Two dimensional modeling of sewage sludge flow in a double-axis continuous paddle dryer

Abstract

A two-dimensional model based on the theory of Markov chain has been developed to determine the Residence Time Distribution (RTD) of municipal sewage sludge in a double-axis continuous paddle dryer. Based on the experiments, the paper proposes further corrections to simulate the transition. To characterize the sludge transition in the dryer, the parameter of internal recirculation based on one dimensional model is further developed. In addition, two parameters, the internal forward coefficient between two axes and the internal forward coefficient in one axis are introduced to characterize the new model. In absence of available correlation, solid hold-up of each cell in dryer and both the recirculation parameters are identified by fitting the model to experiments. Through analysis, the model demonstrates its ability to describe the sludge flow in a double-axis continuous paddle dryer by the experimental and simulation RTD curve. Finally, an analysis of influence factors highlights that recirculation coefficients are critical for the model while solid hold-up Hu of each cell controls the mean residence time and the final moisture content. In addition, the geometric residence time of sludge flow has a negligible effect on sludge flow for it has no effect on dimensionless variance. Moreover, compared with the recirculation coefficient between different axes R, the recirculation coefficient in one axis r has a negligible effect. In addition, recirculation parameters have no effect on mean residence time of sludge flow.