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Chemical Looping Combustion of Coal for CO2 Capture: Process Simulation and
Optimisation using Aspen Plus
Presented by Sanjay Mukherjee
Post Graduate Researcher University of Surrey, UK
Supervisor Co‐SupervisorDr. Prashant Kumar Dr Ali Hosseini
Dr Aidong Yang
Department of Civil & Environmental Engineering
University of Surrey, UK
POINTS FOR DISCUSSION
PROJECT OBJECTIVES
CARBON CAPTURE AND STORAGE (CCS)
CHEMICAL LOOPING COMBUSTION (CLC)
ASPEN PLUS SIMULATION
RESULTS
CONCLUSION
FUTURE WORK
1. Developing and optimising industrial scale flow sheet models of coal power plantswith CLC process and comparing it with conventional CO2 capture technologies.
2. To develop a kinetics based model of CLC process for industrial scale coal powerplant with direct and indirect coal combustion process and investigating theoptimum operating condition with various oxygen carriers.
3. Perform system level energy, exergy and cost analysis of CLC process to determinethe robustness and feasibility of a CLC system with changing loads and fuel types.
PROJECT OBJECTIVES
Capture Technologieso Chemical Absorption (MEA/DMEA/DEA)o Physical Absorption (Selexol/Rectisol)o Physical Adsorption (Pressure/Vacuum/thermal Swing adsorption)o Chemical Looping Combustion
CARBON CAPTURE AND STORAGE (CCS)
Conventional Process
CASE DESCRIPTION
Case 1 : Base case without CO2 capture.
Case 2.1: IGCC with Pressure swing adsorption (PSA) producing electricity only.Case 2.2: IGCC with PSA producing combined electricity and H2.
Case 3.1: IGCC with selexol producing electricity only.Case 3.2: IGCC with selexol producing combined electricity and H2.
Case 4.1: IGCC with CLC producing electricity only.Case 4.2: IGCC with CLC producing combined electricity and H2.
FLOWSHEET MODEL CASES
CONVENTIONAL PROCESS (PSA)
ASU Gasification Unit
Syngas Cooling
Sulphur Removal
WGS Reactor
SteamTurbine Unit
CO2Compressor
PSA - CO2
Cooled Syngas
Syngas
Steam
CO2 to Storage
(I)
CO2
O2
Clean Syngas
Coal
HRSG
Combined Cycle Gas Turbine Unit
Power
H2 CompressionAir
Purified H2
(II)
Water
Tail Gas-1
Air
Flue Gas
Heat
Heat
SyngasSteam
H2H2
Flue GasN2
PSA -H2
Tail Gas-2
H2O
CONVENTIONAL PROCESS (SELEXOL)
ASU Gasification Unit
Syngas Cooling
Sulphur Removal
WGS Reactor
SteamTurbine Unit
CO2Compressor
AGR - CO2
Cooled Syngas
Syngas
Steam
CO2 to Storage
(I)
CO2
O2
Clean Syngas
Coal
HRSG
Combined Cycle Gas Turbine Unit
Power
H2 CompressionAir
Purified H2
(II)
Water
Tail Gas-1
Air
Flue Gas
Heat
Heat
SyngasSteam
H2H2
Flue GasN2
PSA -H2
Tail Gas-2
H2O
CLC WITH ELECTRICITY ONLY
ASU Gasification Unit
Syngas Cooling
Sulphur Removal
FR 1
Air reactor/ Oxidiser
Air Turbine
CO2 Separator
HRSG
Steam Turbine Unit
Cooled Syngas
Heat
AirCoal
Syngas
AirFe/FeOFe2O3
Water
Exhaust Air
CO2 to Storage
SteamCO2
Air In
O2 Depleted Air
O2
Clean Syngas
Ex Gas-1
CO2Compressor
Condensate
Ex Gas-2Power
FR 2Fe3O4
CLC WITH ELECTRICITY & H2
ASU Gasification Unit
Syngas Cooling
Sulphur Removal
FR 1
Steam reactor
Air Reactor
CO2 Separator
HRSG
Steam Turbine Unit
Cooled Syngas
Heat
AirCoal
Syngas
SteamFe/FeOFe2O3
Water
Exhaust Air
CO2 to Storage
SteamCO2
Air InO2 Depleted Air
O2
Clean Syngas
Ex Gas-1
CO2Compressor
Condensate
Ex Gas-2
Power
FR 2Fe3O4
Air Turbine
Fe3O4
ASPEN PLUS SIMULATION
Fuel used is Illinois # 6 type coal.
