Construction planning of cement grinding station

According to the Detailed Rules for the Implementation of the Production License for Cement Products (hereinafter referred to as the Detailed Rules) issued by the National Office of Industrial Products Production License on April 4, 2007, cement enterprises are divided into four types according to their production processes: cement plants, clinker plants, grinding stations and preparation plants. The grinding station includes: cement grinding, cement homogenization and preparation, cement packaging and bulk production.

The author's enterprise plans to build a grinding station with an annual output of 600,000 tons. Since 2007, the project has been investigated and a large number of research data have been obtained. Now write some questions about the construction of grinding station enterprises for the reference of peers. According to Article 3.7 of the Detailed Rules, the scale of the newly-built grinding station after June 65438+1October 65438+July 2006 shall be at least 600,000 tons/year. The construction of this scale grinding station is aimed at the owner who intends to build a new grinding station. The following discussion is basically limited to building a grinding station with an annual output of 600,000 tons. The technological process with an annual output of 600,000 tons of cement can be adopted:

Scheme 1: roller press +φ 3.2× 13m ball mill;

Scheme 2: φ 3.8× 13m closed-circuit grinding;

Scheme 3: clinker fine crusher +φ 3.2× 13m ball mill.

The consensus of Grade A Design Institute is to adopt Scheme I, on the grounds that:

(1) roller press is a technology introduced in the mid-1980s. After more than 20 years of digestion and transformation, it has been proved to be an advanced and mature pre-grinding technology.

(2) Using the roller press can greatly improve the output of the mill, thus reducing the use specifications of the mill and greatly reducing the purchasing cost of the mill. The φ 3.2× 13m ball mill is an edge drive mill, and the cost of each mill is 2.6-2.65 million yuan. The φ 3.8× 13m ball mill is the center drive mill, and the cost of each mill is 4.8-4.85 million yuan. The difference between the two is 2.2 million yuan.

(3) The use of roller press can significantly save electricity, increase the mixing ratio of additives in cement, and prolong the service life of internal grinding equipment, thus reducing the manufacturing cost of cement and improving the efficiency of grinding station.

(4) Using roller press can greatly reduce the noise of ball milling, which is beneficial to the physical and mental health of front-line workers. According to experts from Hefei Institute, after the clinker is rolled, the maximum steel ball diameter of the ball mill can be reduced from 90 mm or 100mm to below 60mm, and the noise of the mill can be reduced from 100 ~ 1 10 dB to below 70 or 60 dB.

The biggest advantage of the second scheme is that the system maintenance is simple, and the system mill is even called "fool mill", but the power consumption per ton of cement is generally around 35 ~ 36 kWh, which has no advantage of low operating cost and lacks market competitiveness. In contrast, the first scheme increases the roller press system and the complexity of operation and maintenance. However, according to our investigation results, the faults of roller press are mainly manifested in two aspects: hydraulic system and roller surface wear. The stability of the former is greatly improved after using foreign parts, while the latter usually needs surfacing on the roll surface after running for 6000 ~ 7000 hours (one year) (some manufacturers using low-voltage electricity regularly spend two hours to open the roll surface for inspection during peak hours every day, and the surfacing effect is better in time when there are wear points on the roll surface). In the first overall scheme, the system operation rate can reach more than 72%.

Scheme 3 is recommended by some provincial cement design institutes and private enterprises, but the owners are often worried about the crushing effect and operation stability of fine crusher. Fahrenheit mill, impact fine crusher and ball mill are often recommended in fine crusher. It is said that they have good running stability. Theoretically, ball milling can only improve the system output, but not reduce the power consumption. This conclusion has been verified in a grinding station in Chaohu City, Anhui Province: the enterprise uses a ball mill with φ 3.2× 13m open-circuit mill, and the power of the ball mill system is nearly 360 kW (the power of the ball mill is 320kW, and the rest is the power of dust removal and conveying equipment). After operation, the output of the system increased by 6 ~ 8 tons per hour. The configuration of roller press can be divided into "roller press+disperser" and "roller press +V machine".

