Process simulation and economic analysis of calcium looping gasification for coal to synthetic natural gas

Abstract

The calcium looping (CL) gasification process is an attractive approach for synthetic natural gas (SNG) production from coal, with the elimination of energy-intensive air separation, water-gas shift, and CO2 removal units. This study is to provide an impartial assessment of the conventional SNG process and the innovative CL-SNG process based on process simulation using ASPEN Plus. The estimated coal to synthetic natural gas conversion efficiency of the CL-SNG process is nearly 64.2%. The amount of sour water needs to be further purified in the calcium looping process is 40% lower than that of the conventional process. Besides, the capital investment of the CL-SNG process is about 10.6% lower than the conventional process while the total annual operation cost in the CL-SNG plant is relatively high due to the progressive deactivation of CaO sorbents. The sensitivity analysis shows that the operating cost of the CL-SNG process could be further lowered with the improvement of CO2 sorbent performance. The formation of CaSO4 from the combustor could consume the syngas in the gasifier and reduce the SNG yield, and sulfur is suggested to be transformed to SO2 under mild reducing environment in the combustor in this study.