Slag Vertical Roller Mill Better than Ball Mill for BFC

Granulated blast furnace slag, a by-product of pig iron production, has been used as an important component of blast furnace cement for many years, due to its latent hydraulic properties.

The replacement of a certain clinker portion by blast furnace slag does not only mean to save raw materials and thermal energy for pyroprocessing, but also provides for advantageous characteristics of the blast furnace cements:

• Low heat of hydration helps to prevent cracks in the concrete due to temperature stresses,

• High resistance against sulphate attack,

• High resistance against alkali-aggregate reaction,

• High binding capacity of chlorides in blast furnace slag cement pastes,

• The low electrical conductivity of concrete made with blast furnace cement resulting in a positive effect on the corrosion protection of the concrete reinforcement.

For a long time, the applicable standards allowed cement clinker and granulated blast furnace slag to be ground together in tube mills, but especially by utilization of tube mills the clinker mainly accumulates in the fines fraction, while the granulated slag accumulates in the coarse range.

Because the proportion of pulverized blast furnace slag predominates in the blast furnace cement, the slag can only inadequately participate in the hydration as a result. The consequence is loss of quality. Intergrinding in roller mills provides very similar particle size distributions for clinker and slag and thus provides a better quality of the blast furnace cement.

Therefore, it is an indisputable fact that it is necessary to grind the granulated blast furnace slags to high fineness in order to generate good strength properties. The intergrinding of clinker and granulated blast furnace slag inevitably necessitates the energetically unfavourable grinding of the clinker to higher fineness as necessary. The only way to avoid this is to grind clinker and slag separately. The vertical roller mill meets the demands.

Compared with ball mill, slag vertical mill has these advantages.

1. High grinding efficiency and low power consumption. This kind of machine consumes 20-30% lower power. And with the growing of moisture content, its energy-saving effect will be more obvious.

2. Strong dry ability. Air is used to send materials, and the temperature of the air can be controlled according to the moisture content of materials. And this mill can be used to dry materials with moisture content as high as 12~15%, which is much higher than the special dryer.

3. Large feeding size. The feeding size can be as large as 5% of the diameter of the grinding diameter, that is, 40 to 100mm. Therefore, secondary grinding is unnecessary for large-scale and medium vertical mill.

4. Stable chemical composition and even particle size products.

5. Simple process flow and small in size.