Dual-objective optimization of biofuel-based solid oxide fuel cell energy system for hydrogen fuel and desalinated water production

Abstract

In this research study, the combination of both mentioned solutions and their effects on the efficiency of the system, its environmental concerns, operation cost, and maintenance cost are explored. The intended purpose of the current study was to propose a regenerative cycle that implements multiple sub-cycles to enhance the first and second-law efficiencies of the system and reduce the cost rates. The aforementioned system consists of a gas turbine (Brayton) cycle, a steam turbine (Rankine Cycle), an ORC, a single-effect Li-Br absorption chiller, a reverse osmosis desalination unit, a SOFC, and thermoelectric generators to obtain higher efficiency and electricity, even from the system low-grade waste heat. The dual-objective optimization considering the minimum cost rate and maximum exergy efficiency of the system is proposed. To achieve this goal, a genetic algorithm is implemented for better optimization and the Pareto frontier is represented along with a scatter of distribution plots to determine the optimum outputs of the function and their respective values for the decision variables. The optimization using design parameters lead to the best point with the exergy efficiency of 61.3% and cost rate of 0.27$/s for an interest rate of 12%. Although the environmental aspects are not included in the optimization, the design of the system is tried to be as environmental-friendly as it can be. The decision variables were the most crucial ones that affect the system the most. Isentropic efficiencies of pumps, compressors, and turbines along with the fuel mass flow rate, and pressure ratio in pumps and compressors are considered decision variables. The other decision variable which plays an undeniable role in the efficiency of the system is the temperature difference between the inlet and outlet of the Rankine Cycle HRSG. In the end, the optimizations were repeated for four different interest rates. The projected results illustrated the negative effect of increasing interest rates on both the exergy efficiency and cost rate of the system.