JPS6248537B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for regenerating a poisoned denitrification catalyst containing at least vanadium and titania used for catalytic reduction removal of nitrogen oxides in exhaust gases discharged from various combustion devices in the presence of ammonia. Nitrogen oxides contained in the exhaust gas emitted from various combustion devices are one of the causes of air pollution, and various methods have been proposed for their removal. Many catalytic reduction methods have been put into practical use, in which exhaust gas is brought into contact with a catalyst to decompose nitrogen oxides into nitrogen and water. As the denitrification catalyst used in this catalytic reduction method, catalysts containing vanadium and titania are most often used because they have excellent activity and long life. However, when these denitration catalysts containing vanadium and titania are used for a long period of time, the dust contained in the exhaust gas can accumulate, and the SO ₂ gas contained in the exhaust gas can be converted to SO ₃ by the denitration catalyst. Ammonium sulfate is produced by the reaction, and the ammonium sulfate adheres to and accumulates on the denitrification catalyst, resulting in so-called catalyst poisoning, which inevitably causes a significant decrease in the denitrification properties. Conventionally, as a method for regenerating such a poisoned denitrification catalyst, for example, after washing with water,
A method of firing at 500℃ (Japanese Unexamined Patent Publication No. 51-80696), a method of washing with water or a dilute inorganic acid solution or spraying with steam (Japanese Unexamined Patent Application No. 52-27091), and a method of contacting with an oxalic acid aqueous solution to remove the vanadium component. A method of impregnating and supporting a vanadium compound after extracting a portion and firing it (Japanese Patent Application Laid-Open No. 1983-
10294) etc. have been proposed and implemented. These cleaning treatment methods remove to some extent dust adhering to the catalyst and water-soluble substances that cause catalyst deterioration, and are therefore highly effective in restoring catalyst performance. However, it increased with catalyst poisoning.
It was not possible to sufficiently reduce and recover the SO ₂ conversion rate, and this was not necessarily a satisfactory method for regenerating the denitrification catalyst. The denitrification catalyst regeneration method of the present invention was developed to solve these conventional drawbacks, and is a catalyst regeneration method that is particularly excellent in recovering the characteristics of catalyst performance and SO ₂ conversion rate. In a method for regenerating a denitrification catalyst containing at least vanadium and titania in which nitrogen oxides are removed by catalytic reduction in the presence of ammonia, the poisoned catalyst is washed with water or an inorganic acid solution, and then immersed in a solution containing tungsten, 0.01Kg~10 in terms of _WO3 per ^1m3 of apparent volume of catalyst
This is a denitrification catalyst regeneration method in which the catalyst is impregnated and supported with kg of tungsten compound, then dried and calcined at 400 to 650°C. The present invention will be explained in more detail below. A vanadium-titania catalyst, a vanadium-tungsten-titania catalyst, or at least vanadium or titania containing one or more catalytically active substances such as molybdenum, iron, copper, chromium, nickel, cobalt, and cerium in these components. The so-called poisoned denitrification catalyst, which has degraded denitrification performance due to long-term use, is removed from room temperature to
Clean with ultrasonic cleaning, etc. in water at 90°C or warm water, or in an inorganic acid solution such as hydrochloric acid or sulfuric acid with a concentration of 10% or less. This cleaning removes dust that has entered the catalyst surface and inside, as well as water-soluble poisoning substances that have reacted with alkali metal compounds and catalyst components. In this case, the time required for cleaning varies depending on the adhesion status of dust and poisonous substances, the temperature of the cleaning liquid, the concentration of inorganic acid, stirring conditions, etc., but is usually about 10 minutes to 3 hours. The catalyst from which dust and poisonous substances have been removed by this cleaning is dried, and the catalyst is immersed in a solution containing tungsten to reduce the apparent volume of the catalyst to 1 m ³ .
0.01Kg to 10Kg in terms of WO ₃ per unit, preferably
After impregnating and supporting the catalyst with 0.1Kg to 3Kg of tungsten compound, the temperature is 400℃ to 650℃, preferably 500℃.
This is a catalyst regeneration method that involves firing at ~600℃. In addition,
Solutions containing tungsten used for impregnation include:
It is preferable to use ammonium paratungstate dissolved in an organic solvent such as monoethanolamine or methanolamine, or a commercially available aqueous tungstic acid solution. In addition, as a method for impregnating and supporting WO ₃ , the concentration of WO ₃ may be adjusted according to the target amount of support and impregnation may be carried out at once, or it may be carried out by repeatedly impregnating and supporting using a solution with a thin concentration. However, if the supported amount of WO ₃ is less than 0.01 Kg/m ³ , it is not preferable because the recovery effect on the denitrification rate and SO ₂ conversion rate is small.
This is because even if m ³ or more is supported, neither the denitrification rate nor the SO ₂ conversion rate can be expected to improve much, and it is economically meaningless. Furthermore, the reason why the calcination temperature after supporting is set to 400°C to 650°C is because the supported tungsten compound cannot completely convert into WO ₃ at temperatures below 400°C.
This is because at temperatures above 0.degree. C., the vanadium component contained in the original catalyst melts, leading to a decrease in the specific surface area of the catalyst, resulting in a decrease in the denitrification rate and an increase in the SO ₂ conversion rate. The denitrification catalyst containing at least vanadium and titania that can be regenerated in the present invention may be a so-called coated catalyst in which an active substance is supported on a base material such as mullite or cordierite, or a so-called solid catalyst in which the catalyst is formed of an active substance. The shape of the catalyst may be honeycomb, pellet, pipe, etc. Next, the present invention will be specifically explained using examples. A honeycomb catalyst (hereinafter referred to as catalyst A) consisting of 3.0% V ₂ O ₅ and 97% TiO ₂ as catalyst components;
Honeycomb catalyst (hereinafter referred to as catalyst B) consisting of V ₂ O ₅ 1.0%, WO ₃ 7.0%, TiO ₂ 92%, V ₂ O ₅ 1.0%,
Honeycomb catalyst (hereinafter referred to as catalyst C) consisting of MoO ₃ 5.5%, TiO ₂ 93.5%, V ₂ O ₅ 2.0%, Fe ₂ O ₃ 3.0%,
Honeycomb catalyst (hereinafter referred to as catalyst D) consisting of CuO 2.5%, TiO ₂ 92.5%, V ₂ O ₅ 1.0%, MoO ₃ 3.0%,
A honeycomb catalyst (hereinafter referred to as catalyst E) consisting of 5.0% WO ₃ and 91.0% TiO ₂ was used for 12,000 hours in boiler exhaust gas under the conditions shown in Table 1.
As shown in Table 2, the denitrification rate and SO ₂ conversion rate at 380°C showed a decrease in catalyst performance compared to the initial stage.

