Energy Saving Sludge Incineration in Stuttgart's Central Sewage Works, F.R.G.

Abstract

The sludge of the main sewage works of Stuttgart is incinerated since 20 years around the clock. Now it was necessary to renew and extend great parts of the old installations. The new conception ought to avoid odors and save energy. It is now in operation for about one and a half years and enables not only an autothernic incineration but also an extensive utilization of the excess heat. Gravity thickening and mechanical dewatering (centrifuges) are same as before. New are the construction of the incinerator (now fluidized bed oven) and the devices for using the heat. The hot gases leaving the incinerator have a temperature of about 900 °C and are in practice odorless. They are cooled in a steam boiler down to 250 °C. The produced steam heats sludge dryers (rotating disc system) which reduce the water content of the centrifuges sludge cake down to about 50%. The 100 °C warm vapor of the dryers is condensed with liquid sludge before its dewatering, and the warm centrate can be finally used for heating purposes (rooms and digesters).