How Sludge Filter Presses Work And Their Benefits

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Sludge filter presses are a type of dewatering equipment designed specifically for removing water from sludge. They consist of a series of filter plates that are compressed, allowing water or filtrate to pass through while retaining the dewatered solids or filter cake.

This blog post will discuss how sludge filter presses work and their main advantages, including:

• The basic mechanics of sludge filter presses
• Types of filter plates and frames used
• How the dewatering process occurs
• The benefits of high percent solids capture
• Other key advantages
• Factors to consider when choosing a sludge filter press
• Tips for effective operation and maintenance

How Sludge Filter Presses Work

The basic components and mechanics of a sludge filter press are:

• Filter plates &#; These consist of a filter cloth or membrane sandwiched between rigid plates. The filter media separates solids from liquids under pressure.
• Slurry feed &#; The slurry or sludge to be dewatered is fed into the space between the plates.
• Hydraulic frame &#; The plates are secured in a frame that can be tightened hydraulically. As pressure is applied, water passes through the filter media but solids are captured.
• Filtrate discharge &#; The filtered water or filtrate drains out of the end of the filter press.
• Cake discharge &#; The dewatered solids or filter cake builds up between the plates and is discharged when the press is opened.

Types of Filter Plates

There are two main types of filter plates in sludge filter presses:

• Frame plates &#; Provide structure but have no filter media. They separate the active filter plates.
• Filter plates &#; Contain the filter cloth or membrane to separate solids and liquids. Common types include:
• Flat plates &#; Simple and basic style with a flat surface area.
• Tortional plates &#; Have grooves to increase the surface area for filtration.
• Membrane plates &#; Use advanced filter membranes instead of cloths.

How Dewatering Occurs

As pressure is applied in the filter press between cycles:

• Water in the slurry is forced through the small openings in the filter media.
• Solids in the slurry accumulate on the surface of the filter cloth or membrane.
• The solids build up to form a filter cake, which becomes denser and holds together as more water is removed.
• The filtrate flows out through channels to be discharged or collected for reuse.

Benefits of High Percent Solids Capture

• Water recovery &#; Up to 99% of water can be removed, allowing for recycle and reuse.
• Reduced volume &#; A thicker filter cake takes up less space, lowering disposal costs.
• Lower energy costs &#; Less sludge means less energy needed for heating and pumping.
• Reduced chemicals &#; Thicker sludge requires less polymer addition for dewatering.
• Compliance with regulations &#; Many wastewater discharge limits based on total solids.
• Cost savings &#; Higher dewatered solids content directly correlates to lower operating expenses.

Other Key Advantages of Sludge Filter Presses

• Ability to handle a wide range of sludges and slurries
• Continuous or batch operation modes available
• Simple and robust design requires little maintenance
• Modular design for ease of installation and expansion
• Compact footprint conserves space
• Flexibility to optimize cycle times and pressures based on application needs

Factors to Consider When Choosing

When selecting a filter press, consider:

• Flow rates and throughput needs
• Final dewatered solids content required
• Space and facility footprint available
• Capital and operating costs
• Type of sludge or slurry to be dewatered
• Disposal and reuse requirements
• Level of automation desired

Tips for Operation and Maintenance

• Start slowly and work up to maximum operating pressure.
• Allow a dwell time at pressure for best dewatering results.
• Apply vacuum to the filtrate chamber where possible.
• Flush and rest the press between cycles for optimal performance.
• Inspect and replace seals, gaskets and worn parts as needed.
• Replace filter cloths and membranes when flow rates begin to decrease.

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.

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

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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.

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