JPH06226103A - Recycling of exhaust gas treatment catalyst and treatment of exhaust gas - Google Patents

Abstract

PURPOSE:To obtain a method of recycling an exhaust gas treatment catalyst by which to make it possible to recycle a catalyst with excellent desulfurization/ denitration activities by water-washing a carbonaceous catalyst used for exhaust gas desulfurization and denitration after thermal treatment. CONSTITUTION:In an exhaust gas treatment device, an exhaust gas is guided to a moving bed reactor 3 filled with a carbonaceous catalyst 4 with ammonia injected from a line 2, through a line 1. Further, the exhaust gas comes in contact with the descending carbonaceous catalyst 4 to be desulfurized/ denitrated. A clean gas after treatment is released into an atmosphere from a line 5. The carbonaceous catalyst 4 in the reactor 3 is extracted from below after exhaust gas treatment, then is heated to 300 to 600 deg.C by a heater 6 in an inert gas atmosphere, and sulfuric acid and its ammonium salt are desorbed as SO2, NH3 and N2. This catalyst 4 after heating is loaded in a separator 7 and the pulverized catalyst and dust are removed. After that, the catalyst 4 is sent to a waver washer 8 to have an alkali metal salt removed by water wash, and is returned to the top of the reactor 3 after drying.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for regenerating an exhaust gas treatment catalyst and an exhaust gas treatment method.

[0002]

As a method for treating exhaust gas containing sulfur oxides (SO _x ) and nitrogen oxides (NO _x ) such as boiler exhaust gas, iron plant sintering exhaust gas, waste incinerator exhaust gas, etc.,
After mixing ammonia with the exhaust gas, a method is known in which the exhaust gas is passed through a single reactor filled with a carbonaceous catalyst such as activated carbon or activated coke to treat SO _{x at} a relatively low temperature, It has the advantages that NO _x can be removed at the same time and that the catalyst can be reused.

In this method, SO _{x in} the exhaust gas, for example SO _2, is converted to sulfuric acid and its ammonium salt (acidic ammonium sulfate, ammonium sulfate, etc.) and adsorbed on the carbonaceous catalyst, as shown in the following formula. SO ₂ + 1 / 2O ₂ + H ₂ O → H ₂ SO ₄ H ₂ SO ₄ + NH ₃ → NH ₄ HSO ₄ NH ₄ HSO ₄ + NH ₃ → (NH ₄ ) ₂ SO ₄ Also, NO _x in exhaust gas, for example NO As shown in the formula, ammonia is reduced to nitrogen and removed. NO + NH ₃ + 1 / 4O ₂ → N ₂ + 3 / 2H ₂ O

In addition to the method using a single reactor as described above, exhaust gas with a high SO _x concentration can be used as it is.
Alternatively, after mixing with ammonia and passing through a first reactor filled with a carbonaceous catalyst to remove most of SO _x in advance, ammonia is mixed with the treated gas leaving the first reactor to obtain A method has been proposed in which the mixed gas is introduced into a second reactor filled with a carbonaceous catalyst and further processed to obtain a high desulfurization rate and a high denitration rate (Japanese Patent Publication No. 63-500).
No. 52).

In any of the above exhaust gas treatment methods, it is necessary to regenerate and recycle the inactivated (deactivated) carbonaceous catalyst after being subjected to exhaust gas treatment. A washing method and a heat treatment method have been proposed.

[0006]

However, in the water treatment method, since the by-product is recovered as dilute sulfuric acid, the equipment is significantly corroded, and the adsorbed oil cannot be desorbed and the performance of the carbonaceous catalyst is deteriorated. There is a problem and it has not been put to practical use.

The heat treatment is carried out by heating the catalyst inactivated by adsorption of sulfuric acid and its ammonium salt (ammonium acid sulfate, ammonium sulfate, etc.) to 300 to 600 ° C., and the sulfuric acid and its ammonium salt are expressed by the following formula. Is decomposed into SO ₂ , NH ₃ , N _{2 and the} like to be eliminated from the catalyst, and the eliminated SO ₂ has the advantage that it can be further reacted and reused as sulfuric acid, sulfur, gypsum and the like.

