In the 1990s, the European and American cement industries began to experiment with the use of vertical mills to grind cement on the basis of the very successful industrial production and application of raw meal vertical mills. The initial production practice showed that in addition to the previously estimated structural strength of the mill, In addition to problems such as vibration and abrasion, it was also found that the construction performance of vertical mill cement has changed compared with that of the circular flow ball mill widely used at that time. The main performance is that its standard consistency requires a little higher water and the fluidity of the cement paste is slightly worse. The early strength is slightly lower. ......

1. The development history and application status of cement vertical mill

In the 1990s, the European and American cement industries began to experiment with the use of vertical mills to grind cement on the basis of the very successful industrial production and application of raw meal vertical mills. The initial production practice showed that in addition to the previously estimated structural strength of the mill, In addition to problems such as vibration and abrasion, it was also found that the construction performance of vertical mill cement has changed compared with that of the circular flow ball mill widely used at that time. The main performance is that its standard consistency requires a little higher water and the fluidity of the cement paste is slightly worse. The early strength is slightly lower. In production practice, people quickly discovered that the reason for the change in the construction performance of vertical mill cement was mainly caused by the change in the average particle size and particle composition distribution of the cement. Because this situation happened more than 30 years ago around 1960. At that time, the cement grinding system was evolving from an open-flow tube mill to a loop ball mill. The cement construction performance of the loop ball mill was "slightly poor". In the cement industry in Europe and the United States, there has been a debate and hesitation about whether to use open flow or circle flow for cement grinding for nearly 10 years (the author had contributed an article abroad to publish my humble opinion). After several improvements in the cement industry's own process equipment, as well as coordination and cooperation with concrete construction, this problem has finally been properly resolved. As a result, the cement loop grinding system replaced the open-flow tube mill and developed rapidly. Based on this experience, when Europe and the United States encountered the so-called vertical mill cement performance problem again in 1990, the cement industry and the concrete industry were both psychologically and technically "familiar with the road", calmly dealt with it, quickly solved the problem, and promoted the smooth promotion of cement vertical mills. Created favorable conditions. In 2015, the selection rate of cement vertical mills in Europe and the United States reached about 60%.

With the passage of time, the cement vertical mill system has been continuously improved in terms of mechanical structure strength, transmission reducer, mill vibration, liner wear, reliability and operation rate, and flexible and convenient control of its cement performance. And gradually improve. In Europe and the United States until 2000, cement vertical mills have overcome various problems, showing their advantages of high efficiency, economy, energy saving, low noise, and small area, and are welcomed by the majority of users. The selection rate of vertical mills in cement grinding systems in new cement projects in the world (except Mainland China) has increased from 15% in 2000 to 45% in 2005, as shown in Figure 1. After that, the US watch continued to maintain this momentum. In 2015, the selection rate of its cement vertical mill continued to rise to 70%. But globally (except Mainland China) it rose slightly to 53%. According to the report of the German Winston (OneStone) consulting company, in 2015, about 2,610 sets of cement grinding systems were put into production globally (except mainland China), of which there were 538 cement vertical mills, accounting for about the total cement output that year. 23% (414 million tons).

  The use of cement vertical mills in my country's cement industry first began in 2005. Yunnan Kunming Dongjun Cement Factory introduced two OK 33-4 vertical mills from Smith Company to produce cement and finely grind slag, creating my country’s cement vertical mills. First, achieved a zero breakthrough. Because of the successful application of cement vertical mills in Dongjun Plant and its good operating practices, cement vertical mills have begun to gain a place in domestic new cement projects. By 2010, the domestic selection rate of cement vertical mill systems rose to 8%. Through practice, the advantages of the cement vertical mill system have gradually been recognized by more users, showing a slight trend of promotion. In 2015, its selection rate has reached 30% (Figure 1). From 2000 to 2015, the cumulative number of vertical mills sold by various suppliers in my country is listed in Table 1. As many as 210 cement (slag) vertical mills were put into production in my country's cement plants in 2015, accounting for about 9% (216 million tons) of the total cement output that year.

2. the main obstacles to the further promotion and selection of cement vertical mills in my country

Although the long-term production practice of more than 600 cement vertical mills at home and abroad has shown that, compared with the grinding system of roller press + ball mill, cement vertical mill has the advantages of energy saving, investment saving, low production cost, low noise, and changing product varieties ( Cement, slag powder) has many advantages such as rapid and convenient, small area, open-air installation and so on. However, in the minds of many Chinese cement companies, there are still some "worries" that the performance of the vertical mill cement may not be as good as the semi-final system, for fear of the cement market. Looking back on the exchanges with foreign experts over the years, the author found that internationally, no matter if it is a developed country, a new country or a less advanced country, they seem to have basically no such "worries" and don't care much about it. Because colleagues in developed countries are "comers" and have personal experience, there is no need to "worry." Colleagues in emerging countries and less advanced countries often quickly dispelled this hearsay "worry" after learning the fact that more than 600 cement vertical mills have been successfully operated. Only our Chinese expert colleagues still have such strong "worries"?

