JP6298296B2 - Water treatment system and method - Google Patents

Description

  The present invention relates to a water treatment system and method for discharged water generated in, for example, a boiler plant or a chemical plant facility.

  For example, in a process plant such as a power plant or a chemical plant, discharged water is generated from, for example, a boiler, a reactor, a wet cooling tower of a condenser, a water treatment device, or the like. Various treatment apparatuses have been proposed to treat such discharged water, but all have a problem of increasing costs. In order to solve these problems, it is characterized by neutralizing alkaline blow water by spraying cooling water (blow water) of a boiler cooling tower into a flue as a mist having a droplet diameter of 20 to 120 microns. There is a proposal of a boiler with a wastewater treatment device (Patent Document 1).

  In addition, there is a proposal of a wastewater treatment apparatus that increases the amount of wastewater that can be evaporated by spraying discharged water into a flue (Patent Document 2).

JP-A-8-47693 Japanese Patent Laid-Open No. 2001-29939

  However, according to the invention of Patent Document 1, wastewater can be treated easily and at low cost, but the amount of wastewater increases with respect to the heat energy (temperature, flow rate) of the exhaust gas, and the evaporation treatment is performed. There is a problem that processing cannot be performed when the required energy increases.

  Further, according to the invention of Patent Document 2, the amount of drainage can be reduced by the concentrating device, but in the concentrating device, a part of the steam generated in the boiler is extracted, so that the output of the steam turbine is reduced. There is a problem.

  In addition, exhaust gas discharged from boiler plants may contain trace amounts of harmful substances such as mercury in addition to nitrogen oxides and sulfur oxides. To prevent this, mercury countermeasures are necessary.

  Therefore, for example, in the process plant equipment of a power plant or chemical plant, for example, waste water from a boiler, a reactor, a wet cooling tower of a condenser, a water treatment device, etc. is low-cost and accompanied by a decrease in boiler efficiency. However, there is an urgent need for the emergence of efficient treatment technologies that take mercury emission countermeasures into consideration.

  This invention makes it a subject to provide the water treatment system and method of the waste_water | drain which generate | occur | produces in plant equipment in view of the said problem.

The first invention of the present invention for solving the above-mentioned problems is a wet desulfurization apparatus that removes sulfur oxides in boiler exhaust gas, and dehydration that separates gypsum from desulfurization effluent containing gypsum slurry from the wet desulfurization apparatus. A mercury removal unit that introduces separation water from the dehydration device, introduces a chelating agent, and immobilizes heavy metals in the separation water; and a solid component that separates solids in the separation water from the mercury removal unit. A liquid separation unit, a mixing unit that mixes the separated water from the solid-liquid separation unit with discharged water generated in plant equipment, and a desalination treatment device that removes salt in the mixed water mixed in the mixing unit. the has a spraying means for spraying the concentrated water was salinity concentrated in desalination apparatus, and the spray drying apparatus spray dried with a portion of the boiler exhaust gas, provided with a, the desalination apparatus, Ca Contains divalent ions Installed on the downstream side of the scale inhibitor supply unit, the scale inhibitor supply unit that supplies scale inhibitor to the mixed water, and separates the mixed water into reclaimed water and concentrated water enriched with the Ca ions. A first desalting apparatus, a crystallization tank which is provided downstream of the first desalting apparatus and crystallizes gypsum from the concentrated water, the crystallized gypsum, and the first desalting A separation unit that separates the concentrated water from the device; a second desalination device that is installed downstream of the separation unit and separates the concentrated water into reclaimed water and concentrated water enriched with the Ca ions; It is in the water treatment system characterized by having .

According to a second aspect of the present invention, there is provided a wet desulfurization device that removes sulfur oxides in boiler exhaust gas, a dehydration device that separates gypsum from desulfurization effluent containing gypsum slurry from the wet desulfurization device, and separated water from the dehydration device. A mixing section for mixing with the discharged water generated in the plant equipment, a reaction tank for introducing the mixed water mixed in the mixing section and introducing a chelating agent to immobilize heavy metals in the separated water, and the reaction tank A solid-liquid separation unit for solid-liquid separation of the solid content in the mixed water from, a desalting apparatus for removing salt in the mixed water after the solid-liquid separation, and a concentrated water salt-concentrated in the desalting apparatus A spray-drying device for spray-drying using a part of the boiler exhaust gas, and the desalting apparatus is for mixed water containing divalent ions of Ca ions, Scale to supply scale inhibitor An inhibitor supply unit; a first desalination device that is installed downstream of the scale inhibitor supply unit and separates the mixed water into reclaimed water and concentrated water enriched with the Ca ions; and A crystallization tank for crystallization of gypsum from the concentrated water, a separation unit for separating the crystallized gypsum and the concentrated water from the first demineralizer; A water treatment system comprising: a second desalting apparatus that is installed on the downstream side of the separation unit and separates the concentrated water into reclaimed water and concentrated water in which the Ca ions are concentrated .

  A third aspect of the present invention is the water treatment according to the first or second aspect, further comprising a membrane treatment unit that treats the separated water after separation by the solid-liquid separation unit with a membrane having monovalent selectivity. In the system.

  A fourth invention is the water treatment system according to any one of the first to third inventions, wherein the desalting apparatus removes divalent salt in the discharged water.

According to a fifth invention, in the first or second invention, the desalting apparatus is further installed on a downstream side of the separation unit, a separation unit that separates the concentrated water from the second desalination device, in water treatment systems, characterized in that it has a third desalination device for separating the concentrated water to the recycled water and concentrated water in which the Ca ions are concentrated.

A sixth invention is the water treatment system according to the first or second invention, further comprising an oxidation-reduction potentiometer for measuring the oxidation-reduction potential of the mixed water introduced into the first desalting apparatus.

A seventh invention is characterized in that, in the sixth invention, the value (X) of the oxidation-reduction potential in the mixed water measured by the oxidation-reduction potentiometer is -0.69 V <X <1.358 V. In the water treatment system.

The eighth invention comprises a wet desulfurization step for removing sulfur oxides in boiler exhaust gas, a dehydration step for separating gypsum from desulfurization effluent containing gypsum slurry from the wet desulfurization step, and separated water from the dehydration step. Introducing and introducing a chelating agent to immobilize heavy metals in the separated water, a solid-liquid separation step for solid-liquid separation of the solid content in the separated water from the mercury removal step, and from the solid-liquid separation unit The separated water is mixed with the discharged water generated in the plant equipment, the desalinating process for removing the salt in the mixed water mixed in the mixing process, and the concentration obtained by concentrating the salt in the desalting process A spray-drying step of spray-drying water using a part of the boiler exhaust gas, and the desalting treatment step with respect to the mixed water containing divalent ions of Ca ions. Supply scale An inhibitor supply step; a first desalting step that is installed downstream of the scale inhibitor supply step and separates the mixed water into reclaimed water and concentrated water enriched with the Ca ions; and A crystallization step for crystallizing gypsum from the concentrated water, a separation unit for separating the crystallized gypsum and the concentrated water from the first desalting step, provided downstream of the desalting step; A water treatment method comprising a second desalting step, which is installed downstream of the separation unit and separates the concentrated water into reclaimed water and concentrated water enriched with the Ca ions .

According to a ninth aspect of the invention, there is provided a wet desulfurization step for removing sulfur oxides in boiler exhaust gas, a dehydration step for separating gypsum from desulfurization effluent containing gypsum slurry from the wet desulfurization step, and separated water from the dehydration step. A mixing step for mixing with the discharged water generated in the plant equipment, a precipitation step for introducing the mixed water mixed in the mixing step, and introducing a chelating agent to immobilize heavy metals in the separated water, and the precipitation step A solid-liquid separation step for solid-liquid separation of the solid content in the mixed water, a desalting treatment step for removing salt in the mixed water after the solid-liquid separation, and a concentrated water salt-concentrated in the desalting treatment step, A spray-drying step of spray-drying using a part of boiler exhaust gas, and the desalting treatment step supplies scale inhibitor to mixed water containing divalent Ca ions. Agent supply process A first desalting step that is installed downstream of the scale inhibitor supply step and separates the mixed water into reclaimed water and concentrated water enriched with the Ca ions; and downstream of the first desalting step A crystallization step for crystallizing gypsum from the concentrated water, a separation unit for separating the crystallized gypsum from the concentrated water from the first desalting step, and a downstream of the separation unit And a second desalting step for separating the concentrated water into reclaimed water and concentrated water enriched with Ca ions .

A tenth aspect of the present invention is the water treatment according to the eighth or ninth aspect , further comprising a membrane treatment step of treating with a membrane having monovalent selectivity with respect to the separated water after separation in the solid-liquid separation step. Is in the way.

An eleventh invention is the water treatment method according to the eighth or ninth invention, wherein the desalting treatment step removes divalent salt in the discharged water.

In a twelfth aspect of the invention according to the eighth or ninth aspect , the desalting treatment step is further installed on the downstream side of the separation step of separating the concentrated water from the second desalting step, and the separation step, in water treatment method characterized by having a third desalting step in which the Ca ions of the concentrated water and reclaimed water is separated into concentrated water which has been concentrated.

A thirteenth invention is the water treatment method according to the eighth or ninth invention, further comprising a redox potential measuring step for measuring a redox potential of the mixed water introduced into the first desalting step. .

In a fourteenth aspect based on the thirteenth aspect , the value (X) of the redox potential in the mixed water measured in the redox potential measuring step is −0.69 V <X <1.358 V. It is in the water treatment method.

  According to the present invention, it is not necessary to treat the waste water discharged in the plant equipment with the industrial waste water treatment equipment, and it is possible to eliminate waste water generated in the plant or to reduce the amount of waste water and to take measures against mercury discharge. It becomes.

