/smash/get/diva2:15031/FULLTEXT01.pdf

/smash/get/diva2:15031/FULLTEXT01.pdf
Thermodynamic Properties of CO2 Mixtures and Their
Applications in Advanced Power Cycles with CO2 Capture
Processes
Hailong Li
Energy Processes
Department of Chemical Engineering and Technology
Royal Institute of Technology
Stockholm, Sweden
KTH, Royal Institute of Technology
School of Chemical Science and Engineering
Department of Chemical Engineering and Technology
Division of Energy Processes
SE-100 44 Stockholm
Sweden
Copyright © Hailong Li, 2008
All rights reserved
TRITA-CHE Report 2008:58
ISSN 1654-1081
ISBN 978-91-7415-091-9
Hope it is something…
Abstract:
The thermodynamic properties of CO2 mixtures are essential for the design and operation of
CO2 capture and storage (CCS) systems. A better understanding of the thermodynamic
properties of CO2 mixtures could provide a scientific basis to define a proper guideline of CO2
purity and impure components for the CCS processes according to technical, safety, and
environmental requirements. However, the available accurate experimental data cannot cover
the entire operation conditions of the CCS processes. In order to overcome the shortage of
experimental data, theoretical modelling and estimation are used as a supplemental approach.
In this thesis, the available experimental data on the thermodynamic properties of CO2 mixtures
were first collected; their applicability and gaps for theoretical model verification and calibration
were also determined according to the required thermodynamic properties and operation
conditions of CCS. Then, in order to provide recommendations concerning calculation
methods for the engineering design of CCS, a total of eight equations of state (EOS) were
evaluated for the calculations concerning vapour liquid equilibrium (VLE) and volume of CO2
mixtures, including N2, O2, SO2, Ar, H2S, and CH4.
With the identified equations of state, the preliminary assessment of the impact of impurity was
further conducted regarding the thermodynamic properties of CO2 mixtures and the different
processes involved in the CCS system. Results show that the increment of the mole fraction of
non-condensable gases would make purification, compression, and condensation more difficult.
Comparatively, N2 can be separated more easily from the CO2 mixtures than O2 and Ar.
Moreover, a lower CO2 recovery rate is expected for the physical separation of CO2/N2 under
the same separation conditions. In addition, the evaluations of the acceptable concentration of
non-condensable impurities show that the transport conditions in vessels are more sensitive to
the non-condensable impurities, thus, requiring very low concentration of non-condensable
impurities in order to avoid two-phase problems.
Meanwhile, the performances of evaporative gas turbine integrated with different CO2 capture
technologies were investigated from both technical and economical aspects. It is concluded that
the evaporative gas turbine (EvGT) cycle with chemical absorption capture has a smaller
penalty on electrical efficiency, but a lower CO2 capture ratio than the EvGT cycle with
O2/CO2 recycle combustion capture. Therefore, although EvGT + chemical absorption has a
higher annual cost, it has a lower cost of electricity because of its higher efficiency. However,
considering its lower CO2 capture ratio, EvGT + chemical absorption has a higher cost to
capture 1 ton CO2. In addition, the efficiency of EvGT + chemical absorption can be increased
by optimizing Water/Air ratio, increasing the operating pressure of stripper, and adding a flue
gas condenser condensing out the excessive water.
Language: English.
Keywords: thermodynamic property, vapour liquid equilibrium, volume, equation of state,
interaction parameter, CO2 mixtures, evaporative gas turbine, chemical absorption, oxy-fuel
combustion, cost evaluation, CO2 capture and storage
I
II
Table of Contents
Abstract .............................................................................................................................. I
Table of Contents............................................................................................................ III
List of Tables .................................................................................................................... V
List of Figures................................................................................................................ VII
List of Papers and Technical Reports ............................................................................ IX
Acronyms ........................................................................................................................ XI
1
Introduction ...........................................................................................................- 1 1.1
Global Warming and CO2 Capture and Storage (CCS) .................................................. - 1 -
1.2
Problems and Challenges.................................................................................................. - 2 -
1.3
Objectives ........................................................................................................................ - 3 -
1.4
Methodology..................................................................................................................... - 3 -
1.5
Outline of the Thesis........................................................................................................ - 4 -
Part I: Thermodynamic Properties of CO2 Mixtures ................................................... - 7 2
Method Evaluations for the Thermodynamic Property Calculations of CO2
Mixtures ........................................................................................................................ - 7 2.1
Necessary Thermodynamic Properties and Potential Operation Conditions of CCS ........... - 7 -
2.2
Available Experimental Data and Gaps Regarding CO2 and CO2 Mixtures.................. - 9 -
2.3
Evaluation of Calculation Models on Thermodynamic Properties of CO2 Mixtures......... - 11 -
2.4
Discussions....................................................................................................................- 19 -
3
Impact of Impurity on Thermodynamic Properties of CO2 Mixtures and Different
Processes Involved in the CCS Systems ......................................................................- 21 3.1
Impact of Impurity on Thermodynamic Properties of CO2 Mixtures................................ - 22 -
3.2
Impact of Impurity on the Different Processes Involved in the CCS Systems..................... - 25 -
3.3
Discussions....................................................................................................................- 32 -
Part II: Evaporative Gas Turbine Cycles Integrated with CO2 Capture.....................- 35 4
Evaporative Gas Turbine Cycles Integrated with Different CO2 Capture
Technologies................................................................................................................- 35 4.1
System Configurations.................................................................................................... - 35 -
4.2
Thermodynamic Performances of Various Systems .......................................................... - 38 -
4.3
Economic Evaluation on Various Systems ..................................................................... - 43 -
III
4.4
Investigation of EvGT Integrated with MEA Based Chemical Absorption Capture Regarding
Electrical Efficiency ..................................................................................................................... - 45 4.5
Discussions....................................................................................................................- 48 -
5 Conclusions...............................................................................................................- 51 Appendix......................................................................................................................- 53 References....................................................................................................................- 57 Acknowledgements......................................................................................................- 63 -
IV
List of Tables
Table 2.1 Major thermodynamic properties of CO2 mixtures required by the CCS system design
and engineering evaluation ....................................................................................................... - 7 Table 2.2 Estimated operation conditions (P and T) of the CCS processes .............................. - 8 Table 2.3 Summary of the available experimental data for pure CO2 ....................................... - 10 Table 2.4 Summary of the experimental data for binary CO2 mixtures.................................... - 10 Table 2.5 Summary of TPxy ranges of the VLE experimental data for binary CO2 mixtures ........
.................................................................................................................................................... - 11 Table 2.6 Summary of TPxy ranges of the volume experimental data for binary CO2 mixtures....
.................................................................................................................................................... - 11 Table 2.7 Summary of studied cubic EOS for VLE calculations .............................................. - 15 Table 2.8 Correlated kij for different binary CO2 mixtures based on VLE experimental data ........
.................................................................................................................................................... - 16 Table 2.9 AAD of EOS on the calculated VLE properties of binary CO2 mixtures.............. - 16 Table 2.10 Supplement cubic EOS for volume calculations ...................................................... - 17 Table 2.11 Correlated kij for different binary CO2 mixtures based on volume experimental data..
.................................................................................................................................................... - 18 Table 2.12 AAD of EOS on both gas and liquid volumes of binary CO2 mixtures (%) .................
.................................................................................................................................................... - 19 Table 2.13 Recommended equations of state and their corresponding accuracies for predicting
VLE and volume of different CO2 mixtures ....................................................................... - 20 Table 3.1 Relationship between thermodynamic properties and system parameters ............. - 21 Table 3.2 Acceptable maximum mole fraction of impurities at the given temperatures and
pressures .................................................................................................................................... - 31 Table 4.1 Input data and assumptions for the simulations of gas turbine, compressors,
chemical absorption and dehydration ................................................................................... - 39 Table 4.2 Compositions and properties of feed streams and outlet streams ........................... - 40 Table 4.3 Comparison on electricity generation and internal electricity consumption between
combined cycle and EvGT cycle (in % of fuel LHV) ........................................................ - 43 Table 4.4 Assumptions made in the cost calculation................................................................... - 43 Table 4.5 Annual costs of different systems ................................................................................. - 44 -
V
VI
List of Figures
Figure 1.1 Strategy to reduce global CO2 emissions ..................................................................... - 1 Figure 1.2 Basic principles of three CO2 capture technologies for fossil fuel power generation....
...................................................................................................................................................... - 2 Figure 1.3 Flow chart of this study................................................................................................... - 4 Figure 2.1 Potential pressure and temperature windows of the CCS systems ........................... - 8 Figure 2.2 Relationship between calculation accuracy and binary interaction parameter .….- 15 Figure 2.3 AAD on Ps, ys,CO2, and Ps+ys,CO2 of CO2/CH4 at different kij................................... - 15 Figure 2.4 AAD of PR EOS on Ps, ys,CO2, gas density and liquid density of CO2/CH4 at different
kij ................................................................................................................................................. - 18 Figure 3.1 Comparison of VLE characteristics among the binary CO2 mixtures containing noncondensable impurities............................................................................................................ - 22 Figure 3.2 VLE characteristics of the CO2 mixtures containing condensable impurity SO2 ...... …
.................................................................................................................................................... - 23 Figure 3.3 Heat capacities of different components at different temperatures ....................... - 24 Figure 3.4 Enthalpy of different gaseous CO2 mixtures ............................................................ - 24 Figure 3.5 Volumes and densities of CO2 mixtures at different CO2 compositions............... - 25 Figure 3.6 Simple process flow diagram of purification.............................................................. - 26 Figure 3.7 Relative volatilities of the non-condensable components involved in CO2 mixtures ...
.................................................................................................................................................... - 27 Figure 3.8 Energy consumption of isothermal compression work at different CO2 compositions
.................................................................................................................................................... - 28 Figure 3.9 Discharging temperature and energy consumption of isentropic compression at
different CO compositions and pressures............................................................................ - 28 Figure 3.10 Comparison on the compression work of isothermal and isentropic processes - 29 Figure 3.11 Energy consumption of external refrigeration required by CO2 liquefaction at
different CO2 compositions and operation conditions ...................................................... - 30 Figure 3.12 Effective CO2 volumes of different CO2 mixtures at different CO2 mole and mass
concentrations .......................................................................................................................... - 32 Figure 4.1 System sketch of System I (reference system): EvGT cycle without CO2 capture ........
.................................................................................................................................................... - 36 Figure 4.2 System sketch of System II: EvGT cycle with chemical absorption CO2 capture - 37 Figure 4.3 System sketch of System III: EvGT cycle with O2/CO2 recycle combustion CO2
capture ....................................................................................................................................... - 38 Figure 4.4 Breakdown of electricity generation and power consumption (in % of fuel LHV).......
.................................................................................................................................................... - 41 Figure 4.5 Breakdown of the heat recovered for district heating and heat consumption (in % of
fuel LHV) .................................................................................................................................. - 41 Figure 4.6 CO2 emissions per kWh produced electricity and the CO2 capture ratio .............. - 42 Figure 4.7 Comparison of capture cost of chemical absorption and O2/CO2 ........................ - 44 Figure 4.8 Comparison of CO2 capture costs ............................................................................... - 45 Figure 4.9 Electrical efficiency of EvGT without/with CO2 capture at different Water/Air ratio
.................................................................................................................................................... - 46 Figure 4.10 Specific energy requirement and reboiler temperature at different stripper pressures
.................................................................................................................................................... - 46 Figure 4.11 Configuration of heat exchangers.............................................................................. - 47 Figure 4.12 Electrical efficiency at different stripper pressures ................................................. - 47 Figure 4.13 Specific reboiler duty and electrical efficiency at different condenser temperatures ...
.................................................................................................................................................... - 48 VII
VIII
List of Papers and Technical Reports
This thesis is based on the following papers, referred to by the Roman numerals I- VIII, and
technical reports, referred to by the Roman numerals IX and X.
Papers (appended):
I.
H. Li, X. Ji, J. Yan. A new modification on RK EOS for gaseous CO2 and gaseous
mixtures of CO2 and H2O. International Journal of Energy Research, 2006. 30:135-148.
II.
H. Li, J. Yan. IMPACTS OF IMPURITIES IN CO2-FLUIDS ON CO2 TRANSPORT
PROCESS. In: Proceedings of the ASME Turbo Expo 2006, Barcelona, Spain May 8-11th
2006. Paper No. GT2006-90954.
III.
H. Li, J. Yan. PRELIMINARY STUDY ON CO2 PROCESSING IN CO2 CAPTURE
FROM OXY-FEUL COMBUSTION. In: Proceedings of the ASME Turbo Expo 2007,
Montreal, Canada May 14-17th 2007. Paper No. GT2007-27845.
IV.
H. Li, J. Yan, J. Yan, M. Anheden. Impurity impacts on the purification process in oxyfuel combustion based CO2 capture and storage system. Applied Energy, 2008, In Press.
V.
H. Li, J. Yan, Evaluating cubic equations of state for calculation of vapour-liquid
equilibrium of CO2 and CO2 mixtures for CO2 capture and storage processes. Applied
Energy, 2008, In Press.
VI.
H. Li, J. Yan, PERFORMANCE COMPARISON ON THE EVAPORATIVE GAS
TURBINE CYCLES COMBINED WITH DIFFERENT CO2 CAPTURE
OPTIONS. Accepted by the International Green Energy Conference IV, Beijing, China
2008.
VII.
H. Li, S. Flores, J. Yan. Integrating Evaporative Gas Turbine with Chemical Absorption
for Carbon Dioxide Capture. Accepted by the International Green Energy Conference IV,
Beijing, China 2008.
VIII.
H. Li, J. Yan, Impacts of Equations of State (EOS) and Impurities on the Volume
Calculation of CO2 Mixtures in the Applications of CO2 Capture and Storage (CCS)
Processes. Manuscript.
Technical Reports (not appended):
I.
H. Li, J. Yan, J. Yan, M. Anheden. Evaluation of Existing Methods for the
Thermodynamic Property Calculation of CO2 mixture. KTH-Vattenfall, 2007.
II.
H. Li, J. Yan, J. Yan, M. Anheden. Preliminary Assessment of Impurity Impacts of CO2
mixture on CO2 Processing and Transport Process. KTH-Vattenfall, 2007.
IX
X
Acronyms
Nomenclature:
a, b
a1, a2
C, c
c1, …, c5
G
h
kij
L
M
n
P
R
T
V, v
u, w
x
X
y
Z
α
ζ
Parameters in cubic equations of state
Parameters of modified RK equation
Heat capacity J/(mol·K)
Constant to calculate heat capacity
Gas
Enthalpy kJ/mol
Binary interaction parameter
Liquid
General representative of parameters
Mole number
Pressure MPa
Gas constant J/(mol·K)
Temperature K
Molar volume mol/l
Parameters in 3P1T equation of state
Mole fraction in liquid phase
Total mole fraction
Mole fraction in vapour phase
Compressibility
Relative volatility
Binary interaction parameter of PT equation of state
Abbreviation:
AAD
ACCR
ASU
Abs
BP
BWR
CC
CCR
CCS
Comp
CS
Dev
DBDP
DP
ECV
EOR
EOS
Equ.
EvGT
FCT
FP
GHG
HAT
IGCC
Absolute average deviations %
Actual CO2 capture ratio
Air separation unit
Absolute value
Bubble point
Benedict-Webb-Rubin
Combined cycle
CO2 capture ratio
CO2 capture and storage
Compressibility
Carbon steel
Deviation
Difference between bubble point and dew point
Dew point
Effective CO2 volume
Enhanced oil recovery
Equation of state
Equation
Evaporative gas turbine
Flue gas condensing temperature
Flat plate
Green house gases
Humid air turbine
Integrated gasification combined cycle
XI
IPCC
ISRK
LHV
MEA
MPR
MSRK
O&M
PR
PSRK
PT
PUR
RK
SRK
SS
STIG
STP
TEG
TET
TIT
TRA
T-S
VLE
W/A
Intergovernmental Panel on Climate Change
Improved Soave-Redlich-Kwong
Lower heating value
Mono-methyl ethanolamine
Modified Peng-Robinson
Modified Soave-Redlich-Kwong
Operation and maintenance
Peng-Robinson
Predictive- Redlich-Kwong-Soave
Patel-Teja
Purification
Redlich-Kwong
Soave-Redlich-Kwong
Stainless steel
Steam injection gas turbine
Stripper pressure
Triethylene glycol
Turbine exit temperature
Turbine inlet temperature
Transport
Tube-shell
Vapour liquid equilibrium
Water/Air ratio
Subscript:
c
cal
exp
g
i, j
l
s
0
Critical
Calculated
Experimental
Gas
Component labels
Liquid
Saturated
Reference status
XII
1 Introduction
1 Introduction
1.1 Global Warming and CO2 Capture and Storage (CCS)
Emissions of greenhouse gases (GHG) have been associated with a rise in the global average
temperature. The global average temperature has been increased by 0.74K since the late 1800s
and, according to the Intergovernmental Panel on Climate Change (IPCC), is expected to
further increase by another 1.1 to 6.4K by the end of 21st century [1]. A global warming may
lead to serious consequences. For example, the average sea level has risen by 10 to 20cm during
the past century, and an additional increase of 9 to 88cm is expected by the year 2100 [2].
