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How to properly use new ceramic grinding bodies in cement ball mill

Date:2019-07-03 17:18 Source:未知Views:

Preface


At present, the status quo of the cement industry is not optimistic. The problems ahead are overcapacity, weak market demand, falling profit margins, increasing environmental pressures, and increasing competition in the cement market. How to reduce production costs and improve the competitiveness of enterprises after the traditional technological transformation measures have been put in place has become the top priority for the industry.

As we all know, the current ball mill grinding is still the main way of cement grinding. The wear of the cement grinding power and the steel grinding steel segment and other metal grinding bodies occupy an important part of the cost of cement grinding. As a cement grinding and grinding body, the use of high-chromium cast balls and segments makes the grinding and cost of cement grinding much lower, and is recognized by the industry. However, due to its high quality, the grinding machine has high power, high operating current and high energy consumption for grinding, which is an inherent problem in the grinding operation.

In recent years, a new type of high-quality wear-resistant alumina ceramic grinding body has emerged. The introduction of this new type of grinding body is undoubtedly a bright light in the industry, changing the status quo of cement grinding machine grinding body relying on metal grinding materials for a long time. The energy-saving and environmental protection of grinding has injected fresh vitality, which not only responds to the national call for energy conservation and emission reduction, but also reduces the production cost of enterprises, and also improves the economic and social benefits of enterprises. In the current environment where the cement industry is not prosperous, it is favored by cement grinding operations and has become a hot topic in the industry.

1 Alumina ceramic grinding body performance


The new alumina ceramic abrasive body is currently generally referred to as a high temperature ceramic sintered body having an alumina content of about 92%, having a spherical shape (grinding ball) and a cylindrical shape (grinding section). The alumina ceramic sintered body has characteristics of high temperature resistance, high hardness, wear resistance, corrosion resistance, low expansion coefficient, high thermal conductivity, light weight, and high brittleness.

As a grinding medium, its high hardness and high wear resistance are properties. Light weight is the premise of energy saving and low grinding efficiency; large brittleness is its outstanding shortcoming and large breakage rate.

After the ball mill uses the new alumina ceramic grinding body, it has the following advantages over the high chromium steel ball:

1) Reduce the power consumption of cement grinding


Reduce the load of the ball mill by more than 30%, the current of the mill main machine can be reduced by more than 20%, and the electricity consumption per ton of cement is reduced by more than 15%. Take Φ4.2 m×13 m cement ball mill as an example: with steel ball and steel section grinding body, the mill output is about 210 t/h, and the average power consumption of cement is about 30 kWh/t. With the new alumina ceramic grinding body, the average power consumption of the mill can be reduced to below 25 kWh/t. If the electricity fee is calculated at 0.6 yuan/kWh, the manufacturing cost per ton of cement can be saved by 3.0 yuan, and the annual cost of grinding mill is 1 million tons of cement, saving about 3 million yuan.

2) Conducive to the safe operation of equipment


The new alumina ceramic abrasive body has low wear and extended maintenance intervals. The metal abrasive body is worn at 30 to 40 g/t of cement. The wear of the new alumina ceramic grinding body is about 50% of the metal grinding body, the service life is lengthened, the maintenance workload is greatly reduced; the overall quality of the grinding machine is reduced, the friction of the sliding bearing bush is reduced, and the temperature is lowered, which is beneficial to grinding. Safe operation and longevity of the equipment.

3) Good compatibility of cement and admixture


After using the new alumina ceramic grinding body, the cement temperature is reduced by 20 °C or more, the overgrinding phenomenon is alleviated, the particle distribution is optimized, the particle size is reduced by ≤1 μm, the particle size of 3~32 μm is increased, the water consumption of the standard consistency of cement is reduced, cement The compatibility with concrete admixtures is improved and is welcomed by the downstream concrete industry, which is beneficial to market sales.

4) Conducive to environmental protection


The new alumina ceramic grinding body does not bring in chromium ions, which is conducive to environmental protection, production of green cement, and meets the requirements of GB 31893-2015 national standards.

