Energy Conservation and Optimization in Condensate Splitter

Energy Conservation and Optimization in Condensate Splitter
A publication of
CHEMICAL ENGINEERINGTRANSACTIONS
VOL. 35, 2013
Guest Editors:PetarVarbanov, JiříKlemeš,PanosSeferlis, Athanasios I. Papadopoulos, Spyros Voutetakis
Copyright © 2013, AIDIC ServiziS.r.l.,
ISBN 978-88-95608-26-6; ISSN 1974-9791
The Italian Association
of Chemical Engineering
www.aidic.it/cet
DOI: 10.3303/CET1335230
Energy Conservation and Optimization in Condensate
Splitter Plant
Eid M. Al-Mutairi*, Husamelden Elkawad
Department of Chemical Engineering
King Fahd University of Petrolem Minerals, Saudi Arabia, Dhahran, 31261
mutairi@kfupm.edu.sa
In this work, energy integration of a heat exchanger network (HEN) of the Plant Refinery was carried out
using the Pinch Analysis Technology through (Heat-int) software. From the operating data, the HEN data
was extracted, then the heat exchanger network data were analysed through varying the Pinch
temperature and the amount of hot and cold utilities were observed. Also the effects of Pinch temperature
on the area of heat exchangers were done. The percentages of changing in hot and cold utilizes beside
the area of heat exchangers were investigated and the percentages of utilities and area changing with
Pinch temperature were done. The main problem of the exiting heat exchanger network came from cross
Pinch temperature, seven heat exchangers with total energy of 183.1 MMBTU/h crosses the Pinch Point
that violated the Pinch rules. Cross Pinch Point with different Pinch temperature was found to occur, so
attention must be taken with these temperatures.
The area efficiency of the current heat exchangers is 0.397 comparing with the ideal area with the same
amount of hot utility. Retrofitting of the current heat exchangers was done by replacing some heat
exchangers and adding new units. The reduced in hot and cold utilities were 6.79% and 27.9%
respectively with 10.6% decreases in the area.
1. Introduction
Pinch technology is a methodology derived from simple scientific principles, by which it is possible to
design new plants with optimum energy and capital costs. Also it’s used with existing processes to improve
the performance.
The condensate splitter plant produced high quality of naphtha, stabilized naphtha, LPG, heavy naphtha,
kerosene, light and heavy diesel and atmospheric gas oil (AGO) for domestic uses and exportation.
In this work we are going to extract and analyse the information data to find the quantities of hot and cold
utilities required for the crude distillation unit (CDU) and then investigate the effects of changing the Pinch
temperature on the current heat exchanger network (HEN) using Heat-int software.
The Pinch Analysis technique has been used globally to target hot and cold energy requirement for crude
distillation units (CDU) specifically and for any distillation column – see (Ajay et al., 2010) for general heat
integration of distillation columns and (Nakaiwa et al,, 2003) for internally heat integrated distillation
columns. Al-Riyami (2001) studied the effects of changing the Pinch temperature of a fluid catalytic
cracking plant on the hot and cold utilizes and the area of the heat exchanger networks. Ajao and Akande
(2009) investigated the energy integration of the crude pre heat train of Kaduna refinery where they found
out the optimum Pinch temperature for the pre-heat train using Pinch Analysis techniques. Salomeh (2008)
used the Heat-Int software which is based on methods of Pinch Technology to design, optimize and
improve the integrated heat exchanger network of crude oil preheating Process in distillation unit in Arak
refinery.
Revamping projects using pinch design method were conducted for existing oil refineries to improve their
operation and achieve more energy savings (Liebmann and Dhole, 1995). On the other hand, the stage
model has been applied to many CDUs such as work of Promvitak et al. (2009).
Please cite this article as: Al-Mutairi E.M., Elkawad H., 2013, Energy conservation and optimization in condensate splitter plant, Chemical
Engineering Transactions, 35, 1381-1386 DOI:10.3303/CET1335230
1381
2. Process Description
The process consists of desalting units, stabilized feed and the crude distillation units as shown in the
block diagram in figure (1).
Condensate
Crude distillation unit
Desalting unit
Fraction Overhead& CDU Overhead
Stabilizer Unit
Final Products
LPG & Light Naphtha
Figure 1: The Process Block Diagram
The splitter plant Refinery of the crude condensate produced a high quality of Naphtha, stabilized
Naphtha, Liquefied Petroleum Gas (LPG), Heavy Naphtha, Kerosene, Light and Heavy diesel and
atmospheric Gas Oil (AGO) for domestic uses and exporting.
