JPH1015345A - Combustion exhaust gas purification method and apparatus - Google Patents

Abstract

(57) [Problem] To improve the denitration performance when purifying combustion exhaust gas containing nitrogen oxides and sulfur oxides, and prolong the life of the denitration catalyst. SOLUTION: A moving bed type desulfurization layer 3 in which a combustion exhaust gas 1 containing a nitrogen oxide and a sulfur oxide is first filled with a desulfurizing agent 4 is provided.
The desulfurizing agent 4 is introduced from a direction perpendicular to the moving direction of the desulfurizing agent 4 and desulfurized. The exhaust gas after desulfurization is divided into two or more according to the degree of desulfurization activity of the desulfurization layer 3. The separated exhaust gas is individually temperature-controlled by the exhaust gas temperature-controlling devices 5a and 5b, respectively, and then subjected to ammonia catalytic reduction and denitration in the denitration layers 7a and 7b. [Effect] Purification of combustion exhaust gas with high denitration performance and long life of the denitration catalyst can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for producing nitrogen oxides (NOx) and sulfur oxides (SOx) contained in flue gas, particularly flue gas containing NOx and SOx generated in a sintering process of an ironworks. The present invention relates to a method and an apparatus for purifying combustion exhaust gas in which desulfurization is performed by a moving-bed type desulfurization layer filled with a desulfurizing agent, and then ammonia-catalytic reduction and denitration is performed by a denitration layer filled with a manganese dioxide catalyst.

[0002]

2. Description of the Related Art As a method for purifying exhaust gas generated from a sintering process in an ironworks, as described in "Fuel Conversion and SOx / NOx Countermeasure Technology" (published by Project News, p. After the combustion exhaust gas at 150 ° C is wet desulfurized by the lime / gypsum method, high-performance dust removal is performed by a wet electric precipitator, and the exhaust gas is further heated to 400 ° C by a gas-gas heat exchanger and a heating furnace. A method for catalytic reduction denitration is known. As the catalyst to cause ammonia catalytic reduction denitration, for example, "fresh catalyst Chemistry" (Sankyo Shuppan, page 109) as described in, V ₂ O ₅ -TiO ₂ based catalyst most widely known.

On the other hand, for example, JP-A-6-210138 discloses that a flue gas is first introduced into a moving bed type desulfurization layer filled with a desulfurizing agent such as iron ore from a direction perpendicular to the moving direction of the desulfurizing agent. A method is disclosed in which, after desulfurization, exhaust gas from which SO _{2 has been} removed is subjected to ammonia catalytic reduction denitration using a manganese dioxide-based catalyst such as a Mn ore catalyst.

However, the gas processing method for denitration by V ₂ O ₅ -TiO ₂ based catalyst after wet desulfurization by lime-gypsum method, a large amount becomes process-produced gypsum is a big problem in the desulfurization process, the denitrification process , V ₂ O ₅
-To advance the denitration reaction on the TiO ₂ -based catalyst,
It is necessary to raise the temperature of the sintering exhaust gas of 00 to 150 ° C. to about 300 to 400 ° C., which requires enormous gas heating costs, and that the V ₂ O ₅ —TiO ₂ based catalyst is expensive. It becomes a problem.

On the other hand, the flue gas is first introduced into a moving-bed type desulfurization layer filled with a desulfurizing agent from a direction perpendicular to the moving direction of the desulfurizing agent and dry desulfurized, and then manganese dioxide such as a manganese ore catalyst is used. gas treatment method for ammonia catalytic reduction denitration by system catalysts for desulfurization, that post-treatment of desulfurization by-product is easy, for denitration, manganese-based catalysts dioxide compared with V ₂ O ₅ -TiO ₂ based catalyst Since the denitration reaction can proceed at low temperature, V ₂ O ₅ —TiO
_It has the advantages of significantly reducing gas heating costs compared to _2- system catalysts, and the fact that manganese dioxide-based catalysts such as manganese ore are inexpensive, and is an excellent method for desulfurization and denitration of sintering exhaust gas. I can say. The ammonia-catalytic reduction denitration activity of the manganese dioxide-based catalyst appears at a low temperature of about 100 ° C., and the initial denitration activity increases as the reaction temperature increases.

