JP3637458B2 - Ammonia nitrogen removal method - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for removing ammonia nitrogen present in a liquid such as condensate demineralized reclaimed water in a thermal power plant as ammonia gas.
[0002]
[Prior art]
For example, condensate in a thermal power plant is usually desalted with an ion exchange resin to form condensate demineralized reclaimed water, and the reclaimed water generally contains ammonia nitrogen in an amount exceeding environmental standards. Conventionally, an ammonia diffusion (stripping) method has been frequently used as a method of reducing ammonia nitrogen in such condensate demineralized reclaimed water to be below the environmental standard.
[0003]
[Problems to be solved by the invention]
However, this stripping method requires a complicated facility and a large site area, and also has a problem of consuming a great deal of energy. Moreover, since it is not environmentally preferable to release ammonia together with evaporated water into the atmosphere, in order to avoid this, further post-treatment facilities are required. Even if such facilities are provided, ammonia as a resource is also required. It is not easy to recover.
Accordingly, an object of the present invention is to provide a method for removing ammoniacal nitrogen for solving such problems.
[0004]
[Means for Solving the Problems]
The present invention relates to electrodialysis in which an ammonium salt is precipitated and removed by adding an acid to a liquid containing ammoniacal nitrogen, and the resulting liquid containing ammonium ions is alternately arranged with a cation exchange membrane and an anion exchange membrane. This is a method of removing ammoniacal nitrogen treated by an apparatus.
As a dialysis unit of the electrodialysis apparatus, a dilution chamber for introducing a solution containing ammonium ions, a first concentration chamber adjacent to the cation exchange membrane side of the dilution chamber, and an anion exchange membrane side of the dilution chamber are adjacent to each other. The second concentration chamber includes a hydroxide ion chamber in which a hydroxide ion-containing liquid flows adjacent to the anion exchange membrane side of the first concentration chamber. Further, the pH of the first concentrating chamber is maintained at an alkalinity so as to be an equilibrium condition for generating ammonia from ammonium ions moving from the dilution chamber and hydroxide ions moving from the hydroxide ion chamber. And the produced | generated ammonia is taken out from a 1st concentration chamber as gas, It is characterized by the above-mentioned.
[0005]
【Example】
Next, the ammonia nitrogen removing method of the present invention will be described in more detail.
FIG. 1 is an example of a processing flow sheet for carrying out the ammonia nitrogen removing method of the present invention, wherein 1 is a pH adjusting tank, 2 is a pump, 3 is a hollow fiber membrane filter, and 4 is an electrodialysis apparatus.
The liquid a containing ammonia nitrogen is mixed with the acid b added in the pH adjusting tank 1, and the pH is adjusted to 4 or less, preferably about 2 to 4, whereby the ammonia nitrogen precipitates as an ammonium salt. It is removed from the pipe c. The acid to be added is preferably a mineral acid such as hydrochloric acid or sulfuric acid. Ammonium ions (NH ₄ ions) that do not precipitate and inorganic ions such as sulfuric acid (SO ₄ ions) are left in the solution when sulfuric acid is used as the acid.
The liquid containing ammonium ions from the pH adjusting tank 1 is sent by the pump 2 through the pipe d to the hollow fiber membrane filter 3 to remove fine solid particles. By removing the solid particles, the effective treatment time of the dialysis membrane in the electrodialysis apparatus can be greatly extended.
[0006]
The reclaimed water from which the solid particles have been removed is introduced into the dilution chamber of the electrodialyzer 4 through the pipe e, where a liquid in which a certain amount of ammonia ions and other inorganic ions have been reduced by the electrodialysis treatment is discharged through the pipe f. And reused or released out of the system.
As will be described later, the electrodialysis apparatus 4 includes a large number of cation exchange membranes and anion exchange membranes alternately arranged, and the dilution chamber, the first concentration chamber, the second concentration chamber, and the hydroxide ion chamber partitioned by them are dialysis units. It has become. Then, a liquid containing sodium hydroxide (NaOH) as a hydroxide ion supply liquid is introduced into the hydroxide ion chamber through the pipe g and flows out from the pipe h. Further, a liquid containing an alkaline agent, for example, sodium hydroxide (NaOH) liquid is introduced into the first concentration chamber through the pipe k in order to maintain the room at a high pH, and the NaOH liquid flows out from the first concentration chamber through the pipe m. To do. Also, ammonia as a gas rises in the first concentration chamber and is taken out from the pipe i. Further, a liquid containing inorganic ions such as SO ₄ ions and Na ions concentrated in the second concentration chamber flows out from the pipe j.
