JP3381973B2 - 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.

[0002]

2. Description of the Related Art Ammonia (NH ₃ ) is mixed with combustion exhaust gas from boilers containing sulfur oxides (SOx) and nitrogen oxides (NOx), sintering furnace exhaust gas from iron mills, waste incinerator exhaust gas, etc. A method of desulfurizing and denitrifying exhaust gas by passing it through a cross-flow moving bed reactor filled with a carbonaceous catalyst such as activated carbon or activated coke is well known.

According to this method, in addition to the advantage that desulfurization and denitration are simultaneously performed by the action of the carbonaceous catalyst, the chemical consumption in the heating regeneration of the carbonaceous catalyst is reduced, and the carbon is repeatedly used by adsorption and regeneration. There is an advantage that the activity of the quality catalyst is improved.

By the way, in this method, when the amount of treated gas increases, a large amount of carbonaceous catalyst is required.
Among the carbonaceous catalysts, low-quality carbonaceous catalysts that are inexpensive, have low activation, and have a small specific surface area (usually 100 to 300 m ² / g) are used.

[0005]

However, when this low-quality carbonaceous catalyst is used, the initial desulfurization / denitration performance is inferior and it takes 1000 to 2000 hours or more to obtain the desired performance. . The reason why a long period of time is required until the desired desulfurization / denitration state is obtained is that the NH ₃ gas injected for denitration causes a small amount due to gasification of carbon constituting the carbonaceous catalyst during heating and regeneration. This is because the development of pores is suppressed and the increase in specific surface area becomes slow.

This problem can be solved by using a high-quality carbonaceous catalyst having high activity instead of the low-quality carbonaceous catalyst for the initial filling, but not only the cost becomes high, but also the high quality having a large specific surface area is provided. The carbonaceous catalyst causes another problem that it is easy to cause a temperature rise in the catalyst packed bed and is apt to ignite.

In addition, at the beginning of exhaust gas treatment, NH
_A method has also been proposed in which the exhaust gas is desulfurized without injecting _3, and NH ₃ is injected after the carbonaceous catalyst is activated by the repeated use of the carbonaceous catalyst to inject the exhaust gas to desulfurize and denitrate. 63-1889 gazette). Although this method is excellent, it is still insufficient in that it requires several hundred hours to reach the desired performance.

Further, in the case of the moving bed system, it is possible to improve the desulfurization / denitration rate to some extent by operating at a high catalyst transfer amount, but there is a drawback that the mechanical wear due to the movement of the catalyst becomes large. However, there is a problem that the activated catalyst surface is worn and scraped off, which delays the activation.

Therefore, an object of the present invention is to provide an exhaust gas treatment method capable of obtaining desired desulfurization / denitration performance from the initial stage of operation of exhaust gas treatment even when a low-quality carbonaceous catalyst is used.

[0010]

The above-mentioned object of the present invention is to
Exhaust gas containing Ox and NOx is introduced into a moving bed reactor filled with a carbonaceous catalyst for desulfurization / denitration treatment in the presence of NH ₃ , while the carbonaceous catalyst is inactivated by contact with the exhaust gas. In the method for treating exhaust gas in which the carbon dioxide is heated and regenerated in the regenerator, it was achieved by introducing an oxygen-containing gas into the regenerator to oxidize and activate the carbonaceous catalyst before the start of the desulfurization and denitration treatment.

Therefore, according to the present invention, exhaust gas containing sulfur oxides (SOx) and nitrogen oxides (NOx) is introduced into a moving bed reactor filled with a carbonaceous catalyst to desulfurize in the presence of NH _3. In the exhaust gas treatment method in which the carbonaceous catalyst deactivated by contact with the exhaust gas is heated and regenerated in the regenerator while performing the denitration treatment, an oxygen-containing gas is introduced into the regenerator before the desulfurization / denitration treatment operation is started. A method for treating exhaust gas is characterized in that a carbonaceous catalyst is oxidized and activated.

[0012]

[Operation] When the exhaust gas is introduced into a moving bed reactor filled with a carbonaceous catalyst to perform desulfurization / denitration treatment in the presence of NH ₃ ,
Sulfuric acid (H ₂ SO ₄ ), acidic ammonium sulphate (NH ₄ HSO ₄ ), ammonium sulphate ((NH ₄ ) ₂ SO ₄ ), etc. are adsorbed on the carbonaceous catalyst that has been inactivated by contact with the exhaust gas. The reaction that occurs when this catalyst is heated and regenerated in the regenerator is very complicated and difficult to clarify, but it is presumed that the following reaction occurs in the regenerator.

