JPH078973A - Liberation of ammonia - Google Patents

Abstract

PURPOSE:To provide a method for liberating ammonia from a waste soln. containing fixed ammonia without generating the clogging problem of an apparatus and economical as compared with a conventional method and a method capable of throwing away a product generated by reaction to the sea. CONSTITUTION:A slurry prepared by preliminarily adding a light burnt magnesium powder to a strong alkali aq. soln. is held for a definite time to be improved in activation capacity and added to a waste soln. containing fixed ammonia to decompose fixed ammonia.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for releasing ammonia from an effluent containing fixed ammonia such as ammonium sulfate and ammonium chloride.

[0002]

2. Description of the Related Art Recently, not only in lakes and marshes, but also in closed sea areas such as Tokyo Bay and the Seto Inland Sea, nitrogen (ammonia),
Eutrophication due to phosphorus has become a problem, and various regulations have become strict.

In order to remove the free ammonia (NH ₃ ) existing in the waste water, the air diffusion method in which the ammonia content is transferred from the water phase to the gas phase and treated by aeration by contacting the waste water with air is an urban sewage treatment system. It is applied to the processing of.

In addition, regarding ammonia stripping, "Chemical Factory" VOL. 20, No. 11, p.
85-91 (1976), "Chemical Factory" VOL. Two
1, No. 12, p. 32 to 35 (1977), a general method for dissipating free ammonia is a distillation column system using steam, in which steam is blown into the wastewater, and the liberated ammonia is converted into ammonia water in a condenser. Although it is collected, it has a drawback that energy cost is required because a large amount of steam is used to heat waste water or vaporize ammonia water and a part of water.

Further, when removing ammonia from an effluent containing so-called fixed ammonia, which is an ammonia salt, sodium hydroxide or calcium hydroxide is added to adjust the pH value to 11 or more, and the ammonium salt is added. After separating it into free ammonia, it is possible to dissipate it using an inert gas such as air, or to supply it to a distillation column as described above and blow steam from below to distill off ammonia. Has been.

It has been widely practiced to release ammonia from fixed ammonia by adding sodium hydroxide or calcium hydroxide. Taking ammonium sulfate as an example, it is represented by the following reaction formula. You can

(NH ₄ ) ₂ SO ₄ +2 NaOH → Na ₂
SO ₄ + 2H ₂ O + 2NH ₃ ↑ (NH ₄ ) ₂ SO ₄ + Ca (OH) ₂ → CaSO ₄ +2
H ₂ O + 2NH ₃ ↑

The alkali used at this time greatly affects the economic efficiency and also has different characteristics.

Although sodium hydroxide has a good reaction efficiency, it is practically problematic because it is expensive and the cost of chemicals becomes enormous when it is carried out on a large scale industrially. Calcium hydroxide is inexpensive, but due to the growth of gypsum crystals generated by the reaction, the heat exchanger and the packed tower are easily clogged, and the operation of the device,
Difficult to manage. In addition, the equipment for separating the product, gypsum, becomes large, which requires construction costs and a vast site. Recently, the marketability of gypsum has become poor and it has become difficult to sell it, and if it is to be discarded, processing costs for disposal will be higher.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of releasing ammonia from an effluent containing fixed ammonia which is more economical than conventional ones and does not cause problems such as clogging of equipment. It is a thing. Furthermore, it is a method that allows the products produced by the reaction to be directly dumped into the sea.

[0011]

According to the present invention, a slurry solution prepared by previously adding lightly burned magnesium powder to a strong alkaline aqueous solution is maintained for a certain period of time to improve the activity, and then the above-mentioned slurry solution is added to a drainage containing fixed ammonia. Is a method of liberating ammonia, characterized in that fixed ammonia is decomposed by adding.

In order to solve the above-mentioned problems, the present invention has been variously studied and inexpensive light-burned magnesium is used as a raw material.

That is, in the light burned magnesium used as a raw material in the present invention, MgC is a basic component often produced in China.
O ₃ Rishomadoite (Magnesite, Magnesite)
Is obtained by firing in a kiln or the like, and is commercially available as powder. Although the composition contains some impurities,
Most are magnesium oxide (MgO).

The activity of the light-baked magnesium is improved by adding it as a powder to an aqueous solution of a strong alkali such as sodium hydroxide or potassium hydroxide and holding it for a while. Although the mechanism that the activity is improved here is unknown, the reactivity of magnesium oxide is improved,
It means that the decomposition reaction of fixed ammonia can be carried out efficiently.

Further, in order to accelerate the above reaction, it is preferable to use light burned magnesium powder as fine as possible, and it is desirable that the average particle size is about 50 μm or less.

Light burned magnesium as a raw material is disclosed in Japanese Patent Publication No. 3-6.
A slurry solution of magnesium hydroxide that has been previously dehydrated with an aqueous alkali solution by the method disclosed in Japanese Patent No. 0774 is called hydromagnesium (hereinafter abbreviated as hydromag).

