Reducing CO 2 emissions for an IGCC power generation system: Effect of variations in gasifier and system operating conditions

Abstract

In an integrated gasification combined cycle (IGCC) power generation system, the effectiveness of the gasification process significantly affects system performance while the optimization of system operating conditions is essential for improved utilization of the syngas. The benefits to the gasifier and IGCC system are currently investigated through a sensitivity analysis of gasifier and system operating conditions. In the analysis, the following are varied: (i) thermal operating conditions of the IGCC system, (ii) inlet conditions of the gasifier (steam–coal, oxygen–coal ratios) and (iii) fuel (four solid fuels are considered). The thermal operating conditions used here are variations in the inlet temperatures at three locations within the IGCC system (the gas turbine combustion chamber, the gas turbine and the heat recovery steam generator). The operating effectiveness of the gasifier and the IGCC system are analysed considering fuel utilization based on estimates of relative and specific net work output rates, combined cycle efficiency and CO 2 emissions. The analysis is discussed on the basis of the increase in gasification of the fixed carbon in the source fuel (i.e. from partial to full gasification) thus comparing the proposed IGCC system for the entire range of gasification. Results from the analysis suggest that increasing gasification: (i) increases efficiency, (ii) marginally decreases net work output rate, (iii) reduces coal consumption, thus reducing CO 2 emissions. Char combustion in the supplementary firing chamber helps to reduce CO 2 emissions for the same work output. Partial gasification above 70% of fixed carbon yields lower CO 2 emissions for all conditions discussed. Increasing the compressed air inlet temperature to the gas cycle increases CO 2 emissions. A higher steam-to-coal ratio yields lower specific CO 2 emissions and a lower oxygen-to-coal ratio yields lower CO 2 emissions. Higher carbon content in the fuel yields higher CO 2 emissions, especially at above 60% gasification.