Optimisation and modelling of pyrolysis processes focused on the treatment of municipal solid waste scaled towards decentralised energy from waste systems
Energy from Waste (EfW) technologies are beneficial for both energy generation and as a waste management option. However they face significant challenges due to the heterogeneous nature of municipal solid waste. The overall aim of the research reported in this thesis was therefore to explore some of the problems which hinder the development of commercial scale EfW technologies. A laboratory scale pyrolysis reaction rig has been developed to investigate the effect of temperature, residence time and fuel type on the pyrolysis products. Investigations were also undertaken to establish the composition of gas produced from the pyrolysis of typical waste feedstocks in two commercial scale pyrolysis rigs. An empirical model has been developed to predict the pyrolysis behaviours on a larger scale and comparisons have been made with data from the commercial scale rigs.\ud The research findings showed that the majority of the reduction of mass during pyrolysis occurred within the first 5-10 minutes with a loss of up to 70 % at 550 °C and up to 77 % at 700 °C for paper, newspaper and cardboard. Paper, newspaper and cardboard behaved similarly with solid, liquid and gaseous fractions of approximately 33 %, 53 % and 13 % respectively. Products from the plastics components varied significantly; PET produced the highest gaseous products (42 %) and HDPE produced the highest solid products (45 %). An increase in pyrolysis temperature increased the gaseous products from paper to 34 % to the detriment of liquid and solid yields. The main gases produced from the pyrolysis were found to be CO2, CO and H2, except for the pyrolysis of PVC where the main gases produced, from the high content of hydrochloride, were not identified in this study. An increase in pyrolysis temperature was found to increase the production of CO and H2. The gas produced from commercial rig 1 mostly consisted of CO2 due to the low temperature and the addition of air to the pyrolysis chamber. The gas produced from commercial rig 2 consisted of high volumes of CO and H2 suggesting the rig was operating at a temperature above 550 °C. An empirical model was developed based on laboratory data to allow prediction the effect of a change in MSW composition on the pyrolysis gas. It was found that the addition of newspaper to a waste mix led to a higher production of CO and therefore a higher HHV.\ud In general, the results of this study suggest that the laboratory scale pyrolysis rig used in this study and the empirical models developed, can be employed to predict the behaviour of larger scale commercial pyrolysis systems. However, further experimental investigation on the pyrolysis behaviours of mixed waste samples, especially plastic fractions, is hereby proposed.