8 Column
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8 Column
8.1 Column Sub-Flowsheet .................................................................. 4
8.2 Column Theory............................................................................. 11
8.2.1
8.2.2
8.2.3
8.2.4
Three Phase Theory................................................................ 14
Detection of Three Phases....................................................... 15
Initial Estimates..................................................................... 15
Pressure Flow........................................................................ 19
8.3 Column Installation ..................................................................... 24
8.3.1 Input Experts ........................................................................ 26
8.3.2 Templates ............................................................................. 26
8.4 Column Property View................................................................. 35
8.4.1 Design Tab............................................................................ 37
8.4.2 Parameters Tab...................................................................... 52
8.4.3 Side Ops Tab ......................................................................... 76
8.4.4 Rating Tab............................................................................. 81
8.4.5 Worksheet Tab....................................................................... 84
8.4.6 Performance Tab.................................................................... 85
8.4.7 Flowsheet Tab........................................................................ 97
8.4.8 Reactions Tab .......................................................................102
8.4.9 Dynamics Tab.......................................................................109
8.4.10 Perturb Tab.........................................................................111
8.5 Column Specification Types ....................................................... 113
8.5.1
8.5.2
8.5.3
8.5.4
8.5.5
Cold Property Specifications....................................................113
Component Flow Rate............................................................114
Component Fractions.............................................................114
Component Ratio ..................................................................115
Component Recovery.............................................................115
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8.5.6 Cut Point .............................................................................116
8.5.7 Draw Rate............................................................................116
8.5.8 Delta T (Heater/Cooler) .........................................................116
8.5.9 Delta T (Streams) .................................................................117
8.5.10 Duty..................................................................................117
8.5.11 Duty Ratio..........................................................................117
8.5.12 Feed Ratio..........................................................................118
8.5.13 Gap Cut Point .....................................................................118
8.5.14 Liquid Flow.........................................................................119
8.5.15 Physical Property Specifications.............................................119
8.5.16 Pump Around Specifications..................................................120
8.5.17 Reboil Ratio ........................................................................121
8.5.18 Recovery............................................................................121
8.5.19 Reflux Feed Ratio ................................................................122
8.5.20 Reflux Fraction Ratio............................................................122
8.5.21 Reflux Ratio........................................................................123
8.5.22 Tee Split Fraction ................................................................123
8.5.23 Tray Temperature ................................................................123
8.5.24 Transport Property Specifications...........................................124
8.5.25 User Property .....................................................................124
8.5.26 Vapor Flow .........................................................................125
8.5.27 Vapor Fraction ....................................................................125
8.5.28 Vapor Pressure Specifications................................................125
8.5.29 Column Stream Specifications...............................................126
8.6 Column-Specific Operations........................................................127
8.6.1
8.6.2
8.6.3
8.6.4
Condenser ...........................................................................128
Reboiler...............................................................................147
Tray Section .........................................................................162
Tee .....................................................................................180
8.7 Running the Column ...................................................................181
8.7.1 Run.....................................................................................182
8.7.2 Reset ..................................................................................183
8.8 Column Troubleshooting.............................................................184
8.8.1 Heat and Spec Errors Fail to Converge .....................................185
8.8.2 Equilibrium Error Fails to Converge ..........................................189
8.8.3 Equilibrium Error Oscillates.....................................................189
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8.9 References..................................................................................189
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8.1 Column Sub-Flowsheet
For detailed information
about sub-flowsheet
manipulation, refer to
Chapter 3 - Flowsheet in
the HYSYS User Guide.
The Column is a special type of sub-flowsheet in HYSYS. A subflowsheet contains equipment and streams, and exchanges
information with the parent flowsheet through the connected
internal and external streams. From the main simulation
environment, the Column appears as a single, multi-feed multiproduct operation. In many cases, you can treat the column in
exactly that manner.
You can also work inside the Column sub-flowsheet. You can do
this to “focus” your attention on the Column. When you move
into the Column build environment, the main simulation is
“cached.” All aspects of the main environment are paused until
you exit the Column build environment. When you return to the
Main Environment, the Desktop re-appears as it was when you
left it.
You can also enter the Column build environment when you
want to create a custom column configuration. Side equipment
such as pump arounds, side strippers, and side rectifiers can be
added from the Column property view in the main simulation.
However, if you want to install multiple tray sections or multiple
columns, you need to enter the Column build environment.
Once inside, you can access the Column-specific operations
(Tray Sections, Heaters/Coolers, Condensers, Reboilers, etc.)
and build the column as you would any other flowsheet.
In this chapter, the use of
the Column property view
and Column Templates are
explained. Section 8.6 Column-Specific
Operations, describes the
unit operations available in
the Column build
environment.
If you want to create a custom column template for use in other
simulations, on the File menu select the New command, and
then select the Column sub-command. Since this is a column
template, you can access the Column build environment directly
from the Basis environment. Once you have created the
template, you can store it on disk. Before you install the
template in another simulation, ensure that the Use Input
Experts checkbox in the Session Preferences view is unchecked.
Having a Column sub-flowsheet provides a number of
advantages:
•
•
isolation of the Column Solver.
optional use of different Property Packages.
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•
•
èóë
construction of custom templates.
ability to solve multiple towers simultaneously.
Isolation of the Column Solver
One advantage of the Column build environment is that it allows
you to make changes, and focus on the Column without
requiring a recalculation of the entire flowsheet. When you enter
the Column build environment, HYSYS clears the Desktop by
caching all views that were open in the parent flowsheet. Then
the views that were open when you were last in the Column
build environment are re-opened.
Once inside the Column build environment, you can access
profiles, stage summaries, and other data, as well as make
changes to Column specifications, parameters, equipment,
efficiencies, or reactions. When you have made the necessary
changes, simply run the Column to produce a new converged
solution. The parent flowsheet cannot recalculate until you
return to the parent build environment.
While in the Column sub-flowsheet, you can view the
Workbook or PFD for both the Parent flowsheet or subflowsheet by using the Workbooks option or PFDs option in
the Tools menu.
PFD icon
The sub-flowsheet environment permits easy access to all
streams and operations associated with your column. Click the
PFD icon to view the sub-flowsheet. If you want to access
information regarding column product streams, click the
Workbook icon to view the Column workbook, which displays
the Column information exclusively.
Workbook icon
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Independent Fluid Package
HYSYS allows you to specify a unique fluid package for the
Column sub-flowsheet. Here are some instances where a
separate fluid package is useful:
•
•
•
If a column does not use all of the components used in
the main flowsheet, it is often advantageous to define a
new fluid package with only the components that are
necessary. This speeds up the column solution.
In some cases, a different fluid package can be better
suited to the column conditions. For example, if you want
to redefine Interaction Parameters such that they are
applicable for the operating range of the column.
In Dynamic mode, different columns can operate at very
different temperatures and pressures. With each fluid
package, you can define a different dynamic model
whose parameters can be regressed in the appropriate
temperature and pressure range, thus, improving the
accuracy and stability of the dynamic simulation.
Ability to construct Custom Column
Configurations
Complex custom columns
and multiple columns can
be simulated within a
single sub-flowsheet
using various
combinations of subflowsheet equipment.
Column arrangements
are created in the same
way that you build the
main flowsheet:
• accessing various
operations.
• making the
appropriate
connections.
• defining the
parameters.
Custom column configurations can be stored as templates, and
recalled into another simulation. To create a custom template,
on the File menu select the New command, and then select the
Column sub-command. When you store the template, it has a
*.col extension.
There exists a great deal of freedom when defining column
configurations, and you can define column setups with varying
degrees of complexity. You can use a wide array of column
operations in a manner which is straightforward and flexible.
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Use of Simultaneous Solution Algorithm
The Column sub-flowsheet uses a simultaneous solver whereby
all operations within the sub-flowsheet are solved
simultaneously. The simultaneous solver permits you to install
multiple unit operations within the sub-flowsheet
(interconnected columns, for example) without the need for
Recycle blocks.
Dynamic Mode
There are several major differences between the dynamic
column operation and the steady state column operation. One of
the main differences is the way in which the Column subflowsheet solves.
In steady state if you are in the Column sub-flowsheet,
calculations in the main flowsheet are put on Hold until the focus
is returned to the main flowsheet. When running in dynamics,
calculations in the main flowsheet proceed at the same time as
those in the Column sub-flowsheet.
Another difference between the steady state column and the
dynamic column is with the column specifications. Steady state
column specifications are ignored in dynamics. To achieve the
column specifications when using dynamics, control schemes
must be added to the column.
Finally, although it is possible to turn off static head
contributions for the rest of the simulation, this option does not
apply to the column. When running a column in Dynamic mode,
the static head contributions are always used in the column
calculations.
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Column Property View
Side equipment (pump
arounds, side strippers,
etc.) is added from the
Column property view.
The Column property view (the representation of the Column
within the main or parent flowsheet) essentially provides you
with complete access to the Column. You can enter the Column
sub-flowsheet to add new pieces of equipment, such as
additional Tray Sections or Reboilers.
Ú·¹«®» èòï
For more information,
refer to Section 8.4 Column Property View.
From the Column property view, you can change feed and
product connections, specifications, parameters, pressures,
estimates, efficiencies, reactions, side operations, and view the
Profiles, Work Sheet, and Summary. You can also run the
column from the main flowsheet just as you would from the
Column sub-flowsheet.
If you want to make a minor change to a column operation (for
instance, resize a condenser) you can call up that operation
using the Object Navigator without entering the Column subflowsheet. Major changes, such as adding a second tray section,
require you to enter the Column sub-flowsheet. To access to the
Column build environment, click the Column Environment
button at the bottom of the Column property view.
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If you make a change to
the Column while you are
working in the parent, or
main build environment,
both the Column and the
parent flowsheets are
automatically
recalculated.
èóç
Main/Column Sub-flowsheet
Relationship
Unlike other unit operations, the Column contains its own subflowsheet, which in turn, is contained in the Parent (usually the
main) flowsheet. When you are working in the parent flowsheet,
the Column appears just as any other unit operation, with
multiple input and output streams, and various adjustable
parameters. If changes are made to any of these basic column
parameters, both the Column sub-flowsheet and parent
flowsheet are recalculated.
When you install a Column, HYSYS creates a sub-flowsheet
containing all operations and streams associated with the
template you have chosen. This sub-flowsheet operates as a
unit operation in the main flowsheet. Figure 8.2 shows this
concept of a Column sub-flowsheet within a main flowsheet.
Main Flowsheet / Sub-flowsheet
Concept
Consider a simple absorber in which you want to remove CO2
from a gas stream using H2O as the solvent. A typical approach
to setting up the problem would be as follows:
1. Create the gas feed stream, FeedGas, and the water solvent
stream, WaterIn, in the main flowsheet.
2. Click the Absorber icon from the Object Palette, and specify
the stream names, number of trays, pressures, estimates,
and specifications. You must also specify the names of the
outlet streams, CleanGas and WaterOut.
3. Run the Column from the main flowsheet Column property
view.
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A sub-flowsheet stream
that is connected to a
stream in the main
flowsheet is
automatically given the
same name with
“@Sub-flowsheet tag”
attached at the end of
the name. An example
is the stream named
“WaterIn” has the subflowsheet stream
named “[email protected]”.
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When you connected the streams to the tower, HYSYS created
internal streams with the same names. The Connection Points or
“Labels” serve to connect the main flowsheet streams to the
sub-flowsheet streams and facilitate the information transfer
between the two flowsheets. For instance, the main flowsheet
stream WaterIn is “connected” to the sub-flowsheet stream
WaterIn.
Ú·¹«®» èòî
The connected streams do not necessarily have the same
values. All specified values are identical, but calculated
stream variables can be different depending on the fluid
packages and transfer basis (defined on the Flowsheet tab).
When working in the main build environment, you “see” the
Column just as any other unit operation, with a property view
containing parameters such as the number of stages, and top
and bottom pressures. If you change one of these parameters,
the sub-flowsheet recalculates (just as if you had clicked the
Run button); the main flowsheet also recalculates once a new
column solution is reached.
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If you delete any streams
connected to the column
in the main flowsheet,
these streams are also
deleted in the Column
sub-flowsheet.
èóïï
However, if you are inside the Column sub-flowsheet build
environment, you are working in an entirely different flowsheet.
To make a major change to the Column such as adding a
reboiler, you must enter the Column sub-flowsheet build
environment. When you enter this environment, the main
flowsheet is put on “hold” until you return.
8.2 Column Theory
For information regarding
the electrolyte column
theory, refer to Section
1.6.8 - HYSYS Column
Operation in the HYSYS
OLI Interface
Reference Guide.
Multi-stage fractionation towers, such as crude and vacuum
distillation units, reboiled demethanizers, and extractive
distillation columns, are the most complex unit operations that
HYSYS simulates. Depending on the system being simulated,
each of these towers consists of a series of equilibrium or nonequilibrium flash stages. The vapour leaving each stage flows to
the stage above and the liquid from the stage flows to the stage
below. A stage can have one or more feed streams flowing onto
it, liquid or vapour products withdrawn from it, and can be
heated or cooled with a side exchanger.
The following figure shows a typical stage j in a Column using
the top-down stage numbering scheme. The stage above is j-1,
while the stage below is j+1. The stream nomenclature is shown
in the figure below.
Ú·¹«®» èòí
Lj-1
Vj
F = Stage feed stream
VSDj
Fj
Stage j
Qj
Rj
LSDj
Vj+1
Lj
L = Liquid stream
travelling to stage below
V = Vapor stream
travelling to stage above
LSD = Liquid side draw
from stage
VSD = Vapor side draw
from stage
Q = Energy stream
entering stage
More complex towers can have pump arounds, which withdraw
liquid from one stage of the tower and typically return it to a
stage farther up the column. Small auxiliary towers, called
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sidestrippers, can be used on some towers to help purify side
liquid products. With the exception of Crude distillation towers,
very few columns have all of these items, but virtually any type
of column can be simulated with the appropriate combination of
features.
It is important to note that the Column operation by itself is
capable of handling all the different fractionation applications.
HYSYS has the capability to run cryogenic towers, high pressure
TEG absorption systems, sour water strippers, lean oil
absorbers, complex crude towers, highly non-ideal azeotropic
distillation columns, etc. There are no programmed limits for the
number of components and stages. The size of the column
which you can solve depends on your hardware configuration
and the amount of computer memory you have available.
The column is unique among the unit operations in the methods
used for calculations. There are several additional underlying
equations which are used in the column.
The Francis Weir equation is the starting point for calculating the
liquid flowrate leaving a tray:
L N ã C lw h
1.5
(8.1)
where:
LÒ = liquid flowrate leaving tray N
C = units conversion constant
= density of liquid on tray
l© = weir length
h = height of liquid above weir
The vapour flowrate leaving a tray is determined by the
resistance equation:
F vap ã k
P friction
(8.2)
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where:
Fvap = vapour flowrate leaving tray N
k = conductance, which is a constant representing the
reciprocal of resistance to flow
P friction = dry hole pressure drop
For columns the conductance, k, is proportional to the
square of the column diameter.
The pressure drop across a stage is determined by summing
the static head and the frictional losses.
It is possible to use column stage efficiencies when running a
column in dynamics. The efficiency is equivalent to bypassing a
portion of the vapour around the liquid phase, as shown in the
figure below, where n is the specified efficiency.
Ú·¹«®» èòì
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HYSYS has the ability to model both weeping and flooding inside
the column. If P friction is very small, the stage exhibits weeping.
Therefore it is possible to have a liquid flow to the stage below
even if the liquid height over the weir is zero.
For the flooding condition, the bulk liquid volume approaches
the tray volume. This can be observed on the Holdup page in the
Dynamics tab, of either the Column Runner or the Tray Section
property view.
8.2.1 Three Phase Theory
For non-ideal systems with more than two components,
boundaries can exist in the form of azeotropes, which a simple
distillation system cannot cross. The formation of azeotropes in
a three phase system provides a thermodynamic barrier to
separating chemical mixtures.
Distillation schemes for non-ideal systems are often difficult to
converge without very accurate initial guesses. To aid in the
initialization of towers, a Three Phase Input Expert is available
to initialize temperatures, flows, and compositions. Refer to
Section 8.3.2 - Templates for further details on the three
phase capabilities in HYSYS.
For non-ideal multicomponent systems, DISTIL is an
excellent tool for determining process viability. This
conceptual design software application also determines the
optimal feed tray location and allows direct export of column
specifications to HYSYS for use as an initial estimate.
Contact your local AspenTech representative for details.
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8.2.2 Detection of Three
Phases
Look at the Trace
Window for column
convergence messages.
Whenever your Column converges, HYSYS automatically
performs a Three Phase Flash on the top stage. If a second
liquid phase is detected, and no associated water draw is found,
a warning message appears.
If there is a water draw, HYSYS checks the next stage for a
second liquid phase, with the same results as above. This
continues down the Tower until a stage is found that is two
phase only.
If there is a three phase stage below a stage that was found
to be two phase, the three phase stage is not detected
because the checking would have ended in the previous two
phase stage.
HYSYS always indicates the existence of the second liquid
phase. This continues until the Column reverts to VLE operation,
or all applicable stages have water draws placed on them.
8.2.3 Initial Estimates
Initial estimates are optional values that you provide to help the
HYSYS algorithm converge to a solution. The better your
estimates, the quicker HYSYS converges.
There are three ways for you to provide the column with initial
estimates:
•
•
Refer to Section 8.3.2 Templates for more
information regarding
default specifications.
•
Provide the estimate values when you first build the
column.
Go to the Profiles or Estimates page on the Parameters
tab to provide the estimate values.
Go to the Monitor or Specs page on the Design tab to
provide values for the default specifications or add your
own specifications.
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It is important to remember, when the column starts to solve for
the first time or after the column has been reset, the
specification values are also initial estimates. So if you replaced
one of the original default specifications (overhead vapour flow,
side liquid draw or reflux ratio) with a new active specification,
the new specification value is used as initial estimates. For this
reason it is recommended you provide reasonable specification
values initially even if you can replace them while the column is
solving or after the column has solved.
Although HYSYS does not require any estimates to converge
to a solution, reasonable estimates help in the convergence
process.
Temperatures
Temperature estimates can be given for any stage in the
column, including the condenser and reboiler, using the Profiles
page in the Parameters tab of the Column property view.
Intermediate temperatures are estimated by linear
interpolation. When large temperature changes occur across the
condenser or bottom reboiler, it would be helpful to provide an
estimate for the top and bottom trays in the tray section.
If the overhead product is a subcooled liquid, it is best to
specify an estimated bubble-point temperature for the
condenser rather than the subcooled temperature.
Mixing Rules at Feed Stages
When a feed stream is introduced onto a stage of the column,
the following sequence is employed to establish the resulting
internal product streams:
1. The entire component flow (liquid and vapour phase) of the
feed stream is added to the component flows of the internal
vapour and liquid phases entering the stage.
2. The total enthalpy (vapour and liquid phases) of the feed
stream is added to the enthalpies of the internal vapour and
liquid streams entering the stage.
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èóïé
3. HYSYS flashes the combined mixture based on the total
enthalpy at the stage Pressure. The results of this process
produce the conditions and composition of the vapour and
liquid phases leaving the stage.
In most physical situations, the vapour phase of a feed stream
does not come in close contact with the liquid on its feed stage.
However if this is the case, the column allows you to split all
material inlet streams into their phase components before being
fed to the column. The Split Inlets checkbox can be activated in
the Setup page of the Flowsheet tab. You can also set all the
feed streams to a column to always split, by activating the
appropriate checkbox in the Options page from the Simulation
tab of the Session Preferences view.
Basic Column Parameters
Regardless of the type of column, the Basic Column Parameters
remain at their input values during convergence.
Pressure
The pressure profile in a Column Tray Section is calculated using
your specifications. You can either explicitly enter all stage
pressures or enter the top and bottom tray pressures (and any
intermediate pressures) such that HYSYS can interpolate
between the specified values to determine the pressure profile.
Simple linear interpolation is used to calculate the pressures on
stages which are not explicitly specified.
You can enter the condenser and reboiler pressure drops
explicitly within the appropriate operation view. Default pressure
drops for the condenser and reboiler are zero, and a non-zero
value is not necessary to produce a converged solution.
If the pressure of a Column product stream (including side
vapour or liquid draws, side stripper bottom streams, or internal
stream assignments) is set (either by specification or
calculation) prior to running the Column, HYSYS “backs” this
value into the column and uses this value for the convergence
process. If you do specify a stream pressure that allows HYSYS
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ݱ´«³² ̸»±®§
to calculate the column pressure profile, it is not necessary to
specify another value within the column property view. If you
later change the pressure of an attached stream, the Column is
rerun.
Recall that whenever a change is made in a stream, HYSYS
checks all operations attached to that stream and
recalculates as required.
Number of Stages
The number of stages that you specify for the tray section does
not include the condenser and bottom reboiler, if present. If
sidestrippers are to be added to the column, their stages are not
included in this number. By default, HYSYS numbers stages from
the top down. If you want, you can change the numbering
scheme to bottom-up by selecting this scheme on the
Connections page of the Design tab.
HYSYS initially treats the stages as being ideal. If you want your
stages to be treated as real stages, you must specify efficiencies
on the Efficiencies page of the Parameters tab. Once you provide
efficiencies for the stages, even if the value you specify is 1,
HYSYS treats the stages as being real.
Stream
The feed stream and product stream location, conditions, and
composition are treated as Basic Column Parameters during
convergence.
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ݱ´«³²
èóïç
8.2.4 Pressure Flow
In the following sections, the pressure flow specifications
presented are the recommended configurations if no other
equipment, such as side strippers, side draws, heat exchanger,
etc., are connected. Other combinations of pressure flow
specifications are possible, however they can lead to less stable
configurations.
Regardless of the pressure flow specification configuration,
when performing detailed dynamic modeling it is recommended
that at least valves be added to all boundary streams. Once
valves have been added, the resulting boundary streams can all
be specified with pressure specifications, and, where necessary,
flow controlled with flow controllers.
Absorber
The basic Absorber column has two inlet and two exit streams.
When used alone, the Absorber has four boundary streams and
so requires four Pressure Flow specifications. A pressure
specification is always required for the liquid product stream
leaving the bottom of the column. A second pressure
specification should be added to the vapour product of the
column, with the two feed streams having flow specifications.
The column shows the
recommended pressure
flow specifications for a
stand alone absorber
column.
If there are down stream unit operations attached to the liquid
product stream, then a column sump needs to be simulated.
There are several methods for simulating the column sump. A
simple solution is to use a reboiled absorber, with the reboiler
duty stream specified as zero in place of the absorber. Another
option is to feed the liquid product stream directly into a
separator, and return the separator vapour product to the
bottom stage of the column.
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ݱ´«³² ̸»±®§
Refluxed Absorber
The basic Refluxed Absorber column has a single inlet and two
or three exit streams, depending on the condenser
configuration. When used alone, the Refluxed Absorber has
three or four boundary streams (depending on the condenser)
and requires four or five pressure-flow specifications; generally
two pressure and three flow specifications. A pressure
specification is always required for the liquid product stream
leaving the bottom of the column. The extra specification is
required due to the reflux stream and is discussed in Section
8.6 - Column-Specific Operations.
The column shows the
recommended pressure
flow specifications for a
stand alone refluxed
absorber with a partial
condenser.
If there are down stream unit operations attached to the liquid
product stream, then a column sump needs to be simulated.
There are several methods for simulating the column sump. A
simple solution is to use a distillation column, with the reboiler
duty stream specified as zero in place of the refluxed absorber.
Another option is to feed the liquid product stream directly into
a separator, and return the separator vapour product to the
bottom stage of the column.
