JP3483288B2 - Exhaust gas treatment method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating exhaust gas, and more particularly, to recovering and reusing a carbonaceous catalyst powdered by treating exhaust gas as a granular carbonaceous catalyst having a low dust content. The present invention relates to a method for treating exhaust gas that enables the above.

[0002]

2. Description of the Related Art A moving bed reactor containing a carbonaceous catalyst such as activated carbon after injecting ammonia into an exhaust gas containing sulfur oxides (hereinafter referred to as SOx) and nitrogen oxides (hereinafter referred to as NOx) The SOx in the exhaust gas is adsorbed on the carbonaceous catalyst for desulfurization while simultaneously contacting the exhaust gas with the carbonaceous catalyst in a cross-flow, and at the same time, NOx is reacted with ammonia to denitrate. It is known as a desulfurization denitration method. In this method, the carbonaceous catalyst that adsorbs SOx and is discharged from the bottom of the reactor is transferred to a regenerator for heating and regeneration, and the regenerated carbonaceous catalyst is circulated to the above reactor again. It is customary.

Such a flue gas desulfurization denitration method utilizing a moving bed not only can treat exhaust gas containing dust, but also has an advantage that it does not have the trouble of waste water treatment as seen in the wet method. However, pulverization of the carbonaceous catalyst could not be avoided due to the use of the moving bed.
The pulverized carbonaceous catalyst is incinerated in a boiler or the like, and it is necessary to replenish with a new carbonaceous catalyst commensurate with the amount of the pulverized carbonaceous adsorbent.

On the other hand, in Japanese Patent Publication No. 61-61855, a powdered carbonaceous catalyst generated along with the movement of the carbonaceous catalyst is recovered and regenerated into a granular carbonaceous catalyst to produce the moving bed. A method of circulating to the reactor is disclosed.

[0005]

SOx in exhaust gas,
Dust is contained in addition to NOx, so that dust is mixed in the pulverized carbonaceous adsorbent generated by the movement in the moving bed reactor. If the dust concentration in the exhaust gas introduced into the reactor is several tens mg / Nm ³ or less, the powdered carbonaceous catalyst can be molded and regenerated into a granular carbonaceous adsorbent having a small dust content. Dust concentration in exhaust gas is 100m
If it is g / Nm ³ or more, the amount of dust in the pulverized carbonaceous catalyst becomes very large, so that even if the granular carbonaceous catalyst is molded and regenerated, only a very high dust content is obtained. Therefore, in the method described in Japanese Patent Publication No. 61-61855, only the pulverized carbonaceous catalyst generated in the heating regenerator, in which dust is substantially removed, is molded and regenerated to obtain a granular carbonaceous catalyst. However, this method has a drawback that the reuse ratio of the pulverized carbonaceous catalyst is low.

Therefore, an object of the present invention is to treat an exhaust gas capable of molding and regenerating a granular carbonaceous catalyst having a small dust content from a pulverized carbonaceous catalyst with a high recovery rate even when the dust concentration in the exhaust gas is high. To provide a method.

[0007]

The present invention has been made in order to achieve the above-mentioned object, and after injecting ammonia into exhaust gas containing sulfur oxide or sulfur oxide and nitrogen oxide, the front catalyst bed is used. And a cross-flow type moving bed reactor divided into a rear catalyst bed and dust in the exhaust gas in the front catalyst bed, and then desulfurization or desulfurization in the rear catalyst bed.
While performing denitration treatment, after being subjected to exhaust gas treatment, the carbonaceous catalyst in the rear catalyst bed was regenerated by a heating regenerator, and the heated and regenerated granular carbonaceous catalyst and the pulverized carbonaceous catalyst were separated,
The gist is a method for treating exhaust gas, which comprises recovering a pulverized carbonaceous catalyst and molding and regenerating it into a granular carbonaceous catalyst.

[0008]

The present invention will be further described with reference to the following examples.

Example 1 FIG. 1 shows an apparatus used in the method for treating exhaust gas in this example. The method for treating exhaust gas in this example will be described below with reference to FIG.

