This invention relates to an apparatus for separating a base liquid
into a permeate fraction and a retentate fraction comprising:
a semi-permeable membrane for separating the base liquid into the fractions;
a base liquid flow path disposed on a first side of said membrane, and
permeate flow channel means disposed on the opposite second side of the membrane
and being provided on a support for carrying said membrane, such that a portion
of the base liquid entering said base liquid flow path and comprising said permeate
fraction flows through the membrane and into said permeate flow channel means.
An apparatus of this general type is disclosed in WO-A-82/00102.
In the known apparatus referred to as a membrane plasmapheresis module a folded
membrane is positioned between structured surfaces of adjacent plates defining
a blood inlet port and a blood outlet port positioned at the ends of one first
flow path on one side of the membrane and further defining a plasma outlet port
adjacent one end of separate, second flow paths extending along the other side
of the membrane.
Generally, this invention pertains to the art of separating a liquid
into fractions by pressure-driven flow through semi-permeable membranes, known
as ultrafiltration, and more particularly, to apparatus adapted to accomplish
Ultrafiltration is the general term applied to the process of separating
a liquid into fractions by pressure-driven flow through semi-permeable membranes.
By proper selection of the membrane material, it is possible to separate liquids
based upon molecular weight, thus obtaining a permeate of extremely high purity.
Such processes find wide application in a number of industries, as for separating
milk used in cheese making into whey and milk precheese product, and in concentrating
antibiotics from a fermentation broth.
Two distinctions are important in identifying the position of the
present invention in relation to the art. First, the art classifies filtration
processes into microfiltration, ultrafiltraton, and hyperfiltration (or reverse
osmosis). The distinction between these processes is based primarily upon the pore
size of the membranes employed and the pressure at which the systems operate.
Microfiltration operates at a relatively large pore size (0.02-2.0 µm) and low
pressure [21 to 105 N/cm² (30-150 psi)]. Hyperfilatration, or reverse osmosis,
operates at pore sizes from the range of 5-15 angstroms down to the micromolecular
and ionic size range (molecular weights of 150 and below), and at pressures in
the range of 141 to 703 N/cm² (200-1000 psi). Ultrafiltration operates at values
between these two processes, at molecular weight cutoffs ranging from 200 to 350,000
and pore diameters of from about 10 to 1000 angstroms. Although the preferred
embodiment of the present invention is directed primarily toward ultrafiltration,
the invention would operate equally well in a microfiltration role, and it could
be adapted to hyperfiltration equipment as well.
Second, the field of ultrafiltration encompasses several means of
effecting the separation of a liquid into fractions. At the outset, it should be
understood that ultrafiltration does not operate in a manner analogous to "filtering"
processes, in which a liquid is passed through a filter disposed transverse to
the flow path, with undesirable solids being retained by the filter and the objective
being a clarified liquid output. Rather, ultrafiltration seeks to separate a base
liquid into two fractions by placing the liquid in the presence of a semi-permeable
membrane; one portion of the liquid (termed the permeate) will pass through the
membrane, and the other will remain in the base liquid stream, termed the retenate.
Thus, ultrafiltration systems pass a base liquid across, rather than through, the
filration means. Also, depending upon the specific application, one fraction or
the other may be the desired product of the process. For example, in cheese manufacure,
the desired product is the retenate (precheese liquid), while in a juice manufacturing
process the object is the permeate, a clarified fruit juice.
Several methods of ultrafiltration have been suggested by the art.
Of primary concern to the present invention are the methods classified as "plate
and frame" ultrafiltration, in which a series of plates support semi-permeable
membranes, and the base liquid is passed across these membranes for filtration.
Other methods include spiral membrane apparatus, in which the membrane is wrapped
in a perforate collection tube, the base liquid being passed throught the tube
longitudinally. A membrane also may be presented in tubular form, with the base
liquid passed within the tube and the permeate passing through the tube and collecting
within the membrane housing. Alternatively, hollow fiber membranes have been offered,
with a bundle of hollow fiber membranes contained within a tubular housing. Base
liquid is passed though the cores of the fibers, and permeate is collected from
the channels surrounding the fibers. The disadvantages of these methods, when
compared to the present invention, will be clear to those skilled in the art.
