Converting Agricultural Residues to Bioenergy by Microwave-Induced Torrefaction
Date Issued
2010
Date
2010
Author(s)
Wang, Mei-Ju
Abstract
Torrefaction is a mild pyrolysis process which improves properties of fuel. This study utilized single-mode microwave irradiation to induce torrefaction of biomass wastes. Comparing to the conventional method, microwave-induced torrefaction is more rapid, efficient and economical. In this study, two types of agricultural residues, rice husk and sugarcane residue were torrefied under an inert atmosphere in an industrial microwave device. . Different parameters, including microwave power level, processing time, water content of biomass and particle size of biomass, were varied in the experiments to optimize the process.
Based on the experimental results, it could be concluded that increasing microwave power enhanced the heating rate and the maximal temperature of torrefaction. However, it is worthwhile noting that torrefaction might go beyond the original expectation when the microwave power was relatively too high. On the other hand, when the microwave power fell below a level, the reaction would not reach completion. This study suggests that the microwave power should be set between 250 W - 350 W for torrefaction of these two agricultural residues. Furthermore, the caloric value enhancement of processed rice husk could reach 26% under a microwave power of 250 W. With regards to processed sugarcane residue, the caloric value enhancement could achieve 57% under the same operating condition.
This study also investigated the effects of water content and particle sizes of biomass on the torrefaction process. Under lower microwave power settings, water content of biomass, ranging 5 to 10%, helped to increase mass reduction and caloric value. Moreover, particle size of biomass was also an important process parameter. When the particle size was too small, the torrefaction process would adversely go beyond expectation and ended up with a reduction in the caloric value.
Microwave-induced torrefaction also changed properties of the solid char. Elemental analysis showed that carbon content of the solid char also increased with the microwave power applied. However, oxygen content of the solid char decreased during the process. It implied that microwave-induced torrefaction is more efficient than the conventional method for O/C ratio reduction.
In conclusion, microwave-induced torrefaction can shorten the processing time when compared to the conventional method. It can achieve more efficient torrefaction. The results of this study suggest that microwave-induced torrefaction be a promising technology with a great potential.
Subjects
microwave-induced torrefactio
pyrolysis
agricultural residues
O/C ratio
caloric value
Type
thesis
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