Years of cement production practice shows that cement particle gradation should be distributed continuously within a certain size range. Generally speaking, the cement particles smaller than 32 μm are beneficial to reduce bleeding and early strength, but as the size of particles gets smaller, although the hydration activity increases, the voidage of particles will also increase when they accumulate, the coagulation time will become longer, and the compatibility with admixture will become worse. Therefore, the proportion of cement particles smaller than 3 μm is better less than 10%. Due to the particles of 10 to 24μm have a significant effect on early strength, accounting for 55% to 65% of the best. As to particles larger than 64 μm which only play a filling role, the smaller the number, the better. All in all, the optimal cement particle size distribution should match the particle’s bulk density with its hydration activity. Only when these conditions are met can we produce high-quality cement.
At present, there are a lot of enterprises whose cement production can meet the above requirements, and the quality, output, efficiency and other indicators are at the leading level in the cement industry. Customers generally highly approve of the cement they produce. After some investigations, it is found that these enterprises all adopt the ball mill of closed-circuit grinding system as cement grinding equipment. Why they choose the ball mill closed-circuit grinding system? And what are its advantages?
The Comparison between Open-circuit & Closed-circuit Grinding System of Ball Mill
Open-circuit Grinding System
The open-circuit grinding system of the ball mill is shown as follows: materials (including clinker, gypsum, mixed materials, etc.) mixed according to a certain proportion will be directly stored in the steel silo as finished cement products after being ground by the ball mill.
The open-circuit grinding system has the characteristics of simple production process, less equipment, simple maintenance, small investment, etc., but it still has many insuperable shortcomings. For example, we usually choose to extend the grinding time to ensure the ground cement reaches a higher fineness, which may reduce the output and increase electricity consumption, abrasion and the temperature of cement after grinding. What’s more, it prolongs the staying time of a lot of fine powders in the ball mill, resulting in the excessive content of materials under 3μm, greatly decreasing the crushing efficiency. In addition, too much fine powder will increase the amount of water needed for cement. And high cement temperature will cause gypsum dehydration, affect the comprehensive performance of cement, easily lead to the process admixture volatilization in concrete mixing.
If we properly reduce the cement fineness requirements, shorten the material grinding time is the most direct way. Then there will be an increase in production, a decrease in power consumption and abrasion, while the content of particles larger than 64 μm will also increase significantly. These cement particles in concrete are very difficult to hydration, only filling role, augment the amount of clinker in cement and seriously affect the economic benefits of enterprises. Of course, even if we set a more appropriate cement fineness, it is difficult to change the current situation that the flow velocity in the open-circuit ball mill is only 1/2-1/3 of that in the closed-circuit ball mill with the same specification, which will lead to poor comprehensive performance of finished cement, low system output and unsatisfactory enterprise benefits.
Closed-circuit Grinding System
The closed-circuit grinding system of the ball mill is shown as follows: materials mixed in a certain proportion will firstly enter the cement ball mill for grinding and then be sent to the powder concentrator by bucket elevator. The powder concentrator divides the materials into coarse and fine materials. Fine material is the material that reaches the fineness requirement of the finished product. They will be collected by bag filter and sent directly into the cement silo. The coarse materials should be sent back to the ball mill for regrinding.
The technological process of closed-circuit grinding system is complex and the cost of equipment, investment and maintenance are relatively high, but the distribution of cement particles which are processed by this system is reasonable so that they can prepare high-performance concrete. In addition, the closed-circuit grinding system has the characteristic of high efficiency, high output, low cement temperature, and good comprehensive benefit. Generally, the output of the closed-circuit ball mill is 15% ~ 25% higher than that of the open-circuit ball mill with the same size. However, the superiority of the closed-circuit grinding system is closely related to the comprehensive performance of the powder concentrator, the selection of ball mill’s technological parameters, the arrangement method of pipeline and the level of production management. As long as we carry out the project according to the law of the closed-circuit grinding process, operate carefully and strengthen management, we can ensure the production of this system to run smoothly and efficiently.
AGICO Cement Ball Mill & Cement EPC Project
The closed-circuit grinding system is not suitable for any cement plant. On the one hand, its process is relatively complex and the number of equipment is large. On the other hand, it has strict requirements for related equipment and production management. If these basic requirements can not be met, its productive result is not as good as an open-circuit cement grinding system. The rejection of the closed-circuit grinding process by some enterprises is based on the fact that the output and quality of the system are not high due to the insufficient equipment or inadequate management so that they conclude that closed-circuit grinding process is inferior to open-circuit grinding. But the most fundamental reason is that these enterprises did not carry on the project construction according to the law of closed-circuit grinding process. Because, at present, the cement that has the best quality all comes from the closed-circuit grinding system is the best proof.
AGICO Cement is a cement equipment manufacturer with more than 20 years’ experience. We are the long-term partner of many large and medium-sized cement enterprises in different countries, providing cement equipment and EPC project construction. The closed-circuit grinding system ball mill for cement grinding and the matching powder concentrator and dust collector all have the characteristic of high wear resistance, smooth running and long service life.
Technical Advantages & Performance Characteristics
- The main bearing of the ball mill adopts sliding bearing and the seal adopts a compound seal.
- The hollow shaft and the main gear of the ball mill both adopt steel casting. The cylinder body is inlaid with wear-resisting lining plate, which has good wear resistance and smooth running.
- The main bearing uses the double high and low-pressure thin oil as lubrication. It is equipped low-speed transmission device which is easy to repair and start.
- The big and small gears of ball mill adopt the fog lubrication to prolong their service life and smooth running
In addition, we also provide the EPC cement project construction service. It includes cement plant design, equipment onsite installation, real-time commissioning, spare parts service, equipment maintenance and equipment operation training. High-quality equipment and efficient service make AGICO a trustworthy partner for you!