Introduction

Ceramic ball as cement grinding body is not a new thing, the white cement industry early use of cast stone ball that is low density grinding body, and later used a kind of artificial silica ball in the white cement pipe mill application can be said to be the ancestor of ceramic ball in cement grinding application. As a new wear-resisting material in cement grinding system, ceramic ball has the obvious advantages of energy saving and reducing the temperature of cement grinding, and has shown the tendency to replace high chromium ball. But due to the ceramic ball manufacturers and cement manufacturers on the ceramic ball communication, communication is not enough, the application of ceramic ball grinding body has the following problems:

(1) Ceramic ball manufacturers product quality is uneven, high crushing rate, affect the grinding effect;

(2) Ceramic ball production enterprises exaggerated propaganda, in fact, there is no lack of ceramic ball trial failure cases, but most are successful. Therefore, it is necessary to analyze and discuss the electric saving mechanism of ceramic grinding body from theory and practice.

Performance comparison between high chromium ball and ceramic ball

See Table 1 for the composition and performance comparison of the ceramic ball mainly pushed by XX Company with the high-chromium ball.

Table 1 Physical and chemical parameters of ceramic spheres of XX Company

Items	Indicators
Alumina content /%	≥90
Density/(g–cm-3)	≥3.6∽3.8
Rockwell hardness/HRA	≥80
The compressive strength/MPa	≥460
Fracture toughness/( MPa–m-1/2)	KIC≥4.8
Bending strength/MPa	≥290
Coefficient of thermal conductivity	20
Coefficient of thermal expansion	7.2×10-6

According to Table 1, ceramic ball products have the following characteristics:

(1) High hardness. Its Rockwell hardness is Hra80 ~ 90, second only to diamond, far exceeding the wear resistance of wear resistant steel and stainless steel.

(2) Excellent wear resistance. The wear resistance is equivalent to 266 times of manganese steel and 171.5 times of high chromium cast iron. Under the same working condition, the service life of the equipment can be extended at least 10 times.

(3) Light weight. Its density is 3.6 ~ 3.9g/cm³, only half of that of steel, which can greatly reduce the load of equipment.

02 ceramic balls can be promoted as prerequisites

2.1 Grinding process is the key

The traditional ball mill without roller press or the pre-grinding system with roller press into the mill particle range is wide, the ball mill into the grinding particle size of 0 ~ 25mm; Combined grinding system with roller press grinding particle size of 0 ~ 3mm. The single weight of the grinding body in the first or second warehouse of the mill is large, which provides a certain impact and crushing ability, so it is more appropriate to use the steel ball with large density and diameter as the grinding body.

With the V-type separator used in the roller press system, the particle size of the semi-finished products by air selection is less than 1mm. After grinding/crushing in the first warehouse, the particle size of the materials entering the second warehouse is less than 0.5mm. At this time, the grinding body can use low-density ceramic balls to replace the high-chromium balls as grinding materials. So the roller press +V type separator + mill system is a prerequisite for the use of ceramic balls.

2.2 Comparison between ceramic ball and high chromium ball in terms of calculation of traditional process

A company with 4.2m×13m mill as an example, the second warehouse using ceramic ball, the loading capacity of the original steel ball about half the mass.

(1) Comparison of mill power before and after. Loading capacity: G₁=67+158=225t before trial; after trial (2 storehouse ceramic ball) G₂=73+84=157t. According to the calculation formula:

the same mill other parameters are fixed, power and transfer into 0.8 power proportional relationship.

, It can be seen that the theoretical power reduction ratio of ceramic ball is 25%.

(2) The comparison of the output before and after the grinding machine. According to the calculation formula:

, the same mill with other parameters fixed, the output and loading into the square proportional relationship. According to the formula

 know the use of ceramic ball output decreased to 16.46% in theory, if the use of high chromium ball output is Q₂= 145T /h, then use ceramic ball after mill output Q₂= 121T /h, reduce 16.55%.

(3) Process power consumption calculation (mainly the power consumption of the mill). Assumption mill power for rated power 3200KW, the use of ceramic ball Q₁= 145T /h before grinding host unit power consumption is 3200/145=22.1kWh/t, switch to ceramic ball after power reduction 25%, 3200-3200×25%= 2400KW,Q₂= 121T /h when grinding host unit power consumption is 2400/121=19.84kWh/t, if the station does not reduce 2400/145=16.55kWh/t.

