Water softener abstract
A water softener and a method of operating the same are provided
to allow for the efficient use of either NaCl or KCl as the regenerant
salt. A user interface is provided to allow the user to indicate
to the computer controlling the water softener whether NaCl or KCl
is being used. The computer controller adjusts the fill time and
brine time, depending on the type of regenerant salt used and on
the temperature of the brine.
Water softener claims
We claim:
1. A method for operating a water softener having a resin bed and
a brine tank, said water softener being connected to a source of
water, to provide a first mode of operation wherein a first salt
type is used for regeneration and a second mode of operation wherein
a second salt type is used for regeneration, the method comprising
the steps of: a. selecting a salt type; b. adding a quantity of
salt to the brine tank; the salt being of the selected salt type;
c. adding a first quantity of water to the brine tank if said selected
salt type is the first salt type, said first quantity of water being
determined by the solubility of said selected salt type, whereby
the water forms a brine of a desired concentration; d. adding a
second quantity of water to the brine tank if said selected salt
type is the second salt type, said second quantity of water being
in addition to the first quantity of water and being determined
by the solubility of said second salt type, said second quantity
of water forming a brine of the desired concentration; and e. exposing
the resin bed to said brine to regenerate the resin bed.
2. The method of claim 1 wherein the desired concentration is
a saturated brine with a predetermined quantity of the selected
salt in solution.
3. The method of claim 1 wherein said first salt type is sodium
chloride and said second salt type is potassium chloride.
4. The method of claim 1 wherein said second quantity of water
is about twenty-five percent of said first quantity of water.
5. The method of claim 1 further comprising the steps of: a. determining
the temperature of the brine; and b. calculating said second quantity
of water based on said temperature.
6. The method of claim 5 wherein said second salt type is potassium
chloride.
7. The method of claim 1 further comprising the steps of: a. measuring
the water temperature of the source water; and b. calculating said
second quantity of water based on said water temperature.
8. The method of claim 7 wherein said second salt type is potassium
chloride.
9. The method of claim 1 further comprising the steps of: a. measuring
the temperature of said brine; and b. calculating said second quantity
of water based on said temperature.
10. The method of claim 9 wherein said second salt type is potassium
chloride.
11. A method for regenerating a water softener, having a resin
bed and a brine tank, comprising the steps of: a. commencing a flow
of water into the brine tank, said brine tank containing a quantity
of a regenerant salt, whereby regenerant salt dissolves to form
a brine; b. measuring the temperature of said brine; c. calculating
a theoretical water quantity necessary to dissolve a predetermined
quantity of the regenerant salt based on said temperature; d. maintaining
and measuring said flow of water until the measured quantity of
water in the brine tank equals the theoretical water quantity; and
e. exposing the resin bed to said brine to regenerate the resin
bed.
12. The method of claim 11 further comprising the steps of: a.
measuring the temperature of said brine at regular intervals of
time; b. re-calculating a theoretical water quantity based on the
most recently measured brine temperature and the regenerant salt
selected; and c. maintaining said flow of water so that the measured
quantity of water is at least as great as the most recently re-calculated
theoretical quantity of water.
13. A water softener connected to a source of water, comprising:
a. a brine tank; b. a resin tank; c. a resin bed disposed in said
resin tank; d. a piping system connecting said brine tank to said
resin tank; e. salt selection means for selecting a salt type from
a plurality of salt types; d. water quantity means for calculating
and measuring a quantity of water based on said selected salt type;
and e. means for connecting said brine tank to the source of water,
f. whereby said brine tank is filled with said quantity of water
to form a brine, and said brine may be transferred through said
piping system to said resin tank to regenerate said resin bed.
14. The water softener claimed in claim 13 including a. a temperature
sensor disposed in said brine tank for measuring the temperature
of the brine therein; b. said water quantity means includes means
for calculating a theoretical fill time based on said temperature;
and c. means for filling said brine tank with water for an amount
of time at least as great as said theoretical fill time.
15. A water softener, comprising: a. a resin tank; b. a resin bed
disposed in said resin tank; c. a brine tank for preparing a salt
solution for regenerating the resin bed; d. a piping system connecting
said brine tank to said resin tank; e. salt selection means for
selecting a regenerative salt type from a plurality of salt types;
f. water dispensing means for measuring and placing either a first
quantity of water in the brine tank when a first salt type is selected
or a second quantity of water in the brine tank when a second salt
type is selected, said second quantity of water being greater than
the first quantity of water; said water interacting with a salt
in the brine tank to form a brine; g. means for connecting said
brine tank to a source of water; h. brine draw means for withdrawing
brine from the brine tank and running the brine to the resin tank
and through the resin bed, whereby the resin bed is washed with
a first quantity of brine having a volume substantially equal to
the first quantity of water if the first salt type is selected and
a second quantity of brine having a volume substantially equal to
the second quantity of water if the second salt type is selected.
16. In a water softener having a resin tank, a resin bed disposed
in the resin tank, a brine tank intended to contain a salt for regenerating
the resin bed, the improvement comprising: a brine feed-water selection
means for selecting either a predetermined first quantity of water
or a variable second quantity of water, either of said quantities
to be added to the brine tank during regeneration, the first water
quantity being associated with a first salt type, the second water
quantity being associated with a second salt type, the second water
quantity being greater than the first water quantity.
17. The water softener of claim 16 wherein the second water quantity
is between 10.2% and 27.2% greater than the first water quantity.
18. The water softener of claim 16 wherein the second water quantity
is about 25% greater than the first water quantity.
19. The water softener of claim 15 and including a temperature
sensing means for determining the temperature of the brine, and
wherein the water dispensing means adjusts the quantity of water
for the second water quantity whereby it is substantially equal
to 2Q=1Q+1QRT, wherein 2Q equals the second water quantity and 1Q
equals the first water quantity and R equals an adjustment rate
per degree Fahrenheit of the brine below 80 degrees Fahrenheit and
T equals the temperature of the brine in degrees Fahrenheit, and
the adjustment rate is in the range of 0.0054 to 0.0058.
