U.S. patent application number 10/080302 was filed with the patent office on 2003-08-21 for multi-path split cell spacer and electrodialysis stack design.
This patent application is currently assigned to EET Corporation. Invention is credited to Sferrazza, Alois.
Application Number | 20030155243 10/080302 |
Document ID | / |
Family ID | 27733190 |
Filed Date | 2003-08-21 |
United States Patent
Application |
20030155243 |
Kind Code |
A1 |
Sferrazza, Alois |
August 21, 2003 |
Multi-path split cell spacer and electrodialysis stack design
Abstract
An electrodialysis method and apparatus include a source of
concentrate fluid, a source of dilute fluid, a collector of treated
concentrate fluid, a collector of dilute fluid, an anode and a
cathode. A plurality of generally planar spacers are interleaved
with a plurality of membranes to define a plurality of cells
providing electrically conductive fluid connection between the
anode and the cathode. Each of the spacers comprises a gasket that
defines a first aperture and a second aperture. Each of said first
and second apertures define an independent cell between interleaved
membranes. The symmetrical, multiple split cell spacer
configuration channels fluid flow through two or more narrow and
elongated paths. The split cell arrangement allows for operation of
the stack in parallel or in series. The invention improves the ion
removal efficiency of a given membrane area, requires significantly
less energy than other electrodialysis systems and substantially
reduces stack assembly, materials and fabrication costs.
Inventors: |
Sferrazza, Alois;
(Knoxville, TN) |
Correspondence
Address: |
PITTS AND BRITTIAN P C
P O BOX 51295
KNOXVILLE
TN
37950-1295
US
|
Assignee: |
EET Corporation
830 Corridor Park Boulevard, Suite 400
Knoxville
TN
37932
|
Family ID: |
27733190 |
Appl. No.: |
10/080302 |
Filed: |
February 21, 2002 |
Current U.S.
Class: |
204/520 ;
204/523; 204/635; 204/636; 204/638 |
Current CPC
Class: |
B01D 63/084 20130101;
C02F 1/4693 20130101; Y02A 20/134 20180101; B01D 61/50 20130101;
B01D 2313/14 20130101; B01D 2313/345 20130101; Y02A 20/131
20180101; Y02A 20/124 20180101 |
Class at
Publication: |
204/520 ;
204/523; 204/635; 204/636; 204/638 |
International
Class: |
B01D 061/46; B01D
061/50 |
Claims
Having thus described the aforementioned invention, we claim:
1. In an electrodialysis system comprising a source of concentrate
fluid, a source of dilute fluid, a collector of treated concentrate
fluid; a collector of used dilute fluid, an anode, a cathode, a
plurality of generally planar spacers, a plurality of membranes
interleaved with said spacers to define a plurality of cells
providing electrically conductive fluid connection between said
anode and said cathode, each of said spacers comprising: a gasket
defining a first aperture and a second aperture, each of said first
and second apertures defining an independent cell between
interleaved membranes.
2. The apparatus of claim 1 wherein said apertures have the shape
of an abbreviated rectangle having squares removed from two
diagonally opposed corners.
3. The apparatus of claim 2 wherein all corners of said apertures
are rounded.
4. The apparatus of claim 1 wherein a conduit provides flow
communication between said first aperture and said second
aperture.
5. The apparatus of claim 1 wherein one or more bolts extend
through said spacers between said first aperture and said second
aperture.
6. The apparatus of claim 5 wherein said bolts are coated with an
electrically resistant material.
7. A method of electrodialysis treatment comprising providing a
source of concentrate fluid, providing a source of dilute fluid,
providing a collector of treated concentrate fluid; providing a
collector of used dilute fluid, providing an anode, providing a
cathode, securing a plurality of generally planar spacers and a
plurality of membranes interleaved with said spacers to define a
plurality of cells, providing electrically conductive fluid
connection between said anode and said cathode, wherein each of
said spacers comprises a gasket defining a first aperture and a
second aperture, each of said first and second apertures defining
an independent cell between two common interleaved membranes.
8. A method in accordance with claim 6 wherein said apertures have
the shape of an abbreviated rectangle having squares removed from
two diagonally opposed corners.
9. The method of claim 8 wherein all corners of said apertures are
rounded.
10. The method of claim 8 and further comprising the step of
providing flow communication from said first aperture to said
second aperture.
