Method of controlling material flow rate and temperature in Ball Mill MillDate: 2019-08-20 Views:
With the advent of summer, the temperature of clinker increases sharply, which makes the temperature rise sharply. In order to improve the grinding condition and reduce the grinding temperature, it is necessary to strengthen the ventilation in the mill. However, with the increase of ventilation in the mill, the flow rate of the material in the mill is increased, the circulation load is increased, the efficiency of powder selection is reduced, and the output is reduced. Try to control the flow rate of the material in the mill by adjusting the gradation of the steel ball, but the effect is not obvious. Here are the options given
1. Reasons for the high temperature of grinding cement
Due to the impact and friction between a large number of grinding bodies and liner, a large amount of heat is generated, which increases the cement temperature; the temperature of the grinding material is too high to increase the temperature of the grinding cement; the ventilation of the mill is not good, or because of the limitation of technological conditions, the ventilation is not enough, so that the heat in the mill can not be taken away in time, and the temperature of the grinding cement is increased. Due to the large size of the mill, the proportion of heat dissipation on the surface of the unit cement output cylinder becomes smaller, which can not effectively drain away the heat, thus increasing the temperature of the grinding cement; the fineness of cement requires too fine, the material flow rate in the mill decreases, and the heat taken away by the material decreases greatly, which makes the cement temperature rise. Because of the high seasonal temperature, the temperature of the grinding material is high and the heat dissipation of the system is slow, and finally the phenomenon of high temperature of the grinding and finished cement is formed.
2. Harm of high temperature of grinding cement
The gypsum is dehydrated into semi-hydrated gypsum and even part of anhydrous gypsum is produced, which makes the cement produce false setting, affects the quality of cement, and is easy to caking cement into storage, and seriously affects the storage, packaging and transportation of cement. Make the packing paper bag brittle, increase the damage rate, the working environment of the workers deteriorate;
It is also unfavorable to the mill machine itself. For example, the bearing temperature rises and lubrication action is reduced, which will cause certain thermal stress on the cylinder and cause the liner screw to break. Even the mill cannot operate continuously, endangering the safety of the equipment;It is easy to agglomerate cement due to electrostatic attraction, which will adhere to the grinding body and lining plate seriously, resulting in ball-wrapped forging, reducing the grinding efficiency and reducing the mill output;It increases the temperature of the selected powder machine, the adhesion of the inner wall and the wind blade of the separator, and the electrostatic attraction between the particles is stronger, which affects the dispersibility of the material after the material is spread, the efficiency of the powder separation is directly reduced, the circulating load rate of the grinding system is increased, and the cement mill is reduced. Taiwan time output. High cement temperature will affect the construction performance of cement, produce rapid setting, concrete slump loss is large, and even easy to produce temperature difference stress of cement concrete, resulting in concrete cracking and other hazards.
3. Method of lowering the temperature of the cement for grinding.
Reduce the temperature of the grinding clinker:
(1) The material management shall be strengthened, and the clinker with high temperature shall be prevented from entering the grinding head bin to prevent the red material from entering the grinding head.
(2) spray water in the cooler to reduce clinker temperature.
(3) spray water on the feed grinding clinker belt.
The above two water spraying measures have obvious cooling effect, but they also have side effects. The water spray in the cooler easily makes part of the water vapor into the crusher at the end of the cooler, and the water vapor captures the clinker dust to form a bond on the inner wall of the crusher, which affects the normal operation of the crusher over time. Spraying water on the clinker belt will reduce the strength of cement.
a. Strengthen the heat dissipation of the grinding system
The grinding system has a large number of equipment and pipes, and the surface of heat dissipation is very large. Strengthening the heat dissipation of the system mainly uses the surface of the system to strengthen the cooling and heat dissipation, such as ejecting atomized water to the outer wall of the powder separator, making the sink along the outside of the screw conveyor, and so on. The test results show that the cement temperature is reduced but not obvious, and it is easy to cause water intake in the equipment, so it should be used carefully.
B, mixed with grinding aids
The decrease of the temperature in the mill is helpful for increasing the output of the table hour, and the increase of the output at the table hour is helpful in reducing the temperature of cement. In view of the high temperature of the grinding system, the over-grinding phenomenon in the mill is serious and the powder separation efficiency of the separator is decreased. By using the grinding aid, the adhesion degree in the mill is reduced, the efficiency of the separator can be improved, so as to a certain extent, the temperature of the grinding cement is reduced.
C, strengthen the ventilation of the mill
Strengthening the ventilation of the mill can take away a part of the heat, but according to the calculation of the heat balance of the mill, the heat carried away by the ventilation of the mill usually accounts for only 20% of the total heat discharged from the mill. Although strengthening the inner ventilation can reduce the material temperature, the ventilation in the grinding is limited by the resistance of the system, the lock air, the air leakage and so on, as well as the fineness of the products. therefore, there is a certain limit to reduce the temperature of the grinding material by increasing the ventilation inside the mill.