[0007]
Next, FIG. 2 is a diagram schematically showing the electrodialysis apparatus 4 used in the present invention. For example, a large number of cation exchange membranes C and anion exchange membranes A are alternately arranged between an anode plate 5 platinum-plated on a titanium plate and a cathode plate 6 made of a stainless steel plate. As the anion exchange membrane A, for example, a membrane of a styrene / divinylbenzene copolymer system containing a quaternary ammonium salt as an ion exchange group of 1.5 to 3.0 (meq / g dry resin) is used. As C, for example, a styrene / divinylbenzene copolymer film containing 1.5 to 3.0 (meq / g dry resin) of a sulfonic acid group as an ion exchange group is used. An anolyte flows between the anode plate 5 and the anion exchange membrane A adjacent thereto, and a catholyte flows between the cathode plate 6 and the cation exchange membrane C adjacent thereto.
[0008]
The logarithm of the ion exchange membrane varies depending on the concentration of ammonia ions contained in the liquid, the desired treatment amount, etc., but generally about 200 to 900 pairs are used. A dilution chamber 10 for introducing a liquid containing ammonium ions is disposed between the pair of cation exchange membrane C and anion exchange membrane A, and the first concentration chamber is adjacent to the cation exchange membrane C side of the dilution chamber 10. 11. The water in which the second concentration chamber 12 is disposed adjacent to the anion exchange membrane A side of the dilution chamber 10 and the hydroxide ion-containing liquid flows adjacent to the anion exchange membrane A side of the first concentration chamber 11. An acid ion chamber 13 is disposed. The dilution chamber 10, the first concentration chamber 11, the second concentration chamber 12, and the hydroxide ion chamber 13 constitute a dialysis unit U, and a large number of such dialysis units are arranged between the anode plate 5 and the cathode plate 6. Has been.
[0009]
As described above, when sulfuric acid is used as the acid, a solution containing ammonium ions (NH ₄ ions) and sulfate ions (SO ₄ ions) is introduced into the dilution chamber 10 through the pipe e, where these ions are negative-anode. Electrophoresis is performed by an electric field formed between the plates. NH ₄ ions (cations) migrate in the direction of the cathode plate 6, pass through the cation exchange membrane C, and move to the first concentration chamber 11. NH ₄ ions in the first concentration chamber 11 try to migrate further toward the cathode plate 6, but are blocked by the anion exchange membrane A at the boundary with the hydroxide ion chamber 13.
On the other hand, SO ₄ ions (anions) migrate in the direction of the anode plate 5, pass through the anion exchange membrane A, and move to the second concentration chamber 12. The SO ₄ ions in the second concentrating chamber 12 try to migrate further in the direction of the anode plate 5, but are blocked by the cation exchange membrane C at the boundary with the hydroxide ion chamber 13 constituting the next dialysis unit and concentrated solution. Remain in. Thus, NH ₄ ions in the dilution chamber 10 move to the first concentration chamber 11, and SO ₄ ions move to the second concentration chamber 12.
[0010]
The liquid containing sodium hydroxide introduced into the hydroxide ion chamber 13 in the center of the figure by the pipe g is ionized into sodium ions (Na ions) that are cations and hydroxide ions (OH ions) that are anions. . Na ions migrate in the direction of the cathode plate 6 by the electric field formed between the negative and positive electrode plates, pass through the cation exchange membrane C, and move to the second concentration chamber 12 constituting the next dialysis unit. Na ions in the second concentration chamber 12 try to migrate further toward the cathode plate 6 but are blocked by the anion exchange membrane A.
On the other hand, OH ions migrate in the direction of the anode plate 5, pass through the anion exchange membrane A, and move to the first concentration chamber 11. The OH ions in the first concentration chamber 11 try to migrate further in the direction of the anode plate 5, but are blocked by the cation exchange membrane C at the boundary with the dilution chamber 10. Thus, Na ions in the hydroxide ion chamber 13 move to the second concentration chamber 12 constituting the next dialysis unit, and OH ions move to the first concentration chamber 11.
As described above, NH ₄ ions and SO ₄ ions introduced into the dilution chamber 10 are diluted and discharged out of the system from the pipe f or recirculated. Further, the NaOH introduced into the hydroxide ion chamber 13 is diluted and flows out from the pipe h, is replenished with a new NaOH solution, and is recirculated.
