Over the last three decades the vertical roller mill has become the preferred ball mill for grinding of raw materials. The grinding efficiency of the vertical roller mill combined with an ability to dry, grind and classify within a single unit gives the vertical roller mill a decided advantage over a ball mill system. However, despite these benefits, applications of the vertical roller mill for cement grinding are less prevalent.
In the cement grinding process, we can use either cement ball mill or cement vertical roller mill. What is the difference between the two?
The grinding process in ball mills and vertical roller mills differ fundamentally. In a ball mill the comminution takes place by impact and attrition. The comminution in the vertical roller mill takes place by exposing a bed of material to a pressure sufficiently high to cause fracture of the individual particles in the bed.
It is characteristic of grinding in vertical roller mills that the energy input to the material per pass between roller and table is small, for which reason a large number of passes are required to obtain the necessary specific energy input to the material. This leads to a very high internal material circulation factor.
Cost of operation
The most significant advantage of a vertical roller mill compared to a ball mill system is related to the consumption of electrical energy of the two systems, the specific energy consumption of the vertical roller mill is 25% – 40% lower than for the ball mill system.
Maintenance of wear parts
Wear parts for a ball mill, i.e. grinding balls, liner plates and other mill internals are either very easy to maintain or they have a long life time. The grinding charge is simply maintained by adding more grinding balls to the mill as the mill charge becomes worn and the power consumption and the output capacity decrease.
Also for a vertical roller mill the performance will deteriorate as a consequence of progressive wear of the grinding parts. This, however, is not only reflected in a reduced capacity, but also in a higher specific energy consumption and a higher level of mill vibrations.