JP2015029934A - Desalination apparatus and desalination method, and method for co-producing fresh water, salt and valuable-material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a desalination apparatus and desalination method capable of removing multi-valent ions contained in the desalinated water from an electrodialysis unit as well as removing boron, and improving the purity of the recovered valuable-material, and to provide a method for co-producing fresh water, salt and valuable-material.SOLUTION: The desalination apparatus comprises: a desalination unit 12 for obtaining a fresh water Wwhose salt content in the supplied feed seawater (raw water) W has been removed, and a salt-content enriched water Wwhose salt content in the feed seawater (raw water) W has been enriched; an electrodialysis unit 13 for obtaining an enriched saline water Wand a diluted saline water Wby electrodialyzing the salt content enriched water W; a reactive crystallization unit 23 for recovering the residual ions in the diluted saline water Was a valuable-material 61 to obtain a desalinated water W; a boron removal unit 51 for removing boron in the desalinated water W; and a recirculation line Lfor recirculating the boron removed liquid whose boron has been removed, to the feed seawater (raw water) W on the inlet side of the desalination unit 12 as a recirculation water W.

Description

  The present invention relates to a desalination apparatus and a desalination method for producing fresh water and salt in one facility using an electrodialysis section, and a method for co-production of fresh water, salt and valuables.

  Conventionally, a drinking water and salt production apparatus including a reverse osmosis membrane device and an electrodialysis unit has been proposed (see, for example, Patent Document 1). In such a production apparatus, raw water containing salt such as seawater is supplied to the reverse osmosis membrane device to produce desalted water by desalting, while the concentrated salt water concentrated by the reverse osmosis membrane device is supplied to the electrodialysis unit. Then, further concentrate to make concentrated brine. And the salt is manufactured by carrying out the evaporative crystallization of the obtained concentrated brine with an evaporator.

  In addition, it has been proposed to return the concentrated salt-enriched water to the raw water supply line to increase the production amount of the produced water (see, for example, Patent Document 2).

Japanese Patent No. 2887105 JP-A-9-290260

By the way, in the proposal of patent document 2 mentioned above, when returning salt concentration water to the raw | natural water side, after removing monovalent salt (Na salt) in an electrodialysis part, it is making it return to the raw | natural water side as it is. Therefore, the salt concentration of monovalent salt (Na) in the reverse osmosis membrane device is reduced, and the power reduction in the reverse osmosis membrane device is possible. However, since multivalent ions such as divalent ions accumulate in the desalted solution from the electrodialysis unit, scale deposition of calcium sulfate (CaSO ₄ ) or the like occurs on the membrane in the reverse osmosis membrane device. There's a problem.

By returning the demineralized water from the electrodialysis unit to the inlet side of the reverse osmosis membrane device, valuable materials (for example, chloride) recovered by various crystallization means such as evaporation crystallization, cooling crystallization, reaction crystallization, etc. There is a problem that the purity of sodium (NaCl), potassium chloride (KCl), magnesium hydroxide (Mg (OH) ₂ ), etc. is lowered by the precipitate derived from the circulating divalent ions.

  Further, since the demineralized water from which monovalent ions have been removed contains boron, there is a problem in that when this is circulated and reused, the boron concentration of the production water increases.

  The present invention has been made in view of such circumstances, and removes polyvalent ions contained in the demineralized water from the electrodialysis section and removes boron to improve the purity of valuable materials to be recovered. An object of the present invention is to provide a desalination apparatus and a desalination method, and a method for co-producing fresh water, salt and valuables.

  A first invention for solving the above-mentioned problems is a desalination unit for obtaining fresh water from which salt in raw water has been removed and salt-enriched water in which salt in the raw water is concentrated, and electrodialyzing the salt-enriched water to concentrate An electrodialysis unit for obtaining brine and diluted brine, a reaction crystallizing unit for recovering residual ions in the diluted brine as valuable materials, and a salt removal water, and a boron removal unit for removing boron in the salt removal water; A desalination apparatus comprising: a circulation line for circulating the boron removal liquid from which boron has been removed to the raw water on the inlet side of the desalination section as circulating water.

According to the present invention, boron contained in the salt-removed water from which the polyvalent ions remaining in the diluted brine are removed by the reaction crystallization part is removed by the boron removal part, so that the boron in the circulating water returned to the desalination part In the circulating water whose concentration is lowered and recirculated, there is no accumulation of multivalent ions, and scale deposition on the membrane of the desalination part is prevented.
Moreover, since boron is removed, accumulation of boron in fresh water and salt-enriched water is prevented. Further, the removed boron can be recovered as a valuable material.

  The second invention is characterized in that, in the first invention, when removing boron in the boron removing section under an alkaline condition, an acid supply section is provided for supplying an acid to the circulating water after the boron removal. Located in the desalination unit.

  According to the present invention, after removing boron under alkaline conditions, it can be adjusted to a pH suitable for desalination in the desalination unit.

  According to a third invention, in the first invention, an evaporation crystallization part for evaporating and crystallization of the concentrated brine, a solid-liquid separation part for solid-liquid separating the concentrated sodium chloride slurry from the evaporation and crystallization part, Fresh water comprising an electrochemical treatment unit that obtains an aqueous sodium hydroxide solution and hydrochloric acid using the solid-liquid separated sodium chloride, and a hydrochloric acid supply line that supplies the hydrochloric acid to the inlet side of the desalination unit In the device.

