JP3360854B2 - Exhaust gas treatment method using carbon material - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas containing SOx and NOx, particularly an exhaust gas containing a large amount of SOx but having a small amount of NOx to be removed. The present invention relates to an exhaust gas treatment method suitable for treating wastewater. 2. Description of the Related Art As a method for treating SOx and NOx-containing exhaust gas such as combustion exhaust gas of various fossil fuels or exhaust gas from a sintering furnace of an ironworks, ammonia is added to these exhaust gases, and a moving bed of carbon material is treated. Through a cross flow and contact
There is a method of adsorbing SOx and decomposing and removing NOx. In this method, SOx is adsorbed on the carbon material mainly in the form of sulfuric acid. Therefore, when the amount of SOx contained in the exhaust gas is large, the added ammonia is consumed in the form of ammonium salt, so that the amount of ammonia contributing to the denitration reaction is reduced, and a large amount of ammonia is required to advance the denitration reaction. Ammonia needs to be added and is not economical. In addition, ammonium salts precipitate in the moving bed, especially on the exhaust gas inlet side, block the carbon material, hinder smooth movement in the moving bed, and generate a large amount of ammonia during the regeneration of the carbon material. There is a problem in that it contaminates by-products such as corrosion and recovered sulfur. As a method for solving such a problem, S
When treating an exhaust gas containing a large amount of Ox and containing SOx and NOx, two moving bed reactors are installed, and ammonia is added to the exhaust gas or supplied to the first moving bed without adding ammonia. Mainly to desulfurize and reduce the amount of SOx to 1
There is a method of reducing the concentration to about 00 ppm or less, then adding ammonia, and then supplying the second layer to mainly perform denitration and remove the remaining SOx. This method is an extremely effective method when treating exhaust gas containing a large amount of SOx and having a high content of NOx to be removed. However, in actual exhaust gas, the content of NOx is often small in spite of the large content of SOx, and it is often not necessary to remove the entire amount of NOx when treating the exhaust gas. In such a case, it is inefficient to install two moving bed reactors, and a method capable of treating with one reactor has been desired. In addition, in any of these methods, since the denitration reaction is performed in the presence of free ammonia, there is a problem of so-called leak ammonia, in which ammonia is mixed into the treated exhaust gas. [0004] Further, in order to solve the problems occurring in such a desulfurization and denitration method, attempts have been made to devise a method of adding ammonia. For example, SOx and NO
When ammonia is added to the exhaust gas containing x and supplied to the moving bed of the carbonaceous adsorbent, especially when the temperature is low,
As a method to solve the problem that a large amount of ammonium salt is generated near the exhaust gas inlet and thereby promotes powdering of the adsorbent, ammonia is not directly added to the exhaust gas but ammonia is previously adsorbed. A method of supplying an adsorbent to a moving bed has been proposed (JP-A-2-266).
No. 18, etc.). According to this method, since the ammonia is uniformly supplied into the bed, the ammonium salt is not excessively generated in part and powdering of the adsorbent is reduced,
Further, there is an advantage that ammonia on the downstream side of the gas is used for denitration without being consumed by SOx. However, also in this case, the amount of ammonia corresponding to SOx
Problems such as the consumption of ammonia due to the reaction with x and the presence of leaked ammonia are not much different from the case where ammonia is directly introduced into exhaust gas. Further, a method of using two moving bed reactors, there is a method of increasing the catalytic activity ammoniated After heating reproduced inertness phased carbonaceous catalyst (JP 60-220129 Issue publication). However, also in this method, essentially, the above-mentioned two moving bed reactors are installed, and ammonia is added to the exhaust gas or supplied to the first moving bed without adding ammonia to mainly perform desulfurization. S
There is no difference from the method of reducing the amount of Ox to about 100 ppm or less, then adding ammonia, and then supplying it to the second layer to mainly perform denitration and remove the remaining SOx. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned prior art problems by wasting ammonia by reacting with SOx, obstructing the flow of a moving bed of carbon material due to precipitation of ammonium salts, and treating exhaust gas. An object of the present invention is to provide a simple exhaust gas treatment method using a single moving bed reactor which has no problem such as mixing of ammonia into the inside. [0007] In order to achieve the above object, the present invention provides a desulfurization denitration tower, a regeneration section, and an ammonia treatment.