[0006]

However, after the flue gas is introduced into the moving bed type desulfurization layer in a direction perpendicular to the moving direction of the desulfurizing agent and dry desulfurized, the catalyst is subjected to ammonia catalytic reduction denitration with a manganese dioxide catalyst. in gas treatment method, the SO ₂ in few ppm levels leaks downstream of the denitration layer without being desulfurized in the desulfurization layer manganese dioxide catalyst is poisoned, the denitration performance gradually decreases, especially the reaction when the temperature is high Is a significant disadvantage that the denitration performance is significantly reduced. Therefore, when denitration is performed at a low temperature, the denitration performance decreases slowly but the initial denitration performance is low.On the other hand, when denitration is performed at a high temperature, the initial denitration performance is high but the degradation of the denitration performance is fast, and the DeNOx performance is low. Therefore, it is desired that the manganese dioxide-based catalyst has high denitration performance and a long catalyst life.

Accordingly, an object of the present invention is to provide a method and an apparatus for purifying combustion exhaust gas having high denitration performance and a long life of a denitration catalyst.

[0008]

According to the method for purifying combustion exhaust gas of the present invention, a combustion exhaust gas containing nitrogen oxides and sulfur oxides is first transferred to a moving bed type desulfurization layer filled with a desulfurizing agent in a moving direction of the desulfurizing agent. In the flue gas purification method of introducing from the vertical direction and desulfurizing, then introducing into a denitration layer filled with a manganese dioxide catalyst and performing ammonia catalytic reduction denitration, the exhaust gas after passing through the desulfurization layer is divided into at least two or more, This is a method for purifying combustion exhaust gas, wherein the temperature of each of the divided exhaust gases is individually adjusted and denitration is performed.

As a method of dividing the exhaust gas after passing through the desulfurization layer, a method of dividing the exhaust gas according to the degree of the desulfurization activity, specifically, a method of dividing the exhaust gas into a plurality according to the remaining amount of SO ₂ is preferable. The temperature of the exhaust gas divided in a state where SO ₂ remains remains as low as possible to prevent SO ₂ from reacting with a manganese dioxide catalyst to form manganese sulfate, and react with ammonia to react with ammonium sulfate or acidic ammonium sulfate. The reaction temperature may be adjusted to produce an ammonium compound such as

[0010] Further, the combustion exhaust gas purifying apparatus of the present invention converts a combustion exhaust gas containing nitrogen oxides and sulfur oxides into a moving bed type desulfurization layer filled with a desulfurizing agent in a direction perpendicular to the moving direction of the desulfurizing agent. In a combustion exhaust gas purifying apparatus for introducing and desulfurizing, and then introducing into a denitration layer filled with a manganese dioxide catalyst and performing catalytic NOx reduction by ammonia, at least two exhaust gases passing through the desulfurization layer are provided after the moving bed type desulfurization layer. A flue gas purifying apparatus characterized in that the flue gas is divided into two or more parts and each of the divided flue gases is provided with a temperature control device for increasing the temperature of the flue gas and a denitration layer thereafter.

According to the present invention, the factor of the decrease in the denitrification performance of a manganese dioxide catalyst due to SO ₂ depends on the reaction temperature. When the reaction temperature is low, ammonia compounds such as ammonium sulfate and ammonium ammonium sulfate produced by the reaction of SO ₂ and ammonia ( SO ₂ + 2NH ₃ + H ₂ O + 1 / 2O ₂ → (NH ₄ )
₂ SO ₄ , SO ₂ + NH ₃ + H ₂ O + ／ O ₂ → NH
₄ HSO ₄ or the like is the main cause of the decrease in the denitration performance, while when the reaction temperature is high, manganese dioxide reacts with SO ₂ to form manganese sulfate (reaction formula: MnO ₂ + SO ₂ → MnSO). ₄ ) is the main cause of the decrease in the denitration performance, and the decrease in the denitration performance of the manganese dioxide catalyst was made based on the finding that the influence of manganese dioxide conversion to manganese sulfate was particularly large.