11. An electrodialysis system comprising a source of concentrate
fluid, a source of dilute fluid, a collector of treated concentrate
fluid; a collector of used dilute fluid, an anode, a cathode, a
plurality of generally planar spacers, a plurality of membranes
interleaved with said spacers to define a plurality of cells
providing electrically conductive fluid connection between said
anode and said cathode, each of said spacers comprising: a gasket
defining an aperture defining an independent cell between
interleaved membranes, said aperture having the shape of an
abbreviated rectangle having squares removed from two diagonally
opposed corners.
12. The apparatus of claim 11 wherein all corners of said apertures
are rounded.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable
BACKGROUND OF THE INVENTION
[0003] 1. Field of Invention
[0004] This invention pertains to a method and apparatus for the
purification and reuse or disposal of polluted liquids.
[0005] More particularly, this invention pertains to an
electrodialysis stack for the removal and concentration of ions
from aqueous solutions and certain aqueous/organic solutions.
[0006] 2. Description of the Related Art
[0007] There are presently a number of systems for treating and
recycling aqueous and aqueous/organic waste streams on the market.
Present state of the art systems, including de-ionization methods
that are available to industrial waste stream generators, are
deficient in their ability to consistently and economically produce
a cleansed fluid of sufficient quality that can be continuously
recycled and reused, especially in the case of small to medium
volume liquid waste generation. The initial high cost of purchasing
many of these systems is beyond the economic resources of many
businesses, thus prohibiting cost-effective recycling for
environmental compliance or beneficial reuse.
[0008] Multi-cell electrodialysis stacks are normally built up of
membrane sheets separated from each other by suitable gaskets. For
efficient separations, the distance (gap) between the sheets is as
small as possible. In most designs, a spacer is introduced between
the individual membrane sheets, both to assist in supporting the
membrane and to help control the liquid flow distribution. The
stacks for most electrodialysis processes are assembled in the same
fashion as a plate-and-frame filter press, the gaskets
corresponding to the frames and the membrane sheets corresponding
to the plates. The manifolds that are needed to distribute the
process fluids to the various compartments or channels are formed
by ingenious patterns of mating holes and slots punched in the
gaskets and sometimes in the membranes themselves, prior to
assembly of the stack. Several different gasket and spacer
materials and arrangements and channel geometries have been
utilized or proposed.
[0009] In typical electrodialysis systems, the flow pattern within
each compartment (i.e., between any two successive membranes) is
determined by the configuration of the spacer element used between
the membranes. Two distinctively different flow arrangements are
typically used. One is known as the tortuous-path design; the other
makes use of the sheet-flow principle. The most serious design
problem for both flow arrangements for multi-membrane and
multi-cell stacks is that of assuring uniform fluid flow to the
various compartments and effective transport of the ions to the
membrane surfaces. These difficulties are the major obstacles to
simple, single stage demineralization of brackish liquids.
[0010] In particular, reducing concentration polarization is one of
the most important design issues for electrodialysis. Concentration
polarization is the reduction of ion concentrations near the
membrane surface compared to those in the bulk solution flowing
through the membrane compartment. With substantial concentration
polarization, electrolytic water splitting in order to provide the
requisite electric current carriers through the membranes occurs
due to the deficiency of solute ions adjacent to the membranes that
can carry the current. This water splitting is extremely
detrimental to electrodialysis efficiency. The tendency of
concentration polarization to take place at the surface of the
membranes is due to the hydrodynamic characteristic of channel
flow, in which there is a central turbulent core of flow bounded by
thin viscous boundary layers adjacent to the confining surfaces.
These viscous boundary layers impose a resistance to the passage of
ions much greater than that of a layer of like thickness in the
turbulent core, and hence increase the likelihood of polarization
at the membrane surfaces. Polarization is objectionable not only
from the standpoint of the inefficient increase in energy
consumption, but also the change of pH of the concentrate stream as
a result of water splitting, which tends to cause scale
deposition.
[0011] When dealing with fluids with very low total dissolved
solids (TDS), back diffusion can take place. Back diffusion occurs
when the ion concentration in the concentrate stream is
substantially higher than the ion concentration in the
de-mineralized stream. The result is that some of the ions from the
concentrate stream diffuse back through the membrane, against the
force of the DC potential, into the de-mineralized stream.
[0012] The number of cells in a stack is limited mainly by the
practical considerations of assembly and maintenance requirements.
