THE PYROLYSIS OF MUNICIPAL SOLID-WASTE

Municipal solid waste in the form of refuse-derived fuel (RDF) was pyrolysed in a static batch reactor at pyrolysis temperatures from 300 to 720-degrees-C and at heating rates from 5 to 80 K min-1. Compositions and properties of the derived gases, pyrolytic oils and solid char were determined in relation to pyrolysis temperatures and heating rates. In addition, the separated components of the waste were individually pyrolysed in a thermogravimetric analyser (TGA) and compared with the thermal degradation of the total waste. Results from the static batch reactor showed that as the pyrolysis temperature was raised the percentage mass of solid char fell, whereas gas and oil products rose. At 20 K min-1 heating rate and 720-degrees-C pyrolysis temperature the product yield was 29.4% char, 53.2% liquid and 17.6% gas. There was a small effect of heating rate on product yield. The gases were identified as CO, CO2, H-2, CH4, C2H6, C3H8, with lower concentrations of other hydrocarbon gases. The calculated calorific value of the gases was high and they rose with heating rate, ranging from 13.9 MJ m-3 at 5 K min-1 to 18.0 MJ m-3 at 80 K min-1. The calorific values were: derived oils 25 MJ kg-1, and chars 19 MJ kg-1; they were essentially independent of the heating rates. Elemental analysis of the oils showed that they were highly oxygenated. FT-ir analysis of the oils indicated the presence of carboxylic acids, alcohols, phenols, alkanes, alkenes, ketones or aldehydes, aromatic, polyaromatic and substituted aromatic groups. The oils showed an increase in aromatic groups as the temperature of pyrolysis was raised. Separated components of the waste, including different plastics, paper, cardboard, fabric and wood, were pyrolysed in a thermogravimetric analyser at the same conditions as in the static batch reactor. The TGA thermograms indicated the different thermal-degradation profiles of the waste components, and showed that the lower-temperature thermal degradation of RDF can be attributed to cellulosic waste, and the higher-temperature degradation to plastic waste.