According to the introduction of Hefei Institute, the roller press is equipped with crusher, the φ 3.2× 13m ball mill is equipped with HFCG 120×50 system, and the roller press equipped with V-type machine needs to be added one by one. Although the output of the system can be increased by about 15%, the investment is increased and the power consumption per ton of cement is increased by 1 ~ 2 kWh. The V-type machine with roller press and V-type machine has no moving parts, so the operation rate is higher than that with roller press and disperser, the operation and maintenance are simpler, and the separation and classification effect is better than that with disperser. In addition, if a heat source is introduced (building a hot blast stove and other facilities), the slag can be dried at the same time, and the moisture content of the slag entering the system is below 10%.

A company in Nanjing introduced that the choice of roller press configuration is based on the temperature of clinker. If the clinker temperature is not high, you can choose a roller press with a disperser. On the contrary, the configuration of roller press +v-type machine should be adopted. The roller press should avoid the entry of iron, which will seriously damage the roller surface. Therefore, the materials entering the roller press must be equipped with iron remover and metal detector. The former directly removes iron, and the latter manually removes non-magnetic metal parts such as manganese steel after detection.

Regarding the maintenance difficulty and cost of the roller press system in operation, experts from Hefei Institute of Cement said: In daily operation, as long as we pay attention to ensuring lubrication and tighten the anchor bolts, we can ensure the operation rate of more than 90%. The cost of surfacing welding on the roller surface is about 20,000 yuan for a period of 6000 hours (generally 8000 hours). After five cycles of operation, the shaft sleeve needs to be replaced, and the cost is about 300,000 yuan.

In general, the wind wheel in the disperser is replaced every three months. If wear-resistant covered electrode surfacing is used, the service life will be longer. At present, the impact plate in V-type machine is made into drawer structure, which is convenient to replace. It is worth mentioning that the blades of the circulating fan in this system must adopt wear-resistant technology, otherwise they will wear out quickly. Different units have different views on the choice of open circuit or closed circuit for ball mill. Conch Design Institute thinks that closed-circuit technology should be chosen, and the quality adaptability of ground cement is not good, mainly because concrete mixing stations with high cement temperature are not welcome. Hefei Institute thinks that the water consumption of standard consistency cement in open circuit technology is low, and the mixing station welcomes it. Both companies in Nanjing believe that the closed-circuit process is definitely superior to the open-circuit process in terms of advanced grinding technology. However, for the mill with the specification of φ 3.2× 13m, the large length and diameter are designed for the open circuit process. A company thinks that if the closed-circuit process is adopted, the length of the mill should be reduced to11m.

In fact, a senior cement expert introduced in the survey that developed countries stopped arguing about the opening and closing of ball mills in the 1980s and adopted closed-circuit process instead. A large courtyard vigorously promoted that their open-flow high-precision grinding originated in Denmark, but in the 1990s, the Danes themselves stopped open-flow grinding and switched to closed-circuit grinding. The production of cement should be refined. In developed countries, a grinding station can produce more than 70 kinds of cement at most, all of which are regulated by closed-circuit technology. China South China Institute of Technology advocates the use of open-circuit grinding in Guangdong, while the vast majority in the north advocate the use of closed-circuit grinding.

In fact, compared with closed-circuit grinding, open-circuit grinding only saves investment and is convenient for maintenance and management. The closed-circuit mill is easy to adjust and has stronger adaptability to the quality change and moisture of raw materials. The newly-built grinding station buys clinker from several clinker production enterprises, and the grindability of clinker is bound to be different. At this time, the output of closed-circuit grinding and the fineness of cement have little change because of easy adjustment, which is better than open-circuit grinding. However, when the comprehensive moisture content of ground mineral materials exceeds 65438 0.5%, the output of open-circuit grinding is greatly reduced. For example, the grinding station proposed by our company will produce cement in the future, on the one hand, it will be sold to the concrete mixing station, and on the other hand, it will produce cement concrete sleepers in our company. These two kinds of requirements for cement fineness are just the opposite: the former should not be too fine. Otherwise, the adaptability of water reducer in cement concrete is not good. The latter should not be too thick, otherwise the early strength of cement will not come up, which will affect the early strength of cement sleepers. The fineness of this cement only needs to be adjusted in the closed circuit process.

