Demonstration-scale high temperature slagging gasification of sewage sludge

Abstract

This study explores the treatment of sewage sludge via high temperature slagging gasification process as a strategic waste management approach to convert this challenging waste stream into highly stabilized and reusable slag which can be applied in the construction industry as building material. A demonstration scale slagging gasification research facility for municipal solid waste (MSW) with a designed treatment capacity of 11.5 tonnes per day is employed to determine the feasibility of the mono sewage sludge slagging gasification in the direct melting furnace system (DMFS), to understand the suitable operation controls, engineering requirements, and technical challenges of the sludge gasification process, and to assess the generation and properties of the resulted by-products. For comparison, slagging gasification testing of MSW, the co-gasification of MSW with sewage sludge (at approximately 1:1 ratio) and the mono sewage sludge slagging gasification are performed, respectively, with a total operation period of around 300 hours. Significant fluctuations of the temperature profiles in the slagging gasifier are observed during mono sewage sludge operation. Additional biomass charcoal was required to aid the melting of ash residue from sludge. SO2 and NOx emissions from the mono sludge operation are higher than usual MSW operation with spikes of SO2 observed. Substantial amount of particulates are deposited on the wall of the slagging gasifier and the duct connecting the gasifier to secondary combustion chamber (SCC). Slag generated from the mono sludge operation shows superior leaching performance according to the waste acceptance criteria set by the EU Landfill Directive and is comparable to MSW slag, demonstrating the capacity of the slagging gasifier to treat diverse waste streams. Life cycle assessment (LCA) illustrates the advantages, limitations and hotspots of the gasification process for further improvement.