  According to the present invention, after removing boron under alkaline conditions, it can be adjusted with hydrochloric acid to a pH suitable for desalination in the desalination unit. At this time, since hydrochloric acid can be produced in the desalination apparatus, hydrochloric acid can be supplied on-site. As a result, it is not necessary to purchase medicines from the outside, and storage facilities are not required, so that the production efficiency of fresh water production can be improved.

  A fourth invention is the desalination apparatus according to the third invention, further comprising a sodium hydroxide aqueous solution supply line for supplying the sodium hydroxide aqueous solution to the reaction crystallization part.

According to the present invention, an aqueous sodium hydroxide solution can be supplied on-site as a chemical agent under alkaline conditions in the reaction crystallization part, and a magnesium salt can be recovered by crystallization reaction under alkaline conditions.
In addition, since the multivalent ions are separated in the reaction crystallization part, there is no accumulation of multivalent ions during the recirculation circulation, and scale deposition on the membrane of the desalination part is prevented from occurring. The
Moreover, when recovering a salt as a valuable material, a highly pure salt can be recovered. As a result, it is possible to improve the recovery efficiency of valuable materials.

  A fifth invention is the desalination apparatus according to the third or fourth invention, further comprising a hydrochloric acid supply line for supplying the hydrochloric acid to the reaction crystallization part.

  According to the present invention, hydrochloric acid can be supplied on-site as a chemical agent under acidic conditions in the reaction crystallization part, and by removing the carbonic acid component under acidic conditions, precipitation of calcium carbonate is suppressed, and hydroxylation is achieved. Magnesium can be recovered with high purity.

  The sixth invention uses the desalination apparatus according to any one of the first to fifth inventions to remove salt from raw water to obtain fresh water, and from the concentrated salt water after desalination, sodium chloride and valuable resources In the method of co-production of fresh water, salt and valuables.

  According to the present invention, fresh water from which boric acid has been removed is produced, and valuables such as hydrochloric acid and sodium hydroxide are recovered using a part of sodium chloride generated in the desalination apparatus. Since the desalination process is performed using hydrochloric acid and sodium hydroxide, there is no need to purchase chemicals from the outside, and no storage facilities are required. Production efficiency of production of fresh water, sodium chloride and valuable resources Can be improved.

  The seventh invention includes a desalination step for obtaining fresh water from which salt in raw water has been removed and salt-enriched water in which salt in raw water is concentrated, electrodialyzing the salt-enriched water, An electrodialysis step to obtain residual ions in the diluted brine, and a reaction crystallization step to obtain salt-removed water, a boron removal step to remove boron in the salt-removed water, and the boron removal And a circulation step of circulating the boron removal solution as circulating water to the raw water on the inlet side of the desalination step.

According to the present invention, since the boron contained in the salt-removed water from which the polyvalent ions remaining in the diluted brine have been removed in the reaction crystallization step is removed by the boron removing unit, the circulating water W ₂₁ returned to the desalination step. There is no accumulation of multivalent ions in the circulating water W ₂₁ which is reduced in the concentration of boron in the recycled water, and scale deposition on the membrane in the desalination process is prevented from occurring.
Moreover, since boron is removed, accumulation of boron in fresh water and salt-enriched water is prevented. Further, the removed boron can be recovered as a valuable material.

  8th invention has the acid supply process which supplies an acid to the circulating water after said boron removal, when performing boron removal in a boron removal process in 7th invention on alkaline conditions, The fresh water characterized by the above-mentioned. It is in the conversion method.

  According to the present invention, after removing boron under alkaline conditions, it can be adjusted to a pH suitable for desalination in the desalination step.

  According to a ninth invention, in the seventh invention, an evaporation crystallization step of evaporating and crystallization of the concentrated brine, a solid-liquid separation step of solid-liquid separating the concentrated sodium chloride slurry from the evaporation crystallization step, The method comprises an electrochemical treatment step for obtaining a sodium hydroxide aqueous solution and hydrochloric acid using the solid-liquid separated sodium chloride, and a hydrochloric acid supply step for supplying the hydrochloric acid to the inlet side of the desalination step. It is in the desalination method.

  According to the present invention, after removing boron under alkaline conditions, it can be adjusted with hydrochloric acid to a pH suitable for desalination in the desalination step. At this time, since hydrochloric acid can be produced in the desalination apparatus, hydrochloric acid can be supplied on-site. As a result, it is not necessary to purchase medicines from the outside, and storage facilities are not required, so that the production efficiency of fresh water production can be improved.

  A tenth invention is the desalination method according to the ninth invention, wherein the sodium hydroxide aqueous solution is supplied to the reaction crystallization step.

According to the present invention, an aqueous sodium hydroxide solution can be supplied on-site as a chemical agent under alkaline conditions in the reaction crystallization step, and the magnesium salt can be recovered by crystallization reaction under alkaline conditions.
In addition, since the multivalent ions are separated in the reaction crystallization process, there is no accumulation of multivalent ions in the recirculated circulation, and scale deposition on the membrane of the desalination process is prevented from occurring. The
Moreover, when recovering a salt as a valuable material, a highly pure salt can be recovered. As a result, it is possible to improve the recovery efficiency of valuable materials.