The author believes that this is obviously related to the fact that all provinces, regions, cities, prefectures, and villages in our country have been very accustomed to using circulatory ball mill cement and roller press semi-final cement in the past 50 years; because it is the only form of cement in my country, The scale of application is extremely large, reaching 38 billion tons: the geographical space is extremely wide, all over the country: the duration is extremely long, more than half a century: the cumulative number of building materials construction employees is extremely large, nearly 200 million people. Therefore, the cement and concrete construction industry in my country has developed a fixed habit for it. The psychological and production and operation habits are extremely tenacious. In the short term, it is a psychological obstacle for them to accept the newly arrived vertical mill cement. It will take a certain amount of time to eliminate this psychological barrier nationwide. This is the special situation caused by the development history of my country's cement industry. It is also the further promotion of cement vertical mills in my country to increase the proportion of vertical mill cement in total cement production (for example, from 9% in 2015 to 15% in 2020) Left and right) the first obstacle faced is also the main obstacle.

  The second obstacle is the legendary so-called cement vertical mill system is complex and difficult to control. This obstacle is relatively simple and easy to explain. Because it only involves technical issues in the production and operation management of the cement vertical mill system. In fact, the current cement vertical mill system has a complete means and method to comprehensively control the construction performance of its cement products, which can ensure the particle size composition and distribution, characteristic particle size, uniformity coefficient (RRB curve slope), Water demand, fluidity, early strength of cement and other indicators, if not better than those, are at least not inferior to circulating ball mill cement. It can completely realize the full coverage of cement-related performance control (Figure 2), and the control is convenient, timely and accurate, and responds quickly. There are four main control methods, namely, the height of the retaining ring, the air volume (wind speed) in the mill, the grinding pressure and the speed of the powder separator; the control range and precision of each method, and their impact on the cement performance, are shown in Table 2. And listed in Table 3. Correspondingly, in the case of different retaining ring heights, the relationship between the grinding pressure and the uniformity coefficient of the cement particle size composition; and in the case of different air volumes (wind speeds) in the mill, the speed of the separator and the uniformity of the cement The correlation of the coefficients is shown in Figure 3 and Figure 4 respectively. According to the operation guide in Table 3, single or multiple comprehensive control methods can be adopted, and various properties of finished cement products can be gradually controlled and adjusted in production practice, which can fully meet the goal of market demand.

In the initial stage of trial production of cement vertical mill, the above-mentioned control measures and methods are adopted, and through communication and coordination with the concrete client, the mutual adaptation process can be completed within 1 to 2 months, and gradually becomes normal.化. In the second half of 2005, I experienced this process during the commissioning of the OK 33-4 cement vertical mill of Dongjun Plant. The general production technicians of the cement plant can do this job. By the beginning of 2006, Dongjun's cement was very popular in the Kunming market, and the price was slightly higher, and customers welcomed it. It took less than half a year for OK 33-4 cement vertical mill from trial production to the announcement of the first success of vertical mill cement in the Chinese market. So far, the two cement (slag) vertical mills have been running smoothly for 12 years, and Dongjun Plant is very satisfied.

As for the comparison of the performance indicators of vertical mill cement and ball mill cement, more than 100 sets of practical data have been released at home and abroad. my country’s Hefei Institute, Tianjin Institute and some cement plants have reported many results in this regard. The conclusions are positive for the vertical mill cement, so I will not list them all. The data of Jiang Xiiyadong is particularly recommended here to illustrate the problem. Since 2007, Jiangxiiyadong has become the second manufacturer in my country to introduce and choose cement vertical mill system after Yunnan Dongjun. If Dongjun decided to choose the cement vertical mill first in 2003, he did have the foresight and courage to "eat crabs", which is admirable. In 2006, Yadong made a clear and shrewd decision to choose a cement vertical mill. Because this is a well-conceived measure taken by Yadong after a comprehensive assessment, and it reflects the scientific foresight of its management. In addition, because Jiangxi East has both roller press + ball milled semi-finished cement and vertical mill cement in the same factory, both of them use the same clinker, admixture, and gypsum to grind to the same variety and label. The comparison conditions of the cement are perfect (there are also examples abroad); in addition, the production and operation management level of Jiangxi East is excellent, the sampling and testing are rigorous, and the data is accurate and reliable. Therefore, Yadong’s comparative data and results will be more convincing and convincing.

Table 4 shows many tests conducted by Yadong around 2008. Under normal production and operation conditions, the average value of the test data of 17 comparative samples was extracted in parallel and evenly rhythmically within 1 month each time, which is highly representative and objective. Sex.

