Engineering analysis of a rotary dryer : drying of wood particles

Graduation date: 1984Rotary dryers are the most commonly used wood drying system in the particleboard industry. These dryers also play an increasingly important role in drying wood residues for fuel. Many potential benefits may be realized through an improved understanding of the rotary drying process. A rotary dryer simulation model was developed, in the form of a computer program, for the purpose of analyzing the drying behavior of wood particles. The model is applicable to single pass rotary drums, with or without a centerfill flighting section. Modifications to the base program could be made to allow for alternative rotary drum designs, such as multiple pass drums. The approach used in the model development analyzed the rotary drying process in a sequential manner. Beginning with a study of particle residence time in a rotary drum, the process of heat transfer, and then mass transfer, were incorporated to yield a complete rotary dryer simulation model. The resultant computer program does not require empirical constants or equations developed for a particular rotary dryer system. Experiments on a commercially manufactured rotary dryer were performed to check the performance of the simulation model as a predictor of overall residence time and drying behavior. The variables tested were drum rotation rate, gas flow rate, and inlet gas temperature. Measurements of gas temperature, particle temperature, and particle moisture content were obtained along the drum length. Comparison between the predictions and the measured results were good, indicating a percent root mean square error of 22.2 in the prediction of the outlet particle moisture content. A series of computer simulation trials were performed to check the affect of inlet particle moisture content, blend-box gas temperature, drum diameter, air leakage, drum length, gas volumetric flow rate, particle size, particle sphericity, drum speed, and angle of repose on dryer behavior. It was discovered that an optimal gas flow rate exists at which the greatest extent of drying may be achieved. In addition, the presence of centerfill flights enhances the extent of drying in a rotary dryer. The rotary dryer simulation model developed in this study should prove useful for optimizing process parameters in the drying of wood particles