It is mainly used for solid-liquid separation. It is widely used in the chemical and pharmaceutical industries for filtering materials through pressure. It is particularly advantageous for the separation of viscous and fine materials.
The use of the filter press is explained in detail.
Filter Presses are used for the separation of solids and liquids. Compared to other solid-liquid separation equipment, the filter press has a higher solids content and a better separation effect than the filtered cake. The basic principle of solid-liquid separation is that the mixed liquor flows through the filter media (filter cloth) and the solids stay on the filter cloth and gradually accumulate on the cloth to form a filter cake. The filtrate part, on the other hand, penetrates the filter cloth and becomes a clear liquid without solids.
Filter presses are commonly used in the mining, sludge and food industries as filtration and separation equipment. They were used in chemical production in the early 18th century and are still widely used in the chemical, pharmaceutical, metallurgical, dye, food, brewing, ceramic and environmental industries. The filter press consists of a number of filter plates and filter frames stacked together to form a filter chamber, with pressure as the driving force for filtration. There are three types of filter presses: plate and frame filter presses, chamber filter presses and vertical filter presses, which are operated intermittently.
The working principle of a filter press is.
The first is positive pressure strong pressure dehydration, also known as into the slurry dehydration, that is, a certain number of filter plate under the action of strong mechanical force is closely arranged in a row, the filter plate surface and the filter plate surface between the formation of the filter chamber, the filter material under strong positive pressure is sent into the filter chamber, the filter material into the filter chamber, the solid part of the filter media (such as filter cloth) retained by the filter cake, the liquid part through the filter media and discharge the filter chamber, so as to achieve solid-liquid separation. As the positive pressure increases, the solid-liquid separation becomes more complete, but the high positive pressure is not cost effective in terms of energy and cost. After pulp dehydration, the filter press equipped with a rubber squeeze membrane, the compression medium (such as gas and water) enters the back of the squeeze membrane to push the squeeze membrane to further dehydrate the squeeze filter cake, called squeeze dehydration. After pulp dehydration or extrusion dehydration, compressed air enters the filter chamber on one side of the filter cake through the filter cake and carries liquid water from the other side of the filter cake through the filter cloth to discharge the filter chamber and dehydration, called wind-blown dehydration. If both sides of the filter chamber are covered with filter cloth, the liquid part can be discharged from the filter chamber through the filter cloth on both sides of the filter chamber, which is called double-sided dewatering of the filter chamber. After the dewatering is completed, the mechanical pressure of the filter plate is lifted and the single piece is gradually pulled away from the filter plate and the filter chamber is opened separately for unloading the cake as a major work cycle is completed. Depending on the nature of the filter material, the filter press can be set up to feed pulp dewatering, extrusion dewatering, wind-blown dewatering or single or double-sided dewatering, with the aim of minimising the water content of the filter cake.
Filter presses are used for the separation of solids and liquids. Compared with other solid-liquid separation equipment, the filtered mud cake from the belt filter press has a higher solids content and excellent separation effect. The basic principle of solid-liquid separation is that the mixed liquid flows through the filter medium (filter cloth), the solids stay on the filter cloth and gradually accumulate on the filter cloth to form a filter mud cake. The filtrate part, on the other hand, penetrates the filter cloth and becomes a clear liquid without solids.
As the filtration process proceeds, cake filtration begins, the thickness of the mud cake gradually increases and the filtration resistance increases. The longer the filtration time, the higher the separation efficiency. Specially designed filter cloths can retain particles with a particle size of less than 1 μm. In addition to the excellent separation effect and the high solids content of the mud cake, the filter press offers further separation processes.
The filtration process can be combined with an effective washing of the filter cake at the same time.
Valuable material can thus be recovered and a high purity filter cake can be obtained.
Filtration method.
The way the filtrate flows out is divided into open-flow filtration and dark-flow filtration. In open-flow filtration, a spigot is provided at the bottom of each plate and the filtrate flows intuitively from the spigot. For concealed flow filtration, each filter plate is equipped with an outlet channel hole underneath, and the outlet holes of several filter plates are connected into a single outlet channel, which is discharged by a pipe connected to the outlet hole underneath the stopper.
