Torrefaction as a way to increase the waste energy potential

Abstract

Torrefaction is the thermal treatment process that has beneficial effects to upgrade the properties of solid fuels. Torrefaction of waste is currently of special interest due to the possible improvements of waste properties in terms of its application as an energy source. The unfavorable properties of waste fuel (low grindability, low energy density, high moisture content, irregular shape and size, biological instability and hydrophilicity) can be significantly reduced by the application of the torrefaction process. This article focuses on the beneficial effects of municipal solid waste torrefaction. It was observed that the torrefaction significantly avoids the fragmentation of waste pellets during mechanical treatment and enhances the durability and hydrophobicity. Maximal water uptake after 72h immersion was 0.72 kg of water/kg of fuel (dry) in the case of raw MSW pellets, whereas this value in the case of torrefied MSW pellets was 0.34 kg of water/kg of fuel (dry). For torrefied MSW, the durability, the compression strength and the shear strength were kept at the almost invariable level of >99%, >3 MPa, and >33 MPa. Due to a poor ability to grind, a torrefied waste application should be rather considered in a fluidized bed or grate furnace technologies.