Investigations On Energy Recovery Potential of Sewage Sludge Through Thermochemical Conversion Methods

Abstract

Waste disposal is one of the major challenges faced by countries worldwide. Strict environmental regulations and opportunities for waste to energy conversion have resulted in increased interest in the recycling and utilization of wastes. The present work deals with investigations on energy harnessing from sewage sludge (SS) generated from waste-water treatment plants, adopting a thermo-chemical conversion route. The complex reactions during the thermo-chemical conversion processes depend on the physical and chemical properties of the feedstock. Detailed characterisation of a non-conventional biomass feedstock like sewage sludge is essential for assessing its behaviour during the thermo- chemical conversion processes. A comprehensive study of relevant physical and chemical properties of sewage sludge was performed initially to assess its distinct characteristics. newlineGasification and pyrolysis have been identified as the potential methods for the valorisation of dewatered sewage sludge. The feasibility of sewage sludge as feedstock in a typical downdraft gasifier was experimentally tested. Temperature and equivalence ratio (ER) significantly influenced the product gas generated during the sludge gasification. The average mole fraction of the product gas components: H2, CO, CO2 and CH4 were found to be 9.76%, 11.80%, 9.84% and 2.97%, respectively, for the temperature range of 900 K to 1150 K. The effect of temperature on the mole fractions of the product components, cold gas efficiency, carbon conversion efficiency, and lower heating value of the product gas was systematically studied. newlineModel-based analysis of gasification, with sewage sludge as the feedstock was also carried out through the formulation of a Stoichiometric Thermodynamic Equilibrium Model (STEM). A good agreement between the simulation results through STEM and experimental results were observed. Investigations on suitability of sewage sludge for gasification in a fluidised bed system were also carried out