H ₂ SO ₄ + 1 / 2C → SO ₂ + 1 / 2C
O ₂ + H ₂ O (NH ₄ ) ₂ SO ₄ → 4/3 NH ₃ + SO ₂ + 1 / 3N
₂ + 2H ₂ O NH ₄ HSO ₄ → 1/3 NH ₃ + SO ₂ + 1 / 3N ₂ +
2H ₂ O

However, the exhaust gas contains dust such as an alkali metal salt of K, Na or the like, which is attached to the carbonaceous catalyst. The heat treatment method removes the alkali metal salt. I can't. It is known that this alkali metal salt causes a decrease in the activity of the carbonaceous catalyst for catalytic reduction of NO _x with ammonia, and the carbonaceous catalyst regenerated by the heat treatment method sufficiently recovers the denitration activity. There was a drawback that it could not be done.

Therefore, the first object of the present invention is to remove not only sulfuric acid and its ammonium salt but also alkali metal salt from the catalyst used for exhaust gas treatment, so that the catalyst is excellent not only in desulfurization activity but also in denitration activity. An object of the present invention is to provide a method for regenerating an exhaust gas treatment catalyst that can regenerate the exhaust gas.

A second object of the present invention is to provide an exhaust gas treatment method incorporating a method for regenerating an exhaust gas treatment catalyst that achieves the first object.

[0012]

A method for regenerating an exhaust gas treatment catalyst according to the present invention that achieves the above object is characterized in that a carbonaceous catalyst used for desulfurization / denitration treatment of exhaust gas is heat-treated and then washed with water. To do. In addition, the exhaust gas treatment method of the present invention (hereinafter referred to as the exhaust gas treatment method (I) of the present invention) that achieves the above-mentioned object is an exhaust gas containing sulfur oxides and nitrogen oxides at about 60 to 180 ° C. together with ammonia and carbon. It is characterized in that it is supplied to a moving bed reactor filled with a high quality catalyst for desulfurization / denitration treatment, and the carbonaceous catalyst used for desulfurization / denitration treatment of exhaust gas is heat-treated and then washed with water for regeneration.

Another object of the present invention to achieve the above object
One of the exhaust gas treatment methods (hereinafter referred to as the exhaust gas treatment method (II) of the present invention) is a carbonaceous catalyst filled with an exhaust gas containing sulfur oxides and nitrogen oxides at about 60 to 180 ° C. alone or together with ammonia. After being supplied to the first moving bed reactor and subjected to desulfurization / denitration treatment, ammonia is mixed with the processing gas discharged from the first moving bed reactor, and then the second moving bed reactor filled with a carbonaceous catalyst is mixed. It is characterized in that the carbonaceous catalyst which is supplied and desulfurized / denitrified and the exhaust gas desulfurized / denitrified is heat-treated and then washed with water to be regenerated.

The present invention will be described in detail below. In the method for regenerating the exhaust gas treatment catalyst of the present invention, the catalyst provided for regeneration is
It is a carbonaceous catalyst used for desulfurization and denitration of exhaust gas. Examples of the carbonaceous catalyst include activated carbon, activated coke, and those in which oxides such as vanadium pentoxide and iron are supported.

The method for regenerating an exhaust gas treatment catalyst of the present invention may be carried out on a carbonaceous catalyst which is continuously or intermittently discharged from a reactor during desulfurization / denitration treatment of exhaust gas,
Further, the carbonaceous catalyst discharged from the reactor after the desulfurization / denitration treatment of the exhaust gas may be carried out.

