Multiobjective Optimization of a Novel Biogas-Based SOFC-sCO2-VAR System with Anode Gas Recirculation: Energy, Exergy, and Economic Analysis

Abstract Conventional fuels, such as natural gas, used in solid oxide fuel cells (SOFCs), often leave a portion unutilized, leading to harmful emissions. To address this problem, a biogas-fueled SOFC (which has lower carbon footprints and renewable in nature) with an anode gas recirculation (AGR) unit has been integrated, which recycles unreacted gases to improve fuel utilization and overall system efficiency. At the same time, the system has been further modified by integrating the supercritical carbon dioxide ( sCO 2 ) Brayton cycle and vapor absorption refrigeration system (VARS). Biogas is reformed externally to hydrogen-enriched syngas, then supplied to anodes of SOFCs. The unused fuel is recycled through the AGR loop, reducing fresh fuel consumption and improving energy efficiency, and the rest is supplied to the burner for complete combustion. The system’s residual heat is efficiently exploited through a sCO 2 Brayton cycle, VARS, and a dedicated heat exchanger for hot water. The individual system of the proposed hybrid system was validated against published results using engineering equation solver (EES) software. System performance was analyzed for varying current densities, AGR, and SOFC operating temperatures. The SOFC produced 174.4 kW with an energy efficiency of 48.9% without AGR and 53.2% with AGR. The overall system achieved an energy efficiency of 78%, an exergy efficiency of 75%, and an overall cost rate of 22.15 USD / h . The system was technoeconomically optimized using a multiobjective grey wolf algorithm, revealing an inherent trade-off between thermodynamic efficiency and economic performance. Under the TOPSIS-selected optimal condition, the proposed system achieved a 59% efficiency with a reduced cost rate of 11.02 USD / h .