Technical Field
The present invention relates to a water treatment
process and a water treatment system for reproducing water to
5 be treated containing Ca ions (Ca2+) , sulfate ions (S04
2~) ,
carbonate ions, and silica.
Background Art
It is known that industrial waste water, saline water,
10 and sewage contain large amounts of ions and silica. In
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
15 silica in the cooling water are 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
treatment, a reverse osmosis membrane device, a nanofiltration
membrane device, an ion-exchange equipment, and the like are
known.
Among ions contained in the water mentioned above,
25 monovalent cations such as Na+, K+, and NH4
+ 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 S04
2~ and C032~,
and silica are scale-forming components. Salts and silica of
scale-forming components have low solubility in water, and
30 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 large amounts of Ca2+,
S04
2~, carbonate ions (C03
2~, HC03") , and silica. An example of
2
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,
CI ions: 200 mg/L, S04 ions: 120 mg/L, P04 ions: 5 mg/L, Si02
ions: 35 mg/L. Among these, the concentrations of Ca ions, Mg
5 ions, S04 ions, and HC03 ions are high, and as a result of
their reaction, scales (CaS04, CaC03, etc.) are formed. In
addition, depending on the concentration percentage, silica
components present in waste water also serve as scale
components adhering to the instrument, etc. When scales are
10 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 production of scales.
Here, examples of plants using a water-cooling-type
15 cooling tower are plants equipped with power generation
facilities (power generation facilities include those for
business purposes for electric power selling and those for
industrial purposes for in-house electricity use, and the
power generation is thermal power generation, geothermal power
20 generation, etc.), plants equipped with power generation
facilities and cooling facilities, etc. In addition, plants
include ordinary chemical plants, steel plants, mining plants,
oil field plants, gas field plants, mechanical plants, etc.
As a process for removing Ca ions, a lime soda process is
25 known. According to the lime soda process, sodium carbonate is
added to water to be treated, and Ca ions in 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
30 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.
3
Citation List
Patent Literature
PTL 1 U.S. Pat. No. 7815804
Summary of Invention
5 Technical Problem
The lime soda process requires the addition of sodium
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.
10 Meanwhile, in the case where SO42" is contained in water to be
treated, it is not removed by the lime soda process. That 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-
15 exchange equipment, the treatment of 1 mol of Ca ions results
in the production of 2 mol of Na+, and water the 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-
20 exchange equipment is further treated in a reverse osmosis
membrane device to remove ion components. 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
25 increased treatment load. In addition, with the device of
Patent Literature 1, S04
2~ is not removed but remains in the
treated water, and it has been difficult to obtain high water
recovery.
In addition, the waste water treatment device of Patent
30 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.
An object of the present invention is to provide a water
4
treatment process and a water treatment system, which are
capable of reproducing water containing salts with high water
recovery.
5 Solution to Problem
A first aspect of the present invention is a water
treatment process including:
a first scale inhibitor supplying step of supplying a
calcium scale inhibitor which is a scale inhibitor for
10 inhibiting the deposition of a scale containing calcium to
water to be treated containing Ca ions, S04 ions, carbonate
ions, and silica;
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
15 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 after the first scale inhibitor
20 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 that gypsum is
crystallized from the first concentrated water;
wherein the water treatment process further includes
25 after the first crystallizing step,
a second scale inhibitor supplying step of supplying the
calcium scale inhibitor and a silica scale inhibitor which is
a scale inhibitor for inhibiting the deposition of silica to
the water to be treated;
30 a second demineralizing step of separating the water to
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
5
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 water.
5 A second aspect of the present invention is a water
treatment system including:
a first scale inhibitor supplying section that supplies a
calcium scale inhibitor which is a scale inhibitor for
inhibiting the deposition of a scale containing calcium to
10 water to be treated containing Ca ions, S04 ions, carbonate
ions, and silica;
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
15 water to be treated;
a first demineralizing section that is installed on the
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,
20 the S04 ions, the carbonate ions, and the silica are
concentrated and treated water; and
a first crystallizing section including a first
crystallizing tank that is installed on the downstream side of
the first demineralizing section and crystallizes gypsum from
25 the first concentrated water and a first seed crystal
supplying section that supplies seed crystals of gypsum to the
first crystallizing tank;
wherein the water treatment system further includes on
the downstream side of the first crystallizing section with
30 respect to the water to be treated ;
a second scale inhibitor supplying section that supplies
the calcium scale inhibitor and a silica scale inhibitor which
is a scale inhibitor for inhibiting the deposition of silica
6
to the water to be treated;
a second demineralizing section that is installed on the
downstream side of the second scale inhibitor supplying
section and separates the water to be treated into second
5 concentrated water in which the Ca ions, the S04 ions, the
carbonate ions, and the silica are concentrated and treated
water; and
a second crystallizing section including a second
crystallizing tank that is installed on the downstream side of
10 the second demineralizing section and crystallizes gypsum from
the second concentrated water and a second seed crystal
supplying section that supplies seed crystals of gypsum to the
second crystallizing tank.
According to the first aspect and the second aspect, in
15 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 water treatment.
20 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 step, even when a scale
25 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, SO4 ions, carbonate ions, and silica can be treated
with high water recovery. In addition, the amount of chemicals
30 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 first aspect and the second aspect, owing to the
7
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
production of scales in the second demineralizing section and
5 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 is present,
gypsum can be crystallized and separated from the water to be
10 treated. As a result, the water to be treated containing Ca
ions, SO4 ions, and silica can be treated with high water
recovery, and the operation cost can be reduced. Further, this
is also advantageous in that high-purity gypsum can be
recovered.
15 In the above aspect, the water treatment process includes
a downstream side demineralizing step of separating the second
concentrated water after the second crystallizing step on the
most downstream of the water to be treated into concentrated
water and treated water, and recovering the separated treated
20 water.
In the above aspect, the water treatment system includes,
on the downstream side of the second crystallizing section on
the most downstream of the water to be treated, a downstream
side demineralizing section that separates the second
25 concentrated water discharged from the second crystallizing
section into concentrated water and treated water.
When the downstream side demineralizing step and the
downstream side demineralizing section are provided, the water
recovery can be further improved. In addition, in the
30 invention, the number of moles of ions in the water to be
treated is significantly reduced. Accordingly, the amount of
salts flowing into the downstream side demineralizing section
can be reduced, and thus the power of the downstream side
8
demineralizing section can be reduced.
In the above aspect, it is preferable that the water
treatment process includes a second pH adjusting step of
adjusting the second concentrated water to a pH at which a
5 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
treatment system includes a second pH adjusting section that
10 is installed on the 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 a scale inhibition
function of the calcium scale inhibitor is reduced, and the
15 deposition of the gypsum is promoted.
In this case, it is preferable that after the second
crystallizing step, the second 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 exerts
20 its function.
It is also preferable that the water treatment system
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
25 of the pH in the second pH adjusting section to 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
30 the second concentrated water to a pH at which the silica is
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
9
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
5 the second crystallizing section.
As a result of this configuration, the formation of
scales containing calcium in the downstream side
demineralizing section can be suppressed.
In the first aspect, it is preferable that the water
10 treatment process includes a first upstream side precipitating
step of precipitating 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, before the
first scale inhibitor supplying step and the first pH
15 adjusting 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 first deaerating step of removing
C02 from the water to be treated before the first upstream side
precipitating step or after the first upstream side
20 precipitating step and before the first scale inhibitor
supplying step and the first pH adjusting step.
In the second aspect, it is preferable that the water
treatment system includes, on the upstream side of the first
scale inhibitor supplying section and the first pH adjusting
25 section located on the most upstream of the water to be
treated, a first 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
30 preferable that the water treatment system includes a first
deaerating section that removes C02 from the water to be
treated on the upstream side of the first upstream side
precipitating section or on the downstream side of the first
10
upstream side precipitating section and on the upstream side
of the first scale inhibitor supplying section and the first
pH adjusting section.