Reboiled Absorber
A Reboiled Absorber column has a single inlet and two exit
streams. When used alone, the Reboiled Absorber has three
boundary streams and so requires three Pressure Flow
specifications; one pressure and two flow specifications. A
pressure specification is always required for the vapour product
leaving the column.
The column shows the
recommended pressure
flow specifications for a
stand alone reboiled
absorber.
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ݱ´«³²
èóîï
Distillation Column
The basic Distillation column has one inlet and two or three exit
streams, depending on the condenser configuration. When used
alone, the Distillation column has three or four boundary
streams but requires four or five pressure-flow specifications;
generally one pressure and three or four flow specifications. The
extra pressure-flow specification is required due to the reflux
stream, and is discussed in Section 8.6 - Column-Specific
Operations.
Ú·¹«®» èòë
The column shows the
recommended pressure-flow
specifications for a stand alone
distillation column with a partial
condenser.
The column shows the
recommended pressure-flow
specifications for a stand alone
three phase distillation column
with a partial condenser.
The Three Phase Distillation column is similar to the basic
Distillation column except it has three or four exit streams. So
when used alone, the Three Phase Distillation column has four
to five boundary streams, but requires five or six pressure-flow
specifications; generally one pressure and four to five flow
specifications.
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Condenser and Reboiler
The following sections provide some recommended pressureflow specifications for simple dynamic modeling only. The use of
flow specifications on reflux streams is not recommended for
detailed modeling. If the condenser liquid level goes to zero, a
mass flow specification results in a large volumetric flow
because the stream is a vapour.
It is highly recommended that the proper equipment be added
to the reflux stream (e.g., pumps, valves, etc.). In all cases,
level control for the condenser should be used to ensure a
proper liquid level.
Partial Condenser
The partial condenser has three exit streams:
•
•
•
overhead vapour
reflux
distillate
All three exit streams must be specified when attached to the
main tray section. One pressure specification is recommended
for the vapour stream, and one flow specification for either of
the liquid product streams. The final pressure flow specification
can be a second flow specification on the remaining liquid
product stream, or the Reflux Flow/Total Liquid Flow value on
the Specs page of the Dynamics tab of the condenser can be
specified.
Fully-Refluxed Condenser
The Fully-Refluxed condenser has two exit streams:
•
•
overhead vapour
reflux
A pressure specification is required for the overhead vapour
stream, and a flow specification is required for the reflux
stream.
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Total Condenser
A Total condenser has two exit streams:
•
•
reflux
distillate
There are several possible configurations of pressure flow
specifications for this type of condenser. A flow specification can
be used for the reflux stream and a pressure flow spec can be
used for the distillate stream. Two flow specifications can be
used, however, it is suggested that a vessel pressure controller
be setup with the condenser duty as the operating variable.
Reboiler
The Reboiler has two exit streams:
•
•
boilup vapour
bottoms liquid
Only one exit stream can be specified. If a pressure constraint is
specified elsewhere in the column, this exit stream must be
specified with a flow rate.
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8.3 Column Installation
The first step in installing a Column is deciding which type you
want to install. Your choice depends on the type of equipment
(for example, reboilers and condensers) your Column requires.
HYSYS has several basic Column templates (pre-constructed
column configurations) which can be used for installing a new
Column. The most basic Column types are described in the table
below.
Basic Column Types
Icon
Description
Absorber
Tray section only.
Liquid-Liquid
Extractor
Tray section only.
Reboiled Absorber
Tray section and a bottom stage
reboiler.
Refluxed Absorber
Tray section and an overhead
condenser.
Distillation
Tray section with both a reboiler and
condenser.
Three Phase
Distillation
Tray section, three-phase condenser,
reboiler. Condenser can be either
chemical or hydrocarbon specific.
There are two ways that you can add a basic Column type to
your simulation:
You can also add a basic
Column type by pressing
the F12 hot key.
1. In the Flowsheet menu, click the Add Operation command.
The UnitOps view appears.
2. Click the Prebuilt Columns radio button.
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3. From the list of available unit operations, select the column
type.
4. Click the Add button. The Input Expert view appears. Refer
to Section 8.3.1 - Input Experts for more information.
OR
You can also open the
Object Palette by
pressing the F4 hot key.
1. In the Flowsheet menu, click the Palette command. The
Object Palette appears.
2. Double-click the column type icon, as described in the table
above. The Input Expert view appears.
There are also more complex Column types, which are described
in the table below.
You can also add a
complex Column type by
pressing the F12 hot
key.
Complex Column Types
Description
3 Sidestripper Crude
Column
Tray section, reboiler, condenser, 3
sidestrippers, and 3 corresponding pump
around circuits.
4 Sidestripper Crude
Column
Tray section, reboiler, condenser, an
uppermost reboiled sidestripper, 3 steamstripped lower sidestrippers, and 3
corresponding pump around circuits.
FCCU Main Fractionator
Tray section, condenser, an upper pump
around reflux circuit and product draw, a midcolumn two-product-stream sidestripper, a
lower pump around reflux circuit and product
draw, and a quench pump around circuit at
the bottom of the column.
Vacuum Reside Tower
Tray section, 2 side product draws with pump
around reflux circuits and a wash oil-cooled
steam stripping section below the flash zone.
To add a complex column type to your simulation:
1. In the Flowsheet menu, click the Add Operation command.
The UnitOps view appears.
2. Click the Prebuilt Columns radio button.
3. From the list of available unit operations, select the column
type.
4. Click the Add button. The column property view appears.
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ݱ´«³² ײ-¬¿´´¿¬·±²
8.3.1 Input Experts
Input Experts guide you through the installation of a Column.
The Input Experts are available for the following six standard
column templates:
•
•
•
•
•
•
Absorber
Liquid-Liquid Extractor
Reboiled Absorber
Refluxed Absorber
Distillation
Three Phase Distillation
Details related to each column template are outlined in Section
8.3.2 - Templates. Each Input Expert contains a series of input
pages whereby you must specify the required information for
the page before advancing to the next one. When you have
worked through all the pages, you have specified the basic
information required to build your column. You are then placed
in the Column property view which gives comprehensive access
to most of the column features.
Refer to Chapter 12 Session Preferences in
the HYSYS User Guide
for details on how to
access the Session
Preferences view.
It is not necessary to use the Input Experts to install a column.
You can disable and enable the use of Input Experts on the
Options page in the Simulation tab of the Session Preferences
view. If you do not use the Input Experts, you move directly to
the Column property view when you install a new column.
8.3.2 Templates
Press F12 to access the
UnitOps view, which
allows you to add a
column template.
HYSYS contains a number of column templates which have been
designed to simplify the installation of columns.
A Column Template is a pre-constructed configuration or
“blueprint” of a common type of Column, including Absorbers,
Reboiled and Refluxed Absorbers, Distillation Towers, and Crude
Columns. A Column Template contains the unit operations and
streams that are necessary for defining the particular column
type, as well as a default set of specifications.
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Ú·¹«®» èòê
All Column templates can be viewed by selecting the Prebuilt
Columns radio button.
When you add a new Column, HYSYS gives you a choice of the
available templates. Simply select the template that most
closely matches your column configuration, provide the
necessary input in the Input Expert view (if applicable), and
HYSYS installs the equipment and streams for you in a new
Column sub-flowsheet. Stream connections are already in place,
and HYSYS provides default names for all internal streams and
equipment. You can then make modifications by adding,
removing or changing the names of any streams or operations
to suit your specific requirements.
Clicking the Side Ops button on the final page of the Column
Input Expert opens the Side Operations Input Expert wizard,
which guides you through the process of adding a side operation
to your column.
In addition to the basic Column Templates which are included
with HYSYS, you can create custom Templates containing
Column configurations that you commonly use.
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HYSYS Column Conventions
Column Tray Sections, Overhead Condensers, and Bottom
Reboilers are each defined as individual unit operations.
Condensers and Reboilers are not numbered stages, as they are
considered to be separate from the Tray Section.
By making the individual
components of the
column separate pieces of
equipment, there is
easier access to
equipment information,
as well as the streams
connecting them.
The following are some of the conventions, definitions, and
descriptions of the basic columns:
Column Component
Description
Tray Section
A HYSYS unit operation that represents the series
of equilibrium trays in a Column.
Stages
Stages are numbered from the top down or from
the bottom up, depending on your preference.
The top tray is 1, and the bottom tray is N for the
top-down numbering scheme. The stage
numbering preference can be selected on the
Connections page of the Design tab on the
Column property view.
Overhead Vapor
Product
The overhead vapour product is the vapour
leaving the top tray of the Tray Section in simple
Absorbers and Reboiled Absorbers. In Refluxed
Absorbers and Distillation Towers, the overhead
vapour product is the vapour leaving the
Condenser.
Overhead Liquid
Product
The overhead liquid product is the Distillate
leaving the Condenser in Refluxed Absorbers and
Distillation Towers. There is no top liquid product
in simple Absorbers and Reboiled Absorbers.
Bottom Liquid
Product
The bottom liquid product is the liquid leaving the
bottom tray of the Tray Section in simple
Absorbers and Refluxed Absorbers. In Reboiled
Absorbers and Distillation Columns, the bottom
liquid product is the liquid leaving the Reboiler.
Overhead Condenser
An Overhead Condenser represents a combined
Cooler and separation stage, and is not given a
stage number.
Bottom Reboiler
A Bottom Reboiler represents a combined heater
and separation stage, and is not given a stage
number.
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Default Replaceable Specifications
Replaceable specifications are the values, which the Column
convergence algorithm is trying to meet. When you select a
particular Column template, or as you add side equipment,
HYSYS creates default specifications. You can use the
specifications that HYSYS provides, or replace these
specifications with others more suited to your requirements.
The available default replaceable specifications are dependent
on the Basic Column type (template) that you have chosen. The
default specifications for the four basic column templates are
combinations of the following:
•
•
•
•
•
Refer to the Monitor
Page and Specs Page
in Section 8.4.1 Design Tab for more
information.
Overhead vapour flowrate
Distillate flowrate
Bottoms flowrate
Reflux ratio
Reflux rate
The specifications in HYSYS can be set as specifications or
changed to estimates.
The provided templates contain only pre-named internal
streams (streams which are both a feed and product). For
instance, the Reflux stream, which is named by HYSYS, is a
product from the Condenser and a feed to the top tray of the
Tray Section.
The pressure for a tray section stage, condenser or reboiler
can be specified at any time on the Pressures page of the
Column property view.
In the following schematics, you specify the feed and product
streams, including duty streams.
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ݱ´«³² ײ-¬¿´´¿¬·±²
Absorber Template
The only unit operation contained in the Absorber is the Tray
Section, and the only streams are the overhead vapour and
bottom liquid products.
A schematic
representation of the
Absorber.
There are no available specifications for the Absorber, which is
the base case for all tower configurations. The conditions and
composition of the column feed stream, as well as the operating
pressure, define the resulting converged solution. The
converged solution includes the conditions and composition of
the vapour and liquid product streams.
The Liquid-Liquid Extraction Template is identical to the
Absorber Template.
The remaining Column templates have additional equipment,
thus increasing the number of required specifications.
Reboiled Absorber Template
The Reboiled Absorber template consists of a tray section and a
bottom reboiler. Two additional streams connecting the Reboiler
to the Tray Section are also included in the template.
Ú·¹«®» èòé
When you install a Reboiled Absorber (i.e., add only a Reboiler
to the Tray Section), you increase the number of required
specifications by one over the Base Case. As there is no
overhead liquid, the default specification in this case is the
overhead vapour flow rate.
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Refluxed Absorber Template
The Refluxed Absorber template contains a Tray Section and an
overhead Condenser (partial or total). Additional material
streams associated with the Condenser are also included in the
template. For example, the vapour entering the Condenser from
the top tray is named to Condenser by default, and the liquid
returning to the Tray Section is the Reflux.
Ú·¹«®» èòè
When you install a Refluxed Absorber, you are adding only a
Condenser to the base case. Specifying a partial condenser
increases the number of required specifications by two over the
Base Case. The default specifications are the overhead vapour
flow rate, and the side liquid (Distillate) draw. Specifying a total
condenser results in only one available specification, since there
is no overhead vapour product.
Either of the overhead vapour or distillate flow rates can be
specified as zero, which creates three possible combinations for
these two specifications. Each combination defines a different
set of operating conditions. The three possible Refluxed
Absorber configurations are listed below:
•
•
•
Partial condenser with vapour overhead but no side liquid
(distillate) draw.
Partial condenser with both vapour overhead and
distillate draws.
Total condenser with distillate but no vapour overhead
draw.
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Distillation Template
If you select the Distillation template, HYSYS creates a Column
with both a Reboiler and Condenser. The equipment and streams
in the Distillation template are therefore a combination of the
Reboiled Absorber and Refluxed Absorber Templates
Ú·¹«®» èòç
Reflux Ratio
The number of specifications for a column with both a Reboiler
and Condenser depends on the condenser type. For a partial
condenser, you must specify three specifications. For a total
condenser, you must specify two specifications. The third default
specification (in addition to Overhead Vapor Flow Rate and Side
Liquid Draw) is the Reflux Ratio.
Ú·¹«®» èòïð
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The Reflux Ratio is defined as the ratio of the liquid returning to
the tray section divided by the total flow of the products (see
the figure above). If a water draw is present, its flow is not
included in the ratio.
As with the Refluxed Absorber, the Distillation template can have
either a Partial or Total Condenser. Choosing a Partial Condenser
results in three replaceable specifications, while a Total
Condenser results in two replaceable specifications.
The pressure remains
fixed during the Column
calculations.
The pressure in the tower is, in essence, a replaceable
specification, in that you can change the pressure for any stage
from the Column property view.
The following table gives a summary of replaceable column
(default) specifications for the basic column templates.
Templates
Vapour Draw
Reboiled
Absorber
X
Distillate Draw
Reflux Ratio
Refluxed
Absorber
Total Condenser
Partial
Condenser
X
X
X
Distillation
Total Condenser
Partial
Condenser
X
X
X
X
X
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Three Phase Distillation Template
The same standard
column types exist for a
three phase system that
are available for the
“normal” two phase
(binary) systems.
If you select the Three Phase Distillation template, HYSYS
creates a Column based on a three phase column model.
Ú·¹«®» èòïï
Using the Three Phase Column Input Expert, the initial view
allows you to select from the following options:
•
•
•
•
Distillation
Refluxed Absorber
Reboiled Absorber
Absorber
Each choice builds the appropriate column based on their
respective standard (two phase) system templates.
If the Input Expert is turned off, installing a Three Phase column
template opens a default Column property view for a Distillation
type column equipped with a Reboiler and Condenser.
The key difference between using the standard column
templates and their three phase counterparts lies in the solver
that is used. The default solver for three phase columns is the
“Sparse Continuation” solver which is an advanced solver
designed to handle three phase, non ideal chemical systems,
that other solvers cannot.
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When using the Three Phase Column Input Expert some
additional specifications can be required when compared with
the standard (binary system) column setups.
Ú·¹«®» èòïî
It requires some expertise to
set up, initialize, and solve
three phase distillation
problems. Additional modeling
software applications such as
DISTIL, use residue curve maps
and distillation region diagrams
to determine feasible designs,
and can greatly assist in the
initial design work. Contact
your local AspenTech
representative for details.
Clicking the Side Ops button on the final page of the Three
Phase Column Input Expert opens the Side Operations Input
Expert wizard, which guides you through the process of adding a
side operation to your column.
8.4 Column Property View
Column Runner icon
Column Runner is
another name for the
sub-flowsheet Column
property view.
The column property view is sectioned into tabs containing
pages with information pertaining to the column. The column
property view is accessible from the main flowsheet or Column
sub-flowsheet. In the Column sub-flowsheet, the column
property view is also known as the Column Runner, and can be
accessed by clicking the Column Runner icon.
The column property view is used to define specifications,
provide estimates, monitor convergence, view stage-by-stage
and product stream summaries, add pump-arounds and sidestrippers, specify dynamic parameters and define other Column
parameters such as convergence tolerances, and attach
reactions to column stages.
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There are some
differences in the Column
property view; in the
main flowsheet, and in
the Column subflowsheet. These
differences are noted.
ݱ´«³² Ю±°»®¬§ Ê·»©
The column property view is essentially the same when
accessed from the main flowsheet or Column sub-flowsheet.
However, there are some differences:
•
•
•
The Connections page in the main flowsheet column
property view displays and allows you to change all
product and feed stream connections. In addition, you
can specify the number of stages and condenser type.
The Connections page in the sub-flowsheet Column
property view (Column Runner) allows you to change the
product and feed stream connections, and gives more
flexibility in defining new streams.
In the main flowsheet Column property view, the
Flowsheet Variables and Flowsheet Setup pages allow
you to specify the transfer basis for stream connections,
and permit you to view selected column variables.
In order to make changes or additions to the Column in the
main simulation environment, the Solver should be active.
Otherwise HYSYS cannot register your changes.
Column Convergence
The Run and Reset buttons are used to start the convergence
algorithm and reset the Column, respectively. HYSYS first
performs iterations toward convergence of the inner and outer
loops (Equilibrium and Heat/Spec Errors), and then checks the
individual specification tolerances (refer to the section on the
Specification Tolerances for Solver for more information).
The Monitor page displays a summary of the convergence
procedure for the Equilibrium and Heat/Spec Errors. An example
of a converged solution is shown in the following figure:
Ú·¹«®» èòïí
A summary of each of the tabs in the Column property view are
in the following sections.
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8.4.1 Design Tab
Column Runner is
another name for the
sub-flowsheet Column
property view.
The following sections detail information regarding the Column
property view pages. All pages are common to both the Main
Column property view and the Column Runner, unless stated
otherwise.
Connections page (Main Flowsheet)
If you have modified
the Column Template
(e.g., - added an
additional Tray
Section), the
Connections page
appears differently than
what is shown in Figure
8.14.
The main flowsheet Connections page allows you to specify the
name and location of feed streams, the number of stages in the
tray section, the stage numbering scheme, condenser type,
names of the Column product streams, and Condenser/Reboiler
energy streams.
Ú·¹«®» èòïì
The streams shown in this view reside in the parent or main
flowsheet; they do not include Column sub-flowsheet streams,
such as the Reflux or Boilup. In other words, only feed and
product streams (material and energy) appear on this page.
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ݱ´«³² Ю±°»®¬§ Ê·»©
The appearance of the Connections page varies depending
on the template you are using. See Figure 8.15 for the
Connections page of a Stripper Crude.
When the column has complex connections, the Connections
page changes to the view shown in the figure below.
Ú·¹«®» èòïë
You can also split the feed streams by activating the Split
checkbox associated to the stream.
Click the Edit Trays button to open the Tray Section Details view.
You can edit the number of trays in the column, and add or
delete trays after or before the tray number of your choice in
this view.
Ú·¹«®» èòïê
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Connections page (Column Runner)
If you specify a new
stream name in any of
the cells, this creates the
stream inside the
Column. This new
stream is not
automatically transferred
into the main flowsheet.
The Connections page displayed in the Column Runner (inside
the Column sub-flowsheet) appears as shown in the following
figure.
You can connect or
disconnect streams from
this page, as well as
change the stream
location.
All feed and energy streams, as well as the associated stage,
appear in the left portion of the Connections page. Liquid,
vapour, and water product streams and locations appear on the
right side of the page.
Ú·¹«®» èòïé
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ݱ´«³² Ю±°»®¬§ Ê·»©
Monitor Page
The Monitor page is primarily used for editing specifications,
monitoring Column convergence, and viewing Column profile
plots. An input summary, and a view of the initial estimates can
also be accessed from this page.
Ú·¹«®» èòïè
HYSYS displays the iteration number, step size, and
Equilibrium and Heat/Spec errors in this area during
the iteration process.
Profiles are where
plots of column
temperatures, flows,
and pressures appear
during convergence.
The Current checkbox
shows the current
specs that are being
used in the column
solution. You cannot
activate or deactivate
this checkbox.
Specification types,
the value of each
specification, the
current calculated
value and the
weighted error appear
here.
Buttons for working with specifications.
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Optional Checks Group
In the Optional Checks group, you find the following two
buttons:
Refer to Section 1.3 Object Status Window/
Trace Window in the
HYSYS User Guide for
details concerning the
Trace Window.
Button
Function
Input Summary
Provides a column input summary in the Trace
Window. The summary lists vital tower information
including the number of trays, the attached fluid
package, attached streams, and specifications.
You can click the Input Summary button after you
make a change to any of the column parameters to
view an updated input summary. The newly defined
column configuration appears.
View Initial
Estimates
Opens the Summary page of the Column property
view, and displays the initial temperature and flow
estimates for the column. You can then use the
values generated by HYSYS to enter estimates on the
Estimates page.
These estimates are generated by performing one
iteration using the current column configuration. If a
specification for flow or temperature has been
provided, it is honoured in the displayed estimates.
Profile Group
During the column calculations, a profile of temperature,
pressure or flow appears, and is updated as the solution
progresses. Select the appropriate radio button to display the
desired variable versus tray number profile.
Specifications Group
New specifications can also
be added via the Specs
page.
Each specification, along with its specified value, current value,
weighted error, and status is shown in the Specifications group.
You can change a specified value by typing directly in the
associated Specified Value cell. Specified values can also be
viewed and changed on the Specs and Specs Summary pages.
Any changes made in one location are reflected across all
locations. Refer to Section 8.5 - Column Specification Types
for a description of the available specification types.
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Double-clicking on a cell within the row for any listed
specification opens its property view. In this view, you can
define all the information associated with a particular
specification. Each specification view has three tabs:
•
•
•
Parameters
Summary
Spec Type
This view can also be accessed from both the Specs and Specs
Summary pages. Further details are outlined in the section on
the Specification Property View.
Spec Status Checkboxes
Spec Status checkboxes
The status of listed specifications are one of the following types:
Status
Description
Active
The active specification is one that the convergence
algorithm is trying to meet. An active specification always
serves as an initial estimate (when the Active checkbox is
activated, HYSYS automatically activates the Estimate and
Current checkboxes). An active specification always
exhausts one degree of freedom.
An Active specification is one which the convergence
algorithm is trying to meet initially. An Active specification
has the Estimate checkbox activated also.
Estimate
An Estimate is considered an Inactive specification because
the convergence algorithm is not trying to satisfy it. To use
a specification as an estimate only, deactivate the Active
checkbox. The value then serves only as an initial estimate
for the convergence algorithm. An estimate does not
exhaust an available degree of freedom.
An Estimate is used as an initial “guess” for the
convergence algorithm, and is considered to be an Inactive
specification.
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Status
Description
Current
This checkbox shows the current specs being used by the
column solution. When the Active checkbox is activated,
the Current checkbox automatically activates. You cannot
alter this checkbox.
When Alternate specs are used and an existing hard to
solve spec has been replaced with an Alternate spec, this
checkbox shows you the current specs used to solve the
column.
A Current specification is one which is currently being used
in the column solution.
Completely
Inactive
To disregard the value of a specification entirely during
convergence, deactivate both the Active and Estimate
checkboxes. By ignoring a specification rather than deleting
it, you are always able to use it later if required. The
current value appears for each specification, regardless of
its status. An Inactive specification is therefore ideal when
you want to monitor a key variable without including it as
an estimate or specification.
A Completely Inactive specification is ignored completely by
the convergence algorithm, but can be made Active or an
Estimate at a later time.
The degrees of freedom value appears in the Degrees of
Freedom field on the Monitor page. When you make a
specification active, the degrees of freedom is decreased by
one. Conversely, when you deactivate a specification, the
degrees of freedom is increased by one. You can start column
calculations when there are zero degrees of freedom.
