Field
The present invention relates to a water treatment
system and a water treatment method for effluent generated,
for example, in a boiler plant or a chemical plant facility.
5
Background
For example, in a process plant like a power generation
plant or a chemical plant, effluent is generated, for
example, from a boiler, a reactor, a wet-type cooler for a
10 steam condenser, or a water treatment device. Various types
of treatment devices have been suggested to perform
treatment of such effluent, but any of those devices can
only be implemented with an increase in costs. To address
such a problem, a suggestion has been made on a boiler with
15 an effluent treatment device which is characterized in that
cooling water (blow water) in a cooler of the boiler is
sprayed into a flue gas duct as a mist of droplets having a
diameter of 20 to 120 micron, thereby neutralizing the
alkaline blow water (Patent Literature 1).
20 There has also been a suggestion on an effluent
treatment device in which effluent is sprayed into a flue
gas duct, thereby increasing the amount of effluent that can
be vaporized (Patent Literature 2).
2 5 Citation List
Patent Literature
Patent Literature 1: Japanese Patent Application Laidopen
No. 8-47693
Patent Literature 2: Japanese Patent Application Laid-
30 open No. 2001-29939
2
Summary
Technical Problem
However, the invention according to Patent Literature 1
can perform treatment of effluent with ease and at low costs,
5 but raises the problem in that an increase in the amount of
effluent relative to the heat energy (the temperature and
the flow rate) of the flue gas may cause an increase in the
energy required to vaporize the effluent with the result
that the effluent cannot be treated.
10 On the other hand, the invention of Patent Literature 2
makes it possible to reduce the amount of effluent by a
concentrating device, but raises the problem of causing
degradation in the output of the steam turbine because the
concentrating device bleeds part of the steam generated in
15 the boiler.
Therefore, the emergence of such a technique is desired
which can efficiently perform treatment of effluent at low
costs without degradation in boiler efficiency, the effluent
being generated in a process plant facility such as a power
20 generation plant or a chemical plant, for example, from a
boiler, a reactor, a wet-type cooler of a steam condenser,
or a water treatment device.
In view of the aforementioned problems, it is an object
of the present invention to provide a water treatment system
25 and a water treatment method for effluent generated in a
plant facility.
Solution to Problem
According to a first aspect of the present invention in
30 order to solve the above-problems, there is provided a water
treatment system including: a flue gas treatment system that
performs treatment of boiler flue gas; and a spray drying
device that includes a spraying unit, which sprays effluent
3
generated in a plant facility, and that performs spray
drying using some of the boiler flue gas.
According to a second aspect of the present invention,
there is provided the water treatment system according to
5 the first aspect, further including a desalination device
that removes salt content present in the effluent, wherein
the spray drying device performs spray drying of
concentrated water from which salt content has been
concentrated by the desalination device.
10 According to a third aspect of the present invention,
there is provided the water treatment system according to
the second aspect, wherein the desalination device includes
a membrane separating unit.
According to a fourth aspect of the present invention,
15 there is provided the water treatment system according to
the second aspect, wherein the desalination device removes
bivalent salt content present in the effluent.
According to a fifth aspect of the present invention,
there is provided the water treatment system according to
20 the first or second aspect, wherein the flue gas treatment
system includes a wet desulfurization device, and the
spraying unit of the spray drying device has separator
liquid, which is obtained by separating gypsum from the wet
desulfurization device, introduced thereto and performs
25 spray drying of the separator liquid along with the effluent.
According to a sixth aspect of the present invention,
there is provided a water treatment method including: flue
gas-treating that includes performing treatment of boiler
flue gas; and spray-drying that includes spray drying using
30 a spray drying device that has a spraying unit, which sprays
effluent generated in a plant facility, and that performs
spray drying using some of the boiler flue gas.
According to a seventh aspect of the present invention,
4
there is provided the water treatment method according to
claim 6, further comprising desalinating that includes
removing salt content present in the effluent, wherein the
spray-drying, by the spray drying device, includes
5 performing spray drying of concentrated water from which
salt content has been concentrated by the desalination
device.
According to an eighth aspect of the present invention,
there is provided the water treatment method according to
10 the seventh aspect, wherein the desalinating includes
membrane-separating.
According to a ninth aspect of the present invention,
there is provided the water treatment method according to
the seventh aspect, wherein the desalinating includes
15 removing bivalent salt content present in the effluent.
According to a tenth aspect of the present invention,
there is provided the water treatment method according to
the sixth or seventh aspect, wherein the flue gas treatment
system includes wet-desulfurizing, and the spray-drying has
20 separator liquid, which is obtained by separating gypsum at
the wet-desulfurizing, introduced thereat and includes
performing spray drying of the separator liquid along with
the effluent.
25 Advantageous Effects of Invention
The present invention eliminates the need of performing
treatment of effluent discharged in a plant facility by an
industrial effluent treatment facility and can eliminate the
need of draining the effluent generated in the plant or
30 reduce the amount of effluent.
Brief Description of Drawings
FIG. 1 is a schematic view illustrating a water
treatment system according to a first embodiment for
5
effluent generated in a plant facility.
FIG. 2 is a schematic view illustrating a water
treatment system according to the first embodiment for
effluent generated in another plant facility.
5 FIG. 3 is a schematic view illustrating a water
treatment system according to the first embodiment for
effluent generated in another plant facility.
FIG. 4 is a schematic view illustrating a spray drying
device according to the first embodiment.
10 FIG. 5 is a schematic view illustrating a water
treatment system according to a second embodiment for
effluent generated in a plant facility.
FIG. 6 is a block diagram illustrating an example of a
desalination device according to this embodiment.
15 FIG. 7 is a block diagram illustrating an example of
another desalination device according to this embodiment.
FIG. 8 is a block diagram illustrating an example of
another desalination device according to this embodiment.
FIG. 9 is a schematic view illustrating a water
20 treatment system according to a third embodiment for
effluent generated in a plant facility.
FIG. 10 is a schematic view illustrating a water
treatment system according to the third embodiment for
effluent generated in another plant facility.
25 FIG. 11 is a schematic view illustrating a water
treatment system according to the third embodiment for
effluent generated in another plant facility.
FIG. 12 is a schematic view illustrating a water
treatment system according to the third embodiment for
30 effluent generated in another plant facility.
FIG. 13 is a schematic view illustrating an example of
a separating device which employs a cold lime method.
FIG. 14 is a photomicrograph of gypsum obtained by
6
crystallization.
FIG. 15 is a photomicrograph of gypsum obtained by
crystallization.
FIG. 16 is a view illustrating a result of a simulation
5 of pH dependency on the amount of precipitation of gypsum.
FIG. 17 is a view illustrating a result of a simulation
of pH dependency on the amount of precipitation of calcium
carbonate.
FIG. 18 is a view illustrating a result of a simulation
10 of pH dependency on the amount of precipitation of silica.
FIG. 19 is a schematic view illustrating a water
treatment system according to a fourth embodiment for
effluent generated in a plant facility.
Description of Embodiments
15 Now, referring to the attached drawings, preferred
embodiments of the present invention will be described in
more detail below. Note that the present invention will not
be limited by these embodiments, but may also include those
that are made up of a combination of each of a plurality of
20 embodiments, if any.