Since the failure of a single membrane can seriously impair stack
performance, the necessity to be able to disassemble and reassemble
a stack to replace a membrane, and the necessity to be able to
perform this quickly and easily, effectively limits the number of
membranes that can be practically utilized in a stack. As a result,
it is often desirable to use several smaller modular-size stacks
rather than one large one. This problem has been attacked by using
several small subassemblies or packs containing about 50 to 100
cell pairs (CP), and arranging as many as 10 of these packs in
series in a single clamping press. A single set of electrodes may
be used for the entire assembly (stack) or several electrodes may
be used to provide electric staging. However, use of single
electrodes for larger assemblies typically causes end-cell heating
that results in rapid membrane deterioration.
[0013] The present invention serves to expand the possible
applications of electrodialysis in that it represents an efficient,
small scale electrodialysis system with a configuration allowing
cost-effective small-scale applications, while making the large
scale applications even more cost-competitive than they currently
are.
[0014] In accordance with the present invention, a unique gasket
design reduces hydraulic pressure drop across the cell stack
assembly by eliminating narrow inlet/outlet manifold cutouts
inherent with conventional designs. The reduction of hydraulic
pressure permits the use of higher flow rates that further reduce
concentration polarization, as well as thinner membranes, resulting
in improved desalting efficiency, especially for sparingly
conductive solutions, and also less sensitivity to the presence of
suspended matter.
[0015] The novel multiple split cell design can be operated in
parallel as a roughing de-mineralizer (or operated in a batch
recirculation mode) or operated in series allowing for single-pass
continuous flow. When operated in the series mode, the split cell
design permits separate voltage and flow control when a higher
purity fluid is desired. The split cell design permits separate
cell control of concentrate stream salinity content. The roughing
cell may be operated with a higher concentrate stream TDS, with the
salinity of the polish cell concentrate stream correspondingly
reduced to the salinity content of the de-mineralized stream. This
prevents back diffusion and allows for efficient removal of ions in
feed water of low TDS. In short, the split cell design incorporates
the benefits of hydraulic and electrical staging without the
inherent complexity and expense of commercial electrodialysis
systems.
[0016] The split cell design minimizes the voltage potential across
the stack, thereby reducing end-cell heating that leads to membrane
deterioration.
[0017] It is an object of the present invention to provide a
simpler stack assembly of low production cost. Stack assembly cost
is reduced as a result of the novel split cell/gasket geometry. A
reduced number of expensive machined components are required.
Simpler and lighter components lower material costs for a given
membrane area. Inexpensive center bolts provide an alternative to
typical hydraulic force application arrangements, which also
improves the uniformity of the clamping force distribution on the
gasket area. Threaded bolts also reduce assembly labor time, i.e.,
it is easier to hold the configuration in place and also facilitate
change-out of membranes when they are spent, as the cell geometry
reduces stress on the end points as is found inherent with some
conventional stack assemblies.
[0018] It is another object of the present invention to provide an
apparatus and method that allows for the cost-effective arrangement
of two or more split membrane cells that enables the ingenious
arrangements of plumbing for optimizing deionization
processing.
[0019] The cell gasket geometry can be more easily and
inexpensively fabricated from a larger range of materials in
comparison to conventional designs, allowing the process to be used
in more harsh environments through the use of a wide range of
chemically resistant materials. It is still another object of the
present invention to provide an apparatus and method that combines
a unique arrangement of small to intermediate scale unit operations
for the economical recovery/reclamation of a wide range of fluids
and that can also be scaled to a large system size, further
improving the economics of large scale electrodialysis systems by
reducing both capital and operating costs.
BRIEF SUMMARY OF THE INVENTION
[0020] According to one embodiment of the present invention, a
dialysis stack is provided in which each generally planar gasket
defines a first cell and a second cell. A membrane is located
adjacent to each side of each gasket. A turbulence spacer is
located within each cell. Each cell is provided with an inlet and
an outlet to provide fluid access into and out of each cell. Fluid
flows sequentially through the two cells defined in each gasket.
Preferably, the fluid flows through a plurality of first cells
defined by a plurality of spacers and then flows through a
plurality of second cells defined in the plurality of spacers.
