Pyrolysis of sewage sludge : kinetic study

Abstract

A suitability of applying sewage sludge as pyrolysis material was realized as it has, on aeraged, volatile matters of 40 wt% and heating value of 9.7 MJ/kg. According to a survey of great number of sludge samples by thermogravimetric technique, five mass loss behaviors were found. The overall decomposition is under 600 C with a maximum rate at approximately 300C allthough decomposition at as high a 700C is possible according to carbonate degradation. Either pseudo single-,bi- or multi-component can be applied in general case with the confirmation of the primary gas evolution data. However, reaction can be more elucidated by analyzing sludge according to the biomass compositions such as lignin cellulose, hemicellulose and extractives. It is possible to compare between the sewage sludge and those compounds, including complex protein, in terms of mass loss behavior by themogravimetric and functionality by Fourier Transform Infrared Spectroscopy. That means, all those compounds might compose in sludge and effect to the overall decomposition kinetics. By reverse direction, the formulation of the blobal mass loss curve from individual components and detection of gas evolution confirms this hypothesis in low temperature region (<400C). At higher temperature, it is believed that the sludge is denatured caused by the reaction at low temperature, resulting in the extended decomposition at such high temperature.