Study on Relations Between Abnormal Vibration and Friction Characteristics of a Roller Depending on Water Content for Three Types of Fined Coal

Abstract

In coal-fired power generation, it is necessary to pulverize coal, and a vertical roller mill with excellent crushing efficiency has become the mainstream. However, In the process of pulverization by compression and shear, abnormal vibrations, which are considered to be self-excited vibration, occurs rarely. As a method of reducing self-excited vibration, adding water has been empirically performed in the field. Since the powder state changes due to water addition, it is necessary to investigate how the vibration characteristics and slip characteristics change. In this paper, we examined the effects of adding water to Artificial coal, Sub-bituminous coal A, and Sub-bituminous coal B with different powder characteristics on the dynamic friction characteristics and dynamic response generated between the roller and the powder. Investigating the relation between the RMS value of the horizontal acceleration response and the slip ratio indicates the degree of slippage of the roller. Next, we investigated the relation between the dynamic frictional characteristics generated during rolling and the slip ratio and found that the Slip-Stick phenomenon remarkably appeared at the test machine speed at which the vibration acceleration was maximum even when water was added. Also, a frequency analysis showed that when the vibration acceleration increased, the resonance frequency decreased, and the phenomenon of uniting was confirmed for all types of coal, suggesting that the abnormal vibration that occurred was self-excited vibration.