D, cooling by leaching water from mill cylinder
In small mill, cylinder water is usually used to reduce the temperature of grinding cement. According to the calculation of heat balance of mill, the heat emitted by radiation on the surface of cylinder accounts for about 6% of the total heat, so its effect is limited. Moreover, after the mill is large, the surface area of the cylinder per unit output of the mill decreases a lot, and the proportion of heat dissipation from the surface of the mill cylinder to the total heat is getting smaller and smaller. The thickening of the steel plate of the mill cylinder and the thickening of the liner also hinder the heat conduction. The traditional method of leaching water on the surface of the mill cylinder to improve the heat dissipation efficiency is limited, and its effect is very limited for the mill with a diameter of more than 3m. Moreover, with the scaling of the cylinder surface, the efficiency will decrease significantly (1mm thick scaling is equivalent to the thermal resistance of 40mm thick steel plate). The drenching water on the surface of the cylinder wastes resources and pollutes the environment, so it is no longer used in large grinding system.
Using cement cooler
The cement cooler can greatly reduce the cement temperature, and the cooling effect is good. The cement temperature of the outlet cooler can reach below 70 ℃, which is easy to operate and control. There are many kinds of cement coolers, such as vertical spiral lifting cement cooler, heat pipe oblique slot cement cooler, heat pipe fluidized bed cement cooler and so on. Although the cooling effect of cement cooler is very good, it also has the following defects:
(1) the cement cooler can only cool the ground cement, which has no effect on reducing the internal temperature of cement mill, avoiding gypsum dehydration, preventing ball packing forging, increasing the output of cement mill, avoiding the excessive temperature of mill bearing and so on.
The investment is large, the required space is large, and the amount of cooling water is large.
(3) because of the wear of cement to the cooling equipment, there are hidden dangers of leakage and so on.
The spiral hoist cooler also strictly requires that there is no mixing of particles in the cooled cement, otherwise the screw will not work.
After the cement cooler is used for a long time, because the cooling water is impure or contains high calcium, the outer surface of the barrel in contact with the water will be crud and rusted. As the moisture in the air condenses on the inner wall, a layer of cement is generated on the inner side surface of the barrel in contact with the cement. The appearance of the above phenomenon can lead to a significant decrease in the cooling efficiency.
(6) because the gap between the spiral hoist cooler cylinder and the spiral blade is very small, and the rotor with the spiral blade rotates, the concentric degree and coaxiality of the two are required to be very high. In particular, the welding of large diameter cylinder is more difficult, slightly less attention, welding deformation and transportation deformation will occur, so it is very difficult to large-scale.
Adopt Internal spray cooling system
Grinding spray cooling technology has been widely used in foreign cement mills, and it is a mature means of internal grinding cooling. In order to greatly reduce the temperature of grinding cement, the most effective way is to use the internal spray cooling system. Theoretically, the spray can bring out the desired heat. By injecting atomized water into the mill, it vaporizes rapidly, absorbs the heat in the mill, and brings it out of the mill by the ventilation inside the mill, especially when the mill is in a high temperature state, and by injecting atomized water into the high temperature area of the tail warehouse of the mill, its effect is immediate, the temperature of the grinding cement can be controlled below 95 ℃, and the output of the cement mill can be increased by about 8%. .
4. How to ensure Safety by using Internal spray cooling system
As we all know, using in-mill spray cooling system is the most effective method to reduce the grinding temperature, which can significantly reduce the temperature of grinding cement. But many manufacturers have palpitations and worry about accidents. In the actual production, it is often due to the imperfect design of the grinding water spray system, resulting in production accidents. Therefore, the key technology of in-mill spray cooling system is how to ensure safety and reliability.
In order to ensure foolproof, the grinding spray cooling system of Wuhan Yisheng Technology Co., Ltd. has taken the following safety measures:
A, using high pressure air atomization anti-blocking sprinkler, through high pressure air atomization of water, at the same time atomized water into the grinding. The nozzle design is ingenious, unique, anti-wear, atomization, anti-blocking effect;
B, the high pressure water pump is controlled by frequency conversion to realize stepless adjustment of water injection and metering device.
c. PC control is adopted to realize the automatic control of the temperature of the cement discharged by detecting the exhaust gas temperature of the dust collector and automatically adjusting the amount of water spraying according to the temperature, and effectively preventing condensation of the dust collector and pipe blockage;
D, the pump control system and the mill motor linkage, stop grinding, can automatically stop spraying water, to avoid human negligence caused by accidents;
E, by detecting the air pressure of high pressure air, as long as the air pressure is abnormal or out of gas, the spray water will be stopped automatically to ensure the atomization effect of grinding water.
And f. the water cut-off protection, when the water is stopped, the water pump can be automatically shut down, high-pressure air is injected into the water path of the spray gun, the residual water in the spray gun is removed, and the spray head is prevented from being blocked.
G, the maximum amount of water injection can be set according to the need, so as to avoid excessive water injection and increase the water content of the material in the mill, which can affect the performance of cement or lead to the deterioration of grinding state.
H. The abnormal protection of the working condition can automatically stop the water spraying as long as the abnormal condition is found, so as to ensure no loss.