The preferred plate-and-frame processes depend, of course, on the
presentation of a large membrane area to the base liquid, and it is known in the
art to employ membrane supports, with membrane material disposed on both sides
of a plate and the plates arranged in a stack. Generally, such a stack is provided
with input and output flow passages for the base liquid, disposed on opposite
sides of the stack such that liquid can flow to one side of a plate and thence
between the membranes of adjacent plates, allowing the base liquid to come into
intimate contact, under pressure, with the membrane surface to permit ultrafiltration.
Because one pass through the system generally does not suffice to provide complete
extraction of the desired constituents, the retenate usually is recirculated through
the ultrafiltration apparatus several times. Further, it is known to divide the
stack into subassemblies, each subassembly having input and output passages, such
that liquid flows in parallel across the membranes of all support members of a
subassembly, and the output of one subassembly flows to the input of a succeeding
The apparatus available to date has exbhibited a number of problems.
Ultrafiltration equipment is evaluated based on two criteria -- the concentration
ratio, reflecting the maximum concentration to which the base liquid can be processed
(defined as the ratio of initial volume of base liquid to the final volume after
processing), and the flux rate, defined as the volume of permeate that passes
through a given area of membrane per unit of time, generally expressed as gallons
of permeate per square foot of membrane per day (GFD). These two factors will
determine the specifications of an ultrafiltration apparatus chosen for a particular
Typical of the apparatus offered by the art is the ellipsoidal structure
seen in US-A-3,872,015. As disclosed, the apparatus is similar to that discussed
above, with each plate-like member being ellipsoidal in form. Each plate also has
two openings formed toward the ends of the major axis, so that when the stack
is formed by passing retaining bolts through the aligned openings, inlet and outlet
passages are formed. Curved grooves in the surface of the plate extend from one
opening to the other. These grooves generally can be described as forming a set
of concentric ellipses of increasingly smaller periphery. Blocking members placed
in one opening of periodically-spaced members serve to divide the stack into subassemblies,
Base liquid flows through the inlet passage of a subassembly and
passes into the gap between adjacent membranes. The fluid pressure of the base
liquid forces both membranes against the respective plate surfaces, so that liquid
flows within channels corresponding to the surface grooves. Given that the fluid
pressure at the head of all channels is equal and that the flow path in the outer
channels is significantly longer than that of the inner channels, basic principles
of fluid dynamics would lead one to expect the flow velocity in the inner channels
to be significantly greater than in the outer channels. That expectation is borne
out in operation. As the viscosity of the retenate increases, fluid velocity in
the outer channels decrease, ultimately dropping to zero, at which point the channel
plugs. The relatively short inner channels in effect "short-circuit" the flow
pattern, and this process continues as the base liquid becomes more concentrated
with repeated recirculation through the system.
The assignee of this patent has attempted to alleviate this problem
by eliminating the central portion of the plate, leaving an ellipsoidal ring, and
by increasing the depth of the outer (longer) channels. That design does ameliorate
the plugging problem, but at the expense of reduced output (from reduced membrane
area) and higher cost (from inefficient production of membrane material -- the
cutout central section cannot be put to other use). Moreover, observation of this
design reveals that the uneven flow rate leads to uncertainty as to which channels
will plug first, as sometimes an inner channel plugs, and at other times an outer
channel will become blocked. The problems with this design stem directly from
the provision of flow channels of uneven length, and appear inherent in such configurations.
An alternative approach is disclosed in US-A-Re. 30,632 (a reissue
of US-A-3,831,763). The basic structure of this device is similar to that discussed
above, but here the plates are rectangular, and joining members are disposed between
adjacent plates to promote sealing and to define the space into which the base
liquid flows between plates. Each plate has two openings, defining inlet and outlet
passages, and intermediate plates, having only one such opening, serve to divide
the stack into subassemblies. A depression is formed into the surface of both sides
of a plate, and packing material is carried therein to permit collection of permeate,
and the membranes are carried atop this material. A variant form of this device,
offered by the assignee of this patent, substitutes raised ridges, formed in the
surface of the depression and extending across same.
