JPS6018450B2 - Method for treating exhaust gas containing nitrogen oxides - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating exhaust gas containing nitrogen oxides discharged from various boilers and the like.

Conventionally, many catalysts have been known that reduce nitrogen oxides such as N◯ and N02 in the presence of ammonia and decompose them into nitrogen and water.

Typical examples include titania, vanadium, tungsten, molybdenum, iron, copper, etc. Even when these useful catalysts are used, for example, 300
When used at a relatively low temperature of 0.00 or lower, reaction products between S02 and S03 gases in the exhaust gas and ammonia are formed on the catalyst surface, resulting in a decrease in catalyst activity and a disadvantage of lack of durability. Furthermore, when used at temperatures above 300 pm, dust components contained in the exhaust gas, especially alkali metal salts, adhere to the catalyst surface and gradually react with the catalyst component elements to form alkali metal salts. It also had the disadvantage that the catalyst components were worn out by the components, resulting in a decrease in activity. In addition to the reduction in catalyst activity, a large amount of SQ gas contained in the exhaust gas is oxidized and converted to S03 by the catalyst component, forming compounds with ammonia and sulfuric acid mist, which corrodes the catalytic reaction equipment and boiler equipment. It had drawbacks such as being stowed away.

The present inventors conducted research to solve the above-mentioned drawbacks, and found that by supporting at least one or more protective film layers of titanium oxide, zirconium oxide, and tin oxide on the surface of the catalyst, Even when exhaust gas containing sulfur oxides and dust components is treated without loss of activity,
The catalyst component is not worn out by the dust components contained in the exhaust gas, nor is it poisoned by the dust components, and has extremely stable denitrification performance over a wide temperature range of 150 to 650 oo without deterioration of activity over a long period of time. The present invention was achieved by discovering and developing a catalyst that can be maintained for a long period of time. That is, the present invention provides a protective film layer of 1 to 100 μm consisting of at least one of titanium oxide, zirconium oxide, and tin oxide on the surface of the known catalyst used for the purpose of removing nitrogen oxides as described above. This protective film layer does not necessarily have to be in the form of an oxide when it is supported on the catalyst, but it has the form of an oxide at the end of the calcination after holding. It is fine as long as it is something.

The protective film layer is preferably formed of porous material having a porosity of about 30% to 70%, and the protective film layer is preferably made up of 95% particles with a particle size of 1 μm or less.
The best thing to do is to be moderate.

As for the material of the protective film layer, at least one or more of titanium oxide, zirconium oxide, and tin oxide are most effective in improving the durability of the catalyst. No significant effect on improving the durability of the catalyst was observed. The thickness of the material is best between 1 and 100 mm, and if the thickness exceeds 100 mm, the gas permeability becomes poor and the denitrification properties deteriorate. Moreover, if the thickness is less than 1 mm, the effect as a protective film for the catalyst will be reduced, which is not preferable. The raw materials for preparing the protective film layer of at least one of titanium oxide, zirconium oxide, and tin oxide of the present invention include titanium oxide, zirconium oxide, tin oxide, and various compounds that produce these oxides when heated. For example, titanic acid, titanium hydroxide, titanium sulfate, zirconium hydroxide, tin halide, tin sulfate, etc. can be mixed with water, aqueous ammonia,
Hydroxide precipitated with a caustic alkali or the like and titanium oxide obtained by thermally decomposing the hydroxide are also preferred raw materials. In addition, a method for supporting a protective film layer consisting of at least one of titanium oxide, zirconium oxide, and tin oxide on the catalyst surface includes at least one or more of titanium oxide, zirconium oxide, and tin oxide, which are appropriately used. It is also possible to crush the oxide with water or other binders and solvents as necessary, make it into a slurry, and spray it onto the base catalyst, or to mix the base catalyst in the slurry and then dry it. Then, it may be fired at 400 to 600 qC.

Furthermore, a base catalyst is impregnated in a solution of zirconyl sulfate, zirconyl nitrate, zirconyl ammonium carbonate, zirconyl chloride, titanium tetrachloride, zirconium tetrachloride, tin tetrachloride, titanium sulfate, etc., and titanium, zirconium, and tin are adsorbed. After drying, it may be fired at 400 to 6004°C. In addition, the form of the base catalyst supporting the protective film layer consisting of at least one or more of titanium oxide, zirconia oxide, and tin oxide may be formed into the final use form such as a commonly used bead shape or honeycomb shape. preferred catalysts.
Furthermore, in order to actually remove nitrogen oxides,
Ammonia is used as a reducing agent to reduce the amount of nitrogen oxides in the exhaust gas.
It is added by 5 moles or more, preferably about 1 to 2 moles.

