Cross-Flow Filtration; Trans-Membrane Pressure; Cross-Flow Rates - Burkert T-CUT Manuel D'utilisation

Type T-CUT
StructureandFiltration
6.2.1 Cross-flow Filtration
Pipe membrane
Feed
Figure 2:

Cross-flow filtration

In cross-flow filtration, the product to be filtered flows through the membrane installed in the filter module. The
difference in pressure between the membrane pipes which the product crosses and the filtrate void causes part
of the fluid to flow as a filtrate (permeate) through the membrane. The remaining part is fed into the circuit as con-
centrate or retentate.
More heavily contaminated water is frequently treated using the cross-flow operation. In comparison with dead-
end operation, a higher volume flow is fed into the module here. The main part of the water which is fed in washes
over the membrane (cross-flow) and is recirculated. The resulting flow and turbulence reduces the formation of a
covering layer and ensures a consistent permeate output.
6.2.2 Trans-membrane Pressure
The trans-membrane pressure is identified by the pressure loss over the module.
Drop in pressure through the module: ∆p = p
Trans-membrane pressure:
The permeate flow increases with the trans-membrane pressure.
Please note that while high trans-membrane pressures produce a thicker and denser covering layer, the permeate
flow increases only slightly and membrane fouling may result in a decline in the permeate flow in the long term.
Therefore, while moderate trans-membrane pressures mean that there are no peak permeate flow rates at the
start phase of filtration, this will pay off in the form of high and stable permeate flow rates in the long term.
6.2.3 Cross-flow Rates
Higher cross-flow rates will limit the thickness of the developing covering layer and enable the flow rate of the
permeate to be kept high.
The standard flow rate (cross-flow rate) per module can be found in the specific data sheet. The cross-flow
rate of 3–4 m/s is usually indicated here. The optimum flow rates for membrane applications will vary and are
dependent on the composition of the fluid to be filtered.
Retentate
Pressure
(Concentrate)
Filtrate (permeate)
– p
IN
= p + p
p
IN
TMP
2
OUT
– p
OUT
Perm
Filtration time
english
11