JPH0417701B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for regenerating an ammonia catalytic reduction denitrification catalyst used for combustion exhaust gas such as boiler exhaust gas.

[Background technology]

As a method for removing nitrogen oxides from combustion exhaust gas, an ammonia catalytic reduction method in which ammonia is used as a reducing agent and reduced by a catalyst is widely adopted.

When dust is contained in the combustion exhaust gas, in order to prevent clogging due to dust during use, it is common practice to use catalyst shapes such as honeycomb, cylinder, and plate shapes in parallel flow. Honeycomb-shaped catalysts with pore shapes such as hexagonal, square, rectangular, and triangular are often used because they have a large gas contact area and are highly economical.

These NO _x removal catalysts gradually degrade in performance when used in combustion exhaust gas, so in order to maintain high denitrification performance, it is necessary to replace the catalyst or reactivate the catalyst whose performance has deteriorated. . It is economically disadvantageous to replace all catalysts with degraded performance with new catalysts because the catalysts are expensive and disposal of used catalysts is also expensive. It is useful to use it as

The present inventors have found that the
As a result of intensive studies on the performance deterioration phenomenon of ammonia catalytic reduction denitrification catalysts whose main component is TiO ₂ , we found that the deterioration in catalyst performance is due to the accumulation of alkaline components such as Na and K contained in the dust in the exhaust gas in the catalyst. It was determined that this was the main cause. Catalysts whose performance has deteriorated in this way can be regenerated by washing them with water, but it is difficult to restore them to the performance equivalent to that of a new catalyst, and it is not always possible to restore them to the performance equivalent to that of a new catalyst. There were some flaws that I can't talk about.

Through subsequent studies, the present inventors found that the performance of an ammonia catalytic reduction denitrification catalyst containing TiO ₂ as a main component is closely related to the S content in the catalyst, and that the catalyst regenerated by water washing has a high S content. It was found that the content was lower than that of the new catalyst. Therefore, the present invention was completed by discovering that by further impregnating the water-washed catalyst with sulfuric acid and heating and calcining it, S content could be replenished to the catalyst and effective performance recovery could be carried out.

[Object of the present invention]

That is, an object of the present invention is to provide a method for regenerating an ammonia catalytic reduction denitrification catalyst mainly composed of TiO ₂ which has deteriorated in performance and restores the performance to that of a new catalyst.

[Configuration of the present invention]

The present invention, as a means for achieving the above object, consists in impregnating or spraying a sulfuric acid aqueous solution onto a catalyst with reduced performance, and then firing the catalyst. That is, the present invention involves impregnating or spraying an aqueous sulfuric acid solution on an ammonia catalytic reduction denitrification catalyst mainly composed of _TiO2 , which has deteriorated in performance, and then calcining it at 300 to 650°C to replenish the S content in a fixed manner to the catalyst. This is a unique method for regenerating ammonia catalytic reduction denitrification catalysts.

The catalyst targeted by the present invention is a catalyst mainly composed of TiO ₂ , such as TiO ₂ −V ₂ O ₅ system, TiO ₂ −WO ₃ −
It is effective for V ₂ O ₅ type and TiO ₂ -WO ₃ type catalysts, and in addition to the method of impregnating or spraying sulfuric acid after washing with water and firing, there is also a method of immediately impregnating or spraying sulfuric acid on the catalyst with decreased performance and firing. It's good to wear. The firing temperature is
The temperature is preferably 300 to 650°C, preferably 400 to 500°C for about 1 hour.

It goes without saying that any catalyst containing TiO ₂ as a main component can be applied regardless of its shape.

EXAMPLES The present invention will be specifically explained below with reference to Examples.

Example 1 TiO _{2 -WO} 3 -V ₂ O ₅ catalyst TiO ₂ 91% with performance deterioration degree K (performance of degraded catalyst or performance of catalyst to be regenerated)/Ko (performance of new catalyst) = 0.63,
When the sample (WO ₃ 8%, V ₂ O ₅ 1%) was immersed in 5 times its volume of water for 60 minutes and washed with water, K/Ko was restored to 0.88. After further impregnating this catalyst with 1NH ₂ SO ₄ aqueous solution
After firing at 450°C for 1 hour, K/Ko was restored to 0.99.

Example 2 TiO ₂ −WO ₃ V ₂ O ₅ with degraded performance of K/Ko=0.50
Catalyst ( _TiO2 89.7%, _WO3 10%, _{V2O5 0.3} %),
After immersing in 1NH ₂ SO ₄ aqueous solution for 5 minutes, overnight (16 hours)
After air drying and baking at 450℃ for 1 hour,
Performance recovered to K/Ko=0.95. the same catalyst again
After immersing in 0.1NH ₂ SO ₄ aqueous solution for 5 minutes, overnight (16 hours)
When air-dried and fired at 450°C for 1 hour, K/
Performance recovered to Ko=0.93.

[Effects of the present invention]

As described in detail above, the present invention has an extremely large regeneration effect by impregnating or spraying a sulfuric acid aqueous solution on a catalyst with degraded performance and then firing it. This produces an effect that can be expected to significantly reduce the cost of the catalyst in the device.

Claims (1)

[Claims] 1 An ammonia contact method characterized by impregnating or spraying an aqueous sulfuric acid solution on an ammonia catalytic reduction denitrification catalyst mainly composed of _TiO2 , which has deteriorated in performance, and then calcining it at 300 to 650°C to fix and replenish the S content to the catalyst. Regeneration method of reduction denitrification catalyst.