Control of working condition parameters of vertica

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Control of working condition parameters of vertical mill in cement plant

MPs vertical mill is a kind of grinding machine that uses the principle of material bed crushing to grind materials. It has been widely used in cement, coal, power and other industries. MPs vertical mill is a full air swept mill. After being extruded, the materials entering the mill are thrown off the side of the disc and sunk to the nozzle ring under the action of centrifugal force, which is blown up and dispersed by the high-speed wind, and the metals and heavy ores will settle under the nozzle ring and be discharged. The fine powder is brought to the upper part of the vertical mill, sorted by the separator, and the finished product is collected with the gas into the dust collector, and the coarse powder is recycled back. Coarse powder and particles are thrown up, and with the decrease of wind speed, they lose their support, settle on the disk surface, and enter the grinding track by centrifugal force for a new round of circulation. In multiple cycles, heat transfer between particles and gas makes water evaporate. Therefore, MPs vertical mill integrates many advantages of material grinding, transportation, powder separation, drying, and separation of metal blocks and heavy ores. Under normal conditions, the vertical mill can operate smoothly as long as it passes short-term process commissioning. However, how to optimize process parameters to ensure quality, ensure that the whole set of prices is also relatively expensive, ensure safety, improve production, reduce energy consumption, improve operation rate, and continuously improve economic benefits are the central issues of the management and operation of vertical mills. The following is a brief discussion on these problems

1. ventilation in the mill and temperature control at the inlet and outlet

1.1 source and matching of the air entering the mill

most of the hot air entering the mill uses the exhaust gas of the rotary kiln system, and some process systems use the hot air stove to provide hot air. In order to adjust the temperature of the air and save energy, cold air and circulating air can also be added before entering the mill

the process system adopts a hot blast stove to supply hot air. In order to save energy, 20% - 50% circulating air can be mixed according to the water content of the material. The system that uses the waste gas of precalcining kiln as the hot air source hopes that all the waste gas can be used in the mill. If there is surplus, the waste gas can be directly discharged into the dust collector through the pipeline. If it is not enough for all the waste gas to enter the mill, it can be determined to add some cold air or circulating air according to the temperature of the waste gas entering the mill

1.2 control of air volume, wind speed and air temperature

throughout history (1) selection principle of air volume

the concentration of dust (finished product) in the grinding gas should be between 550 ~ 750g/m3, generally less than 700g/m3

the wind speed of the outlet pipeline is generally 20m/s, and horizontal layout is avoided

the wind speed standard at the nozzle ring is 90m/s, and the maximum fluctuation range is 70% - 105%

when the grindability of materials is poor and the mill output is low, it is often necessary to choose a larger model of vertical mill. Under comparative conditions, when the outlet air volume is appropriate, the air speed of the nozzle ring is low. Iron plate should be used to block the hole of the nozzle ring behind the grinding roll as required, so as to reduce the ventilation area and increase the air speed. How many holes to block shall be determined by wind balance calculation

it is allowed to adjust the air volume within the range of 70% - 105% according to the specific situation of the vertical mill, but the system in series with the kiln mill shall not affect the flue gas emission of the kiln

(2) control principle of air temperature

the temperature of raw mill outlet air is not allowed to exceed 120 ℃. Otherwise, the soft connection will be lost, and the dividing wheel of the cyclone may expand and stop; The outlet air temperature of coal mill depends on the coal quality. If the volatile matter is high, the outlet air temperature of coal mill should be lower, otherwise it can be higher. Generally, it should be controlled below 100 ℃ to avoid burning, explosion and other phenomena of the system

in the system of heating air with hot blast stove, as long as the moisture of the material out of the mill meets the requirements and the air temperature into the dust collector is more than 16 ℃ higher than the dew point, the air temperature at the inlet and outlet can be appropriately reduced to save energy

when drying and grinding, the inlet air temperature should not exceed 200 ℃, so as not to deteriorate the lubricating oil in the grinding roll

1.3 prevention of system air leakage

system air leakage refers to the air leakage at the vertical mill body, outlet pipe, dust collector, etc. Under the condition of constant total air volume, the air leakage of the system will reduce the wind speed at the nozzle ring, resulting in serious slag spitting. Due to the reduction of outlet wind speed, the discharge of finished products is less, the circulating load is increased, and the differential pressure is increased. Due to the vicious cycle, the total air volume is reduced, which is easy to cause full grinding and vibration shutdown. It will also make the conveying capacity in the mill insufficient and reduce the output. In addition, it can also reduce the air temperature entering the dust collector, which is prone to condensation

if in order to maintain 3, equipped with all experimental accessories required for the physical experiment of wood-based panel; The wind speed at the nozzle ring will increase the ventilation volume, which will increase the load of the fan and dust collection and waste energy. At the same time, it is also limited by the capacity of fans and dust collectors. Therefore, the air leakage of the system is harmful without any benefit, which must be overcome. MPs limo German side requires that the air leakage of the system is 4%. According to our national conditions, it should be designed according to the style of 10% air leakage, so the air leakage of the system must not be 10%

2. Selection of several parameters

2.1 selection of tensioning force

the grinding force of the vertical mill mainly comes from the hydraulic tensioning device. In general, the selection of tension pressure is related to the material characteristics and the thickness of the material layer of the grinding disc, because the vertical mill is crushed by the material bed, and the extrusion pressure is transmitted between the particles. When the strength of the material is exceeded, it is crushed. The greater the extrusion pressure is, the higher the degree of crushing is. Therefore, the harder the material, the higher the tension force is required; Similarly, the thicker the material layer, the greater the tension required. Otherwise, the effect is not good

for materials with good fragility, excessive tension is a waste. In the case of thin material layer, it often causes vibration. For materials with poor fragility, the required tension is large, and the thin material layer will achieve better crushing effect. Another important basis for the selection of tensioning force is the current of the main motor of the mill. Under normal working conditions, it is not allowed to exceed the rated current, otherwise the tension should be reduced

2.2 selection of separator speed

the main factors affecting the fineness of products are the separator speed and the wind speed there. When the rotating speed of the separator is constant, the greater the wind speed is, the coarser the product fineness is. When the wind speed is constant, the faster the rotating speed of the separator is, the greater the centrifugal force obtained by the product particles there is, the smaller the particle diameter that can pass through, and the finer the product fineness is. Generally, the air flow out of the mill is stable, and the wind speed there does not change much. Therefore, controlling the speed of separator is the main means to control the fineness of products. The particle size of the products of the vertical mill is relatively uniform, and it should be controlled within a reasonable range. Generally, the residue of 0.08mm sieve is controlled at about 12%, which can meet the requirements of the rotary kiln for the fineness of raw materials and pulverized coal. Over fineness not only reduces the output and wastes energy, but also has a high and wide control accuracy and control range, and improves the circulating load in the mill, causing pressure

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