No.12, Haotian Street, Liangxiang, Fangshan District, Beijing-102401, China
Regarding whether the ball mill is open or closed, the opinions of the various units are different. Conch Design Institute believes that the closed-circuit process should be selected. The quality of the open-grinding mill is not suitable for the quality of the cement. The main reason is that the concrete temperature mixing concrete mixing station is not welcome. Hefeiyuan believes that the open standard of cement standard consistency water consumption is low, and the mixing station is welcome. Both companies in Nanjing believe that the advanced process of the grinding process is definitely a closed circuit process that is better than the open circuit. However, the specific grinding machine with the specification of Φ3.2×13m has a long diameter and is designed for the open circuit. One company believes that if a closed circuit process is used, the length of the mill should be reduced to 11m.
In fact, a senior cement expert in the survey introduced that in the 1980s, developed countries stopped talking about the opening and closing of ball mills and turned to closed-circuit processes. A large hospital tried to sell their high-flow fine grinding from Denmark, but in the 1990s, the Danes themselves did not open the flow mill and turned to the closed-circuit process. The production of cement should be developed in the direction of refinement. A grinding station in developed countries can produce more than 70 varieties of cement, all of which are adjusted by closed circuit. China's South China Institute of Technology advocates the use of open-circuit process grinding in Guangdong, and most of the northern countries advocate the use of closed-circuit processes.
In fact, compared with closed-circuit grinding, the open-circuit process mill is only a little investment, and it is convenient to maintain and manage. However, the closed-circuit grinding is easy to adjust, and the adaptability of raw material quality and moisture is stronger. In the new grinding station, when clinker is purchased from several clinker production enterprises, the clinker wearability is inevitably different. At this time, the closed-circuit grinding output and the fineness of the grinding cement are not changed much because of easy adjustment, which is superior to the open-circuit grinding. When the comprehensive moisture content of the milled material exceeds 1.5%, the output of the open road mill decreases greatly. For example, in the grinding station proposed by our unit, the cement produced in the future will be sold to the concrete mixing station on the one hand and the cement concrete sleeper on the other hand. The requirements for cement fineness are the opposite: the former cannot be too thin. Otherwise, the adaptability of the water reducing agent in cement and concrete is not good. The latter should not be too thick, otherwise the cement will not come early, affecting the early strength of the cement sleeper. Such cement fineness needs to be adjusted only in the closed circuit process.
Some experts who recommend the use of open-circuit process grinding believe that the open-flow process grinds the cement because it has a wider particle size distribution than the closed-circuit mill, so the standard consistency requires less water, and the concrete mixing station is welcome. In this regard, senior cement experts believe that the closed-circuit process mill can completely adjust the particle size of the grinding cement by adjusting the separator. China's powder separator industry has a tendency to pursue high-selection powder efficiency unilaterally, not good! The efficiency of powder selection is about 70%. The first generation of classifier has about 30% qualified fine powder into the coarse powder; the second generation classifier has about 20% to 25% qualified fine powder to enter the coarse powder; the third generation classifier only has about 5% to 8% The qualified fine powder enters the coarse powder. The powder selection efficiency can be adjusted to allow about 14% of the fine powder to enter the coarse powder. In this way, the particle size distribution of the milled cement in the closed-circuit process mill is widened, and the standard consistency water demand is improved. However, the mill output will decrease, and the internal grinding and the grading adjustment of the grinding body can be simultaneously made to slow the flow rate of the material in the mill, and the circulating load is increased to increase the mill output. In fact, there are many factors affecting the water requirement of cement standard consistency. The particle size distribution of cement is only one aspect. For a detailed discussion of this issue, please refer to the author's other article, "On the impact of water consumption of cement standard consistency on concrete water consumption."
As for the temperature of the open road grinding cement, the average person may think that there is no such problem in the grinding station, and the temperature of the cement produced by the online cement company is easy to be high. In fact, some of the authors investigated the use of roller press + Φ3.2 × 13m open flow mill enterprises, the temperature of the cement in winter is about 120 ° C, and in summer it is as high as 140 ° C. Another on-line roller press + Φ3.8×13m open-circuit mill, after the production, the mill temperature is high due to the high temperature inside the mill, causing the mill to stop. Senior cement experts said that developed countries are controlling the factory cement temperature, and China will soon control it. Through the study, the author summarizes the four major shortcomings of high cement temperature: poor compatibility with water reducer in concrete; easy to cause early cracks in concrete; easy to cause pseudo-coagulation of gypsum dewatering cement; easy to make cement standard consistency water demand high. Therefore, it is unwise to use the open flow system in the new grinding station ball mill system. When using the closed-circuit grinding process, if the O-Sepa separator is used to introduce the cold-air powder, the cement temperature can be reduced by 30-40 °C compared with the open-path mill.
For the Φ3.2×13m mill with a relatively long diameter and more suitable for open flow grinding, the author believes that the length of the mill can be shortened by two meters, that is, the Φ3.2×11m mill is used as the closed-circuit mill. This can reduce the purchase cost of the mill and reduce the amount of grinding body grinding in the mill to reduce the basic construction cost of the mill. It can also reduce the power of the mill motor by 200kW, thus reducing the power consumption per ton of cement. This is also an economically valuable option. Of course, it is also possible to use a Φ3.2×13m mill as a closed-circuit mill, which is more advantageous for increasing the specific surface area of the milled cement and increasing the blending amount of the mixture.