A Simple and Effective Model for Modeling of Convective Drying of Sewage Sludge: The Reaction Engineering Approach (REA)

Sludge drying is an essential step to reduce the cost of waste treatment but design of sewage sludge dryer is still relatively complicated since the drying kinetics is influenced signficantly by shrinkage, cracking and skin formation which occur during drying. In this study, the REA (reaction engineering approach) is implemented for the first time to model the convective drying of sewage sludge, a highly shrinkable material. The equilibrium activation energy (ΔEv,b) is evaluated according to the corresponding drying air humidity and temperature. This is combined with the relative activation energy (ΔEv/ΔEv,b), generated from one accurate drying run to produce the activation energy, which describes the internal behavior of the samples during drying. A good agreement between experimental and predicted data is observed. The REA is shown to perform comparable or even better than the classical diffusion-based model. It can be said that the REA can model the convective drying of sewage sludge well. The REA can be implemented for further applications including design and evaluation of sludge dryer.