JP3059136B2 - Regeneration method of denitration catalyst - 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 regenerating a denitration catalyst, and more particularly to a method for regenerating a denitration catalyst which is considered to be difficult to regenerate due to a decrease in denitration performance, and which enables effective reuse. About the method.

[0002]

In recent years, from the viewpoint of prevention of air pollution, nitrogen oxides generated from a boiler and various combustion furnaces As a method for removing the (hereinafter referred to as NO _x.), Using ammonia as a reducing agent, catalytically by catalytic Ammonia catalytic reduction, which decomposes into nitrogen and water, is widely used. NO _x removal catalysts are currently in practical use, in order to prevent blockage by dust in the exhaust gas, and to widen the gas contact area,
A honeycomb-shaped catalyst having a square hole shape is mainly used. As the catalyst component, those containing titanium oxide as a main component are excellent, and vanadium,
Those containing tungsten or the like is generally used, TiO ₂ mainly binary -WO ₃ catalyst or TiO ₂ -Mo
O ₃ catalyst and ternary TiO ₂ —V ₂ O ₅ —WO ₃
A catalyst or a TiO ₂ —V ₂ O ₅ —MoO ₃ catalyst is used. The performance of these denitration catalysts tends to gradually decrease as the usage time as a catalyst increases, and the cause of the performance deterioration also differs depending on the difference in the fuel of an exhaust gas generation source such as a boiler.

For example, in the case of heavy oil fired boiler exhaust gas,
Sodium mainly contained in dust in the exhaust gas accumulates in the catalyst, and the performance of the catalyst deteriorates. In the exhaust gas of coal-fired boilers, calcium contained in dust in the exhaust gas mainly adheres to the catalyst surface, generates anhydrous calcium sulfate contained in the exhaust gas, covers the catalyst surface, and enters the inside of the catalyst. The diffusion of NO and NH ₃ gas is hindered, and the performance of the catalyst is reduced. Conventionally, it has been known that washing with water and an aqueous solution of hydrochloric acid is effective in regenerating a catalyst with reduced performance due to these causes of deterioration.

[0004]

SUMMARY OF THE INVENTION The present inventors have proposed a coal-fired
Conducting regeneration tests on catalysts used in boiler exhaust gas
In the process, conventional washing with water or hydrochloric acid aqueous solution,
Some catalysts have almost no regeneration effect on catalyst performance.
And confirmed. After investigating the cause, there was water
Or on the surface of a catalyst that does not show regeneration effect with hydrochloric acid aqueous solution
Is arsenic (As_TwoO _Five) Is found to be present at high concentrations
did.

In general, when a denitration catalyst is applied to an exhaust gas using gas as a fuel, almost no deterioration in performance is observed. However, in recent years, some of the catalysts used in the exhaust gas of a coal-fired boiler using poor coal that has been increasing tend to have large performance degradation. Then, as a result of investigating these deteriorated catalysts, as described above, arsenic was present at a high concentration on the catalyst surface, and the conventional washing with water or hydrochloric acid showed almost no regeneration effect. Further, as a result of investigating the cause of the accumulation of arsenic on the surface of the coal-fired catalyst with respect to the fuel of the exhaust gas generation source, a high concentration of arsenic compound is present in the coal, and As ₂ O ₃ ( It exists in the state of diarsenic trioxide, is adsorbed on the catalyst, is oxidized on the catalyst by the following reaction formula (1), and is fixed on the catalyst in the form of stable As ₂ O ₅ (diarsenic pentoxide). You. As ₂ O ₃ + O ₂ → As ₂ O ₅ (1) From these facts, when the cause of catalyst deterioration is an arsenic compound accumulated on the catalyst surface, conventional washing with water or an aqueous hydrochloric acid solution can There was a problem that there was almost no regeneration effect.

