Improvements in Pyrolysis of Wastes in an Externally Heated Rotary Kiln : (Measurements of the Overall Heat Transfer Coefficient from the Wall to Wastes)

概要

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Externally heated rotary kilns are the most appropriate furnaces to dispose of solid wastes using pyrolysis reactions. The goal of this study was to improve heat transfer in externally heated rotary kilns for waste pyrolysis. We experimentally evaluated the overall heat transfer coefficient km-w as it is an important property of heat transfer. The model wastes were pyrolyzed using an externally heated batch-type rotary-kiln pyrolyzer. Six pairs of thermocouples were attached to the inner and outer surfaces of the drum wall to measure the radial heat flux through it. The heat flux qm was calculated using the radial temperature gradient in the wall. km-w was calculated using the formula, km-w=qm/AdT, where A is the internal surface area of the wall, and dT is the difference in temperature between the inner surface of the wall and the wastes. qm and dT had the highest values when pyrolysis began. However, km-w had the lowest value when pyrolysis began and rose with an increase in waste temperature. When the mean temperature of the kilns inner wall was 555 °C, km-w rose from 22 W/m2K to 55 W/m2K. Consequently, a higher km-w appeared closer to the end of the drum in a continuous-type kiln.