(173c) Synthesis of Liquid Fuel from Woody Biomass by A Bench-Scale Btl Plant

Transportable liquid fuel such as hydrocarbon and dimethyl ether (DME) produced from biomass as a sustainable energy resource is an extremely promising carbon neutral fuel because CO2 generated by the use of liquid fuel produced from biomass can be offset by CO2 fixed by photosynthesis. In addition, this liquid fuel is clean, emitting none of the air pollutants such as SOx, NOx, and particulate matter. In particular, hydrocarbon fuel such as gasoline, light oil, and kerosene is applicable to the conventional engine. Accordingly, in view of petroleum saving and environmental protection, the synthesis process of hydrocarbon fuel as a transportable liquid fuel from biomass is one of the highest interests among the conversion technologies of biomass to energy. In the present work, on a bench-scale, the conversion of biomass into a transportable liquid fuel (BTL) system consisting of biomass gasification, gas cleaning, and FT synthesis was constructed. The synthesis of hydrocarbon liquid fuel from woody biomass was sequentially carried out. Eucalyptus tip (30 mm squares) was employed as a woody biomass sample. The ultimate analysis (daf basis) was as follows; C: 51.0 wt%, H: 6.0 wt%, N: 0.2 wt%, S: 0.015 wt%, O (diff.): 42.8 wt%. The proximate analysis was as follows; moisture: 10.5 wt%, volatile matter: 73.1 wt%, fixed carbon: 15.8 wt%, ash: 0.6 wt%. This bench-scale BTL plant consists of gasifier, scrubber, compressor, desulphurization tower, decarbondioxide installation, and FT synthesis reactor. A downdraft fixed bed gasifier was employed in the oxygen-enrichment gasification step. The biomass feed rate was approximately 9 kg/h on a dry basis. The oxygen concentration in the gasifying agent was in the range of 21.0 to 31.5 vol.%. The temperature of the combustion zone and reduction zone inside the gasifier was from 900 to 1000 oC, from 800 to 850 oC, respectively. The product gas flow rate was adjusted 18 Nm3/h using a roots blower installed downstream of the gasifier. The sulfur compounds derived from woody biomass gasification deactivate the FT catalyst. Therefore, in the gas cleaning step, the concentration of sulfur compounds has to be decreased less than 1 ppm. In this process, the sulfur compounds such as H2S and COS were removed by a scrubber and desulphurization tower packed with activated carbon. In the gas compression step, the cleaned gas has to be compressed up to several MPa in order to enhance liquid fuel yield in the FT synthesis step. Moreover, the partial pressure of syngas was increased by removing CO2 from cleaned gas on the decarbondioxide installation. In the FT synthesis step, a slurry bed reactor was employed. The inner diameter was 100 mm, and the length was 1500 mm. Hexadecane was employed as a solvent. 600 g of Co catalyst was used. Prior to run, the catalyst was reduced for 10 hours at 400 oC. The reaction pressure and temperature were 3 MPa and in the range of 280 to 300 oC. The slurry was stirred at 650 rpm. The feed gas rate was 18.5 NL/min. The reaction time was for 6 hours. The obtained gas and liquid fuel were quantitatively analyzed by GC-TCD, GC-FID, and GC-FPD. With increasing the oxygen concentration in the gasifying agent, the carbon conversion on a carbon basis increased from 91.9 to 96.2 C-mol%, and CO increased from 22.8 to 30.1 vol.%, and H2 concentration increased from 16.8 to 23.7 vol.%. CO2 and CH4 concentrations were approximately 11 and 2 vol.% and independent of the oxygen concentration. In the oxygen concentration of 27.6 vol.%, the product gas was 21.9 vol.% of H2, 29.3 vol.% of CO, 11.0 vol.% of CO2, 2.0 vol.% of CH4, 0.4 vol.% of C2 hydrocarbon, 35.5 vol.% of N2, 9.1 ppm of H2S, and 5.3 ppm of COS . The H2S, COS, and CO2 in the obtained gas in this case were removed through the desulphurization tower and decarbondioxide installation during gas compression up to 13 MPa. As a result, the cleaned gas was 25.2 vol.% of H2, 30.8 vol.% of CO, 40.6 vol.% of N2, 2.5 vol.% of CH4 0.9 vol.% of CO2, less than 5 ppbv of H2S, and less than 5 ppbv of COS. The hydrocarbon liquid fuel was produced from the cleaned gas by the FT reactor. As a result, the CO conversion was 36.2%, H2 conversation was 76.7%. The selectivity of CO2, CH4, C2, C3, C4, and C5+ was 14.6%, 8.3%, 1.3%, 1.6%, 1.2%, and 73.0%, respectively. From this result, 1.9 L of liquid fuel was obtained from 13 kg of woody biomass on a dry basis by the bench-scale BTL plant per day. In the future work, we are planning to scale up to the production capacity of 16 L of liquid fuel per day.