Therefore, IPCC has stated that global GHG emissions should be reduced by 50 to 80 percent
by the year 2050 [3].
The largest contributor amongst the greenhouse gases is carbon dioxide (CO2), which is
released by burning such fossil fuels as coal, oil and natural gas, and by the burning of forests.
Carbon dioxide capture and storage (CCS), which involves the capture, transport and long-term
storage of carbon dioxide, is a technically feasible method of making substantial reductions of
CO2 emissions. CCS is a critical technology amongst a portfolio of measures to limit climate
change to a manageable level, along with improving the efficiency of energy conversion and/or
utilization, and switching to renewable energy resources. The importance of CCS has been
highlighted in Figure 1.1 as one of the key elements in the strategy of reducing greenhouse gas
emissions [4]. At present, the main application for CCS is in power generation systems [5].
Figure 1.1 Strategy to reduce global CO2 emissions [4]
As shown in Figure 1.2, there are three main technology options for CO2 separation from
power plants: post-combustion capture, pre-combustion capture, and oxy-fuel combustion
capture. Post-combustion capture means capturing CO2 from the flue gases produced by the
combustion of fossil fuels and biomass in air. It is a downstream process, in which the CO2 in
flue gas at near atmospheric pressure is typically removed by a chemical absorption process
using absorbents such as alkanolamines. Pre-combustion capture is to separate the fuel-bound
carbon before the fuel is combusted. This involves a reaction between fuel and oxygen to
primarily give a ‘synthesis gas’ or ‘fuel gas’, which contains carbon monoxide and hydrogen. The
carbon monoxide reacts with steam in a catalytic reactor, called a shift converter, to give CO2
and more hydrogen. CO2 is then separated, usually by a physical or chemical absorption
-1-
1 Introduction
process. Oxy-fuel combustion capture means capturing CO2 from the flue gases produced in
oxy-fuel combustion. The oxy-fuel combustion is the combustion taking place in a
denitrogenation environment, resulting in a flue gas mainly consisting of H2O and CO2. The
technical-economic comparison of the three CO2 capture technologies is still under way
especially for large-scale industrial applications. A preferable technology may highly depend on
its further development and commercialization of the technologies.
Figure 1.2 Basic principles of three CO2 capture technologies for fossil fuel power generation
1.2 Problems and Challenges
The thermodynamic properties of CO2 mixtures are essential for the design and operation of
the CCS systems. How a specific operation parameter affects the performance and costs of the
CO2 capture system highly depends upon the knowledge of thermodynamic properties of CO2
mixtures. For example, the vapour-liquid equilibrium (VLE) of CO2 mixtures is the basic
parameters to design necessary purification processes for CO2 mixtures captured from the flue
gas of coal-fired power generation. Meanwhile, for CO2 transportation, it is preferable to
transport CO2 in a high-density state and avoid the occurrence of two-phase flow in order to
reduce the energy consumption and investment costs, and to secure operation safety. In order
to guarantee the right operation conditions, the accurate thermodynamic properties of CO2
mixtures are of great importance to control and adjust parameters for the CCS system
operation.
Therefore, a better understanding of the thermodynamic properties of CO2 mixtures could
provide a scientific basis to define a proper guideline of CO2 purity and impure components for
the CCS processes according to technical, safety and environmental requirements. The more
knowledge of the thermodynamic properties, the more accurate, more economic, and safer
guidelines of CO2 purity could be defined. Moreover, new CO2 capture system development
and technical breakthrough will also rely upon a deeper understanding of the thermodynamic
properties of CO2 mixtures and the related impurities. The existence of impurities, however,
makes it more difficult.
-2-
1 Introduction
The most precise way to study the thermodynamic properties of CO2 mixtures is via
experiments. However, there are some critical issues regarding experimental data. Those CCS
processes cover a large range of operation conditions from normal atmosphere to supercritical
state, and involve multi-component mixtures; therefore, the limited experimental data cannot
satisfy the requirements of the engineering applications.
In order to break the limitations of experiments, theoretical mathematic models are usually used
to predict thermodynamic properties. Due to the rapidly developing research on CCS, there has
been an increasing interest in finding proper theoretical models to predict the thermodynamic
properties of CO2 mixtures. So far, there are many available models of various types. It has
been proven that the reliabilities of models vary for different properties, components and
conditions [6-8]. However, only a little work has been done regarding several CO2 mixtures; and
no comprehensive evaluations and recommendations are addressed concerning the applications
in the CCS systems. For example, Carroll only studied Peng-Robinson (PR) [9] and RedlichKwong-Soave (SRK) equations of state (EOS) [10] for the VLE calculations of the binary CO2
mixtures including CH4 and H2S [11-12].
1.3 Objectives
One of the main objectives of this thesis is to study the thermodynamic properties of CO2
mixtures and analyze their impacts on the processes of CCS. In order to properly conduct the
work, it is necessary to find or develop the proper models for the thermodynamic property
calculation.
Another important objective is to have an overview of the advanced power cycles combined
with different CO2 capture technologies, from both technical and economic aspects, by
applying the results, obtained from the property study, in the system simulations. A novel gas
turbine cycle, evaporative gas turbine cycle (EvGT), was investigated as it is integrated with
chemical absorption capture and oxy-fuel combustion capture.
1.4 Methodology
Figure 1.3 illustrates the flow chart of this study. The required thermodynamic properties and
operation conditions of CCS were first identified in order to make the study more specific; then
the available experimental data on the thermodynamic properties of CO2 mixtures were
collected. Based upon the data, different theoretical models were evaluated and the
recommendations of calculation methods were provided regarding the engineering design of
CCS systems. With the determined appropriate methods, the impacts of impurities upon the
thermodynamic properties of CO2 mixtures and the performances of different processes
involved in CCS were investigated. The results would be helpful to the design and optimization
of the power cycles combined with different CO2 capture technologies.
In this study, our self-programming codes are used to conduct the calculations about the
thermodynamic property and investigate the impacts of impurities on some processes involved
in CCS, such as compression and flash purification; while the humid gas turbine cycles
integrated with CO2 capture are simulated with Aspen Plus.
-3-
1 Introduction
Figure 1.3 Flow chart of this study
1.5 Outline of the Thesis
The thesis is a summary of eight scientific papers, which are appended, and two technical
reports. The research can be divided into two parts: Thermodynamic Properties of CO2
Mixtures, which includes Chapter 2 and 3; and Evaporative Gas Turbine Cycles Integrated with
CO2 capture, which includes Chapter 4.
Chapter 2 investigates the calculation methods about the thermodynamic properties of CO2
mixtures. Section 2.1 summarizes the required thermodynamic properties, the possible
operation conditions, such as temperature and pressure windows for different the CCS
processes, and the potential impurities. In Section 2.2, experimental data are collected
concerning those required properties, and the experimental data gap is identified for the
method evaluations. In Section 2.3, various theoretical models on the thermodynamic property
calculation are evaluated based upon the collected experimental data. Finally suggestions on
-4-
1 Introduction
method selection are provided in Section 2.4. The presented material is based upon Papers I, V
and VIII and Report I
Chapter 3 investigates the impacts of impurities upon the thermodynamic properties of CO2
mixtures and the different processes involved in the CCS systems. It has been identified that
impurities affect the CCS processes through their impacts upon the thermodynamic properties
of CO2 mixtures. The basic material is taken from Papers II - IV and Report II.
Chapter 4 addresses the study of the advanced power cycles combined with CO2 capture
processes. Section 4.1 introduces three system configurations including EvGT, EvGT +
Chemical Absorption CO2 Capture, and EvGT + Oxy-fuel Combustion. In Section 4.2 and 4.3,
those systems are analyzed from the view points of both thermodynamic efficiency and
investment cost respectively. In Section 4.4, several issues regarding the electrical efficiency are
investigated. Results given in this chapter are based upon Paper VI and VII.
Chapter 5 summarizes the conclusions found during the course of this research.
-5-
1 Introduction
-6-
2 Method Evaluations for the Thermodynamic Property Calculations of CO2 Mixtures
Part I: Thermodynamic Properties of CO2 Mixtures
2 Method Evaluations for the Thermodynamic Property
Calculations of CO2 Mixtures
2.1 Necessary Thermodynamic Properties and Potential Operation
Conditions of CCS
2.1.1
Required Thermodynamic Properties and Their Relation to Engineering
Design
The major thermodynamic properties of CO2 mixtures required by the design of the CCS
systems have been identified based upon main processes and corresponding components as
shown in Table 2.1 [13]. Meanwhile VLE and volume are the basis for other property
calculations. Therefore VLE and volume are considered to be the most important properties in
this study.
Table 2.1 Major thermodynamic properties of CO2 mixtures required by the CCS system design and engineering
evaluation
Capture
Compression
Purification
Refrigeration
Transportation
Pipeline
Small tanks
Large tanks
Storage
Injection
Storage
2.1.2
Thermodynamic properties
Phase equilibrium Volume
Enthalpy
Entropy
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
Operating Windows of the CCS Processes
In order to determine the data needs for the evaluation of CO2 thermodynamic properties in
the CCS processes, the operating window should be defined with the regions of phases and the
CCS processes. The operation conditions of the temperatures and pressures provide the basis
upon which to identify the relevant experimental data requirements and applied range, in which
property models should preferably be used to minimize the uncertainties.
A typical CCS procedure from a fossil fuel power generation normally consists of four steps:
CO2 capture from flue gas, CO2 processing (compression, dehydration,
purification/liquefaction, and further compression/pumping), CO2 transport and CO2 storage.
The four steps make up a process chain for CCS. The operation conditions of the CCS
processes are estimated in terms of pressure and temperature in Table 2.2 [13]. Some subprocesses or options for these CCS processes are indicated in Table 2.2 as well. The P-T
-7-
2 Method Evaluations for the Thermodynamic Property Calculations of CO2 Mixtures
windows are illustrated in Figure 2.1, mainly based on the estimated operation conditions of the
CCS processes.
Table 2.2 Estimated operation conditions (P and T) of the CCS processes
CCS process
CO2 compression/purification
Initial compression
Dehydration
Purification
Further compression/pumping
CO2 transport
Pipeline
Small tanks
Large tanks
CO2 storage
P (MPa)
0 to 11
0 to 3
2 to 3
2 to 5
5 to 11
0.5 to 20
7.5 to 20
1.5 to 2.5
0.5 to 0.9
0.1 to 50
T (K)
219.15 to 423.15
293.15 to 423.15
283.15 to 303.15
219.15 to 248.15
283.15 to 303.15
218.15 to 303.15
273.15 to 303.15
238.15 to 248.15
218.15 to 228.15
277.15 to 423.15
100
Storage in Hydrocarbon Reservoir
Storage in Ocean
Dense Phase
Liquid
Pressure (MPa)
10
Transportation in Pipeline
Critical Point
Liquid
Transportation in Vessels
Solid
Gas
Compression Process
1
Triple Point
0.1
200
250
300
350
Temperature (K)
400
450
500
Figure 2.1 Potential pressure and temperature windows of the CCS systems
2.1.3
Impurities in CO2 Mixtures
Generally there are no strong technical barriers to provide high purity of CO2 from the flue gas
of fossil fuel fired power plants. However, high purity requirements are likely to induce
additional costs and energy requirements resulting in a loss of power plant efficiency. It is of
importance to find an optimal balance amongst the requirements from purification, transport,
storage, legal and environmental aspects.
The characteristics of the CO2 streams captured from the power generation may vary
depending on the CO2 capture technology used for CCS. The CO2 streams captured from post-
-8-
2 Method Evaluations for the Thermodynamic Property Calculations of CO2 Mixtures
combustion with an amine solution is relatively clean. H2O is the main impurity. However,
relative high levels of impure components are expected in the captured CO2 streams from oxyfuel combustion, and a more complicated composition of the CO2 streams is found in the
Integrated Gasification Combined Cycle (IGCC) cases, mainly including different
hydrocarbons, such as CH4.
Based on the fuel conversion processes for power generation and the speciation of major
impurities, the captured CO2 streams could be categorised into two types [14]:
− Oxidising CO2 streams with residual O2 and contaminated sulphur components mainly
with SO2 (e. g. CO2 captured from oxy-fuel and post combustions); and,
− Reducing CO2 streams with almost no residual O2 and contaminated sulphur
components mainly with H2S (e. g. CO2 captured from coal gasification processes such
as IGCC).
The major differences of the two types of captured CO2 streams are the concentrations of noncondensable impurities such as N2, Ar, and O2 and types of impurities due to the different
redox conditions in the CO2 streams, for example the oxidising sulphur species SO2 existing in
oxidising CO2 streams while the reducing species H2S existing in reducing CO2 streams.
Therefore, the impurities, including N2, O2, Ar, H2O, CH4, SO2, and H2S, are considered for the
study of the thermodynamic properties of their CO2 mixtures in this research, which may cover
the most interest non-CO2 components existing in the captured CO2 streams.
2.2 Available Experimental Data and Gaps Regarding CO2 and CO2
Mixtures
Accurate experimental data of both pure CO2 and CO2 mixtures (CO2 + impurities) are
required to verify the reliabilities of calculation models and calibrate parameters contained in
the models.
Since the 1980s, many experiments with higher accuracy have been conducted for pure CO2
properties. For the thermodynamic properties of CO2 mixtures, investigations were also carried
out but focused mainly on the impurities, such as water, hydrocarbons, nitrogen, and hydrogen
sulphide due to their importance for production and processing of natural gas resources and for
using the CO2 mixture for enhanced oil recovery (EOR) process. As a result, there are a lot of
available experimental data about the mixtures of CO2/H2O, CO2/N2, CO2/CH4, and
CO2/H2S, which cover a wide range of temperature and pressure. However, the experimental
data of the CO2 mixtures containing O2, Ar, and SO2 are limited, although such impurities in
CO2 are important for the CCS processes, especially the oxy-fuel combustion technology.
Available experimental data of pure CO2 are summarized in Table 2.3. Different kinds of
properties including volume, Cp, VLE, and excess enthalpy are included.
-9-
2 Method Evaluations for the Thermodynamic Property Calculations of CO2 Mixtures
Table 2.3 Summary of the available experimental data for pure CO2
Source
Year
Type
T (K)
P (MPa)
Holste et al [15]
1987
Volume
215-448
0.1-50.0
Ernst et al [16]
1989
Cp
303.15-393.15
0.1-90
Duschek [17]
1990
VLE
217-340
0.3-9.0
Gilgen et al [18]
Brachthuser [19]
1992
1993
220-360
233-523
0.3-13.0
0.8-30.1
Möller et al [20]
1993
Volume
Volume
Excess
Enthalpy
Uncertainty
P: ±0.01%;
T: ±0.01K;
P: ±0.02%;
T: ±0.003Ka
V:±(0.015~0.04)%
V: ±(0.02~0.04)%
230-350
15-18
-
Fenghour [21]
1995
Volume
329.82-697.81
3.032-34.203
Klimeck et al [22]
2001
Volume
240-470
0.5-30
P: ±0.02%;
T: ±0.01K;
P: ±0.016%’
T: ±0.004Kb;
Available experimental data of the CO2 mixtures containing those impurities (N2, O2, Ar, SO2,
CH4, H2O and H2S) are summarized in Table 2.4. They are mainly about the properties of VLE
and volume. Meanwhile almost all of them are about binary CO2 mixtures.
