JP3150519B2 - Regeneration method of denitration catalyst - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a deposition or titanium spent the denitration performance was increased decreased SO ₂ oxidizing ability by the accumulation of dust components - a reproducing method of tungsten and / or molybdenum-based denitration catalyst.

[0002]

2. Description of the Related Art As a method for removing NOx from exhaust gas, a catalytic reduction method for reducing NOx to harmless nitrogen in the presence of a catalyst using ammonia as a reducing agent has been put to practical use. However due to the presence of high concentrations of SO ₂ in the process gas in the boiler exhaust gas treatment using sulfur high oil (C heavy oil), the SO ₂ produced simultaneously with the NOx reduction reaction for removing the sulfur trioxide (SO ₃₎ High concentration of SO ₃
Is generated and easily binds with the unreacted portion of NH ₃ used as a reducing agent in the low-temperature region to form ammonium sulfate and other compounds, so that the clogging phenomenon in various devices such as a downstream heat exchanger and a dust collector It is necessary to improve the ability of
As a catalyst used in the above method and exhibiting excellent activity, there is a titanium-tungsten and / or molybdenum-based denitration catalyst. Even with this catalyst, dust containing heavy metals such as vanadium, nickel and iron and alkali salts such as sodium sulfate are present in the combustion exhaust gas of heavy oil having a high sulfur content in addition to SO _2. The components in the dust adhere to and accumulate on the catalyst surface, which degrades the denitration performance of the catalyst and reduces
A phenomenon in which the O ₂ oxidizing ability increases is observed. This decrease in the denitration performance is mainly caused by the accumulation of alkali components such as Na and K contained in the dust in the exhaust gas on the catalyst.
₍₂₎ The increase in oxidation ability is mainly caused by the accumulation of vanadium contained in dust in exhaust gas on the catalyst.

[0003]

[Problems that the Invention is to Solve reduces the thus denitrification performance, titanium SO ₂ oxidation ability is raised - as described in JP 60-209252 Laid as a reproduction method of the tungsten and / or molybdenum-based denitration catalyst There is a method.
In this method, in regenerating a used vanadium-tungsten-titania denitration catalyst, first, the used catalyst is washed with water or a dilute inorganic acid aqueous solution, and then washed with an oxalic acid aqueous solution.
It removes vanadium compounds that cause an increase in O ₂ oxidizing ability. Tungsten as a catalyst component is simultaneously eluted by this treatment, and the denitration performance is reduced. Therefore, the tungsten compound is washed with an oxalic acid aqueous solution and then impregnated with a tungsten compound again. In this method, the tungsten component must be impregnated and fired again after the cleaning operation, and there is a problem that the cost is increased. Further, in this method, if the tungsten component is not impregnated and supported after oxalic acid washing, the denitration performance of the catalyst does not recover, and the strength of the catalyst also decreases. The present invention solves the above-mentioned problems of the prior art, and provides a method for regenerating a titanium-tungsten and / or molybdenum-based denitration catalyst capable of restoring the activity of a catalyst only by a washing operation.

[0004]

SUMMARY OF THE INVENTION The present invention is directed to a dust component.
Denitration performance decreases due to adhesion or accumulation and SO ₂ oxidation ability
Raised used titanium and tungsten and / or moly
A catalyst comprising a composite oxide with butene, or the composite acid
Regenerating a catalyst in which a vanadium compound is supported on a chloride
Then, after washing the catalyst with water or a dilute inorganic acid aqueous solution,
Wash with 0.1 to 5% by weight aqueous oxalic acid, then add water
Features to remove oxalic acid remaining in catalyst by washing
Of the used denitration catalyst.

[0005] The catalyst process of the present invention is applied to form a composite oxide with the catalyst or pre-titanium and tungsten and / or molybdenum consisting composite oxide of titanium and tungsten and / or molybdenum, the composite oxide This is a catalyst in which a vanadium compound is supported on a substance .

[0006] Such a catalyst of the composite oxide type is obtained by calcining a sol-formed metatitanic acid containing at least one compound selected from a tungsten compound and a molybdenum compound, and applying the calcined product or the vanadium oxide to the calcined product. A method in which an appropriate amount of an auxiliary agent and water are added to the mixture, mixed, and kneaded, and then extruded in a lattice shape using an extruder, dried, and fired (Japanese Patent Publication No. 1-1808, etc.).
It can be manufactured by such as. For example, adding a predetermined amount of an aqueous solution of ammonium paratungstate or an aqueous solution of ammonium molybdate to metatitanic acid, dehydrating, molding,
A method of baking after drying, or a method of adding a predetermined amount of an aqueous solution of ammonium paratungstate or an aqueous solution of ammonium molybdate to metatitanic acid, dehydrating, impregnating with an aqueous solution of ammonium metavanadate after drying, drying after forming, and firing is preferable. It is.

