Torrefaction of biomass from municipal solid waste fractions I: Temperature profiles, moisture content, energy consumption, mass yield, and thermochemical properties

In this study, construction demolition waste (CDW) and grass clippings (GC) from municipal solid waste (MSW) were torrefied in a blown glass reactor using microwave irradiation with respect to microwave power levels (250, 500 and 750 W), torrefaction residence time (15, 30 and 45 min), moisture content (12, 16 and 20% w.b.) for CDW and 64% w.b. for GC, under nitrogen-activated inert condition. This investigation reflects that microwave power levels and torrefaction time have positive correlation on the temperature profiles. It shows that higher microwave power level contributed to higher heating rate and final temperature. Microwave power level and torrefaction time have negative correlation with the moisture content of CDW and GC after the torrefaction process. The higher the power level and torrefaction time, the higher the reaction temperature and the lower the moisture content of the torrefied MSW. Increasing the microwave power level and torrefaction residence time resulted to a corresponding increase in the thermochemical properties of the materials. As a result of torrefaction of CDW, elemental carbon increased by 1.3-39% over that of the non-torrefied CDW; while the elemental carbon of torrefied GC increased by 9-21% over that of the non-torrefied GC. The results show that the wetter the sample the less torrefaction energy is consumed and the more efficient the torrefaction process. At 500 W power level and 15 min torrefaction residence time of CDW, torrefaction energy of 4338 MJ/t and 3862 MJ/t were expended for 12 and 20% m.c., respectively.