Vacuum filter is a device that uses vacuum negative pressure as the driving force to achieve solid-liquid separation. Under the action of vacuum negative pressure (0.04-0.07MPa), the liquid in the suspension is sucked out through the filter medium (filter cloth), while the solid particles are trapped by the medium, so as to realize the separation of liquid and solid. In terms of structure, the filtering section is arranged along the horizontal length direction, which can continuously complete operations such as filtering, washing, drying, and filter cloth regeneration. Rubber belt filter has the advantages of high filtration efficiency, large production capacity, good washing effect, low water content of filter cake, flexible operation and low maintenance cost. The rubber belt filter can be widely used in solid-liquid separation in the fields of metallurgy, mining, chemical industry, papermaking, food, pharmaceuticals, environmental protection, etc., especially for gypsum dehydration (FGD) in flue gas desulfurization.
Product Introduction
Vacuum filter is a solid-liquid separation machine that forms vacuum filtration by negative pressure, and creates negative pressure at the outlet of the filtrate as the driving force for filtration.
Working Principle
The basic principle of vacuum filtration [2] is: under the action of vacuum negative pressure (0.04-0.07MPa), the liquid in the suspension is sucked out through the filter medium (filter cloth), while the solid particles are retained by the medium. So as to realize the separation of liquid and solid. The vacuum filter uses a surface filtration mechanism. When the liquid in the suspension flows to the filter medium, the solid particles larger or similar to the pore size of the filter medium will first form an initial layer on the surface of the medium by bridging the pores of the filter medium. It is larger than its pore channel, which traps smaller particles, so the continuously deposited solid particles gradually form a filter cake with a certain thickness on the initial sedimentation layer.
The vacuum filter forms a negative pressure at the outlet of the filtrate as the driving force for filtration. This filter is divided into batch operation and continuous operation. The intermittently operated vacuum filter can filter suspensions of various concentrations, and the continuously operated vacuum filter is suitable for filtering thick suspensions containing more solid particles.
The intermittent operation filter has been developed because it can realize automatic operation, and the filter area is getting larger and larger. In order to obtain a filter residue with low moisture content, a mechanically squeezed filter has been developed.
Separate the container into upper and lower chambers with filter media, which constitutes a simple filter. Suspension is added to the upper cavity and enters the lower cavity through the filter medium under pressure to become filtrate. The solid particles are trapped on the surface of the filter medium to form filter residue (or filter cake).
During the filtration process, the filter residue layer on the surface of the filter medium gradually thickens, the resistance of the liquid through the filter residue layer increases and the filtration speed decreases. When the filter chamber is full of filter residue or the filtering speed is too low, stop filtering, remove the filter residue, and regenerate the filter medium to complete a filtration cycle.
The liquid must overcome the resistance to pass through the filter residue layer and the filter medium, so there must be a pressure difference on both sides of the filter medium, which is the driving force for filtering. Increasing the pressure difference can speed up the filtration, but the deformed particles under pressure will easily block the pores of the filter medium when the pressure difference is large, and the filtration will slow down instead.
Suspension filtration has three methods: filter residue layer filtration, deep layer filtration and sieving filtration. The filter residue layer filtration refers to the formation of the initial filter residue layer after the initial stage of filtration. After that, the filter residue layer plays a major role in filtering. At this time, both large and small particles are retained; deep filtration means that the filter medium is thick and the suspension contains There are few solid particles, and the particles are smaller than the pores of the filter medium. When filtering, the particles are adsorbed in the pores after entering; sieve filtration means that the solid particles trapped by the filter are larger than the pores of the filter medium, and the inside of the filter medium does not absorb solid particles. Filtration methods, such as rotating drum filter sieve to filter out coarse particles in sewage.
In the actual filtration process, the three methods often appear simultaneously or one after another. The processing capacity of the filter depends on the filtering speed. When the solid particles in the suspension are large and the particle size is uniform, the pores of the filtered filter residue layer are relatively unobstructed, and the filtrate passes through the filter residue layer at a higher speed. The application of coagulant to gather the fine particles into larger agglomerates is beneficial to increase the filtration speed.
For suspensions with fast solid particles settling speed, apply a filter on the top of the filter medium to make the filtration direction consistent with the direction of gravity. The coarse particles settle first, which can reduce the clogging of the filter medium and the filter residue layer; in the suspension that is difficult to filter ( Coarse solid particles such as diatomaceous earth, expanded perlite, etc. are mixed into the colloid, which can make the filter residue layer loose; when the filtrate has a high viscosity, the suspension can be heated to reduce the viscosity. These measures can speed up the filtration speed.
Classification and characteristics
Intermittent vacuum filter
The mechanism of the vacuum filter is basically the same as that of the pressure filter, except that the pressure on one side of the filter medium is lower than the atmospheric pressure, and the driving force is smaller. Vacuum filter: simple structure, filtering driving force is greater than gravity filter. Vacuum leaf filter: simple structure, suitable for general mud-like material filtration, but the operating conditions are poor and the labor intensity is high .
Continuous vacuum filter
External filter surface rotary drum vacuum filter: It can operate continuously and automatically, can effectively carry out filtration, washing, and dehydration. The operation site is clean and easy to inspect and repair. The disadvantage is high cost, the use range is limited by the vapor pressure of hot liquid or volatile liquid, materials with low boiling point or volatile at operating temperature cannot be filtered, and it is difficult to handle slurry with high solid content and large change in particle characteristics, and filter cake The moisture content is about 30%, rarely less than 10%, mainly used in the chemical and food industries.