20. In a water softener having a resin tank, a resin bed disposed
in the resin tank, and a brine tank for preparing a brine for regenerating
the resin bed, the improvement comprising: a. a brine feed-water
means for filling the brine tank with water to prepare a brine;
b. a temperature sensing means for determining the temperature of
the brine; and c. adjustment means coupled with the feed-water means
and the temperature sensing means for changing the quantity of water
fed into the brine tank in accordance with the temperature sensed
by the temperature sensing means.
21. The water softener of claim 20 wherein the adjustment means
adjusts the water quantity at a rate substantially equal to -0.0029
times the temperature sensed.
22. The water softener of claim 20 wherein the brine feed-water
adjustment means adjusts the water quantity substantially in accordance
with -0.0077 times the temperature sensed.
23. The water softener of claim 20 including a salt selection means,
the salt selection means being coupled with the adjustment means,
wherein the adjustment means adjusts the water quantity at a rate
per degree change in the temperature sensed, said rate being substantially
in accordance with (the solubility quotient -1) divided by 40 wherein
the solubility quotient equals the solubility at 80.degree. F. of
the salt selected divided by the solubility at 40.degree. F. of
the salt selected.
24. A method for regenerating a water softener having a resin bed
and a brine tank, said water softener being connected to a source
of water, the method comprising the steps of: a. selecting a salt
type from the group consisting of sodium chloride and potassium
chloride; b. adding to the brine tank a quantity of salt of said
selected salt type; c. adding to the brine tank a first quantity
of water to form a brine, said first quantity of water being determined
by the amount of salt desired for regeneration at a standard solubility;
d. determining the solubility of the salt in the brine; e. adding
to the brine tank an additional quantity of water if the solubility
of the brine is determined to be different than the standard solubility;
and f. exposing the resin bed to said brine to regenerate the resin
bed.
25. The method of claim 24 wherein said standard solubility is
about 2.99 pounds per gallon and said additional quantity of water
is at least 16 percent of the first quantity of water.
26. The method of claim 25 wherein said additional quantity of
water is about twenty-five percent of said first quantity of water.
27. The method of claim 24 wherein said standard solubility is
about 2.99 pounds per gallon and further comprising the steps of:
a. selecting a temperature parameter; and b. calculating said additional
water quantity as being substantially equal to (6.91-[0.029 brine
temperature])10.sup.-1(80-brine temperature) as a percent.
28. The method of claim 24 further comprising the steps of: a.
measuring the temperature of the source water; and b. calculating
said additional water quantity as being substantially equal to (74.9+0.0029
times the water source temperature raised to the second power-1.309
times the water source temperature) as a percent.
29. The method of claim 24 further comprising the steps of: a.
determining the temperature of said brine; and b. calculating said
additional water quantity as being a function of (the amount of
salt desired in the brine.div.solubility of the salt at 80.degree.
F.) ([solubility of the salt at 80.degree. F..div.solubility of
the salt at said temperature determined]-1).
30. The method of claim 24 wherein the regenerant salt is potassium
chloride and further comprising the steps of: a. measuring the temperature
of the brine; and b. calculating said additional water quantity
as being substantially equal to (6.91-[0.029 brine temperature])10.sup.-1(80-brine
temperature) as a percent.
31. A method for regenerating a water softener with a salt having
a solubility which varies in accordance with the temperature of
the brine, the water softener having a resin bed and a brine tank
and being connected to a source of water, the method comprising
the steps of a. adding the salt to the brine tank; b. determining
the quantity of salt desired for regeneration; c. adding a first
quantity of water to the brine tank to form a brine, said first
quantity of water being approximately equal to a theoretical amount
as if the brine were at room temperature, said theoretical amount
being said quantity of salt desired for regeneration divided by
the solubility of the salt at room temperature; d. determining the
temperature of the brine; e. determining the solubility of the brine
at the temperature determined; f. adding an additional quantity
of water to the brine tank, said additional quantity being determined
as a function of the solubility of the salt at the temperature determined;
and g. exposing the resin bed to said brine to regenerate the resin
bed.
32. The method of claim 31 wherein the function is substantially
equal to the solubility difference divided by the solubility product,
the solubility difference being determined by subtracting the solubility
at the determined temperature from the solubility at room temperature,
the solubility product being determined by multiplying the two solubilities.
33. The method of claim 31 wherein said additional quantity is
substantially equal to (the amount of salt desired for regeneration.div.the
solubility of the salt at the temperature determined) minus (the
amount of salt desired for regeneration.div.solubi- lity of the
salt at room temperature).
Water softener description
[0001] This application is a continuation in part of U.S. application
Ser. No. 09/016203 filed Jan. 30 1998.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to the art of water softening
systems. More particularly, the present invention is directed to
a method and apparatus for the efficient use of potassium chloride
as the regenerant in a water softener.
[0004] 2. Description of Related Art
[0005] A number of different methods and systems are known in the
art for softening water. The water softening process involves the
replacement of "hard" ions, such as calcium and magnesium,
with "soft" ions such as sodium and potassium. Soft water
is often desirable because it is less likely to leave deposits on
plumbing fixtures.
[0006] Water softeners typically utilize an ion exchange material,
typically present as a resin bed, to soften water. In the water
softening process untreated water is brought into contact with the
resin bed where "hard" ions are exchanged for "soft"
ions to provide a source of softened water. After prolonged contact
with untreated water, however, the capacity of the resin bed to
soften water becomes exhausted. When this occurs, the resin bed
may be regenerated by exposing it to a brine solution containing
the desired "soft" ions, which process restores its water
softening capacity.
