JPS6251656B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides an improved method for cleaning and reactivating a nitrogen oxide removal catalyst when its performance deteriorates due to the accumulation of poisonous substances during use. Nitrogen oxides in exhaust gas (hereinafter referred to as NOx)
is said to be one of the causes of photochemical smog when it reacts with hydrocarbons in the atmosphere due to the action of ultraviolet rays.
Development of NOx removal methods is underway. especially,
The so-called ammonia catalytic reduction method, in which NOx in exhaust gas is rendered harmless on a catalyst using ammonia as a reducing agent, is currently the mainstream method for removing NOx. In general, for processing dirty gas containing dust and SOx, such as exhaust gas from heavy oil-fired boilers or coal-fired boilers, it is most suitable in consideration of SOx resistance, dust toxicity resistance, dust clogging resistance, dust abrasion resistance, etc. It is necessary to select appropriate catalyst specifications.
Al ₂ O ₃ is widely used in LNG-fired boilers and other applications.
By using TiO ₂ as a carrier instead of _{TiO 2} , the SOx resistance becomes _{sufficient .}
Catalysts on which active components such as Fe ₂ O ₃ and MoO ₂ are supported are used. In addition, as catalyst shapes that do not become clogged with dust, we use catalysts shaped like granules, cylinders, or ellipsoids in a moving bed, or fixed catalyst structures such as plates, pipes, grids, or honeycombs. A method of using a bed to allow exhaust gas to pass through in parallel has been compared, and currently grid-shaped catalysts are the mainstream as they are economical and easy to maintain. A highly hard lattice catalyst has also been developed for denitrification reactions on the high-dust side of coal-fired boilers, and has virtually no problems in practical use. However, even with a parallel-flow lattice catalyst using TiO ₂ as a carrier, if the catalyst surface gets wet with water with dust attached to it, or if the boiler evaporator tube or economizer water supply pipe breaks, the catalyst surface may become contaminated with dust from the furnace. If steam or water wets the catalyst, K,
Because the catalyst contains Na, Mg, etc., the amount of poisonous substances such as K, Na, Mg, etc. increases rapidly inside the catalyst, causing unexpected performance deterioration and causing an accident in which the boiler cannot operate. There is also. Furthermore, when the denitrification device no longer exhibits the expected performance due to such an emergency accident, it is necessary to restore the performance in a short period of time while the catalyst remains filled. If the performance of the catalyst deteriorates due to water-soluble poisonous substances such as K, Na, Mg, etc., it can be regenerated by washing with normal water, but in exhaust gas containing Ca such as coal-fired exhaust gas, In some cases, poisonous substances that are difficult to dissolve in water, such as calcium sulfate, accumulate on or inside the catalyst, and in such cases, cleaning with water alone may not reactivate the catalyst to a usable state. difficult to do. The present invention was made to improve the insufficiency of the reactivation method using water. That is, in the present invention, when removing nitrogen oxides from exhaust gas by an ammonia catalytic reduction method, a catalyst whose performance has deteriorated is washed with an organic acid aqueous solution or a mixed solution of an organic acid aqueous solution and an inorganic acid aqueous solution at room temperature or with heating. The present invention relates to a method for regenerating a catalyst, characterized in that the catalyst is regenerated through treatment. In the method of the present invention, the organic acid aqueous solution is
Concentration 0.01-10% by weight, preferably 0.5-3% by weight
dilute aqueous solutions of organic acids such as acetic acid, formic acid, and ethylenediaminetetraacetic acid, and mixed aqueous solutions of organic acids and inorganic acids with concentrations of 0.01 to 5.
A mixed solution of a dilute aqueous solution of an inorganic acid such as hydrochloric acid, sulfuric acid, nitric acid, etc. in % by weight is used. The reason for setting the concentration of the organic acid aqueous solution to 0.01 to 10% by weight is that the higher the concentration of the organic acid aqueous solution, the easier it is to elute poisonous substances such as calcium sulfate, but even if the concentration is 10% by weight or more, it is difficult to increase the concentration. The effect is almost unchanged for 0.01, which is economically disadvantageous.
This is because if the amount is less than % by weight, the effect of eluting poisonous substances cannot be obtained. It is also necessary to select the concentration of the organic acid aqueous solution depending on the concentration of the poisonous substance.
If the concentration of poisonous substances is low, the concentration of the organic acid aqueous solution may be low, but for more effective and economical treatment,
0.5-3% by weight is suitable. When mixing an inorganic acid aqueous solution with this organic acid aqueous solution, the concentration of the inorganic acid aqueous solution should be 0.01 to 5% by weight. This is because even if the concentration is higher than %, the effect will hardly change even though the concentration is increased, and this will be economically disadvantageous. Further, the above organic acid aqueous solution or mixed aqueous solution of an organic acid and an inorganic acid is used at room temperature or under heating at 25 to 90°C. This is because, although the elution of poisonous substances increases by increasing the temperature, the elution of active ingredients also increases accordingly, so it is not preferable to increase the temperature unnecessarily, and it is also economically disadvantageous. Furthermore, the washing time is 5 to 90 minutes, preferably 30 to 60 minutes.
It's a minute. A cleaning effect cannot be obtained with a cleaning time of less than 5 minutes, and the longer the cleaning time, the higher the effect.
However, even if the cleaning time is 60 minutes or more, the cleaning effect will hardly change, so 30 to 60 minutes is preferable for efficient cleaning in a short time. The method of the present invention can efficiently elute and remove calcium-containing poisonous substances such as calcium sulfate, which are difficult to dissolve in water, in a short time _.
Catalysts that combine active ingredients such as V ₂ O ₅ , WO ₃ , Fe ₂ O ₃ , MoO _{2 ,} etc.; catalysts shaped into granules, cylinders, ellipsoids, etc.; plate-shaped catalysts;
It can be applied to the regeneration of coated and solid catalysts of pipe-shaped, lattice-shaped, honeycomb-shaped catalyst structures, etc. Furthermore, the cleaning method is not particularly limited, and can be either normal spray cleaning or immersion cleaning. The catalyst from which poisonous substances have been removed is dried by a normal drying method and subsequently used as a denitrification catalyst. The method of the present invention is particularly effective as a method for regenerating catalysts applied to coal-fired exhaust gas, but is not limited thereto, and can also be used as a method for regenerating catalysts applied to heavy oil-fired exhaust gas, garbage incinerator exhaust gas, etc. The method is simple and has great practical effects. Next, examples of the method of the present invention will be given, but the method of the present invention is not limited to these examples. Example 1 In detoxifying NOx in coal-fired exhaust gas by ammonia catalytic reduction method using a lattice catalyst containing vanadium as a catalyst component, 600Nm ³ /H
scale equipment, temperature 300-380℃, space velocity
3000hr ^-1 , ammonia/NOx ratio = 0.85, SOx concentration
A catalyst durability test was conducted for 12,000 hours under conditions of 1,100 to 1,400 ppm and a dust concentration of 15 to 20 g/m ³ N. As a result of sampling the catalyst and conducting an activity test under the conditions shown in Table 1, the initial NOx removal rate was 83%.
Activity decreased to 51%. This catalyst was immersed in 4 times the volume of water at room temperature for 60 minutes, dried, and then subjected to an activity test under the same conditions as above. As a result, the denitrification rate recovered to 55%. Similarly, using an acetic acid solution with a concentration of 3% by weight, the deteriorated catalyst was added to the acetic acid solution at room temperature in a 4-fold volume ratio.
After soaking and drying for 60 minutes, an activity test was conducted under the same conditions, and the denitrification rate recovered to 79%.