Feed rate of coal is 132.9 t/hr.
Hematite (Fe2O3) is used as oxygen carrier.
Aluminum oxide (Al2O3) and Silicon carbide (SiC)are used as inert support material.
Ultimate Analysis
Value
Ash 10.91
Carbon 71.72
Hydrogen 5.06
Nitrogen 1.41
Cholrine 0.33
Sulphur 2.82
Oxygen 7.75
Proximate analysis Wt%
Moisture 5
Fixed Carbon 49.72
Volatiles 39.37
Ash 10.91
ASPEN PLUS SIMULATION
Integration of steam generated in gasification, syngas treatment andchemical looping unit.
Steam is generated at 124 atm and 600 OC.
Exit pressure for steam turbines are 30, 20 and 0.046 bars.
Isentropic efficiency of compressors and expanders are between 0.8 to0.9.
H2 is compressed to 60 atm and CO2 to 150 atm.
ASPEN PLUS SIMULATION
Reactor operating conditionFuel reactor : 30 bars and 1121 oCAir reactor : 30 bars and 1300 oCSteam reactor : 30 bars and 550 oC
Gibbs free energy minimisation model for both reactors were used.
Pressure ratio of GT: 21
Acid gas removal (AGR) method used for H2S capture with more than 99%yield.
RESULTS (1)
BaseCase
(Case 1)
PSA(Case 2.1)
Selexol(Case 3.1)
CLC(Case 4.1)
Coal Input (Kg/s) 36.9 36.9 36.9 36.9
Gas Turbine output (MW) 278.3 233.2 227.8 166.7
Steam Turbine output (MW) 258.2 280 278.2 327.5
Gross electricity produced(MW) 536.5 513.2 506.0 494.2
Total ancillary power consumed(MW)
81.5 108.1 116.82 96.6
Net electricity produced (MW) 455.0 405.1 389.2 397.6
Net electrical efficiency (%) 42.5 37.8 36.4 37.2
Overall exergy efficiency (%) 36.2 32.2 31.0 31.6
CO2 specific emissions (t/MWh) 0.608 0.083 0.054 0.0
CO2 capture efficiency (%) 0 89.9 93.5 100
Cases with Electricity Production Only
Comparison of PSA, Selexol and CLC process on the basis of (a)Net electrical efficiency and CO2 emissions, and (b) Gross powerproduction, net power production and power consumption.
RESULTS (2)
0
20
40
PSA Selexol CLC
CO2 emissions Net electrical efficiency
CO2em
issions (1
0‐2t/MW)
Net electrical efficien
cy (%
)
0
200
400
600
PSA Selexol CLC
Gross Power Power ConsumedNet Power
Power (M
W)
(a)(b)
Amount of CO2 captured per unit energy and efficiency penalty with reference to the base case.
RESULTS (3)
Plant Data PSA Selexol CLC
Net electrical efficiency penalty (%)4.7 6.1 5.3
Decrease in net electrical efficiency in relative to the base case (%) 11.0 14.3 12.5
CO2 captured per MW decrease in energy production than the base case (t) 4.9 3.9 4.8
CO2 captured per unit decrease in net electrical efficiency (t) 52.0 42.1 52.5
Comparison of CO2 compression work between PSA, Selexol and CLC process.