[0007] The brine needed for regeneration may be formed by dissolving
in a quantity of water a regenerant salt having the desired "soft"
ions. Typical regenerant salts are sodium chloride and potassium
chloride. The type of regenerant salt used determines what type
of "soft" ions will be present in the softened water.
In particular, sodium chloride results in sodium ions being introduced
into the softened water, and potassium chloride results in potassium
ions being introduced into the softened water.
[0008] Many water softeners regenerate the resin bed automatically.
In such systems the resin bed is in service most of the time softening
water. When the water softener system determines that regeneration
is required, it stops softening water and instead regenerates the
resin by exposing it to It) the brine. A number of different methods
are known for automatically determining when to initiate a regeneration.
Some of these methods are described in U.S. Pat. Nos. 5544072
and 4722797 which are incorporated herein by reference. Typically,
in such methods, regenerations are performed before the resin bed
is completely exhausted, in order to ensure that the user does not
run out of soft water.
[0009] In addition to determining when to regenerate, many systems
automatically select the amount of regenerant to be used in a regeneration
step. The regenerant is often provided in the form of dry regenerant
salt located in a vessel separate from the resin bed, termed the
"brine tank." A measured amount of water is introduced
into the brine tank in order to dissolve the desired amount of regenerant,
forming a brine. Typically, the rate at which water enters the brine
tank, the "fill rate," is fixed, so that the fill time
determines the amount of water introduced and therefore the amount
of regenerant salt dissolved. The brine is then transferred from
the brine tank to the resin bed, so that the resin bed is exposed
to a known amount of regenerant during the regeneration process.
The used brine is then disposed of as waste.
[0010] Sodium chloride (NaCl) has been the regenerant salt most
commonly used in water softeners. However, the use of potassium
chloride (KCl) as the regenerant is an attractive alternative. The
potassium ions added to soft water from softeners regenerated with
KCl are more beneficial to human health as well as to plant life
than the sodium ions added to soft water from softeners regenerated
with NaCl. The use of KCl as the regenerant also often results in
less chloride being present in the waste brine, making its disposal
less environmentally damaging.
[0011] Most water softeners, however, are designed for NaCl regenerant
and lack the flexibility to operate adequately if KCl is used as
the regenerant instead. In particular, if KCl is used as the regenerant,
the resin bed may become exhausted prematurely, i.e., before it
is regenerated. As a result, the user would run out of soft water.
The problem becomes more acute as a function of water temperature
and softener efficiency, i.e., the colder the water is that is used
to form the brine and the more efficiently the water softener uses
regenerant salt, the more likely premature exhaustion is.
[0012] Moreover, the use of KCl as the regenerant is more complicated
than the use of NaCl for a number of reasons. First, in certain
operational regimes, namely, when the resin bed is used most efficiently,
the resin bed requires a greater amount of KCl than NaCl for regeneration.
Second, the solubility of KCl in water is highly temperature dependent,
unlike NaCl. In particular, the solubility of KCl in cold water
is greatly reduced relative to NaCl. As a result, when cold water
is used to form the brine, a greater amount of water is required
to dissolve the KCl. Third, the dissolution of KCl in water is significantly
endothermic, so that the KCl cools the water as it dissolves, thereby
lowering its solubility even more. Finally, KCl dissolves in water
at a slower rate than NaCl.
[0013] U.S. Pat. Nos. 5544072 and 4722797 each disclose a method
and apparatus for operating a water softener. These references also
disclose that either potassium chloride or sodium chloride may be
used as the regenerant, but they do not suggest any changes to the
water softening method or apparatus depending on whether NaCl or
KCl is used. Such changes are required, however, because of the
different characteristics of these two salt types. As a practical
matter, then, water softeners in accordance with these references
do not have the flexibility to be able to use either NaCl or KCl
at the option of the user. Moreover, these references do not disclose
any way of accounting for the more complicated characteristics of
KCl, such as its temperature dependent solubility, in order to use
KCl as a regenerant in an efficient and reliable manner.
SUMMARY OF THE INVENTION
[0014] The principal object of the present invention is to provide
a water softener and a method of operating the same to allow for
the efficient and reliable use of KCT as the regenerant salt.
[0015] Another object of the present invention is to provide a
water softener method and apparatus having the flexibility to allow
either NaCl or KCl to be used as the regenerant salt at option of
the user.
[0016] Yet another object of the present invention is to provide
a method and apparatus for filling the brine tank of a water softener
to account for changes in the brine temperature occurring during
the course of the fill and thereby to ensure that the required amount
of regenerant salt is dissolved.
[0017] In accordance with the present invention, a water softener
and a method of operating the same are provided to allow for the
efficient and reliable use of either NaCl or KCl as the regenerant
salt. A user interface is provided to allow the user to indicate
to the computer controlling the water softener whether NaCl or KCl
is being used. The computer controller adjusts the fill time and
brine time depending on the type of regenerant salt used. The temperature
of the brine is measured at regular intervals as water is being
supplied to the brine tank to dissolve the KCl. At each interval
the computer calculates the amount of water needed to dissolve the
required amount of KCl, and the fill ends when the amount of water
added is approximately equal to the required amount calculated at
the most recent time interval.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a graph which illustrates curves representing
the capacity of a typical resin bed as a function of the salt dosage
used to regenerate it. The solid line corresponds to the use of
NaCl as the regenerant, and the dotted line corresponds to the use
of KCl.
[0019] FIG. 2 is a schematic representation of an automatic water
softener in accordance with the present invention.
[0020] FIG. 3 is a schematic representation of a user interface
for the water softener in accordance with the present invention.
[0021] FIG. 4 is a graph showing the relationship between brine
temperature and the water volume equivalency of KCl with respect
to NaCl.