Two problems have arisen in the application of this device to fields
requiring operation over wide viscosity ranges. First, the inclusion of joining
members (typically, gaskets) at the outer periphery of each plate limits the pressure
at which the base liquid can be introduced into the inlet passages. Of course,
such a limitation restricts the overall flow rate and the resultant output.
This design also does not prevent deposition of solids from the base
liquid, particularly in high-viscosity applications. As with the previous device,
the problem stems from the basic principles of fluid dynamics. It is well known
that fluid flow within a channel is not uniform but exhibits a velocity profile
from one side of the channel to the other. Velocity is lowest at the sides of
the channel (indeed, it is zero within a boundary layer in contact with the channel
wall). Further, the velocity differential across the channel is related to the
viscosity of the fluid (higher viscosity produces a higher differential) and to
the size of the channel (wider channels result in a more pronounced zone of significantly
lower velocity). These theoretical predictions again are seen to occur in practice.
When employed in an antibiotic application, where the base fluid contains a high
level of suspended solids, flow velocity of the broth at the edges of this device
is not sufficiently high to avoid deposition, restricting the flow to an increasingly
small area toward the center of each plate. Output suffers, both from the reduced
permeate flow and from the increased requirement to clean and change membranes.
A common shortcoming of these devices is the failure to provide uniform
flow across the surface of each plate, at flow rates that offer economically-attractive
permeate recovery. It is to these problems that the present invention is directed.
It is an object of this invention to provide an ultrafiltration apparatus
that permits improved operation over a wide range of base liquid viscosities and
especially an improved membrane support for an ultrafiltration apparatus.
This object is accomplished by means of an apparatus of the type
indicated at the outset and being characterized according to the present invention
in that said base liquid flow path is subdivided into a plurality of sealingly
separated base liquid flow channels which are substantially mutually parallel and
substantially equally dimensioned such that the fluid velocity of the base liquid
is substantially uniform across the membrane, and that the base liquid flow channels
are provided for channelling the flow of the base liquid, such that the base liquid
flows substantially tangentially across the membrane.
It is an advantage of the invention that it provides a membrane support
for an ultrafiltration apparatus that allows for uniform flow across the surface
of the support.
Yet another advantage of the invention is the provision of an ultrafiltration
apparatus that offers improved performance in reducing the turbulence associated
with the transition from one stack subassembly to another such subassembly.
These and other objects are advantages in the present invention.
In a preferred embodiment, an ultrafiltration apparatus includes a plurality of
support panels arranged to form a stack. Each panel is generally flat and rectangular
in shape, with two flat faces identically formed. Raised edges run around the
periphery of one face of each panel to allow base liquid to flow between adjacent
panels in the stack. Two apertures are formed near the periphery of each panel,
preferably on opposite sides thereof. Panels are stacked with these apertures
in alignments to form inlet and outlet ducts. Two types of rings are carried around
the perimeter of each aperture, with rings of the same type disposed on one panel
face. Distribution rings inlcude distribution apertures in the periphery of the
ring to direct fluid flow in selected directions, and sealing rings have flat
upper surfaces. Panels are stacked with the distribution rings of one panel bearing
against the sealing rings of the adjacent panel, effecting a seal within the duct.
A membrane is carried on each face of each panel, overlying the raised edges thereof,
so that the clamping force exerted by such eges of adjacent panels forms a seal
for the stack as a whole.
Longitudinal ribs, running from one aperture to the other and preferably
spaced equidistantly, are formed in both faces of each panel, with longitudinal
channels disposed on either side of each such rib. In the area between such channels
is a plurality of transverse ribs, with transverse channels lying between adjacent
such ribs. To provide optimum retenate flow, the top surface of these transverse
ribs lies below the top surface of the longitudinal ribs, and to provide optimum
permeate flow, the bottom of the transverse channels lies above the bottom of
the longitudinal channels. A connecting channel, preferably at least equal in depth
to the longitudinal channels, extends around the portion of the support member
surface into which the longitudinal and transverse ribs are formed. A permeate
extraction port, preferably located at the top of the support member, communicates
with the connecting channel and permits collection of permeate; this duct is adapted
for connection to fluid communication means, such as plastic tubing, for conveying
the permeate to a collection means. Permeate collects in the transverse channels,
flows to the longitudinal channels and thence to the connecting channel, and exits
through the permeate extraction port.
