Preventing transport of sewage sludge over long distances and avoiding incalculable costs by outsourcing sludge disposal were the objectives of this project. Under the leadership of the public utility Stadtwerke Crailsheim GmbH, 27 municipalities in southern Germany set up a special-purpose association, KSV GmbH. This special-purpose association disposes of the regional sewage sludge in a Pyrobustor.
Approximately 18,000 tons of dewatered sewage sludge, containing roughly 25% dry matter, are collected every year from the participating municipalities. Prior to thermal treatment in the Pyrobustor, the sewage sludge is converted into granulated material with 88% dry matter.
The Pyrobustor is sized for a throughput of 1450 lbs/hour or 5,070 tons/year (at 7,800 hours/year operation) of dry, granulated material with a calorific value of 5,244 Btu/lb. In this case, surplus heat discharged from the system after the combustion chamber is used to generate steam. The 175 psig, 375ºF saturated steam is used for heating the drying plant thus closing the energy cycle. Primary energy from fossil fuel is not required.
The heat energy which is not needed for drying the sewage sludge can be delivered costeffectively to neighboring plants.
Uses of the Pyrobustor outlined here can play a major role in solving the problems with sewage sludge disposal. With the Pyrobustor, sewage sludge is converted into usable heat energy and inert ash, disposable in landfills. One aspect of particular interest is the possibility of erecting the Pyrobustor plant on the site of the waste water treatment plant with a direct link to the sludge drier. It goes without saying that the manner in which the heat is used to save primary energy can be selected in accordance with the specific case concerned.
Considerable interest is being displayed at present, especially by municipal authorities and special-purpose associations. Use of the Pyrobustor offers them economic and ecological advantages and above all certainty for disposability of the sludge.