[0022] FIG. 5 is a graph showing the relationship between brine
temperature and the water volume adjustment rate to obtain equivalent
amounts of KCl in solution.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0023] Water hardness is typically expressed in terms of grains
per gallon, which represents the weight in grains of calcium carbonate
(CaCO.sub.3) which would be needed to be dissolved in one gallon
of water to achieve that level of hardness. The capacity of a resin
bed, which represents the amount of water of a given hardness it
can soften before becoming exhausted, is therefore expressed in
grains as follows:
C=H.times.V
[0024] where C=capacity of the resin bed in grains, H=the hardness
of the water in grains per gallon, and V=the amount of water in
gallons at that hardness that can be treated by the resin bed before
exhausting it.
[0025] When the resin bed becomes exhausted, it may be regenerated
by exposing it to a brine comprising a quantity of regenerant salt
dissolved in water. The salt dosage, dissolved in water as a brine,
required to regain the desired capacity depends on the efficiency
of the resin bed. The efficiency, E, of a resin bed is defined as
follows:
E=C/D
[0026] where D=the dosage of regenerant salt applied to the resin
bed in pounds, and C=the capacity of the resin in grains resulting
from that salt dosage.
[0027] The water softening process, to the extent that it involves
the removal of calcium ions, involves the exchange of either two
Na.sup.+ ions or two K.sup.+ ions for one Ca.sup.2+ ion. Since the
molecular weights of CaCO.sub.3 KCl, and NaCl are 100.09 74.56
and 58.44 respectively, and since 1 pound=7000 grains, the theoretical
efficiency is 5995 grains/lb. when NaCl is used and 4699 grains/lb.
when KCl is used. Theory thus predicts that NaCl is 28% more efficient
as a regenerant salt than KCl, with the result that more KCl would
be required for regeneration in order to achieve the same capacity.
[0028] In practice, however, resin beds approach their theoretical
efficiencies only when low salt dosages are used. The reason for
this is that the capacity cannot be increased without limit by increasing
the salt dosage. With higher salt dosages, the resulting capacity
levels off and gradually approaches a limiting value. Put another
way, as the salt dosage is increased, the efficiency falls increasingly
below its theoretical value. Moreover, it has been found that for
sufficiently high salt dosages, the amount of NaCl and KCl needed
to achieve the same capacity becomes essentially the same.
[0029] This general trend is illustrated schematically in FIG.
1 which is a graph of the capacity of a typical resin bed in grains
as a function of NaCl and KCl dosage in pounds. The NaCl curve is
a solid line, and the KCl curve is a dotted line. As shown in that
graph, when low salt dosages are used, NaCl results in a greater
capacity than the same dosage of KCl. However, with higher salt
dosages the resulting capacity becomes nearly independent of the
type of salt used.
[0030] Many water softeners operate in the regime where NaCl and
KCl have nearly the same efficiency. However, a more efficient use
of regenerant salt is obtained by using lower salt dosages, albeit
at the cost of more frequent regeneration. In this regime, then,
the lower efficiency of KCl, as compared to NaCl, must be compensated
for by increasing the KCl dosage during regeneration.
[0031] Preferably, curves for KCl and NaCl like those in FIG. 1
are generated for each resin bed to determine the salt dosage required
to achieve the desired capacities. Such data is typically obtained
by exhausting the resin bed until the effluent water has a hardness
of one grain per gallon. The resin bed is then regenerated with
a regenerant brine having a selected salt dosage. Water of a known
hardness is passed through the resin bed until the effluent water
reaches a hardness of one grain per gallon. The amount of water
that has passed through the resin bed is measured, and from this
quantity the capacity of the resin bed may be calculated.
[0032] This procedure is then repeated for various salt dosages
to generate the curve of capacity versus salt dosage as in FIG.
1.
[0033] An automatic water softener 10 adapted to use potassium
chloride in accordance with the present invention is shown schematically
in FIG. 2. When water softener is "in service" it is designed
to treat hard water to provide a source of soft water. Periodically,
water softener 10 automatically goes out of service, thereby ceasing
the softening of water, and enters a "regeneration cycle"
designed to regenerate its capability to soften water.
[0034] With reference to FIG. 2 water softener 10 preferably includes
a source pipe 12 connected to a source of hard water 14 a destination
pipe 16 connected to a destination 18 intended to use the softened
water, and a drain pipe 20 connected to a drain 22. Pipes 12 16
and 20 are also connected to a control valve 24. A resin bed 26
preferably comprising particles of ion exchange resin, is disposed
in a resin tank 28. A pipe 30 and a pipe 32 connect resin tank 28
to control valve 24. A brine tank 34 holds a quantity of a regenerant
salt 36 typically NaCl or KCl, and is connected to an aspirator
valve 38 by a pipe 40. Pipe 40 includes a brine valve 42. Pipes
44 and 46 connect aspirator valve 38 to control valve 24. Control
valve 24 may be configured to interconnect pipes 12 16 20 30
32 44 and 46 in a number of different ways hereinafter described.
[0035] Water softener 10 preferably includes a micro computer controller
48 having a user interface 50. User interface 50 shown schematically
in FIG. 3 preferably includes an LCD display 60 and various buttons,
such as a "SELECT" button 62 an "UP" button
64 and a "DOWN" button 66 to allow the user to selectively
view and enter in information. A timer 52 is provided to enable
controller 48 to measure time durations. A water meter 54 is placed
in either pipe 30 or pipe 32 to enable controller 48 to measure
the amount of water flowing through resin tank 28. A temperature
sensor 56 is preferably disposed in brine tank 34 to enable controller
48 to measure the temperature therein. Temperature sensor 56 is
preferably a thermocouple or a semiconductor device. Controller
48 sets the configuration of control valve 24.
[0036] When in service, hard water from source 14 passes through
supply pipe 12 to control valve 24 which is configured so that
the hard water then flows through pipe 30 to resin tank 28. In resin
tank 28 the hard water passes through resin bed 26 where it is
softened by an ion exchange process. The soft water flows out from
resin tank 28 through pipe 32 to control valve 24. Control valve
24 is configured to direct the soft water from pipe 32 to pipe 16
where it is directed to its destination 18.
