H₂ recovery and CO₂ capture after water-gas shift reactor using synthesis gas from coal gasification

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 CO₂ 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% H₂ at 2100kPa to imitate coal gasification. The CO₂ enrichment and H₂ recovery tests at 673K and 2100kPa with the high-pressure membrane module after the WGS reaction presented the enriched CO₂ concentration and H₂ recovery ratios of ~92% and ~96%, respectively. The long-term stability test showed that the CO₂ concentration decreased to 78.2%, and CO was generated and reached to 8.8% in the retentate stream after 47h because of reverse WGS and CO₂ hydrogenation reaction on 316L stainless steel module. The stability test for ~3137h 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 ~100h and showed that the WGS catalysts and membrane module made of 310S would be stable under real conditions.