An efficient biogas-assisted Brayton cycle combined with a trigeneration plant with power, heat, water, and methanol outputs: Design and multi-criteria analysis

Addressing sustainability challenges in high-temperature power generation, this study proposes a novel thermal design for a biogas-assisted Brayton cycle integrated within a multi-generation framework. The system utilizes preheated fuel and air for combustion and is coupled with a steam methane reforming unit connected to a gas turbine. To enhance energy recovery and overall performance, a supercritical CO2 cycle and a thermal desalination unit are incorporated in a cascading configuration. Furthermore, a syngas-based methanol production unit is embedded within the SMR subsystem, enabling simultaneous production of electricity, heat, freshwater, and methanol. A comprehensive assessment is performed using thermodynamic, exergoeconomic, and environmental analyses. To determine optimal performance, two bi-objective optimization scenarios, exergy-power and exergy-cost, are conducted using the Multi-Objective Particle Swarm Optimization algorithm. The exergy-power scenario yields superior results, achieving a net power output of 13,018 kW, thermal load of 5855 kW, freshwater production of 2.52 kg/s, and methanol output of 0.491 kg/s. Correspondingly, the system attains thermal and exergy efficiencies of 41.63 % and 33.33 %, a total unit product cost of 8.15 $/GJ, and a payback period of 2.79 years. These results underscore the proposed system's viability as a high-efficiency, low-cost, and environmentally sustainable energy solution.