Technical Field
The present invention relates to a water treatment
process and a water treatment system for reproducing water
to be treated containing Ca ions (Ca2+), sulfate ions (S042-),
carbonate ions, and silica.
Background Art
It is known that industrial waste water, saline water,
and sewage contain large amounts of ions and silica. In
10 addition, in a cooling tower, heat is exchanged between a
high-temperature exhaust gas discharged from the boiler,
etc., and cooling water. As a result of this heat exchange,
some of the cooling water turns into steam, and,
accordingly, ions and silica in the cooling water are
15 concentrated. Therefore, the cooling water discharged from
the cooling tower (blowdown water) has increased
concentrations of ions and silica.
Water containing a large amount of ions is subjected to
a demineralization treatment and then discharged into the
20 environment. As devices that perform the demineralization
25
treatment, a
nanofiltration
reverse osmosis
membrane device, an
and the like are known.
Among ions contained
monovalent cations such as
in the
Na+,
membrane device, a
ion-exchange equipment,
water mentioned above,
and NH,+ and anions such
as Cl- and N03- are highly soluble in water. On the other
hand, divalent metal ions such as Ca2+, anions such as S042-
and C03 2-, and silica are scale-forming components. Salts and
silica of scale-forming components have low solubility in
30 water, and thus they tend to be deposited as scales. In
particular, the saline water, industrial waste water, and
blowdown water from a cooling tower mentioned above contain
2
large amounts of Ca2+, S04
2-, carbonate ions (C032-, HC03-), and
silica. An example of the property is as follows: pH: 8, Na
ions: 20 mg/L, K ions: 5 mg/L, Ca ions: 50 mg/L, Mg ions: 15
mg/L, HC03 ions: 200 mg/L, Cl ions: 200 mg/L, so, ions: 120
5 mg/L, P04 ions: 5 mg/L, Si02 ions: 35 mg/L. Among these, the
concentrations of Ca ions, Mg ions, so, ions, and HC03 ions
are high, and as a result of their reaction, scales (Caso,,
CaC03, etc.) are formed. In addition, depending on the
concentration percentage, silica components present in waste
10 water also serve as scale components adhering to the
instrument, etc. When scales are produced in the device that
performs a demineralization treatment, the treatment
capacity is reduced. Therefore, it is required to perform a
demineralization treatment without allowing for the
15 production of scales.
Here, examples of plants using a water-cooling-type
cooling tower are plants equipped with power generation
facilities (power generation facilities include those for
business purposes for electric power selling and those for
20 industrial purposes for in-house electricity use, and the
power generation is thermal power generation, geothermal
power generation, etc.), plants equipped with power
generation facilities and cooling facilities, etc. In
addition, plants include ordinary chemical plants, steel
25 plants, mining plants, oil field plants, gas field plants,
mechanical plants, etc.
As a process for removing Ca ions, a lime soda process
is known. According to the lime soda process, sodium
carbonate is added to water to be treated, and Ca ions in
30 the water to be treated are deposited/precipitated as
calcium carbonate and thereby removed from the water.
Patent Literature 1 discloses a waste water treatment
3
device including a combination of a chemical softening
device, an ion-exchange equipment, a reverse osmosis
membrane device, and the like using the lime soda process.
Citation List
5 Patent Literature
PTL 1 U.S. Pat. No. 7815804
Summary of Invention
Technical Problem
The lime soda process requires the addition of sodium
10 carbonate for the treatment, and thus the treatment cost is
high. In the lime soda process, when 1 mol of Ca ions are
precipitated as calcium carbonate, 2 mol of Na+ is produced.
Meanwhile, in the case where so,2 - is contained in water to
be treated, it is not removed by the lime soda process. That
15 is, in the lime soda process, water after the treatment
contains an increased number of moles of ions.
Also in the case where Ca ions are removed using an
ion-exchange equipment, the treatment of 1 mol of Ca ions
results in the production of 2 mol of Na+, and water the
20 after treatment contains an increased number of moles of
ions.
According to the system of Patent Literature 1, water
that has been treated by the lime soda process and in an
ion-exchange equipment is further treated in a reverse
25 osmosis membrane device to remove ion components.
30
Accordingly, the system of Patent Literature 1 has a problem
in that because of the increased number of moles of ions,
the osmotic pressure in the reverse osmosis membrane device
is high, resulting in an increased treatment load. In
addition, with the device of Patent Literature
not removed but remains in the treated water,
been difficult to obtain high water recovery.
4
1, so, 2 - is
and it has
In addition, the waste water treatment device of Patent
Literature 1 requires a large amount of chemicals for the
reproduction of the ion-exchange equipment, and thus there
has also been the problem of high treatment cost.
5 An object of the present invention is to provide a
water treatment process and a water treatment system, which
are capable of reproducing water containing salts with high
water recovery.
10 Solution to Problem
A first aspect of the present invention is a water
treatment process including:
a second scale inhibitor supplying step of supplying a
calcium scale inhibitor which is a scale inhibitor for
15 inhibiting the deposition of a scale containing calcium and
a silica scale inhibitor which is a scale inhibitor for
inhibiting the deposition of silica to water to be treated
containing Ca ions, S04 ions, carbonate ions and silica;
a second demineralizing step of separating the water to
20 be treated into second concentrated water in which the Ca
ions, the S04 ions, the carbonate ions and the silica are
concentrated and treated water after the second scale
inhibitor supplying step; and
a second crystallizing step of supplying seed crystals
25 of gypsum to the second concentrated water so that gypsum is
crystallized from the second concentrated water,
wherein the water treatment process further comprises,
after the second crystallizing step:
a first scale inhibitor supplying step of supplying the
30 calcium scale inhibitor to the water to be treated;
a first pH adjusting step of adjusting the water to be
treated to a pH at which the silica is soluble in the water
5
5
to be treated;
a first demineralizing step of separating the water to
be treated into first concentrated water in which the Ca
ions, the S04 ions, the carbonate ions and the silica are
concentrated and treated water
inhibitor supplying step and the
and
after the first scale
first pH adjusting step;
a first crystallizing step of supplying seed crystals
of gypsum to the first concentrated water so that gypsum is
10 crystallized from the first concentrated water.
15
A second aspect of the present invention is a water
treatment system including:
a second scale
supplies a calcium
inhibitor supplying
scale inhibitor which
inhibitor for inhibiting the deposition
section
is a
of a
that
scale
scale
containing calcium and a silica scale inhibitor which is a
scale inhibitor for inhibiting the deposition of silica to
water to be treated containing Ca ions, so, ions, carbonate
ions and silica;
20 a second demineralizing section that is positioned on a
downstream side of the second scale inhibitor supplying
section and separates the water to be treated into second
concentrated water in which the Ca ions, the so, ions, the
carbonate ions and the silica are concentrated and treated
25 water; and
a second crystallizing section including a second
crystallizing tank that is positioned on a downstream side
of the second demineralizing section and crystallizes gypsum
from the second concentrated water and a second seed crystal
30 supplying section that supplies seed crystals of gypsum to
the second crystallizing tank,
wherein the water treatment system comprises, on a
6
downstream side of the second crystallizing section with
respect to the water to be treated:
a first scale inhibitor supplying section that supplies
the calcium scale inhibitor to the water to be treated;
5 a first pH adjusting section that supplies a pH
adjuster to the water to be treated to adjust the pH of the
water to be treated to such a value that the silica is
soluble in the water to be treated;
a first demineralizing section that is positioned on a
10 downstream side of the first scale inhibitor supplying
section and the first pH adjusting section and separates the
water to be treated into first concentrated water in which
the Ca ions, the S04 ions, the carbonate ions and the silica
are concentrated and treated water; and
15 a first crystallizing section including a first
crystallizing tank that is positioned on a downstream side
of the first demineralizing section and crystallizes gypsum
from the first concentrated water and a first seed crystal
supplying section that supplies seed crystals of gypsum to
20 the first crystallizing tank.
In the first aspect and the second aspect, owing to the
effects of the calcium scale inhibitor and the silica scale
inhibitor supplied in the second scale inhibitor supplying
step and the second scale inhibitor supplying section, the
25 production of scales in the second demineralizing section
and the second demineralizing step can be inhibited. In
addition, by adding seed crystals of gypsum to the second
concentrated water in the second crystallizing section and
the second crystallizing step, even when a scale inhibitor
30 is present, gypsum can be crystallized and separated from
the water to be treated. As a result, the water to be
treated containing Ca ions, so, ions, and silica can be
7
treated with high water recovery, and the operation cost can
be reduced. Further, this is also advantageous in that highpurity
gypsum can be recovered.
According to the first aspect and the second aspect, in
5 the first scale inhibitor supplying step, the first scale
inhibitor supplying section, the first pH adjusting step,
and the first pH adjusting section, a calcium scale
inhibitor is added, and also the water to be treated is
adjusted to a pH at which silica is soluble, followed by a
10 water treatment. Accordingly, the production of scales in
the first demineralizing section and the first
demineralizing step can be inhibited. In addition, by adding
seed crystals of gypsum to the first concentrated water in
the first crystallizing section and the first crystallizing
15 step, even when a scale inhibitor is present, gypsum can be
crystallized and separated from the water to be treated. As
a result, while inhibiting the production of scales, the
water to be treated containing Ca ions, S04 ions, carbonate
ions, and silica can be treated with high water recovery. In
20 addition, the amount of chemicals required for the treatment
and the power required for the operation can be reduced, and
also maintenance is facilitated. Accordingly, the operation
cost can be reduced.
In the above aspect, the water treatment process
25 includes a downstream side demineralizing step of separating
the first concentrated water after the first crystallizing
step on the most downstream of the water to be treated into
concentrated water and treated water, and recovering the
separated treated water.
30 In the above aspect, the water treatment system
includes, on the downstream side of the first crystallizing
section on the most downstream of the water to be treated, a
8
5
downstream side demineralizing section
first concentrated water discharged
crystallizing section into concentrated
water.
that separates the
from the first
water and treated
When the downstream side demineralizing step and the
downstream side demineralizing section
water recovery can be further improved.
invention, the number of moles of ions
are provided, the
In addition, in the
in the water to be
treated is significantly reduced. Accordingly, the amount of
10 salts flowing into the downstream side demineralizing
section can be reduced, and thus the power of the downstream
side demineralizing section can be reduced.
In the above aspect, it is preferable that the water
treatment process includes a second pH adjusting step of
15 adjusting the second concentrated water to a pH at which a
scale inhibition function of the calcium scale inhibitor is
reduced, thereby promoting the deposition of the gypsum in
the second crystallizing step.
In the above aspect, it is preferable that the water
20 treatment system includes a second pH adjusting section that
is installed on the downstream side of the second
demineralizing section and supplies
second concentrated water to adjust
a pH adjuster to the
the pH of the second
concentrated water to such a value that a scale inhibition
25 function of the calcium scale inhibitor is reduced, and the
deposition of the gypsum is promoted.
In this case, it is preferable that after the second
crystallizing step,
adjustment of the
the second concentrated water after the
pH in the second pH adjusting step is
30 adjusted to a pH at which the calcium scale inhibitor exerts
its function.
It is also preferable that the water treatment system
9
includes, on the downstream side of the second crystallizing
section, a third pH adjusting section that supplies a pH
adjuster to the second concentrated water after the
adjustment of the pH in the second pH adjusting section to
5 adjust the pH of the second concentrated water to such a
value that the calcium scale inhibitor exerts its function.
Alternatively, in the above aspect, the water treatment
process may include a second pH adjusting step of adjusting
the second concentrated water to a pH at which the silica is
10 soluble in the second crystallizing step. In the above
aspect, it is preferable that the water treatment system
includes a second pH adjusting section that is installed on
the downstream side of the second demineralizing section and
supplies a pH adjuster to the second concentrated water to
15 adjust the pH of the second concentrated water to such a
value that the silica is soluble in the second concentrated
water in the second crystallizing section.
As a result of this configuration, the formation of
scales containing calcium in the downstream side
20 demineralizing section can be suppressed.
In the first aspect, it is preferable that the water
treatment process includes a second upstream side
precipitating step of precipitating at least calcium
carbonate from the water to be treated so that the
25 concentration of the calcium carbonate in the water to be
treated is reduced, before the second scale inhibitor
supplying step on the most upstream side of the water to be
treated. In this case, it is preferable that the water
treatment process includes a second deaerating step of
30 removing C02 from the water to be treated before the second
upstream side precipitating step or after the second
upstream side precipitating step and before the second scale
10
inhibitor supplying step.
In the second aspect, it is preferable that the water
treatment system includes, on the upstream side of the
second scale inhibitor supplying section located on the most
5 upstream of the water to be treated, a second upstream side
precipitating section that precipitates at least calcium
carbonate from the water to be treated so that the
concentration of the calcium carbonate in the water to be
treated is reduced. In this case, it is preferable that the
10 water treatment system includes a second deaerating section
that removes C02 from the water to be treated on the upstream
side of the second upstream side precipitating section or on
the downstream side of the second upstream side
precipitating section and on the upstream side of the second
15 scale inhibitor supplying section.
In this way, by previously
from the water to be treated
removing calcium carbonate
before flowing into the
demineralizing section, the deposition of calcium carbonate
as scales during the water treatment can be inhibited. By
20 removing calcium carbonate, the purity of gypsum
crystallized in the crystallizing step and the crystallizing
section can be increased.
In the above aspect, it is preferable that the water to
be treated contains metal ions, and the water treatment
25 process includes a first precipitating step of precipitating
at least one of calcium carbonate and a metal compound so
that the concentration of at least one of the calcium
carbonate and the metal ions is reduced from the first
concentrated water, after the first crystallizing step. It
30 is preferable that the water treatment process includes a
second precipitating step of precipitating at least one of
calcium carbonate and a metal compound so that the
11
concentration of at least one of the calcium carbonate and
the metal ions is reduced from the second concentrated
water, after the second crystallizing step.
In this case, at least one of seed crystals of the
5 silica and a precipitant for the silica is supplied to the
first concentrated water in the first precipitating step. In
the second precipitating step, at least one of seed crystals
of the silica and a precipitant for the silica is supplied
to the second concentrated water.
10 In the above aspect, it is preferable that the water to
be treated contains metal ions, and the water treatment
system includes, on
crystallizing section,
the downstream side of the first
a first precipitating section that
precipitates at least one of calcium carbonate and a metal
15 compound so that the concentration of at least one of the
calcium carbonate and the metal ions in the first
concentrated water is reduced. It is preferable that the
water treatment system includes, on the downstream side of
the second crystallizing section, a second precipitating
20 section that precipitates least one of calcium carbonate and
a metal compound so that the concentration of at least one
of the calcium carbonate and the metal ions in the second
concentrated water is reduced.
In this case, at least one of seed crystals of the
25 silica and a precipitant for the silica is supplied to the
first precipitating section. At least one of seed crystals
of the silica and a precipitant for the silica is supplied
to the second precipitating section.
By removing calcium carbonate and a metal compound from
30 the water to be treated in the precipitating section and the
precipitating step provided after the crystallizing section
and the crystallizing step, high water recovery can be
12
,,
5
10
15
obtained.
The dissolution state of silica changes depending on
the pH of the water to be treated, but silica tends not to
be deposited only by changing the pH. Thus, seed crystals of
silica are added in the precipitating section and the
precipitating step to promote the deposition of silica,
whereby the silica removal efficiency can be improved. As a
result, the water recovery can be further improved, and the
operation power can be further lowered.
In the water treatment process of the above aspect, it
is preferable that when the water to be treated contains Mg
ions, the amount of the precipitant for silica to be
supplied is adjusted according to the concentration of the
Mg ions.
In the above aspect, it is preferable that when the
water to be treated contains Mg ions, the amount of the
precipitant for silica to be supplied
to the concentration of the Mg
is adjusted according
ions in the first
precipitating section. It is preferable that when the water
20 to be treated contains Mg ions, the amount of the
precipitant for silica to be supplied is adjusted according