In this way, by previously removing calcium carbonate
5 from the water to be treated before flowing into the
demineralizing section, the deposition of calcium carbonate as
scales during the water treatment can be inhibited. By
removing calcium carbonate, the purity of gypsum crystallized
in the crystallizing step and the crystallizing section can be
10 increased.
In the above aspect, it is preferable that the water to
be treated contains metal ions, and the water treatment
process includes a first precipitating step of precipitating
at least one of calcium carbonate and a metal compound so that
15 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 is preferable that the
water treatment process includes a second precipitating step
of precipitating at least one of calcium carbonate and a metal
20 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.
In this case, at least one of seed crystals of the silica
25 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.
30 In the above aspect, it is preferable that the water to
be treated contains metal ions, and the water treatment system
includes, on the downstream side of the first crystallizing
section, a first precipitating section that precipitates at
11
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 first concentrated water is reduced. It
is preferable that the water treatment system includes, on the
5 downstream side of the second crystallizing section, a second
precipitating 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.
10 In this case, at least one of seed crystals of the 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.
15 By removing calcium carbonate and a metal compound from
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
obtained.
20 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,
25 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,
30 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
12
for silica to be supplied is adjusted according to the
concentration of the Mg ions in the first precipitating
section. It is preferable that when the water to be treated
contains Mg ions, the amount of the precipitant for silica to
5 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 water
to be treated contains Mg ions, the first concentrated water
in the first precipitating step is adjusted to a pH at which a
10 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 to a pH at
which the magnesium compound is soluble. It is preferable that
the second concentrated water in the second precipitating step
15 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 precipitating step, the second concentrated water
is adjusted to a pH at which the magnesium compound is
soluble.
20 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
25 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 adjusted to a pH at which
30 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.
13
In the case where Mg ions are contained in the water to
be treated, Mg ions react with silica in the concentrated
water in the precipitating step and the precipitating section,
resulting in precipitation. In the present invention, the
5 amount of precipitant to be supplied is 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
10 magnesium compound 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 suppressing the formation of scales in the
demineralizing section located on the downstream side of the
15 precipitating section.
In the above aspect, it is preferable that when the water
to be treated contains Mg ions, the water to be treated in the
first upstream side precipitating step is adjusted to a pH at
which a magnesium compound is deposited so that the
20 concentration of the Mg ions is reduced, and, after the first
upstream side precipitating step, the water to be treated is
adjusted to a pH at which the magnesium compound is soluble.
In the above aspect, it is preferable that when the water
to be treated contains Mg ions, the water to be treated in the
25 first 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, on the
downstream side of the first upstream side precipitating
section, the water to be treated is adjusted to a pH at which
30 the magnesium compound is soluble.
In this way, in the case where Mg ions are contained in
the water to be treated, by efficiently removing Mg ions
before a demineralization treatment, the formation of scales
14
containing magnesium in the course of water treatment can be
inhibited.
In the above aspect, it is preferable that moisture is
evaporated from the concentrated water in the downstream side
5 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
10 is recovered. It is preferable that the water treatment system
includes, on the downstream side of 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.
15 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.
20 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 S04
2_ can be removed as gypsum
25 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 used,
30 they can be removed from the water to be treated while
inhibiting the production of scales containing magnesium
during the treatment.
Water treated by the present invention has a
15
significantly reduced number of moles of ions on the
downstream side. Therefore, the power of the demineralizing
section located downstream can be significantly reduced.
Further, the present invention is also advantageous in
5 that high-purity gypsum can be crystallized and recovered.
Brief Description of Drawings
Fig. 1 is a schematic diagram of a water treatment system
according to the first reference embodiment.
10 Fig. 2 shows 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.
Fig. 4 is a graph showing the pH dependency of the amount
15 of silica dissolved.
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
20 performed using simulated water in which gypsum is
supersaturated with changing the concentration of seed
crystals.
Fig. 7 is a microphotograph of gypsum crystallized under
Condition 5.
25 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
30 system according to the third reference embodiment.
Fig. 11 is a schematic diagram of a water treatment
system according to the first embodiment.
Fig. 12 is a schematic diagram of a water treatment
16
system according to the fourth reference 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
5 treatment system according to the sixth reference embodiment.
Fig. 15 is a schematic diagram explaining a water
treatment system according to the seventh reference
embodiment„
Fig. 16 is a schematic diagram explaining a water
10 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+, S04
2~, carbonate
15 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.
20 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
configured such that two water treatment sections are
25 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, and it is also
possible that three or more water treatment sections are
30 connected.
Each water treatment section includes, from the upstream
side of the water to be treated, a first demineralizing
section 10 (10a, 10b) and a first crystallizing section 20
17
(20a, 20b) . The concentration sides of the first
demineralizing sections 10a and 10b are connected to the first
crystallizing sections 20a and 20b, respectively. The water
treatment section includes a first scale inhibitor supplying
5 section 30 (30a, 30b) and a first pH adjusting section 40
(40a, 40b) in the flow path on the upstream side of each first
demineralizing section 10 (10a, 10b).
The first scale inhibitor supplying section 30 (30a, 30b)
is made up of a tank 31 (31a, 31b), a valve VI (Via, Vlb), and
10 a control section 32 (32a, 32b). The control sections 32a and
32b are connected to the valves Via and Vlb, respectively. The
tanks 31a and 31b have stored therein a scale inhibitor.
The scale inhibitor used in this reference embodiment
serves to inhibit the deposition of scales containing calcium
15 in the water to be treated. It will be hereinafter 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
20 to the surface of crystal nucleus of gypsum or 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,
25 there is another type of 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 phosphonicacid-
based scale inhibitors, polycarboxylic-acid-based scale
30 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
be treated, a scale inhibitor that inhibits the deposition of
18
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".
Examples of magnesium scale inhibitors include
5 polycarboxylic-acid-based scale inhibitors, etc. A specific
example is FLOCON 2 95N (trade name, manufactured by BWA).
Although Fig. 1 shows only one first scale inhibitor
supplying section 30a/30b in each position, in the case where
two or more kinds of scale inhibitors are loaded, it is
10 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.
The first pH adjusting section 40 (40a, 40b) is made up
of a tank 41 (41a, 41b), a valve V2 (V2a, V2b) , a control
15 section 42 (42a, 42b), and a pH meter 43 (43a, 43b). The tanks
41a and 41b have stored therein an alkali as a pH adjuster.
The alkali is calcium hydroxide or sodium hydroxide, for
example. Calcium hydroxide is particularly preferable because
Ca ions are recovered as gypsum in the below-mentioned
20 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 connected to the valves V2a
and V2b and the pH meters 43a and 43b, respectively.
In Fig. 1, the first demineralizing sections 10a and 10b
25 are reverse osmosis membrane devices. In addition, the first
demineralizing sections 10a and 10b may also be
electrodialyzers (ED), electro dialysis reversal devices
(EDR), electro de-ionization devices (EDI), ion-exchange
equipments (IEx), capacitive de-ionization devices (CDI),
30 nanofilters (NF), evaporators, etc.
Here, in a nanofilter (NF) , an electrodialyzer (ED) , an
electro dialysis reversal device (EDR), an electro deionization
device (EDI), and an capacitive de-ionization
19
device (CDI), scale components (divalent ions, Ca2+, Mg2+, etc.)
are selectively removed, while monovalent ions such as Na+ and
CI" permeate. The use of these demineralizers suppresses an
increase in the ion concentration of ions that serve as scale
5 components in concentrated water. Accordingly, the water
recovery can be improved, and also energy saving (e.g., the
reduction of pump power, etc.) can be achieved.
