Cryogenic method for H2 and CH4 recovery from a rich CO2 stream in pre-combustion carbon capture and storage schemes

The pre-combustion carbon capture technology based on coal gasification or methane reforming followed by (water gas shift reactors assisted with Pd-alloys membranes) WGS-MR is considered very promising for the production of a rich hydrogen stream that can be combusted in combined cycles. However, recovery of the total H2 content is not feasible and a part of it remains in the retentate side. The requirement for upstream high pressure operation of the necessary reforming step has a drawback: complete reforming of CH4 is not possible; thus small but significant amounts remain in the rich CO2 stream. These CH4 amounts not only affect the efficiency of the process but also are against regulations for the allowed composition of carbon dioxide for storage. Therefore, an efficient purification step before its compression is of high importance. The current work models a cryogenic method for the separation of combustibles from a rich-CO2 stream and evaluates its effects on the efficiency of the pre-combustion carbon capture system. The modeling study is performed with AspenPlus™. A study on the effect of operating parameters of the (Purification & Compression Unit) PCU integration on the performance is presented.