Variables such as the duty of the reboiler stream, which is
specified in the Workbook, or feed streams that are not
completely known can offset the current degrees of freedom. If
you feel that the number of active specifications is appropriate
for the current configuration, yet the degrees of freedom is not
zero, check the conditions of the attached streams (material and
energy).You must provide as many specifications as there are
available degrees of freedom. For a simple Absorber there are
no available degrees of freedom, therefore no specifications are
required. Distillation columns with a partial condenser have
three available degrees of freedom.
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Specification Group Buttons
The four buttons which align the bottom of the Specifications
group allow you to manipulate the list of specs. The table below
describes the four buttons.
You can also double-click
in a specification cell to
open its property view.
Button
Action
View
Move to one of the specification cells and click the View
button to display its property view. You can then make any
necessary changes to the specification. Refer to the section
on the Specification Property View for more details.
To change the value of a specification only, move to the
Specified Value cell for the specification you want to
change, and type in the new value.
Add Spec
Opens the Column Specifications menu list, from which you
can select one or multiple (by holding the CTRL key while
selecting) specifications, and then click the Add Spec(s)
button.
The property view for each new spec is shown and its name
is added to the list of existing specifications. Refer to
Section 8.5 - Column Specification Types for a
description of the available specification types.
Update
Inactive
Updates the specified value of each inactive specification
with its current value.
Group Active
Arranges all active specifications together at the top of the
specifications list.
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Specs Page
Remember that the
active specification
values are used as initial
estimates when the
column initially starts to
solve.
Adding and changing Column specifications is straightforward. If
you have created a Column based on one of the templates,
HYSYS already has default specifications in place. The type of
default specification depends on which of the templates you
have chosen (refer to the Default Replaceable Specifications
in Section 8.3.2 - Templates for more details).
Ú·¹«®» èòïç
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ݱ´«³² Ю±°»®¬§ Ê·»©
Column Specifications Group
The following buttons are available:
Button
Action
View
Opens the property view for the highlighted specification.
Alternatively, you can object inspect a spec name and select
View from the menu. Refer to the section on the Specification
Property View for more details.
Add
Opens the Column Specifications menu list, from which you can
select one or multiple (by holding the CTRL key while selecting)
specifications, and then click the Add Spec(s) button.
The property view for each new spec is shown, and its name is
added to the list of existing specifications. Refer to Section 8.5
- Column Specification Types for a description of the
available specification types.
Delete
Removes the highlighted specification from the list.
From the Default Basis drop-down list, you can choose the basis
for the new specifications to be Molar, Mass or Volume.
Available Specification
Types view
The Update Specs from Dynamics button replaces the specified
value of each specification with the current value (lined out
value) obtained from Dynamic mode.
Specification Property View
Figure 8.20 is a typical property view of a specification. In this
view, you can define all the information associated with a
particular specification. Each specification property view has
three tabs:
•
•
•
Parameters
Summary
Spec Type
This example shows a component recovery specification which
requires the stage number, spec value, and phase type when a
Target Type of Stage is chosen.
Specification information is shared between this property view,
and the specification list on both the Monitor and Specs
Summary pages. Altering information in one location
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automatically updates across all other locations.
For example, you can enter the spec value in one location, and
the change is reflected across all other locations.
Ú·¹«®» èòîð
Provide the name
of the
component(s) to
which the
specification
applies.
Provide basic
spec information
on the
Parameters tab.
Specify the stage
to which the
specification
applies.
Specify Liquid or
Vapor phase for
the specification.
The Summary tab is used to specify tolerances, and define
whether the specification is Active or simply an Estimate.
Ú·¹«®» èòîï
Specify the interval for use with a Ranged Spec Value.
Define as either a Fixed or
Ranged Spec. A Ranged Spec
allows the solver to meet a
Spec over an interval
(defined according to the
Upper and Lower spec
values).
Define as either a Primary or
Alternate Spec. An Alternate
Spec can replace another hard
to solve spec in situations
where the column is not
converging.
The Spec Type tab (as shown in Figure 8.21) can be used to
define specifications as either Fixed/Ranged and Primary/
Alternate. By default, all specifications are initially defined as
Fixed and Primary. Advanced solving options available in HYSYS
allow the use of both Alternate and Ranged Spec types.
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The following section further details the advanced solving
options available in HYSYS.
Ranged and Alternate Specs
The reliability of any solution method depends on its ability to
solve a wide group of problems. Some specs like purity,
recovery, and cut point are hard to solve compared to a flow or
reflux ratio spec. The use of Alternate and/or Ranged Specs can
help to solve columns that fail due to difficult specifications.
If the Column solves on
an Alternate or Ranged
Spec, the status bar
reads “Converged Alternate Specs”
highlighted in purple.
Configuration of these advanced solving options are made by
selecting the Advanced Solving Options button located on the
Solver page. The advanced solving options are only available for
use with either the Hysim I/O or Modified I/O solving methods.
Refer to Advanced Solving Options Button in Section 8.4.2
- Parameters Tab for further details.
Fixed/Ranged Specs
When the solver attempts
to meet a Ranged spec,
the Wt. Error becomes
zero when the Current
Value is within the
Ranged interval (as
shown on the Monitor
page).
When an existing spec is
replaced by an alternate
spec during a column
solution, the Current
checkbox becomes
deactivated for the
original (not met) spec
and is activated for the
alternate spec.
The number of active
Alternate specs must
always equal the number
of inactive Alternate
specs.
For a Fixed Spec, HYSYS attempts to solve for a specific value.
For a Ranged Spec, the solver attempts to meet the specified
value, but if the rest of the specifications are not solved after a
set number of iterations, the spec is perturbed within the
interval range provided for the spec until the column converges.
Any column specification can be specified over an interval. A
Ranged Spec requires both lower and upper specification values
to be entered. This option (when enabled), can help solve
columns where some specifications can be varied over an
interval to meet the rest of the specifications.
Primary/Alternate Specs
A Primary Spec must be met for the column solution to
converge. An Alternate Spec can be used to replace an existing
hard to solve specification during a column solution. The solver
first attempts to meet an active Alternate spec value, but if the
rest of the specifications are not solved after a minimum
number of iterations, the active Alternate spec is replaced by an
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inactive Alternate spec. This option (when enabled), can help
solve columns where some specifications can be ignored
(enabling another) to meet the rest of the specifications and
converge the column.
Both Ranged or Alternate Specs must be enabled and
configured using the Advanced Solving Options Button
located on the Solver page of the Parameters tab before they
can be applied during a column solution.
Specification Tolerances for Solver
The Solver Tolerances feature allows you to specify individual
tolerances for your Column specifications. In addition to HYSYS
converging to a solution for the Heat/Spec and Equilibrium
Errors, the individual specification tolerances must also be
satisfied. HYSYS first performs iterations until the Heat/Spec
(inner loop), and Equilibrium (outer loop) errors are within
specified tolerances (described in Section 8.4.2 - Parameters
Tab).
The Column specifications do not have individual tolerances
during this initial iteration process; the specification errors are
“lumped” into the Heat/Spec Error. Once the Heat/Spec and
Equilibrium conditions are met, HYSYS proceeds to compare the
error with the tolerance for each individual specification. If any
of these tolerances are not met, HYSYS iterates through the
Heat/Spec, and Equilibrium loops again to produce another
converged solution. The specification errors and tolerances are
again compared, and the process continues until both the inner/
outer loops and the specification criteria are met.
Specific Solver Tolerances can be provided for each individual
specification. HYSYS calculates two kinds of errors for each
specification:
•
•
an absolute error
a weighted error
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The absolute error is simply the absolute value of the difference
between the calculated and specified values:
Errorabsolute = |Calculated Value - Specified Value|
When the Weighted and
Absolute Errors are less
than their respective
tolerances, an Active
specification has
converged.
(8.3)
The Weighted Error is a function of a particular specification
type. When a specification is active, the convergence algorithm
is trying to meet the Weighted Tolerances (Absolute Tolerances
are only used if no Weighted Tolerances are specified, or the
weighted tolerances are not met).
Therefore, both the weighted and absolute errors must be less
than their respective tolerances for an active specification to
converge. HYSYS provides default values for all specification
tolerances, but any tolerance can be changed. For example, if
you are dealing with ppm levels of crucial components,
composition tolerances can be set tighter (smaller) than the
other specification tolerances. If you delete any tolerances,
HYSYS cannot apply the individual specification criteria to that
specification, and Ignore appears in the tolerance input field.
The specification tolerance feature is simply an “extra” to permit
you to work with individual specifications and change their
tolerances if desired.
Specification Details Group
You can edit any
specification values (in
the Column property
view) shown in blue.
For a highlighted specification in the Column Specifications
group, the following information appears:
•
•
•
•
Spec Name
Convergence Condition. If the weighted and absolute
errors are within their tolerances, the specification has
converged and Yes appears.
Status. You can manipulate the Active and Use As
Estimate checkboxes. Refer to the Monitor Page for
further details concerning the use of these checkboxes.
Dry Flow Basis. Draw specifications are calculated on a
dry flow basis by activating the Dry Flow Basis checkbox.
This option is only available for draw specifications. The
checkbox is greyed out if it does not apply to the
specification chosen.
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•
•
•
èóëï
Spec Type. You can select between Fixed/Ranged and
Primary/Alternate specs. Refer to the section on the
Ranged and Alternate Specs for more details.
Specified and Current Calculated Values.
Weighted/Absolute Tolerance and Calculated Error.
Specs Summary Page
You can edit any
specification details shown
in blue.
You can double-click in a
specification cell to open
its property view. Refer to
the section on the
Specification Property
View for more details.
The Specs Summary page lists all Column specifications
available along with relevant information. This specification
information is shared with the Monitor page and Specs page.
Altering information in one location automatically updates
across all other locations.
Ú·¹«®» èòîî
Subcooling Page
The Subcooling page is
not available for LiquidLiquid Extractor.
The Subcooling page allows you to specify subcooling for
products coming off the condenser of your column. You can
specify the condenser product temperature or the degrees to
subcool. For columns without condensers, such as absorbers,
this page requires no additional information.
Notes Page
For more information,
refer to Section 1.3.2 Notes Page/Tab.
The Notes page provides a text editor where you can record any
comments or information regarding the specific unit operation,
or your simulation case in general.
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8.4.2 Parameters Tab
The Parameters tab shows the column calculation results, and is
used to define some basic parameters for the Column solution.
The Parameters tab consists of six pages:
•
•
•
•
•
•
Profiles
Estimates
Efficiencies
Solver
2/3 Phase
Amines
Profiles Page
The Profiles page shows the column pressure profile, and
provides estimates for the temperature, net liquid and net
vapour flow for each stage of the column. You can specify tray
estimates in the Temperature column, Net Liquid column and
Net Vapour column, or view the values calculated by HYSYS.
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The graph in Figure 8.23 depicts the pressure profile across the
column.
Ú·¹«®» èòîí
At least one iteration
must have occurred for
HYSYS to convert
between bases. In this
way, values for the
compositions on each
tray are available.
Use the radio buttons in the Flow Basis group to select the flow
type you want displayed in the Net Liquid and Net Vapour
columns. The Flow Basis group contains three radio buttons:
•
•
•
Molar
Mass
Volume
The buttons in the Steady State Profiles group are defined as
follows:
Button
Function
Update from
Solution
Transfers the current values that HYSYS has
calculated for the trays into the appropriate cells.
Estimates that have been Locked (displayed in blue)
are not updated. The Column Profiles page on the
Performance tab allows you to view all the current
values.
Clear
Deletes values for the selected tray.
Clear All Trays
Deletes values for all trays.
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Button
Function
Lock
Changes all red values (unlocked estimates, current
values, interpolated values) to blue (locked), which
means that they cannot be overwritten by current
values when the Update from Solution button is
clicked.
Unlock
Changes all blue values (locked) to red (unlocked).
Unlocked values are overwritten by current values
when the Update from Solution button is clicked.
Stream Estimates
Displays the temperature, molar flow, and enthalpy of
all streams attached to the column operation.
Although the Profiles page is mainly used for steady state
simulation, it does contain vital information for running a
column in dynamics. One of the most important aspects of
running a column in dynamics is the pressure profile. While a
steady state column can run with zero pressure drop across a
tray section, the dynamic column requires a pressure drop. In
dynamics, an initial pressure profile is required before the
column can run. This profile can be from the steady state model
or can be added in dynamics. If a new tray section is created in
Dynamic mode, the pressure profile can be obtained from the
streams if not directly specified. In either case, the closer the
initial pressure profile is to the one calculated while running in
dynamics, the fewer problems you encounter.
Estimates Page
To see the initial
estimates generated by
HYSYS, click the View
Initial Estimates button on
the Monitor page.
The Estimates page allows you to view and specify composition
estimates.
When you specify estimates on stages that are not adjacent to
each other, HYSYS cannot interpolate values for intermediate
stages until the solution algorithm begins.
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ݱ´«³²
Estimates are NOT
required for column
convergence.
èóëë
You can specify tray by tray component composition estimates
for the vapour phase or liquid phase. Each composition estimate
is on a mole fraction basis, so values must be between 0 and 1.
Ú·¹«®» èòîì
HYSYS interpolates intermediate tray component values when
you specify compositions for non-adjacent trays. The
interpolation is on a log basis. Unlike the temperature
estimates, the interpolation for the compositions does not wait
for the algorithm to begin. Select either the Vap or Liq radio
button in the Phase group to display the table for the vapour or
liquid phase, respectively.
The Composition Estimates group has the following buttons:
HYSYS does not ask for
confirmation before
deleting estimates.
Button
Action
Clear Tray
Deletes all values, including user specified (blue) and
HYSYS generated (red), for the selected tray.
Clear All Trays
Deletes all values for all trays.
Update
Transfers the current values which HYSYS has calculated
for tray compositions into the appropriate cells. Estimates
that have been locked (shown in blue) cannot be
updated.
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Button
Action
Restore
Removes all HYSYS updated values from the table, and
replaces them with your estimates and their
corresponding interpolated values. Any cells that did not
contain estimates or interpolated values are shown as
<empty>. This button essentially reverses the effect of
the Update button.
If you had entered some estimate values, click the Unlock
Estimates button, and click the Update button. All the
values in the table appear in red. You can restore your
estimated values by clicking the Restore button.
Normalize
Trays
Normalizes the values on a tray so that the total of the
composition fractions equals 1. HYSYS ignores <empty>
cells, and normalizes the compositions on a tray provided
that there is at least one cell containing a value.
Lock Estimates
Changes all red values (unlocked estimates, current
values, interpolated values) to blue (locked), which
means that they cannot be overwritten by current values
when the Update button is clicked.
Unlock
Estimates
Changes all blue values (locked) to red (unlocked).
Unlocked values are overwritten by current values when
the Update button is clicked.
Efficiencies Page
Fractional efficiencies
cannot be given for the
condenser or reboiler
stages, nor should they be
set for feed or draw
stages.
The Efficiencies page allows you to specify Column stage
efficiencies on an overall or component-specific basis.
Efficiencies for a single stage or a section of stages can easily be
specified.
The functionality of this page is slightly different when
working with the Amines Property Package. Refer to the
section on Special Case - Amines Property Package for more
information.
HYSYS uses a modified Murphree stage efficiency. All values are
initially set to 1.0, which is consistent with the assumption of
ideal equilibrium or theoretical stages. If this assumption is not
valid for your column, you have the option of specifying the
number of actual stages, and changing the efficiencies for one
or more stages.
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To specify an efficiency to
multiple cells, highlight
the desired cells, enter a
value in the Eff. MultiSpec field, and click the
Specify button.
The data table on the Efficiency page gives a stage-by-stage
efficiency summary.
The efficiencies are fractional, i.e., an efficiency of 1.0
corresponds to 100% efficiency.
Overall stage efficiencies can be specified by selecting the
Overall radio button in the Efficiency Type group, and entering
values in the appropriate cells.
Component-specific efficiencies can be specified by selecting the
Component radio button, and entering values in the appropriate
cells.
Special Case - Amines Property Package
When solving a column for a case using the Amines Property
Package, HYSYS always uses stage efficiencies for H2S and CO2
component calculations. If these are not specified on the
Efficiencies page of the Column property view, HYSYS calculates
values based on the tray dimensions. Tray dimensions can be
specified on the Amines page of the Parameters tab. If column
dimensions are not specified, HYSYS uses its default tray values
to determine the efficiency values.
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The Reset H2S, CO2
button, and the Transpose
checkbox are available
only if the Efficiency Type
is set to Component.
ݱ´«³² Ю±°»®¬§ Ê·»©
If you specify values for the CO2 and H2S efficiencies, these are
the values that HYSYS uses to solve the column. If you want to
solve the column again using efficiencies generated by HYSYS,
click the Reset H2S, CO2 button, which is available on this page.
Run the column again, and HYSYS calculates and displays the
new values for the efficiencies.
Activate the Transpose checkbox to change the component
efficiency matrix so that the rows list components and the
columns list the stages.
For more information on the Amines Property Packages, refer to
Appendix C - Amines Property Package of the HYSYS
Simulation Basis guide.
Solver Page
You can manipulate how the column solves the column variables
on the Solver page.
Ú·¹«®» èòîê
The Solving Method
Group, Acceleration
Group, and Damping
Group will have different
information displayed
according to the options
selected within the group.
Refer to the
corresponding sections
for more information.
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Solving Options Group
Specify your preferences for the column solving behaviour in the
Solving Options group.
Ú·¹«®» èòîé
Maximum Number of Iterations
The Column convergence process terminates if the maximum
number of iterations is reached. The default value is 10000, and
applies to the outer iterations. If you are using Newton's
method, and the inner loop does not converge within 50
iterations, the convergence process terminates.
Equilibrium and Heat/Spec Tolerances
Convergence tolerances are pre-set to very tight values, thus
ensuring that regardless of the starting estimates (if provided)
for column temperatures, flow rates, and compositions, HYSYS
always converges to the same solution. However, you have the
option of changing these two values if you want. Default values
are:
•
•
Inner Loop. Heat and Spec Error: 5.000e-04
Outer Loop. Equilibrium Error: 1.000e-05
Because the default values are already very small, you should
use caution in making them any smaller. You should not make
these tolerances looser (larger) for preliminary work to reduce
computer time. The time savings are usually minor, if any. Also,
if the column is in a recycle or adjust loop, this could cause
difficulty for the loop convergence.
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Equilibrium Error
The value of the equilibrium error printed during the column
iterations represents the error in the calculated vapour phase
mole fractions. The error over each stage is calculated as one
minus the sum of the component vapour phase mole fractions.
This value is then squared; the total equilibrium error is the sum
of the squared values. The total equilibrium error must be less
than 0.00001 to be considered a converged column.
Heat and Spec Error
The heat and specification error is the sum of the absolute
values of the heat error and the specification error, summed
over each stage in the tower.
This total value is divided by the number of inner loop
equations. The heat error contribution is the heat flow
imbalance on each tray divided by the total average heat flow
through the stage.
The specification error contribution is the sum of each individual
specification error divided by an appropriate normalization
factor.
For component(s) flow, the normalization factor is the actual
component(s) flow; for composition, it is the actual mole
fraction; for vapour pressure and temperature it is a value of
5000; etc. The total sum of heat and spec errors must be less
than 0.0005 to be considered a converged column.
The allowed equilibrium error and heat and spec error are
tighter than in most programs, but this is necessary to avoid
meta-stable solutions, and to ensure satisfactory column heat
and material balances.
Save Solution as Initial Estimate
This option is on by default, and it saves converged solutions as
estimates for the next solution.
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Super Critical Handling Model
Supercritical phase behaviour occurs when one or more Column
stages are operating above the critical point of one or more
components. During the convergence process, supercritical
behaviour can be encountered on one or more stages in the
Column. If HYSYS encounters supercritical phase behaviour,
appropriate messages appear in the Trace Window.
HYSYS cannot use the equation of state or activity model in the
supercritical range, so an alternate method must be used. You
can specify which method you want HYSYS to use to model the
phase behaviour. There are three choices for supercritical
calculations:
Refer to Section 1.3 Object Status Window/
Trace Window in the
HYSYS User Guide for
details on the Trace
Window.
Model
Description
Simple K
The default method. HYSYS calculates K-values for the
components based on the vapour pressure model being
used. Using this method, the K-values which are
calculated are ideal K-values.
Decrease
Pressure
When supercritical conditions are encountered, HYSYS
reduces the pressure on all trays by an internally
determined factor, which can be seen in the Trace
Window when the Verbose option is used. This factor is
gradually decreased until supercritical conditions no
longer exist on any tray, at which point, the pressure in
the column is gradually increased to your specified
pressure. If supercritical conditions are encountered
during the pressure increase, the pressure is once
again reduced and the process is repeated.
Adjacent Tray
When supercritical conditions are encountered on a
tray, HYSYS searches for the closest tray above which
does not have supercritical behaviour. The nonsupercritical conditions are substituted in the phase
calculations for the tray with supercritical conditions.
Trace Level
The Trace Level defines the level of detail for messages
displayed in the Trace Window, and can be set to Low, Medium,
or High. The default is Low.
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Initialize from Ideal KŽs
When this checkbox is checked, HYSYS initializes its column
solution using ideal K values which are calculated from vapour
pressure correlations. The ideal K-value option, which is also
used by HYSIM, increases the compatibility between HYSIM and
HYSYS.
By default, the Initialize from Ideal K's checkbox is deactivated.
HYSYS uses specified composition estimates or generates
estimates to rigorously calculate K-values.
Two Liquids Check Based on
This option allows you to specify a check for two liquid phases in
the column. The check is based on one of the following criteria:
•
•
•
No 2 Liq Check. Disables the two liquid check.
Tray Liquid Fluid. The calculation is based on the
composition of the liquid in the column.
Tray Total Fluid. The calculation is based on the overall
composition of the fluid in the column.
Tighten Water Tolerance
When this checkbox is checked, HYSYS increases the
contribution of the water balance error to the overall balance
error in order to solve columns with water more accurately. The
default setting for this checkbox is unchecked.
Solving Method Group
The Solving Method drop-down list allows you to select the
column solution method.
Ú·¹«®» èòîè
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The display field, which appears below the drop-down list,
provides explanations for each method, and is restated here:
Only a simple Heat
Exchanger Model
(Calculated from
Column) is available in
the Column subflowsheet. The Simple
Rating, End-Point, and
Weighted models are
not available.
Method
Explanation
HYSIM InsideOut
General purpose method, which is good for most
problems.
Modified HYSIM
Inside-Out
General purpose method, which allows mixer, tee, and
heat exchangers inside the column sub-flowsheet.
Newton Raphson
Inside-Out
General purpose method, which allows liquid-phase
kinetic reactions inside the Column sub-flowsheet.
Sparse
Continuation
Solver
An equation based solver. It supports two liquid phases
on the trays, and its main use is for solving highly nonideal chemical systems and reactive distillation.
Simultaneous
Correction
Simultaneous method using dogleg methods. Good for
chemical systems. This method also supports reactive
distillation.
OLI Solver
Only used to calculate the column unit operation in an
electrolyte system.
Inside-Out
With the “inside-out” based algorithms, simple equilibrium and
enthalpy models are used in the inner loop to solve the overall
component and heat balances as well as any specifications. The
outer loop updates the simple thermodynamic models with
rigorous model calculations.
Open the Trace Window
at the bottom of the
HYSYS Desktop to view
messages regarding the
convergence of the
column.
General Features of the Solving Methods
The following table displays the general features of all the
HYSYS column solving methods.