H ₂ SO ₄ → SO ₃ + H ₂ O (1) (NH ₄ ) ₂ SO ₄ → NH ₄ HSO ₄ + NH ₃ (2) NH ₄ HSO ₄ → NH ₃ + SO ₃ + H ₂ O (3) 2 / 3NH ₃ + SO ₃ → SO ₂ + H ₂ O + 1 / 3N ₂ (4) SO ₃ + 1 / 2C → SO ₂ + 1 / 2CO ₂ (5) SO ₃ + C → C ... O + SO ₂ (6) C ... O + NH ₃ → C ... Red (7) (Note that C ... O in the formulas (6) and (7) is considered to be an acidic oxide in which carbon (C) and oxygen (O) are bound, but its binding form is unknown. C in formula (7)
... Red is considered to be a basic nitrogen compound in which carbon (C) and a reducing compound (Red) are bound to each other, but the binding form thereof is unknown. ) Sulfuric acid, acidic ammonium sulfate, and ammonium sulfate adsorbed on the catalyst are decomposed into SO ₃ , NH ₃ , and H ₂ O by the reactions of formulas (1) to (3), and most of NH ₃ is represented by formula (4). The reaction decomposes into N ₂ . Also, SO ₃ is calculated by the formula (5)
Is simultaneously reduced to SO ₂ by the reaction of, and at the same time, carbon is gasified to cause the development of pores. Furthermore, equations (6) and (7)
The reaction also proceeds to produce an acidic oxide effective for the denitration reaction and a basic nitrogen compound effective for the desulfurization reaction.

When NH ₃ is injected from the beginning of the operation according to the conventional method, the reaction of the formula (4) occurs at a high rate, and the erosion of the catalyst due to the reaction of the formula (5) does not proceed and the development of pores slows down. Then, the production of the acidic oxide exhibiting the denitration activity by the reaction of the formula (6) is delayed, and the production of the basic nitrogen compound effective for the desulfurization activity produced by the reaction of the formula (7) is also delayed.

According to the method of the present invention, when the carbonaceous catalyst is brought into contact with the oxygen-containing gas before the start of operation, the reaction of the following formula proceeds.

C + O ₂ → CO ₂ (8) C + 1 / 2O ₂ → CO (9) C + O ₂ → C ... O (10) That is, the carbon constituting the carbonaceous catalyst is changed by the reactions of the formulas (8) and (9). When gasified, the pores develop and the specific surface area increases. Further, the reaction of the formula (10) produces an acidic oxide C ... O effective for the denitration reaction, and this acidic oxide further reacts with NH ₃ according to the reaction represented by the above formula (7) to be effective for the desulfurization reaction. A basic nitrogen compound (C ... Red) is produced.

Therefore, according to the exhaust gas treatment method of the present invention,
The desired desulfurization / denitration performance can be obtained immediately after the start of the desulfurization / denitration treatment operation.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of an apparatus for carrying out a general exhaust gas treatment method.

In FIG. 1, the exhaust gas containing SOx and NOx is mixed in line 1 with the ammonia supplied via line 2 and introduced into a cross flow type moving bed reactor 3. The exhaust gas introduced into the reactor 3 is 60-18
It is preferable that the temperature is controlled to about 0 ° C.

After the exhaust gas comes into contact with the carbonaceous catalyst bed 4 descending in the reactor 3 for desulfurization and denitration treatment, the clean gas leaving the reactor 3 is discharged directly or through a dust collector into the atmosphere from a line 5. Is released to.

The carbonaceous catalyst inactivated in the reactor 3 is withdrawn from the lower part of the reactor 3 and supplied to the regenerator 6. The carbonaceous catalyst desorbs SOx by being heated to 300 to 500 ° C. in the regenerator 6 under an inert gas atmosphere (under an inert gas supply or under an SO ₂ gas atmosphere generated without using an inert gas). Then played.

The regenerated carbonaceous catalyst is circulated to the upper part of the reactor 3 via a line 8 by a conveyor or the like after removing powdered catalyst and dust by a separator 7 such as a vibrating screen. On the other hand, the high-concentration SOx-containing gas recovered by the regenerator 6 is sent to a by-product manufacturing process of sulfuric acid, sulfur, gypsum, etc. via the line 9.

