Principle, faults and solutions of plate and frame filter press
working principle:
The plate and frame filter press consists of five major parts: filter plate, hydraulic system, filter press frame, filter plate transmission system and electrical system.
First, hydraulic force is applied to compress the plate and frame group, and the precipitated sludge enters from the middle and is distributed between each filter cloth. Due to the tight plate and frame, the sludge cannot overflow. Under the high pressure of the screw pump and diaphragm pump, the moisture in the mud seeps out of the filter cloth and flows into the return pipe, while the mud cake remains in the cavity. Afterwards, the plate and frame are relieved of pressure, the filter plates are pulled apart, and the mud cake falls down by gravity.
The plate and frame filter press is suitable for general suspensions.
The solid particle concentration of a suitable suspension is generally below 10% (that is, the moisture content is above 90%).
The operating pressure is generally 0.3-0.6 MPa.
The filter area can be increased or decreased with the number of plates and frames used. The plate frame is usually square, the inner side length of the filter frame is 320-2000 mm, and the frame thickness is 16-80 mm.
The filtration area is 20-1200 square meters (the 300, 500 plate and frame we often say refers to the filtration area).
The plate and frame are pressed by manual screw, electric screw and hydraulic pressure.
Boards and frames are manufactured from materials such as wood, cast iron, cast steel, stainless steel, polypropylene and rubber.
Diaphragm frame
The previous process is the same as that of ordinary plate and frame.
Add filter plate expansion design. Gas is introduced into the filter plate to cause it to expand and deform, squeezing the filter cake in the middle of the filter plate, thereby reducing the moisture in the filter cake.
Gas backflush technology is used. When the filter press stops feeding, high-pressure gas is passed into the filter cake of the filter plate to dry the sludge.
The biggest feature of the diaphragm filter press is that it can perform secondary drying and pressing of the filter cake. The special design of its filter chamber allows it to automatically reduce the feed valve in half after the filter chamber is filled with filter cake, leading to gas or gas in the filter chamber. The liquid causes the filter cloth to swell and deform, thereby achieving a secondary squeeze on the filter cake and further reducing the moisture.
Further access to the gas can also further reduce the moisture in the filter cake. High-pressure air passes through the filter cake to separate the water, structural water and other moisture in the filter cake, and is dried by secondary blowing.
Diaphragm filter press operation:
The first is to tighten:
The entire machine needs to be inspected before operation: check whether the filter cloth is folded or overlapped, and whether the power supply is connected properly. After inspection, the pressing operation can be carried out. First press the "Start" button and the oil pump starts to work. Then press the "Compression" button again. The piston will push the pressing plate for compression. When the pressing force reaches the set high point pressure, , the hydraulic system automatically stops.The second is the feed:
When the filter press is tightened, the feeding operation can be carried out: turn on the feeding pump, and slowly open the feeding valve, and the feeding pressure gradually increases to normal pressure. At this time, observe the liquid output from the filter press and the leakage between the filter plates. After filtration for a period of time, the liquid output from the filter press outlet hole gradually decreases. This indicates that the filter residue in the filter chamber is gradually filling. When the liquid outlet does not come out, When there is no liquid or only a very small amount of liquid, it proves that the filter residue in the filter chamber has been completely filled to form a filter cake. If you need to wash or air-dry the filter cake, you can do it later. If you don't need washing or air-drying, you can unload the cake.The third is to wash or air dry:
After the filter cake of the filter press is filled, shut down the feed pump and feed valve. Start the washing pump or air compressor, slowly open the washing liquid inlet or air inlet valve, and wash or air-dry the filter cake. After the operation is completed, close the lotion pump or air compressor and its valve to proceed with the cake unloading operation.The fourth is to unload the cake:
First, close the feed pump and feed valve, the washing liquid or air inlet device and valve, and then press and hold the "Release" button on the operation panel. The piston rod drives the pressing plate to return. After returning to the appropriate position, release the button. Press and hold the "Release" button, manually pull the filter plate piece by piece to remove the filter cake, and at the same time clean the filter residue stuck on the sealing surface to prevent the filter residue from being caught on the sealing surface, affecting the sealing performance and causing leakage. At this point, one operation cycle is completed.Common faults and solutions
▪️Damage to the plate itself
The reasons for damage to the plate itself include:1/When the sludge is too thick or dry blocks are left behind, it will cause the feed port to be blocked. At this time, there is no medium between the filter plates and only the pressure of the hydraulic system itself is left. At this time, the plates themselves are easily prone to being pressurized for a long time. cause damage.