In the method for purifying combustion exhaust gas of the present invention,
The flue gas is introduced into the moving bed type desulfurization layer filled with the desulfurizing agent from the direction perpendicular to the moving direction of the desulfurizing agent and desulfurized,
The combustion exhaust gas after the desulfurization treatment is divided into at least two or more, and appropriate temperature control and ammonia catalytic reduction denitration are performed on each of the divided exhaust gas. By dividing the exhaust gas that has passed through the desulfurization layer into two or more, it is divided into exhaust gas according to the degree of desulfurization, and appropriate denitration can be performed according to the respective desulfurization state of the divided exhaust gas. As a result, the denitration rate can be increased as a whole, and the manganese dioxide catalyst life can be prolonged.

First, the method of desulfurizing exhaust gas with a moving bed type desulfurization layer is not particularly limited as long as it is a cross-flow moving bed system in which combustion exhaust gas is introduced from a direction perpendicular to the moving direction of a desulfurizing agent and desulfurized. There is nothing to do. The type of the desulfurizing agent is not particularly limited as long as it has high desulfurizing performance. For example, a carbonaceous substance such as activated carbon or iron ore can be used as the desulfurizing agent. The residence time of the desulfurizing agent varies depending on the equipment specifications.

The exhaust gas that has passed through the desulfurization layer is divided according to the degree of desulfurization activity, and it is preferable to divide the exhaust gas according to the remaining amount of SO ₂ . Usually, SO ₂ is free from almost no SO ₂ remaining (for example, a desulfurization rate of 99%).
%) And an exhaust gas in which SO ₂ remains (for example, a desulfurization rate of 99% or less). SO
_The exhaust gas in which ₂ remains may be further divided into a plurality according to the degree of the remaining amount of SO ₂ (desulfurization rate). Then, the divided exhaust gas is heated and adjusted by a temperature adjusting device in accordance with the remaining amount of SO ₂ , and then ammonia is added to the exhaust gas.

The adjusting heating of the exhaust gas, the SO ₂ free flue gas to a high temperature, to adjust the exhaust gas SO ₂ remained in the low temperature is desirable to improve denitrification rate. Since the manganese dioxide-based catalyst does not turn into manganese sulfate for the SO ₂ -free gas, it is possible to maintain a high denitration rate for a long time by adjusting the temperature to a high temperature and denitrating. In addition, the gas in which SO ₂ remains remains as low as possible so that the SO ₂ does not react with the manganese dioxide-based catalyst to form manganese sulfate and reacts with ammonia to produce an ammonium compound. To denitrate. As a result, it is possible to suppress a decrease in the denitration performance and to reduce the gas heating cost.

The denitration layer may be either a moving layer or a fixed layer. The residence time of the manganese dioxide catalyst in the case of a moving bed varies depending on the equipment specifications. As the manganese dioxide catalyst used for denitration, in addition to a commercially available manganese dioxide catalyst, manganese ore containing manganese dioxide is preferable,
The specific surface area is 1 m ² / g or more, and the size is 1 to 100.
A mm diameter is desirable.

[0017]

FIG. 1 shows an example of a combustion exhaust gas purifying apparatus according to the present invention. The combustion exhaust gas 1 containing NOx and SO ₂ is sent to the moving bed type desulfurization layer 3 filled with the desulfurizing agent 4 through the exhaust gas pipe 2 from a direction perpendicular to the moving direction of the desulfurizing agent 4 to perform dry desulfurization. The desulfurizing agent 4 introduced from above the desulfurization layer 3 has a high desulfurization activity at the upper portion of the desulfurization layer 3 and can be almost completely desulfurized, but gradually loses the desulfurization activity as it descends in the desulfurization layer 3. Tiki, desulfurization layer 3
The desulfurization rate decreases in the lower part of. Therefore, in the present invention, the exhaust gas after desulfurization is divided into at least two or more. FIG.
Is an example in which the exhaust gas having a high desulfurization activity passing through the upper portion of the desulfurization layer 3 and the exhaust gas having a low desulfurization activity passing through the lower portion of the desulfurization layer 3 are divided into two. The division may be made into three or more parts depending on the degree of the desulfurization activity.

