Dynamic behaviour of sewage sludge incineration in a large-scale bubbling fluidised bed in relation to feeding-rate variations

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 O2 and 22–45 min for temperatures. Depending on the fluctuation frequency, the corresponding phase shifts are 39–96° for outlet O2, 138–336° for bed temperature and 80–336° for freeboard temperature.