[0011]
In the first concentration chamber 11, there are NH ₄ ions moved from the dilution chamber 10 and OH ions moved from the hydroxide ion chamber 13. The NH ₄ ions and OH ions are reversible between ammonia (NH ₃ ). To react. FIG. 3 shows the results of measuring the abundance ratio of NH ₃ and NH ₄ ions when the indoor pH is changed using temperature as a parameter.
As can be seen from FIG. 3, the reaction shifts to the NH ₃ side as the indoor pH increases. However, the reaction is almost 100% NH even if the temperature changes by maintaining at least the pH of 12 or higher. Equilibrate in the state shifted to the ₃ side. The inside of the first concentration chamber 11 is maintained at such a high pH, at least at such a temperature, by a NaOH solution introduced from the pipe k at a high pH under which the reaction equilibrates to the nearly 100% NH ₃ side. The NH ₄ ions moved into the chamber 11 are separated as gaseous ammonia (NH ₃ ) and can be efficiently taken out and recovered from the pipe i. On the other hand, a liquid containing NaOH flows out from the first concentration chamber 11 through the pipe m, but this is recirculated.
[0012]
[Experimental example]
Next, the Example of this invention comprised like the flow sheet of FIG. 1 is shown.
Condensate demineralized regenerated water containing ammonia nitrogen at 0.3 liter / hour was supplied to the pH adjustment tank 1 from the pipe a, and sulfuric acid was added thereto to adjust the pH to 3. The pH-adjusted reclaimed water was then subjected to solid dial removal to 0.2 ppm as SS with the hollow fiber membrane filter 3 and then introduced into the electrodialysis apparatus 4 for electrodialysis treatment. The effective membrane area of the electrodialysis apparatus 4 is 1.72 dm / pair, and the number of built-in membrane pairs is 1.
A NaOH solution having a concentration of pH 12 was flowed into the hydroxide ion chamber 13 at 0.3 liter / hour, and an NaOH solution having a concentration of pH 12 was flowed into the first concentration chamber at 0.3 liter / hour to maintain the pH at 12. As a result, 1.3 liter / hour of ammonia as a gas was recovered from the pipe i. On the other hand, an NaOH solution substantially free of ammonium ions flowed out from the pipe m.
[0013]
【The invention's effect】
According to the method of the present invention, ammonia nitrogen can be efficiently removed without requiring complicated facilities or a large site area and without consuming a great deal of energy. Furthermore, according to the method of the present invention, ammonia can be easily separated and recovered as a gas, so that environmental problems do not occur, and the recovered ammonia can be effectively used as a resource.
[Brief description of the drawings]
FIG. 1 is a process flow sheet for carrying out the method for removing ammoniacal nitrogen of the present invention.
FIG. 2 is a schematic diagram illustrating the principle of an electrodialysis apparatus used in the method of the present invention.
FIG. 3 is a view showing an equilibrium condition between ammonium ions and ammonia.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 pH adjustment tank 2 Pump 3 Hollow fiber membrane filter 4 Electrodialyzer 5 Anode plate 6 Cathode plate 10 Dilution chamber 11 First concentration chamber 12 Second concentration chamber 13 Hydroxide ion chamber A Anion exchange membrane C Cation exchange membrane

Claims (2)

An acid is added to a liquid containing ammonia nitrogen to precipitate and remove ammonium salts, and a liquid containing ammonium ions is processed by an electrodialysis apparatus 4 in which cation exchange membranes C and anion exchange membranes A are alternately arranged. A method for removing ammonia nitrogen, which is a dialysis unit U of the electrodialyzer 4, a dilution chamber 10 for introducing a liquid containing ammonium ions, and a first concentration adjacent to the cation exchange membrane C side of the dilution chamber 10. Chamber 11, the second concentration chamber 12 adjacent to the anion exchange membrane A side of the dilution chamber 10, and the water in which the hydroxide ion-containing liquid flows adjacent to the anion exchange membrane A side of the first concentration chamber 11 An acid ion chamber 13 is included, and the pH of the first concentrating chamber 11 becomes an equilibrium condition for generating ammonia from ammonium ions moving from the dilution chamber 10 and hydroxide ions moving from the hydroxide ion chamber 13. Maintaining the alkaline method of removing ammonia nitrogen, characterized in that retrieving the ammonia formed from the first concentrating compartment 11 as a gas thereby. The method for removing ammoniacal nitrogen according to claim 1, wherein the pH of the first concentration chamber 11 is maintained at a high alkalinity of 12 or more.

Images