Design principles for IGCC with CO 2 Capture

Transcription

1 Design principles for IGCC with CO 2 Capture Adel F. Sarofim, University of Utah, Reaction Engineering International Presentation at Pacificorp, Salt Lake City July 6, 2006 Based on Tutorial presented at The 31st International Technical Conference on Coal Utilization & Fuel Systems Clearwater, Florida May 22, 2006

2 Background Costs of Different Options for CO 2 Capture: Repowering Applications (Marion et al., 04)

3 IGCC with CO 2 Capture and H 2 Production (Holt, 05)

4 Selected Gasifier Designs (Holt, 05)

5 Outline Criteria for Selection of Gasifier and Gasifier Operating Conditions High Temperature vs Low Temperature? Tar and HC formation Factors Determining Operating Temperature Slagging temperature Carbon burnout Refractory lifetime Factors Determining O 2 /Coal Ratio Operating Temperature Cost of O 2 Soot Formation Factors Determining H 2 O/Coal Ratio Cold Gas Efficiency Water/Gas Shift Reaction

6 Criteria (Cont.) Factors Governing Slurry vs Dry Feed Ease of Feeding to High Pressure Reactor Cost of Vaporization of Water Factors Determining Operating Pressure End Use Reactor Volume Factors Determining Quench of Gases for Gasifier Radiant Chamber Heat Exchanger Water Quench Gas Recycle Factors Determining Upflow vs Downflow Influence of Coal Quality

7 Gasifier Model, Bockelie et al., 06 Model Development Computational Fluid Dynamic (CFD) + Process models Allows modification of Process conditions, burner characteristics Fuel type, slurry composition gross geometry Generic Configurations: downflow / upflow 1 stage / 2 stage Improved physical models reaction kinetics upflow high pressure and gasification slag, ash, soot, tar formation downflow

8 Gasifier Process Model, Bockelie et al. 06 Fast running Process Model for Gasifier Design inputs for CFD model indicator for proper slag flow Consists of three submodels Zonal Equilibrium model Quench model Particle burnout model Oxidant Unburned Carbon Coal Transport Fluid Zonal Equilibrium Model T = K Q loss Quench Model -dt/dt Iterate between the submodels Unburned carbon from Carbon Burnout to Zonal Equilibrium T and Gas Composition from Zonal Equilibrium to Carbon Burnout Coal Particle Burnout Model Temperature Unburned Carbon Residence Time: τ

9 Difficulty of Obtaining Data on Gasification Conditions Ruprecht et al., Fuel (1988)

10 Gasifier Reactions (Holt, 2005) Model is based on the above reactions with energy, material balances, and instantaneous devolatilization, equilibrium gas phase chemistry, and kinetic char gasification reactions.

11 Selection of Temperature

12 Carbon Conversion vs Time in PFR; Contributions of Volatile Release and Gasification Reactions (Roberts, Tinney, & Harris, CCSD, 06); symbols refer to different coals.

13 Modeling of Effect of T and P on Carbon Conversion Efficiency, Bockelie et al., 06 Firing Conditions System Pressure = 18 atm tpd Subbituminous o11% H 2 O, 10% ash Slurry Feed: 74% solids (wt.) Oxidant (wt %) o95% O 2, 5% N 2 O 2 : C (molar) = 0.40 Inlet Stoichiometry ~ 0.54 Schematic of one-stage, slurry-feed, downflow gasifier and process conditions.

14 Higher Carbon Conversion Efficiencies Are More Readily Achieved by Increasing Temperature Than Increasing Residence Time, Bockelie et al., Carbon Conversion, % Increase Stoichiometric Ratio 1360 K, SR = K, SR = K, SR = τ / τ (1623 K) Figure 4. Carbon conversion vs. residence time for selected stoichiometric ratios (70 atm.)

15 Effect of CO Inhibition on Carbon Gasification Rate (Roberts, Tinney, & Harris, CCSD, 06); symbols refer to different coals.

16 Increasing Furnace Temperature Increases Carbon Conversion Efficiency at the Expense of the Liner Life Carbon Conversion (% Per Pass) Startup Liner Commercial Liner Liner Life (Months) Humphrey Pittsburg #8 Tampa Electric Final Report to DOE

17 H 2 O / Coal (daf) Refractory Refractory: K Exit temperature, K 30 atm, slurry feed adiabatic, 98% burnout O 2 / Coal (daf) Bockelie et al.)

18 Selection of O 2 /Carbon Ratio

19 Graphite mole fraction 30 atm, slurry feed adiabatic, 98% burnout 0.7 H 2 O / Coal (daf) Slagging Low O 2 /Coal ratios lead to soot formation O 2 / Coal (daf) Bockelie et al.)

