Plate and Frame

WHAT IS A PLATE AND FRAME FILTER PRESS?

Plate and frame filter presses have been used for many years, and predate the recessed chamber filter press, which is the type that most people think of today when they hear the term “filter press”. Although recessed chamber presses are now more of the norm, the plate and frame design has some advantages with certain applications and is still used today.

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PLATE AND FRAME FILTER PRESS DESIGN OVERVIEW

The plate and frame design utilizes a flat, solid plate (known as a “flush plate”) covered by a filter press cloth, with a hollow frame between each plate. A metal skeleton holds and clamps the filter plates together to create a chamber, which is formed by the flush plate on each side of a frame. Filter cake is collected within the frame. Historically, plates were made of wood or cast iron. Today, the most common material is polypropylene.

HOW DOES A PLATE AND FRAME FILTER PRESS WORK?

The slurry is pumped into a corner hole and flows into each frame, allowing solid particles to accumulate on the filter cloths. The remaining filtered liquid (also known as filtrate) then moves to a drainage port in the flush plate and into a corner hole that is not being used for feeding the slurry. The filtrate then travels to discharge piping and is directed to the next step in the process.

After a period of time, the frames become filled with solids, the slurry feed pump turns off, and the filter press is ready to open. Each frame should now contain a filter cake, which is the end result of the solids forming on the filter cloths. The filter cakes are then scraped out of the frames using a spatula, ideally falling into a cake hopper placed below the press.

ADVANTAGES OF THE PLATE AND FRAME DESIGN

The primary advantages of plate and frame presses are the ability to quickly change the filter cloths as well as the ability to use a wider range of materials for the filtration medium, including paper, which is often used for fine filtration applications.

For example, in a process where immediate particle retention is important, filter paper may be required as fine solids would either blind off the filter cloth or simply pass through it. Note that filter cloths are still in place to support the filter paper. The filter cloths are reused, but the filter paper is replaced after every filtration cycle.

Plate and frame presses are best suited for projects where filtration area is more important than volume. This is why plates and frames have their greatest prominence in polishing applications (as opposed to dewatering projects), where the feed solids concentration is often well below 1% by weight.

Polishing applications are sized for a particular filtration area based on the process flow rate and the known flux rate (volume per area per unit of time). To avoid dips in achievable filtration flow as the press fills with solids, polishing applications usually include a redundant filter press that is also sized to accept 100% of the desired process flow.

DISADVANTAGES OF PLATE AND FRAME PRESSES

One disadvantage of the plate and frame design is the potential for building uneven pressure between frames, which can lead to plate damage. This issue stems from the fact that the frame is being fed through a small opening in the corner, which can lead to blockage. This clogging can cause one frame to become full while the next frame in-line remains empty.

Another disadvantage is the potential for leakage. The filter plates used in plate and frame presses are non-gasketed, which allows them to wick liquid under pressure. This type of filter press is usually mounted on a raised platform or positioned over a pit where any leaked liquids can be collected more conveniently.

Recessed Chamber

WHAT IS A RECESSED CHAMBER FILTER PRESS?

A recessed chamber filter press utilizes filter plates that form a series of cavities between them when they are clamped together. Suspended particulates collect on the filter cloths and build up inside each cavity space to form a filter cake. Compare this to the hollow frames of the plate and frame design where solids are collected.

RECESSED CHAMBER FILTER PRESS DESIGN OVERVIEW

The skeleton of a recessed chamber filter press is constructed in a similar fashion as a plate and frame press where the plates hang on a steel frame, and the frame acts as a clamping device for the filter plates. Both types of presses also utilize a hydraulic cylinder and pump for opening, closing, and clamping the press.

As with plate and frame filter plates, recessed chamber plates are most commonly made from polypropylene. However, recessed chamber plates can be either gasketed or non-gasketed. Gasketed plates offer greater protection from leakage, but can also require a more time-intensive cloth changing process. Non-gasketed cloths or plate and frame cloths can have latex applied to the edges to help minimize (but not eliminate) wicking.

HOW DOES A RECESSED CHAMBER FILTER PRESS WORK?