HYSIM
I/O
Modified
HYSIM I/O
Newton
Raphson
I/O
Sparse
Continuation
Simultaneous
Correction
OLI
Component
Efficiency
Handling
Yes
Yes
No
Yes
No
Yes
Total Efficiency
Handling
Yes
Yes
No
Yes
No
Yes
Additional Side
Draw
Yes
Yes
Yes
Yes
Yes
Yes
Vapour Bypass
Yes
Yes
No
Yes
No
No
Pump Arounds
Yes
Yes
No
Yes
No
Yes
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HYSIM
I/O
Modified
HYSIM I/O
Newton
Raphson
I/O
Sparse
Continuation
Simultaneous
Correction
OLI
Side Stripper
Yes
Yes
No
Yes
No
No
Side Rectifier
Yes
Yes
No
Yes
No
No
Mixer & Tee in
Sub-flowsheet
No
Yes
No
No
No
No
Three Phase
Yes
(water
draw)
Yes (water
draw)
No
Yes
No
Yes
Chemical
(reactive)
No
No
Yes
Yes
Yes
Inter
nal
reacti
ons
Acceleration Group
By default, the Accelerate
K value & H Model
Parameters checkbox is
deactivated.
When activated, the Accelerate K value & H Model Parameters
checkbox displays two fields, which relate to an acceleration
program called the Dominant Eigenvalue Method (DEM).
Ú·¹«®» èòîç
The DEM is a numerical solution program, which accelerates
convergence of the simple model K values and enthalpy
parameters. It is similar to the Wegstein accelerator, with the
main difference being that the DEM considers all interactions
between the variables being accelerated. The DEM is applied
independently to each stage of the column.
Use the acceleration option if you find that the equilibrium
error is decreasing slowly during convergence. This should
help to speed up convergence. Notice that the Accelerate K
value & H Model Parameters checkbox should NOT be
activated for AZEOTROPIC columns, as convergence tends to
be impeded.
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The listed DEM parameters include:
Parameter
Description
Acceleration
Mode
Select either Conservative or Aggressive. With the
Conservative approach, smaller steps are taken in the
iterative procedure, thus decreasing the chance of a
bad step.
Maximum
Iterations
Queued
Allows you to choose the number of data points from
previous iterations that the accelerator program uses
to obtain a solution.
Damping Group
Choose the Damping method by selecting either the Fixed or
Adaptive radio button.
Ú·¹«®» èòíð
Fixed Damping
If you select the Fixed radio button, you can specify the
damping factor. The damping factor controls the step size used
in the outer loop when updating the simple thermodynamic
models used in the inner loop. For the vast majority of
hydrocarbon-oriented towers, the default value of 1.0 is
appropriate, which permits a full adjustment step. However,
should you encounter a tower where the heat and specification
errors become quite small, but the equilibrium errors diverge or
oscillate and converge very slowly, try reducing the damping
factor to a value between 0.3 and 0.9. Alternatively, you could
enable Adaptive Damping, allowing HYSYS to automatically
adjust this factor.
Changing the damping factor has an effect on problems
where the heat and spec error does not converge.
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There are certain types of columns, which definitely require a
special damping factor.
Use the following table as a guideline in setting up the initial
value.
The Azeotropic checkbox
on the Solver page of the
Parameters tab must be
activated for an azeotropic
column to converge.
Type of Column
Damping Factor
All hydrocarbon columns from demethanizers to
debutanizers to crude distillation units
1.0
Non-hydrocarbon columns including air separation,
nitrogen rejection
1.0
Most petrochemical columns including C2= and
C3= splitters, BTX columns
1.0
Amines absorber
1.0
Amines regenerator, TEG strippers, sour water
strippers
0.25 to 0.50
Highly non-ideal chemical columns without
azeotropes
0.25 to 0.50
Highly non-ideal chemical columns with azeotropes
0.50 to -1.0*
As shown in the table above, an azeotropic column requires the
azeotrope checkbox to be enabled. There are two ways to
indicate to HYSYS that you are simulating an azeotropic column:
•
Enter a negative damping factor, and HYSYS
automatically activates the Azeotropic checkbox.
The absolute value of the damping factor is always
displayed.
•
Enter a positive value for the damping factor, and
activate the Azeotropic checkbox.
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Adaptive Damping
If you select the Adaptive radio button, the Damping matrix
displays three fields. HYSYS updates the damping factor as the
column solution is calculated, depending on the Damping Period
and convergence behaviour.
Damping Period
Description
Initial Damping Factor
Specifies the starting point for adaptive
damping.
Adaptive Damping Period
The default Adaptive Damping Period is ten.
In this case, after the tenth iteration, HYSYS
looks at the last ten errors to see how many
times the error increased rather than
decreased. If the error increased more than
the acceptable tolerance, this is an indication
that the convergence is likely cycling, and the
current damping factor is then multiplied by
0.7. Every ten iterations, the same analysis is
done to see if the damping factor should be
further decreased. Alternatively, if the error
increased only once in the last period, the
damping factor is increased to allow for
quicker convergence.
Reset Initial Damping
Factor
If this checkbox is activated, the current
damping factor is used the next time the
column is solved. If it is deactivated, the
damping factor before adaptive damping was
applied is used.
Initialization Algorithm Radio Buttons
There are two types of method for the initialization algorithm
calculation:
•
•
Standard Initialization radio button uses the tradition
initialization algorithm in Hysys.
Program Generates Estimations radio button uses a
new functionality that handles the cases where the
traditional initialization does not.
Ú·¹«®» èòíï
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The following list situations when the Program Generates
Estimations (PGE) initialization method is used:
•
•
The PGE initialization handles systems with more than 25
components while the standard initialization does not
handle systems with more than 25 components without
the user’s initial estimation.
When column does not converge with the standard
initialization method (default), switching to PEG may
converge the column. The new algorithm eliminates the
discrepancy in the temperature and component
estimates, which may exist in standard initialization.
Initial Estimate Generator Parameters
You can enable the initial estimate generator (IEG) by activating
the Dynamic Integration for IEG checkbox. The IEG then
performs iterative flash calculations (NRSolver, PV, and PH) to
provide initial estimates for the temperature and composition
profiles. No user estimates are required when the Dynamic
Integration for IEG checkbox is activated.
Ú·¹«®» èòíî
Click the Dynamic Estimates Integrator button, and the Col
Dynamic Estimates view appears as shown in the figure below.
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Col Dynamic Estimates View
The Col Dynamic Estimates view allows you to further define the
dynamic estimates parameters.
Ú·¹«®» èòíí
You can set parameters for the time period over which the
dynamic estimates are calculated, as well as set the calculation
tolerance. An activated Active checkbox indicates that the
Dynamic Integration for IEG is on. Select either the Adiabatic or
Isothermal radio button to set the dynamic initialization flash
type.
If you want to generate the dynamic estimates without running
the column, you can do so from this view by clicking the Start
button. If you want to stop calculations before the specified time
has elapsed, click the Stop button. You do not have to manually
click the Start button to generate the estimates; if the Dynamic
Integration for IEG option is active, HYSYS generates them
automatically whenever the column is running.
If you are running
simulation with an
iterative solving
procedure where the
column has to be
calculated several times,
it is a good idea to select
this option to save on
calculation time.
The Shortcut Mode checkbox allows you to bypass this step once
a set of estimates is generated, that is, once the column has
converged.
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Advanced Solving Options Button
When you click the Advanced Solving Options button, the
Advanced Solving Options property view appears.
Ú·¹«®» èòíì
If the Column
converges on an
Alternate or Ranged
Spec, the status bar
reads “Converged Alternate Specs”
highlighted in purple.
The “use” checkboxes must
be selected in order to
enable a particular option.
These checkboxes are only
enabled if the corresponding
spec type exists.
All the Alternate active specs
can be replaced on an
individual spec basis or all
specs simultaneously. The
alternative (active) spec
with the larger error is
replaced with an alternative
inactive spec with minimum
error.
The order in which the solving options are executed is based on the
priority.
On the Advanced Solving Options property view, each solving
option (i.e., Alternate, Ranged, and Autoreset) has a solving
priority and also a checkbox option. To use a particular solving
option, you have to activate the corresponding checkbox. You
must also specify the priority of the solving method. This is the
order in which the solving options are executed (either first,
second or third).
When a column is in
recycle, by default, the
solver switches to the
original set of specs after
each recycle iteration or
the next time the column
solves.
Advanced solving options cannot be used until the minimum
number of iterations are met. If the column is not solved after
the minimum number of iterations, the solver switches to an
advanced solving option according to the solving priority. This
process is repeated until all the solving options have been
attempted or the column converges.
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2/3 Phase Page
This page is not available
for Liquid-Liquid
Extractor.
The 2/3 Phase page is relevant only when you are working with
three-phase distillation. On this page, you can check for the
presence of two liquid phases on each stage of your column.
Ú·¹«®» èòíë
The Liquid Phase Detection table lists the liquid molar flow rates
on each tray of the tray section, including the reboiler and the
condenser.
By default, HYSYS selects
Pure for all hydrocarbon,
and Rigorous for all
chemical based
distillations. This default
selection criteria is based
on the type of fluid
package used but you
can always change it.
In order for HYSYS to check for two liquid phases on any given
stage, activate the checkbox in the Check column. If a second
liquid phase is calculated, this is indicated in the Detected
column, and by a calculated flowrate value in the L2Rate
column. The buttons in the Liquid Phase Detection group serve
as aids in selecting and de-selecting the trays you want to
check.
The 2nd Liquid Type group allows you to specify the type of
calculation HYSYS performs when checking for a second liquid
phase. When the Pure radio button is selected, HYSYS checks
only for pure water as the second phase. This helps save
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calculation time when working with complex hydrocarbon
systems. When you want a more rigorous calculation, select the
Rigorous radio button.
Checking for liquid phases in a three phase distillation tower
greatly increases the solution time. Typically, checking the
top few stages only, provides reasonable results.
Auto Water Draws Button
The Auto Water Draws
facility is available for IO
and MIO solvers.
The Auto Water Draws (AWD) option allows for the automatic
adding and removing of total aqueous phase draws depending
on the conditions in the converged column.
The Two Liquids Check
Based on drop-down list
is located in the
Parameters tab of the
Solver page in the Solving
Options group.
AWD updating process is based on direct check of stage fluid
phases. The direct check follows the Two Liquids Check Based on
control criteria for detecting the aqueous phase. AWD mode is
not available if No 2 Liq Check option is selected.
To manipulate the AWD option, click the Auto Water Draws
button to open the Auto Water Draws view.
Ú·¹«®» èòíê
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The Auto Water Draws
button is available in
both column subflowsheet and main
flowsheet.
èóéí
The Auto Water Draws view contains the following objects:
Object
Description
On
Check this checkbox to activate the Auto Water Draws
mode.
Threshold
The threshold value allows variation of the condition
for 2nd liquid phase. The default value in this cell is
0.001 (same as for Two Liquids Check based on
control).
If you delete the value in this cell, the threshold is set
to minimum possible value.
The All option results
typically in multiple
water draws with small
flows, and the From Top
or From Bottom option
results typically in fewer
water draws.
Keep draws
If this checkbox is checked, the added draws are not
removed.
Preserve
estimates
If this checkbox is checked, the converged values are
preserved as estimates for the next column run.
Reset
If this checkbox is checked, the column Reset option is
performed before each column run.
Strategy
There are three options of strategy to select from in
the Strategy group:
• All. All required changes in water draw
configuration are done simultaneously.
• From Top.Updates on the topmost stage from
required is performed.
• From Bottom. Updates on the bottommost stage
from required is performed.
To AWD
All existing water draws are converted to AWDs.
From AWD
Converts all AWDs to regular draws.
Restore
Restores the last successful (i.e., column equation
were solved) AWD configuration.
Delete
Deletes all AWDs.
Two more columns are added in the table on the 2/3 Phase page
when in Auto Water Draws mode. These two columns are called
AWD and No AWD
•
The Amines Property
Package is an optional
property package that
must be purchased in
addition to the base
version of HYSYS.
For more information on
the Amines Property
Package, refer to the
Appendix C - Amines
Property Package in
the HYSYS Simulation
Basis guide.
•
Set AWD mode for attached water draw by checking the
checkboxes under the AWD column.
If the checkbox in the No AWD column is checked, no
AWD will be attached to corresponding stage.
Amines Page
The Amines page appears on the Parameters tab only when
working with the Amines Property Package. There are two
groups on the Amine page:
•
•
Tray Section Dimensions for Amine Package
Approach to Equilibrium Results
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Tray Section Dimensions for Amine Package
When solving the column using the Amines package, HYSYS
always takes into account the tray efficiencies, which can either
be user-specified, on the Efficiencies page, or calculated by
HYSYS. Calculated efficiency values are based on the tray
dimensions specified. The Amines page lists the tray section
dimensions of your column, where you can specify these values
that are used to determine the tray efficiencies in the Tray
Section Dimensions for Amine Package group.
The list includes:
•
•
•
•
•
Tray Section
Weir Height
Weir Length
Tray Volume
Tray Diameter
If tray dimensions are not specified, HYSYS uses the default tray
dimensions to determine the efficiency values.
Approach to Equilibrium Results
Approach to Equilibrium values are used for the design,
operation, troubleshooting, and de-bottlenecking for the
absorption and regeneration columns in an amine plant. When
you are modeling an amine column in HYSYS, you can calculate
the Approach to Equilibrium values after the column converges.
With this capability, you can adjust the flowrate of amine to
achieve a certain Approach to Equilibrium value recommended
by literature or in-house experts for the amine column. The
extension is compatible with all of the major amine and
mixtures of amines (i.e., MEA, DEA, TEA, DGA, DIPA, MDEA, and
any mixtures of these amines).
The extension can only be used on a pre-converged amine
treating unit simulation with the Amine Property Package.
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The Approach to Equilibrium extension calculates the Approach
to Equilibrium value of rich amine from the bottom of the
absorber column in two methods:
•
•
Partial Pressure
Amine Molar Loading
Method 1 Partial Pressure
In this method, the Approach to Equilibrium is defined as the
partial pressure of the acid gas in the rich amine stream exiting
the absorber relative to the partial pressure of the acid gas in
the main feed gas stream entering the absorber.
The Approach to Equilibrium calculation are as follows:
H2S ã 100%
ppH2S rich amine exiting the absorber
óóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóó
ó
ppH2S feed gas entering the absorber
(8.4)
CO2 ã 100%
ppCO2 rich amine exiting the absorber
óóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóó
ppCO2 feed gas entering the absorber
(8.5)
The Approach to Equilibrium results based on H2S and CO2 are
expressed in percentages. When both H2S and CO2 are present,
the highest Approach to Equilibrium percentage is usually
reported, although both values should be reported.
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Amine Molar Loading
Amine Molar Loading is defined as the loading of the rich amine
solution leaving the absorber divided by the equilibrium amine
loading, assuming that the amine is at equilibrium with the feed
gas and is at the same temperature as the rich amine leaving
the absorber. The temperature of the rich amine and the amine
in equilibrium with the feed gas are the same. The result is
expressed as a percentage as follows:
Approach
to Equilibrium
Rich amine loading
ã 100%
mole of amine
in mole AG
óóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóó
Equilibrium loading
in mole AG
(8.6)
mole of amine
In general, the Approach to Equilibrium value calculated by the
Partial Pressure method is greater than the one calculated by
the Amine Molar Loading method.
8.4.3 Side Ops Tab
The Side Ops tab is not
available in the LiquidLiquid Extractor.
Some solver methods
do not allow side ops.
Refer to the table in the
section on the General
Features of the
Solving Methods for
more information.
Side strippers, side rectifiers, pump arounds, and vapour
bypasses can be added to the Column from this tab. To install
any of these Side Operations, click the Side Ops Input Expert
button or on the appropriate Side Ops page, click the Add
button.
•
•
If you are using the Side Ops Input Expert, a wizard
guides you through the entire procedure of adding a side
operation to your column.
If you are using the Add button, complete the form which
appears, and then click the Install button. Specifications
that are created when you add a side operation are
automatically added to the Monitor page and Specs page.
For instance, when you add a side stripper, product draw
and boilup ratio specs are added. As well, all appropriate
operations are added; for example, with the side stripper
(reboiled configuration), a side stripper tray section and
reboiler are installed in the Column sub-flowsheet.
You can view or delete any Side Operation simply by positioning
the cursor in the same line as the Operation, and clicking the
View or Delete button.
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If you are specifying Side Operations while in the Main
simulation environment, make sure that the Solver is Active.
Otherwise, HYSYS cannot register your changes.
Side Strippers Page
You can install a reboiled or steam-stripped side stripper on this
page. You must specify the number of stages, the liquid draw
stage (from the Main Column), the vapour return stage (to the
Main Column), and the product stream and flow rate (on a
molar, mass or volume basis).
For the reboiled configuration, you must specify the boilup ratio,
which is the ratio of the vapour to the liquid leaving the reboiler.
For the steam-stripped configuration it is necessary to specify
the steam feed.
The property view of the side stripper is shown in the figure
below.
Ú·¹«®» èòíé
To change the side
stripper draw and return
stages from the Column
property view, the Solver
must be Active in the
Main simulation
environment.
When you click the Install button, a side stripper tray section is
installed, as well as a reboiler if you selected the Reboiled
configuration.
By default, the tray section is named SS1, the reboiler is named
SS1_Reb, and the reboiler duty stream is named SS1_Energy.
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As you add additional Side strippers, the index increases (e.g., SS2, SS3, etc.).
Side Rectifiers Page
As with the side stripper, you must specify the number of
stages, the liquid draw stage, and the vapour return stage.
Ú·¹«®» èòíè
The vapour and liquid product rates, as well as the reflux ratio
are also required. These specifications are added to the Monitor
page and Specs page of the Column property view.
When you install the side rectifier, a side rectifier tray section
and partial condenser are added. By default, the tray section is
named SR_1, the condenser is named SR_1_Cond, and the
condenser duty stream is named SR_1_Energy.
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Pump Arounds Page
When you install the pump around, a Cooler is also installed.
The default pump around specifications are the pump around
rate and temperature drop. These are added on the Monitor
page and Specs page of the Column property view.
When installing a Pump
Around, it is necessary to
specify the draw stage,
return stage, molar flow,
and duty.
After you click the Install button, the Pump Around property
view changes significantly, as shown in the figure below,
allowing you to change pump around specifications, and view
pump around calculated information.
Ú·¹«®» èòíç
Vap Bypasses Page
As with the Pump Around, it is necessary to specify the draw
and return stage, as well as the molar flow and duty for the
vapour bypass. When you install the vapour bypass, the draw
temperature and flowrate appear on the vapour bypass view.
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The vapour bypass flowrate is automatically added as a
specification. The figure below shows the vapour bypass view
once the side operation has been installed.
Ú·¹«®» èòìð
Side Draws Page
The Side Draws page allows you to view, and edit information
regarding the side draw streams in the column. The following is
the information included on this page:
•
•
•
•
•
•
Draw Stream
Draw Stage
Type (Vapour, Liquid or Water)
Mole Flow
Mass Flow
Volume Flow
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8.4.4 Rating Tab
The Rating tab has several pages, which are described in the
table below.
Page
Description
Tray
Sections
Provides information regarding tray sizing. On this page,
you can specify the following:
• Tray Section (Name)
• Uniform Section. When checked all tray stages have
the same physical setup (diameter, tray type, etc.).
• Internal Type (tray type)
• Tray Diameter
• Tray Space
• Tray Volume
• Disable Heat Loss Calcs
• Heat Model
• Rating Calculations
• Hold Up (ft3). If you delete the weir height, you can
then enter the hold up value, and the weir height is
back-calculated.
• Weeping Factor. The value is used to adjust the
weeping in dynamic mode for low pressure drops.
Vessels
Provides information regarding vessel sizing. On this page,
you can specify the following:
• Vessel (Name)
• Diameter
• Length
• Volume
• Orientation
• Vessel has a Boot
• Boot Diameter
• Boot Length
• Hold Up (ft3)
Equipment
Contains a list of Other Equipment in the Column flowsheet.
Pressure
Drop
Contains information regarding pressure drop across the
column. On this page you can specify the following
information:
• Pressure Tolerance
• Pressure Drop Tolerance
• Damping Factor
• Maximum Pressure Iterations
• Top and Bottom column pressures
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Tray Sections Page
The required size
information for the tray
section can be calculated
using the Tray Sizing
utility.
The Tray Sections page contains all the required information for
correctly sizing the column tray sections. The tray section
diameter, weir length, weir height, and the tray spacing are
required for an accurate and stable dynamic simulation. You
must specify all the information on this page. With the exception
of the tray volume, no other calculations are performed on this
page.
Ú·¹«®» èòìï
For multipass trays, simply enter the column diameter and the
appropriate total weir length.
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Vessels Page
The Vessels page contains the necessary sizing information for
the different vessels in the column sub-flowsheet.
Ú·¹«®» èòìî
Equipment Page
This page is not
available in the LiquidLiquid Extractor.
The Equipment page contains a list of all the additional
equipment, which is part of the column sub-flowsheet. The list
does not contain equipment, which is part of the original
template. Any extra equipment, which is added to the subflowsheet (pump arounds, side strippers, etc.) is listed here.
Double-clicking on the equipment name opens its property view
on the Rating tab.
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Pressure Drop Page
This page is not
available in the LiquidLiquid Extractor.
The Pressure Drop page allows you to specify the pressure drop
across individual trays in the tray section. The pressure at each
individual stage can also be specified. The Pressure Solving
Options group allows you to adjust the following parameters:
•
•
•
•
Pressure Tolerance
Pressure Drop Tolerance
Damping Factor
Maximum Pressure Iterations
Ú·¹«®» èòìí
8.4.5 Worksheet Tab
The Column Environment
also has its own
Workbook.
The Worksheet tab contains a summary of the information
contained in the stream property view for all the streams
attached to the unit operation. The PF Specs page contains a
summary of the stream property view’s Dynamics tab. Refer to
Section 1.3.1 - Worksheet Tab for more information.
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8.4.6 Performance Tab
You can view the results
in molar, mass or liquid
volume, by selecting the
appropriate basis radio
button.
On the Performance tab, you can view the results of a converged
column on the Summary page, Column Profiles page, and
Feeds/Products page. You can also view the graphical and
tabular presentation of the column profile on the Plots page.
Summary Page
The Summary page gives a tabular summary of the feed and
product stream compositions, flows or the % recovery of the
components in the product streams. When you select the
Recovery radio button, the feed table displays the feed stream
flowrate.
Ú·¹«®» èòìì
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Column Profiles Page
The liquid and vapour
flows are net flows for
each stage.
The Column Profiles page gives a tabular summary of Column
stage temperatures, pressures, flows, and duties.
Ú·¹«®» èòìë
The Heat Loss column is
empty unless you select a
heat flow model in the
column sub-flowsheet of
Main TS view on the
Rating tab.
You can change the basis for which the data appears by
selecting the appropriate radio button from the Basis group.
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Feeds/Products Page
The Feeds/Products page gives a tabular summary of feed and
product streams tray entry/exit, temperatures, pressures, flows,
and duties.
Ú·¹«®» èòìê
You can split a feed
stream into its phase
components either on the
Setup page of the
Flowsheet tab in the
column view or on the
Options page of the
Simulation tab in the
Session Preference view.
You can change the basis of the data by selecting the
appropriate radio button from the Basis group. For the feeds and
draw Streams, the VF column to the right of each flow value
indicates whether the flow is vapour (V) or liquid (L). If the feed
has been split, a star (*) follows the phase designation. If there
is a duty stream on a stage, “Energy” appears in the Type
column. The direction of the energy stream is indicated by the
sign of the duty.
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Plots Page
On the Plots page, you can view various column profiles or assay
curves in a graphical or tabular format.
Ú·¹«®» èòìé
Activate the Live Updates checkbox to update the profiles with
every pass of the solver (i.e., a dynamic update). It is
deactivated by default, and performance of the column can be a
bit slower if the checkbox is on and a profile is open.