Through the above-mentioned comparative tests, Yadong concluded: “The water requirements, fluidity of cement paste and early strength of cement that people are worried about for vertical mill cement are all up to the standard, and are slightly better than conventional ball mill cement. Vertical mill cement Compared with the roller press + ball mill, the unit power consumption is 4~6kWh/t, which is more than 12 kWh/t than the circle ball mill” (China Cement, 2009, Issue 10, pages 49~52). In fact, this conclusion is no different from the results of comparative tests at home and abroad at that time. After reviewing this conclusion carefully now, I wonder if you, who still have such concerns, will start to rethink and dispel them at this moment. Or turn the worries into a basic tendency to be reassuring? !

  As of the end of 2015, Smith has more than 400 cement tube mills and ball mills operating in global cement plants, about 80 cement semi-final grinding roller presses, and about 135 cement (slag) vertical mills. According to the big data analysis of the actual production and operation of these mills, representative statistical averages of the production and maintenance costs of the three cement grinding systems were selected, as shown in Table 5.

 The data in Table 5 is completely derived from the big data analysis of Smith's existing cement grinding machines, which are representative averages of countries in the world, or can be used as a rough relative quantitative reference. It can be seen that the production, operation and maintenance costs of the cement vertical mill, the metal wear of the grinding media, and the relative ton investment are lower than those of the cement circle ball mill and the semi-final grinding system of roller press + ball mill.

  3. Development of cement vertical mill

  The development of cement vertical mill is mainly manifested in large-scale or super-large scale. For example, Smith's largest OK mill has been developed into OK 62-6, with a cement production capacity of 750t/h, a slag of 550t/h, a grinding disc diameter of 8.2m, 6 grinding rollers, and a transmission power of 12000~16000kW, as shown in Figure 5 and Shown in Figure 6. The OK 62-6 vertical mill is suitable for 10000~12000 t/d clinker (cement) production lines and cement (slag) grinding stations with an annual output of 4 million tons.

Another manifestation of the development of cement vertical mills is intelligence. The vertical mill system can pre-set the specified indicators in the memory of the intelligent operating system according to the customer's requirements for cement performance, especially construction performance, during the production transfer of the vertical mill The intelligent software will intermittently monitor various indicators in real time, and carry out automatic adjustment and tracking detection in time, so that cement performance is always under supervision of production.

  At present, the intelligent vertical mill system, including its operating economic indicators and product performance quality monitoring and adjustment functions, has entered the stage of industrial-scale production test and R&D, debugging and improvement, and it will soon be put on the market. According to relevant research and development experts, the vertical mill intelligent system enjoys greater advantages compared to the semi-final grinding of roller press + ball mill. Because its equipment is small and simple, the control method is highly targeted, the target is accurate, the control is convenient and fast, the feedback response is fast, and the research and development technology is less difficult. This is an important favorable condition for the early practical application of the vertical mill intelligent system.

 4. conclusion

Nowadays, in the field of cement grinding systems in the world cement industry, there are mainly three systems widely used in the field of circular ball mills, roller press + ball mill semi-finished and vertical mills. Open flow tube mills are rarely used anymore. Cylindrical roller mills Still trying to develop, the roller press final grinding may be an option for new attempts.

  On the issue of cement construction performance, 100 years ago, there was only one kind of cement open-flow tube mill in the world. Because there was no choice, people knew very little about the so-called cement construction performance. So naturally accepted the open flow tube mill. Unexpectedly, this acceptance has been more than half a century, and the cement and concrete industries have developed a deep-rooted habit of milling cement. Until around 1960, when the open flow tube mill evolved and transformed to the circular flow ball mill, developed countries such as Europe and the United States had a strong "entanglement" with the resulting changes in cement construction performance, and even hesitated in the debate for nearly 10 years. In 2017, the open-flow tube mill was eventually replaced by the circle ball mill, because technological progress is an eternal theme.

  However, at that time, we in China did not seem to feel the kind of "entanglement" in Europe and America, because we were far from developing to the stage where we could feel it. At present, when cement vertical mills are gradually being promoted in our country, due to changes in cement properties, a European and American "entanglement" around 1960 has been repeated in my country's cement concrete industry, creating a psychological obstacle to the promotion of cement vertical mills. History tells us that this phenomenon has its roots and is understandable.

  But what is certain is that my country’s current "entanglement and hesitation" can never be so long, and the final expected result must be optimistic. In fact, cement vertical mills have formed a trend in my country and have entered the track of gradual promotion. Because all kinds of cement grinding process equipment technology systems are constantly innovating and evolving, every user will choose the most suitable cement grinding equipment according to the actual specific situation and its most important concerns. People should respect it. The independent choice of each owner.

  It is true that various cement grinding systems more or less have their own strengths and weaknesses, not to mention the continuous development of various innovations and technological advancements. As an industry expert, the main responsibility and ethics when disseminating and introducing new processes, new technologies, and new equipment is to provide relevant materials, data and information (including personal opinions and suggestions) to the public in an objective, fair, fair and truthful manner in accordance with current reality , For reference and comments of colleagues in the industry, mutual discussion and common improvement.

This article is transferred from China Cement Association

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