[0007]

In the method of the present invention, by washing with water before oxalic acid washing, the vanadium component which causes an increase in SO ₂ oxidizing ability is hardly eluted, but other dust components such as an alkali metal component and unburned carbon. And the like, so that the mixing of dust components into the oxalic acid solution is extremely small as compared with the case where oxalic acid washing is performed directly without washing with water, so that the effect of vanadium elution by oxalic acid is sufficiently exhibited.
In addition, after washing with an aqueous oxalic acid solution, it is necessary to store the oxalic acid component before filling it in the reactor. When refilling and restarting, the residual oxalic acid is scattered, which is not preferable.However, in the method of the present invention, the oxalic acid component remaining in the catalyst is reduced because the oxalic acid aqueous solution is further washed with water after washing. Such trouble does not occur because it has been completely removed.

Further, as a titanium-tungsten and / or molybdenum-based catalyst, a catalyst comprising a composite oxide of titanium and tungsten and / or molybdenum or a composite oxide of titanium and tungsten and / or molybdenum is formed in advance, and because it uses was supported vanadium compound oxide catalyst, not that the denitration performance decreases since once made of tungsten or molybdenum is hardly eluted is supported active metal catalyst at the time of cleaning by oxalic acid aqueous solution, reproduction At this time, an operation such as reloading of the active metal is not required.

[0009]

【Example】

(Preparation of catalyst) (1) Titanium oxide was formed into a honeycomb shape having a pitch of 7 mm (width: 15 mm).
(0 mm, height 150 mm, length 500 mm), dried, impregnated with a predetermined concentration of ammonium metavanadate aqueous solution and ammonium paratungstate aqueous solution into a honeycomb carrier fired at 550 ° C., dried, fired at 500 ° C., and oxidized. A titanium-vanadium-tungsten catalyst (catalyst A) was obtained. (2) A predetermined concentration of ammonium paratungstate was added to metatitanic acid, dehydrated, molded, dried and calcined at 500 ° C. to obtain a titanium oxide-tungsten catalyst (catalyst B). (3) A predetermined concentration of ammonium paratungstate is added to metatitanic acid, dehydrated, dried, impregnated with a predetermined concentration of ammonium metavanadate aqueous solution, formed, dried, and then dried.
The mixture was calcined at 00 ° C. to obtain a titanium oxide-vanadium-tungsten-based catalyst (catalyst C). (4) A predetermined concentration of ammonium molybdate is added to metatitanic acid, dehydrated and dried, then impregnated with a predetermined concentration of ammonium metavanadate aqueous solution, molded, dried, and then dried at 500 ° C.
To obtain a titanium oxide-vanadium-molybdenum catalyst (catalyst D). Table 1 shows the compositions of these catalysts A, B, C and D.

[0010]

[Table 1]

(Preparation of Spent Catalyst Sample) The catalysts A, B, C and D prepared as described above were charged into a denitration apparatus installed in a heavy oil combustion boiler exhaust gas having a sulfur content of 5% by weight.
A durability test (aging) for 000 hours was performed, and the obtained sample was used as a used catalyst sample. The denitration conditions are gas volume 70
000 m ³ N / h, temperature 380 ° C., NH ₃ / NOx =
0.8 (molar ratio). Thereafter, the catalyst was extracted, and changes in denitration rate, SO ₂ oxidizing ability, and content of vanadium (V), tungsten (W), or molybdenum (Mo) in the catalyst were examined. The results are as shown in Table 2. Although the denitration rate was hardly reduced, an increase in SO ₂ oxidizing ability and an increase in vanadium content were observed.

