Synthetic natural gas production by sorption enhanced steam hydrogasification based processes for improving CH4 yield and mitigating CO2 emissions

Abstract Two new processes for synthetic natural gas (SNG) production based on the sorption enhanced steam hydrogasification (SE-SHR) are proposed. Experimental work was conducted on the gasification of coal and biomass feedstocks with a fixed quantity of quicklime as the sorbent. Results showed that SE-SHR can significantly increase H 2 yield beyond the initial H 2 input and minimize CO 2 production. The SE-SHR parametric study was carried out by using lignite as a typical feedstock. By varying hydrogen to carbon molar ratio (H 2 /C) and steam to carbon molar ratio (Steam/C), the product gas composition and yield during SE-SHR and conventional steam hydrogasification (SHR) were obtained. The increase of H 2 /C enhanced the productions of H 2 and CH 4 and decreased the productions of CO and CO 2 . On the other hand, due to the domination of steam gasification reaction, the yields of H 2 , CO and CO 2 were increased with the increase of Steam/C. The new SNG processes include SE-SHR coupled with water gas shift (WGS) and SE-SHR coupled with methanation. The simulation of individual WGS or methanation unit based on the preliminary bench-scale data was conducted using Aspen Plus software to obtain the final SNG composition. Results showed that the SE-SHR-Methanation process results in high CH 4 production with self-sustained H 2 supply and near zero CO 2 emissions. The optimum gasification conditions for this process using lignite were H 2 /C of 1.08 and Steam/C of 2.22. Finally, a preliminary pilot-scale simulation of SE-SHR-Methanation process was conducted based on the predetermined optimum condition to evaluate the overall material and energy balance. It showed that carbon conversion efficiency to CH 4 was as high as 39.8%.