Tray by Tray Properties Group
To view a column profile, follow this generalized procedure:
Electrolyte Properties are
only available for cases
with an electrolyte
system.
1. Select a profile from the list in the Tray by Tray Properties
group. The choices include: Temperature, Pressure, Flow,
Transport Properties, Composition, K Value, Light/Heavy Key,
and Electrolyte Properties.
2. In the Column Tray Ranges group, select the appropriate
radio button:
Radio Button
All
Action
Displays the selected profile for all trays connected to the
column (i.e., main tray section, side strippers, condenser,
reboiler, etc.).
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The main tray section
along with the condenser
and reboiler are
considered one section,
as is each side stripper.
Plots and tables are
expandible views that
can remain open without
the column property
view.
To make changes to the
plot, right-click in the
plot area, and select
Graph Control from the
menu. Refer to Section
10.4 - Graph Control
in the HYSYS User
Guide.
èóèç
Radio Button
Action
Single Tower
From the drop-down list, select a tray section.
From/To
Use the drop-down lists to specify a specific range of the
column. The first field contains the tray that is located at a
higher spot in the tower (i.e., for top to bottom tray
numbering, the first field could be tray 3 and the second
tray 6).
3. After selecting a tray range, click either the View Graph
button or the View Table button to display a plot or table
respectively.
Ú·¹«®» èòìè
Depending on the profile selected, you have to make further
specifications. For certain profiles, there is a Properties button
on both the profile plot and table. By clicking this button, the
Properties view appears, where you can customize the display of
your profile. Changes made on the Properties view affect both
the table and plot.
A description of the specifications available for each profile type
are outlined in the following table.
Profile Type
Description
Temperature
Profile
Displays the temperature for the tray range selected.
No further specification is needed.
Pressure Profile
Displays the pressure of each tray in the selected
range. No further specification is needed.
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Profile Type
Description
Flow Profile
Displays the flow rate of each tray in the selected
range. You can customise the data displayed using the
Properties view.
In the Basis group, select molar, mass or liquid volume
for your flow profile basis.
In the Phase group, activate the checkbox for the flow
of each phase that you want to display. Multiple flows
can be shown. If three phases are not present in the
column, the Heavy Liquid checkbox is not available,
and thus, the Light Liquid checkbox represents the
liquid phase.
In the Tray Flow Basis group, you can specify the stage
tray flow basis by selecting the appropriate radio
button:
• Net. The net basis option only includes interstage
flow.
• Total. The total basis option includes draw and
pump around flow.
The Properties Profile
table displays all of the
properties for the
phase(s) selected.
Transport
Properties
Profile
Displays the selected properties from each tray in the
selected range. You can customise the data displayed
using the Properties view:
In the Basis group, select molar or mass for the
properties profile basis.
In the Phase group, activate the checkbox for the flow
of each phase that you want to display on the graph.
Multiple flows can be shown. If three phases are not
present in the column, the Heavy Liquid checkbox is
not available.
In the Axis Assignment group, by selecting a radio
button under Left, you assign the values of the
appropriate property to the left y-axis. To display a
second property, choose the radio button under Right.
The right y-axis then shows the range of the second
property. If you want to display only one property on
the plot, select the None radio button under Right.
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Profile Type
Description
Composition
Displays the selected component’s mole fraction of
each tray in the selected range. You can customise the
data displayed using the Properties view.
In the Basis group, select molar, mass or liquid volume
for the composition profile basis.
In the Phase group, activate the checkbox for the flow
of each phase that you want to display. Multiple flows
can be shown. If the three phases are not present in
the column, the Heavy Liquid checkbox is not
available, and thus, the Light Liquid checkbox
represents the liquid phase.
Choose either Fractions or Flows in the Comp Basis
group by selecting the appropriate radio button.
The Components group displays a list of all the
components that enter the tower. You can display the
composition profile of any component by activating the
appropriate checkbox. The plot displays any
combination of component profiles.
K Values Profile
Displays the K Values of each tray in the selected
range. You can select which components you want
included in the profile using the Properties view.
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Profile Type
Description
Light/Heavy Key
Profile
Displays the fraction ratio for each stage. You can
customise the data displayed using the Properties
view.
In the Basis group, select molar, mass or liquid volume
for the profile basis.
In the Phase group, select Vapour, Light Liquid or
Heavy Liquid for the profile phase.
In the Light Key(s) and Heavy Key(s) groups, you can
select the key component(s) to include in your profile.
Electrolyte
Properties
Profile
Displays the pH and ionic strength or the scale index
depending on which radio button you select in the
Graph Type group.
When you select the pH, Ionic Strength radio button,
you can see how the pH value and ionic strength
decrease or increase from tray to tray.
The Solid Components group displays a list of the
solids that could form in the distillation column. You
can activate or deactivate the checkboxes to display or
hide the scale tendency index value for the solid
components in the table or graph.
The scale tendency index value refers to its tendency
to form at the given tray conditions. Solids with a scale
tendency index greater than 1 form, if the solid
formation is governed by equilibrium (as oppose to
kinetics), and if there are no other solids with a
common cation or anion portion which also has scale
tendency greater than 1.
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Assay Curves Group
Ú·¹«®» èòìç
From the Assay Curves group, you can create plots and tables
for the following properties:
•
•
•
•
Boiling Point Assay
Molecular Weight Assay
Density Assay
User Properties
For each of the options, you can display curves for a single tray
or multiple trays. To display a plot or table, make a selection
from the list, and click either the View Graph button or the View
Table button. The figure below is an example of how a Boiling
Point Properties plot appears.
Ú·¹«®» èòëð
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Data Control View
Click the Profile Data Control button, which is located on bottom
left corner of every plot and table, to open the Data Control
property view. This view is common to all plots and tables on
the Curves page. For a selected curve, all changes made on the
Data Control property view affect the data of both the plot and
table.
The Data Control property view consists of five groups as shown
in the figure below.
Ú·¹«®» èòëï
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The following table describes each data control option available
according to group name.
Group
Description
Style
Select either the Multi Tray or Single Tray radio button. The
layout of the Data Control property view differs slightly for
each selection.
For the Single Tray selection, you must open the dropdown list and select one tray.
If you select Multi Tray, the drop-down list is replaced by a
list of all the trays in the column. Each tray has a
corresponding checkbox, which you can activate to display
the tray property on the plot or table.
Refer to Chapter 4 HYSYS Oil Manager in
the HYSYS Simulation
Basis guide for details on
boiling point curves.
Properties
Displays the properties available for the plot or table. Each
Curve option has its own distinct Properties group. For a
single tray selection, you can choose as many of the boiling
point curves as required. Activate the checkbox for any of
the following options:
TBP,ASTM D86,D86 Crack Reduced, D1160 Vac, D1160
ATM, and D2887. When multiple trays have been chosen in
the Style group, the checkbox list is replaced by a dropdown list. You can only choose one boiling point curve when
displaying multiple trays.
Basis
Select molar, mass or liquid volume for the composition
basis.
Phase
Activate the checkbox for the flow of each phase that you
want displayed. Multiple flows can be shown. If there are
not three phases present in the column, the Heavy Liquid
checkbox is not available, and thus, the Light Liquid
checkbox represents the liquid phase.
Visible
Points
The radio buttons in the Visible Points group apply to the
plots only. Select either the 15 Points or 31 Points option to
represent the number of data points which appear for each
curve.
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TBP Envelope Group
The curve allows you to
view product stream
distillation overlaid on
the column feed
distillation. This gives a
visual representation of
how sharp the
separations are for each
product. The sharpness
of separation is adjusted
using section and
stripper efficiencies and
front and back end
shape factors.
The TBP Envelope group contains only the View Graph button.
You can click the View Graph button to display a TBP Envelope
curve as shown in the figure below.
Ú·¹«®» èòëî
Click the Profile Data Control button located on the view above
to open a view for customizing your TBP Envelope curve.
Ú·¹«®» èòëí
Select either a wet or
dry basis. Dry basis is
the default selection.
Select a basis to define
your TBP profile here.
Select from either 100
or 200 data points for
your TBP plot.
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8.4.7 Flowsheet Tab
The Flowsheet tab contains the following pages:
•
•
•
•
Setup
Variables
Internal Streams
Mapping
Setup Page
The Setup page defines the connections between the internal
(sub-flowsheet) and external (Parent) flowsheets.
Ú·¹«®» èòëì
To split all material inlet
streams into their phase
components before
being fed to the column,
activate the Split All
Inlets checkbox.
If one of the material
feed stream Split
checkbox is deactivated,
the Split All Inlets
checkbox deactivates
too.
If you deactivate the
Split All Inlets checkbox,
none of the material
inlet stream Split
checkboxes are affected.
The Labels, as noted previously, attach the external flowsheet
streams to the internal sub-flowsheet streams. They also
perform the transfer (or translation) of stream information from
the property package used in the parent flowsheet into the
property package used in the Column sub-flowsheet (if the two
property packages are different). The default transfer basis used
for material streams is a P-H Flash.
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The Transfer Basis is significant only when the sub-flowsheet
and parent flowsheet Property Packages are different.
See the Summary page of
the Performance tab to
verify the split feed
streams. An asterisk (*)
following the phase
indicator in the VF column
indicates a split stream.
Flash Type
Action
T-P Flash
The pressure and temperature of the material stream are
passed between flowsheets. A new vapour fraction is
calculated.
VF-T Flash
The vapor fraction and temperature of the material stream
are passed between flowsheets. A new Pressure is
calculated.
VF-P Flash
The vapor fraction and pressure of the material stream are
passed between flowsheets. A new temperature is
calculated.
P-H Flash
The pressure and enthalpy of the material stream is passed
between flowsheets. This is the default transfer basis.
User Specs
You can specify the transfer basis for a material Stream.
None
Required
No calculation is required for an energy stream. The heat
flow is simply passed between flowsheets.
When the Split checkbox for any of the inlet material streams is
activated, the stream is split into its vapour and liquid phase
components. The liquid stream is then fed to the specified tray,
and the vapour phase to the tray immediately above the
specified feed tray.
Energy streams and material streams connected to the top tray
(condenser) cannot be split. The checkboxes for there variables
appear greyed out.
Ú·¹«®» èòëë
The Flowsheet Topology group provides stage information for
each element in the flow sheet.
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Flowsheet Variables Page (Main)
The Variables page allows you to select and monitor any
flowsheet variables from one location. You can examine subflowsheet variables from the outside Column property view,
without actually having to enter the Column sub-flowsheet
environment.
You can also use the
Specifications page to
view certain variables.
Select the variable by
adding a specification,
and ensure that the Active
and Estimate checkboxes
are not activated. The
value of this variable
appears in the Current
value column, and this
“pseudo-specification” do
not affect the solution.
You can add, edit or delete variables in the Selected Column
flowsheet Variables group.
Ú·¹«®» èòëê
Adding a Variable
Refer to Section 11.21 Variable Navigator in
the HYSYS User Guide
for information on the
Variable Navigator.
To add a variable in the Selected Column Flowsheet Variables
group:
1. Click the Add button.
2. From the Variable Navigator, select each of the parameters
for the variable.
3. Click the OK button.
4. The variable is added to the Selected Column Flowsheet
Variables group.
Editing a Variable
If you decide that you do
not want to keep the
changes made in the
variable navigator, click
the Cancel button.
You can edit a variable in the Selected Column Flowsheet
Variables group as follows:
1. Highlight a variable.
2. Click the Edit button.
3. Make changes to the selections in the Variable Navigator.
4. Click the OK button.
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Deleting a Variable
You can remove a variable in any of the following ways:
•
Select a variable, and click the Delete button.
•
Select a variable, click the Edit button, and then click the
Disconnect button on the Variable Navigator.
OR
Internal Streams Page
On the Internal Streams page, you can create a flowsheet
stream that represents any phase leaving any tray within the
Column. Streams within operations attached to the main tray
section (i.e., side strippers, the condenser, the reboiler, etc.) can
also be targeted. Each time changes occur to the column, new
information is automatically transferred to the stream which you
have created.
Ú·¹«®» èòëé
To demonstrate the addition of an internal stream, a stream
representing the liquid phase flowing from tray 7 to tray 8 in the
main tray section of a column is added:
1. Click the Add button.
2. In the Stream drop-down list, type the name of the stream
named Liquid.
3. In the Stage drop-down list, select tray 6 or simply type 6,
which locates the selection in the list.
4. In the Type drop-down list, select the phase that you want to
represent. The options include Vapor, Liquid or Aqueous.
Select Liquid in this case.
5. From the Net/Total drop-down list, select either Net or Total.
For the stage 6 liquid, select Net.
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•
•
èóïðï
Net represents the material flowing from the Stage you
have selected to the next stage (above for vapour, below
for liquid or aqueous) in the column.
Total represents all the material leaving the stage (i.e.,
includes draws, pump around streams, etc.).
Mapping Page
The Mapping page contains a table that displays the inlet and
outlet streams from the column sub-flowsheet, and component
maps for each boundary stream.
Ú·¹«®» èòëè
For more detail on the
actual map collections
and component maps
themselves, refer to
Chapter 6 Component Maps in
the HYSYS Simulation
Basis guide.
If the fluid package of the column is the same as the main
flowsheet, component maps are not needed (because
components are the same on each side of the column
boundary). None Req'd is the only option in the drop-down list
of the Into Sub-Flowsheet and Out of Sub-Flowsheet columns. If
the fluid packages are different, you can choose a map for each
boundary stream. HYSYS lists appropriate maps based on the
fluid package of each stream across the boundary.
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Click the Overall Imbalance Into Sub-Flowsheet button or
Overall Imbalance Out of Sub-Flowsheet button to view any
mole, mass of liquid volume imbalance due to changes in fluid
package. If there are no fluid package changes, then there are
no imbalances.
8.4.8 Reactions Tab
This tab is not available
for the Liquid-Liquid
Extractor.
Reactive distillation has been used for many years to carry out
chemical reactions, in particular esterification reactions. The
advantages of using distillation columns for carrying out
chemical reactions include:
•
•
•
•
the possibility of driving the reaction to completion
(break down of thermodynamic limitations for a
reversible reaction), and separating the products of
reactions in only one unit, thus eliminating recycle and
reactor costs.
the elimination of possible side reactions by continuous
withdrawal of one of the products from the liquid phase.
the operation at higher temperatures (boiling liquid),
thus increasing the rate of reaction of endothermic
reactions.
the internal recovery of the heat of reaction for
exothermic reactions, thereby replacing an equivalent
amount of external heat input required for boil-up.
For any column in an electrolyte flowsheet, there is no
option to add any reaction (reaction set) to the column.
Conceptually, electrolyte thermo conducts a reactive and
phase flash all together. HYSYS does not provide options to
allow you to add external reactions to the unit operation.
The Reactions tab allows you to attach multiple reactions to the
column. The tab consists of two pages:
•
•
Stages. Allows you select the reaction set, and its scope
across the column.
Results. Displays the reaction results stage by stage.
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Before adding a reaction to a column, you must first ensure that
you are using the correct column Solving Method. HYSYS
provides three solving methods which allow for reactive
distillation.
Solving Method
Reaction Type
Reaction Phase
Sparse Continuation
Solver
Kinetic Rate, Simple Rate,
Equilibrium Reaction
Vapor, Liquid
Newton Raphson
Inside-Out
Kinetic Rate, Simple Rate
Liquid
Simultaneous
Correction
Kinetic Rate, Simple Rate,
Equilibrium Reaction
Vapor, Liquid,
Combined Phase
The Sparse Continuation Solver method allows you to attach
a reaction set to your column, which combines reaction
types. Other solvers require that the attached reactions are
of a single type.
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Stages Page
The Stages page consists of the Column Reaction Stages group.
The group contains the Column Reaction Stages table and three
buttons.
Ú·¹«®» èòëç
Column Reaction Stages Table
The table consists of four columns, which are described in the
table below.
Column
Description
Column
Reaction Name
The name you have associated with the column reaction.
This is not the name of the reaction set you set in the
fluid package manager.
First Stage
The highest stage of the stage range over which the
reaction is occurring.
Last Stage
The lowest stage of the stage range over which the
reaction is occurring.
Active
Activates the associated reaction thereby enabling it to
occur inside the column.
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The view also contains three buttons that control the addition,
manipulation, and deletion of column reactions.
Button
Description
New
Allows you to add a new column reaction set via the
Column Reaction view. For more information of the
Column Reaction view and adding new reactions, refer to
the section on the Column Reaction View.
Edit
Allows you to edit the column reaction set whose name is
currently selected in Column Reaction Stages table. The
selected reaction’s Column Reaction view opens. For
more information on the Column Reaction view, refer to
the section on the Column Reaction View.
Delete
Allows you to delete the column reaction set whose name
is currently selected in the Column Reaction Stages table.
Column Reaction View
The Column Reaction view allows you to add and revise column
reactions.
Ú·¹«®» èòêð
The Reaction Set
Information group
allows you to select the
reaction set, and the
scope of its application.
The Reaction
Information group
contains thermodynamic
and stoichiometric
information about the
reaction you are
applying to the selected
section of the column.
The Column Reaction view shown in the above figure consists of
two groups:
•
•
Reaction Set Information
Reaction Information
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Reaction Set Information Group
The Reaction Set Information group consists of six objects:
Objects
Description
Name
The name you would like to associate with the column
reaction. This is the name that appears in the Column
Reaction Name column of the Column Reaction Stages
table.
Reaction
Set
Allows you to select a reaction set from a list of all the
reaction sets attached to the fluid package.
First Stage
The upper limit for the reaction that is to occur over a range
of stages.
Last Stage
The lower limit for the reaction that is to occur over a range
of stages.
Delete
Deletes the Column Reaction from the column.
Active
Allows you to enable and disable the associated column
reaction.
Reaction Information Group
The Reaction Information group contains the Reaction field,
which allows you to select a reaction from the reaction set
selected in the Reaction Set field. Click the View Reaction button
to open the selected reaction’s Reaction view. This group also
contains three sub-groups, which allow you to view or specify
the selected reactions properties:
Sub-group
Description
Stoichiometry
Allows you to view and make changes to the
stoichiometric formula of the reaction currently
selected in the Reaction drop-down list. The group
contains three columns:
• Components. Displays the components involved
in the reaction.
• Mole Wt. Displays the molar weight of each
component involved in the reaction.
• Stoich Coeff. Stoichiometric coefficients
associated with the reaction.
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You can make changes to
the fields in these groups.
These changes affect all
the unit operations
associated with this
reaction. Click the View
Reactions button for more
information about the
attached reaction.
èóïðé
Sub-group
Description
Basis
Consists of two fields:
• Base Component. Displays the reactant to which
the reaction extent is calculated. This is often the
limiting reactant.
• Reaction Phase. Displays the phase for which
the kinetic rate equations for different phases can
be modeled in the same reactor. To see the
possible reactions, click the Reaction Information
button in the View Reaction group.
Heat and Balance
Error
Consists of two fields:
• Reaction Heat. Displays the reaction heat.
• Balance Error. Displays any error in the mass
balance around the reaction.
Results Page
The Results page displays the results of a converged column.
Ú·¹«®» èòêï
The page consists of a table containing six columns. The
columns are described in the following table:
Column
Description
1st column
Displays the name/number of the column stage.
Rxn Name
The name of the reaction occurring at this stage.
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The Rxn Extent results
appear only if the Sparse
Continuation Solver is
chosen as the Solving
Method.
ݱ´«³² Ю±°»®¬§ Ê·»©
Column
Description
Base Comp
The name of the reactant component to which the
calculated reaction extent is applied.
Rxn Extent
The consumption or production of the base component in
the reaction.
Spec % Conv
Displays the percentage of conversion specified by you.
Act % Conv
Displays the percentage of conversion calculated by HYSYS.
If you have more than one reaction occurring at any particular
stage, each reaction appears simultaneously.
Design Tips for Reactive Distillation
ïAlthough
the column unit operations allows for multiple column
reactions and numerous column configurations, a general
column topography can be subdivided into three sections:
•
•
•
Rectifying Section
Reactive Section
Stripping Section
Ú·¹«®» èòêî
Rectifyin
g Section
Reactive
Section
Strippin
g
While the Rectifying and Stripping Sections are similar to
ordinary distillation, a reactive distillation column also has a
Reactive Section. The Reactive Section of the column is where
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the main reactions occur. There is no particular requirement for
separation in this section.
There are several unique operational considerations when
designing a reactive distillation column:
•
•
•
•
The operating pressure should be predicated on the
indirect effects of pressure on reaction equilibrium.
The optimum feed point to a reactive distillation column
is just below the reactive section. Introducing a feed too
far below the reactive section reduces the stripping
potential of the column and results in increased energy
consumption.
Reflux has a dual purpose in reactive distillation.
Increasing the reflux rate enhances separation and
recycles unreacted reactants to the reaction zone
thereby increasing conversion.
Reboiler Duty is integral to reactive distillation as it must
be set to ensure sufficient recycle of unreacted, heavy
reactant to the reaction zone without excluding the light
reactant from the reaction zone, if the reboiler duty is too
high or too low, conversion, and purity can be
compromised.
8.4.9 Dynamics Tab
The Dynamics tab contains the following pages:
•
•
•
Vessels
Equipment
Holdup
If you are working exclusively in Steady State mode or your
version of HYSYS does not support dynamics, you are not
required to change any information on the pages accessible
through this tab.
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Vessels Page
The Vessels page contains a summary of the sizing information
for the different vessels contained in the column sub-flowsheet.
In addition, it contains the possible dynamic specifications for
these vessels.
Ú·¹«®» èòêí
Equipment Page
This page is not
available for the LiquidLiquid Extractor.
The Equipment page displays the same information as the
Equipment page on the Rating tab. The difference is that
double-clicking on the equipment name opens its property view
on the Dynamics tab.
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Holdup Page
The Holdup page contains a summary of the dynamic
information calculated by HYSYS.
Column
Description
Pressure
Displays the calculated stage pressure.
Total Volume
Displays the stage volume.
Bulk Liq Volume
Displays the liquid volume occupying the stage.
8.4.10 Perturb Tab
The Perturb tab is only available in the Column Runner view. The
Perturb tab allows you to control the way column solver
calculates the partial derivatives. There are two types of
independent controls.
Control
Description
Low Level Analytic
The Analytic property derivatives checkbox allows
you to turn On and Off low level analytic
derivatives support (i.e., derivatives of
thermodynamic properties like Fugacity, Enthalpy,
and Entropy by Temperature, Pressure, and
Composition).
At present this facility is available for Peng
Robinson or Soave-Redlich-Kwong property
packages in Sparse Continuation Solver context.
Optimizer Level
Analytic
HYSYS Optimizer (RTO+) allows calculation of
column analytic derivatives by stream
Temperature, Pressure, Component Flow, Column
Spec specified value, and Tear Variables.
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The Sparse analytic page allows you to select a particular
method of column analytic derivatives calculation.
Ú·¹«®» èòêì
The Perturb method parameters group provides tuning
parameters for analytic column derivatives calculator.
•
•
•
Rigorous properties checkbox. If active, rigorous
thermodynamic properties are applied in Jacobi matrix
calculation. If inactive, simple models (controlled by
Control panel of Sparse solver) are applied instead for
Enthalpy and Fugacity of thermodynamic phases. The
last option may expedite derivative calculations.
Warm restart checkbox. If active, additional Sparse
linear solver information is preserved between Analytic
derivative calculator calls (faster solution of linear
system). If inactive, no Sparse linear solver information
is stored (memory economy).
Skip Sparse Solve checkbox. If active, Column solution
phase is skipped (may allow faster execution).