  An eleventh invention is the desalination method according to the ninth or tenth invention, wherein the hydrochloric acid is supplied to the reaction crystallization step.

  According to the present invention, hydrochloric acid can be supplied on-site as a chemical agent under acidic conditions in the reaction crystallization step, and by removing the carbonic acid component under acidic conditions, precipitation of calcium carbonate is suppressed, and hydroxylation is achieved. Magnesium can be recovered with high purity.

According to the present invention, boron contained in the salt-removed water from which polyvalent ions remaining in the diluted brine by electrodialysis are removed by the reaction crystallization part is removed by the boron removal part. There is no accumulation of multivalent ions in the recycled water that is reduced in the concentration of boron in the water and recycled, and scale deposition on the membrane of the desalination unit is prevented from occurring.
Moreover, since boron is removed, accumulation of boron in fresh water and salt-enriched water is prevented. Further, the removed boron can be recovered as a valuable material.

FIG. 1 is a schematic view of a desalination apparatus according to the first embodiment of the present invention. FIG. 2 is a schematic view of another desalination apparatus according to the first embodiment of the present invention. FIG. 3 is a schematic view of a desalination apparatus according to the second embodiment of the present invention. FIG. 4 is a schematic view of a desalination apparatus according to the third embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, this invention is not limited to each following embodiment, It can implement by changing suitably. Moreover, the structure of the desalination apparatus which concerns on each embodiment can be implemented combining suitably.

(First embodiment)
FIG. 1 is a schematic view of a seawater desalination apparatus according to the first embodiment of the present invention, and FIG. 2 is a schematic of another seawater desalination apparatus according to the first embodiment of the present invention. FIG.
As shown in FIG. 1, the seawater desalination apparatus 10 </ b> A includes fresh water W ₁₁ from which salt in the supplied seawater (raw water) W supplied by the seawater line L ₁₁ has been removed and salinity in the supplied seawater (raw water) W. In the desalination section 12 for obtaining the concentrated salt water W ₁₂ , the electrodialysis section 13 for electrodialyzing the salt water W ₁₂ and obtaining the concentrated brine W ₁₃ and the diluted brine W ₁₄ , and the diluted brine W ₁₄ and the recovered residual ions as valuables 61, the reactive crystallization analyzing unit 23, demineralized water W _20, the boron removal unit 51 for removing boron in demineralized water W _20, the boron removal liquid boron has been removed, A circulation line L ₂₁ circulated as circulating water W _{21 in} the supply seawater (raw water) W on the inlet side of the desalination unit 12 is provided.

According to the present invention, the boron 60 included in demineralized water W in ₂₀ was removed by reactive crystallization analyzing unit 23 multivalent ions remaining in the diluted brine W _14, since removing a boron removal unit 51, desalination The concentration of boron in the circulating water W ₂₁ returned to the section 12 is reduced, and there is no accumulation of multivalent ions in the circulating water W ₂₁ that is recycled, and scale deposition on the membrane of the desalination section 12 occurs. It is prevented.
Moreover, since boron is removed, accumulation of boron in fresh water and salt-enriched water is prevented. Further, the removed boron can be recovered as the valuable material 61.

Desalination unit 12, distilling the feed seawater W, together with obtaining a fresh W ₁₁ salinity in the feed seawater W is removed to obtain a salinity concentrate W ₁₂ salinity in the feed seawater W enriched. Although it does not specifically limit as the desalination part 12, The membrane separation method using a reverse osmosis membrane apparatus etc. can be applied besides the evaporation method.

Here, as the reverse osmosis membrane device, for example, a plurality of reverse osmosis membrane elements (reverse osmosis membrane modules) are provided in a container, and fresh water W ₁₁ obtained by processing with each reverse osmosis membrane element and salinity connect the retentate line for leading out (discharge) the concentrated water W ₁₂ from each container and (concentrated water discharge path) permeate tube (freshwater discharge path) is arranged.

  As a reverse osmosis membrane of a reverse osmosis membrane device, a general reverse osmosis (RO) membrane (hereinafter also referred to as “RO membrane”), an NF (Nanofiltration) membrane (hereinafter also referred to as “NF membrane”), etc. Can be used.

Further, in the present embodiment, the supply seawater W as raw water is treated with desalination unit 12 to obtain a fresh W ₁₁ and salinity concentrate W _12, water other than seawater so long as it contains a salt May be used as raw water. As the supply seawater W, for example, pumped seawater, seawater once used in the plant as a refrigerant, or the like can be used.

The electrodialysis unit 13 includes an electrodialysis membrane (ED: Elecrodialysis membrane) 13a. Electrodialysis unit 13, salinity salinity concentrate W ₁₂ electrodialysis to salinity concentrate W ₁₂ salinity concentrate enriched brine W of ₁₃ and salt concentration water W in ₁₂ was removed by electrodialysis membrane 13a Diluted brine W ₁₄ is obtained.
As an electrodialysis method, for example, a cation exchange membrane that transmits only cations and an anion exchange membrane that transmits only anions are alternately arranged, and voltage is applied from both ends of the cation exchange membrane and the anion exchange membrane. It is configured so that a direct current can be applied by applying it. In the electrodialysis unit 13, concentrated obtained by treating the salt concentration water W ₁₂ brine W ₁₃ and diluted brine W _14, respectively, they are discharged by the discharge line L _14, L _15.

