Filter press operation and precautions

 The filter press can be operated only after the filter press equipment is in place and the external pipelines are connected, and the three-wire circuit is delivered (an independently protected circuit breaker junction box must be set up). Before operating the filter press, it is necessary to The following preparations:

 

Check the vertical and horizontal positions of the frame and plates; check whether the frames and plates are skewed and whether the centers are aligned; Check whether the filter cloth is folded or damaged; Check whether the pipe hole joints at the end of the thrust plate are connected correctly and whether the bolts are tightened , whether the gasket is properly padded.

 

1. 1.Press the filter plate tightly (maintain pressure)

（1）Turn on the power switch and the power indicator light will turn on;

（2） Move all filter plates to the end of the thrust plate and place them in the center of the two beams;

（3）Press the "press" button, and the piston rod pushes the compression plate to compress the filter plate/frame until the hydraulic working pressure value is reached (see the pressure gauge, see the product insert for specific values), and the hydraulic system automatically controls the pressure at the pressure gauge Between the upper and lower limits, automatic pressure maintenance is implemented. (The pressing force generated by the filter press pressing device must not only resist the filtering pressure or pressing pressure, but also must ensure the sealing of the filter chamber.)

Warning: In order to prevent the permanent deformation of the filter plate and the strength of the filter press, the pressing force is not allowed to be too high. The operator should comply with the specified data. When the filter chamber is compacted, there must be a telescopic compensation function in the length. The reason is: the change in length caused by the compaction of the filter cloth and the reaction of the elasticity of the filter plate, as well as the change in length caused by thermal expansion and contraction;

Note: Most filter presses are designed with telescopic compensation function. That is, the anchor screw holes of the hydraulic cylinder base bracket are long waist-shaped. When installing, tighten the two nuts and keep a 2mm gap between the washer and the bracket plane to ensure that the hydraulic cylinder end can expand and contract slightly during the compression process - horizontal movement. In some larger models, the connection between the cylinder base and the bracket is equipped with a needle roller connection, which can also ensure that the hydraulic cylinder end can expand and contract slightly during the compression process - horizontal movement.

Warning: Pressing force that is too small may cause leakage in the filter chamber. If it is too large, it will damage the filter plate, piston rod and filter press frame, and even affect life safety. Our company has locked the product and pressing force value (overflow threshold). The upper limit of the electric contact pressure gauge is adjusted to the hydraulic working pressure value, and the lower limit is the hydraulic working pressure minus 2Mpa; the lower limit of the automatic pull plate hydraulic working pressure is the hydraulic working pressure minus 2-4Mpa. Users must not make adjustments without authorization. If you find any situation such as liquid spraying in the filter chamber, please call or send us an email and we will answer your questions. ·When out of service, do not leave the filter press in a compressed state. ·When pressing, no foreign matter (including residual filter cake or human limbs) should be placed in the filter press.

 

2. 2.Feed filtration (washing)

Feed filtration means that the suspension is forced into the filter chamber of the filter press, and the filtrate flows out through the filter medium. A filter cake is formed in the filter chamber, and the filtrate is discharged from the filtrate discharge hole through open flow or undercurrent. The formation of filter cake in the filter chamber; feeding is mainly achieved by relying on the feed pump. A suitable feed pump can be selected for each set of filtration equipment. The size of the feed pump depends on the composition of the filtered material and the filtration rate. Select the feed pump according to the properties and characteristics of the filtered material. The feeding method can be made into center feeding, upper feeding, lower feeding, and corner feeding according to your process requirements; the feeding position can also be double-head feeding (from the thrust plate and the compression plate) according to your process requirements. end), middle-end feed (adding a movable thrust plate in the middle of the filter chamber), etc. Feeding system users need to take care of themselves.

Note: Avoid fluctuations in feed pressure or instantaneous pressure drops as much as possible, otherwise it will lead to uneven filter cake thickness, bending of the filter plate, and reduced filtration capacity.
The valves for filtrate, washing liquid and compressed air must be activated according to the operating procedures and must not be opened at the same time.
The temperature of the filtered slurry must be controlled at <100°C, and the filtrate must not be mixed with impurities, otherwise it will easily block the feed port.
The allowable feed pressure and the required feed pressure are usually determined by the dehydration performance of the filter cake. Decide. The feed pressure is also subject to: The operating pressure allowed by the filter press; The pressure value allowed by the filter plate and limited by the temperature curve.

Information: Pre-coating filtration is to apply a layer of filter aid on the filter cloth in the filter chamber. Relying on its thin coating, it can achieve better separation effect and make it easier to unload the cake. Diatomaceous earth is a commonly used filter aid.