FIG. 1 is a schematic diagram of a water treatment system for discharged water generated in a plant facility according to the first embodiment. FIG. 2 is a schematic diagram of the spray dryer according to the first embodiment. FIG. 3 is a configuration diagram illustrating an example of a desalting apparatus according to the present embodiment. FIG. 4 is a configuration diagram illustrating an example of another desalting apparatus according to the present embodiment. FIG. 5 is a configuration diagram illustrating an example of another desalting apparatus according to the present embodiment. FIG. 6 is a configuration diagram illustrating an example of another desalting apparatus according to the present embodiment. FIG. 7 is a configuration diagram illustrating an example of another desalting apparatus according to the second embodiment. FIG. 8 is a schematic diagram of a water treatment system for discharged water generated in a plant facility according to the third embodiment. FIG. 9 is a schematic diagram of a water treatment system for discharged water generated in a plant facility according to the fourth embodiment. FIG. 10 is a photomicrograph of gypsum obtained by crystallization. FIG. 11 is a photomicrograph of gypsum obtained by crystallization. FIG. 12 is a schematic view of an example of a separation apparatus by the cold dry method. FIG. 13 is a schematic diagram of a water treatment system for discharged water generated in a plant facility according to the fifth embodiment. FIG. 14 is a diagram showing a simulation result of the pH dependence of the amount of gypsum deposited. FIG. 15 is a diagram showing a simulation result of the pH dependency of the precipitated amount of calcium carbonate. FIG. 16 is a diagram showing a simulation result of the pH dependence of the silica precipitation amount.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, this invention is not limited by this Example, Moreover, when there exists multiple Example, what comprises combining each Example is also included.

FIG. 1 is a schematic diagram of a water treatment system for discharged water generated in a plant facility according to the first embodiment.
As shown in FIG. 1, a water treatment system for discharged water generated in a plant facility according to the present embodiment includes an exhaust gas treatment system 18 for treating boiler exhaust gas (hereinafter referred to as “exhaust gas”) 12 from a boiler 11, and desulfurization. After fixing mercury in the waste water 41 in the mercury removing unit, the waste water 22 is mixed with the mixing unit 110 and the desalinating device 30 for removing the salt in the mixed water, and after the desalinating unit 30 is processed. And a spray drying device 23 for spray drying the concentrated water 31 using a part 12a of the boiler exhaust gas 12.

In the case of a coal fired boiler 11 using coal as a fuel or a heavy oil fired boiler 11 using heavy oil as a fuel, the exhaust gas treatment system 18 illustrated in FIG. 1, from the exhaust gas 12, nitrogen oxide (NO _x ), A device that removes harmful substances such as sulfur oxide (SO _x ) and mercury (Hg), a denitration device 13 that removes nitrogen oxides, an air preheater 14 that recovers the heat of the exhaust gas 12, and a post-heat recovery device A dust collector 15 that removes soot and dust in the exhaust gas 12, a wet desulfurization device 16 that removes sulfur oxides contained in the exhaust gas 12 after dust removal, and a chimney 17 that discharges the purified gas after desulfurization. I have.

In the present embodiment, as the wet desulfurization apparatus 16, sulfur oxides contained in the exhaust gas 12 are removed by a desulfurization method using a lime / gypsum method. When removing this sulfur oxide, lime slurry (not shown) is supplied, and gypsum 32 is removed from the gypsum slurry, which is desulfurization waste water 41 discharged from the wet desulfurization device 16 via the discharge line L ₃₁ by the dehydrator 42. It is separated. The separated water 43 separated by dewatering device 42 is returned as make-up water via line L ₃₂ back to the wet desulfurization system 16. Reference numeral L ₃₃ shows a slurry circulation line for circulating the desulfurized gypsum slurry.

In this embodiment, a dehydrating device 42 for separating gypsum 32 from desulfurization waste water 41 containing gypsum slurry from the wet desulfurization device 16 and separated water 43 from the dehydrating device 42 are introduced by a separation water line L ₃₄ , and a chelating agent. 102 is a mercury removal unit that removes mercury in the separation water 43 and a solid-liquid separation unit that solid-liquid separates the solid content (heavy metal sludge) 104 in the separation water 43 from the reaction vessel 101. 103, and by adding the chelating agent 102, the mercury (Hg) in the separated water 43 is immobilized.

A chelating agent 102 is added to the reaction tank 101 by an adding device (not shown), and the chelating agent 102 is subjected to an adsorption treatment of mercury (Hg) in the separated water 43.
In addition to the chelating agent 102, for example, a pH adjusting agent alkaline agent for adjusting pH), a coagulant (for example, sulfuric acid band, PAC, iron salt, etc.), and a flocculant such as a polymer flocculant are added to the reaction tank 101. You may make it do.
Mercury in the separation water 43 forms an insoluble polymer complex by the chelating agent 102 which is a heavy metal scavenger, and agglomerates the polymers with, for example, a sulfuric acid band.

Thereafter, the heavy metal (such as Hg) sludge 104 is separated by the solid-liquid separation unit 103, and the separated water from the solid-liquid separation unit 103 is discharged by the separated water discharge line L ₃₅ and mixed with the discharged water 22 from the cooling tower 21. The water is mixed in the section 110 to obtain mixed water 111.

  As the solid-liquid separation unit 103, for example, a coagulation sedimentation tank, a coagulation membrane separation tank, a membrane separation tank, a sand filtration tank, or the like can be used. If the separated water 43 after solid-liquid separation has a high water quality requirement, the water quality may be improved by passing a chelate resin.

The pH adjuster has the separated water 43 as an alkali side, and for example, slaked lime Ca (OH) ₂ , sodium hydroxide (NaOH), or the like can be used. For example, a pH range (for example, pH 7) in which a sulfate band can aggregate. To be near).

  In the embodiment of FIG. 1, the mercury removal unit has been described using the reaction tank 101, but the present invention is not limited to this, and for example, a gypsum crystallizer, a solidification tank, an ion exchange apparatus, or the like is used. Thus, mercury in the separated water 43 may be removed.

The gypsum crystallizer takes in mercury as mercury sulfate (HgSO ₄ ) and coprecipitates it when gypsum (CaSO ₄ ) is produced, and removes mercury in the separated water 43.

In the precipitation apparatus, for example, iron sulfide, sodium sulfide, or the like is added to the separated water 43 and immobilized as mercury sulfide (HgS) by the following reaction.
Hg ²⁺ + S ^2- → HgS ↓
The immobilized mercury sulfide is removed in a coagulation sedimentation tank, a coagulation membrane separation tank, a membrane separation tank, a sand filtration tank, an activated carbon adsorption tank, or the like.

The ion exchange device allows the separation water 43 to pass through the cation exchange resin and the anion exchange resin to adsorb Hg ²⁺ to the cation exchange resin, and to adsorb the mercury complex (HgCl ³⁻ , HgCl ₄ ²⁻ , HgS ₂ ²⁻ etc.) are adsorbed and removed.

In addition, when using a precipitation apparatus, since it isolate | separates with a precipitation apparatus already, the solid-liquid separation part 103 becomes unnecessary. In addition, when the chelate resin tower is used, sludge is not generated, and similarly, the solid-liquid separation unit 103 is unnecessary.

  In this embodiment, a chelating agent 102 is added and precipitated in the reaction tank 101 as the mercury removing unit, and the separation water 43 containing the precipitate is removed as heavy metal sludge 104 in the solid-liquid separation unit 103. ing. Thereafter, the separation water 43 from the solid-liquid separation unit 103 is mixed with the discharged water 22 generated in the plant facility by the mixing unit 110, and the salt content in the mixed water 111 is removed by the desalination treatment apparatus 30. I am doing so.

  Then, the concentrated water 31 that has been salt-concentrated by the desalting apparatus 30 is introduced into the spray drying apparatus 23, where it is spray-dried using a part 12 a of the exhaust gas 12 from the boiler 11.

  As a result, the concentrated water 31 introduced into the spray-drying device 23 has the mercury in the separated water 43 obtained by separating the gypsum 32 from the desulfurization waste water 41 discharged from the wet desulfurization device 16 removed. When the concentrated water 31 discharged from 30 is spray-dried, mercury elution of the spray-dried product is prevented. In addition, the mercury content in the gypsum 32 in the desalting apparatus 30 can be reduced.

  As a result, the mercury content of the spray-dried dry salt can be reduced by removing mercury from the desulfurization waste water 41 from the wet desulfurization apparatus 16.

  In the water treatment system according to the present embodiment, the gypsum 32 is separated from the wet desulfurization device 16 that removes sulfur oxides in the boiler exhaust gas 12 from the boiler 11 and the desulfurization waste water 41 that includes the gypsum slurry from the wet desulfurization device 16. A dehydrator 42, a mercury removal unit (for example, the reaction tank 101) that introduces the separation water 43 from the dehydration device 42, introduces the chelating agent 102 and immobilizes heavy metals in the separation water 43, and a mercury removal unit A solid-liquid separation unit 103 that solid-liquid separates the solid content (heavy metal sludge) 104 in the separated water 43 and a mixing unit that mixes the separated water 43 from the solid-liquid separation unit 103 with the discharged water 22 generated in the plant equipment. 110, a desalting apparatus 30 for removing the salt content in the mixed water 111 mixed in the mixing unit 110, and a spraying means for spraying the concentrated water 31 that has been concentrated with the desalinating apparatus 30; So that comprises a spray-drying apparatus 23 for spray-dried using a portion 12a of the flue gas 12.

  As a result, by removing mercury from the desulfurization effluent 41, gypsum generated in the gypsum crystallization process of the subsequent desalination treatment apparatus 30, and mercury content in the spray dried salt in the spray drying process of the spray drying apparatus 23 The amount can be reduced. In connection with this, the elution amount of mercury of spray-dried salt can also be reduced.

As shown in FIG. 1, the spray drying device 23 sprays or sprays the concentrated water 31 and gas introduction means for introducing a part 12 a of the exhaust gas 12 through the branch line L ₁₁ branched from the exhaust gas line L _10. Spraying means. Then, the concentrated water 31 sprayed by the heat of the part 12a of the introduced exhaust gas 12 is evaporated and dried.

