Enhancing efficiency and reduced CO2 emission in hybrid biomass gasification with integrated SOFC-MCFC system based on CO2 recycle

The burning of fossil fuels at an ever-increasing rate is accompanied by significant anthropogenic CO2 emissions that are surpassing the carbon cycle in nature. Fuel cell (FC) technology serves as the fundamental basis for hybrid energy systems, which exhibit potential in addressing environmental and energy concerns. This study harnesses the gasification of biomass as a renewable resource in conjunction with two types of high-temperature fuel cells. The investigated system includes a gasifier, solid oxide fuel cell, molten carbonate fuel cell, gas turbine, and steam turbine. In this system, the oxidation of unused fuel through sustainable technology is facilitated by positioning the molten carbonate fuel cell downstream of the solid oxide fuel cell. Additionally, this placement enhances the recirculation of CO2 within the system. A comprehensive examination has been undertaken to ascertain the effects of many variables on energy and exergy efficiency, levelised cost of energy, and CO2 emission index. Moreover, the Sankey diagram of the system under investigation was implemented to examine the exergy interaction between its various components. Also, in order to ascertain the optimal point of the system, two sets of objective functions—levelised cost of energy paired with CO2 emission index, and exergy efficiency coupled with levelised cost of energy—were chosen for multi-objective optimisation utilizing genetic algorithm method. The findings of sensitivity analysis reveal a consistent positive correlation between the levelised cost of energy and both energy and exergy efficiency across nearly all parameters examined. Furthermore, the results of parametric study indicate that CO2 recirculation within the system is of utmost importance in mitigating its emission. The effectiveness of the system is evidenced by multi-objective optimisation with levelised cost of energy and CO2 emission index as objective functions results, which show a commendable exergy efficiency of 41.52 % alongside a reduced cost of 26.98 $/GJ and a CO2 emission index of 0.124 kg/kWh. Additionally, the investigated system is able to achieve an exergy efficiency of 47.68 % with a levelised cost of energy of 31.95 $/GJ and a CO2 emission index of 0.141 kg/kWh at the optimum point with the objective functions of exergy efficiency and levelised cost of energy. Additionally, comparing the outcomes of performed optimisations with findings from research performed on a power generation system incorporating waste management, as well as an integrated system featuring a high temperature fuel cell, reveals improvements in exergy efficiency, levelised cost of energy, and CO2 emission index. These comparisons highlight the advancements in efficiency, cost, and environmental impact achieved by the optimised system.