Here, the supply line L ₁₃ supplies the salinity concentrate W ₁₂ from desalination unit 12 is partly branched into the electrodialysis unit 13 side, salinity concentrate W ₁₂ not branch, through the supply line L ₁₃ And discharged to the outside as drainage 17.

The reaction crystallization unit 23 crystallizes multivalent ions by a reaction crystallization method.
For example, when crystallizing calcium salt (Ca salt), it is recovered as a valuable material (calcium sulfate, calcium carbonate, etc.) 61 under alkaline conditions and acidic conditions.

  Here, calcium hydroxide is used for the crystallization reaction under alkaline conditions. For example, sulfuric acid or hydrochloric acid is used in the crystallization reaction under acidic conditions.

The reaction crystallization unit 23 first removes the Ca salt by reaction crystallization, and then recovers it as a valuable material (Mg salt) 61 under alkaline conditions.
Here, using sulfuric acid and hydrochloric acid to supply before recovery of magnesium hydroxide, the pH of the diluted brine W ₁₄ is lowered and the carbonic acid component in the water is volatilized / reduced by the following reaction formulas (1) and (2). By removing it, precipitation of calcium carbonate is suppressed. Thereby, magnesium oxide can be recovered with high purity.
Ca (HCO ₃ ) ₂ + 2HCl → CaCl ₂ + 2H ₂ O + 2CO ₂ ↑ (1)
Ca (HCO ₃ ) ₂ + H ₂ SO ₄ → CaSO ₄ + 2H ₂ O + 2CO ₂ ↑ (2)

The boron removing unit 51 removes the polyvalent ions in the reaction crystallization unit 23 and removes boron 60 from the desalted water W ₂₀ supplied through the circulation line L ₂₁ . Boron can be removed using an ion exchange resin, a boron adsorption resin, or the like.

  Here, as the ion exchange resin, for example, as a boron adsorption resin, “Diaion (registered trademark) CRB (trade name)” manufactured by Mitsubishi Chemical Corporation, “Amberlite IRA 743 (trade name)” manufactured by Rohm and Haam, Dow Developland GmbH & Co. “Dow XUS43594 (trade name)” manufactured by OHG can be used. An ion exchange resin capable of selectively exchanging ions with boron (such as borate ions) and recovering boron may be used.

  Further, when boron is collected and removed by an adsorption method, for example, a boron removing unit having an adsorbent capable of adsorbing and recovering boron such as a cerium-based adsorbent and a chelate-based adsorbent may be used.

  Further, except that boron is collected by adsorption and / or ion exchange, it may be removed, for example, by electrodialysis.

Boron is dissociated in an ionic state as boric acid as shown in the following formula (3). Since the desalted water W ₂₀ is on the alkali side (pH 9 to 11) due to the reaction crystallization to remove the Mg salt, the proportion of ionic boric acid concentration is higher than before the reaction crystallization, and the pH on the alkali side is higher. A higher value is advantageous for ion exchange.
B (OH) ₃ + H ₂ O⇔B (OH) ₄ ⁻ + H ⁺ (3)

The circulation line L ₂₁ circulates the boron-removed water from which boron has been removed to the supplied seawater (raw water) W on the inlet side of the desalination unit 12 as the circulating water W ₂₁ .

According to the present embodiment, boron (B) contained in the demineralized water W ₂₀ obtained by removing the polyvalent ions remaining in the diluted brine W ₁₄ by the reaction crystallization unit 23 is removed by the boron removing unit 51. As a result, the boron concentration in the circulating water W ₂₁ returned to the desalination unit 12 is reduced, and there is no accumulation of multivalent ions in the circulating water W ₂₁ that is recycled. Scale precipitation is prevented from occurring and boron is removed, so that accumulation of boron in fresh water and salt-enriched water is prevented. Further, the removed boron can be recovered as a valuable material.

Installation position of boron removal unit 51 may be either before or after the branch portion 53 branches the demineralized water W ₂₀ of the circulation line L ₂₁ in branch line L _21A (see FIG. 2).

  Here, when it is desired to recover a large amount of boron as a valuable material, a boron removing unit 51 is disposed between the reaction crystallization unit 23 and the branching unit 53 on the upstream side as shown in FIG. Is done.

On the other hand, in the desalination apparatus 10B shown in FIG. 2, the boron removal part 51 is arrange | positioned in the downstream of the branch part 53. FIG. With this arrangement, it is only necessary to remove boron in the circulating water W ₂₁ circulated in the circulation line L ₂₁ , so that the capacity of the boron removing unit 51 can be minimized.

By recycling and reusing the circulating water W ₂₁ that the boron is removed, it is possible to reduce the supply amount of the supply seawater W, for example, when installing the pretreatment device to the upstream side of the desalination unit 12, The size of the pretreatment device can be reduced.
Further, in the circulating water W ₂₁ , monovalent ions are removed by the electrodialysis unit 13, and the salt concentration of polyvalent ions is reduced by the reaction crystallization unit 23, so that the total salt concentration is reduced, For example, when a reverse osmosis membrane device is used as the desalination unit 12, it is possible to reduce power when the raw water is at a high pressure.
Here, hydrochloric acid and sodium hydroxide obtained from sodium chloride obtained in the desalination apparatus can be used for regeneration of the boron adsorption resin.