Separate anodes and cathodes provide electrical energy to the two
parallel sets of first cells and second cells. Separate rectifiers
can be used to apply specific electric potential across the first
set of cells and second cells when operated in series, or a single
rectifier can power both the first and second cell sets when
operated in parallel. A system of bolts extending through parallel
compression plates are used to secure the plurality of spacers and
interleaved membranes in register to define conduits extending
between the plurality of cells.
[0021] The electrodialysis stack is included in an electrodialysis
system. The system includes a mixing tank for the solution being
processed. Mixed solution is passed through filters for removing
particulate matter and potential precipitants. The filtered
solution is collected in a dilute tank. Concentrated fluid is
collected in a concentrate tank. Electrolyte is provided from an
electrolyte tank to an anode chamber and to a cathode chamber. The
anode chamber and the cathode chamber have an electrically
conductive fluid connection through the cell stack. The membranes
alternate between anion exchange membranes and cation exchange
membranes. The cells alternate between concentrate stream cells and
dilution stream cells.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0022] The above-mentioned features of the invention will become
more clearly understood from the following detailed description of
the invention read together with the drawings in which:
[0023] FIG. 1 is a laterally exploded view of a cell stack
embodying various of the features of the present invention;
[0024] FIG. 2 is a plan view of a cell stack embodying various
features of the present invention;
[0025] FIG. 3 is a side elevation view of a cell stack embodying
various features of the present invention;
[0026] FIG. 4 is an end elevation view of a cell stack embodying
various features of the present invention;
[0027] FIG. 5 is an elevation view of an electrodialysis system
embodying various features of the present invention;
[0028] FIG. 6 is a flow diagram of an electrodialysis system
embodying various features of the present invention;
[0029] FIG. 7a is a schematic diagram of split cell spacer having
two cells arranged in series;
[0030] FIG. 7b is a schematic diagram of split cell spacer having
two cells arranged in parallel;
[0031] FIG. 7c is a schematic diagram of split cell spacer having
three cells arranged in series;
[0032] FIG. 7d is a schematic diagram of split cell spacer having
three cells arranged in parallel;
[0033] FIG. 7e is a schematic diagram of split cell spacer having
four cells with two parallel cells arranged in series with two
parallel cells;
[0034] FIG. 7f is a schematic diagram of split cell spacer having
four cells arranged in series; and
[0035] FIG. 7g is a schematic diagram of split cell spacer having
four cells with three cells arranged in parallel arranged in series
with a single polish cell.
DETAILED DESCRIPTION OF THE INVENTION
[0036] Referring to the drawings, wherein similar reference numbers
denote similar elements throughout the several drawings, there are
disclosed a method and an apparatus for electrodialysis treatment
of a fluid in which a salt is dissolved. One example of such a
fluid is used antifreeze, which can be cleaned and recycled in
accordance with the present invention.
[0037] In FIG. 1 there is illustrated one embodiment of an
electrodialysis cell stack 10, exploded laterally. At one end is an
electrode stream spacer 12 defining two rectangular apertures 14
and 14'. In the depicted embodiment the electrode stream spacer is
approximately 14 inches by 24 inches, though it will be recognized
that various sizes may be used. Also defined in the electrode
stream spacer 12 are eight conduit apertures 16a, 16b, 16c, 16d,
16e, 16f, 16g and 16h.
[0038] Adjacent to the electrode stream spacer 12 is an anion
exchange membrane 18, many of which are well known in the art. One
commercially available material is Neosepta AFN produced by
Tokuyama Corporation. The anion exchange membrane 18 is shaped and
sized substantially identically to the electrode stream spacer 12
and includes conduit apertures 19a-h in register with the conduit
apertures 16a-h defined in the electrode stream spacer 12.
[0039] Adjacent to the anion exchange membrane 18 is a concentrate
split cell spacer 20 defining two apertures 22 and 22'. Each of the
apertures 22 and 22' has the shape of an abbreviated rectangle in
which two squares have been removed from diagonally opposed corners
and all corners have been rounded. Conduit apertures 24a, 24c, 24e
and 24h are defined in the concentrate split cell spacer. The
concentrate split cell spacer 20 is shaped and sized substantially
identical to the electrode stream spacer 12. The aperture 22 is in
register with the rectangular aperture 14 and the aperture 22' is
in register with the rectangular aperture 14'.
[0040] A concentrate turbulence spacer 28 is located within the
aperture 22 and a concentrate turbulence spacer 28' is located
within the aperture 22'. Each of the concentrate turbulence spacers
28 and 28' are formed from a mesh to maintain turbulence within the
apertures 22 and 22' as concentrate fluid passes through the
apertures 22 and 22'.