In the method for regenerating an exhaust gas treating catalyst of the present invention, the carbonaceous catalyst used for desulfurizing and denitrifying the exhaust gas is first heat-treated to remove sulfuric acid and its ammonium salt adsorbed on the carbonaceous catalyst. This heat treatment introduces the carbonaceous catalyst into a heater, and in order to prevent the oxidative consumption of the carbonaceous catalyst, in an inert carrier gas atmosphere such as N ₂ , CO ₂ or combustion exhaust gas having a low oxygen content, the temperature is 300 to 600 ° C. It is preferable to carry out at the temperature of. Alternatively, it may be carried out without using any inert carrier gas. The reason why the temperature of 300 to 600 ° C. is preferable is as follows. That is,
When the temperature is lower than 300 ° C, the desorption of sulfuric acid and its ammonium salt adsorbed on the catalyst from the catalyst is not sufficiently performed,
When the temperature exceeds 600 ° C., desorption of sulfuric acid and its ammonium salt from the catalyst is sufficiently carried out, but a large amount of energy is required to raise the temperature. On the other hand, 3
This is because when the temperature is from 00 to 600 ° C., the above problem does not occur, and sulfuric acid and its ammonium salt can be desorbed from the catalyst at a relatively low cost.

According to the method for regenerating an exhaust gas treating catalyst of the present invention, it is preferable to remove the pulverized catalyst and dust by a separator such as a vibrating screen after the heat treatment.

In the method for regenerating the exhaust gas treating catalyst of the present invention, it is an essential requirement to carry out a water washing treatment after the above heat treatment. This water washing treatment is carried out by introducing the catalyst after heat treatment into a vessel for water washing and immersing it in water or spraying (spraying) water. In this case, it may be carried out in a single step, or in several steps. It may be divided into two steps.

As described above, in the catalyst after the heat treatment, alkali metal salts such as Na and K, which have an adverse effect on denitration, remain without being desorbed. Since the alkali metal salt is removed, it is possible to regenerate the catalyst that has recovered not only desulfurization performance but also denitration performance. Also, this washing process differs from the conventional washing method.
Since it is carried out after desorption of sulfuric acid and its ammonium salt, there is no problem of equipment corrosion due to dilute sulfuric acid or generation of ammonia-containing wastewater. The generated wastewater contains a small amount of catalyst powder and dust.
Alternatively, it is possible to directly treat the particles by spraying them into the inlet of a dust collector installed in front of the reactor or the exhaust gas line at the inlet of the reactor.

The catalyst which has been heated and regenerated at 300 to 600 ° C. by the conventional method is usually indirectly cooled by air or water in the lower part of the heating regenerator and then discharged from the heating regenerator. The amount of water adsorbed by the carbonaceous catalyst is extremely low (1% or less), and when this catalyst is circulated and supplied to the upper part of the reactor, the water in the exhaust gas is rapidly adsorbed and the temperature of the catalyst bed rises, which may lead to overheating accident There is. On the other hand, in the present invention, it is possible to circulate the catalyst having the adsorbed water content adjusted to several% to several tens% by performing drying after washing with water in the reactor, so that it is possible to avoid an abrupt temperature rise. is doing.

Next, an exhaust gas treating method (I) of the present invention incorporating the above method for regenerating the exhaust gas treating catalyst will be described with reference to FIG. In the exhaust gas treatment device shown in FIG.
The exhaust gas is introduced into the moving bed reactor 3 filled with the carbonaceous catalyst 4 via the line 1. As is clear from the examples described below, the exhaust gas is 60 to 180 ° C. in the reactor 3.
In particular, it is preferable that the treatment is carried out at a temperature of 100 to 150 ° C. from the viewpoint of increasing the denitration rate, so that it is preferable to control the temperature of the exhaust gas introduced into the reactor 3. The moving bed reactor 3 is preferably a cross flow type.