to the concentration of the Mg ions in the second
precipitating section.
In the above aspect, it is preferable that when the
25 water to be treated contains Mg ions, the first concentrated
water in the first precipitating step is adjusted to a pH at
which a magnesium compound is deposited so that the
concentration of the Mg ions is reduced, and after the first
precipitating step, the first concentrated water is adjusted
30 to a pH at which the magnesium compound is soluble. It is
preferable that the second concentrated water in the second
precipitating step is adjusted to a pH at which a magnesium
13
compound is deposited so that the concentration of the Mg
ions is reduced, and after the second precipitating step,
the second concentrated water is adjusted to a pH at which
the magnesium compound is soluble.
5 In the above aspect, it is preferable that when the
water to be treated contains Mg ions, the first concentrated
water in the first precipitating section is adjusted to a pH
at which a magnesium compound is deposited so that the
concentration of the Mg ions is reduced, and, on the
10 downstream side of the first precipitating section, the
first concentrated water is adjusted to a pH at which the
magnesium compound is soluble. It is preferable that when
the water to be treated contains Mg ions, the second
concentrated water in the second precipitating section is
15 adjusted to a pH at which a magnesium compound is deposited
so that the concentration of the Mg ions is reduced, and, on
the downstream side of the second precipitating section, the
second concentrated water is adjusted to a pH at which the
magnesium compound is soluble.
20 In the case where Mg ions are contained in the water to
be treated, Mg ions react with silica
water in the precipitating step and
section, resulting in
invention, the amount
precipitation.
of precipitant
in the
the
In
to be
concentrated
precipitating
the present
supplied is
25 adjusted according to the balance between Mg ions and silica
in the concentrated water, whereby the precipitant is
efficiently supplied. In the case where the concentration of
Mg ions in high relative to silica, the pH of the
concentrated water is adjusted so that a magnesium compound
30 is deposited in the precipitating step and the precipitating
section. Subsequently, the concentrated water is adjusted to
a pH at which the magnesium compound is soluble, thereby
14
suppressing the formation of scales in the demineralizing
section located on the downstream side of the precipitating
section.
In the above aspect, it is preferable that when the
5 water to be treated contains Mg ions, the water to be
treated in the second upstream side precipitating step is
adjusted to a pH at which a magnesium compound is deposited
so that the concentration of the Mg ions is reduced, and,
after the second upstream side precipitating step, the water
10 to be treated is adjusted to a pH at which the magnesium
compound is soluble.
In the above aspect, it is preferable that the water to
be treated in the second upstream side precipitating section
is adjusted to a pH at which a magnesium compound is
15 deposited so that the concentration of the Mg ions is
reduced, and, on the downstream side of the second upstream
side precipitating section, the water to be treated is
adjusted to a pH at which the magnesium compound is soluble.
In this way, in the case where Mg ions are contained in
20 the water to be treated, by efficiently removing Mg ions
before a demineralization treatment, the formation of scales
containing magnesium in the course of water treatment can be
inhibited.
In the above aspect, it is preferable that moisture is
25 evaporated from the concentrated water in the downstream
30
side demineralizing step, so that a solid in the
concentrated water is recovered.
In the above aspect, it is preferable that moisture is
evaporated from the concentrated water in the downstream
side demineralizing step, so that a solid in the
concentrated water is recovered. It is preferable that the
water treatment system includes, on the downstream side of
15
the concentrated water of the downstream side demineralizing
section, an evaporator that evaporates moisture from the
concentrated water to recover a solid in the concentrated
water.
5 According to the water treatment process and the water
treatment system thus configured, when solid matters
produced in the course of water treatment are discharged out
of the system as waste, the volume of waste can be reduced.
10 Advantageous Effects of Invention
According to the water treatment system and the water
treatment process of the present invention, while inhibiting
the production of scales such as calcium carbonate and
silica during the treatment, Ca2+ and S042 - can be removed as
15 gypsum from the water to be treated. Accordingly, the water
recovery can be further improved.
Also in the case where magnesium ions are contained in
the water to be treated, when the water treatment system or
the water treatment process of the present invention is
20 used, they can be removed from the water to be treated while
inhibiting the production of scales containing magnesium
during the treatment.
Water treated
significantly reduced
by the
number
present
of moles
invention
of ions
has
on
a
the
25 downstream side. Therefore, the power of the demineralizing
section located downstream can be significantly reduced.
Further, the present invention is also advantageous in
that high-purity gypsum can be crystallized and recovered.
Brief Description of Drawings
30 Fig. 1 is a schematic diagram of a water treatment
system according to the first reference embodiment.
Fig. 2 shows simulation results for the pH dependency
16
of the amount of gypsum deposited.
Fig. 3 shows simulation results for the pH dependency
of the amount of calcium carbonate deposited.
Fig. 4 is a graph showing the pH dependency of the
5 amount of silica dissolved.
10
Fig. 5 shows the results of gypsum deposition
experiments performed using simulated water in which gypsum
is supersaturated with changing the pH of the simulated
water.
Fig. 6 shows the results of gypsum deposition
experiments performed using simulated water in which gypsum
is supersaturated with changing the concentration of seed
crystals.
Fig. 7 is a microphotograph of gypsum crystallized
15 under Condition 5.
20
25
30
Fig. 8 is a microphotograph of gypsum crystallized
under Condition 3.
Fig. 9 is a schematic diagram of a water treatment
system according to the second reference embodiment.
Fig. 10 is a schematic diagram of a water treatment
system according to the third reference embodiment.
Fig. 11 is a schematic diagram of a water treatment
system according to the fourth reference embodiment.
Fig. 12 is a schematic diagram of a water treatment
system according to the first embodiment.
Fig. 13 is a schematic diagram explaining a water
treatment system according to the fifth reference
embodiment.
Fig. 14 is a schematic diagram explaining a water
treatment system according to the sixth reference
embodiment.
Fig. 15 is a schematic diagram explaining a water
17
5
10
15
treatment system according to the seventh reference
embodiment.
Fig. 16 is a schematic diagram explaining a water
treatment system according to the eighth reference
embodiment.
Description of Embodiments
Water that is an object to be treated in the present
invention (water to be treated) contains Ca2+ r
carbonate ions, and silica. Specifically, the water to be
treated (raw water) is saline water, sewage, industrial
waste water, blowdown water from a cooling tower, or the
like. The water to be treated may also contain metal ions,
such as Mg ions.
First Reference Embodiment
Fig. 1 is a schematic diagram of a water treatment
system according to the first reference embodiment of the
present invention. The water treatment system 1 of Fig. 1 is
20 configured such that two water treatment sections are
connected in the flow direction of the water to be treated.
In the water treatment system 1 of this reference
embodiment, depending on the properties of the water to be
treated, the number of water treatment sections may be one,
25 and it is also possible that three or more water treatment
sections are connected.
Each
upstream
water
side
demineralizing
treatment section includes,
of the water to be treated,
section 10 (lOa, lOb) and
from
a
a
the
first
first
30 crystallizing section 20 (20a, 20b). The concentration sides
of the first demineralizing sections lOa and lOb are
connected to the first crystallizing sections 20a and 20b,
18
respectively. The water treatment section includes a first
scale inhibitor supplying section 30 (30a, 30b) and a first
pH adjusting section 4 0 ( 4 Oa, 4 Ob) in the flow path on the
upstream side of each first demineralizing section 10 (lOa,
5 lOb).
The first scale inhibitor supplying section 30 (30a,
30b) is made up of a tank 31 (31a, 31b), a valve Vl (Vla,
Vlb), and a control section 32 (32a, 32b). The control
sections 32a and 32b are connected to the valves Vla and
10 Vlb, respectively. The tanks 3la and 3lb have stored therein
a scale inhibitor.
The scale inhibitor used in this reference embodiment
serves to inhibit the deposition of scales containing
calcium in the water to be treated. It will be hereinafter
15 referred to as "calcium scale inhibitor".
The calcium scale inhibitor suppresses the crystal
nucleation of gypsum or calcium carbonate in the water to be
treated. At the same time, the calcium scale inhibitor
adheres to the surface of crystal nucleus of gypsum or
20 calcium carbonate contained in the water to be treated (seed
crystals, small-diameter scales deposited due to the
exceeding of the saturation concentration, etc.), and
functions to suppress the crystal growth of gypsum or
calcium carbonate. Alternatively, there is another type of
25 calcium scale inhibitor, which has the function of
dispersing particles in the water to be treated (inhibiting
aggregation), such as deposited crystals.
Examples of calcium scale inhibitors include
phosphonic-acid-based scale inhibitors, polycarboxylic-acid-
30 based scale inhibitors, and mixtures thereof. A specific
example is FLOCON260 (trade name, manufactured by BWA).
In the case where Mg ions are contained in the water to
19
be treated, a scale inhibitor that inhibits the deposition
of scales containing magnesium (e.g., magnesium hydroxide)
in the water to be treated can be used. It will be
hereinafter referred to as "magnesium scale inhibitor".
5 Examples of magnesium scale inhibitors include
polycarboxylic-acid-based scale inhibitors, etc. A specific
example is FLOCON 295N (trade name, manufactured by BWA).
Although Fig. 1 shows only one first scale inhibitor
supplying section 30a/30b in each position, in the case
10 where two or more kinds of scale inhibitors are loaded, it
is preferable that two or more first scale inhibitor
supplying sections are installed. In this case, the scale
inhibitors are sorted according to kind and stored in the
respective tanks.
15 The first pH adjusting section 40 (40a, 40b) is made up
20
of a tank 41 (4la, 4lb), a valve V2 (V2a, V2b), a control
section 42 (42a, 42b), and a pH meter 43 (43a, 43b). The
tanks 4la and 4lb have stored therein an alkali as a pH
adjuster. The alkali is calcium hydroxide or sodium
hydroxide,
preferable
for example. Calcium hydroxide
because Ca ions are recovered as
is particularly
gypsum in the
below-mentioned crystallizing step, and thus the amount of
ions that reach the demineralizing section on the downstream
side is reduced. The control sections 42a and 42b are
25 connected to the valves V2a and V2b and the pH meters 43a
and 43b, respectively.
In Fig. 1, the first demineralizing sections lOa and
lOb are reverse osmosis membrane devices. In addition, the
first demineralizing sections lOa and lOb may also be
30 electrodialyzers (ED), electro dialysis reversal devices
(EDR), electro de-ionization devices (EDI), ion-exchange
equipments (IEx), capacitive de-ionization devices (CDI),
20
nanofilters (NF), evaporators, etc.
Here, in a nanofilter (NF), an electrodialyzer (ED), an
electro dialysis reversal device (EDR) , an electro deionization
device (EDI), and a capacitive de-ionization
5 device (CDI), scale components (divalent ions, Ca2+, Mg2+,
etc.) are selectively removed, while monovalent ions such as
Na+ and cl- permeate. The use of these demineralizers
suppresses an increase in the ion concentration of ions that
serve as scale components in concentrated water.
10 Accordingly,
energy saving
be achieved.
the water recovery can be improved,
(e.g., the reduction of pump power,
and also
etc.) can
In addition, in the case where the water to be treated
is blowdown water from a cooling tower, the reclaimed water
15 does not have to be pure water, and what is necessary is
that scale components (divalent ions, Ca2+, Mg2+, etc.) are
removed. Accordingly, it is advantageous to use a nanofilter
(NF), etc.
Although only one first demineralizing section lOa/lOb
20 is shown in Fig. 1, the system may also be configured such
that two or more demineralizers are connected in parallel or
in series in the flow direction of the water to be treated.
The first crystallizing section 20 (20a, 20b) is made
up of a first crystallizing tank 21 (2la, 2lb) and a first
25 seed crystal supplying section 22 (22a, 22b) . The first seed
crystal supplying sections 22a and 22b are connected to the
first crystallizing tanks 2la and 2lb, respectively. The
first seed crystal supplying sections 22a and 22b have a
seed crystal tank 23 (23a, 23b), a valve V3 (V3a, V3b), and
30 a control section 24 (24a, 24b).
and 24b are
respectively.
connected to the
The seed crystal
21
The control sections 24a
valves V3a and V3b,
tanks 23a and 23b store
gypsum particles as seed crystals.
In the water treatment system 1 of Fig. 1, a first
precipitating section 50 (50a, SOb) may be installed on the
downstream side of each of the first crystallizing sections
5 20a and 20b. The first precipitating sections 50a and SOb
each include a first precipitating tank 51 (51a, 5lb) and a
first filtration device 52 (52a, 52b).
The water treatment system 1 includes a downstream side
demineralizing section 60 on the downstream side of the
10 water to be treated of the first crystallizing section 20b
located on the most downstream.
In Fig. 1, the downstream side demineralizing section
60 is a reverse osmosis membrane device. The downstream side
demineralizing section 60 may also be an electrodialyzer
15 (ED), an electro dialysis reversal device (EDR), an electro
de-ionization device (EDI), an ion-exchange equipment, a
capacitive de-ionization device (CDI), a nanofilter (NF), an
evaporator, etc.
In the water treatment system 1, a precipitating tank
20 71 and a filtration device 72 are installed as a first
upstream side precipitating section 70 on the upstream side
of the first scale inhibitor supplying section 30a and the
first pH adjusting section 40a which are located on the most
upstream of the water to be treated. The precipitating tank
25 71 and the filtration device 72 have the same configuration
as the first precipitating tank 51 and the first filtration
device 52 of the first precipitating section 50.
In particular, in the case where Mg ions are contained
in the water to be treated, the first upstream side
30 precipitating section can be configured such that two or
more precipitating tanks 71 are connected in series in the
flow direction of the water to be treated.
22
..
In the water treatment system 1 shown in Fig. 1, a
first deaerating section 73 may be provided on the upstream
side of the first upstream side precipitating section 70.
Specifically, the first deaerating section 73 is a
5 deaeration tower equipped with a filler for removing carbon
dioxide or is a separation membrane. On the upstream side of
the water to be treated of the first deaerating section 73,
a pH adjusting section (not shown) that adjusts the water to
be treated to a pH at which carbonate ions are present in
10 the form of C02 may be installed.
The first deaerating section 73 may also be installed
on the downstream side of the water to be treated of the
first upstream side precipitating section 70 and on the
upstream side of the first scale inhibitor supplying section
15 30a and the first pH adjusting section 40a.
It is also possible that a deaerating section having
the same configuration as the first deaerating section 73 is
installed in the flow path between the first demineralizing
section 10 and the first crystallizing section 20, in the
20 flow path between the first crystallizing section 20 and the
first precipitating section 50, and on the downstream side
of the first precipitating section 50 and in the flow path
between it and the first demineralizing section lOb or the
downstream side demineralizing section 60.
25 In the case where the concentration of Ca ions in the
water to be treated is high, an ion-exchange equipment (not
shown) may be installed on the downstream of the filtration
device 72 and on the upstream of the first scale inhibitor
supplying section 30a and the first pH adjusting section 40a
30 which are located on the most upstream. The ion-exchange
equipment may be an ion-exchange resin column or an ionexchange
membrane device, for example.
23
When gypsum in the water to be treated flowing into the
first demineralizing section lOa is already supersaturated,
because ions are further concentrated in the first
demineralizing section lOa, the resulting gypsum
5 concentration is even higher. In this case, the loading of a
large amount of calcium scale inhibitor is required.
Further, the concentration of gypsum may become too high for
the calcium scale inhibitor to exert its effect, resulting
in the production of scales in the first demineralizing
10 section lOa.
Thus, in the case where gypsum
to be treated) is supersaturated,
upstream side crystallizing section
in the raw water (water
it is possible that an
(not shown) having the
same configuration as the first crystallizing tanks 2la and
15 2lb are provided on the upstream of the first scale
inhibitor supplying section 30a and the first pH adjusting
section 40a on the most upstream, so that the concentration
of gypsum is reduced, and then the water to be treated is
fed to the first demineralizing section lOa.
20 A process for treating water to be treated using the
water treatment system 1 of the first reference embodiment
will be described hereinafter.
First, the deposition behaviors of gypsum, silica, and
calcium carbonate in water will be explained. Fig. 2 shows
25 simulation results for the pH dependency of the amount of
gypsum deposited. Fig. 3 shows simulation results for the pH
dependency of the amount of calcium carbonate deposited. In
the figures, the abscissa is pH, and the ordinate is the
amount of gypsum or calcium carbonate deposited (mol). Using
30 a simulation software manufactured by OLI, the simulation
was performed under the conditions where 0. 1 mol/L of each
solid component was mixed with water, and H2S04 and Ca (OH) 2
24
5
10
15
were added as an acid and an alkali, respectively.
Fig. 4 is a graph showing the pH dependency of the
amount of silica dissolved (source: Fig. 4 of u.s. Pat. No.
7815804). In the figure, the abscissa is pH, and the
ordinate is the amount of silica dissolved (mg/L).
From Fig. 2' it can be understood that gypsum
deposition has no pH dependency, and deposition is possible
over the entire pH range. However, when a calcium scale
inhibitor is added, in a high-pH region, gypsum is present
in the state of being dissolved in water. From Fig. 3,
calcium carbonate is deposited when the pH is more than 5.
From Fig. 4, silica tends to dissolve in water when the pH
is 10 or more.

