Study on Material Motion and Combustion Characteristics in Rotary Kiln

Abstract

We study the solid waste stream in a rotary kiln with L/D ≥ 10 in this paper. The particle trace is determined based upon the vector force analysis on it, and therefore, the distance and time of single particle motion in a circle are deduced. Using filling method, the mean distance and the mean residence time of material flow are then calculated, in which the motion results from the material beyond the critical angle of motion θ falling because of the kiln’s rotation. The influence of the filling angle of particles on the axial velocity is also analyzed. At the same time some experiments on different solid waste streams in the rotary kiln are carried on so that the equation of flow derived by theoretical analysis is modified according to the experimental results. Industrial analysis is done on several typical kinds of solid waste from two paper plants. Moreover, on a small scale rotary burning device, we conducted hot test on the solid waste from the paper plants to study the dependence of burnout rate on the residence time and the temperature inside the kiln. The results indicate that the water content and volatile content are high in the solid waste from paper plants. Hence, to ensure the high burnout rate, the solid waste has to stay in a rotary kiln for a long enough residence time at high temperature, which requires, in turn, that the rotary velocity of a rotary kiln be lower than 10 rpm, the inclination angle less than 2°, and the temperature inside higher than 800 °C. In addition, we conducted hot test on typical municipal residential waste in South China, from which we come to the conclusion that without enough air supply, clinker and slag are formed when the inside temperature is 850 °C.