Torrefaction of Rice Straw and Biofiber
Date Issued
2012
Date
2012
Author(s)
Yang, Tuz-Zi
Abstract
Because of the greenhouse effect, environmental pollution and shortage of fossil fuel, the development of renewable energies is an important issue for the future. The most widely used renewable energy is biomass energy. However, the biomass has encountered several limitations in energy generation, including high moisture, hydrophilicity, low heating value, low energy density and low grindability, while biodegradable. Torrefaction can assist biomass overcoming those disadvantages so as to be applicable to the existing heating and energy generation systems. Therefore, torrefaction is one of the suitable pretreatments for converting agricultural waste to energy.
In this study, rice straw and biofiber were torrefied at 280, 300 and 320 oC with the residence times from 10 to 60 min. The biofiber examined is the product from the autoclaving of municipal solid waste. Key propesties of solid product (biofuel or biochar) and gas products were analyzed. The results indicate that after torrefation, biofiber becomes spontaneously combustible, thus lowering the heating value. For example, at 280 °C with 60 min torrefaction time, the high heating value in wet basis (HHMW) of torrefied biofiber is about 4309 kcal/kg. Therefore, it is suitable to co-fire the biofiber with coal directly without torrefaction.
HHMW of rice straw of 5025 kcal/kg torrefied at 280 °C for 50 min meets the coal standarnds D (HHMW > 5000 kcal/kg) of Taiwan Power Co. Torrefaction is completed when gas production rate and CO2 concentration decrease slowly after peakvalues. The mass yield, heating vale and pellet diameter of rice straw exhibit highly positive correlation. Therefore, these formation can be used to fleetly check whether the operation has reached the goal of torrefaction. For example, in batch reactor, one can directly estimate the heating value of biochar from mass yield. In continuous reactor, the mass yield and heating value can be directly estimated by the pellet diameter of biochar. The results indicate that the biochar from rice straw has the potential to replace a part of coal for either direct firing or co-firing.
Subjects
Rice straw
biofiber
torrefaction
energy density
predict heating value
Type
thesis
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