And a regeneration tower having a cooling section and a SOx of 1
Method for treating exhaust gas containing at least 00 ppm and NOx
And without adding ammonia in the exhaust gas,
From ammonia-treated carbon material flowing down in the desulfurization and denitration tower
Exhaust gas is passed through the moving bed by cross-flow to reduce SOx
NOx is decomposed and removed while being adsorbed on carbon material.
The carbon material exiting the desulfurization and denitration tower at 40
After heating to 0 to 600 ° C. to discharge SO ₂ ,
1 for 1 mole of NOx to be removed in the near processing section
400 to 60 while supplying ~ 1.5 mol of ammonia
Ammonia treatment of carbon material by heating to 0 ° C, then cooling
Means for circulating through the section to the desulfurization and denitration tower . The exhaust gas to be treated by the method of the present invention is:
The exhaust gas has an SOx content of 100 ppm or more and a relatively small amount of NOx to be removed. The allowable range of the NOx content in the exhaust gas that can be treated by this method is determined by the operating conditions such as the supply amount of the carbon material and the reaction temperature and the NOx content rate allowed in the treated exhaust gas. Although it cannot be said, if the amount of NOx to be removed is 3 mg or less per 1 g of the carbon material in the moving bed, the treatment of the present invention can be sufficiently performed. Further, the carbon material used in the present invention includes:
Any activated carbon material having a strength that can be used in a moving bed reactor can be used without any particular limitation, but semi-coke obtained by preliminarily carbonizing coal is used as a main raw material, and coal having cohesive properties is used as an auxiliary material. A molding activated coke obtained by mixing, kneading, adding, binding and kneading, followed by molding, dry distillation, and activation is particularly preferable. Hereinafter, the method of the present invention will be described in detail with reference to a schematic diagram showing an example of a flow according to the exhaust gas treatment method of the present invention in FIG. SOx content is 100ppm
The SOx and NOx-containing exhaust gas described above is discharged from the exhaust gas line 3 to the desulfurization and denitration tower 1 without adding ammonia.
And passed through the moving bed of the carbon material moving from the upper side to the lower side in the column in a cross flow with respect to the flow of the carbon material. During contact with the carbon material, SOx and NOx in the exhaust gas are adsorbed or decomposed and removed, and the treated exhaust gas is discharged out of the system. The carbon material that flows down in the desulfurization and denitration tower 1 and adsorbs and inactivates SOx is discharged from the lower part of the desulfurization and denitration tower, and is guided to the regeneration tower 2 through the inactivation carbon material line 4. Then, 400 to 600 in the regeneration section 2a at the top of the regeneration tower
Heated to ℃ and regenerated. The gas containing SO ₂ at a high concentration generated here is discharged from the SO ₂ -containing gas line 7 and sent to a by-product recovery step, where by-products such as high-purity SO ₂ gas and sulfur or sulfuric acid are recovered. . Regeneration temperature is 40
0 it takes a long time for reproduction is less than ° C., playback there may become insufficient, also, undesirably exceeds 600 ° C. surface properties of the activated carbon material charge is changed when denitration ratio is decreased. The heat-regenerated carbon material is heated to 400 ° C. to 600 ° C. in the presence of ammonia supplied from the ammonia supply line 6 in the ammonia treatment section 2 b downstream of the regeneration tower.
After being heated at the temperature of 3 and subjected to ammonia treatment, the cooling unit 2
After passing through the activated carbon material line 5, the waste gas is discharged from the regeneration tower via c and sent to the desulfurization and denitration tower, where it is recycled. The activated carbon material consumed during circulation may be supplemented by appropriately supplying a new carbon material from outside the system. The amount of ammonia used here depends on the amount of NOx to be removed in the desulfurization and denitration tower.
