Improved Efficiency of Sewage Sludge Incineration by Preceding Sludge Drying

Abstract

Normally, mechanical dewatering of sewage sludges is not sufficient for a self-supporting combustion, even if combustion is ensured in the fluidized bed furnace. The heat balance can be compensated by firing additional fuels of higher calorific value and a preceding sludge drying using the heat, which is generated during combustion. The most favoured solution is an indirect drying in special equipment adapted to the state of the sewage sludge to be burnt. Heating surfaces and the steam transfer the thermal energy of the flue gases to the mechanically dewatered sludge. The development of malodours and pollutants in the vapours is controlled by an appropriate process flow. The process entails not only an economy of primary energy but also an increase in the furnace throughput. In Wuppertal-Buchenhofen, the fluidized bed fired sludge incineration plant has been operating for 12 years.In the near future it will be brought up to date by retrofitting such a drying system. The foreseeable effects have already been investigated and operational experience gained with other plants has been taken into account. The technical modifications, which are being considered, the operational influences expected, as well as all consequences with regard to investment and operating costs, have been outlined.