Thermodynamic and economic analysis of a novel biomass oxy-fuel combustion system for power and methanol cogeneration with cryogenic carbon capture and purge gas recycle

Developing carbon-neutral pathways for the co-production of electricity and renewable fuels is essential for deep decarbonization. In this study, an integrated biomass oxy-combustion, cryogenic carbon capture, and methanol synthesis polygeneration system is proposed to enhance the utilization of biomass carbon, green hydrogen, and process waste energy. The system incorporates biomass oxy-combustion to increase the CO2 concentration in flue gas, thereby facilitating low-temperature carbon capture, while a CO2 heat pump cycle is introduced to recover mid- and low-grade waste heat from MS for refrigeration supply, based on the principle of cascading utilization of chemical and thermal energy. In addition, the hydrogen-containing purge gas from MS is recycled to the oxy-fuel boiler as auxiliary fuel, enabling cross-system integration of material and energy flows. Thermodynamic analysis shows that the proposed system achieves an overall energy efficiency of 62.11%, which is 5.66 percentage points higher than that of the individual system, while the exergy efficiency increases by 4.3%. The net power output is increased by 8.90 MW without additional biomass consumption. Economic results indicate that the proposed system yields an additional NPV of 44.8 M$ over the plant lifetime and shortens the DPP by 2.17 years compared with the reference system. Sensitivity analysis indicates that the system performs best at around 250 °C with an optimal excess oxygen ratio of 1.1, while carbon recovery rate and fixed carbon content in biomass strongly affect hydrogen and oxygen absorption. These results demonstrate a promising route for efficient and economically viable power-MeOH cogeneration under near carbon-neutral conditions.