Effect of Rice Husk Torrefaction on Syngas Production and Quality

The aim of this study was the production of a good quality gasification gas (syngas) with rice husk residues. This material was torrefied before gasification with the aim of improving this last process, and the effect of torrefaction time and temperature was investigated. The variation of temperature from 200 to 300 degrees C decreased moisture and volatile matter and, consequently, increased higher heating value (HHV). The increase of reaction time from 30 to 60 min at 250 or 300 degrees C had a milder effect than the rise of torrefaction temperature. The optimum conditions for the rice husk torrefaction prior to gasification were 250 degrees C and 30 min, as the torrefied material presented an HHV of 22.1 MJ/kg daf and an ash content of 17.7%. The torrefaction increased the rice husk in extractives 14.8% (vs 12.6% in the raw material), mainly in nonpolar extractives and lignin (36.4% vs 28.9%). Py-GC/MS analyses determined that raw rice husk presented a monomeric composition of lignin (H/G/S) of 4:12:1 and ratio of carbohydratesto lignin of 3.3 while the torrefied material showed, respectively, 3:9:2 and 3.9. Compared with the raw rice husks, the gasification of torrefied rice husk at 250 degrees C presented a syngas poorer in CO2 (39% vs 24%) and richer in H-2 (31% vs 36%) and CO (17% vs 24%) and produced less tar (7.6 g/m(3) vs 3.5 g/m(3)) but released more pollutants (186 vs 92 ppmv of H2S and 1284 vs 734 ppmv of NH3).