In FIG. 1, SOx or SOx and NOx
After injecting ammonia into the exhaust gas containing carbon, it is introduced via line 1 into a cross flow type moving bed reactor 2 filled with a granular carbonaceous catalyst. The exhaust gas introduced into the reactor 2 is 6
It is preferable that the temperature is controlled to about 0 to 180 ° C. The cross-flow type moving bed reactor 2 is divided into a front catalyst bed 4 and a rear catalyst bed 5 by a porous partition 3 such as a screen and a louver, and the front catalyst bed 4 and the rear catalyst bed 4 are separated. The volume ratio with the catalyst bed 5 is set to 1: 5.

The exhaust gas introduced into the reactor 2 first contacts the front carbonaceous catalyst bed 4 descending in the reactor 2 to remove dust, and then contacts the rear catalyst bed 5 for desulfurization.
It is denitrified. It is needless to say that desulfurization or desulfurization / denitration is partially performed in the front catalyst bed 4. Then, the processing gas is discharged to the atmosphere via the line 6 directly or after being subjected to dust collection processing.

On the other hand, the carbonaceous catalyst discharged from the bottom of the front catalyst bed 4 in the reactor 2 captures dust in the exhaust gas and contains a lot of dust. Therefore, the carbonaceous catalyst is pulled out from the bottom portion and the dust and the catalyst are separated by the screen 7. The separated catalyst is combined with the carbonaceous catalyst discharged from the bottom of the rear catalyst bed 5, and then supplied to the heating regenerator 9 through the line 8. The catalyst is heated in the regenerator 9 at 300 to 600 in a high temperature inert gas atmosphere.
The catalyst powder is regenerated by heating to 0 ° C., the catalyst powder is separated by a separator 10 such as a vibrating screen, and then circulated to the top of the reactor 2 through a line 11.

On the other hand, the high-concentration SOx-containing gas recovered by the heating regenerator 9 is subjected to cleaning treatment, etc.
Via, it is sent to the process for recovering by-products such as sulfuric acid, sulfur, gypsum, etc.

The pulverized carbonaceous catalyst separated and recovered by the screen 10 is further pulverized by a pulverizer 13, and then a binder such as pitch and tar is optionally added together with water and kneaded by a kneader 14. Then, it is formed into granules by the forming machine 15. In this case, the finely powdered carbonaceous catalyst may be mixed with coal powder, which is a raw material of the carbonaceous catalyst, or the like, and similarly molded.
It should be noted that coal and pitch may be added by the crusher 13 and pulverized together with the pulverized carbonaceous catalyst. The molded product is carbonized and activated in a furnace 16 such as a kiln in the presence of steam at about 700 to 1000 ° C. Carbonization and activation may be performed separately. In this case, carbonization is about 400 to 700 ° C. and activation is about 700 to 700 ° C.
It is performed at 1000 ° C. The regenerated catalyst molding is fed to the top of the reactor 2 via lines 17 and 11, or to the top of the regenerator 9 via lines 17 and 19.

According to this embodiment, the front carbonaceous catalyst bed 4
Since the dust in the exhaust gas can be removed with, the catalyst discharged from the rear carbonaceous catalyst bed is partially pulverized, but the dust content is small. Therefore, the catalyst with a small dust content is sent to the heating regenerator, and after heating and regenerating, the pulverized carbonaceous catalyst separated from the heated and regenerated granular carbonaceous catalyst (the one pulverized in the rear catalyst bed, the heating regenerator). (Including those pulverized in step 1) also has a small dust content, so by molding and regenerating this, a granular carbonaceous catalyst having a low dust content can be obtained.

Further, according to the present embodiment, in addition to the carbonaceous catalyst pulverized by the heating regenerator, the carbonaceous catalyst pulverized in the catalyst bed at the rear can be molded and regenerated into the granular carbonaceous catalyst. There is an advantage that the reuse rate of the catalyst is extremely high.

