Economic analysis of CO2 capture from natural gas combined cycles using Molten Carbonate Fuel Cells

Abstract

Driven by the search for high efficiency power generation with low CO2 emissions, several works in the last years investigated the integration of gas turbine cycles and high temperature fuel cells to arrange power plants with CO2 capture.One of the most promising configurations in a mid-term perspective relies on the use of Molten Carbonate Fuel Cells (MCFC) as “active CO2 concentrator” in natural gas combined cycles (NGCC). This work presents an assessment of the economic perspectives of the two most promising configurations, previously analyzed through detailed simulations carried out at Politecnico di Milano, discussing their potential for the long-term (2025+) technology portfolio of an electric utility.The fuel cell cathode side receives the gas turbine exhausts, in order to transfer CO2 from this stream to the anode side. While doing this, the MCFC requires about 20% of the total fuel input and contributes to the plant electric power output by a similar fraction. Downstream the MCFC is placed the heat recovery steam generator (HRSG); exhaust heat released to the cell effluents is recovered in the bottoming steam cycle.Two different approaches were considered for purification of the CO2-rich flow exiting the fuel cell anode: (i) a cryogenic process that separates CO2 from the residual combustible compounds, which are recycled back to the gas turbines, or (ii) an oxy-combustion of residual combustible species, followed by heat recovery, cooling and water separation by condensation. In all cases, purification yields a high purity CO2 stream, pumped to liquid form for storage.Both these plant configurations can capture up to 70–85% of CO2 with small or negligible efficiency penalties compared to a baseline NGCC while increasing remarkably the plant power output, thus yielding relevant advantages with respect to competitive CO2 capture technologies. Moreover, the relatively limited power output of the fuel cell section suggests a plausible mid-term feasibility of the proposed concept, by taking into account that largest existing MCFC plants built so far surpassed the 50MWel size.After an introduction about MCFC technological status and economic outlook, this work analyzes the economic performances of the proposed plants in order to evaluate their economic viability, considering all plant components and adopting a detailed bottom-up approach to determine the component cost distribution and the total plant costs. The final effect on cost of electricity and CO2 capture cost are addressed, allowing to evidence whether and how this solution might be competitive in the future. It is shown that current MCFC costs do not allow an economic advantage with respect to ‘traditional’ carbon capture cycles (i.e., NGCC with ammines scrubbing); while the situation would change assuming more aggressive mid-term MCFC cost targets. The breakeven specific costs that MCFC should achieve to successfully compete on an economic basis results close to 1500€/kWel (in terms of Total Equipment Cost, TEC) for a cost of natural gas equal to 6.5€/GJ, increasing to 2000€/kWel assuming NG cost of 9€/GJ.