Solid-oxide electrolyzer coupled biomass-to-methanol systems

Biomass-derived fuels are attractive due to the reduced greenhouse gas emissions and the potential contribution to the development of the agricultural industry. Particularly, 2nd generation biofuels, e.g., synthetic biodiesel as a high-performance and alternative mobility fuel, can be produced via biomass-gasification based processes. There are mainly three types of biomass gasification processes: (1) moving- or fixed-bed gasifier for coal gasification with oxidizing blast gas (air + hot syngas) (2) fluidized-bed gasifier that uses air (oxidant agent) to fluidize the bed and the added carbon-containing particle, and (3) entrained flow gasifier that uses pure oxygen to reach high operating temperature. The entrained flow gasifier seems to be a promising choice with high scale-up potential, due to the high-pressure operation and none N2 diluted syngas production, which can lead to the compact design of down-stream equipment. Particularly, the syngas produced contains no tar, and low methane and CO2. The disadvantage of this gasification technology is the need of high-purity O2 supply of, usually from an air separation unit (ASU). Therefore, solid-oxide electrolysis offers very good opportunity of integrating with entrained-flow gasifier, due to that (1) possible pure oxygen production to avoid the ASU, (2) high operating temperature for better heat integration with the original gasification process, and (3) hydrogen production via steam electrolysis for adjusting the syngas composition. In this paper, the integration of the SOE in the EFG-based biomass to methanol systems (SOEC case) is investigated and technically compared with the traditional biomass-to-liquid system (base case), whose syngas composition is adjusted by water-gas-shift reactors. The results show that, the mass yield of the methanol is set as around 69.4 t/hr, SOEC case can achieve higher energy efficiency, the energetic efficiencies of the base case and SOEC case were 47.95% and 59.1%, respectively.