RESULTS (4)
Case Electrical efficiency
(%)
CO2captured
(t)
CO2compression
Work (MW)
Compression work per tonne of CO2
captured(MW/t)
Electrical efficiency w/o CO2
compression(%)
Base Case 42.5 0 0 0 42.5
PSA 37.8 244.7 26 0.289 40.3
Selexol 36.4 257.2 28 0.299 38.9
CLC 37.2 278.3 10 0.036 38.1
RESULTS (5)
PSA(Case 2.2)
Selexol(Case 3.2)
CLC(Case 4.2)
Coal Input (Kg/s) 36.9 36.9 36.9
H2 production (MWth) 528.0 528.0 528.0
Net electricity produced (MW) 150.6 141.3 137.0
Net electrical efficiency (%) 14.1 13.2 12.8
Overall energy produced (MWe+th) 678.6 669.3 665.0
Overall energy efficiency (%) 63.4 62.5 62.1
Overall exergy efficiency (%) 54.0 53.3 52.9
CO2 capture efficiency (%) 89.9 93.5 100
Combined electricity and H2 Production Only
RESULTS (6)
Trade-off between electrical, H2 and overall efficiency for CLC process case 4.2
0
20
40
60
100 200 300 400 500
Electrical Efficiency H2 Efficiency Overall Efficiency
H2Output (MW)
Efficiency (%
)
RESULTS (7)
Integration between ASU and gas turbine
0
100
200
300
400
case 2.1 case 3.1 case 2.2 case 3.2 case 4.1 case 4.2
With N2 With out N2
MW
RESULTS (7)
Effect of (a) air reactor temperature, and (b) excess air reactor air on the power output for CLC process (Case 4.1).
0
100
200
300
400
500
600
7 8 9 10 11 12 13
Gas Turbine Power Steam Turbine Power Gross Electric Power Net Electric Power
Power (MW)
Temperature (100oC)0 5 10 15 20
Amount of excess air (%)(a) (b)
CONCLUSION
The IGCC with CLC process (case 4.1) has a net electrical efficiencyof 37.2% and CO2 capture efficiency of 100% which clearlyindicates the suitability of CLC process for CO2 capture in IGCCpower plants .
Cases 4.1 and 4.2 with CLC process show an increase in the netelectrical efficiency by 3.03% and 1.37%, respectively, when N2stream from ASU is used in AR.
The sensitivity analyses performed on CLC process shows that it isfavourable to operate the air reactor at higher temperatures formore power output.
The cooling of air reactor by using excess air supply instead of water/steam tends to increase the net power output of the CLC system.
FUTURE WORK (1)
Objective 2:To develop a kinetics based model of CLC based industrial scale coal powerplant with direct and indirect coal combustion process and investigatingthe optimum operating condition with various oxygen carriers.
Methodology: Equation based modelling of CLC system using component mass and
energy balance over each reactor unit. This model will be used in aspen plus to develop a complete power
plant model. Experimental CLC reactor models in Tsinghua university will be used to
validate the model. Data available on novel OC particles will be used for optimising the
plant performance.
FUTURE WORK (1)
Expected Outcome :
Kinetics based model would be able to predict the exact behavior ofthe complete system even with small changes in the governingparameters or OC carrier performance.
It will be used for sensistivity analysis to check the suitability andflexibility of the system to changing loads.
FUTURE WORK (2)
Objective 3:Perform system level energy, exergy and cost analysis of the CLC process todetermine the robustness and feasibility of a CLC system with changingloads and fuel types.
Methodology: A detailed energy and exergy analysis would be performed for each
process unit in the flow sheet model with different types of fuels andOCs to recover energy from the major areas of exergy losses.
A lifecycle cost estimation of the complete system would be carried outto obtain the cost of CO2 avoided in a CLC system for comparison withother capture technologies.
FUTURE WORK (2)
Expected Outcome :
The work performed under objective 3 will provide optimum operatingconditions with respect to energy and cost for a CLC system.
Combined results from objective 2 and 3 will be used to evaluate therobustness and feasibility of a CLC system with changing loads andfuel types.
Acknowledgement
I would like to begin by sincerely thanking my projectsupervisors, Dr Prashant Kumar and Dr Ali Hosseini for theirconstant support, guidance and mentorship over the courseof this project so far.
I would like to express my special gratitude and thanks to DrAidong Yang for his help and support.
I am very grateful to Engineering and Physical SciencesResearch Council (EPSRC) and Department of Civil andEnvironmental Engineering, University of Surrey for theirfunding and financial support in this project.
THANK YOUContacts:Sanjay Mukherjee ([email protected])Dr. Prashant Kumar ([email protected])Dr. Aidong Yang ([email protected])Dr. Ali Hosseini ([email protected])