JP3675667B2 - How to remove ammonia in waste water - Google Patents

Description

【００１８】
表２の結果から、実施例１〜実施例３のいずれも、アンモニアの高い除去率が得られたことが判る。また、各実施例共、放散塔の閉塞の心配もなく、３〜６ヵ月の連続運転が可能であった。
【００１９】
【発明の効果】
請求項１記載の発明方法によれば、放散塔における閉塞の虞がなく、長期連続運転が可能である。また、９８％以上の高いアンモニア除去率を得ることができる。従って、沈殿物を生成し易い物質を含むアンモニア含有排水のストリッピングに特に適している。
請求項２記載の発明方法によれば、前記効果に加えて、アンモニアの放散塔をコンパクトな装置で構成することができる。
【図面の簡単な説明】
【図１】本発明の好適な実施形態を示すフローチャートである。
【符号の説明】
１０ 放散塔
１１ 水平領域
１２ 導入領域
１３ 排出領域
１４ ノズル
２０ アンモニア回収塔
３０ 反応槽
３２ ポンプ[0001]
[Industrial application fields]
The present invention relates to a method for removing ammonia from wastewater containing ammonia, and more particularly to an improved ammonia stripping method.
[0002]
[Prior art]
The ammonia stripping method is a removal method suitable for treating a relatively high concentration of ammonia-containing wastewater or ammonia-containing wastewater having a large concentration fluctuation, targeting factory wastewater, city water, lake water, and the like. In this method, the pH of water to be treated is raised to convert ammonium ions into free ammonia, and the ammonia is removed from the water to be treated by moving it to air by air stripping.
Conventionally, a stripping tower that performs air stripping is filled with a plastic filler or the like in order to sufficiently contact the air and the water to be treated, and the water to be treated is sprinkled from the top of the tower after pH adjustment, It falls while repeating the formation and destruction of water droplets between fillers. During this time, the water droplets come into contact with air, and ammonia is used as a gas to dissipate from the water into the air.
[0003]
The pH of the water to be treated is adjusted with an alkali source such as sodium hydroxide, calcium hydroxide, calcium oxide, magnesium hydroxide, magnesium oxide, and is usually relatively inexpensive calcium hydroxide, calcium oxide, magnesium hydroxide. Magnesium oxide and the like are used. However, if these inexpensive alkali sources are used, they react with carbon dioxide in the air or sulfate contained in the water to be treated to produce calcium or magnesium carbonates or sulfates. As a result of adhering as a scale between the packing materials inside the tower, it is necessary to block the inside of the diffusion tower, hinder long-term continuous operation, and to frequently clean the inside.
In addition, when the wastewater to be treated contains substances that cause precipitation due to alkali, such as aluminum sulfate, water glass, etc., the scale adheres to the packed bed no matter what alkali source is used, and the above problem May occur.
[0004]
[Problems to be solved by the invention]
The present invention does not depend on the type of alkali source to be added, and wastewater that can be continuously operated for a long time without clogging the diffusion tower, even for ammonia-containing wastewater mixed with substances that cause precipitation due to alkali. The present invention provides a method for removing ammonia therein.
[0005]
[Means for Solving the Problems]
The present invention provides a method for transferring ammonia from water to be treated into water by adding alkali to ammonia-containing wastewater and bringing it into contact with air circulating between the ammonia recovery tower and the ammonia recovery tower. The inside of the chamber is made hollow and divided into two or more regions, the treated water brought into contact with the circulating air in the former region is extracted to promote the ammonia conversion reaction in the reaction tank, and then returned to the latter region of the stripping tower. It is a means.
The region is preferably formed to extend in the horizontal direction, and the water to be treated is sprayed in the horizontal direction.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be specifically described with reference to FIG. 1 which is a flowchart showing a preferred embodiment of the present invention.
[0007]
FIG. 1 shows a stripping tower 10, an ammonia recovery tower 20, a reaction tank 30, and the like, which are main components for carrying out the present invention.
The diffusion tower 10 is formed with a region 11 extending in the horizontal direction, and an introduction region 12 and a discharge region 13 that are bent in the vertical vertical direction at both ends of the region 11. In the present embodiment, the horizontal region 11 is divided into three parts 11a, 11b, and 11c, and each horizontal region 11a, 11b, 11c, the introduction region 12, and the discharge region 13 are provided with nozzles 14 for spraying water to be treated. Equipped. Accordingly, a total of five regions are formed in the present embodiment. The inside of the stripping tower 10 is a cavity and is not equipped with a filler.
The horizontal region 11 of the stripping tower 10 is slightly inclined (about 1 to 10 degrees), and weirs 15, 15, and 15 are provided in the horizontal regions 11a, 11b, and 11c to easily collect treated water.
[0008]
The ammonia recovery tower 20 is the same as a conventionally known one, and a vertical tower is filled with Raschig rings 21 and the like, and air circulates between the diffusion tower 10.
[0009]
The reaction tanks 30a, 30b, 30c, and 30d are for extracting the treated water that has contacted the circulating air in the introduction region 12 and the horizontal regions 11a, 11b, and 11c, and promoting the ammonia conversion reaction. Are preferred. The treated water converted to free ammonia is returned to the subsequent regions, that is, the horizontal regions 11a, 11b, 11c and the discharge region 13 by the pumps 32a, 32b, 32c, 32d.
[0010]
In the ammonia stripping method, if all the ammonia in the water exists as free ammonia such as ammonia water, the packed bed required for stripping is determined by the temperature, pH, weight ratio L / G of the water to be treated and the amount of circulating air. Is determined. However, since the packed bed is not provided in the method of the present invention, the corresponding reduction in contact efficiency is compensated by nozzle spraying. The inventors confirmed by experiments that one nozzle spray corresponds to a packed bed height of 1.5 m.
[0011]
If inexpensive magnesium hydroxide or magnesium oxide is used as the alkali source, the conversion reaction to free ammonia proceeds only about 50%. However, if this free ammonia is stripped, the reaction between the remaining ammonium salt and magnesium proceeds and half of it again becomes free ammonia. Therefore, in the method of the present invention, considering that the reaction rate between the ammonium salt and magnesium is slower than the diffusion rate of ammonia, the diffusion tower is divided into a plurality of regions, and reaction vessels are provided between the regions. is there.
[0012]
The ammonia-containing wastewater is adjusted to a high pH value by adding an alkali, and the treated water 1 is sprayed into the diffusion tower 10 from the nozzle 14 in the introduction region 12. The water 1 to be treated comes into contact with the circulating air, descends the introduction region 12, and is extracted from the line 16a and introduced into the reaction tank 30a. The treated water 1 that has undergone the conversion reaction to ammonia in the reaction tank 30 a is sent to the horizontal region 11 a by the pump 32 a and sprayed from the nozzle 14. Hereinafter, the water 1 to be treated comes into contact with air in the horizontal regions 11a, 11b, 11c and the discharge region 13 to release ammonia, and is sent from the discharge line 2 in the discharge region 13 to a wastewater treatment facility (not shown) outside the system. It is done.
[0013]
The temperature in the stripping tower 10 is preferably 85 ° C to 95 ° C. For this purpose, in addition to preheating the air, water vapor may be blown into the circulating air. Moreover, it is desirable to adjust beforehand that the pH value of the to-be-treated water 1 is 9 or more in the discharge region 13. Accordingly, the pH of the water 1 to be treated in the introduction region 12 is preferably 10.5 or more. Moreover, you may adjust pH by adding an alkali with each reaction tank 30a, 30b, 30c, 30d. The weight ratio L / G of the water to be treated and the amount of circulating air in the stripping tower 10 is preferably 1 to 10, particularly preferably about 1 to 5.
[0014]
The circulating air introduced into the discharge area 13 flows in the stripping tower 10 in the direction opposite to the treated water 1 and then returns from the top of the introduction area 12 to the bottom of the ammonia recovery tower 20 via the line 3. It is. This circulating air is extracted from the top of the recovery tower 20 after coming into contact with the recovery liquid containing sulfuric acid in the ammonia recovery tower 20 and returned to the discharge region 13 via the line 4. Sulfuric acid is supplied to the ammonia recovery tower 20 from the line 5, and the recovery liquid containing sulfuric acid is circulated in the recovery tower 20 from the top to the bottom by the pump 22. A part of the recovered liquid containing ammonia and absorbing ammonium sulfate is branched from the line 6 and sent to an ammonium sulfate recovery facility (not shown) outside the system.
[0015]
【Example】
About the factory waste water of average ammonia concentration 1500mg / l (maximum 3500mg / l), the ammonia stripping process was performed by the flow shown in FIG. Table 1 shows the composition of industrial wastewater, and Table 2 shows the treatment conditions and results.
[0016]
[Table 1]
Ammonium sulfate: 5800 mg / l (up to 11600 mg / l)
Sodium sulfate: 1.5-2.5% by weight
Sulfuric acid: 1700 mg / l
Aluminum sulfate: 1800 mg / l
Chlorine: 300 mg / l
Other solid content: Small amount [0017]
[Table 2]