[0037] When the resin bed 26 loses its capacity to effectively
soften the water passing through it, regeneration is necessary.
The regeneration cycle preferably includes the following steps:
(1) fill; (2) brine draw; (3) slow rinse; (4) backwash; and (5)
fast rinse. During the fill step, a quantity of water flows into
brine tank 34 to dissolve a quantity of the salt 36 therein in order
to make the amount of brine necessary for regeneration. Specifically,
control valve 24 is configured so that hard water from source 14
flows through pipe 12 to pipe 30 to resin tank 28. The hard water
passes through resin bed 26 and flows out through pipe 32 to control
valve 24. Control valve 24 is configured to direct this water to
pipe 44 and then to pipe 40 through aspirator valve 38. Brine valve
42 opens in response to the flow of water in pipe 40 allowing the
water to enter brine tank 34. The water filling brine tank 34 dissolves
a quantity of the salt 36 to form a brine, whereby the brine is
substantially saturated. Temperature sensor 56 preferably measures
the temperatures of the water and of the resulting brine. The duration
of the fill step determines the amount of water that enters brine
tank 34 and therefore the amount of regenerant salt dissolved and
available for regeneration.
[0038] During the brine draw step, control valve 24 is configured
so that hard water from pipe 12 is directed to pipe 44 whereupon
it flows through aspirator valve 38 to pipe 46. This flow through
aspirator valve 38 creates suction on pipe 40 by the Venturi effect.
Brine valve 42 is open, so that the suction on pipe 40 draws the
brine in brine tank 34 formed during the fill step, up into pipe
40 which then flows through aspirator valve 38 to pipe 46. Control
valve 24 is configured so that the water and brine from pipe 46
are directed through pipe 30 to resin tank 28. The brine entering
resin tank 28 flows through resin bed 26 thereby regenerating it,
and flows out through pipe 32 as waste. The waste is directed to
drain 22 via pipe 20 for its disposal. The duration of the brine
draw step is sufficiently long so as to withdraw all or nearly all
of the brine from brine tank 34. Preferably, brine valve 42 closes
automatically when the level of brine in brine tank 34 falls below
a prescribed point.
[0039] During the slow rinse step, brine valve 42 is closed, and
brine is no longer withdrawn from brine tank 34. However, water
keeps flowing as in the brine draw step. In particular, the configuration
of control valve 24 is the same as for the brine draw step. The
remaining brine continues to flow through resin bed 26 until replaced
with incoming water in order to achieve maximum ion exchange and
to continue to flush out any hardness minerals or brine which may
remain in resin tank 28.
[0040] During the backwash and fast rinse steps, control valve
24 is configured so that hard water from pipe 12 is directed to
pipe 30 and flows into resin tank 28. The water flows out of resin
tank 28 through pipe 32 and is directed to drain 22 via pipe 20.
During the backwash step, the water flows up through resin bed 26
lifting up and expanding the resin bed 26 and flushing out iron
minerals, dirt, sediments, hardness minerals, and any remaining
brine. During the fast rinse step, a fast flow of water is directed
downward through resin bed 26 to pack it and prepare it for service.
[0041] Controller 48 determines when to regenerate resin bed 26
and to what capacity. Various methods maybe used for these determinations,
such as those described in U.S. Pat. Nos. 5544072 and 4722797.
The necessary capacity will, in general, depend on the hardness
of the water to be treated. User interface 50 therefore preferably
includes means by which the user can enter the water hardness, expressed
in grains per gallon, into controller 48. To accommodate the use
of different types of regenerant salt, user interface 50 also enables
the user to specify the type of salt used, e.g., Eli whether NaCl
or KCl is used.
[0042] Preferably, the user-adjustable parameters, which typically
include the time of day for regeneration, the water hardness, and
the type of regenerant salt used, are shown as various "screens"
on display 60 with each parameter having its own screen. At each
screen, the user is able to scroll up and down through the available
values for the parameter by pressing "UP" button 64 and
"DOWN" button 66 respectively. The user indicates the
desired value for the parameter by pressing "SELECT" button
62 whereupon the value is stored by computer controller 48 and
the next "screen" is shown on display 60. In this way,
the user is able to scroll through the available salt types, such
as NaCl and KCl, and to make a selection. Other means for indicating
the regenerant salt type, such as other types of computer interfaces
or mechanical switches, could also be used.
[0043] From the desired capacity to which resin bed 26 is to be
regenerated, the required salt dose may be determined from empirical
data as described above. The salt dosages, D, for each desired regenerated
capacity, C, are programmed into controller 48 for the various salt
types intended to be used, such as NaCl and KCl. Thus, from the
type of salt used and the regenerated capacity required, controller
48 is able to determine the salt dosage, D, needed for regeneration.
[0044] The value of D, the salt dosage, determines the amount of
water that must be supplied to brine tank 34 during the fill step,
based on the solubility of that salt. Preferably, the amount of
water added during the fill step is determined by the fill time,
the flow rate being a fixed quantity. The required fill time may
thus be calculated as follows:
[0045] F=D/(R.times.S)
[0046] where F=fill time in minutes, D=the salt dosage in pounds,
R=the fill rate in gallons per minute, and S=the solubility of the
salt in pounds per gallon. When KCl is used as the regenerant salt,
however, an added complication arises in that its solubility is
markedly temperature dependent over the typical range of water temperatures
encountered, namely, 34.degree. F. to 80.degree. F., whereas the
solubility of NaCl is relatively constant over this range. In particular,
the solubilities of NaCl and KCl are both approximately 2.99 lbs./gal.
at 80.degree. F. At lower temperatures, the solubility of KCl is
significantly less than that of NaCl as summarized in Table 1. The
information in Table 1 has been generated from empirical data linearized
in the range of 34.degree. F. to 80.degree. F., with the solubility
of NaCl taken to be a constant 2.99 lbs./gal. The data of Table
1 is representative only, in that results can be affected by the
water chemistry in the particular application.
