• Njeng, Alex Stéphane Bongo
• Clausse, Marc
• Dirion, Jean-Louis
• Vitu, Stéphane
• Debacq, Marie

Abstract

Rotary kilns are gas-solid reactors firstly used in the cement and lime industry. Nowadays, they are utilized in numerous other material processing operations such as calcining of petroleum coke, uranium dioxide production, reduction of ore in extractive metallurgy or pyrolysis of solid waste, for example.The device consists generally of an inclined cylinder, equipped or not with lifters, rotated axially and which can be either directly or indirectly heated. In the above-mentioned unit operation, hydrodynamic, thermal and chemical processes are strongly linked. Among the most important parameters influencing transfers (and reactions) occurring within the kiln is the residence time of solids. Hence, it is worth to characterize the influence of operational conditions on this key parameter. The best method to achieve this goal remains on the residence time distribution (RTD) measurement using the tracer technique. Several studies have been reporting on rotary kilns or drums of different size, but only few of them have been conducted on the solids behavior by the mean of RTD measurement. Nevertheless few authors reported the effect of operating parameters on the mean residence time (MRT) of solids and hold up. Others proposed correlations to predict the RTD curves or the MRT. Scarcer are investigations on the RTD in flighted rotary kilns. Finally, in these studies, the range of variation of the operating parameters is narrow in most cases. The aim of this experimental work is to understand and qualify the flow of solid materials in a rotary kiln using the tracer impulse-response technique. The solid material used was homogeneous sand with a particle size distribution of 0.4 to 0.8 mm. To characterize the material flow, sodium chloride of similar size distribution than the bulk flow was injected at the feed inlet. At the discharge end, samples were continuously collected. The samples were dissolved in distillated water and the conductivity was measured. Thus, RTD curves could be established. The effect of operating parameters, namely, rotational speed and slope of the kiln, dam height and feed rate of solids is investigated through the RTD curve, as well as the MRT of solids. Moreover, the effect of the presence of lifters and the shape of these lifters on the RTD is studied and discussed.

Topics

• pyrolysis
• impedance spectroscopy
• Sodium
• cement
• lime
• Uranium