Comparison of torrefaction and hydrothermal treatment as pretreatment technologies for rice husks

Many agricultural waste residues are generated in Southeast Asia while some areas in the region still do not have electricity. This study explores the potential effective utilization of agricultural residues in Southeast Asia to generate power. Firstly, visualization of the potential for energy generation was completed using a geographic information system (GIS). Secondly, a comparison of effectiveness was completed between the torrefaction and hydrothermal treatment of low-grade agricultural residues as pretreatment techniques for the modification of agricultural residues. In this study, the feasibility of utilizing rice residues was analyzed (i.e., rice husks, which are produced in large quantities in Southeast Asia) to determine their suitability for pretreatment as feedstock for power plants. This was assessed experimentally by focusing on the pyrolytic characteristics of the husks and the rate of ash change both before and after treatment, while the subsequent implications on transportation costs were also noted. The results indicated that the percentage of ash in torrefied rice husks was 26.7%, whereas the percentages of ash in rice husks that were treated with water or an NaOH solution were 13.96% and 8.87%, respectively. The reduction in transportation costs after compression was 90.8% for hydrothermal treatment and 88.7% for torrefaction.