2.3 Measures to prevent production reduction by using ceramic balls

The same specifications of the mill using ceramic ball and the use of high chromium ball, using the same grinding body filling rate, grinding material ratio and grinding particle size (fineness or surface area) is the same, the ceramic ball as grinding body of the grinding machine output is bound to reduce, and do not reduce the output can take the following measures:

(1) The density of ceramic ball is light and the bulk density is small. It can be used to appropriately increase the grinding weight of the second warehouse and increase the filling rate of the grinding body (from 30% of the high chromium ball to about 39% ~ 45%) to make up for its shortcomings.

(2) Change the mill system process, from the original open flow mill production into closed circuit mill production, closed circuit mill output 20% ~ 30% to make up for the original open flow mill output reduction.

(3) The use of reasonable mill structure, the use of a new control flow double compartment plate, optimize the structure and arrangement of the activation ring, prolong the residence time inside the mill.

(4) Optimize the grading of ceramic balls and find out the optimal grading and grinding body surface area per unit weight.

(5) improve the surface area of the material into grinding (strictly control the particle size of the material into grinding), strengthen the crushing and grinding ability of the first warehouse, to adapt to the crushing ability of the ceramic ball in the second warehouse to create conditions, that is, the grinding effect forward, make up for the lack of grinding ability.

03 Use ceramic ball as grinding body case

The company to #4 lines with 4.2m×12.5m open flow mill for experiment, on June 27, 2016, the second warehouse with ceramic ball grinding body for debugging. From June 27 to July 9, 2016, the loading capacity of the second warehouse was 93% (the total amount was 86t), the roller press operated frequently and the extrusion effect was poor. The output decreased greatly while the power consumption decreased not significantly, as shown in Table 2.

Table 2 Comparison of system operation before commissioning and use of ceramic ball

Time	Output per hour /(t–h1)	Process power consumption / (kW–h-1)
P–O42.5R	P–O42.5	P–O42.5R	P–O42.5
One year before the transformation	142.35	161.18	35.21	31.17
On July 9	105.81	122.1	35.19	30.84
Before August 13	129.17	132.16	31.61	27.55
After August 13	135.8	166.1	30.87	25.96
August to October	136.26	163.71	31.11	26.68

According to the above situation, the system will be adjusted as follows from July 10 to July 26:

(1) a warehouse (high chromium ball), in the feeding tongue plate to increase the baffle, to avoid the material directly rushed far into the compartment plate; Adjust the intermediate feeding device of the middle compartment plate, reduce the flow rate of the material in one warehouse (adjust to the minimum), and extend the residence time of the material in one warehouse; Increase the loading capacity of high chromium ball in one warehouse, improve the crushing and grinding ability.

(2) the second chamber (ceramic ball), after adding grinding body to 100% (86T), the filling rate reaches 39%; Optimize the activation ring, block the lower part of the activation ring, reduce the feeding area, prolong the material grinding time. Through the above measures, the output of grinding machine has been increased and the process power consumption has been reduced. Then, on August 13, the roller press was optimized and adjusted again to improve the powder selection efficiency of the V-type separator and increase the surface area of the material into the mill to about 210m²/kg, so as to meet the functional requirements of ceramic ball grinding. After operation from August to October, the stable operation results of the system are shown in Table

(3)As can be seen from Table 3, after the trial of ceramic balls, the power consumption of P•O42.5R cement process decreased by 4.10kWh/t and 11.64%; The power consumption of P•O42.5 cement process decreased by 4.49kWh/t, down by 14.40%. P•O42.5 production increased by 2.53t/11, increased by 1.58%; The production of P•O42.5R decreased by 6.09t/h and 4.28%.

04 Conclusions

The mechanism of ceramic ball and high chromium ball as grinding body is quite different, change the way of thinking, to create necessary conditions for the application of ceramic ball, can play its energy saving effect. However, due to the poor adaptability of ceramic balls to materials, it is suggested to strictly control the water content of grinding materials, adopt materials with better easy grinding performance, and use less or forbid steel slag and slag. According to the use of ceramic ball, if the high chromium ball reduces the loading capacity and the size of grinding body in the second bin, increases the specific surface area of grinding body per unit, finds out the best point of output and power consumption, and does not pursue high output, it can also achieve the purpose of reducing power consumption.

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