Thermo-economic analyses of concepts for increasing carbon capture in high-methane syngas integrated gasification combined cycle power plants

•Increasing carbon capture in IGCCs with high CH4 syngas.•Combusting separated CH4 in sequestration stream is most cost and water effective.•Recycling separated CH4 back to gasifier has highest efficiency.•Cost of electricity for 90% carbon capture ranges from 138.1 $/MWh to 143.4 $/MWh. An integrated gasification combined cycle (IGCC) power plant with transport gasifier and advanced pressure swing adsorption based warm gas CO2 removal technology for carbon capture is analyzed with respect to its maximum carbon capture yield. The carbon capture was limited to 88.6% due to high CH4 content in the syngas. The plant efficiency in this scenario is 33.76% resulting in a 1st year cost of electricity (COE) of 136.0 $/MWh with CO2 transport, storage and monitoring (TS&M). The high CH4 content in the syngas is a result of employing a highly efficient, low temperature gasifier designed for low rank feedstocks such as subbituminous coal, lignite and biomass. In order to increase the carbon capture in high methane syngas IGCCs to reach the U.S. Department of Energy target of 90% carbon capture, three pathways also based on warm gas CO2 removal were studied: (1) combustion of syngas in the CO2 purification section while raising steam, (2) syngas reforming in an external adiabatic reformer and (3) syngas recycling to the gasifier. Although the recycling option (3) has the highest efficiency, the combustor option (1) was the most economical with a COE of 138.1 $/MWh with TS&M. For scenario (1), the 1st year carbon capture cost with TS&M is 53.3 $/tonne compared to a corresponding IGCC without carbon capture and 75.0 $/tonne compared to a supercritical boiler plant (SCBP) without carbon capture. For the 1st year of operation, the avoided cost with TS&M compared to the corresponding IGCC without carbon capture is 65.4 $/tonne. Compared to the SCBP without carbon capture the 1st year avoided cost is 87.2 $/tonne.