Cyclic waste heat recovery strategies in a novel biomass driven all-in-one system for sustainable power, hydrogen and freshwater production; thermo-economic assessment and ANN/GA optimization

This study presents a novel, highly integrated biomass-driven system designed for the co-production of electricity, hydrogen, and freshwater. The system enhances sustainability and resource efficiency by combining biomass combustion and gasification with a Brayton cycle and a cascaded Organic Rankine cycle (CORC). The CORC utilizes a biphenyl-diphenyl oxide (BDO) mixture as the working fluid in its top tier. The system also integrates proton exchange membrane electrolyzers (PEMEs) for hydrogen generation and a reverse osmosis (RO) unit for seawater desalination. In the proposed system, syngas and high-temperature flue gases from biomass combustion and gasification drive gas turbines to generate electricity. Waste heat is then recovered through high/low pressure gas turbines (HPGT and LPGT) and converted into additional electrical power using a thermoelectric generator and the CORC. At base conditions, the Brayton cycle and RO unit account for the majority of operational costs, at 37.5 % and 23.6 %, respectively. A sensitivity analysis reveals that freshwater pricing has the greatest economic impact, significantly influencing the net present value (NPV) and payback period (PP). Based on parametric analysis, increasing biomass mass flow rates enhances system outputs linearly while maintaining exergy efficiency near 22 %. Conversely, elevated moisture content negatively affects performance by reducing power, hydrogen, and freshwater output, while increasing emissions and exergy destruction. Finally, using machine learning combined with genetic algorithm optimization, we identified optimal trade-offs between exergy efficiency and cost, with an ideal solution achieving 24.59 % efficiency at a cost of 416.21 $/h.