Torrefaction of Municipal Solid Waste (MSW) Pellets using Microwave Irradiation with the Assistance of the Char of Agricultural Residues

In this study, the effects of the addition of char of agricultural residue (corncob, palm shell, straw, and bagasse) as a microwave absorber on the microwave torrefaction of municipal solid waste (MSW) pellets at 500-800 W for 4-12 minutes were investigated. The experimental results revealed that the torrefied MSW pellets with the addition of microwave absorbers had lower mass yields but higher temperatures than did the torrefied MSW pellet without the addition of microwave absorber. The addition of char of bagasse resulted in the lowest mass yield and the highest temperature of the torrefied MSW pellet. Moisture was completely removed from the MSW pellets after being torrefied for 8-12 minutes. The addition of microwave absorber and the increases in torrefaction time and microwave power caused the mass yield and the remaining amount of volatile matter (VM) of the torrefied MSW pellet to decrease. However, the remaining amount of fixed carbon (FC) was found to be relatively constant, approximately at the amount of FC in the raw MSW pellet. A decrease in VM content was found to be highest for the torrefied MSW pellet with the addition of char of bagasse. The amount of carbon (C) was found to be highest, whereas the amount of oxygen (0) was found to be lowest, for the torrefied MSW pellet with the addition of char of bagasse. The heating values of the torrefied MSW pellets with the addition of microwave absorbers were found to increase from that of the raw MSW pellet, and the heating values of the torrefied MSW pellets with the addition of char of straw and bagasse were equivalent to that of sub-bituminous coal. The use of microwave power of 650 W and the addition of char of bagasse were the most suitable combination, as they yielded the torrefied MSW pellet with the highest heating value, a reasonably high energy yield, and an appropriate amount of VM. (C) 2017 The Authors. Published by Elsevier Ltd.