[0041] Adjacent to the concentrate turbulence spacer 28 is a cation
exchange membrane 29, many of which are well known in the art. One
commercially available material is Neosepta CMX produced by
Tokuyama Corporation. The cation exchange membrane 29 is shaped and
sized substantially identical to the electrode stream spacer 12 and
includes conduit apertures 30a-h in register with the conduit
apertures 16a-h defined in the electrode stream spacer 12.
[0042] Adjacent to the cation exchange membrane 29 is a dilution
stream split cell spacer 32 defining two apertures 34 and 34'. Each
of the apertures 34 and 34' has the shape of an abbreviated
rectangle in which two squares have been removed from diagonally
opposed corners and all corners have been rounded. The apertures 22
and 22' are mirror images of the apertures 34 and 34'. Conduit
apertures 36b, 36d, 36e and 36g are defined in the dilution stream
split cell spacer 32. The dilution stream split cell spacer 32 is
shaped and sized substantially identically to the electrode stream
spacer 12. The aperture 34 is in register with the rectangular
aperture 14 and the aperture 34' is in register with the
rectangular aperture 14' to provide electrically conductive fluid
connection to the apertures 14 and 14', respectively.
[0043] A dilution stream turbulence spacer 38 is located within the
aperture 34 and a concentrate turbulence spacer 38' is located
within the aperture 34'. Each of the concentrate turbulence spacers
38 and 38' is formed from a mesh to maintain constant turbulence
within the apertures 34 and 34' as dilution fluid passes through
the apertures 34 and 34'.
[0044] Adjacent to the dilution stream turbulence spacer 38 is an
anion exchange membrane 40, which is identical to anion exchange
membrane 18. The anion exchange membrane 40 defines conduit
apertures 42a-h in register with the conduit apertures 16a-h
defined in the electrode stream spacer 12.
[0045] Adjacent to the anion exchange membrane 40 is a concentrate
split cell spacer 44 defining two apertures 46 and 46'. The
concentrate split cell spacer is identical to the concentrate split
cell spacer 20 and defines conduit apertures 48a, 48c, 48f and 48h.
The aperture 46 is in register with the rectangular aperture 14 and
the aperture 46' is in register with the rectangular aperture 14'
to provide electrically conductive fluid connection to the
apertures 14 and 14', respectively
[0046] A concentrate turbulence spacer 50 is located within the
aperture 46 and a concentrate turbulence spacer 50' is located
within the aperture 46'. Each of the concentrate turbulence spacers
50 and 50' is formed from a mesh to maintain constant turbulence
within the apertures 46 and 46' as concentrate fluid passes through
the apertures 46 and 46'.
[0047] Adjacent to the concentrate turbulence spacer 50 is a cation
exchange membrane 52, many of which are well known in the art. The
cation exchange membrane 52 is shaped and sized substantially
identically to the electrode stream spacer 12 and includes conduit
apertures 54a-h in register with the conduit apertures 16a-h
defined in the electrode stream spacer 12.
[0048] Adjacent to the cation exchange membrane 52 is an electrode
stream spacer 56 defining two rectangular apertures 58 and 58'. The
electrode stream spacer 56 is substantially identical to the
electrode stream spacer 12. Also defined in the electrode stream
spacer 56 are eight conduit apertures 60a-h, which are in register
with the conduit apertures 16a-h respectively.
[0049] A first end section 62b of the aperture 22 overlays the
conduit apertures 19b and 30b to cooperatively define a concentrate
outlet port for the aperture 22. A diagonally opposed second end
section 62e overlays conduit apertures 19e and 30e to cooperatively
define a concentrate inlet for the aperture 22. A first end section
62d of the aperture 22' overlays the conduit apertures 19d and 30d
to cooperatively define an outlet port for the aperture 22'. A
diagonally opposed second end section 62g of the aperture 22'
overlays the conduit apertures 19g and 30g to cooperatively define
an inlet port for the aperture 22'.
[0050] A first end section 64a of the aperture 34 overlays the
conduit apertures 30a and 42a to cooperatively define a dilution
outlet port for the aperture 34. A diagonally opposed second end
section 64f overlays conduit apertures 30f and 42f to cooperatively
define a dilution inlet for the aperture 34. A first end section
64c of the aperture 34' overlays the conduit apertures 30c and 42c
to cooperatively define an outlet port for the aperture 34'. A
diagonally opposed second end section 64h of the aperture 34'
overlays the conduit apertures 30h and 42h to cooperatively define
an inlet port for the aperture 34'.