Some experts who recommend the open-circuit mill believe that the cement produced by the open-circuit mill has a wider particle size distribution than that produced by the closed-circuit mill, so the water requirement of standard consistency is lower, which is welcomed by the concrete mixing station. In this regard, senior cement experts believe that the closed-circuit mill can completely adjust the particle size of ground cement by adjusting the classifier. There is a tendency of one-sided pursuit of high efficiency in China classifier industry, which is not good! The efficiency of powder selection is about 70%. About 30% qualified fine powder enters the coarse powder in the first generation classifier; About 20% ~ 25% of qualified fine powder enters the coarse powder in the second generation classifier; In the third generation classifier, only about 5% ~ 8% qualified fine powder enters coarse powder. The separation efficiency can be adjusted to make about 14% of qualified fine powder enter coarse powder. In this way, the particle size distribution of cement produced by closed-circuit grinding becomes wider and the water demand of standard consistency increases. However, the mill output will decrease, and the mill output can be improved by simultaneously reforming the mill and adjusting the gradation of the mill body, slowing down the material flow rate in the mill and increasing the circulating load. In fact, there are many factors that affect the standard consistency water demand of cement, and the particle size distribution of cement is only one aspect. For a detailed discussion on this issue, please refer to another article by the author, The Influence of Water Consumption of Standard Consistency of Cement on Water Consumption of Concrete.

Regarding the temperature of open-circuit grinding cement, most people may think that this problem does not exist in grinding stations, and the cement temperature of online cement enterprises is easy to be high. In fact, in some enterprises that adopt roller press +φ+φ3.2× 13m open flow grinding, the cement temperature is approximately 120℃ in winter and as high as 140℃ in summer. Another online roller press +φ3.8× 13m open-circuit mill was put into operation, but the temperature in the mill was too high, which caused the bearing bush temperature to be too high and the mill stopped. According to senior cement experts, developed countries control cement temperature, and China will soon control it. Through research, the author summarizes four shortcomings of cement at high temperature: poor compatibility with water reducer in concrete; It is easy to cause early cracks in concrete; It is easy to cause gypsum dehydration and cement false coagulation; It is easy to increase the water consumption of standard consistency of cement. Therefore, it is unwise to use open flow system in the ball mill system of the newly-built grinding station. When the closed-circuit grinding process is adopted, if the O-Sepa classifier is used to introduce cold air for powder separation, the grinding temperature of cement can be reduced by 30 ~ 40℃ compared with that of open-circuit grinding.

As for the argument that φ3.2× 13m mill is more suitable for open-flow mill, the author thinks that the mill length can be shortened by two meters, that is, φ 3.2× 1 1m mill can be used as a closed-circuit mill. This can not only reduce the purchasing cost of the mill, but also reduce the bearing capacity of the grinding body in the mill, thus reducing the civil engineering cost of the mill foundation. 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 economic choice. Of course, φ3.2× 13m mill can also be used as a closed-circuit mill, which is more conducive to improving the specific surface area of cement and increasing the admixture content. The above is only the author's summary of some views formed in the investigation of mill station construction. In fact, various options have their own advantages and disadvantages. There is no perfect plan. The key is that the owners should be clear about their goals when making choices. When choosing, we should consider the advanced nature and maturity of the scheme, and also consider whether the quality of employees in this enterprise is appropriate. For example, from the perspective of saving power consumption per ton of cement and reducing operating costs, the final grinding system of vertical mill is definitely the most advanced. However, due to the unsatisfactory material of grinding roller and the particle size distribution of cement produced by domestic vertical mill (one compound is introduced for grinding cement in JISCO, and the system output is still problematic), it is not suitable for use at present. Therefore, according to the current technical level, considering that the grinding station has a certain cost advantage after operation and ensures the quality of cement, the author agrees to adopt the roller press+closed-circuit grinding process in the grinding station.