Further, in this embodiment, since a portion 12a of the exhaust gas 12 flowing into the air preheater 14 from the exhaust gas line L ₁₀ is branched via a branch line L _11, high temperature exhaust gas 12 (350 to 400 ° C. ) And spray drying of the concentrated water 31 can be performed efficiently. Incidentally, the exhaust gas 12b contributed to the drying is recycled into the exhaust gas line L ₁₀ between the air preheater 14 and the dust collector 15 via a gas delivery line L _12. In addition, you may make it return the exhaust gas 12b which contributed to drying to the one or several places of the back flow side of the air preheater 14, and the front flow side of the dust collector 15. FIG.

FIG. 2 is a schematic diagram of the spray drying apparatus according to the first embodiment. As shown in FIG. 2, the spray drying device 23 of the present embodiment includes a spray nozzle 24 that sprays the discharged water 22 introduced from the cooling tower 21 through the introduction line L ₂₁ into the spray drying device main body 23 a, An inlet 23b for introducing a part 12a of the exhaust gas 12 for drying the spray liquid 22a provided in the spray drying apparatus main body 23a, and an outlet 23b provided in the spray drying apparatus main body 23a. A drying region 25 for drying and an exhaust port 23c for discharging the exhaust gas 12b contributing to drying are provided. Reference numeral 26 denotes a solid material separated by the spray drying apparatus main body 23a, and V ₁ and V ₂ denote flow path opening / closing valves.

Here, an example of the balance between the gas amount of the part 12a of the exhaust gas 12 introduced into the spray drying device 23 and the liquid spray amount of the concentrated water 31 is shown.
When the gas amount of part 12a of the exhaust gas 12 to be introduced is sprayed from the spray nozzle 24 with a liquid amount of 100 kg / H of the concentrated water 31 per 1000 m ³ / H, the gas temperature decreases by 200 ° C.
In addition, the moisture concentration in the gas increases by 10%. For example, when the moisture concentration in the gas of the part 12a of the exhaust gas to be introduced before spraying is 9%, the moisture concentration in the gas of the exhaust gas 12b contributing to drying after spraying is 19%, which is increased by about 10%.
The decrease in the gas temperature of 200 ° C. is substantially equal to the temperature of the exhaust gas 12 after passing through the air preheater 14.

However, the bypass amount of the portion 12a of the exhaust gas 12 to the spray-drying apparatus 23 are the order of about 5%, when the gas 12b that has contributed to the drying bypassed returns to the exhaust gas line L _10, the moisture increase is 10 % / 20 = about 0.5%.

In addition, the gas temperature of the exhaust gas 12 passing through the exhaust gas line L ₁₀ is reduced by 200 ° C. because the air is preheated by the air preheater 14 and supplied to the boiler 11. There will be no temperature difference. That is, when the gas temperature at the inlet side of the air preheater 14 is 350 ° C., the gas temperature that has decreased after passing through the air preheater 14, the branch line L _11, and the gas feed line L ₁₂ is spray dried. The gas temperature of the exhaust gas 12b that has contributed to drying by the apparatus 23 is similarly reduced by 200 ° C., so that the temperature is substantially equivalent.

  According to the present embodiment, the concentrated water 31 discharged from the cooling tower 21 and discharged from the desalting apparatus 30 is introduced into the spray drying apparatus 23 via the spray nozzle 24, and the spray liquid 22 a is supplied to the exhaust gas 12. Since it is dried by the heat of the part 12a, it is not necessary to separately treat the discharged water 22 with an industrial waste water treatment facility, and it is possible to realize no drainage of the discharged water 22 generated in the plant.

  In the present embodiment, the discharge water 22 generated in the plant equipment will be described by taking blow drainage from the cooling tower 21 as an example. However, the present invention is not limited to this, and it is from a power plant or a chemical plant. It can be applied to discharged water in general.

  Here, as drainage cases of coal-fired power plant and oil-fired power plant, as drainage that is generated regularly, other than cooling water, for example, condensate demineralizer regeneration drainage, condensate demineralizer pre-filtration Exhaust device regeneration wastewater, turbidity filtration device regeneration wastewater, makeup water treatment device regeneration wastewater, laboratory miscellaneous wastewater, desulfurization device wastewater, miscellaneous wastewater, sampling wastewater, domestic wastewater, ash waste water, lifting coal cleaning wastewater, etc. can do. Examples of non-steady-state wastewater other than the regularly generated wastewater include, for example, air preheater washing wastewater, gas gas heater (GGH) washing wastewater, chimney washing wastewater, chemical washing wastewater, startup wastewater, coal storage wastewater, and coal pier Examples include drainage and drainage such as tank yards. In addition to the cooling tower cooling water, examples of the cooling water include bearing cooling water and condenser cooling water.

  The denitration device 13 installed in the exhaust gas treatment system 18 of the present embodiment is not essential, and the nitrogen oxide concentration and mercury concentration in the exhaust gas 12 from the boiler 11 are very small, or these are contained in the exhaust gas 12. When the substance is not included, the denitration apparatus 13 shown in FIG. 1 can be omitted.

The drying back destination of the gas feed line L ₁₂ contribution to exhaust gas 12b to from the spray drying apparatus 23, when the temperature drop is small, may be in the upstream side of the air preheater 14.

  According to the present embodiment, for example, various effluents generated in process plant equipment of a power plant or a chemical plant can be efficiently processed at low cost and without being accompanied by a decrease in boiler efficiency.

As shown in FIG. 1, the water treatment system of the mixed water 111 in which the discharged water 22 generated in the plant facility according to the present embodiment and the separated water 43 are mixed is present in the discharged water 22 from the cooling tower 21. In order to remove salt, a desalting apparatus 30 is provided. Then, the concentrated water 31 that has been desalted by the desalting treatment apparatus 30 is introduced into the spray drying apparatus 23 via the supply line L ₂₁ . In FIG. 1, reference numeral L ₂₄ is an introduction line for introducing the discharged water 22 into the desalting apparatus 30.

Next, a water treatment system for the mixed water 111 will be described with reference to FIGS. 1 and 3.
FIG. 3 is a configuration diagram illustrating an example of a desalting apparatus according to the present embodiment.
As shown in FIG. 3, the desalting apparatus 30 </ b> A according to the present embodiment applies the scale inhibitor 74 to the mixed water 111 of the discharged water 22 containing divalent ions such as Ca ions and the separated water 43. A first desalting salt which is installed downstream of the scale inhibitor supply unit to be supplied and separates the discharged water 22 into reclaimed water 33a and concentrated water 31a enriched with the Ca ions and the like. The device 55A is provided downstream of the first desalination device 55A, and the seed crystal gypsum 32a is supplied to the concentrated water 31a of the first desalination device 55A, so that the first desalination device 55A A crystallization tank 61 for crystallizing the gypsum from the concentrated water 31a, a liquid cyclone 62 as a separation unit for separating the crystallized gypsum 32 and the concentrated water 31a from the first desalinator 55A, and the liquid Installed downstream of the cyclone 62 And a second desalinator 55B that separates the concentrated water 31a into reclaimed water 33b and the concentrated water 31b in which the Ca ions and the like are concentrated. Yes.

  In the embodiment shown in FIG. 3, the first desalting device 55A and the second desalting device 55B use reverse osmosis membrane devices (RO) having reverse osmosis membranes 55a and 55b. Instead of this reverse osmosis membrane device, for example, a nanofiltration membrane (NF), an electrodialyzer (ED), a polarity switching electrodialyzer (EDR), an electroregenerative pure water device (EDI), an ion exchange resin device (IEx) ), An electrostatic desalting apparatus (CDl), an evaporator, and the like are also applicable as appropriate.

  The crystallization tank 61 includes a liquid cyclone 62 that is a separation unit, and the separated gypsum 32 is dehydrated by a dehydrator 63. As a modification of the present embodiment, the liquid cyclone 62 that is a separation unit can be omitted. In this case, the bottom of the crystallization tank 61 and the dehydrator 63 are directly connected.

The scale inhibitor 74 suppresses the formation of crystal nuclei in the mixed water 111 and is adsorbed on the surface of crystal nuclei (seed crystals, small-scale scales deposited exceeding the saturation concentration) contained in the discharged water 22. Thus, it has a function of suppressing crystal growth.
The scale inhibitor 74 also has a function of dispersing particles in water such as precipitated crystals (preventing aggregation). The scale inhibitor 74 is, for example, a phosphonic acid scale inhibitor, a polycarboxylic acid scale inhibitor, and a mixture thereof. Examples of the scale inhibitor 74 include “FLOCON 260 (trade name, manufactured by BWA)”, but the present invention is not limited thereto.

Moreover, when Mg ^<2+> is contained in the discharged water 22, the scale inhibitor which prevents the scale (For example, magnesium hydroxide, magnesium carbonate, magnesium sulfate) containing magnesium in the discharged water 22 is used. it can. Hereinafter, it is referred to as “magnesium scale inhibitor”.
Examples of magnesium scale inhibitors include polycarboxylic acid scale inhibitors. A specific example is “FLOCON295N (trade name)” manufactured by BWA.

  In this embodiment, after supplying the scale inhibitor 74 to the upstream flow path of the first demineralizer 55A, the first pH adjuster for introducing, for example, an acid or the like as the first pH adjuster 75A is provided. It is connected.

  An acid (for example, sulfuric acid) or an alkali agent (for example, calcium hydroxide or sodium hydroxide) is supplied as the first pH adjuster 75A.

Here, the precipitation behavior of gypsum, silica, and calcium carbonate in the discharged water 22 will be described with reference to FIGS.
FIG. 14 is a simulation result of the pH dependence of the amount of gypsum deposited. FIG. 15 is a simulation result of the pH dependence of the calcium carbonate deposition amount. FIG. 16 is a simulation result of the pH dependence of the silica precipitation amount. In these figures, the horizontal axis represents pH, and the vertical axis represents the amount of precipitation (mol) of gypsum, calcium carbonate, and silica, respectively. The simulation was performed using simulation software manufactured by OLI under the condition that 0.1 mol / L of each solid component was mixed in water and H ₂ SO ₄ as an acid and Ca (OH) ₂ as an alkali were added.