1TABLE 1 Temp. (.degree. F.) KCl Solubility (lbs./gal.) KCl/NaCl
Difference (%) 34 2.35 27.2% 36 2.38 25.7% 38 2.40 24.2% 40 2.43
22.8% 42 2.46 21.4% 44 2.49 20.1% 46 2.51 18.8% 48 2.54 17.5% 50
2.57 16.2% 52 2.60 14.9% 54 2.63 13.7% 56 2.65 12.5% 58 2.68 11.4%
60 2.71 10.2% 62 2.74 9.1% 64 2.76 8.0% 66 2.79 6.9% 68 2.82 5.9%
70 2.85 4.9% 72 2.88 3.8% 74 2.90 2.8% 76 2.93 1.9% 78 2.96 0.9%
80 2.99 0.0%
[0047] To accommodate the use of KCl, the fill times should be
adjusted on the basis of water temperature to reflect the temperature
dependent solubility of KCl. The simplest approach to account for
this effect is not to measure the actual water temperature at all
but to simply assume a typical water temperature and to increase
accordingly the fill time for KCl by a fixed percentage relative
to the fill time that would be required if NaCl were used. An increase
in the fill time of 25% is found to be a reasonably adequate approximation
for the most typical water temperatures encountered.
[0048] A more accurate system includes temperature sensor 56 in
order to enable controller 48 to determine the temperature of the
water being supplied to brine tank 34. Temperature sensor 56 is
preferably located in brine tank 34 but may alternatively be located
upstream, such as in source pipe 14. Controller 48 is programmed
with the solubilities of KCl at various water temperatures, so that
when KCl is used as the regenerant salt controller 48 measures the
water temperature and sets the required fill time accordingly.
[0049] Alternatively, the water temperature may be a user-adjustable
parameter entered into computer controller 48 by means of user interface
50 as previously described.
[0050] The temperature of the brine formed in brine tank 34 does
not remain constant during the course of the fill. An example of
how the brine temperature changes during the course of a fill when
KCl is used as the regenerant salt is shown in tabular form in Table
2. This temperature changed is caused by two factors. First, before
the fill begins, the temperatures of the water and of brine tank
34 with dry regenerant salt 36 present within will not in general
be equal, so that the brine temperature will naturally equilibrate
during the course of the fill. Second, the dissolution process of
the salt also changes the temperature of the brine. In particular,
the dissolution of KCl is significantly endothermic, so that the
dissolution process itself cools the brine.
[0051] The temperature change of the brine during the course of
the fill thus presents an added difficulty in the case of KCl because
of its temperature dependent solubility. Temperature sensor 56 should
thus measure the temperature during the course of the fill, preferably
at regular intervals such as every minute. Typical results under
this method are tabulated in Table 2.
2TABLE 2 Required Sample Fill Required Fill Time Temp Solubility
Water Fill Time (Min) (.degree. F.) (lbs/gal) (gal) (min) 0 60 2.7048
2.219 7.40 1 56 2.6492 2.265 7.55 2 52 2.5937 2.3133 7.71 3 48 2.5381
2.3640 7.88 4 46 2.5103 2.3902 7.97 5 44 2.4826 2.4168 8.06 6 42
2.4548 2.4442 8.15 7 41 2.4409 2.4581 8.19 8 40 2.4270 2.4722 8.24
8.24 -- END OF FILL --
[0052] The adjustment in water volume to add to the brine tank
to account for the difference in solubility of potassium chloride
at different temperatures is as is found in Table 1. Based on Table
1 the average change in solubility (pounds of salt per gallon of
water) of KCl is 0.014 pounds per gallon per "minus" degree
Fahrenheit over the range of 80.degree. F. to 34.degree. F. Thus,
the KCl solubility, in pounds per gallon, is related to the temperature
of the brine solution as follows:
KCl solubility=2.99-(80-brine temperature )(0.014)
[0053] To determine the water volume equivalency (i.e., the gallons
of water to add to obtain one pound of KCl in solution as compared
to the amount of water to obtain one pound of NaCl in solution,
at a temperature) the relationship is NaCl solubility.div.KCl solubility
at the temperature. Thus, the water volume equivalency of KCl is
1.27234@34.degree. F., 1.23045@40.degree. F., 1.16342@50.degree.
F., 1.10332 at 60.degree. F., 1.04912@70.degree. F., and 1.0000
at 80.degree. F.
[0054] Based on the above, the water adjustment rate for temperature,
sometimes referred to as WARFT, (additional percentage of water
required for equivalent KCl in solution per degrees below 80.degree.
F.) is 0.592% more water per degree over the temperature range of
80.degree. F. to 34.degree. F.; calculated by change in water equivalency
rate over the temperature range divided by the temperature difference,
i.e., (1.27234-1.0000).div.46. Additional adjustment rates over
different temperature ranges, as determined from the data, are:
0.49% for the range 800 to 70.degree.; 0.52% for the range 80.degree.
to 60.degree.; 0.55% for the range 80.degree. to 50.degree.; and
0.58% for the range 80.degree. to 40.degree.. Each of these rates
is the percent increase in water required, that is, in addition
to the water determined for a brine solution at 80.degree. F., for
each .degree. F. the brine temperature is below 80.degree. F. Thus,
it is believed that good results can be obtained if the water volume
is adjusted at a rate in the range of 0.49% to 0.59% per .degree.
F. difference, and the preferred range is 0.55% to 0.58% per .degree.
F. difference. Accordingly, if the temperature in the brine tank
is 40.degree. F., the amount of water to be added to the brine tank
should be increased by about 23.2% (determined by adjustment rate
of +0.58%/.degree. F., times a temperature difference of 40.degree.)
in addition to the amount of water which would be added if the temperature
were at 80.degree. F.