Washing method:
When the filter cake needs to be washed, there are sometimes one-way washing and two-way washing, dark flow one-way washing and two-way washing. In the open flow one-way washing, the washing liquid enters from the washing liquid inlet hole of the stopper plate, passes through the filter cloth and then through the filter cake, and flows out from the non-porous filter plate, when the liquid outlet nozzle of the porous plate is closed and the liquid outlet nozzle of the non-porous plate is open. The two-way washing of the open flow is that the washing liquid is washed twice from both sides of the inlet hole above the stopper plate, i.e. the washing liquid is washed from one side first and then from the other side, and the outlet of the washing liquid is diagonal with the inlet, so it is also called two-way cross washing. The concealed one-way flow is that the washing liquid enters the perforated plate from the inlet hole of the stopper plate, passes through the filter cloth and then through the filter cake, and flows out from the non-perforated filter plate. Dark flow two-way washing is the washing liquid from the two washing liquid inlet holes on both sides above the stop plate, that is, washing liquid first from one side and then from the other side, the outlet of washing liquid is diagonal direction, so also called dark flow two-way cross washing.
Classification of filter presses
Plate and frame filter presses
The filter press consists of a set of filter chambers with alternating filter plates and filter frames. The surface of the filter plate is grooved and its projections are used to support the filter cloth. The corners of the filter frame and plate are perforated to form a complete channel for the flow of suspended liquor, washing water and filtrate. The plates and frames are supported on the crossbeam by handles on each side and are pressed by a pressing device. The filter cloth between the plates and frames acts as a sealing gasket. The suspension is pumped into the filter chamber by the feed pump and forms a sludge on the filter cloth until it fills the chamber. The filtrate flows through the filter cloth and along the grooves of the filter plate to the edge channels of the plate and frame, where it is discharged centrally. When filtration is complete, the sludge is washed with clear washing water. After washing, compressed air is sometimes introduced to remove the remaining washing liquid. The filter press is then opened to remove the filter residue, clean the filter cloth, re-press the plate and frame and start the next working cycle.
The plate and frame filter press is suitable for suspensions with a large or nearly incompressible sludge. The suitable concentration of solids in the suspension is generally below 10% and the operating pressure is generally 0.3 to 0.6 MPa, with special cases up to 3 MPa or more. The filtration area can be increased or decreased depending on the number of plates and frames used. The plate and frame are usually square, the inner length of the frame is 200 to 2000 mm, the frame thickness is 16 to 80 mm and the filter area is 0.5 to 1200 m. The plate and frame are pressed together with a manual screw, an electric screw and hydraulic pressure. The plates and frames are made of wood, cast iron, cast steel, stainless steel, polypropylene and rubber.
Chamber filter presses
The structure and working principle of the chamber filter press is similar to that of the plate and frame filter press, with the difference that the filter plates are recessed on both sides and each two plates are combined to form a chamber, eliminating the need for a filter frame, with a circular hole in the centre of the plate. The suspension flows into the chambers from this. This type of filter is suitable for suspensions that need to be filtered under high pressure without washing the residue.
Vertical filter presses
The filter plates are stacked horizontally and up and down to form a group of chambers and occupy a small footprint. It uses a continuous filter belt and after filtration is completed, the belt is moved to unload and clean the filter belt, making the operation automatic. The filter press has a wide range of applications and a relatively simple structure. The pressing and pulling apart of the plate and frame, the unloading of the slag and the cleaning of the filter cloth can all be automated, which is conducive to the development of the filter press into a large scale. With the addition of a flexible rubber diaphragm in the filter chamber of the filter press, high pressure water or compressed air can be used to compress the slag at the end of filtration with the help of the rubber diaphragm, so that the slag can be further pressed and de-liquified, forming a diaphragm press filtration with variable volume of the filter chamber and compressed slag, the pressure of which can reach 1 to 2 MPa.
Application areas for filter presses
Mineral processing industry:
with the development of modern industry, mineral resources are increasingly depleted, the mined ore has been faced with the “poor, fine, mixed” situation, for this reason, people have to grind the ore finer, and the “fine, mud, sticky” materials for solid-liquid separation. Today, in addition to the high demand for energy saving and environmental protection, enterprises have put forward higher and wider requirements for solid-liquid separation technology and equipment. The social demand for mineral processing, metallurgy, petroleum, coal, chemical, food, environmental protection and other industries has driven the application of solid-liquid separation technology and equipment, and the breadth and depth of its application areas are still expanding.
Sewage treatment industry:
After flocculation, the sludge is transported to the belt filter press, where the free water is separated under the action of gravity, forming a non-flowing sludge, and the sludge is gradually squeezed under the action of squeezing pressure and shear force, finally forming a filter cake and discharged. It is widely used in the sewage treatment of urban domestic sewage, textile printing and dyeing, electroplating, paper making, leather, brewing, food processing, coal washing, petrochemical, calcium carbide slag, starch slag, wine slag, textile activated sludge and other industries.