Analysis of a Rotary Dryer: Drying of Wood Particles

Rotary dryers, long used by the particleboard industry, are being put to growing use in the area of hogged fuel drying. Lack of information about the design and operating technology of rotary dryers, however, combined with demand for greater efficiency in all modes of production, call for a closer examination of the rotary drying process. This study involved the development of a computer program that simulates the rotary drying process. The simulation model is based on a theoretical development of momentum, heat, and mass transfer fundamentals. Two sets of data generated by experiments with a commercial dryer were compared to the simulation program’s predictions. A radioactive tracer technique was used for retention time measurements. A separate drying experiment generated temperature and moisture content readings along the length of the dryer. The simulation program’s predictions were very close to the actual measured results, with a percent root mean square error of 14.2 for retention time and 22.2 for the outlet particle moisture content. The gas particle interaction controls the retention time and the rate of heat transfer; this interaction results in an optimum gas flow rate which maximized drying. The sequential development of the simulation model allowed a detailed examination of the physical processes involved in rotary drying and put into perspective many of the interrelationships among the numerous rotary drying parameters, including gas flow rate, gas temperature, particle moisture content, and particle size.

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