  From FIG. 14, it can be understood that there is no pH dependence of gypsum deposition, and precipitation occurs in the entire pH range. However, when a calcium scale inhibitor is added, gypsum exists in a dissolved state in water at a high pH range. From FIG. 15, calcium carbonate precipitates when the pH exceeds 5. From FIG. 16, silica tends to dissolve in water when the pH is 10 or more.

  Therefore, in consideration of the precipitation behavior of gypsum (calcium sulfate), silica, and calcium carbonate in the mixed water 111, the following first pH adjustment to third pH adjustment are performed.

1) First pH adjustment mode (pH 10 or more)
In the first pH adjustment mode, the pH in the mixed water 111 is measured by the pH meter 76 on the upstream side of the first desalting apparatus 55A, and is controlled so that the pH value becomes a predetermined pH of 10 or more.
This is because, as shown in FIG. 16, silica is dissolved when the pH is 10 or more.
In the case of this first pH adjustment, a scale inhibitor (calcium scale inhibitor) 74 in an amount that suppresses adhesion between gypsum and calcium carbonate is supplied as a substance to be scaled to the reverse osmosis membrane 55a.

2) Second pH adjustment mode (pH 10 or less)
In the second pH adjustment mode, the pH in the mixed water 111 is measured by the pH meter 76 on the upstream side of the first desalting apparatus 55A, and is controlled so that the pH value becomes a predetermined pH of 10 or less.
This is because, as shown in FIG. 16, silica is precipitated when the pH is 10 or less.
In the case of this second pH adjustment, the substances that scale to the reverse osmosis membrane 55a are gypsum, calcium carbonate, and silica, and an amount of the scale inhibitor 74 that suppresses all these adhesions is supplied.

  Here, as the scale inhibitor 74 for silica, there are two types of inhibitors: a calcium scale inhibitor and one that prevents silica from depositing as scale in the water to be treated (referred to as “silica scale inhibitor”). Is used. Examples of silica scale inhibitors include polycarboxylic acid scale inhibitors and mixtures thereof. A specific example is FLOCON260 (trade name, manufactured by BWA).

3) Third pH adjustment mode (pH 6.5 or less)
In the third pH adjustment mode, the pH in the mixed water 111 is measured by the pH meter 76 on the upstream side of the first desalting apparatus 55A, and controlled so that the pH value becomes a predetermined pH of 6.5 or less. To do.
This is because, as shown in FIG. 15, calcium carbonate is dissolved when the pH is 6.5 or lower.
In the case of this third pH adjustment, as a substance that adheres to the reverse osmosis membrane 55a, an amount of a scale inhibitor (calcium scale inhibitor, silica scale inhibitor) 74 that suppresses the adhesion of gypsum and silica is supplied.

  Table 1 summarizes the first pH adjustment mode to the third pH adjustment mode.

  As shown in Table 1, when pH is 10 or more, a scale inhibitor (calcium scale inhibitor) 74 is supplied to suppress the scale of gypsum and calcium carbonate (◯ in the table), and the silica is dissolved. Therefore, it is not necessary to supply a scale inhibitor (× in the table).

  Moreover, in the case of pH 10 or less and 6.5 or more, a scale inhibitor (calcium scale inhibitor, silica scale inhibitor) 74 is supplied to suppress all scales of gypsum, calcium carbonate, and silica ( ○ in the table).

  In addition, in the case of pH 6.5 or lower, scale inhibitor (calcium scale inhibitor, silica scale inhibitor) 74 is supplied to suppress the scale of gypsum and silica (O in the table), Since it is dissolved, the supply of the calcium scale inhibitor only needs to prevent the scale of only gypsum, so the supply amount is smaller than in the case of the second pH adjustment (× in the table).

  When the silica concentration in the concentrated water 31a after being concentrated by the first desalting apparatus 55A is equal to or higher than a predetermined concentration, the ability of the silica scale inhibitor is limited. Therefore, when the silica concentration is a predetermined concentration (for example, 200 mg / L) or less, the first, second, or third pH adjustment step is performed, and when the silica concentration is a predetermined concentration (for example, 200 mg / L) or more. It is preferable to carry out the first pH adjustment step (silica dissolution).

  In addition, a second pH adjusting unit for introducing an acid that is the second pH adjusting agent 75B is connected to the crystallization tank 61. The introduction of the acid that is the second pH adjusting agent 75B may be connected to the upstream line of the crystallization tank 61.

Thus, the first pH adjuster 75A is not limited to an acid. For example, by maintaining the alkali side, gelation of silicon oxide (SiO ₂ ) can be prevented. On the other hand, when the alkali side is used, calcium carbonate (CaCO ₃ ) or magnesium hydroxide (Mg (OH) ₂ ) may be precipitated. For this purpose, a scale inhibitor 74 is added to suppress the generation of scale.

  Therefore, it is preferable that the first pH adjusting agent 75A supplied on the upstream side of the first and second desalting apparatuses 55A and 55B is an acid or an alkali.

The second pH adjuster 75B supplied to the crystallization tank 61 is preferably an acid. Here, the reason why the second pH adjusting agent 75B supplied to the crystallization tank 61 is limited to an acid is, for example, to invalidate the calcium-based scale inhibitor 74 and precipitate calcium as gypsum (CaSO ₄ ). .

Incidentally, scale inhibitor 74, if a carboxylic acid ^{type, -COO - ··· Ca 2+ ··· -} OOC- as in, and H ⁺ dissociation of the tip of the carboxyl group, -COO ^- is Ca ^It is bound to ²⁺ . When the pH is lowered to an acid state, like the —COOH Ca ²⁺ HOOC—, H ^{+ at} the tip of the carboxyl group is not dissociated, and at the same time, the bond between the carboxyl group and the calcium ion Ca ²⁺ is released. As a result, the ionic calcium concentration increases, becomes supersaturated, and calcium salts such as gypsum precipitate.

  In the water treatment system of the present embodiment, the precipitation tank 53 and the filtration device 54 may be installed upstream of the supply portion of the scale inhibitor 74. An oxidation unit (not shown) that oxidizes by supplying an oxidant such as air may be installed upstream of the settling tank 53.

Similarly, a settling tank 53 and a filtration device 54 are installed between the hydrocyclone 62 and the second desalting device 55B. An acid or the like that is the third pH adjusting agent 75C is introduced into the flow path between the filtration device 54 and the second desalting device 55B.
In the case of the third pH adjusting agent 75C, an acid or an alkali can be used similarly to the first pH adjusting agent 75A.

  A method for treating the mixed water 111 using the water treatment system shown in FIG. 3 will be described below.

Here, as an example of the properties of the discharged water 22 from the cooling tower 21 treated in the present invention, the pH is 8, the Na ion is 20 mg / L, the K ion is 5 mg / L, the Ca ion is 50 mg / L, and the Mg ion. Is 15 mg / L, HCO ₃ ion is 200 mg / L, Cl ion is 200 mg / L, SO ₄ ion is 120 mg / L, PO ₄ ion is 5 mg / L, and SiO ₂ ion is 35 mg / L. , Ca ions, Mg ions, SO ₄ ions, and HCO ₃ ions are high in concentration, and a scale (CaSO ₄ , CaCO _3, etc.) is generated by the reaction of their presence.

<Pretreatment process>
First, in the precipitation tank 53 and the filtering device 54, metal ions in the discharged water 22 are roughly removed as metal hydroxides.
When the discharged water 22 shows strong acidity, an alkaline agent (for example, Ca (OH) ₂ ) 71 and a polymer (for example, an anionic polymer (Mitsubishi Heavy Mechatronics) are added to the discharged water 22 in the addition tank 52 adjacent to the upstream side of the settling tank 53. System Co., Ltd., trade name: Hishiflock H ₃ O ₅ )) 72 is charged, and the pH in the precipitation tank 53 is controlled to be alkaline (for example, pH: 8.5 to 11).

In this pH region, the solubility of calcium carbonate and metal hydroxide is low, and when calcium carbonate and metal hydroxide become supersaturated, calcium carbonate and metal hydroxide precipitate and precipitate at the bottom of the precipitation tank 53.
Also, the solubility of the metal hydroxide depends on the pH. The solubility of metal ions in water increases with acidity. Since the solubility of many metal hydroxides is low in the above pH range, the metal contained in the discharged water 22 is precipitated as a metal hydroxide at the bottom of the precipitation tank 53. Here, the deposit 53a is separately discharged from the bottom.

The discharged water 22 that is the supernatant liquid in the settling tank 53 is discharged from the settling tank 53. An iron-based flocculant (for example, FeCl ₃ ) 73 is added to the discharged discharged water 22, and solid contents such as calcium carbonate and metal hydroxide in the discharged water 22 are aggregated together with Fe (OH) ₃ .
The mixed water 111 is fed to the filtration device 54. The solid content aggregated together with Fe (OH) ₃ is removed by the filtration device 54.

Fe is acidic and tends to precipitate as a hydroxide among metals. When the mixed water 111 containing a large amount of Fe ions flows into the first demineralizer 55A, a scale containing Fe is generated in the first demineralizer 55A. Etc. precipitate. For this reason, in this embodiment, considering the prevention of scale generation in the first demineralizer 55A, the mixed water 111 is supplied after the alkali pretreatment and before flowing into the first demineralizer 55A. The treatment conditions in the precipitation tank 53, the addition amount of FeCl _3, and the like are appropriately set so that the Fe ion concentration therein is 0.05 ppm or less. Depending on the water quality of the mixed water 111, the pretreatment can be omitted.