In the case where the water to be treated is industrial
waste water, etc., before the water to be treated flows into
the first upstream side precipitating section 70, a step of
removing oils, floating particles, and the like from the
water to be treated and a step of removing organic
20 substances by a biological treatment or a chemical oxidation
treatment are performed.

In the water treatment system 1 of Fig. 1, the water to
be treated before flowing into the first deaerating section
25 73 is adjusted to a low pH. Carbonic acid in the water to be
treated is in the following equilibrium depending on the pH
of the water to be treated.
Chemical Formula 1
C02 t H2C03 t HCO} + H+ t CO~-+ 2H+ . . . ( 1 )
30
25
In the case where the pH is as low as 6. 5 or less, it
is mainly present as HC03- and C02 in the water to be
treated.
The water to be treated containing C02 flows into the
5 first deaerating section 7 3. C02 is removed from the water
to be treated in the first deaerating section 73. When the
water to be treated has been previously adjusted to a pH at
which carbonate ions are present as C02, carbon dioxide can
be efficiently removed.
10 The water to be treated, whose carbonate ion
concentration has been reduced in the first deaerating step,
is fed to the first upstream side precipitating section 70.

In the first upstream side precipitating section 70,
15 some of Ca ions and carbonate ions are previously removed
from the water to be treated as calcium carbonate.
In the case where metal ions other than Ca ions are
contained in the water to be treated, in the first upstream
side precipitating section 70, some of the metal ions are
20 previously removed from the water to be treated as a metal
compound having low solubility in water. This metal compound
is mainly a metal hydroxide, but may also include a
carbonate.
In the precipitating tank 71, Ca(OH) 2 and an anionic
25 polymer (manufactured by Mitsubishi Heavy Industries
Mechatronics Systems, Ltd. , trade name: Hishifloc H30 5) are
loaded to the water to be treated, and the pH in the
precipitating tank 71 is controlled to 4 or more and 12 or
less, and preferably 8.5 or more and 12 or less.
30 As shown in Fig. 3, the solubility of calcium carbonate
is low in this pH range. When calcium carbonate is
supersaturated, calcium carbonate is deposited and
26
precipitated at the bottom of the precipitating tank 71.
The solubility of a metal compound depends on pH. A
more acidic pH leads to a higher solubility of metal ions in
water. For many metal compounds, the solubility is low in
5 the above pH range. In the above pH range, a metal compound
having low solubility in water aggregates in the
precipitating tank 71, resulting in precipitation at the
bottom of the precipitating tank 71.
The precipitated calcium carbonate and metal compound
10 are discharged from the bottom of the precipitating tank 71.
Mg ions form salts that are poorly soluble in water,
and thus are components that tend to be deposited as scales.
Mg(OH)z is deposited at pH 10 or more.
In the case where the water to be treated containing Mg
15 ions is treated by the water treatment system 1 of this
reference embodiment, the pH of the water to be treated in
the precipitating tank 71 is adjusted to a pH at which a
magnesium
deposited.
compound (mainly magnesium hydroxide) is
Specifically, the pH of the water to be treated
20 is adjusted to 10 or more, preferably 10.5 or more, and more
preferably 11 or more. Accordingly, a magnesium compound is
deposited from the water to be treated, precipitated at the
bottom of the precipitating tank 71, and removed. As a
result, some of Mg ions in the water to be treated are
25 removed, resulting in a decrease in the concentration of Mg
ions in the water to be treated.
be
In the above case,
treated after being
it is preferable that the water to
discharged from the first upstream
side precipitating section 70 is adjusted to a pH at which
30 the above magnesium compound is soluble. Specifically, the
pH is adjusted to less than 10. Accordingly, the formation
of scales in devices and steps on the downstream side,
27
particularly the first demineralizing section lOa and the
first demineralizing step, can be inhibited.
In the case where two or more stages of precipitating
tanks 71 are provided, Mg ions in the water to be treated
5 can be reliably removed, and the concentration of Mg ions in
the water to be treated fed to the downstream side can be
reduced.
10
The supernatant
the water to be
precipitating tank
in the precipitating tank 71, which is
treated, is discharged
71. FeCb is added to the
from the
discharged
water to be treated, and solids in the supernatant, such as
calcium carbonate and a metal compound, aggregate with
Fe(OH)3.
The water to be treated is fed to the filtration device
15 72. The solids aggregated with Fe(OH)3 are removed through
the filtration device 72.
In the case where the first deaerating step is
performed after the first upstream side precipitating step,
the pH of the water to be treated is adjusted to a pH at
20 which carbonate ions can be present as C02, specifically 6. 5
or less.
25
30
Incidentally, depending on the properties of the water
to be treated, the first deaerating step and the first
upstream side precipitating step may be omitted.
In the case where an ion-exchange equipment is
installed, Ca ions in the water to be treated are removed by
the ion-exchange equipment. In the case where Mg ions are
contained in the water to be treated, the Mg ions are also
removed by the ion-exchange equipment.
In the case where gypsum in the raw water is
supersaturated, seed crystals of gypsum are loaded to the
water to be treated in the upstream side crystallizing
28
section installed immediately after the filtration device
72, and gypsum is crystallized, thereby reducing the
concentration of gypsum in the water to be treated. The
water to be treated having a reduced concentration of gypsum
5 is fed to the first demineralizing section lOa.

The control section 32a of the first scale inhibitor
supplying section 30a opens the valve Vla and supplies a
predetermined amount of calcium scale inhibitor to the water
10 to be treated from the tank 3la. The control section 32a
adjusts the opening of the valve Vla so that the
concentration of the calcium scale inhibitor is a
predetermined value set according to the properties of the
water to be treated.
15 In the case where Mg ions are contained in the water to
be treated, a magnesium scale inhibitor is supplied to the
water to be treated in the first scale inhibitor supplying
step in the same manner as above. In this case, the calcium
scale inhibitor and the magnesium scale inhibitor are stored
20 in the tank of each of two or more first scale inhibitor
supplying sections, and each control section adjusts the
amounts of calcium scale inhibitor and magnesium scale
inhibitor to be supplied.

25 The control section 42a of the first pH adjusting
section 40a controls the pH of the water to be treated at
the entrance of the first demineralizing section lOa to such
a value that silica is soluble in the water to be treated.
Specifically, the pH of the water to be treated fed to the
30 first demineralizing section lOa is adjusted to 10 or more,
preferably 10.5 or more, and more preferably 11 or more.
The pH meter 43a measures the pH of the water to be
29
treated at the entrance of the first demineralizing section
lOa. The control section 4 2a adjusts the opening of the
valve V2a so that the value measured by the pH meter 43a is
a predetermined pH control value, and allows an alkali to be
5 loaded to the water to be treated from the tank 4la.

