ANALYSIS OF THE DRYING OF RESIDUAL SLUDGE: FROM THE EXPERIMENT TO THE SIMULATION OF A BELT DRYER

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Abstract
The drying of residual sludge is a current environmental problem not sufficiently described in the literature, hence research investigations on this dewatering process are required. This paper proposes a modelling of a conveyor dryer belt. However the study of residual sludges dewatering in order to design or simulate drying equipment requires some experimental investigations. An analysis in terms of drying kinetics is proposed in this paper. Specific experiments were also needed in order to better describe some particular aspects such as crusting, shrinkage, and particle size impact. According to these data some analytical expressions have been derived and integrated in a belt dryer model. The set of air operating conditions (T, RH, v) was reduced to a single parameter, the drying potential. The results of the simulations show that a conveyor belt dryer is not well adapted to activated sludge. This is essentially due to a crust phenomenon. For a PVC industrial sludge this kind of dryer is more efficient and allows drying with reasonable residence times. Several simulations were run in order to point out the relevant parameters of the process.