Water softener abstract
System and method for purifying and recycling spent brine in a
water softener are provided. The system may be made up of a cation
exchange resin tank fluidly coupled for passing spent brine comprising
monovalent and divalent ions. A fluid mixer valve is coupled to
the resin tank and to a water tank to dilute the spent brine to
a desired concentration of a regenerant salt, e.g., NaCl. An ion-separation
device is fluidly coupled to the fluid mixer valve to receive the
diluted spent brine and separate the diluted spent brine into first
and second streams. The first of the streams comprises monovalent
ions and the second of the streams comprises divalent ions.
Water softener claims
What is claimed is:
1. A water softener comprising: a cation exchange resin tank fluidly
coupled for passing spent brine comprising monovalent and divalent
ions; and an ion-separation device fluidly coupled to the resin
tank to receive the spent brine and separate the spent brine into
first and second streams, the first of the streams substantially
comprising monovalent ions and the second of the streams substantially
comprising divalent ions.
2. The water softener of claim 1 wherein the ion-separation device
comprises a nanofiltration membrane.
3. The water softener of claim 1 wherein the first of the streams
comprises regenerated brine and is coupled to a brine storage tank
for further reuse for cation exchange resin regeneration.
4. The water softener of claim 3 wherein the second of the streams
comprises a dischargeable stream comprising hardness-causing ions.
5. The water softener of claim 1 wherein the monovalent ions are
selected from the group consisting of sodium and chloride.
6. The water softener of claim 1 wherein the divalent ions are
selected from the group consisting of calcium, magnesium and carbonates.
7. A water softener comprising: a cation exchange resin tank fluidly
coupled for passing spent brine comprising monovalent and divalent
ions; a fluid mixer valve coupled to the resin tank and to a water
tank to dilute the spent brine to a desired concentration of a regenerant
salt; and an ion-separation device fluidly coupled to the fluid
mixer valve to receive the diluted spent brine and separate the
diluted spent brine into first and second streams, the first of
the streams substantially comprising monovalent ions and the second
of the streams substantially comprising divalent ions.
8. The water softener of claim 7 wherein the ion-separation device
comprises a nanofiltration membrane.
9. The water softener of claim 7 wherein the first of the streams
comprises a diluted stream of monovalent ions and is coupled to
a filter device for providing a concentrated stream of monovalent
ions and a stream of substantially demineralized water.
10. The water softener of claim 9 wherein the filter device for
providing the concentrated stream of monovalent ions and the stream
of demineralized water comprises a reverse osmosis filter.
11. The water softener of claim 9 wherein the second of the streams
comprises a dischargeable stream comprising hardness-causing ions.
12. The water softener of claim 9 wherein said water tank is coupled
to receive the demineralized water.
13. The water softener of claim 12 wherein said water tank is coupled
to the fluid mixer valve to supply water for diluting the spent
brine.
14. The water softener of claim 7 further comprises a pump device
fluidly coupled to draw liquid through the fluid mixer valve from
a spent brine holding tank and said water tank, said liquid to be
delivered to the ion-separation device.
15. The water softener of claim 9 wherein said concentrated stream
of monovalent ions comprises regenerated brine.
16. The water softener of claim 7 wherein said regenerant salt
comprises sodium chloride.
17. A method for purifying and recycling spent brine in a water
softener, the method comprising: passing from a cation exchange
resin tank spent brine comprising monovalent and divalent ions;
diluting the spent brine to a desired concentration of a regenerant
salt; and separating the diluted spent brine into first and second
streams, the first of the streams substantially comprising monovalent
ions and the second of the streams substantially comprising divalent
ions.
18. The method of claim 17 wherein the first of the streams comprises
a diluted stream of monovalent ions and said method further comprises
filtering said first stream for providing a concentrated stream
of monovalent ions and a stream of substantially demineralized water.
19. The method of claim 17 wherein the second of the streams comprises
a dischargeable stream comprising hardness-causing ions and said
method further comprises discharging said second stream to a sewer.
20. The method of claim 18 wherein said concentrated stream of
monovalent ions comprises regenerated brine.
21. The water softener of claim 17 wherein said regenerant salt
comprises sodium chloride.
