Thermodynamic analysis of methanol synthesis combining straw gasification and electrolysis via the low temperature circulating fluid bed gasifier and a char bed gas cleaning unit

Abstract The phase-out of fossil fuels in the heavy transportation sector will require energy-dense biofuels like methanol, and will likely require that a wide range of biomasses are utilized. In this framework, gasification of straw and subsequent upgrading to methanol represents a potentially advantageous conversion route. In this study, the established low-temperature circulating fluid bed (LTCFB) gasifier is coupled to a partial oxidation (POX) and char bed reactor, which enables a relatively robust and effective conversion of tars - making the product gas suitable for methanol synthesis. Five scenarios producing methanol via traditional air-separation units and electrolysis were thermodynamically modeled and analyzed in Aspen Plus. The analysis showed state-of-the-art biomass-to-methanol energy efficiencies up to 54–56% and overall carbon conversions above 57%. A parametric analysis on the POX temperature revealed the potential to increase efficiency and the carbon conversion up to 58% and 68%, respectively. The proposed systems outperform alternative systems framed on straw gasification, and exceed in terms of efficiency and overall carbon conversion other solutions based on wood-gasification.