[0051] A first end section 66b of the aperture 46 overlays the
conduit apertures 42b and 54b to cooperatively define a concentrate
outlet port for the aperture 46. A diagonally opposed second end
section 66e overlays conduit apertures 54e and 42e to cooperatively
define a concentrate inlet for the aperture 46. A first end section
66d of the aperture 46' overlays the conduit apertures 42d and 54d
to cooperatively define an outlet port for the aperture 46'. A
diagonally opposed second end section 66g of the aperture 46'
overlays the conduit apertures 42g and 54g to cooperatively define
an inlet port for the aperture 46'.
[0052] In FIGS. 2 and 3 the cell stack 10 is depicted as it is
mounted with threaded bolts 68 between an opposed pair of
electrolyte flow distribution endplates 70a and 70b. Preferably,
the bolts 68 are coated with a plastic or other high electrically
resistant material. The threaded bolts 68 are arranged around the
periphery of the end plates 70a and 70b and also extend through the
space between the split cells as shown in FIG. 4. As depicted in
FIG. 5, a cathode 72 extends through the endplate 70a and an anode
74 extends through the endplate 70b. A rectifier 75 applies a
potential between the cathode 72 and the anode 74. An electrolyte
solution supplied to the endplates 70a and 70b, a concentrate
stream sequentially supplied to the apertures 22, 22', 46' and 46
and a dilution stream sequentially supplied to the apertures 34 and
34' provide electrically conductive fluid connection between the
cathode 72 and the anode 74.
[0053] The split-cell spacers comprise EPDM (ethylene propylene
diene terpolymer) sold under the name Nordel by E. I. Du Pont de
Nemours and Company. When assemble and secured with threaded bolts
68 no glue or other adhesive is required between the membranes and
the spacers.
[0054] Referring now to FIG. 6, there is depicted a flow diagram of
an electrodialysis system adapted for using the cell stack
described hereinabove. The system is portable and may be easily
moved to locations where fluids require cleaning. For example, used
antifreeze is stored in a mixing tank 76, where it is mixed with a
metal reducing agent to precipitate metals in the fluid. The mixing
tank 76 is in flow communication with a desalinated tank 78 through
a filter pump 80, a 1 micron filter 82, a carbon adsorber 84 and a
second 1 micron filter 86.
[0055] The desalinated tank 78 is in flow communication by
conduits, through a pump 88 to the conduit apertures 60f, 54f, 48f
and 42f (in series) to enter the inlet of aperture 34. The outlet
of the aperture 34 is connected in flow communication with the
inlet of the aperture 34' by a conduit 91. The outlet of the
aperture 34' is in flow communication with the desalinated tank by
conduit apertures 30c, 24c, 19c and 16c.
[0056] An electrolyte is stored in an electrolyte rinse tank 90,
which is connected through conduits to the inlets 92a and 92b of
the end plates 70a and 70b, respectively. The outlets 94a and 94b
from the endplates 70a and 70b, respectively, are connected back to
the electrolyte rinse tank 90. A pump 96 circulates the
electrolyte.
[0057] A pump 100 sends concentrated brine from a concentrate brine
tank 98 through the conduit apertures 60e and 54e to enter the
inlet of aperture 46. From the outlet of the aperture 46 the brine
is directed through the conduit apertures 42b, 36b and 30b to the
inlet of the aperture 22. From the outlet of the aperture 22 the
brine is directed through the conduit apertures 19e and 16e, a
conduit 102, and conduit apertures 60g and 54g to the inlet of
aperture 46'. From the outlet of the aperture 46' the brine is
directed through the conduit apertures 42d, 36d and 30d to the
outlet of the aperture 22'. From the outlet of the aperture 22' the
brine is directed back to the concentrated brine tank 98 via the
conduit apertures 19g and 16g. The concentrated brine tank 98 is in
flow communication with a concentrate neutralization tank 104.
[0058] In operation, electrolyte is circulated between the
electrolyte rinse tank 90 and the end plates 70a and 70b. The pH of
the electrolyte is monitored for maintenance in a generally
constant range. As required, neutralization acid may be added from
the tank 104.
