Abstract
Utilization of rice straw as an alternative fuel source to fossil fuel has been considered. However, properties such as water content, low heating value, less grindability, high bulk density, and high ash content are problems in such a biomass fuel supply chain. This study attempted to produce wood pellets mixed with torrefied rice straw (WPTRS) to solve the problems related to using rice straw as fuel. For that, preferred torrefaction conditions, such as torrefaction temperature and holding time, were determined by indicators of the grindability, energy loss, and heating value. As a result, the preferred grindability was found at torrefaction temperatures of over 220 °C. In terms of energy, we derived two viewpoints: i.e., if minimum energy loss is prioritized, the preferred torrefaction temperature is 220 °C, and for an increase in the heating value of rice straw, 280 °C was preferred. Next, WPTRS was produced using rice straw torrefied at 220 °C and 280 °C, and by changing the mixing ratio of rice straw to wood. Burning tests were conducted to clarify the WPTRS characteristics and the results revealed that the torrefaction at a temperature of 280 °C increased WPTRS’s heating value. In addition, the basicity can be used as a good indicator for clinker production when wood and rice straw are used as fuel.
Highlights
Renewable and sustainable energy is of global interest because fossil fuels have been exhausted and greenhouse gases are being emitted
For torrefaction temperatures less than 220 °C, the remaining heating value rate (RHVR) was still over 95%
The lower heating value (LHV) of torrefied rice straw increased with the torrefaction temperature because the reduction in weight of the rice straw accompanied by torrefaction was larger than the decrease in the volatile content of the rice straw
Summary
Renewable and sustainable energy is of global interest because fossil fuels have been exhausted and greenhouse gases are being emitted. In Japan, solar and wind power generation and electricity saving have been promoted by the feed-in tariff scheme. The share of biomass energy in electricity and heat is still low [2]. During 2011, Nanporo was the first town in Hokkaido that started a business to use rice straw pellets. To mitigate the clinker problem, Nanporo introduced a co-combustion process of rice straw pellets and wood pellets in the ratio of 1:1 [7]. The above shortcomings of rice straw for utilization as biomass fuels can be overcome by applying torrefaction, torrefaction requires energy. Our approach is to produce pellets using both wood and
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