By the way, as a carbonaceous catalyst for dry desulfurization / denitration, a relatively large particle catalyst is used from the viewpoint of pressure loss (usually,
The diameter is about 4 to 20 mm, and the length is about 5 to 30 mm). In order to produce such a large-sized carbonaceous catalyst, it is necessary to activate the inside (gasification of carbon to develop pores). This is difficult and requires a large kiln, or requires a long residence time in the kiln for the furnace, resulting in very poor productivity. However, in this example, the pulverized carbonaceous catalyst to be molded and regenerated has pores developed and its surface area increased due to the circulating use of the exhaust gas treatment device.
Therefore, there is an advantage that activation after granulating the pulverized carbonaceous catalyst can be carried out very easily.

Further, since the pulverized carbonaceous catalyst contains a nitrogen compound which improves desulfurization or denitration activity, there is also an advantage that the molded and regenerated granular carbonaceous catalyst has excellent catalytic activity.

Example 2 FIG. 2 shows an apparatus used in the method for treating exhaust gas in this Example. The difference from the apparatus used in Example 1 is that the moving bed reactor 2 has two There is one inlet, one for the front catalyst bed and one for the rear catalyst bed. In the exhaust gas treatment method of this example, the following substances (a) and / or (b) were used instead of the carbonaceous catalyst used in Example 1 in the front catalyst bed 4.
Is filled.

(A) A substance having a dust removing function in exhaust gas, for example, silica sand, limestone, coke or iron ore,
Ore such as sinter or bauxite or ceramics such as alumina.

(B) Contains vanadium, iron, copper, manganese, tungsten, etc. on the basis of substances having a function of removing dust in exhaust gas and denitrifying exhaust gas, such as activated alumina, titanium oxide, activated silica, zeolite, etc. Dust removal and denitration catalyst.

The substances (a) and / or (b) in the front catalyst bed 4 come in contact with the exhaust gas introduced through the line 1 while descending through the catalyst bed 4 to remove dust in the exhaust gas. Remove. When the above-mentioned substance (b) which also has a denitration action is used, denitration is performed together with the removal of dust.

The substances (a) and / or (b) which have been subjected to the removal of dust and have become dust-containing are guided to the screen 7 from the bottom of the front catalyst bed 4 to remove the dust. , Through the line 18 from the inlet for the front catalyst bed to the front catalyst bed 4. When the catalyst performance deteriorates, the dust may be removed by the screen 7, followed by heating regeneration (usually 250 to 500 ° C.) and supply to the front catalyst bed 4 via the line 18.

According to this embodiment, since the dust in the front catalyst bed 4 is removed by using a substance other than the carbonaceous catalyst, the total amount of the pulverized carbonaceous catalyst generated in the exhaust gas treatment is the same as in the above embodiment. Kneading, molding, carbonization, as in 1
After the activation treatment, there is an advantage that it can be molded and regenerated into a granular carbonaceous catalyst having a small dust content.

Although the present invention has been described with reference to the first and second embodiments, the present invention includes the following application examples and modifications.

(1) In Examples 1 and 2, the volume ratio between the front catalyst bed and the rear catalyst bed was set to 1: 5, but the volume ratio is not limited to this value and is usually 1: 5. 1-1: 20
It is appropriately determined between The parameters for determining the volume ratio are the type of substance packed in the front catalyst bed for removing dust, the content of dust in the exhaust gas and SOx, N
For example, the content of Ox.

(2) When coal powder, which is a raw material for the carbonaceous catalyst, is added when the powdered carbonaceous catalyst is molded and regenerated,
Various types of coal can be used, but the use of caking coal such as bituminous coal has the advantage of reducing the amount of binder such as pitch and tar required for molding. In addition, the use of coal powder that has been previously oxidized or previously subjected to carbonization (carbonization) has the advantage that activation becomes easier.

(3) Vanadium in powdered carbonaceous catalyst,
By adding a compound such as iron, copper or manganese, molding, and carbonizing and activating the compound, a granular carbonaceous catalyst having more excellent performance can be obtained.

(4) In Examples 1 and 2, the pulverized carbonaceous catalyst was molded and recycled into the granular carbonaceous catalyst in the exhaust gas treating apparatus and reused. It can also be transported to the carbonaceous catalyst manufacturing plant of and remolded there.

