JPH10225617A - Method for removing mercury in combustion gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently remove mercury by bringing the combustion gas contg. mercury and oxygen into contact with the zeolite contg. silver. SOLUTION: Two kg of Na-A type zeolite is introduced into 20l of an aq. 0.72mmol/l silver nitrate soln. and agitated at room temp. for 16hr to exchange silver ion. The zeolite is then cleaned and dried to obtain a zeolite contg. 0.1wt.% silver. Subsequently, 25 pts.wt. of attapulgite is mixed with 100 pts.wt. of the silver-contg. zeolite, the mixture is formed into a pellet having 3mm diameter, and the pellet is calcined at 650 deg.C for 4hr to obtain a mercuty absorbing and removing agent 1. The agent 1 thus prepared is brought into contact with a combustion gas contg. mercury and oxygen to remove the mercury. The used agent 1 is calcined at 200-800 deg.C by using air, reducing gas, etc., and reutilized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing harmful mercury contained in flue gas containing oxygen. More specifically, the present invention relates to a method for removing mercury from waste incineration exhaust gas using a zeolite adsorbent containing silver.

[0002]

2. Description of the Related Art To remove trace amounts of mercury contained in oxygen-free hydrocarbon gas such as naphtha cracked gas and natural gas,
Methods using silver-containing zeolites have been proposed (US Pat. No. 4,892,567, US Pat. No. 4,874,745).
No. 25). It is necessary that the silver in the zeolite used in these methods be used in the form of a metal by a reduction treatment, or in the form of an ion or element.

On the other hand, as a method for removing mercury from refuse incineration exhaust gas in which oxygen coexists, it is known to add a mercury absorbing liquid to a cooling absorption tower or the like for removing hydrochloric acid. As the mercury absorbing solution, a mixed solution of potassium permanganate-sulfuric acid, an aqueous solution of hypochlorous acid-brine, an aqueous solution of thiouric acid, sodium sulfide, sodium thiosulfate and the like are used. However, this method has a problem of treating the wastewater that has absorbed mercury.

[0004] As a method of directly treating waste incineration exhaust gas in the gas phase, a method of contacting the exhaust gas with an activated carbon adsorbent has been proposed (Japanese Patent Application Laid-Open No. 60-129124). Further, a method has been proposed in which carbon powder is injected into exhaust gas to adsorb mercury and then trapped (JP-A-4-34).
No. 6822).

However, these methods are not economical because the mercury removing ability is not sufficient and the adsorbent cannot be regenerated.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for efficiently removing and purifying mercury in a combustion exhaust gas in which oxygen coexists.

[0007]

Means for Solving the Problems As a result of diligent studies on the above-mentioned problems, the present inventors brought silver-containing zeolite into contact with combustion exhaust gas containing mercury and oxygen, and reduced silver by a conventional reduction treatment. It has been found that mercury can be adsorbed on the zeolite side without the need to make it into a metallic, ionic or elemental form, whereby mercury in the combustion exhaust gas can be removed, and the present invention has been completed.

That is, the gist of the present invention is a method for removing mercury from flue gas, which comprises contacting flue gas containing mercury and oxygen with zeolite containing silver.

In the present specification, the term "adsorption" means that mercury is drawn into the zeolite side by various methods, and not only physical adsorption and chemical adsorption but also amalgam. It may mean that it is formed.

Hereinafter, the present invention will be described in more detail.

The type of zeolite used in the method of the present invention is not particularly limited as long as it can contain silver, and A-type zeolite, X-type zeolite,
Y-type zeolite, L-type zeolite, mordenite, ZS
M-5 or the like can be used. Of these, A-type zeolite and X-type zeolite are preferably used from the economical point of view. As the cations in the zeolite, alkali metal ions such as Na and K, hydrogen ions, ammonium ions, and the like are used. When the exhaust gas contains an acidic gas such as hydrochloric acid or a sulfur compound, Ca is used. , Ba, Sr or the like may be used in exchange for alkaline earth metal ions.

The silver raw material (hereinafter referred to as "silver source") contained in the zeolite used in the method of the present invention can be exemplified by silver nitrate, silver oxide, silver chloride, silver sulfate and the like.