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8.5 Column Specification
Types
This section outlines the various Column specification (spec)
types available along with relevant details. Specs are added and
modified on the Specs Page or the Monitor Page of the
Design tab.
Adding and changing Column specifications is straightforward. If
you have created a Column based on one of the templates,
HYSYS already has default specifications in place. The type of
default specification depends on which of the templates you
have chosen (refer to the Default Replaceable Specifications
in Section 8.3.2 - Templates for more details).
8.5.1 Cold Property
Specifications
Ú·¹«®» èòêë
Cold
Property
Description
Flash Point
Allows you to specify the Flash Point temperature (ASTM
D93 flash point temperature closed cup) for the liquid or
vapour flow on any stage in the column.
Pour Point
Allows you to specify the ASTM Pour Point temperature for
the liquid or vapour flow on any stage in the column.
RON
Allows you to specify the Research Octane Number for the
liquid or vapour flow on any stage.
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8.5.2 Component Flow Rate
The flow rate (molar, mass or volume) of any component, or the
total flow rate for any set of components, can be specified for
the flow leaving any stage. If a side liquid or vapour draw is
present on the selected stage, these are included with the
internal vapour and liquid flows.
Ú·¹«®» èòêê
8.5.3 Component Fractions
The mole, mass or volume fraction can be specified in the liquid
or vapour phase for any stage. You can specify a value for any
individual component, or specify a value for the sum of the mole
fractions of multiple components.
Ú·¹«®» èòêé
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èóïïë
8.5.4 Component Ratio
The ratio (molar, mass or volume fraction) of any set of
components over any other set of components can be specified
for the liquid or vapour phase on any stage.
Ú·¹«®» èòêè
8.5.5 Component Recovery
Component recovery is the molar, mass or volume flow of a
component (or group of components) in any internal or product
stream draw divided by the flow of that component (or group) in
the combined tower feeds. As the recovery is a ratio between
two flows, you specify a fractional value. Also, there is no need
to specify a Flow Basis since this is a ratio of the same
component between specified stream and the combined tower
feeds.
Ú·¹«®» èòêç
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8.5.6 Cut Point
While initial and final cut
points are permitted, it is
often better to use 5 and
95 percent cut points to
minimize the errors
introduced at the
extreme ends of boiling
point curves.
This option allows a cut point temperature to be specified for the
liquid or vapour leaving any stage. The types are TBP, ASTM
D86, D1160 Vac, D1160 ATM, and ASTM D2887. For D86, you
are given the option to use ASTM Cracking Factor. For D1160,
you are given an Atmospheric Pressure option. The cut point can
be on a mole, mass or volume fraction basis, and any value from
0 to 100 percent is allowed.
Ú·¹«®» èòéð
8.5.7 Draw Rate
The molar, mass or volume flowrate of any product stream draw
can be specified.
Ú·¹«®» èòéï
8.5.8 Delta T (Heater/Cooler)
The temperature difference across a Heater or Cooler unit
operation can be specified. The Heater/Cooler unit must be
installed in the Column sub-flowsheet, and the HYSIM InsideOut, Modified HYSIM Inside-Out or Sparse Continuation solving
methods must be selected on the Solver page of the Parameters
tab.
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8.5.9 Delta T (Streams)
The temperature difference between two Column sub-flowsheet
streams can be specified.
Ú·¹«®» èòéî
8.5.10 Duty
You can specify the duty for an energy stream.
Ú·¹«®» èòéí
8.5.11 Duty Ratio
You can specify the duty ratio for any two energy streams. In
addition to Column feed duties, the choice of energy streams
also includes pump around duties (if available).
Ú·¹«®» èòéì
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8.5.12 Feed Ratio
This type of specification
is useful for turn down or
overflash of a crude feed.
The Feed Ratio option allows you to establish a ratio between
the flow rate on or from any stage in the column, and the
external feed to a stage. You are prompted for the stage, flow
type (Vapor, Liquid, Draw), and the external feed stage.
Ú·¹«®» èòéë
8.5.13 Gap Cut Point
The Gap Cut Point is defined as the temperature difference
between a cut point (Cut Point A) for the liquid or vapour leaving
one stage, and a cut point (Cut Point B) on a different stage.
Ú·¹«®» èòéê
This specification is best
used in combination with
at least one flow
specification; using this
specification with a
Temperature
specification can produce
non-unique solutions.
You have a choice of specifying the distillation curve to be used:
•
•
•
•
•
TBP
ASTM D86
D1160 Vac
D1160 ATM
ASTM D2887
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You can define Cut Point A and Cut Point B, which together must
total 100%. The cut points can be on a mole, mass or volume
basis.
8.5.14 Liquid Flow
The net molar, mass or volume liquid (Light or Heavy) flow can
be specified for any stage.
Ú·¹«®» èòéé
8.5.15 Physical Property
Specifications
The mass density can be specified for the liquid or vapour on
any stage.
Ú·¹«®» èòéè
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8.5.16 Pump Around
Specifications
Ú·¹«®» èòéç
The Pump Around Rate,
as well as the Pump
Around Temperature
Drop are the default
specifications HYSYS
requests when a pump
around is added to the
column.
Specification
Description
Flow Rate
The flow rate of the Pump Around can be specified
in molar, mass or liquid volume units.
Temperature Drop
Allows you to specify the temperature drop across a
Pump Around exchanger. The conditions for using
this specification are the same as that stated for the
Pump Around return temperature.
Return
Temperature
The return temperature of a Pump Around stream
can be specified. Ensure that you have not also
specified both the pump around rate and the duty.
This would result in the three associated variables
(flow rate, side exchanger duty, and temperature)
all specified, leaving HYSYS with nothing to vary in
search of a converged solution.
Duty
You can specify the duty for any Pump Around.
Return Vapor
Fraction
You can specify the return vapour fraction for any
Pump Around.
Duty Ratio
To specify a Pump Around duty ratio for a Column
specification, add a Column Duty Ratio spec
instead, and select the Pump Around energy
streams to define the duty ratio. Refer to Section
8.5.11 - Duty Ratio for further details.
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8.5.17 Reboil Ratio
You can specify the molar, mass or volume ratio of the vapour
leaving a specific stage to the liquid leaving that stage.
Ú·¹«®» èòèð
8.5.18 Recovery
The Recovery spec is the recovery of the total feed flow in the
defined outlet streams (value range between 0 and 1).
molar
flow of draw streamó
óóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóó
ã % recovery
total molar feed flow
(8.7)
Ú·¹«®» èòèï
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8.5.19 Reflux Feed Ratio
The Reflux Feed Ratio spec is the fraction of the reflux flow
divided by the reference flow for the specified stage and phase.
reflux flow
óóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóóó ã reflux feed ratio
reference flow
(8.8)
Ú·¹«®» èòèî
8.5.20 Reflux Fraction Ratio
The Reflux Fraction Ratio spec is the fraction or % of liquid that
is being refluxed on the specified stage (value range between 0
and 1).
Ú·¹«®» èòèí
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8.5.21 Reflux Ratio
The Reflux Ratio
specification is normally
used only for top stage
condensers, but it can be
specified for any stage.
For a Partial Condenser:
• Checking the Include
Vapour checkbox,
gives the following
equation for the
reflux ratio:
R
Reflux Ratio ã óóóóóóóóóóóóóó
VõD
• Unchecking the
Include Vapour
checkbox, gives the
following equation
for the reflux ratio:
Ró
Reflux Ratio ã óóó
D
where:
R = liquid reflux to
column
V = vapour product
D = distillate
product
Refer to Section 5.5 Tee for details on the Tee
operation.
The Reflux Ratio is the molar, mass or volume flow of liquid
(Light or Heavy) leaving a stage, divided by the sum of the
vapour flow from the stage plus any side liquid flow.
Ú·¹«®» èòèì
Reflux Ratio view for
general column
Reflux Ratio view for three
phase distillation column
8.5.22 Tee Split Fraction
The split fraction for a Tee operation product stream can be
specified. The Tee must be installed within the Column subflowsheet and directly attached to the column i.e., to a draw
stream, in a pump around circuit, etc. Also, the Modified HYSIM
Inside-Out solving method must be selected.
Tee split fraction specifications are automatically installed as you
install the tee operation in the Column sub-flowsheet; however,
you can select which specifications become active on the
Monitor page or Specs page. Changes made to the split fraction
specification value are updated on the Splits page of the tee
operation.
8.5.23 Tray Temperature
The temperature of any stage can be specified.
Ú·¹«®» èòèë
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8.5.24 Transport Property
Specifications
The viscosity, surface tension or thermal conductivity can be
specified for the liquid leaving any stage. The viscosity or
thermal conductivity can be specified for the vapour leaving any
stage. A reference temperature must also be given.
The computing time required to satisfy a vapour viscosity
specification can be considerably longer than that needed to
meet a liquid viscosity specification.
Ú·¹«®» èòèê
8.5.25 User Property
A User Property value can be specified for the flow leaving any
stage. You can choose any installed user property in the
flowsheet, and specify its value. The basis used in the
installation of the user property is used in the spec calculations.
Ú·¹«®» èòèé
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8.5.26 Vapor Flow
The net molar, mass or volume vapor flow can be specified for
any stage. Feeds and draws to that tray are taken into account.
Ú·¹«®» èòèè
8.5.27 Vapor Fraction
The vapour fraction of a stream exiting a stage can be specified.
Ú·¹«®» èòèç
8.5.28 Vapor Pressure
Specifications
Two types of vapour pressure specifications are available:
•
•
true vapour pressure (@100°F)
Reid vapour pressure.
Ú·¹«®» èòçð
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Vapor Type
Description
Vapor
Pressure
The true vapour pressure at 100°F can be specified for the
vapour or liquid leaving any stage.
Reid Vapor
Pressure
Reid vapour pressure can be specified for the vapour or
liquid leaving any stage. The specification must always be
given in absolute pressure units.
8.5.29 Column Stream
Specifications
Column stream specifications must be created in the Column
sub-flowsheet. Unlike other specifications, the stream
specification is created through the stream’s property view, and
not the Column Runner Specs page. To be able to add a
specification to a stream:
Only one stream
specification can be
created per draw stream.
•
•
The Modified HYSIM Inside-out solving method must be
chosen for the solver.
The stream must be a draw stream.
The Create Column Stream Spec button on the Conditions page
of the Worksheet tab is available only on Stream property views
within the Column sub-flowsheet. When you click on the Create
Column Stream Spec button, the Stream Spec view appears.
Ú·¹«®» èòçï
Creating a new stream
specification for a stage,
or activating a
specification
automatically deactivates
all other existing draw
stream specifications for
that stage.
For draw streams from a separation stage (tray section stage,
condenser or reboiler) only a stream temperature specification
can be set. For a non-separation stage streams (from pumps,
heaters etc.) either a temperature or a vapour fraction
specification can be set. For any given stage, only one draw
stream specification can be active at any given time.
Once a specification is added for a stream, the button on the
Conditions page of the Worksheet tab changes from Create
Column Stream Spec to View Column Stream Spec, and can be
clicked to view the Stream Specification view.
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You can only add Column Stream Specifications via the
Stream property view of a draw stream within the Column
sub-flowsheet.
8.6 Column-Specific
Operations
Only the operations which
are applicable to a
Column operations are
available within the
Column sub-flowsheet.
The procedure for installing unit operations in a Column subflowsheet is the same as in the main flowsheet (refer to Section
1.2.1 - Installing Operations for details). The UnitOps view
for the Column is activated by selecting the Add Operation
command from the Flowsheet menu in the menu bar, or by
pressing F12.
Ú·¹«®» èòçî
The unit operations available within the Column sub-flowsheet
are listed in the following table. Most operations shown here are
identical to those available in the main flowsheet in terms of
specified and calculated information, property view structure,
etc.
There are also additional unit operations which are not available
in the main flowsheet. They are:
•
•
•
Condenser (Partial, Total, 3-Phase)
Reboiler
Tray Section
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The Bypasses and Side Operations (side strippers, pump
arounds, etc.) are available on the Side Ops page of the Column
property view. Available unit operations in the Column subflowsheet are:
Refer to Section 7.25.4 Access Column or SubFlowsheet PFDs in the
HYSYS User Guide for
more information
Operation Category
Types
Vessels
3-Phase Condenser, Partial Condenser, Reboiler,
Separator, Total Condenser, Tray Section
Heat Transfer
Equipment
Cooler, Heater, Heat Exchanger
Rotating Equipment
Pump
Piping Equipment
Valve
Logicals
Balance, Digital Pt, PID Controller, Selector Block,
Transfer Function Block
You can open a view of the Column PFD from the main build
environment. This PFD only provides you with the ability to
modify stream and operation parameters. You cannot add
and delete operations or break stream connections. These
tasks can only be performed in the Column sub-flowsheet
environment.
8.6.1 Condenser
The Condenser is used to condense vapour by removing its
latent heat with a coolant. In HYSYS, the condenser is used only
in the Column Environment, and is generally associated with a
Column Tray Section.
There are four types of Condensers:
The Partial Condenser can
be used as a Total
Condenser simply by
specifying the vapour
flowrate to be zero.
Condenser Type
Description
Partial
Feed is partially condensed; there are vapour
and liquid product streams. The Partial
Condenser can be operated as a total
condenser by specifying the vapour stream to
have zero flowrate.
Total
Feed is completely condensed; there is a liquid
product only.
Three-Phase - Chemical
There are two liquid product streams and one
vapour product stream.
Three-Phase Hydrocarbon
There is a liquid product streams and a water
product stream and one vapour product
stream.
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The Condenser property view uses a Type drop-down list, which
allows you to switch between condenser types without having to
delete and re-install a new piece of equipment.
Ú·¹«®» èòçí
Partial Condenser icon
Total Condenser icon
Three-Phase Condenser
icon
When you switch between the condenser types, the pages
change appropriately. For instance, the Connections page for the
Total Condenser does not show the vapor stream. If you switch
from the Partial to Total Condenser, the vapor stream is
disconnected. If you then switch back, you have to reconnect
the stream.
When you add a Column to the simulation using a pre-defined
template, there can be a condenser attached to the tower (for
example, in the case of a Distillation Column). To manually add
a Condenser, press F12, and make the appropriate selection
from the UnitOps view, or click a Condenser icon from the
Column Palette.
The Condenser property view has the same basic five tabs that
are available on any unit operation:
•
•
•
•
•
Design
Rating
Worksheet
Performance
Dynamics
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It is necessary to specify the connections and the parameters
for the Condenser. The information on the Dynamics tab are not
relevant in steady state.
Design Tab
The Design tab contains options to configure the Condenser.
Connections Page
On the Connections page, you can specify the operation name,
as well as the feed(s), vapour, water, reflux, product, and
energy streams.
Ú·¹«®» èòçì
The Connections page shows only the product streams, which
are appropriate for the selected condenser. For example, the
Total Condenser does not have a vapour stream, as the entire
feed is liquefied. Neither the Partial nor the Total Condenser has
a water stream.
The Condenser is typically used with a tray section, where the
vapour from the top tray of the column is the feed to the
condenser, and the reflux from the condenser is returned to the
top tray of the column.
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Parameters Page
Ú·¹«®» èòçë
It is better to use a duty
spec than specifying the
heat flow of the duty
stream.
The condenser parameters that can be specified are:
•
•
•
Pressure Drop
Duty
Subcooling Data
Pressure Drop
The Pressure Drop across the condenser (Delta P) is zero by
default. It is defined in the following expression:
P ã P v ã P l ã P feed Š P
(8.9)
where:
P = vessel pressure
Pv = pressure of vapour product stream
Pl = pressure of liquid product stream
Pfeed = pressure of feed stream to condenser
P = pressure drop in vessel (Delta P)
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You typically specify a pressure for the condenser during the
column setup, in which case the pressure of the top stage is
the calculated value.
Duty
If you specify the duty, it
is equivalent to installing
a duty spec, and a degree
of freedom is used.
The Duty for the energy stream can be specified here, but this is
better done as a column spec (defined on the Monitor page or
Specs page of the Column property view). This allows for more
flexibility when adjusting specifications, and also introduces a
tolerance.
The Duty should be positive, indicating that energy is being
removed from the Condenser feed.
The steady state condenser energy balance is defined as:
Hfeed - Duty = Hvapour + Hliquid
(8.10)
where:
Hfeed = heat flow of the feed stream to the condenser
Hvapour = heat flow of the vapour product stream
Hliquid = heat flow of the liquid product stream(s)
SubCooling
In steady state,
SubCooling applies only to
the Total Condenser.
There is no SubCooling in
dynamics.
In some instances, you want to specify Condenser SubCooling.
In this situation, either the Degrees of SubCooling or the
SubCooled Temperature can be specified. If one of these fields is
set, the other is calculated automatically.
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Estimate Page
On the Estimate page you can estimate the flows and phase
compositions of the streams exiting the Condenser.
Ú·¹«®» èòçê
You can enter any value for fractional compositions, and click
the Normalize Composition button to have HYSYS normalize the
values such that the total equals 1. This button is useful when
many components are available, but you want to specify
compositions for only a few. HYSYS also specifies any <empty>
compositions as zero.
HYSYS re-calculates the phase composition estimates when you
click the Update Comp. Est. button. Clicking this button also
removes any of the estimated values you entered for the phase
composition estimates.
Click the Clear Comp. Est. button to clear the phase
compositions estimated by HYSYS. This button does not remove
any estimate values you entered. You can clear the all estimate
values by clicking the Clear All Comp. Est. button.
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User Variables Page
The User Variables page enables you to create and implement
your own user variables for the current operation. For more
information refer to Section 1.3.3 - User Variables Page/
Tab.
Notes Page
The Notes page provides a text editor where you can record any
comments or information regarding the specific unit operation,
or your simulation case in general. For more information, refer
to Section 1.3.2 - Notes Page/Tab.
Rating Tab
The Rating tab contains options that are applicable in both
Steady State and Dynamics mode.
Sizing Page
The Sizing page contains all the required information for
correctly sizing the condenser.
Ú·¹«®» èòçé
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You can select either vertical or horizontal orientation, and
cylinder or sphere. You can either enter the volume or
dimensions for your condenser. You can also indicate whether or
not the condenser has a boot associated with it. If it does, then
you can specify the boot dimensions.
Nozzles Page
Refer to Section 1.6.2
- Nozzles in the HYSYS
Dynamic Modeling
guide for more
information.
The Nozzles page contains information regarding the elevation
and diameter of the nozzles. The information provided in the
Nozzles page is applicable only in Dynamic mode.
Ú·¹«®» èòçè
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Heat Loss Page
The Heat Loss page allows you to specify the heat loss from
individual trays in the tray section. You can choose either a
Direct Q, Simple, or Detailed heat loss model or no heat loss
from the Heat Loss Mode group.
Ú·¹«®» èòçç
Direct Q Heat Loss Model
The Direct Q model allows you to either specify the heat loss
directly, or have the heat loss calculated from the Heat Flow for
the condenser.
Ú·¹«®» èòïðð
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Simple Heat Loss Model
The Simple model allows you to calculate the heat loss from
these specified values:
•
•
Overall U value
Ambient Temperature
Ú·¹«®» èòïðï
Detailed Heat Loss Model
Refer to Section 1.6.1
- Detailed Heat Model
in the HYSYS Dynamic
Modeling guide for
more information.
The Detailed model allows you to specify more detailed heat
transfer parameters.
Ú·¹«®» èòïðî
Worksheet Tab
The PF Specs page is
relevant to dynamics
cases only.
The Worksheet tab contains a summary of the information
contained in the stream property view for all the streams
attached to the Condenser. Refer to Section 1.3.1 Worksheet Tab for more information.
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Performance Tab
In steady state, the
displayed plots are all
straight lines. Only in
Dynamic mode, when the
concept of zones is
applicable, do the plots
show variance across the
vessels.
The Performance tab has the following pages:
•
Plots
Ú·¹«®» èòïðí
•
•
Tables
SetUp
From these pages you can select the type of variables you want
to calculate and plot, view the calculated values, and plot any
combination of the selected variables. The default selected
variables are temperature, pressure, heat flow, enthalpy, and
vapor fraction. At the bottom of the Plots or Tables page, you
can specify the interval size over which the values should be
calculated and plotted.
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Dynamics Tab
The Dynamics tab contains the following pages:
•
•
•
•
Specs
Holdup
StripChart
Heat Exchanger
You are not required to modify information on the Dynamics tab
when working in Steady State mode.
Specs Page
The Specs page contains information regarding initialization
modes, condenser geometry, and condenser dynamic
specifications.
Ú·¹«®» èòïðì
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Model Details
In the Model Details group, you can specify the initial
composition and amount of liquid that the separator should start
with when you start dynamics. This is done via the initialization
mode which is discussed in the table below.
The Initialization Mode
can be changed any
time when the integrator
is not running. The
changes cause the
vessel to re-initialize
when the integrator is
started again.
Initialization Mode
Description
Initialize from
Products
The composition of the holdup is calculated from a
weighted average of all products exiting the
holdup. A PT flash is performed to determine other
holdup conditions. The liquid level is set to the
value indicated in the Liq Volume Percent field.
Dry Startup
The composition of the holdup is calculated from a
weighted average of all feeds entering the holdup.
A PT flash is performed to determine other holdup
conditions. The liquid level in the Liq Volume
Percent field is set to zero.
Initialize from User
The composition of the liquid holdup in the
condenser is user specified. The molar composition
of the liquid holdup can be specified by clicking the
Init Holdup button. The liquid level is set to the
value indicated in the Liq Volume Percent field.
The condenser geometry can be specified in the Model Details
group. The following condenser geometry parameters can be
specified in the same manner as the Geometry group on Sizing
page of the Rating tab:
•
•
•
•
Volume
Diameter
Height (Length)
Geometry (Level Calculator)
The Liquid Volume Percent value is also displayed in this group.
You can modify the level in the condenser at any time. HYSYS
then uses that level as an initial value when the integrator is
run.
Refer to the section on
the Nozzles Page for
more details.
The Fraction Calculator determines how the level in the
condenser and the elevation and diameter of the nozzle affects
the product composition. There is only one Fraction Calculation
mode available, it is called Use Levels and Nozzles. The
calculations are based on how the nozzle location and vessel
liquid level affect the product composition.
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Dynamic Specifications
The Dynamic Specifications group contains fields, where you can
specify what happens to the pressure and reflux ratio of the
condenser when you enter dynamic mode.
The Fixed Pressure Delta P field allows you to impose a fixed
pressure drop between the vessel and all of the feed streams.
This is mostly supported for compatibility with Steady State
mode. In Dynamic mode, you are advised to properly account
for all pressure losses by using the appropriate equipment such
as valves or pumps or static head contributions. A zero pressure
drop should preferably be used here otherwise you may get
unrealistic results such as material flowing from a low to a high
pressure area.
The Fixed Vessel Pressure field allows you to fix the vessel
pressure in Dynamic mode. This option can be used in simpler
models where you do not want to configure pressure controllers
etc., or if the vessel is open to the atmosphere. In general the
specification should not be used, because the pressure should
be determined by the surrounding equipment.
The Reflux Flow/Total Liquid Flow field provides you with a
simple reflux ratio control option, and the ratio determines the
reflux flow rate divided by the sum of the reflux and distillate
flow rates.
This option allows you to set up simple models without
having to add the valves, pumps, and controller that would
normally be present. This option does not always give
desirable results under all conditions such as very low levels
or reversal of some of the streams.
The Add/Configure Level Controller button installs a level
controller on the distillate (liquid) outlet stream if one is not
already present. If this stream has a valve immediately
downstream of the vessel, the controller is configured to control
the valve rather than the stream directly. In any case, the
controller is configured with some basic tuning parameters, but
you can adjust those.