(5) In Examples 1 and 2, the regeneration of the pulverized carbonaceous catalyst in the moving bed reactor and the heating regenerator was explained. However, the pulverized carbonaceous catalyst generated in the exhaust gas treating apparatus (for example, catalyst transportation) Needless to say, a pulverized carbonaceous catalyst generated in a conveyor or air transportation) or a pulverized carbonaceous catalyst generated in another device is also a target of regeneration in the present invention.

Next, the method of the present invention will be described with reference to experimental examples.

Experimental Example (a) SO ₂ 500 whose dust was previously removed by an electrostatic precipitator
ppm, NOx 200ppm, dust 150mg / N
10000 Nm ³ / h of boiler exhaust gas containing m ³ was taken out, NH ₃ was mixed with 300 ppm of this, and the mixture was introduced into the exhaust gas treatment apparatus (dry desulfurization / denitration apparatus) shown in FIG. 1. The moving bed reactor is divided into two parts by a screen, the front catalyst bed is filled with 4.17 m ³ of activated carbon, and the rear catalyst bed is filled with 20.8 m ³ of activated carbon. The residence time of activated carbon in the front catalyst bed was set to 20 hours, and the residence time of activated carbon in the rear catalyst bed was set to 45 hours. The dust-rich activated carbon discharged in the catalyst bed in front of the reactor was separated by the lower screen and fed to the regenerator, and the dust-rich activated carbon powder separated by the screen was discarded. All other activated carbon powder was collected. The breakdown of the activated carbon powder was 2.6% of dust and 97.4% of activated carbon powder, and the activated carbon powder having a very small dust content was recovered (this recovered material is referred to as A).

As a comparative experimental example, the result of recovering all of the active carbon powder generated in the catalyst bed in front of the reactor was as follows:
The dust content was 18.6% and the activated carbon powder content was 81.4%, and the dust content was remarkably high (this collected product is referred to as B).

15% pitch for each of recovered materials A and B
The mixture was added and mixed and pulverized to 50 mesh or less, a small amount of water or the like was added thereto, and the mixture was kneaded, and then pressure-molded into a granular body of about 10 mmφ × 12 mm. Each molded body was activated with steam at a temperature of 900 ° C. to produce regenerated activated carbon (regenerated activated carbon A and regenerated activated carbon B, respectively).

1 liter of each of them was packed into a reaction tube having an inner diameter of 5 cm as a fixed bed. SO ₂ 500pp
m, NO 200 ppm, O ₂ 6%, H ₂ O 7% and N ₂ gas were mixed with 350 ppm of NH _3, and the mixed gas was heated to 140 ° C. in each reactor at 0.4 hour / hour.
The mixture was passed through at a flow rate of Nm ³ / h for 100 hours, and changes in SO ₂ removal rate and NO removal rate with time were measured. For comparison, when starting the operation of the above-mentioned exhaust gas treatment device, with respect to the fresh granular activated carbon (new activated carbon) supplied to the exhaust gas treatment device, changes with time in SO ₂ removal rate and NO removal rate were measured under the same conditions. did. Passing gas for each activated carbon sample 10
Table 1 shows the results of the SO ₂ removal rate after 0 hour and the NO removal rate after passing gas for 20 hours.

As shown in Table 1, the regenerated activated carbon A is superior in its performance to the regenerated activated carbon B produced by using the pulverized activated carbon having a large dust content as a raw material, and the regenerated activated carbon C is remarkably superior in performance to the new activated carbon C. It turns out that is excellent.

[0037]

[Table 1]

Experimental Example (b) An exhaust gas treating apparatus was operated in the same manner except that the catalyst in front of the reactor of Experimental Example (a) was filled with alumina balls having a diameter of 4 mm. In this case, the breakdown of the recovered activated carbon powder was 3.2% dust and 96.8% activated carbon powder (this recovered product is referred to as C).

