H_2 recovery and CO_2 capture after water-gas shift reactor using synthesis gas from coal gasification

摘要

In this study, a combined test of the WGS (water-gas shift) reactor and a Pd-based composite membrane was carried out for pre-combustion CO_2 capture in a coal gasifier. The two series of WGS reactions, i.e., a high-temperature shift and a low-temperature shift, were performed under a gas composition of 60% CO and 40% H_2 at 2100 kPa to imitate coal gasification. The CO_2 enrichment and H_2 recovery tests at 673 K and 2100 kPa with the high-pressure membrane module after the WGS reaction presented the enriched CO_2 concentration and H_2 recovery ratios of ～92% and ～96%, respectively. The long-term stability test showed that the CO_2 concentration decreased to 78.2%, and CO was generated and reached to 8.8% in the retentate stream after 47 h because of reverse WGS and CO_2 hydrogenation reaction on 316L stainless steel module. The stability test for ～3137 h showed that these catalytic activities could be successfully prevented using steel with higher Cr and Ni contents, such as 310S. The WGS-membrane combination test using the outlet gas from a real coal gasifier was continued for ～ 100 h and showed that the WGS catalysts and membrane module made of 310S would be stable under real conditions.