In addition, the obtained mixed gas contains titanium oxide, zirconia oxide,
The space velocity (space velocity based on the sky column) of 200 to 1
00000/hour preferably 5000-50000/hour
Let it pass within the time range. Furthermore, the temperature during the reaction is 150
-650qo is preferably in the range of 250-500°C. In addition, in the case of flue gas, various measures are required for the type of reactor in which the present invention is carried out, since the flow rate of the gas to be treated is large. A variety of reactor types for use with catalysts can be used.

Next, the present invention will be explained in detail based on examples.

Composition ratio is V2051%, W035%, Ti02 in weight%
94%, 6 willows on one side, 3 square cells with wall thickness of 1 willow
Prepare a honeycomb-shaped catalyst with a length of 15 cm made of needles, dip the honeycomb catalyst into a slurry that forms a protective film layer made of the materials listed in Table 1, and after taking it out, add 120 qo of honeycomb catalyst.
After drying with hot air for 3M, the catalyst was calcined at 500 oo for 3 hours to obtain a catalyst supporting a protective film layer of the present invention as shown in Table 1.

The thickness of the protective film layer supported on the surface of this catalyst is
It was as described in the table. To evaluate the performance of these catalysts, six of the same catalysts were filled in a stainless steel reactor with an inner diameter of 800 mm and a length of 1,000 mm, and the NOx removal rate was measured by contacting with B heavy oil-fired boiler exhaust gas under the following conditions. The change over time and the conversion rate of S02 to S03 were also measured.

The results are shown in Table 1. In addition, the test exhaust gas contained NOx: 150-20 pm, S0x: 400-50 pm.
Snake pm, 02: 3-6%, duct: Contains 9/N of 50, gas temperature 350CC, SV value 10000Hr
-1, a durability test was conducted at NH3/NO=1.1. Measurement of N○x is carried out using chemiluminescence method reduced pressure type NO.
/NQ analyzer (Yanagimoto Seisakusho model ECL-77A). In addition, when measuring the conversion rate of SQ to S03, stop the injection of ammonia and wait 5 hours before measuring the conversion rate of SQ to S03 using the NDIR method.
The S02 concentration at the inlet and outlet was detected using two analyzers, and the conversion rate to S03 was determined using the following equation. S02 Conversion rate Mochi 0 Entrance S0
2 concentration - outlet S02 concentration XI.

〇Inlet S02 concentration For comparison, the same test as above was conducted on a catalyst without a protective film layer and a catalyst using a protective film layer of a material and thickness other than those specified in the present invention, and the results were as follows. are listed in Table 1.

As is clear from the results in Table 1, according to the method of the present invention, the durability of the catalyst is extremely high, and a high denitrification rate can be stably obtained for a long period of time. While the conversion was extremely low, the durability of the catalysts in both the conventional example and the comparative example was poor, and the conversion of S02 to S03 was extremely high.

As mentioned above, titanium oxide of 1 to 100 degrees on the surface,
In the method of the present invention, nitrogen oxides are removed at a temperature of 150 qC to 650 °C by mixing exhaust gas and ammonia in the presence of a catalyst carrying a protective film layer consisting of at least one or more of zirconia oxide and tin oxide. According to the research, this method not only improves the durability of the catalyst compared to conventional catalysts without a protective film layer, but also has an extremely excellent effect of suppressing the oxidation reaction that converts S02 in exhaust gas to S03. It is capable of removing nitrogen oxides from exhaust gas emitted from various combustion furnaces stably and at a high rate over a long period of time.
This is an industrially extremely useful method for treating nitrogen oxides.

Claims (1)

[Claims] 1 Exhaust gas containing nitrogen oxides is applied to the surface at 1 to 100%
Nitrogen oxide, which is mixed with ammonia in the presence of a catalyst supporting a protective film layer consisting of at least one of titanium oxide, zirconium oxide, and tin oxide of μ, and heated in a temperature range of 150 to 650°C. A method for treating exhaust gas containing