Slurry is pumped into the filter press through the feed (most commonly in the center of the plate) and the solids are distributed evenly in each chamber throughout the press (1). Solids begin to build on the filter cloths. Most of the solid/liquid separation is accomplished by the particulates building on the cloths. At first, some fines pass through, but eventually the solids begin to form a layer on the cloths (2). This layer traps the fine particles and eventually forms a filter cake. The filter cake then serves as a depth filter as the dewatering process continues.

The filtrate (liquid) usually exits the filter pack (plates) through corner ports into a manifold. When the correct valves in the manifold are open, the filtrate exits the press through a single point, the filtrate outlet. The filtrate is then directed via discharge piping to the next step in the process.

As the filter press builds pressure, the solids build within the chambers until they are completely full of filter cake (3). Once the chambers are full, the fill cycle is complete, and the filter press is ready to be emptied (4). The press is then opened, and the plates are moved apart. As the plates are shifted, the filter cake falls from each chamber into a cake hopper or drum below the press. A spatula can be used to scrape the cake from the cloths if needed.

ADVANTAGES OF THE RECESSED CHAMBER DESIGN

One of the main advantages of the recessed chamber plate design is the ability to feed a large center hole versus a small opening in the corner of the plate. The large hole in the center of the plates allows the chambers to fill faster and more evenly, with less risk of clogging and causing plate damage due to unequal pressure. This is especially important in applications with high feed solids.

However, it’s also important to note that a larger feed inlet (combined with gaining one more filtrate outlet in a center feed configuration) is important in large-scale polishing applications with high flux rates (for example, a Merrill-Crowe process). If the filter plate inlets, outlets, and internal porting are not large enough, the calculated press flow rate will not be achievable.

Another advantage is the ability to achieve higher feed pressure with the recessed chamber design. The “frame” or sealing surface of the recessed chamber plate is all connected to the center web. This keeps the “frame” from bowing out under high pressures.

Contact us to discuss your requirements of filter press plates. Our experienced sales team can help you identify the options that best suit your needs.

Also, filter cake release is generally easier with a recessed plate. When the press is opened, and the plates are shifted, the cake either falls out or is quickly scraped off the cloths using a spatula. Cake release may not be as fast with a plate and frame press, as the filter cake is held by a non-tapered frame and may require more manipulation for removal.

DISADVANTAGES OF RECESSED CHAMBER PRESSES

Although recessed chamber presses have several advantages over plate and frame, one disadvantage is the limitation on cake thickness, which is dictated by the depth of the chamber. Recessed chamber plates cannot be easily swapped out for a wider or narrower frame as in a plate and frame press. This makes the plate and frame design better suited for applications where testing variations in filter cake thickness is important.

Another disadvantage can be seen in changing filter cloths. The plate and frame design allows for a simple drape-over cloth, whereas recessed chamber either requires pounding filter cloths into the plates (gasketed) or securing cloths to the plates using cloth dogs and zip ties or hook-and-loop fasteners (non-gasketed).

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Filter press technology plays a vital role in industry, especially in the field of solid-liquid separation. As one of the key equipment, recessed plate filter presses are widely used in a variety of industries, including chemical, pharmaceutical, food and beverage, and environmental engineering.

Introduction of the recessed plate filter press

The basic principle of the recessed plate filter press is to utilize the space between the filter plate and the filter frame to form a filter chamber, and by applying pressure to the mixture, the liquid is filtered through the filter cloth or the filter paper, while the solid particles are retained in the filter cloth, forming a filter cake. In this way, the purpose of solid-liquid separation is realized.

Recessed plate filter presses usually consist of a filter plate, a filter frame, and a pressing device. The filter plate has grooves that can be used to install filter cloth or paper and can be pressed under a certain pressure to improve filtration efficiency. The frame is a frame around the plate to hold the plate in place and form the filter chamber.

Working process of the concave plate filter press

• Slurry feed: First, the slurry or mixture to be treated is injected through the feed pipe into the inlet of the filter press. The slurry contains solid particles and liquid components.
• Cake formation: After the slurry enters the filter press, under pressure, the liquid components are filtered out through the filter cloth or paper, while the solid particles are retained on the filter cloth to form a cake. With the continuous feeding of the slurry and the increase of pressure, the thickness of the filter cake gradually increases.
• Filtrate discharge: The clear filtrate enters the retention chamber through the filter cloth and is discharged through the discharge pipe. Typically, the filtrate is cascaded through multiple chambers of the filter press to ensure that the final liquid is clear.
• Cake handling: Once the cake reaches a certain thickness, the feed to the filter press is stopped and the cake can be removed from the press using an extraction device after a certain period of curing and compaction. The filter cake can usually be used for reprocessing or disposal, such as incineration, recycling, or disposal of waste.