[0055] Additionally, the data in Table 1 shows that the rate of
water adjustment for temperature differences for potassium chloride
is substantially linear in the range of temperatures ordinarily
expected for the brine, and has been found to be directly related
to the water temperature as follows: the rate equals [0.488+0.0029
(70-brine temperature)].div.100 which equals (6.91-0.029 brine
temperature)10.sup.-3. As an example, using this relationship to
determine the water adjustment rate for brine solution at 60.degree.
F., the rate equals [0.488+0.0029 (70-60)].div.100 i.e., 0.00517
increase per degree of brine temperature difference from 80.degree.
F., and at 34.degree. F. the rate is [0.488+0.0029 (70-34)].div.100=0.00592
increase in water per degree of brine temperature difference from
80.degree. F. These rates can be used to determine a water adjustment
adder, which is WARFT times (80-temperature of brine solution),
and a water adjustment multiplier which is 1+water adjustment adder.
Thus water adjustment rates and multipliers, based on the above
relationships are as follows:
3 Water Adjustment Brine Temperature Water Adjustment Rate Multiplier
34.degree. 0.00592 1.27232 40.degree. 0.00575 1.23000 50.degree.
0.00546 1.16380 60.degree. 0.00517 1.10340 70.degree. 0.00488 1.04880
[0056] Referring now to Table 2 the required fill time is directly
related to the volume of water desired. In the example of Table
2 the fill rate is 0.3 gallons per minute. With a constant fill
rate, the brine fill time determines the volume of water added to
the brine tank, and the amount of the salt that can be in solution.
The fill time can be adjusted according to the same water adjustment
multiplier set forth above to obtain the desired quantity of water
in the brine tank and a desired amount of KCL in solution, i.e.,
the brine, and which will be available to be delivered to the resin
bed for regeneration. For example, if six pounds of KCl were to
be delivered to the resin bed for regeneration, the volume of water
to be delivered to the brine tank at 80.degree. F. would be about
2.00 gallons and the brine fill time would be 6.666 minutes at a
water delivery rate of 0.3 gallons per minute. If the brine temperature
were 40.degree. F., the water adjustment rate would be about 0.00575%
increase per degree of temperature difference from 80.degree. F.,
which temperature difference is 40.degree., thus, the water adjustment
adder is 0.00232 i.e., 23.2% for a water adjustment multiplier
of 1.23. Using that adjustment, the volume of water required @40.degree.
F. is about 2.46 gal. (2.000@80.degree.+2.000.times.0.23) and the
brine fill time is about 8.2 minutes (6.666+6.666.times.0.23). Both
of which compare favorably with 2.4722 gal. and 8.24 minutes as
shown in Table 2.
[0057] The volume of water for the brine fill for KCL can be determined
from the following relationships: 1 Water To Brine Tank ( gallons
) = Salt Salt Solubility ( 1 + WARFT .times. dT )
[0058] Thus the gallons of water required at a brine temperature
of BT is 2 Gallons of Water = Salt Salt solubility ( 1 + [ 0.488
+ 0.0029 ( 70 - BT ) ] ( 80 - BT ) ) 10 - 2
[0059] which for potassium chloride equal salt (519.2-3.086BT+9.6(BT).sup.-
2 10.sup.-3)10.sup.-3 and 3 Brine Tank Fill Time ( minutes ) = Salt
( 1 + WARFT .times. dT ) Salt Solubility .times. WDR
[0060] which for potassium chloride equals: 4 = Salt WDR ( 519.2
- 3086 BT + 9.6 ( ( 40 ) 2 10 - 3 ) 10 - 3
[0061] Wherein:
[0062] Salt=pounds of KCl salt desired for regeneration of resin
bed.
[0063] Salt Solubility=solubility at 80.degree. F., which is 2.99
lbs/gal for KCl
[0064] WARFT=water adjustment rate for temperature (increase per
degree below 80.degree.)
[0065] dT=temperature differential between brine temperature and
80.degree. F.
[0066] WDR=water delivery rate to brine tank (gallons per minute)
[0067] BT=temperature of the brine.
[0068] Based on the results of Table 2 it can be seen that an
additional quantity of water in the brine tank is required to dissolve
equivalent amounts of potassium chloride depending upon the brine
temperature, for example about 11% more at 60.degree. F. (0.219.div.2.00)
and about 16% more at 52.degree. F. (0.3133.div.2.00) and about
24% more at 40.degree. F. (0.4722.div.2.00). This increased water
allows an amount of potassium chloride to be present in the brine
which is substantially equivalent to the amount of sodium chloride
which would be present in an amount of brine without the additional
water.
[0069] Also note from Table 2 that the final brine temperature
is approximately 20 degrees lower than the temperature at the start
of the fill, i.e., the temperature started at 60.degree. F. and
ended at 40.degree. F. Thus, the temperature selected for determining
the water adjustment rate and the water adjustment factor should
be about 20.degree. less than the temperature of the water admitted
to the brine tank. If the temperature of the source water is used
to determine the water adjustment rate and multiplier, the relationship
discussed above would be adjusted for that 20.degree. difference
by substituting (source water temperature-20) for brine temperature
which results in the relationships:
WARFT=(6.91-(0.029[SWT-20])10.sup.-3
=(7.49-0.029 SWT)10.sup.-3
[0070] where SWT=source water temperature, and
[0071] Water Adjustment Multiplier=1+WARFT.times.dT
=1+(6.91-[0.029(SWT-20)])10.sup.-3(dT)
=1+(7.49-0.029(SWT))10.sup.-3(100-SWT)
=1+[0.749+2.9(SWT).sup.210.sup.-5-0.01039SWT]
[0072] The KCl Water Volume Equivalency (WVE) is based on the KCl
Solubility presented in Table 1. The KCl Water Volume Equivalency
at a given brine temperature is the gallons of water to obtain the
amount of KCl in solution which is equal to an amount of NaCl in
solution. It can be determined from Table 1 by dividing the NaCl
Solubility (2.99 pounds per gallon of water) by the KCl solubility
(see second column of Table 1 for soluability at different temperatures).
