CO2 CAPTURE FROM AIR-BLOWN GASIFICATION-BASED COMBINED CYCLES

This paper focuses on an air-blown gasification-based combined cycle where CO2 is removed from the coal-derived gas before fuelling the combustion turbine. On the basis of public information from Mitsubishi Heavy Industries (MHI), the air-blown gasifier was modeled and its performance was investigated by the authors in a previous study. Here, with reference to a possible IGCC power plant with such a gasification technology, the possibility of removing CO2 from the coal-derived fuel gas is considered. The main differences between the two IGCCs, without and with CO2 capture, are gas used for coal loading (N-2 or CO2), the layout of the syngas cooling and treatment sections (owing to the presence of water-gas shift reactions and CO2 absorption process) and the composition of the fuel used in the combustion turbine. The results highlight that IGCC efficiency reduces by about 10.8% points when realizing CO2 capture, mainly due to the steam consumption in shift reactors and CO2 solvent regeneration and to power consumption for CO2 compression. However, the calculated efficiency penalty is in line with the values typical of IGCCs with oxygen-blown gasifier and CO2 capture. The power balances of the assessed cases are reported in detail and the main technical issues are discussed in the paper. The results of a sensitivity analysis are also reported to assess the effects of different steam to carbon ratios in the shift reactors.