 

3.Filter Cake Washing: Washing is an additional processing step in the separation process. (You can decide whether to wash or not when ordering according to the process requirements?) Through washing, the filtrate stock solution or mother liquor is replaced with washing liquid. Washing means that the medium enters the filter chamber from one side of the washed filter plate, and then is pressed into the entire chamber, that is, through the filter cake, and the washed filtrate is discharged from the filter plate. The flow direction of the washing medium can also be reversed.

Note: Before washing the filter cake, use a membrane filter plate to compact the filter cake, so as to obtain the best washing effect. (This is only possible when the pressing pressure must be slightly higher than the washing pressure). Usually the working pressure of the filter chamber ≥ diaphragm pressure ≈ washing pressure. Filter cake drying (air drying) The filter cake can be dried with air. The compressed air blows the filter cake like filter cake washing and discharges the filtrate in the filter cake capillary. This process can be carried out before, during and after membrane pressing.

 

3. 4.Diaphragm pressing (secondary dehydration)

Membrane press is usually used to compact the filter cake during filter cake washing and to press out the remaining filtrate in the filter cake during dehydration. Squeezing is achieved by introducing the squeezing medium (compressed air or water) into each membrane filter plate to create squeezing pressure.

Danger: When compressed air is used for squeezing, energy accumulation occurs due to the compressibility of the air. If the pressing force of the filter press is insufficient, the expansion of the compressed air will cause damage to the filter press frame, filter plate, etc. In serious cases, it will damage or even endanger personnel safety. （1) The required pressing pressure is usually determined by the dewatering performance of the filter cake. The pressing pressure is also subject to: The operating pressure allowed by the filter press, The pressure value allowed by the membrane filter plate and limited by the temperature curve. (2) The amount of pressing media, volume flow rate, increase in pressing pressure, etc. involve many factors such as the volume of the filter chamber, the volume of the filter cake, the inherent dehydration rate of the filter cake, the life of the diaphragm, and operational safety. It can only be determined by experience. (3) The solids volume within the filtration chamber (ideal filling of the chamber) is determined by many factors. All these factors are related to the filtration cycle and the service life of the diaphragm.

Warning: In view of the above reasons, the filtration pressure (feed pressure) of our company's diaphragm filter press is 0.6-0.8Mpa, and the pressing pressure is 1.0Mpa-1.6Mpa or less than the working pressure value in the filter chamber.

Information: According to practical experience, the final filling capacity of the diaphragm filter press is 60-80% of that of the general chamber filter press, and should not be less than this number. In the absence of feasible reference values, optimal filling must be determined experimentally. When using a diaphragm filter press, an air compressor and air storage tank are required. The tank should be equipped with a safety valve. If the gas tank is used exclusively for filter presses, install a shut-off valve at the outlet and connect it to the distribution pipeline; if one tank is used for multiple purposes, install a shut-off valve at the outlet and install a pressure reducing valve and connect it to the distribution pipeline. To prevent thermal expansion of compressed air and failure of the pressure reducing valve, a safety valve must also be installed on the distribution pipeline. Exhaust (discharge of pressing medium): The compressed air must be completely exhausted into the atmosphere after pressing. Therefore, an exhaust valve is installed on the distribution pipe to quickly drain the compressed air.

Warning:The exhaust pipe should be placed away from people and the working condition of the exhaust system should be checked regularly. Use a silencer for exhaust according to circumstances and needs. Attention should be paid to the fact that the exhaust system is blocked and the exhaust is insufficient and incomplete, causing safety accidents. Before the compressed air (or water) is completely exhausted, do not press the "release" button to release the pressing force of the filter plate to avoid damaging the diaphragm.

 

4. 5.Opening the filter plate and unloading the cake

The hydraulic filter press manually pulls the plate to discharge the slag. In the automatic type, press the "pull plate forward" button, and the plate box will automatically pull the filter plates apart piece by piece and unload the slag. After pulling the last filter plate, the plate box returns to its original position. The extra large filter press is equipped with pull-plate pause and continuation control devices on both sides of the beam, which can be manually controlled at will. In order to adapt to the different time requirements that may occur when unloading slag from filter plates one by one.

 

5. Clean and inspect the filter cloth

Remove the residue on the joint surface of the filter cloth and filter plate, check whether the filter cloth is damaged or wrinkled, and clean the machine. It is recommended that all filter plates be moved to the end of the thrust plate and centered between the two beams. Then enter the next work cycle.

 

Note:The residual filter cake remaining in the filter chamber must be removed. Residues blocking the suspension feed port must be removed to ensure smooth flow. There must be no filter cake residue on the sealing surface (all around edges) of the filter plate. Unremoved filter cake residue and dirt deposits produced by not cleaning for a long time will reduce the filtration effect and cause deformation and spraying of the sealing edge. Therefore, if necessary, protect the sealing edges from leaks by cleaning them with high-pressure cleaning equipment.