CN1778718A

CN1778718A - Treatment for softening seawater by single-decalcification

Info

Publication number: CN1778718A
Application number: CN 200510023314
Authority: CN
Inventors: 蔡梅初
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-01-06
Filing date: 2005-01-06
Publication date: 2006-05-31
Anticipated expiration: 2025-01-06
Also published as: CN1332894C

Abstract

A treatment for softening seawater single decalcification is prepared by taking imsoluble lime salts such as CaCO3, CaSO3, CaC2O4 etc. as inducing crystal seeds, taking corresponded sodium salts such as Na2CO3, Na2SO3, Na2C2O4 etc. as precipitant, induction crystallizing between normal temperature and boiling point in reactor and adjusting the softened seawater pH<=7.5. The final end of induction crystallization is CaCl2+Na2CO3-CaCO3+2NaCl and residual Ca in seawater<=40mg/L.

Description

Treatment method for single decalcification softening of seawater

Technical Field

The invention relates to a treatment method for single decalcification and softening of seawater, belonging to the technical field of seawater desalination pretreatment.

Background

Due to the shortage of fresh water resources, people are constantly engaged in the research of seawater desalination. At present, various methods for desalinating seawater are actually used in two types, one is a distillation method, and the other is a membrane treatment method. The two methods for desalting seawater at present have the problems of equipment corrosion prevention, cost and the like, and a large amount of concentrated seawater is discharged, so that the warm concentrated seawater with the additive causes pollution to local sea areas. The utilization rate of seawater desalinated by the existing distillation method is only 50 percent, and the membrane treatment method is about 67 percent, because of the high content of Ca in the seawater⁺⁺、Mg⁺⁺And SO₄ ^--The seawater has high hardness, and the serious scaling phenomenon of the seawater in the process of desalination and concentration is caused. If Ca in seawater is to be treated⁺⁺、Mg⁺⁺、SO₄ ^--The prior art has high cost and poor operability, which is unacceptable.

Disclosure of Invention

The invention aims to provide a pretreatment method for single decalcification softening of seawater, which is beneficial to the extreme concentration of seawater, thereby obtaining fresh water, industrial salt, bittern and useful calcium salt, and realizing zero discharge.

The technical scheme of the single decalcification softening treatment method of seawater of the invention is as follows: taking insoluble calcium salt of more than 0.1% as inducing seed crystal, taking corresponding sodium salt as precipitant, performing induced crystallization at any temperature ranging from normal temperature to boiling point, performing induced crystallization in a reactor, inducingCa in softened seawater after crystal guide treatment⁺⁺Can be reduced to 40mg/L, and can be concentrated extremely without scale formation when the pH is less than or equal to 7.5. The treatment method takes the difficultly soluble calcium salt (such as CaCO)₃、CaSO₃、CaC₂O₄、CaF₂、Ca₃(PO₄)₂Etc.) as an induction seed and a corresponding sodium salt (e.g., Na)₂CO₃、Na₂SO₃、Na₂C₂O₄、NaF、Na₃PO₄Etc.) as precipitant, and the induced crystallization can be carried out under the conditions of normal temperature or heating, and the reaction result of the induced crystallization is as follows, taking calcium carbonate as an example:

therefore, from the overall reaction results, Na wasadded₂CO₃All will be converted into sodium chloride, the pH of the aqueous solution will remain the same, and Na will be added in slight excess₂CO₃After reaction, MgCO is generated₃·Mg(OH)₂And converted into sodium chloride, and if the pH value of normal seawater is between 7.5 and 8.4, the pH value of softened seawater after reaction is between 7.5 and 8.6. Therefore, the hydrochloric acid consumption is very little when the pH value is adjusted to be less than or equal to 7.5 (6.5-7.5). Residual calcium content (Ca) of treated seawater⁺⁺Calculated) is less than or equal to 40 mg/L. The method can be used for extremely concentrating without scaling within the pH range of less than or equal to 7.5, so that the utilization rate of the seawater is almost 100 percent, and zero emission is completely realized when the method is used for seawater desalination. The industrial salt value obtained is sufficient to offset all the costs, whether for desalination (distillation) or salting, which costs zero as fresh water.

