A novel flare gas recycling system for distributed energy, renewable fuel, and purified water production: Multi-objective 4E analysis and optimization

Flaring of associated natural gas in oil and gas fields leads to substantial energy loss and severe environmental degradation. This study proposes a novel multi-generation energy system that utilizes flare gas as a valuable resource for the simultaneous production of electricity, hot water, chilled water, freshwater, and hydrogen. The integrated configuration consists of an external combustion gas turbine (ECGT) cycle, a Rankine steam cycle, a lithium bromide absorption chiller, a reverse osmosis desalination unit, and a proton exchange membrane (PEM) electrolyzer. A detailed 4E (energy, exergy, economic, and environmental) analysis is carried out using Engineering Equation Solver (EES), while a multi-objective optimization employing the NSGA-II algorithm in MATLAB is performed to maximize exergy efficiency and minimize the levelized cost of energy (LCOE) and environmental impacts (EI). In the base case, the system achieves an energy efficiency of 53.06 % and an exergy efficiency of 50.44 %, while generating 6320 kW of electricity, 61,308 kg/h of hot water, 7099.2 kg/h of chilled water, 235.1 kg/h of freshwater, and 0.59 kg/h of hydrogen. Optimization improves the exergy efficiency to 72.29 %, and reduces both LCOE and EI by approximately 35 %. The results highlight the system's technical and environmental viability as a sustainable flare gas recovery solution in hydrocarbon-producing regions.