Table 2.4 Summary of the experimental data for binary CO2 mixtures
*
Source
Caubet [23]
Reamer et al [24]
Steckel [25]
Year
1901
1944
1945
Type
TPVX
TPxy
PTxy
Mixture
CO2/SO2
CO2/CH4
CO2/H2S
T (K)
291-416
311-511
221-288.15
P (MPa)
2.7-10.5
1.4-69
0.1-3.6
Bierlein et al [26]
1953
PTVX
CO2/H2S
273-370
1.5-8.5
Donnelly et al [27]
1954
TPxy
CO2/CH4
CO2/O2, CO2/N2,
CO2/N2/O2
167-301
2.0-7.4
273.15
5.5-12
Muirbrook et al [28, 29]
1965
TPxy
Kestin et al [30]
1966
TPVX
CO2/Ar
293.15-303.15
0.101-2.58
Greenwood [31]
1969
TPxy
CO2/H2O
723-1073
Up to 50
Fredenslund et al [32]
1970
TPxy
CO2/O2
223.15-283.15
1-13
Arai et al [33]
1971
PVTx
CO2/N2, CO2/CH4
253-288
5-15
Sarashina et al [34]
1971
PVTx
CO2/Ar
288.15
5.69-9.77
Davalos et al [35]
Altunin et al [36]
Mraw et al [37]
1976
1977
1978
PTxy
Comp
TPxy
CO2/CH4
CO2/Ar
CO2/CH4
230-250
303.15
89-208
0.9-8.5
0.29-10.75
0.5-6.3
Somait et al [38]
1978
TPxy
CO2/N2
270
3-12
Zawisza and
Malesinska [39]
Dorau et al [40]
1981
TPVX
CO2/H2O
323-473
Up to 3.3
1983
TPxy
CO2/N2
223.15-273.15
3-20
Patel and Eubank [41]
1988
TPVX
CO2/H2O
323-498
Up to 10.34
Esper et al [42]
1989
TPVX
CO2/N2
205-320
0.1-48
Sterner and Bodnar [43]
1991
TPVX
CO2/H2O
673-973
200-600
Fenghour [44]
1994
TPVX
CO2/H2O
415-700
6-35
Seitz and Blencoe [45]
1999
TPVX
CO2/H2O
673
10-100
If partial pressure of CO2 was less than 5MPa, uncertainty was 1.5 percent.
- 10 -
Uncertainty
V: ±0.02%
T: ±0.02K
P: ±0.1%
P: ±0.5% *
T: ±1K
P: ±0.5%
T: ±0.02K
P: ±0.01atm
T: ±0.01K
P: ±0.01atm
T: ±0.01K
P: ±0.015atm
T: ±0.02K
P: ±0.03%
T: ±0.05K
P: ±0.01%;
T: ±0.01K
P: ±0.015%
T: ±0.01K
P: ±1%
T: ±1% oC
P: ±0.02%
T: ±0.01K
P: ±0.01MPa
T: ±0.01K
2 Method Evaluations for the Thermodynamic Property Calculations of CO2 Mixtures
Tables 2.5 and 2.6 summarized the ranges of T, P, x and y of the experimental data on VLE
and volume. There are still some gaps between available experimental data and requirements of
method for the evaluation and calibration. For example, there are few experimental data on
VLE of CO2/SO2 at temperatures below 290K; there are few experimental data on VLE of
CO2/Ar, except at the temperature of 288.15K and pressure 5~10MPa; and there are no
experimental data on volume of CO2/O2. Moreover only a few of the experimental data are
available for multi-component CO2 mixtures such CO2/N2/O2.
Table 2.5 Summary of TPxy ranges of the VLE experimental data for binary CO2 mixtures
CO2
CO2/O2
CO2/N2
CO2/SO2
CO2/H2S
CO2/Ar
CO2/CH4
CO2/H2O
T (K)
P (MPa)
xCO2
yCO2
No. of Exp. Point
216.58-303.90
223.15-283.15
253.15-288.15
295.15-338.45
255.15-363.15
288.15
193.15-270
276.15-642.7
0.52-7.32
1.01-12.16
2.35-13.95
2.12-6.43
2.03-8.11
5.69-8.38
0.68-8.41
Up to 310
0.62-0.999
0.43-1.00
0.01-0.97
0.83-0.94
0.026-0.99
0~0.99
0.18-0.91
0.43-1.00
0.75-0.93
0.05-0.97
0.79-0.94
0.026-0.917
0~0.99
27
72
67
91
77
10
82
>1000
Table 2.6 Summary of TPxy ranges of the volume experimental data for binary CO2 mixtures
Phase
CO2
CO2/O2
CO2/N2
CO2/SO2
CO2/H2S
CO2/Ar
CO2/CH4
CO2/H2O
Vg
Vl
Vg
Vl
Vg
Vl
Vg
Vl
Vg
Vl
Vg
Vl
Vg
Vl
T (K)
215.00-697.81
NA
NA
253.15-288.15
253.15-288.15
287.15-347.35
299.15-341.15
278.05-304.86
275.07-306.27
293.15-303.15
288.15
219.7-300
273-293
323-1073
278-471
P (MPa)
0.30-50.00
2.35-14.51
2.43-14.51
0.10-7.60
5.67-10.64
3.50-6.99
3.50-6.99
0.10-2.50
7.51-9.78
0.1-14.3
6-14
Up to 600
0-31
xCO2
0.85-1
0.125-0.927
0.83-0.90
0.83-0.94
0.56-0.96
0-0.99
yCO2
No. of Exp. Point
>1000
0.49-1
120
64
120
36
16
16
16
4
245
47
>2000
>300
0.125-0.927
0.83-0.90
0.84-0.92
0.45-0.96
0.-0.99
2.3 Evaluation of Calculation Models on Thermodynamic Properties of
CO2 Mixtures
2.3.1
Introduction of the Calculation Models
The correlation and prediction of mixture behaviours are one of the central topics in applied
thermodynamics. There are generally two types of thermodynamic methods for phase
equilibrium calculations: liquid activity coefficient based models and equation-of-state based
models. Activity coefficient models are the best way to represent highly non-ideal liquid
mixtures at low pressures, and can be used to describe mixtures of any complexity. The
equation of state methods can be applied over wide ranges of temperature and pressure,
including sub-critical and super-critical regions. For ideal or slightly non-ideal systems, the
thermodynamic properties for both the vapour and liquid phases can be computed with a
minimum amount of component data. However, the EOS method has relatively poor accuracy
- 11 -
2 Method Evaluations for the Thermodynamic Property Calculations of CO2 Mixtures
for liquid phase calculations. Considering the wide range of operation conditions of the CCS
processes and many required thermodynamic properties, EOS may be more applicable than
activity coefficient methods, because activity coefficient method can only be used in low
pressure cases (usually those lower than 10atm) [47] and has more complicated procedure to
calculate other thermodynamic properties, such as volume, enthalpy, and entropy.
A semi-empirical EOS relates volume, pressure, temperature and composition of substances in
mathematical forms [46]. Any thermodynamic property can be obtained from it by using
appropriate thermodynamic relations [48]. However, the development of such semi-empirical
equations requires a great deal of experimental data on wide range to the corresponding
substance. The shortage of those experimental data makes the progress slow and limited to a
few pure fluids nowadays.
EOS can be divided into two categories: specialized EOS, such as Span’s EOS [49] for CO2,
and general EOS, such as van der Waals EOS [50]. Compared with the latter, specialized
equations have a better accuracy; however, their applications are limited to certain substances.
For example, Span’s EOS can only be applied to CO2. Meanwhile the general equations can be
further divided into two types: equations with simple structures, such as Redlich-Kwong (RK)
EOS [51]; and equations with complex structures, such as Benedict-Webb-Rubin (BWR) EOS
[52]. Although the general equations with complex structure may give better results, as they
contain more parameters, their calculation procedures on the thermodynamic properties are
more complicated, especially when calculating some derived properties such as enthalpy and
entropy. In addition, also due to the complicated calculation procedure, it is more difficult to
integrate the general equations with complex structure into some commercial software, such as
Aspen Plus [47] and IPSpro [53], if they are not originally included.
Thus, from an engineering standpoint, a general EOS with simple structure and reasonable
accuracy is more preferable. Cubic equations of state have very simple structures. Since van der
Waals proposed his EOS in 1873, numerous modified versions of cubic EOS with two or more
parameters have been developed to improve predictions of volumetric and phase equilibrium
properties of fluids. It has been well established that a cubic EOS can satisfactorily model phase
equilibrium. In this work, RK was modified for gaseous CO2 and gaseous mixtures of
CO2/H2O; moreover the reliabilities of cubic equations of state were evaluated for predicting
the thermodynamic properties of CO2 mixtures.
2.3.2
A New Model for Gaseous CO2 and Gaseous Mixtures of CO2/H2O
Since the 1980s, new experiments on gaseous CO2 and gaseous mixtures of CO2/H2O have
been conducted. However, little work on equation of state has been done regarding the
requirements of engineering applications. Under such a situation, a new correlation was
developed with the consideration of new experimental data.
It has been verified that RK EOS [50] can represent vapour and liquid behaviours effectively. It
was proposed in 1949 as:
P=
RT
a
−
v − b v(v + b )T 1 / 2
(2.1)
Where ‘a’ and ‘b’ are parameters. Parameter ‘a’ reflects intermolecular attraction, and parameters
‘b’ reflects molecular size (repulsive forces). For simple non-polar gases, they can be calculated
from critical data.
- 12 -
2 Method Evaluations for the Thermodynamic Property Calculations of CO2 Mixtures
a=
0.42748 R 2Tc2.5
Pc
(2.2)
0.08664 RTc
b=
Pc
According to Bottinga’s conclusions [54], if the parameters ‘a’ and ‘b’ were expressed by
functions, RK EOS can describe properties more accurately, even for polar gases. Therefore, in
the current research, and based upon more precisely measured PVTs properties, RK EOS will
be modified for better precision for gaseous CO2 and for larger application range for gaseous
mixtures of CO2 and H2O. New description of parameter ‘a’ for gaseous CO2 is given in Equ.
2.3.
a = a1 + a 2 P
2.3457 × 10 5 1.3612 × 10 3
−
− 4.8365 × 10 −3 T + 9.9191
2
T
T
−2
1.9141 × 10
1.0132 × 10 − 4
a2 =
−
− 1.3654 × 10 −10 T + 0.1934 × 10 − 6
2
T
T
0.08664 RTc
b=
Pc
a1 =
(2.3)
For gaseous CO2/H2O, we modified the mixing rules:
a = ∑ ∑ yi ⋅ y j ⋅ aij
(2.4)
b = ∑ yi ⋅ bi
(2.5)
i
j
i
With
a ij = a ji = 40 . 1248 + 4 . 5108 × 10
−7
⋅T
2 .5
⋅e
1 . 6060 ×10 3 4 . 9003 ×10 5 1 . 4556 ×10 8
−
+
T
T2
T3
(2.6)
Compared with experimental data, the absolute average deviation (AAD), which is defined as:
∑
AAD =
⎛ M cal − M exp ⎞
⎟ × 100%
abs⎜
⎟
⎜
M exp
⎠
⎝
N
(2.7)
of the new model is 1.68% for the volume of gaseous CO2 in the range 220-700K and 0.1400MPa except for the critical region (295-315K and 6.5-9.5MPa); and 0.93% for the volume of
gaseous CO2/H2O in the range 323-1073K and 0.1-600MPa. Calculated results on other
thermodynamic properties, such as enthalpy and heat capacity, also fit the experimental data
well. More detailed results were summarized in Paper I.
- 13 -
2 Method Evaluations for the Thermodynamic Property Calculations of CO2 Mixtures
2.3.3
Evaluations of Cubic EOS for Predicting VLE and Volume of CO2
mixtures
2.3.3.1 Prediction of VLE
Five cubic EOS widely used in the petroleum and gas industries are evaluated for the
calculation on VLE properties, including Peng-Robinson (PR) [9], Patel-Teja (PT) [55], RedlichKwong (RK), Redlich-Kwong-Soave (SRK) [56], and 3P1T [57]. All studied equations of state
are summarized in Table 2.7 with the features as described below:
− PR EOS is proposed based upon RK EOS. It is capable of predicting the liquid volume as
well as vapour pressure in order to further improve VLE predictions. It is recommended
for hydrocarbon processing applications, such as gas processing, refinery, and
petrochemical processes.
− PT EOS has two substance dependent parameters which are obtained from the liquid
volume and vapour pressure data, and correlated with an acentric factor. The 3-parameter
PT equation has been shown to give satisfactory results for both vapour pressure and
volume even for heavy and polar compounds. It is also recommended for hydrocarbon
processing applications.
− RK EOS is the earliest modification of van der Waals EOS; it improved the intermolecular
attraction. It is more applicable for the system at low pressures.
− SKR EOS is another modification of RK EOS by introducing a temperature-dependent
function to modify the attraction parameter. It was one of the most popular EOS in the
hydrocarbon industry. SRK is capable of predicting VLE for liquid mixtures; however, it is
not very satisfactory for predictions of liquid compressibility.
− 3P1T EOS is an equation of van der Waals type. It was primarily developed for non-polar
compounds, however, it was claimed to be able to be applied for polar substances as well
[57].
The semi-empirical equations of state have been developed by using pure component data. The
application of these equations has been extended to a multi-component system by defining
mixing rules to evaluate the average parameters required in the calculations. In this study, the
conventional random van der Waals mixing rules were employed for all of EOS. In the mixing
rules, there is one very important parameter, binary interaction parameter kij, which accounts
for the attraction forces between pairs of non-similar molecules. Theoretically, it is a
modification of intermolecular attraction when calculating thermodynamic properties of
mixtures. The value of kij is more sensitive to derivative or partial properties such as fugacity
coefficients than to total properties such as mixture molar volumes. For that reason, values of
kij have most often been determined from VLE data.
Since the determination of kij requires a large amount of experimental data, the calibrated binary
interaction parameters are not known for all the binary systems and EOS. If the calibrated kij is
unknown, for approximate calculation the difference of attraction forces, which are between
non-similar molecules and between similar molecules, can be ignored, and different molecules
can be regarded as same. Thus, values of kij would be taken as zero (if (1-kij) is used in the
mixing rules, such as RK EOS) or unity (if (kij) is used in the mixing rules, such as PT EOS).
- 14 -
2 Method Evaluations for the Thermodynamic Property Calculations of CO2 Mixtures
Table 2.7 Summary of studied cubic EOS for VLE calculations
EOS
Function Form
PR
P=
Mixing Rule
a = ∑∑ xi x j ai1 / 2 a1j / 2 (1 − k ij ) ;
RT
a
−
V − b V (V + b ) + b(V − b )
i
j
b = ∑ xi bi ; kij=kji;
i
P=
PT
a = ∑∑ xi x j ai1 / 2 a1j / 2ξ ij ;
RT
a(T )
−
V − b V (V + b ) + c(V − b )
i
j
b = ∑ xi bi ; c = ∑ xi ci ; ξ ij = ξ ji
i
a = ∑∑ xi x j a a
a 0 .5
RT
T
P=
−
V − b V (V + b )
RK
i
1/ 2 1/ 2
i
j
i
(1 − k );
ij
j
b = ∑ xi bi ; kij=kji
i
P=
SRK
a = ∑∑ xi x j ai1 / 2 a1j / 2 (1 − k ij ) ;
RT
a
−
V + c − b (V + c )(V + b + c )
i
j
b = ∑ xi bi ; c = ∑ xi ci ; kij=kji
i
3P1T
P=
i
a = ∑∑ xi x j ai1 / 2 a1j / 2 (1 − k ij ) ;
RT
a
− 2
V − b V + ubV + wb 2
i
j
b = ∑ xi bi ; kij=kji
i
However, an inappropriate kij may cause a poor calculating accuracy of an EOS. Figure 2.2
shows the sum of average absolute deviation (AAD), on the saturated pressure and AAD on
the saturated vapour fraction of CO2 (ys,CO2) at different binary interaction parameter kij, (to PT
EOS, it is (1-kij)). It is clear that AAD changes with the variation of kij.