Water softener description
BACKGROUND OF THE INVENTION
[0001] The present invention is generally related to water softeners,
and, more particularly, to system and techniques for the filtration
and reuse of spent brine, such as may be produced during the regeneration
of salt-based ion-exchange water softening systems.
[0002] Residential water softeners typically use cation exchange
resins, which remove ions, such as calcium and magnesium ions, which
commonly contribute to the hardness of water. During the ion exchange
process, the resin releases a cation, e.g., a divalent cation, into
the softened water. Periodically, preferably when the resin bed
becomes saturated with the divalent cations, the resin is regenerated
by flushing it with a concentrated regenerant aqueous solution,
such as salt (e.g., sodium chloride) brine. In the process, the
cations producing hardness (calcium and magnesium, for instance)
are released into the regeneration stream that is disposed of into
the municipal sewer system.
[0003] Unfortunately, excess sodium chloride from the regenerant
brine solution is also discarded to the sewer system. Because many
municipalities nowadays treat sewer water for agricultural irrigation
or other purposes, discharge of brine is often no longer acceptable
because the discharged brine would introduce excessive salinity
to the agricultural fields and present environmental pollution of
the ponds and nearby lands being irrigated. As a consequence, many
municipalities may enact regulations effectively banning the discharge
of brine from the regeneration of residential water softeners.
[0004] In addition, residential users must periodically buy pelletized
salt in heavy bags and carry them to the location of the ion exchange
softener, which is often not easily accessible.
BRIEF DESCRIPTION OF THE INVENTION
[0005] In view of the foregoing considerations, the inventors of
the present invention have innovatively recognized a brine regeneration
system by which the mixture of monovalent ions (e.g., brine salt)
and divalent ions (e.g., hardness-causing ions) in the spent regeneration
stream are separated. This allows for the brine to be recycled and
reused for additional cycles of resin regeneration while the hardness
ions may be discharged in an environmentally friendly fashion to
the sewer system.
[0006] Generally, the present invention fulfills the foregoing
needs by providing in one aspect thereof, a water softener comprising
a cation exchange resin tank fluidly coupled for passing spent brine
comprising monovalent and divalent ions. A fluid mixer valve is
coupled to the resin tank and to a water tank to dilute the spent
brine to a desired concentration of a regenerant salt (sodium chloride
or NaCl). An ion-separation device is fluidly coupled to the fluid
mixer valve to receive the diluted spent brine and separate the
diluted spent brine into first and second streams. The first of
the streams substantially comprises monovalent ions and the second
of the streams substantially comprises divalent ions.
[0007] In another aspect thereof, the present invention further
fulfills the foregoing needs by providing a method for purifying
and recycling spent brine in a water softener. The method allows
passing from a cation exchange resin tank spent brine comprising
monovalent and divalent ions. The method further allows for diluting
the spent brine to a desired concentration of a regenerant salt.
The diluted spent brine is separated into first and second streams.
The first of the streams substantially comprises monovalent ions
and the second of the streams substantially comprises divalent ions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The features and advantages of the present invention will
become apparent from the following detailed description of the invention
when read with the accompanying drawings in which:
[0009] FIG. 1 illustrates a schematic representation of an exemplary
system for purifying spent brine in a water softener; and
[0010] FIG. 2 illustrates a schematic representation of an exemplary
system for purifying and recycling spent brine in a water softener.
DETAILED DESCRIPTION OF THE INVENTION
[0011] Below is generic background information solely for the purpose
of providing a cursory description of one exemplary operation of
a typical water softener. This background information in no way
should be construed as limiting the scope of the present invention
described further below. As shown in FIG. 1 an exemplary water
conditioner system 10 may comprise at least two tanks: a resin tank
12 and a brine (e.g., salt) tank 14. The resin tank is filled with
a resin that, for example, comprises relatively small beads of a
suitable material, e.g., cross-linked polystyrene sulfonic acid.
This resin may be referred to in the art as a cation resin. The
beads may be constructed to exhibit a permanent electrical charge.
The charge may cause the beads to attract positively charged ions.
For example, the resin may be initially placed into service with
Na.sup.+ ions on the beads. When the hardness ions (e.g., calcium
or Ca.sup.2+ and magnesium or Mg.sup.2+) come in contact with the
sodium ions (Na.sup.+), such ions would displace the Na.sup.+ on
the beads. The Na.sub.+ is eventually dissolved into the water.