It is explained in the above-mentioned publication that activated magnesium hydroxide can be obtained by allowing light burned magnesium to have a liquidity of pH 11 or more and being soaked for 2 to 3 hours while being heated to 85 ° C. or more. There is. However, in the present invention, it is not necessary to carry out the activation treatment at high temperature for a long time as described above, and it is possible to improve the target activity by a simpler treatment, decompose the fixed ammonia, and serve to strip ammonia. can do.

On the other hand, as magnesium hydroxide, those sold as a reagent and so-called seawater mugs produced from magnesium chloride in seawater as a raw material are known. That is, since magnesium chloride exists as magnesium in seawater, it is produced by adding magnesium hydroxide to seawater and precipitating magnesium hydroxide by utilizing the difference in solubility based on the following reaction.

MgCl ₂ + Ca (OH) ₂ → CaCl ₂
+ Mg (OH) ₂

These magnesium hydroxides can also be used when liberating ammonia from the effluent containing fixed ammonia as in the present invention, but they are low in efficiency and need to be used in large quantities. However, in both cases, the manufacturing process is complicated, the price is higher than light burned magnesium, and the processing cost is high.

In addition, the commercially available 30% slurry of seawater mug has a very high viscosity and is difficult to handle, and it also has a problem in management of the apparatus because it accompanies a calcium content. The feature is to use one based on lightly burned magnesium without using magnesium oxide.

In the present invention, a solution in the form of a slurry in which the activity of light-baked magnesium as a raw material is improved in advance with a strong alkaline aqueous solution is added to an effluent containing fixed ammonia to decompose the fixed ammonia. When ammonium sulfate is used as an example, it can be represented by the following reaction formula.

(NH ₄ ) ₂ SO ₄ + Mg (OH) ₂ → M
gSO ₄ + 2H ₂ O + 2NH ₃ ↑ (NH ₄ ) ₂ SO ₄ + MgO → MgSO ₄ + H ₂ O + 2
NH ₃ ↑

Although it is not clear which of the above reactions is dominant, there is essentially no difference as a reaction product regardless of which reaction is used. What is important in the present invention is that the light burned magnesium slurry is provided with an activity for decomposing fixed ammonia regardless of the method disclosed in Japanese Patent Publication No. 3-60774, as will be seen from the examples described later. It is possible.

The magnesium sulfate produced as described above has a high solubility in water and is almost dissolved in the liquid. Moreover, since MgSO ₄ is originally a component of seawater, the residual solution containing this can be discharged directly to the sea. Therefore, it is not necessary to provide a process for separating and treating gypsum as in the case of using calcium hydroxide.

In the present invention, the lightly burnt magnesium powder as a raw material is
It is important to treat with an aqueous solution of strong alkali to improve the activity. To improve this activity, it is sufficient to add light-baked magnesium powder to an aqueous solution in which a strong alkali such as sodium hydroxide or potassium hydroxide is dissolved, and keep it at room temperature for a certain period of time. Even more effective, but up to about 50 ° C is sufficient.

The processing time is at least 20 minutes,
It is more preferably 30 minutes or more. The upper limit is not essentially defined, but it is desirable to determine it in consideration of production efficiency.

The ratio of light burned magnesium and strong alkali used is expressed by the equivalent ratio of magnesium content to alkali, and is 0.02 to 0.1, preferably 0.03 to 0.06 with respect to the former 1. It is more preferably around 0.05.

If the light-burning magnesium solution is added to the alkaline aqueous solution prepared in advance as described above to the drainage solution containing the fixed ammonia such as ammonium sulfate or ammonium chloride, the slurry solution having the improved activity is added and reacted. Good. In this case, the light-burned magnesium treated with a strong alkali may be slightly more than 1 mol in terms of an equivalent ratio with respect to the amount of fixed ammonia in the target effluent.

An example of equipment for carrying out the present invention industrially is shown in FIG. FIG. 2 is a conceptual diagram of equipment for releasing ammonia from an effluent containing ammonium sulfate (ammonium sulfate).

The light burned magnesium powder as a raw material is stored in the hopper 1 and, if necessary, charged into the alkali treatment tank 2. An aqueous solution of sodium hydroxide is contained in the alkaline treatment tank 2, and the light-burned magnesium powder is stirred and then maintained for a predetermined time to improve the activity. After that, it is sent to the decomposition reaction tank 3.

On the other hand, the waste liquid containing ammonium sulfate of fixed ammonia passes through the heat exchanger 6 to reach a high temperature (50 to 100).
(.Degree. C.) after being heated by the heat recovered from the treated water, it enters the decomposition reaction tank 3 and reacts in the tank to release ammonia.

The liquid containing free ammonia after the decomposition reaction is sent to the stripping tower 4, where it is contacted with a high temperature gas saturated with water at 50 to 100 ° C. to separate the ammonia content.

