May 01, 2011· Typically, an electrical motor of the ball mill uses about 14–15 kWh/tonne of raw mix. On the other hand, a VRM motor uses about 7–8 kWh/tonne. On an overall basis, a VRM consumes about 20% lower specific energy than a conventional closed circuit ball mill. A VRM is widely used for raw material and coal grinding in the cement industry. 5.1.3.