In addition, in the case where the water to be treated is
blowdown water from a cooling tower, the reclaimed water does
10 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 is
shown in Fig. 1, the system may also be configured such that
15 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 (21a, 21b) and a first seed
crystal supplying section 22 (22a, 22b) . The first seed
20 crystal supplying sections 22a and 22b are connected to the
first crystallizing tanks 21a and 21b, respectively. The first
seed crystal supplying sections 22a and 22b have a seed
crystal tank 23 (23a, 23b) , a valve V3 (V3a, V3b) , and a
control section 24 (24a, 24b) . The control sections 24a and
25 24b are connected to the valves V3a and V3b, respectively. The
seed crystal 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, 50b) may be installed on the
30 downstream side of each of the first crystallizing sections
20a and 20b. The first precipitating sections 50a and 50b each
include a first precipitating tank 51 (51a, 51b) and a first
filtration device 52 (52a, 52b).
20
The water treatment system 1 includes a downstream side
demineralizing section 60 on the downstream side of the water
to be treated of the first crystallizing section 20b located
on the most downstream.
5 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 (ED) ,
an electro dialysis reversal device (EDR), an electro deionization
device (EDI), an ion-exchange equipment, a
10 capacitive de-ionization device (GDI), a nanofilters (NF), an
evaporator, etc.
In the water treatment system 1, a precipitating tank 71
and a filtration device 72 are installed as a first upstream
side precipitating section 70 on the upstream side of the
15 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 71 and the
filtration device 72 have the same configuration as the first
precipitating tank 51 and the first filtration device 52 of
20 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 precipitating
section can be configured such that two or more precipitating
tanks 71 are connected in series in the flow direction of the
25 water to be treated.
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 deaeration
30 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
21
pH at which carbonate ions are present in the form of CO2 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
5 upstream side precipitating section 70 and on the upstream
side of the first scale inhibitor supplying sectipn 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
10 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 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
15 and the first demineralizing section 10b or the downstream
side demineralizing section 60.
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
20 device 72 and on the upstream of the first scale inhibitor
supplying section 30a and the first pH adjusting section 40a
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.
25 When gypsum in the water to be treated flowing into the
first demineralizing section 10a is already supersaturated,
because ions are further concentrated in the first
demineralizing section 10a, the resulting gypsum concentration
is even higher. In this case, the loading of a large amount of
30 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 section 10a.
22
Thus, in the case where gypsum in the raw water (water to
be treated) is supersaturated, it is possible that an upstream
side crystallizing section (not shown) having the same
configuration as the first crystallizing tanks 21a and 21b are
5 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 10a.
10 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
15 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 a
20 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 H2SO4 and Ca(OH)2 were
added as an acid and an alkali, respectively.
Fig. 4 is a graph showing the pH dependency of the amount
25 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
30 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
23
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
5 the first upstream side precipitating section 70, a step of
removing oils, floating particles, and the like form the water
to be treated and a step of removing organic substances by a
biological treatment or a chemical oxidation treatment are
performed.
10
In the water treatment system 1 of Fig. 1, the water to
be treated before flowing into the first deaerating section 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
15 the water to be treated.
Chemical Formula 1
C02 Z H2C03 Z HCO^ +H+Z CO]~ + 2H+ • • • (1 )
In the case where the pH is as low as 6.5 or less, it is
20 mainly present as HC03~ and C02 in the water to be treated.
The water to be treated containing C02 flows into the
first deaerating section 73. 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
25 carbonate ions are present as C02, carbon dioxide can be
efficiently removed.
The water to be treated, whose carbonate ion
concentration has been reduced in the first deaerating step,
is fed into the first upstream side precipitating section 70.
30
In the first upstream side precipitating section 70, some
24
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
5 side precipitating section 70, some of the metal ions are
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(0H)2 and an anionic
10 polymer (manufactured by Mitsubishi Heavy Industries
Mechatronics Systems, Ltd., trade name: Hishifloc H305) 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.
15 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
precipitated at the bottom of the precipitating tank 71.
The solubility of a metal compound depends on pH. A more
20 acidic pH leads to a higher solubility of metal ions in water.
For many metal compounds, the solubility is low in 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
25 tank 71.
The precipitated calcium carbonate and metal compound 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.
30 Mg(OH)2 is deposited at pH 10 or more.
In the case where the water to be treated containing Mg
ions is treated by the water treatment system 1 of this
reference embodiment, the pH of the water to be treated in the
25
precipitating tank 71 is adjusted to a pH at which a magnesium
compound (mainly magnesium hydroxide) is deposited.
Specifically, the pH of the water to be treated is adjusted to
10 or more, preferably 10.5 more, and more preferably 11 or
5 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 removed, resulting in a
decrease in the concentration of Mg ions in the water to be
10 treated.
In the above case, it is preferable that the water to be
treated after being discharged from the first upstream side
precipitating section 70 is adjusted to a pH at which the
above magnesium compound is soluble. Specifically, the pH is
15 adjusted to less than 10. Accordingly, the formation of scales
in devices and steps on the downstream side, particularly the
first demineralizing section 10a and the first demineralizing
step, can be inhibited.
In the case where two or more stages of precipitating
20 tanks 71 are provided, Mg ions in the water to be treated can
be reliably removed, and the concentration of Mg ions in the
water to be treated fed to the downstream side can be reduced.
The supernatant in the precipitating tank 71, which is
the water to be treated, is discharged from the precipitating
25 tank 71. FeCl3 is added to 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
72. The solids aggregated with Fe(OH)3 are removed through the
30 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 which carbonate
26
ions can be present as C02, specifically 6.5 or less.
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.
5 In the case where an ion-exchange equipment is installed,
Ca ions in the water to be treated are removed by the ionexchange
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.
10 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 section
installed immediately after the filtration device 72, and
gypsum is crystallized, thereby reducing the concentration of
15 gypsum in the water to be treated. The water to be treated
having a reduced concentration of gypsum is fed to the first
demineralizing section 10a.

The control section 32a of the first scale inhibitor
20 supplying section 30a opens the valve Via and supplies a
predetermined amount of calcium scale inhibitor to the water
to be treated from the tank 31a. The control section 32a
adjusts the opening of the valve Via so that the concentration
of the calcium scale inhibitor is a predetermined value set
25 according to the properties of the water to be treated.
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
30 scale inhibitor and the magnesium scale inhibitor are stored
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
27
inhibitor to be supplied.

The control section 42a of the first pH adjusting section
40a controls the pH of the water to be treated at the entrance
5 of the first demineralizing section 10a 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 first
demineralizing section 10a is adjusted to 10 or more,
preferably 10.5 or more, and more preferably 11 or more.
10 The pH meter 43a measures the pH of the water to be
treated at the entrance of the first demineralizing section
10a. The control section 42a 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
15 loaded to the water to be treated from the tank 41a.

In the first demineralizing section 10a, the pH-adjusted
water to be treated is treated. In the case where the first
demineralizing section 10a is a reverse osmosis membrane
20 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 nonpermeate
side of the reverse osmosis membrane, there is
25 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 (first concentrated
30 water).
As shown in Fig. 4, as a result of the first
demineralizing step, silica is contained in the first
concentrated water in the state of being dissolved in the
28
water to be treated. Even in the case where gypsum and 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.
5 In the case where Mg ions are contained in the water to
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
containing magnesium is suppressed by the magnesium scale
10 inhibitor.
The first concentrated water is fed toward the first
crystallizing section 20a.

The first concentrated water discharged from the first
15 demineralizing section 10a is stored in the first
crystallizing tank 21a of the first crystallizing section 20a.
The control section 24a of the first seed crystal supplying
section 22a opens the valve V3a and adds seed crystals of
gypsum to the first concentrated water in the first
20 crystallizing tank 21a from the tank 23a.
The pH of the first concentrated water from the first
demineralizing section 10a is 10 or more. As mentioned above,
gypsum is in the state of being dissolved in water in a highpH
region where a calcium scale inhibitor is present. However,
25 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 system 1 of Fig. 1,
the crystal-grown gypsum having a large diameter (e.g., having
a particle diameter of 10 urn or more, more preferably 20 una or
30 more) is precipitated at the bottom of the first crystallizing
tank 21a. The precipitated gypsum is discharged from the
bottom of the first crystallizing tank 21a.