2 Application method of alumina ceramic grinding body


Traditional ceramic abrasive bodies have been used for many years on wet grinding. Because of its inherent shortcomings such as high brittleness, low toughness, and easy breakage, it is often used in cement grinding to cause problems such as large damage and low grinding efficiency. For wear resistant materials, the harder the material is generally more wear resistant, but the wear resistance is not completely proportional to the hardness. As a ceramic grinding body, the toughness is also considered. Hardness and toughness are a pair of contradictory uniforms. Conventional alumina wear-resistant materials with high toughness and high hardness are generally brittle. The covalent bond crystal phase structure is the source of brittleness of alumina ceramics. How to improve toughness (toughening) is the focus of research, but at present it can only achieve a little improvement. Therefore, the hardness and brittleness are the nature of the alumina ceramic material; at the same time, the production process has a great influence on the performance of the material, such as ratio, grinding fineness, molding method, calcination system, and the like. For example, the molding method can be divided into press molding and rolling forming, and two kinds of ceramic grinding bodies of the same material and the same specifications are tested, and the breakage rate of press molding is lower than that of the roll forming type.

At present, there are not many companies that have the ability to manufacture ceramic grinding products for cement grinding, and the use time in the industry is relatively short. The problems in the process of use still need to be solved, and it is impossible to take ordinary ceramic grinding bodies. Fill the cement ball mill. Because the new alumina ceramic grinding body has certain selectivity to the mill equipment and the grinding material, the existence of these problems, if not solved well, will affect the promotion and application of the new alumina ceramic grinding body. The original wet grinding abrasive body is directly loaded into the cement mill, which will cause the grinding body to be severely broken, the breaking rate exceeds 2.0%, and the peeling debris is directly blocked on the quilting of the grinding plate, resulting in an increase in ventilation resistance. The finished product cannot be discharged in time, which greatly affects the production of the Taiwanese machine and the normal production operation of the mill.

2.1 Adaptability of ceramic grinding bodies


The new alumina ceramic grinding body has certain selectivity for ball mills and grinding materials. It should be noted that the alumina ceramic grinding body is different from the metal grinding body in that it has excellent wear resistance which is incomparable with steel balls under low stress and small angle wear conditions, but for large impact force, the breaking rate under the condition of front impact Will increase, contrary to the characteristics of the metal abrasive body. According to statistics, the impact toughness of high-chromium steel balls is ≥4 J/cm2, and the impact toughness of ceramic balls is ≤1.5 J/cm2. Therefore, if the ceramic ball is used in a warehouse with crushing as the main, it will cause too high. damage rate. This is also the main reason why the new alumina ceramic grinding body is suitable for the multi-bin ball mill tail bin which is mainly based on the sloping mode, and is not suitable for the ball mill which is mainly used for the throwing method. Even if a variety of toughening materials are added to the new ceramic grinding body, the ceramic grinding body is only suitable for the grinding machine system with pre-grinding equipment such as a roller press, and the grinding grain size of 80 μm sieve is required to be <40 %. It has been verified by many experiments that the new alumina ceramic grinding body is more suitable for the grinding of blast furnace slag, fly ash and limestone, and the grinding efficiency is higher than that of the metal grinding body.

2.2 Mill adjustment


The promotion and use of the new alumina ceramic grinding body in the cement industry is not a simple job. It is necessary to systematically organize, analyze and analyze the parameters of the mill structure, grinding body, process parameters and grinding materials. And the corresponding adjustments can be made to achieve the desired effect of the new type of grinding body.

It is necessary to do a good job in the investigation of the cement ball mill, and thoroughly understand and master the raw material grindability, grinding main and auxiliary equipment, process flow, central control room operating parameters, and finished product quality indicators. The inspection projects of the mill mainly include:

1) Roller system technology: equipment specification model, main engine power, nominal output, actual output; raw material particle size, grain size, raw material moisture, moisture content, product size, etc.

