Sterlitech™
Sepa CF Cell: Frequently Asked Questions
Q. What
is the difference between Sepa CF and Sterlitech HP4750?
Q. Does the feed spacer penetrate
the membrane?
Q. How do I calculate Reynolds
number based on the feed cross-flow velocities for the various feed
spacers?
Q. How do I distinguish between
the low foulant (34ml) feed spacer and the high foulant (68ml) feed
spacer when I hold them in my hands?
Q. Is the low foulant spacer
the same as the permeate carrier?
Q. In the instruction manual of
the Sepa CF, tubular and mesh spacers are mentioned. Can I
conclude that the tubular is the low foulant and the mesh is the
high foulant?
Q. Could the filter cloth of
industrial filters be used in Sepa filtration units, after cutting
it to proper size?
Q. How
is the Sepa System repassivated?
Q. Can I use the Sepa CF membrane
cell without spacers?
Q. How can I set the maximum
flow from my Sepa CF?
Q. What is the definition of GFD?
Q. Will there be a difference in flow rate on the Sepa CF if it is run continuously or in intervals?
Q. What fluid do I use in my Hydraulic hand pump for my Sepa CF?
Q. What is the proper way to store the membranes for the Sepa CF after they have been used?
Q.
What is the difference between Sepa CF and Sterlitech HP4750?
A. The Sterlitech HP4750 is an enclosed batch system
(limited to 300ml) with direct filtration under pressure.
There is a stir bar mixing the solution and pressures up to 1000
psi may be applied.
The Sepa CF is a crossflow
system that allows continuous sampling and testing under different
pressure and flow rate parameters depending on the pump and fluid.
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Q.
Does the feed spacer penetrate the membrane?
A. The mesh spacer usually leaves an imprint on the membrane which
is not a problem - unless too thick of a mesh is used - then it
could damage the membrane.
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Q.
How do I calculate Reynolds number based on the feed cross-flow
velocities for the various feed spacers?
A. The Sepa CF cell
for use with high fouling spacer has a flow area width and height
of 3.7 inches by 0.068 inches. Once a spacer material is placed
in the channel the actual flow channel cross section is significantly
reduced. We have not calculated that. We typically operate
the cell and estimate the Reynolds number at the transition from
laminar to turbulent flow by monitoring the increase in pressure
drop as the crossflow is increased.
Another usage implementation
which we have used is the placement of a rubber gasket in the flow
channel. A specifically sized flow channel can be cut out
of the gasket to define a flow channel of the desired cross section.
We actually have done
more study of the CF cell for use with standard spacer (3.7 in.
by 0.034 in. cell cross-section). We evaluated that cell for
various cross flow velocities at various feed flow rates.
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Q.
How do I distinguish between the low foulant (34ml) feed spacer
and the high foulant (68ml) feed spacer when I hold them in my hands?
A. The low foulant
has smaller squares and bends slightly easier. It feels lighter.
It is not stiff like the medium foulant. The high foulant
spacer has corragated ridges in it like cardboard. No holes.
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Q.
Is the low foulant spacer the same as the permeate carrier?
A. No, the low foulant
spacer is under the membrane and the permeate carrier is on top.
The membrane is sandwiched between the spacer and permeate carrier.
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Q.
In the instruction manual of the Sepa CF, tubular and mesh spacers
are mentioned. Can I conclude that the tubular is the low
foulant and the mesh is the high foulant?
A. The mesh spacer
is a low (34 ml) and also the medium spacer (68 ml).
The tubular spacer is for high foulants
(68 ml) and looks like corregated cardboard.
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Q.
Could the filter cloth of industrial filters be used in the Sepa
filtrations units, after cutting it to proper size?
A. The Sepa CF can
potentially work for any media that can be fitted into the chamber.
One thing that could be
an issue for some types of filter media is whether or not a sufficient
seal is made between the O-ring and the media. For membranes,
this is not a problem because membranes have a relatively smooth
surface, which affords good mechanical seal when pressed together.
A large fiber woven material, for example, may need to be modified
or filled with some type of potting compound to level the surface
in order to get a non-bypass seal.