【table】

[Table] The five poisoned catalysts with degraded performance were cleaned using an ultrasonic cleaning device in water or an aqueous solution of an inorganic acid with an amount three times the apparent volume of the catalyst under the conditions shown in Table 3. Immersing the catalyst in a monoethanolamine solution of ammonium tungstate in WO ₃
The catalysts were impregnated and supported in the amount shown in Table 3 in terms of the amount of catalyst, dried, and calcined under the conditions shown in Table 3 to obtain regenerated catalysts No. 1 to No. 33. Then, the denitrification rate and SO ₂ conversion rate of these regenerated catalysts were comparatively measured under the exhaust gas conditions shown in Table 1. The results are shown in Table 3. For comparison, those outside the scope of the present invention are listed as comparative examples, and those made using the conventional method are listed as conventional examples in Table 3.

【table】

[Table] As is clear from the results in Table 3, according to the catalyst regeneration method of the present invention, both the denitrification rate and the SO ₂ conversion rate can be completely restored to their initial characteristics.
Both the denitrification rate and the SO ₂ conversion rate could not be recovered to their initial values in the cases outside the scope of the present invention and those using the conventional method. As described above, in the present invention, after cleaning the poisoned denitrification catalyst containing vanadium and titania, both the denitrification rate and the SO ₂ conversion rate can be completely restored to their initial values by a simple operation of impregnating and supporting a predetermined amount of tungsten. It is an extremely useful regeneration method for denitrification catalysts containing vanadium and titania, which are currently used in large quantities to remove nitrogen oxides from boiler exhaust gas in thermal power plants, etc., and is an industrially useful method. This is a method for regenerating poisoned denitrification catalysts.

Claims (1)

[Claims] 1 In a method for regenerating a denitrification catalyst containing at least vanadium and titania in which nitrogen oxides in exhaust gas are removed by catalytic reduction in the presence of ammonia, the poisoned catalyst is washed with water or an inorganic acid solution and then immersed in a solution containing tungsten. per 1 ^m3 of apparent volume of catalyst
A catalyst is impregnated and supported with 0.01Kg to 10Kg of tungsten compound in terms of WO ₃ , and then dried at 400 to 650℃.
A method for regenerating a denitrification catalyst, which is characterized by firing the denitrification catalyst.