Advantages of the recessed plate filter press

• High efficiency: The recessed plate filter press adopts a multi-layer filter plate and filter cloth structure, which can realize efficient solid-liquid separation, fast cake formation, and clear filtrate.
• Easy to operate: The operation of the filter press is relatively simple, only need to set the operating parameters, start the equipment can run automatically. The operator usually only needs to monitor the running status of the equipment and does not need too much technical training.
• Low maintenance cost: The maintenance cost of the recessed plate filter press is relatively low because of its simple structure, few parts, and components, which are not easy to be damaged and have a long maintenance cycle. Usually only needs regular cleaning and lubrication of key components to ensure the normal operation of the equipment.
• Wide range of applications: The recessed plate filter press is suitable for a variety of solid-liquid separation scenarios, including chemical, pharmaceutical, food processing, environmental protection, and other industries. Different models and specifications of the filter press can be customized and adjusted according to different process requirements, with strong adaptability and flexibility.
• Energy saving: The recessed plate filter press is usually driven by hydraulic or mechanical pressure, which consumes less energy and saves energy compared with other filter presses.
• Friendly operating environment: the noise generated by the recessed plate filter press in the process of operation is low, and the wastewater and waste residue discharged can meet the environmental standards after treatment, in line with modern environmental requirements.

Areas of application for recessed plate filter presses

Recessed plate filter presses are widely used in various industries, and they play a key role in solid-liquid separation and are mainly used in the following fields:

Mining: In the field of mining, recessed plate filter presses are commonly used to extract useful components from metal ores, such as extracting solid particles from metal ores such as gold, silver, and copper, and separating them from water. The solid particles in the slurry are separated from the water by the filter press, thus realizing the concentration and purification of the ore.

Chemical: In chemical production, recessed plate filter presses are widely used in the separation, filtration, and recovery of chemical raw materials. For example, in the organic synthesis process, solid particles and solvents in the reaction mixture need to be separated, and the recessed plate filter press can efficiently accomplish this task.

Food processing: In the food processing industry, recessed-plate filter presses are commonly used for clarification and filtration of liquid foodstuffs such as fruit juices, wines, and beverages. Solid particles, suspended solids, and impurities in the liquid can be removed by the filter press, thus improving the quality and purity of the food.

Wastewater treatment: Recessed plate filter presses are used for solid-liquid separation and sludge dewatering in wastewater treatment processes. Through the filter press, solid particles and suspended solids in wastewater can be separated, thus purifying the water quality, meeting the discharge standard, and protecting the environment.

Environmental protection: Recessed plate filter press is also widely used in environmental protection projects, such as the treatment of industrial wastewater, municipal wastewater, solid waste, and so on. The useful substances in the waste can be recycled and utilized through the filter press, and at the same time, the volume of the waste can be reduced to reduce environmental pollution.

Difference between plate and frame filter press and recessed plate filter press

There are some obvious differences between plate and frame filter presses and recessed plate filter presses in terms of structure and working principle:

Structural difference:

• Plate and frame filter press: its filter plate and frame are separated, and the filter media forms a filter cake on the plate, which is then compacted. After the cake is formed, the pressure is applied to the filter material through the filter plate and the filter frame.
• Recessed Plate Filter Press: The filter plate of the recessed plate filter press has a grooved or recessed structure, which forms a filtrate channel on the surface of the plate while forming the filter cake.

The cake is discharged in this manner:

• Plate and frame filter press: Cake is discharged manually and usually requires downtime.
• Recessed plate filter press: after the formation of the filter cake, the filtrate is discharged through the grooves, and the filter cake can be continuously discharged during operation.

Scope of application:

• Plate and frame filter press: suitable for processing thin suspensions, which require frequent downtime to clean up the filter cake during processing.
• Recessed plate filter press: suitable for processing concentrated suspension, the cake can be discharged continuously during the process, which improves production efficiency.

Summary

In short, the requirements for solid-liquid separation in industrial production can be met using recessed plate filter presses, which quickly and efficiently separate solid particles from liquids in suspension to obtain a dry cake and a clear filtrate.