The denitration rate and SO ₂ oxidation rate were measured as follows. 150mm width, 150mm height,
Four honeycomb catalysts having a length of 500 mm were filled in an activity test device, and the combustion exhaust gas generated in a combustion furnace was about 225 m ³ N /
h into the test apparatus, gas temperature 380 ° C., NH ₃ / N
Ox = 1.0 (molar ratio), inlet NOx200ppm, inlet SO ₂ 1000 ppm, inlet SO ₃ 10 ppm, after 20 hours aging in an atmosphere of the remaining N ₂ and CO _2,
NOx concentration, SO ₂ concentration and SO ₃ at the test equipment
To determine the concentration to obtain the NOx removal efficiency and SO ₂ oxidation rate by the following equation. Denitration rate (%) = 100 x (NOx at inlet-NOx at outlet) /
Inlet NOx SO ₂ oxidation rate (%) = 100 × (Outlet SO ₃ −Inlet SO
₃ ) / SO _{2 at the} entrance

[0013]

[Table 2]

Example 1 A sample of the used catalyst (sample after 10000 hours in Table 2) was immersed in water having a volume ratio of 4 times for 1 hour, and then taken out. It was immersed in a 1% by weight aqueous oxalic acid solution (4 times in volume ratio) for 1 hour, washed with an aqueous oxalic acid solution, and then dried with hot air at 110 ° C. Denitration rate before and after oxalic acid solution wash, SO ₂ oxidation ability and vanadium in the catalyst (V), investigating changes in the content of tungsten (W) and molybdenum (Mo). The results are shown in Table 3. In each sample, the vanadium content increased by aging was removed, and the SO ₂ oxidizing ability (SO ₂ oxidizing rate) was restored to the initial value. However, the amount of tungsten or molybdenum in the catalyst did not change before and after washing with oxalic acid in catalysts B, C and D in which titanium and tungsten or molybdenum formed a composite oxide, but did not. No comparative example
In a certain catalyst A, the amount of tungsten in the catalyst was reduced, and a reduction in the denitration rate was recognized.

(Example 2) The catalyst which was washed with an oxalic acid aqueous solution in Example 1 and the catalyst which was washed with an oxalic acid aqueous solution and then immersed in 4 times the volume of water for 1 hour and washed with water,
After leaving at room temperature for one week and drying with hot air at 110 ° C., the compressive strength was measured. The measurement of the compressive strength was performed by a method of compressing a honeycomb-shaped sample from the side. The results are shown in Table 3. When the catalyst was dried while being washed with an oxalic acid aqueous solution, the strength of all the catalysts was reduced. However, the strength was prevented by washing with an oxalic acid aqueous solution and then washing with water. You can see what you can do. Further, the denitration rate, SO ₂ oxidizing ability, and the contents of vanadium (V), tungsten (W) and molybdenum (Mo) in the catalyst do not change by washing with oxalic acid aqueous solution.

[0016]

[Table 3]

[0017]

[Table 4]

[0018]

Deposition of dust components according to the present invention or the denitration performance decreases due to the accumulation of titanium spent for SO ₂ oxidation ability is increased -
Washing the tungsten and / or molybdenum-based denitration catalyst with water,
Upon regeneration by washing with an aqueous oxalic acid solution, washing with an aqueous oxalic acid solution and then washing with water can prevent a decrease in the strength of the catalyst itself and troubles caused by scattering of residual oxalic acid. Further, as a titanium-tungsten and / or molybdenum-based catalyst, a catalyst composed of a composite oxide of titanium and tungsten and / or molybdenum or a composite oxide of titanium and tungsten and / or molybdenum is formed in advance, and If a catalyst carrying a vanadium compound is used, tungsten and molybdenum, which are active metals once supported on the catalyst, are less likely to elute during washing with an oxalic acid aqueous solution. This eliminates the need for operations such as reloading.

Continuation of the front page (72) Inventor Yoshiaki Obayashi 4-6-22 Kanonshinmachi, Nishi-ku, Hiroshima-shi, Hiroshima Mitsubishi Heavy Industries, Ltd. Hiroshima Research Laboratory (56) References JP-A-60-209252 (JP, A) JP-A Sho 54-10294 (JP, A) JP 60-41611 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 21/00-38/74 B01D 53/86 B01D 53 / 94 B01D 53/96

Claims (1)

(57) [Claims] Claims: 1. Used titanium whose denitration performance has been reduced due to adhesion or accumulation of dust components and SO ₂ oxidation ability has been increased.
From composite oxide with tungsten and / or molybdenum
Or a vanadium compound to the composite oxide
A method for regenerating a supported catalyst, comprising washing the catalyst with water or a dilute inorganic acid aqueous solution, then washing with a 0.1 to 5% by weight aqueous oxalic acid solution, and further removing oxalic acid remaining on the catalyst by washing with water. A method for regenerating a used denitration catalyst, which comprises removing the catalyst.