Effect of Rice Husk Torrefaction on Syngas Production and Quality

Abstract

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 °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 °C had a milder effect than the rise of torrefaction temperature. The optimum conditions for the rice husk torrefaction prior to gasification were 250 °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 °C presented a syngas poorer in CO2 (39% vs 24%) and richer in H2 (31% vs 36%) and CO (17% vs 24%) and produced less tar (7.6 g/m3 vs 3.5 g/m3) but released more pollutants (186 vs 92 ppmv of H2S and 1284 vs 734 ppmv of NH3).

Enhancement of thermochemical properties on rice husk under a wide range of torrefaction conditions

“…This result can be attributed to the decreasing trend in the yields and calorific values of RH-torrefied products produced at longer residence time because of more releases of carbon and hydrogen by the intense devolatilization at the strict torrefaction conditions. Similar trends were obtained for the torrefaction of RH at 300 °C by increasing residence time from 30 to 60 min [48].…”

Torrefaction of Sorghum Straw Pellets in a Stationary Reactor with a Feeding Screw

“…Torrefaction is often used as a pretreatment method prior to pyrolysis/gasification to improve the quality of pyrolysis products and the yields of desired products. 9,10 The yields of H 2 and CO from the gasification of torrefied biomass increase, 11 which increases the calorific value of biogas. The decomposition of hemicellulose during torrefaction decreases the hydroxyl and O-acetyl groups in the biomass, decreasing the water and acids in bio-oil volatilized from biomass fast pyrolysis, 12,13 and the fracture of lignin side branches during high-temperature torrefaction decreases the production of phenols with side branches in bio-oil.…”

Integration of Gasification and Solid Oxide Fuel Cells (SOFCs) for Combined Heat and Power (CHP)

“…Milling to reduce particle size is another common pretreatment, but particle size depends on technology, fixed beds may process wastes up to 50 mm, while entrained flows require much smaller particles usually below 500 µm and fluidized beds in between (0.5-5 mm). On the contrary, some feedstocks require pelletization to increase density prior to gasification, decrease moisture and pathogen contents, facilitate inlet operation and improve uniformity and homogeneity inside the gasifier [10]. Torrefaction has also been considered as a pretreatment operation, as it increases energy density and feedstocks hydrophobic characteristics, thus allowing open air transportation and storage.…”

“…Torrefaction has also been considered as a pretreatment operation, as it increases energy density and feedstocks hydrophobic characteristics, thus allowing open air transportation and storage. Torrefaction treats feedstocks at 200-300 • C under minor air conditions for around 30 min [10].…”