Membrane processes for CO2 removal and fuel utilization enhancement for solid oxide fuel cells

Incomplete oxidation on the anode side of a solid oxide fuel cell (SOFC) leaves a considerable amount of unused fuel (e.g., H2 and CO) in the anode exhaust. In order to enhance fuel utilization, CO2-selective membranes can be employed to remove the CO2 in the anode exhaust before returning the recovered fuel to the SOFC. In this study, two membrane processes have been designed for integration with a SOFC system, one with an air sweep (SOFC-MBair) and the other with a vacuum (SOFC-MBvac), on the permeate side. The transport properties of developed membranes were applied to the processes, and techno-economic analysis (TEA) was carried out to estimate the CO2 removal cost of each process. The parameters investigated were the anode exhaust recycle percentage, stack fuel utilization of the SOFC, power output, as well as the area and transport properties of the membranes. Notably, at 100% anode exhaust recycle, the system fuel utilization can be boosted to >99% for both processes. By tuning the stack fuel utilization, a steam-to-carbon ratio above 1.5 is achievable. It was found that the SOFC-MBvac process can achieve a lower CO2 removal cost than the SOFC-MBair process. For the SOFC-MBvac process, by considering the value of the recovered fuel, the CO2 removal cost not only can be fully rebated by the recovered fuel value, but also there is a profit of about $38 per tonne of CO2 captured. Moreover, by taking into account a CO2 sale price of $40/tonne for enhanced oil recovery, a profit of about $66 per tonne of CO2 captured may be achieved. Furthermore, more cost reduction or profit is attainable by developing membranes with higher CO2 permeances. In addition, a zero-carbon electricity generation can be achieved by the SOFC-MBvac process.