Meanwhile, when the pH 10 is or more, silica is present
29
in the state of being dissolved in the first concentrated
water in the first crystallizing tank 21a. Even in the case
where the concentration of silica in the first concentrated
water exceeds the saturation solubility, because seed crystals
5 of silica are not present, silica is deposited as floating
matters in a colloidal 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
10 inhibitor has been added, the deposition of calcium 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
15 previously reduced. As a result, in the first crystallizing
tank 21a, 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
20 crystallization rate increases with a decrease in pH.
Fig. 5 shows the result of gypsum deposition experiments
with changing the pH of simulated water in the case where a
scale inhibitor (FLOCON260) is added to simulated water
(containing Ca2+, S04
2~, Na+, and Cl~) in which gypsum is
25 supersaturated. The experimental conditions are as 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 (Condition
30 3), 3.0 (Condition 4),
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
30
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, the ordinate
5 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 in
the case where seed crystals are present, gypsum is
10 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.
In the case where carbonate ions are contained in the
water to be treated, under low-pH conditions, carbonate ions
15 are removed from the water to be treated as CO2 as in chemical
formula (1). In addition, as can be understood from Fig. 3, in
the case where the pH is low, calcium carbonate is in a
dissolved state.
From these results, when the first crystallizing step is
20 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
crystallizing tank 21a. In the case where the first
crystallizing step is performed at low pH, a third pH
25 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 10a
and the first crystallizing tank 21a. The pH adjusting section
has the same configuration as the below-mentioned second pH
30 adjusting section.
Meanwhile, in order to change the pH in the course of
water treatment, it is necessary to supply a large amount of
chemicals (acid or alkali) . The use of an acid or an alkali
31
leads to an increase in the amount of ions transferred to the
downstream side of the first crystallizing section 20a, and
this causes an increase in the power of demineralizing
sections on the downstream side (in Fig. 1, the first
5 demineralizing section 10b or the downstream side
demineralizing section 60). In terms of operation cost, it 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
10 seed crystals. Fig. 6 shows the results of gypsum deposition
experiments with changing the amount of seed crystals to be
added in the case where a calcium scale inhibitor (FLOCON260)
is added to simulated water. The experimental conditions were
the same as in Fig. 5 except that the pH was 4.0, and that
15 gypsum (CaS04-2H20) was added as seed crystals in the following
amounts:
The amount of seed crystals to be added: 0 g/L (Condition
3), 3 g/L (Condition 5), 6 g/L (Condition 6), 3 g/L (Condition
7) .
20 Under Conditions 5 and 6, seed crystals and sulfuric acid
for pH adjustment were added to the simulated water having
added thereto a scale inhibitor. Under Condition 7, seed
crystals pre-immersed with the above scale inhibitor were
added to the simulated water having added thereto a scale
25 inhibitor, and sulfuric acid was added for pH adjustment.
Two hours immediately after the pH adjustment, the
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 (%).
30 From the results of Fig. 6, it can be understood that
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%
32
(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
5 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 with 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 with a calcium scale
inhibitor, when the pH is reduced to 4.0, the function of the
15 scale inhibitor is reduced.
Fig. 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 5,
20 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
urn or more, preferably 20 um or more, the resulting gypsum has
25 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
and an anionic polymer (Hishifloc H305) are loaded to the
33
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 or
less. In the first precipitating tank 51a, calcium carbonate
5 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 tank
51a.
10 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 be treated, such as
calcium carbonate and a metal compound, aggregate with Fe(OH)3.
15 The water to be treated is fed to the first filtration
device 52a. The solids aggregated with Fe(OH)3 are removed
through the first filtration device 52a.
Silica in the supernatant in the first crystallizing
section 20a may be removed from the first concentrated water
20 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 step
is determined according to the properties of the water to be
treated or the first concentrated water.
25 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
precipitating tank 51a. In this case, silica is separated from
the treated water in demineralizing sections located on the
30 downstream side (the first demineralizing section 10b 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
34
into the first concentrated water in the first 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 MgS04 or Na aluminate (Na[Al(OH) 4] ) ,
5 for example. In the case where silica is removed, it is
preferable that the first concentrated water in the first
precipitating tank 51a 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
10 the case where MgS04 is used as a precipitant for silica,
magnesium silicate is deposited. The 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.
15 In the case where Mg ions are contained in the water to
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
20 the content of silica in the first concentrated 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
25 precipitation with silica. In order to remove an excess of
silica that is not consumed by precipitation with Mg ions, a
precipitant for silica (MgS04) is supplied. With respect to
the amount of precipitant for silica to be supplied, according
to the content of silica and the content of Mg ions in the
30 first precipitating step, the precipitant is supplied in such
an amount that the excess of silica is consumed.
In the case where the first concentrated water in the
first precipitating step has a higher concentration of Mg ions
35
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 residual Mg
ions is discharged from the first precipitating tank 51a,
5 scales containing Mg may be deposited in demineralizing
sections of subsequent stages (the first demineralizing
section 10b in Fig. 1; in the case of the first precipitating
section on the most downstream, the downstream side
demineralizing section 60).
10 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
in the first precipitating tank 51a, thereby reducing the
15 concentration of Mg ions in the first concentrated water in
the first precipitating tank 51a. Further, after the first
precipitating step, the first concentrated water discharged
from the first precipitating tank 51a is adjusted to a pH at
which the magnesium compound is soluble, specifically to a pH
20 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
the first filtration device 52a of the first water treatment
25 section of the previous stage flows into the water treatment
section of the subsequent stage as water to be treated. In 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.
30
The concentrated water (first concentrated water) that
has passed through the first precipitating section 50b located
on the most downstream of the water to be treated is fed to
36
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 section 60 is discharged
5 out of the system. The installation of the downstream side
demineralizing section 60 makes it possible to further recover
treated water from water that has been treated in a water
treatment section. Accordingly, the water recovery is
improved.
10 In the water treatment system 1 of this reference
embodiment, ions are concentrated in the first demineralizing
section 10. However, gypsum, calcium carbonate, silica, etc.,
have been removed in the first crystallizing section, the
first precipitating section, etc. Accordingly, the water
15 flowing into the downstream side demineralizing section 60 has
a smaller number of moles of ions than before the treatment.
Accordingly, the osmotic pressure is low in the first
demineralizing section 10b or the downstream side
demineralizing section 60 located downstream, and the required
20 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
25 contained in the concentrated water are deposited 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 for evaporation
30 can be reduced.
Second Reference Embodiment
Fig. 9 is a schematic diagram of a water treatment system
37
of the second reference embodiment of the present invention.
In Fig. 9, the same configurations as in the first reference
embodiment are indicated with the same reference numerals. In
the water treatment system 100 of the second reference
5 embodiment, a first separating section 180 (180a, 180b) is
installed on the downstream side of the 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
10 the water treatment system 100 of this reference embodiment,
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 are
connected.
15 In Fig. 9, the first separating section 180 (180a, 180b)
includes a classifier 181 (181a, 181b) and a dehydrator 182
(182a, 182b). The classifiers 181a and 181b are liquid
cyclones, for example. The dehydrators 182a and 182b are belt
filters, for example.
20 Although the first separating section 180 has only one
classifier installed in Fig. 9, it is also possible that two
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 reference
25 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.

30 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 in the first
38
crystallizing tanks 21a and 21b.
The first concentrated water discharged from the first
crystallizing tanks 21a and 21b contains gypsum having various
particle diameters, as well as calcium carbonate and silica
5 deposited due to the exceeding of the saturation
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.