This sodium generally leaves the resin tank and may be delivered
to the tap with the treated water. When most of the Na.sup.+ is
removed from the resin beads, regeneration equipment should start
the regeneration process. The resin may then be regenerated by drawing
in a relatively high concentration of brine (e.g., NaCl or KCl)
solution from the brine tank. This salt solution is washed over
the depleted resin. The salt solution may contain Na.sup.+ and chloride
ions (Cl.sup.-). The Na.sup.+ is placed back onto the resin beads
and the Ca.sup.2+, Mg.sup.2+ and Cl.sup.- are washed down the drain.
The resin may then be rinsed with fresh water to remove any remaining
residual salt. Additional water may be added to the brine tank to
dissolve salt for the next regeneration cycle. The equipment may
then command a service mode and there would be treated water available
from the softener.
[0012] In accordance with aspects of the present invention, the
exemplary embodiment illustrated in FIG. 1 uses a nanofiltration
membrane 20 to separate the spent brine into two streams: stream
22 comprises regenerated or purified brine (essentially monovalent
ions, such as sodium and chloride) and stream 24 comprises waste
hardness (essentially divalent ions, such as calcium, magnesium
and carbonates) in order to deal with the environmental requirements
for discharge to sewer. It will be appreciated by those skilled
in the art that a nanofiltration membrane is just one example of
a device that can separate the monovalent ions from the divalent
ions that may be present in the spent brine. For some applications,
a "loose" reverse osmosis (RO) device, electrodialysis
device, or deionization device may be used in lieu of or in combination
with the nanofiltration membrane.
[0013] The foregoing embodiment may be useful for cases where the
nanofiltration membrane 20 is capable of separating the divalent
ions in the presence of a high concentration of monovalent ions.
In practice, many nanofiltration membranes (as presently available
in the market) may not be able to achieve complete separation of
hardness at high monovalent ion concentration. As an example, presently
commercially available nanofiltration membranes will separate divalent
ions from water at efficiencies approaching 99% or better whenever
the concentration of monovalent ions is substantially close to zero
(e.g., approximately below 0.1% wt NaCl). However, the efficiency
to separate divalent ions that produce hardness may decrease to
approximately 50% when the monovalent concentration is at approximately
1% wt NaCl or higher.
[0014] In one exemplary embodiment, the concentrated brine from
a regeneration cycle of the ion exchange softener, may be typically
saturated at approximately near 20-26% NaCl. It would be desirable
to reuse the brine multiple times without discharging it to the
sewer system. As described in greater detail below in the context
of FIG. 2 another embodiment is contemplated to effectively separate
hardness when the nanofiltration membranes alone may not be able
to achieve the separation to a satisfactorily high degree in the
presence of high brine (e.g., NaCl) concentrations.
[0015] Referring Now to FIG. 2:
[0016] A concentrated brine (stream 50) for regenerating an ion
exchange softening system resin may be obtained in a brine storage
tank 52 from pelletized salt (sodium chloride), for example. Stream
50 leaving the brine storage tank is passed to an ion-exchange resin
bed in a resin tank 54 where the concentration of sodium may be
reduced from close to saturation (approximately 26% wt NaCl or so)
to approximately from about 1/5.sup.th to about {fraction (1/10)}.sup.th
of its saturation point (stream 56). This stream is commonly called
spent brine because it comprises a residual amount of brine plus
the divalent cations removed from the resin bed during resin regeneration.
Stream 56 may be collected in a spent brine storage tank 58.
[0017] Stream 56 may be diluted with a stream 60 which may comprise
either fresh water or predominantly softened water, from a ratio
of approximately about 1:1 to about 10:1 or higher, passing through
a suitable mixing valve 62 or equivalent device. The purpose of
this diluting step is to reduce the concentration of sodium chloride
in stream 56 so as to produce a diluted stream 64 equal to or below
the concentration of monovalent ions that a nanofiltration membrane
66 can tolerate to separate the divalent (hardness) ions at high
efficiencies (typically 70% or higher, and up to about 99% hardness
removal in one exemplary embodiment).