The method is used for pretreatment of seawater by a membrane method, and can also avoid the scaling phenomenon.

Drawings

FIG. 1 is a schematic view of a normal-temperature water-bath type induced crystallization device for single decalcification and softening of seawater according to the present invention;

FIG. 2 is a schematic diagram of a high-temperature (tank type) reaction device for single decalcification and softening of seawater according to the invention.

Detailed Description

The invention discloses a treatment methodfor single decalcification softening of seawater, which is characterized by comprising the following steps: taking more than 0.1 percent of insoluble calcium salt as an induction seed crystal, taking corresponding sodium salt as a precipitator, carrying out induction crystallization at any temperature ranging from normal temperature to boiling point, wherein the induction crystallization is carried out in a reactor, and the corrected PH of softened seawater subjected to the induction crystallization is less than or equal to 7.5. Wherein the insoluble calcium salt is: CaCO₃、CaSO₃、CaC₂O₄、CaF₂、Ca₃(PO₄)₂Etc., wherein said corresponding sodium salt precipitating agents are respectively: na (Na)₂CO₃、Na₂SO₃、Na₂C₂O₄、NaF、Na₃PO₄And the like. The reactor is a water pool type induced crystallization or tank type induced crystallization reaction device. The operating method of the water pool type induced crystallization comprises the following steps: pre-storing inducing crystal seed with sea water amount over 0.1% in a water tank, filling normal temperature sea water into inducing crystallization water tank, adding precipitant into the water tank for mixing, stirring intermittently in the water tank with stirrer 8, reacting at normal temperature for 2-3.5 hr, standing, clarifying, and taking clarified liquid to correct pH to less than 7.5.

A specific example of the room temperature water bath will be described below with reference to fig. 1.

Seawater 12 is introduced into the induced crystallization tank 7 by a pump 1 or a high-level water tank, and calcium carbonate powder with the total amount of seawater of more than 0.1 percent is prestored in the tank. Adding Ca contained in seawater under stirring⁺⁺Sodium carbonate (added by dissolving seawater into 10% solution) 1.5 times the total equivalent is used as precipitant, and is added by precipitant feeder 9, and then intermittently stirred to make CaCO₃Keeping the suspension state. Naturally reacting for 3 hours at the normal temperature of 25 ℃ to obtain Ca in the seawater⁺⁺The concentration is reduced from 400mg/L to below 40 mg/L.Then stopThe mixture is stirred and kept stand for about 5 minutes, and the reactant can be clarified. Then, a filtrate valve 5 is opened, an emptying valve 4 is opened, the clarified decalcified seawater can flow into a softened water storage tank 2 through a filter pipe 6, the filtrate flows into the tank tangentially when flowing, so that the filtrate rotates, a proper amount of hydrochloric acid is dripped from an acid storage tank 3 at the moment to adjust the pH value of the softened water to be less than or equal to 7.5 (6.5-7.5), and the softened water can be sent to a using process through a pump 1.

After the second circulation, CaCO in the crystallization tank is induced₃The amount was quantitatively increased while stopping the stirring after the reaction was completed. Opening the communicating butterfly valve 10 to make the reaction suspension enter the quantitative separation tank 11, and then when standing and clarifying, settling CaCO in the separation tank 11₃The reactor is removed and the clarified demineralized water is filtered out, and the liquid level in the quantitative separation tank 11 is also reduced to the minimum. The communication butterfly valve 10 is then closed again for the next cycle, and so on.

Quantitative CaCO precipitated from separation tank₃Can be taken out manually (or a mechanical material taking device can be arranged), is dried to be sold as a product after being centrifuged and washed by fresh water to be qualified, and is used for filling rubber, paint or plastic. The centrifugate andthe leacheate were combined in a softening water tank.

