Design and Balance-of-Plant of a Demonstration Plant With a Solid Oxide Fuel Cell Fed by Biogas From Waste-Water and Exhaust Carbon Recycling for Algae Growth

The design and balance-of-plant of a novel anaerobic digestion (AD) biogas solid oxide fuel cell (SOFC) plant is assessed. Biogas from waste-water treatment plant is the fuel feeding the SOFC system. Simultaneous multigeneration of electricity, heat and a fuel (algae, in our case) via exhaust carbon recycling is accomplished in the proposed plant configuration. CO₂ capture from the SOFC anode exhaust is carried out through an oxy-combustion reactor that completes the oxidation of spent fuel still available downstream of the fuel cell. The captured CO₂, after water condensation, is thus fed to an array of photo-bioreactors where C biofixation in algae is achieved. The design of the main plant sections, including the gas cleaning unit, fuel processor, SOFC “hot-box,” oxy-combustor, CO₂/H₂O condensation unit and photo-bioreactors, is provided. A system analysis of a full-scale version of the biogas SOFC power plant with optimized heat integration is finally analyzed to fully understand the potential of the proposed integrated energy system. An overall electrical efficiency exceeding 52% (LHV basis) was calculated. Sensitivity analyses have been carried out in order to study the influence of fuel utilization, internal reforming, biogas composition and steam-to-carbon ratio on both SOFC and overall plant performance.