First, the condensate crude from storage is preheated by the resulting products from the Crude Distillation
Unit (CDU). The crude enters the desalting unit to remove the dissolved salts. Then it’s entering the first
distillation column (Flash Column). The bottom product from the flash columns heated in two furnaces
using flue fuel gases then enters a second distillation column (CDU) .The top product is routed as feed to
the condensate fractionator, while medium naphtha sent to the fractionator’s top and light naphtha is
routed to the fractionator’s overhead/cold condensate exchanger. The distillations products are then used
to pre-heat the feedstock before storing in the tanks or sends to exporting ports.
3. Data Extraction
The source temperature (Ts), target temperature (Tt), flow –rate and heat capacity and of each streams in
the heat exchangers network were extracted. Also the areas of each heat exchanger in the network were
extracted. The physical properties of the products from the crude distillation unit are shown in Table 1.
Table 1: The Physical Properties of the Crude Distillation Unit Products
No
Stream Name
Type
1
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Fractionators overhead
Heavy naphtha
Kerosene
Light diesel
Heavy diesel
Fraction bottom
Dirty was oil
Factional feed
Pre flash column overhead
Hot crude
Crude
Cold
Cold
Cold
Cold
Cold
Cold
Cold
Hot
Cold
Hot
Hot
Density
3
lb/ft
0.41
39
38
42
42
42
40
40
0.63
40
48
Viscosity CP
Specific gravity
0.01
0.18
0.17
0.24
0.24
0.3
0.21
0.01
0.2
0.84
0.78
0.81
0.83
0.85
0.88
0.87
0.87
0.78
0.78
4. Heat Exchangers Network
The process includes 128 streams with cold streams and hot streams. Also it’s includes process to
process heat exchangers and hot and cold utilities heat exchangers. The hot exchanger’s utility uses
steam and flue gases, and the cold utilities heat exchangers uses sea water and air as coolants. The
energy consumptions of the exiting process are shown on the grand composite curve in Figure 2.
1382
Figure 2: The Current Heat Exchanger Network Grand Composite Curve
0
From the diagram, the pinch temperature of the network is 28.85 F, the amounts of the hot and cold
utilities are 329 MMBTU/h and 429.8 MMBTU/h, the processes to processes heat exchanges is 893.2
MMBTU/h. The percentage of the energy consumptions are as shown in Table 2.
Table 2: Existing Utilities Percentage
Hot Utilities
Flue Gases
150 Psig
99.998 %
0.001 %
Cold Utilities
Air Cooling
Sea Water
0.178 %
4.1 Capital, Utilities and Total Cost of the Existing Heat Exchanger Network
The annual costs and the area of the existing network are shown in Table 3.
Table 3: The Current Heat Exchanger Network Data
Commodity
Hot Utility Cost
Cold Utility Cost
Total Utility Cost
Capital Cost
Total Network Cost
Total Area
Process area
Utility area
Amount
4.44
32,000
32,000
8,390
72,400
432.0
29.0
141.6
Unit
3
10 SAR/y
3
10 SAR/y
3
10 SAR/y
3
10 SAR/y
3
10 SAR/y
3 2
10 ft
3 2
10 ft
3 2
10 ft
Table 4: The Current Heat Exchanger Cross Pinch Energy
1.
2.
3.
4.
5..
6.
7.
Heat Exchanger No.
E231
E101
E201
E222
E350
E211
E241
Total Energy
Energy (MMBTU/h)
1.70
47.9
9.27
22.4
27.2
144.4
12.2
183.1
1383
4.2 Analysing of Exiting Heat Exchanger Network
The existing network consists from 64 heat exchangers (process to process heat exchangers, two
furnaces, three utilities and air fans cooling heat exchangers).Through analyzing the network to determine
the inappropriate uses of energy consumption, either through crossing the Pinch temperature or
inappropriate using for utilities. Table 4 shows the heat exchangers that violated the pinch rule.
4.3 Analysing the Heat Exchangers Network at Different Pinch Temperature
When applying different pinch temperatures for the exiting heat exchangers network, some heat
exchangers violated one of the Pinch rules, heat transfer across Pinch. Table 5 below shows the numbers
of heat exchangers that violated this rule and the amount of heat transfer through the Pinch. Figure 3
shows the loss of energy due to cross pinch temperature decreases as the pinch temperature increases.
Table 5: The Current Heat Exchanger Cross Pinch Energy
o
Heat Exchanger No.