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Q.
How is the Sepa System repassivated?
A. Passivation is
a process that will remove free iron deposits and will add future
protection to your Sepa System. To passivate the Sepa System,
swab the entire unit with either a 20% Nitric Acid (1st choice)
or Phosphoric Acid (2nd choice) solution. Make sure to use
good Nitric Acid or Phosphoric Acid handling precautions such as
gloves, eye goggles, etc. when performing passivation. Rinse
unit off with conditioned water such as distilled.
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Q.
Can I use the Sepa CF membrane cell without spacers?
A. Using the cell without any
spacers will usually cause wrinkles in the membrane. The depth
of the cell is made to accommodate the spacer that will fit in it
(34 or 68 ml).
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Q.
How can I set the maximum flow from my Sepa CF?
A. Most separations
and flux through membranes are controlled by the nature of the fluid.
For salt rejecting membranes, such as RO and NF, the dominant variables
are operating pressure and osmotic pressure (a solute concentration-dependent
property which reduces net operating pressure with increased solute
concentrate).
The pumping rate or fluid
velocity across the membrane is another important operating parameter;
an increased velocity results in improved mixing of the layer of
feed solution directly above the membrane. The removal of
fluid through the membrane results in accumulation of rejected solutes
in this layer, often referred to as the boundary layer. The
boundary layer can contribute a significant resistance to flux through
the membrane as levels of solutes increase.
The accumulation of solutes
in the boundary layer is often the most limiting factor in membrane
flux, particularily for the larger pored membranes (NF, UF, and
MF). There generally is a finite operating pressure, above
which provides little or no flux benefit.
An increase in the feed
solution velocity across the membrane, combined with turbulence
promoting mesh spacers, can provide the optimal combination of operating
conditions. Consideration of energy imput and mechanical load
due to pressure drop across the membrane are practical limitations
for operation of membrane systems.
To find maximum flux, we set the feed
flow to a maximum practical rate, and increase the operating pressure
incrementally while monitoring flux (filtrate) output. A given
operating pressure will yield a certain maximum output for a specific
feed solution.
If the feed solution becomes
more concentrated, such as occurs for a dewatering objective, the
optimal operating pressure will typically decrease as the solute
concentration increases (the exception to this would be if the osmotic
pressure increase due to concentration becomes significant).
The input energy may be better applied to higher cross flow velocity
if practical.
A practical method may include operation
at a pressure setting slightly lower than the maximum initial rate
determined. This is produce highest flow, best flux, and least
amount of build up on membrane.
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Q. What is the definition of GFD?
A. GFD = Gallons Per Square Foot of Membrane Per Day
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Q. Will there be a difference in flow rate on the Sepa CF if it is run continuously or in intervals?
A. If permeate flow rate verses time for both membranes are plotted will there be a difference?
There should be a difference in the plots - at least initially. There is typically a "conditioning" affect that occurs as the result of mechanical compression, some of this affect is reversible to an observable amount if operation is intermittent.
This will yield a "zigzag" appearance to a graph of operation vs. time or cumulative hours of operation. The trend with the intermittent operation would be to gradually approach a standard.
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Q. What fluid do I use in my Hydraulic hand pump for my Sepa CF?
A. The unit uses standard grade hydraulic oil. It has a reservoir located under the handle at the furthest end with a cap on the reservoir.
The amount of oil used will depend on the length of line, hose.
The recommended oil has a viscosity rating at 100°F.
SUS rating 150-165
SAE 10 wt oil Hydraulic oil (do not use other types of oils)
General purpose
150-165 thickness
Rating 210°F 42-45
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Q. What is the proper way to store the membranes for the Sepa CF after they have been used?
A. We recommend that the membranes for the Sepa CF be kept wet once used. Either keep the water fresh (change every couple of days), or add ~0.5 sodium metabisulfite (preferred) to keep bacteria from growing.
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Sepa CF Cell Applications.
Sepa CF Cell Benefits
and Features.
Sepa CF Cell Pricing
information.
Sepa CF Cell Specifications.
Sepa CF Cell Principles
of Operation.
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