JPS618116A - Method for deodorizing waste gas - Google Patents

Abstract

PURPOSE:To lower energy cost, in a method for deodorizing dust-containing waste gas, by introducing waste gas into a reactor packed with a deodorizing and oxidizing catalyst at 250-700 deg.C without preliminarily applying dust removal treatment to said waste gas. CONSTITUTION:Dust-containing waste gas is introduced into a reactor comprising a deodorizing catalyst integrally molded into a honeycomb shape without receiving dust revoval treatment at 250-700 deg.C, pref., 300-600 deg.C and the superficial velocity of 0.5-10m/s, pref., 1-5m/s. If the superficial velocity is set to this degree, no dust is adhered to the surface of the catalyst and the accumulation thereof is prevented. As the deodorizing catalyst, any one having oxidizing activity may be used and, concretely, one of oxides of Ti, Al, Si and Zr, one of oxides of Cu, Cr, Fe, V, Mn, W, Ni, Co, Mo and Pb and, further, a platinum element are used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for deodorizing exhaust gas containing a high concentration of dust and organic compounds having a bad odor. To be more specific, the present invention uses heat that contains a large amount of hard inorganic dust discharged from scrap preheating furnaces, etc., and also contains malodorous organic compounds such as aldehydes generated from the thermal decomposition of paints, oils, fats, and plastics. The object of the present invention is to provide a deodorizing method for making gas odorless and pollution-free using a deodorizing oxidation catalyst.

For equipment that heats and melts scrap with an electric arc to make steel, so-called scrap preheating furnace equipment has been developed that saves energy by preheating the raw material scrap using high-temperature gas discharged from the electric furnace. In recent years, the number of installed bases has been increasing.

Raw material scrap is heated in a preheating furnace to 3006C to 600C by high-temperature gas discharged from the electric furnace, thereby reducing the amount of electricity consumed in the electric furnace. This includes empty cans and scrap car parts, and the paints, oils and fats applied to their surfaces, as well as synthetic resins and other contaminants mixed into these scraps, are heated in a preheating furnace. This causes thermal decomposition and is emitted as foul-smelling gases such as aldehydes, causing foul-smelling pollution.

In addition, these exhaust gases contain 10 to 50 y of hard inorganic dust such as iron oxide, zinc oxide, or manganese oxide.
/NM3, making it increasingly difficult to deodorize the exhaust gas of this system.

[Prior art]

The following methods can be considered for deodorizing this type of so-called dirty gas.

(a) Direct combustion deodorization method (b) Scrubber cleaning method using water, alkaline water, etc. (c) Catalytic combustion method using oxidation catalyst Usually, when adopting a method to deodorize scrap preheating furnace exhaust gas, the following points must be considered: These are efficiency and equipment and operating costs.

The direct combustion deodorizing method in (a) is suitable for treating this kind of dirty gas, but it requires a gas temperature of 700 to 900.
℃ and residence time is required to fully oxidize the malodorous substances.

Considering the large amount of gas emitted, the fuel cost required to raise the temperature of the exhaust gas is enormous, and may end up negating the energy-saving benefits that were the original purpose of installing a preheating furnace. do not have.

In addition, this system is difficult to adopt because it generates a large amount of nitrogen oxides due to the accumulation of exhaust gas in a high temperature range, which may cause secondary pollution.

The scrubber cleaning method (b) has the disadvantage of poor deodorizing efficiency and the high cost of wastewater treatment. As a method superior to the above two treatment methods, the catalytic combustion method using an oxidation catalyst (c) is superior to the above two treatment methods. Yes, this method is 150~4
Since it exhibits its oxidative deodorizing effect at a relatively low temperature of 50°C, fuel costs are low and there is no need for secondary treatment such as wastewater treatment. In addition, since it can be processed at low temperatures, there is no need to worry about the generation of nitrogen oxides. However, on the other hand, it has weaknesses such as clogging of the catalyst layer due to dust coexisting in the exhaust gas or deterioration of catalyst activity due to the accumulation of poisonous substances.

