Multi-variable study of a novel multigeneration system using biogas separation unit and LNG cold energy utilization, producing electricity, cooling, heat, fresh water, liquid CO2, biomethane, and methanol

Biogas fuel has gained recognition as a highly suitable alternative to fossil fuels, attributed to its renewable nature and remarkable energy density. Biogas fuel utilization facilitates the integration of combined energy systems equipped with multi-generational structures, rendering them suitable for long-term planning and management. Hence, this study presents a unique approach to using biogas for multigeneration, exhibiting enhanced thermodynamic efficiencies and negative carbon dioxide emissions. To achieve the stated objective, an innovative system is devised that involves the utilization of a biogas separation unit in integration with several other components, including a LNG cold energy utilization unit, an ammonia Rankine cycle, a desalination unit, a Kalina cycle, a solid oxide electrolyzer cell, a biomethane combined cycle, and a methanol synthesis unit. The newly devised configuration is simulated through the Aspen HYSYS software and assessed from energy, exergy, environmental, and economic considerations. Based on the research findings, the suggested methodology exhibits energy and exergy efficiencies of 91% and 83%, correspondingly. Furthermore, the evaluation of the entire unit cost of the product and the levelized energy cost reveals values of 4.81 $/GJ and 0.033 $/kWh, respectively. The carbon dioxide emission intensity of the newly implemented process is calculated to be -0.1041 kg/kWh. The economic aspects reveal a favorable net present value of 1470.6 M$ and a payback period of 5.29 years.