JPH044023B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for regenerating a denitrification catalyst,
In particular, the present invention relates to a regeneration method for reducing SO _x flowing out from the catalyst in the reuse of a denitrification catalyst used for SO _x -containing gas.

Catalysts used in exhaust gas denitrification equipment using the ammonia catalytic reduction method have been put into practical use, except for those for extremely dirty gases such as coal exhaust gas, and have been operating smoothly to date. However, the performance of the catalyst deteriorates due to poisonous components such as SO _x in the exhaust gas or a decrease in surface area due to heat. For this reason, some catalysts currently in operation need to be replaced. Regarding the treatment of this deteriorated catalyst, it is thought that it is most rational to regenerate and use it, and various methods of regenerating it are being studied.

Catalysts used to treat SO _x -containing exhaust gas accumulate SO ₄ ^2- in the catalyst, so in order to reuse the catalyst, the accumulated SO ₄ ^2- must be removed by some means. The SO ₃ flowing out from the denitrification equipment causes problems such as blockage and corrosion of the air preheater located downstream of the denitrification equipment. In order to remove the SO ₄ ^2- accumulated in the catalyst that causes such problems, cleaning with water or NH ₃ water has been considered, but soluble components in the catalyst may also flow out, so wastewater treatment equipment is required. There is a problem in that the installation of a catalyst is required, leading to an increase in the cost of the catalyst.

An object of the present invention is to provide a method for regenerating a denitrification catalyst that eliminates the drawbacks of the prior art described above, fixes SO ₄ ^2- in the spent catalyst, and reduces outflow of SO ₃ .

The feature of the method for regenerating a denitrification catalyst of the present invention for the above _purpose is that it ^is used for the denitrification treatment of SO _x -containing exhaust gas, and calcium (Ca) or / and barium (Ba)
oxides, hydroxides, or carbonates. This allows SO ₄ ^2- in the catalyst to be fixed in the catalyst as a stable sulfate of the element, thereby reducing the amount of SO ₃ flowing out from the catalyst.

When a catalyst is used for denitration treatment of SOx _- containing exhaust gas,
A large amount of SO ₄ ^2- accumulates in the catalyst. If this catalyst is to be reused, the accumulated SO ₄ ^2-
If the concentration of _SO
SO ₄ ^2- must be removed or fixed in a form that prevents it from flowing out. In the case of the method of removing SO ₄ ^2- from the catalyst by washing with water, etc., as described in the above-mentioned section of the prior art, it is necessary to install wastewater treatment equipment, etc., which increases the cost of the catalyst. conducted research into fixing the accumulated SO ₄ ^2- in a form that makes it difficult to leak out. the result,
It has been found that when oxides, hydroxides, or carbonates of alkaline earth metals such as Ca and Ba are added as additives, the effect of preventing sulfate root efflux is remarkable, and the effect on activity is small. As well,
It has also been found that the addition of these compounds has the effect of significantly improving the denitrification performance. The present invention is based on the results of such research and study regarding the present invention.

In the following, the present invention will be explained in detail with reference to Examples along with comparative examples for illustrating its effects.

First, we will describe how to measure the SO ₃ outflow amount and the NOx removal rate in the performance evaluation of the regenerated catalyst.

Method for measuring SO ₃ outflow amount SO ₃ outflow amount was measured under the following conditions.

Measurement conditions for SO ₃ outflow amount Superficial velocity: 20000h ^-1 Temperature: 350℃ Gas composition NO: 200ppm O ₂ : 3% CO ₂ : 12% H ₂ O: 12% N ₂ : Measurement method for residual denitrification rate Denitrification The rate was measured under the following conditions.

Measurement conditions for denitrification rate Superficial velocity: 20000h ^-1 Temperature: 350℃ Gas composition NO: 200ppm NH ₃ : 240ppm O ₂ : 3% CO ₂ : 12% H ₂ O: 12% N ₂ : Residual comparative examples and implementation Examples 1, 2, 3, 4 Titanium oxide (TiO ₂ ) and iron oxide (Fe ₂ O ₃ ) used for about 2 years in heavy oil exhaust gas (SO _x concentration about 500 ppm)
and vanadium pentoxide (V ₂ O ₅ ), the SO ₄ ^2- content of the catalyst was about 10% by weight. This catalyst is crushed to 100 mesh or less using a crusher, and Ca
(OH) ₂ was added to SO ₄ ^2- in the catalyst in the following proportions in each of Comparative Examples and Examples 1 to 4, namely: Comparative Example 0 (not added) Example 1...50 mol% Example 2... 100 mol% Example 3... 150 mol% Example 4... 200 mol%, added water and kneaded with a kneader, then dried, crushed, and formed into tablets of 7φ x 7 ^L. 450
It was calcined at ℃ for 2 hours to obtain a regenerated catalyst. The SO ₃ outflow amount and denitrification rate were measured using the above measurement method for each of the catalysts of Comparative Example, Examples 1, 2, 3, and 4. The results are as shown in the solid curve in the graph of Figure 1. It was hot.

Examples 5, 6, 7, 8 Ca(OH) ₂ in the cases of Examples 1 to 4 above
In each of Examples 5, 6, 7 _{, and 8, the same procedure was performed except that Ba(OH) 2.8H 2 O} was used.
The ratio of Ba(OH) 2.8H ₂ O to SO ₄ ^2- in the catalyst is as follows: Example 5...50 mol% _Example 6...100 mol% Example 7...150 mol% Implementation Example 8... 200 mol% was added and the regenerated catalyst was prepared in the same manner as in Examples 1 to 4. The SO ₃ outflow amount and denitrification rate were measured for each catalyst using the measurement method described above. , as shown by the broken line curve in the graph of FIG.

As shown in the graph of Figure 1, the regenerated catalyst of the comparative example, which is simply re-tablet of the spent catalyst, has a high effluent SO ₃ concentration of 50 ppm, while Ca
(OH) ₂ or Ba(OH) ₂・_8H2O , 50, 100,
Catalysts containing 150 and 200 mol % of SO ₃ will flow less. On the other hand, the denitrification rate improves up to about 100 mol%.
It can be seen that when it exceeds 150 mol%, it decreases.
In this way, by adding an appropriate amount of Ca(OH) ₂ or Ba(OH) _{2.8H 2 O} to regenerate the denitrification catalyst, it is possible to reduce the SO ₃ outflow without reducing the denitrification rate, making it an effective regeneration method. It can be seen that it is.

As can be seen from the above explanation, according to the present invention, a used catalyst with an increased SO ₄ ^2- content can be regenerated as a catalyst with a small amount of SO ₃ effluent without reducing the denitrification rate. . Another effect is that the denitrification activity of the deteriorated catalyst is improved when the amount of regeneration additive added is up to 150 mol%.

[Brief explanation of drawings]

FIG. 1 is a graph showing the results of measuring the SO ₃ outflow amount and denitrification rate of the regenerated catalyst in Comparative Example and Examples 1 to 8.

Claims (1)

[Claims] 1 A process of powdering the ammonia catalytic reduction denitrification waste catalyst containing sulfate radicals (SO ₄ ^2- ) used in the denitrification treatment of exhaust gas containing sulfur oxides, and adding calcium to the powdered denitrification waste catalyst containing sulfate radicals. (Ca) or barium (Ba) or both, oxides, hydroxides, or carbonates and water are added and kneaded, molded and dried, and then heated and fired to form the sulfate groups. A method for regenerating a denitrification catalyst, comprising at least a step of fixing it as a sulfate.