Functional principle and primary components of TRF-Filtration
Functional principle
The functional principle of the patented TRF-Filtration method is simple. It is based on an agitator tank with filter membranes attached to its agitators. This prevents the major problem in membrane filtration of fluids: the formation of a layer over the membrane and the subsequent reduction or blockage of the membrane pores.
This layer usually occurs through agglomeration of the molecules that are separated by the membrane pores and the concentration of such molecules at the membrane surface. In a continuous filtration process this effect can be prevented only by fulfilling both these criteria:
- There must be an exchange of the various concentration levels between the membrane surfaces and the fluid.
- Shearing forces are produced at the membrane surface to cause continuous mechanical cleansing. This is best achieved via a highly turbulent cross flow.
In general, agitator tanks produce significantly higher shearing forces and turbulences with significantly less power consumption than is possible with linear flow through a tank or pipe. TRF-Filtration economically utilizes the many directions of flow produced at the membrane surface in the agitator/filter tank for continuous filtration. These simple physical principles highlight the advantages of TRF-Filtration over primarily linear-flow conventional cross-flow membrane systems as used in pipe modules or disc filters.
| figure 1: linear cross flow | figure 2: multidirectional flows in TRF-filter tanks |
 |
 |
Primary components of TRF-Filtration
The heart of TRF-Filtration is a closed filter tank in which one or more rotating assemblies are driven by motors. The rotor and its drive have an innovative patented design. Filtered fluids can be collected in the rotor and discharged from the inside of the filter tank via the rotor accumulating, the rotor hub, and the inside bore of the shaft of the rotor drive; thereby the filtered fluids are not mixed with unfiltered fluids in the tank. Filter modules are mounted fix to a accumulating rotor via screw thread and are sealed even against high pressure in the tank. The filter modules consist of stable stainless steel planetary shafts on which filter discs are stacked, separated and sealed by means of spacers. The filter disc usually consists of a base disc with a drainage surface structure on both sides that allows cleansed filtrate/permeate to flow to the center of the disc. The flat membrane discs are attached to both sides of these base discs via a plastic frame and hermetically sealed.
| figure 3 : rotor und filter modules | figure 4: rotor drive, gear box, V-belt, motor |
 |
 |
Process Description of TRF-Filtration
During filtration operation the filtration tank is filled with the fluid to be filtered by means of a pump with a pressure-dependent performance curve. Then the air bleed valve is closed and, after a delay, the rotor is engaged. The rotational speed of the drive motor is controlled by means of a frequency converter, and the rotor speed is adapted to the properties of the respective membranes and fluids. The interplay between rotating filter modules, flow breakers and other control parameters of TRF-Filtration creates a highly turbulent situation inside the agitator/filter tank through the interaction of a large number of directions of flow and pulsation frequencies. Even for highly viscous media, this achieves the required exchange of concentration through turbulence at the membrane surface as well as the shearing forces necessary for cleansing the membranes – and all this with significantly reduced energy.
In the TRF-filter tank, filtrate flows through the membranes into the inside of the filter discs and from there via planar shaft, collective rotor and its accumulator and hub, to the inside bore of the drive shaft, and from there out of the tank. Outside the filter tank the filtrate/permeate is directed through a flow meter.
The concentration of the suspension in the filter tank continues to rise because the filtrate/permeate continuously flows through the membrane and new feed material enters the tank in relation to the drop in pressure.
In batch operation, this manner of concentration enrichment can continue until the viscosity of the solution reaches a certain ceiling due to the rise in solid matter content; up to that point, the throughput remains economical. Then the suspension concentrate is drained through a valve in the floor of the tank. Under continuous operation, this concentrate drain valve is open continuously or at certain intervals to achieve controlled drainage.
figure 5: primary components III TRF-filter module |
figure 6: structure of TRF-filter discs: base disc, membrane |
 |
|
figure 7: |
|
 |