Solids Motion In Rotary Kilns: Characteristic Parameters And Their Detection

Rotary kilns are heat exchanger widely used in the chemical and metallurgical industries due to their calcination ability and good product quality. However, rotary kilns belong to the huge energy-consuming equipments, especially in small plants where the process automation level are rather poor, resulting in the low efficiency of the producing process.Automatic control of rotary kilns was realized in some advanced big companies. Such control systems aim to maintain the calcination temperature within a given range by using intelligent control based on measured process signals such as temperature, pressure and flow rate. However, due to lack of the measuring technology, these control system ignored the important process information-the solids motion which actually exerts determining effect on the energy transport within the kiln.The solids motion in industrial rotary kilns is typically in the so-called Slumping mode, and the repose angle is the characteristic parameter describing the motion features. In this paper, experimental study was carried out on a rotating cylinder to investigate the slumping process of the solids using image processing technology. The evolution of the repose angle with time was measured and the range of repose angle was obtained. The avalanche time, which is one of the most important parameter influencing the heat transfer process, was investigated with varying filling degrees. Experimental data were then used to test different theoretical models from the literature. It was demonstrated that the model from Mellmann can predict the avalanche time well.There has been no research work reporting the online detection of the repose angle of the solids in rotary kilns. In this paper, an image processing-based method is proposed to measure the repose angle by image sampling, region segmentation, edge detection and linear fitting. To test the effectiveness of the algorithm, Matlab simulation was carried out using the image sequences taken from an alumina rotary kiln. The measured profile of the repose angle shows a periodic feature, reflecting the motion behavior of the solids well.The research field of this paper belongs to the interdisciplinary field of granular materials and control engineering. The research results give new insight in the theoretical study of dynamics of the granular materials and provide new quantitative process information which can be used to improve the automatic monitoring- and control of rotary kilns.