What Is a Filter Press?

The filter press uses a special filter medium to apply a certain pressure to the object, which is a kind of mechanical equipment that makes the liquid dialysis. It is a commonly used solid-liquid separation equipment. It was used in chemical production in the early 18th century and is still widely used in chemical, pharmaceutical, metallurgy, dyes, food, brewing, ceramics and environmental protection industries.

Function: The solid in the mixed liquid is extracted to realize the role of solid and liquid separation.

Subjects: coal technology (first-level discipline); mining machinery engineering (second-level discipline); coal preparation machinery (third-level discipline).

History: The first filter press equipment appeared in the early 18th century and was used in the chemical industry.

Filter press use range:

Environmental protection industries such as medicine, chemical industry, standard parts, pharmaceutical, metallurgy, non-standard screws, dyes, food, brewing, ceramics, oil refining, sewage treatment, etc. ^[1]

The structure of the filter press consists of three parts:

The hydraulic pressure mechanism of the filter press is composed of a hydraulic station, a cylinder, a piston, a piston rod, and a Huffland card hydraulic station where the piston rod is connected to the pressure plate. Direction valve, pressure gauge, oil circuit, fuel tank.

Filtration method: The filtrate flows out into clear flow filtration and dark flow filtration. Open-flow filtration. A water nozzle is installed on the liquid outlet below each filter plate, and the filtrate intuitively flows out of the water nozzle. Underflow filtration, a liquid outlet channel hole is provided below each filter plate, and the liquid outlet holes of several filter plates are connected to form a liquid outlet channel, which is discharged through a pipe connected to the liquid outlet holes below the thrust plate.

Washing method: When the filter cake needs to be washed, there are sometimes one-way washing and two-way washing, and underflow one-way washing and two-way washing. ^[2]

1. As a mature dewatering equipment, the filter press is widely used in the field of environmental protection and has become an important equipment for sewage sludge treatment.

2. The mechanical dehydration of sludge is mainly to remove the capillary water between sludge particles. The moisture content of sludge after ordinary mechanical dehydration is usually 65% -80%, which is a mud cake.

3. In the past, mechanical dewatering equipment mainly included belt filter presses, plate and frame filter presses, and decanter centrifuges. Currently, box filter presses, vertical hydraulic filter presses, diaphragm machines, and high pressure plate and frame machines are commonly used.

4. When sludge is used for landfill, sludge dewatering can greatly reduce the accumulation of sludge and save costs during transportation. When composting sludge, dewatering of sludge can ensure smooth composting (during the composting process) Generally, sludge is required to have a lower moisture content); if sludge incineration and centralized treatment are performed, a high sludge dehydration rate can greatly reduce heat energy consumption and reduce the cost of hazardous materials treatment.

5. However, the sludge composition is complex, the relative density is small, the particles are fine, and it is often in a colloidal state, which determines its characteristics that it is not easy to dehydrate, so far. Except for the ultra-high pressure vertical hydraulic filter press, the other filter presses have added drying processes to reduce the residual oil (liquid) rate.

6. Low power consumption of belt filter press. The plastic cake filter press has a low water content, but the decanter centrifuge has a strong adaptability to sludge flow fluctuations, good sealing performance, large processing capacity, and small footprint. In the past, most sewage treatment plants in China used centrifuges, belt filter presses and plate and frame filter presses, and small sewage treatment plants generally used concentrated dewatering machines. At present, box-type filter presses, diaphragm filter presses, and ultra-high pressure vertical hydraulic filter presses are unique in technology and are ideal equipment for sludge dewatering.

Belt filter press:

Continuous work, belt press dewatering machine has 3 working areas, namely gravity dewatering zone, wedge press dewatering zone and shear press dewatering zone. The type of press is a two-dimensional press, mainly used for sludge dewatering, but its application The scope is expanding. The dewatering effect of the belt filter press relies more on chemical agents, resulting in higher sludge treatment costs.

