Environmental Performance and Operational Analysis of a Sewage Sludge Fermentation Solid Oxidation Fuel Cell System Using Fe₂O₃ and Kanuma Clay

Abstract

This study discussed the performance of an integrated indirect gasification solid oxidation fuel cell (IIG-SOFC) in consideration of LCA thinking. Generally, hydrogen sulfide (H₂S) in gasified biomass causes cell voltage in a stack to decline over time. Although the biomass resource such as sewage sludge are carbon-neutral, a decline in SOFC performance creates environmental disadvantage of global warming potential (GWP); as such, it is necessary to remove H₂S via adsorption, and typically, ferric oxide (Fe₂O₃) is used for desulfurization. However, Fe₂O₃ imposes a considerable environmental burden of abiotic depletion potential (ADP). Kanuma clay (Kc) which is a natural sorbent was proposed as a viable substitute in our previous study, but Kc is characterized by a low adsorption capacity. As such, limitations associated with the adsorption column size and frequency with which adsorbents should be changed mean that utilizing a large amount of Kc does not necessarily result in a high desulfurization rate. Therefore, we investigated the optimal performance of IIG-SOFC utilizing Kc using exergy analysis and LCA. As a result, the maximum exergy efficiency was 28.2%. Likewise, the smallest GWP and ADP was achieved at a desulfurization rate of 100%, Kc usage ratio of 4.5%, and adsorption temperature of 120 °C.