E101
E241
E211
E231
E222
E350
E202
Total
Pinch temperature 10 F
Heat Transferred
(MMBTU/h)
3.23
18.92
4.32
19.76
7.48
17.93
0.293
103.61
o
Pinch temperature 15 F
Heat Transferred
(MMBTU/h)
12.80
26.92
3.34
18.18
7.48
14.03
2.35
84.14
o
Pinch temperature 20 F
Heat Transferred
(MMBTU/h)
16.14
14.95
2.35
16.60
7.48
10.14
1.76
69.43
Figure 3: Cross Pinch Temperature Energy vs. different Pinch Temperatures
4.4 Determination of area efficiency for Retrofit Design
In retrofit design the area efficiency measures the performance of the exiting heat exchangers network
with the ideal network. The closer the exiting heat exchangers area to the curve, best performance is given
by the installed heat exchangers area. As shown in Figure 4, the efficiency of exiting heat exchangers area
2
is 0.397, whereas the exiting and target areas for the energy recovery were 432,100 and 190,022 ft .
1384
Figure 4: Energy Area Plot of the CDU Heat Exchangers Area vs. Energy Recovery
4.5 Adjusting the Current Heat Exchangers Network
When pinch analysis was applied to the current heat exchangers network, seven heat exchangers (E221,
E241, E231, E101, E211, E222, E 350 and E202) crossed the pinch temperature as shown in Table 6. In
order to avoid this situation, some arrangement for the network design is suggested as shown in Figure 5
in general manner. The solutions steps are:1. Determine the heat exchangers that cross the pinch temperature
2. Find out which stream violate the pinch rule
3. Move the exiting heat exchangers either below or above the pinch point, calculate the new are needed
4. Calculate the area for heat exchanger for the remaining energy recovery
After these steps, the expected energy saving were 6.79 % and 27.9 % for hot and cold utilities required.
Table 6: Heat Exchangers Crossing Pinch Temperature
Heat Exchanger Stream Crossing Pinch Temperature Energy Transferred (MMBtu/h)
Hot stream
Cold stream
1. E101
hot
42.8
2. E241
hot + cold
17.4
10.7
3. E211
hot + cold
3.4
9.6
4. E231
hot
10.9
5. E222
hot
4.0
6. E350
hot
4.1
7. E201
hot
4.6
In this procedure, the old heat exchangers that violated the pinch rules will be replaced by efficient heat
exchangers. The area will be reduced by 10.5 % in the new design.
Table 7: Heat Exchangers retrofit of current network
HE
E101
E201
E231
E222
E241
E350
E211
3 2
Old Area (10 ft )
5.50
4.31
5.14
3.62
9.21
4.88
7.40
3 2
New Area (10 ft )
6.01
3.68
4.08
3.64
3.08
10.1
5.22
1385
Solution
Pinch temp.
Pinch temp.
Figure 5: Suggested Solution for the Current Heat Exchangers Network
5. Conclusions
In conclusion, the Heat Integration of the heat exchanger network (HEN) of The Plant Refinery was carried
out using the Pinch Analysis. It was found that retrofitting of the existing HEN can save a lot of energy.
Modifications of current HEN were illustrated to show merits and benefits of integrating the energy within
the plant.
Acknowledgements
The authors thank King Fahd University of Petroleum & Minerals (KFUPM) for the financial support.
References
Ajay M., Amiya K. J., 2010, A New intensified heat integration in distillation column. Ind. Eng. Chem. Res.,
49. 9534-9541.
Ajao K.R, Akande H.F., 2009, Energy Integration of Crude Distillation Unit Using Pinch Analysis,
Researcher, 1(2), 54–66.
Al-Riyami B.A., Klemes J., Perry S., 2001, Heat integration retrofit analysis of a heat exchanger network of
a fluid catalytic cracking plant. Applied Thermal Engineering 21, 1449-1487.
Liebmann K., Dhole V.R., 1995, Integrated crude distillation design, Comput. Chem. Eng. 19(1), S119–
S124.
Nakaiwa M., Huang, K., Endo T., Ohmori, T., Akiya, T., Takamatsu T., 2003, Internally heat integrated
distillation columns: A review. Chemical Engineering Research and Design, 81(1), 162–177.
Promptak P., Siemanond K.,Bunluesriruang S., Raghareutai V., 2009, Retrofit Design of Heat Exchanger
Networks of Crude Oil Distillation Unit. Chemical Engineering Transactions, 18, 99-104.
Salomeh C., Reza D., Afshin M., 2008, Modification of Preheating Heat Exchanger Network in Crude
Distillation Unit of Arak Refinery Based on Pinch Technology, WCECS 2008, San Francisco, USA,
123-127.
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