[0059] Concentrated brine is circulated from the tank 98,
sequentially through the apertures 46, 22, 46' and 22' and then
back to the tank 98. The concentration of the brine is monitored
for maintenance in a generally constant range. As required, water
may be added to the tank 98. A "feed and bleed" mode of operation
is provided for make-up water. The pH is also monitored and
controlled.
[0060] The fluid to be cleaned, such as used antifreeze, is entered
into the mixing tank 76 where a stirrer 106 maintains agitation of
the fluid with a metal reducing agent. The fluid is then pumped
through the filter 82, the carbon adsorber 84 and the filter 86 to
the desalinated tank 78. The fluid is circulated from the
desalinated tank 78, sequentially through the apertures 34 and 34',
and then back to the desalinated tank. As is well recognized in the
field of electrodialysis, the potential applied between the cathode
72 and anode 74 induce the ions of salts in the fluid to pass
through the membranes into the brine solution passing through the
adjacent aperture, thus increasing the concentration of salts in
the brine solution and reducing the concentration of salts in the
treated fluid. By cycling the fluid repeatedly through the
apparatus, the concentration of salts can be reduced to the desired
minimal level. A conductivity sensor 108 monitors the fluid as it
leaves the pump 88 to determine when a satisfactory level has been
reached. A control panel 110 provides visual readouts and controls
for operating the system.
1 Conventional Multi- Multi-path Split Cell Parameter Compartment
Stack (Operated in parallel) Glycol content % w. 40.0 40.0 Glycol
Retention % 91.8 99.9 Starting conductivity 3,800 3,800
(.mu.Mho/cm) Finish Conductivity (.mu.Mho/ 1,000 1,000 cm) Cell
pair Volage (V) 1.0 1.0 Membrane type Conventional Conventional
Solution temperature (.degree. F.) 76 76 Production Rate 0.44 2.0
(m.sup.3/day/m.sup.2 of membrane) Gasket Material EPDM EPDM
[0061] (The anion exchange membrane used was Neosepta AFN produced
by Tokuyama Corporation. The cation exchange membrane used was
Neosepta CMX produced by Tokuyama Corporation.)
[0062] The multi-path split cell system was substantially less
costly to produce than the conventional multi-compartment stack,
yet operated at a production rate over four times greater.
[0063] Studies indicate that the configuration of the invention is
a substantial improvement over traditional designs. Example 2 shows
the production rate and typical % removal of NaCl for the current
invention; those skilled in the art will recognize these values
allow the invention to be economically competitive for a variety of
feeds. Example 3 shows typical membrane area and energy
requirements for desalination using traditional ED stack designs
contrasted with the performance of the current invention. Those
skilled in the art will recognize that the improved design of the
current invention results in a stack requiring significantly less
membrane area and that is significantly more energy efficient.
2 1. NaCl Feed Production Rate % NaCl Concentration
(m.sup.3/m.sup.2 day) Removal 1.65 g/L 5.74 91 16.5 g/L 1.50 99
[0064]
3 NaCl Feed Traditional % Concentration Designs** Split cell
Reduction A. Membrane Area (m.sup.2) for 1 m.sup.3/day Capacity* 1
g/L 0.3 0.17 42% 10 g/L 1.2 0.67 44% B. Energy Requirements
(kw-hr/m.sup.3 product)* 1 g/L 1.2 0.26 78% 10 g/L 3.4 2.67 21%
*For a product concentration of 500 ppm TDS. **Source: Strathmann,
H., "Design and Cost Estimates", in Membrane Handbook, pp. 246-254,
W.S.W. Ho and K.K Sikar, eds., Van Nostrand Reinhold, New York
(1992).
[0065] An important variable describing an ED system is the current
utilization efficiency. The current utilization efficiency is
primarily influenced by the ED stack design and flow velocities but
also to a lesser extent by the concentration and composition of the
feed stream. For a given ED stack (gasket design, spacer design,
etc.) and feed stream, the current efficiency is [1,2,3,4,5]: 1 =
zFQ f ( C inlet d - C outlet d ) NI .times. 100 % ( 1 )
[0066] where
[0067] .xi.=current utilization efficiency, %
[0068] z=charge of ion
[0069] F=Faraday's constant, 96,485 Amp-s/mol
[0070] Q.sub.f=diluate flow rate, L/s
[0071] C.sup.d.sub.inlet=diluate ED cell inlet ion concentration,
mol/L
[0072] C.sup.d.sub.outlet=diluate ED cell outlet ion concentration,
mol/L
[0073] N=number of cell pairs
[0074] I=applied current, Amps.
