Data-driven optimization of an innovative environmentally friendly power-methanol co-production system utilizing biogas-driven S-Graz cycle, biogas steam reforming, and CO2 capture-hydrogenation process

This study proposes an eco-friendly, multi-integrated system for co-producing electricity and methanol. The system incorporates a biogas-driven S-Graz cycle and a biogas steam reforming (BSR) unit for hydrogen generation, which is subsequently used in a methanol synthesis unit via carbon dioxide hydrogenation. The feasibility of the proposed configuration is assessed through thermodynamic, exergoeconomic, exergoenvironmental, and sustainability analyses. Sensitivity analysis reveals the steam-to-carbon molar ratio as the most influential parameter, with a mean sensitivity index of 0.377. To optimize system performance, a hybrid artificial neural network (ANN) and multi-objective grey wolf optimization (MOGWO) method is implemented under two scenarios: (i) sustainability index vs. methanol cost, and (ii) methanol production rate vs. methanol cost. The second scenario yields the best trade-off, achieving a methanol production rate of 3.25 m3/h at a cost of 0.5771 $/kg. Additionally, the system achieves an exergetic efficiency of 46.5 %, a sustainability index of 2.97, a net present value of 160 M$, and a payback period of 4.77 years. This study demonstrates the potential of integrating methanol production with a biogas-driven, multi-integrated system to enhance biogas utilization, improve thermodynamic efficiency, and support sustainable methanol production.