Support panels are assembled into a stack, with end plates located
on each end of the stack. A compressive force is applied to the stack through the
end plates to retain panels in position and effect the respective seals. In a
preferred form, the stack is subdivided into modules, each module including a number
of panels, by providing turbulence reduction flanges within the stack. These units
receive fluid from the outlet duct of a module and directs that fluid to the opposite
side of the stack for introduction into the inlet duct of a succeeding module.
It having been found that optimum performance occurs when fluid flow across a panel
is directed from bottom to top (with respect to gravity), the inlet duct of each
module is positioned at the bottom of the stack and the outlet duct is positioned
at the top.
Rather than providing means for blocking the flow in each duct and
forcing the fluid to flow in opposite directions in successive subassemblies, as
taught in the art, the present invention employs turbulence reduction flanges
to divide the stack into subassemblies. These components direct fluid flow from
the top of one subassembly to the bottom of the succeeding subassembly, providing
bottom-to-top fluid flow throughout the apparatus. Such flow produces improved
performance by reducing the turbulence in the base liquid, as well as improving
permeate delivery by insuring that the permeate extraction port always is located
at areas of lowest pressure on the panel. Also, this design eliminates uneven
flow due to entrapped air in the system.
The invention is further explained with reference to the accompanying
drawings in which:
- FIGURE 1 is a pictorial showing an embodiment of the membrane support of the
- FIGURE 2 is a detail side view taken along plane II-II of Fig.1;
- FIGURE 3 is a detail cross-sectional side view taken along plane III-III of
- FIGURE 4 is a pictorial showing the area IV of Fig. 2;
- FIGURES 5(a) and (b) are pictorials depicting the distribution ring and sealing
ring of the embodiment shown in Fig. 1;
- FIGURE 6 is a schematic side view of the ultrafiltration apparatus of the invention.
This invention generally includes a plurality of panels, each carrying
two semi-permeable membranes, arranged in a stack. Flow passages exist between
the membranes carried by adjacent panels. The stack is subdivided into a number
of modules, each containing a number of panels. A base liquid is introduced into
the first module, flows in parallel across the panels of that module, and then
flows to succeeding modules, where the parallel flow pattern is repeated. Between
modules, the liquid flows through a turbulence reducing flange that dissipates
turbulence to increase permeate delivery. Understanding of the invention will be
facilitated by first considering the individual panels in detail, and then considering
the apparatus as a whole.
Fig. 1 shows a support panel 10 of the present invention. As seen,
the panel is generally flat and rectangular in form, with two faces 12, 14. Discussion
herein will focus on the face shown, but it should be understood that the two
faces are identical, except as specifically noted. The panel preferably is formed
of a molded plastic material, as will be understood by those in the art. For use
in the antibiotic industry, where freedom from possible contamination is important,
it is preferred to employ a polysulfone plastic, formed into a single-piece plate.
The panel shape is not critical, except as it affects the flow pattern, as discussed
below. In the embodiment shown, the panel dimensions are about 53 cm by about
38 cm (21 inches by about 15 inches). A raised edge 13 runs around the perimeter
of one panel face, this being the only point of dissimilarity between the faces.
Preferably, this edge includes two ridges, each having a rounded upper surface.
The function of these ridges is explained below.
Two apertures 16 are formed in the periphery of the panel, preferably
centered on the panel's long axis. To assure optimum flow in preselected directions,
as discussed below, it is preferred to form these apertures as flattened ovals,
with the flat side oriented toward the center of the panel. The size of the apertures
is chosen consistent with the hydraulic requirements of the overall design.