In view of the above problems, the inventors of the present invention have found that when the use time of the denitration catalyst increases and the catalyst performance deteriorates, the catalyst can be regenerated while avoiding the conventional performance deterioration due to sodium or calcium content. The present inventors have made intensive studies to develop a regeneration method capable of regenerating a denitration catalyst in which arsenic is present on the surface of the catalyst and the regeneration effect cannot be obtained by washing with water or an aqueous hydrochloric acid solution. As a result, the present inventors convert the arsenic compound into a water-soluble compound by washing the used denitration catalyst with an aqueous sulfuric acid solution or an aqueous ammonia solution, and remove the arsenic compound accumulated on the catalyst surface. We have found that this problem can be solved. The present invention has been completed from such a viewpoint.

[0007]

That is, according to the present invention, in regenerating a denitration catalyst having a reduced denitration performance, the concentration of sulfuric acid or ammonia in the cleaning solution is set to 0.05 to 20% by weight, and the temperature of the cleaning solution is set to 10 to 20% by weight. An object of the present invention is to provide a method for regenerating a denitration catalyst, comprising washing the catalyst while maintaining the temperature at 90 ° C. Here, by setting the temperature of the cleaning liquid to 20 to 80 ° C., the hardly soluble arsenic compound accumulated on the catalyst surface can be more effectively removed. Also, the present invention
After washing the denitration catalyst whose denitration performance has decreased under the above conditions,
The present invention also provides a method for regenerating a denitration catalyst in which a catalytically active component is impregnated and supported on the denitration catalyst. Here, as the catalytically active component to be impregnated and supported, for example, vanadium, tungsten, or the like, which easily elutes, may be used. According to the regeneration method of the present invention, a catalyst in which an arsenic compound has conventionally been discarded as non-renewable can be regenerated, and can be effectively used again as a denitration catalyst. Hereinafter, the present invention will be described in detail.

[0008]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to nitrogen oxidation in flue gas.
The performance of the denitration catalyst used for removing
When the lower cause is As compound accumulated on the catalyst surface,
The medium is sulfuric acid (H _TwoSO_Four) Or ammonia (NH_Three) Water soluble
AsO accumulated on catalyst surface after washing with liquid_FiveDissolve and touch
It is for regenerating the medium. Here, reproduced according to the present invention
The denitration catalyst is composed mainly of titanium oxide,
Containing vanadium, tungsten or molybdenum
Specifically, binary TiO 2_Two-WO_Three
Catalyst, TiO_Two-MoO_ThreeCatalyst or ternary Ti
O_Two-V_TwoO_Five-WO_ThreeCatalyst, TiO_Two-V_TwoO_Five-M
oO_ThreeCatalysts and the like can be mentioned.

In the present invention, the concentration of sulfuric acid or aqueous ammonia in the cleaning solution is set to 0.05 to 20% by weight, and the temperature of the cleaning solution is maintained at 10 to 90 ° C. to clean the denitration catalyst whose performance has deteriorated. The cleaning method is not particularly limited, and the purpose of the cleaning is achieved by bringing the denitration catalyst into contact with a sulfuric acid aqueous solution or an aqueous ammonia solution. Specifically, the denitration catalyst is immersed in an alkaline aqueous solution, or the denitration catalyst is statically immersed in a sulfuric acid aqueous solution or an ammonia aqueous solution, or bubbling air or forced convection is generated in the static denitration catalyst to update the liquid. And the like. In this washing, if the concentration of the aqueous sulfuric acid solution or the aqueous ammonia solution is low, a sufficient regeneration effect cannot be obtained. On the other hand, in the case of a high concentration, although the regeneration effect is recognized, in order to maintain the strength of the catalyst during catalyst molding,
Glass fibers mainly composed of clay or silica such as acid clay and diatomaceous earth are added in an amount of several percent to several tens percent. For this reason,
Since a part of the silica content contained in these substances dissolves, the strength of the catalyst decreases, and the strength is lower than that required in an actual plant. Therefore, in order to maintain the strength of the catalyst and obtain a regenerating effect, it is necessary to wash with a 0.05 to 20% by weight aqueous sulfuric acid solution or aqueous ammonia solution.