[First Embodiment]
FIG. 1 is a schematic view illustrating a water
treatment system according to a first embodiment for
effluent generated in a plant facility. FIGS. 2 and 3 are
25 schematic views illustrating a water treatment system
according to the first embodiment for effluent generated in
another plant facility.
As shown in FIG. 1, the water treatment system
according to this embodiment for effluent generated in a
30 plant facility includes: a flue gas treatment system 18 for
performing treatment of a boiler flue gas (hereafter
referred to as the "flue gas") 12 from a boiler 11; and a
spray drying device 23 which has a spraying unit (not
7
illustrated in FIG. 1) for spraying effluent 22 generated in
the plant facility, for example, in a cooler 21 and which
employs part 12a of the boiler flue gas 12 for spray drying.
The flue gas treatment system 18 illustrated in FIG. 1
5 removes, from the flue gas 12, hazardous substances such as
nitrogen oxide (NOx), sulfur oxide (SOx), and mercury (Hg) ,
for example, in the case of a coal combustion boiler which
employs coal as fuel or a heavy-oil combustion boiler which
employs heavy oil as fuel. The flue gas treatment system 18
10 includes: a denitrification device 13 for removing nitrogen
oxide; an air preheater 14 for recovery of heat of the flue
gas 12; a precipitator 15 for removing soot and dust in the
flue gas 12 after the recovery of heat; a desulfurization
device 16 for removing sulfur oxide contained in the flue
15 gas 12 after the removal of dust; and a stack 17 for
discharging a clean gas cleaned after desulfurization.
The spray drying device 23 includes a gas introduction
unit for introducing part 12a of the flue gas 12 through a
branch line Ln branched from a flue gas line Lio and a
20 spraying unit for dispersing or spraying the effluent 22.
Further, the heat of part 12a of the flue gas 12 being
introduced is employed to vaporize and dry the effluent 22
which has been dispersed.
Furthermore, in this embodiment, part 12a of the flue
25 gas 12 flowing into the air preheater 14 is branched from
the flue gas line Li0 through the branch line Ln, so that the
flue gas 12 is at a high temperature (350 to 400°C) and thus
the effluent 22 can be sprayed and dried with efficiency.
Note that flue gas 12b having contributed to drying is fed
30 back through a gas feed line Li2 to the flue gas line Li0
between the air preheater 14 and the precipitator 15. Note
that the flue gas 12b having contributed to drying may also
be fed back to one of or a plurality of points upstream of
8
the air preheater 14 or downstream of the precipitator 15.
FIG. 4 is a schematic view illustrating the spray
drying device according to the first embodiment. As shown in
FIG. 4, the spray drying device 23 of this embodiment
5 includes: a spray nozzle 24 for spraying, into a spray
drying device main body 23a, the effluent 22 introduced from
the cooler 21 through an introduction line L21; an inlet port
23b which is provided on the spray drying device main body
23a so as to introduce part 12a of the flue gas 12 for
10 drying a sprayed liquid 22a; a drying region 25 which is
provided in the spray drying device main body 23a so as to
dry the effluent 22 by part 12a of the flue gas 12; and a
discharge outlet 23c for discharging the flue gas 12b having
contributed to drying. Note that symbol 26 denotes a solid
15 substance separated in the spray drying device main body 23a.
Here is shown an example of a balance between the gas
amount of part 12a of the flue gas 12 introduced into the
spray drying device 23 and the amount of a sprayed liquid of
the effluent 22.
20 The temperature of the gas is lowered by 200°C when the
spraying unit 24 sprays a liquid amount of lOOkg/H of the
effluent 22 per a gas amount of 1000m3/H of the part 12a of
the flue gas 12 introduced.
Furthermore, the water concentration of the gas is
25 increased by 10%. For example, when part 12a of the flue gas
introduced before the spray has a water concentration of 9%
in the gas, the flue gas 12b having contributed to drying
will have a water concentration of 19% in the gas after the
spraying, with the result of an increase of about 10%.
30 The gas temperature with a decrease of 200°C is
generally equal to the temperature of the flue gas 12 after
having passed through the air preheater 14.
However, since the bypass amount of the part 12a of the
9
flue gas 12 into the spray drying device 23 is approximately
about 5%, the bypassed gas 12b having contributed to drying
has an increase in water content of about 0.5% (= 10%/20)
when having been fed back to the flue gas line Lio.
5 Furthermore, the flue gas 12 passing through the flue
gas line Li0 is reduced by 200°C in the gas temperature in
the same manner because air is preheated in the air
preheater 14 and then supplied to the boiler 11. Thus, the
flue gas 12 will have no temperature difference when having
10 been bypassed and returned. That is, when the gas
temperature at the inlet to the air preheater 14 is 350°C,
the gas that has passed through the air preheater 14 to have
a reduced temperature and the flue gas 12b having
contributed to drying in the spray drying device 23 through
15 the branch line Ln and the gas feed line Li2 are reduced by
200°C in the gas temperature in the same manner and thus have
a generally equal temperature.
According to this embodiment, the effluent 22
discharged from the cooler 21 is introduced through the
20 spray nozzle 24 into the spray drying device 23 in order to
dry the sprayed liquid 22a by the heat of the part 12a of
the flue gas 12. This eliminates the need of separately
performing treatment of the effluent 22 in an industrial
effluent treatment facility, thus eliminating the need of
25 draining the effluent 22 generated in a plant.
In this embodiment, the blow drain from the cooler 21
has been described as an example of the effluent 22
generated in a plant facility. However, the present
invention is not limited thereto, but may also be generally
30 applied to effluent from a power generation plant or a
chemical plant.
Here, examples of effluent in the coal thermal power
plant or oil thermal power plant as the effluent generated
10
regularly other than cooling water may include condensate
desalination device recycled effluent, condensate
desalination device pre-filter recycled effluent, cleansing
filter recycled effluent, makeup water treatment device
5 recycled effluent, analysis chamber miscellaneous effluent,
desulfurization device effluent, miscellaneous effluent,
sampling effluent, domestic effluent, ash disposal excess
water, and coal unloading and transporting facility cleaning
effluent. Examples of the irregular effluent other than the
10 regularly generated effluent may include air preheater
cleaning effluent, gas-gas heater (GGH) cleaning effluent,
stack cleaning effluent, chemical cleaning effluent, startup
effluent, coal-storage yard effluent, coal unloading pier
effluent, and effluent from tank yards. Furthermore,
15 examples of cooling water may include, other than the cooler
cooling water, bearing cooling water and steam condenser
cooling water.
Here, the denitrification device 13 provided in the
flue gas treatment system 18 of this embodiment is not
20 indispensable. When the flue gas 12 from the boiler 11 has a
trace concentration of nitrogen oxide or mercury or such
substances are not contained in the flue gas 12, for example,
the denitrification device 13 shown in FIG. 1 can be
eliminated as in the system shown in FIG. 2.