In the first demineralizing section lOa, the pHadjusted
water to be treated is treated. In the case where
the first demineralizing section lOa is a reverse osmosis
10 membrane device, the water that has passed through the
reverse osmotic membrane is recovered as treated water. Ions
and scale inhibitors contained in the water to be treated
cannot pass through the reverse osmosis membrane. Therefore,
on the non-permeate side of the reverse osmosis membrane,
15 there is concentrated water having a high concentration of
ions. Also in the case where other demineralizers, such as a
capacitive de- ionization device, are used, for example, the
water to be treated is separated into treated water and
concentrated water having a high concentration of ions
20 (first concentrated water).
As shown in Fig. 4, as a result of the first
demineralizing step,
concentrated water in
water to be treated.
silica is contained in the first
the state of being dissolved in the
Even in the case where gypsum and
25 calcium carbonate in the first concentrated water are
concentrated to the saturation concentration or higher, the
production of scales is suppressed by the calcium scale
inhibitor.
In the case where Mg ions are contained in the water to
30 be treated, the concentration of Mg ions contained in the
first concentrated water increases as a result of the first
demineralizing step. However, the production of scales
30
containing magnesium is suppressed by the magnesium scale
inhibitor.
The first concentrated water is fed toward the first
crystallizing section 20a.
5
The first concentrated water discharged from the first
demineralizing section lOa is stored in the first
crystallizing tank 21a of the first crystallizing section
20a. The control section 24a of the first seed crystal
10 supplying section 22a opens the valve V3a and adds seed
crystals of gypsum to the first concentrated water in the
first crystallizing tank 21a from the tank 23a.
The pH of the first concentrated water from the first
demineralizing section lOa is 10 or more. As mentioned
15 above, gypsum is in the state of being dissolved in water in
a high-pH region where a calcium scale inhibitor is present.
However, when seed crystals are sufficiently present, even
when a scale inhibitor is present, gypsum is crystallized
using the seed crystals as nuclei. In the water treatment
20 system 1 of Fig. 1, the crystal-grown gypsum having a large
diameter (e.g., having a particle diameter of 10 ~m or more,
more preferably 20 ~m or more) is precipitated at the bottom
of the first crystallizing tank 2la. The precipitated gypsum
is discharged from the bottom of the first crystallizing
25 tank 2la.
Meanwhile, when the pH 10 is or more, silica is present
in the state of being dissolved in the first concentrated
water in the first crystallizing tank 2la. Even in the case
where the concentration of silica in the first concentrated
30 water exceeds the saturation solubility, because seed
crystals
floating
of silica are not present,
matters in a colloidal
31
silica is deposited as
form or the like and
unlikely to be precipitated.
With reference to Fig. 3, calcium carbonate tends to be
deposited at pH 10 or more. However, because the calcium
scale inhibitor has been added, the deposition of calcium
5 carbonate is suppressed in the first crystallizing tank 21a.
In addition, in the case where the first upstream side
precipitating section or the first deaerating section is
provided, the concentration of calcium carbonate has been
previously reduced. As a result, in the first crystallizing
10 tank 2la, calcium carbonate is unlikely to be crystallized
using the seed crystals of gypsum as nuclei.
Incidentally, although gypsum is crystallized
independent of pH when seed crystals of gypsum are present,
the crystallization rate increases with a decrease in pH.
15 Fig. 5 shows the result of gypsum deposition
experiments with changing the pH of simulated water in the
case where a scale inhibitor ( FLOCON2 60) is added to
simulated water (containing Ca2+, S042-, Na+, and cl-) in which
gypsum is supersaturated. The experimental conditions are as
20 follows:
The degree of gypsum supersaturation in simulated water
(25°C): 460%,
The amount of scale inhibitor to be added: 2.1 mg/L,
pH: 6.5 (Condition 1), 5.5 (Condition 2), 4.0
25 (Condition3), 3.0 (Condition4),
30
The amount of seed crystals to be added: 0 g/L.
Two hours and 6 hours immediately after the pH
adjustment, the concentration of Ca in the simulated water
treated under each condition was measured using an atomic
absorption spectrometer (manufactured by Shimadzu
Corporation, AA-7000), and the degree of supersaturation was
calculated. The results are shown in Fig. 5. In the figure,
32
the ordinate is the degree of supersaturation (%).
With reference to Fig. 5, even under conditions where
seed crystals are absent, the crystallization rate increases
with a decrease in pH. From this, it can be understood that
5 in the case where seed crystals are present, gypsum is
crystallized even under Condition 1 (pH 6.5), and the
relation of the crystallization rate is such that the
crystallization rate increases with a decrease in pH as
shown in Fig. 5.
10 In the case where carbonate ions are contained in the
water to be treated, under low-pH conditions, carbonate ions
are removed from the water to be treated as C02 as in
chemical formula (1). In addition, as can be understood from
Fig. 3, in the case where the pH is low, calcium carbonate
15 is in a dissolved state.
From these results, when the first crystallizing step
is performed under low-pH conditions, because of the low
content of calcium carbonate and silica, high-purity gypsum
is crystallized and recovered from the bottom of the first
20 crystallizing tank 21a. In the case where the first
crystallizing step is performed at low pH, a third pH
adjusting section (not shown) that supplies an acid as a pH
adjuster is installed in the first crystallizing tank 21a or
in the flow path between the first demineralizing section
2 5 1 Oa and the first crystallizing tank 21a. The pH adjusting
section has the same configuration as the below-mentioned
second pH adjusting section.
Meanwhile, in order to change the pH in the course of
water treatment, it is necessary to supply a large amount of
30 chemicals (acid or alkali). The use of an acid or an alkali
leads to an increase in the amount of ions transferred to
the downstream side of the first crystallizing section 20a,
33
and this causes an increase in the power of demineralizing
sections on the downstream side (in Fig. 1, the first
demineralizing section lOb or the downstream side
demineralizing section 60). In terms of operation cost, it
5 is more advantageous that the pH is not changed between the
first demineralizing step and the first crystallizing step.
The gypsum crystallization rate depends on the loading
of seed crystals. Fig. 6 shows the results of gypsum
deposition experiments with changing the amount of seed
10 crystals to be added in the case where a calcium scale
inhibitor ( F10CON2 60) is added to simulated water. The
experimental conditions were the same as in Fig. 5 except
that the pH was 4. 0, and that gypsum (Caso,-2H20) was added
as seed crystals in the following amounts:
15
20
The amount of seed crystals to be
(Condition 3), 3 g/1 (Condition 5), 6 g/1
g/1 (Condition 7)
added: 0 g/1
(Condition 6), 3
Under Conditions 5
acid for pH adjustment
and 6, seed crystals and sulfuric
were added to the simulated water
having added thereto a scale inhibitor. Under Condition 7,
seed crystals pre-immersed in the above scale inhibitor were
added to the simulated water having added thereto a scale
inhibitor, and sulfuric acid was added for pH adjustment.
Two hours immediately after the pH adjustment, the
25 concentration of Ca in the simulated water treated under
each condition was measured by the same technique as in Fig.
5. In Fig. 6, the ordinate is the degree of supersaturation
(%) •
From the results of Fig. 6, it can be understood that
30 although the degree of supersaturation was 215% under
Condition 3 where seed crystals are not added, the degree of
supersaturation decreases to 199% (Condition 5) and 176%
34
5
(Condition 6) with an increase in the concentration of seed
crystals, leading to an increase in the gypsum deposition
rate. Also under high-pH conditions, similarly, the gypsum
deposition rate tends to increase with an increase in the
loading of seed crystals. Condition 5 and Condition 7 are
the same test conditions, except for whether the used seed
crystals are not immersed or immersed in a scale inhibitor.
Also under Condition 7 where seed crystals have a scale
inhibitor previously adhering thereto, the degree of
10 supersaturation is 199%, and it has been confirmed that
gypsum is deposited at the same level as under Condition 5.
That is, the results under Condition 5 and 7 show that
independent of the immersion time of seed crystals in a
calcium scale inhibitor, when the pH is reduced to 4.0, the
15 function of the scale inhibitor is reduced.
Figs. 7 and 8 each show a microphotograph of gypsum
resulting from crystallization. Fig. 7 shows results under
Condition 5 (seed crystals added), and Fig. 8 shows results
under Condition 3 (no seed crystals added). Under Condition
20 5, gypsum having a larger size was deposited than under
Condition 3. Generally, the water content decreases with an
increase in the size of deposited gypsum. A low water
content leads to high-purity gypsum. When the average
particle diameter is 10 flm or more, preferably 20 fJm or
25 more, the resulting gypsum has a sufficiently reduced water
content. The "average particle diameter" in the present
invention is a particle diameter measured by the method
specified in JIS Z 8825 (laser diffractometry).
30

The supernatant (first concentrated water) in the first
crystallizing section 20a is fed to the first precipitating
section 50a. In the first precipitating section 50a, Ca(OH) 2
35
and an anionic polymer (Hishifloc H305) are loaded to the
first concentrated water after the crystallizing step, and
the pH in the first precipitating tank 51a is controlled to
4 or more and 12 or less, and preferably 8.5 or more and 12
5 or less. In the first precipitating tank 51a, calcium
carbonate and a metal compound are precipitated and removed
from the first concentrated water. The precipitated calcium
carbonate and metal compound having low solubility in water
are discharged from the bottom of the first precipitating
10 tank 5la.
The water to be treated, which is the supernatant in
the first precipitating tank 51a, is discharged from the
first precipitating tank 51a. FeCl3 is added to the
discharged water to be treated, and solids in the water to
15 be treated, such as calcium carbonate and a metal compound,
aggregate with Fe(OH) 3 •
The water to be treated is fed to the first filtration
device 52 a. The solids aggregated with Fe (OH) 3 are removed
through the first filtration device 52a.
20 Silica in the supernatant in the first crystallizing
section 20a may be removed from the first concentrated water
in the first precipitating step, or may also be fed to the
downstream side without being removed.
Whether silica is removed in the first precipitating
25 step is determined according to the properties of the water
to be treated or the first concentrated water.
In the case where silica is not removed, the first
precipitating step is performed without supplying seed
crystals of silica and a precipitant for silica to the first
30 precipitating tank 51a. In this case, silica is separated
from the treated water in demineralizing sections located on
the downstream side (the first demineralizing section lOb
36
and the downstream side demineralizing section 60).
In the case where silica is removed, at least one of
seed crystals of silica and a precipitant for silica is
supplied into the first concentrated water in the first
5 precipitating section 50a from a supply section (not shown).
The seed crystals of silica are a silica gel, for example,
and the precipitant for silica is Mgso,, for example. In the
case where silica is removed, it is preferable that the
first concentrated water in the first precipitating tank 51a
10 is adjusted to pH 8 or more and 10 or less. In the case
where seed crystals of silica are used, silica is
crystallized using the seed crystals as nuclei. In the case
where MgS04 or Na aluminate (Na[Al(OH),]) is used as a
precipitant for silica, magnesium silicate is deposited. The
15 crystallized silica or the crystallized magnesium silicate
is precipitated at the bottom of the first precipitating
tank 51a and discharged from the bottom of the first
precipitating tank 51a.
In the case where Mg ions are contained in the water to
20 be treated, Mg ions react with silica in the first
concentrated water in the first precipitating step,
resulting in precipitation. The steps for silica/Mg ion
removal vary depending on the balance between the content of
Mg ions and the content of silica in the first concentrated
25 water in the first precipitating tank 51a.
In the case where the first concentrated water in the
first precipitating step has a lower concentration of Mg
ions relative to the silica content, Mg ions are consumed by
precipitation with silica. In order to remove an excess of
30 silica that is not consumed by precipitation with Mg ions, a
precipitant for silica (MgSO,) is supplied. With respect to
the amount of precipitant for silica to be supplied,
37
according to
ions in the
supplied in
consumed.
the content of silica and the
first precipitating step, the
such an amount that the excess
content of Mg
precipitant is
of silica is
5 In the case where the first concentrated water in the
first precipitating step has a higher concentration of Mg
ions relative to the silica content, Mg ions remain as a
result of the precipitation of Mg ions and silica. When the
first concentrated water having a high concentration of
10 residual Mg ions is discharged from the first precipitating
tank 51 a, scales containing Mg may be deposited in
demineralizing sections of subsequent stages (the first
demineralizing section lOb in Fig. 1; in the case of the
first precipitating section on the most downstream, the
15 downstream side demineralizing section 60).
Thus, the first concentrated water in the first
precipitating tank 51a is adjusted to such a value that a
magnesium compound (mainly magnesium hydroxide) can be
deposited. Accordingly, a magnesium compound is precipitated
20 in the first precipitating tank 51 a, thereby reducing the
concentration of Mg ions in the first concentrated water in
the first precipitating tank 5la. Further, after the first
precipitating step, the first concentrated water discharged
from the first precipitating tank 5la is adjusted to a pH at
25 which the magnesium compound is soluble, specifically to a
pH of less than 10. Accordingly, the deposition of scales
containing Mg in a demineralizing section can be suppressed.
In the case where the treatment is performed in several
stages, the first concentrated water that has passed through
30 the first filtration device 52a of the first water treatment
section of the previous stage flows into the water treatment
section of the subsequent stage as water to be treated. In
38
5
the water treatment section of the subsequent stage, the
steps from the first scale inhibitor supplying step to the
first precipitating step mentioned above are performed.

