Operation of Tube Mills in Cement Plant

Grinding systems with tube mills have been operated throughout the world for many decades. Many practical ways to operate these mills in an easy way have been developed and many improvements introduced, including the application of new technologies.

But still, the operation of tube mills involves a large number of items and routines which importance often is not sufficiently considered by the responsibles. Many times a great deal of facts are neglected and even fundamental procedures are unconcernedlycarried out, leading to constant drawbacks.

Any grinding system should be operated in such a way as to obtain the necessary product quality and to achieve the maximum mill output. As soon as an efficiency drop is observed then the reasons should be investigated. There are many different grinding systems and each system underlies its own and specific conditions. It is obvious that no standard instruction can be given for all possibilities and cases. This paper serves as general guide line for better mill operation and the procedure of practical mill assessment.

In a cement plant, the largest portion of electrical energy costs is related to cement grinding. Any improvement in grinding efficiency results in considerable savings. Subsequent guide lines refer therefore in the first place to cement grinding plants, where the procedure for raw mills and coal mills is similar and can be derived from this. Raw and coal mills include additionally the drying aspects which have to be assessed.

Normal operation can be defined as the day to day operation of the mill system with a continuous mill output and a steady cement quality. Any common disturbance can easily be equilibrated with normal means of mill control, either manually or automatically with a closed loops control system. As abnormal operation can be defined all operating conditions beyond the normal range. In this case, either the required mill output rate and/or the required quality cannot be reached relative to the recorded normal operating conditions. As soon as deviations from the normal operation are encountered, the possible reasons have to be assessed in order to undertake necessary measures for correction. Often an abnormal operation can be counteracted by corrections through corresponding actions of the mill operator or the maintenance crew. If normal operation can not be reestablished by such procedures, the execution of a performance test of the mill system is indicated.