Electrochemical Carbon Separation in a SOFC–MCFC Polygeneration Plant With Near-Zero Emissions

Abstract

The modularity and high efficiency at small-scale make high temperature (HT) fuel cells an interesting solution for carbon capture and utilization at the distributed generation (DG) scale when coupled to appropriate use of CO2 (i.e., for industrial uses, local production of chemicals, etc.). The present work explores fully electrochemical power systems capable of producing a highly pure CO2 stream and hydrogen. In particular, the proposed system is based upon integrating a solid oxide fuel cell (SOFC) with a molten carbonate fuel cell (MCFC). The use of these HT fuel cells has already been separately applied in the past for carbon capture and storage (CCS) applications. However, their combined use is yet unexplored. The reference configuration proposed envisions the direct supply of the SOFC anode outlet to a burner which, using the cathode depleted air outlet, completes the oxidation of the unconverted species. The outlet of the burner is then fed to the MCFC cathode inlet, which separates the CO2 from the stream. This layout has the significant advantage of achieving the required CO2 purity for liquefaction and long-range transportation without requiring the need of cryogenic or distillation plants. Furthermore, different configurations are considered with the final aim of increasing the carbon capture ratio (CCR) and maximizing the electrical efficiency. Moreover, the optimal power ratio between SOFC and MCFC stacks is also explored. Complete simulation results are presented, discussing the proposed plant mass and energy balances and showing the most attractive configurations from the point of view of total efficiency and CCR.