In particular, with granular oxidation catalysts and nicum-type catalysts with small openings (through-hole diameter) commonly used for deodorization, when a gas containing high concentration of dust, such as scrap preheating furnace exhaust gas, is passed through, the dust is quickly removed. Accumulation and clogging occur, leading to a sudden increase in pressure loss, and the product becomes unusable.

Therefore, exhaust gas containing a high concentration of dust, etc.
After installing an electrostatic precipitator and bag filter to remove dust, gas is passed through a reactor filled with an oxidation catalyst.
Generally, it is deodorized, but due to the heat resistance of the dust remover equipment, the temperature of the exhaust gas is lowered considerably and then passed through the dust remover, and then the temperature is raised again to the temperature required for deodorization. It is necessary to pass it through a catalyst layer.

The temperature of the scrap preheating furnace exhaust gas at the outlet of the preheating furnace is 300 to 600°C, and after lowering the gas temperature and removing dust with a dust remover as described above, the temperature is raised again, and the temperature is raised again with an oxidation catalyst. Deodorizing treatment involves an extremely large amount of heat loss, and no matter how good the deodorizing effect is,
This may not be economically viable for practical use.

[Problem that the invention seeks to solve]

The present inventors took advantage of the superior efficiency of the catalytic combustion method for deodorizing the foul-smelling exhaust gas containing high concentrations of dust as described above, and developed this method as a more economical treatment method in terms of energy costs. The present invention has been completed through repeated research into a method of deodorizing exhaust gas by passing it through a reactor filled with an oxidation catalyst without having to perform dust removal treatment in advance.

[Means for solving problems] The present invention is specified as follows.

(1) When deodorizing a malodorous gas that contains a large amount of dust (10 to 50 f/NM), the exhaust gas can be deodorized to 250 to 50 f/NM without pre-dedusting the dust mixed therein.
A method for deodorizing exhaust gas, characterized in that the exhaust gas is introduced into a reactor filled with a deodorizing oxidation catalyst at a temperature in the range of 700°C, preferably 300 to 600°C.

(2) The method according to (1) above, wherein the catalyst is integrally molded into a honeycomb shape and has an average through-pore diameter in the range of 3 to 12 g, preferably 4 to 8 mm.

(3) The superficial velocity of the exhaust gas when introduced into the reactor is adjusted to a range of 0.5 to 10 meters/second, preferably 1 to 5 meters/second (S, T, P). The method according to (1) or (2) above, characterized in that:

[For production]

The reason why the present invention limits the deodorizing catalyst to one integrally molded into a honeycomb shape is because the dust present in the exhaust gas is composed of hard oxides such as iron, zinc, and manganese. In the case of a catalyst whose surface layer is thinly coated with activated alumina and catalytic material 1 on a light honeycomb type carrier, the surface of the catalyst is scraped off by the dust contained therein, and the catalyst material on the surface layer peels off, resulting in significant activity deterioration. This is because there is no need to worry.

In other words, even if the surface of the catalyst is scraped by dust, a new active surface appears and the activity does not deteriorate due to catalyst surface peeling.

The average opening of the catalyst that is integrally molded into a honeycomb shape is preferably in the range of 3 to 12 holes.If the opening is smaller than this, the catalyst will become clogged with dust and the pressure drop in the catalyst layer will increase. In addition, when the opening is 128 or more, the contact efficiency becomes poor, the blow-through of the process gas becomes large, and the oxidative deodorizing efficiency decreases.

The superficial velocity of the exhaust gas introduced into the reactor is 0.5 to 10,
Preferably, 1 to 5 meters/second (8, T, P) is suitable. This is because dust adhering to the surface of the catalyst can be blown away to prevent dust from accumulating.

The composition of the catalyst integrally molded into a honeycomb shape may be any composition as long as it contains a catalytically active substance with recognized oxidation activity.

In particular, an oxidation catalyst C in which the molded catalyst itself has a BET surface area of 10 i/9 or more, especially 5oy7 or more.
If available, it will be used effectively.