<Scale inhibitor supply process>
In the supply unit that supplies the scale inhibitor 74, a predetermined amount of the scale inhibitor 74 is supplied to the mixed water 111 from a tank (not shown). A control unit (not shown) adjusts so that the concentration of the scale inhibitor 74 becomes a predetermined value set according to the properties of the mixed water 111.

<First pH adjustment step>
The supply part of the pH adjusting agent 75 in the first pH adjusting step is a scale (gypsum, calcium carbonate) containing Ca by the scale inhibitor 74 with respect to the pH of the mixed water 111 on the inlet side of the first desalting apparatus 55A. To a value (for example, about pH 5.5) that suppresses precipitation of. The management measures the pH of the mixed water 111 on the inlet side of the first desalinator 55A.
In the modification in which the first pH adjusting unit is not provided, the first pH adjusting step is omitted.

<Upstream separation process>
In the first desalting apparatus 55A, the mixed water 111 whose pH is adjusted is treated. The permeated water that has passed through the reverse osmosis membrane 55a of the first desalting apparatus 55A is recovered as reclaimed water 33a from which the salt content has been removed.

  In this upstream separation step, the ions and the scale inhibitor 74 contained in the mixed water 111 cannot permeate the reverse osmosis membrane 55a. Therefore, the non-permeate side of the reverse osmosis membrane 55a becomes the concentrated water 31a having a high ion concentration. The concentrated water 31a of the first demineralizer 55A is fed toward the crystallization tank 61. For example, also when other desalting apparatuses such as an electrostatic desalting apparatus are used, the mixed water 111 is separated into treated water and concentrated water having a high ion concentration.

Here, in the first desalting apparatus 55A, when the pH is high, silica is present as ionic silica on the surface of the reverse osmosis membrane 55a.
Specifically, in the case of 200 mg SiO ₂ / L or more, for example, it can exist as ionic silica at a high pH.
On the other hand, in the first desalting apparatus 55A, when the pH is low, it is precipitated as gel-like silica.
Specifically, for example, at 200 mg SiO ₂ / L or less, it can exist as ionic silica at a high pH.
If the pH is low, the gelation can be suppressed (or the gelation time can be extended) by using the scale inhibitor 74 at 200 mg SiO ₂ / L or less.

In the first desalting apparatus 55A, when the pH is high, calcium ions (Ca ²⁺ ) can be precipitated as CaCO ₃ crystals on the surface of the reverse osmosis membrane 55a. Precipitation is prevented by supplying.

Further, in the first desalting apparatus 55A, when the pH is high, magnesium ions (Mg ²⁺ ) precipitate as Mg (OH) ₂ and MgSiO ₃ crystals on the surface of the reverse osmosis membrane 55a at a high pH. However, precipitation is prevented by supplying the scale inhibitor 74 for Mg.

<Second pH adjustment step>
In a control unit (not shown), the pH of the concentrated water 31a from the first desalinator 55A in the crystallization tank 61 is a value at which gypsum in the concentrated water 31a can be precipitated by reducing the function of the scale inhibitor 74. (For example, pH 4 or less).

<Crystalling process>
The concentrated water 31 a whose pH has been adjusted by the second pH adjusting agent 75 </ b> B is stored in the crystallization tank 61. When the seed crystal supply unit is installed, the seed crystal supply unit adds the seed crystal seed gypsum 32 a to the concentrated water 31 a in the crystallization tank 61.
The addition of the second pH adjuster 75B invalidates the function of the scale inhibitor 74 in the crystallization tank 61. For this reason, the gypsum 32 supersaturated in the crystallization tank 61 is crystallized. When seed crystal gypsum 32a is added separately as a seed crystal in this crystallization step, the gypsum 32 grows using the seed crystal gypsum 32a as a nucleus.
Here, a part of the gypsum 32 separated by the dehydrator 63 is used as the seed crystal gypsum 32a.

When supplying the seed crystal gypsum 32a, the pH passing through the first desalting apparatus 55A may be set to the alkali side without performing the first pH adjustment by adding the first pH adjusting agent 75A. In this case, the purity of the gypsum 32 is somewhat lower than that in the case of adjusting the pH by adding an acid which is the first pH adjusting agent 75A. This is because calcium carbonate (CaCO ₃ ) crystals are produced when the pH is on the alkali side. Therefore, so that the purity is lowered due to gypsum (CaSO ₄₎ to calcium carbonate (CaCO ₃₎ are mixed.

  As in this example, in the second pH adjusting step of adding an acid as the second pH adjusting agent 75B, the water content is increased by adjusting the pH to a predetermined value and adding the seed crystal gypsum 32a in the crystallization step. A low-purity gypsum 32 can be deposited.

The silica in the concentrated water 31a gels at a low pH, and reacts with Ca ²⁺ and Mg ²⁺ in the concentrated water 31a to form, for example, a reaction product of CaSiO ₃ and MgSiO ₃ and precipitate.

  Here, FIGS. 10 and 11 are photomicrographs of gypsum obtained by crystallization. FIG. 10 shows an observation result when seed crystal gypsum 32a which is a seed crystal is added as a condition. FIG. 11 shows an observation result when seed crystal gypsum 32a which is a seed crystal is not added as a condition.

  As shown in FIG. 10, large gypsum precipitated when seed crystal gypsum 32a was added. In general, the larger the precipitated gypsum, the lower the water content. If the average particle size is 10 μm or more, preferably 20 μm or more, gypsum having a sufficiently reduced water content can be obtained. Here, the “average particle diameter” in the present invention is a particle diameter measured by a method (laser diffraction method) defined by JlSZ8825.

  From the results of FIGS. 10 and 11, high-purity gypsum having a low water content can be precipitated by adjusting the pH to a predetermined value in the second pH adjustment step and adding a seed crystal in the crystallization step. The larger the amount of seed crystal added (the higher the seed crystal concentration in the crystallization tank 61), the higher the precipitation rate of gypsum 32. The amount of seed crystal gypsum 32a, which is a seed crystal, is appropriately set based on the residence time in the crystallization tank 61, the concentration of the scale inhibitor 74, and the pH.

  Further, the gypsum 32 having an average particle diameter of 10 μm or more, preferably 20 μm or more is separated from the concentrated water 31a by the liquid cyclone 62 which is a separation part. A part of the gypsum 32 collected by the dehydrator 63 adjacent to the hydrocyclone 62 serving as the separation unit is stored in a seed crystal tank (not shown) via a seed crystal circulation unit (not shown). A part of the collected gypsum 32 is supplied to the crystallization tank 61 as seed crystal gypsum 32a.

  Here, acid treatment may be applied to the stored gypsum 32 in the seed crystal tank. When the scale inhibitor 74 adheres to the gypsum 32 separated by the dehydrator 63, the function of the adhesion scale inhibitor is reduced by acid treatment. The type of acid used here is not particularly limited, but sulfuric acid is optimal in consideration of power reduction in the second desalinator 55B.

  The gypsum 32 crystallized in the crystallization tank 61 has a wide particle size distribution. However, since the gypsum 32 of 10 μm or more is separated and recovered from the concentrated water 31a by the liquid cyclone 62, a large gypsum can be used as a seed crystal. If a large seed crystal is added, a large amount of large gypsum can be crystallized. That is, it is possible to obtain high-quality gypsum with a high recovery rate. In addition, the large gypsum can be easily separated by the hydrocyclone 62, and the hydrocyclone 62 can be reduced in size and the power can be reduced. Large gypsum can be easily dehydrated by the dehydrating device 63, so that the dehydrating device 63 can be reduced in size and power can be reduced.

  Here, since the water treatment system of FIG. 3 is an open system except for the reverse osmosis membrane device, the mixed water 111 and the concentrated water 31a come into contact with the air and the carbonate ions are dissolved in the water. However, as described above, the mixed water 111 and the concentrated water 31a are adjusted in the pH region where the solubility of calcium carbonate is high in the first pH adjusting step and the second pH adjusting step. The carbonate ions in the concentrated water are reduced in the previous stage of the crystallization tank 61 or in the crystallization tank 61, and the calcium carbonate is below the saturation solubility. Furthermore, since the pH is lowered by adding an acid as the pH adjusting agent 75, the carbonate ion concentration is low from the equilibrium formula (1) below. Therefore, in the crystallization tank 61, calcium carbonate is maintained at a concentration sufficiently lower than the saturation concentration, and calcium carbonate does not crystallize. For this reason, the recovered gypsum 32 contains almost no calcium carbonate. Thereby, the purity of the gypsum 32 becomes high.

CO ₂ + H ₂ O⇔H ₂ CO ₃ ⇔HCO ₃ ⁻ + H ⁺ ⇔CO ₃ ²⁻ + 2H ⁺ (1)

Moreover, the solubility of the salt containing a metal is high in an acidic region. Even if the metal remains in the mixed water 111 even after the pretreatment (precipitation tank 53), the pH of the concentrated water 31a of the first demineralizer 55A is reduced as described above in the first pH adjustment step. If it is, the hydroxide containing a metal will not precipitate in the crystallization process. Further, when the mixed water 111 has a property containing a large amount of Fe ions, since the Fe concentration is reduced through the pretreatment described above, the hydroxide containing Fe (OH) ₃ in the crystallization tank 61 is reduced. Almost no precipitation occurs.

  Thus, if the water treatment method and water treatment system of the present embodiment are used, impurities such as calcium carbonate and metal hydroxide in the mixed water 111 including the discharged water 22 discharged from the cooling tower 21 are hardly included. High purity gypsum 32 can be separated and recovered as a valuable resource.

  Here, when gypsum 32 having a large average particle size of 10 μm or more, preferably 20 μm or more is crystallized, the crystallization speed generally decreases, so that the residence time in the crystallization tank 61 becomes longer. In the present embodiment, the pH is adjusted so as to reduce the function of the scale inhibitor 74, and the seed crystal concentration is increased to ensure an appropriate crystallization rate.