10 When the first concentrated water flows into the
classifiers 181a and 181b, gypsum having a predetermined size,
for example, gypsum having an average particle diameter of 10
um or more, sediments at the bottom of the classifiers 181a
and 181b, and gypsum having a small particle diameter, calcium
15 carbonate, and silica remain in 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
20 first precipitating sections 50a and 50b.
In this reference embodiment, seed crystals are added to
cause crystallization. Therefore, gypsum having an average
particle diameter of 10 um or more is mainly deposited, and
the proportion of gypsum having a small diameter is low.
25 Through the first separating step, gypsum having a low water
content and containing no impurities (i.e., high-purity
gypsum) can be separated and recovered with high recovery.
Some of the gypsum recovered in the first separating
sections 180a and 180b may be circulated through the seed
30 crystal tanks 23a and 23b as seed crystals.
Third Reference Embodiment
Fig. 10 is a schematic diagram of a water treatment
39
system of the third reference embodiment of the present
invention. The water treatment system 200 of Fig. 10 is
configured such that two water treatment sections are
connected in the flow direction of the water to be treated.
5 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 are
connected.
In the water treatment system 200 of the third reference
10 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
crystallizing section 220 (220a, 220b). The concentration
sides of the second demineralizing sections 210a and 210b are
15 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 the flow
path on the upstream side of each second demineralizing
section 210 (210a, 210b).
20 The second scale inhibitor supplying sections 230a and
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 second
25 scale inhibitor supplying sections 230a and 230b have stored
therein a scale inhibitor.
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
30 deposition of silica as scales in the water to be treated
(referred to as "silica scale inhibitor"). Examples of silica
scale inhibitors include phosphonic-acid-based scale
inhibitors, polycarboxylic-acid-based scale inhibitors, and
40
mixtures thereof. A specific example is FLOCON260 (trade name,
manufactured by BWA).
Fig. 10 shows two tanks 231a. For example, a calcium
scale inhibitor is stored in one tank 231a, and a silica scale
5 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
10 de-ionization device (EDI), an ion-exchange equipment, a
capacitive de-ionization device (CDI), a nanofilters (NF), an
evaporator, etc.
Although only one second demineralizing section 210 is
shown in Fig. 10, the system may also be configured such that
15 two or more demineralizers are connected in parallel or in
series in the flow direction of the water to be treated.
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). The
20 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 224 (224a,
224b). The control section 224 is connected to the valve V5.
25 The seed crystal tank 223 stores gypsum particles as seed
crystals.
In the water treatment system 200 of the third reference
embodiment, a second pH adjusting section 240 (240a, 240b) may
be installed between the second demineralizing section 210 and
30 the 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
41
pH adjuster. The acid used may be hydrochloric acid, sulfuric
acid, nitric acid, or the like, for example. Sulfuric acid is
particularly preferable because S04
2_ is removed as gypsum in
the crystallizing step, and thus the amount of ions that reach
5 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 243 may be installed in the
flow path between the second demineralizing section 210 and
the second crystallizing section 220 as shown in Fig. 10, or
10 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
of the second scale inhibitor supplying section 230a located
15 on the most upstream of the water to be treated. The second
upstream side precipitating section 270 has the same
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
20 flow direction of the water to be treated.
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
25 as the first deaerating section 73 of the 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
30 side of the second scale inhibitor supplying section 230a.
It is also possible that a deaerating section having the
same configuration as the second deaerating section 273 is
installed in the flow path between the second demineralizing
42
section 210a and the second crystallizing section 220a, in the
flow path between the second crystallizing section 220 and the
second precipitating section 250, and on the downstream side
of the second precipitating section 250 and in the flow path
5 between it and the second demineralizing section 210b or the
downstream side demineralizing section 60.
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
10 scale inhibitor supplying section 230a located on the most
upstream. In addition, depending on the concentration of
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
15 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 side of
the second crystallizing section 220 as shown in Fig. 10. The
20 second separating section 280 has the same configuration as
the first separating section 180 and includes a classifier 281
(281a, 281b) and a dehydrator 282 (282a, 282b).
In the water treatment system 200 of Fig. 10, a second
precipitating section 250 (250a, 250b) may be installed on the
25 downstream side of the second crystallizing section 220. The
second precipitating section 250 has the same configuration as
the first precipitating section 50 and includes a second
precipitating tank 251 (251a, 251b) and a second filtration
device 252 (252a, 252b).
30 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
evaporator (not shown in Fig. 10) may be installed on the
43
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
5 will be described hereinafter.

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

10 In the same manner as in the first deaerating step
described in the first reference embodiment, CO2 in the water
to be treated is removed in the second deaerating section 273,
whereby the concentration of carbonate ions in the water to be
treated is reduced.
15
In the second upstream side precipitating section 270,
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
20 to be treated, in the second upstream side precipitating
section 270, some of a metal compound having 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
25 step.
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
30 is deposited in the second upstream side 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
44
soluble on the downstream side of the second upstream side
precipitating section 270. 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
5 demineralizing section 210 and the second demineralizing step,
can be inhibited.
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 which carbonate
10 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
precipitating step may be omitted.
In the case where an ion-exchange membrane device is
15 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.
In the case where an upstream side crystallizing section
is installed, the concentration of gypsum in the water to be
20 treated is reduced in the upstream side crystallizing section
through the same steps as in the first reference embodiment.

The control section 232a of the second scale inhibitor
supplying section 230a opens the valve V4a and supplies a
25 predetermined amount of calcium scale inhibitor to the water
to be treated from the tank 231a. The control section 232b 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
30 control section 232a and the control section 232b adjust the
valve opening of the valve V4a and the valve V4b,
respectively, so that the concentrations of the calcium scale
inhibitor and the silica scale inhibitor are predetermined
45
values set according to the properties of the water to be
treated.
In the water treatment system 200 of the third reference
embodiment, the pH adjustment of the water to be treated
5 immediately before flowing into the second demineralizing
section 210 is optionally performed.
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
10 demineralizing section 210a. As shown in Fig. 3, the
solubility of calcium carbonate in water is high when the pH
of the water to be treated is 6.5 or less. In addition, as in
formula (1), in the above pH range, carbonic acid is present
mainly in the form of HC03~ and C02 in water. The water to be
15 treated flowing into the second demineralizing 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 be
20 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 section 210a, and the
25 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 the
30 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
46
from the non-permeate side of the reverse osmosis membrane as
concentrated water (second concentrated water).
As a result of the treatment in the second demineralizing
section 210a, gypsum and silica is concentrated in the second
5 concentrated water. However, the production of scales is
suppressed by the calcium scale inhibitor and the silica scale
inhibitor.
Also in the case where other demineralizers, such as a
capacitive de-ionization device, are used, for example, the
10 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.

15 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
section 220a.
20 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. The pH
meter 243a measures the pH of the second concentrated water.
25 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.

The second concentrated water is stored in the second
30 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
47
second concentrated water in the second crystallizing tank
221a. Although the second concentrated water contains a
calcium scale inhibitor, when seed crystals are loaded, gypsum
is crystallized, followed by crystal growth.
5 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 elapse of
6 hours. Under Condition 1, the scale inhibitor exerts its
function to suppress the deposition of gypsum. Meanwhile, >
10 under Condition 4 and Condition 2, the degree of
supersaturation decreases.
That is, it has been confirmed that even when seed
crystals are not loaded, a decrease in pH leads to a decrease
in the function of the scale inhibitor, whereby gypsum is
15 crystallized. In addition, according to the results of Fig. 5,
the deposition rate increases with a decrease in pH.
In Fig. 6, as a comparison with Condition 5 (pH 4.0),
under Condition 7 (pH 4.0), seed crystals pre-immersed with
the above calcium scale inhibitor were added to simulated
20 water having added thereto a calcium scale inhibitor, and
sulfuric acid was added for pH adjustment. Condition 5 and
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
25 simulated water was measured by the same technique as in Fig.
3.
