STUDY OF SLAGGING/FOULING PROBLEMS IN SEWAGE SLUDGE FLUIDISED-BED INCINERATOR

摘要

Nowadays, the fluidised bed technology is one of the mostly used for the specific incineration of urban sludge. Although this technology is particularly suitable for sludge combustion, slagging/fouling can occur within the furnace, on the flue gas duct and/or heat exchanger. Numerous physical and chemical mechanisms are acting for the deposit formation and the bed agglomeration. Specifically during sludge combustion, condensation is a significant or even dominant phenomena. Operating combustion conditions and particles properties have also to be taken into account for a better understanding of the deposit formation and the bed agglomeration. However the sludge mineral matter, constituting 20% to 40% of their dry matter and the whole fly ashes, is often considered as the major slagging/fouling factor. More precisely we identified that Iron, Phosphorus, Chlorine and Sodium are the elements the more responsible for slagging/fouling while Calcium allows to decrease the ash fouling nature.Physical predicting methods exist but the ratios linked with the mineral content are the most employed. Above a certain limit, the molar ratios Ca/P and Ca/Na enable to predict that there is a little chance for slagging/fouling to occur. The usefulness of the combined ratios (Ca+Al)/P and Ca/(Fe+P) has been proved.