Water treatment process and water treatment system

• US 9,950,936 B2
• Filed: 03/30/2015
• Issued: 04/24/2018
• Est. Priority Date: 07/05/2013
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Heavy Industries Engineering, Ltd. (Mitsubishi Heavy Industries, Ltd.)
• Original Assignee: Mitsubishi Heavy Industries, Ltd.
• Inventors: Eda, Masayuki, Okino, Susumu, Yoshiyama, Ryuji, Sakurai, Hideaki, Ukai, Nobuyuki, Suzuki, Hideo, Nakashoji, Hiroshi, Yoshioka, Shigeru
• Primary Examiner(s): Perrin, Clare M
• Application Number:
  US14/672,807
• Publication Number:
  US 20150203380A1
• Time in Patent Office: 1,121 Days
• Field of Search: None
• CPC Class Codes: B01D 19/0005 with one or more auxiliary substances
• CPC Class Codes: B01D 2311/04 Specific process operations in the feed stream; Feed pretreatment
• CPC Class Codes: B01D 2311/12 Addition of chemical agents
• CPC Class Codes: B01D 2311/18 pH control
• CPC Class Codes: B01D 2311/2642 Aggregation, sedimentation, flocculation, precipitation or coagulation
• CPC Class Codes: B01D 2311/2649 Filtration
• CPC Class Codes: B01D 2311/2657 Deaeration
• CPC Class Codes: B01D 61/025 Reverse osmosis; Hyperfiltration
• CPC Class Codes: B01D 61/04 Feed pretreatment
• CPC Class Codes: B01D 61/42 Electrodialysis; Electro-osmosis ; Electro-ultrafiltration; Membrane capacitive deionization
• CPC Class Codes: B01D 65/08 Prevention of membrane fouling or of concentration polarisation
• CPC Class Codes: B01D 9/0036 Crystallisation on to a bed of product crystals; Seeding
• CPC Class Codes: C02F 1/04 by distillation or evaporation
• CPC Class Codes: C02F 1/20 by degassing, i.e. liberation of dissolved gases degasification of liquids in general B01D19/00; arrangement of degassing apparatus in boiler feed supply F22D
• CPC Class Codes: C02F 1/42 by ion-exchange ion-exchange in general B01J
• CPC Class Codes: C02F 1/441 by reverse osmosis
• CPC Class Codes: C02F 1/442 by nanofiltration
• CPC Class Codes: C02F 1/4691 Capacitive deionisation
• CPC Class Codes: C02F 1/4693 electrodialysis
• CPC Class Codes: C02F 1/52 by flocculation or precipitation of suspended impurities C02F1/463 takes precedence
• CPC Class Codes: C02F 1/5281 : Installations for water purification using chemical agents
• CPC Class Codes: C02F 1/66 : by neutralisation; pH adjustment for degassing C02F1/20; using ion-exchange C02F1/42; for flocculation or precipitation of suspended impurities C02F1/52; for removing dissolved compounds C02F1/58
• CPC Class Codes: C02F 2001/007 : Processes including a sedimentation step
• CPC Class Codes: C02F 2001/5218 : Crystallization
• CPC Class Codes: C02F 2101/10 : Inorganic compounds
• CPC Class Codes: C02F 2101/101 : Sulfur compounds
• CPC Class Codes: C02F 2103/023 : Water in cooling circuits
• CPC Class Codes: C02F 2209/06 : pH
• CPC Class Codes: C02F 5/10 : using organic substances
• CPC Class Codes: C02F 9/00 : Multistage treatment of water, waste water or sewage
• CPC Class Codes: Y02A 20/124 : Water desalination
• CPC Class Codes: Y02A 20/131 : Reverse-osmosis

Abstract

In a water treatment system (1) and a water treatment process, a scale inhibitor is supplied to water to be treated containing Ca ions, SO₄ ions, carbonate ions, and silica, and the water to be treated is adjusted to a pH at which silica is soluble. The pH-adjusted water to be treated containing the calcium scale inhibitor is separated in a demineralizing section (10) into concentrated water and treated water. In a crystallizing section (20), seed crystals of gypsum are supplied to the concentrated water, whereby gypsum is crystallized and removed. Silica in the water to be treated is removed from the concentrated water on the downstream side of the crystallizing section (20). Calcium carbonate in the water to be treated is removed from the concentrated water on the upstream side of the demineralizing section (10) or the downstream side of the crystallizing section (20).

Claims

1. A water treatment process comprising:

a scale inhibitor supplying step of supplying a calcium scale inhibitor which is a scale inhibitor for inhibiting the deposition of a scale containing calcium to water containing Ca²⁺ ions, SO₄²⁻

ions, carbonate ions and silica;

a pH adjusting step of adjusting the water to a pH of 10 or more at which the silica is soluble in the water;

a demineralizing step of separating the water into concentrated water in which the Ca²⁺ ions, the SO₄²⁻

ions, the carbonate ions and the silica are concentrated and treated water after the scale inhibitor supplying step and the pH adjusting step; and

a crystallizing step of supplying seed crystals of gypsum to the concentrated water so that gypsum is crystallized from the concentrated water; and

an upstream side precipitating step of precipitating at least calcium carbonate from the water so that the concentration of the calcium carbonate in the water is reduced, before the scale inhibitor supplying step and the pH adjusting step.

