2008 Volume 87 Issue 9 Pages 737-743
The bench-scale production of hydrocarbon liquid fuel was successful from woody biomass via gasification. The production capacity of the biomass-to-liquid (BTL) plant used in this study was 1.9 L of hydrocarbon liquid from 13 kg of woody biomass per day. The BTL process involved the following steps: gasification of the woody biomass, wet and dry gas cleaning, gas compression, the removal of carbon dioxide, and the Fischer-Tropsch (FT) synthesis reaction. In the gasification step, oxygen-enriched air gasification was carried out using a downdraft fixed-bed gasifier. By increasing the oxygen content, which acts as a gasifying agent, from 21.0 to 31.5 vol%, the conversion to gas on a carbon basis increased from 91.9 to 96.3 C-mol%, while the concentrations of CO and H2 increased from 22.8 to 30.1 vol% and from 16.8 to 23.7 vol%, respectively. The product gas obtained with an oxygen content of 27.6 vol% was subsequently converted to a liquid fuel through the gas cleaning and FT synthesis reaction steps. The concentrations of H2S and COS produced in the gasification step decreased to less than 5 ppb through the scrubber and desulfurization tower for the wet and dry gas cleaning, respectively. The concentration of the syngas (CO + H2) increased from 48.1 to 56.0 vol%, while that of CO2 decreased from 12.1 to 0.6 vol% after the cleaned gas was passed through a carbon dioxide removal tower. Subsequently, the cleaned gas was compressed up to 12.6 MPa using compressors to obtain a feed gas for the FT synthesis reaction, and its composition was as follows: 30.8 vol% of CO, 25.2 vol% of H2, 0.9 vol% of CO2, 2.5 vol% of CH4, 40.6 vol% of N2, <5 ppb of H2S, and <5 ppb of COS. In the FT synthesis step, the hydrocarbon fuel was synthesized in a slurry bed reactor using hexadecane as the solvent and Co/SiO2 catalyst. The selectivity to hydrocarbon with a carbon chain length of more than 5 carbon atoms as a liquid fuel, i.e., a C5+ selectivity of 73.0% was obtained along with a chain growth probability of 0.85 under the following conditions: 3 MPa, 280 to 310°C, and when the ratio of catalyst weight to feed gas rate (W/F) was 86.9 g h/mol.