20 Selection of H 2 O/Coal Ratio

21 Slurry Fed Gasifiers Bockelie et al. H 2 O / Coal (daf) Temperature limit O 2 / Coal (daf) CGE (HHV), % 30 atm, slurry feed Adiabatic, 98% burnout Illinois #6 Cool Water Tampa CGE, cold gas efficiency, is the ratio of heat of combustion of cooled gasification products divided by heat of combustion

22 Dry Feed Gasifiers CGE (HHV), % 30 atm, dry feed adiabatic, 98% burnout Steam / Coal (daf) Temperature limit Shell Gasifier Illinois #5 Drayton Petcoke SUFco Pike County Texas lignite O 2 / Coal (daf)

23 Peak Cold Gas Efficiencies Depend on Coal C/O ratios (Single-stage gasifier, 30 atm, dry feed, steam/coal(daf) = 0.1), Bockelie et al.

24 Comparison Table 3 of Compositions (Dry) for Slurry Fed Gasification, Bockelie et al. Case CW Model CW Model CW Model CW Model CW Model CW Model Exit Temperature, K Carbon Conversion, % Mole Fraction: CO H CO CH Ar+N H 2 S+COS HHV of Syngas, MJ/kg

25 Comparison Table 5 of Compositions (Dry) for Dry Fed Gasification, Bockelie et al. Case Shell Model Shell Model Shell Model Shell Model Exit Temperature, K Carbon Conversion, % > > > Mole Fraction (dry): CO H CO N others HHV of Syngas (dry), MJ/kg Cold-Gas Efficiency (LHV), %

26 Holt scheme to have advantages of slurry and dry fed gasification Steam Coal/Water Slurry Steam Flash Cyclone Dry Coal Syngas N 2 or CO 2 Gasifier

27 Selection of Pressure

28 Effect of Doubling Pressures on Gasification Rate, Roberts et al., 05

29 Residence Time (Reactor Volume) Dependence Varies Between 1/P (Diffusion limit) and 1/P 2 (1 st Order Kinetics) τ / τ (18 atm) Pressure, atm Figure 3. Required residence time for 98% carbon conversion versus pressure.

30 Quench Systems Radiant Gas Quench Fire Tube Heat Exchanger Water injection

31 Composition of Exit Gases Are Frozen as Gases Cool Down Downstream of the Gasifier Exit, Bockelie et al.)

32 Water Gas Shift Equilibrium Temperatures is Lower than Exit Gas Temperatures by Amounts that Depend on Cooling Rate and Exit Temperatures (1311, 1500, and 1687K) Bockelie et al.)

33 Costs and Potential Improvements

34 Avoided Cost of CO 2, $/mt, Holt 2005

35 Gary J. Stiegel, Presention to GCEP, March 15, 2005

36 Utah Clean Coal Center Tasks Gasification issues (Pugmire, Whitty, Fletcher, Baxter) Improving burnout efficiency Increasing refractory lifetime Increasing injector lifetime Improved slag models Other issues Hg capture (Lighty, Silcox, Pugmire) Oxyfuel Combustion (Wendt, Eddings) Sequestration (Deo) Integration Simulation (Smith)

37 CFD to Evaluate Injector Heat Flux

38 Injector using 1.5D geometry Oxidant Slurry Oxidant Inner tip Outer tip

39 Injector using 1.5D geometry Gasifier top face Outer nozzle oxidant 5% 75% 30% 85% 50%

40 50% oxidant to the outer nozzle Heat flux, MW/m Inner tip Outer tip Top surface Baseline 1.5D 3.0D

41 Acknowledgements Neville Holt, Mike Bockelie, Martin Denison, Zumao Chen, Gary Stiegel, John Marion, CCSD (Harris, Roberts, & Tinney)

42 Flowing Slag Model (Bockelie et al.) T s Model accounts for: Wall refractory properties Back side cooling Fire side flow field + heat transfer Particle deposition on wall Local Deposition Rate Fuel ash properties Composition (ash, carbon) Burning on wall Slag model computes Slag viscosity Tcv = critical viscosity ash composition Slag surface temperature Liquid & frozen slag layer thickness Heat transfer through wall [Dogan et al, GTC2002] Solid Slag Layer Refractory Lining Metal Wall T Ambient T w2 T w1 T w Coolant T i x S Liquid Slag y u (x, y) Q radiation Q convection Hot Particles Hot Gas Based on work by [Benyon], [CCSD], [Senior], [Seggiani] For model details see - Pittsburgh Coal Conference 2002