Heat transfer in an externally heated rotary kiln: Preliminary results obtained with a new experimental device
Résumé
Rotary kilns are widely used gas/solid reactors encountered in several branches of the chemical industry. They are a key element in the production processes of cement, lime and pigments, for the reduction of ore in extractive metallurgy and for the pyrolysis of solid waste. They are also used to convert uranium fluoride into uranium dioxide for the production of nuclear fuel.
In this kind of device, hydrodynamic, thermal and chemical modelling processes are linked, as it is clear that the temperature profiles of the solid and the gas in the kiln directly influence the chemical reaction kinetics that occur. It is thus essential to be able to calculate precisely the temperature of the solid and of the gas at any point in the kiln and to understand the heat exchanges in the kiln.
Various correlations are reported in the literature for estimating the heat transfer coefficients in rotary kiln. However, for a given kiln, the heat transfer coefficient values calculated by using these correlations are highly scattered. Moreover, experimental measurements of heat transfer in rotary kilns are scarce.
The aim of this work is thus to design and construct an adaptable experimental setup to study heat exchange in rotary kilns. A key point is that the operating mode of the experimental setup must be similar to those of the rotary kilns used for the conversion of uranium. In particular, our kiln is externally heated and equipped with lifters.
The design of our experimental device will be described, focusing on the heating mode chosen and on the instrumentation. A special attention will also be devoted to the preliminary results obtained concerning the influence of the solid flow rate and the rotational speed on the heat transfer coefficient between the wall of the rotary kiln and the solid flowing through the kiln.