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Gasification of sawdust in a fluidized bed Shake, Fon-Yun


Hemlock sawdust with an average size of 0.67 mm and moisture content 5% was gasified in a 7.6 cm diameter fluidized bed with four different fluidizing media, namely, nitrogen, carbon dioxide, air and a mixture of steam and nitrogen. The static bed height was 20 cm and the bed material was 0.55 mm diameter Ottawa sand. The bed was operated at 1 - 1.5 times the minimum fluidization velocity. The major objective of the present study was to examine the quality of the gas produced with the different gasifying media as a function of the reactor temperature. Due to the difficulty in controlling the solid feedrate, it was not possible to maintain the gas/dry solid ratio (w/w) constant for runs using a particular fluidizing medium. The dry solid feedrate varied from 0.03 to 0.24 g/s, and for most runs, it was in the vicinity of 0.1 g/s. Both production rate and quality of the gas generally increased with temperature and were very sensitive to the type of fluidizing medium used. For nitrogen pyrolysis, the net gas heating value increases from 11.7 to 13.7 MJ/std.m³ when the temperature is increased from 410 to 690°C. Addition of steam to nitrogen produced gases of heating values 6.5 to 14.6 MJ/std.m³ on a nitrogen free basis, as temperature increased from 420 to 600°C. Carbon dioxide pyrolysis produces a gas with heating value-3.68-12.78 MJ/std.m³ between the temperature range 420-517°C. In contrast to the above systems, only low-Btu gas is produced with air gasification between 440 and 670°C. The calorific value of the raw gas produced at 670°C is 1.35 MJ/std.m³.

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