As a result, as shown in Fig. 6, the degree of
supersaturation was 199% or less both under Condition 5 and
Condition 7. From this, it can be said that independent of the
30 immersion time of seed crystals with a calcium scale
inhibitor, when the pH is reduced to 4.0, the function of the
calcium scale inhibitor is reduced.
In consideration of the effects of the calcium scale
48
inhibitor, the pH of the second concentrated water is 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,
5 the function of the calcium scale inhibitor can be
significantly reduced. 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
10 promoted. According to the kind of scale inhibitor, 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 loaded in
15 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. 3, calcium carbonate
dissolves in water at pH 6.0 or less.
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 221a in the second separating
section 280a is classified, the purity of the recovered gypsum
49
can be increased.

In the case where the second separating section 280a is
installed, the second concentrated water containing solid
5 matters deposited in the second crystallizing tank 221a is
transferred to the second separating section 280a. In the
second concentrated water in the second crystallizing tank
221a, gypsum deposited by crystallization is present. In
addition, the second concentrated water may also contain
10 silica deposited because of an increase in the silica
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
15 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
20 of 10 um 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, high-purity gypsum can
be recovered. Some of the recovered gypsum may be circulated
25 through the seed crystal tank 223a as seed crystals.
In the case where the second separating section 280a is
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 tank 221a.
30 The supernatant of the second crystallizing tank 221a is fed
to the second precipitating section 250a.

The supernatant (second concentrated water) in the second
50
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
5 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.
In the second precipitating step, it is also possible
10 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.
In the case where the treatment is performed in several
15 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. In the water treatment section of the
20 subsequent stage, the steps from the second scale inhibitor
supplying step to the second precipitating step mentioned
above are performed.

The second concentrated water that has passed through the
25 second precipitating section 250b located on the most
downstream of the water to be treated is treated in the
downstream side demineralizing section 60. The water that has
passed through the downstream side demineralizing section 60
is recovered as water to be treated. The concentrated water in
30 the downstream side demineralizing section 60 is discharged
out of the system.
Also in this reference embodiment, an evaporator (not
shown) may be installed on the downstream on the concentrated-
51
water side of the downstream side demineralizing section 60.
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
5 scale inhibitor is reduced, as a third pH adjusting step, the
pH of the second concentrated water may be adjusted 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,
10 and more preferably 6.0 or more. The third pH adjusting step
is performed after the second crystallizing step and before
the second demineralizing step, or after the second
crystallizing step and before the downstream side
demineralizing step.
15 In the water treatment system 200 of this reference
embodiment, in order to perform the third pH adjusting step, 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
20 second demineralizing section immediately thereafter (in Fig.
10, between the second crystallizing section 220a and the
second demineralizing sections 210b, particularly the second
precipitating section 250a and the second demineralizing
section 210b). In addition, a third pH adjusting section (not
25 shown in Fig. 10) having the same configuration as the second
pH adjusting section is installed between the second
precipitating section 250b and the downstream side
demineralizing section 60 on the most downstream. Accordingly,
even in the case where the second concentrated water is
30 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 inhibitor.
52
In the water treatment system 200 of this reference
embodiment, silica is concentrated by the treatment in the
second water treatment section. When the concentration of
silica in the second concentrated water is equal to or higher
5 than the concentration at 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
10 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
15 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 crystallizing
20 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 crystallizing
section 220 can be increased.
25 First Embodiment
Fig. 11 is a schematic diagram of a water treatment
system of the first 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
30 numerals.
In the water treatment system 300 of the first
embodiment, the water treatment section described in the first
reference embodiment is installed. On the downstream side of
53
the water to be treated of this water treatment section, the
water treatment section described in the third reference
embodiment is installed.
In the water treatment system 300 of Fig. 11, a first
5 separating section 180 is installed on the downstream side of
the first crystallizing section 20. In addition, a second
separating section 280, which is the same as the first
separating section 180, is installed on the downstream side of
the second crystallizing section 220.
10 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.
The water treatment system 300 of the first embodiment
15 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 located on the most
upstream of the water to be treated.
20 Further, the water treatment system 300 of the first
embodiment includes a first deaerating section 73, 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
25 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
30 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 first
54
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 first precipitating
section 50 and the second demineralizing section 210.
5 Also in the water treatment system 300 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 first scale inhibitor
supplying section 30 and the first pH adjusting section 40.
10 In Fig. 11, the water treatment sections from the first
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
15 for each section, two or more stage of water treatment
sections are connected.
In the water treatment system 300 of the first
embodiment, first, water to be treated is treated by the water
treatment process described in the first reference embodiment
20 and the second reference embodiment. First concentrated water
after being treated by the process of the first reference
embodiment and the second reference embodiment is treated as
water to be treated through the steps form the second scale
inhibitor supplying step to the second precipitating step
25 described in the third reference embodiment.
Second concentrated water that has passed through the
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
30 demineralizing section 60 is recovered as treated water. The
concentrated water in the downstream side demineralizing
section 60 is discharged out of the system.
Also in this embodiment, an evaporator (not shown) may be
55
installed on the downstream on the concentrated-water side of
the downstream side demineralizing section 60.
In the first embodiment, in the case where the second
concentrated water is adjusted to a pH at which the function
5 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.
Fourth Reference Embodiment
Fig. 12 is a schematic diagram of a water treatment
10 system of the fourth reference embodiment of the present
invention. In Fig. 12, the same configurations as in the first
to third reference embodiments are indicated with the same
reference numerals.
In the water treatment system 400 of the fourth reference
15 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 section, the
water treatment section described in the first reference
embodiment is installed.
20 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
25 crystallizing section 20 located on the most downstream.
The water treatment system 400 of the fourth reference
embodiment 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
30 230 located on the most upstream of the water to be treated.
Further, the water treatment system 400 of the fourth
reference embodiment has a second deaerating section 273,
which is the same as in the third reference embodiment, on the
56
upstream side of the second upstream side precipitating
section 270 as shown in Fig. 12. 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
5 and on the upstream side of the second scale inhibitor
supplying section 230.
Incidentally, a deaerating section having the same
configuration as the second deaerating section 273 may be
installed in the flow path between the second demineralizing
10 section 210 and the second crystallizing section 220, in the
flow path between the first crystallizing section 20 and the
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
15 precipitating section 250 and the first demineralizing section
10.
Also in the water treatment system 400 of this reference
embodiment, an ion-exchange equipment (not shown) and an
upstream side crystallizing section (not shown) may be
20 provided on the upstream of the second scale inhibitor
supplying section 230.
In the water treatment system 400 of this reference
embodiment shown in Fig. 12, a first separating section 180
and a second separating section 280 may be installed on the
25 downstream side of the first crystallizing tank 21 and the
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
30 supplying section 30 to the first precipitating section 50 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.
57
In the water treatment system 400 of the fourth reference
embodiment, first, water to be treated is treated by the water
treatment process described in the third reference embodiment.
Second concentrated water after being treated by the process
5 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 described in
the first reference embodiment and the second reference
embodiment.
10 First concentrated water that has passed through the
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
15 concentrated water in the downstream side demineralizing
section 60 is discharged out of the system.
Also in this reference embodiment, an evaporator (not
shown) may be installed on the downstream on the concentratedwater
side of the downstream side demineralizing section 60.
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 performed.
25 Also by the water treatment system 300 of the first
embodiment and the water treatment system 400 of the fourth
reference embodiment, water to be treated containing ions can
be treated with high water recovery.
In particular, the fourth reference embodiment is
30 configured such 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
58
ions fed to the downstream side is further reduced. Further,
the purity of the gypsum recovered in the second crystallizing
section 220 can be increased.
5 Fifth Reference Embodiment
According to the fifth reference embodiment of the
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 reference
10 embodiments 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 configuration is also applied to the second
crystallizing tank 221.