[0018] A pumping device 68 can be used to draw fluid from the spent
brine holding tank 58 and/or a recycled water tank 70 to the nanofiltration
membrane 66. In one exemplary embodiment, typical pressures for
a stream 72 entering the nanofiltration membrane 66 need not be
much higher than pressures found in residential city water supplies.
If necessary for a given application, the pressure can be increased
slightly with the pumping device 68 (or an auxiliary pump) to approximately
about 100-150 psi.
[0019] Stream 72 comprises a diluted hard water stream that enters
the nanofiltration membrane 66 and is separated into two streams:
a concentrated stream of divalent ions, such as calcium, magnesium
and carbonates (stream 74) and a diluted softened stream (stream
75) that comprises just the monovalent ions (e.g., sodium and chloride)
and is essentially free of hardness. Stream 74 is discharged to
the sewer as a safe discharge essentially free of the sodium chloride
monovalent ions. In one exemplary embodiment, multiple passes through
nanofiltration membrane 66 may be performed in an optional loop
arrangement (not shown in FIG. 2) to achieve higher separation efficiencies.
[0020] The diluted soft stream (stream 75) may be pumped through
a pumping device 76 to a sufficiently high level of pressure, e.g.,
approximately 70 psi or higher, and passes through a reverse osmosis
(RO)-type membrane device 78 where the demineralized water (stream
80) is available for further recirculation and eventually the dilution
of stream 56. The purpose of RO device 78 may be two-fold: 1) to
reclaim the water present in stream 75 (i.e, the dilute spent brine)
for further utilization, and 2) to reconstitute the brine for further
reuse. The reclaimed water stream 80 is sent back to the recycled
water tank 70 for further use as diluent. The reconstituted brine
stream 82 is sent to brine storage 52 to make more brine and/or
increase its salt concentration.
[0021] In one exemplary embodiment, a bleed stream 75A, a bleed
stream 82A, and a bleed stream 60A could be added off stream 75
stream 82 and stream 60 respectively, to allow for draining or
discharging of fluids used in the cleaning or maintenance of membrane
device 66 membrane device 78 and storage device 70 respectively.
[0022] Unlike sea water desalination, the pressure in the RO membrane
device does not have to be very high because the osmotic pressure
of a diluted water stream is relatively low. In some applications
one may use a loose reverse osmosis (RO) device, an electrodialysis
device, or a deionization device in lieu of RO device 78.
[0023] As will be appreciate by those skilled in the art, a general
rule typically employed in water treatment is that for every 100
mg/L of ions in the treated water, the osmotic pressure that needs
to be overcome is about 1 psi. For instance, assuming that stream
75 comprises a total dissolved solids (TDS) concentration of 1%
wt (10000 mg/L or ppm), this would require approximately 100 psi
of osmotic pressure, which is a pressure level readily achievable
with a small pump in a residential system. The monovalent ions present
in stream 75 are separated and concentrated in stream 82 the reconstituted
brine.
[0024] In one exemplary embodiment, a design goal would be to provide
a relatively high water separation efficiency in the RO membrane,
for example at least 50% or higher, in order to bring the concentration
of monovalent ions to at least 3% wt NaCl, so that most of the water
is recovered as stream 80 and sent to the recycled water tank 70.
The reconstituted brine (stream 82) will then comprise a small volume
of liquid with high a concentration of NaCl and can be used for
further regeneration of the water softener cation exchange resin
as regenerated brine.
[0025] It is further desirable to achieve good separation efficiency
of the divalent ions at the nanofiltration membrane 66 so that the
working capacity for water hardness removal of the cation exchange
resin does not decrease with time. It is also desirable to have
a good separation (permeation) efficiency of water from the RO-type
membrane to avoid the possibility that the brine storage tank 52
overflows with low salt concentration liquid.
[0026] In operation, performing separations in a diluted stream
loop as illustrated in FIG. 2 allows the nanofiltration membrane
66 to operate more efficiently (i.e., achieve a higher level of
separation between monovalent and divalent ions) while avoiding
a reduction in the softening capacity of the ion exchange resin
bed.
[0027] While the preferred embodiments of the present invention
have been shown and described herein, it will be obvious that such
embodiments are provided by way of example only. Numerous variations,
changes and substitutions will occur to those of skill in the art
without departing from the invention herein. Accordingly, it is
intended that the invention be limited only by the spirit and scope
of the appended claims.
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