Study Of Thermal Process And Optimum Structure In Carbon Rotary Kilns

The carbon rotary kiln is a kind of rotary cylindrical equipment for aluminum industrial calcination of carbon product such as petroleum coke. It has been used to calcinate petroleum coke only for nearly 30 years in China. As a result, there are wide differences between home and abroad in kiln output, energy consumption, calcining quality and kiln working life. Therefore, how to improve calcining quality and increase kiln output are becoming more urgent questions for the researchers. Then the paper is around these questions to study.In the paper, thermal measurements are carried out on a carbon rotary kiln in Henan province and physical parameters about petroleum coke are tested. Then, we calculate the material balance and the thermal balance. From the calculated results, we can know the carbon burning loss and utilization of energy. Meanwhile, the numerical simulations are conducted on gas and solid areas of the kiln using Fluent and Matlab softwares. It illustrates explicitly the flow field, temperature filed and compositional concentration field. And then the paper focuses on the impacts of the supply rate and positions of the secondary air and tertiary air and the kiln lining with turn-down rig structure on the kiln working condition.In the paper, solids movements are further researched. For practical engineering, the rolling motion is often chosen as an ideal design work condition. Here, characteristics of rolling motion are made simple analysis and its necessary conditions to occur are deduced. From the induced conditions, rolling motion happens by adjusting the kiln inner wall friction and the rotation speed. As the rotation speed ranges from 1.1 to 3.7 rpm for practical kiln and from 1.0 to 8.0 rpm for our experimental kiln, the solids mode of motion is rolling. According to the previous numerical model for predicting the depth of the solid bed, formula about the particle mean residence time of the straight kiln is deduced. Changing the numerical model for the solid bed depth of the straight kiln, formula about the particle mean residence time of the variable diameter kiln is got.The formulae calculate the residence time as a function of the kiln radius, kiln length, discharge dam height, kiln inclination, rotation speed, material volumetric flow rate, angle of repose of the solids and particle mean diameter.A laboratory rotary kiln is set up and hot experiments are carried on it in this work. The experimental results show that, kiln temperature increases with the calcination time. Kiln temperature changes significantly at around the kiln inlet and outlet and gently at the middle part of the kiln. The influences of operational and structural parameters on the mean residence time of solids (MRT) and the kiln output are also presented on the experimental rotary kiln. Experimental results show that the increase of rotation speed and kiln slope reduces MRT and increases kiln output. Also, kiln output increases with increasing charge dam height. MRT increases when the rotation speed is lower than 2.0 rpm but decreases when the rotation speed is higher than 2.0 rpm with increasing dam height. The product of MRT and mass flow rate (i.e. kiln output) increases approximately linearly with the mass flow rate per kiln rotation at the same kiln slope. Results of formulae about MRT calculation are compared with measurements. The comparison shows that, calculated results of the residence time of solids agree well with measurements. No fitting parameter is necessary.Finally, the paper summarizes the experiment results and simulated results and makes some recommendations so as to accomplish the aim of calcining quality improvement, kiln output increment and energy reduction.