A practical range is 1 to 1.5 moles per mole. The amount of ammonia used is less than 1 mol or the heating temperature is 400
If the temperature is lower than ℃, the effect of the ammonia treatment is not sufficient. Even if the amount of ammonia used exceeds 1.5 mol, the effect that the excess ammonia contributes to the improvement of the denitration rate is small. On the other hand, if the heating temperature during the ammonia treatment exceeds 600 ° C., the surface properties of the activated carbon material change as in the regeneration treatment, and the denitration rate is undesirably reduced. The ammonia treatment is conveniently carried out in the regeneration tower from the viewpoint of thermal efficiency, but an ammonia treatment device may be provided after the regeneration tower and carried out there. Also,
The regeneration of the activated carbon material and the ammonia treatment are preferably performed continuously using a moving bed type processing apparatus, but can also be performed using a batch type processing apparatus. The carbon material thus treated with ammonia usually contains almost no free ammonia. However, when the amount of free ammonia contained in the carbon material is relatively large, such as when the amount of ammonia used is large, it is inconvenient. Alternatively, the amount of free ammonia can be further reduced by a method such as purging with an inert gas. [0015] The surface of the ammonia-treated carbon material thus obtained is sufficiently activated as a denitration catalyst, and the SOx and NOx-containing exhaust gas having an SOx content of 100 ppm or more is treated using this. In this case, it has a sufficient desulfurization ability without adding ammonia and a denitration performance capable of decomposing about 3 mg of NOx per 1 g of carbon material. [0016] Ammonia treatment in the present invention is not merely to adsorb ammonia on the carbon material, NOx
An active nitrogen group effective for decomposition is generated on the surface of the carbon material to impart activity as a denitration catalyst. Accordingly, the type of the treating agent is not limited to ammonia, and a reducing nitrogen compound such as urea can be used, but ammonia is most suitable. In the method of the present invention, the content of SOx is 1
This method is suitable for treating SOx and NOx-containing exhaust gas which has a large amount of 00 ppm or more but has a relatively small content of NOx to be removed. However, it is needless to say that the method is effective for a gas having a SOx content of less than 100 ppm. is there. EXAMPLES The method of the present invention will be described more specifically with reference to the following examples. (Example 1) A test was performed using activated coke which was repeatedly used in a desulfurization and denitration reaction and had stable performance. A desulfurization and denitration reaction was carried out using this activated coke, and 300 ml of inactivated activated coke was filled in a reaction tube, and the activated coke was placed under a N ₂ atmosphere.
Regeneration was performed by heating at 00 ° C. for 1 hour. Then ammonia 1
A gas diluted with 68 mg of N ₂ was introduced and heated at 500 ° C. for 1 hour to carry out an ammonia treatment. The ammoniated activated coke was cooled N ₂ until purged while _{140 ℃, SO 2 500ppm, NO} 40ppm, O 2 5
%, H ₂ O 7%, and the remaining N ₂ , a mixed gas was introduced, and a desulfurization and denitration test was performed on a fixed bed at SV 400 Hr ⁻¹ and a temperature of 140 ° C. In this test, the integrated denitration rate after 20 hours was 90% (the amount of NOx removed during this period was 0.92 mg in terms of NO ₂ per 1 g of activated coke), and after 70 hours. The integrated denitration rate was 70% (the amount of NOx removed during this period was 1 g of activated coke, N
2.50 mg in terms of O ₂ ). Also, the amount of ammonia used for the treatment of activated coke and the amount of NO removed
The ratio with the amount of x is a molar ratio, and is 2.75 after 20 hours.
It was 1.01 after 70 hours. [0019] (Example 2) addition to the 400 ° C. The regeneration temperature and ammonia treatment temperature <br/> Similarly operating as in Example 1, was subjected to desulfurization and denitrification test. In this test, the integrated denitration rate after elapse of 20 hours was 71%.
(The amount of NOx removed during this period was 0.72 mg in terms of NO ₂ per gram of activated coke), and the integrated denitration rate after 70 hours had passed was 50% (N removed during this period).
The amount of Ox was 1.7 in terms of NO ₂ per gram of activated coke.
8 mg). The ratio of the amount of ammonia used for the treatment of the activated coke to the amount of NOx removed was 3.49 in a molar ratio after 20 hours and 1.42 in a period of 70 hours. . (Comparative Example 1) The ammonia treatment after regeneration was not performed, and 150
Besides the addition of ppm of ammonia in the same manner as in Example 1, it was subjected to desulfurization and denitrification test. In this test, 2
The integrated denitration rate after the lapse of 0 hours is 84% (the amount of ammonia supplied during this period is 254 mg, and the amount of removed NOx is 0.86 m _{2 in} terms of NO ₂ per gram of activated coke.
g). The integrated denitration rate after 70 hours is 5
4% (the amount of ammonia supplied during this period was 889 mg, and the amount of removed NOx was N / g of activated coke.
