Briefly explain the reasons for the low vacuum of the vacuum filter
Abstract: After the vacuum filter is replaced by the factory equipment, the vacuum degree of the filter is low, the processing volume is not up, and the production is restricted. Based on the analysis of the equipment system, the corresponding solution is proposed to alleviate the problem. The contradiction restricting production has achieved good economic benefits. Key words: vacuum filter, vacuum, vacuum pump 1 Working principle and structure of vacuum filter The vacuum filter is mainly used for filtration and dewatering of flotation clean coal in coal preparation plant. Vacuum filters rely on vacuum as a driving force for dehydration. During the filtration process, the movement of the liquid is generally considered to be a laminar motion along the tube. However, the porosity and curvature of the filter media and filter cake vary widely, and the flow of the filtrate is much more complicated than the movement of the liquid in the desired capillary. At any instant, the volume of filtrate passing through the filtering surface is proportional to the area of ​​the filtering surface and the pressure difference across the sides. If the area is doubled, the flow rate of the filtrate is also doubled. When the pressure difference is doubled, the flow rate of the filtrate is also doubled, but the viscosity of the liquid and its flow resistance decrease the flow rate of the filtrate. Thereby reducing the flow rate of the filtrate. Therefore, the volume of the filtrate passing through the filtering surface is inversely proportional to the viscosity of the liquid and the resistance of the filtration. During filtration, the filtrate passes through the porous membrane and the cake layer above it as it passes over the filtration surface, so the filtration resistance includes the resistance of the filter cake and membrane (also known as the filter medium). Express the above analysis as a formula: μ is the viscosity of the liquid, Pa·s; R is the resistance of the filter cake, L/m; Y is the resistance of the filter medium (diaphragm), L / m; K is a proportionality constant. When the filter is working properly, the resistance of the filter cake is several times greater than the resistance of the filter medium. The resistance of the filter cake depends on its thickness and properties (particle size, porosity, gel content, etc.). During the filtration process, the thickness of the filter cake is gradually increased, which is determined by the amount of filtrate per unit area and the solid content of the coal slurry, and the nature of the filter cake also affects the ease of liquid flow. The filter of the disc vacuum filter consists of several fan-shaped filter plates. The fan-shaped filter plate is covered with a filter cloth and fixed on the hollow shaft. The filtrate hole on the hollow shaft communicates with the filter plate cavity, the shaft end is connected with the distribution head of the filter, and the distribution head is pumped and blown. Gas action. The figure below shows the working principle of the disc vacuum filter. The filter plate is placed in the tank body, and the liquid surface of the coal slurry in the tank is below the axis of the hollow shaft, and the filter plate rotates clockwise, and sequentially passes through the filtration zone (I) drying zone (II) and the filter cake falling zone (V). When the filter plate is in the filtration zone, it is connected to the vacuum pump. Under the pumping action of the vacuum pump, the coal slurry is attached to the surface of the filter cloth and filtered. When the filter plate is in the drying zone, it is still connected with the vacuum pump. Connected, because the filter plate has left the coal slurry at this time, the pumping action is only to let the air pass through the filter cake, and the moisture in the pores is taken away to further dehydrate; when the filter plate is in the falling area of ​​the filter cake, it is turned Connected to the blower, the filter cake on the filter plate is blown off by blowing. In the middle of the three work areas, there are transition zones (II, IV, VI), and the transition zone is a dead zone, which is used to prevent the filter plates from colliding with each other when moving from one work area to another. If there is a string of gas, the filtering effect will be greatly reduced. The filter zone should be of an appropriate size. 2 low vacuum analysis Vacuum filters rely on vacuum as a driving force for dehydration. The degree of vacuum directly affects the productivity of the filter, the moisture of the product and the solids content of the filtrate. The higher the degree of vacuum, the greater the amount of treatment and the lower the moisture of the filter cake. However, the excessively high degree of vacuum tends to increase the solid content of the filtrate and affect the filtration effect. When vacuum filter is used to treat flotation clean coal, the general vacuum should be between 0.050.067Mpa. After upgrading the 429# vacuum filter from PG116-12 to GPY-120, the vacuum of the equipment system has been at a relatively low level, and the processing capacity is not going up, which affects normal production. The reason for the low degree of vacuum is relatively complicated, and is closely related to the structure of the coal cake, the concentration of the feed, the filtration operation, the leakage of the vacuum filter, the piping system, and the working state of the vacuum pump. The following is only an analysis of the system and equipment. 