J. Yang et al., Determination of the overall heat transfer coefficient in a vacuum pyrolysis moving and stirred bed reactor, CHEM ENG R, 78(A4), 2000, pp. 633-642
A novel moving and stirred bed reactor with a high heat transfer capacity h
as been operated to achieve the thermal decomposition of used tyre particle
s under vacuum. The overall heat transfer coefficient determined in this re
actor reaches 200-250 W m(-2) K-1, a value exceeding the levels obtained in
conventional rotary kilns and multiple hearth furnaces. In order to design
large scale stirred bed vacuum pyrolysis reactors, both experimental and t
heoretical studies were carried out to understand the heat transfer mechani
sm and to determine the heat transfer coefficient in the reactor as a funct
ion of the operating conditions. In this work, the heat transfer coefficien
ts under different agitation speeds up to 22.5 rpm were measured. The heat
transfer coefficient was found to increase with the agitation speed, propor
tionally to (1/t(mix))(1/2). A Schlunder's modified model was used to descr
ibe the correlation between the heat transfer coefficient and the operating
conditions. Calculation of the partial heat transfer coefficients during t
he three pyrolysis evolution periods revealed the influence of the chemical
reactions, the phase change and the feedstock thermal property variation o
n the overall heat transfer coefficient during the vacuum pyrolysis of tyre
particles.