Ammonia is injected into line 1 through line 2. The exhaust gas mixed with ammonia comes into contact with the carbonaceous catalyst 4 descending in the moving bed reactor 3 to be desulfurized and denitrated. The treated clean gas is discharged to the atmosphere through line 5 directly or through a dust collector. The carbonaceous catalyst 4 in the moving bed reactor 3 is subjected to treatment of exhaust gas, then withdrawn from the lower part of the reactor 3, and heated by a heater 6 under an inert gas atmosphere.
When heated to 00 to 600 ° C., sulfuric acid and its ammonium salt are desorbed as SO ₂ , NH ₃ and N ₂ . The heated catalyst is passed through a separator 7 such as a vibrating screen to remove powdered catalyst and dust. Then, the catalyst is sent to the water washing device 8 and washed with water to remove the alkali metal salt.
The catalyst after washing with water is returned to the upper part of the moving bed reactor 3 by a conveyor after being dried to a predetermined water content. The high temperature SO ₂ gas recovered by the heater 6 is supplied to a manufacturing process of a by-product (sulfuric acid, sulfur, gypsum, etc.) via a line 9.

Next, an exhaust gas treating method (II) of the present invention incorporating the above method for regenerating the exhaust gas treating catalyst will be described with reference to FIG. In the exhaust gas treatment device shown in FIG.
Similar to the exhaust gas treatment method (I), the exhaust gas whose temperature is controlled to 60 to 180 ° C., particularly 100 to 150 ° C. is the first moving bed reaction in which the carbonaceous catalyst 4 is filled through the line 1 alone or together with ammonia. It is introduced into the vessel 3. Exhaust gas is first
After being subjected to desulfurization / denitration (mainly desulfurization) by contacting with the carbonaceous catalyst 4 descending in the moving bed reactor 3 of No. 1, it is discharged from the first moving bed reactor 3. The discharged gas is introduced into the second moving bed reactor 10 via the line 5. At this time, ammonia is injected through the line 2. Exhaust gas is second
Line 12 after desulfurization / denitration (mainly denitration) treatment by contacting with the carbonaceous catalyst 11 descending in the moving bed reactor 10 of
Directly or through dust collection process, and then released into the atmosphere. On the other hand, the carbonaceous catalyst discharged from the second reactor 10 is supplied to the upper portion of the first reactor 3 through the line 13, and the catalyst discharged from the lower portion of the first reactor 3 is heated. 300 to 6 under high temperature inert gas atmosphere in the vessel 6.
Heat treatment is performed at 00 ° C., and sulfuric acid and its ammonium salt are desorbed as SO ₂ , NH ₃ , and N ₂ . The catalyst after the heat treatment is passed through a separator 7 such as a vibrating screen and further washed with water in a water washer 8 and then dried to a predetermined water content,
It is returned to the upper part of the second reactor 10 via a line 14 and is recycled. The heating and washing with water may be carried out continuously for the catalyst discharged from the reactor 3, but only a part of
Alternatively, it may be carried out intermittently at the time when the decrease in the activity of the catalyst becomes remarkable. It may also be performed after the exhaust gas treatment is completed. The high-temperature SO ₂ gas recovered by the heater 6 is supplied to a manufacturing process of by-products (sulfuric acid, sulfur, gypsum, etc.) via a line 9.

[0024]

The present invention will be further described with reference to the following examples.
The invention is not limited to these examples only.

Example 1 An exhaust gas treatment apparatus having a cross flow type moving bed reactor and a heater attached thereto was used. 10,000 Nm ³ / h of coal-fired boiler exhaust gas was introduced into a cross-flow type moving bed reactor filled with a carbonaceous catalyst (activated carbon) of 16.6 m ³ to perform desulfurization and denitration treatment, while being used for exhaust gas treatment. A carbonaceous catalyst was taken out after 3,000 hours from an exhaust gas treating apparatus in which heating and regeneration of the carbonaceous catalyst was carried out at 400 ° C. with a heater, and washed with water as follows. That is, the carbonaceous catalyst discharged from the heater was introduced into a water washing device, and immersed and washed three times with 1.5 liters of water per liter of catalyst to remove alkali metal salts such as K and Na. Next, the carbonaceous catalyst discharged from the water washing device was dried at 120 ° C. for 1 hour to regenerate the carbonaceous catalyst. Since the sulfuric acid and its ammonium salt were quantitatively desorbed by the heat treatment, the carbonaceous catalyst regenerated by washing with water had the same desulfurization performance as the catalyst regenerated by heating. The denitration performance of the carbonaceous catalyst regenerated by washing with water was examined by the following model experiment. That is, after charging 1 liter of the regenerated carbonaceous catalyst into the fixed bed reactor,
_{O 300ppm, NH 3 300ppm, O} 2 3.
A model mixed gas containing 8% and H ₂ O 7.8% and the rest being N ₂ gas was flowed into the catalyst-filled reactor at a rate of 10 liters per minute (SV 600 h ⁻¹ ), and left the reactor. The NO removal rate was determined by measuring the NO concentration in the gas, and compared with the NO removal rate in the case of the regenerated carbonaceous catalyst regenerated only by heat treatment. The results are shown in Figure 3. From FIG. 3, when the exhaust gas treatment temperature in the carbonaceous catalyst-filled reactor is the same temperature, and when the catalyst that has been heat-treated and washed with water is used (see the same figure, solid line (A)), regeneration is performed only by heat treatment. It was revealed that the NO removal rate was higher and the NOx removal performance was superior to the case where the above catalyst was used (see the same figure, dotted line (a)).