The method of incorporating silver into the zeolite is not particularly limited as long as the object can be achieved, but ion exchange, impregnation-supporting, kneading, and physical mixing methods such as dry mixing can be used. it can. Among these, an ion exchange method is mentioned as a method of incorporating silver into zeolite in a higher dispersion. The ion exchange method may be a commonly used method, and is performed by adding zeolite to an aqueous solution in which a soluble silver source such as silver nitrate is dissolved, stirring, washing, and drying. Moreover, it can also be baked as needed. The temperature for firing is 200 ° C to 8 ° C.
It can be carried out at 00 ° C. in an atmosphere of air, nitrogen, reducing gas or the like. The firing time is not particularly limited, but usually about 5 minutes to 50 hours is sufficient.

The content of silver in the zeolite used in the method of the present invention is not particularly limited as long as it can adsorb mercury in the combustion gas sufficiently. The silver content is preferably in the range of 0.01 to 20% by weight, more preferably 0.02 to 2% by weight, based on the total amount of the zeolite contained.

As described above, the zeolite containing silver (hereinafter referred to as "mercury adsorption and removal agent") used in the method of the present invention can be prepared.

The mercury adsorption / removal agent used in the method of the present invention can be used by mixing with a binder such as a clay mineral and molding. Examples of the binder used in molding include clay minerals such as kaolin, attapulgite, montmorillonite, bentonite, allophane, and sepiolite. Alternatively, the mercury adsorption / removal agent may be wash-coated on a cordierite or metal honeycomb substrate and used.

As a method for forming the mercury adsorption / removal agent, a commonly used method, for example, a method such as press molding or tumbling granulation can be employed. The shape of the mercury adsorption / removal agent depends on the specific method of removing mercury in the exhaust gas, such as filling the tower with the mercury adsorption / removal agent or using it in a batch process. As a shape,
A spherical shape, an elliptical spherical shape, a disk shape, a column shape, a pellet shape, and the like can be adopted, and a diameter of about 0.5 to 5 mm is usually used. Further, if necessary, the particles can be classified using a sieve or the like.

The mercury adsorption / removal agent thus prepared removes mercury by contacting with a flue gas containing mercury and oxygen. The combustion exhaust gas to be used in the method of the present invention must be a combustion exhaust gas containing mercury and oxygen, but is also effective when hydrochloric acid, a sulfur compound or the like is contained.

The concentration of mercury contained in the combustion exhaust gas is not particularly limited as long as it is a concentration normally contained.
To obtain better reaction efficiency, 0.1 p
It is preferably from 10 to 10 ppm, more preferably from 1 to 1 ppm.

The concentration of oxygen in the combustion exhaust gas is not particularly limited as long as it is normally contained, but in order to remove mercury more efficiently, the oxygen concentration must be 0.5 to 0.5% by volume. Preferably it is 20%.

The type of the combustion exhaust gas is not particularly limited, but examples thereof include an exhaust gas discharged from an internal combustion engine such as a boiler and a diesel engine, and a waste incineration exhaust gas. Of these, a waste combustion exhaust gas is preferable. Further, among the refuse incineration exhaust gas, the exhaust gas from the cooling absorption tower of the refuse incineration plant and the exhaust gas from the tower bottom tank of the cooling and absorption tower are preferable. Here, the cooling absorption tower is installed to remove hydrochloric acid and sulfur compounds, and a caustic solution is used as the cooling absorption liquid. The bottom tank of the cooling absorption tower is installed as a facility for collecting and circulating cooling absorption water. Further, the waste gas incineration gas may be a waste gas from a dry or semi-dry type removing device for hydrochloric acid and sulfur compounds.

The linear velocity, temperature, etc., for removing mercury in the combustion exhaust gas containing oxygen by the method of the present invention are not particularly limited.
The temperature is preferably 1 to 5 m / s, and the temperature is preferably in the range of room temperature to 100 ° C. The linear velocity is preferably 0.05 to 1 m / s, and the temperature is preferably in the range of room temperature to 70 ° C. Here, the room temperature means an outside air temperature when mercury is removed.

Further, the mercury adsorption / removal agent used in the method of the present invention can be regenerated and reused by firing it with air, a reducing gas or the like after it is actually used. The firing temperature is 200 ° C. to 8
It can be performed at 00 ° C. The firing time is not particularly limited as long as the shape can be maintained, but usually about 5 minutes to 50 hours is sufficient.

[0024]

The present invention will be described below in more detail with reference to Examples. However, the present invention is not limited to only these examples.

