(177f) A Hybrid Biomass-Methane Gasification System for High Conversion and Selectivity to H2 and CO
Biomass is highly oxygenated which prevents it from being economically converted to fungible liquid hydrocarbon fuels. One way to offset this high oxygen content is to co-process natural gas, which has previously been shown to significantly increase end-product yield and overall carbon conversion with gasification as the primary conversion step for the biomass. However, most hybrid processes consider a parallel design where the two feedstocks are converted in separate reactors. Presented is a co-feed system to simultaneously gasify biomass and reform natural gas noncatalytically in a steam-only atmosphere. An external heat source is used to obtain high temperatures to thermally convert tars in-situ; likewise light hydrocarbons and methane are reformed into CO and H2. Experimentally it was shown that the ratio of input biomass to methane has influence on the product gas ratios, however operating temperature is the most significant parameter affecting both conversion and selectivity. At 1500°C it is possible to obtain a product gas composition of H2/CO ≈ 2.0 and CO2/CO ≤ 0.25 with an overall carbon conversion ≥ 95% and selectivity to CO ≥ 90%. These results imply a two-fold increase in end-product yield per kilogram of input carbon compared to conventional biomass gasifiers. An oxygen-blown gasifier was simulated and gasifier efficiencies (LHV basis) were compared for the autothermal and allothermal configurations showing comparable performance depending on input steam and the ability of the allothermal reactor to transfer thermal energy to the reacting medium. Practical limitations of indirectly heated gasifiers include selection of a heat source, high temperature material considerations, and heat transfer limitations for particle sizes above 100 μm.