Item

Background

Vertical roller mill for
cement grinding

Application
Finishing process

In the cement grinding process, grinding system using the tube mill is widely applied forlong 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 issent to dust collectors such as cyclone and/or bag filter.

Descriptions

The advantage of the vertical roller mill for cement (comparison with the tube 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 tube 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, andquality trouble due to the excessive rise of temperature of cement is less likely tooccur.
4) The installation area of the vertical roller mill is about half of tube mill grinding
system.
But the introduction of a pre-grinding grinder has become mainstream in Japan, and theabove-mentioned technology is spreading mainly overseas.

Results

Electrical power consumption can be reduced by 30 % (compared with the tube mills).

Costestimation
Relatedmatters

External circulating system to vertical roller mill for cement.

Reference-1-Item

Background

High efficiency grinding of
blast furnace slag

Application
Finishing process

In the past, slag grinding is performed in a tube mill with dryer. This requires
relatively higher power consumptions, and efficiency improvement in this process
has become a great concern.
Improvements in slag grinding efficiency wasdeveloped and implemented with existing cement manufacturing technology.
Improvements in the grinding process to produce fine granulated blast furnace slag
suitable for use in the production of blast furnace cement was achieved with pregrinding and vertical mill technologies used in cement manufacturing.
1. The installation of vertical mill
In a vertical coal mill, drying, grinding, and separating/classifying of groundmaterial are done simultaneously. The hot air used for drying is supplied with a
hot wind generator. Slag contains iron grain, which could damage the rotatingtable and aggravate grinding efficiency. Hence, the removal of these irongrains before commencing the grinding process, using an external circulation
system with a magnetic-separator device, is crucial.
2. The installation of pre-grinding equipment
There are cases where a vertical mill is installed to the existing tube mill toenhance grinding efficiency while reducing power consumption. With the use ofvertical mill, pre-grinding and cement grinding processes are performed
separately. Reduction in the size of grinding media used in the tube mill is
expected to improve grinding efficiency. However this would partially ruin
overall efficiency improvement level.

Descriptions
Separater

Bag
Filter
Separater

External Circulation

Vertical M ill
Heat Generator

Tube M ill

Fig. The example of the combination of tube mills andvertical mill

Results

Reduction in unit electricity consumption (Blended value 4,000cm 2/g)
* Tube mill 70kWh/t (approx., excluding drying)* Vertical mill
<40kWh/t (including separator, wind-chamber/fan, conveyor
systems, and etc)

Costestimation

About 7.3 million US$ including cost of supplemental facilities and construction fees
[40t/h] [1US$=¥110]

Relatedmatters
Reference

Introduction of vertical raw material mill, vertical cement mill, vertical coal mill.

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