Two rings, shown in Figs. 5(a) and (b), are carried in each aperture,
one at each face. A distribution ring 18 (Fig.5(a)) includes a series of distribution
ports 26 defined by raised teeth 25 formed in the perimeter of the ring, as will
be discussed in more detail below. A sealing ring 19 (Fig. 5(b)) has a substantially
flat upper surface 24. One ring of each type is carried in each aperture, disposed
at opposite ends thereof, arranged so that rings of the same type are carried on
the same face of a panel. Both types are fabricated from relatively soft material,
such as polypropylene plastic, and the combined thickness of both rings is approximately
equal to the distance between the surfaces of adjacent apertures to provide a sealing
function, as discussed below. Any suitable mounting means can be employed, but
it has been found effective to provide mounting recesses 20 around the perimeter
of the aperture, to be engaged by lugs (not shown) projecting from the ring.
Those in the art will understand that other ring designs could be
used to provide functions identical to the means preferred here. For example, both
rings could have identical teeth, similar to the teeth 25, rather than have one
ring with such teeth. It has been found that the chosen design provides the best
performance, combined with ease of manufacture.
The structure of a panel surface can be seen in the various views
of Figs. 1, 2, 3, and 4. Longitudinal ribs 28 extend between the apertures, pairs
of such ribs defining flow channels 30. These channels are mutually parallel,
of equal dimensions, and the number of such channels is chosen to provide uniform
flow across the face of the panel, as would be appreciated by those skilled in
the art. The embodiment depicted in Fig. 1 has a total of 18 channels and 16 longitudinal
ribs, the outermost channels not having ribs at the outer periphery, that number
of channels having proved effective to achieve such uniform flow. Two longitudinal
channels 32 lie on either side of each longitudinal rib. The top surfaces of the
longitudinal ribs should be relatively flat and slightly below the top surface
of the raised edge 13.
Between the longitudinal ribs and channels is a series of transverse
ribs 34 and channels 36, lying generally at right angles to the longitudinal ribs
and channels. As seen more clearly in Fig. 2, the tops of the transverse ribs
34 are slightly below the tops of the longitudinal ribs 28, and the bottoms of
the transverse channels 36 lies above that of the longitudinal channels 32. The
relative depths of the transverse and longitudinal channels is not critical, but
it has been found that the arrangement shown is effective in obtaining the desired
flow pattern, as will be discussed in more detail below.
Other combinations of ribs and channels could be substituted for
those discussed above. For example, a single longitudinal channel could be located
between each pair of longitudinal ribs. Or, one could dispense with the transverse
ribs and channels by providing a series of intermediate longitudinal ribs between
the longitudinal ribs discussed, these intermediate ribs having tops at a lower
level than those of the primary longitudinal ribs. Alternatively, one could utilize
an internal permeate drainage system, as is known in the art, rather than the
permeate flow system described above. Such systems carry significant disadvantages,
however, such as a tendency to leak (most serious in food and antibiotic applications),
and a limitation on the permeate flow rate. In addition, such plates are more
difficult to manufacture, and hence more costly, than single-piece designs.
A connecting channel 37 encircles the portion of the face into which
the ribs and channels are formed. This channel has a depth preferably at least
equal to that of the longitudinal channels, and it intersects each longitudinal
channel to receive fluid flow from same. Permeate extraction port 39 intersects
the connecting channel at a convenient point, and provides a fluid flow path through
the side of the panel. As shown, this duct projects outward from the side of the
panel, for connection with a means for collecting permeate, such as plastic tubing.
Other collection means would require alternate duct structures, as would be clear
to those in the art.
Mounting lugs 40 project outward from the side of the panel and adapt
the panel for mounting on a suitable carrier, such as a rack. Those in the art
will understand methods for adapting the panel to other mounting arrangements
that might be desireable.
Operation of a single panel is illustrated in Fig. 3. The panel is
prepared for operation by placing a semi-permeable membrane 38 upon the panel face.
Choice of a suitable membrane material depends upon the specific application,
as is well-known to those in the art. Next, rings are inserted into the apertures,
with distribution rings 18 being employed at one panel face and sealing rings
19 on the opposite face. It should be noted that Fig. 3 depicts slight spaces between
the rings, panel and membrane; these gaps are present for clarity, as the components
in fact come into intimate contact.