To the recovered material, 15% of pitch was added and mixed and pulverized to 50 mesh or less, and a small amount of water or the like was added and kneaded, and then pressure-molded into a granular body of about 10 mmφ × 12 mm,
Regenerated activated carbon was produced in the same manner as in Experimental Example (a) (this is referred to as regenerated activated carbon C). Further, 50% of coal (Brown coal briquette produced in Australia) was mixed with the recovered material C to similarly produce regenerated activated carbon (this is referred to as regenerated activated carbon D). 1 liter of fixed bed reactor was filled with each regenerated activated carbon,
Similar to the experimental example (a), changes with time of SO ₂ removal rate and NO removal rate were measured. As shown in Table 2, the regenerated activated carbon C showed good performance. Also, with respect to the regenerated activated carbon produced by mixing coal, it was possible to obtain the one having a performance higher than that of the new activated carbon shown in Table 1.

[0040]

[Table 2]

[0041]

As described above, according to the present invention, the carbonaceous catalyst pulverized by treating the exhaust gas can be regenerated into a granular carbonaceous catalyst having a small dust content with 100% or an extremely high recovery rate. A method was provided.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an apparatus used for exhaust gas treatment in Example 1.

FIG. 2 is a schematic diagram of an apparatus used for exhaust gas treatment in Example 2.

[Explanation of symbols]

1 line 2 moving bed reactor 3 Porous partition 4 Front catalyst bed 5 Rear catalyst bed 6 lines 7 screen 8 lines 9 heating regenerator 10 separator 11 lines 12 lines 13 crusher 14 Kneader 15 molding machine 16 furnaces 17 lines 18 lines 19 lines

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ identification code FI B01D 53/81 53/96 (58) Fields surveyed (Int.Cl. ⁷ , DB name) B01D 53/96

Claims (7)

(57) [Claims] 1. An ammonia gas is injected into an exhaust gas containing sulfur oxides or sulfur oxides and nitrogen oxides, and then introduced into a cross-flow moving bed reactor divided into a front catalyst bed and a rear catalyst bed. After removing dust in the exhaust gas in the front catalyst bed, desulfurization or desulfurization / denitrification treatment is performed in the rear catalyst bed, while the carbonaceous catalyst in the rear catalyst bed used for exhaust gas treatment is regenerated with a heating regenerator. After that, the particulate carbonaceous catalyst that has been heated and regenerated is separated from the pulverized carbonaceous catalyst, the pulverized carbonaceous catalyst is recovered, and the exhaust gas treatment method is characterized by molding and regenerating the granular carbonaceous catalyst. . 2. The front catalyst bed is made of a granular carbonaceous catalyst, and the carbonaceous catalyst is used for removing dust in the exhaust gas, and then sent to the dust separator from the bottom of the front catalyst bed to remove the dust. The method according to claim 1, which is sent to a heat regenerator after separation. 3. The front catalyst bed is made of a substance having a function of removing dust in the exhaust gas, and the substance is used for removing dust in the exhaust gas and then sent to the dust separator from the bottom of the front catalyst bed. The method of claim 1, wherein the dust is separated and then circulated to the top of the front catalyst bed. 4. The method according to claim 3, wherein the substance having a dust removing action is selected from the group consisting of silica sand, limestone, coke or iron ore, sinter, ores such as bauxite, or ceramics such as alumina. . 5. The front catalyst bed is made of a substance having a dust removal effect in exhaust gas and a denitration effect on the exhaust gas, and the substance is subjected to dust removal in the exhaust gas and denitration of the exhaust gas, and then the bottom part of the front catalyst bed. 2. The process according to claim 1, which is sent to a dust separator from which the dust is separated and then circulated to the front catalyst bed. 6. Dust removal containing vanadium, iron, copper, manganese, tungsten, etc., based on at least one substance selected from activated alumina, titanium oxide, activated silica and zeolite as a substance having a dust removing and denitrifying action. The method according to claim 5, which is a denitration catalyst. 7. The method according to claim 1, wherein the pulverized carbonaceous catalyst is mixed with coal, which is a raw material for the carbonaceous catalyst, to regenerate a molded carbonaceous catalyst.