25 Furthermore, the desulfurization device 16 provided in
the flue gas treatment system 18 of this embodiment is not
indispensable. When the flue gas 12 from the boiler 11 has
a trace concentration of sulfur oxide or such a substance is
not contained in the flue gas 12, for example, the
30 desulf urization device 16 shown in FIG. 1 can be eliminated
as in the system shown in FIG. 3.
Furthermore, the gas feed line L12 for the flue gas 12b
from the spray drying device 23 having contributed to drying
11
may be fed back to upstream of the air preheater 14 when a
temperature drop is not significant.
According to this embodiment, it is possible to
efficiently perform treatment of various types of effluent
5 at low costs without degradation in boiler efficiency, the
effluent being generated in a process plant facility such as
a power generation plant or a chemical plant.
[Second Embodiment]
Now, a description will be made to a water treatment
10 system according to a second embodiment for effluent
generated in a plant facility. FIG. 5 is a schematic view
illustrating the water treatment system for effluent
generated in a plant facility. As shown in FIG. 5, the
water treatment system according to this embodiment for
15 effluent generated in a plant facility has a desalination
device 30 to remove salt content present in the effluent 22
from the cooler 21. Then, the water treatment system draws
concentrated water 31, which has been desalinated in a
desalination device 30A, into the spray drying device 23
20 through the supply line L2i. Note that this embodiment may
also include such a mode in which the denitrification device
or the desulfurization device is not provided as in the flue
gas treatment system 18 shown in FIGS. 2 and 3. In FIG. 5,
symbol L24 denotes an introduction line for introducing the
25 effluent 22 into the desalination device 30A.
FIG. 6 is a block diagram illustrating an example of
the desalination device according to this embodiment. As
shown in FIG. 6, the desalination device 30A according to
this embodiment includes: a scale inhibitor supply unit for
30 supplying a scale inhibitor 74 to the effluent 22 containing
bivalent ions such as Ca ions; a first desalination device
55A which is disposed downstream of the scale inhibitor
supply unit and separates the effluent 22 into recycled
12
water 33a and the concentrated water 31 into which the Ca
ions or the like are concentrated; a crystallization basin
61 which is disposed downstream of the first desalination
device 55A and supplies seed crystal gypsum 32a to the
5 concentrated water 31 in the first desalination device 55A
so as to crystallize the gypsum from concentrated water 31a
from the first desalination device 55A; a liquid cyclone 62
serving as a separation unit to separate crystallized gypsum
32 from the concentrated water 31a from the first
10 desalination device 55A; and a second desalination device
55B which is disposed downstream of a separation unit 62 and
separates the concentrated water 31a into recycled water 33b
and the concentrated water 31b into which the Ca ions or the
like are concentrated.
15 In the embodiment shown in FIG. 6, the first
desalination device 55A and the second desalination device
55B employ a reverse osmosis membrane device (RO) which has
reverse osmosis membranes 55a and 55b, respectively.
Instead of the reverse osmosis membrane device, it is also
20 possible to employ, as appropriate, for example, a nano
filtering film (NF), an electro-dialyzer (ED), a polarity
reversible electro-dialyzer (EDR), an electro-deionization
device (EDI), an ion-exchange resin device (lEx), a
capacitive desalination device (CD1), or an evaporator.
25 The crystallization basin 61 includes the liquid
cyclone 62 serving as a separation unit, and the separated
gypsum 32 is dewatered by a dehydrator 63. Note that as a
modified example of this embodiment, the liquid cyclone 62
or the separation unit can be eliminated. In this case, the
30 bottom of the crystallization basin 61 and the dehydrator 63
are directly connected to each other.
The scale inhibitor 74 has a function of reducing the
generation of a crystal nuclear in the effluent 22, and also
13
a function of reducing crystal growth by causing it to be
adsorbed to the surface of a crystal nuclear contained in
the effluent 22 (seed crystals or reduced-diameter scales
which are precipitated beyond the saturated concentration).
5 Furthermore, the scale inhibitor 74 also has a function
of dispersing particles such as precipitated crystals in
water (or to prevent aggregation). The scale inhibitor 74 is,
for example, a phosphonic acid-based scale inhibitor, a
poly-carboxylic acid-based scale inhibitor, or a mixture
10 thereof. Examples of the scale inhibitor 74 may include
"FLOCON 260 (trade name, manufactured by BWA)" although the
present invention is not limited thereto.
This embodiment has a first pH control unit connected
to introduce an acid or a pH control agent 75 after the
15 scale inhibitor 74 is supplied to a flow path upstream of
the first desalination device 55A. This embodiment also has
a second pH control unit connected to introduce the acid or
the pH control agent 75 into the crystallization basin 61.
Alternatively, the second pH control unit may also be
20 connected to introduce the acid or the pH control agent 75
into a line upstream of the crystallization basin 61.
In the water treatment system of this embodiment, there
may be disposed a sedimentation basin 53 and a filter 54
upstream of the supply unit for the scale inhibitor 74.
25 There may also be disposed an oxidation unit 51 upstream of
the sedimentation basin 53 so as to supply air for oxidation.
Furthermore, in the same manner, the sedimentation
basin 53 and the filter 54 are disposed between the liquid
cyclone 62 and the second desalination device 55B. On a flow
30 path between the filter 54 and the second desalination
device 55B are disposed a third pH control unit for
introducing the acid or the pH control agent 75.
Now, a description will be made to how to perform
14
treatment of effluent or water to be treated using the water
control system of the first embodiment.
Here, by way of example, the properties of the effluent
22 from the cooler 21 to be treated according to the present
5 invention may include: a pH of 8, Na ions of 20 mg/L, K ions
of 5 mg/L, Ca ions of 50 mg/L, Mg ions of 15 mg/L, HC03 ions
of 200 mg/L, CI ions of 200 mg/L, S04 ions of 120 mg/L, P04
ions of 5 mg/L, and Si02 ions of 35 mg/L, in which of these
ions, the Ca ions, Mg ions, S04 ions, and HC03 ions have a
10 high concentration, so that reactions in the presence
thereof may lead to the generation of scales (such as CaS04
and CaC03) .

First, in the sedimentation basin 53 and the filter 54,
15 metal ions in the effluent 22 are roughly removed as a metal
hydroxide.
When the effluent 22 shows strong acidity, an alkaline
agent (for example, Ca(OH)2) 71 and a polymer (for example,
anion based polymer (manufactured by MITSUBISHI HEAVY
20 INDUSTRIES MECHATRONICS SYSTEMS, LTD., trade name: Hishifloc
H305) ) 72 are supplied to the effluent 22 in an adjacent
dispensing basin 52 upstream of the sedimentation basin 53
so as to control the pH in the sedimentation basin 53 within
an alkaline pH region (for example, a pH of 8.5 to 11).
25 In this pH region, calcium carbonate and metal
hydroxides have a low solubility, so that when calcium
carbonate and metal hydroxides become supersaturated, the
calcium carbonate and the metal hydroxides are precipitated
and then sedimented on the bottom of the sedimentation basin
30 53.
Furthermore, the solubility of the metal hydroxides
depends on the pH. Metal ions have a higher solubility in a
stronger acid water. Since many metal hydroxides have a low
15
solubility within the aforementioned pH region, metals
contained in the effluent 22 are sedimented as metal
hydroxides on the bottom of the sedimentation basin 53.
