Optimization of low-temperature torrefaction for rice straw upgrading

Rice straw is an agricultural waste most left in the field and is burned prior to the next crop. It is a biomass resource which has high potential to be used as an alternative fuel. However, it contains low fixed carbon and high volatile matters, giving low fuel characteristics. Hence, upgrading rice straw via low temperature torrefaction is of interest. Torrefaction is a thermal chemical process similar to drying, but it requires higher temperature with air absence environment. In this present work, central composite design is used for experimental plan. Two pertinent parameters, temperature and reaction time vary in ranges of 200-300 °C and 25.7-54.3 minutes, respectively. Optimization of the torrefaction is made by considering energy yield (%) and specific energy consumption (Wh/g) used during the process. The results show that at 200°C, 40 min, the test gives the best energy yields and specific energy consumption by 96.16% and 23.73 Wh/g and at 215°C, 30 min, the second best of 94.06% and 25.50 Wh/g are obtained. These two conditions are recommended for rice straw torrefaction.