Integration of solid oxide fuel cell (SOFC) and chemical looping combustion (CLC) for ultra-high efficiency power generation and CO2 production

This work presents a thermodynamic analysis of the integration of solid oxide fuel cells (SOFCs) with chemical looping combustion (CLC) in natural gas power plants. The fundamental idea of the proposed process integration is to use a dual fluidized-bed CLC process to complete the oxidation of the H2-CO-rich anode exhausts from the SOFC in the CLC fuel reactor while preheating the air stream to the cathode inlet temperature in the CLC air reactor. Thus, fuel oxidation can be completed in N2-free environment without the high energy and economic costs associated to O2 production, avoiding at the same time the high temperature and high cost heat exchanger needed in conventional SOFC plants for air preheating. In the proposed configurations, the CLC plant is operated at mild conditions (atmospheric pressure and temperature in the range of 700–800 °C), already demonstrated in several pilot plants. Two different scenarios have been investigated: in the first one, the SOFC is designed for large-scale power generation (100 MWLHV of heat input), featuring a heat recovery steam cycle and CO2 capture for subsequent storage. In the second scenario, the system is designed for a small-scale plant, producing 145 kg/h of pure CO2 for industrial utilization, as a possible early market application.

The main parameters affecting the plant performance, i.e. SOFC voltage (V) and S/C ratio at SOFC inlet, have been varied in a sensitivity analysis. Three different materials (Ni, Fe and Cu-based) are also compared as oxygen carriers (OCs) in the CLC unit. The integrated plant shows very high electric efficiency, exceeding 66%LHV at both small and large scale with a carbon capture ratio (CCR) of nearly 100%. It was found that, except for the cell voltage, the other operating parameters do not affect significantly the efficiency of the plant. Compared to the benchmark SOFC-based hybrid cycles using conventional CO2 capture technologies, the SOFC-CLC power plant showed an electric efficiency ∼2 percentage points higher, without requiring high temperature heat exchangers and with a simplified process configuration.