2) Mill system technology (double closed circuit): host specification model, host power, nominal output; powder selection equipment type, host current, host power, actual power; effective inner diameter and warehouse length, each warehouse grading, total load , the form of the compartment board, etc.

3) Process parameters: product variety; 80 μm and 45 μm sieve residue, specific surface area, Taiwan time production, unit power consumption; slag and steel slag ratio.

Firstly, the operating parameters of the mill system are calibrated, including the production time of the mill, the operation of the roller press, the particle size of the milled material, the flow rate of the material in the mill, the wind speed, the negative pressure of the inlet and outlet, the powder selection efficiency of the separator and the cycle load rate; The mill filling rate, the maximum ball diameter and the average ball diameter are measured in detail; the form of the mill liner, the compartment board and the discharge jaw are statistically organized. In this way, it is confirmed whether the mill system is suitable for the new alumina ceramic grinding body, and the unsuitable mill should not be tried hard. Of course, most mills are adapted. Then, the gradation adjustment of the grinding body is performed according to the change data of the material sieve residue curve, and the gradation of the grinding body filling rate and the ball diameter of each stage is confirmed. At present, the new ceramic grinding body is mainly suitable for the tail end of the mill, and it must be matched with the front grading. The grain size of the grinding material using pre-grinding equipment such as roller presses is usually <3 mm or even <1 mm. Due to the reduced particle size of the grinding material, the average ball diameter of the grinding body in the ball mill grinding machine must be reduced. In general, the ball diameter of the largest ball in a warehouse should not exceed Φ60 mm. Reasonable grading is to allow the particles entering the tail bin to be fully ground by the new abrasive body, and the position of the partition plate should be adjusted according to the particle size of the grinding machine to increase the length of the fine grinding bin. After the test, in general, the tailings should be increased by 3% to 6% compared with the metal grinding body, and the maximum ball diameter needs to be one size larger. The loading amount is about 60% of the original metal grinding body, so that the total grinding body after replacement is required. The surface area cannot be lower than that of the metal abrasive body to ensure sufficient grinding performance. Before adding a new ceramic grinding body, a part of fly ash or slag powder is spread in the warehouse as a starting buffer.

After the mill is in normal operation, it is necessary to pay close attention to the changes of various system parameters. The parameters such as the host current, the inlet and outlet of the mill, and the temperature of the grinding gas will change greatly, and should be adjusted in time according to the change of the grinding condition. The process parameters of the grinding equipment should be adapted or close to the previous ones to ensure the safe operation of the mill system. At the same time, the post operator adapts to the new grinding condition as soon as possible, and saves electricity and reduces consumption under the premise of stabilizing the production and quality of the cement grinding system. Due to the non-metallic structural characteristics of the new abrasive body, the electrostatic adsorption decreases or disappears after the grinding body is replaced. The flow rate of the material in the grinding is often accelerated or even out of control. Since the material does not have enough residence time in the grinding, the material cannot be fully ground. Well, it will lead to an increase in the circulating load of the classifier, a sharp increase in the material in the mill, a misalignment of the ball, an increase in the current of the hoist, a drop in the yield of the mill and a decrease in the current of the finished hoist, and repeated vicious cycles, making the mill system impossible. Normal operation affects production. During on-site commissioning, the flow rate of the material in the mill is allowed to change, the cycle load of the classifier is slightly higher, and the output fluctuation of the table occurs. As long as the parameters of the mill and the output of the machine are stabilized, and the quality index of the finished product meets the control requirements, it can be gradually Adjustment and debugging. If there is still uncontrollable situation after the adjustment of the mill system, it is necessary to communicate with the plant equipment management personnel, modify the grinding inner lining plate, the silo slab and the discharge slab, analyze the reasons, and take Make practical and feasible transformation plans to adapt to changes in grinding conditions. Only by fully understanding the mill equipment system can the full effect of the new alumina ceramic grinding body be fully utilized, thereby achieving the goal of energy saving and consumption reduction.

