Evaluation of ash related problems during sewage sludge combustion

A good function of waste-to-energy installation requires knowledge of the combustion characteristics of the fuel and fusion characteristics of the ash produced in the combustion process. Sewage sludge could be considered as renewable fuel due the high quantity of organics of sufficiently high calorific value. The combustion of sewage sludge can cause operating problems due to high ash content containing mineral compounds. This paper presents the oxide composition of three kinds of sewage sludge ashes and the influence on the slagging and fouling process in combustion. For comparation, two coal samples were selected, a low and a high rank coal. The mineral matter were investigated by the X-ray fluorescence analytical technique using the Rigaku CG X-ray Spectrofluorimeter. The evaluation of slagging and fouling process was performed on the basis of some indices: the basic oxides, the base-to-acid ratio, the slagging index and the fouling index. The conclusion based on experimental studies is that depending on mineral content the sewage sludge ash can cause high to moderate slagging and fouling hazard.