Small-scale air Brayton cycle fueled by green methanol – thermodynamic analysis

Faced with the challenges of depleting fossil fuel resources, ensuring continuity of energy supply, but at the same time climate security, technological solutions are being sought to support the energy transition. Biomass is an important part of energy scenarios, particularly in the context of distributed energy development. The paper considers a small-scale unit for the generation of electrical energy operated under the regenerative air Brayton cycle fueled with green methanol, produced from waste biomass. While offering the low-quality biomass-to-power generation pathway with efficiency exceeding 30%, it is a technology competitive against classic steam systems developed to date, additionally supporting the circular economy implementation. A comprehensive thermodynamic analysis is carried out to assess the impact of key cycle operating parameters on the system performance to find their optimum ranges in terms of efficiency and potential cost of regenerative heat exchanger. Effects of pressure ratio, excess-air ratio, and compressor and turbine efficiencies on the heat regeneration effectiveness, system efficiency, and related heat transfer surface area of the high-temperature recuperator, were examined. A system of non-linear equations with non-ideal gas model for fluids was solved via a developed in-house code. The calculation results indicated on the optimum compression ratio ranging within ∼ 1.6–2.9, and the system efficiency increase from 23% to 33% for compressor efficiency varied within 60%–80%, respectively. The maximum techno-economically justified heat exchange surface was estimated at 40 m2.