① Maintaining a stable material bed with appropriate layer thickness and a stable material bed is the foundation and key to the normal operation of vertical abrasive bed grinding.
The thickness of the material layer can be adjusted by adjusting the height of the retaining ring. The appropriate thickness and its corresponding relationship with the mill output should be identified first during the debugging phase. The material layer is too thick, which reduces the grinding efficiency; If the material layer is too thin, it will cause vibration. The thickness of the material layer should increase appropriately with the expansion of the mill. The thickness of the material layer is influenced by various operating parameters. If the rolling pressure increases, more fine powder will be produced, and the material layer will become thinner; The roller pressure decreases, the grinding disc material becomes thicker, and the corresponding return material is more, resulting in a thicker material layer. Increase the wind speed inside the mill, enhance internal circulation, and thicken the material layer; Reduce wind speed, minimize internal circulation, and thin the material layer. The thickness of the material bed after compaction by the grinding roller in a general mill should not be less than 40-50mm.
The thickness of the material layer is closely related to the material properties. Some materials, such as those that are too dry or too fine, have a low coefficient of internal friction, resulting in good fluidity and difficulty in forming a normal material layer, or the material layer is very unstable, causing operational difficulties and severe vibration. In this situation, it is advisable to increase the height of the material blocking ring and reduce the roller pressure appropriately. But the fundamental solution is to increase the water spray inside the mill to increase the viscosity of the material and reduce its fluidity. The general water spray rate is 2% to 3%, and sometimes it needs to be increased to 6% to 7%. At this time, in order to control the moisture content of the grinding material and increase the enthalpy of the gas entering the grinding process.
② Seeking suitable roller pressing, vertical grinding is achieved by applying high pressure to the material bed for crushing. As the pressure increases, the output increases but no longer changes after reaching a certain critical value. Due to the fact that the grinding machine is a multi-stage cycle for grinding, the actual roller pressure is much lower than the critical value. The increase in pressure requires an increase in power, which poses an economic pressure issue for unit energy consumption. Suitable roller pressing should take into account both output and energy consumption. This value depends on the material properties, particle size, and feeding amount. For a specific factory's raw materials, the appropriate usage pressure and the corresponding relationship between pressure and production capacity should be identified. During operation, follow the principle of high roller pressure when the material flow is large, and try to maintain stability as much as possible. Otherwise, it may not only affect the grinding effect, but also cause fluctuations in the material layer, leading to problems such as slag discharge and vibration.
Under normal load conditions, the actual operating pressure can be between 70% and 90% of the maximum operating pressure. During the debugging phase, when operating under low load, it is necessary to correspondingly reduce the workload.
③ Control the wind speed reasonably, and the vertical mill system mainly relies on airflow to circulate animal materials. The wind speed at the wind ring of the wind swept system can reach up to 60-90m/s; The semi wind swept wind speed can be reduced to 40-50 m/s. Reasonable wind speed can form a good internal circulation, making the material layer on the disc appropriate and stable, and achieving high grinding efficiency. In the production process, when the area of the wind ring is determined, the wind speed is determined by the air volume. A reasonable air volume should be related to the feeding amount, such as a large feeding amount resulting in a large strain of air volume; The feeding amount is small, and the air volume needs to be reduced. A small amount of wind can cause excessive slag discharge, gradual thinning of the material layer, and vibration of the grinding machine. At this time, increasing the air volume appropriately will make the material layer thicker, which is beneficial for grinding; If the material is small and the wind is strong, it is also possible that the material is swept out too much, the material bed is too thin, and vibration occurs. At this time, reducing the air volume appropriately is beneficial for stable production. But this situation usually does not occur under normal load conditions, because the fan air volume has been limited and cannot be too large; During debugging, it may occur during low load operation.
The air volume of the fan is affected by system resistance and can be adjusted by adjusting the fan air volume. The differential pressure, inlet negative pressure, and outlet negative pressure of the grinder can all reflect the size of the air flow. A large differential pressure and negative pressure both indicate high wind speed and air volume; If the differential pressure and negative pressure are small, the corresponding wind speed and air volume will be small. Therefore, ensuring the stability of these parameters also controls the stability of the air volume. The stability of air flow also ensures the stability of the material bed to a certain extent.
The differential pressure of the mill also reflects the size of the material flow inside the mill. With a certain air volume, a large material flow and high concentration result in a large pressure drop; Small material flow, low concentration, and low pressure drop. Therefore, the feeding of the mill can be adjusted by controlling the differential pressure of the mill.
④ Adjust a certain temperature for grinding Vertical mill is a drying and grinding system, and the temperature at the mill outlet is a comprehensive indicator to measure whether the drying operation is normal. If the temperature is too low, it indicates insufficient drying capacity, high moisture content in the finished product, low grinding and powder selection efficiency, which may cause condensation in the dust collection system. If it is too high, it indicates that the cooling and humidification of the flue gas are not enough, which will also affect the dust collection effect. Generally, the temperature for grinding is controlled at 80-90 ℃.
(2) Abnormal situation analysis
Under normal circumstances, the vertical grinding operation is very stable, but if it loses control, it will result in a large amount of slag discharge or severe vibration.
1. The possible situations for large-scale slag discharge are:
Dry material, fine particles, fast flow rate, and inability to retain material on the disc. Improvement measures include spraying water to increase the viscosity and resistance of the material flow, and appropriately raising the height of the material blocking ring;
The solution is to increase the pressure appropriately, as the material is large, the particles are coarse, the pressure is low, and it cannot be crushed.
The wind speed is low and the air volume is low, so it cannot be blown. At this time, the air volume should be increased.
The possible reasons for severe vibration are as follows.
Hard foreign object entering: Sudden vibration occurs inside the grinding machine. Iron removal should be strictly enforced.
Improper material dropping point: biased to one side, may cause periodic vibration. The material should be fed into the center of the grinding disc.
Particle size variation: Particles that are too large and change in size frequently cause oscillation of the grinding roller. Appropriate feeding should be controlled.
Unstable material flow: When feeding, there are too many and too few, and the moisture content is too high and too low, making it difficult for the roller to adapt to the air flow and causing the grinding roller to bounce. Efforts should be made to stabilize the material flow.
The material layer is too thin: the dry and fine particles of the material cause the material to run and form a material layer, with too little buffering and severe vibration. Material flow resistance should be improved.
The material layer gradually becomes thinner: unbalanced air supply, low ventilation, increased slag discharge, and less circulating material; Unbalanced material pressure, high material volume and low pressure, decreased grinding efficiency, excessive slag discharge and insufficient circulating material. All of these will cause the material layer to gradually thin and cause vibration. Improvement measures: Appropriate process parameters should be adjusted.
The rigidity of the hydraulic system is too strong, and the accumulator is not functioning. The charging pressure of the accumulator can be appropriately reduced.