40
Absolute Average Deviation (%)
2
AAD on Ps + AAD on ys,CO (%)
VLE of CO2/CH4
PR EOS
AAD on Ps
AAD on ys,CO
AAD on Ps + AAD on ys,CO
25
35
30
25
20
VLE of CO2/N2 at 270K
PR EOS
*
PT EOS
RK EOS
SRK EOS
3P1T EOS
15
10
5
-0.20
-0.15
-0.10
-0.05
0.00
Value of kij
0.05
0.10
0.15
20
2
2
15
10
5
0.20
Figure 2.2 Relationship between calculation
accuracy and binary interaction parameter
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
Value of kij
Figure 2.3 AAD on Ps, ys,CO2, and Ps+ys,CO2 of
CO2/CH4 at different kij
In order to improve the accuracy of cubic equations and evaluate EOS precisely, the binary
interaction parameters of various binary CO2 mixtures must first be determined. Usually, the
binary interaction parameter kij is considered to be independent of temperature, composition,
and volume [58]. However, there are also some different conclusions that kij is temperature and
composition dependent [59-61]. As kij is determined by matching the predicted values with
experimental data, it should be considered as a fitting parameter only and not a rigorous
physical parameter [7]. Hence, in this study, the value of kij is still regarded as a constant.
- 15 -
2 Method Evaluations for the Thermodynamic Property Calculations of CO2 Mixtures
The saturated pressures and saturated vapour compositions have been calculated from the
known saturated temperatures (Ts) and saturated liquid compositions (xs). Figure 2.3 shows the
AAD of PR EOS on Ps, ys,CO2, and Ps+ys,CO2 of CO2/CH4 at different kij. This clearly displays
that for various properties, the binary interaction parameter may be calibrated as different
values. Since both saturated pressure and saturated vapour composition are important to the
CCS processes, here kij is calibrated as the value that makes the sum of AAD on Ps and ys,CO2
minimum (For CO2/Ar and CO2/SO2. because xs and ys are not known at dew points and
bubble points, respectively, no AAD on ys,CO2/xs,CO2 are calculated. In these cases, the value of
kij that makes the AAD on Ps minimum is chosen.). The flow chart of the procedure for
regressing kij is shown in Appendix A. Based upon the experimental data listed in Table 2.4, kij
was calibrated for each EOS concerning each binary mixture. Since CO2/H2O has been
examined intensively in previous studies [62, 63], here H2O is excluded. Results are given in
Table 2.8.
Table 2.8 Correlated kij for different binary CO2 mixtures based on VLE experimental data
CO2/CH4
CO2/O2
CO2/H2S
CO2/N2
CO2/Ar
CO2/SO2
PR
0.103
0.115
0.099
-0.011
0.228
0.047
PT
0.903
0.898
0.907
1.043
0.806
0.953
RK
0.084
0.178
0.083
0.089
-0.084
-0.041
SRK
0.104
0.118
0.106
-0.011
0.224
0.048
3P1T
-0.050
0.105
0.098
-0.032
-0.128
0.083
With the new calibrated kij, VLE of different binary CO2 mixtures were calculated using
different EOS; and the calculated results were compared with experimental data. Table 2.9
summarizes the absolute average deviations of EOS. All of the studied EOS have various
performances for various mixtures; and comparatively PR, PT and SRK are superior to RK and
3P1T for all of the studied mixtures. It should be stressed that although 3P1T is primarily
developed for non-polar compounds, it doesn’t show any advantages in the VLE calculations
of CO2/CH4, CO2/O2, CO2/N2, and CO2/Ar. For detailed analysis of these binary CO2
mixtures, please refer to Paper V and Report VIII.
Table 2.9 AAD of EOS on the calculated VLE properties of binary CO2 mixtures
CO2/CH4
CO2/O2
CO2/H2S
CO2/N2
CO2/Ar
CO2/SO2
Ps
ys,CO2
Ps
ys,CO2
Ps
ys,CO2
Ps
ys,CO2
Ps
ys,CO2
Ps
ys,CO2
PR
2.91
3.12
5.12
3.91
1.22
4.54
6.04
3.80
5.01
4.76
-
PT
2.32
3.62
4.54
3.74
3.65
10.82
5.86
3.76
5.00
4.79
-
- 16 -
RK
5.25
20.31
6.30
13.19
3.95
11.91
14.17
9.95
8.01
10.62
-
SRK
2.66
3.71
4.97
4.65
1.32
4.49
11.28
6.08
5.32
4.33
-
3P1T
21.52
28.49
9.65
7.85
3.32
4.79
9.65
7.85
25.75
12.02
-
2 Method Evaluations for the Thermodynamic Property Calculations of CO2 Mixtures
2.3.3.2 Prediction of Volume
For the calculation on volume, 3P1T was replaced by three other equations due to its poor
performance on VLE.
− MSRK and MPR EOS include a translation along the volume axis. Applications of this
improved method to pure liquid, mixtures of liquids or gases, and petroleum fluids show
that markedly superior volume estimations are obtained, except in the neighbourhood of
the pure-component critical points; nonetheless, critical volumes for mixtures can be
estimated correctly [64].
− ISRK [65] EOS is another modification of SRK, by introducing a temperature dependent
volume correction. ISRK can provide accurate volumes for polar and non-polar pure
substances both near to and far from the critical point. It can also be easily extended to
mixtures, and the calculation results show that it can shift the critical locus towards
experimental values and give good results for the liquid volumes of mixtures.
Table 2.10 Supplement cubic EOS for volume calculations
EOS
Function Form
Mixing Rule
MPR
a=
RT
a
P=
−
V − b (V + c )(V + b + 2c ) + (b + c )(V − b)
∑∑ x x a
i
i
1/ 2 1/ 2
i
j
a
(1 − k );
ij
j
b = ∑ xi bi ; c = ∑ xi ci ; kij=kji
i
MSRK
j
RT
a
−
P=
V − b (V + c )(V + b + 2c )
i
1/ 2 1/ 2
i
j
a = ∑∑ xi x j a a
i
(1 − k );
ij
j
b = ∑ xi bi ; c = ∑ xi ci ; kij=kji
i
i
a = ∑∑ xi x j ai1 / 2 a1j / 2 (1 − k ij ) ;
ISRK
P=
RT
a(T )
−
V + c − b (V + c )(V + b + c )
i
j
⎛ bii + b jj
b = ∑ ∑ x i x j ⎜⎜
i
j
⎝ 2
c = ∑ xi ci ; kij=kji; lij=lji
⎞
⎟(1 − l ij ) ;
⎟
⎠
i
It has been mentioned that the proper value of kij may be different for different properties.
Therefore, the kij calibrated from VLE data may not result in a high accuracy on the volume
calculation. Figure 2-4 shows the AAD of PR EOS on the saturated pressure, the saturated
vapour fraction of CO2 (ys,CO2), the gas volume and liquid volume of CO2/CH4 at different
values of binary interaction parameter kij. It demonstrates that in order to pursue high
calculation accuracy on volume, kij should be calibrated separately for gas and liquid phases.
Table 2.11 lists the calibrated kij for volume calculations on both vapour and liquid phases.
- 17 -
2 Method Evaluations for the Thermodynamic Property Calculations of CO2 Mixtures
Absolute Average Deviation (%)
30
CO2/CH4
PR EOS
AAD on Ps
AAD on ys,CO
AAD on gas volume
AAD on liquid volume
25
2
20
15
10
5
0
0,0
0,1
0,2
Value of kij
Figure 2.4 AAD of PR EOS on Ps, ys,CO2, gas volume and liquid volume of CO2/CH4 at different kij
Table 2.11 Correlated kij for different binary CO2 mixtures based on volume experimental data
CO2/CH4
CO2/H2S
CO2/N2
CO2/Ar
CO2/SO2
*
G
L
G
L
G
L
G
L
G
L
PR
0.049
0.008
0.038
0.012
-0.001
-0.017
0.027
0.002
-0.085
0.004
PT
0.963
1.002
0.960
1.004
1.015
1.029
0.990
1.015
1.090
0.996
RK
0.008
-0.077
0.031
-0.073
-0.019
-0.129
0.0
-0.077
-0.091
-0.026
SRK
0.018
-0.056
0.033
-0.064
-0.037
-0.104
0.007
-0.065
-0.092
-0.026
MPR
-0.006
-0.120
-0.014
-0.082
-0.053
-0.154
-0.031
-0.124
-0.148
-0.122
MSRK
-0.032
-0.192
-0.015
-0.181
-0.095
-0.258
-0.043
-0.200
-0.156
-0.175
ISRK*
0.033/0.189
-2.225/-0.375
-0.055/0.125
-0.900/-0.085
-0.104/0.099
-0.490/0.050
0.015/0.320
-0.015/0.335
-0.500/-0.500
-0.700/-0.115
kij/lij
Tables 2.12 shows the absolute average deviations of equations of state on the gas and liquid
volumes of CO2 mixtures respectively, which were calculated with different values of kij. It is
same to the calculations on VLE properties that the performances of EOS vary for various
mixtures. More concrete evaluations are available in Paper VIII.
- 18 -
2 Method Evaluations for the Thermodynamic Property Calculations of CO2 Mixtures
Table 2.12 AAD of EOS on both gas and liquid volumes of binary CO2 mixtures (%)
CO2/CH4
CO2/H2S
CO2/N2
CO2/Ar
CO2/SO2
Vg
Vl
Vg
Vl
Vg
Vl
Vg
Vl
Vg
Vl
PR
2.95
4.17
4.71
3.03
1.58
1.74
5.96
2.37
13.02
9.43
PT
2.34
3.70
5.57
2.43
0.98
1.77
6.08
2.12
13.06
9.28
RK
2.56
5.19
8.84
4.95
1.47
5.97
6.43
4.86
14.26
11.96
SRK
2.56
5.12
7.34
4.18
1.50
4.99
6.45
4.66
14.00
10.84
MPR
4.49
5.50
3.37
4.30
2.85
3.79
7.21
3.99
11.64
10.51
MSRK
3.97
6.08
4.26
4.97
2.59
6.16
7.16
5.48
12.76
12.15
ISRK
7.42
8.33
7.21
4.99
5.17
7.46
6.24
4.64
8.83
13.21
2.4 Discussions
2.4.1
Experimental Data
Regarding the CO2 mixture, the TPX ranges of experimental data do not completely match the
operation conditions of the CCS processes. This will result in poor evaluation results of the
theoretical models because no sufficient experimental data are available for verifying the
models. For example, there are only 4 experimental results at the same temperature about VLE
and liquid volume of CO2/Ar. Based upon such experimental data, the verified model may not
be able to provide accurate results, when temperatures are beyond this temperature. Moreover,
the experimental data of CO2/SO2 mixtures are old. Updated experimental data are, therefore,
needed to reduce the uncertainty of the evaluations.
2.4.2
Calculation Models
To all cubic EOS considered in this study, kij has significant effects on the calculating accuracy
and the application range of an EOS. Those equations have better accuracy on VLE with
calibrated kij than with the default value of kij. Therefore, if a new impurity is introduced in CO2
mixtures, the calibrated kij of CO2/new-impurity should be obtained in order to assure a high
reliability. Moreover, as aforementioned, kij was calibrated as a constant in the calculations of
CO2 mixtures. To further improve calculation accuracy, there are two options to handle kij. One
way is that kij could be calibrated to a function of temperature and pressure, perhaps even of
composition, when sufficient experimental data are available. The other way is to calibrate kij in
narrow T, P, x and y ranges, by which the calculation accuracies could be improved for most
interested conditions. This, however, will seriously reduce the applicability in extended ranges.
2.4.3
Suggestions Regarding Method Selections
Calculating accuracies of different EOS on VLE and volume are evaluated. With recommended
EOS, the most of AAD on parameters of VLE are within 5%, while AAD on volume are
within 10% except those of CO2/SO2. Detailed results are summarized in Table 2.13.
- 19 -
2 Method Evaluations for the Thermodynamic Property Calculations of CO2 Mixtures
Table 2.13 Recommended equations of state and their corresponding accuracies for predicting VLE and volume
of different CO2 mixtures
Mixtures
CO2/O2
CO2/N2
CO2/SO2
CO2/Ar
CO2/H2S
CO2/CH4
2.4.4
ACD on VLE (%)
EOS
Ps
PT
4.54
PT
5.86
SRK
4.33
PT
5.00
PR
1.22
PR
2.91
ys
3.74
3.76
4.54
3.12
ACD on Volume (%)
EOS
Vg
EOS
PT
0.98
PR
ISRK
8.83
PT
PR
5.96
PT
MPR
3.37
PT
PT
2.34
PT
Vl
1.74
9.28
2.12
2.43
3.70
Future Work
Based upon the above analysis, to improve the reliability of evaluation, future work is necessary
in the areas of:
− Carrying out more accurate experiments, especially on VLE of CO2/Ar, CO2/SO2, and
CO2/N2, VLE at pressures higher than 8.5MPa, and on volume of CO2/O2, CO2/SO2
and CO2/Ar;
− Including evaluations on the ternary CO2 mixture to further verify the theoretical
models for the calculations of multi-components systems;
− Calibrating the binary interaction parameter to a polynomial instead of a constant, or in
a narrow application range to further improve the calculation accuracy on VLE of EOS.
- 20 -
3 Impact of Impurity on Thermodynamic Properties of CO2 Mixtures and Different Processes
Involved in the CCS Systems
3 Impact of Impurity on Thermodynamic Properties of CO2
Mixtures and Different Processes Involved in the CCS Systems
By changing the thermodynamic properties of CO2 mixtures, impurities have great impact on
system design, operation, and optimization. For example, the relationships between
thermodynamic properties and some system parameters of CO2 purification and transportation
are summarized in Table 3.1.
Table 3.1 Relationship between thermodynamic properties and system parameters
DP
VLE
BP
DBDP
Heat Capacity
Enthalpy and
entropy
Volume
Operation
conditions
PUR
TRA
√
√
Energy
consumption
PUR
TRA
√
√
√
√
√
√
Configuration
Design
PUR
TRA
√
Performance
PUR
√
√
TRA
√
√
√
√
The variation of impurity content will influence the VLE properties of CO2 mixtures, which
mainly mean the boiling and condensing behaviours. Physical separation shall be conducted in
two-phase area, which implies that at a constant temperature, the operation pressure should be
above the condensing pressure and below the boiling pressure of the mixtures. Different from
separation, transportation must be carried out above their boiling pressure for safety issues.
Therefore, when the VLE properties are changed, the operation conditions of the CO2
compression/purification (e.g. the discharging pressure of compression and the condensation
temperature) and transport systems should also be changed accordingly. Meanwhile, the CO2
purity of the separation product is the CO2 mole fraction of bubble point. Thus, when the
boiling behaviour is changed, the performance of separation would be changed. In addition, the
configuration of separation unit is tightly related to the difference between boiling and dew
points. If there is a big difference between boiling and dew points, separation system can be
simpler. For instance, multi-stage flash may be used instead of distillation column, which is
required for separating mixtures with close boiling and dew points.
The variation of impurity content will also influence the enthalpy, entropy and heat capacity of
CO2 mixtures. Since the energy consumptions of compression and refrigeration are determined
by the enthalpy and entropy changes in those processes, as a result, impurities can have impacts
on the energy consumption.
Moreover the variation of impurity content will vary the effective CO2 volumes (ECV) of CO2
streams, which is defined as:
ECV =
VCO2
(3.1)
VCO2 − mixture
- 21 -
3 Impact of Impurity on Thermodynamic Properties of CO2 Mixtures and Different Processes
Involved in the CCS Systems
ECV can directly affect the efficiencies and economic issues of CO2 transport and storage;
therefore, it is significant to the design of CO2 transport and storage systems.
Compared with other approaches for CO2 capture, such as pre-combustion capture and postcombustion capture, relatively high levels of impurities are expected in the captured CO2
streams from oxy-fuel combustion. So it presents more challenges for CO2 processing
processes, which includes dehydration, purification and compression [66]. Here efforts were
mainly focused on the impurities appearing in the oxidizing CO2 streams captured from oxycoal combustion. In this chapter, the impact of impurities on the thermodynamic properties of
CO2 mixtures was firstly analyzed; then the impact of impurities was further discussed
concerning different processes involved in the CCS systems.
