Comparison of Preanode and Postanode Carbon Dioxide Separation for IGFC Systems

Abstract

This paper examines the arrangement of a solid oxide fuel cell (SOFC) within a coal gasification cycle, this combination generally being called an integrated gasification fuel cell cycle. This work relies on a previous study performed by the National Energy Technology Laboratory (NETL) that details thermodynamic simulations of integrated gasification combined cycle (IGCC) systems and considers various gasifier types and includes cases for 90% CO2 capture (2007, “Cost and Performance Baseline for Fossil Energy Plants, Vol. 1: Bituminous Coal and Natural Gas to Electricity,” National Energy Technology Laboratory Report No. DOE/NETL-2007/1281). All systems in this study assume a Conoco Philips gasifier and cold-gas clean up conditions for the coal gasification system (Cases 3 and 4 in the NETL IGCC report). Four system arrangements, cases, are examined. Cases 1 and 2 remove the CO2 after the SOFC anode. Case 3 assumes steam addition, a water-gas-shift (WGS) catalyst, and a Selexol process to remove the CO2 in the gas cleanup section, sending a hydrogen-rich gas to the fuel cell anode. Case 4 assumes Selexol in the cold-gas cleanup section as in Case 3; however, there is no steam addition, and the WGS takes places in the SOFC and after the anode. Results demonstrate significant efficiency advantages compared with IGCC with CO2 capture. The hydrogen-rich case (Case 3) has better net electric efficiency compared with typical postanode CO2 capture cases (Cases 1 and 2), with a simpler arrangement but at a lower SOFC power density, or a lower efficiency at the same power density. Case 4 gives an efficiency similar to Case 3 but also at a lower SOFC power density. Carbon deposition concerns are also discussed.