2.1 There is a leak in the system to reduce the vacuum. Mainly manifested in (1) the vacuum line between the filter, the vacuum pump to the steam separator, the interface of the filtrate pipeline flange and the leaking of the valve is not strict. (2) The secondary filter system leaks between the two steam separators. (3) The operating level of the slurry in the filter is lower than that of the hollow shaft, causing air leakage at the hollow shaft of the filter. (4) The sealing of the filter fan blade and the hollow shaft interface is not strict, resulting in air leakage. (5) The filter cloth is damaged and leaks. (6) There is no airtightness at both ends of the dispensing head hose to generate air leakage. (7) Leakage is caused by poor airtightness between the friction discs of the distribution head. (8) The filter has a large shaft and wind, which reduces the vacuum. 2.2 The vacuum filter model is changed, the gas volume is increased and the vacuum pump is not updated to make the vacuum degree not available. (1) Equipment characteristics of PG116-12 and GPY-120 vacuum filter: (2) Analysis of gas distribution map of each zone of PG116-12 and GPY-120 vacuum filter The drying zone of the GPY-1 vacuum filter is 140 degrees, which is 58 degrees higher than the 82 degree of the PG116 vacuum filter, an increase of nearly 70%. Therefore, at the same speed, the gas consumption of the filter is bound to increase significantly. As a result, the system vacuum is not improved. (3) PG116-12 and GPY-120 vacuum filter filter fan structure are different, the gas volume is different. The GPY-120 vacuum filter uses a variable chamber filter fan whose main purpose is to increase the shedding rate of the filter cake. The working principle is to realize the self-shedding of the filter cake by means of the displacement generated by the flexible filter strip in the vacuum zone and the discharge zone. However, due to the fine particle size of the flotation clean coal in our plant, the content of the mud material is large, the filter cake is sticky, and the cake thickness is small. The effect of taking off cake is obviously low. Practice has proved that the variable cavity filter fan has poor adaptability to the nature of the filter material of the factory. On the other hand, due to the small thickness of the filter cake on the variable chamber filter fan, the resistance of the filter cake becomes smaller, and the relative gas consumption is also increased, which also affects the improvement of the degree of vacuum. 2.3 The vacuum pump has been used for more than 20 years, the equipment is aging, and the technical performance is reduced. The performance curve of the 2YK-110 water ring vacuum pump is shown in Figure 4. The 2YK-110 water ring vacuum pump currently in use is installed and put into operation in 82 years, and has been used for more than 20 years. Its performance is mainly reflected in: (1) The gap between the impeller and the distributor, the impeller and the front and rear covers is increased, which affects the performance of the vacuum pump. Move the PS curve down as a whole. (2) Poor water quality, easy to form scale attached to the impeller blades and the surface of the distributor, affecting the performance of the vacuum pump, causing the pumping volume to decrease and the power to increase. (3) The amount of water replenishment has a great influence on the degree of vacuum, the amount of exhaust gas and the shaft power. In principle, the amount of makeup water should be given in accordance with the amount of water that must be discharged as the exhaust gas is exhausted. Generally it is 3121114m/h. (4) The sealing effect of the vacuum pump is deteriorated. (5) Leakage at the packing. (6) The temperature of the water ring in the pump is high. (7) A set of data observed on February 4, 2005 is shown in Table 2. It can be seen from Table 2 that the vacuum degree of the vacuum pump can reach 0.05Mpa, but the power consumption increases greatly. 3 Conclusion Through the above analysis of the system and equipment, and based on the observation of the use of 429#. The main reasons for the low vacuum are: (1) The special coal quality of the factory causes the filter cake layer of the vacuum filter to be thin, the gas consumption is increased, and the vacuum degree is not improved. (2) Due to the system leakage and the structure of the GPY-120 filter, it is necessary to use a large gas consumption. The performance of the original vacuum pump is reduced, and the gas consumption cannot meet the requirements, so the vacuum cannot be obtained. 4 Take measures In the current state of existing equipment: (1) It is necessary to strengthen the inspection and maintenance of the filter to ensure that the filter system does not leak air. (2) Strengthen the inspection and maintenance of the vacuum pump and improve the operation of the equipment. (4) Replace the variable chamber filter fan with the original cast aluminum filter fan. (5) From a long-term perspective, in view of the status of coal quality in factories, we should actively conduct research and select more advanced, reliable and energy-saving equipment to dewater the flotation clean coal.
P is the pressure difference between the two sides of the filter surface, Pa;
(3) Strengthen the operation of the post driver to operate the vacuum filter system at a relatively good working point to meet the production needs.