3.1 Impact of Impurity on Thermodynamic Properties of CO2 Mixtures
According to Table 3.1, the impact of impurity on VLE, Heat capacity, enthalpy and volume
were investigated respectively, considering their importance to the system design and operation.
3.1.1
Impact on VLE
Figure 3.1 shows an example of the phase diagrams of CO2/Ar, CO2/N2 and CO2/O2 at
223.15K. In the area marked A, the CO2 mixtures are in the liquid phase; in the area marked as
C, they are in the gas phase; in the area marked as B, which is between A and C, two phases coexist. In order to better understand the VLE behaviours of CO2 mixtures in the CCS
applications, the concentration ranges of impurities were reduced to the probable
concentrations of impurities that appear in the CCS processes. Referring to the composition
windows of different components presented in the Section 2.1, the mole fractions of Ar, N2
and O2 were set between 0-5%, 0-15%, and 0-7% respectively, as shown in the right side
diagrams in Figure 3.1.
8
20
T=223.15K
CO2/Ar
CO2/N2
CO2/O2
18
16
6
Pressure (MPa)
Pressure (MPa)
14
A: Liquid
12
10
8
Dew Point Curve
Bubble Point Curve
6
T=223.15K
CO2/Ar
CO2/N2
CO2/O2
7
5
A: Liquid
4
3
Dew Point Curve
Bubble Point Curve
2
B: Liquid+Gas
4
B: Liquid+Gas
1
2
C: Gas
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0
0.90
C: Gas
0.91
0.92
0.93
0.94
0.95
0.96
0.97
0.98
0.99
1.00
Fraction of CO2 (mol)
Fraction of CO2 (mol)
Figure 3.1 Comparison of VLE characteristics among the binary CO2 mixtures containing non-condensable
impurities: Ar, O2 and N2
Compared with the saturated state of pure CO2, the increment of non-condensable gases makes
both the boiling pressure and condensing pressure of CO2 mixtures rise. For relatively high
purity of CO2, for example, CO2 >70 mol %, the impurities have a more clear impact on
bubble point than on dew point. Comparatively, the variation of N2 has the most remarkable
impacts on both the dew points and the bubble points of CO2 mixtures. Moreover, CO2/N2
has the biggest difference between bubble and dew points. The VLE characteristics of various
CO2 mixtures are shown in more details in Paper IV.
- 22 -
3 Impact of Impurity on Thermodynamic Properties of CO2 Mixtures and Different Processes
Involved in the CCS Systems
Different from the impacts of the non-condensable gases, SO2 has the opposite impact of on
the VLE properties of CO2 mixtures. Figure 3.2 shows the VLE characteristics of CO2/SO2.
Since SO2 has a higher critical point than CO2, the presence of SO2 in CO2 mixtures will make
the condensing temperature increase at a certain pressure or conversely, make the condensing
pressure decrease at a certain temperature.
1.6
CO2/SO2
223.15K
227.15K
243.15K
248.15K
1.4
Pressure (MPa)
1.2
Dew point curve
Bubble point curve
1.0
0.8
0.6
0.4
0.2
0.0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
Mole Fraction of CO2
0.7
0.8
0.9
1.0
Figure 3.2 The VLE characteristics of the CO2 mixtures containing condensable impurity SO2
3.1.2
Impact on Heat Capacity
The heat capacity, enthalpy, and entropy are the important thermodynamic parameters of CO2
mixtures, because they affect the heat transfer and energy consumption of the CO2
compression/purification processes.
The temperature-dependent heat capacities of pure substance (CCO2, CSO2, CN2, CO2 and CAr)
have been calculated based upon an empirical equation [67]:
2
C ⎤
C ⎤
⎡C
⎡C
C = C1 + C 2 ⎢ 3 /sinh( 3 ) ⎥ + C 4 ⎢ 5 /cosh( 5 ) ⎥
T ⎦
T ⎦
⎣T
⎣T
2
(3.2)
and shown in Figure 3.3. The heat capacities of the pure substances decrease in an order of CSO2
> CCO2 > CO2 > CN2 > CAr. It is also clear that the heat capacities of O2, N2 and Ar are less
temperature dependence.
The heat capacity of a CO2 mixture could be calculated by following equation:
n
Cmixture = ∑ Ci × X i
(3.3)
i
where Ci is the heat capacity of pure component. At the same operating temperature, the
presence of SO2 will increase, while the presence of Ar, O2 and N2 will decrease the heat
capacities of CO2 mixtures. This implies that the CO2/SO2 mixture may absorb or release more
- 23 -
3 Impact of Impurity on Thermodynamic Properties of CO2 Mixtures and Different Processes
Involved in the CCS Systems
heat for the same changes in temperature at compared with that of CO2/N2, CO2/O2 and
CO2/Ar mixtures.
40
-1
-1
Heat Capacity (JK mol )
35
30
CO2
SO2
Ar
N2
O2
25
20
15
220
230
240
250
260
270
280
290
300
310
Temperature (K)
Figure 3.3 Heat capacity of different components at different temperatures
3.1.3
Impact on Enthalpy
The enthalpy of real gas can be calculated with the following equation:
h(t , p ) = ∫
T
T0
∑yc
0
i p ,i
⎡
⎛ ∂v ⎞ ⎤
v −T⎜
⎟ ⎥ dP
⎢
p →0
⎝ ∂T ⎠ p ⎥⎦
⎢⎣
dT + ∫
p
(3.4)
Figure 3.4 shows the enthalpies of different CO2 mixtures at 303.15K and 3MPa. It is clear that
only the presence of SO2 increases the enthalpy of CO2 mixtures, which is mainly due to its
heat capacity being higher than that of CO2. More discussion about the impacts of impurities
on enthalpy and entropy will be given in the analysis on energy consumption later.
-36
303.15K, 3MPa
CO2/SO2
CO2/Ar
CO2/O2
CO2/N2
-34
Enthalpy (kJ/kg)
-32
-30
-28
-26
-24
-22
-20
0.90
0.92
0.94
0.96
0.98
1.00
Mole Fraction of CO2
Figure 3.4 Enthalpy of different gaseous CO2 mixtures
- 24 -
3 Impact of Impurity on Thermodynamic Properties of CO2 Mixtures and Different Processes
Involved in the CCS Systems
3.1.4
Impact on Volume
The impact of impurity on the volumes of CO2 mixtures depends upon the molecular weights
of impurities. Since the molecular weight of SO2 is higher, while those of Ar, O2 and N2 are
lower than that of CO2, only SO2 increases the molecular weight of CO2 mixtures. As a result
SO2 makes the volumes of CO2 mixtures increase while others make them decrease. Figure 3.5
shows the volumes and densities of binary CO2 mixtures at different CO2 compositions.
0.060
1050
0.051
0.048
1000
950
3
278.15K, 11MPa
CO2/SO2
CO2/Ar
CO2/O2
CO2/N2
Density (kg/m )
0.054
3
Volume (m /mol)
0.057
900
Volume
Density
850
800
0.045
750
0.042
0.86
0.88
0.90
0.92
0.94
0.96
0.98
700
1.00
Mole Fraction of CO2
Figure 3.5 Volumes and densities of CO2 mixtures at different CO2 compositions
3.2 Impact of Impurity on the Different Processes Involved in the CCS
Systems
3.2.1
Impact of Impurity on Purification
In order to satisfy the requirements of transportation and use the storage reservoir efficiently,
non-condensable gases, such as O2, N2 and Ar should be removed from the CO2 streams
captured in the O2/CO2 recycle combustion. In this study, CO2 purification process has been
investigated with a focus on the physical separation of non-condensable gases. A simplified
process flow diagram of purification is shown in Figure 3.6. The purification process includes
three steps: CO2 stream compression, CO2 stream condensation/liquefaction, and noncondensable gas separation. After water removal, the CO2 stream goes into the separation
column, in which the CO2 stream is condensed and non-condensable gases are separated. Then
the CO2 stream with higher purity will be transported to storage reservoirs by different
measures.
The principle of physical separation is that the liquid/gas concentration of a component in a
non-azeotropic mixture can be increased or decreased by varying the temperature or pressure
of the mixture. Since those CO2 mixtures containing O2, N2, and Ar are non-azeotropic, CO2
streams can be purified by a physical separation, for example, using a distillation column or in a
flash system.
- 25 -
3 Impact of Impurity on Thermodynamic Properties of CO2 Mixtures and Different Processes
Involved in the CCS Systems
WA STE
COM
FEED
SEP1
PUR
SEP2
HEA
WA TER1
WA TER2
PRODUCT
Figure 3.6 Simple process flow diagram of purification
The impact of impurity on non-condensable gas separation process is evaluated from the
following aspects:
− Impacts on the operation conditions;
− Impacts on the purity of the liquid CO2 product delivered to transport;
− Impacts on separation efficiency; and,
− Impacts on system configuration.
The operation conditions of purification are mainly determined by the dew points of CO2
mixtures. Since the presence of non-condensable impurities increases the condensing pressures
of CO2 mixtures at a certain temperature, or decreases the condensing temperatures at a certain
pressure, the increment of mole fractions of impurities increases either compression work or
the energy demand of refrigeration. Comparatively, condensing CO2 mixtures containing N2
requires a lower condensing temperature or a higher condensing pressure than condensing
mixtures containing other non-condensable gases. Therefore, the operation conditions of CO2
purification can be more sensitive to the changes of N2 concentration in CO2 mixtures.
The purity of the liquid CO2 obtained from the separation process is mainly determined by the
bubble points of the CO2 mixtures. From Figure 3.1, it can be found that the purity of liquid
CO2 mixtures decreases with the increase in pressure at a given temperature. It is also found
that less N2 exists in the liquid CO2 product compared to that of Ar and O2 at certain
temperatures and pressures. This means that under the same operation conditions of
purification, CO2 purity of purification products is in an order of separating CO2/N2 >
separating CO2/Ar > separating CO2/O2.
How easily a non-condensable component can be separated from its corresponding CO2
mixture can be evaluated by relative volatility [68] of the components, which is defined by:
α AB =
y Ae / x Ae
y Be / x Be
(3.5)
where αAB is the relative volatility of component A compared to component B when the twocomponent mixture under equilibrium conditions, yAe/yBe and xAe/xBe are the mole fractions of
component A/B in vapour and liquid phase, respectively. As shown in Figure 3.7, N2 has a
- 26 -
3 Impact of Impurity on Thermodynamic Properties of CO2 Mixtures and Different Processes
Involved in the CCS Systems
higher relative volatility compared to Ar and O2. This means that N2 can be more easily
separated from the CO2 mixtures compared to the separation of Ar and O2. It can also be
found that pressure has more remarkable impacts on the relative volatilities of the noncondensable gases at low temperatures, such as 223,15K. These characteristics should be taken
into account for the optimization of separation conditions.
100
Separating impurity from CO2
N2
O2
Ar
Relative Volatility
80
60
223.15K
243.15K
40
20
1
2
3
4
5
6
7
Pressure (MPa)
Figure 3.7 Relative volatilities of the non-condensable components involved in CO2 mixtures
The system configuration of CO2 purification is related to the difference between bubble and
dew points of CO2 mixtures. McCabe et al. [68] indicates:” flash distillation is used most for
separating components which boil at widely different temperatures. It is not effective in
separating components of comparable volatility since both the condensed vapour and residual
liquid are far from pure”. As the differences between bubble points and dew points of CO2/N2,
CO2/O2 and CO2/Ar are large; they can be purified by a flash system. Examples for simulating
purification by flash and distillation tower are given in Paper IV.
3.2.2
Impact of Impurity on Compression
Compression can be conducted in a number of ways, such as undergoing an isothermal path, a
polytropic path, or an isentropic path. If we ignore the change of kinetic energy and potential
energy, theoretical compression work is reduced as the compression path approaches the
isothermal from the isotropic.
In an actual compression process, the isothermal compression is unable to be realized and
consequently it is a polytropic process. Due to the diversification of polytropic compression,
the impact of impurity on isothermal compression and isentropic compression, which are the
top and bottom limits of polytropic compression work, was studied instead.
Figure 3.8 shows the work required for compressing different CO2 streams isothermally at
different outlet pressures and different CO2 compositions. Under the same operation
conditions, compressing CO2/SO2 will consume the least work, while compressing CO2/N2 will
require the most work. Meanwhile, compression work increases along with the increments of
Ar, O2 and N2; while decreases along with the increment of SO2 linearly, if the outlet pressure is
constant.
- 27 -
3 Impact of Impurity on Thermodynamic Properties of CO2 Mixtures and Different Processes
Involved in the CCS Systems
Compression Work (kJ/kg)
220
Outlet Pressure
3MPa
4MPa
210
200
190
180
Inlet: 303.15K, 0.1MPa
CO2/SO2
CO2/Ar
CO2/O2
CO2/N2
170
0.86
0.88
0.90
0.92
0.94
0.96
0.98
1.00
Mole Fraction of CO2
Figure 3.8 Energy consumption of isothermal compression at different CO2 compositions
Figure 3.9 shows the discharging temperatures and energy consumption of isentropic
compression. It can be seen that Ar, O2, and N2 make discharging temperature increase, while
SO2 makes it decrease. Comparatively, the discharging temperature is more sensitive to the
fraction variation of Ar than other impurities. Meanwhile impurities affect the isentropic
compression work in similar ways as they affect the discharging temperature.
400
680
Inlet: 303.15K, 0.1MPa
CO2/SO2
CO2/Ar
CO2/O2
CO2/N2
Outlet Pressure
3MPa
4MPa
660
650
Outlet Pressure
3MPa
4MPa
390
380
Compression Work (kJ/kg)
Discharging Temperature (K)
670
640
630
620
610
370
360
350
340
330
320
600
Inlet: 303.15K, 0.1MPa
CO2/SO2
CO2/Ar
CO2/O2
CO2/N2
310
590
0.86
0.88
0.90
0.92
0.94
0.96
0.98
1.00
0.86
0.88
0.90
0.92
0.94
0.96
0.98
1.00
Mole Fraction of CO2
Mole Fraction of CO2
Figure 3.9 Discharging temperature and energy consumption of isentropic compression at different CO2
compositions and pressures
Figure 3.10 compares the compression work between isothermal and isentropic processes. It is
clear that the energy consumption difference becomes larger along with the rise of the
concentrations of non-condensable gases. This implies that it is more desirable to compress the
CO2 mixture containing non-condensable gases in the process that is close to isothermal
compression. In other words, intercooling shall be considered in the compression of CO2/O2,
CO2/N2 and CO2/Ar, especially at relatively high impurity concentrations.
- 28 -
3 Impact of Impurity on Thermodynamic Properties of CO2 Mixtures and Different Processes
Involved in the CCS Systems
190
Compression Work Difference (kJ/kg)
185
180
175
170
165
Outlet Pressure
3MPa
4MPa
160
155
150
145
140
Inlet Condition: 303.15K, 0.1MPa
CO2/SO2
CO2/Ar
CO2/O2
CO2/N2
135
0.86
0.88
0.90
0.92
0.94
0.96
0.98
1.00
Mole Fraction of CO2
Figure 3.10 Comparison on the compression work of isothermal and isentropic processes
3.2.3
Impact of Impurity on Refrigeration/Liquefaction
In order to liquefy CO2 mixtures, two ways can be applied to remove heat from the gas
processing system: (1) cooling the gas by transferring heat to a cold reservoir (external
refrigeration); and, (2) using Joule-Thomson effect, which is called self-refrigeration. In this study,
the external refrigeration is investigated to understand the impacts of the impurities on the
demands of refrigeration for the phase separation of the CO2 mixtures.
Figure 3.11 shows the energy consumption of external refrigeration at different inlet and outlet
temperatures and pressures. Refrigeration duty rises along with the drop of the discharging
temperatures of refrigeration and operating pressures. Meanwhile, refrigeration decreases with
the increments of non-condensable impurities; while increases with the increments of SO2 due
to the impact of impurity on heat capacity. In addition, there is a turning point on their curves
of the required refrigeration for liquefying CO2/Ar, CO2/O2 and CO2/N2. Before and after that
point, the increasing rates of the energy demand with the decrements of impurity are different.