Next, the overall operation of the desalination apparatus 10A according to the present embodiment will be described.
Supplying sea water W supplied to the desalination unit 12 will and salinity concentrated water W ₁₂ salinity of fresh water W ₁₁ and in the feed seawater W which salt has been removed in the feed seawater W by desalination process is concentrated. The fresh water W ₁₁ is discharged through the supply line L ₁₂ and used as the production water 14. A part of the salt-concentrated water W ₁₂ is supplied to the electrodialysis unit 13 through the supply line L ₁₃ and a part thereof is discharged as the waste water 17.

The salt concentration water W ₁₂ supplied to the electrodialysis unit 13 is diluted by further concentrating the salt content in the salt concentration water W ₁₂ by the electrodialysis membrane 13a and removing the salt content in the concentrated brine W ₁₃ and the salt concentration water W _12. Brine W ₁₄ Here, the concentrated brine W ₁₃ is rich in monovalent salts (Na (sodium) salt, K (potassium) salt, etc.) contained in the salt-enriched water W ₁₂ . The diluted brine W ₁₄ is rich in polyvalent salts (Mg (magnesium) salt, Ca (calcium) salt, etc.) contained in the salt-enriched water W ₁₂ .

The diluted brine W ₁₄ from the electrodialysis unit 13 is sent to the reaction crystallization unit 23, and multivalent ions are crystallized by the reaction crystallization method.
By this reaction crystallization, for example, calcium salt (Ca salt) and magnesium salt, which are multivalent ions, are recovered as valuables 61.

The demineralized water W ₂₀ from which polyvalent ions have been removed in the reaction crystallization unit 23 is sent to the boron removing unit 51 where boron is removed by, for example, an ion exchange membrane method, a boron adsorption resin method, or the like.

The acid supply unit 52 uses the pH of the circulating water W ₂₁ as the desalination condition of the desalination unit 12, and the pH is adjusted by an acid 52 a such as sulfuric acid or hydrochloric acid. Thereby, when boron is removed under alkaline conditions, it can be adjusted to a pH suitable for desalination in the desalination unit 12.

Boron-removed water from which boron has been removed is circulated as circulating water W _{21 in} the supply seawater (raw water) W on the inlet side of the desalination unit 12.

Here, in the desalination apparatus 10A according to the present embodiment, as in the prior art, the diluted brine W ₁₄ from the electrodialysis unit 13 is not directly circulated to the supply seawater side through the circulation line, but once the reaction crystallization unit. multivalent ions recovered as valuable product 61, after further removal of boron demineralized water W ₂₀ boron removal unit 51 at 23, so that recycled as circulating water W _21. As a result, the salinity concentration of polyvalent ions in the circulating water W ₂₁ returned to the desalination unit 12 as circulating water is reduced, so that power in the desalination unit 12 can be reduced and boron is removed. So boron accumulation is prevented.

In addition, since the polyvalent ions are separated by the reaction crystallization unit 23, there is no accumulation of polyvalent ions in the recycled water W ₂₁ , and for example, a reverse osmosis membrane device is used as the desalination unit 12. In some cases, scale deposition on the reverse osmosis membrane is prevented.
Moreover, since there is no accumulation of multivalent ions and boron as circulating water, when recovering a salt as a valuable material, a highly pure salt can be recovered. As a result, it is possible to improve the recovery efficiency of valuable materials.

Further, in the desalination method of the present embodiment, a desalination step of obtaining fresh water W ₁₁ from which salt in raw water (supply seawater) W has been removed and salt-enriched water W ₁₂ from which salt in raw water has been concentrated, to electrodialysis said salinity concentrated water W _12, and electrodialysis to obtain a the concentrated brine W ₁₃ and diluted brine W _14, to recover the residual ions in the dilute brine W ₁₄ as valuables 61, and demineralized water W ₂₀ A reaction crystallization step, a boron removal step for removing boron in the desalted water W ₂₀ , and a boron removal solution from which boron has been removed are circulated as the circulating water W _{21 in} the raw water on the inlet side of the desalination unit 12. And a circulation step.

Therefore, according to the desalination apparatus and method of the present embodiment, boron (B) contained in demineralized water W in ₂₀ was removed by reactive crystallization analyzing unit 23 multivalent ions remaining in the diluted brine W _14, since removing boron removal unit 51, to reduce the boron concentration in the circulating water W ₂₁ back to the desalination unit 12, the circulation water W ₂₁ to be recirculated, no accumulation of multivalent ions, desalination The occurrence of scale deposition on the film of the portion 12 is prevented. Moreover, since boron is removed, accumulation of boron in fresh water and salt-enriched water is prevented. Further, the removed boron can be recovered as a valuable material.

(Second Embodiment)
Next, a desalination apparatus according to the second embodiment of the present invention will be described. Below, it demonstrates centering around difference with the desalination apparatus which concerns on the said 1st Embodiment. In addition, about the component same as the desalination apparatus which concerns on the said 1st Embodiment, the same code | symbol is attached | subjected and duplication of description is avoided.

