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Power cycles with CO 2 capture – combining solide oxide fuel cells and gas turbines. Dr. ing. Ola Maurstad. Outline of the presentation. A technology status for power plants with CO 2 capture (efficiencies, capture costs, timeframes) A hybrid SOFC/GT power cycle with CO 2 capture.
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Power cycles with CO2 capture – combining solide oxide fuel cells and gas turbines Dr. ing. Ola Maurstad
Outline of the presentation • A technology status for power plants with CO2 capture (efficiencies, capture costs, timeframes) • A hybrid SOFC/GT power cycle with CO2 capture
Commercial power cycles • The dominating technology for new power generation plants based on natural gas: the combined cycle (CC) • It combines a gas turbine cycle with a steam turbine and achieves electrical efficiencies close to 60 % (LHV) • The specific investment cost is around $500/kWe • Compared to coal fired power plants the emissions of CO2 is only around 50 % per kWh electricity (due to the higher efficiency and the lower carbon content of natural gas)
Gas fired power plants with CO2 capture • To fulfill the Kyoto agreement Norwegian emissions of CO2 must be reduced • The electricity consumption is increasing yearly • Norway has large reserves of natural gas • We also have geological structures under the sea with great storage capacity for CO2 • The less costly alternative would be to use CO2 for enhanced oil recovery (EOR) • Therefore, one option in reducing the emissions are gas fired power plants with CO2 capture • Other options include renewable energy, energy efficiency and energy modesty
Principles for power plants with CO2 capture 1: Post-combustion principle 2: Pre-combustion principle 3: Oxy-fuel principle = direct stoichiometric combustion with oxygen
65 63 61 Combined Cycle 59 SOFC+CO2 capture 57 55 Efficiency potential incl. CO2 compression (2%-points) 53 Chemical Looping Combustion Post-combustion amin-absorption 51 AZEP 49 Pre-combustion, NG reforming 47 Oxy-fuel Combined Cycle 45 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Time until commercial plant in operation given massive efforts from t=0 Year
Risk for not succeeding AZEP High Chemical Looping Combustion SOFC+CO2 capture Medium Oxy-fuel Combined Cycle Pre-comb. NG reform. Low Post-comb. amin-abs. CC 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0 4.4 4.8 5.2 5.6 .. Combined Cycle additional cost €-cent/kWhel 2.4 (Norway)
Risk for not succeeding AZEP High Chemical Looping Combustion SOFC+CO2 capture Medium Oxy-fuel Combined Cycle Pre-comb. NG reform. Low Post-comb. amin-abs. CC 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Time until commercial plant in operation given massive efforts from t=0 Year
Working principle of a SOFC Source: http://www.seca.doe.gov/
Reforming Water/gas shift The solide oxide fuel cell (SOFC) Fuel Anode Electrolyte ZrO2 Electrons 900-1000 °C Oxygen ions Cathode Air
Technology status of SOFCs • The major developers of SOFCs is Siemens Westinghouse, but several others • The cost of the SOFCs is the major barrier for market introduction • SECA – Solid State Energy Conversion Alliance • A 10-year program led by Dept. of Energy, USA to accelerate the commercialization of SOFCs • Cost target for 3-10 kW module by 2010: $ 400/kW • Projected costs assuming mass production of existing cell designs are $1500-4500 • SECA yearly budget is around 20 million $
Reforming Water/gas shift Fuel Anode Electrolyte ZrO2 Electrons 900-1000 °C Oxygen ions Cathode Air Combining SOFCs and gas turbines Vann Heat exchanger Natural gas Exhaust Combustor SOFC withinternal reforming Compressor ~ Turbine Scale250 kW-10 MW Efficiency (net AC/LHV) ~60-70% Air
Benefits of SOFC/GT systems • Electrical efficiencies as high as those for combined cycle plants at much smaller scale (1/1000) • Very low emissions of NOx, SOx
Technology status SOFC/GT system • 220 kWe demonstration systemin operation at NFCRC, USA • Designed and fabricated bySiemens Westinghouse (operational in 2000) • 53 % electrical efficiency (net AC/LHV) achieved • Conceptual designs by SW have shown electrical efficiencies approaching 60 % (300 kW to 20 MW systems) • More complex and/or expensive systems in the literature promise much higher efficiencies (e.g. 70 %) • Other planned demonstration systems have not always appeared on schedule ...
Adding CO2 capture to the process • The SOFC is especially well suited for capture of CO2 • CO2 is present only in the anode exit stream (not mixed with nitrogen), and at high partial pressure • The afterburner oxidizes the rest of the fuel so that the exhaust consists only of CO2 and H2O • The water vapor is then condensed by cooling and removed => resulting in a pure stream of CO2, ready for compression Source: Shell Technology Norway AS
Simplified system description Efficiency (net AC/LHV): 65 – 68 %
Afterburner solutions • Several solutions are possible (both mature and unmature technologies) • Cryogenic separation • Chemical absorption • Second SOFC • Oxygen permeable membrane • Hydrogen permeable membrane
Technology status SOFC/GT with CO2 capture • No demonstration system exists • Aker Kværner and Shell are working with the technology in cooperation with Siemens Westinghouse • A demonstration system for an atmospheric SOFC with CO2 capture was planned operational in Kollsnes, Norway before 2004 – has not appeared • Specific investment cost for a SOFC/GT system with CO2 capture based on today’s equipment has been estimated to $5000-8000/kWe
Technological challenges • Development of low-cost and reliable SOFC (and afterburner) units • Component matching and system integration • Development of suitable micro gas turbines for small scale solutions • Development of new power converters