Torrefaction of landfill food waste for possible application in biomass co-firing

摘要

Highlights•Temperature had a more pronounced effect on quality of biochar as compared to residence time.•Biochar had similar fuel properties to bituminous coal.•Aromatic compounds responsible for tar formation were produced at high temperatures.•High temperatures were associated with low energy yield.AbstractGreenhouse gas emissions and municipal solid waste management have presented challenges globally. This study aims to produce a high-quality biochar with properties close to bituminous coal from landfill food waste (FW). FW was analyzed by proximate and ultimate analyses to determine its fuel properties and elemental composition before torrefaction. Temperature was varied from 200 to 300 °C at a constant residence time of 40 min and 10 °C/min heating rate. Calorific value, mass yield, energy yield and energy density were computed and used to determine the quality of the resulting biochar. Quality of raw food waste was also determined by elemental analysis. Thermal evolution was then investigated using hyphenated Thermogravimetric Analysis (TGA) and Fourier Transform Infra-Red Spectrometry (FTIR). Torrefaction was done at 225 °C, 275 °C and 300 °C. The calorific value was upgraded from 19.76 MJ/kg for dried raw food waste to 26.15 MJ/kg for torrefied food waste at the appropriate conditions which were 275 °C, 40 min and 10 °C/min. The higher heating value was comparable to that of bituminous coal from Anglo Mafube in South Africa. Elemental analysis of biochar showed an increase in carbon content with temperature due to loss of oxygen containing volatiles. This agreed with TG curves and FTIR spectra which confirmed release of H2O, CO and CO2. This resulted in a more hydrophobic solid fuel with high energy density. Food waste can therefore be upgraded to a biochar with similar fuel properties as pulverized coal used in coal fired boilers.