When arsenic accumulated on the surface of the catalyst exists in a form that is not easily dissolved, a large regeneration effect may not be obtained with a sulfuric acid aqueous solution or an ammonia aqueous solution at a low temperature. In such a case, by setting the temperature of the washing solution of the aqueous sulfuric acid solution or the aqueous ammonia solution to 10 to 90 ° C, preferably 20 to 80 ° C, the hardly soluble arsenic compound accumulated on the catalyst surface can be removed. On the other hand, when the temperature of the washing solution of the sulfuric acid aqueous solution or the ammonia aqueous solution increases, vanadium or tungsten, which is the active component of the catalyst, elutes from the catalyst, and the denitration performance decreases due to a decrease in the concentration of the active component in the catalyst. There is. Therefore, in the present invention, if necessary, after removing the arsenic compound, washing with water and drying, vanadium or tungsten can be impregnated and supported so that the active component concentration in the catalyst becomes the same as before regeneration. . As a method for supporting vanadium, vanadium pentoxide, ammonium metavanadate,
A method of immersing the catalyst in an aqueous solution in which a vanadium compound such as vanadyl sulfate is dissolved in water, an organic acid, or an amine solution is exemplified. As a method for supporting tungsten, there is a method in which a catalyst is immersed in an aqueous solution in which a tungsten compound such as ammonium paratungstate, tungsten trioxide, or tungsten chloride is dissolved in water, hydrochloric acid, an amine solution, or an organic acid.

According to the reproducing method of the present invention as described above,
Arsenic compounds accumulated in the catalyst (mainly diarsenic pentoxide: As ₂
O ₅ ) can be removed by washing. That is,
When washing with a sulfuric acid aqueous solution, the dissolution of the arsenic compound is promoted as an arsenic acid (H ₃ AsO ₄ ) aqueous solution as shown in the following reaction formula (2) to remove the arsenic compound accumulated on the catalyst surface. Can be. As ₂ O ₅ + 3H ₂ O → 2H ₃ AsO ₄ (2) When washing with an aqueous ammonia solution, the arsenic compound is converted into a water-soluble ammonium arsenic as shown in the following reaction formula (3). It can be converted to ((NH ₄ ) ₃ AsO ₄ ) and the arsenic compound accumulated on the catalyst surface can be easily removed. _{As 2 O 5 + 6NH 3 +} 6H 2 O → 2 (NH 4) 3 AsO 4 · 3 H 2 O ··· (3)

On the other hand, when a sparingly soluble arsenic compound accumulates on the catalyst surface, it is effective to increase the temperature of the cleaning solution in order to enhance the cleaning effect. However, when the temperature is increased, the cleaning effect is increased, but the elution of the active component such as vanadium of the catalyst is increased, and the concentration of the active component remaining in the catalyst may decrease. This removes the arsenic compound that is the cause of the performance degradation,
Apparently, the denitration performance does not recover. Therefore, if the active components in the catalyst are largely eluted due to the washing conditions, the catalyst is impregnated with vanadium or the like as appropriate to recover the catalyst performance. It is effective to measure. Less than,
The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0013]

EXAMPLE 1 A honeycomb-shaped denitration catalyst having a pitch of 7.4 mm and a shape shown in FIG. 1 (TiO ₂ = 89.2% by weight, WO ₃ = 10.
2% by weight, V ₂ O ₅ = 0.6% by weight) was used in the flue gas of the coal-fired boiler A plant for about 23,000 hours. In regenerating the above denitration catalyst whose denitration performance has been reduced by this use, the H ₂ SO ₄ concentration is 0.03%, 0.05
%, 0.3%, 1%, 20% or 30% aqueous solutions were used as the washing liquids, respectively, so that the volume ratio of the washing liquid to the denitration catalyst (washing liquid / denitration catalyst) was 4.0,
After immersing the denitration catalyst in a cleaning solution at 20 ° C. for 4 hours,
Washed and dried. These regenerated catalysts are referred to as catalysts 1 to 6 in ascending order of sulfuric acid concentration.