FIG. 3 is a schematic view of a desalination apparatus according to the second embodiment of the present invention.
As shown in FIG. 3, desalination apparatus 10C according to this embodiment, the desalination apparatus 10A of the first embodiment, an evaporation crystallization analyzing unit 21 for further evaporation crystallization concentrated brine W _13, evaporation crystallization A solid-liquid separation unit 22 for solid-liquid separation of the concentrated sodium chloride slurry from the analyzing unit 21; and an electrochemical processing unit 30 for obtaining hydrochloric acid 32 and a sodium hydroxide aqueous solution 33 using the solid-liquid separated sodium chloride; And a hydrochloric acid supply line L25 for supplying the obtained hydrochloric acid 32 to the inlet side of the desalination unit. In the present embodiment, the pretreatment device 11 is installed, and the reverse osmosis membrane device 12 </ b> A is used as the desalination unit 12.

In the present embodiment, a pretreatment device 11 that removes impurities and the like in the supplied seawater W is provided. The pre-processing unit 11, a suspension of such particles or colloids in sea water, and treated water W ₁₀ before microorganisms were removed, such as algae and shellfish, decrease water permeability of the reverse osmosis membrane 12a of the reverse osmosis unit 12A This is to suppress the phenomenon (fouling phenomenon). And this pre-processing apparatus 11 is a sand filter formed by adding chemical | medical agents, such as an inorganic type and an organic type coagulant | flocculant, a disinfectant, etc. in the supply seawater W, for example, and filling the container with sand as a filter medium. Pass water to remove suspended matter and microorganisms in seawater. In addition, a backwash pump or the like for backwashing the sand filter to recover the filtration performance is provided. A biofilm may be formed on the surface of a carrier such as sand in the filter, and the pretreatment of seawater may be performed using both the filtration performance and the degradation performance of the BOD component by the biofilm. Note that, for example, when pretreated seawater is desalinated with respect to seawater used as cooling water for a plant, this pretreatment device may be omitted.

The evaporative crystallization unit 21 evaporates and crystallizes the concentrated brine W ₁₃ supplied from the electrodialysis unit 13 to obtain a salt (sodium chloride (NaCl)) and also obtains evaporated water W ₁₅ . Further, the evaporated water W ₁₅ from the evaporative crystallization unit 21 merges with the fresh water W ₁₁ via the supply line L ₁₆ and the supply line L ₁₂ and is discharged as the production water 14.

Here, the evaporative crystallization unit 21 can be exemplified by, for example, a multi-effect evaporator, a thin film evaporator or a drum dryer, and the discharge for discharging the precipitate sodium chloride slurry S ₁ obtained by the evaporation process. A line L ₁₇ is connected to the solid-liquid separator 22.

The solid-liquid separation unit 22 performs solid-liquid separation on the concentrated sodium chloride slurry S ₁ from the evaporative crystallization unit 21, and obtains sodium chloride (solid) 34 as a valuable material.
Further, the sodium chloride removal slurry S ₂ from which sodium chloride has been separated is discharged through the discharge line L ₁₈ .
Further, the separated sodium chloride is discharged through the discharge line L ₂₁ , and a part thereof is introduced into the dissolving part 29. The remaining sodium chloride (solid) 34 is discharged through the discharge line L ₂₂ as a valuable resource.

The dissolution unit 29 uses a part of the separated sodium chloride to dissolve with fresh water W ₁₁ to obtain a sodium chloride aqueous solution. For this dissolution, the fresh water W ₁₁ obtained by the desalination treatment and the evaporated water W ₁₅ are supplied from one or both of the supply lines L ₃₁ and L ₃₂ . Dissolved sodium chloride aqueous solution is supplied to the electrochemical processing unit 30 via a supply line L _23.

  The electrochemical treatment unit 30 obtains a hydrochloric acid 32 and a sodium hydroxide (NaOH) aqueous solution 33 by electrochemical treatment such as electrolysis or electrodialysis using the supplied sodium chloride aqueous solution.

In the present embodiment, the hydrochloric acid supply line L ₂₅ for supplying hydrochloric acid (HCl) 32 is connected to the seawater line L ₁₁ so as to be supplied to the inlet side of the reverse osmosis membrane device 12A.
A pH meter 54 for measuring pH is installed on the inlet side of the reverse osmosis membrane device 12A to adjust the pH with hydrochloric acid.

In this embodiment, a hydrochloric acid supply line L ₂₅ for supplying hydrochloric acid 32 and a sodium hydroxide aqueous solution supply line L ₂₆ for supplying sodium hydroxide aqueous solution 33 are connected to a supply line L ₁₂ for discharging fresh water W _11. Has been.

Further, a hydrochloric acid supply line L ₂₅ for supplying hydrochloric acid 32 to supply hydrochloric acid 32 and aqueous sodium hydroxide solution 33 for cleaning the reverse osmosis membrane device 12 and the boron removing unit 51 when the desalination apparatus is shut down. The sodium hydroxide aqueous solution supply line L ₂₆ for supplying the sodium hydroxide aqueous solution 33 may be connected to a predetermined cleaning line.