The membrane and panel cooperate to separate the base fluid into
two fractions. Fluid flows through the distribution ports 26 and into the gap between
the panels, following the path of arrow A, in contact with the membrane surface.
As it does so, permeate penetrates the membrane and is collected and removed.
The distribution ports are disposed in relation to the flow channels 30, and direct
fluid toward those portions of the membrane overlying those channels. Also, the
longitudinal ribs 28 of adjacent panels bear against one another (as discussed
in connection with the overall operation of the apparatus, below), confining retenate
flow within the confines of the base liquid flow channels. Because these channels
are relatively narrow, fluid velocity is relatively uniform across each channel,
and hence across the entire face of the panel. Fluid pressure forces the membrane
against the transverse ribs 34; the tops of the transverse ribs are lower than
those of the longitudinal ribs, and thus the membrane is urged against their respective
top surfaces and the sides of the longitudinal ribs.
Permeate flows through the membrane to collect in transverse channels
36. It should be noted that these channels (and the longitudinal channels 32) are
below the level of the membrane, which is supported by the longitudinal and transverse
ribs. It has been found that provision of such channels, permitting the permeate
to flow between the panel and the bottom surface of the membrane, without making
contact with the membrane, results in a relatively free permeate flow and a higher
permeate flow rate (or flux). From the transverse channels, permeate flows to the
longitudinal channels 32 and thence to the connecting channel 37, which receives
the permeate from all of the longitudinal channels. Permeate extraction port 39,
in fluid communication with the connecting channel, provides an exit point to
conduct the permeate to suitable collection means (not shown).
Turning to a consideration of the device as a whole, the ultrafiltration
apparatus is assembled by stacking panels, with apertures 16 in alignment, as seen
in Fig. 6. The alignment of apertures results in the formation of two ducts within
Panels are arranged with raised edges 13 (which lie only on one face
of each panel) extending in the same direction, and each such edge is brought into
contact with the corresponding flat surface on the opposite face of the adjacent
panel, clamping the outer portions of the membranes to form an outer seal for the
stack. Also, the distribution rings 18 of one panel make contact with the top
surfaces 24 of sealing rings 19 of the adjacent panel, sealing the ducts formed
within the stack. Additionally, longitudinal ribs 28 on both faces of each panel
make contact, further clamping the membranes and sealing the base liquid flow paths
30 from one another. End plates 41 are placed at either end of the stack, as seen
in Fig. 6. These plates should be sufficiently durable to withstand the compressive
force necessary to effect stack sealing, and also should be sized to bear completely
against an entire panel.
The stack may be supported in any suitable manner known to the art.
Preferably, a rack (not shown) is provided, indluding means (not shown) for receiving
mounting lugs 40, or whatever mounting means is chosen. Also, those in the art
will understand that means for applying a compressive force to the stack must be
provided, such as readily-available hydraulic press means.
As is known in the art, it is desirable to subdivide the stack into
modules. For this purpose, turbulence reduction flanges 46 are inserted into the
stack at appropriate intervals. As discussed above, the art teaches the use of
a blocking means to accomplish this purpose, resulting in a flow pattern in which
fluid travels in opposite directions in successive modules. It has been found,
however, that optimum performance is achieved by causing fluid to flow across a
membrane in an upward direction (as used herein, terms such as "top", "bottom",
"up" and "down" are used with respect to the direction of gravity). Therefore,
the stack according to the present invention is arranged with panels oriented
vertically, and with the ducts located at the top and bottom of the stack. The
ducts located at the bottom of the stack are inlet ducts 48 and those at the top
of the stack are outlet ducts 50.
The relatively rough surface of the duct interior (resulting from
stacking panels) inherently produces turbulence, a condition exacerbated by the
abrupt change in flow direction at the end of the duct. Further, turbulence increases
from duct to duct, so that, for example, the fluid within the fourth module of
a stack experiences significantly greater turbulence than the fluid within the
first module. Increased turbulence has been observed to lead to early plugging
of panel channels and to delamination of membrane material, particularly in modules
located toward the end of a stack. Therefore, measures to reduce turbulence would
serve to increase performance. As shown in Fig. 6, the turbulence reduction flange
includes a conduit 42 formed through the divider, which accepts the output from
an outlet duct 50 and conducts fluid to the inlet duct 48 of the succeeding module.