<Recovery process>
Concentrated water 31a containing gypsum 32 is discharged from the crystallization tank 61 and fed to the liquid cyclone 62 as a separation unit, and the gypsum 32 is separated from the discharged concentrated water 31a. The gypsum 32 having an average particle size of 10 μm or more settles at the bottom of the hydrocyclone 62, and the gypsum having a small particle size remains in the supernatant. The gypsum 32 settled on the bottom of the hydrocyclone 62 is transferred to the dehydrator 63 and further dehydrated and collected. By the recovery step, the high-purity gypsum 32 having a low moisture content and no impurities can be separated and recovered at a high recovery rate. In this embodiment, since seed crystals are added for crystallization, gypsum 32 having an average particle size of 10 μm or more is mainly precipitated, and the proportion of small-diameter gypsum is reduced. Here, the separated liquid 64 separated by the dehydrating device 63 may be supplied to the spray drying device 23 and spray dried.

  In addition to supplying the spray drying device 23 to spray drying, the separation liquid 64 is introduced into the concentrated water 31a discharged from the hydrocyclone 62, and is treated together with the concentrated water 31a by the second desalting device 55B. Anyway.

  When the liquid cyclone 62 that is a separation unit is omitted as a modification of the present embodiment, concentrated water on the sedimentation side is discharged from the bottom of the crystallization tank 61. In the concentrated water at the bottom of the crystallization tank 61, a large crystallized gypsum 32 has settled. If the concentrated water mainly containing the large gypsum 32 is dehydrated by the dehydrator 63, the high-purity gypsum 32 can be recovered. Further, since the moisture content of the gypsum 32 is low, it is not necessary to increase the volume of the dehydrator 63.

<Downstream separation process>
The supernatant-side concentrated water 31 a discharged from the hydrocyclone 62 is fed to the settling tank 53 and the filtration device 54. The gypsum 32 and calcium carbonate remaining in the concentrated water after the separation step and the metal hydroxide remaining in the concentrated water are removed in the same steps as the precipitation tank 53 and the filtration device 54 described above.

  The concentrated water 31a discharged from the filtration device 54 is supplied to the second desalting device 55B. Before flowing into the second desalinator 55B, the scale inhibitor 74 may be additionally added to the concentrated water 31a.

Further, after adding scale inhibitor 74, an acid or alkali is a pH adjusting agent 75 to the concentrated water 31a may be supplied.

  In the second desalting apparatus 55B, the concentrated water 31a from the first desalting apparatus 55A is processed. The water that has passed through the reverse osmosis membrane 55b of the second desalting apparatus 55B is recovered as recycled water 33b as permeated water. The concentrated water 31b of the second desalting apparatus 55B is introduced into the spray drying apparatus 23 where it is spray dried.

  When the second desalting apparatus 55B is installed, the recycled water 33b can be further recovered from the concentrated water 31a on the supernatant liquid side after the gypsum 32 is crystallized, so that the water recovery rate is further improved.

The concentrated water 31a from the first desalting apparatus 55A has a low ion concentration because the gypsum 32 has been removed by the treatment in the crystallization tank 61. For this reason, since the 2nd desalination apparatus 55B can make an osmotic pressure low compared with the case where the gypsum 32 is not removed, required motive power is reduced.
An evaporator (not shown) may be installed. In the evaporator, water is evaporated from the concentrated water, and ions contained in the concentrated water are precipitated as a solid and recovered as a solid. Since water is collected upstream of the evaporator and the amount of concentrated water is significantly reduced, a compact evaporator can be obtained, and the energy required for evaporation can be reduced.

  In the present embodiment, as the desalination treatment apparatus, a first desalination apparatus 55A for desalting after introducing the scale inhibitor 74 into the mixed water 111 of the discharged water 22 of the cooling tower 21 and the separated water 43; The "desalting / crystallizing device" having a crystallization tank 61 for crystallizing gypsum 32 after the first desalting device 55A and a liquid cyclone 62 for separating the crystallized gypsum 32 is used. The present invention is not limited to this.

Here, the gypsum 32 crystallized in the crystallization tank 61 of the desalting apparatus 30 is discharged through the gypsum discharge line L ₂₂ as shown in FIG. 1, and the recycled water 33 (33a, 33b) is Through the reclaimed water supply line L ₂₃ , the separated water 43 is joined to a return line L ₃₂ that returns to the desulfurization device 16 and used as makeup water for gypsum slurry used in the wet desulfurization device 16.

As a desalting apparatus other than the “desalting / crystallization apparatus” as shown in FIG. 3, as another embodiment, a separation apparatus using the cold dry method shown in FIG. 12 may be used.
FIG. 12 shows an outline of an example of a separation apparatus by the cold dry method.
As shown in FIG. 12, the desalination apparatus using the cold dry method adds mixed water 111 to calcium hydroxide (Ca (OH) ₂ ) 92 in an addition tank 91 and calcium carbonate (CaCO ₃ ) in a settling tank 93. 94 is settled and removed.
Next, sodium carbonate (NaCO ₃ ) 96 is added in the addition tank 95, and calcium carbonate (CaCO ₃ ) 94 is precipitated in the sedimentation tank 97 and removed.
Thereafter, an iron-based flocculant (for example, FeCl ₃ ) 73 is added to agglomerate suspended solids (for example, floating solids such as gypsum, silica, calcium carbonate, magnesium hydroxide). Thereafter, in the same manner as the operation shown in FIG. 3, when the treatment is performed by the first desalting apparatus 55A, the scale inhibitor 74 and the pH adjuster 75 are introduced to perform the membrane separation treatment.

In addition, OPUS (Optimized Pretreatment and Unique Separation), which is treated with a reverse osmosis membrane after degassing and free oil removal of water to be treated, chemical softening, filtering floating solid particles such as metals, etc. Method (Veolia) or water to be treated is removed by chemical softening means or ion exchange resin, for example, Ca and Mg, then acid is added to adjust pH to the acid side, and CO ₂ gas is separated. Thereafter, the pH can be adjusted to the alkali side to prevent ionization and precipitation, and a HERO (High Efficiency Reverse Osmosis) method (GE) or the like, which is treated with a reverse osmosis membrane, can be exemplified.

In the first and second desalting apparatuses 55A and 55B of this embodiment, the “RO membrane” is used as the membrane separation means, but the “NF membrane” may be used as the separation membrane.
When using this NF membrane, like the RO membrane, although the divalent ion can be removed, since the monovalent ions are not completely removed, it can be supplied for example to the desulfurization makeup water of the desulfurization apparatus However, it is preferable to use the supply destination of the reclaimed water as, for example, feed water for the cooling tower. This is because the NF film cannot remove the scale inhibitor 74.

  By the water treatment system of the present embodiment, divalent metals (for example, calcium salt, magnesium salt, etc.), sulfate ions and carbonate ions contained in the mixed water 111 can be separated efficiently. In addition, when the RO membrane is used, it is possible to remove barium salt and strontium salt in addition to calcium salt and magnesium salt.

  According to the present embodiment, it is possible to remarkably increase the amount of drainage (before concentration) that can be spray-dried by concentrating the mixed water 111 using a desalting apparatus 30A as shown in FIG. For example, by using a desalting crystallizer, if the recovery rate of the recycled water is 95%, 100 / (100−95) = 20 times as much drainage can be eliminated.

FIG. 4 is a configuration diagram illustrating an example of another desalting apparatus according to the present embodiment. In the desalination treatment apparatus 30A shown in FIG. 3, a precipitation tank 53 and a filtration apparatus 54 are installed on the upstream side of the first desalination apparatus 55A, and the metal content in the mixed water 111 is used as a metal hydroxide to obtain a calcium content. Is precipitated and removed as calcium carbonate, but the present invention may not be provided with this pretreatment.
As shown in FIG. 4, in the desalination processing apparatus 30B of the present embodiment, a first desalting apparatus 55A, a crystallization tank 61, a liquid cyclone 62, and a second desalting apparatus 55B are installed. In order to prevent the scale from adhering to the reverse osmosis membranes 55a and 55b of the first and second desalting devices 55A and 55B, the scale inhibitor 74 is added on the upstream side of the desalting devices 55A and 55B. ing. In addition, as the pH adjuster 75, an acid (for example, sulfuric acid etc.) and an alkali agent (sodium hydroxide, calcium hydroxide, etc.) are added.
Depending on the type of the mixed water 111, no pretreatment is required, and the configuration of the desalting apparatus is simplified.

Examples of the mixed water 111 to be processed by such a simplified desalting apparatus 30B include discharged water having a low carbonate ion concentration. Further, the present invention can also be applied to discharged water having a low concentration of scale components such as Ca ²⁺ and Mg ²⁺ .
Here, the pH adjusting agent 75 includes an acid and an alkali agent. Examples of the acid used for lowering the pH include general pH adjusters such as hydrochloric acid, sulfuric acid, and citric acid. Moreover, as an alkali agent used when raising pH, common pH adjusters, such as sodium hydroxide and calcium hydroxide, can be illustrated, for example.

FIG. 5 is a configuration diagram illustrating an example of another desalting apparatus according to the present embodiment.
Further, as in the desalting apparatus 30C shown in FIG. 5, a third desalting apparatus 55C is further installed downstream of the concentrated water side of the second desalting apparatus 55B to perform a three-stage desalting process. You may do it.
If the 3rd desalination apparatus 55C provided with the reverse osmosis membrane 55c is installed, since the reclaimed water 33c can further be collect | recovered from the concentrated water 31b, the water recovery rate will further improve to 97%. In addition, between the 2nd desalination apparatus 55B and the 3rd desalination apparatus 55C, the pretreatment means of the precipitation tank 53 shown in FIG. 3, the filtration apparatus 54, the scale inhibitor 74, and the pH adjuster 75 are installed. Although added, this is omitted in FIG.

