Thermo-economic analysis and multi-criteria optimization of an integrated biomass-to-energy power plant

A biomass-driven integrated system comprising anaerobic digestion, gasification, proton exchange membrane electrolyzer (PEME), Sabatier reactor, solid oxide fuel cell (SOFC), a gas turbine, steam turbine and organic Rankine cycle (ORC) was proposed in this study. Biomass feedstocks in form of animal waste served as input in the digester and converted to biogas, and crop residue was converted to syngas in the gasifier. Upgraded syngas and methane from the bio-conversion process was fed to a SOFC-GT topping cycle, with heat recovery bottoming cycles of steam turbine and organic Rankine cycles. The proposed system was assessed from energy, exergy and economic viewpoints in Engineering Equation Solver (EES) software. Parametric analysis was performed to ascertain the effect of design parameters on the plant's performance. Lastly, a multi-criteria optimization was performed using multi-objective genetic algorithm (MOGA) in MATLAB to maximize exergy efficiency and minimize levelized cost of electricity, as well as selection of best ORC working fluid from six preselected candidates (MM, MDM, cyclopentane, cyclohexane, R1233zd(E), and R600a). According to the results, at optimum point the plant can attain energy and exergy efficiencies of 54.81 % and 44.87 %, respectively. The total power output is 9.05 MW, with levelized cost of electricity of 111.8 $/MWh. Hydrogen of 0.0023 kg/s with PEME efficiency of 73.73 % was obtained and further used in upgrading the syngas from LHV of 4.20-37.78 MJ/kg.