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ball mill in cement plants

Something About The Real Application Of Ball Mill In Cement Plants

Ball mill, also called ball mill grinder, is a kind of grinding equipment, mainly used for fine pulverizing various materials such as ore, cement, chemical raw materials, glass, etc. It is widely used in mining, metallurgy, cement, chemicals, and building materials industries.

Mining Industry

In the mining industry, ball mills are primarily used for grinding various metal ores, such as copper ore, iron ore, lead-zinc ore, etc., to facilitate subsequent processing processes such as flotation and beneficiation.

Chemical Industry

In the chemical industry, ball mills are applied for grinding various chemical raw materials, such as dyes, pigments, coatings, etc., to improve the physical and chemical properties of the products, as well as enhance quality and profitability.

Building Materials Industry

In the building materials industry, ball mills are used for grinding various raw materials such as limestone, gypsum, coal ash, etc. The application of the ball mill enables thorough fine grinding of building raw materials, enhancing production efficiency and product quality.

Cement Industry

In the cement industry, ball mills represent the final stage of cement production and also the most energy-intensive one. Its main function is to grind cement clinker, along with additives such as gypsum and performance-enhancing materials, to an appropriate fineness, forming a certain particle size distribution, increasing the hydration area, and accelerating the hydration rate to meet the requirements of cement slurry setting and hardening.

ball mill applications

The Application Of Ball Mills In A Cement Production Line

Basic Information Of The Cement Production Line

There is a 4000t/d cement production line, and the main configuration of the grinding station is three traditional ball mills. Due to the small specifications and aging of the ball mills, with a single unit output of about 100t/h, it is no longer sufficient to meet the production demand. Therefore, the production line has been reconfigured with a joint grinding system consisting of a new type of energy-saving ball mill, a V-type cement separator, and a dynamic cement separator.

The production process of the joint grinding system is as follows: the materials are lifted by a bucket elevator into the ball mill for grinding, and then fed into the V-type cement separator. Coarse particles selected by the separator return to the ball mill for further grinding, while fine powder enters the dynamic cement separator, which selects the final product. Coarse powder selected by the dynamic cement separator is fed into the ball mill through a chute for another round of grinding.

Ball Mill Operation Status

During the initial phase of operation, adjustments to the internal structure of the ball mill are not permitted. Therefore, coarse powder selected by the dynamic cement separator can only be directly introduced into the original ball mill system via a chute. The final product selected is collected by a bag dust collector and mixed with the product ground by the ball mill before being stored. At this stage, the system’s output is approximately 165-175t/h. According to measurements, the specific surface area of the final product selected by the separator ranges from 2800-3100cm2/g (R40μm: 8%-10%), while the specific surface area of the product ground by the ball mill ranges from 3350-3450cm2/g (R40μm: 8%10%). The specific surface area obtained by mixing the two is 3100-3200cm2/g (R40μm: 8%10%). When converted to the specific surface area required by the design contract, which is 3600m2/g, the output is only 138-147t/h.

To increase the specific surface area, one approach is to increase the rotational speed of the dynamic separator. However, if the speed is raised without changing the circulation fan’s settings, it can lead to excessive re-grinding of coarse particles, causing the ball mill to become overfilled with material. In such a situation, the only option is to reduce the airflow by decreasing the circulation fan speed or adjusting the circulation air valve to decrease the air volume. However, when the circulation air valve is opened to 55% and the circulation fan is operating at 95%, and if the ball mill’s slant plate is opened to 90%, instability in the roller gap may occur after running for a period, resulting in a further decrease in output.

ball mill grinding station agico

At this point, with the set pressure of the ball mill is 10MPa and the operating power is 51% of the design power, the ball mill is not generating sufficient output. The current entering the two bucket elevators is 185A and 148A, respectively, which are 53% and 64% of the rated current, indicating that the operating power is clearly low, consistent with the ball mill. To increase the output of the ball mill, the material throughput and the operating pressure of the mill should be increased. However, if the slant plate opening of the ball mill is too large, it can lead to unstable operation. Additionally, there is still 1MPa of pressure increase potential in the ball mill, but it’s insufficient to achieve the required output with a specific surface area of over 3600cm2/g. It would be challenging to attain this high specific surface area through the ball mill alone, and it would also result in a significant increase in power consumption.

In addition, we need to pay attention to the fact that the system must ensure that the ball mill is not over-ground by reducing the airflow of the circulating fan and the circulating air valve. It is estimated that after reducing the airflow, the actual air volume through the V-type separator will inevitably decrease significantly, to the point where it cannot meet the design airflow requirements, thereby reducing the classification efficiency. This leads to an increase in the fines content entering the ball mill, thereby disrupting the operational stability of the ball mill. Under normal circumstances, the valve opening of the circulating fan can reach more than 90%, and the ball mill can operate normally. However, ball mills previously configured have power close to or slightly larger, and the internal structure of the mill has been adjusted accordingly. Therefore, the problem to be solved is how to further increase the power consumption of the ball mill and ensure the stability of its operation without changing the structure.

Measures To Address The Issue

Given the aforementioned issue, we can make the following adjustments without modifying the internal structure of the ball mill, aiming to maximize the synergy and production efficiency of the ball mill:

Adjust the internal grading of the ball mill: we should remove some large balls from the first and second chambers and add smaller balls with diameters of ϕ20mm and ϕ15mm. This adjustment aims to lower the internal flow rate and increase its grinding capacity.

Make a three-way valve: the three-way valve allows for the partial return of coarse powder from the dynamic separator to the ball mill for further grinding. This setup aims to minimize over-grinding due to the insufficient grinding capacity of the ball mill. Simultaneously, it effectively eliminates over-grinding in the ball mill caused by inadequate airflow from the V-type separator.

Increasing the operating pressure of the ball mill and adjusting the airflow control valve between the dynamic separator and the V-type separator allows for fine-tuning to identify the optimal balance point of the ball mill system.

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