Thus at 40.degree. the KCl Water Volume Equivalency is 2.99.div.2.43=1.230
gallons of water for KCl to have the same amount of KCl in solution
as one gallon of NaCl solution. Accordingly, the KCl Water Volume
Equivalency at various temperatures is as follows:
4 Temp (.degree. F.) KCl Water Volume Equivalency 34 1.272 40 1.230
50 1.163 60 1.103 70 1.049 80 1.000
[0073] which are stated above as the Water Adjustment Multipliers.
[0074] The KCl Water Equivalency values can be used to determine
the KCl water volume desired, based on the temperature of the brine.
To do so, KCl Water Equivalency is plotted against Brine Temperature,
as shown in FIG. 4. The KCl Equivalency can be determined at each
temperature from the relationship between the KCl Equivalency and
Brine Temperature, which relationship is determined from the slope
of the plot of the points; which relationship is KCl Water Volume
Equivalency=1.103+0.0065(60.degree- .-Brine Temperature) in the
temperature range from 60.degree. to 34.degree.. The relationship
also closely approximates the KCl Water Volume Equivalency in other
selected temperature ranges. These relationships can also be stated
as formulas with other numerical factors for different temperature
ranges and "curves" believed to be the best "fit"
to the plotted values.
[0075] Further, the Water Adjustment Rate (WAR) for KCl, as set
forth above, is determined from the data in Table 1 and Table 2.
The WAR is based on the additional water needed to put equal amounts
of KCl in solution, i.e., equal to the amount of NaCl which is desired
if NaCl were to be used. The WAR is the percent increase in water
per change of temperature of the brine solution from the standard
temperature of 80.degree. F.; 80.degree. F. was selected because
the solubility of KCl is substantially the same as the solubility
of NaCl at that temperature, i.e., 2.99 lbs. per gallon (see Table
1), and then varies from the solubility of NaCl when the brine temperature
is cooler than 80.degree. F. as shown in Table 1. Using 40.degree.
F. as an example WAR for KCl can be determined by calculating the
extra water required to put an equivalent amount of KCl in solution
at 400 which is the KCl Water Volume Equivalency of 1.230 gallons
minus the amount of water for NaCl which is 1.000 gallon. The result
is 0.230 gallons extra water required at 40.degree.. The difference
in temperature from the standard is 40.degree.(i.e., 80.degree.-40.degree.).
Thus the WAR for brine temperature at 40.degree. is 0.230 gallons.div.40.degree.=0.00575
gallons/degree difference from 80.degree. and its units are increased
percent volume of water per degree of temperature. WARs for selected
other temperatures, determined in the same manner as above, are
as follows:
5 Brine Temp (.degree. F.) Water Adjustment Rate 34 0.00592 40
0.00575 50 0.00546 60 0.00517 70 0.00488 80 -0-
[0076] These values can be plotted as shown in FIG. 5. And the
relationship between the WAR for KCl and Brine Temperature can be
determined from the plot, by well known algebra analysis, to be
WAR for KCl=[0.488+0.0029(70-Brine Temperature)].div.100 for brine
temperatures in the range of 60.degree. to 34.degree.. Thus, the
relationship set forth above (i.e., the rate of water adjustment
for temperature differences for potassium chloride is substantially
linear in the range of temperatures ordinarily expected for the
brine, and has been found to be directly related to the water temperature
as follows: the rate equals [0.488+0.0029(70-brine temperature)].div.100
which equals (6.91-0.029 brine temperature)10.sup.-3) is derived
from Table 1.
[0077] The preferred method of using KCl as the regenerant is described
as follows. At regular time intervals during the fill, the temperature
at temperature sensor 56 is measured. From this temperature, the
solubility of the salt is calculated, and from this value the required
volume of fill water and ultimately the required fill time may be
calculated, as shown in Table 2. The fill then proceeds until the
required fill time is approximately equal to the actual fill time.
[0078] Even after the fill ends, the brine temperature is often
observed to continue to drop when KCl is used. This may be due to
the dissolution rate of KCl which is less than that of NaCl. In
other words, the KCl continues to dissolve even after the flow of
water stops, thereby cooling the brine even further. The temperature
drop is observed to be fairly small --typically 2.degree. F. The
temperature drop reduces the solubility of KCl even further, so
that less dissolved KCl is present in the brine as result. The way
to compensate for this effect is to add more water during the fill
step by increasing the fill time. Typically, a 1% increase in the
fill time is all that is required.
[0079] When the fill time is adjusted, the brine draw time must
also be adjusted to ensure that the required amount of brine is
withdrawn from brine tank 34. Typically, the ratio of the brine
draw time to the fill time is a fixed quantity, so that the brine
draw time may be taken to be the fill time multiplied by this quantity.
The slow rinse time is typically fixed. Preferably, controller 48
calculates the necessary brine draw time based on the fill time
actually used. The total "brine time" is then the sum
of this necessary brine time and the slow rinse time. Controller
48 maintains control valve 24 in the brine draw/slow rinse configuration
for this "brine time" to ensure that the required amount
of brine is withdrawn. In the case where the fill time for KCl is
increased by 25% relative to NaCl, a corresponding increase in the
"brine time" for KCl of approximately 12.5% relative to
NaCl is found to be sufficient.
[0080] The above described embodiments are merely illustrative
of the features and advantages of the present invention. Other arrangements
and advantages may be devised by those skilled in the art without
departing from the spirit and scope of the present invention. Accordingly,
the invention should not be deemed to be limited to the above detailed
description but only by the claims that follow. |