Here, sediments 53a are discharged separately from the
5 bottom.
The effluent 22, which is a supernatant liquid in the
sedimentation basin 53, is discharged from the sedimentation
basin 53. An iron-based flocculant (for example, FeCls) 73 is
added to the discharged effluent 22, so that solids such as
10 calcium carbonate or metal hydroxides in the effluent 22 are
flocculated as Fe(OH)3.
The effluent 22 is fed to the filter 54. The filter 54
removes the solid to which Fe(OH)3 has been flocculated.
Among metals, Fe is acidic and tends to be precipitated
15 as a hydroxide. The effluent 22 which contains a large
amount of Fe ions and flows into the first desalination
device 55A will cause scales containing Fe to be generated
in the first desalination device 55A and as well an iron
hydroxide or the like to be sedimented in the
20 crystallization basin 61. Thus, in this embodiment, by
taking into account the prevention of generation of scales
in the first desalination device 55A, treating conditions in
the sedimentation basin 53 and the amount of FeCl3 to be
added and the like are set as appropriate so that the
25 effluent 22 has an Fe ion concentration of 0.05 ppm or less
after pretreating of alkali and before flowing into the
first desalination device 55A. Note that the aforementioned
pretreating can be eliminated depending on the water quality
of the effluent 22.
30

In the supply unit for supplying the scale inhibitor 74,
a predetermined amount of the scale inhibitor 74 is supplied
16
from a tank (not shown) to the effluent 22. The control unit
(not shown) provides control so that the concentration of
the scale inhibitor 74 has a predetermined value that is set
depending on the property of the effluent 22.
5
The supply unit of the pH control agent 75 for second
pH control provides control so that the effluent 22 at the
entrance of the first desalination device 55A has a pH value
(for example, a pH of about 5.5) at which the scale
10 inhibitor 74 reduces the precipitation of scales (gypsum and
calcium carbonate) that contain Ca. Control is achieved by
measuring the pH of the effluent 22 at the entrance of the
first desalination device 55A.
Note that in a modified example which is not provided
15 with the second pH control unit, the second pH control step
is eliminated.

The first desalination device 55A performs treatment of
the effluent 22 of which pH has been controlled. The water
20 having passed through the reverse osmosis membrane 55a of
the first desalination device 55A is collected as the
recycled water 33a from which salt content has been removed.
In the upstream separation step, the ions and the scale
inhibitor 74 contained in the effluent 22 cannot pass
25 through the reverse osmosis membrane 55a. Thus, the
concentrated water 31a has a high ion concentration before
passing through the reverse osmosis membrane 55a. The
concentrated water 31a in the first desalination device 55A
is fed toward the crystallization basin 61. For example,
30 when another desalination device such as a capacitive
desalination device is employed, the effluent 22 is
separated into treated water and concentrated water of a
17
high ion concentration.

The control unit (not shown) provides control so that
the concentrated water 31a from the first desalination
5 device 55A in the crystallization basin 61 has a pH value at
which the function of the scale inhibitor 74 is lowered and
the gypsum in the concentrated water 31a can be precipitated
(for example, a pH of 4 or less).

10 The concentrated water 31a of which pH has been
adjusted in the first pH control step is stored in the
crystallization basin 61. When a seed crystal supply unit
is disposed, the seed crystal supply unit adds a seed
crystal or the seed crystal gypsum 32a to the concentrated
15 water 31a in the crystallization basin 61.
In the first pH control step, the function of the scale
inhibitor 74 is lowered in the crystallization basin 61.
Thus, the gypsum supersaturated in the crystallization basin
61 is crystallized. When the seed crystal gypsum 32a is
20 separately supplied as the seed crystal in the
crystallization step, the crystal growth of the gypsum 32
occurs with the supplied seed crystal gypsum 32a as a
nucleus.
Here, part of the gypsum 32 separated by the dehydrator
25 63 is employed as the seed crystal gypsum 32a.
When the seed crystal gypsum 32a is supplied,, no
adjustment is made to the pH by the addition of the pH
control agent 75, so that the pH of a liquid passing through
the first desalination device 55A may be on the alkaline
30 side. In this case, the purity of the gypsum 32 is slightly
lower than that when the acid 75 is added to adjust the pH.
This is because the pH on the alkaline side causes the
18
crystal of calcium carbonate (CaC03) to be generated. This
causes the calcium carbonate (CaC03) to be mixed with the
gypsum (CaS04) and thus the purity to be lowered.
As in this embodiment, in the first pH control step in
5 which an acid is added as the pH control agent 75, the pH is
controlled to a predetermined value and in the
crystallization step, the seed crystal gypsum 32a is added,
thereby allowing a high purity gypsum 32 low in water
content to be precipitated.
10 Here, FIGS. 14 and 15 each are a photomicrograph of
gypsum obtained by crystallization. FIG. 14 shows an
observation result under a condition with the seed crystal
gypsum 32a or a seed crystal added. FIG. 15 shows an
observation result under a condition with the seed crystal
15 gypsum 32a or a seed crystal not added.
As shown in FIG. 14, when the seed crystal gypsum 32a
is added, greater pieces of gypsum were precipitated. In
general, the greater the precipitated gypsum, the lower the
water content becomes. With an average grain size of 10 |jjn
20 or more, preferably 20 \xm or more, such gypsum of a
sufficiently reduced water content can be obtained. Here,
"the average grain size" used in the present invention is
the grain size which is measured by the method (the laser
diffraction method) that is specified in J1SZ8825.
25 From the results of FIGS. 14 and 15, the pH can be
adjusted to a predetermined value in the first pH control
step and then the seed crystal is added in the
crystallization step, thereby allowing high purity gypsum
low in water content to be precipitated. The greater the
30 amount of added seed crystal (the higher the seed crystal
concentration in the crystallization basin 61), the greater
the speed of precipitation of the gypsum 32 becomes. The
amount of the seed crystal or the seed crystal gypsum 32a
19
added is set, as appropriate, on the basis of the residence
time, the concentration of the scale inhibitor, and the pH
in the crystallization basin 61.
Furthermore, the liquid cyclone 62 serving as a
5 separation unit separates, from the concentrated water 31a,
the gypsum 32 which has an average grain size of 10 urn or
greater or preferably 20 |j,m or greater. Part of the gypsum
32 collected in the dehydrator 63 adjacent to the liquid
cyclone 62 serving as a separation unit is stored in a seed
10 crystal tank 65 through a seed crystal circulation unit (not
shown) , Part of the collected gypsum 32 is supplied from
the seed crystal tank 65 to the crystallization basin 61.
Here, in the seed crystal tank 65, the stored gypsum 32
undergoes acid treatment. When the scale inhibitor 7 4 is
15 adhered to the gypsum 32 separated in the dehydrator 6314,
the acid treatment lowers the function of the adhered scale
inhibitor. Although the type of the acid used here is not
limited to a particular one, sulfuric acid is the optimum
one by taking into account the power saving of the second
20 desalination device 55B.
