Research Status, Development and Problems of Vertical Mill

1 Research status of vertical mill at home and abroad
1.1 vertical mill in overseas development

The first vertical mill was born in 1925 and was developed by German experts. In 1935, vertical mills were first applied to the cement field. Vertical mills have been well developed in Europe and used in the United States and Canada. Due to the relatively high cost of fuel costs at the time, Europe and Canada also vigorously developed and applied vertical grinding technology. The United States is also increasingly interested in the research of vertical grinding equipment. And at the end of 1973, the first grinding equipment was put into use in the United States. Due to the energy saving and high efficiency of grinding equipment, many countries have also introduced vertical grinding technology. These countries include Argentina, Congo, Japan, Egypt, Hexige and New Zealand. At the end of the last century, along with the tremendous economic development of East Asian countries, the East Asian cement sector has also experienced rapid development. Large international companies have invested in Southeast Asian countries, making large-scale cement production lines springing up in various regions, and vertical grinding technology has also developed rapidly.

In the 1960s, vertical pulverizers made a qualitative leap abroad and developed along the trend of large-scale. In the cement field in Europe and the United States and China, vertical mills are widely used in the field of cement raw material processing. The vertical grinding technology developed rapidly in the 1970s, when a large vertical mill with a capacity of 500t/h appeared.

In the 1990s, the grinding technology developed rapidly, mainly due to the development of technologies such as finite element, parameter optimization and fluidics. On the other hand, the development of remanufacturing engineering and the application of wear-resistant materials directly promoted The application and promotion of the mill has improved the use time of the vertical mill, saved the cost of the enterprise, and ensured the requirement of the vertical grinding capacity of the large dry-process cement production line. The market share of the vertical mill in the cement industry reached a percentage. More than ninety.

In general, in recent years, countries have vigorously advocated policies for energy conservation and consumption reduction, cement production has become large-scale, and vertical mills have grown to large-scale. The technology has made new progress, mainly as follows:
(1 ) Design presents new ideas

With its production capacity, the LM mill is designed to be compact, minimal and cost-effective. Along with the development of the large-scale grinding machine, the thickness of the mill bed is too high, the ability of the mill to dry the finished product is not well matched with the ability to grind the raw materials, and some properties are degraded, such as the efficiency of the grinding machine, so In the mill design, there is a new idea, using the design idea of ​​large grinding disc and small grinding roller, in order to achieve the vertical grinding and kiln synchronous operation, also based on cost considerations, using 6 roller mills, 4 of which are roller Grinding work, a new idea for 2 roll repairs.

(2 ) All external circulation of materials
The original mill is equipped with a wind ring. In order to ensure the constant internal pressure of the mill, a large amount of wind is required to be used, and the power consumption is huge. A new design idea is proposed for this, and the material is changed from partial outer circulation to full outer circulation. Transfer all materials to the outside of the classifier. This process is implemented by the hoist.

(3 ) Enhanced material adaptability
In order to meet the drying requirements, materials with a water content of up to 12% to 25% require a high temperature gas of about 600 degrees. In order to grind highly abrasive materials, the grinding roller adopts a new type of scheme: the width of the grinding roller is reduced, and the diameter of the grinding roller is increased, and the thickness of the sleeve is increased. This scheme reduces the friction and wear, and the grinding roller and the grinding roller The speed between the discs is better, and the amount of grinding material allowed per time is increased.

1.2 Vertical grinding in the domestic development
In 1940, vertical mill began to be applied in China, and it was applied to the field of white cement for the first time. In the 1950s, small vertical mills were used in domestic cement companies. Beginning in the late 1970s, cement plants began to adopt a new dry process outside the kiln. Domestic experts began to develop and research equipment for vertical grinding and grinding of raw materials. In the early 1980s, the domestic research and development results of the vertical mill technology were obtained. The Tianjin Cement Research and Design Institute developed the TKM series vertical mill. The Hefei Cement Industry Design and Research Institute also achieved success and successfully developed the HRM model with a daily output of 2,500 tons. Vertical mill, and developed other models of this type of mill.

At the same time, China began to introduce large-scale vertical grinding technology abroad, and developed and designed different types of grinding machines on the basis of absorption and digestion. For example, CITIC Heavy Machinery Co., Ltd. and Smith Company have cooperated and developed the LGM5024 vertical pulverizer, which has been applied in Jilin cement production. The production line is 5,000 tons per day and can grind moisture content less than 12%. Material.

In addition, Shenyang Heavy Machinery Factory has developed a variety of ML series vertical mill equipment and applied it to the cement clinker production line, and the structure has been improved compared with the previous one, adding external circulation, buffering parts, etc., and also developed MLK series mills for slag production.

HRM vertical mill

By absorbing foreign technology, Hefei Cement Design Institute has developed a vertical grinding machine with a daily output of 5000.0 tons of HRM on the basis of these digestions. This type of mill is suitable for the clinker production line. The grinding structure is the same as the MPS. The machine has its own characteristics, such as the reversible roller, and is manufactured by Deli Machinery Manufacturing Co., Ltd. It has been found in production that the mill has the characteristics of low operating cost, less power consumption, and higher efficiency compared with tube mills, compared with other similar equipment in foreign countries. This type of vertical mill can produce 5,000 tons per day, so it can compete with imported equipment.