FIG. 6 is a configuration diagram illustrating an example of another desalting apparatus according to the present embodiment.
Further, as in the desalination treatment apparatus 30 </ b> D shown in FIG. 6, a deaeration unit 50 that is a carbon dioxide separation unit that separates carbon dioxide is provided on the upstream side of the addition tank 52. Specifically, the deaeration unit 50 is a deaeration tower or a separation membrane provided with a filler that diffuses carbon dioxide.

In the desalting apparatus 30D of FIG. 6, the mixed water 111 before flowing into the deaeration unit 50 is adjusted to a low pH. Carbonic acid in the mixed water 111 is in an equilibrium state according to its pH. When the pH is as low as 6.5 or lower, the mixed water 111 exists mainly in the state of HCO ₃ ⁻ and CO ₂ . The mixed water 111 containing CO ₂ flows into the deaeration unit 50. CO ₂ is removed from the mixed water 111 in the deaeration unit 50.

  In the present embodiment, similarly to FIG. 5, a third desalinator 55C is further installed downstream of the second desalinator 55B on the concentrated water side to perform a three-stage desalting process.

Next, a water treatment system according to Example 2 will be described. FIG. 7 is a schematic diagram of a water treatment system according to the present embodiment. About the member which overlaps with the water treatment system of Example 1, the same code | symbol is attached | subjected and the overlapping description is abbreviate | omitted.
As shown in FIG. 7, the water treatment system according to the present embodiment is provided with an oxidation-reduction potential (ORP) meter 130 that measures the oxidation-reduction potential in the mixed water 111 introduced into the first desalination apparatus 55A. Yes.
And when the value of the oxidation-reduction potential of the mixed water 111 introduced into the first desalting apparatus 55A is outside the predetermined value range, the oxidizing agent 132 is supplied from the oxidizing agent supply unit 131. .
Although mercury is removed from the separated water 43 separated from the desulfurization drainage before the mixing in the mixing unit 110, mercury may remain in the separated water 43 in some cases.

Since this residual mercury takes various forms, it can be removed by the RO membrane in the ionic state and does not permeate to the permeate side, but in the case of metallic mercury, it is nonpolar and liquid. Permeates the RO membrane.
Therefore, by controlling the value of the oxidation-reduction potential in the mixed water 111 within a predetermined range, the form of mercury is converted into an ionic state and removed by the RO membrane.

  Here, it is preferable to control so that the value (X) of the oxidation-reduction potential in the mixed water 111 measured by the oxidation-reduction potentiometer 130 is in the range of −0.69 V <ORP value (X) <1.358 V. .

This is because when the ORP value (X) exceeds “1.358 V”, the chloride Cl ⁻ becomes chlorine gas (Cl ₂ ), which is not preferable.
The lower limit value of the ORP value (X) varies depending on the coexisting substances. The lower limit value of the ORP is −0.69 V or more, preferably 0.2680 V or more, more preferably 0.6125 V or more, and further preferably 0.796 V. is there. Most of the salts in the wastewater are Cl ⁻ and SO ₄ ²⁻ .
Hg (l) is oxidized to Hg ₂ Cl ₂ (solid) at +0.2680 V or higher and Hg ₂ SO ₇ (solid) at +0.6125 V or higher. The waste water contains S ²⁻ , I ⁻ and Br ^−, but the amount is smaller than that of Cl ⁻ and SO ₄ ²⁻ .
On the other hand, when no impurities are contained at all, +0.798 V is required to oxidize Hg (l) to Hg ₂ ²⁺ .

Rationale of 1.358V upper limit value Cl ^- because the standard electrode potential of the oxidation of the Cl ₂ is + 1.3583V. On the other hand, since the reaction from Cl ⁻ to ClO ⁻ is +0.89 V, the upper limit value is at least +1.3583 V or less, preferably +0.89 V or less.

Therefore, the oxidizing agent 132 is introduced by ORP control so that mercury does not reduce.
As a result, mercury is not metal mercury but is maintained as mercury oxide, and chlorine gas, which is a repellent substance for the RO membrane, is maintained in the form of chloride ions. Therefore, it is possible to operate without removing the mercury while removing the mercury.

  Here, it is preferable to use air as the oxidizing agent 132. By using air as the oxidant 132, it is possible to oxidize under mild conditions while suppressing damage to the RO membrane.

In addition, after supplying the oxidizing agent 132, a solid-liquid separation device 133 is installed on the upstream side of the first desalting device 55A, and solidified mercury (for example, mercury chloride (HgCl ₂ ) or the like in the mixed water 111). ) May be separated. Thereby, solidified mercury (for example, mercury chloride (HgCl ₂ )) is prevented from adhering to the surface of the RO membrane, and a decrease in the desalting capability can be suppressed.

Next, a water treatment system according to Example 3 will be described. FIG. 8 is a schematic diagram of a water treatment system according to the present embodiment. About the member which overlaps with the water treatment system of Example 1, the same code | symbol is attached | subjected and the overlapping description is abbreviate | omitted.
As shown in FIG. 8, the water treatment system according to this embodiment includes a UF (Ultrafiltration Membrane) membrane 122 on the downstream side of the solid-liquid separation unit 103 from which the heavy metal sludge 104 is separated and on the upstream side of the mixing unit 110. And an NF membrane device 121 having an NF membrane (nanofiltration membrane) 121a.

In this embodiment, by adding the chelating agent 102, the solid-liquid separation unit 103 removes and separates mercury, and then desalting with a membrane. The membrane for this membrane treatment is preferably an NF membrane.
Sends back in return line L ₃₆ in the wet desulfurization system 16 as return water 123a a portion of permeate 123 of NF membrane 121 a, and the discharge water 22 of the concentrate 124 NF membrane 121 from the rear stage of the cooling tower 21 It mixes with the mixing part 110, and it is set as the mixed water 111.

By desalted NF membrane 121 a, multivalent ions to the concentrate 124 side (e.g. _{^{Ca 2+, Mg 2+, SO 4}} 2-) was concentrated and monovalent ions (such as Na in the permeate 123 side ⁺ , Cl ⁻ ) can be concentrated.
Here, the salt contained in the waste water from the wet desulfurization apparatus 16 is mainly calcium chloride (CaCl ₂ ). Thus, by membrane separation by NF membrane 121 a having a monovalent selectivity, concentrate 124 is downstream of the gypsum raw materials gypsum crystallization (e.g. Ca ^2+, SO ₄ ^2-) while concentrating, the subsequent first It is possible to reduce Cl ⁻ as a load on the RO membrane of the first desalting apparatus 55A.

Accordingly, it is possible to reduce the concentration of soluble evaporated residue (TDS) supplied to the first desalting apparatus 55A in the subsequent stage and to increase the concentration rate.
Thereby, the concentrated water 31a from the 1st desalination apparatus 55A can be reduced. As a result, the spray drying device 23 for spray drying concentrated water can be downsized.

In order to prevent clogging of the desalination apparatus according to NF membrane 121 a, may be added to the scale inhibitor.

According to this embodiment, after the treatment with mercury process the separated water 43 with a chelating agent 102, by desalting by further NF membrane 121 a, it is possible to selectively enrich the multivalent ions, thereby, The concentration rate at the RO membrane in the first desalting apparatus 55A is increased, and the spray drying apparatus 23 is reduced in size.

The deliquescent materials are mainly CaCl ₂ and MgCl ₂ , but since these divalent cations (Ca ²⁺ , Mg ²⁺ ) and chloride ions Cl ⁻ can be separated by the NF membrane, spray drying The problem of deliquescence of dry salt in the device 23 is reduced.

  The concentrated water 124 of the NF membrane becomes rich in multivalent ions, and gypsum is collected by the crystallization device, concentrated by RO after crystallization, and the RO concentrated water can be spray dried by the spray drying device 23.

Next, a water treatment system according to Example 4 will be described. FIG. 9 is a schematic diagram of a water treatment system according to the present embodiment. About the member which overlaps with the water treatment system of Example 1, the same code | symbol is attached | subjected and the overlapping description is abbreviate | omitted.
As shown in FIG. 9, the water treatment system according to the present embodiment includes a wet desulfurization device 16 that removes sulfur oxide in the boiler exhaust gas 12 from the boiler 11, and a desulfurization that includes gypsum slurry from the wet desulfurization device 16. A dehydrator 42 that separates the gypsum 32 from the waste water 41, a mixing unit 110 that mixes the separated water 43 from the dehydrator 42 with the discharged water 22 generated in the plant facility, and a mixing that is mixed in the mixing unit 110 Solid-liquid separation of reaction tank 101 in which water 111 is introduced and chelating agent 102 is introduced to immobilize heavy metals in separated water 43 and solid content (heavy metal sludge) 104 in mixed water 111 from reaction tank 101 Spraying the solid-liquid separation unit 103 to perform, the desalination treatment device 30 for removing the salt content in the mixed water 111 after the solid-liquid separation, and the concentrated water 31 concentrated in the salt content by the desalination treatment device 30 It has a step, and spray-drying apparatus 23 for spray-dried using a portion 12a of the boiler flue gas 12, in which comprises a.
By mixing the discharged water 22 from the cooling tower 21 with the separated water 43, impurities contained in the discharged water 22 of the cooling tower 21 can be removed using the chelating agent 102.

  Unlike the treatment system of the first embodiment, the amount of water introduced into the first desalinator 55A increases, so that the salt concentration decreases and the load on the RO membrane can be reduced.

Next, a water treatment system according to Example 5 will be described. FIG. 13 is a schematic diagram of a water treatment system according to the present embodiment. About the member which overlaps with the water treatment system of Example 1, the same code | symbol is attached | subjected and the overlapping description is abbreviate | omitted.
As shown in FIG. 13, the water treatment system according to the present embodiment adds the chelating agent 102 to the concentrated water 31 supplied to the spray drying device 23.
In this embodiment, a chelating agent 102 for immobilizing heavy metal remaining in the concentrated water 31 is added to the line L ₂₁ for supplying the concentrated water 30 from the desalting treatment device 30 to the spray drying device 23. It is added from the part.