The gypsum crystallized in the crystallization basin 61
has a broad grain size distribution. However, since grains
of the gypsum 32 equal to or greater than 10 |om are
separately collected from the concentrated water 31a in the
25 liquid cyclone 62, those pieces of gypsum having greater
grain sizes can be used as a seed crystal. If larger grains
of seed crystal are available, then larger grains of gypsum
can be crystallized in a greater amount. That is, it is
possible to obtain high-quality gypsum with a high
30 collection rate. Furthermore, larger grains of gypsum can be
easily separated in the liquid cyclone 62, so that the
liquid cyclone 62 can be reduced in size, and as well power
can be saved. Larger grains of gypsum can be more easily
20
dewatered in the dehydrator 63, so that the dehydrator 63
can be reduced in size and as well power can be saved.
Here, since the water treatment system of FIG. 6 is an
open system other than the reverse osmosis membrane device,
5 the effluent 22 and the concentrated water 31a are in
contact with air, causing carbonate ions to be dissolved
therein. However, as described above, in the first pH
control step or the second pH control step, the effluent 22
or the concentrated water 31a is adjusted to be within a pH
10 region where a high solubility of calcium carbonate is shown.
In the preceding stage of the crystallization basin 61 or in
the crystallization basin 61, carbonate ions in the
concentrated water have been reduced, with the calcium
carbonate at saturation solubility or less. Furthermore,
15 since the addition of an acid as the pH control agent 75
provides a low pH region, the equilibrium equation in (1)
below shows an environment of a lower carbonate ion
concentration. This causes calcium carbonate to be
maintained at a sufficiently low concentration in the
20 crystallization basin 61 as compared with the saturated
concentration, allowing no calcium carbonate to be
crystallized. Thus, the collected gypsum 32 contains almost
no calcium carbonate. This allows the gypsum 32 to have a
high purity.
25 C02 + H20 <-» H2C03 <-> HCO3" + H+ <-» CO32" + 2H+ ... (1)
Furthermore, in the acid region, salt containing metal
has a high solubility. Even when metal is left in the
effluent 22 even after the pretreatment (the sedimentation
basin 53), hydroxides containing metal will never be
30 precipitated in the crystallization step if the pH of the
concentrated water 31a in the first desalination device 55A
is reduced in the first pH control step as described above.
Furthermore, when the effluent 22 has a property of
21
containing a large amount of Fe ions, the Fe concentration
is reduced through the aforementioned pretreatment, and thus
almost no hydroxide containing Fe(OH)3 is sedimented in the
crystallization basin 61.
As described above, the use of the water treatment
method and the water treatment system of this embodiment
make it possible to separately collect, as valuables, the
high-purity gypsum 32 which contains almost no impurities
such as calcium carbonate or metal hydroxides in the
effluent 22 discharged from the cooler 21.
Here, when greater grains of gypsum 32 having an
average grain size of 10 um or greater, preferably 20 um or
greater, are crystallized, the crystallization speed is
reduced in general and thus the residence time in the
crystallization basin 61 is elongated. In this embodiment,
the pH is adjusted so as to lower the function of the scale
inhibitor 74, and the seed crystal concentration is
increased to ensure an appropriate crystallization rate.

20 The concentrated water 31a containing the gypsum 32 is
discharged from the crystallization basin 61 and fed to the
liquid cyclone 62 serving as a separation unit, allowing the
gypsum 32 to be separated from the discharged concentrated
water 31a. Grains of gypsum 32 having an average size of 10
25 um or greater is settled on the bottom of the liquid cyclone
62, whereas grains of gypsum having a size less than 10 um
are left in the supernatant liquid. The gypsum 32 settled on
the bottom of the liquid cyclone 62 is transferred to the
dehydrator 63 and further dewatered and then collected. In
30 the collection step, it is possible to separate and collect,
at a high collection rate, the gypsum 32 which has a low
water content and a high purity without containing any
22
10
impurity. In this embodiment, since seed crystal is added
for crystallization, grains of gypsum 32 having an average
size of 10 \xm or greater are mainly precipitated, so that
those pieces of gypsum having reduced grain diameters are
5 found at a low percentage. Here, separator liquid 64
separated in the dehydrator 63 may also be supplied to the
spray drying device 23 for spray drying.
Furthermore, other than being supplied to the spray
drying device 23 for spray drying, the separator liquid 46
10 may also be drawn into the discharged concentrated water 31a
in the liquid cyclone 62 so as to be treated in the second
desalination device 55B together with the concentrated water
31a.
When the liquid cyclone 62 serving as a separation unit
15 is eliminated as a modified example of this embodiment, the
concentrated water on the settlement side is discharged from
the bottom of the crystallization basin 61. In the
concentrated water on the bottom of the crystallization
basin 61, larger crystallized grains of gypsum 32 are
20 settled. If the concentrated water containing mainly greater
grains of gypsum 32 can be dewatered in the dehydrator 63,
the gypsum 32 of a high purity can be collected.
Furthermore, since the gypsum 32 has a low water content,
the dehydrator 63 does not need to increase its volume.
25
The concentrated water 31a on the supernatant side
discharged from the liquid cyclone 62 is fed to the
sedimentation basin 53 and the filter 54. In the same steps
as those of the sedimentation basin 53 and the filter 54
30 mentioned above, the gypsum 32 and calcium carbonate left in
the concentrated water after the separation step and the
metal hydroxides left in the concentrated water are removed.
The concentrated water 31a from the first desalination
23
device 55A discharged from the filter 54 is fed to the
second desalination device 55B. Before the concentrated
water 31a in the first desalination device 55A is allowed to
flow into the second desalination device 55B, the scale
5 inhibitor 7 4 may also be additionally added thereto.
Furthermore, after the scale inhibitor 74 was added to
the concentrated water 31a from the first desalination
device 55A, the acid 75 may also be supplied thereto.
In the second desalination device 55B, the concentrated
10 water 31a from the first desalination device 55A is treated.
The water having passed through a reverse osmosis membrane
55b of the second desalination device 55B is collected as
transmitted water or the recycled water 33b. The
concentrated water 31b in the second desalination device 55B
15 is discharged from the system.
The provision of the second desalination device 55B
makes it possible to further collect the recycled water 33b
from the concentrated water 31a on the supernatant liquid
side after the gypsum 32 was crystallized. This allows for
20 providing a further improved water collection rate.
The concentrated water 31a from the first desalination
device 55A has a low ion concentration because the gypsum 32
has been removed by the treatment in the crystallization
basin 61. Thus, it is possible for the second desalination
25 device 55B to provide a reduced osmotic pressure when
compared with the case in which the gypsum 32 is not removed,
thus allowing required power to be saved.
Furthermore, it is also acceptable to provide an
evaporator (not illustrated in FIG. 6) . In the evaporator,
30 water is vaporized from the concentrated water, and ions
contained in the concentrated water are precipitated as a
solid and then collected as a solid. Since the water is
collected upstream of the evaporator to considerably reduce
24
the amount of the concentrated water, the evaporator can be
made compact and the energy required for vaporization can
also be saved.