The reason for this difference comes from the fact that CO2 mixtures are partially condensed
before the point, and the decrement of impurities will increase the liquid fraction. Due to the
latent hear of phase change, the energy consumption of refrigeration increases faster when
more fractions are liquefied.
- 29 -
3 Impact of Impurity on Thermodynamic Properties of CO2 Mixtures and Different Processes
Involved in the CCS Systems
410
400
Outlet Temperature
223.15K
243.15K
Outlet Pressure:
3MPa
360
390
Refrigeration (kJ/kg)
Refrigeration (kJ/kg)
380
400
340
320
Inlet: 303.15K, 3MPa
CO2/SO2
CO2/Ar
CO2/O2
CO2/N2
300
280
260
0.86
0.88
0.90
0.92
0.94
0.96
0.98
380
Pressure:
3MPa
4MPa
Outlet Temperature:
223.15K
370
360
350
Inlet: 303.15K
CO2/SO2
CO2/Ar
CO2/O2
CO2/N2
340
330
320
1.00
0.86
0.88
Mole Fraction of CO2
0.90
0.92
0.94
0.96
0.98
1.00
Mole Fraction of CO2
Figure 3.11 Energy consumption of external refrigeration required by CO2 liquefaction at different CO2
compositions and operation conditions
3.2.4
Impact of Impurity on CO2 Transportation
To improve transportation efficiency, it is preferable to transport CO2 in a high-density state.
The desired state of the CO2 fluids is different based upon the means of transportation. For
transportation in vessels, liquid phase in low pressure is desirable [13]. If CO2 is transported in
pipeline, liquid phase in high pressure, or supercritical phase is desirable. However, regardless
of which transport method is used, phase change must be avoided to ensure the safety of
transportation.
3.2.4.1 Acceptable Concentration Ranges of Non-condensable Impurities
To guarantee the safe transportation of CO2 mixtures, the concentrations of non-condensable
impurities should be restricted in appropriate ranges. According to the estimated T-P windows
for CO2 transport (Table 2.2) and possible concentration ranges of the impurities, the potential
of phase changes under such conditions is presented. Results on the acceptable maximum mole
fraction of impurities at the given temperature and pressure are summarized in Table 3.2.
As shown in Table 3.2, very low contents of the non-condensable impurities should be kept for
the CO2 products for the vessel transport. Especially, the operation conditions of the transport
in large tanks should be carefully investigated again, because the VLE calculations show that the
CO2 mixtures may be in a gas phase even when the purity of CO2 is 100%. For example, at
218.15K, 5bar cannot satisfy the requirement transporting CO2 mixtures in liquid phase.
- 30 -
3 Impact of Impurity on Thermodynamic Properties of CO2 Mixtures and Different Processes
Involved in the CCS Systems
Table 3.2 Acceptable maximum mole fraction of impurities at the given temperatures and pressures
Temperature (K)
Large tank
Small tank
218.15
223.15
228.15
238.15
243.15
Acceptable N2 content in CO2/N2 mixtures (mol%)
0.5
Gas[1]
Gas[1]
Gas[1]
0.7
0.18
0.03
Gas[1]
0.9
0.45
0.30
0.10
1.0
Gas[1]
Gas[1]
1.5
0.57
0.14
2.0
1.52
1.12
2.5
2.30
2.10
8.0
>9.0
Acceptable Ar content in CO2/Ar mixtures (mol%)
0.5
Gas[1]
Gas[1]
Gas[1]
0.7
0.24
0.03
Gas[1]
0.9
0.60
0.40
0.12
Gas[1]
1.0
Gas[1]
1.5
0.45
0.11
2.0
1.20
0.88
2.5
1.97
1.67
8.0
>9.0
Acceptable O2 content in CO2/O2 mixtures (mol%)
0.5
0.05
Gas[1]
Gas[1]
0.7
0.43
0.14
Gas[1]
0.9
0.83
0.52
0.25
1.0
Gas[1]
Gas[1]
1.5
0.65
0.21
2.0
1.59
1.14
2.5
2.55
2.09
8.0
>9.0
Pressure
(MPa)
Pipeline
273.15 283.15
293.15
303.15
Gas[1]
Gas[1]
0.63
1.62
-
-
-
-
-
9.54
15[2]
7.88
15[2, 3]
5.70
15[2, 3]
4.33
15[2, 3]
Gas[1]
Gas[1]
0.50
1.29
-
5[2, 3]
5[2, 3]
5[2, 3]
5[2, 3]
5[2, 3]
5[2, 3]
4.60
5[2, 3]
Gas[1]
Gas[1]
0.64
1.59
-
7[2, 3]
7[2, 3]
7[2, 3]
7[2, 3]
6.04
7[2, 3]
4.68
7[2, 3]
248.15
Notes: [1] in gas phase even for pure CO2; [2] the max tested impurities content in corresponding CO2 mixtures; [3] in supercritical liquid phase
or supercritical fluid phase.
3.2.4.2 Transport Efficiency
In most cases, CO2 is transported and stored in a supercritical state. The volume of CO2
mixtures significantly affects the efficiency and safety of CO2 transportation and storage. For
example, the higher the effective CO2 volume is, the more efficiently the CO2 can be
transported, and the more efficiently the pore space in geological media can be used for storage.
In addition, the buoyancy forces decrease with the increase of CO2 mixture density. It would be
easier to reduce CO2 leakage from the top rock layer of storage sites if the buoyancy force is
lower.
Figure 3.12 shows the effective CO2 volumes, calculated based on Equ. 3.1 under different
mole concentrations and mass concentrations of CO2. It is clear that occupied volumes by the
given amount of impurities in corresponding CO2 mixtures are in the following order: VN2 >
VO2 > VAr > VSO2. This means that N2 has the worst impact on CO2 transport efficiency and
storage capacity, amongst all of impurities. Therefore its concentration should be kept as low as
possible.
- 31 -
1,05
1,05
1,00
1,00
0,95
0,95
Effective CO2 Volume
Effective CO2 Volume
3 Impact of Impurity on Thermodynamic Properties of CO2 Mixtures and Different Processes
Involved in the CCS Systems
0,90
278.15, 11MPa
CO2/SO2
CO2/Ar
CO2/O2
CO2/N2
0,85
0,80
0,75
0,90
0,85
278.15K, 11MPa
CO2/SO2
CO2/Ar
CO2/O2
CO2/N2
0,80
0,75
0,70
0,70
0,86
0,88
0,90
0,92
0,94
0,96
0,98
1,00
0,86
0,88
0,90
0,92
0,94
0,96
0,98
1,00
Mass Fraction of CO2
Mole Fraction of CO2
Figure 3.12 Effective CO2 volumes of different CO2 mixtures at different CO2 mole and mass concentrations
3.3 Discussions
3.3.1
Impact of Impurity on the Thermodynamic Properties
In this chapter, the impacts of the impurities appearing in the oxidizing CO2 stream (e.g.
captured from oxy-fuel combustion) were mainly studied. However, it is different from the
impurities appearing in the reducing CO2 stream (e.g. captured from IGCC) that H2S is found
instead of SO2. Moreover, H2 is also important in the reducing CO2 stream. Therefore, for the
study on reducing CO2 steams, the impacts of H2S and H2 should be investigated as well.
Current studies focus on the binary CO2 mixture. However, the real flue gases are multicomponent CO2 mixtures. When there is more than one impurity, the changes of the properties
of CO2 mixtures and performances of different processes still remain unclear. Several questions
must be answered before the evaluation results from the binary systems could be applied to the
multi-component systems. For example, would the impact of impurity on thermodynamic
properties be consistent in binary mixtures and multi-component mixtures? If there are several
impurities, can the total impacts of impurities be decided simply by summing up the impact of
any impurity? Which calculation methodologies are more suitable for the assessment of
thermodynamic properties of the multi-component CO2 mixtures?
In addition, hydrate formation and corrosion are tightly related to the content of water involved
in CO2 mixtures. H2O is an important component for corrosion evaluation, especially for the
CO2 processing equipments located before the dehydration. However, the existence of other
impurities, such as O2, N2, and Ar may change the solubility of water vapour. Therefore, it is
essential to study the solubility of H2O in multi-component CO2 mixtures.
3.3.2
Compression
The results on the theoretical compression work of isothermal compression and isentropic
compression have given some insights into the compression work of a multi-stage polytropic
compression. However, the required compression power of an actual compression process is
far from the theoretical compression work and is affected by many factors in addition to the
impacts of impurities on the thermodynamic properties of CO2 mixtures. For example, the
impact of impurity on the transport properties of CO2 mixtures, such as viscosity and heat
conductivity, is also of great importance for the evaluation of the compression processes.
- 32 -
3 Impact of Impurity on Thermodynamic Properties of CO2 Mixtures and Different Processes
Involved in the CCS Systems
3.3.3
Refrigeration
As mentioned in Chapter 3.2.3, there are two ways to liquefy CO2 streams. Comparatively
liquefaction by external refrigeration is usually adopted when the process does not require very
low temperatures [14]. Therefore, using Joule-Thomson effect to liquefy CO2 streams might be
more appropriated according to the desired operation conditions. In this research, the impact
of impurity on the energy demand of refrigeration has been discussed based upon external
refrigeration. However, impurities would have an impact on the energy consumption of selfrefrigeration as well; because various impurities have different kinds of impacts on the latent
heat of CO2 mixtures and evaporating conditions. Therefore, further study should be
conducted regarding the impact of impurity on self-refrigeration. In addition, the energy
demand of refrigeration strongly depends upon the operation pressure. Hence, how to balance
the energy consumption of compression and refrigeration is essential to the system
optimization for CO2 compression and purification.
3.3.4
Future Work
Based upon the current discussion, more work should be conducted to supplement the analysis
of the impact of impurity on the thermodynamic properties of CO2 mixtures. This includes:
− Investigating the impacts of H2S and H2 on the thermodynamic properties and the CCS
processes; and,
− Investigating the impact of impurity in multi-component CO2 mixtures and offering
some general indications on the trends of this impact. Since very few experimental data
about CO2/O2/N2 exist, they will be used to verify the conclusions.
- 33 -
3 Impact of Impurity on Thermodynamic Properties of CO2 Mixtures and Different Processes
Involved in the CCS Systems
- 34 -
4 Evaporative Gas Turbine Cycles Integrated with Different CO2 Capture Technologies
Part II: Evaporative Gas Turbine Cycles Integrated with
CO2 Capture
4 Evaporative Gas Turbine Cycles Integrated with Different CO2
Capture Technologies
Performance of integrating CO2 capture into a gas turbine cycle is significant in developing the
innovative and optimal methods for CO2 mitigation. A variety of system configurations to
reach high efficiency and low CO2 capture cost have been studied. For example, performance
analysis has been conducted regarding the combined cycles (CC) integrated with different CO2
capture technologies [69-72]. However, few studies are available concerning the integration of
CO2 capture with another advanced power cycle, the humidified gas turbine cycles.
Normally, humidified gas turbines include steam injection gas turbines (STIG) and evaporative
gas turbines, also known as humid air turbine (HAT). The driving forces for gas turbine
humidification have been the potentials of high electrical efficiency, specific power output,
reduced specific investment cost, decreased formation of nitrogen oxides (NOx) in the
combustor, and, improved part-load performance compared with combined cycles [73]. In
addition, compared with STIG, EvGT has a lower irreversibility, because water is injected into
the cycle by humidification tower, which has a small temperature difference between the hot
and cold fluids. This study is intended to analyze the integration of CO2 capture with EvGT
cycles.
Two CO2 capture technologies are considered here including chemical absorption with MEA
and O2/CO2 recycle combustion. The MEA-based chemical absorption technology is suitable
for dilute systems and low CO2 concentrations, and can be easily applied to the existing power
plants. Thus far, this is the only commercially available option for CO2 capture [74-78]. In the
O2/CO2 recycle combustion option, the most promising features are the nearly 100% CO2
capture and the simple CO2 stream processing procedure, which does not involve absorption
and stripping steps. However, on the other hand, it requires an air separation unit (ASU) to
supply oxygen for combustion [79-81].
In this chapter, the performances of different configurations have been analyzed and compared
from both technical and economical perspectives, in order to characterize and understand the
features of the integration of EvGT with CO2 capture process.
4.1 System Configurations
Two systems, as well as a reference system, are simulated with natural gas as fuel input. These
include:
− System I (reference case): EvGT cycle without CO2 capture;
− System II: EvGT cycle + chemical absorption capture; and,
− System III: EvGT cycle + O2/CO2 recycle combustion.
In order to avoid corrosion and the formation of ice or hydrate in CO2 compression and
transportation, the captured CO2 streams will go through a dehydration process, after which the
water content would be lower than 0.05% [82]. Furthermore, to achieve high cycle efficiency,
- 35 -
4 Evaporative Gas Turbine Cycles Integrated with Different CO2 Capture Technologies
waste heat is recovered for district heating from flue gas and the discharging streams of CO2
compressors, stripper, and dehydrator through condensers or heat exchangers.
4.1.1
EvGT Cycle without CO2 Capture
The basic idea of EvGT cycle is injecting water by evaporation, which will increase the mass
flow rate through the turbine and, consequently, augment the specific power output. The
EvGT cycle has a high efficiency, due to that fact the waste heat in the exhaust gas is recovered
by humid air in the recuperator and by water in the economizer. A system sketch of EvGT
cycle without CO2 capture is shown in Figure 4.1. Water is heated close to saturation by the
compressed air in the aftercooler, and flue gas in the feedwater heater and economizer. The
heated water enters at the top of a humidification tower and is brought into counter-current
contact with the compressed air that enters as the bottom of the tower. The tower is a column
with a packing that is either structured or dumped. Some of the water is evaporated and the air
is humidified. The water evaporates at the water boiling point corresponding to the partial
pressure of water in the mixture, (i.e., water evaporates below the boiling point that
corresponds to the total pressure in the tower). Therefore, low temperature heat, which cannot
be used to evaporate water in a boiler, can be recovered in an EvGT cycle. Since the water
vapour content in the air increases as the air passes upward through the tower, the boiling
temperature also increases. This ensures a close matching of the air and water temperature
profiles and small exergy losses, compared to the evaporation in a conventional steam boiler.
Figure 4.1 System sketch of System I (reference system): EvGT cycle without CO2 capture
4.1.2
EvGT Cycle with Chemical Absorption CO2 Capture
A system sketch of EvGT cycle with chemical absorption capture is shown in Figure 4.2. As
opposed to System I, instead of being condensed in the feedwater heater, the flue gas enters the
reboiler of MEA stripper to support the heat required for MEA regeneration; afterward, it goes
- 36 -
4 Evaporative Gas Turbine Cycles Integrated with Different CO2 Capture Technologies
through the recuperator and economizer. Then it is condensed in a heat exchanger, in which
heat is recovered for district heating as well. After heat recovery, flue gas flows through the
absorber counter-currently with the absorbent where the absorbent reacts chemically with CO2.
The rich solvent containing chemically bound CO2 is then sent to the top of the stripper via a
lean/rich cross heat exchanger, being heated to a temperature close to that of the stripper
operating temperature. At an elevated temperature, the chemically bound CO2 is released and
absorber is regenerated in the stripper. After compression and dehydration, the recovered CO2
will be transported to the storage reservoir through different means.
Figure 4.2 System sketch of System II: EvGT cycle with chemical absorption CO2 capture
4.1.3
EvGT Cycle with O2/CO2 Recycle Combustion CO2 Capture
A system sketch of EvGT cycle with O2/CO2 recycle combustion capture (oxy-fuel
combustion) is shown in Figure 4.3. O2/CO2 recycle combustion takes place in a
denitrogenation environment; it produces a flue gas that consists of mainly H2O and CO2.
Therefore, a simplified flue gas processing procedure can be used instead of conventional
means, such as chemical absorption, to achieve a low cost for CO2 capture. For instance, flue
gas could be compressed directly and transported to the storages after condensation and
dehydration, without further purification. However, in the denitrogenation combustion, the
nitrogen removal may cause the flame temperature to be extremely high and decrease the mass
flow rate through the gas turbine. In order to compensate for the reduced mass flow, after
condensation, a large fraction of flue gas is recycled back into the combustor. In addition,
compared with the CO2 capture approach of chemical absorption, relatively high levels of
impurities are expected in the captured CO2 streams from O2/CO2 recycle combustion. Here,
the major impurity is oxygen, due to the existing amount of excess oxygen.
