Introduction

Stacked disc modules have a long history in Food and Beverage applications. They arose out of the need to package sheet-based depth filter technology in more user-friendly, modular closed systems, especially for small batch production or medium flow rate applications. Due to the relative high dirt holding capacity and filtration performance of filter sheet-based products, they provided an optimal and cost-effective solution for handling food and beverage fluids.

The filtration effect of these sheet-based products is based on a combination of surface, depth, and adsorptive filtration. Selected combinations of cellulose, different types of filter aids, or other ingredients in the filter matrix result in a highly porous structure, which achieves effective filtration, including coarse to fine particle removal, colloidal removal, and final filtration.

Classic stacked disc modules represent first generation module design, but they have performance disadvantages.

SUPRAdisc II modules eliminate the disadvantages of classic stacked disc modules. They offer increased capacity, reliability, handling advantages, and robustness, which satisfies customer needs and requirements for a higher performing product.

SUPRAdisc II modules are ideal for many food and beverage applications.

Basic construction of classic stacked disc modules

To better appreciate the design advancements of SUPRAdisc II filter modules, an understanding of the basic features and construction of stacked disc modules should be considered.

Since their inception, classic stacked disc modules have been manufactured leaving the cells of media fully exposed within the filter housing (Figures 1 and 2).

• Individual cells are made from two sheets of depth filter media with a polypropylene separator in between them. This separator is sandwiched inside the cell, on the downstream side of the two sheets, as the flow path is from the outside surface of the sheets to the inside (Figure 3).
• A polypropylene seal around the outside edge is used to bind the two sheets together, thus forming one complete cell.
• The cells are stacked on top of each other until the desired height is achieved.
• End caps are then affixed to the center core, thus locking each cell in place and forming a complete stacked disc module.

Design limitations of classic stacked disc modules

Classic stacked disc modules have inherent design limitations.

• Depth media is exposed
  • The integrity of the media can be compromised during shipping, handling, installation and removal. Extra care must be taken to avoid damage.
  • Modules can fall apart when removed from the housing.
• Individual cell proximity to one another is very close. During steaming, rinsing, or filtration, the cells may shift or warp causing individual cells to touch. This causes blinding of portions of each cell, which reduces the effective filtration area.
• Classic stacked disc designs do not withstand any back pressure. With only the downstream support layer (the separator), even as little as 0.05 bar (0.7 psid) of back pressure can rupture the unsupported media in these modules. This is seen as a half moon tear on either the top sheet of the top module or the bottom sheet of the lowest module in the stack, creating fluid bypass areas and compromising filtrate quality.
• Classic stacked disc modules are sensitive to high temperature operations such as hot water sanitization, steaming, or hot filtration. Deformation caused by high temperature exposure is a common problem (Figure 4).

Construction technology of SUPRAdisc II modules

SUPRAdisc II modules (Figure 5) incorporate a double separator concept.

• Alternating outside separators, discs of depth media, and inside separators are affixed to a rigid polypropylene core until the desired height is achieved.
• Two techniques are used to connect the separators:
  • For 287 mm (12 inch) diameter modules, the unique Clip-Seal Interlock is created by using a hydraulic ram to apply pressure and snap and lock the outside to the inside separators. Each disc of filter media is thus sealed in between the separators.
  • For 410 mm (16 inch) diameter modules, the inside/outside separators are connected by ultrasonic welding.
• Locking end caps are then applied to the center core, creating a complete module.

Design features of SUPRAdisc II modules

The unique separator design provides both upstream and downstream support of the filter media. The media is sealed inside a polypropylene cage assembly and is no longer exposed. The unique Clip-Seal Interlock and the welded design connects the outside to the inside separators resulting in an extremely robust design (Figures 6,7).

Each sheet of filtration media is individually sealed and separated. Depth sheets cannot come into contact with each other, eliminating blinding of the media.

Due to the separator channels, SUPRAdisc II modules have close to 100 % effective filtration area that is dimensionally stable during shipment and handling, filtration and removal.

Deformation or cell collapse is no longer an issue and sheet damage during use is minimized. Backflushing to regenerate the modules is now possible.

Backflushing SUPRAdisc II modules

With the use of a backflush set consisting of supporting discs and intermediate distance discs (Figure 8), modules can be backflushed either with water or product in order to remove contaminants and prolong their life.

For more detailed information on backflushing and availability of backflush sets, please contact Pall.

Benefits of SUPRAdisc II modules

SUPRAdisc II modules offer a multitude of benefits that overcome the disadvantages of the classical stacked disc design (Figures 9, 10, 11). These benefits result in important cost savings.

• Longer onstream life, due to highest utilization of the filter sheet area, no blinding of filter surfaces, open design of the separators, optimized drainage, and distribution of incoming fluid to each filter sheet via the outside separator
• Repeated use is possible due to regenerability of the modules with backflushing
• Higher operational security, due to resilience against vacuum or back pressure shocks, and no cell or module deformation from hot operation or sanitization and steaming
• Better handling before and after operation, due to robust design and protection of filter media from exposure and damage
• Higher yields, as rest filtration in reverse flow mode is possible
• High filtrate quality, without chance of bypass, due to module design and use of proven and reliable filter media recipes

SUPRAdisc housings

SUPRAdisc II modules are used in SUPRAdisc housings. Up to 4 modules can be stacked in a housing without concern of deformation or loss of module integrity. This is due to the solid design of the inner tubular core. This center core is capable of carrying the load of the saturated wet weight of the modules, minimizing the compressive forces on individual filter cells, and subsequently the filter sheets.

For further technical and ordering information on Pall SUPRAdisc housings, please consult Pall.

SUPRAdisc II Module Types

Standard Range

Available in 287 mm (12 inch) and 410 mm (16 inch) diameters, SUPRAdisc II Standard Range modules contain single layer Pall filter sheet media, in K, T, and IR grades (Figure 12).

HP Range

Available only in 410 mm (16 inch) diameter, the SUPRAdisc II HP Range combines 2 different grades of Pall filter sheet media into a single module. A coarse layer on the upstream side and a fine layer on the downstream side allows pre-clarification and clarification in one assembly. Each of the sheet layers is separated by a separator (Figures 13, 14).

A wide range of upstream and downstream sheet combinations is available.

SUPRAdisc II HP modules are not designed for backflushing.

Benefits of SUPRAdisc II HP modules

• Enhanced clarification abilities for fluids with wide particle size distribution, due to graded particle removal. Larger particles are retained by the top sheet layer, thus avoiding plugging of the finer sheet material below. In turn, the downstream layer enables increased efficiency of the upstream layer.
• Up to 30 % higher filtration efficiency than in single layer formats
• Reduced capital expenditure for small batch processing, due to two-step filtration in one housing
• Reduced rinsing water and cleaning chemical consumption