In regenerating a honeycomb-shaped denitration catalyst whose denitration performance has been reduced by the above-mentioned use, the NH ₃ concentration must be 0.03%, 0.05%, 1%, 20% or 30%.
Each of the aqueous solutions was used as a washing solution, and the denitration catalyst was immersed in the washing solution at 20 ° C. for 4 hours so that the volume ratio between the washing solution and the denitration catalyst was 4.0.
Dried. These regenerated catalysts are referred to as catalysts 7 to 11 in ascending order of ammonia concentration.

Comparative Example 1 In regenerating a denitration catalyst used in the same manner as in Example 1, water or a 1% HCl aqueous solution was used as a washing solution, and the volume ratio between the washing solution and the catalyst was 4.0. The catalyst was immersed in a cleaning solution at 20 ° C. for 4 hours, washed with water and dried. The catalyst treated with water is catalyst 51, and the catalyst treated with aqueous HCl is catalyst 6
Let it be 1.

Example 2 A honeycomb-shaped denitration catalyst having a pitch of 7.4 mm (TiO ₂
= 89.2 wt%, WO ₃ = 10.2 wt%, V ₂ O ₅
= 0.6% by weight) in coal-fired boiler B plant
Used for 5,000 hours. In regenerating the above-mentioned denitration catalyst whose denitration performance has been reduced by this use, aqueous solutions each having an H ₂ SO ₄ concentration of 0.3%, 1% or 20% are used as a washing solution, and the volume ratio of the washing solution to the denitration catalyst is used. Is 4.0 and the temperature of the cleaning solution is 10
The denitration catalyst was immersed in a cleaning solution at a temperature of 20 ° C., 20 ° C., 80 ° C., and 90 ° C. for 4 hours, then washed with water and dried. These regenerated catalysts are referred to as catalysts 12 to 23 as shown in Table 3 below. Further, these catalysts 12 to 23 were immersed in a solution in which vanadium pentoxide was dissolved in oxalic acid to prepare the same vanadium concentration in the catalyst as before washing. These regenerated catalysts are referred to as catalysts 24-35 as shown in Table 3 below.

When the honeycomb-shaped denitration catalyst whose denitration performance has been reduced by the above use is regenerated, an aqueous solution having an NH ₃ concentration of 1.0% is used as a washing solution, and the volume ratio of the washing solution to the denitration catalyst is 4. At 0 ° C., 20 ° C., 80 ° C., and 90 ° C., the denitration catalyst was immersed in the cleaning solution for 4 hours, washed with water, and dried. These regenerated catalysts are referred to as catalysts 36 to 39 in ascending order of the temperature of the washing liquid. Further, these catalysts 36 to 39 were immersed in a solution in which vanadium pentoxide was dissolved in oxalic acid, and prepared so that the vanadium concentration in the catalysts was the same as before the washing. These regenerated catalysts are referred to as catalysts 40 to 44.

Comparative Example 2 In regenerating a denitration catalyst used in the same manner as in Example 2, water or a 1% HCl aqueous solution was used as a cleaning solution, and the volume ratio of the cleaning solution to the denitration catalyst was 4.0.
The denitration catalyst was immersed in a cleaning solution at 20 ° C. for 4 hours, washed with water and dried. Here, the catalyst treated with water is referred to as catalyst 52, and the catalyst treated with aqueous HCl is referred to as catalyst 62. Further, this catalyst 62 was immersed in a solution of vanadium pentoxide in oxalic acid to prepare the same vanadium concentration in the catalyst as before washing. This regenerated catalyst is referred to as a catalyst 63.