3 examples


A cement company is equipped with a Φ3.8 m×13 m double closed-circuit mill, which is combined with a roller press to form a P-O42.5R, P·O42.5 and P·C32.5R cement. The system host device configuration is shown in Table 1, and the system process flow is shown in Figure 1. It can be seen from Table 1 and Figure 1 that the system is a two-cylinder double closed-circuit cement grinding system consisting of a pre-pulverizing machine with a V-type classifier and a ball mill with an O-Sepa classifier.
Table 1 mill system parameters



Figure 1 Grinding system process

According to the trial plan, after the calibration of the mill system was carried out, the use plan of the ceramic grinding body was established. Because the roller surface of the roller press is heavily worn, it indicates that there are unstable large particles entering the grinding. When it is determined that the ball diameter ratio of the mill is not changed, the Φ40 mm metal grinding body is added 5 t to ensure that there are some large particles in the grinding part. Sufficient impact force; the load of Ercang ceramic grinding body is 56% of the mass of the metal grinding body, and the ball diameter is Φ13 mm~Φ25 mm. The new alumina ceramic grinding body was replaced on June 11, 2016. At the beginning of use, the current of the mill main engine dropped significantly, but there was a phenomenon that the grinding fineness was rough, the powder selection machine current and the lifter hoist current increased, and the circulating load of the powder separator increased. It was initially judged that after replacing the ceramic grinding body. The phenomenon of electrostatic adsorption is alleviated, the phenomenon of fine powder aggregation is eliminated, the flow rate of the material in the mill is fast, and the grinding is insufficient. Accordingly, it is determined to adjust from the mill parameters and appropriately change the mill discharge system to adapt to the grinding characteristics of the ceramic abrasive body. Since the wind speed in the mill directly affects the flow rate of the material, by adjusting the opening degree of the circulating air valve in the mill, the opening degree and the rotation speed of the separator 1 and the secondary air valve, the flow rate of the material in the mill can be effectively slowed down; The measures of quilting the squeegee of the squeegee are kept so that the material in the mill maintains sufficient grinding time. After adjustment and optimization, the changes in the operating parameters of the mill system are shown in Table 2, and the conditions in the mill are shown in Figure 2.
Table 2 Technical parameters of mill system (P·O42.5 cement)




Figure 2 Photo of the condition inside the mill

It can be seen from Table 2 that the loading capacity of the grinding body is greatly reduced, and the temperature of the main machine of the mill and the temperature of the tail end of the grinding machine are greatly reduced, and the energy consumption of the mill is obviously reduced.

See Table 3 for a comparison of the particle composition of the finished cement with the metal abrasive body after using the new alumina ceramic abrasive body. It can be seen from Table 3 that in the distribution of the cement particles of the new alumina ceramic grinding body, the characteristic particle size and the median diameter are reduced, and the amount of particles <1 μm is reduced, that is, the phenomenon of over-grinding is alleviated. The number of 3 to 25 μm particles contributing to the strength of the cement increases, and the distribution of the powder particles is improved, which is advantageous for the late strength of the cement.

Table 3 Cement particle composition
Tables 4 and 5 are concrete slump tests prepared by grinding cement using a new alumina ceramic abrasive body. It can be seen that the concrete slump is significantly increased, and the slump loss over time is significantly reduced. Because the temperature inside the mill is reduced, the optimization of the cement particle composition can reduce the water consumption of the standard consistency of the cement, increase the fluidity of the cement, reduce the adsorption of the concrete admixture, and improve the compatibility of the cement and concrete admixture. In this way, the cement performance is further improved, so that downstream customers have better choices.
Table 4 C30 concrete material ratio
Table 5 Concrete slump test (June 2016)

4 Conclusion


At present, the use of new alumina ceramic grinding bodies is not long. Different cement enterprises have different process configurations. There are no fixed adjustment measures that can be followed. It is necessary to take corresponding measures according to different situations, ultimately achieving energy saving, extending equipment maintenance cycle and reducing maintenance costs. And the purpose of environmentally friendly production, to maximize the effectiveness of the new alumina ceramic grinding body.

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