The raw material batching station is provided with 4 reservoirs, which store cement clinker, limestone, volcanic ash and gypsum respectively. Each material is discharged from each batching warehouse by a certain proportion of the quantitative feeder, and sent to the raw material by the belt conveyor. station. Before entering the mill, the material is passed through a de-ironing device and a metal detector, and the material containing the metal object is discharged to the waste bin through a three-way valve. The grinding material is sent to the center of the grinding disc through the lock air feeding valve, and moves to the edge of the grinding disc under the action of centrifugal force. After being ground by the grinding roller, it is thrown out, and the milled material is blown by the high-speed airflow at the wind ring. The coarse material falls back to the grinding disc for re-grinding. At the same time, the fine material is dried and brought into the classifier for sorting.
The qualified material is ground with the airflow, and the product is sent to the cement storage tank after being collected by the bag dust collector. The unqualified materials are re-grinded under the action of the blades of the classifier to the grinding disc and the newly added materials, and the cycle is repeated to achieve the purpose of selecting the qualified cement.
The vertical roller mill system integrates grinding, drying, sorting and conveying. The components must be coordinated with each other to maintain stable and efficient operation of the system. A parameter change will affect the stability of the whole system. The debugging and groping summary, we should pay attention to the following parameters when debugging.
2.1 The amount of water sprayed in the mill
The stable operation of the vertical roller mill is guaranteed to ensure the stability of the material layer. The main function of the water spray is to stabilize the material layer. Insufficient water spray will cause the material layer to be unstable, causing the vertical roller mill to vibrate and stop; excessive water spray will cause the inner knot of the mill, reduce the grinding efficiency, block the water spray pipe, and increase the system energy consumption. Therefore, the control of the amount of water spray is particularly important in ensuring the stable operation of the cement vertical roller mill system.
In the initial stage of commissioning, the vertical roller mill started to run for a few minutes, and then it stopped and stopped, and normal grinding could not be performed. The analysis believes that it is mainly impossible to form a stable layer when the roller is lowered, and the water spray should be appropriately increased. Through multiple trials and explorations, under normal conditions, the water spray volume is controlled at 3~5 t/h, which can ensure the stable operation of the vertical roller mill and reduce the knot in the mill.
2.2 Grinding pressure difference
The internal pressure difference between the mills refers to the difference between the static pressure at the inlet of the vertical roller mill and the outlet of the vertical roller mill. The stability of the mill pressure difference is very important for the normal operation of the whole system. The operator can understand the working condition in the mill through the pressure difference, which is one of the main parameters. The change in the internal pressure difference depends on the change in fluid resistance in the mill, and the change in fluid resistance depends mainly on the amount of suspended material in the mill. The amount of suspended material depends not only on the amount of feed but also on the amount of material circulating in the mill. The feed amount is controlled by the batching station and is usually stable, so the pressure difference directly reflects the amount of material circulating.
In the initial stage of commissioning, the vertical roller mill suddenly jumped after 10 minutes of stable operation. Through observation, it is found that within 10 min of operation, the differential pressure of the vertical roller mill increases slowly, and the return amount of the return conveyor belt is large. After a period of operation, the mill current fluctuates drastically, and the vertical roller mill has a sharp pressure difference. Increase, then the mill vibrates and stops. According to the analysis, the pressure difference of the vertical roller mill increases because the material suspended in the mill is too much. In the initial stage of grinding, the material in the mill is thicker and cannot be selected by the classifier in time. The cyclic load is increasing and can only pass. The discharge conveyor belt discharges the outside of the mill, and the material of the return conveyor belt is milled together with the new material through the external circulation, further increasing the feeding amount, resulting in more and more materials in the grinding machine, eventually causing full grinding and vibration jumping. stop. Therefore, in the initial stage of grinding, the speed of the powder separator should be appropriately reduced, and the material in the mill should be selected in time. The pressure difference in the mill tends to be stable. When the amount of return is small, the speed of the powder separator is increased to improve the product quality. In normal operation, the mill pressure differential should be controlled at 3 000 to 4 000 kPa.
During the commissioning process, after the vertical roller mill can run stably for a period of time, the system capacity can be gradually increased, each time increasing by 5 t/h. By adjusting the parameters appropriately, it is found that the vertical roller mill can operate stably under different production conditions. However, the fineness of the cement is not high, and the speed of the powder separator cannot be further improved. When the speed of the separator is increased to a certain extent (about 90 r/min), the mill current fluctuation will increase, and the pressure difference within the mill will increase sharply, causing the vertical roller mill to vibrate. After repeated adjustments, the situation has not been improved, and the specific surface area of the cement has been maintained at 3,000 to 3,200 m2/kg, which cannot improve the product quality. The analysis believes that: increase the speed of the powder separator, the internal pressure difference increases, indicating that there are too many circulating materials in the mill, and the fine powder cannot be discharged in time; the fineness of the product is not high, indicating that the speed of the powder separator is too low, and the powder separator cannot effectively Sorting the material may be a problem with the classifier. By checking the rotor blades of the classifier, it was found that the rotor blade position was shifted, and the high deviation reached 13°. After correcting the rotor blade angle of the classifier, the situation was significantly improved.
2.3 Grinding temperature
After the system was running for a period of time, it was found that after the cement was stored in the cement storage for a period of time, the phenomenon of forming a ball appeared. The analysis believes that the main moisture content of cement is high. In the case where the amount of water sprayed by the vertical roller mill cannot be reduced, in order to reduce the moisture of the product, it is necessary to increase the temperature of the system and increase the temperature of the mill.
Under normal conditions, the air temperature should be controlled at around 90 °C. The hot air inside the cement vertical roller mill acts to dry the moisture of the product, and the low wind temperature will cause the moisture content of the cement product to be too high. The finished product of cement requires less than 0.5% of water. When the grinding temperature is lower than 65 °C, the product requirements are not met. After the cement is stored for a period of time, the phenomenon of ball formation will occur, and the inner layer of the grinding material will be too thick. Properly increasing the grinding temperature can improve the milling efficiency and reduce the internal knot. However, if the grinding temperature is too high, it will cause the inner layer of the grinding machine to become thin and vibrate, which is not conducive to the service life and safety of the equipment, and also wastes energy.
2.4 Layer thickness and grinding pressure
The thickness of the layer is determined by the wearability of the material. For materials that are difficult to grind, the thickness of the layer should be appropriately reduced to increase the proportion of qualified particles in the extruded material. Conversely, for a material that is easy to grind, even if the material layer is thick, a large amount of qualified particles can be produced, which can increase the yield accordingly. The thickness of the layer is affected by factors such as water spray, milling temperature, ventilation, product fineness and milling pressure, among which the grinding pressure is a key factor. For materials with good grindability, the grinding pressure is too large, resulting in waste. In the case of thin material layer, it will also cause vibration, and the material with poor wearability needs to increase the grinding pressure, and the material layer will be thinner. Grinding effect. Another important basis for the selection of the grinding pressure is the main motor current of the mill, which is not allowed to exceed the rated current under normal operating conditions.