Example 2 The same procedure as in Example 1 was carried out except that the iron plant sintering exhaust gas was used in place of the coal-fired boiler exhaust gas. As a result, the desulfurization performance of the regenerated carbonaceous catalyst was the same as in Example 1. Further, as shown in FIG. 3, the denitration performance of the carbonaceous catalyst regenerated by heating and washing with water (solid line (B) in the figure) is the denitration performance of the carbonaceous catalyst regenerated only by the heat treatment (FIG. 3). It was far superior to the dotted line (b)) in FIG.

[0027]

As described in detail above, according to the present invention,
By removing not only sulfuric acid and its ammonium salt but also alkali metal salts from the catalyst that has been subjected to desulfurization / denitration treatment of exhaust gas, it is possible to regenerate a catalyst excellent in desulfurization activity and denitration activity, and a method for regenerating an exhaust gas treatment catalyst and An exhaust gas treatment method incorporating the method for regenerating this exhaust gas treatment catalyst has been provided.

[Brief description of drawings]

FIG. 1 is a schematic view showing an exhaust gas treatment method of the present invention.

FIG. 2 is a schematic view showing another exhaust gas treatment method of the present invention.

FIG. 3 is a graph showing the relationship between the exhaust gas treatment temperature and the NO removal rate of the carbonaceous catalyst.

[Explanation of symbols]

1 ... Line, 2 ... Line, 3 ... Moving bed reactor, 4 ... Carbonaceous catalyst, 5 ... Line, 6 ... Heater, 7 ... Separator, 8 ... Water washer, 9 ... Line, 10 ... Moving bed reactor , 11 ... Carbonaceous catalyst, 12 ... Line, 13 ... Line, 14 ... Line.

Claims (3)

[Claims] 1. A method for regenerating an exhaust gas treatment catalyst, which comprises heat-treating a carbonaceous catalyst that has been subjected to desulfurization / denitration treatment of exhaust gas and then washing with water. 2. An exhaust gas containing sulfur oxides and nitrogen oxides at a temperature of about 60 to 180 ° C. is supplied together with ammonia to a moving bed reactor filled with a carbonaceous catalyst for desulfurization / denitration treatment and desulfurization of exhaust gas. A method for treating exhaust gas, which comprises subjecting a carbonaceous catalyst that has been subjected to denitration treatment to heat treatment, followed by washing treatment with water and regeneration. 3. Desulfurization and denitration treatment by supplying exhaust gas containing sulfur oxides and nitrogen oxides at about 60 to 180 ° C. alone or together with ammonia to a first moving bed reactor filled with a carbonaceous catalyst. Then, ammonia is mixed with the process gas discharged from the first moving bed reactor and supplied to the second moving bed reactor filled with a carbonaceous catalyst for desulfurization / denitration treatment, and desulfurization / denitration of exhaust gas. A method for treating exhaust gas, which comprises subjecting a carbonaceous catalyst subjected to treatment to heat treatment, followed by washing treatment with water and regeneration.