The exhaust gas after the division is treated by providing a temperature control device for raising the exhaust gas temperature and a denitration layer for each exhaust gas. In the case of this example, a temperature controller 5a and a denitration layer 7a are provided for exhaust gas having a high desulfurization activity, and a temperature controller 5b and a denitration layer 7b are provided for each exhaust gas having a low desulfurization activity. I have.

Before sending the exhaust gas whose temperature has been increased by the temperature control devices 5a and 5b to the denitration layers 7a and 7b, an ammonia addition device 6a is provided in a gas pipe connecting the temperature control devices 5a and 5b and the denitration layers 7a and 7b. Add ammonia via 6b.

The denitration layers 7a and 7b may be either a moving layer or a fixed layer. When the fixed layers are used, manganese dioxide is periodically used to prevent the denitration layers from being blocked by dust contained in exhaust gas. It is desirable to extract the system catalyst and remove accumulated dust.

The exhaust gas after the denitration is discharged from the exhaust gas pipe 2 through the chimney 8.

[0022]

Next, the present invention will be further described with reference to examples.

When the gas temperature is 100 ° C. and NOx is 200 pp
A combustion exhaust gas containing 150 ppm of m and SO ₂ was purified using the apparatus of the present invention shown in FIG. On the other hand, an example in which the purification treatment was performed without dividing the exhaust gas was also performed for comparison.

The processing conditions were as shown in Table 1.

[0025]

[Table 1]

The conditions for dividing the exhaust gas and the conditions for raising the temperature of the exhaust gas are as shown in Table 2.

[0027]

[Table 2]

With respect to the denitrated gas treated under the above conditions, the results of analyzing the NOx concentration and SO ₂ concentration in the gas are also shown in Table 2. As is clear from Table 2, according to the present invention, high denitration performance was obtained. As a result, the service life of the denitration catalyst was extended.

[0029]

According to the method and apparatus for purifying combustion exhaust gas of the present invention, high denitration performance can be obtained and the life of the manganese dioxide-based denitration catalyst can be extended.

[Brief description of the drawings]

FIG. 1 is a diagram showing one example of a combustion exhaust gas purifying apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Combustion exhaust gas 2 Exhaust gas pipe 3 Desulfurization layer 4 Desulfurizer 5a, 5b Temperature control device 6a, 6b Ammonia addition device 7a, 7b Denitration layer 8 Chimney

Claims (5)

[Claims] 1. A flue gas containing nitrogen oxides and sulfur oxides is first introduced into a moving bed type desulfurization layer filled with a desulfurizing agent from a direction perpendicular to the moving direction of the desulfurizing agent, and then desulfurized. In a method of purifying flue gas that is introduced into a denitration layer filled with a system catalyst and catalytically reduces and denitrates ammonia, the exhaust gas after passing through the desulfurization layer is divided into at least two or more, and the temperature of each of the divided exhaust gas is individually adjusted to denitrate. A method for purifying a combustion exhaust gas. 2. The exhaust gas after passing through the desulfurization layer is divided according to the degree of desulfurization activity of the desulfurization layer.
The method for purifying combustion exhaust gas according to the above. 3. The method for purifying exhaust gas according to claim ₂ , wherein the division according to the degree of desulfurization activity of the exhaust gas is performed based on the remaining amount of SO _{2 in} the exhaust gas. 4. The method according to claim 3, wherein the temperature of the exhaust gas divided while the SO ₂ remains is adjusted to a reaction temperature at which ammonia reacts with ammonia to produce an ammonium compound.
The method for purifying combustion exhaust gas according to the above. 5. A flue gas containing nitrogen oxides and sulfur oxides is first introduced into a moving bed type desulfurization layer filled with a desulfurizing agent from a direction perpendicular to the moving direction of the desulfurizing agent, and then desulfurized. In a combustion exhaust gas purifying device that introduces into a denitration layer filled with a system catalyst and performs ammonia catalytic reduction denitration, after a moving bed type desulfurization layer, the exhaust gas that has passed through the desulfurization layer is divided into at least two or more, A flue gas purifying device comprising a flue gas heating temperature controller and a subsequent denitration layer provided for each of the flue gases.