Thermodynamic performance of IGCC with oxycombustion

Transcription

1 Thermodynamic performance of IGCC with oxycombustion CO 2 capture G.Lozza, M. Romano, A. Giuffrida Dip. Energia, Politecnico di Milano, Italy

2 Purpose of the study CO 2 capture from coal power plant. Configurations proposed: USC with amine capture or with oxy-combustion IGCC with pre-combustion capture Investigate novel plant configurations, to obtain better thermodynamic and environmental performance Near-term solutions requiring the development of components not available in today s marketplace, but not requiring unproven technologies Investigated configurations: Reference IGCC, without and with capture Oxy-combustion, with semi-closed H 2 O-CO 2 power cycle, present technology Oxy-combustion, with co-capture capture CO 2 -SO 2, advanced technology Oxy-combustion, Hot Gas Desulfurization, advanced technology Detailed thermodynamic analysis and optimization

3 The reference cases Calculations by means GS code, developed in our Department and used for power plant on-design performance prediction No capture: A status-of-the-art IGCC combined cycle based: An oxygen-blown dry-feed entrained-flow gasifier (Shell type) Syngas cooling by syngas quench and HP steam gen. Power cycle based on a FB-technology gas turbine With pre-combustion capture: Same basic plant configuration and calculation assumptions CO conversion to hydrogen by means of two Water-Gas-Shift reactors (HT: bulk conversion, LT: finishing ) H 2 S/CO 2 removal by Selexol in two separate absorbers; largest solvent fraction for CO 2 removal with pressure-swing swing regeneration; smaller fraction for H 2 S removal with stripper regeneration.

4 Pre-combustion CO 2 capture 4 gasification island 8 9 slag scrubber ECO EVA+SH 11 to HP 24 dry solids removal B A HT-WGS 30 to LP LP- EVA LT- WGS HP-EVA 19 A saturator B 2 22 from HP power island from LP, to Selexol and sour water strippers heat recovery steam generator coal feeding 7 6 dry coal chiller lean solvent CO2 absorber H2S, CO2 removal section gaseous CO2 O2 waste nitrogen ASU air N2 air separation section H2S absorber flash chiller stripper semi-lean solvent H2S/CO2 to Claus flash chambers 23

5 r dry feed Oxy-fuel IGCC Syngas from conventional gasification is burnt with high- purity oxygen in a semi-closed CO 2 -H 2 O Joule cycle: CO 2 to lock-hoppers. A CO 2 compressor recycles CO 2 to the oxy-combustor Larger pressure ratio to optimize cycle efficiency A CO 2 cryogenic purification system is needed to eliminate incondensable gases during compression 4 coal 2 CO2 for 1 Gasif 5 HP SC O2 from HP eco 3 Gasification island drier 6 20 to coal drying Oxygen island 11 steam turbine 12 LP eco O2 compr. filter CO2C LP eva + SH 8 CO2 island cryogenic expander 7 ASU combustor 9 waste nitrogen air compr. Power island CO2T HTT coolant HP eco/boiler 19 LPT SH/RH IPT HPT 17 m.d knockout liquid CO2

6 Oxy-fuel IGCC: present vs. advanced technology 6 The gas turbine must be re-designed, using known methodologies and present technology. Large development costs can be anticipated. Present technology: Conventional gasification with H 2 S separation by Selexol Advanced technology with CO 2 -SO 2 co-sequestration: High pressure gasifier Hot Gas Filtration (550 C) H 2 S not separated (sent to burner) Improved gas turbine, due to the mid-long term application Blade coolant cooling to improve TIT

7 Hot Gas Desulfurization 7 To avoid Co-sequestration of CO 2 and SO 2 Reactions ZnO + H 2 S ZnS + H 2 O ZnS + 3/2 O 2 ZnO + SO 2 C C Regeneration gas with 2% O 2 to avoid ZnSO 4 formation 18 Filter 16 Lost sorbent Fresh sorbent 13 Raw syngas 11 H2S free syngas Desulfurizer 28 Regenerator 27 Filter N2 from ASU Air Turbo-charger 17 Regeneration off-gas