[0075] Those skilled in the art will recognize that current
utilization efficiencies should be >70% for efficient use of ED
for desalting typical brackish water feeds, and that current
utilization decreases as the product water concentration decreases.
Chart 1 shows that the invention provides excellent current
utilization efficiencies (>90%) over a wide range of product
water concentrations. The figure also shows that good current
utilizations are achieved even when producing high quality product
(<5 mg/L Cl.sup.-). Also, studies indicate that the invention is
capable of producing a product with extremely low conductivity
levels (down to as low as 2.6 .mu.Mho/cm). Those skilled in the art
will recognize that this represents a substantial improvement
compared to traditional ED designs, which are typically limited to
product with conductivities >30 .mu.Mho/cm. As a result, the
invention would represent a new pretreatment option for production
of ultrapure water.
[0076] While the depicted embodiment has been described in terms of
three split cell spacers and four membranes, it will be recognized
that additional split cell spacers and membranes are desirable to
speed the process. Such additional apparatus would function in
substantially the same manner.
[0077] As depicted schematically in FIGS. 7a to 7g, the split cells
may be arranged with more than two cells and the cells may be
arranged in a variety of parallel, serial and parallel/serial
arrangements. FIG. 7a depicts the arrangement described herein
above. FIG. 7b depicts an arrangement wherein the two split cells
are arranged in parallel. FIG. 7c depicts a split cell having three
apertures that are arranged serially. FIG. 7d depicts a split cell
having three apertures that are arranged in parallel. FIG. 7e
depicts a split cell having four apertures that are arranged with
two parallel cells arranged serially with another set of parallel
cells. FIG. 7f depicts a split cell having four apertures that are
arranged serially. FIG. 7g depicts a split cell having four
apertures with three cells arranged in parallel and all three
serially feeding the fourth cell. It will be recognized by those
skilled in the art that the multiple cells may be arranged in a
variety of ways to accommodate many different electrodialysis
situations.
[0078] Benefits of the process include a recovery rate in excess of
95%, high throughput and low capital and operating cost. The system
does not generate hazardous by-products. It is easy to operate,
control and automate, and easy to maintain. Also, studies indicate
that the invention is capable of producing a product with extremely
low conductivity levels (down to as low as 2.6 .mu.Mho/cm). Those
skilled in the art will recognize that this represents a
substantial improvement compared to traditional ED designs, which
are typically limited to product with conductivities >30
.mu.Mho/cm. As a result, the invention would represent a new
pretreatment option for production of ultrapure water.
[0079] The multi-path split-cell spacer design permits use of a
single or multiple central bolts, eliminating the need for an
expensive hydraulic clamping assembly for applying central pressure
on the stack and providing a uniform force distribution over the
gasket area, improving the seals between membranes and improving
ion removal efficiency, while also reducing assembly labor time.
Expensive machined components are replaced with simpler, lighter
components having lower material costs, for a given membrane area
assemblies.
[0080] In addition to the described use of the method and apparatus
to clean used antifreeze, the system may be used to clean and/or
recycle: wash water (vehicular, laundry, mop water, trailer/tank
washout, textile rinses, metal, aqueous parts cleaners), oil and
gas field fluids (glycol base natural gas dehydration fluids,
glycol/water heat transfer fluids, amines from treatment of natural
gas, produced water), other thermal transfer fluids (secondary
coolants from HVAC systems and coolants from ice-skating rinks),
cooling water reuse, nuclear wastewater, mixed (nuclear and
hazardous) wastewater, hazardous wastewater, desalination of sea or
brackish water, drinking water production and pretreatment for
ultra-pure water production.
[0081] While the present invention has been illustrated by
description and while the illustrative embodiments have been
described in considerable detail, it is not the intention of the
applicant to restrict or in any way limit the scope of the appended
claims to such detail. Additional advantages and modifications will
readily appear to those skilled in the art. The invention in its
broader aspects is therefore not limited to the specific details,
representative apparatus and methods, and illustrative examples
shown and described. Accordingly, departures may be made from such
details without departing from the spirit or scope of applicant's
general inventive concept.
* * * * *