Rotary drum vacuum filter with inner filter surface
It is suitable for filtering the suspension of solid particles with uneven thickness. It does not require a stirring device. The machine has low cost and can adapt to changes in feed concentration. If it needs to operate at high temperatures, it is easy to take heat preservation measures. The disadvantage is that the surface of the drum cannot be fully utilized, and the filter cake needs a certain viscosity, otherwise it is easy to fall off, resulting in a decrease in the vacuum degree and a change in the feed flow rate; it is difficult to replace the filter cloth.
Disc vacuum filter
The price is the lowest based on the unit filtering area, and the floor space is small, but the humidity of the filter cake is higher than that of the rotary drum vacuum filter. Because the filter surface is vertical, the filter cake has uneven thickness, is easy to crack, is not easy to wash, the thin layer filter cake is difficult to discharge, the filter cloth wears quickly, and it is easy to block. It is easy to handle materials with low sedimentation speed and easy to filter. It is not suitable for processing non-sticky materials. The application range is the same as that of rotary drum vacuum filters.
Turntable vacuum filter
The structure is simple, the washing effect is good, the washing liquid is separated from the filtrate, and the processing capacity of a single filter is large for the fast dewatering slurry. The disadvantage is that it covers a large area, the filter cloth wears quickly, and is easy to block.
Turn-over disc vacuum filter
It can filter viscous materials and has strong adaptability. It is suitable for separating slurry with a solid content of more than 20%, high density, easy separation and full washing of the filter cake. It is often used in chemical, light industry and other industries.
Maintenance of the turn-over type vacuum filter;
1. It is difficult to control the installation accuracy of rotating parts and the deviation process is slow;
2. The fatigue damage of the filter steel structure is slow;
3. The acidic medium has a slow corrosive effect on parts;
Belt vacuum filter: There are three types: fixed chamber type, mobile chamber type, and intermittent movement of the filter belt. The belt vacuum filter has a horizontal filter surface, and it has high filtration efficiency, good washing effect, and adjustable filter cake thickness. The filter cloth can be washed on both sides at the same time, flexible operation and low maintenance cost. It can be used in the chemical, pharmaceutical, and food industries. It has excellent separation performance for the slurry with a faster settling speed, and it is even better when the filter cake needs to be washed.
Purpose of vacuum filter
Vacuum belt filter press is a new type of filtration equipment with a high degree of automation. Its products are widely used in : thermoelectricity, chemical industry, pharmaceuticals, papermaking, building materials, smelting, rubber, food and other fields. The vacuum belt filter press is a new type of filtration equipment with a high degree of automation. Its products are widely used in: thermoelectricity, chemical industry, pharmaceuticals, papermaking, building materials, smelting, rubber, food and other fields.
Prospects of vacuum filter
New types of filtration equipment under development include: mechanical squeezing filtration equipment; dynamic filters that can achieve filtration without a filter residue layer; large-scale filtration equipment for coal washing sewage treatment, chemical and petroleum industries.
In terms of filtration theory research, the measurement of filter resistance and porosity of the filter residue layer, filtration speed, simulation and amplification of filtration equipment, thin liquid clarification filtration and dynamic filtration mechanism, and filtration media research are all important topics. The use of electronic computers to control filtering operations is the development direction of filtering equipment.
The vacuum filter appeared
The filter is a device that uses porous filter media to intercept solid particles in the mixture of liquid and solid particles to achieve solid and liquid separation. Filters are widely used in chemical, petroleum, pharmaceutical, light industry, food, mineral processing, coal and water treatment sectors.
Filtration technology has been used in production in ancient China, and paper made of plant fibers has been used in 200 BC. In 105 AD, Cai Lun improved the papermaking method. During the papermaking process, he dipped plant fiber pulp on the dense thin bamboo curtains. The water was filtered through the gaps of the bamboo curtains, and a thin layer of wet pulp remained on the bamboo curtains. Serve paper.
Most of the earliest filtration was gravity filtration. Later, pressure filtration was used to increase the filtration speed, and then vacuum filtration appeared. The rotary drum vacuum filter invented at the beginning of the 20th century realized the continuous filtration operation. Since then, various types of continuous filters have appeared one after another.
Installation, use and maintenance
After the equipment is unpacked, remove the packing grease and check whether the fasteners, meters, switches and wiring heads are loose or fall off .
Switch on the power supply and ground protection.
Open the water pipe valve, and continuously supply an appropriate amount of water to the vacuum pump, so that the water ring necessary for vacuuming is formed in the pump, and the purpose of cooling can be achieved. In order to ensure the performance and safe operation of the pump, it is advisable to run for no more than 10 minutes each time. If you need to reuse it, you must replace the circulating water to ensure that the water temperature does not exceed 30°C. (Note: If the amount of supplemental water is too small, a water ring cannot be formed, and the calibrated vacuum cannot be achieved; if the water volume is too large, unnecessary water will be added. Power consumption and the power consumption of the motor, and make a harsh noise).
Before driving, open the large and small filter disc valves, and close the rest.
Test drive, if there is a screaming sound, you should immediately adjust and add water until there is no screaming, close the opened filter disc valve, observe the pointer of the vacuum gauge, and the machine can be used normally after reaching the calibration value.
When using a fixed filter disc to filter materials, first lock the filter disc, wet the filter cloth and filter paper on the filter plate with a small amount of clean water, then pour the pulp into the filter disc, and open the valve of the filter disc used. Normal work can be performed repeatedly intermittently or continuously.
To prevent backwater from entering the vacuum system during shutdown, the valve should be closed first, and then the pump should be stopped. After the work is finished, if you do not use it temporarily within 1-2 days, you must open the screw plug at the bottom of the pump cover, drain the water in the pump, and then stop. The screw plug must be tightened when used.
After stopping for a long time and before restarting, remove the motor protective cover, and turn the motor fan blade by hand to make it start after turning flexibly.