[Table] Example 2 The same deteriorated catalyst as in Example 1 was used at a concentration of 3.
After being immersed in an acetic acid solution at 60° C. for 60 minutes and dried, an activity test was carried out under the same conditions as in Example 1. As a result, the denitrification rate recovered to 82%. Example 3 A catalyst degraded in the same manner as in Example 1 was immersed in a formic acid solution at room temperature at a concentration of 3% by weight and a volume ratio of 4 times for 60 minutes, and after drying, an activity test was conducted under the same conditions as in Example 1. , the denitrification rate recovered to 77%. Example 4 A catalyst degraded in the same manner as in Example 1 was immersed in an ethylenediaminetetraacetic acid solution at room temperature at a concentration of 3% by weight and a volume ratio of 4 times for 60 minutes, and after drying, an activity test was conducted under the same conditions as in Example 1. As a result, the denitrification rate recovered to 81. Example 5 A catalyst degraded in the same manner as in Example 1 was immersed in an acetic acid solution at room temperature at a concentration of 3% by weight and a volume ratio of 4 times for 30 minutes, and after drying, an activity test was conducted under the conditions shown in Table 1. As a result, The denitrification rate recovered to 70%. In addition, when the degraded catalyst was immersed in a hydrochloric acid solution with a concentration of 1% by weight and a 4x volume ratio at room temperature for 30 minutes, and after drying, an activity test was conducted in the same manner, the denitrification rate was recovered to 62%. Furthermore, the deteriorated catalyst was immersed for 30 minutes at room temperature in a mixed solution of 3% by weight acetic acid solution and 1% by weight hydrochloric acid solution at a volume ratio of 4 times, and then dried.
As a result of conducting an activity test under the conditions shown in the table, the denitrification rate recovered to 82%. This experiment shows that regeneration treatment takes some time when an organic acid or inorganic acid solution is used alone, but when a mixed solution of an organic acid and an inorganic acid is used, the regeneration treatment time can be shortened due to a synergistic effect. The results obtained in Examples 1 to 5 above are summarized in FIGS. 1 and 2. FIG. 1 is a chart showing the denitration rate of the catalysts regenerated in Examples 1 to 4, and FIG. 2 is a chart showing the relationship between the regeneration time and the denitrification rate of the catalyst. As is clear from Figures 1 and 2, cleaning treatment with water does not easily recover the activity, but cleaning treatment with an organic acid solution has a high activity recovery rate, and cleaning treatment with a mixed solution of organic and inorganic acids shows that the activity recovery rate is high. In treatment, compared to cleaning treatment with organic acid or inorganic acid alone solution,
The cleaning time is reduced, confirming the effectiveness of the method of the present invention. In addition, in Figures 1 and 2, ○・ is the initial one,
● is after 12000 hours, △・ is after cleaning treatment with water in Example 1, □・ is after cleaning treatment with acetic acid solution in Example 1, ▽・ is after cleaning treatment with acetic acid solution in Example 2 × indicates the cleaning treatment with the formic acid solution of Example 3, ◇・ indicates the cleaning treatment with the ethylenediaminetetraacetic acid solution of Example 4, ○ indicates the cleaning treatment with the acetic acid solution of Example 5, △ indicates the cleaning treatment with the acetic acid solution of Example 5. □ indicates the cleaning treatment using a hydrochloric acid solution in Example 5; □ indicates the cleaning treatment using a mixed solution of acetic acid and hydrochloric acid in Example 5.

[Brief explanation of the drawing]

Figures 1 and 2 are charts showing the results obtained in Examples.

Claims (1)

[Claims] 1. When removing nitrogen oxides from exhaust gas by the ammonia catalytic reduction method, by cleaning the catalyst whose performance has decreased with an organic acid aqueous solution or a mixed solution of an organic acid aqueous solution and an inorganic acid aqueous solution at room temperature or under heating. A method for regenerating a catalyst, the method comprising regenerating a catalyst.