15 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
first pH measuring section 543 may be installed in the flow
path that connects the first demineralizing section 10 and the
20 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 of the seed
crystal supplying section. 22.
In the fifth reference embodiment, as shown in Fig. 13, a
25 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 to
the control section 542 of the pH adjusting section 540. The
pH adjusting section 540 controls the pH of the first
30 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 case where the amount of seed
59
crystals of gypsum to be supplied to the second crystallizing
tank 221 is controlled, the pH meter 243a described in the
third reference embodiment corresponds to the second pH
measuring section, and the control section 242 of the second
5 pH adjusting section corresponds to the control section 542.
Seed crystals stored in the seed crystal tank 23 of the
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
10 separated by the classifier 181, whose particle diameter is
equal to or greater than a predetermined particle diameter, or
gypsum after being dehydrated by the dehydrator 182.
The control of the amount of seed crystals to be supplied
in the fifth reference embodiment is performed through the
15 following steps. Hereinafter, the case where the amount of
seed crystals 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 the
first concentrated water in the first crystallizing tank 21.
20 The measured pH value is sent to the control section 24 of the
seed crystal supplying section 22.
The control section 24 stores the pH range where the
scale inhibition function of a calcium scale inhibitor is
reduced. Specifically, as described for the second
25 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
30 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 be supplied.
In the case where the measured value is greater than the above
60
pH range, the control section 24 increases the opening of the
valve V3 to increase the amount of seed crystals of gypsum to
be supplied.
Gypsum is deposited when seed crystals are present.
5 However, in the case where the calcium scale inhibitor exerts
its function, the crystallization rate is low. 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
10 crystallization rate can be obtained even when the amount of
seed crystals is small.
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.
15 In this reference embodiment, it is also possible that
the pH is regularly measured during continuous operation, 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, for
20 example, and the amount of seed crystals to be supplied is
increased or decreased based on the obtained time-dependent
variation.
Sixth Reference Embodiment
25 The sixth reference embodiment of the present invention
is a water treatment system 600 provided with at least 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
30 separating section is directly supplied to a first
crystallizing tank or a second crystallizing tank as seed
crystals.
The configuration that controls the amount of seed
61
crystals to be supplied to the first crystallizing tank 21 in
this reference embodiment will be described with reference to
Fig. 14. The same configuration is also applied to the second
crystallizing tank 221.
5 In Fig. 14, a first circulation line 601, which 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
10 performs transfer so that some of the gypsum 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,
15 this reference embodiment may also be 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
20 reference embodiment, the valve V8, and the valve V9.
The control of the amount of seed crystals to be supplied
in the sixth reference embodiment is performed through the
following steps. Hereinafter, the case where the amount of
seed crystals to be supplied is constantly controlled during
25 continuous operation will be explained as 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.
The control section 610 stores the pH range where the
30 scale inhibition function of a calcium scale inhibitor is
reduced. Through the same steps as in the fifth reference
embodiment, the control section 610 compares the value
measured by the first pH measuring section 543 with the above
62
pH range to adjust the opening of the valve V8 and the valve
V9.
In the fifth reference embodiment and the sixth reference
embodiment, a seed crystal concentration measuring section
5 (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
crystallizing tank 21. The seed crystal concentration
measuring section measures the concentration of seed crystals
10 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 section 610 stores
the threshold for the concentration of seed crystals, and
increases the amount of seed crystals to be supplied in the
15 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
20 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 first
concentration measuring section is preferably installed on the
downstream side of the first separating section 180, but may
25 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 the control section
610.
In the case of the second crystallizing tank 221, a
30 second concentration measuring section is installed in place
of the first concentration measuring section.
The first concentration measuring section measures at
least one of the concentration of Ca ions and the
63
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.
5 The concentration of Ca ions and the concentration of
sulfate ions measured by the first concentration measuring
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
10 lead to a higher crystallization rate.
The control section 24 and the control section 610 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
15 ions and the concentration of sulfate ions measured by the
first concentration measuring section is equal to or 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
20 concentration of Ca ions and the concentration of sulfate ions
measured by the first concentration measuring 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.
25 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 higher
than the threshold, the control section 610 increases the
opening of the valve V8 and the valve V9 to increase the
30 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,
64
the control section 610 reduces the opening of the valve V8
and the valve V9 to reduce the amount of seed crystals to be
supplied.
Also in the case of the second crystallizing tank 221,
5 the amount of seed crystals to be supplied is controlled
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 Ca ions and the concentration of sulfate ions after the
10 crystallizing step, the amount of seed crystals used can be
reduced.
Seventh Reference Embodiment
Fig. 15 is a partial schematic diagram of a water
15 treatment system of the seventh reference embodiment of the
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
20 such that the gypsum separated from the first concentrated
water in the first crystallizing section 20 in the water
treatment system of the fourth reference embodiment is
recovered and supplied to the second crystallizing tank 221 of
the second crystallizing section 220. Also in the water
25 treatment system of the first embodiment, the same
configuration can be employed.
As described in the first reference embodiment, the pH of
concentrated water (first concentrated water) in the first
crystallizing tank 21 of the first crystallizing section 20 is
30 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 demineralizing
step. In this case, the first crystallizing step is performed
65
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
embodiment, in the second crystallizing section 220 (second
5 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 calcium carbonate
recovered in the first crystallizing section 20 is supplied to
10 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 concentrated water. By using
the water treatment system 300 of the seventh reference
15 embodiment, water to be treated can be treated with high water
recovery, and also high-purity gypsum can be recovered.
{Eighth Reference Embodiment}
Fig. 16 is a partial schematic diagram of a water
treatment system of the eighth reference embodiment of the
20 present invention. In Fig. 16, the same configurations as in
the second reference embodiment are indicated with the same
reference numerals.
Incidentally, the eighth reference embodiment will be
described hereinafter using a water treatment process
25 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.
In Fig. 16, the water treatment system 800 includes, for
30 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 181a and 181b
are installed. The size of gypsum to be separated is different
66
between the first classifier 181a located on the most upstream
and the first classifier 181b located on the downstream side.
In this reference embodiment, the size of gypsum to be
separated by the first classifier 181b is smaller than that of
5 gypsum to be separated by the first classifier 181a. For
example, the first classifier 181a is a classifier that
separates particles having an average particle diameter of 10
um or more, and the first classifier 181b is a classifier that
separates particles having an average particle diameter of 5
10 um or more.
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.
15 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.
20 In the water treatment system 800 of the eighth reference
embodiment, the following treatment is performed in the first
separating step.
In the first classifier 181a located on the most
upstream, gypsum having an average particle diameter of 10 jam
25 or more is classified and sedimented at the bottom of the
first classifier 181a. The sedimented gypsum is discharged
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
30 mainly contains particles having a particle diameter of less
than 10 um (gypsum, calcium carbonate, silica, etc.).
In the first classifier 181b located on the downstream
side, gypsum having an average particle diameter of 5 jam or
67
more is classified and sedimented at the bottom of the first
classifier 181b. The supernatant in the first classifier 181b
is fed to the first precipitating section 50.
The sedimented gypsum is discharged from the first
5 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 the
first crystallizing tank 21.
The circulated gypsum functions as seed crystals in the
10 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 um
or more is fed from the first crystallizing tank 21 to the
first classifier 181a together with the first concentrated
15 water, then separated from the first concentrated water by the
first classifier 181a, and transferred to the dehydrator 182.
The supernatant in the first classifier 181b contains
particles having a relatively small diameter of less than 5
um, such as those having a particle diameter of about 2 to 3
20 um. 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
crystallizing tank 21, and an increased amount of gypsum flows
25 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 that connects the
bottom of the first precipitating tank 51 to the first
30 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.
68
10
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 leads to the
reduction of the amount of gypsum particles having a
relatively small diameter flowing out to the downstream side.
Accordingly, the water recovery can be improved, and also the
amount of waste resulting from the water treatment can be
reduced.