TRM53 raw material equipment

Tianjin Cement Design Institute has also developed TRM53 raw material equipment by absorbing domestic and foreign technologies. The mill has the same structural characteristics as MPS structure, such as high production efficiency, good drying performance, compact structure and wide adaptability. Features. After operation, the system consumes about 15 degrees of electricity per hour. The effect of drying the moisture by the exhaust gas is better. The grinding grain size of the raw materials reaches 120mm. The life of each wear part is within the design range, which can meet the relevant requirements of the daily production line. This marks that the mill technology has reached the level of similar products.
In addition, domestic universities and research institutes have done a lot of research on vertical grinding. On the one hand, the structural optimization of the key parts of the vertical mill has been carried out to improve the grinding ability and fineness of the vertical mill, and the results have been achieved; on the other hand, the process parameters are optimized. Through the series of test analysis, to optimize the process parameters such as wind speed.

Chen Shijiao and Yang Fangxia from Chongqing University conducted a dynamic study on the TRM mill, and studied the dynamic characteristics of the mill from both theoretical and finite element software. Firstly, the loading system of the pulverizer is analyzed, and the simplified model is used to represent the mechanical model. The equivalent mass conversion and the centroid instantaneous velocity analysis are carried out. The mathematical calculation software is used to solve the differential equation and the natural frequencies of the system are solved. . Another modal analysis is performed by ANSYS, and the low-order natural frequency is obtained by post-processing. The results obtained by the two methods are consistent, which provides a theoretical basis for studying the dynamic performance of the mill.

Professor Li Qiang of Jilin University made a corresponding research on the vertical mill, especially for the MLS453 mill, and carried out the finite element analysis of the grinding disc under two working conditions, and analyzed the data of the stress and strain of the grinding disc. The maximum equivalent stress is less than its allowable stress, and the displacement is also small, and the stiffness is also reasonable.

Yang Honggang of Hebei University of Technology studied the vertical mill with a daily output of 5000t. The static analysis of the rocker arm and the base of the key components was carried out. The research found that the components were designed reasonably and met the relevant requirements.

Deng Xiaolin of Hefei Cement Design Institute analyzed the relevant components of HRM4800, analyzed the stress status of the main components, and verified that the structural work meets the design requirements and the reliability is good.

Zhang Xiaozhong and Dong Liming from Xi'an University of Architecture and Technology used ADAMS software to establish a parametric model of the mill. In this process, there are a large number of physical prototypes, and the project is replaced by a virtual prototype, focusing on the stability of the vertical mill in the startup phase. Sex.
Professor Shen Zuwu from Wuhan University of Technology and Huang Jiquan from Sinoma Construction Company conducted a meta-analysis of the mill transfer device and established a finite element model. From the perspective of statics, the rationality of the design was verified and the design practice was instructive.

Zhang Shuguang of Sinoma Construction Company and Chen Zubing of Wuhan Institute of Technology conducted an analysis of the temperature field of the grinding disc. The analysis process used the APDL parametric language. The analysis found that the temperature field of the grinding disc changed from 31.3 degrees Celsius to 179.5 degrees Celsius, and the bottom of the grinding disc The temperature is the smallest, the temperature is the largest at the edge of the disc, and the maximum deformation and the coupled field thermal stress are within the allowable range, which verifies that the structure meets the relevant requirements for operation.

Hou Zhiqiang and Hou Shujun of Hebei University of Technology analyzed the internal air flow of the mill. Using fluid dynamics analysis software, the study found that there are huge vortices inside the mill, and understand the specific characteristics of the internal air flow. The existence of the vortex will consume the energy of the system and also the stability of the mill. The impact of reducing the efficiency and service life of the mill improves the internal optimization and redesign of the mill.

Yang Linjian of Sichuan Engineering Vocational and Technical College and Li Jian of China's Double Research conducted a static analysis of the column. The research first built a model in UG and analyzed it in the finite element analysis software. It was found that the equivalent stress of the column occurred at the maximum near the central opening and was 158 MPa. The stress was high, and the structural adjustment should be adjusted accordingly.

1.4 problems
Vertical mill technology is monopolized by foreign companies. Although China has introduced technology from abroad and absorbed and digested the vertical mill design technology, its energy consumption is at least 5 percent higher than that of foreign countries. The main reasons are as follows:
(1) In terms of vertical mill design, a traditional design method based on experience and analogy is obviously insufficient, lacking system and basic data support.
(2) In terms of operation control, the adaptability of the mill should be further improved. When the yield changes or the material fluctuates, the stability of the entire grinding system is not good.
(3) In terms of parameter optimization, study the influence of process parameters such as size and wind speed on the static and dynamic performance of the structure, and whether the system can achieve energy saving and consumption reduction.