[0018]
From the results of Table 2, it can be seen that in all of Examples 1 to 3, a high ammonia removal rate was obtained. In each Example, continuous operation for 3 to 6 months was possible without worrying about blocking of the diffusion tower.
[0019]
【The invention's effect】
According to the first aspect of the invention, there is no risk of blockage in the stripping tower, and long-term continuous operation is possible. Further, a high ammonia removal rate of 98% or more can be obtained. Therefore, it is particularly suitable for stripping ammonia-containing wastewater containing substances that easily generate precipitates.
According to the second aspect of the invention, in addition to the above effect, the ammonia diffusion tower can be constituted by a compact device.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a preferred embodiment of the present invention.
[Explanation of symbols]
10 Dispersion tower 11 Horizontal area 12 Introduction area 13 Discharge area 14 Nozzle 20 Ammonia recovery tower 30 Reaction tank 32 Pump

Claims (1)

In the method of transferring ammonia from the water to be treated to the air by adding alkali to the ammonia-containing waste water and bringing it into contact with the air circulating between the ammonia recovery tower in the diffusion tower, the inside of the diffusion tower is hollow In addition, the spray water is divided into two or more regions extending in the horizontal direction, spray nozzles are provided in each region, and the treated water brought into contact with the circulating air is extracted by spraying the water to be treated in the horizontal direction in the previous stage region. after promoting the ammonia conversion reaction in a reaction vessel Te, to return to a subsequent stage region of the stripping column, a method for removing the ammonia in the waste water, characterized in that spraying in a horizontal direction.

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