As the next generation of advanced adiabatic compressed air energy storage systems is being developed, designing a novel integrated system is essential for its successful adaptation in the various grid load demands. This study proposes a novel design framework for a hybrid energy system comprising a CAES system, gas turbine, and high-temperature solid oxide fuel cells, aiming for power generation and energy storage solutions. The overall model of the hybrid power generation system was constructed in Aspen Plus^TM, and the mass balance, energy balance, and thermodynamic properties of the thermal system were simulated and analyzed. The results demonstrate that the hybrid system utilizes the functional complementarity of CAES and solid oxide fuel cells (SOFCs), resulting in the cascade utilization of energy, a flexible operation mode, and increased efficiency. The overall round-trip efficiency of the system is 63%, and the overall exergy efficiency is 67%, with a design net power output of 12.5 MW. Additionally, thermodynamic analysis shows that it is advisable to operate the system under lower ambient temperatures of 25 °C, higher compressor and turbine isentropic efficiencies of 0.9, a higher fuel utilization of 0.62, and optimal SOFC/MGT split air flow rates of 1.1 kg/s. The results of this article provide guidance for designing innovative hybrid systems and system optimization.

Existing combined heat and power plants usually operate on part-load conditions during low heating demand seasons. Similarly, there are boilers designated for winter use that remain inactive for much of the year. This brings a concern about the inefficiency of resource utilization. Retrofitting existing CHP plants (especially for those with spare boilers) for biofuel production could increase revenue and enhance resource efficiency. This study introduces a novel approach that combines biomass gasification and pyrolysis in a polygeneration process that is based on utilizing existing CHP facilities to produce biomethane, bio-oil, and hydrogen. In this work, a detailed analysis was undertaken of retrofitting an existing biomass combined heat and power plant for biofuel production. The biofuel production plant is designed to explore the polygeneration of hydrogen, biomethane, and bio-oil via the integration of gasification, pyrolysis, and renewable-powered electrolysis. An Aspen Plus model of the proposed biofuel production plant is established followed by a performance investigation of the biofuel production plant under various design conditions. An economic analysis is carried out to examine the profitability of the proposed polygeneration system. Results show that the proposed polygeneration system can achieve 40% carbon efficiency with a payback period of 9 years and an internal rate of return of 17.5%, without the integration of renewable hydrogen. When integrated with renewable-power electrolysis, the carbon efficiency could be significantly improved to approximately 90%; however, the high investment cost associated with the electrolyzer system makes this integration economically unfavorable.

Thermochemical conversion processes of biomass, such as gasification and pyrolysis, can convert a wide range of feedstocks into liquid fuels, including forest residue, agricultural, food, and municipal solid waste. These more widely available and theoretically lower cost feedstocks make biofuel production through thermochemical pathway more cost-competitive. Furthermore, the thermochemical conversion pathway for biomass conversion could be relatively easy to integrate with the existing biomass combined heat and power plant, making it an attractive technology for the future commercialization of biofuel production through biomass. A detailed analysis was undertaken of a retrofitted biomass combined heat and power plant for biofuel production in this work. The biofuel production plant is designed to explore the polygeneration of hydrogen, biomethane, and biooil via the integration of gasification, pyrolysis, and renewable-powered electrolysis. The G-valve in the biomass circulating fluid bed plant, which is generally used for sand and char recycling, is retrofitted in the proposed system to fit the pyrolysis reaction for bio-oil production. Centering around the biomass circulating fluid bed gasifier, the system is also outfitted with a condensation and distillation process for bio-oil production, and a membrane reactor system for biomethane production. A mathematical model of the proposed biofuel production plant is established in Aspen Plus, followed by a performance investigation of the biofuel production plant under various design conditions. The limitations and opportunities of this retrofitted biomass combined heat and power plant for biofuel production are explored in this study.