Solids Motion In Rotary Kilns: Motion Behavior And Real-time Monitoring System

Rotary kilns are large thermal equipments that are widely used in chemical, metallurgy, mining, cement and paper industries. However, rotary kilns also belong to huge energy-consuming equipments. In China, the rotary kiln processes in most small and medium enterprises are poorly automated, leading to high energy consumption and difficulties in completion of the national twelfth five-year-plan.Efforts have been devoted to the automatic control of rotary kiln processes. Such control systems are mainly realized by detecting thermal signals such as temperature, pressure and feed rate, based on which the kiln process are controlled and optimized. However, due to lack of the measuring technology, these control systems ignored the important process information-the solids motion which actually plays an important role in the energy transport inside the kiln.The solids bed in the kiln cross-section includes the cascading layer and stagnant layer. In the paper, image processing technology was used to track single colored particle and the motion behavior of the particle in the cascading layer was analyzed. The time features of the motion were measured and the effects of drum speed and filling degree were studied. Based on measurements, a new dimensionless time variable, fractional residence time was introduced which may serve as an indicator of the heat transfer efficiency.Reports on the real-time monitoring of solids motion for industrial rotary kilns are relatively rare. In this paper, an image-based monitoring system was developed for the solids motion in a ferrite rotary kiln. It consists of image acquisition and display module, image processing module and database module. With it, important motion features of the solids such as the repose angle and filling degree can be detected. Analysis of the data demonstrated that the repose angle can be used to predict the change of thermal conditional inside the kiln. The obtained results provide a new measuring technique for the prediction of thermal process inside the kiln, which are meaningful to the improvement of the automatic control of rotary kilns.