In the exhaust gas treatment method shown in FIG. 1, when an inexpensive low-quality carbonaceous catalyst is used, as described above,
It takes a long time after the desulfurization / denitration treatment is started to obtain desired desulfurization / denitration performance. Therefore, according to the present invention, an oxygen-containing gas is introduced into the regenerator to oxidize the carbonaceous catalyst before the start of the desulfurization / denitrification operation, and the specific surface area is increased by the development of pores in the carbonaceous catalyst. At the same time, it produces an acidic oxide and a basic nitrogen compound on the carbonaceous surface to activate the carbonaceous catalyst in advance.This enables the desired desulfurization / denitration performance from the start of desulfurization / denitration treatment operation. Can be obtained.

Contacting the oxygen-containing gas with a carbonaceous catalyst,
FIG. 2 shows an example of the structure of the regenerator when the catalyst is activated.

In FIG. 2, the new carbonaceous catalyst before the desulfurization / denitration treatment operation is circulated in the desulfurization / denitration apparatus.
The carbonaceous catalyst exiting the bottom of the moving bed reactor 3 is stored in the storage region 11 located at the top of the regenerator 6 and then flows down to the mixing region 12a. The carbonaceous catalyst in the mixing area 12a is then sent to the separation area 14a via the heat transfer tube 13.
After being rectified by the rectifier 15, it is discharged from the lower part of the regenerator 6 as shown in FIG. 1, passed through the separator 7, and then circulated to the top of the moving bed reactor 3 by the line 8. In addition,
The carbonaceous catalyst in the heat transfer tube 13 is supplied to the heating region 17 from the line 16 and is heated to a desired temperature (100 to 400 ° C.) suitable for oxidation by the heating gas discharged from the line 18.
(The temperature when the exhaust gas treatment is performed is 300 to 500 ° C.).

On the other hand, the oxygen-containing gas is supplied from the line 19 to the mixing region 12a and flows in parallel with the carbonaceous catalyst in the heat transfer tube 1.
Line 2 which descends in 3 and is provided above the separation region 14a
It is discharged from the system from 0.

According to the embodiment shown in FIG. 2, the oxygen-containing gas is mixed in the mixing area 12a, the heat transfer tube 13 and the separation area 14.
In step a, the carbonaceous catalyst is activated by contacting with the carbonaceous catalyst so that desired desulfurization / denitration performance can be obtained from the beginning of the desulfurization / denitration treatment operation.

In FIG. 2, lines 19 and 20 are used as an inert gas supply line and an exhaust line after the start of the desulfurization / denitrification operation. The line 19 is closed when no inert gas is used.

In the embodiment of FIG. 3, the oxygen-containing gas is supplied through the line 20.
The regenerator 6 is further supplied to the lower mixing region 14b, and the heat transfer tubes 13 and the upper separation region 12b are sequentially raised,
It differs from the embodiment of FIG. 2 in that it is discharged from the line 19 after being brought into countercurrent contact with the descending carbonaceous catalyst.

The oxygen-containing gas may be of any type as long as it contains oxygen at a concentration capable of activating the carbonaceous catalyst. For example, clean gas after exhaust gas treatment, untreated exhaust gas, gas for heating carbonaceous catalyst, air, or an inert gas such as nitrogen or oxygen added thereto to adjust the oxygen concentration can be used.

In order to maximize the effects of the present invention, as the carbonaceous catalyst, a low-quality one having a low cost, a low activation rate and a small specific surface area is used. Specific examples thereof include coal, which is a carbon-containing substance, pitch, wood, plant-derived substances such as coconut husks, those obtained by activating plastics or the like by carbonization or further steam, and further improve the catalytic activity. For this reason, those supporting metal oxides such as vanadium, iron and copper may be used.

In the present invention, the oxygen-containing gas is supplied to the carbonaceous catalyst in the regenerator 6 not only before the desulfurization / denitrification treatment is started, but also after the start of the operation to activate the carbonaceous catalyst. In this case, a mixed gas obtained by adding a small amount of oxygen-containing gas to an inert gas may be supplied from the line 19 to the mixing region 12a above the regenerator 6 in the embodiment of FIG.
In the embodiment of FIG. 3, the line 20 is supplied to the mixing region 14b below the regenerator 6. In addition, in this case, the regenerator 6 has a temperature gradient, and normally the upper mixing region 12a is
Alternatively, the temperature of the separation region 12b is about 100 to 200 ° C., and the temperature of the lower separation region 14a or the mixing region 14b is about 300.
Since the temperature of the latter is higher than the temperature of the former, when the temperature of the latter is 400 ° C. or higher, when the oxygen-containing gas is introduced according to the embodiment of FIG. It occurs rapidly and the catalyst surface is incinerated. Therefore, it is preferable to adopt the mode of FIG. 2 in which the oxygen-containing gas is supplied to the upper mixing region 12a having a low temperature.