This conduit is shaped to match the profile of the panel apertures, with smooth
sides. In accordance with general principles of fluid dynamics, provision of such
a smooth passageway allows turbulence to dissipate between modules. Preferably,
the turbulence reduction flange is formed as a two-piece unit, with the inner
surfaces molded to produce the conduit. This unit could be joined permanently,
or (as is preferred), one of the units could be provided raised edges similar
to those of the panels, for producing a seal between the unit halves. The choice
of materials for the flange can be made by those in the art; stainless steel or
polysulfone plastic would be most acceptable for food or antibiotic applications.
Operation of the ultrafiltration apparatus proceeds as follows. For
purposes of illustration, Fig. 6 depicts a stack comprising two modules, A and
B, inlcluding three plates 12 in each module. Liquid, which can be, for example,
a fermentation broth employed in the production of antibiotics, is introduced into
the apparatus through an inlet duct 52, located in the leftmost end plate 41 shown
in Fig. 6, by appropriate means (not shown), at a pressure of about 105 N/cm² (150
psi). This liquid flows into inlet duct 48 of module A, and thence through the
distribution ports 26 as discussed above, being directed thereby into the gap
44 between adjacent panels 12, as shown by arrows a. Of course, such flow occurs
on each panel in the module, in parallel. The flow pattern occurring on individual
panels was discussed above.
Fluid then collects in module A outlet duct 50a and flows through
the turbulence reduction flange conduit 42 to the inlet duct 48b of module B, noted
by arrows c. The parallel flow pattern is repeated, with fluid proceeding in the
gaps between panels, following the paths of arrows d. Outlet duct 50b receives
this flow, which exits the apparatus through duct 54 in the rightmost end plate
of Fig. 6, shown by arrows e.
It is important to note that the flow pattern of the present apparatus
differs substantially from prior art apparatus in that flow occurs in the same
direction, from bottom to top, in each module. In this configuration, the permeate
extraction port is always located at the low pressure (outlet) end of the panel,
promoting improved flow of permeate from the system. In the prior art devices
discussed above, of course, half of such ports are located at low pressure areas
and half at high pressure areas. Not only does the present invention provide increased
flow, but also this arrangement eliminates "dead zones" that occur due to air
entrapped on the permeate side of the membrane.
Also, it should be noted that one could divide the stack into panels
oft two types - one having longitudinal ribs twice the height of those disclosed
herein, and the other having a permeate drainage system, such as the transverse
ribs, transverse channels, and longitudinal channels disclosed herein. Although
such means would be within the scope of the present invention, it is prefereable
to employ a single type of plate.
It should also be understood that the apparatus shown in Fig. 6 is
configured for illustrative purposes only. Those in the art will understand the
requirement for more or fewer modules, or for differing numbers of panels within
a module, based upon the application and its requirements.
Operational testing of an ultrafiltration apparatus constructed according
to the present invention confirms that the advantages outlined herein do in fact
occur in practice. A device according to the invention was compared to a unit
constructed alongs the lines of U.S. Patent No. 3,872,015, to Madsen, as discussed
above. Equipment of this type is manufactured by De Danske Sukkerfabriker, a Danish
corporation. The base liquid employed was penicillin broth, and two comparative
outputs were recorded: flux, in gallons of permeate per square foot of membrane
material per day (GFD), and the maximum concentration ratio of the retenate (the
ratio of intial base liquid volume to the volume of fluid remaining after processing).
The two apparatus contained an identical number of plates, with the following
Maximum Concentration Ratio
Clearly, this invention offers substantial benefits over the prior
The apparatus shown in Fig. 6 is configured for illustrative purposes
only. Those in the art will understand the requirement for more or fewer modules,
and for differing numbers of panels in each module, and they will be able to match
such requirements to specific applications.