TWI577642B - Method of recycling ammonia from wastewater and preparing solid calcium sulfate and calcium chloride solution - Google Patents

Description

Method for recovering ammonia from wastewater and preparing calcium sulfate solid and calcium chloride solution 【0001】

The present invention is a wastewater treatment method, and more particularly to a method for recovering ammonia from wastewater while obtaining calcium sulfate solids and calcium chloride solution from the recovery process.

【0002】

Ammonia nitrogen can provide a nutrient source for the growth of aquatic plants, and such as seaweed and aquatic plants multiply, which will lead to the lack of oxygen in the waters, which in turn causes the aquatic organisms to die. Free ammonia nitrogen molecules (unionized fractions) are toxic to aquatic organisms. In general, the water body is dysfunctional and ecologically balanced. To this end, the Environmental Protection Agency has regulated the ammonia nitrogen emissions of the photovoltaic industry, chemical industry, and science parks, and ammonia nitrogen recovery has become an important issue.

[0003]

Ammonia (NH ₃ ) is an exhaust gas pollutant. Generally, factories that produce waste ammonia gas use a wet scrubber to reduce the emission of waste ammonia. In order to effectively adsorb waste ammonia gas, the composition of the washing liquid in the wet scrubber is usually low-priced hydrochloric acid or sulfuric acid, and when the washing liquid is discharged out of the scrubber, it becomes a wastewater containing high ammonia nitrogen.

[0004]

At present, the high-concentration ammonia nitrogen recovery treatment method is air stripping and steam stripping, which is to be blown off by air under alkaline conditions (using air as a carrier gas) or by using steam. Stripping (using water vapor as a carrier gas). Using the difference between the actual concentration of ammonia nitrogen contained in the wastewater and the equilibrium concentration, firstly, the ammonia ion is converted into an ammonia molecule by providing an alkaline environment, and then the volatility of the ammonia molecule is utilized to transfer the ammonia nitrogen in the wastewater from the liquid phase to In the gas phase, the purpose of removing ammonia nitrogen is achieved. Therefore, the method must be carried out under alkaline conditions, usually using calcium hydroxide (Ca(OH) ₂ ) (commonly known as lime milk, slaked lime), sodium hydroxide (NaOH) or potassium hydroxide (KOH), etc. Compounds to increase the pH of wastewater (also known as pH).

[0005]

However, although calcium hydroxide is cheap, it is easy to produce scale (calcium containing calcium) during operation, such as calcium sulfate (CaSO ₄ ) or calcium carbonate (CaCO ₃ ), which causes the efficiency of the equipment to decrease and even cause blockage of the pipeline. The equipment is inoperable, so it is often used in the industry to increase the pH of the wastewater.

[0006]

However, if sodium hydroxide is used to raise the pH value of the wastewater, although no sediment will be produced, the residual liquid after stripping is sodium chloride (NaCl) or sodium sulfate (NaSO ₄ ) solution, and the two solutions are directly reused. It is low in nature and cannot be sold directly. It can only be treated as wastewater.

【0007】

In addition, the ammonia gas blown off by the air stripping method or the steam stripping method can easily cause secondary pollution if it is not collected and escapes.

[0008]

The object of the present invention is to provide a method for recovering ammonia from waste water and preparing calcium sulfate solid and calcium chloride solution, which has the advantages of the conventional air stripping method: high ammonia blowing rate, and no air blowing method, sodium hydroxide method The shortcomings of the calcium hydroxide method: the secondary pollution caused by ammonia emissions, the inability to reuse by-products, and the problem of sediment blocking the pipeline.

【0009】

In order to achieve the foregoing object, the present invention provides a method for recovering ammonia from wastewater and preparing a calcium sulfate solid and a calcium chloride solution, comprising the following steps (A) to (D).

[0010]

Step (A): introducing ammonia nitrogen wastewater into the reaction tank, adding calcium chloride, and utilizing calcium ions (Ca ²⁺ ) in the calcium chloride to combine sulfate ion (SO ₄ ^2- ) and calcium ions in the wastewater to produce sulfuric acid. After the calcium solid is precipitated and the precipitate is removed by a solid-liquid separation device, the wastewater at this time is ammonium chloride (NH ₄ Cl) wastewater, and the converted wastewater is referred to as a reaction liquid, and the reaction liquid is introduced into a stirring mixing tank.

[0011]

Step (B): increasing the pH of the ammonium chloride reaction solution to 11 or more with calcium hydroxide (Ca(OH) ₂ ), introducing the ammonia generator, and warming the reaction liquid (the heating vapor does not come into contact with the reaction liquid) . After removal of ammonia by air stripping, the remaining chloride ions combine with calcium ions to form calcium chloride.

[0012]

Step (C): collecting ammonia dissolved in the ammonia absorption tower after the air is blown off, and absorbing the dissolved ammonia gas by using water or hydrochloric acid to prepare ammonia water or ammonium chloride solution, respectively.