1.93 mg in terms of O ₂ ). The molar ratio of the amount of ammonia supplied during the desulfurization and denitration reaction to the amount of NOx removed was 4.46 after 20 hours, and 6.94 after 70 hours. From this result, it can be seen that the denitration ratio is lower than in the case of Example 1 even though the supply amount of ammonia is larger. (Comparative Example 2) The ammonia treatment after regeneration was not carried out, and 150
Besides the addition of ppm of ammonia by the same procedure as in Example 2, it was subjected to desulfurization and denitrification test. In this test, 2
The integrated denitration rate after 0 hours is 55% (the amount of ammonia supplied during this period is 254 mg, and the amount of removed NOx is 0.56 m _{2 in} terms of NO ₂ per gram of activated coke.
g). The integrated denitration rate after 70 hours is 2
5% (the amount of ammonia supplied during this period was 889 mg, and the amount of NOx removed was N per 1 g of activated coke.
0.89 mg in terms of O ₂ ). The molar ratio of the amount of ammonia supplied during the desulfurization and denitration reaction to the amount of NOx removed was 6.82 after 20 hours, and 14.99 after 70 hours. From this result, it can be seen that the denitration rate is lower than in the case of Example 2 even though the supply amount of ammonia is larger.
In this test, the integrated denitration rates at the lapse of 20 hours and 70 hours, the amount of NOx removed during this period, and the ratio of the amount of ammonia used for the treatment of activated coke to the amount of NOx removed are shown in Table 1. Show. [Table 1] According to the method of the present invention, the SOx and NOx-containing exhaust gas having a high SOx content of 100 ppm or more, but having a relatively small NOx content to be removed, is discharged into the desulfurization and denitration reactor. The desulfurization and denitration treatment can be efficiently performed by one reactor without coexisting ammonia in the reactor. Also, since ammonia is not consumed by SOx at all, the amount of ammonia used can be greatly reduced as compared with the conventional method, and the amount of free ammonia entering the desulfurization and denitration reactor is extremely small. There is no risk that the carbon material will be blocked due to precipitation of ammonium salt, etc.
There is also an advantage that the problem of leak ammonia does not occur.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing an example of a flow according to an exhaust gas treatment method of the present invention. [Description of Signs] 1 desulfurization and denitration tower 2 regeneration tower 2a regeneration section 2b ammonia treatment section 2c cooling section 3 exhaust gas line 4 inactivated carbon material line 5 activated carbon material line 6 ammonia supply line 7 SO ₂ containing gas line

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification code FI B01D 53/94 B01D 53/36 101A B01J 8/12 ZAB ZAB 331 (72) Inventor Kohei Murayama 1 Hibikicho, Wakamatsu-ku, Kitakyushu-shi, Fukuoka Prefecture 3-chome, Mitsui Mining Co., Ltd. Kyushu Research Laboratory (72) Mitsuhiro Takada 2-1-1, Nihonbashi Muromachi, Chuo-ku, Tokyo Mitsui Mining Co., Ltd. (56) References JP-A-59-73030 (JP, A) JP-A-55-51438 (JP, A) JP-A-49-64568 (JP, A)

Claims (1)

(57) [Claims 1] The use of a desulfurization denitration tower and a regeneration tower having a regeneration section, an ammonia treatment section, and a cooling section, wherein SOx is 1
A method for treating exhaust gas containing at least 00 ppm and NOx, without adding ammonia to the exhaust gas,
Ammonia-treated free ammonia flowing down in a desulfurization denitration tower
Exhaust gas is passed through a moving bed made of a carbon material not containing near gas by cross flow to adsorb SOx on the carbon material,
NOx is decomposed and removed, and then the carbon material exiting the desulfurization and denitration tower is heated to 400 to 600 ° C.
After discharging ₂ , the carbon material is heated to 400 to 600 ° C. while supplying 1 to 1.5 mol of ammonia to 1 mol of NOx to be removed in the ammonia treatment section.
Free ammonia-free charcoal treated with ammonia
Raw material and then the free ammonia free ammonia
A method for treating exhaust gas, comprising circulating a near-treated carbon material through the cooling unit to the desulfurization and denitration tower.