A vital requirement for any large-scale filtration system is that the performance scales up from development trials to commercial-scale production. Due to batch-to-batch variability and uncertainty in scale-up performance of a filtration solution, process developers typically apply a safety margin of 30% or greater for filtration area.
Although allowing for process variability is a good engineering practice, adding additional filtration area based on uncertain scale-up performance leads to poor economics of the clarification step.
In developing a design concept for a large-scale, single-use depth filter platform, Pall considered ease-of use and process aspects to derive a system design based on stacking depth-filter capsules vertically within a chassis. This design was preferred to that of a horizontal arrangement to aid installation, venting, and draining of the assembly as well as minimize the footprint needed.
The design of the inlet/outlet manifold (distribution manifold) enables the greatest flexibility in the way the process-scale chassis can be operated (Figure 1). In bottom in/bottom out configuration, the process flow is through the distribution manifold at the bottom of the stack. The alternative operating mode of bottom in/top out or top in/bottom out allows for the process flow to enter and exit from opposite ends of the assembly.
Switching between operating configurations is achieved by the simple addition or removal of the second distribution manifold at the top of the stack. The use of the bottom in/top out or top in/bottom out operating mode is potentially applicable for large area, single-layer systems operated at high feed flow flux rates and/or for ease of product handling. The bottom in/bottom out operating mode will otherwise apply.
Additionally the design of the Pall Stax platform provides users with the flexibility to operate the stack in a serial flow mode, whereby two grades of filter media can be operated in series within one chassis. Furthermore, because of the small footprint, multiple chassis can be placed into a small area.
Filterability trials were conducted to assess the scalability of the Stax platform. The trials focused on operating with single-layer modules, which require a higher feed flow rate through the filter assembly than double layer filters, and will amplify the effect of any hydrodynamic losses through the filter assembly. This provided for the worst-case scenario.
The test program included a comparison of the performance of the Pall Stax assembly with other Pall sheet filter formats to provide scalability data across the product range.