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 (S.Mukherjee@surrey.ac.uk)Dr. Prashant Kumar (P.Kumar@surrrey.ac.uk)Dr. Aidong Yang (A.yang@surrey.ac.uk)Dr. Ali Hosseini (S.hosseini@surrey.ac.uk)