Simulation of industrial pneumatic conveying dryer with constant and falling rates of drying

Abstract

In the present thesis, a comprehensive mathematical model of the pneumatic conveying dryer, which is derived by combining two separate models proposed by Shigeru Matsumoto and David Pei, has successfully been developed. The model is able to describe the entire range of drying behavior which consists of two main periods, namely, surface water evaporation and internal moisture diffusion controlled periods. Testing of the model to validate its general applicability is done by comparison of the simulation results with the full-scaled industrial pneumatic coveying drying of cassava flour and the published industrial drying results of ilmenite, Glauber's salt, calcium carbonate, ammonium sulfate, and PVC resin. The comparison shows that the outlet solid moisture content and air humidity is accurately predicted by the model. However, the predicted solid and air temperatures show some discrepancies from the reported values due to the assumption of negligible heat loss from the dryer in the model. The simulation results are also compared to the predictions of the previous model proposed by W. Tanthapanichakoon and C. Srivotanai which assumes that, below the critical moisture content, the falling drying rate is proportional to the remaining free moisture content. The comparison shows that the present model gives better prediction and does not require an advanced knowledge of the value of the critical moisture content. Furthermore, the model is applied to improve the oprove the operating condition of the same flour dryer at the existing drying capacity and to search for a most suitable operating condition for increasing the drying capacity by 20%. The improved operating condition can reduce the operating cost by 35% when compared with the original operating condition.