Analysis And Model Study On Current Signal Of The Drive Motor For Rotary Kiln

As large process equipments,rotary kilns are widely used in cement,metallurgical and other industries for mixing and heat treatment of granular materials.The stability of kiln operation plays a decisive role in the production efficiency and enterprise's benefit.The electric current of the kiln drive motor is an important parameter reflecting the thermal condition and equipment stability of rotary kilns,and it is also one of the key process variables to be monitored for efficient production and equipment safety.The current of the kiln drive motor is closely related to the power consumed for material movement through the kiln,as well as the power to overcome axis offset of the kiln body.The current research work on the motor current is mainly qualitative analysis based on the sampled current signal and experience of the kiln operator.In contrast,quantitative analysis and modeling of the motor current is relatively rare,which is disadvantageous for accurate judgment of kiln conditions and automatic control of the production process.To solve this problem,motor current is sampled using an experimental rotary kiln and analyzed using Fourier frequency analysis method and Normal Time-Frequency Transform,after which the features of the current signal are extracted.Factors influencing the motor current are then analyzed and a relating model is established,which is theoretically meaningful and useful in practice.Firstly,the kiln drive motor current is studied on an experimental rotary kiln with a diameter of 0.2 meters and a length of 1.5 meters.Ten sets of batch experiments(both ends of the rotary cylinder are closed,without continuous material flow)and five sets of continuous experiments(both ends of the cylinder are open,with continuous material flow through the cylinder)are conducted,with brown corundum as test material.With the real-time current acquisition system,the change of motor current with time at different rotational speeds and material weights can be obtained.By use of the Discrete Fourier transform and the Normal Time-Frequency Transform method,the current signals are analyzed and the characteristic features(current mean,main frequency and corresponding amplitude)are extracted.Results show that,the main component of the current signal is caused by the axis offset of the cylinder,and its frequency is equal to that of the rotary cylinder.Then,factors influencing the power and current of the drive motor are analyzed,based on which equations are given to calculate the drive power for material motion and the drive power for overcoming the axis offset of the rotating cylinder.A model is then established,which relates the motor current with the running parameters of the rotary kiln,such as the axis offset,rotation speed and the material load.Based on the established model and sampled signal of the motor current,it is now possible to estimate the axis offset of the cylinder,which provides a new way for safety monitoring of industrial rotary kilnsFinally,the proposed model is verified by experiments.(1)In batch experiments,the actual axis offset in batch experiment is measured using image processing method.Based on the main components of the acquired motor current and the proposed model,the axis offset of the rotary cylinder is calculated and compared with measured values.It is found that the error between the model calculated axis offset and the measured value is not greater than 0.4 mm.This indicates the effectiveness of the proposed model in the present work.(2)Based on the proposed model,the main component of the motor current is predicted and compared with the measurement.Good agreements are found in the five sets of continuous experiments,with satisfactory accuracy in the aspects of signal frequency and magnitude.The research result of the present work provides an effective tool for quantitative analysis of the motor current of rotary kiln.Based on the proposed model and the current signal,the axis offset of the rotary kiln can be also calculated,which is useful in the safety monitoring of the kiln process.