The effects of rotating speed and internal structure on the performance of an externally heated rotary kiln for waste pyrolysis were investigated. A newly developed method was adopted to evaluate the overall heat transfer coefficient
km-w from the inner wall to the wastes for this purpose. The experimental results revealed that
km-w monotonically increased with the number of lifters and their height. When six lifters 200 mm in height were attached to the inner wall of the kiln, the mean value of
km-w increased from 38.6 W/m
2K to 45.3 W/m
2K at 2.7 rpm. In addition,
km-w increased to 50.1 W/m
2K when the rotating speed was increased to 4.0 rpm. In the water vaporization phase during the course of the pyrolysis process, the height of the lifters had a significant influence on
km-w. However, the number of lifters had a significant impact on
km-w in the pyrolysis phase of the plastic-based wastes. According to measurements, a 10 % increase in
km-w could be obtained when installing lifters to attain a ratio of lifter height
Hl to the thickness of the waste layer
Hw larger than 0.45 or when arc length between two lifters
Ll to the arc length of the interface between the wastes and the kiln wall
Lw was larger than 1.
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