has
The concentrated water (first concentrated water)
passed through the first precipitating section
that
SOb
located on the most downstream of the water to be treated is
fed to the downstream side demineralizing section 60. The
water that has passed through the downstream side
10 demineralizing section 60 is recovered as treated water. The
concentrated water in the downstream side demineralizing
section 60 is discharged out of the system. The installation
of the downstream side demineralizing section 60 makes it
possible to further recover treated water from water that
15 has been treated in a water treatment section. Accordingly,
the water recovery is improved.
20
In the water treatment system 1 of this reference
embodiment, ions are
demineralizing section
carbonate, silica, etc.,
concentrated in the first
10.
have
However, gypsum, calcium
been removed in the first
crystallizing section, the first precipitating section, etc.
Accordingly, the water flowing into the downstream side
demineralizing section
ions than before the
60 has a smaller number of moles of
treatment. Accordingly, the osmotic
25 pressure is low in the first demineralizing section lOb or
30
the downstream side demineralizing section 60 located
downstream, and the required power is reduced.
An evaporator (not shown in Fig. 1) may be installed on
the downstream on the concentrated-water side of the
downstream side demineralizing section 60. In the
evaporator, water is evaporated from the concentrated water,
and ions contained in the concentrated water are deposited
39
as a solid and recovered as a solid. Because water is
recovered on the upstream side of the evaporator, and the
amount of concentrated water significantly decreases, the
evaporator can be reduced in size, and the energy required
5 for evaporation can be reduced.
10
Second Reference Embodiment
Fig. 9 is
system of the
invention. In
first reference
a schematic diagram of a water treatment
second reference embodiment of the present
Fig. 9, the same configurations as in the
embodiment are indicated with the same
reference numerals. In the water treatment system 100 of the
second reference embodiment, a first separating section 180
(180a, 180b) is installed on the downstream side of the
15 first crystallizing sections 20a and 20b. The water
treatment system 100 of Fig. 9 is configured such that two
water treatment sections are connected in the flow direction
of the water to be treated. In the water treatment system
100 of this reference embodiment, depending on the
20 properties of the water to be treated, the number of water
treatment sections may be one, and it is also possible that
three or more water treatment sections are connected.
25
In Fig. 9, the
180b) includes a
dehydrator 182 (182a,
first separating section 180 (180a,
classifier 181 (18la, 18lb) and a
182b). The classifiers 18la and 18lb
are liquid cyclones, for example. The dehydrators 182a and
182b are belt filters, for example.
Although the first separating section 180 has only one
classifier installed in Fig. 9, it is also possible that two
30 or more classifiers are connected in series in the flow
direction of the water to be treated.
In the water treatment system 100 of the second
40
reference embodiment, the water to be treated is treated
through the same steps as in the first reference embodiment,
except that the first separating step is performed
immediately after the first crystallizing step.
5
First concentrated water in the first crystallizing
tanks 21a and 21b is transferred to the first separating
sections 180a and 180b. The first concentrated water
transferred here is water containing solid matters deposited
10 in the first crystallizing tanks 21a and 21b.
The first concentrated water discharged from the first
crystallizing tanks 21a and 2lb contains gypsum having
various particle diameters, as well as calcium carbonate and
silica deposited due to the exceeding of the saturation
15 concentration. Because the deposition of calcium carbonate
and silica has taken place in the absence of seed crystals,
they have small diameters or are floating matters in a
colloidal form.
When the first concentrated water flows into the
20 classifiers 181a and 18lb, gypsum having a predetermined
size, for example,
diameter of 10 )lm or
classifiers 181a and
gypsum having an average particle
more, sediments at the bottom of the
181b, and gypsum having a small
particle diameter, calcium carbonate, and silica remain in
25 the supernatant. The gypsum sedimented at the bottom of the
classifiers 181a and 181b is further dehydrated by the
dehydrators 182a and 182b and recovered. The supernatant
containing gypsum having a small particle diameter, calcium
carbonate, and silica is fed to the first precipitating
30 sections 50a and 50b.
In this reference embodiment, seed crystals are added
to cause crystallization. Therefore, gypsum having an
41
average particle diameter of 10
deposited, and the proportion of
~m or more is mainly
gypsum having a small
diameter is low. Through the first separating step, gypsum
having a low water content and containing no impurities
5 (i.e., high-purity gypsum) can be separated and recovered
with high recovery.
10
Some of the gypsum recovered in the first separating
sections lBOa and 180b may be circulated through the seed
crystal tanks 23a and 23b as seed crystals.
Third Reference Embodiment
Fig. 10 is a schematic diagram of a water treatment
system of the third reference embodiment of the present
invention. The water treatment system 200 of Fig. 10 is
15 configured such that two water treatment sections are
connected in the flow direction of the water to be treated.
Depending on the properties of the water to be treated, the
number of water treatment sections may be one, and it is
also possible that three or more water treatment sections
20 are connected.
In the water treatment system 200 of the third
reference embodiment, each water treatment section includes,
from the upstream side of the water to be treated, a second
demineralizing section 210 (210a, 210b) and a second
25 crystallizing section 220 (220a, 220b). The concentration
sides of the second demineralizing sections 210a and 210b
are connected to the second crystallizing sections 220a and
220b, respectively. The water treatment section includes a
second scale inhibitor supplying section 230 (230a, 230b) in
30 the flow path on the upstream side of each second
demineralizing section 210 (210a, 210b).
The second scale inhibitor supplying sections 230a and
42
230b are each made up of a tank 231 (231a, 231b), a valve V4
(V4a, V4b), and a control section 232 (232a, 232b). The
control sections 232a and 232b are connected to the valves
V4a and V4b, respectively. The tanks 231a and 231b of the
5 second scale inhibitor supplying sections 230a and 230b have
stored therein a scale inhibitor.
10
Scale inhibitors used in the third reference embodiment
are the calcium scale inhibitor described in the first
reference embodiment and a scale inhibitor that inhibits the
deposition of
(referred to
silica as scales
as "silica scale
in the water to be treated
inhibitor") . Examples of
silica scale inhibitors include phosphonic-acid-based scale
inhibitors, polycarboxylic-acid-based scale inhibitors, and
mixtures thereof. A specific example is FLOCON260 (trade
15 name, manufactured by BWA).
20
Fig. 10 shows two tanks 231a. For example, a calcium
scale inhibitor is stored in one tank 231a, and a silica
scale inhibitor is stored in the other tank 231a.
In Fig. 10, the second demineralizing section 210 is a
reverse osmosis membrane device. In addition, the second
demineralizing section 210 may also be an electrodialyzer
(ED), an electro dialysis reversal device (EDR), an electro
de-ionization device (EDI), an ion-exchange equipment, a
capacitive de-ionization device (CDI), a nanofilters (NF),
25 an evaporator, etc.
Although only one second demineralizing section 210 is
shown in Fig. 10, the system may also be configured such
that two or more demineralizers are connected in parallel or
in series in the flow direction of the water to be treated.
30 The second crystallizing section 220 (220a, 220b) is
made up of a second crystallizing tank 221 (221a, 221b) and
a second seed crystal supplying section 222 (222a, 222b).
43
The second seed crystal supplying section 222 is connected
to the second crystallizing tank 221. The second seed
crystal supplying section 222 has a seed crystal tank 223
(223a, 223b), a valve V5 (V5a, V5b), and a control section
5 224 (224a, 224b). The control section 224 is connected to
10
15
the valve V5. The seed crystal tank 223 stores gypsum
particles as seed crystals.
In the water treatment
reference embodiment, a second
(240a, 240b) may be
system 200 of
pH adjusting
the third
section 240
the second
demineralizing section
installed
210 and the
between
second crystallizing
section 220. The second pH adjusting section 240 is made up
of a tank 241 (241a, 241b), a valve V6 (V6a, V6b), a pH
meter 243 (243a, 243b), and a control section 242 (242a,
242b) . The tank 241 has stored therein an acid as a pH
adjuster. The acid used may be hydrochloric acid, sulfuric
acid, nitric acid, or the like, for example. Sulfuric acid
is particularly preferable because so, 2- is removed as gypsum
in the crystallizing step, and thus the amount of ions that
20 reach the demineralizing section on the downstream side can
be reduced. The control section 242 is connected to the
valve V6 and the pH meter 243. The pH meter 2 4 3 may be
installed in the flow path between the second demineralizing
section 210 and the second crystallizing section 220 as
25 shown in Fig. 10, or may also be installed in the second
crystallizing tank 221.
In the water treatment system 200, a precipitating tank
271 and a filtration device 272 are installed as a second
upstream side precipitating section 270 on the upstream side
30 of the second scale inhibitor supplying section 230a located
on the most upstream of the water to be treated. The second
upstream side precipitating section 270 has the same
44
configuration as the first upstream side precipitating
section 70. As in the first reference embodiment, two or
more stages of precipitating tanks 271 may be connected in
series in the flow direction of the water to be treated.
5 In the water treatment system 200, a second deaerating
section 273 may be provided on the upstream side of the
second upstream side precipitating section 270 as shown in
Fig. 10. The second deaerating section 273 has the same
configuration as the first deaerating section 73 of the
10 first reference embodiment.
The second deaerating section 273 may be installed on
the downstream side of the water to be treated of the second
upstream side precipitating section 270 and on the upstream
side of the second scale inhibitor supplying section 230a.
15 It is also possible that a deaerating section having
20
the same configuration as the second deaerating section 273
is installed in the flow path between the second
demineralizing section 210a and the second crystallizing
section 220a, in the flow path between the second
crystallizing
section 250,
precipitating
section 220 and the second precipitating
and on the downstream side of the second
section 250 and in the flow path between it
and the second demineralizing section 210b or the downstream
side demineralizing section 60.
25 As in the first reference embodiment, an ion-exchange
equipment (not shown) may be installed on the downstream of
the filtration device 272 and on the upstream of the second
scale inhibitor supplying section 230a located on the most
upstream. In addition, depending on the concentration of
30 gypsum in the water to be treated, an upstream side
crystallizing section (not shown) having the same
configuration as the second crystallizing section may be
45
installed on the upstream of the second scale inhibitor
supplying section 230a on the most upstream.
In this reference embodiment, a second separating
section 280 (280a, 280b) may be installed on the downstream
5 side of the second crystallizing section 220 as shown in
Fig. 10. The second separating section 280 has the same
configuration as the first separating section 180 and
includes a classifier 281 (28la, 28lb) and a dehydrator 282
(282a, 282b)
10 In the water treatment system 200 of Fig. 10, a second
precipitating section 250 (250a, 250b) may be installed on
the downstream side of the second crystallizing section 220.
The second precipitating section 250 has the same
configuration as the first precipitating section 50 and
15 includes a second precipitating tank 251 (25la, 25lb) and a
second filtration device 252 (252a, 252b).
The water treatment system 200 includes a downstream
side demineralizing section 60 on the downstream side of the
water to be treated of the first water treatment section. An
20 evaporator (not shown in Fig. 10) may be installed on the
downstream on the concentrated-water side of the downstream
side demineralizing section 60.
A process for treating water to be treated using the
water treatment system 200 of the third reference embodiment
25 will be described hereinafter.

The water to be treated is subjected to
pretreatment described in the first reference embodiment.

the
30 In the same manner as in the first deaerating step
described in the first reference embodiment, C02 in the water
to be treated is removed in the second deaerati.ng section
46
273, whereby the concentration of carbonate ions in the
water to be treated is reduced.

In the second upstream side precipitating section 270,
5 some of Ca ions and carbonate ions are previously removed
from the water to be treated as calcium carbonate. In the
case where metal ions other than Ca ions are contained in
the water to be treated, in the second upstream side
precipitating section 270, some of a metal compound having
10 low solubility in water is previously removed from the water
to be treated.
The second upstream side precipitating step is
performed in the same manner as in the first upstream side
precipitating step.
15 In the case where water to be treated containing Mg
ions is treated in the water treatment system 200 of this
reference embodiment, as in the first reference embodiment,
the water to be treated is adjusted to a pH at which a
magnesium compound is deposited in the second upstream side
20 precipitating section 270, and some of Mg ions in the water
to be treated are removed. Subsequently, it is preferable
that the water to be treated is adjusted to a pH at which
the magnesium compound is soluble on the downstream side of
the second upstream side precipitating section 270.
25 Specifically, the pH is adjusted to less than 10.
Accordingly, the formation of scales in devices and steps on
the downstream side, particularly the second demineralizing
section 210 and the second demineralizing step, can be
inhibited.
30 In the case where the second deaerating step is
performed after the second upstream side precipitating step,
the pH of the water to be treated is adjusted to a pH at
47
which carbonate ions can be present as C02, specifically 6.5
or less.
Depending on the properties of the water to be treated,
the second deaerating step and the second upstream side
5 precipitating step may be omitted.
In the case where an ion-exchange membrane device is
installed, in the water treatment system 200 of the third
reference embodiment, Ca ions and Mg ions in the water to be
treated are removed by the ion-exchange membrane device.
10 In the case where an upstream side crystallizing
section is installed, the concentration of gypsum in the
water to be treated is reduced in the upstream side
crystallizing section through the same steps as in the first
reference embodiment.
15
The control section 232a of the second scale inhibitor
supplying section 230a opens the valve V4a and supplies a
predetermined amount of calcium scale inhibitor to the water
to be treated from the tank 231a. The control section 232b
20 of the second scale inhibitor supplying section 230b opens
the valve V4b and supplies a predetermined amount of silica
scale inhibitor to the water to be treated from the tank
231b. The control section 232a and the control section 232b
adjust the valve opening of the valve V4a and the valve V4b,
25 respectively, so that the concentrations of the calcium
scale inhibitor and the silica scale inhibitor are
predetermined values set according to the properties of the
water to be treated.
In the water treatment system 200 of the third
30 reference embodiment, the pH adjustment of the water to be
treated immediately before flowing into the second
demineralizing section 210 is optionally performed.
48
For example, in the configuration of Fig. 10, as a
result of the addition of FeCl3, the water to be treated is
adjusted to about pH 5 to 6 and then flows into the second
demineralizing section 210a. As shown in Fig. 3, the
5 solubility of calcium carbonate in water is high when the pH
of the water to be treated is 6.5 or less.
in formula ( 1) , in the above pH range,
In addition,
carbonic acid
as
is
present mainly in the form of HC03- and C02 in water. The
water to be treated flowing into the second demineralizing
10 section 210a has a reduced concentration of calcium
carbonate. In such a case, it is not necessary to adjust the
pH immediately before the second demineralizing section
210a.
Incidentally, in the case where the pH of the water to
15 be treated, which is to be treated in the second
demineralizing step, is adjusted, it is possible that a pH
adjusting section having the same configuration as the first
pH adjusting section of the first reference embodiment is
installed on the upstream of the second demineralizing
20 section 210a, and the pH-adjusted water to be treated is fed
to the second demineralizing section 210a.

In the second demineralizing section 210a, the water to
be treated containing the scale inhibitors is treated. In
25 the case where the second demineralizing section 210a is a
reverse osmosis membrane device, the water that has passed
through the reverse osmotic membrane is recovered as treated
water. The water containing ions and the scale inhibitors is
discharged from the non-permeate side of the reverse osmosis
30 membrane as concentrated water (second concentrated water).
As a result of the treatment in the second
demineralizing section 210a, gypsum and silica is
49
concentrated in the second concentrated water.
production of scales is suppressed by the
inhibitor and the silica scale inhibitor.
However, the
calcium scale
Also in the case where other demineralizers, such as a
5 capacitive de-ionization device, are used, for example, the
water to be treated is separated into treated water and
concentrated water having a high concentration of ions
(second concentrated water). The second concentrated water
is fed toward the second crystallizing section 220a.
10
In this reference embodiment, the pH of the water to be
treated (second concentrated water) may be adjusted by the
second pH adjusting section 240a between the second
demineralizing section 210a and the second crystallizing
15 section 220a.
The second pH adjusting section 240a controls the pH of
the second concentrated water to such a value that the
function of the calcium scale inhibitor is reduced and
gypsum in the second concentrated water can be deposited.
20 The pH meter 243a measures the pH of the second concentrated
water. The control section 242a adjusts the opening of the
valve V6a so that the value measured by the pH meter 243a is
a predetermined pH control value.
25