  Next, the overall operation of the desalination apparatus 10C according to the present embodiment will be described.

By obtaining the evaporated water W ₁₅ from the concentrated brine W ₁₃ enriched with monovalent ions from the electrodialysis unit 13 by the evaporation crystallization unit 21, the production amount of the produced water 14 can be further increased. Further, as a result of evaporation, the concentrated sodium chloride slurry S ₁ is solid-liquid separated by the solid-liquid separator 22 to obtain valuable sodium chloride (NaCl) 34.

The concentration of the obtained hydrochloric acid 32 is appropriately adjusted by the fresh water W ₁₁ supplied through the fresh water supply line L ₃₃ .

In this embodiment, the pH adjustment of the circulating water W ₂₁ after removing boron, for a suitable pH adjustment of the filtration of the reverse osmosis unit 12A, can be performed on-site by the hydrochloric acid 32. Conventionally, acid (sulfuric acid, hydrochloric acid) was separately purchased for pH adjustment, and the purchased chemical was stored in the desalination plant. However, hydrochloric acid 32 can be supplied on-site. In addition, it is not necessary to purchase chemicals from the outside, and storage facilities and the like are also unnecessary, so that the production efficiency of fresh water production can be improved.

The hydrochloride 32 with sodium hydroxide aqueous solution 33, since an inverse osmosis membrane sodium and apparatus 12A hydrochloric supply line L ₂₅ is fed into the fresh water W ₁₁ on the outlet side of the hydroxide supply line L _26, resulting freshwater W The pH of ₁₁ can be adjusted to any pH value by either one or both of hydrochloric acid 32 and sodium hydroxide aqueous solution 33.

In particular, this adjustment can be easily performed when the pH of the obtained fresh water W ₁₁ is not a desired pH due to the desalination conditions.

Further, it is possible to use either one or both of the resulting hydrochloride 32 or sodium hydroxide solution 33 to adjust the pH of the fresh water W _11, adjusted to pH suitable for example beverages.

Further, in this embodiment, it may be provided with a thermometer to measure the temperature of the pretreated water W ₁₀ in seawater supply line L ₁₁ of the inlet side of the reverse osmosis unit 12A (not shown).
In particular, when the temperature of the supplied seawater W is high, it is preferable to adjust the pH by using hydrochloric acid 32.

(Third embodiment)
Next, a desalination apparatus according to the third embodiment of the present invention will be described. Below, it demonstrates centering around difference with the desalination apparatus which concerns on the said 1st Embodiment. In addition, about the component same as the desalination apparatus which concerns on the said 1st Embodiment, the same code | symbol is attached | subjected and duplication of description is avoided.

FIG. 4 is a schematic view of another desalination apparatus according to the third embodiment.
As shown in FIG. 4, the desalination apparatus 10D according to the present embodiment passes the obtained hydrochloric acid 32 and sodium hydroxide aqueous solution 33 through the hydrochloric acid supply line L ₂₅ and the sodium hydroxide aqueous solution supply line L ₂₆ . It supplies to the reaction crystallization part 23.

  Thereby, the obtained hydrochloric acid 32 is supplied to the reaction crystallization part 23, and by removing the carbonate component under acidic conditions, precipitation of calcium carbonate can be suppressed and magnesium hydroxide can be recovered with high purity. .

  Moreover, the sodium hydroxide aqueous solution 33 obtained by the electrochemical process part 30 can be supplied to the reaction crystallization part 23, and the reaction crystallization of Mg salt on alkaline conditions can be performed.

Thereby, at the time of crystallization in the reaction crystallization unit 23, first, hydrochloric acid 32 is supplied to perform decarboxylation, and then sodium hydroxide can be added to perform reaction crystallization on the alkali side. Mg salt (Mg (OH) ₂ ) can be reacted and crystallized as the valuable material 61.

  As a result, it is possible to solve the problem of separately purchasing an acid or an alkali agent and storing it in the desalination system as in the prior art. As a result, hydrochloric acid 32 and sodium hydroxide aqueous solution 33 can be supplied on-site, and it is not necessary to purchase chemicals from the outside, and storage facilities are not required, thereby improving the production efficiency of fresh water production. Can do.

As described above, according to the desalination apparatus 10D according to the present embodiment, along with the manufacture of fresh water, valuable materials can be manufactured with high purity. Sodium oxide is produced, and high-purity magnesium hydroxide (Mg (OH) ₂ ) can be obtained by reaction crystallization in the alkaline state as the reaction crystallization part 23 using the produced sodium hydroxide. .

Furthermore, in this embodiment, valuable substances (K salt etc.) 62 can be obtained from the sodium chloride removal slurry S ₂ from which sodium chloride has been removed by crystallization in the cooling crystallization unit 24.
Incidentally, the supernatant water W ₁₇ above containing valuable materials in the evaporation crystallization analyzing unit 21 (K salt or the like) via the discharge line L _19, is introduced into the cooling crystallization analyzing unit 24, and is crystallized here.