2. The water treatment process according to claim 1, comprising, after the crystallizing step, a downstream side demineralizing step of performing separation into concentrated water and treated water, and recovering the separated treated water.

3. The water treatment process according to claim 2, wherein moisture is evaporated from the concentrated water in the downstream side demineralizing step, so that a solid in the concentrated water is recovered.

4. The water treatment process according to claim 1, comprising a deaerating step of removing CO₂ from the water before the upstream side precipitating step or after the upstream side precipitating step and before the scale inhibitor supplying step and the pH adjusting step.

5. The water treatment process according to claim 1,

wherein the water contains metal ions;

and

wherein the process comprises a precipitating step of precipitating at least one of calcium carbonate and a metal compound so that the concentration of at least one of the calcium carbonate and the metal ions is reduced from the concentrated water, after the crystallizing step.

6. The water treatment process according to claim 5, wherein at least one of seed crystals of the silica and a precipitant for the silica is supplied to the concentrated water in the precipitating step.

7. The water treatment process according to claim 6, wherein, when the water contains Mg²⁺ ions, the amount of the precipitant for the silica to be supplied is adjusted according to the concentration of the Mg²⁺ ions.

8. The water treatment process according to claim 5,

wherein, when the water contains Mg²⁺ ions, the concentrated water in the precipitating step is adjusted to a pH of 10 or more at which a magnesium compound is deposited so that the concentration of the Mg²⁺ ions is reduced, and

wherein, after the precipitating step, the concentrated water is adjusted to a pH of less than 10 at which the magnesium compound is soluble.

9. The water treatment process according to claim 1,

wherein, when the water contains Mg²⁺ ions, the water in the upstream side precipitating step is adjusted to a pH of 10 or more at which a magnesium compound is deposited so that the concentration of the Mg²⁺ ions is reduced, and

wherein, after the upstream side precipitating step, the water is adjusted to a pH of less than 10 at which the magnesium compound is soluble.

10. A water treatment system comprising:

a scale inhibitor supplying section that supplies a calcium scale inhibitor which is a scale inhibitor for inhibiting the deposition of a scale containing calcium to water containing Ca²⁺ ions, SO₄²⁻

ions, carbonate ions and silica;

a pH adjusting section that supplies a pH adjuster to the water to adjust the pH of the water to 10 or more such that the silica is soluble in the water;

a demineralizing section that is positioned on a downstream side of the scale inhibitor supplying section and the pH adjusting section and separates the water into concentrated water in which the Ca²⁺ ions, the SO₄²⁻

ions, the carbonate ions and the silica are concentrated and treated water;

a crystallizing section including a crystallizing tank that is positioned on a downstream side of the demineralizing section and crystallizes gypsum from the concentrated water and a seed crystal supplying section that supplies seed crystals of gypsum to the crystallizing tank; and

an upstream side precipitating section, on an upstream side of the scale inhibitor supplying section and the pH adjusting section, that precipitates at least calcium carbonate from the water so that the concentration of the calcium carbonate in the water is reduced.

11. The water treatment system according to claim 10, comprising, on a downstream side of the crystallizing section, a downstream side demineralizing section that separates the concentrated water discharged from the crystallizing section into concentrated water and treated water.

12. The water treatment system according to claim 11, comprising, on a downstream side of the concentrated water in the downstream side demineralizing section, an evaporator that evaporates moisture from the concentrated water to recover the solids in the concentrated water.

13. The water treatment system according to claim 10, comprising a deaerating section that removes CO₂ from the water on an upstream side of the upstream side precipitating section or on a downstream side of the upstream side precipitating section and on an upstream side of the scale inhibitor supplying section and the pH adjusting section.

14. The water treatment system according to claim 10,

wherein the water contains metal ions;

and

wherein the system comprises, on a downstream side of the crystallizing section, a precipitating section that precipitates at least one of calcium carbonate and a metal compound so that the concentration of at least one of the calcium carbonate and the metal ions in the concentrated water is reduced.

15. The water treatment system according to claim 14, wherein at least one of seed crystals of the silica and a precipitant for the silica is supplied to the precipitating section.

16. The water treatment system according to claim 15, wherein, when the water contains Mg²⁺ ions, the amount of the precipitant for the silica to be supplied is adjusted according to the concentration of the Mg²⁺ ions in the precipitating section.

17. The water treatment system according to claim 14, wherein, when the water contains Mg²⁺ ions, the concentrated water in the precipitating section is adjusted to a pH of 10 or more at which a magnesium compound is deposited so that the concentration of the Mg²⁺ ions is reduced, and

wherein, on a downstream side of the precipitating section, the concentrated water is adjusted to a pH of less than 10 at which the magnesium compound is soluble.

18. The water treatment system according to claim 10,

wherein, when the water contains Mg²⁺ ions, the water to be treated in the upstream side precipitating section is adjusted to a pH of 10 or more at which a magnesium compound is deposited so that the concentration of the Mg²⁺ ions is reduced, and

wherein, on a downstream side of the upstream side precipitating section, the water is adjusted to a pH of less than 10 at which the magnesium compound is soluble.