Plate Size
Once the cubic foot capacity of a filter press has been determined the next step is, the proper selection of the size of the filter plates, frame, components and any accessories. This will allow you to see exactly where the cu. ft. capacity fits in relation to the volume of each size press. For example a 5 cu. ft. can be sized as a 470 mm, a 630 mm and also an 800 mm. The size selected is determined by the amount of expandability desired. After the plate size is selected, there are many options from which to choose. The following information is a summary of what needs to be considered in order to make the proper selection, Please read each section in turn and note your requirements.
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Plate Construction
Select the type of filter plate material. The standard material is an industrial grade polypropylene. An optional FDA approved food grade polypropylene material, or a high temperature glass filled polypropylene material are also available. Special materials are also available such as Carbon Steel , Stainless steel and Kynar.
Plate Style
The standard is a 100 psi recessed gasketed plate with EPDM seals. Viton seals are available as an option. Also available are non-gasketed plates with quick removal latex edged cloths, where the cloth acts as the gasket. The Non gasketed plates allow for easier change out of the filter cloth, are lower in cost, but are not completely liquid tight during the processing stage. Special membrane squeeze plates have the ability to expand after the chambers are full to “squeeze” additional process liquid out of the filter cake. A “mixed stack” of plates will be provided where every other plate will be a special membrane squeeze plate
Optional Backing Plate
If a shorter cycle is desired, when running low volume applications for example, the capacity of the filter press can be temporarily reduced. This is done by moving the follower (tail) plate forward in the plate stack. The backing or “blank plate” is then placed behind the follower plate acting as extra support. The follower plate will not flex or break when used in this manner.
Plate and Press Pressure Rating
The 100 psi design is standard for most dewatering applications and will produce a cake with approximately 30-35% solids. A 225 psi design can be used to provide an increased yield per cycle and depending on the application can increase the solids in the cake to 50% or more.
Cake Thickness
The 32 mm cake thickness is standard. Options include 25, 38 and 50 mm cake thickness. 25 mm would be used for high viscosity (slimy) materials and 50 mm would be used for easily filtered material.
Cloth Type
ErtelAlsop can provide filter cloths in many different materials, weaves, thread styles, and air permeability values resulting in a wide array of performance characteristics. If possible ErtelAlsop would like to receive samples of the process liquid to conduct filterability tests for cloth selection. If testing is not possible then we will furnish our standard polypropylene filter cloth, a monofilament x multifilament, Sateen weave with a CFM<1.0.
Frame Design
All ErtelAlsop frame configurations are sidebar design. Frames can be designed in Carbon Steel or Stainless Steel.
Volume of Plates/Expansion Spacer
All filter presses are available with optional removable expansion spacer. On presses ordered with a spacer, the first number denotes current plate capacity. The second number in the nomenclature is the maximum capacity the frame will allow.
Discharge/Air Blow-down Piping
The discharge/air blow-down piping is available in either manual or in automatic operation. An optional core blow-down is available to purge the center feed line of residual fluid. Available materials of construction are schedule 80 CPVC, or schedule 40 Stainless Steel.
Feed Style
The feed style can vary for special applications such as pharmaceuticals and some type of food processing. Center feed is standard, however a choice of any corner feed is available.
Automation versus Manual Operation
Manual or semi automatic operation requires input from an operator to start and operation of the filter press, including opening and closing, blow down, plate shifting etc. Fully automated presses require initial start up of operation and then close fill, blow-down, plate shift, discharge and cloth wash is automated. Restarting the press cycle still requires operator input.
Let’s examine the wide variety of factors that influence how Filter Press Cloth performs in your operations.
The type of machine determines the overall strength needed for the filter media. Fabric that may work well on one type of machine may not work at all on another. Tensile strength, elongation properties, flexibility, and durability of the cloth are all important considerations in filter cloth selection. Different types of filters hold and pull fabric in different ways. Some fabrics may work well with one type of filtration equipment, but not with another because of how it stretches, bends, and holds up to stress in the application.
Learn more about the role of yarn fiber materials, filament types, yarn types, and weave patterns in Filter Cloth Selection.
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Each type of filter press cloth has different cake release characteristics. Selecting the proper filter press cloth will help to ensure proper cake formation. The proper amount of filter cake dryness will not only prevent the need for excess cloth scraping but will also contribute to lower expenses in hauling away the filter cake.
Learn more about how proper Filter Cloth Selection will help to ensure a trouble-free press operation with excellent cake formation. Symptoms to look out for regarding your filter press cakes include sticky cakes, thin filter cakes, sloppy filter cakes, and partially formed filter cakes.
Learn more about Filter Cloth Troubleshooting.
How clean does the filter need to be? Some processes may require the cloth to be cleaned after each cycle, or during the process. How is the cloth cleaned, and what is used to clean it? A spray bar may be used to clean cloth on a filter but may also create additional abrasion and wear on the filter press cloth.
Learn about whether Chemical Cleaning is an effective tool in cleaning your filter press cloth.
Learn about Micronics Automatic Cloth Washing Systems and how they are well-suited to extending the life of your properly selected filter press cloth.
Particle size is important when selecting filter cloth. Different fabrics are equipped to handle different particle sizes. If the cloth’s pores are too big, particles will pass through without being caught in the filter. If the pores are too small, the cloth will blind and prevent slurry from passing through. Often, the cake that forms on the cloth is performing much of the filtering. The cloth must have the right pore size to build a cake but still allow liquid to flow through.
Just as particle size is important when selecting filter cloth, so is particle size distribution. In some applications, the particles are all about the same size. In others, large particles are mixed with fine particles. Understanding the particle size distribution helps find the ideal cloth to use as your filter media.
Sometimes, if particle size varies, the material can be processed multiple times in order to efficiently filter. The first pass will catch the largest particles on the cloth but not finer particles. The second pass will allow medium-sized particles to build a thicker cake on top of the largest particles. Additional passes catch and build up finer particles until optimal filtration efficiency is achieved.
The shape of the particles will affect how the cake builds, how it adheres to the cloth, and how much wear may be put on the filter press cloth.
Different types of filter press cloth are equipped to handle different operating conditions. Most fabrics have a maximum operating temperature. Operating outside of that will damage the cloth and affect filtration efficiency. Depending on what the fabric is made of, it may also be susceptible to chemical damage. Filter media selection takes into account susceptibility to chemical attack as well as the operating temperature and consistency of the slurry.
Some types of cloth have an ideal pH range. Many times, both pH and operating temperature need to be considered to ensure the cloth can handle the operating conditions.
The Micronics Engineered Filtration Group can help you select the optimal filter press cloth for your operating conditions which will also help to extend filter press cloth life.
Consider how much material is being processed. How thick does the filter cake need to be? How heavy is the filter cake? If the cloth must support all the weight of the filter cake, the fabric must be strong enough to handle the load of the material being processed.
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