2/ When the feed is insufficient or the feed contains inappropriate solid particles, it will also cause excessive stress on the frame itself and cause damage.
3/If the outflow port is blocked by solids or the feed valve or outlet valve is closed during startup, the pressure will have nowhere to leak, causing damage.
4/When the filter plate is not cleaned thoroughly, sometimes the medium will leak out. Once leaked, small grooves will be washed out on the edges of the plate and frame. The large leakage of the medium will cause the pressure to fail to rise and the mud cake to form. .
Corresponding troubleshooting methods:
(1) Use flexible materials to remove mud from the feed port.
(2) Complete this cycle and reduce the volume of the filter plate.
(3) Check the filter cloth, clean the drain outlet, check the outlet, open the corresponding valve, and release the pressure.
(4) Carefully clean the filter plate and repair the filter plate.
▪️Water seepage between boards and frames
The main causes of water seepage between boards and frames are:1/low hydraulic pressure
2/The filter cloth has wrinkles and holes in the filter cloth
3/There are lumps on the sealing surface.
The treatment method for water seepage between plates and frames is relatively simple, as long as the hydraulic pressure is increased accordingly, the filter cloth is replaced, or the lumps on the sealing surface are removed.
▪️The filter cake cannot be formed or the filter cake is uneven
There are many reasons why the filter cake is not formed or is uneven. Insufficient or too thin feed, or clogging can cause this phenomenon. The main solutions are: adjust the chemical ratio, improve the material supply, clean or replace the filter cloth, clean the blockage, clean the feed hole, clean the drainage hole, clean or replace the filter cloth, increase the pressure or pump power, and start at low pressure. , continuous supercharging and other methods.▪️The filter plate is slow or easy to fall off
Sometimes due to excessive oil stains and stains on the guide rods, the filter plate may move slowly or even fall off. At this time, it is necessary to clean the guide rod in time and apply butter to ensure its lubricity. One thing to note is that it is strictly forbidden to apply thin oil on the guide rod, because the thin oil will easily fall off and make the bottom very slippery. Personnel operating and performing maintenance here may easily fall, causing personal injury.▪️Hydraulic system failure
The hydraulic system of the plate and frame filter press mainly provides pressure. When the oil chamber A is filled with more oil, the piston moves to the left, pressing the filter plate to seal it. When the oil chamber B is filled with more oil, the piston moves to the right and the filter plate loosens. The main reasons for failure to maintain pressure include oil leakage, O-ring wear, and abnormal operation of the solenoid valve. Common solutions are to remove and inspect the valve, replace the O-ring, clean and inspect the solenoid valve, or replace the solenoid valve. The improper advancement of the hydraulic cylinder is obviously because the air is sealed inside. At this time, as long as the system evacuates air, it can usually be solved quickly.▪️Poor separation of filter cake and filter cloth
(1) Check whether there is any change in the fluidity or concentration of the filter material. If the fluidity or concentration is abnormal, extend the filtration time, reduce the moisture content of the filter cake, and ensure that the filter cake and filter cloth are well separated;(2) Check whether the dosage is appropriate and adjust the dosage;
(3) Check whether the capacity and pressure of the feed pump are appropriate. If not, take measures such as changing the filtration time;
(4) The filter cloth is stuck and the mud cake cannot be removed normally. Tie the bottom ends of the filter cloth on both sides of the filter plate or compression plate together, and pull the filter cloth and filter plate together so that the mud cake can be removed smoothly.
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