Mercury removal rate The concentration of mercury in the gas was measured by a pyrolysis-gold amalgam-cold atomic absorption method based on a fertilizer analysis method (1982 edition). The calculation of the mercury removal rate (where Xn and n are process numbers and are integers of 1 or more and correspond to Examples 1 to 5 shown below) is based on the mercury concentration (H
g-0) and the mercury concentration in the treated gas (Hg-
n, where n is the processing number), Xn (%) = (1-
(Hg-n) / (Hg-0)) × 100.

Example 1 A 20% aqueous solution of 0.72 mmol / L silver nitrate was added with Na-
After injecting 2 kg of A-type zeolite (manufactured by Tosoh Corporation),
The mixture was stirred at room temperature for 16 hours to perform silver ion exchange. Next, it was washed and dried to obtain a silver-containing zeolite having a silver content of 0.1% by weight. Using 25 parts by weight of attapulgite with respect to 100 parts by weight of the silver-containing zeolite, 3 mmφ
And baked at 650 ° C. for 4 hours to obtain a mercury adsorption / removal agent 1.

Example 2 After 2 kg of KA type zeolite (manufactured by Tosoh Corporation) was added to 20 L of a 14 mmol / L silver nitrate aqueous solution, the mixture was stirred at room temperature for 16 hours to exchange silver ions. Subsequently, it was washed and dried to obtain a silver-containing zeolite having a silver content of 2% by weight. Using 100 parts by weight of this silver-containing zeolite, 25 parts by weight of attapulgite was formed into pellets having a diameter of 3 mm and baked at 650 ° C. for 4 hours.
I got

Example 3 Ca-A was added to 20 L of a 1.4 mmol / L silver nitrate aqueous solution.
After charging 2 kg of zeolite (manufactured by Tosoh Corporation), the mixture was stirred at room temperature for 16 hours to perform silver ion exchange. Next, it was washed and dried to obtain a silver-containing zeolite having a silver content of 0.2% by weight. Using 25 parts by weight of attapulgite with respect to 100 parts by weight of this silver-containing zeolite, 3 mmφ
Into a pellet, and calcined at 650 ° C. for 4 hours to obtain a mercury adsorption / removal agent 3.

Example 4 Na-X was added to 20 L of a 1.4 mmol / L silver nitrate aqueous solution.
After charging 2 kg of zeolite (manufactured by Tosoh Corporation), the mixture was stirred at room temperature for 16 hours to perform silver ion exchange. Next, it was washed and dried to obtain a silver-containing zeolite having a silver content of 0.2% by weight. Using 25 parts by weight of attapulgite with respect to 100 parts by weight of the silver-containing zeolite, 3 mmφ
Into a pellet, and calcined at 650 ° C. for 4 hours to obtain a mercury adsorption / removal agent 4.

Example 5 25 parts by weight of attapulgite and an aqueous solution of silver nitrate were added to 100 parts by weight of Na-A type zeolite (manufactured by Tosoh Corporation) so that the silver content in the compact was 0.2% by weight. Then, the mixture was kneaded and formed to obtain a 3 mmφ pellet. Next, the mixture was calcined at 650 ° C. for 4 hours to obtain a mercury adsorption / removal agent 5.

Example 6 A mercury removal test was performed using the mercury adsorption and removal agents 1 to 5 obtained in Examples 1 to 5. A column (inner diameter: 30 mm, height: 50 cm) is packed with 360 cc of a mercury adsorption remover,
Gas simulating waste incineration exhaust gas having the composition shown in Table 1
It flowed at a linear velocity of 0.15 m / s at 5 ° C. Table 2 shows the mercury removal rate after the treatment for 3 hours.

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

According to the mercury removal method of the present invention, it is clear that mercury can be efficiently removed from a combustion exhaust gas containing oxygen, and that it can be used repeatedly.

Claims (3)

[Claims] 1. A method for removing mercury from flue gas, comprising contacting flue gas containing mercury and oxygen with zeolite containing silver. 2. The method for removing mercury in flue gas according to claim 1, wherein the flue gas is refuse incineration flue gas. 3. The removal of mercury in flue gas according to claim 2, wherein the refuse incineration exhaust gas is an exhaust gas from a cooling absorption tower of a refuse incineration plant or an exhaust gas from a bottom tank of the cooling absorption tower. Method.