Pretreatment of biomass by torrefaction |
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Authors: | GuiJun Wang YongHao Luo Jian Deng JiangHong Kuang YunLiang Zhang |
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Institution: | (1) CREAR – Research Centre for Renewable Energy and RE-CORD, University of Florence, Florence, Italy;(2) ENEA - Laboratory of Technology and Equipment for Bioenergy and Solar Thermal, C.R. Trisaia, 75026 Rotondella, MT, Italy;(3) Spike Renewables s.r.l., Florence, Italy |
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Abstract: | Agricultural biomass has some drawbacks such as high moisture content, low energy density and wide distribution and as a result,
the cost of transport and storage are high. Moreover, raw biomass has poor grindability so its use in a pulverized boiler
or entrained flow gasifier is difficult. Torrefaction is a mild pyrolysis process carried out at temperatures ranging from
200°C to 300°C to deal with these problems. The cotton stalk and wheat straw were torrefied in a fix-bed reactor at moderate
temperatures (200°C, 230°C, 250°C, 270°C and 300°C) under N2 for 30 min. The biomass chars after torrefaction had higher energy density and improved grindability characteristics compared
with raw biomass and they also showed hydrophobic characteristics. The volatiles consist of a condensable fraction and a non-condensable
fraction. The former mainly contained water and tar (organic products but mainly acetic acid). The non-condensable products
are typically comprised of CO2, CO and a small amount of CH4 and even trace H2. The volatiles increased with an increase in the torrefaction temperature but the solid yield and the energy yield decreased.
However, the grindability and energy density of the biomass char showed great improvement. A kinetic study on the generation
of the main non-condensable gases was undertaken and we conclude that the gases are formed by parallel independent first-order
reactions. Characteristic kinetic parameters for the generation of each gas were determined. |
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Keywords: | agricultural biomass torrefaction pretreatment grindability kinetics |
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