In 1992, an Ohio utility was plagued with pulverizer problems that resulted in unit derating, drive shaft failures, excessive component wear, and bearing failures. ECG was invited to investigate the most frequent problem of main drive-shaft failures. Our engineers constructed a data acquisition system that collects displacement information from the external element springs. Based upon the success of the project, this analysis package was evolved into the Roll Bowl COP application.

The Roll Bowl COP package contains the software and hardware necessary to collect and analyze coal pulverizer operating data, using both time-domain and frequency domain techniques, to reveal the dynamic conditions present within the mill without removing it from service. The results of this analysis are used to optimize the settings and adjustments of the mill and assure the accurate assembly of the grinding elements.

The payoff is longer grinding element life, dramatically improved grinding efficiency, and the virtual elimination of typical drive train failures. The system can also be used to schedule routine preventative maintenance and predict both when a major overhaul will be required, or when a specific component will fail. This allows plant management to plan outages on a condition-based schedule as opposed to a time-based schedule leading to reduced maintenance costs.

Raymond Bowl style mills grind coal by forcing the raw material between a driven bowl and spring loaded rolls. Coal is fed at, or near, the center of the revolving bowl. Centrifugal force feeds the material uniformly to the bowl perimeter where independently sprung rolls exert the pressure necessary for grinding. The Roll Bowl COP (RBC) system utilizes the deflection data of the three rolls to monitor and analyze the grinding elements in the mill. Deflection transducers transmit analog signals to an analog to digital computer board. The DAS software collects and stores the digital displacement information at sampling frequencies that range from 1 to 60 Hz, dependent upon the type of test. Through the use of a brief, non-invasive test, loading symmetry and grinding element conditions are determined. The data is further reduced to determine the frequency components that comprise each wave form. The resulting information allows the performance engineer to monitor the mill by tracking the wear of the rolls, the fatigue stress on the main shaft and compression springs, and the power requirements relative to other similar mills at the plant. Maintenance personnel can then use the RBC system to make minor adjustments to optimize the performance and life of the mill.

The Roll Bowl COP system has been highlighted in the October '98 edition of Power Engineering.