The operation method of the tank type induced crystallization separation device is as follows: the seawater is heated to a preset temperature through a heat exchanger, then enters an induced crystallization tank in a heat preservation state, induced crystal seeds with the seawater amount of more than 0.1 percent are stored in the tank, a precipitator is added beside a hot seawater inlet tank, the seawater is naturally mixed or stirred and mixed through tangential feed liquid, and the decalcified and softened seawater is led out through a reverse filtration device.

A specific example of the use of a high temperature tank reactor is shown below with reference to FIG. 2:

the seawater 12 is pumped into a heat exchanger 23 by a seawater pump 21 (the heat exchanger is heated by steam, and a condensed water storage tank 22 is used for leaching CaCO by a centrifugal machine₃Use), the heated seawater enters the induced crystallization reaction tank 26 in the tangential direction, CaCO with the preset tank capacity of more than 0.1 percent is arranged in the induced crystallization reaction tank 26₃As an induction seed, precipitant Na₂CO₃(dissolved in seawater to about 10%)The right solution) is determined by a precipitant feeding tank 24The quantity is added to the crystallization-inducing reaction tank 26, also tangentially, so that the stirrer can be omitted and the CaCO can still be maintained₃The suspension and mixing of the materials are automatically carried out. The reaction mixture is allowed to move in the crystallization-inducing reaction tank 26 for 6 minutes, and then the reaction mixture is discharged from the apparatus through a demineralized water filtration line 25, and the resulting demineralized water is pH-adjusted (not shown) and then sent to the use step.

After the device passes a certain amount of seawater. Precipitation of CaCO in the crystallization-inducing reaction tank 26₃When the amount of the suspension increases, the lower valve of the reaction tank 26 is periodically opened to allow the suspension to enter the quantitative separation tank 27, the suspension is cooled again, centrifuged by the centrifuge 28, and washed with water, and the centrifuged liquid and the eluate are mixed with demineralized water. Precipitated CaCO qualified by leaching₃And drying to obtain the product.

The device can be operated continuously.

Claims

1. The treatment method for single decalcification softening of seawater is characterized by comprising the following steps: taking more than 0.1 percent of insoluble calcium salt as an induction seed crystal, taking corresponding sodium salt as a precipitator, carrying out induction crystallization at any temperature ranging from normal temperature to boiling point, wherein the induction crystallization is carried out in a reactor, and the corrected PH of softened seawater subjected to the induction crystallization is less than or equal to 7.5.

2. The method of claim 1, wherein the insoluble calcium salt is: CaCO₃、CaSO₃、CaC₂O₄、CaF₂、Ca₃(PO₄)₂。

3. The method for mono-decalcifying and softening sea water according to claim 1, wherein the corresponding sodium salt precipitating agents are respectively: na (Na)₂CO₃、Na₂SO₃、Na₂C₂O₄、NaF、Na₃PO₄。

4. The process of claim 1, wherein the reactor is a pool-type induced crystallization or a tank-type induced crystallization.

5. A process as claimed in claim 4, wherein the pond-type induced crystallization operation is: pre-storing inducing crystal seed with sea water amount over 0.1%, filling normal temperature sea water into inducing crystallizing pond, adding precipitant into the pond, mixing, stirring intermittently in the pond with stirrer, reacting at normal temperature for 2-3.5 hr, standing, clarifying, and correcting pH to 7.5 or less.

6. The seawater single decalcification softening treatment method of claim 4, wherein the pot-type induced crystallization operation method is: the seawater is heated to a preset temperature through a heat exchanger, then enters an induced crystallization tank in a heat preservation state, induced crystal seeds with the seawater amount of more than 0.1 percent are stored in the tank, a precipitator is added beside a hot seawater inlet tank, and the mixture is naturally mixed or stirred and mixed, and then the decalcified and softened seawater is led out through a reverse filtration device.