The ammonia gas separated in the stripping tower 4 may be recovered as ammonia water or an ammonium compound by a conventional method. Further, the treated water after removing the ammonia can be finally discharged into the sea after heat recovery.

Although the above-mentioned operation is a basic operation, it may be modified if necessary. For example, for the ammonia gas discharged from the outlet of the stripping tower 4, after the ammonia is recovered in the absorption tower 5, the high temperature gas discharged from the absorption tower 5 is sent to the stripping tower 4 again to circulate adiabatically between them. If so, the steam for maintaining the high temperature can be reduced, and the system becomes energy-saving.

As described above, when the gas is adiabatically circulated adiabatically, when it is close to the closed state in the system, the breaker 9 is provided so that the pressure is maintained at 1 atm because the fluctuation of the pressure is large. Further, in order to secure the time for the dissolution and decomposition reaction of the light-burned magnesium, the liquid may be circulated between the decomposition reaction tank 3 and the packed bed of each of the multiple stages in the stripping tower 4. In such a case, the pH may decrease as the emission of ammonia progresses and the emission may worsen. In such a case, a small amount of sodium hydroxide or the like may be added to adjust.

[0037]

【Example】

Examples and Comparative Examples Decomposition reaction was carried out using various alkaline compounds for an effluent containing ammonium sulfate of about 8,000 mg / kg (as N). In the reaction, the above-mentioned drainage was put in a container and heated to a boiling state, and then an aqueous solution of the compound shown in Table 1 was added while stirring the drainage, and the amount of ammonia distilled out was measured and analyzed. During the distillation, pure water corresponding to the amount of distillate was supplied to the container so that the amount of liquid remaining in the container was almost constant. Table 1 also shows the amounts of the compounds used and the amount of effluent added to the fixed ammonia.

[0038]

[Table 1]

The results are shown in FIG. The horizontal axis represents the amount of distilled ammonia water, and the vertical axis represents the amount of residual NH ₄ calculated based on the amount of distilled ammonia.

From Table 1, No. 1 of the present invention is shown. In Nos. 1 and 2, lightly burned magnesium powder (average particle size: about 40 μm) was previously added to an aqueous sodium hydroxide solution, stirred, and then held at room temperature for 30 minutes.

No. Nos. 3 and after are comparative examples. For No. 3, the same lightly baked magnesium powder as described above was added to an aqueous sodium hydroxide solution, and the mixture was stirred and then immediately added to the drainage liquid without waiting time. In addition, No. 4 is light burned magnesium,
No. Nos. 5 and 6 are cases in which magnesium hydroxide as a reagent was added individually, and No. 5 was used. No. 7 is a case where the reagent magnesium hydroxide was added to the aqueous sodium hydroxide solution, stirred, and immediately added to the drainage. No. No. 8 is sodium hydroxide, No. 8 No. 9 is the case where calcium hydroxide was used alone.

From FIG. 1, when light-burnt magnesium is previously treated with sodium hydroxide as in the present invention, ammonia can be liberated more efficiently and in a shorter time than untreated light-burnt magnesium or reagent magnesium hydroxide. Recognize. As the alkali, sodium hydroxide is the most effective, and in the case of the present invention, although it is not as good as sodium hydroxide, it can exhibit a performance close to that of calcium hydroxide.

[0043]

INDUSTRIAL APPLICABILITY The present invention makes it possible to use light-burned magnesium, which has not been used industrially until now, in the decomposition reaction of fixed ammonia contained in waste water, and is produced by the reaction. The compound becomes a water-soluble magnesium salt, and post-treatment is easy.

Further, according to the present invention, unlike the seawater mug, since calcium hydroxide is not accompanied, the operation is easy and the equipment cost,
The cost of chemicals is also advantageous compared to the conventional method. In particular, the present invention is economically advantageous, and when the chemical cost is calculated, light burned magnesium + sodium hydroxide is 1/3 of sodium hydroxide.
Below, it is half or less of calcium hydroxide and seawater mug, and 60% or less compared to hydromug, and it is economically advantageous that the manufacturing process of hydromug can be omitted.

[Brief description of drawings]

FIG. 1 is a graph showing the results of the decomposition reaction of fixed ammonia using various compounds in terms of the amount of residual NH ₄ .

FIG. 2 is a conceptual diagram of equipment for liberating ammonia from an effluent containing ammonium sulfate.

[Explanation of symbols]

 1 Hopper 2 Alkali treatment tank 3 Decomposition reaction tank 4 Emission tower 5 Absorption tower 6 Heat exchanger 7 Circulation pump 8 Circulation blower 9 Breaker 11-24 Piping

Claims (1)

[Claims] 1. A slurry solution prepared by previously adding lightly burned magnesium powder to a strong alkaline aqueous solution is maintained for a certain period of time to improve the activity, and then the above slurry solution is added to a waste solution containing fixed ammonia to remove fixed ammonia. A method for liberating ammonia, characterized by decomposing.