The second concentrated water is stored in the second
crystallizing tank 221 of the second crystallizing section
220a. The control section 224a of the second seed crystal
supplying section 222a opens the valve V5 and adds seed
crystals of gypsum from the seed crystal tank 223a to the
30 second concentrated water in the second crystallizing tank
22la. Although the second concentrated water contains a
calcium scale inhibitor, when seed crystals are loaded,
50
gypsum is crystallized, followed by crystal growth.
As shown in Fig. 5, under Condition 1 (pH 6. 5) , the
degree of supersaturation is 460%, and there is no change
from the initial degree of supersaturation even after the
5 elapse of 6 hours. Under Condition 1, the scale inhibitor
exerts its function to suppress the deposition of gypsum.
Meanwhile, under Condition 4 and Condition 2, the degree of
supersaturation decreases.
That is, it has been confirmed that even when seed
10 crystals are not loaded, a decrease in pH leads to a
decrease in the function of the scale inhibitor, whereby
gypsum is crystallized. In addition, according to the
results of Fig. 5, the deposition rate increases with a
decrease in pH.
15 In Fig. 6, as a comparison with Condition 5 (pH 4. 0),
under Condition 7 (pH 4. 0), seed crystals pre-immersed in
the above calcium scale inhibitor were added to simulated
water having added thereto a calcium scale inhibitor, and
sulfuric acid was added for pH adjustment. Condition 5 and
20 Condition 7 are otherwise the same, and gypsum deposition
experiments were performed under such conditions. Two hours
after the pH adjustment, the concentration of Ca in the
simulated water was measured by the same technique as in
Fig. 3.
25 As a result, as
supersaturation was 199%
Condition 7. From this,
the immersion time of
shown in Fig. 6, the degree of
or less both under Condition 5 and
it can be said that independent of
seed crystals in a calcium scale
inhibitor, when the pH is reduced to 4. 0, the function of
30 the calcium scale inhibitor is reduced.
In consideration of the effects of the calcium scale
inhibitor, the pH of the second concentrated water is
51
5
adjusted in the second pH adjusting step to 6. 0 or less,
preferably 5.5 or less, and more preferably 4.0 or less. In
particular, when the second concentrated water is adjusted
to pH 4.0 or less, the function of
inhibitor can be significantly reduced.
the calcium scale
By adjusting the pH
of the second concentrated water to such a value that the
scale inhibition function of the calcium scale inhibitor is
reduced, crystallization in the second crystallizing section
220a is promoted. According to the kind of scale inhibitor,
10 the pH range in the second pH adjusting step is suitably
determined.
With reference to Fig. 4, in the case where pH is low,
silica may exceed the saturation solubility. However, in
this reference embodiment, a silica scale inhibitor is
15 loaded in the second water treatment section. Accordingly,
the deposition of silica is suppressed even at low pH. Even
when silica is deposited in the second crystallizing tank
221a, such silica is present as small-diameter particles or
floating matters in a colloidal form.
20 In addition, with reference to Fig.
carbonate dissolves in water at pH 6.0 or less.
3, calcium
From the above, high-purity gypsum can be recovered in
the second crystallizing tank 221a of the second water
treatment section.
25 Meanwhile, the second concentrated water in the second
crystallizing step may also be adjusted in the second pH
adjusting step to a pH at which silica is soluble in the
second concentrated water. Accordingly, in the second
crystallizing tank 221a, the deposition of silica from the
30 second concentrated water is suppressed. As a result, in the
case where the second concentrated water discharged from the
second crystallizing tank 22la in the second separating
52
section 280a is classified, the purity of the recovered
gypsum can be increased.

In the case where the second separating section 280a is
5 installed, the second concentrated water containing solid
matters deposited in the second crystallizing tank 221a is
transferred to the second separating section 28 Oa. In the
second concentrated water in the second crystallizing tank
221a, gypsum deposited by crystallization is present. In
10 addition, the second concentrated water may also contain
silica deposited because of an increase in the silica
15
20
25
concentration to be equal to or higher than the
concentration at which the silica scale inhibitor exerts its
function due to the quality change or concentration of the
raw water. Silica is present in the second concentrated
water as small-diameter particles or floating matters in a
colloidal form.
Through the same steps as in the second reference
embodiment, the classifier 281a of the second separating
section 280a performs separation into gypsum having a
predetermined size (e.g.' having an average particle
diameter of 10 }lm or more) and a supernatant containing
small-diameter precipitates (gypsum, silica) . Large-diameter
gypsum is further dehydrated by the dehydrator 282a and
recovered. According to this reference embodiment, highpurity
gypsum can be recovered. Some of the recovered gypsum
may be circulated through the seed crystal tank 223a as seed
crystals.
In the case where the second separating section 280a is
30 not installed, gypsum precipitated at the bottom of the
second crystallizing tank 221a of the second crystallizing
section 220a is discharged from the second crystallizing
53
tank 221a. The supernatant in the second crystallizing tank
221a is fed to the second precipitating section 250a.

The supernatant (second concentrated water) in the
5 second crystallizing section 220a or the supernatant (second
concentrated water) discharged from the second separating
section 280a is fed to the second precipitating section
250a.
In the second precipitating step, in the same manner as
10 in the first precipitating step described in the first
reference embodiment, calcium carbonate and metal compounds
in the second concentrated water are removed in the second
precipitating tank 251a and the second filtration device
252a.
15 In the second precipitating step, it is also possible
that in the same manner as in the first precipitating step,
at least one of seed crystals of silica and a precipitant
for silica is added to the second precipitating tank 251a to
remove silica from the second concentrated water.
20 In the case where the treatment is performed in several
25
stages as shown in Fig. 10, the second concentrated water
that has passed through the second filtration device 252a of
the second water treatment section of the previous stage
flows into the water treatment section of the subsequent
stage as water to be treated.
of the subsequent stage, the
inhibitor supplying step to
In the water treatment section
steps from the second scale
the second precipitating step
mentioned above are performed.