Generally, the carbonaceous catalyst heated in the regenerator 6 is directly or indirectly cooled with air, water or the like, but that portion is omitted in FIGS. 2 and 3. .

The present invention is applicable not only to the exhaust gas treatment method shown in FIG. 1 using one moving bed reactor,
It is also applied to an exhaust gas treatment method using a moving bed reactor having more than one base. For example, an exhaust gas containing SOx and Nox is directly or after being mixed with NH ₃ , introduced into a first moving bed reactor filled with a carbonaceous catalyst for desulfurization / denitration treatment, and then NH ₃ is added to the treated gas. Is introduced into a second moving bed reactor filled with a carbonaceous catalyst for desulfurization and denitration treatment, while the carbonaceous catalyst inactivated by contact with the exhaust gas is heated and regenerated. By applying the invention, desired desulfurization / denitration performance can be obtained from the initial stage of the desulfurization / denitration treatment operation.

In the present invention, when the carbonaceous catalyst is treated with the oxygen-containing gas in the regenerator, NH ₃ is allowed to coexist or is treated with the oxygen-containing gas and then further treated with the NH ₃ gas. The quality catalyst can be further activated.

Reactivation by NH ₃ gas containing no oxygen does not cause carbon oxidation, and therefore the temperature is not particularly limited, but from room temperature to 300 to 500 ° C. which is the maximum temperature of the regenerator.
It is convenient to set to.

The present invention will be described in detail below with reference to experimental examples.

Experimental Example 1 A fixed bed reactor having an inner diameter of 52.7 mm was charged with 1 liter of new activated carbon, and 0.5 liter / min at a temperature of 250 ° C.
At this point, air was supplied for 48 hours to activate the activated carbon. Then, as the first cycle, 100 ppm of SO ₂ , 20
N ₂ with 0 pm NO, 5% O ₂ and 8% H ₂ O
280 ppm NH ₃ gas was injected into the gas, and the mixed gas was introduced into the above reactor at 145 ° C. for 30 hours and the flow rate was 0.6N.
It was passed at m ³ / h (corresponding to a space velocity of 600 h ⁻¹ ) and the SO ₂ removal rate and NO removal rate, which varied with the gas passing time, were measured.

After the test of the first cycle was completed, the activated carbon was regenerated at 400 ° C. for 3 hours under N ₂ stream. Second after playback
As a cycle, the mixed gas containing SO ₂ and NO was passed through the reactor under the same conditions, and the SO ₂ removal rate and NO removal rate were measured. Further, the same repeated test was performed up to 5 times. The result of NO removal rate after 30 hours of passing gas is shown in the curve (a) of FIG.

In Comparative Experimental Example 1, the NO and SO ₂ removal rates were measured in the same manner as in Experimental Example 1 except that activation by air was not performed. The result of the NO removal rate is shown in the curve (b) of FIG.

As is apparent from the results of FIG. 4, the activated carbon activated by air has a significantly improved denitration performance,
It was discovered that the denitration performance was stable at an early stage. The SO ₂ removal rate was 100% in each cycle of Experimental Example 1 and Comparative Experimental Example 1.

Experimental Example 2 A fixed bed reactor having an inner diameter of 52.7 mm was charged with 1 liter of new activated carbon, and at a temperature of 250 ° C., 0.5 liter / min.
At this point, air was supplied for 48 hours to activate the activated carbon. After that, N ₂ gas containing 0.5% NH ₃ at 400 ° C. was further supplied at 0.5 liter / min for 10 hours for reactivation. After the activation operation was completed, the first cycle was 1000 ppm SO ₂ , 200 ppm NO, 5
750 pp for N ₂ gas containing 10% O ₂ and 8% H ₂ O
m ₃ NH ₃ gas was injected, and this mixed gas was passed through the above reactor at 145 ° C. for 30 hours at a flow rate of 0.6 Nm ³ / h (corresponding to a space velocity of 600 h ⁻¹ ) and changed with the gas passage time. The SO ₂ removal rate and the NO removal rate were measured.

After the test of the first cycle was completed, the activated carbon was regenerated at 400 ° C. for 3 hours under N ₂ stream. Second after playback
As a cycle, the above mixed gas was passed through the reactor under the same conditions, and the SO ₂ removal rate and the NO removal rate were measured. Further, the same repeated test was performed up to 5 times. The results of the NO removal rate of 30 hours after the passing gas curve of Fig. 5 (a1), SO ₂
The result of the removal rate is shown in the curve (a2) of FIG.

