Thermochemical treatment of sewage sludge by integration of drying and pyrolysis/autogasification

Abstract

An integrated treatment of sewage sludge by drying and pyrolysis/autogasification was proposed. First, the experiments of sewage sludge (SS) drying and pyrolysis were performed in TG/MS set-up and the kinetic experiments were evaluated. Additionally, SS was investigated by rheometry, elemental analysis and X-ray powder diffraction; the product, – pyrolytic coke was also analyzed by elemental analysis and XRD. Then the experiments were performed in a pilot scale system (at the feed rate of 40 kg/h) containing a contact dryer SHTS, Kenki Co, and Spirajoule® pyrolysis reactor. Two types of SS from a wastewater treatment plant (WWTP) near Compiegne, France with and without lime were investigated. The pyrolysis was performed at temperatures of 400 °C and 800 °C for SS with lime and in 800 °C for SS without lime, for the sludge residence time of 15 and 20 min. The pyrolytic gas possesses high calorific value (up to 19 MJ/m3) and could be totally utilized for low-pressure steam production necessary for SS drying. Based on the obtained results, scaling up of the integrated processes of drying and pyrolysis was performed in a mobile unit with a capacity of 100 kg/h, which was constructed and assembled in a shipping container and tested at a WWTP in Elblag, Poland. The energy balance for the integrated process of drying and pyrolysis/ autogasification is presented in a Sankey's graph.