Therefore, according to the desalination apparatus and method of the present embodiment, fresh water from which boron has been removed is produced, and polyvalent ions contained in the diluted brine W ₁₄ from the electrodialysis unit 13 are valuable by reactive crystallization. (Mg salt, Ca salt, etc.) 61 can be recovered by the reaction crystallization part 23. Further, the valuable material (K salt or the like) 62 contained in the sodium chloride removal slurry S _{2 from} which sodium chloride has been removed can be recovered by the cooling crystallization unit 24. In this embodiment, the crystallization method is used for recovering valuable materials, but the present invention is not limited to this, and valuable materials may be recovered by an adsorption method.

Moreover, the valuable substance was collected, if circulated as circulating water W ₂₁ boron removal water removal boron boron removal unit 51, since the multivalent ions have been removed, to obtain a boron has been removed freshwater Can do. Further, boron can be recovered as a valuable material. Further, the circulating water W _21, since multivalent ions have been removed, it is possible to achieve a significant reduction of the power of the high-pressure pump for supplying the reverse osmosis unit 12A. In addition, since the multivalent ions are separated by the reaction crystallization unit 23, there is no accumulation of multivalent ions (for example, Ca ²⁺ ) in the recirculated water W ₂₁ , and the reverse osmosis membrane device 12 Precipitation of scale (for example, CaSO ₄ etc.) on the reverse osmosis membrane 12a is prevented. Moreover, the purity of the valuables to collect can be improved. Thereby, the efficient co-production method of fresh water, salt, and valuables is realizable.

10A to 10D Desalination device 11 Pretreatment device 12 Desalination unit 12A Reverse osmosis membrane device 12a Reverse osmosis membrane 13 Electrodialysis unit 13a Electrodialysis membrane 14 Production water 21 Evaporation crystallization unit 22 Solid-liquid separation unit 23 Reaction crystallization unit 24 Cooling crystallization part 30 Electrochemical treatment part 31 Hydrochloric acid production part 32 Hydrochloric acid 33 Sodium hydroxide aqueous solution 51 Boron removal part 52 Acid supply part 52a Acid W supply seawater W ₁₀ Pretreatment water W ₁₁ Fresh water W ₁₂ Salt concentration water W ₁₃ Concentrated brine W ₁₄ diluted brine L ₁₁ seawater line L ₂₁ circulation line L ₂₅ hydrochloric acid supply line L ₂₆ sodium hydroxide aqueous solution supply line

Claims (11)

A desalination unit for obtaining fresh water from which salt in raw water has been removed and salt-enriched water in which salt in raw water is concentrated;
Electrodialyzing the salt-enriched water to obtain concentrated brine and diluted brine,
Recovering residual ions in the diluted brine as valuable materials, and a reaction crystallization part to be used as salt-removed water;
A boron removal section for removing boron in the salt removal water;
A desalination apparatus, comprising: a circulation line that circulates the boron removing liquid from which boron has been removed as raw water on the inlet side of the desalination unit. In claim 1,
A desalination apparatus comprising an acid supply unit that supplies an acid to circulating water after boron removal when performing boron removal in the boron removal unit under alkaline conditions. In claim 1,
An evaporation crystallization part for evaporating and crystallization of the concentrated brine;
A solid-liquid separation unit for solid-liquid separation of the concentrated sodium chloride slurry from the evaporative crystallization unit;
Using the sodium chloride separated into the solid and liquid, an electrochemical treatment unit for obtaining a sodium hydroxide aqueous solution and hydrochloric acid,
A desalination apparatus comprising: a hydrochloric acid supply line for supplying the hydrochloric acid to an inlet side of the desalination unit. In claim 3,
A desalination apparatus comprising a sodium hydroxide aqueous solution supply line for supplying the sodium hydroxide aqueous solution to the reaction crystallization part. In claim 3 or 4,
A desalination apparatus comprising a hydrochloric acid supply line for supplying the hydrochloric acid to the reaction crystallization unit.   Using the desalination apparatus according to any one of claims 1 to 5, the salt content in the raw water is removed to obtain fresh water, and sodium chloride and valuable materials are obtained from the salt concentration concentrated water after the desalination treatment. Co-production method of fresh water, salt and valuables. A desalination step of obtaining fresh water from which salt in the raw water has been removed and salinity concentrated water in which the salt in the raw water is concentrated;
Electrodialyzing the salt-concentrated water to obtain concentrated brine and diluted brine,
A reaction crystallization step of recovering residual ions in the diluted brine as valuables and using salt-removed water;
A boron removal step of removing boron in the salt removal water;
And a circulation step of circulating the boron removal liquid from which the boron has been removed to the raw water on the inlet side of the desalination step as circulating water. In claim 7,
In the boron removal in the boron removal step, a desalination method characterized by having an acid supply step of supplying an acid to the circulating water after the boron removal when performing under alkaline conditions. In claim 7,
An evaporation crystallization step of evaporating and crystallization of the concentrated brine;
A solid-liquid separation step for solid-liquid separation of the concentrated sodium chloride slurry from the evaporative crystallization step;
An electrochemical treatment step of obtaining an aqueous sodium hydroxide solution and hydrochloric acid using the solid-liquid separated sodium chloride;
And a hydrochloric acid supply step of supplying the hydrochloric acid to the inlet side of the desalination step. In claim 9,
A desalination method, wherein the aqueous sodium hydroxide solution is supplied to the reaction crystallization step. In claim 9 or 10,
A desalination method, wherein the hydrochloric acid is supplied to the reaction crystallization step.

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