In this paper, a mathematical model is developed for the simulation of a large-scale sewage sludge incineration plant. The model assumes the bed to consist of a fast gas phase, an emulsion phase and a fuel particle phase with specific consideration for thermally-thick fuel particles. The developed model is employed to predict the dynamic response of the bed combustion to fluctuations in sludge feeding-rate. Calculation results indicate that the bed combustion is sensitive to fluctuations with response times greater than 30 min, but severe delays exist for both outlet oxygen level and bed temperatures; from 6 to 13 min for O_2 and 22-45 min for temperatures. Depending on the fluctuation frequency, the corresponding phase shifts are 39-96° for outlet O_2, 138-336° for bed temperature and 80-336° for freeboard temperature.
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