Plate and frame filter press:

1. Intermittent pressure filtering equipment for solid-liquid separation of various suspensions.

2. The box-type filter press was developed after the 1960s. Its characteristics are high filtration pressure, the highest pressure has reached 4.5 MPa; single machine filtration area is large, 2050 square meters of products have come out abroad, the largest filtration area in China has reached 2,000 square meters, the filter cake has a low liquid content, and the pressure after filtration The moisture content of the cake can be further reduced by 5% to 15%; good corrosion resistance, the filter plate can use a variety of reinforced plastics, light weight, good flexibility, corrosion resistance, wide adaptability; low operating costs, can achieve multiple continuous Job, online control. Modern filter presses are mostly box type.

Diaphragm filter press:

1. Intermittent pressure filtering equipment for solid-liquid separation of various suspensions. The filter press is equipped with a rubber press diaphragm to dehydrate the filter cake. The medium that expands the diaphragm can be compressed air (used below 0.7 MPa) or water (used above 0.7 MPa).

2. Ultra-high pressure vertical hydraulic filter press: unique filter cavity structure, the secondary pressing of the sludge, the moisture content of the sludge after pressing is 50%; the residual oil rate of pressing edible oil is low, and the technology is leading in China. First choice by many manufacturers.

Sludge conditioning:

Generally, the domestic sewage sludge is mechanically dehydrated with high-molecular polymers. Generally, it has to undergo "quenching and tempering" treatment. There are various methods of tempering, including thermophysical methods such as "thermal hydrolysis", "hydrothermal drying", "Wet oxidation" and so on, there are physical methods, such as ultrasonic waves, microwaves, etc., most of them are chemical methods. By adding certain inorganic chemical salts (medicines), it can change the polarity of sludge molecular charges, increase particle pores, and improve Filter press characteristics and other effects. At present, the most common and cheapest technology on the market is a combination of "sludge chemical conditioning and filter press treatment". ^[3]

1. The filter press should be installed on a flat concrete foundation. The foot of the thrust plate at the feed end is fixed on the foundation with anchor bolts; the anchor end does not use anchor bolts, or the anchor bolts are locked with two nuts after positioning, leaving an appropriate gap between the nut washer and the foot base. The machine feet can be telescopically retracted. Before positioning, the installer should correct the verticality of the beam and the large plane of the thrust plate.

2. The foundation structure should be designed by the construction engineers according to the equipment load conditions. It is advisable to grout the anchor bolts twice with reserved holes.

3. There should be enough space for operation and maintenance around the filter press. The hydraulic pressure filter press should choose an appropriate place to place the hydraulic station to ensure that the hydraulic station can work normally.

4. Place the filter plate according to the work requirements, and arrange the feeding, washing and draining pipelines. Equipped with filter pressure indicator and return channel to control filter pressure. If it is a diaphragm squeeze type, a compressed air line is arranged.

5. Hydraulic filter press, clean 20 # -40 # hydraulic mechanical oil is injected into the oil tank of the hydraulic station, and the use temperature is> -5 ; if the ambient temperature is low, a hydraulic oil with similar viscosity and low freezing point can be selected. Hydraulic oil must be added through 80-100 mesh strainer.

6. Mechanical or hydraulic pressing device, the starting motor connected to the power supply should work correctly. When the hydraulic pressure is applied, the pressure gauge should rise steadily, and the hydraulic system should have no leakage. Correctly adjust the working pressure of the hydraulic station according to the size of the model. ^[3]

1. Only after the normal filter press is commissioned can the feed work be carried out, and the whole machine must be fully inspected before each shift. Mechanical compaction of transmission components and reduction boxes must be filled with lubricating oil; hydraulic compaction rechecks the oil storage capacity of the fuel tank and the working pressure of the hydraulic station, the hydraulic oil is generally replaced once a year, the hydraulic system should be cleaned once during replacement, the working pressure of the hydraulic station It is less than the maximum working pressure of the oil cylinder, but the minimum must not be lower than the allowable value of the filtering pressure. If it is too small, it will cause large leakage and damage the machine if it is too large.

