In the cement grinding process, grinding system using the ball mill is widely applied for long year. Recently, especially from 1980s, grinding system using the vertical roller mill, which has effective grinding performance, is developed and applied in the cement grinding process.
Basic equipment structure of the vertical roller mill for cement grinding is the same as the vertical roller mill of raw material and coal grindings. The materials such as clinker and gypsum fed into the mill are ground by compression and shearing forces between the grinding table and two or four rollers, which are hydraulically loaded and controlled. Ground cement materials are sent to separator installed in mill upper position by air and classified to coarse particles and fine product. Coarse particles are returned on the grinding table to re-ground and the fine product is sent to dust collectors such as cyclone and/or bag filter.
The advantage of the vertical roller mill for cement (comparison with the ball mill)
1) Highly efficient grinding is possible with considerably low electrical power consumption.
2) The residence time of cement grinding in the vertical roller mill is much shorter than that of ball mill. Since system operational control response is superior, quality management on the cement product is easy.
3) Therefore the vertical roller mill for cement produces little heat for grinding, and quality trouble due to the excessive rise of temperature of cement is less likely to occur.
4) The installation area of the vertical roller mill is about half of ball mill grinding system.