- 37 -
4 Evaporative Gas Turbine Cycles Integrated with Different CO2 Capture Technologies
Figure 4.3 System sketch of System III: EvGT cycle with O2/CO2 recycle combustion CO2 capture
4.2 Thermodynamic Performances of Various Systems
Systems have been simulated in Aspen Plus 2006. For chemical absorption capture process, the
RADFRAC model is used for absorber and stripper columns. Meanwhile, the thermodynamic
and transport properties were modelled using “MEA property insert”, which describes the MEAH2O-CO2 system with electrolyte-NRTL model [83]. In addition, PR equation of state is used
for the calculations of thermodynamic properties in combustion, compression and other
processes based upon our previous studies.
4.2.1
Input Data and Assumptions
Input data and assumptions for the simulations of gas turbine, compressors, chemical
absorption, and dehydration are given in Table 4.1. Compositions and properties of inlet
streams and outlet streams are summarized in Table 4.2.
- 38 -
4 Evaporative Gas Turbine Cycles Integrated with Different CO2 Capture Technologies
Table 4.1 Input data and assumptions for the simulations of gas turbine, compressors, chemical absorption and
dehydration
Parameter
Turbine
Pressure Ratio
Turbine Inlet Temperature (TIT)
Mechanical Efficiency
Unit
Value
20
1523.15
99
K
%
Compressors
Type
Isentropic Efficiency
Intercooling T
Stage Number of Air/Oxygen Compression
Stage Number of CO2 Compression
Mechanical Efficiency
Chemical Absorption
Solvent
Solvent Loading
Stripper Operating P
Pressure Drop in Absorption Column
Isentropic
85
303.15
2
3
98
%
K
%
MPa
mbar
MEA (30wt%)
0.3
0.1
150 [72]
Dehydration
Dryer
Operating P of Dehydration
Operating P of Regeneration
Operating T of Regeneration
MPa
MPa
K
Triethylene glycol (TEG) (99 wt%)
2.0
0.1
477.15 [84]
Others assumptions
Pump mechanical Efficiency
Pressure Drop in Humidification Tower
ΔTmin Gas/Gas
ΔTmin Gas/Liquid
Supplying T for District Heating
CO2 Capture Ratio of Chemical Absorption
Excess Oxygen in Flue Gas
%
%
K
K
K
%
mol%
90
5 [85]
30
20
60
90
3 [69]
Mol CO2
Mol MEA
In Table 4.1, the CO2 capture ratio (CCR) has been defined as:
CCR =
(Mole flow × CO 2 Mole fraction )CO To be transport ed
(Mole flow × CO 2 Mole fraction )Flue gas to be processed
2
Here, the flue gas to be processed is indicated as FBP in the Figure 4.2 and 4.3.
- 39 -
(4.1)
4 Evaporative Gas Turbine Cycles Integrated with Different CO2 Capture Technologies
Table 4.2 Compositions and properties of feed streams and outlet streams
Fuel stream
CH4
LHV
T
P
Air stream
T
P
Composition
N2
O2
Ar
CO2
Relative Humidity
Oxygen stream
T
P
Composition
N2
O2
Energy Consumption
CO2 Streams to be Transported
T
P
4.2.2
%
MJ/kg
K
MPa
100
50
288.15
0.1
K
MPa
288.15
0.1
vol%
vol%
vol%
vol%
%
76.99
20.65
0.921
0.04
60
K
MPa
288.15
0.1
vol%
vol%
MJ/kg O2
1
99
0.9 [70]
K
MPa
293.15
15
Simulation Results and Discussions
With the same turbine inlet temperature and pressure ratio, three systems were simulated.
Concrete evaluation results of EvGT integrated with CO2 capture are given in Paper VI. Here,
the system performance was analyzed from three perspectives: electrical efficiency, heat
recovered for district heating, and CO2 emission.
4.2.2.1 Electrical Efficiency
Figure 4.4 shows the breakdown of electricity generations and power consumptions in
percentage of fuel energy (LHV-based) for the three systems. As can be seen from Figure 4.4,
System I has the highest electrical efficiency, which is defined as:
η=
Net Electricity Generation
Chemical Energy in Feul
(4.2)
with a value of 51.64%. The electrical efficiencies of System II and III are 39.73% and 37.45%
respectively. Therefore, compared to System I, the penalty caused by CO2 capture on electrical
efficiency is 11.91 percentage point for System II and 14.19 percentage point for System III.
- 40 -
Power generation and consumption (in % of fuel LHV)
4 Evaporative Gas Turbine Cycles Integrated with Different CO2 Capture Technologies
Electricity Generation
Power Consumption of Fuel and Air Compressors
Power Consumption of CO 2 Compressors
Power Consumption of ASU
100
80
60
40
20
0
System II
System I
System III
Figure 4.4 Breakdown of electricity generation and power consumption (in % of fuel LHV)
4.2.2.2 Heat Recovery
Recovered heat for district heating and heat consumption
(in % of fuel LHV)
Figure 4.5 shows the breakdown of the heat consumption and the heat recovered for district
heating in percentage of fuel input (LHV-based) for three systems. System III has the largest
amount of heat recovered for district heating, which is about 28.9 in percentage of fuel LHV.
Due to the heat recovered from the discharging flows of CO2 compressors, more heat is
recovered in System II and III than in System I. Meanwhile, because there is no heat demand
by stripper, System III has more recovered heat than System II.
Heat Recovered for District Heating
Heat Consumption of Stripper
Heat Consumption of Dryer Regeneration
40
30
20
10
0
System I
System II
System III
Figure 4.5 Breakdown of the heat recovered for district heating and heat consumption (in % of fuel LHV)
4.2.2.3 CO2 Emission
- 41 -
4 Evaporative Gas Turbine Cycles Integrated with Different CO2 Capture Technologies
The CO2 emission per kWh produced electricity and the actual CO2 capture ratio, which is
defined as:
ACCR =
( Mole flow × CO 2 Mole fraction) CO2 To be transported
Produced CO 2
(4.3)
In combustion
are presented in Figure 4.6. Compared to the CO2 release of the EvGT cycle without CO2
capture, 386g/kWh, the avoided CO2 emissions of System II and III are 335g/kWh and
385g/kWh, respectively. The theoretical CO2 capture ratios of System II and System III are
90% and 100%. However, in the real application, there will be slightly lower than the theoretical
values because CO2 may dissolve in the condensed water in condensers and be lost. Compared
with System III, more water is condensed in System II. As a result, System II has a bigger
reduction of CCR, 0.7 percentage point.
CO2 Emission
Actual CO2 Capture Ratio
350
80
300
250
60
200
40
150
100
CO2 Capture Ratio (%)
CO2 Emission (g CO2/kW.h Electricity)
100
20
50
0
0
System I
System II
System III
Figure 4.6 CO2 emissions per kWh produced electricity and the CO2 capture ratio
4.2.3
Compared with Combined Cycles
Kvamsdal et al. [72] investigated the performance of combined cycles (CC) with various CO2
capture technologies. In Table 4.3, a comparison of electricity generation and internal electricity
consumption is shown between CC and EvGT cycle. The CC always has a higher gross
electricity generation, electricity efficiency, and internal electricity consumptions of Air/Fuel
compressors. However, it has similar electricity consumptions of CO2 compressors and ASU,
compared with the EvGT cycle.
- 42 -
4 Evaporative Gas Turbine Cycles Integrated with Different CO2 Capture Technologies
Table 4.3 Comparison on electricity generation and internal electricity consumption between combined cycle and
EvGT cycle (in % of fuel LHV)
Gross Electricity Generation
Air/Fuel Compressors
CO2 Compressors
Pumps
ASU
Auxiliaries
Net electricity Efficiency
Without CCS
CC
EvGT
95.2
88.5
37.6
35.3
0.3
0.04
0.6
56.7
51.6
MEA Absorption
CC
EvGT
90.9
71.57
37.6
28.2
2.3
2.18
0.6
0.03
2.5
47.9
39.73
O2/CO2 recycle
CC
EvGT
88.5
72
31.1
23.3
3.0
2.3
0.3
0.03
6.4
7.4
0.6
47.0
37.5
4.3 Economic Evaluation on Various Systems
Based upon a gas turbine, LM1600PD, which capacity is 13.78MW and produced by GE
Energy Aeroderivative [86], a preliminary economic calculation was made regarding those three
systems. This gas turbine was considered because it has similar performance (turbine exit
temperature (TET) and pressure ration) to the turbine simulated in Section 4.2.
4.3.1
Assumptions
The assumptions made in the cost calculation are listed in Table 4.4. The fuel price is the
average of Mott MacDonald’s long-run forecast prices up to 2025 for the Netherlands coastal
location [87]. The Operation & Maintenance cost per year is referred to the total capital cost.
And the other fee includes the operating labours cost, local taxation and insurance, and the
auxiliary devices which are not involved in the main equipment list. This is also referred to as
the capital cost.
Table 4.4 Assumptions made in the cost calculation
Parameter
Natural Gas Price
Interest Rate
Operating Life
Operating Hours
Operation & Maintenance
Other Fee
MEA Price
TEG Price
Make-up Water
Cooling Water (288.15K)
4.3.2
Unit
USD/kg
per year
year
hr/yr
%
%
USD/kg
USD/kg
USD/ton
USD/ton
Value
0.4 [87]
8%
20
7500
4 [88]
10
1.5 [89]
1 [90]
1 [91]
0.2 [91]
Capital Costs and Cost of Electricity
Table 4.5 summarizes the annual costs of different systems. The equipment purchase cost is
calculated by CAPCOST [91]. Detailed results are listed in Appendix B. Due to the efficiency
penalty and additional equipment for CO2 capture, System II and III have higher electricity
prices than System I. Meanwhile, compared to System III, although System II has a higher
annual cost, it has a lower electricity price because of its higher efficiency. However,
considering its lower CO2 capture ratio, System II has a higher specific cost to capture CO2.
- 43 -
4 Evaporative Gas Turbine Cycles Integrated with Different CO2 Capture Technologies
Table 4.5 Annual costs of different systems
System I
2698
421
3348
0
0
53
508
7028
0.13
0
Amortized Capital Cost (kUSD)
O&M (kUSD)
Fuel (kUSD)
MEA (kUSD)
TEG (kUSD)
Make-up Water (kUSD)
Cooling Water (kUSD)
Total (kUSD)
Electricity (USD/kWh)
CO2 Capture (USD/tonCO2)
System II
2970
463
4158
86
12
53
508
8250
0.20
47.62
System III
2890
451
4136
0
12
64
578
8131
0.21
38.89
Figure 4.7 shows the breakdown of CO2 capture costs of System II and III. It is apparent that
the O&M is similar in the two systems. Meanwhile, the main components in the overall capture
costs of both methods come from the fuel, due to their large electrical efficiency penalties
caused by CO2 capture. This implies that, to EvGT cycles, improving the cycle efficiency is an
important way to reduce the capture cost.
50
$5.44
40
O&M
Fuel
Capital Cost
$/ton CO2 avoided
$4.31
30
$31.58
$27.81
20
10
$10.60
$6.77
0
Chemical Absorption
O2/CO2
Figure 4.7 Comparison of capture costs of chemical absorption and O2/CO2
There have been some studies examining the capture cost from both coal power plants [84-86]
and gas turbine cycles [92-94]. Figure 4.8 compares the different results in terms of $/ton CO2
captured from different systems. Results from Singh [95], Alston [96], Simbeck [97] and Bill
[98] are included. First of all, the systems with chemical absorption in all studies are more
expensive than the oxy-fuel combustion-based capture systems. Secondly the results on CO2
capture costs of this study are similar to those from coal power plants, while larger than those
of Bill, which are obtained from combined cycle. The big differences of CO2 capture costs
between CC and EvGT mainly come from the big differences of electrical efficiency, for
example, 8.2 and 9.5 percentage point (Table 4.4) for chemical absorption capture and oxy-fuel
combustion capture respectively.
- 44 -
4 Evaporative Gas Turbine Cycles Integrated with Different CO2 Capture Technologies
Chemical Absorption
O2/CO2
Capture Cost ($/ton CO2)
50
40
30
20
10
Th
is
St
ud
y
(N
G)
20
02
)
Bi
ll
(N
G,
20
01
)
Si
m
be
ck
(C
oa
l,
(C
oa
l,
Al
sto
m
Si
ng
h
(C
oa
l,
20
03
)
20
01
)
0
Figure 4.8 Comparison of CO2 capture costs
4.4 Investigation of EvGT Integrated with MEA Based Chemical
Absorption Capture Regarding Electrical Efficiency
In order to improve the electrical efficiency of EvGT cycle integrated with MEA based CO2
capture technology, three important parameters, including Water/Air ratio (W/A), stripper
pressure (STP), and flue gas condensing temperature (FCT), were investigated in a row in this
study. The initial values of STP and FCT are 0.1MPa and 313.15K respectively. After one
parameter is optimized, the optimal value would be used in the following work. All simulations
were conducted with Aspen Plus.
4.4.1
Water/Air Ratio
Water/Air ratio (W/A), which is defined as:
W /A=
Mass flow of evaporated water
Mass flow of Air
(4.4)
It has been verified that there is always an optimum point. This point occurs when both the air
temperature after the recuperation reaches the highest value, and at the same time, the stack
temperature is at the lower limit [99]. Figure 4.9 shows the results of the optimization of
water/air ratio regarding the EvGT without and with CO2 capture. Both electrical efficiencies
first rise; and then, drop along with the increase of W/A. The highest efficiencies are 52.1%
and 41.3%, which were reached at the W/A with values of 0.14 and 0.115 respectively.
Different from the impact of W/A on the total efficiency, the efficiency penalty rises along with
the increase of W/A.
- 45 -
4 Evaporative Gas Turbine Cycles Integrated with Different CO2 Capture Technologies
52
Efficiency (%)
50
EvGT without CCS
EvGT with CCS
48
FCT=313.15K
STP=0.1MPa
46
44
42
0.09
0.10
0.11
0.12
0.13
0.14
0.15
0.16
0.17
Water/Air
Figure 4.9 Electrical efficiency of EvGT without/with CO2 capture at different Water/Air ratio
4.4.2
Stripper Pressure
It has been concluded that increasing the stripper operating pressure would increase the
stripper operating temperature; while decrease the reboiler duty required for MEA regeneration
[83]. This implies that, at a higher operating pressure, the reboiler of stripper may require less
heat but in a higher temperature. Therefore, from the viewpoint of exergy, the heat recovered
back to the combustor through economizer and humidification tower and the heat required by
stripper shall be carefully arranged with the consideration of temperature matching in the heat
exchanging processes. This may reduce the irreversibility caused by heat transfer, and result in
different overall efficiencies of cycle.
Figure 4.10 shows the specific energy requirements to capture 1ton CO2 and the reboiler
temperatures at different STP. Along with the rise of stripper pressure, the energy requirement
decreases; while the reboiler temperature increases. In addition, compared with its reboiler
temperature, reboiler duty is more sensitive to the variation of STP if STP is lower than
0.1MPa.
4,5
405
Reboiler Duty
Reboiler Temperature
400
4,3
395
4,2
390
4,1
385
W/A=11.5%
FCT=313.15K
4,0
380
375
3,9
Reboiler Temperature (K)
Reboiler Duty (GJ/ton CO2)
4,4
370
3,8
365
3,7
0,05
0,10
0,15
0,20
0,25
Stripper Pressure (MPa)
Figure 4.10 Specific energy requirement and reboiler temperature at different stripper pressures
- 46 -
4 Evaporative Gas Turbine Cycles Integrated with Different CO2 Capture Technologies
Considering the temperature match in the heat exchangers, two configurations (Figure 4.11) for
humidification tower and CO2 capture were applied regarding the different heat quality and
quantity requirements. At low STP, for example 0.07MPa, the reboiler temperature is
approximately 366.15K, which is close to the water temperature entering economizer
(353.15K). Thus, Configuration 1 would be applied. On the contrary, at high STP, for example
0.25MPa, the reboiler temperature is approximately 401.15K, which is close to the water
temperature leaving economizer (420.15K). Thus, Configuration 2 would be applied.
