Solar-Driven Biomass Polygeneration with Hierarchical Thermal Cascading for Integrated Water–Energy–Fuel Production

Abstract

Despite extensive research on solar desalination and biomass-to-liquid technologies, fully integrated systems combining thermochemical fuel synthesis, hierarchical solar thermal cascading, supercritical CO₂ power generation, carbon capture, and hybrid desalination remain scarce. This study proposes a novel solar-driven biomass polygeneration system integrating biomass pyrolysis, autothermal reforming, Fischer–Tropsch biodiesel synthesis, dual steam Rankine cycles, a supercritical CO₂ Brayton cycle, MDEA-based carbon capture, and hybrid MED–RO desalination within a hierarchical thermal energy cascading framework. High-temperature solar energy first drives the primary Rankine cycle, while the remaining thermal energy powers the supercritical CO₂ Brayton cycle. Waste heat recovered from syngas cooling and turbine exhaust is further utilized to operate a secondary Rankine cycle and support desalination and solvent regeneration. The hybrid MED–RO configuration enhances freshwater recovery through effective thermal and hydraulic energy integration. Under the design conditions, the proposed system achieved an overall energy efficiency of 63.25% and an exergy efficiency of 49.16%, while producing 1841.48 kg h⁻¹ of biodiesel and 1735.95 t h⁻¹ of freshwater at a levelized water cost of 1.41 $ m⁻³. The levelized electricity cost was 0.049 $ kWh⁻¹, CO₂ emissions were 0.481 t MWh⁻¹, and the economic assessment yielded a net present value of 218 million USD with a payback period of 5.2 years. These results demonstrate that hierarchical thermal cascading effectively enhances resource utilization and provides a promising pathway for sustainable water–energy–fuel production with improved thermodynamic and economic performance.