The Gasification of Sewage Sludge in Bubbling Fluidized Beds

This paper gives the first measurements from a project investigating the gasification of dried sewage sludge in a laboratory scale, bubbling fluidized bed at atmospheric pressure. The aim of the work was to examine the reactions occurring in a fluidized bed gasifier rather than simply treat the reactor as a ‘black box’. Experiments were performed to investigate the rates of drying, devolatilisation, gasification and combustion. Thermogravimetric analysis, as well as batch fluidized bed experiments using mechanically dewatered, dried and pelletised municipal sewage sludges from different regions in the UK were performed. A comparison was made between the different samples of sludge and a low rank coal and softwood biomass. A distributed activation energy model (DAEM) for interpreting the kinetics of devolatilisation was also investigated. The model was able to reduce the results from several TGA experiments to a single curve characterised by a single parameter, the pre-exponential factor, A.