DEVOLATILIZATION AND PYROLYSIS OF REFUSE DERIVED FUELS - CHARACTERIZATION AND KINETIC MODELING BY A THERMOGRAVIMETRIC AND CALORIMETRIC APPROACH

A characterization of pyrolysis behaviour of different refuse derived fuels (RDFs) under heating rates typical of conventional pyrolysis processes is presented. The results of thermogravimetric analysis (TGA) and differential scanning calorimetry (d.s.c.) on different RDFs, and on some materials which have been considered 'key components' towards thermal degradation characteristics of RDFs, are reported. The RDF weight loss curve presents two distinct weight loss steps attributable, respectively, to cellulosic materials and plastic degradation. Samples from different plants and different municipal solid waste (MSW) feedstocks show the same qualitative behaviour. In interpretation of the experimental results, the assumption has been made that the pyrolysis rate of thermal degradation of RDF can be considered as the sum of the rates of the main RDF components: paper (cellulose), wood-like materials (cellulose, lignin and hemicellulose), plastics mainly polyethylene (PE); and that each component contributed to the formation of this sum to an extent proportional to its contribution to the composition of the RDF. On the basis of these data and by means of a simple mathematical approach a method is proposed which provides a simple tool for RDF characterization and, in particular, evaluation of plastic content. A kinetic model has been developed, based on the assumption that the RDF degradation rate is the weighed sum of the rates of primary reacting species: cellulose, lignin, hemicellulose, PE. Simplified kinetic pathways were used for the description of the degradation processes of RDF components. The model allows quantitative prediction of RDF weight loss and char yield at least at the heating rates used in present work.