30 The second concentrated water that has passed through
the second precipitating section 250b located on the most
downstream of the water to be treated is treated in the
54
downstream side demineralizing section 60.
has passed through the downstream side
section 60 is recovered as water to be
The water that
demineralizing
treated. The
concentrated water in the downstream side demineralizing
5 section 60 is discharged out of the system.
Also in this reference embodiment, an evaporator (not
shown) may be installed
concentrated-water side
demineralizing section 60.
on
of
the
the
downstream
downstream
on the
side
10 In the third reference embodiment, in the case where
the second concentrated water is adjusted in the second pH
adjusting step to a pH at which the function of the calcium
scale inhibitor is reduced, as a third pH adjusting step,
the pH of the second concentrated water may be adjusted
15 after the second crystallizing step in order for the calcium
scale inhibitor to exert its function. Specifically, the pH
is preferably adjusted to 4. 0 or more, preferably 5. 5 or
more, and more preferably 6.0 or more. The third pH
adjusting step is performed after the second crystallizing
20 step and before the second demineralizing step, or after the
second crystallizing step and before the downstream side
demineralizing step.
In the water treatment system 200 of this reference
embodiment, in order to perform the third pH adjusting step,
25 a third pH adjusting section (not shown in Fig. 10) having
the same configuration as the second pH adjusting section is
installed between the second crystallizing section and the
second demineralizing section immediately thereafter (in
Fig. 10, between the second crystallizing section 220a and
30 the second demineralizing sections 210b, particularly the
second precipitating section 250a and the second
demineralizing section 210b). In addition, a third pH
55
adjusting section
configuration as
(not shown in Fig. 10) having the same
the second pH adjusting section is
installed between the second precipitating section 250b and
the downstream side demineralizing section 60 on the most
5 downstream. Accordingly, even in the case where the second
concentrated water is treated in the downstream side
demineralizing step, and the concentration of Ca ions is
high on the concentrated-water side, the formation of scales
can be suppressed by the function of the calcium scale
10 inhibitor.
15
In the water treatment system 200 of this embodiment,
silica is concentrated by the treatment in the second water
treatment section.
second concentrated
concentration at
When the concentration of silica in the
water is equal to or higher than the
which the silica scale inhibitor
effectively works, scales of silica may be formed from the
second concentrated water. For example, in the case where
FLOCON260 is used as a silica scale inhibitor, the scaleproduction-
inhibiting effect can be obtained at a silica
20 concentration up to about 200 mg/L. Therefore, the number of
stages of the second water treatment sections is determined
so that silica is concentrated to the concentration at which
the silica scale inhibitor can exert its effect.
By using the water treatment system 200 of the third
25 reference embodiment, water to be treated containing ions
can be treated with high water recovery.
In particular, in the third reference embodiment,
gypsum is mainly deposited in the second crystallizing
section 220. Accordingly, the gypsum recovery in the second
30 crystallizing section 220 is high, and the number of moles
of ions fed to the downstream side is further reduced. In
addition, the purity of the gypsum recovered in the second
56
crystallizing section 220 can be increased.
Fourth reference Embodiment
Fig. 11 is a schematic diagram of a water treatment
5 system of the fourth reference embodiment of the present
invention. In Fig. 11, the same configurations as in the
first to third reference embodiments are indicated with the
same reference numerals.
In the water treatment system 300 of the fourth
10 reference embodiment, the water treatment section described
in the first reference embodiment is installed. On the
downstream side of the water to be treated of this water
treatment section, the water treatment section described in
the third reference embodiment is installed.
15 In the water treatment system 300 of Fig. 11, a first
separating section 180 is installed on the downstream side
of the first crystallizing section 20.
separating section 280, which is the
In addition, a second
same as the first
separating section 180, is installed on the downstream side
20 of the second crystallizing section 220.
A downstream side demineralizing section 60 is
installed on the downstream side of the water to be treated
of the second crystallizing section 220 located on the most
downstream.
25 The water treatment system 300 of the fourth reference
embodiment includes the first upstream side precipitating
section 70 described in the first reference embodiment on
the upstream side of the first scale inhibitor supplying
section 30 and the first pH adjusting section 40 which are
30 located on the most upstream of the water to be treated.
Further, the water treatment system 300 of the fourth
reference embodiment includes a first deaerating section 73,
57
5
which is the same as in the first reference embodiment, on
the upstream side of the first upstream side precipitating
section 70 as shown in Fig. 11. The first deaerating section
73 may also be installed on the downstream side of the water
to be treated of the first upstream side precipitating
section 70 and on the upstream side of the first scale
inhibitor supplying section 30 and the first pH adjusting
section 40.
Incidentally, a deaerating section having the same
10 configuration as the first deaerating section 73 may be
installed in the flow path between the first demineralizing
section 10 and the first crystallizing section 20, in the
flow path between the first crystallizing section 10 and the
15
first precipitating section 50, in
second crystallizing section
precipitating section 250, and in
the flow path between the
220 and the second
the flow path between the
first precipitating section 50 and the second demineralizing
section 210.
Also in the water treatment system 300 of this
20 reference embodiment, an ion-exchange equipment (not shown)
and an upstream side crystallizing section (not shown) may
be provided on the upstream of the first scale inhibitor
supplying section 30 and the first pH adjusting section 40.
In Fig. 11, the water treatment sections from the first
25 scale inhibitor supplying section 30 to the first
precipitating section 50 and from the second scale inhibitor
supplying section 230 to the second precipitating section
250 are each shown as one stage. However, it is also
possible that for each section, two or more stage of water
30 treatment sections are connected.
In the water treatment system 300 of the fourth
reference embodiment, first, water to be treated is treated
58
by the water treatment process described in the first
reference embodiment and the second reference embodiment.
First concentrated water after being treated by the process
of the first reference embodiment and the second reference
5 embodiment is treated as water to be treated through the
steps form the second scale inhibitor supplying step to the
second precipitating step described in the third reference
embodiment.
Second concentrated water that has passed through the
10 second precipitating section 250 on the most downstream is
treated in the downstream side demineralizing section 60.
The water that has passed through the downstream side
demineralizing section 60 is recovered as treated water. The
concentrated water in the downstream side demineralizing
15 section 60 is discharged out of the system.
Also in this
shown) may be
concentrated-water
reference
installed
side
demineralizing section 60.
embodiment,
on the
of the
an evaporator
downstream on
downstream
(not
the
side
20 In the fourth reference embodiment, in the case where
the second concentrated water is adjusted to a pH at which
the function of the calcium scale inhibitor is reduced in
the second pH adjusting step, the third pH adjusting step
described in the third reference embodiment may be
25 performed.
First Embodiment
Fig. 12 is a schematic diagram of a water treatment
system of the first embodiment of the present invention. In
30 Fig. 12, the same configurations as in the first to third
reference embodiments are indicated with the same reference
numerals.
59
In the water treatment system 400 of the first
embodiment, the water treatment section described in the
third reference embodiment is installed. On the downstream
side of the water to be treated of this water treatment
5 section, the water treatment section described in the first
reference embodiment is installed.
10
In the water treatment system 400 of Fig. 12, a first
separating section 180 and a second separating section 280
are installed.
A downstream side demineralizing section 60 is
installed on the downstream side of the water to be treated
of the first crystallizing section 20 located on the most
downstream.
The water treatment system 400 of the first embodiment
15 includes the second upstream side precipitating section 270
described in the third reference embodiment on the upstream
side of the second scale inhibitor supplying section 230
located on the most upstream of the water to be treated.
Further, the water treatment system 400 of the first
20 embodiment has a second deaerating section 273, which is the
same as in the third reference embodiment, on the upstream
side of the second upstream side precipitating section 270
as shown in Fig. 12. The second deaerating section 27 3 may
be installed on the downstream side of the water to be
25 treated of the second upstream side precipitating section
270 and on the upstream side of the second scale inhibitor
supplying section 230.
Incidentally, a
configuration as the
deaerating section having the same
second deaerating section 27 3 may be
30 installed in the flow path between the second demineralizing
section 210 and the second crystallizing section 220, in the
flow path between the first crystallizing section 20 and the
60
first precipitating section 50, in the flow path between the
second crystallizing section 220 and the second
precipitating section 250, and in the flow path between the
second precipitating section 250 and the first
5 demineralizing section 10.
Also in the water treatment system 400 of this
embodiment, an ion-exchange equipment (not shown) and an
upstream side crystallizing section (not shown) may be
provided on the upstream of the second scale inhibitor
10 supplying section 230.
In the water treatment system 400 of this embodiment
shown in Fig. 12, a first separating section 180 and a
second separating section 280 may be installed on the
downstream side of the first crystallizing tank 21 and the
15 second crystallizing tank 221, respectively.
In Fig. 12, the water treatment sections from the
second scale inhibitor supplying section 230 to the second
precipitating section 250 and from the first scale inhibitor
supplying section 30 to the first precipitating section 50
20 are each shown as one stage. However, it is also possible
that for each section, two or more stage of water treatment
sections are connected.
In the water treatment system 400 of the first
embodiment, first, water to be treated is treated by the
25 water treatment process described in the third reference
embodiment. Second concentrated water after being treated by
the process of the third reference embodiment is treated as
water to be treated through the steps form the first scale
inhibitor supplying step to the first precipitating step
30 described in the first reference embodiment and the second
reference embodiment.
First concentrated water that has passed through the
61
first precipitating section 50 on the most downstream is
treated in the downstream side demineralizing section 60.
The water that has passed through the downstream side
demineralizing section 60 is recovered as treated water. The
5 concentrated water in the downstream side demineralizing
section 60 is discharged out of the system.
be
Also in this embodiment, an
installed on the downstream
evaporator (not shown) may
on the concentrated-water
side of the downstream side demineralizing section 60.
10 In the first embodiment, in the case where the second
concentrated water is adjusted to a pH at which the function
of the calcium scale inhibitor is reduced in the second pH
adjusting step, the third pH adjusting step described in the
third reference embodiment may be performed.
15 Also by the water treatment system 300 of the fourth
reference embodiment and the water treatment system 4 00 of
the first embodiment, water to be treated containing ions
can be treated with high water recovery.
In particular, the first embodiment is configured such
20 that gypsum is mainly deposited in the second crystallizing
section 220 on the upstream side of the water to be treated.
Accordingly, the gypsum recovery in the second crystallizing
section 220 is high, and the number of moles of ions fed to
the downstream side is further reduced. Further, the purity
25 of the gypsum recovered in the second crystallizing section
220 can be increased.
Fifth Reference Embodiment
According to the fifth reference embodiment of the
30 present invention, the amount of seed crystals of gypsum to
be supplied to the first crystallizing tank 21 and the
second crystallizing tank 221 in the first to fourth
62
reference embodiments and the first embodiment is
controlled. The configuration that controls the amount of
seed crystals to be supplied to the first crystallizing tank
21 will be described with reference to Fig. 13. The same
5 configuration is also applied to the second crystallizing
tank 221.
In the fifth reference embodiment, a first pH measuring
section 543 that measures the pH of the first concentrated
water in the first crystallizing tank 21 is installed. The
10 first pH measuring section 543 may be installed in the flow
path that connects the first demineralizing section 10 and
the first crystallizing tank 21, or may also be directly
installed in the first crystallizing tank 21. The first pH
measuring section 543 is connected to the control section 24
15 of the seed crystal supplying section 22.
In the fifth reference embodiment, as shown in Fig. 13,
a pH adjusting section 540 is installed. The pH adjusting
section 540 includes a tank 541, a control section 542, and
a valve V7. The first pH measuring section 543 is connected
20 to the control section 542 of the pH adjusting section 540.
25
The pH adjusting section 540 controls the pH of the first
concentrated water in the first crystallizing tank 21 to a
predetermined value based on the value measured by the first
pH measuring section 543.
Incidentally, in the
crystals of gypsum to
crystallizing tank 221 is
case where the amount of seed
be supplied to
controlled, the pH
the second
meter 243a
described in the third reference embodiment corresponds to
the second pH measuring section, and the control section 242
30 of the second pH adjusting section corresponds to the
control section 542.
Seed crystals stored in the seed crystal tank 23 of the
63
first seed crystal supplying section 22 may be new
chemicals. However, in the case where a first separating
section 180 is installed, the seed crystal tank 23 may also
store gypsum separated by the classifier 181, whose particle
5 diameter is equal to or greater than a predetermined
particle diameter, or gypsum after being dehydrated by the
dehydrator 182.
10
The
supplied
control
in the
of the amount of seed crystals to be
fifth reference embodiment is performed
through the following steps.
amount of seed crystals
Hereinafter, the case where the
to be supplied is constantly
controlled during continuous operation will be explained as
an example.
The first pH measuring section 543 measures the pH of
15 the first concentrated water in the first crystallizing tank
21. The measured pH value is sent to the control section 24
of the seed crystal supplying section 22.
20
25
The control section 24 stores the pH range where the
scale inhibition function of
reduced. Specifically, as
a calcium scale
described for
inhibitor is
the second
crystallizing step, the pH range where the scale inhibition
function of a calcium scale inhibitor is reduced is 6. 0 or
less, preferably 5. 5 or less, and more preferably 4. 0 or
less.
The control section 24 compares the value measured by
the first pH measuring section 543 with the above pH range.
In the case where the measured value is within the above pH
range, the control section 24 reduces the opening of the
valve V3 to reduce the amount of seed crystals of gypsum to
30 be supplied. In the case where the measured value is greater
than the above pH range, the control section 24 increases
the opening of the valve V3 to increase the amount of seed
64
crystals of gypsum to be supplied.
Gypsum is deposited when seed crystals are present.
However, in the case where the calcium scale inhibitor
exerts its function, the crystallization rate is low.
5 Accordingly, the amount of seed crystals is increased to
promote crystallization. Meanwhile, in the case where the
function of the calcium scale inhibitor is reduced, a
sufficient crystallization rate can be obtained even when
the amount of seed crystals is small.
10 In this way, by adjusting the amount of seed crystals
to be supplied according to the pH, the amount of seed
crystals used can be reduced.
In this reference embodiment, it is also possible that
the pH is regularly measured during continuous operation,
15 and seed crystals are supplied intermittently.
Alternatively, it is also possible that the time-dependent
variation of pH is obtained at the time of the test run of
the system,
be supplied
for example, and the amount of seed crystals to
is increased or decreased based on the obtained
20 time-dependent variation.
Sixth Reference Embodiment
The sixth reference embodiment of the present invention
is a water treatment system 600 provided with at least
25 either a first separating section 180 or a second separating
section 280. The water treatment system 600 differs from the
fifth reference embodiment in that gypsum separated in the
separating section is directly supplied to a first
crystallizing tank or a second crystallizing tank as seed
30 crystals.
The configuration that controls the amount of seed
crystals to be supplied to the first crystallizing tank 21
65
in this reference embodiment will be described with
reference to Fig. 14. The same configuration is also applied
to the second crystallizing tank 221.
In Fig. 14, a first circulation line 601, which
5 performs transfer so that some of the gypsum sedimented at
the bottom of the classifier 181 of the first separating
section 180 is supplied directly to the first crystallizing
tank 21, is installed. In addition, a second circulation
line 602, which performs transfer so that some of the gypsum
10 after being dehydrated by the dehydrator 182 is supplied
directly to the first crystallizing tank 21, is installed. A
valve V8 is installed in the first circulation line 601, and
a valve V9 is installed in the second circulation line 602.
Incidentally, this reference embodiment may also be
15 configured such that either the first circulation line 601
or the second circulation line 602 is installed.
The control section 610 is connected to a first pH
measuring section 543, which is the same as in the fifth
reference embodiment, the valve V8, and the valve V9.
20 The control of the amount of seed crystals to be
supplied in the sixth reference embodiment is performed
through the following steps.
amount of seed crystals
Hereinafter, the case where the
to be supplied is constantly
controlled during continuous operation will be explained as
25 an example.
The first pH measuring section 543 measures the pH of
the first concentrated water in the first crystallizing tank
21. The measured pH value is sent to the control section
610.
30 The control section 610 stores the pH range where the
scale inhibition function of a calcium scale inhibitor is
reduced. Through the same steps as in the fifth reference
66
5
embodiment, the control section 610 compares the value
measured by the first pH measuring section 543 with the
above pH range to adjust the opening of the valve VS and the
valve V9.
In the fifth reference embodiment and the sixth
reference embodiment, a seed crystal concentration measuring
section (not shown) that measures the concentration of
gypsum seed crystals in the first concentrated water in the
first crystallizing tank 21 may be installed in the first
10 crystallizing tank 21. The seed crystal concentration
measuring section measures the concentration of seed
crystals in the first crystallizing tank 21. The measured
concentration value is sent to the control section 24 or the
control section 610. The control section 24 or the control
15 section 610 stores the threshold for the concentration of
20
seed crystals,
be supplied in
and increases the amount of seed crystals to
the case where the concentration of seed
crystals is equal to or less than the threshold.
As a modification of the fifth reference embodiment and
the sixth reference embodiment, a first concentration
measuring section (not shown) is installed on the downstream
side of the first crystallizing tank 21 and on the upstream
side of the first precipitating section 50. In the case
where the first separating section 180 is provided, the
25 first concentration measuring section is preferably
installed on the downstream side of the first separating
section 180, but may also be installed on the upstream side
of the first separating section 180. The first concentration
measuring section is connected to the control section 24 or
30 the control section 610.
In the case of the second crystallizing tank 221, a
second concentration measuring section is installed in place
67
5
of the first concentration measuring section.
The first concentration measuring section measures at
least one of the concentration of Ca ions and the
concentration of sulfate ions in the first concentrated
water discharged from the first crystallizing tank 21. The
measured concentration is sent to the control section 24 or
the control section 610.
The concentration of Ca ions and the concentration of
sulfate ions measured by the first concentration measuring
10 section depend on the crystallization rate in the first
crystallizing tank 21. In the case where the residence time
is the same, lower concentrations of Ca ions and sulfate
ions lead to a higher crystallization rate.
The control section 24 and the control section 610
15 store the threshold for at least one of the concentration of
Ca ions and the concentration of sulfate ions.
In the case where at least one of the concentration of
Ca ions and the concentration of sulfate ions measured by
the first concentration measuring section is equal to or
20 higher than the threshold, the control section 24 increases
the opening of the valve V3 to increase the amount of seed
crystals to be supplied. In the case where at least one of
the concentration of Ca ions and the concentration of
sulfate ions measured by the first concentration measuring
25 section is lower than the threshold, the control section 24
reduces the opening of the valve V3 to reduce the amount of
seed crystals to be supplied.
In the case where at least one of the concentration of
Ca ions and the concentration of sulfate ions measured by
30 the first concentration measuring section is equal to or
higher than the threshold, the control section 610 increases
the opening of the valve V8 and the valve V9 to increase the
68
amount of seed crystals to be supplied. In the case where at
least one of the concentration of Ca ions and the
concentration of sulfate ions measured by the first
concentration measuring section is lower than the threshold,
5 the control section 610 reduces the opening of the valve VB
and the valve V9 to reduce the amount of seed crystals to be
supplied.
Also in the case of the second crystallizing tank 221,
the amount of seed crystals to be supplied is controlled
10 through the same steps as above.
In this way, by controlling the amount of seed crystals
to be supplied depending on at least one of the
concentration of
ions after the
Ca ions and the concentration of
crystallizing step, the amount
15 crystals used can be reduced.
Seventh Reference Embodiment
sulfate
of seed
Fig. 15 is a partial schematic diagram of a water
treatment system of the seventh reference embodiment of the
20 present invention. In Fig. 15, the same configurations as in
the first to third reference embodiments are indicated with
the same reference numerals.
The water treatment system 700 of Fig. 15 is configured
such that the gypsum separated from the first concentrated
25 water in the first crystallizing section 20 in the water
treatment system of the first embodiment is recovered and
supplied to the second crystallizing tank 221 of the second
crystallizing section 220. Also in the water treatment
system of the fourth reference embodiment, the same
30 configuration can be employed.
As described in the first reference embodiment, the pH
of concentrated water (first concentrated water) in the
69
first crystallizing tank 21 of the first crystallizing
section 20 is not particularly limited. However, in terms of
operation cost, it is more advantageous to perform the first
crystallizing step without changing the pH from the first
5 demineralizing step. In this case, the first crystallizing
step is performed at a pH at which silica is soluble (10 or
more), but the solubility of calcium carbonate is low in
this pH range.
Meanwhile, as described in the third reference
10 embodiment, in the second crystallizing section 220 (second
crystallizing step), gypsum is crystallized in a still lower
pH range. At the pH range in the second crystallizing step
( 6. 0 or less, more preferably 4. 0 or less) , calcium
carbonate is soluble in water. When gypsum containing
15 calcium carbonate recovered in the first crystallizing
section 20 is supplied to the second crystallizing tank 221
of the second crystallizing section 220, calcium carbonate,
which is an impurity, dissolves in the second concentrated
water, and gypsum is present as a solid in the second
20 concentrated water. By using the water treatment system 300
of the seventh reference embodiment, water to be treated can
be treated with high water recovery, and also high-purity
gypsum can be recovered.
25 Eighth Reference Embodiment
Fig. 16 is a partial schematic diagram of a water
treatment system of the eighth reference embodiment of the
present invention. In Fig. 16, the same configurations as in
the second reference embodiment are indicated with the same
30 reference numerals.
Incidentally, the eighth reference embodiment will be
described hereinafter using a water treatment process
70
including a first separating step and a water treatment
system including a first separating section. However, the
same configuration is also applicable to the case of a
second separating step and a second separating section.
5 In Fig. 16, the water treatment system 800 includes,
for one first crystallizing section 20, two or more
classifiers (first classifiers) 181 in the flow direction of
the water to be treated. In Fig. 16, two first classifiers
18la and 18lb are installed. The size of gypsum to be
10 separated is different between the first classifier 18la
located on the most upstream and the first classifier 18lb
located on the downstream side. In this reference
embodiment, the size of gypsum to be separated by the first
classifier 18lb is smaller than that of gypsum to be
15 separated by the first classifier 18la. For example, the
first classifier 18la is a classifier that separates
particles
more, and
having an
the first
average particle diameter of 10
classifier 18lb is a classifier
Jlm or
that
separates particles having an average particle diameter of 5
20 )lm or more.
25
In the case where three or more first classifiers 181
are installed, they are designed such that the size of
gypsum to be separated by each first classifier 181
decreases in the direction from the upstream side toward the
downstream side. The number of first classifiers installed
in the flow direction of the water to be treated and the
particle diameter of solid matters that can be separated by
each classifier are suitably determined in consideration of
the water recovery, gypsum recovery, treatment cost, etc.
30 In the water treatment system 800 of the eighth
reference embodiment, the following treatment is performed
in the first separating step.
71
In the first classifier 181a located on the most
upstream, gypsum having an average particle diameter of 10
~m or more is classified and sedimented at the bottom of the
first classifier 181a. The sedimented gypsum is discharged
5 from the first classifier 181a and fed to the dehydrator
182. The supernatant in the first classifier 181a is fed to
the first classifier 181b on the downstream side. This
supernatant mainly contains particles having a particle
diameter of less than 10 ~m (gypsum, calcium carbonate,
10 silica, etc.).
In the first classifier 181b located on the downstream
side, gypsum having an average particle diameter of 5 ~m or
more is classified and sedimented at the bottom of the first
classifier 181b. The supernatant in the first classifier
15 181b is fed to the first precipitating section 50.
The sedimented gypsum is discharged from the first
classifier 181b. The discharged gypsum is fed to the first
crystallizing tank 21 through a solid matter circulation
line 801 and supplied into the first concentrated water in
20 the first crystallizing tank 21.
The circulated gypsum functions as seed crystals in the
first crystallizing tank 21, and the circulated gypsum is
crystallized, followed by crystal growth. The crystal-grown
circulated gypsum having an average particle diameter of 10
25 ~m or more is fed from the first crystallizing tank 21 to
the first classifier 181a together with the first
30
concentrated
concentrated
water, then
water by the
separated from
first classifier
transferred to the dehydrator 182.
the first
181a, and
The supernatant in the first classifier 181b contains
particles having a relatively small diameter of less than 5
~m, such as those having a particle diameter of about 2 to 3
72
)lm. In particular, in the early stage of the operation of
the water treatment system (immediately after start-up,
etc.), gypsum is discharged from the first crystallizing
tank 21 before it grows to a sufficient size in the first
5 crystallizing tank 21, and an increased amount of gypsum
flows into the first precipitating tank 51. In such a case,
a large amount of gypsum is contained in the precipitate in
the first precipitating tank 51. Thus, in this reference
embodiment, it is also possible that a circulation line 802
10 that connects the bottom of the first precipitating tank 51
to the first crystallizing tank 21 is provided, and solid
matters containing gypsum precipitated at the bottom of the
first precipitating section 51 are circulated through the
first crystallizing tank 21.
15 According to this reference embodiment, the amount of
gypsum recovered in the first separating section is
increased, and also the water content of the recovered
gypsum can be reduced. The use of the water treatment steps
and the water treatment system of this reference embodiment
20 leads to the reduction of the amount of gypsum particles
having a relatively small diameter flowing out to the
25
30
downstream side. Accordingly, the water recovery can be
improved, and also the amount of waste resulting from the
water treatment can be reduced.
Reference Signs List
1, 100, 200, 300, 400, 500, 600, 700, 800: Water treatment
system
10: First demineralizing section
20: First crystallizing section
21: First crystallizing tank
22: First seed crystal supplying section
73
23, 223: Seed crystal tank
24, 32, 42, 224, 232, 242, 542, 610: Control section
30: First scale inhibitor supplying section
31, 41, 231, 241, 541: Tank
5 40: First pH adjusting section
43, 243: pH meter
50: First precipitating section
51: First precipitating tank
52: First filtration device
10 60: Downstream side demineralizing section
70: First upstream side precipitating section
71: Precipitating tank
72: Filtration device
73: First deaerating section
15 180: First separating section
181, 181a, 181b, 281: Classifier
182, 282: Dehydrator
210: Second demineralizing section
220: Second crystallizing section
20 221: Second crystallizing tank
222: Second seed crystal supplying section
230: Second scale inhibitor supplying section
240: Second pH adjusting section
250: Second precipitating section
25 251: Second precipitating tank
252: Second filtration device
280: Second separating section
540: pH adjusting section
543: First pH measuring section
30 601: First circulation line
602: Second circulation line
801, 802: Solid matter circulation line

