Investigation of municipal sludge gasification potential: Gasification characteristics of dried sludge in a pilot-scale downdraft fixed bed gasifier

This study presents the research results acquired from conducting municipal sludge gasification in a downdraft type gasifier at pilot scale. The assessment of the results was not only focused on syngas characteristics, but also on the gasification residues: char ash and glassy material. The gasification temperature was varied from 1000 to 1150 °C during the gasification trials. The produced high quality syngas was transferred to the engine to generate the electricity. About 1 kWh electrical power was achieved for approximately 1.2 kg municipal sludge gasified. Most of the heavy metals available in the sludge was found as fixed form in the glassy material. The gasification residues evaluated as valuable materials regarding their characteristics have reuse potential for different beneficial usage alternatives. Based on the costs for the investment and operation and incomes, the return on the investment for this pilot scale system was roughly found as 3.3 years. This study showed that the municipal sludge had an important fuel merit and the energy recovery from the sludge was possible via the gasification application. In this paper, the research results were discussed in detail to make better insight to full-scale applications as a promising alternative for sludge disposal.