[0013]

Step (D): first adjust the pH of the reaction solution after stripping to below 4 with hydrochloric acid, and let the calcium carbonate in the reaction solution (the calcium hydroxide in step B absorbs carbon dioxide (CO ₂ ) in the air) or residual The unreacted calcium hydroxide reacts with hydrochloric acid. After the pH value is stable, the calcium hydroxide is slowly added gradually, and the pH of the reaction solution is controlled to be between 6 and 9, and finally filtered by a solid-liquid separation device. The reaction solution removes insoluble impurities such as citrate and sulfate to obtain a finished calcium chloride solution.

[0014]

In the present invention, the calcium sulfate in the step (A) has a high purity and has the potential to be developed into a calcium sulfate nanowire (rod). The calcium chloride solution in the step (B) can be used as a medicament for wastewater treatment and can be used to remove fluoride ions in the wastewater. The ammonia water in step (C) can be directly concentrated and sold directly, while the ammonium chloride solution can be further concentrated to ammonium chloride powder for sale. The concentration of the calcium chloride solution in step (D) is between 15 and 20% and can be used to dilute a commercially available calcium chloride solution (concentration 36%).

[0015]

The above and other objects, features and advantages of the present invention will become more apparent and understood.

[0032]

1‧‧‧ sulfate removal tank

2‧‧‧ filter press

3‧‧‧Stirring mixing tank

4‧‧‧Boiler

5‧‧‧Blowers

6‧‧‧Ammonia generator

7‧‧‧Ammonia absorption tower

8‧‧‧Ammonia absorption tank

9‧‧‧ice water machine

10‧‧‧ filter press

11‧‧‧ calcium chloride storage tank

S10~S120‧‧‧Steps

[0016]

1 and 2 are flow charts showing a method for recovering ammonia from wastewater and preparing calcium sulfate solid and calcium chloride solution according to an embodiment of the invention;

Figure 3 is a schematic diagram showing the relative amounts of ammonia molecules and ammonium ions at different pH values and different temperature conditions.

[0017]

1 and 2 are flow charts of a method for recovering ammonia from wastewater and preparing calcium sulfate solid and calcium chloride solution according to an embodiment of the invention, wherein step S30 and step S70 can be combined. Referring to Figure 3, it shows the effect of pH and temperature on the ratio of ammonia to ammonium.

[0018]

Referring to FIG. 1 first, in step S10, ammonium sulfate wastewater (hereinafter referred to as the reaction liquid) and calcium chloride solution are poured into the sulfate removal tank (1) and stirred to remove sulfate ions in the reaction liquid.
CaCl ₂ + (NH ₄ ) ₂ SO ₄ →CaSO ₄ (solid) + 2NH ₄ Cl (liquid)

[0019]

In step S20, the reaction liquid is then introduced into a solid-liquid separation device, for example, a filter press (2), and the solid-liquid separation is carried out to separate calcium sulfate in the reaction liquid to obtain a calcium sulfate solid. At this time, the reaction liquid was ammonium chloride wastewater.

[0020]

In step S30, the reaction liquid is introduced into the stirring mixing tank (3), calcium hydroxide is added, the pH of the reaction liquid is raised to 11 or more (in practice, the pH is increased to pH=11.3 to 11.5), and then the reaction liquid is introduced into the ammonia generator (6). in.

[0021]

The equilibrium reaction formula of NH ₃ and NH ₄ ⁺ (please refer to Figure 3):
NH ₃ + H ₂ O NH ₄ ⁺ + OH ^- knows that at this time, the ammonium ion in the reaction liquid is converted into an ammonia molecule in an alkaline environment.

[0022]

In step S40, the reaction liquid is warmed, for example, the steam supplied from the boiler (4) heats the reaction liquid in the ammonia generator (6) (this vapor does not come into contact with the reaction liquid).

[0023]

In step S50, air is blown into the ammonia generator (6) by the pressure feed type blower (5).

[0024]

In step S60, ammonia in the reaction liquid is blown off by air stripping. The remaining reaction solution is mainly a calcium chloride solution.

[0025]

In step S70, the ammonia gas blown in step S60 is introduced into the ammonia absorption tower (7) to be absorbed by the ammonia absorption liquid. If the ammonia absorbing liquid is water, the temperature of the ammonia absorbing liquid (ie, water) is cooled by cooling to dissolve the ammonia gas in the ammonia absorbing liquid (ie, water), and the obtained finished product is ammonia water: H ₂ O + NH ₃ → NH ₄ ⁺ + OH ^- (Please refer to Figure 3). If the ammonia absorbing liquid is hydrochloric acid, the obtained product is an ammonium chloride solution: HCl + NH ₃ → NH ₄ ⁺ + Cl ^- .

[0026]

In step S80, the ammonia absorption liquid is stored in the ammonia absorption liquid storage tank (8) for recycling to the ammonia absorption tower (7), and the new ammonia absorption liquid is replaced when the ammonia absorption liquid reaches the desired concentration.