2. It is forbidden to start the factory when the number of filter plates is less than the specified number, so as not to damage the parts. Check the arrangement of the filter plates before feeding, the filter cloth must not be folded to prevent large leakage; the filter plates must be neatly arranged and pressed tightly after unloading the cake.

3. After everything is normal, press the filter plate to press and filter. The filter pressure and filter temperature must be within the specified range. Excessive filter pressure will cause leakage. If the filter temperature is too high, the plastic filter plate will easily deform. Suspension during feeding Make the concentration uniform. There must be no impurities; the filter cloth and filter plate must be rinsed after unloading the cake, and the residue is not allowed to be stuck on the sealing surface or the feeding channel, otherwise it will affect the unblocking of the feed and the tightness of the filter plate, which may cause the two sides of the filter plate. Unbalanced pressure causes deformation and damage of the filter plate.

4. The selection of filter cloth must meet the filtering technology requirements of filter paddles. The new filter cloth should be shrunk before production, and the opening diameter should be smaller than the filter plate diameter. When supporting the filter plate, the cloth holes and plate holes should be relatively concentric, and the feeding holes The cloth should be close to the cylinder wall, otherwise it will cause unclear filtration, low filtration rate, rupture of the cloth cylinder, and the consequences of the intended filtration purpose cannot be achieved.

5. In the initial stage of the filter press, the filter is turbid. When a layer of filter cake is formed on the filter cloth, the filtrate will become clear. If the filtrate is always turbid or mixed, the filter cloth may be damaged or the hole between the cloth and the plate may deviate. At this time, the valve should be closed or the feed should be stopped to replace the filter cloth. A small amount of leakage caused by the capillary phenomenon of the filter cloth is allowed between the filter plates.

6. When moving the filter plate, the force should be even and appropriate. Don't bump or hit, so as not to damage the sealing surface and the filter handle. After a period of use, the filter cloth will harden and its performance will decline. Therefore, regular inspections are needed. If changes are found to affect the filtration rate, the corresponding low concentration of weak acid and alkali can be used for neutralization and cleaning to restore the filter cloth's function. If it cannot be recovered, replace it in time.

7. The slurry, washing liquid or compressed air valve must be activated according to the operating procedure, and cannot be activated at the same time. The compressed air pressure cannot exceed the filtration pressure when the diaphragm is squeezed. ^[3]

1) In the working state of the filter press, the suspension will definitely occur. If the sales are not in place at the time of suspension, it will have a serious impact on subsequent work. Through observation and analysis during the operation of the machine, it is found that this phenomenon occurs because the feed pipe of the fast-opening diaphragm filter press uses a steel ring rubber pipe. Under the action of pressure filtration, the pipe itself will form a reaction. The force is applied to the pressure plate, which will offset the force of the oil cylinder to a certain extent, causing the pressure plate to rebound, and when the suspension is stopped, the push pin will not be in place, and a machine failure will occur.

Based on this situation, the following transformation plan is proposed: the orientation of the feeding hose and protective sleeve of the quick-opening diaphragm filter press is adjusted to a certain extent, specifically, by turning 180 ° from the original basis, and turning the clockwise bending into the counterclockwise bending. In this way, the reaction force in the feed pipe not only does not cancel the force of the oil cylinder, but also strengthens the squeezing effect, thereby ensuring the working state of the compaction plate and preventing the failure problem that occurs during suspension.

2) When the filter press is working, the tensioning and loosening of the filter plate is performed on the main beam track. During the operation, derailment occurs from time to time. The study found that the main reason for this phenomenon was that when the filter plate was tightened, the small chain connected to the filter plate fell off, resulting in inconsistent work progress on both sides of the track, which led to failure.

Based on the problem of the small chain connection method, the following transformation scheme is proposed: In the original equipment, the 7-ring small chain of the small chain is reduced to a 3-ring small chain. Observational studies have shown that the occurrence of twisted chains is an important reason for the small chain to fall off. After the small chain structure is modified in this way, when detecting the operation of the small chain, the 3 ring can detect the problem in time than the 7 ring to prevent the occurrence of the twist . ^[4]