8 Calculation method and assumptions 8 Performance calculated by GS code, developed at Energy Dept, Politecnico di Milano Used since two decades to calculate the performance of any type of power plant Built-in in correlations for components efficiency prediction GT blade cooling models Assumptions from literature and industrial experience Gasification and ASU Gasification pressure, bar Gasification temperature, C Heat losses, % LHV Carbon conversion Temperature of O 2 to gasifier, C Moderator steam, kg H2O /kg coal N 2 to lock hoppers, kg/kg dry-coal Quenched syngas temperature, C Cold recycle syngas temperature, C Min. T in syngas coolers, C Oxygen purity, % mol. ASU electric consumption, kwh/t O Gas turbine and steam cycle Fuel temperature, C GT turbine inlet temperature, C GT pressure ratio Pressure levels, bar SH/RH temperature, C Pinch point/sub-cooling T, C Condensing pressure, bar Minimum stack temperature, C CO 2 compression Number of inter-cooled stages Inter-cooling temperature, C Inter-coolers pressure loss, % Compressors isentropic efficiency, % Table 1 Assumptions for the reference IGCC plants, present technology. Water Gas Shift Reactors Selexol Plant Steam to carbon at first reactor inlet 1.5 L/G ratio (wt. basis) in H 2 S/CO 2 HT reactor outlet temperature, C 400 absorption columns LT reactor outlet temperature, C 210 CO 2 flash tanks pressures, bar Reboiler heat duty, MW th Table 2 Additional assumptions for the IGCC plant with pre-combustion capture. CO 2 to gasifier lock hoppers, kg/kg coal GT pressure ratio Fuel side pressure loss at combustor, % O 2 content at combustor outlet, % mol. Table 3 Varied assumptions for the oxy-fuel IGCC plant, present technology. Gasification temperature, C Gasification pressure,bar Carbon conversion Temperature of O 2 to gasifier, C Syngas temperature to GT, C Steam pressures HP/RH, bar LP evaporation pressure, bar SH/RH steam temperature, C Table 4 Varied assumptions for the oxy-fuel IGCC plant, advanced technology / / / /8/3.5/ / /600 ZnO to TiO 2 mol.ratio in fresh sorbent System pressure, MPa Desulphurization temperature, C Sorbent loss, % in wt O 2 mol.fraction in regeneration mixture Regeneration temperature, C ZnS to ZnO mol.ratio in regen.sorbent Pressure loss at the hot gas filter, % Table5 Assumptions for Hot Gas Desulfurization. 2%

9 Results of the performance analysis 9 Case Reference IGCC Precombustion IGCC 1335 no Oxy- IGCC Advanced oxy-igcc Advanced oxy-igcc + HGD 1400 no TIT, C Sulfur co-sequestration 1335 no 1400 yes Electric/mechanical power MW Gas turbine (2 units) GT auxiliaries Steam Turbine Steam cycle pumps ASU Lock hoppers N 2 compress Syngas recycle fan Syngas compressor N 2 compressor for fuel dilution Aux. for H 2 S / CO 2 removal CO 2 compression Auxiliaries for heat rejection Miscellaneous BOP Net power output, MW el Fuel input LHV, MW th Cold Gas Efficiency, % Net LHV efficiency, % CO 2 captured, % CO 2 spec.emissions, g/kwh Table 6 Performance of the plants considered in the paper.

10 Conclusions Very interesting performance can be predicted for Oxy-fuel IGCC: Environmental: NOx and SOx not wasted to the atmosphere, but mostly solved within the stream to sequestration Environmental: 95-99% 99% carbon capture, depending on the solutions adopted for incondensable gases stream Efficiency: better than 45% by adopting advanced solutions, specific to oxy-fuel configurations (not applicable to decarbonization): Hot Gas Filtration Co-sequestration of CO2-SO2 or Hot Gas Desulfurization Drawbacks: the gas turbine must be re-designed, using known methodologies and present technology. A larger attention may be devoted to Oxy-fuel IGCC in the R&D programs

11 Oxy-fuel CO 2 capture: present technology 11 waste nitrogen air separation section O2 ASU aria drier CO2 island cryogenic expander 18 8 gasification island 6 coal 22 lock hopper to HP SH 7 20 liquid CO slag ECO EVA dry solids removal 26 from IP COS hydr power island from HP 25 to coal drier HRSG AGR scrubber to deaerator 27 to MDEA and sour water strippers