Synthesis Gas Production via Non-catalytic and Catalytic Gasification of Lignin with High-moisture Content
Kenji KOIDO, Yutaro WATANABE, Teppei NUNOURA, Kiyoshi DOWAKI
Lignin slurry as a model compound of ethanol-fermentation residue was gasified to produce synthesis gas (carbon monoxide (CO)/hydrogen (H2) for a feedstock of liquid fuel synthesis as an alternative to the petrol and diesel oil, and for hydrogen source applied to a fuel of fuel cells. With increasing moisture content, the gasification of the wet biomass produces less char and tar, whereas more input enthalpy of water is required to achieve reaction temperature (750-950 ℃). Based on the features, the optimum moisture content of the biomass exists. The optimum moisture content and reaction temperature were investigated for effective production of synthesis gas. From the typical results of gasification of the lignin slurry in fixed-bed downdraft type gasifier, conversion to-gas ranged from 45.5 to 78.4 C-mol%, while char yield ranged from 11.2 to 55.1 C-mol%. The cold-gas efficiency varied from 71.9 to 95.6% for moisture content of 73-90 wt.%.For the results of a catalyst (NiO/CaO-Al2O3) loading, the conversion-to-gas and cold-gas efficiency respectively ranged from 75.5 to 92.1% and from 89.0 to 108.2% for a moisture content of 80 wt.% with increasing the NiO/CaO-Al2O3 catalyst loading from 0.00 to 0.41 g-catalyst/g-feedstock. The results for the catalyst loading (CL) of 0.00-0.41 g-catalyst/g-feedstock showed that conversion to-gas and cold-gas efficiency increased by about 20 % compared to the results for non catalytic gasification with CL increase. H2 and CO in product gas composition slightly increased with CL. In comparison of the results of equilibrium constants between non-catalytic and catalytic gasification, the catalyst had few effect on equilibrium temperature for both the water-gas shift and steam methane reforming reactions, and large effects on conversion at T = 800-950℃ and cold-gas effciency at 900℃.
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