In this embodiment, employed as a desalination device
5 is "the desalination/crystallization device" which includes:
the first desalination device 55A for desalinating the
effluent 22 after the scale inhibitor 74 was introduced in
the effluent 22; the crystallization basin 61 for
crystallizing the gypsum 32 after the first desalination
10 device 55A; and the liquid cyclone 62 for separating the
crystallized gypsum 32. However, the present invention is
not limited thereto.
As a desalination device other than the
"desalination/crystallization device" shown in FIG. 6, it
15 may also be acceptable to employ, as another embodiment, a
separating device which employs a cold lime method as shown
. in FIG. 13.
FIG. 13 schematically illustrates an example of a
separating device which employs the cold lime method.
20 As shown in FIG. 13, the desalination device which
employs the cold lime method adds calcium hydroxide (Ca(OH)2)
92 to the effluent 22 in a dispensing basin 91 and allows
calcium carbonate (CaCOs) 94 to be settled in a sedimentation
basin 93 and then removed.
25 Next, sodium carbonate (NaC03) 96 is added in a
dispensing basin 95, and calcium carbonate (CaCOs) 94 is
settled in a sedimentation basin 97 and then removed.
Subsequently, an iron-based flocculant (for example,
FeCl3) 73 is added to flocculate suspended solids (for
30 example, floating solid substances such as gypsum, silica,
calcium carbonate, and magnesium hydroxide). Subsequently,
like the operation shown in FIG. 6, the scale inhibitor 74
and the pH control agent 75 are introduced for membrane
25
separation treatment when treatment is performed in the
first desalination device 55A.
Other examples may include: an Optimized Pretreatment
and Unique Separation (OPUS) method (provided by Veolia) in
5 which after water to be treated is degassed and free oil is
removed therefrom, chemical softening is performed to filter
floating solid-state particles such as metals, and then a
reverse osmosis membrane is used for treatment; and a High
Efficiency Reverse Osmosis (HERO) method (provided by GE) in
10 which water to be treated is treated by chemical softening
or an ion-exchange resin to remove, for example, Ca and Mg,
an acid is then added to adjust pHwo, a C02 gas is separated,
then the pH is adjusted to alkali for ionization to prevent
precipitation, and then a reverse osmosis membrane is used
15 for treatment.
Furthermore, the first and second desalination devices
55A and 55B of this embodiment employ an "RO membrane" as
the membrane separating unit. However, an "NF membrane" may
also be used as a separation membrane.
20 When the NF membrane is used, like the RO membrane,
bivalent ions can be removed, but monovalent ions cannot be
completely removed. Thus, for example, the recycled water
cannot be supplied as desulfurization makeup water to the
desulfurization device and is preferably supplied, for
25 example, to the cooler as feedwater. This is because the NF
membrane cannot remove the scale inhibitor 74.
The water treatment system of this embodiment can
efficiently separate bivalent metals (for example, calcium
salt or magnesium salt), sulfuric acid ions, and carbonate
30 ions, which are contained in the effluent 22. Furthermore,
when the RO membrane is used, it is possible to remove
barium salt and strontium salt in addition to calcium salt
and magnesium salt.
26
According to this embodiment, it is possible to
considerably increase the amount of effluent (before being
concentrated) that can be sprayed and dried by concentrating
the effluent 22 using the desalination device 30 as shown in
5 FIG. 6. For example, the desalination crystallization device
can be used to eliminate 20 times (= 100/(100 - 95)) the
effluent to be drained if the collection rate of the
recycled water is 95%.
Here, the desulfurization device 16 used in the flue
10 gas treatment system 18 of this embodiment may be any one of
the wet-type desulfurization device, the dry-type
desulfurization device, and the semi-dry-type
desulfurization device. However, to eliminate the need of
draining the effluent, the dry-type desulfurization device
15 may be preferably applied.
FIG. 7 is a block diagram illustrating an example of
another desalination device according to this embodiment.
In the desalination device 30A shown in FIG. 6, the
oxidation unit 51, the sedimentation basin 53, and the
20 filter 54 are disposed upstream of the first desalination
device 55A to sediment and remove metal components and
calcium components in the effluent 22 as metal hydroxides
and calcium carbonate, respectively. However, the present
invention may also be configured so as to eliminate the
25 pretreatment.
As shown in FIG. 7, a desalination device 30B of this
embodiment is provided with the first desalination device
55A, a crystallization basin 61, the liquid cyclone 62, and
the second desalination device 55B, in which upstream of the
30 first and second desalination devices 55A and 55B, the scale
inhibitor 74 is added at each position so as to prevent the
scale from being adhered to the membranes 55a and 55b of the
first and second desalination devices 55A and 55B. Note that
27
the pH control agent 75 to be added is an acid (for example,
sulfuric acid) or an alkaline agent (such as sodium
hydroxide).
Depending on the type of the effluent 22, the
5 pretreatment is eliminated and the desalination device is
constructed in a simplified manner.
Examples of the effluent 22 to be treated in such a
simplified desalination device 30B may include effluent that
has a low carbonate ion concentration. Furthermore, the
10 simplified desalination device 30B may also be applied to
effluent which has a low concentration of scale components
such as Ca2+ or Mg2+.
Here, the pH control agent 75 to be used is an acid or
an alkaline agent. Examples of an acid to be used to lower
15 pH may include typical pH control agents such as
hydrochloric acid, sulfuric acid, and citric acid.
Furthermore, examples of an alkaline agent to increase pH
may include typical pH control agents such as sodium
hydroxide.
20 FIG. 8 is a block diagram illustrating an example of
another desalination device according to this embodiment.
Furthermore, as with a desalination device 30C shown in
FIG. 8, downstream of the concentrated water side of the
second desalination device 55B, a third desalination device
25 55C may also be provided to provide three-stage desalination
treatment.
Provision of the third desalination device 55C that
includes a reverse osmosis membrane 55c will allow recycled
water 33c to be further collected from the concentrated
30 water 31b, thus providing an improved water collection rate
of 97%. Note that between the second desalination device 55B
and the third desalination device 55C are disposed the
sedimentation basin 53, a pretreatment unit of the filter 54,
28
and addition of the scale inhibitor 74 and the acid 75, as
shown in FIG. 6, however, these components are not shown in
FIG. 8.
[Third Embodiment]
5 Now, a description will be made to a water treatment
system according to a third embodiment for effluent
generated in a plant facility. FIG. 9 is a schematic view
illustrating the water treatment system for effluent
generated in a plant facility. As shown in FIG. 9, the water
10 treatment system according to this embodiment for effluent
generated in a plant facility is provided with a wet-type
desulfurization device as a desulfurization device of the
flue gas treatment system 18, in which part 43a of a
separated liquid 43 after the gypsum 32 was separated from
15 desulfurization effluent 41 from the wet-type
desulfurization device 16 is introduced through a supply
line L34 to the spray drying device 23.
In this embodiment, other than the effluent 22 from the
cooler 21, part 43a of the separator liquid 43 for which the
20 gypsum 32 has been separated from the desulfurization
effluent 41 from the wet-type desulfurization device 16 that
employs a limestone/gypsum method is also sprayed and dried
in the spray drying device 23 so as to completely eliminate
the need of draining the effluent in the plant.