  In this embodiment, the chelating agent 102 is mixed into the concentrated water 30 before being supplied to the spray drying device 23, so that the dry salt in the exhaust gas 12 b generated by the spray drying device 23 is sufficiently contained in the chelating agent 102. Mixed.

  The solid content 141 separated by the solid content separator 140 is then landfilled as it is.

Here, when adding the chelating agent 102, it is necessary to handle it at or below the heat resistant temperature. For this reason, the temperature (T ₁ ) of the exhaust gas 12b at the end of drying of the spray dryer 23 is maintained at 200 ° C. or lower, preferably 150 ° C. or lower.

Note that the temperature of the spray droplet during drying in the spray drying device 23 is about 80 ° C., and the temperature does not increase any more. For this reason, the temperature at the start of drying is not limited. The inlet temperature (T ₂ ) of the branched exhaust gas 18a to the spray dryer 23 is, for example, about 350 ° C. Therefore, either or both of the evaporation amount of the dehydrated filtrate droplets and the flow rate of the branched exhaust gas 12a are changed, and the temperature (T ₁ ) of the exhaust gas 12b is maintained at 200 ° C. or lower, preferably 150 ° C. or lower. Thus, there is no deterioration of the chelating agent 102, and elution of heavy metals when the solid content 141 is landfilled is eliminated.

  According to the present embodiment, after adding the chelating agent 102 that immobilizes heavy metals in the concentrated water 30, drying with the spray drying device 23 prevents elution of heavy metals such as mercury from the solid content 141. be able to.

Further, a coagulant may be added together with the chelating agent 102 .
As the flocculant, a coagulant that forms solid nuclei and a polymer flocculant that increases flocs of the solid can be used.

  Here, examples of the coagulant include a sulfate band, iron chloride, and PAC. Examples of the polymer flocculant include “Takifloc (trade name; manufactured by Taki Chemical Co., Ltd.) anionic, nonionic, cationic, and amphoteric)”, “Epofloc L-1 (trade name); Etc.

11 Boiler 12 Boiler exhaust gas (exhaust gas)
18 Exhaust gas treatment system 21 Cooling tower 22 Discharged water 23 Spray drying device 30 Desalination treatment device 31 (31a to 31c) Concentrated water 33 (33a to 33c) Reclaimed water 55A to 55C First to third desalination devices 61 Crystallization tank 62 Hydrocyclone 74 Scale inhibitor 75 pH adjuster 101 Reaction tank 102 Chelating agent 103 Solid-liquid separator 104 Heavy metal sludge 110 Mixer 111 Mixed water

Claims (14)

A wet desulfurization device for removing sulfur oxides in boiler exhaust gas;
A dehydrator for separating gypsum from the desulfurization effluent containing gypsum slurry from the wet desulfurization apparatus;
A mercury removing unit that introduces separated water from the dehydrator and introduces a chelating agent to immobilize heavy metals in the separated water;
A solid-liquid separation unit for solid-liquid separation of the solid content in the separated water from the mercury removal unit;
A mixing section for mixing the separated water from the solid-liquid separation section with the discharged water generated in the plant equipment;
A desalting apparatus for removing salt in the mixed water mixed in the mixing unit;
A spray means for spraying the concentrated water salt-concentrated in the desalination treatment apparatus, and a spray drying apparatus for spray drying using a part of the boiler exhaust gas ,
The desalting apparatus is
An anti-scale agent supply unit for supplying an anti-scale agent to the mixed water containing divalent ions of Ca ions;
A first demineralizer installed on the downstream side of the scale inhibitor supply unit and separating the mixed water into reclaimed water and concentrated water enriched with the Ca ions;
A crystallization tank provided on the downstream side of the first demineralizer and crystallizing gypsum from the concentrated water;
A separation unit for separating the crystallized gypsum and the concentrated water from the first desalting apparatus;
A water treatment system , comprising: a second desalting apparatus that is installed on the downstream side of the separation unit and separates the concentrated water into reclaimed water and concentrated water in which the Ca ions are concentrated . A wet desulfurization device for removing sulfur oxides in boiler exhaust gas;
A dehydrator for separating gypsum from the desulfurization effluent containing gypsum slurry from the wet desulfurization apparatus;
A mixing unit for mixing the separated water from the dehydrator with the discharged water generated in the plant facility;
A reaction vessel for introducing mixed water mixed in the mixing section, and for injecting a chelating agent to immobilize heavy metals in separated water;
A solid-liquid separation unit for solid-liquid separation of the solid content in the mixed water from the reaction vessel;
A desalting apparatus for removing salt in the mixed water after the solid-liquid separation;
A spray means for spraying the concentrated water salt-concentrated in the desalination treatment apparatus, and a spray drying apparatus for spray drying using a part of the boiler exhaust gas ,
The desalting apparatus is
An anti-scale agent supply unit for supplying an anti-scale agent to the mixed water containing divalent ions of Ca ions;
A first demineralizer installed on the downstream side of the scale inhibitor supply unit and separating the mixed water into reclaimed water and concentrated water enriched with the Ca ions;
A crystallization tank provided on the downstream side of the first demineralizer and crystallizing gypsum from the concentrated water;
A separation unit for separating the crystallized gypsum and the concentrated water from the first desalting apparatus;
A water treatment system , comprising: a second desalting apparatus that is installed on the downstream side of the separation unit and separates the concentrated water into reclaimed water and concentrated water in which the Ca ions are concentrated . In claim 1 or 2,
A water treatment system comprising a membrane treatment unit that treats the separated water separated by the solid-liquid separation unit with a membrane having monovalent selectivity. In any one of Claims 1 thru | or 3,
The water treatment system, wherein the desalting apparatus removes divalent salt in the discharged water. In claim 1 or 2 ,
The desalting apparatus further separates the concentrated water from the second desalting apparatus;
Wherein disposed on the downstream side of the separation unit, a water treatment system, characterized in that the concentrated water recycled water and the Ca ions having a third desalination device for separating into a concentrated water which has been concentrated. In claim 1 or 2 ,
A water treatment system comprising an oxidation-reduction potentiometer that measures an oxidation-reduction potential of mixed water introduced into the first desalting apparatus. In claim 6 ,
The value (X) of the oxidation-reduction potential in the mixed water measured by the oxidation-reduction potentiometer is:
-0.69V <X <1.358V, The water treatment system characterized by the above-mentioned. A wet desulfurization process for removing sulfur oxides in boiler exhaust gas;
A dehydration step of separating gypsum from the desulfurization effluent containing the gypsum slurry from the wet desulfurization step;
A mercury removal step of introducing separated water from the dehydration step and introducing a chelating agent to immobilize heavy metals in the separated water;
A solid-liquid separation step for solid-liquid separation of the solid content in the separated water from the mercury removal step;
A mixing step of mixing the separated water from the solid-liquid separation unit with the discharged water generated in the plant facility;
A desalting treatment step for removing salt in the mixed water mixed in the mixing step;
A spray drying step of spray drying the concentrated water salt-concentrated in the desalting treatment step using a part of the boiler exhaust gas ,
The desalting treatment step includes
An anti-scale agent supply step for supplying an anti-scale agent to the mixed water containing divalent ions of Ca ions;
A first desalting step that is installed downstream of the scale inhibitor supply step and separates the mixed water into reclaimed water and concentrated water enriched with the Ca ions;
A crystallization step, which is provided downstream of the first desalting step and crystallizes gypsum from the concentrated water;
A separation unit for separating the crystallized gypsum and the concentrated water from the first desalting step;
A water treatment method characterized by comprising a second desalting step that is installed on the downstream side of the separation unit and separates the concentrated water into reclaimed water and concentrated water enriched with the Ca ions . A wet desulfurization process for removing sulfur oxides in boiler exhaust gas;
A dehydration step of separating gypsum from the desulfurization effluent containing the gypsum slurry from the wet desulfurization step;
A mixing step of mixing the separated water from the dehydration step with the discharged water generated in the plant facility;
Introducing the mixed water mixed in the mixing step, adding a chelating agent and immobilizing heavy metals in the separated water; and
A solid-liquid separation step for solid-liquid separation of the solid content in the mixed water of the precipitation step;
A desalting process for removing salt in the mixed water after the solid-liquid separation;
A spray drying step of spray drying the concentrated water salt-concentrated in the desalting treatment step using a part of the boiler exhaust gas ,
The desalting treatment step includes
An anti-scale agent supply step for supplying an anti-scale agent to the mixed water containing divalent ions of Ca ions;
A first desalting step that is installed downstream of the scale inhibitor supply step and separates the mixed water into reclaimed water and concentrated water enriched with the Ca ions;
A crystallization step, which is provided downstream of the first desalting step and crystallizes gypsum from the concentrated water;
A separation unit for separating the crystallized gypsum and the concentrated water from the first desalting step;
A water treatment method characterized by comprising a second desalting step that is installed on the downstream side of the separation unit and separates the concentrated water into reclaimed water and concentrated water enriched with the Ca ions . In claim 8 or 9 ,
A water treatment method comprising a membrane treatment step of treating the separated water after separation in the solid-liquid separation step with a membrane having monovalent selectivity. In any one of Claims 8 thru | or 10 ,
The water treatment method, wherein the desalting treatment step removes divalent salt in the discharged water. In claim 8 or 9 ,
A separation step in which the desalting step further separates the concentrated water from the second desalting step;
Wherein disposed on the downstream side of the separation process, the water treatment method characterized in that the concentrated water the Ca ion and reclaimed water has a third desalting step of separating into a concentrated water which has been concentrated. In claim 8 or 9 ,
A water treatment method comprising a redox potential measuring step of measuring a redox potential of mixed water introduced into the first desalting step. In claim 13 ,
The value (X) of the oxidation-reduction potential in the mixed water measured in the oxidation-reduction potential measurement step is
-0.69V <X <1.358V, The water treatment method characterized by the above-mentioned.

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