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 0, and 22-45 min for temperatures. Depending on the fluctuation frequency, the corresponding phase shifts are 39-96 degrees for outlet O-2, 138-336 degrees for bed temperature and 80-336 degrees for free-board temperature. (C) 2007 Elsevier Ltd. All rights reserved.