25 In this embodiment, the wet-type desulfurization device
16 removes sulfur oxide in the flue gas 12 in a
desulfurization method by the limestone/gypsum method. When
the sulfur oxide is removed, limestone slurry is supplied,
the gypsum 32 is separated in a dehydrator 42 from the
30 gypsum slurry that is the desulfurization effluent 41 to be
discharged through a discharge line L31 from the
desulfurization device 16, and the separator liquid 43 is
fed back as makeup water through a return line L32 to the
29
desulfurization device 16. Note that symbol L33 denotes a
slurry circulation line through which the desulfurization
gypsum slurry is circulated.
In this embodiment, part 43a of the separator liquid 43
5 is introduced through the supply line L34 into the spray
drying device 23 and then sprayed and dried together with
the effluent 22 so as to eliminate the need of draining the
effluent.
Furthermore, a recycled water 33 obtained by performing
10 treatment of the effluent 22 in the desalination device 30
is joined through a recycled water supply line L23 to the
return line L32, along which the separator liquid 43 is fed
back to the desulfurization device 16, and is then used as
makeup water for the gypsum slurry for use in the
15 desulfurization device 16.
As described above, according to this embodiment, it is
possible to eliminate the need of draining the
desulfurization effluent 41 from the wet-type
desulfurization device 16 as well as to obtain the recycled
20 water 33 (33a, 33b) recovered in the desalination devices
55A and 55B using the desalination device 30, thereby
reusing the same in the plant while reducing the amount of
makeup water to the desulfurization device 16.
Here, the recycled water 33 can be reused in the plant,
25 for example, as cooling water makeup water, desulfurization
device makeup water, and boiler makeup water. However, the
invention is not limited to these uses.
On the other hand, as shown in FIG. 10, the settled
water that contains the settled gypsum 32 from the
30 crystallization basin 61 in the desalination device 30 may
be introduced through a supply line L22 to the dehydrator 42,
which separates the gypsum 32 from the desulfurization
effluent 41 from the desulfurization device 16, so as to
30
separate the gypsum 32 therein.
This can eliminate the provision of the dehydrator 63
which separates the settled liquid from the liquid cyclone
62 in the desalination device 30 shown in FIG. 6.
5 Furthermore, as shown in FIG. 11, a part 43a of the
separated water 43 from the dehydrator 42 may be supplied to
the crystallization basin 61 so as to settle the gypsum 32
in the crystallization basin 61, so that the gypsum 32 is
separated from the concentrated water containing the gypsum
10 32 in the liquid cyclone 62 and the dehydrator 63 which are
shown in FIG. 6.
This can actively separate the gypsum 32 from the
separator liquid 43a of the desulfurization effluent 41 in
the desalination device 30. As a result, it is possible to
15 reduce the load of spray drying in the spray drying device
23.
On the other hand, as shown in FIG. 12, part 43a of the
separated water 43 from the dehydrator 42 may also be
introduced into an introduction line L24, through which the
20 effluent 22 is drawn into the desalination device 30, so
that the separated water from the desulfurization device 16
or part 43a of the separator liquid 43 containing the gypsum
32 is desalinated in the desalination device 30.
This can actively separate the gypsum 32 from the
25 separator liquid 43a of the desulfurization effluent 41 in
the desalination device 30. As a result, it is possible to
reduce the load of spray drying in the spray drying device
23.
This can actively separate the gypsum 32 from the
30 separator liquid 43a of the desulfurization effluent 41 in
the desalination device 30. As a result, it is possible to
reduce the load of spray drying in the spray drying device
23.
31
In the modified examples as shown in FIG. 11 and FIG.
12, it is possible to increase the amount of gypsum to be
recovered. Furthermore, since the amount to be treated in
the spray drying device 23 is reduced, the load of treatment
5 can be reduced and an increase in the load on the
precipitator 15 can be reduced as well. Thus, a considerable
excess in the treatment capacity of the precipitator 15 can
be avoided.
Here, for example, suppose that in a 110MW thermal
10 power plant, the amount of supply water to be supplied to
the cooler 21 is 7900 m3/d and the amount of the effluent 22
from the cooler 21 is 1200 m3/d. In this case, assuming that
the collection rate of the recycled water 33 (33a, 33b, 33c)
in the three-stage treating desalination device 30 shown in
15 FIG. 8 is 97%, a liquid of 1164 m3/d is collected. To apply
the collected recycled water 33 to the makeup water for the
wet-type desulfurization device 16 in the flue gas treatment
system 18 of the 110MW thermal power plant, a liquid amount
of about 1000 m3/d is required, so that the recycled water 33
20 recycled in the desalination device 30 can cover all the
amount that is required.
Furthermore, the liquid amounts of the concentrated
water 31 and part 43a of the separated water 43 to be dried
in the spray drying device 23 are 36 m3/d and 38 m3/d,
25 respectively, thus eliminating the load on the spray drying
device 23.
Furthermore, in this embodiment, the precipitation of
silica in the effluent is not taken into account, and thus,
to take into account the precipitation of silica, the
30 following pH control step is preferably followed.
Here, with reference to FIGS. 16 to 18, a description
will be made to the precipitation behavior of gypsum, silica,
and calcium carbonate in the effluent 22.
32
FIG. 16 shows a simulation result of the dependency of
the amount of precipitation of gypsum on pH. FIG. 17 shows a
simulation result of the dependency of the amount of
precipitation of calcium carbonate on pH. FIG. 18 shows a
5 simulation result of the dependency of the amount of
precipitation of silica on pH. In these drawings, the
horizontal axis represents pH and the vertical axis
represents the respective amounts of precipitation (mol) of
gypsum, calcium carbonate, and silica. The simulations were
10 performed using a simulation software manufactured by OLI
under the conditions that each solid-state component is
mixed by 0.1 mol/L in the water, with H2S04 added as an acid
and Ca(0H)2 added as an alkali.
From FIG. 16, it can be understood that the gypsum is
15 precipitated independently on pH, and precipitated on the
entire pH region. However, once the calcium scale inhibitor
• is added, gypsum is found to be dissolved in the water in
the high pH region. From FIG. 17, calcium carbonate is
precipitated at a pH exceeding 5. From FIG. 18, silica tends
20 to be dissolved in the water at a pH of 10 or greater.
Thus, by taking into account the precipitation behavior
of gypsum (calcium sulfate), silica, and calcium carbonate
in the effluent 22, the first to third pH control will be
provided as follows.
25 1) First pH Control (pH of 10 or greater)
The first pH control is provided to measure the pH of
the effluent 22 upstream of the first desalination device
55A with a pH meter (not shown) in order to control the pH
value to be 10 or greater.
30 This is done because as shown in FIG. 18, silica is
dissolved at a pH of 10 or greater.
In the case of the first pH control, supplied is such
an amount of the scale inhibitor (calcium scale inhibitor)
33
74 that is enough to inhibit the adherence of gypsum and
calcium carbonate (substances to be adhered) to the membrane
55a.
2) Second pH Control (pH of 10 or less)
5 The second pH control is provided to measure the pH of
the effluent 22 upstream of the first desalination device
55A with a pH meter (not shown) in order to control the pH
value to be 10 or less.
This is done because as shown in FIG. 18, silica is
10 precipitated at a pH of 10 or less.