Figure 4.11 Configuration of heat exchangers
According to the above strategy, the results of electrical efficiency at different STP are shown in
Figure 4.12. Although the low temperature heat can be used when STP is low, and exergy loss
caused by high temperature difference of heat transfer may be reduced by applying different
configurations of heat exchangers, electrical efficiency grows with the raise of stripper pressure.
The reason is due to the fast increase of reboiler duty at low STP. Therefore, high STP is
helpful to improve the total efficiency. Moreover, it is similar to the impact of STP on reboiler
duty that efficiency is less sensitive to the variation of STP when it is over 0.2MPa. Therefore
0.2MPa was applied in the following calculations, in order to avoid the quick increment of
investment costs caused by the raise of stripper pressure.
42.0
Electrical Efficiency (%)
41.5
41.0
W/A=11.5%
FCT=313.15K
40.5
40.0
39.5
39.0
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
0.22
0.24
0.26
Stripper Pressure (MPa)
Figure 4.12 Electrical efficiency at different stripper pressures
- 47 -
4 Evaporative Gas Turbine Cycles Integrated with Different CO2 Capture Technologies
4.4.3
Flue Gas Condensing Temperature
In Section 4.2.2, the heat required for MEA regeneration in System II is 3.84GJ/ton CO2,
which is higher than the value 3.45GJ/ton CO2 given in [83]. It has been known that the heat
demand decreases with increasing MEA concentration [83]. Since System II is a humidified gas
turbine cycle, more water is contained in the CO2 stream entering CO2 absorber compared to
the conventional gas turbine cycles. The excessive water would dilute MEA solvent, and result
in a higher reboiler duty. Therefore, decreasing the water content in the CO2 stream can help
reduce the thermal energy requirement of reboiler. In order to remove excessive water, flue gas
should be condensed before entering absorber. The variation of condenser temperature would
firstly change the reboiler duty of striper, and further affect the distribution of heat recovery in
humidification and economizer. As a result, the total efficiency would be changed.
Figure 4.13 shows the specific reboiler duty of stripper at different condenser temperatures.
When the condenser temperature drops from 333.15K to 323.15K, more water is condensed,
so reboiler duty is reduced. However, when condenser temperature drops further, reboiler duty
may increase. The reason for this might be that the low condenser temperature would cause a
low input temperature of reboiler. Although less water is contained, the larger temperature
difference between inlet temperature and operation temperature will increase the reboiler duty.
4,00
41,6
41,4
3,90
Reboiler Duty
Electrical Efficiency
3,85
41,2
3,80
41,0
3,75
40,8
3,70
W/A=11.5%
STP=0.2MPa
3,65
Electrical Efficiency (%)
Reboiler Duty (GJ/ton CO2)
3,95
40,6
3,60
40,4
3,55
300
305
310
315
320
325
330
335
Flue Gas Condenser T (K)
Figure 4.13 Specific reboiler duty and electrical efficiency at different condenser temperatures
Figure 4.13 also shows the electrical efficiency at different condenser temperature. FCT has a
reverse impact on efficiency compared its impact on reboiler duty. In this study, the highest
electrical efficiency appears with a value of 41.6% when FCT is 323.15K.
4.5 Discussions
4.5.1
Economic Benefit
As indicated in Figure 4.5, much heat can be recovered for district heating from EvGT cycles.
However, the economic benefit from heat recovery was not included in the economic
evaluation performed in Section 4.3, because it was not included in other studies either. If it
could be counted, the cost to capture 1 ton CO2 would be further reduced.
- 48 -
4 Evaporative Gas Turbine Cycles Integrated with Different CO2 Capture Technologies
4.5.2
Optimization Regarding EvGT + CO2 Capture
According to the optimization result of EvGT + chemical absorption, increasing the operating
pressure of stripper and adding a flue gas condenser would help to increase the total electrical
efficiency. However, the increased pressure and additional condenser would raise the
investment costs at the same time. Therefore, the economic comparison should be conducted
in any future work in order to understand more comprehensively the integration of EvGT with
CO2 capture.
In addition, to the system of EvGT + O2/CO2, more impurities are expected in the CO2
streams to be transported. However, there are restrictions for different transport conditions
based upon Table 3.5. To control the impurity fraction under the acceptable value, an
additional purification system might be required. Under such a situation, EvGT + O2/CO2 may
have a CO2 capture cost close to EvGT + chemical absorption.
4.5.3
Future Work
The system performance of EvGT + chemical absorption has been investigated. The same
work should be conducted regarding EvGT + O2/CO2. Based upon those investigation results,
further economic evaluation should be performed to obtain more accurate comparison of both
systems.
- 49 -
4 Evaporative Gas Turbine Cycles Integrated with Different CO2 Capture Technologies
- 50 -
5 Conclusions
5 Conclusions
In the first part of this thesis, the thermodynamic properties of CO2 mixtures have been
studied, including the evaluations of various calculation methods and the investigations of the
impacts of impurities on the properties of mixtures and different processes involved in CCS.
The results show that:
− There are some gaps of the experimental data on the thermodynamic properties of CO2
mixtures. The available data cannot cover the operation conditions of different the
CCS processes, which may result in a limited reliability of the evaluation results of
theoretical modelling.
− EOS method is better than activity coefficient method in calculations of
thermodynamic properties of CO2 mixtures; and the reliabilities of EOS vary for the
components, the properties, such as VLE and volume, and the calculating conditions.
− For the thermodynamic property calculations of binary CO2 mixtures, cubic EOS is
more applicable from the viewpoint of engineering application. To VLE properties,
comparatively PR is recommended for the calculations of CO2/CH4 and CO2/H2S; PT
is recommended for the calculations of CO2/O2, CO2/N2 and CO2/Ar; while 3P1T is
recommended for the calculations of CO2/SO2. To volume properties, PT is
recommended for the calculations of CO2/CH4, Vl of CO2/H2S, CO2/Ar and
CO2/SO2, and Vg of CO2/N2; PR is recommended for the calculations of Vl of
CO2/N2 and Vg of CO2/Ar; MPR and ISRK are recommended for the calculations of
Vl of CO2/H2S and Vg of CO2/SO2 respectively.
− Calibrated kij can improve the accuracy of VLE calculation; however it doesn’t mean the
kij calibrated from VLE data will definitely result in a higher accuracy on the volume
calculation as well. Therefore, it is recommended to separate the calculation of
thermodynamic properties into two parts: VLE calculation and volume calculation. In
different cases, various EOS with various parameters should be chosen.
− Impurities have great impacts on the design, operation, and optimization of the CCS
system through their impacts on the thermodynamic properties of CO2 streams: (1) the
presence of SO2 makes the heat capacities of CO2 mixtures raise while the presence of
O2, Ar and N2 makes them decrease. As a result, the enthalpy and entropy of CO2
streams are increased with the increment of SO2, while decreased with the increment of
O2, Ar and N2; (2) the presence of non-condensable gases makes condensation more
difficult; thus, resulting in increased pressure requirements for the condensation of the
CO2 mixtures. Comparatively the operation conditions are more sensitive to the
concentration variations of N2 than those of O2 and Ar; (3) theoretically the isothermal
compression work, the discharging temperature of isentropic compression and the
isentropic compression work are increased with the increments of mole fractions of O2,
Ar and N2; yet they are decreased with the increment of SO2 linearly at the same
discharging pressure. Comparatively the isothermal compression work is more sensitive
to the concentration variations of SO2; while the isentropic compression work is more
sensitive to the concentration variations of Ar; (4) energy consumption of external
refrigeration is increased with the increments of mole fractions of SO2, while decreased
with the increment of Ar, O2 and N2; and (5) the existence of impurities would reduce
the transported mass of CO2 and result in lower transport efficiency and storage
capacity. The occupied volumes by the given concentrations of impurities in
corresponding CO2 mixtures are in following order: VN2 > VO2 > VAr > VSO2.
- 51 -
5 Conclusions
In the second part of this thesis, the performances of EvGT cycles integrated with various CO2
capture technologies have been analyzed, including the technical and economical evaluations.
The results show that:
− The EvGT cycle + chemical absorption capture has a higher electrical efficiency, while
a smaller amount of heat recovered for the district heating than the EvGT cycle +
O2/CO2 recycle combustion capture;
− Compared with the EvGT cycle without CO2 capture, the EvGT + chemical
absorption capture has a smaller penalty on electrical efficiency than the EvGT +
O2/CO2 recycle combustion capture;
− The EvGT cycle + O2/CO2 recycle combustion has a higher CO2 capture ratio and
lower CO2 emissions per kWh produced electricity than the EvGT cycle + chemical
absorption capture;
− Comparatively; the combined cycle has a higher gross electricity generation and
electrical efficiency than the EvGT cycle regardless if it is combined with CO2 capture;
while the difference is smaller if CO2 is captured through chemical absorption;
− Compared to the EvGT + O2/CO2, although the EvGT + chemical absorption has a
higher annual cost, it has a lower electricity price because of its higher efficiency.
However considering its lower CO2 capture ratio, the EvGT + chemical absorption has
a higher cost to capture 1 ton CO2.
− There exists an optimum point of W/A for both the EvGT and the EvGT combined
with CCS. As TIT=1523.15K and pressure ratio=20, the optimal W/A is 14.0% and
11.5% for the EvGT and the EvGT + chemical absorption respectively
− To the EvGT + chemical absorption, increasing the operating pressure of stripper
would help increase the total electrical efficiency; however, the efficiency improvement
becomes smaller if stripper pressure is high. Meanwhile adding a flue gas condenser
condensing out the excessive water is another method to increase the total electrical
efficiency. There is also an optimum point of condensing temperature, considering the
concentration of MEA and inlet temperature of stripper.
- 52 -
Appendix
Appendix:
A: Flow chart of calibrating kij
Figure A- 1 Flow chart of regressing kij
- 53 -
Appendix
B: Summary of capital costs of EvGT and EvGT + CCS.
Table A- 1 Capital costs of EvGT without CCS
Equipment
NO
Capacity
Type
Material
Air Compressor (1st stage)
C-101
2.43 MW
Axial
SS
Capital cost
kUSD
522
Air Compressor (2nd stage)
C-102
2.98 MW
Axial
SS
597
Fuel Compressor
C-103
283 kW
Axial
SS
150
Gas Turbine [86]
J-101
13.78 MW
Axial
SS
Water pump
P-101
5.97 kW
Centrifugal
SS
Combustor
H-101
19.2 MW
Intercooler of air compression
E-101
2.11 MW
T-S
SS
h=0.7 kW/m2C
39.6
Aftercooler
E-102
2.07 MW
T-S
SS
h=0.7 kW/m2C
35.1
SS
h=0.4
kW/m2C
173
kW/m2C
22.6
Recuporator
E-103
7.40 MW
Key parameter
LM1600PD
3.34
CS
FP
7000
1780
Economizer
E-104
2.31 MW
T-S
SS
h=0.7
Heat recovery for district heating
E-105
2.55 MW
T-S
SS
h=0.7 kW/m2C
30.9
Flue Gas Condenser
E-106
4.62 MW
T-S
SS
h=0.7 kW/m2C
35.4
Humidification Tower [85]
SS
Total
136.2
10525.14
- 54 -
Appendix
Table A- 2 Capital costs of EvGT with chemical absorption capture
Equipment
NO
Capacity
Type
Material
Air Compressor (1st stage)
C-101
2.43 MW
Axial
SS
Capital cost
kUSD
522
Air Compressor (2nd stage)
C-102
2.98 MW
Axial
SS
597
Fuel Compressor
C-103
283 kW
Axial
SS
150
Key parameter
Compressor of dehydration
C-104
364 kW
Rotary
SS
689
CO2 compressor
C-105
169 kW
Rotary
SS
133
Gas Turbine
J-101
13.78 MW
Axial
SS
Water pump
P-101
5.97 kW
Centrifugal
SS
Combustor
H-101
19.2 MW
LM1600PD
7000
3.34
CS
1780
Absorber
T-101
SS
Stripper
T-102
SS
Dehydration column
T-103
SS
TEG regeneration column
T-104
SS
Intercooler of air compression
E-101
2.11 MW
T-S
SS
15 sieve layer,
H=15 m,
D=2.51 m
10 sieve layer,
H=10 m,
D=1.18
10 sieve layer,
H=5 m, D=2 m
10 sieve layer,
H=5 m, D=24 m
h=0.7 kW/m2C
Aftercooler
E-102
2.07 MW
T-S
SS
h=0.7 kW/m2C
35.1
Recuporator
E-103
3.79 MW
FP
SS
h=0.4 kW/m2C
63.5
SS
h=0.7
kW/m2C
21.8
kW/m2C
33.8
Economizer
E-104
2.39 MW
T-S
98.5
22.3
36
48.7
39.6
Heat recovery for district heating
E-105
3.10 MW
T-S
SS
h=0.7
Flue Gas Condenser
E-106
3.60 MW
T-S
SS
h=0.7 kW/m2C
35
Stripper economizer
E-107
2.48 MW
T-S
SS
h=1.5 kW/m2C
22.9
SS
h=0.7
kW/m2C
38.5
kW/m2C
24.8
Stripper reboiler
E-108
3.64 MW
T-S
Stripper condenser
E-109
1.00 MW
T-S
SS
h=0.7
Dehydration condenser
E-110
0.647 MW
Air cooler
SS
h=0.3 kW/m2C
20.8
CO2 condenser
E-111
0.425 MW
T-S
SS
h=0.7 kW/m2C
15.3
SS
kW/m2C
18.9
Dehydration reboiler
E-112
1.33 MW
T-S
Humidification Tower
SS
Total
h=0.7
136.2
11586.04
- 55 -
Appendix
Table A- 3 Capital costs of EvGT with O2/CO2
Equipment
Air Compressor (1st stage)
Air Compressor
(2nd
stage)
NO
Capacity
Type
Material
C-101
2.15
Axial
SS
Capital cost
kUSD
481
Key parameter
C-102
2.31
Axial
SS
505
Fuel Compressor
C-103
0.282
Axial
SS
150
Compressor of dehydration
C-104
324 kW
Rotary
SS
523
CO2 compressor
C-105
101 kW
Rotary
SS
Gas Turbine
J-101
13.78 MW
Axial
SS
Water pump
P-101
6.51 kW
Centrifugal
Combustor
H-101
19.2MW
Dehydration column
T-103
SS
TEG regeneration column
T-104
SS
Intercooler of air compression
E-101
T-S
Aftercooler
E-102
T-S
Recuporator
E-103
FP
46.4
LM1600PD
7000
SS
3.43
CS
1780
SS
10 sieve layer,
H=5 m, D=2 m
10 sieve layer,
H=5 m, D=24 m
h=0.7 kW/m2C
37.1
SS
h=0.7 kW/m2C
17.5
SS
h=0.4 kW/m2C
105
kW/m2C
22.1
36
48.7
Economizer
E-104
T-S
SS
h=0.7
Heat recovery for district heating
E-105
T-S
SS
h=0.7 kW/m2C
43.5
kW/m2C
33.3
Flue Gas Condenser
E-106
T-S
SS
h=0.7
Dehydration condenser
E-110
Air cooler
SS
h=0.3 kW/m2C
20.8
CO2 condenser 2
E-111
T-S
SS
h=0.7 kW/m2C
15.3
Dehydration reboiler
E-112
T-S
SS
h=0.7 kW/m2C
18.9
CO2 condenser 1
15.3
Humidification Tower
SS
136.2
ASU [100]
235.74
Total
11274.27
- 56 -
References
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Acknowledgements
Acknowledgements
First and foremost, I would like to thank my supervisor Prof. Jinyue Yan for his continuous
support, encouraging and stimulating guidance since the first day.
I must express special gratitude to Dr. Jinying Yan for giving me valuable suggestions.
I would also like to thank Prof. Mats Westmark and Dr. Marie Anheden for useful discussions
and help.
There are so many colleagues and friends that I would like to thank, especially those at the
Division of Energy Processes for providing a pleasant and creative working environment.
The financial support from the Swedish Energy Agency and Vattenfall is gratefully
acknowledged.
Last but not least, my parents deserve my deepest appreciation for always supporting me
throughout these years. I would like to thank my dear wife Xiaohui Jia and my lovely daughter
Yichen Li for all the happiness they brought to me.
Hailong Li
September 2008
- 63 -
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