Example 3 Comparison of unused and used catalysts of the coal-fired boiler A and B plants, the regenerated catalysts of Examples 1 and 2, and the regenerated catalysts of Comparative Examples 1 and 2 Then, the denitration performance was measured under the conditions shown in Table 1. Example 1
For the regenerated catalyst of Example 2, the average arsenic content in the catalyst and the compressive strength of the catalyst were measured. Tables 2 and 3 show the obtained results. In Tables 2 and 3, the denitration rate (%) and the compressive strength ratio are values defined as follows, respectively. Denitrification rate (%) = {(inlet NO _x - outlet NO _x) / inlet N
O _x ｝ × 100 Compressive strength ratio = Sample / unused catalyst

[0020]

[Table 1] Note) SV: Superficial velocity (h ^-1 ), gas amount / catalyst amount NH ₃ / NO _x : molar ratio

[0021]

[Table 2]

[0022]

[Table 3]

As a result, when the arsenic compound accumulates on the catalyst surface and the catalyst whose denitration performance has been reduced is regenerated, if the concentration of sulfuric acid or ammonia in the washing solution is 0.03% by weight or less, the arsenic removing effect is reduced. It turned out to be small. On the other hand, when the concentration of sulfuric acid or ammonia is 30% by weight or more,
Although the denitration performance is recovered, the clay added to maintain the strength of the catalyst during molding of the catalyst and a part of the silica content in the glass fiber are dissolved, and the strength is reduced. Therefore, the concentration of sulfuric acid or ammonia is 0.03% by weight.
It is necessary to be in the range larger than 30% by weight.

Further, as shown in Example 2, when the arsenic compound accumulated on the catalyst surface is difficult to dissolve, arsenic is difficult to dissolve when the temperature of the cleaning solution is about 10 ° C., so that a sufficient regeneration effect can be obtained. Since the temperature of the cleaning solution is
It is preferable to heat as described above. On the other hand, when the temperature of the cleaning liquid is 90 ° C., the strength of the honeycomb-shaped catalyst is reduced. Therefore, the treatment is preferably performed at a temperature in the range of 20 ° C. to 80 ° C. Further, when the temperature of the washing liquid is set to 20 ° C. or higher, the catalytic performance may be reduced by elution of vanadium which is an active component of the catalyst during washing. In this case, the arsenic compound was dissolved and removed. Later, it was also found that by impregnating the eluted vanadium into the catalyst, sufficient recovery (regeneration) of the catalyst performance was possible.

[0025]

According to the regeneration method of the present invention, it is possible to regenerate a catalyst in which an arsenic compound which has been conventionally discarded as non-renewable is accumulated, and can be effectively used again as a denitration catalyst. In addition, by regenerating and using the catalyst, it contributes to the reduction of industrial waste and has great industrial significance in terms of environment.

[Brief description of the drawings]

FIG. 1 is a perspective view of a honeycomb-shaped denitration catalyst used in an embodiment of the present invention.

[Explanation of symbols]

 1 Honeycomb denitration catalyst L length P pitch

Continuation of front page (56) References JP-A-58-247 (JP, A) JP-A-52-27091 (JP, A) JP-A-51-129889 (JP, A) JP-A-64-80444 (JP) , A) JP-A-52-63891 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 21/00-38/74 B01D 53/94 B01D 53/96 B01D 53/86

Claims (2)

(57) [Claims] Claims 1. An arsenic compound contained in flue gas of a coal-fired boiler
When regenerating the denitration catalyst whose denitration performance has decreased due to poisoning, the concentration of sulfuric acid or ammonia in the cleaning solution is 0.05 to
A method for regenerating an arsenic-poisoned denitration catalyst , comprising: immersing the denitration catalyst in the cleaning solution, washing with water while maintaining the temperature of the cleaning solution at 10 to 90 ° C. at 20% by weight. 2. A method for regenerating an arsenic-poisoned denitration catalyst , comprising washing a denitration catalyst whose denitration performance has been reduced under the conditions of claim 1, and then impregnating and supporting a catalytically active component on said denitration catalyst .