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The default tuning values are as follows:
•
•
Kp = 1.8
Ti = 4 * Residence time / Kp
Holdup Page
The Holdup page contains information regarding the properties,
composition, and amount of the holdup.
Ú·¹«®» èòïðë
For each phase contained within the volume space of the unit
operation, the following is specified:
Holdup
Details
Refer to Section 1.3.7 Advanced Holdup
Properties in the
HYSYS Dynamic
Modeling guide for
more information.
Description
Accumulatio
n
The rate of change of material in the holdup for each phase.
Moles
The amount of material in the holdup for each phase.
Volume
The holdup volume of each phase.
Click the Advanced button to access the view that provides more
detailed information about the holdup of that unit operation.
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èóïìí
StripChart Page
The Stripchart page allows you to select and create default strip
charts containing various variable associated to the operation.
Refer to Section 1.3.4 - Stripchart Page/Tab for more
information.
Heat Exchanger Page
The Heat Exchanger page opens a list of available heating
methods for the unit operation. This page contains different
objects depending on which configuration you select.
Ú·¹«®» èòïðê
•
Refer to Duty Radio
Button for more
information.
•
Refer to Tube Bundle
Radio Button for more
information.
•
If you select the None radio button, this page is blank
and the Condenser has no cooling source.
If you select the Duty radio button, this page contains
the standard cooling parameters and you have to specify
an energy stream for the Condenser.
If you select the Tube Bundle radio button, this page
contains the parameters used to configure a kettle chiller
and you have to specify the required material streams for
the kettle chiller.
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The Tube Bundle options are only available in Dynamics
mode.
If you switch from Duty option or Tube Bundle option to
None option, HYSYS automatically disconnects the energy or
material streams associated to the Duty or Tube Bundle
options.
Duty Radio Button
When the Duty radio button is selected the following heat
transfer options are available.
Ú·¹«®» èòïðé
The Heater Type group has two radio buttons:
The Gas Heater method
is available only for
condensers, because the
heat transfer in the
Condenser depends
more on the surface
area of the vapour
contacting the cooling
coils than the liquid.
•
Gas Heater. When you select this radio button, the duty
is linearly reduced so that it is zero at liquid percent level
of 100%, unchanged at liquid percent level of 50%, and
doubled at liquid percent level of 0%. The following
equation is used:
Q ã 2 Š 0.02L Q Total
(8.11)
where:
Q = total heat applied to the holdup
L= liquid percent level
QTotal = duty calculated from the duty source
The heat applied to the Condenser operation directly
varies with the surface area of vapour contacting the
vessel wall.
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Ú·¹«®» èòïðè
20
16
12
8
4
0
0
2
4
6
8
10
Liquid Percent Level,
Percent Heat Applied to Condenser
•
The Vessel Heater
method is a non-scaling
method.
Vessel Heater. When you select this radio button, 100%
of the duty specified or calculated in the SP cell is applied
to the vessel’s holdup. That is:
Q = QTotal
(8.12)
where:
Q = total heat applied to the holdup
QTotal = duty calculated from the duty source
The Duty Source group has two radio buttons:
•
•
Direct Q
From Utility
When you select the Direct Q radio button, the Direct Q Data
group appears. The following table describes the purpose of
each object in the group.
Object
Description
SP
The heat flow value in this cell is the same value specified
in the Duty field on the Parameters page of the Design tab.
Any changes made in this cell are reflected on the Duty
field on the Parameters page of the Design tab.
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Object
Description
Min.
Available
Allows you to specify the minimum amount of heat flow.
Max.
Available
Allows you to specify the maximum amount of heat flow.
When you select the From Utility radio button, the Utility Flow
Properties group appears.
Ú·¹«®» èòïðç
The cells containing:
• black text indicates
the value is
calculated by
HYSYS and cannot
be changed.
• blue text indicates
the value is entered
by you, and you
can change the
value.
• red text indicates
the value is
calculated by
HYSYS, and you
can change the
value.
The following table describes the purpose of each object that
appears when the From Utility radio button is selected.
Object
Description
Heat Flow
Displays the heat flow value.
UA
Displays the overall heat transfer coefficient.
Holdup
Displays the amount of holdup fluid in the condenser.
Flow
Displays the amount of fluid flowing out of the
condenser.
Min. Flow
Displays the minimum amount of fluid flowing out of
the condenser.
Max. Flow
Displays the maximum amount of fluid flowing out of
the condenser.
Heat Capacity
Displays the heat capacity of the fluid.
Inlet Temp.
Displays the temperature of the stream flowing into
the condenser.
Outlet Temp.
Displays the temperature of the stream flowing out of
the condenser.
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Object
Description
Temp Approach
Displays the value of the operation outlet temperature
minus the outlet temperature of the Utility Fluid. It is
only used when one initializes the duty valve via the
Initialize Duty Valve button.
Initialize Duty
Valve
Allows you to initialize the UA, flow, and outlet
temperature to be consistent with the duty for
purposes of control.
8.6.2 Reboiler
If you choose a Reboiled Absorber or Distillation template, it
includes a Reboiler which is connected to the bottom tray in the
tray section with the streams to reboiler and boilup.
Reboiler icon
The Reboiler is a column operation, where the liquid from the
bottom tray of the column is the feed to the reboiler, and the
boilup from the reboiler is returned to the bottom tray of the
column.
Ú·¹«®» èòïïð
The Reboiler is used to partially or completely vapourize liquid
feed streams. You must be in a Column sub-flowsheet to install
the Reboiler.
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To install the Reboiler operation, press F12 and select Reboiler.
From the UnitOps view or click the Reboiler icon in the Column
Palette.
The Reboiler property view has the same basic tabs that are
available on any unit operation:
•
•
•
•
•
Design
Rating
Worksheet
Performance
Dynamics
It is necessary to specify the connections, and the parameters
for the Reboiler. The information on the Dynamics tab are not
relevant in steady state.
Design Tab
The Design tab contains the following pages:
•
•
•
•
Connections
Parameters
User Variables
Notes
Connections Page
On the Connections page, you must specify the Reboiler name,
as well as the feed(s), boilup, vapor draw, energy, and bottoms
product streams. The vapor draw stream is optional.
Ú·¹«®» èòïïï
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Parameters Page
On the Parameter page, you can specify the pressure drop and
energy used by the Reboiler. The pressure drop across the
Reboiler is zero by default.
Ú·¹«®» èòïïî
The Duty for the energy Stream should be positive, indicating
that energy is being added to the Reboiler feed(s). If you specify
the duty, a degree of freedom is used.
It is recommended to define a duty specification on the
Monitor page or Specs page of the Column property view,
instead of specifying a value for the duty stream.
The steady state reboiler energy balance is defined as:
Hfeed + Duty = Hvapour + Hbottom + Hboilup
(8.13)
where:
Hfeed = heat flow of the feed stream to the reboiler
Hvapour = heat flow of the vapour draw stream
Hbottoms = heat flow of the bottoms product stream
Hboilup = heat flow of the boilup stream
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User Variables Page
For more information
refer to Section 1.3.3 User Variables Page/
Tab.
The User Variables page enables you to create and implement
your own user variables for the current operation.
Notes Page
For more information,
refer to Section 1.3.2 Notes Page/Tab.
The Notes page provides a text editor where you can record any
comments or information regarding the specific unit operation,
or your simulation case in general.
Rating Tab
Rating tab and Dynamics
tab for a Reboiler is the
same as the Rating tab
and Dynamics tab for the
Condenser.
The Rating tab contains the following pages:
•
•
•
Sizing
Nozzles
Heat Loss
Sizing Page
Ú·¹«®» èòïïí
The Sizing page contains all the required information for
correctly sizing the reboiler. You can select either vertical or
horizontal orientation, and cylinder or sphere. You can either
enter the volume or dimensions for your reboiler. You can also
indicate whether or not the reboiler has a boot associated with
it. If it does, you can specify the boot dimensions.
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Nozzles Page
Refer to Section 1.6.2
- Nozzles in the HYSYS
Dynamic Modeling
guide for more
information.
The Nozzles page contains information regarding the elevation
and diameter of the nozzles. The information provided in the
Nozzles page is applicable only in Dynamic mode.
Ú·¹«®» èòïïì
Heat Loss Page
The Heat Loss page allows you to specify the heat loss from
individual trays in the tray section. You can choose either a
Direct Q, Simple or Detailed heat loss model or no heat loss
from the Heat Loss Mode group.
Direct Q Heat Loss Model
The Direct Q model allows you to either specify the heat loss
directly, or have the heat loss calculated from the Heat Flow for
the reboiler.
Ú·¹«®» èòïïë
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Simple Heat Loss Model
The Simple model allows you to calculate the heat loss from
these specified values:
•
•
Overall U value
Ambient Temperature
Ú·¹«®» èòïïê
Detailed Heat Loss Model
Refer to Section 1.6.1 Detailed Heat Model in
the HYSYS Dynamic
Modeling guide for more
information.
The Detailed model allows you to specify more detailed heat
transfer parameters.
Ú·¹«®» èòïïé
Worksheet Tab
The PF Specs page is
relevant to dynamics
cases only.
The Worksheet tab contains a summary of the information
contained in the stream property view for all the streams
attached to the Reboiler. Refer to Section 1.3.1 - Worksheet
Tab for more information.
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Performance Tab
The Performance tab of the Reboiler has the same pages as the
Performance tab of the Condenser:
•
•
•
Plots
Tables
SetUp
Ú·¹«®» èòïïè
From these pages you can select the type of variables you want
to calculate and plot, view the calculated values, and plot any
combination of the selected variables. The default selected
variables are temperature, pressure, heat flow, enthalpy, and
vapor fraction. At the bottom of the Plots or Tables page, you
can specify the interval size over which the values should be
calculated and plotted.
Dynamics Tab
The Dynamics tab contains the following pages:
•
•
•
•
Specs
Holdup
StripChart
Heat Exchanger
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The Dynamics tab for a Reboiler is the same as the Dynamics
tab for the Condenser.
You are not required to modify information on the Reboiler’s
Dynamics tab when working in Steady State mode.
Specs Page
The Specs page contains information regarding initialization
modes, reboiler geometry, and reboiler dynamic specifications.
Ú·¹«®» èòïïç
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Model Details
The Initialization Mode
can be changed any time
when the integrator is
not running. The
changes cause the vessel
to re-initialize when the
integrator is started
again.
In the Model Details group, you can specify the initial
composition and amount of liquid that the separator should start
with when you start dynamics. This done via the initialization
mode which is discussed in the table below.
Initialization
Mode
Description
Initialize from
Products
The composition of the holdup is calculated from a
weighted average of all products exiting the holdup. A
PT flash is performed to determine other holdup
conditions. The liquid level is set to the value indicated
in the Liq Volume Percent field.
Dry Startup
The composition of the holdup is calculated from a
weighted average of all feeds entering the holdup. A PT
flash is performed to determine other holdup
conditions. The liquid level in the Liq Volume Percent
field is set to zero.
Initialize from
User
The composition of the liquid holdup in the reboiler is
user specified. The molar composition of the liquid
holdup can be specified by clicking the Init Holdup
button. The liquid level is set to the value indicated in
the Liq Volume Percent field.
The reboiler geometry can be specified in the Model Details
group. The following reboiler geometry parameters can be
specified in the same manner as the Geometry group on the
Sizing page of the Rating tab:
•
•
•
•
Volume
Diameter
Height (Length)
Geometry (Level Calculator)
The Liquid Volume Percent value is also displayed in this group.
You can modify the level in the condenser at any time. HYSYS
then uses that level as an initial value when the integrator is
run.
The Fraction Calculator determines how the level in the
condenser, and the elevation and diameter of the nozzle affects
the product composition.
There is only one Fraction Calculation mode available, it is called
Use Levels and Nozzles. The calculations are based on how the
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nozzle location and vessel liquid level affect the product
composition. Refer to the section on the Nozzles Page for more
information.
Dynamic Specifications
The Dynamic Specifications group contains fields where you can
specify what happens to the pressure of the reboiler when you
enter dynamic mode.
The Feed Delta P field allows you to impose a fixed pressure
drop between the vessel and all of the feed streams. This is
mostly supported for compatibility with Steady State mode. In
Dynamic mode, you are advised to properly account for all
pressure losses by using the appropriate equipment such as
valves or pumps or static head contributions. A zero pressure
drop should preferably be used here otherwise you may get
unrealistic results such as material flowing from a low to a high
pressure area.
The Fixed Vessel Pressure field allows you to fix the vessel
pressure in Dynamic mode. This option can be used in simpler
models where you do not want to configure pressure controllers
etc., or if the vessel is open to the atmosphere. In general the
specification should not be used, because the pressure should
be determined by the surrounding equipment.
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Holdup Page
The Holdup page contains information regarding the properties,
composition, and amount of the holdup.
Ú·¹«®» èòïîð
For each phase contained within the volume space of the unit
operation, the following is specified:
Refer to Section 1.3.7 Advanced Holdup
Properties in the
HYSYS Dynamic
Modeling guide for
more information.
Holdup Details
Description
Accumulation
The rate of change of material in the holdup for each
phase.
Moles
The amount of material in the holdup for each phase.
Volume
The holdup volume of each phase.
Click the Advanced button to access the view that provides more
detailed information about the holdup of that unit operation.
StripChart Page
The Stripchart page allows you to select and create default strip
charts containing various variable associated to the operation.
Refer to Section 1.3.4 - Stripchart Page/Tab for more
information.
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Heat Exchanger Page
The Heat Exchanger page opens a list of available heating
methods for the unit operation. This page contains different
objects depending on which radio button you select.
Ú·¹«®» èòïîï
•
Refer to Duty Radio
Button for more
information.
•
Refer to Tube Bundle
Radio Button for more
information.
•
If you select the None radio button, this page is blank
and the Condenser has no cooling source.
If you select the Duty radio button, this page contains
the standard heating parameters and you have to specify
an energy stream for the Reboiler.
If you select the Tube Bundle radio button, this page
contains the parameters used to configure a kettle
reboiler and you have to specify the required material
streams for the kettle reboiler.
The Tube Bundle options are only available in Dynamics
mode.
If you switch from Duty option or Tube Bundle option to
None option, HYSYS automatically disconnects the energy or
material streams associated to the Duty or Tube Bundle
options.
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Duty Radio Button
When the Duty radio button is selected the following heat
transfer options are available.
Ú·¹«®» èòïîî
The Heater Type group has two radio buttons:
•
•
When you select the
Liquid Heater radio
button, the Heater
Height as % Vessel
Volume group appears.
This group contains two
cells:
• Top of Heater
• Bottom of Heater
These cells are used to
specify the heater
height.
Liquid Heater
Vessel Heater
For the Liquid Heater method, the duty applied to the vessel
depends on the liquid level in the tank. The heater height value
must be specified. The heater height is expressed as a
percentage of the liquid level in the vessel operation. The
default values are 5% for the top of the heater, and 0% for the
bottom of the heater. These values are used to scale the amount
of duty that is applied to the vessel contents.
Q ã 0
L
B
LŠB
Q ã óóóóóóóóóóóóó Q Total
TŠB
B
L
Q ã Q Total
L
T
T
(8.14)
where:
L = liquid percent level (%)
T = top of heater (%)
B = bottom of heater (%)
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The Percent Heat Applied may be calculated as follows:
Q
Percent Heat Applied ã óóóóóóóóóóóóóóó
Q Total
100%
(8.15)
It is shown that the percent of heat applied to the vessel’s
holdup directly varies with the surface area of liquid contacting
the heater.
Ú·¹«®» èòïîí
ïðð
èð
êð
ìð
îð
Þ
ð
ð
îð
Ì
ìð
êð
èð
ïðð
Liquid Percent Level, L
Percent Heat Applied for a Liquid Heater
When you select the Vessel Heater radio button, 100% of the
duty specified or calculated in the SP cell is applied to the
vessel’s holdup:
Q = QTotal
(8.16)
where:
Q = total heat applied to the holdup
QTotal = duty calculated from the duty source
The Duty Source group has two radio buttons:
•
•
Direct Q
From Utility
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When you select the Direct Q radio button, the Direct Q Data
group appears. The following table describes the purpose of
each object in the group.
Object
Description
SP
The heat flow value in this cell is the same value specified
in the Duty field of the Parameters page on the Design tab.
Any changes made in this cell is reflected on the Duty field
of the Parameters page on the Design tab.
Min.
Available
Allows you to specify the minimum amount of heat flow.
Max.
Available
Allows you to specify the maximum amount of heat flow.
When you select the From Utility radio button, the Utility Flow
Properties group appears.
Ú·¹«®» èòïîì
The cells containing:
• black text indicates
the value is
calculated by
HYSYS and cannot
be changed.
• blue text indicates
the value is
entered by you,
and you can
change the value.
• red text indicates
the value is
calculated by
HYSYS, and you
can change the
value.
The following table describes the purpose of each object that
appears when the From Utility radio button is selected.
Object
Description
Heat Flow
Displays the heat flow value.
Available UA
Displays the overall heat transfer coefficient.
Utility Holdup
Displays the amount of holdup fluid in the reboiler.
Mole Flow
Displays the amount of fluid flowing out of the reboiler.
Min Mole Flow
Displays the minimum amount of fluid flowing out of
the reboiler.
Max Mole Flow
Displays the maximum amount of fluid flowing out of
the reboiler.
Heat Capacity
Displays the heat capacity of the fluid.
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Object
Description
Inlet Temp.
Displays the temperature of the stream flowing into
the condenser.
Outlet Temp.
Displays the temperature of the stream flowing out of
the condenser.
Initialize Duty
Valve
Allows you to initialize the UA, flow, and outlet
temperature to be consistent with the duty for
purposes of control.
8.6.3 Tray Section
At the very minimum, every Column Templates includes a tray
section. An individual tray has a vapour feed from the tray
below, a liquid feed from the tray above, and any additional
feed, draw or duty streams to or from that particular tray. The
property view for the tray section of a Distillation Column
template is shown in the figure below.
Ú·¹«®» èòïîë
The tray section property view contains the five tabs that are
common to most unit operations:
•
•
•
•
•
Design
Rating
Worksheet
Performance
Dynamics
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You are not required to change anything on the Rating tab and
Dynamics tab, if you are operating in Steady State mode.
Design Tab
The Design tab contains the following pages:
•
•
•
•
•
•
Connections
Side Draws
Parameters
Pressures
User Variables
Notes
Connections Page
The Connections page of the Tray Section is used for specifying
the names and locations of vapour and liquid inlet and outlet
streams, feed streams, and the number of stages (see Figure
8.125). When a Column template is selected, HYSYS inserts the
default stream names associated with the template into the
appropriate input cells. For example, in a Distillation Column,
the Tray Section vapour outlet stream is To Condenser and the
Liquid inlet stream is Reflux.
A number of conventions exist for the naming and locating of
streams associated with a Column Tray Section:
•
•
When you select a Tray Section feed stream, HYSYS by
default feeds the stream to the middle tray of the column
(for example, in a 20-tray column, the feed would enter
on tray 10). The location can be changed by selecting the
desired feed tray from the drop-down list, or by typing
the tray number in the appropriate field.
Streams entering and leaving the top and bottom trays
are always placed in the Liquid or Vapor Inlet/Outlet
fields.
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Specifying the location of a column feed stream to be either
the top tray (tray 1 or tray N, depending on your selected
numbering convention) or the bottom tray (N or 1)
automatically results in the stream becoming the Liquid Inlet
or the Vapour Inlet, respectively. If the Liquid Inlet or
Vapour Inlet already exists, your specified feed stream is an
additional stream entering on the top or bottom tray,
displayed with the tray number (1 or N). A similar
convention exists for the top and bottom tray outlet streams
(Vapour Outlet and Liquid Outlet).
Side Draws Page
On the Side Draws page, you can specify the name and type of
side draws taken from the tray section of your column. Use the
radio buttons to select the type of side draw:
•
•
•
Vapor
Liquid
Water
Select the cells to name the side draw stream, and specify the
tray from which it is taken.
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Parameters Page
By default, the Use Tray
Section Name for Stage
Name checkbox is
activated.
You can input the number of trays on the Parameters page. The
trays are treated as ideal if the fractional efficiencies are set to
1. If the efficiency of a particular tray is less than 1, the tray is
modeled using a modified Murphree Efficiency.
Ú·¹«®» èòïîê
You can add or delete trays anywhere in the column by clicking
the Customize button, and entering the appropriate information
in the Custom Modify Number of Trays group. This feature
makes adding and removing trays simple, especially if you have
a complex column, and you do not want to lose any feed or
product stream information. The figure below shows the view
that appears when the Customize button is clicked.
Ú·¹«®» èòïîé
You can add and remove trays by:
When you are adding or
deleting trays, all Feeds
remain connected to their
current trays.
•
Specify a new number of trays in the Current Number
of Trays field. This is the same as changing the number
of theoretical trays on the Connections page. All inlet
and outlet streams move appropriately; for example, if
you are changing the number of trays from 10 to 20, a
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ݱ´«³²óÍ°»½·º·½ Ñ°»®¿¬·±²-
•
stream initially connected to tray 5 is now at tray 10, and
a stream initially connected at stream 10 is now at tray
20.
Add or remove trays into or from individual tray section.
Adding Trays
To add trays to the tray section:
1. Enter the number of trays you want to add in the Number of
Trays to Add/Delete field.
2. Specify the tray number after, which you want to add the
trays in the Tray to Add After or Delete First field.
3. Click the Add Trays button, and HYSYS inserts the trays in
the appropriate place according to the tray numbering
sequence you are using. All streams (except feeds) and
auxiliary equipment below (or above, depending on the tray
numbering scheme) the tray where you inserted is moved
down (or up) by the number of trays that were inserted.
Removing Trays
To remove trays from the tray section:
1. Enter the number of trays you want to delete in the Number
of Trays to Add/Delete field.
2. Enter the first tray in the section you want to delete in the
Tray to Add After or Delete First field.
3. Click the Remove Trays button. All trays in the selected
section are deleted. If you are using the top-down
numbering scheme, the appropriate number of trays below
the first tray (and including the first tray) you specify are
removed. If you are using the bottom-up scheme, the
appropriate number of trays above the first tray (and
including the first tray) you specify are removed.
4. Streams connected to a higher tray (numerically) are not
affected; for example, if you are deleting 3 trays starting at
tray number 6, a side draw initially at tray 5 remains there,
but a side draw initially connected to tray 10 is now at tray
7. Any draw streams connected to trays 6,7 or 8 are deleted
with your confirmation to do so.
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If you select the Side Stripper radio button or Side Rectifier
radio button at the bottom of the view, this affects the pressure
profile. The pressure of the main tray section stage from which
the liquid feed stream is drawn is used as the side stripper
pressure, which is constant for all stages. The pressure of the
main tray section stage from which the vapour feed stream is
drawn is used as the Side Rectifier pressure, which is constant
for all stages.
Pressures Page
The Pressures page displays the pressure on each tray.
Whenever two pressures are known for the tray section, HYSYS
interpolates to find the intermediate pressures. For example, if
you enter the Condenser and Reboiler Pressures through the
Column Input Expert or Column property view, HYSYS calculates
the top and bottom tray pressures based on the Condenser and
Reboiler pressure drops. The intermediate tray pressures are
then calculated by linear interpolation.
Ú·¹«®» èòïîè
User Variables Page
The User Variables page enables you to create and implement
your own user variables for the current operation. For more
information refer to Section 1.3.3 - User Variables Page/
Tab.
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Notes Page
For more information,
refer to Section 1.3.2 Notes Page/Tab.
The Notes page provides a text editor where you can record any
comments or information regarding the specific unit operation,
or your simulation case in general.