As Comparative Experimental Example 2, NO and SO ₂ removal rates were measured in the same manner as in Experimental Example 2 except that activation by air and reactivation by NH ₃ were not performed. The results of NO removal rate and SO ₂ removal rate are shown in the curve (b1
) And the curve (b2) in FIG.

As is clear from the results shown in FIG. 5, the activated carbon after being activated with air and then reactivated with NH ₃ has significantly better desulfurization / denitration performance, and stabilizes to high performance at an early stage. I understand.

[0047] Experimental Example 3 of the exhaust gas as shown in FIG. 1 the new activated carbon catalyst was 1.67 m ³ filled in desulfurization and denitrification apparatus consisting regenerator and 1000 Nm ³ / h at a processable moving bed reactor, passing the exhaust gas Before the treatment, the amount of catalyst transferred was set to 35 kg / h and the activated carbon was circulated and transferred in the system. At this time, set the maximum temperature of the regenerator (volume 0.2 m ³ ) to 250 ° C. and set it to 5 m ³
A combustion exhaust gas (combustion exhaust gas for heating the regenerator, having an O ₂ content of 4%) was supplied at a flow rate of / h. This operation was continued for 5 cycles to activate the activated carbon. Next, when the activated carbon transfer rate was 18.5 kg / h, SO ₂ 500 ppm, NOx 20
After mixing 700 ppm of NH ₃ with 1000 Nm ³ / h of boiler exhaust gas containing 0 ppm of NH ₃ , it was supplied to the reactor to treat the exhaust gas.

The results of the obtained NOx removal rate and SO ₂ removal rate are shown by the curves (a1) and (a2) in FIG.

As Comparative Experimental Example 3, the exhaust gas was treated in the same manner as in Experimental Example 3 except that the activated carbon was not activated before the operation (before the exhaust gas treatment). The obtained NOx removal rate and SO ₂ removal rate results are shown in curves (b1) and (b2) of FIG.
).

As is clear from FIG. 6, when the activated carbon was activated before the operation, it became clear that the removal rate was stabilized at a high rate significantly earlier than when it was not treated.

[0051]

EFFECTS OF THE INVENTION According to the present invention, there is provided a method capable of obtaining desired desulfurization / denitration performance from the start of operation of exhaust gas treatment even when a low quality carbonaceous catalyst is used.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an apparatus for carrying out a general exhaust gas treatment method.

FIG. 2 is a diagram showing an example of a regenerator suitable for carrying out the method of the present invention.

FIG. 3 is a diagram showing another example of a regenerator suitable for carrying out the method of the present invention.

FIG. 4 is a graph showing the NO removal rate in Experimental Example 1.

FIG. 5 is a graph showing NO and SO ₂ removal rates in Experimental Example 2.

FIG. 6 is a graph showing NOx and SO ₂ removal rates in Experimental Example 3.

[Explanation of symbols]

1,2,5,8,9 lines 3 moving bed reactor 4 Carbonaceous catalyst 6 regenerator 7 separator 11 Storage area 12a mixing area 12b separation area 13 Heat transfer tube 14a separation area 14b Mixed area 15 Rectifier 16, 18, 19, 20 lines 17 Heating area

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ identification code FI B01D 53/94 (58) Fields investigated (Int.Cl. ⁷ , DB name) B01D 53/60, 53/56 B01D 53/83 , 53/86

Claims (3)

(57) [Claims] 1. Exhaust gas containing sulfur oxides and nitrogen oxides is introduced into a moving bed reactor filled with a carbonaceous catalyst for desulfurization / denitration treatment in the presence of NH ₃ , while exhaust gas In a method for treating exhaust gas in which a carbonaceous catalyst inactivated by contact is heated and regenerated in a regenerator, an oxygen-containing gas is introduced into the regenerator before the operation of desulfurization / denitration treatment is started to oxidize the carbonaceous catalyst, A method for treating exhaust gas, which is characterized by being activated. 2. The method according to claim 1, wherein the desulfurization / denitration treatment is carried out in one or more moving bed reactors. 3. When the carbonaceous catalyst is treated with the oxygen-containing gas in the regenerator, NH ₃ is allowed to coexist, or after the treatment with the oxygen-containing gas, the carbonaceous catalyst is further treated with the NH ₃ gas. The method for treating exhaust gas according to claim 1 or 2, which is activated.