In the case of the second pH control, supplied is such
an amount of the scale inhibitor 74 that is enough to
inhibit the adherence of all of gypsum, calcium carbonate,
and silica (substances to be adhered) to the membrane 55a.
15 Here, the scale inhibitors 74 to be used for silica
include two types of inhibitors: a calcium scale inhibitor,
and an inhibitor (referred to as "a silica scale inhibitor")
for preventing silica from being precipitated as scales in
the water to be treated. The silica scale inhibitor to be
20 employed may include, for example, a poly-carboxylic acidbased
scale inhibitor and a mixture thereof. A specific
example may include FLOCON260 (trade name, manufactured by
BWA) .
3) Third pH Control (pH of 6.5 or less)
25 The third pH control is provided to measure the pH of
the effluent 22 upstream of the first desalination device
55A with a pH meter (not shown) in order to control the pH
value to be 6.5 or less.
This is done because as shown in FIG. 17, calcium
30 carbonate is dissolved at a pH of 6.5 or less.
In the case of the third pH control, supplied is such
an amount of the scale inhibitor (calcium scale inhibitor or
34
silica scale inhibitor) 74 that is enough to inhibit the
adherence of gypsum and silica (substances to be adhered) to
the membrane 55a.
Table 1 collectively shows the first to third pH
5 control.
Table 1
Gypsum
Calcium carbonate
Silica
pH
10 or
greater
0
0
X
10 to
6.5
0
0
0
6.5 or
less
0
X
0
x:Dissolved (Absence of scale inhibitor)
0:Precipitated (Presence of scale inhibitor)
As shown in Table 1, in the case of a pH of 10 or
greater, the scale inhibitor (calcium scale inhibitor) 74 is
supplied in order to inhibit scales of gypsum and calcium
10 carbonate (circle in the Table), whereas the scale inhibitor
is not required to be supplied because silica is dissolved
(cross in the Table).
Furthermore, in the case of a pH of 6.5 to 10 inclusive,
the scale inhibitor (calcium scale inhibitor and silica
15 scale inhibitor) 74 is supplied in order to inhibit the
scales of all of gypsum, calcium carbonate, and silica
(circle in the Table).
Furthermore, for a pH of 6.5 or less, the scale
inhibitor (the calcium scale inhibitor, the silica scale
20 inhibitor) 74 is supplied in order to inhibit the scales of
gypsum and silica (circle in the Table), whereas since
calcium carbonate is dissolved, a less amount of calcium
scale inhibitor is supplied than that in the case of the
second pH control because scales of only gypsum have to be
25 prevented (cross in the Table).
If the concentration of silica in the first
concentrated water 31a after having been concentrated in the
35
first desalination device 55A is equal to or greater than a
predetermined concentration, then the performance of the
silica scale inhibitor is limited. In this context, with a
silica concentration being a predetermined concentration
5 (for example, 200 mg/L) or less, the second and third pH
control steps should be performed, whereas with a silica
concentration being the predetermined concentration (for
example, 200 mg/L) or greater, the first pH control step
(dissolving of silica) should be preferably performed.
10 This can allow desalination treatment to be performed
while preventing precipitation of silica to the membrane
when a large amount of silica components are found in the
effluent 22.
[Fourth Embodiment]
15 Now, a description will be made to a water treatment
system according to a fourth embodiment for effluent
generated in a plant facility. FIG. 19 is a schematic view
illustrating the water treatment system for effluent
generated in a plant facility. As shown in FIG. 19, the
20 water treatment system according to this embodiment for
effluent generated in a plant facility is the same as the
water treatment system shown in FIG. 5 according to the
second embodiment for effluent generated in a plant facility
except that, instead of the concentrated water 31
25 concentrated in the desalination device 30 being sprayed and
dried in the spray drying device 23, the concentrated water
31 is supplied through the introduction line L2i into between
the air preheater 14 and the precipitator 15 disposed into
the flue gas line Li0 through which the flue gas 12 is
30 discharged from the boiler 11. And, the concentrated water
31 introduced into the flue gas line Li0 is sprayed and dried
using all the amount of the flue gas 12. Note that the
desalination device to be used may be any one of the
36
desalination devices 30A to 30C shown in FIG. 6 to FIG. 8,
and thus will not be repeatedly explained.
Although the spray drying device 23 needs to be
separately provided in the water treatment system according
5 to the second embodiment for effluent generated in a plant
facility, the spray drying device 23 is not required to be
provided in this embodiment. Thus, for example, when the
space for accommodating the spray drying device 23 in the
plant cannot be ensured, all the amount of the flue gas 12
10 can be used to spray and dry the concentrated water 31,
thereby eliminating the need of draining the effluent.
Furthermore, the costs for providing the spray drying device
23 can be saved.
15 Reference Signs List
11 boiler
12 boiler flue gas (flue gas)
18 flue gas treatment system
21 cooler
20 22 effluent
23 spray drying device
30 desalination device
31 (31a to 31c) concentrated water
33 (33a to 33c) recycled water
25 55a to 55c first to third desalination devices
61 crystallization basin
62 liquid cyclone
74 scale inhibitor
75 pH control agent

CLAIMS
1. A water treatment system comprising:
a flue gas treatment system that performs
treatment of boiler flue gas; and
5 a spray drying device that includes a spraying
unit, which sprays effluent generated in a plant
facility, and that performs spray drying using some of
the boiler flue gas.
2. The water treatment system according to claim 1,
10 further comprising a desalination device that removes
salt content present in the effluent, wherein
the spray drying device performs spray drying of
concentrated water from which salt content has been
concentrated by the desalination device.
15 3. The water treatment system according to claim 2,
wherein the desalination device includes a membrane
separating unit.
4. The water treatment system according to claim 2,
20 wherein the desalination device removes bivalent salt
content present in the effluent.
5. The water treatment system according to claim 1 or 2,
wherein
the flue gas treatment system includes a wet
25 desulfurization device, and
the spraying unit of the spray drying device has
separator liquid, which is obtained by separating
gypsum from the wet desulfurization device, introduced
thereto and performs spray drying of the separator
30 liquid along with the effluent.
38
6. A water treatment method comprising:
flue gas-treating that includes performing
treatment of boiler flue gas; and
spray-drying that includes spray drying using a
5 spray drying device that has a spraying unit, which
sprays effluent generated in a plant facility, and that
performs spray drying using some of the boiler flue gas
7. The water treatment method according to claim 6,
further comprising desalinating that includes removing
0 salt content present in the effluent, wherein
the spray-drying, by the spray drying device,
includes performing spray drying of concentrated water
from which salt content has been concentrated by the
desalination device.
5 8. The water treatment method according to claim 7,
wherein the desalinating includes membrane-separating.
9. The water treatment method according to claim 7,
wherein the desalinating includes removing bivalent
salt content present in the effluent.
0 10. The water treatment method according to claim 6 or 7,
wherein
the flue gas treatment system includes wetdesulfurizing,
and
the spray-drying has separator liquid, which is
5 obtained by separating gypsum at the wet-desulfurizing,
introduced thereat and includes performing spray drying
of the separator liquid along with the effluent.