[0027]

In step S90, a cooling device such as an ice water machine (9) is prepared in advance, and when the ammonia absorbing liquid is water, it is used as a temperature for reducing the ammonia absorbing liquid (ie, water), so that ammonia gas is dissolved in the ammonia absorbing liquid (ie, water). )in.

[0028]

Referring to FIG. 2 again, in step S100, in the ammonia generator (6), hydrochloric acid is first added to adjust the pH of the reaction solution after the stripping to below 4, and the calcium carbonate in the reaction solution (calcium hydroxide from step S30). Absorbing carbon dioxide (CO ₂ ) in the air) or residual unreacted calcium hydroxide and hydrochloric acid, after the pH of the reaction liquid is stabilized, slowly raise the pH to 6-9 with calcium hydroxide to obtain chlorine. Calcium semi-finished products.

[0029]

In step S110, the reaction liquid is introduced into a solid-liquid separation device, for example, a filter press (10), and solid-liquid separation is performed to remove insoluble impurities such as citrate or sulfate in the calcium chloride semi-finished product to obtain a finished calcium chloride solution.

[0030]

In step S120, the calcium chloride solution obtained in step S110 is stored in the calcium chloride storage tank (11).

[0031]

Although the present invention has been disclosed in the above preferred embodiments, it is not intended to limit the present invention, and those skilled in the art can make some modifications and refinements without departing from the spirit and scope of the present invention. The scope of protection is subject to the definition of the scope of the attached patent application.

1‧‧‧ sulfate removal tank

2‧‧‧ filter press

3‧‧‧Stirring mixing tank

4‧‧‧Boiler

5‧‧‧Blowers

6‧‧‧Ammonia generator

7‧‧‧Ammonia absorption tower

8‧‧‧Ammonia absorption tank

9‧‧‧ice water machine

S10~S90‧‧‧ steps

Claims (7)

[Item 1] A method for recovering ammonia from wastewater and preparing a calcium sulfate solid and a calcium chloride solution, comprising:
(A) introducing waste water into the sulfate removal tank, adding calcium chloride, using calcium ions in the calcium chloride, and combining with the sulfate ion in the reaction liquid to produce a solid precipitate of calcium sulfate, and the converted wastewater is referred to as a reaction liquid;
(B) introducing the reaction liquid into the stirring mixing tank, increasing the pH value of the reaction liquid with calcium hydroxide, then introducing the ammonia generator, warming the reaction liquid, removing ammonia by air stripping, and remaining chlorine ions and calcium. Ion binding to calcium chloride;
(C) Collecting ammonia dissolved in the ammonia absorption tower after the air is blown off, and absorbing the dissolved ammonia gas by using the ammonia absorption liquid. [Item 2] A method for recovering ammonia from waste water and preparing a calcium sulfate solid and a calcium chloride solution as described in claim 1, wherein after the calcium sulfate precipitate is produced in the step (A), a step (A2) is further included to fix the liquid. The separation device removes the precipitated calcium sulfate. [Item 3] The method for recovering ammonia from wastewater and preparing calcium sulfate solid and calcium chloride solution according to claim 1, wherein step (B) further comprises a step (B2) in the ammonia generator. The pH value of the reaction liquid after the stripping of hydrochloric acid is adjusted to 4 or less, and the calcium carbonate in the reaction liquid or the residual unreacted calcium hydroxide and hydrochloric acid are reacted, and the hydroxide is slowly and gradually added after the pH value is no longer changed. Calcium, increase the pH value to 6~9, at this time the reaction liquid is a semi-finished product of calcium chloride. [Item 4] A method for recovering ammonia from waste water and preparing a calcium sulfate solid and a calcium chloride solution as described in claim 3, wherein a step (B3) is further performed after the step (B2) to remove calcium chloride by a solid-liquid separation device. Insoluble impurities in the semi-finished product give a calcium chloride solution. [Item 5] The method for recovering ammonia from waste water and preparing calcium sulfate solid and calcium chloride solution according to claim 1, wherein in the step (C), when water is used as the ammonia absorption liquid, the ammonia absorption liquid is absorbed and dispersed. Ammonia gas, the finished product is ammonia water. [Item 6] A method for recovering ammonia from waste water and preparing a calcium sulfate solid and a calcium chloride solution as described in claim 5, wherein in step (C), when water is used as the ammonia absorbent, a step (C2) is further included. The temperature of the ammonia absorbing liquid is lowered to dissolve the ammonia gas in the ammonia absorbing liquid. [Item 7] A method for recovering ammonia from waste water and preparing a calcium sulfate solid and a calcium chloride solution according to the first aspect of the patent application, wherein in the step (C), when hydrochloric acid is used as the ammonia absorption liquid, the ammonia absorption liquid is absorbed and dispersed. Ammonia gas, the resulting product is an ammonium chloride solution.