Rating Tab
The Rating tab contains the following pages:
•
•
•
•
•
Sizing
Nozzles
Heat Loss
Efficiencies
Pressure Drop
Sizing Page
The Sizing page contains the required information for correctly
sizing column tray and packed sections. If the Sieve, Valve,
Bubble Cap radio button with the Uniform Tray Data are
selected, the following view is shown.
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The required size
information for the tray
section can be calculated
using the Tray Sizing
utility. Each parameter is
also discussed in Section
14.19 - Tray Sizing.
èóïêç
The tray section diameter, weir length, weir height, and the tray
spacing are required for an accurate and stable dynamic
simulation. You must specify all of the information on this page.
The Quick Size button allows you to automatically and quickly
size the tray parameters. The Quick Size calculations are based
on the same calculations that are used in the Tray Sizing Utility.
HYSYS only calculates the tray volume, based on the weir
length, tray spacing, and tray diameter. For multipass trays,
simply enter the column diameter and the appropriate total weir
length.
When you select the Packed radio button and the Uniform Tray
Data section, the Sizing page changes to the view shown below.
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The stage packing height, stage diameter, packing type, void
fraction, specified surface area, and Robbins factor are required
for the simple dynamic model. HYSYS uses the stage packing
dimensions and packing properties to calculate the pressure
flow relationship across the packed section.
Packing Properties
(Dynamics)
Description
Void Fraction
Packing porosity, i.e., m 3 void space/ m3 packed bed.
Specific Surface Area
Packing surface area per unit volume of packing (m-1).
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Packing Properties
(Dynamics)
Description
Robbins Factor
A packing-specific quantity used in the Robbins correlation, which is
also called the dry bed packing factor (m-1). The Robbins correlation
is used to predict the column vapour pressure drop. For the dry
packed bed at atmospheric pressure, î the Robbins or packing factor
is proportional to the vapour pressure drop.
Static Holdup
Static liquid, hst, is the m 3 liquid/ m 3 packed bed remaining on the
packing after it has been fully wetted and left to drain. The static
liquid holdup is a constant value.
Include Loading Regime
Term
Loading regime term is the second term in the Robbins pressure
drop equation, which is limited to atmospheric pressure and under
vacuum but not at elevated pressures. When pressure is high, (i.e.,
above 1 atm), inclusion of the loading regime term may cause an
unrealistically high pressure drop prediction.
To specify Chimney and Sump tray types, the Non Uniform Tray
Data Option must be selected from the Section Properties
group. The Non Uniform Tray Data Option allows you to model a
column with high fidelity by adjusting tray rating parameters on
a tray by tray basis.
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For a Trayed section of a column, you can adjust the Internal
Type of tray, Tray Spacing, Diameter, Weir Height, Weir Length,
DC Volume, Flow Path and Weeping factor. For a Packed section
of a column, you can adjust the Stage Packing Height, and
Diameter.
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From the Internal Type drop-down list in the Detailed Sizing
Information group, you can select alternative internal tray types
on a tray by tray basis. The Chimney and Sump internals along
with the weeping factor details are mentioned below.
Detailed Sizing
Information
Internal Type
Description
Chimney - This allows a higher liquid level and does
not have any liquid going down to the tray below.
Although vapor can go up through it but it does not
contact the liquid. The Chimney tray type can be
designated on any tray. By default, the weeping factor
is set to 0 and the stage efficiency is set to 5% on the
Efficiencies page. The weir height and tray spacing is
increased for a tray section. For a packed section stage
packing height is increased.
Sump - Only the bottom tray can be designated as a
sump. By default, the efficiency is set to 5%. The tray
spacing for a tray section and the stage packing height
in a packed section are increased when using a Sump.
Weeping Factor
The weeping factor can be adjusted on a tray by tray
basis. It is used to scale back or turn off weeping. By
default the weeping factor is set to 1 for all internal
types except the sump.
Nozzles Page
The Nozzles page contains the elevations at which vapour and
liquid enter or leave the tray section. Refer to Section 1.6.2 Nozzles in the HYSYS Dynamic Modeling guide for more
information.
Heat Loss Page
The Heat Loss page allows you to specify the heat loss from
individual trays in the tray section. You can select from either a
Direct Q, Simple or Detailed heat loss model or have no heat
loss from the tray sections.
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Direct Q Heat Flow Model
The Direct Q model allows you to input the heat loss directly
where the heat flow is distributed evenly over each tray section.
Otherwise you have the heat loss calculated from the Heat Flow
for each specified tray section.
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Using the checkbox, you can temporarily disable heat loss
calculations without losing any Heat Loss data that is entered.
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Simple Heat Flow Model
The Simple model allows you to calculate the heat loss by
specifying:
•
•
The Overall U value
The Ambient Temperature°C
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Detailed Heat Flow Model
Refer to Section 1.6.1 Detailed Heat Model in
the HYSYS Dynamic
Modeling guide for more
information.
The Detailed Heat Flow model allows you to specify more
detailed heat transfer parameters. The detailed properties can
be used on a tray to tray basis based on the temperature profile,
conduction, and convection data specified.
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Efficiencies Page
As with steady state, you can specify tray efficiencies for
columns in dynamics. However, you can only specify the overall
tray efficiency; component tray efficiencies are only available in
steady state.
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Pressure Drop Page
The Pressure Drop page
uses the same
calculation in the Tray
Sizing utility to calculate
the pressure drop for the
tray sections when the
column is running (i.e.,
using the traffics and
geometries to determine
what the pressure drop
is).
The Pressure Drop page displays the information associated with
the pressure drops (or pressures) across the tray section.
Activating the Rating Enabled checkbox turns on the pressure
drop calculations as part of the column solution.
The tray sizing utility calculates a pressure drop across each
tray, you need to fix one end of the column (top or bottom),
allowing the other trays to float with the calculations. You can
select which end of the column to be fixed by selecting the
appropriate radio button in the Fix Tray group.
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The Tray Section Pressure Drop field displays the absolute
overall pressure change between the fixed tray and the last tray
at the other end.
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Worksheet Tab
The PF Specs page is
relevant to dynamics
cases only.
The Worksheet tab contains a summary of the information
contained in the stream property view for all the streams
attached to the Tray Section. Refer to Section 1.3.1 Worksheet Tab for more information.
Performance Tab
The Performance tab contains the following pages:
•
•
•
•
•
Pressure
Temperature
Flow
Summary
Hydraulics
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Pressure Page
The Pressure page contains a table that lists all the pressure for
each tray. The table also includes the names of any inlet
streams associated to a tray and the inlet streams’ pressure.
Temperature Page
The Temperature page contains a table that lists all the
temperature for each tray. The table also includes the names of
any inlet streams associated to a tray and the inlet streams’
temperature.
Flow Page
The Flow page contains a table that lists all the liquid and
vapour flow rates for each tray. The table also includes the
names of any inlet streams associated to a tray and the inlet
streams’ flow rate. You can also change the unit of the flow rates
displayed by selecting the unit from the Flow Basis drop-down
list. There are four possible units:
•
•
•
•
Molar
Mass
Standard Liquid Volume
Actual Volume
Summary Page
The Summary page contains a table that displays the flow rates,
temperature, and pressure for each tray.
Hydraulics Page
The Hydraulics page is
only available in dynamic
mode.
The Hydraulics page contains a table that displays the height
and pressure of Dry Hole DP, Static Head, and Height over Weir.
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Dynamics Tab
The Dynamics tab contains the following pages:
•
•
•
•
Specs
Holdup
Static Head
StripChart
Specs Page
The Specs page contains the Nozzle Pressure Flow k Factors for
all the trays in the tray section. You can select to have HYSYS
calculate the k value for all the trays by clicking the All Stages
button. If you want HYSYS to calculate the k values for certain
trays only, select the desired trays and click the Selected Stages
button. HYSYS only calculates the k values for the selected
stages.
Ú·¹«®» èòïíé
The Use tower diameter method checkbox, when activated,
calculates the k values for the column based on the column
diameter. When the checkbox is deactivated the k values are
calculated using the results obtained from the steady state
model, providing a smoother transition between your steady
state model and dynamic model.
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Weeping can start to
occur on a tray when the
dry hole pressure loss
drops below 0.015 kPa.
It allows liquid to drain
to the stage below even
if the liquid height is
below the weir height.
The Model Weeping checkbox, when activated, takes into
account any weeping that occurs on the tray sections and add
the effects to your model.
The Perform dry start up checkbox allows you to simulate a dry
start up. Activating this checkbox removes all the liquid from all
the trays when the integrator starts.
The Initialize From User checkbox allows you to start the
simulation from conditions you specify. Activating this checkbox,
activates the Init HoldUp button. Click this button to enter the
initial liquid mole fractions of each component and the initial
flash conditions.
The Fixed Pressure Profile checkbox allows you to simulate the
column based on the fixed pressure profile.
Pressure Profile
You do not have to
configure pressure
control systems with
this option. This option
is not recommended for
rigorous modeling work
where the pressure can
typically change on
response to other
events.
The Fixed Pressure Profile checkbox allows you to run the
column in Dynamic mode using the steady state pressure
profile. This option simplifies the column solution for
inexperienced users, and makes their transition from the steady
state to dynamics simulation a bit easier.
The pressure profile of a tray section is determined by the static
head, which is caused mostly by the liquid on the trays, and the
frictional pressure losses, which are also known as dry hole
pressure loses.
The frictional pressure losses are associated with vapour flowing
through the tray section. The flowrate is determined by
Equation (8.17).
flow ã k
density
friction pressure losses
(8.17)
In HYSYS, the k-value is calculated by assuming:
k
Tray diameter
2
(8.18)
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However, if the Fixed Pressure Profile option is selected, then
the static head contribution can be subtracted and hence the
vapour flow and the frictional pressure loss is known. This allows
the k-values to be directly calculated to match steady state
results more closely.
Holdup Page
The Holdup page contains a summary of the dynamic simulation
results for the column. The holdup pressure, total volume and
bulk liquid volume results on a tray basis are contained in this
view. Double-clicking on a stage name in the Holdup column
opens the stage property view.
You can double-click on any cell within each row to view the
advanced holdup properties for each specific tray section.
Static Head Page
Refer to Section 1.6.5
- Static Head in the
HYSYS Dynamic
Modeling guide for
more information.
The Static Head page enables you to select how the static head
contributes to the calculation.
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Since static head contributions are often essential for proper
column modeling, internal static head contributions are
generally considered for the column model in any case, and
should only be disabled under special circumstances.
StripChart Page
Refer to Section 1.3.4
- Stripchart Page/Tab
for more information.
The Stripchart page allows you to select and create default strip
charts containing various variable associated to the operation.
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8.6.4 Tee
Refer to Chapter 5 Piping Equipment for
more details on the
property view of the TEE.
Refer to the section on
the General Features of
the Solving Methods for
information on which
method supports Tee
operation.
The property view for the Tee operation in the Column subflowsheet has all of the pages and inherent functionality
contained by the Tee in the Main Environment with one addition,
the Estimates page.
Ú·¹«®» èòïíç
On the Estimates page, you can help the convergence of the
Column sub-flowsheet's simultaneous solution by specifying flow
estimates for the tee product streams. To specify flow
estimates:
1. Select one of the Flow Basis radio buttons: Molar, Mass or
Volume.
2. Enter estimates for any of the product streams in the
associated fields next to the stream name.
There are four buttons on the Estimates page, which are
described in the table below.
Button
Related Setting
Update
Replaces all estimates except user specified estimates
(in blue) with values obtained from the solution.
Clear Selected
Deletes the highlighted estimate.
Clear Calculated
Deletes all calculated estimates.
Clear All
Deletes all estimates.
If the Tee operation is attached to the column, i.e., via a draw
stream, one tee split fraction specification is added to the list of
column specifications for each tee product stream that you
specify. As you specify the split fractions for the product
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streams, these values are transferred to the individual column
specifications on the Monitor page and Specs page of the
column property view.
The additional pieces of equipment available in the Column
sub-flowsheet are identical to those in the main flowsheet.
For information on each piece of equipment, refer to its
respective chapter (e.g., for information on the Heat
Exchanger, refer to Section 4.3 - Heat Exchanger). All
operations within the Column sub-flowsheet environment
are solved simultaneously.
8.7 Running the Column
Once you are satisfied with the configuration of your Column
sub-flowsheet and you have specified all the necessary input,
the next step is to run the Column solution algorithm.
The iterative procedure begins when you click the Run button on
the Column property view. The Run/Reset buttons can be
accessed from any page of the Column property view.
When you are inside the Column build environment, a Run
icon also appears on the toolbar, which has the same
function as the Run button on the Column property view.
Run icon
Stop icon
On the toolbar, the Run icon and Stop icon are two separate
icons. Whichever icon is toggled on has light grey shading.
When the Run button on the Column property view is clicked,
the Run/Reset buttons are replaced by a Stop button which,
when clicked, terminates the convergence procedure. The Run
button can then be clicked again to continue from the same
location. Similarly, the Stop icon switches to a grey shading with
the Run icon on the toolbar after it is activated.
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When you are working inside the Column build environment, the
Column runs only when you click the Run button on the Column
property view, or the Run icon on the toolbar. When you are
working with the Column property view in the Main build
environment, the Column automatically runs when you change:
•
•
A specification value after a converged solution has been
reached.
The Active specifications, such that the Degrees of
Freedom return to zero.
8.7.1 Run
Refer to Monitor Page
from Section 8.4.1 Design Tab for more
information.
The Run command begins the iterative calculations necessary to
simulate the column described by the input. On the Monitor
page of the Column property view, a summary showing the
iteration number, equilibrium error, and the heat and
specification errors appear. Detailed messages showing the
convergence status are shown in the Trace Window.
The default basis for the calculation is a modified “inside-out”
algorithm. In this type of solution, simple equilibrium and
enthalpy models are used in the inner loop, which solve the
overall component and heat balances, vapour-liquid equilibrium,
and any specifications. The outer loop updates the simple
thermodynamic models with rigorous calculations.
When the simulation is running, the status line at the bottom of
the screen first tracks the calculation of the initial properties
used to generate the simple models. Then the determination of
a Jacobian matrix appears, which is used in the solution of the
inner loop. Next, the status line reports the inner loop errors
and the relative size of the step taken on each of the inner loop
iterations. Finally, the rigorous thermodynamics is again
calculated and the resulting equilibrium, heat, and spec errors
reported. The calculation of the inner loop and the outer loop
properties continues until convergence is achieved, or you
determine that the column cannot converge and click Stop to
terminate the calculation.
If difficulty is encountered in converging the inner loop, the
program occasionally recalculates the inner loop Jacobian. If no
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obvious improvement is being made with the printed equilibrium
and heat and spec errors, click Stop to terminate the
calculations and examine the available information for clues.
Refer to Section 8.8 - Column Troubleshooting for solutions
to some common troubles encountered while trying to achieve
the desired solution.
Refer to Estimates Page
from Section 8.4.2 Parameters Tab for
more information.
Any estimates which appear in the Column Profile page and
Estimates page are used as initial guesses for the convergence
algorithm. If no estimates are present, HYSYS begins the
convergence procedure by generating initial estimates.
8.7.2 Reset
The Reset command clears the current Column solution, and any
estimates appearing on the Estimates page of the Column view.
If you make major changes after getting a converged Column, it
is a good idea to Reset to clear the previous solution. This allows
the Column solver to start fresh and distance itself from the
previous solution. If you make only minor changes to the
Column, try clicking Run before Resetting.
Once the column calculation has started it continues until it has
either converged, has been terminated due to a mathematically
impossible condition, (e.g., being unable to invert the Jacobian
matrix), or it has reached the maximum number of iterations.
Other than these three situations, calculations continue
indefinitely in an attempt to solve the column unless the Stop
button is clicked. Unconverged results can be analysed, as
discussed in Section 8.8 - Column Troubleshooting.
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8.8 Column
Troubleshooting
Although HYSYS does not require any initial estimates for
convergence, good estimates of top and bottom temperatures
and one product accelerate the convergence process. Detailed
profiles of vapour and liquid flow rates are not required.
However, should the column have difficulty, the diagnostic
output printed during the iterations provides helpful clues on
how the tower is performing. If the equilibrium errors are
approaching zero, but the heat and spec errors are staying
relatively constant, the specifications are likely at fault. If both
the equilibrium errors and the heat and spec errors do not
appear to be getting anywhere, then examine all your input
(e.g., initial estimates, specifications, and tower configuration).
In running a column, keep in mind that the Basic Column
Parameters cannot change. By this, it is meant that column
pressure, number of trays, feed tray locations, and extra
attachments such as side exchanger and pump around locations
remain fixed. To achieve the desired specifications the Column
only adjusts variables which have been specified as initial
estimates, such as reflux, side exchanger duties, or product flow
rates. This includes values that were originally specifications but
were replaced, thereby becoming initial estimates. It is your
responsibility to ensure that you have entered a reasonable set
of operating conditions (initial estimates) and specifications
(Basic Column Parameters) that permit solution of the column.
There are obviously many combinations of column
configurations and specifications that makes convergence
difficult or impossible. Although all these different conditions
could not possibly be covered here, some of the more frequent
problems are discussed in the following sections.
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8.8.1 Heat and Spec Errors Fail
to Converge
This is by far the most frequent situation encountered when a
column is unable to satisfy the allowable tolerance. The
following section gives the most common ailments and
remedies.
Poor Initial Estimates
To see the initial
estimates, click the View
Initial Estimates button
on the Monitor page of
the column property view.
Initial estimates are important only to the extent that they
provide the initial starting point for the tower algorithm.
Generally, poor guesses simply cause your tower to converge
more slowly. However, occasionally the effect is more serious.
Consider the following:
•
•
•
Check product estimates using approximate splits. A
good estimate for the tower overhead flow rate is to add
up all the components in your feed which are expected in
the overheads, plus a small amount of your heavy key
component. If the tower starts with extremely high
errors, check to see that the overhead estimate is
smaller than the combined feed rates.
Poor reflux estimates usually do not cause a problem
except in very narrow boiling point separations. Better
estimates are required if you have high column liquid
rates relative to vapour rates, or vice versa.
Towers containing significant amounts of inert gases,
e.g., H2, N2, etc., require better estimates of overhead
rates to avoid initial bubble point problems. A nitrogen
rejection column is a good example.
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Input Errors
Clicking the Input
Summary button on the
Monitor page of the
column property view
displays the column
input in the Trace
Window.
It is good practice to check all of your input just before running
your column to ensure that all your entries, such as the stage
temperatures and product flow rates, appear reasonable:
•
•
•
•
Check to ensure that your input contains the correct
values and units. Typical mistakes are entering a product
flow rate in moles/hr when you really meant to enter it in
barrels/day, or a heat duty in BTU/hr instead of E+06
BTU/hr.
When specifying a distillate liquid rate, make sure you
have specified the Distillate rate for the condenser, not
the Reflux rate.
If you change the number of trays in the column, make
sure you have updated the feed tray locations, pressure
specifications, and locations of other units such as side
exchangers on the column.
If the tower fails immediately, check to see if all of your
feeds are known, if a feed was entered on a non-existent
tray, or if a composition specification was mistakenly
entered for a zero component.
Incorrect Configuration
For more complex tower configurations, such as crude columns,
it is more important that you always review your input carefully
before running the tower. It is easy to overlook a stripping feed
stream, side water draw, pump around or side exchanger. Any
one of these omissions can have a drastic effect on the column
performance. As a result, the problem is not immediately
obvious until you have reviewed your input carefully or tried to
change some of the specifications.
•
Check for trays which have no counter-current vapourliquid traffic. Examples of this are having a feed stream
on a tray that is either below the top tray of an unrefluxed tower or a tower without a top lean oil feed, or
placing a feed stream above the bottom stage of a tower
that does not have a bottom reboiler or a stripping feed
stream below it. In both cases the trays above or below
the feed tray become single phase. Since they do not
represent any equilibrium mass transfer, they should be
removed or the feed should be moved. The tower cannot
converge with this configuration.
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•
•
•
èóïèé
The tower fails immediately if any of the sidestrippers do
not have a stripping feed stream or a reboiler. If this
should occur, a message is generated stating that a
reboiler or feed stream is missing in one of the
sidestrippers.
Make sure you have installed a side water draw if you
have a steam-stripped hydrocarbon column with free
water expected on the top stage.
Regardless of how you have approached solving crude
columns in the past, try to set up the entire crude
column with your first run, including all the side
strippers, side exchangers, product side draws, and
pump arounds attached. Difficulties arise when you try to
set up a more simplified tower that does not have all the
auxiliary units attached to the main column, then assign
product specs expected from the final configuration.
Impossible Specifications
Impossible specifications are normally indicated by an
unchanging heat and spec error during the column iterations
even though the equilibrium error is approaching zero. To get
around this problem you have to either alter the column
configuration or operating pressure or relax/change one of the
product specifications.
•
•
•
•
•
You cannot specify a temperature for the condenser if
you are also using subcooling.
If you have zero liquid flows in the top of the tower,
either your top stage temperature spec is too high, your
condenser duty is too low, or your reflux estimate is too
low.
If your tower shows excessively large liquid flows, either
your purity specs are too tight for the given number of
trays or your Cooler duties are too high.
Dry trays almost always indicate a heat balance problem.
Check your temperature and duty specifications. There
are a number of possible solutions: fix tray traffic and let
duty vary; increase steam rates; decrease product
makes; check feed temperature and quality; check feed
location.
A zero product rate could be the result of an incorrect
product spec, too much heat in the column which
eliminates internal reflux, or the absence of a heat
source under a total draw tray to produce needed vapour.
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Conflicting Specifications
This problem is typically the most difficult to detect and correct.
Since it is relatively common, it deserves considerable attention.
•
•
•
•
•
•
•
•
•
You cannot fix all the product flow rates on a tower.
Avoid fixing the overhead temperature, liquid and vapour
flow rates because this combination offers only a very
narrow convergence envelope.
You cannot have subcooling with a partial condenser.
A cut point specification is similar to a flow rate spec; you
cannot specify all flows and leave one unspecified and
then specify the cut point on that missing flow.
Only two of the three optional specifications on a pump
around can be fixed, i.e., duty and return temperature,
duty and pump around rate, etc.
Fixing column internal liquid and vapour flows, as well as
duties can present conflicts since they directly affect
each other.
The bottom temperature spec for a non-reboiled tower
must be less than that of the bottom stage feed.
The top temperature for a reboiled absorber must be
greater than that of the top stage feed unless the feed
goes through a valve.
The overhead vapour rate for a reboiled absorber must
be greater than the vapour portion of the top feed.
Heat and Spec Error Oscillates
While less common, this situation can also occur. It is often
caused by poor initial estimates. Check for:
•
•
•
Water condensation or a situation where water
alternately condenses and vapourizes.
A combination of specifications that do not allow for a
given component to exit the column, causing the
component to cycle in the column.
Extremely narrow boiling point separations can be
difficult since a small step change can result in total
vapourization. First, change the specifications so that the
products are not pure components. After convergence,
reset the specifications and restart.
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8.8.2 Equilibrium Error Fails to
Converge
This is almost always a material balance problem. Check the
overall balance.
•
•
Check the tower profile. If the overhead condenser is
very cold for a hydrocarbon-steam column, you need a
water draw. Normally, a side water draw should be added
for any stage below 200oF.
If the column almost converges, you may have too many
water draws.
8.8.3 Equilibrium Error
Oscillates
This generally occurs with non-ideal towers, such as those with
azeotropes. Decreasing the damping factor or using adaptive
damping should correct this problem (Refer to Section 8.4.2 Parameters Tab).
8.9 References
ï
Sneesby, Martin G., Simulation and Control of Reactive Distillation,
Curtin University of Technology, School of Engineering, March 1998.
î
Henry, Kister., Distillation Design, (1992), pp 497-499.
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