Economically Advantageous Two-Stage Heat Exchanger Configuration for High-Temperature Exhaust Heat Management in Multi-Generation System Utilized in Heat-Driven Humidification-Dehumidification Desalination Unit and sCO2 Cycle Leveraging Metaheuristic Bat Algorithm

Abstract

This study proposes value-oriented thermal management in a sustainable biomass-based freshwater and hydrogen production system integrating a humidification–dehumidification (HDH) desalination unit with a supercritical CO₂ Brayton cycle and PEM water electrolysis, driven by rice straw biomass. A comprehensive thermodynamic model evaluates system performance, with particular emphasis on freshwater generation under varying operating conditions, including gas turbine pressure ratio, turbine inlet temperature, and biomass feed rate. High-temperature exhaust gases from the gas turbine transfer their thermal energy through two heat exchangers as a cost-effective approach. The first heat exchanger supplies heat to drive the supercritical CO₂ (sCO₂) Brayton cycle, generating additional power. Within the sCO₂ cycle, an internal heat exchanger provides heated air for residential space-heating applications. The second heat exchanger recovers residual exhaust heat to drive the HDH desalination cycle, producing freshwater. The system simultaneously delivers electricity, freshwater, hot air, hydrogen, and oxygen. Performance analyses indicate that increasing the gas turbine pressure ratio enhances electrical power and hydrogen production while reducing thermal outputs such as freshwater and hot air. Conversely, higher turbine inlet temperatures favor freshwater and hot air generation. Results show that freshwater production increases significantly with higher turbine inlet temperature and biomass feed rate, reaching up to 216.8 L/h and 235.3 L/h, while higher pressure ratios reduce water yield due to enhanced energy extraction in the power cycle. A metaheuristic bat algorithm is used for multi-objective optimization to maximize freshwater and hydrogen production while improving overall system efficiency. An optimal configuration achieves high freshwater yield, considerable hydrogen generation, and efficiency exceeding 80%.