Flexible and synergistic methanol production via biomass gasification and natural gas reforming

Abstract

Sustainable liquid fuels are essential for decarbonization of various means of transportation which are challenging to address through electrification or hydrogen use. A possible method for producing low-carbon liquid fuel is through the thermochemical biomass to liquid (BTL) process. In this study, we conduct a technoeconomic-environmental analysis of two processes which take advantage of integration of natural gas reforming and biomass gasification, with the objective of improving the economics. By integrating H₂-rich syngas (a mixture of H₂/CO) obtained from natural gas reforming with carbon-rich syngas from biomass gasification, we harness synergistic effects. This combination allows us to achieve the optimal H₂/CO ratio required for methanol synthesis, while also ensuring efficient carbon utilization. In the first design, natural gas is reformed in an autothermal reformer (ATR) to produce syngas. A Solid Oxide Electrolysis Cell (SOEC) is utilized to supply the O₂ for both gasification and reforming processes. The H₂ produced by the SOEC adjusts the H₂ content in the syngas before the methanol synthesis reactor. In the second design, natural gas is reformed in a gas-heated-reformer (GHR) before an ATR, while an Air Separation Unit (ASU) produces the O₂ for the process. As a benchmark, the economics and flexible operation of both processes are compared to a conventional BTL process. In addition, the techno-economic impact of operating in biomass-only or natural gas-only modes are investigated. For a 134 MW_th plant with 50 % of entering carbon from biomass, the levelized cost of methanol (LCOMeOH) of ATR+SOEC case is 34 % higher than the BTL reference case, while that of ATR+GHR case is 24 % lower than the BTL reference case. A lifecycle analysis (LCA) is conducted for these designs. Utilizing renewable electricity and 50 % biogenic carbon, the ATR+SOEC case emits 908 kgCO_2e /tonne MeOH for a 100-year Global Warming Potential (GWP), while the ATR+GHR case emits 721 kgCO_2e /tonne MeOH. For a 20-year GWP, these emissions are 1055 and 915 kgCO_2e /tonne MeOH, respectively. These emissions correspond to more than 50 % reduction in LCA emissions when compared to natural gas based LCA emissions.