CLAIMS
1. A water treatment process, comprising:
a second scale inhibitor supplying step of
supplying a calcium scale inhibitor which is a scale
inhibitor for inhibiting the deposition of a scale
containing calcium and a silica scale inhibitor which is
a scale inhibitor for inhibiting the deposition of
silica to water to be treated containing Ca ions, so,
ions, carbonate ions and silica;
a second demineralizing step of separating the
water to be treated into second concentrated water in
which the Ca ions, the so, ions, the carbonate ions and
15 the silica are concentrated and treated water after the
second scale inhibitor supplying step; and
a second crystallizing step of supplying seed
crystals of gypsum to the second concentrated water so
that gypsum is crystallized from the second concentrated
20 water,
wherein the water treatment process further
comprises, after the second crystallizing step:
a first scale inhibitor supplying step of
supplying the calcium scale inhibitor to the water to be
25 treated;
a first pH adjusting step of adjusting the water
to be treated to a pH at which the silica is soluble in
the water to be treated;
a first demineralizing step of separating the
30 water to be treated into first concentrated water in
which the Ca ions, the so, ions, the carbonate ions and
the silica are concentrated and treated water after the
75
first scale inhibitor supplying step and the first pH
adjusting step; and
a first crystallizing step of supplying seed
crystals of gypsum to the first concentrated water so
5 that gypsum is crystallized from the first concentrated
water.
2. The water treatment process according to claim 1,
comprising a second pH adjusting step of adjusting the
second concentrated water to a pH at which a scale
10 inhibition function of the calcium scale inhibitor is
reduced, thereby promoting the deposition of the gypsum
in the second crystallizing step.
3. The water treatment process according to claim 2,
wherein, after the second crystallizing step, the second
15 concentrated water after the adjustment of the pH in the
second pH adjusting step is adjusted to a pH at which
the calcium scale inhibitor exhibits its function.
4. The water treatment process according to claim 1,
comprising a second pH adjusting step of adjusting the
20 second concentrated water to a pH at which the silica is
soluble in the second crystallizing step.
25
5. The water treatment process according to claim 1,
comprising, after the first crystallizing step on a most
downstream of the water to be treated, a downstream side
demineralizing step of performing separation into
concentrated water and treated water, and recovering the
separated treated water.
6. The water treatment process according to any one of
claims 1 to 5, comprising a second upstream side
30 precipitating step of precipitating at least calcium
76
carbonate from the water to be treated so that the
concentration of the calcium carbonate in the water to
be treated is reduced, before the second scale inhibitor
supplying step on a most upstream side of the water to
5 be treated.
7. The water treatment process according to claim 6,
comprising a second deaerating step of removing C02 from
the water to be treated before the second upstream side
precipitating step or after the second upstream side
10 precipitating step and before the second scale inhibitor
supplying step.
8. The water treatment process according to any one of
claims 1 to 7,
wherein the water to be treated contains metal
15 ions; and
20
wherein the process comprises a second
precipitating step of precipitating at least one of
calcium carbonate and a metal compound so that the
concentration of at least one of the calcium carbonate
and the metal ions is reduced from the second
concentrated water, after the second crystallizing step.
9. The water treatment process according to claim 8,
wherein at least one of seed crystals of the silica and
a precipitant for the silica is supplied to the second
25 concentrated water in the second precipitating step.
30
10. The water treatment process according to claim 1,
wherein the water to be treated contains metal
ions; and
wherein the process comprises a
precipitating step of precipitating at least
77
first
one of
calcium carbonate and a metal compound so that the
concentration of at least one of the calcium carbonate
and the metal ions is reduced from the first
concentrated water, after the first crystallizing step.
5 11. The water treatment process according to claim 10,
wherein at least one of seed crystals of the silica and
a precipitant for the silica is supplied to the first
concentrated water in the first precipitating step.
12. The water treatment process according to claim 9 or 11,
10 wherein, when the water to be treated contains Mg ions,
the amount of the precipitant for the silica to be
supplied is adjusted according to the concentration of
the Mg ions.
13. The water treatment process according to claim 8,
15 wherein, when the water to be treated contains Mg
ions, the second concentrated water in the second
precipitating step is adjusted to a pH at which a
magnesium compound is deposited so that the
concentration of the Mg ions is reduced, and
20 wherein, after the second precipitating step, the
second concentrated water is adjusted to a pH at which
the magnesium compound is soluble.
14. The water treatment process according to claim 10,
wherein, when the water to be treated contains Mg
25 ions, the first concentrated water in the first
precipitating step is adjusted to a pH at which a
magnesium compound is deposited so that the
concentration of the Mg ions is reduced, and
wherein, after the first precipitating step, the
30 first concentrated water is adjusted to a pH at which
78
5
the magnesium compound is soluble.
15. The water treatment process according to claim 6,
wherein, when the water to be treated contains Mg
ions, the water to be treated in the second upstream
side precipitating step is adjusted to a pH at which a
magnesium compound is deposited so that the
concentration of the Mg ions is reduced, and
wherein, after the second upstream side
precipitating step, the water to be treated is adjusted
10 to a pH at which the magnesium compound is soluble.
16. The water treatment process according to claim 5,
wherein moisture is evaporated from the concentrated
water in the downstream side demineralizing step, so
that a solid in the concentrated water is recovered.
15 17. A water treatment system, comprising:
a second scale inhibitor supplying section that
supplies a calcium scale inhibitor which is a scale
inhibitor for inhibiting the deposition of a scale
containing calcium and a silica scale inhibitor which is
20 a scale inhibitor for inhibiting the deposition of
silica to water to be treated containing Ca ions, 804
ions, carbonate ions and silica;
a second demineralizing section that is positioned
on a downstream side of the second scale inhibitor
25 supplying section and separates the water to be treated
into second concentrated water in which the Ca ions, the
ions, the carbonate ions and the silica are
concentrated and treated water; and
a second crystallizing section including a second
30 crystallizing tank that is positioned on a downstream
side of the second demineralizing
79
section and
crystallizes gypsum from the
and a second
supplies seed
seed crystal
crystals of
crystallizing tank,
second concentrated
supplying section
gypsum to the
water
that
second
5 wherein the water treatment system comprises, on a
downstream side of the second crystallizing section with
respect to the water to be treated:
a first scale inhibitor supplying section that
supplies the calcium scale inhibitor to the water to be
10 treated;
a first pH adjusting section that supplies a pH
adjuster to the water to be treated to adjust the pH of
the water to be treated to such a value that the silica
is soluble in the water to be treated;
15 a first demineralizing section that is positioned
on a downstream side of the first scale inhibitor
supplying section and the first pH adjusting section and
separates the water to be treated into first
concentrated water in which the Ca ions, the S04 ions,
20 the carbonate ions and the silica are concentrated and
treated water; and
a first crystallizing section including a first
crystallizing tank that is positioned on a downstream
side of the first demineralizing section and
25 crystallizes gypsum from the first concentrated water
and a first seed crystal supplying section that supplies
seed crystals of gypsum to the first crystallizing tank.
18. The water treatment system according to claim 17,
comprising a second pH adjusting section that is
30 positioned on a downstream side of the second
demineralizing section and supplies a pH adjuster to the
second concentrated water to adjust the pH of the second
80
concentrated water
inhibition function
reduced, and the
promoted.
to such a value that a scale
of the calcium scale inhibitor is
precipitation of the gypsum is
5 19. The water treatment system according to claim 18,
comprising, on a downstream side of the second
crystallizing section, a third pH adjusting section that
supplies a pH adjuster to the second concentrated water
after the adjustment of the pH in the second pH
10 adjusting section to adjust the pH of the second
concentrated water to such a value that the calcium
scale inhibitor achieves a function.
20. The water treatment system according to claim 17,
comprising a second pH adjusting section that is
15 positioned on a downstream side of the second
demineralizing section and supplies a pH adjuster to the
second concentrated water to adjust the pH of the second
concentrated water to such a value that the silica is
soluble in the second concentrated water in the second
20 crystallizing section.
25
21. The water treatment system according to claim 17,
comprising, on a downstream side of the first
crystallizing section on a most downstream of the water
to be treated,
that separates
from the first
a downstream side demineralizing section
the first concentrated water discharged
crystallizing section into concentrated
water and treated water.
22. The water treatment system according to any one of
claims 17 to 21, comprising, on an upstream side of the
30 second scale inhibitor supplying section located on a
81
most upstream of the water to be treated, a second
upstream side precipitating section that precipitates at
least calcium carbonate from the water to be treated so
that the concentration of the calcium carbonate in the
5 water to be treated is reduced.
10
23. The water treatment system according to claim 22,
comprising a second deaerating section that removes C02
from the water to be treated on an upstream side of the
second upstream
downstream side
side
of
precipitating section or
the second upstream
precipitating section and on an upstream side
second scale inhibitor supplying section.
on a
side
of the
24. The water treatment system according to any one of
claims 17 to 23,
15 wherein the water to be treated contains metal
ions; and
of
wherein the system comprises,
the second crystallizing
on a downstream side
section, a second
precipitating section that precipitates at least one of
20 calcium carbonate and a metal compound.
25
25. The water treatment system according to claim 24,
wherein at least one of seed crystals of the silica and
a precipitant for the silica is supplied to the second
precipitating section.
26. The water treatment system according to claim 17,
wherein the water to be treated contains metal
ions; and
wherein the system comprises, on a downstream side
of the first crystallizing section, a first
30 precipitating section that precipitates at least one of
82
calcium carbonate and a metal compound.
27. The water treatment system according to claim 26,
wherein at least one of seed crystals of the silica and
a precipitant for the silica is supplied to the first
5 precipitating section.
28. The water treatment system according to claim 24,
wherein, when the water to be treated contains Mg ions,
the amount of the precipitant for the silica to be
supplied is adjusted according to the concentration of
10 the Mg ions in the second precipitating section.
29. The water treatment system according to claim 26,
wherein, when the water to be treated contains Mg ions,
the amount of the precipitant for the silica to be
supplied is adjusted according to the concentration of
15 the Mg ions in the first precipitating section.
30. The water treatment system according to claim 24,
wherein, when the water to be treated contains Mg
ions, the second concentrated water in the second
precipitating section is adjusted to a pH at which a
20 magnesium compound is deposited so that the
concentration of the Mg ions is reduced, and
wherein, on a downstream side of the second
precipitating section, the second concentrated water is
adjusted to a pH at which the magnesium compound is
25 soluble.
30
31. The water treatment system according to claim 26,
wherein, when the water to be treated contains Mg
ions, the first concentrated water in the first
precipitating section
magnesium compound
is adjusted to
is deposited
83
a pH at which a
so that the
concentration of the Mg ions is reduced, and
wherein, on a downstream side of the first
precipitating section, the first concentrated water is
adjusted to a pH at which the magnesium compound is
5 soluble.
10
32. The water treatment system according to claim 22,
wherein, when the water to be treated contains Mg
ions, the water to be treated in the second upstream
side precipitating section is adjusted to a pH at which
a magnesium compound is deposited so that the
concentration of the Mg ions is reduced, and
wherein, on a downstream side of the second
upstream side precipitating section, the water to be
treated is adjusted to a pH at which the magnesium
15 compound is soluble.
20
25
33. The water treatment system according to claim 21,
comprising, on a downstream side of the downstream side
demineralizing section with respect to the concentrated
water, an evaporator that evaporates moisture from the
concentrated water to recover the solids in the
concentrated water.