15
20
25
30
Reference Signs List
1, 100, 200, 300, 400, 500, 600, 700, 800
system
10: First demineralizing section
20: First crystallizing section
21: First crystallizing tank
22: First seed crystal supplying section
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
40: First pH adjusting section
43, 243: pH meter
Water treatment
50
51
52
60
70
71
72
73
First precipitating section
First precipitating tank
First filtration device
Downstream side demineralizing section
First upstream side precipitating section
Precipitating tank
Filtration device
First deaerating section
180: First separating section
69
181, 181a, 181b, 281: Classifier
182, 282: Dehydrator
Second demineralizing section
Second crystallizing section
Second crystallizing tank
Second seed crystal supplying section
Second scale inhibitor supplying section
Second pH adjusting section
Second precipitating section
Second precipitating tank
Second filtration device
Second separating section
pH adjusting section
First pH measuring section
First circulation line
Second circulation line
101, 802: Solid matter circulation line
70
CLAIMS
1. A water treatment process comprising:
a first scale inhibitor supplying step of supplying
a calcium scale inhibitor which is a scale inhibitor for
5 inhibiting the deposition of a scale containing calcium
to water to be treated containing Ca ions, S04 ions,
carbonate ions and silica;
a first pH adjusting step of adjusting the water to
be treated to a pH at which the silica is soluble in the
10 water to be treated;
a first demineralizing step of separating the water
to be treated into first concentrated water in which the
Ca ions, the SO4 ions, the carbonate ions and the silica
are concentrated and treated water after the first scale
15 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
that gypsum is crystallized from the first concentrated
20 water,
wherein the water treatment process further
comprises, after the first crystallizing step:
a second scale inhibitor supplying step of supplying
the calcium scale inhibitor and a silica scale inhibitor
25 which is a scale inhibitor for inhibiting the deposition
of the silica to the water to be treated;
a second demineralizing step of separating the water
to be treated into second concentrated water in which the
Ca ions, the S04 ions, the carbonate ions and the silica
30 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
71
that gypsum is crystallized from the second concentrated
water.
2. The water treatment process according to claim 1,
comprising a second pH adjusting step of adjusting the
5 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.
3. The water treatment process according to claim 1 or 2,
10 comprising, after the second crystallizing step on a most
downstream of the water to be treated, a downstream side
demineralizing step of separating the second concentrated
water into concentrated water and treated water, and
recovering the separated treated water.
15 4. The water treatment process according to claim 2, wherein,
after the second crystallizing step, the second
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 exerts its function.
20 5. 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 the silica is
soluble in the second crystallizing step.
6. The water treatment process according to any one of claims
25 1 to 5, comprising a first upstream side precipitating
step of precipitating 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,
before the first scale inhibitor supplying step and the
30 first pH adjusting step on a most upstream side of the
water to be treated.
7. The water treatment process according to claim 6,
comprising a first deaerating step of removing C02 from
7 2
the water to be treated before the first upstream side
precipitating step or after the first upstream side
precipitating step and before the first scale inhibitor
supplying step and the first pH adjusting step.
5 8. The water treatment process according to any one of claims
1 to 7,
wherein the water to be treated contains metal ions;
and
wherein the process comprises a first precipitating
10 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.
15 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 first
concentrated water in the first precipitating step.
10. The water treatment process according to claim 1 or 2,
20 wherein the water to be treated contains metal ions;
and
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
25 least one of the calcium carbonate and the metal ions is
reduced from the second concentrated water, after the
second crystallizing step.
11. The water treatment process according to claim 10, wherein
at least one of seed crystals of the silica and a
30 precipitant for the silica is supplied to the second
concentrated water in the second precipitating step.
12. The water treatment process according to claim 9 or 11,
wherein, when the water to be treated contains Mg ions,
73
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,
•i 5 wherein, when the 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
10 wherein, after the first precipitating step, the
first 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
15 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
wherein, after the second precipitating step, the
20 second concentrated water is adjusted to a pH at which
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 first upstream side
25 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 upstream side precipitating
step, the water to be treated is adjusted to a pH at
30 which the magnesium compound is soluble.
16. The water treatment process according to claim 3, wherein
moisture is evaporated from the concentrated water in the
downstream side demineralizing step, so that a solid in
7 4
the concentrated water is recovered.
A water treatment system comprising:
a first scale inhibitor supplying section that
supplies a calcium scale inhibitor which is a scale
inhibitor for inhibiting the deposition of a scale
containing calcium to water to be treated containing Ca
ions, S04 ions, carbonate ions and silica;
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
installedinstalled 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
SO4 ions, the carbonate ions and the silica are
concentrated and treated water; and
a first crystallizing section including a first
crystallizing tank that is installed 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 the first crystallizing tank,
wherein the water treatment system further
comprises, on a downstream side of the first
crystallizing section with respect to the water to be
treated:
a second scale inhibitor supplying section that
supplies the calcium scale inhibitor and a silica scale
inhibitor which is a scale inhibitor for inhibiting the
deposition of silica to the water to be treated;
a second demineralizing section that is installed on
75
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 SO4 ions, the
carbonate ions and the silica are concentrated and
treated water; and
a second crystallizing section including a second
crystallizing tank that is installed on a downstream side
of the second demineralizing section and crystallizes
gypsum from the second concentrated water and a second
seed crystal supplying section that supplies seed
crystals of gypsum to the second crystallizing tank.
The water treatment system according to claim 17,
comprising a second pH adjusting section that is installed
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 a scale inhibition function of the
calcium scale inhibitor is reduced, and the deposition of
the gypsum is promoted.
The water treatment system according to claim 17,
comprising, on a downstream side of the second
crystallizing section on a most downstream of the water to
be treated, a downstream side demineralizing section that
separates the second concentrated water discharged from
the second crystallizing section into concentrated water
and treated water.
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 adjusting
section to adjust the pH of the second concentrated water
to such a value that the calcium scale inhibitor exerts a
76
function.

Claim
1. The water treatment system according to claim 17,
comprising a second pH adjusting section that is installed
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 crystallizing section.
2. The water treatment system according to any one of claims
17 to 21, comprising, on an upstream side of the first
scale inhibitor supplying section and the first pH
adjusting section located on a most upstream of the water
to be treated, a first 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.
3. The water treatment system according to claim 22,
comprising a first deaerating section that removes C02
from the water to be treated on an upstream side of the
first upstream side precipitating section or on a
downstream side of the first upstream side precipitating
section and on an upstream side of the first scale
inhibitor supplying section and the first pH adjusting
section.
4. The water treatment system according to any one of claims
17 to 23,
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 precipitating
section that precipitates 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
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ions in the first concentrated water is reduced.
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 first
5 precipitating section.
26. The water treatment system according to claim 17 or 18,
wherein the water to be treated contains metal ions;
and
wherein the system comprises, on a downstream side
10 of the second crystallizing section, a second
precipitating section that precipitates 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 in the second concentrated water is
15 reduced.
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 second
precipitating section.
20 28. The water treatment system according to claim 25, 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 in
the first precipitating section.
25 29. The water treatment system according to claim 27, 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 in
the second precipitating section.
30 30. The water treatment system according to claim 24,
wherein, 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
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magnesium compound is deposited 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
5 adjusted to a pH at which the magnesium compound is
soluble.
31. The water treatment system according to claim 26,,
wherein, when the water to be treated contains Mg
ions, the second concentrated water in the second
10 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
precipitating section, the second concentrated water is
15 adjusted to a pH at which the magnesium compound is
soluble.
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 first upstream side
20 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 first upstream
side precipitating section, the water to be treated is
25 adjusted to a pH at which the magnesium compound is
soluble.
33. The water treatment system according to claim 19,
comprising, on a downstream side of the concentrated water
in the downstream side demineralizing section, an
30 evaporator that evaporates moisture from the concentrated
water to recover the solids in the concentrated water.