That is, more specifically, an oxide of at least one element selected from the group consisting of titanium, aluminum, silicon, and zirconium, and copper, chromium, iron, vanadium, tungsten, manganese, nickel, cobalt, molybdenum, An oxidation catalyst comprising an oxide of at least one element selected from the group consisting of lead and color, and optionally containing a platinum group element such as platinum, palladium, or um, fully exhibits the effects of the present invention. .

Example 1 Binary oxide containing titanium and silicon [Tiov/s
+ot = 4 (molar ratio)] Powder 1500F
900 mA' of water and 752 starch were added, mixed well, and kneaded well with a kneader. After kneading while adding an appropriate amount of water, each hole diameter (equivalent diameter of the through hole) is 4 mm.
It was extruded into three types of honeycomb molds each having a pore size of 64 mm at 6 mm and 18 mW, and then dried and fired. Oxalic acid 5002 was dissolved in 6 oocc of water, and ammonium metavanadate 467 was added thereto, and the molded body was impregnated for 2 minutes, dried, and fired. The thus obtained molded body was immersed in an aqueous palladium nitrate solution having a palladium concentration of 1.6 P pd/l for 2 minutes, and then dried and fired.

The composition of the finished catalyst obtained is (Ti0z/5
iO2) 'vt05: Pd=89.95:
10: BET surface area 1157d/? at 0.05? Met.

Using this catalyst, a test machine was installed to conduct a deodorization test on the exhaust gas from a scrap preheating furnace.

To determine the deodorizing efficiency, the odor multiple and concentration of acetaldehyde contained in the gas at the inlet and outlet of the catalyst layer were measured using a three-point comparison method using a public method. Table 1 shows the results obtained.
Shown below.

Table 1 Test results (Initial data) Test conditions S V = 10,0OOI (r' temperature 350
The average amount of dust during the test was 26 r/NM, and the superficial velocity in the reactor was 28 m/s (sTp).The difference in the gas concentration before treatment is due to the difference in test time, and the concentration fluctuation in the exhaust gas in the preheating furnace is due to the difference in the gas concentration before treatment. This is because there is.

Example 2 A run test was conducted over a period of 10 days using the same catalyst used in Example 1 with a pore diameter of 6 mm and using the same scrap preheating furnace exhaust gas.

As for the determination of deodorizing efficiency, Example 1 was used on the first day and after 10 days.
A similar gas analysis was performed. The results are shown in Table 2.

Comparative Example 1 Example 2 using a conventional type honeycomb catalyst as a comparative example
A run test was conducted in parallel. The honeycomb contact seat used had an equivalent through-hole diameter of 1.5 mm.

A cordierite honeycomb carrier (210 cells/square inch) on which activated alumina was supported and 0.3% by weight of palladium as a catalyst material was used. The results are shown in Table 2.

Table 2 Test results Test conditions (Example 2) 8V 10,0OOHr' Temperature 350℃~4
Average dust t during oo℃ test 20~30f/NM
s Reactor superficial velocity 2.8 m/s (STP) (
Comparative example) 8V 10,000Hr' Temperature 350℃~4
Average dust amount during 00℃ test: 20-30 ri/NM
”Surface velocity in reactor 0.85 m/s (8TP
) Regarding the catalyst with a pore size of 6, no increase in ΔP in the catalyst layer was observed for 10 days, and the treatment performance after 10 days was similar to the data on the first day.

However, with the conventional catalyst used as a comparative example, high processing efficiency was obtained on the first day's data, but a sharp increase in ΔP occurred after one day, and eventually blockage occurred in the cell, so subsequent tests were continued. I can't do it anymore.

Claims (3)

[Claims] (1) When deodorizing a malodorous gas containing 10 to 50 g/NM^3 of dust, the exhaust gas is oxidized for deodorization at a temperature in the range of 250 to 700°C without removing the dust mixed therein. An exhaust gas deodorizing method characterized by introducing the gas into a reactor filled with a catalyst. (2) The method according to claim (1), wherein the catalyst is integrally molded into a honeycomb shape and has an average through-pore diameter in the range of 3 to 12 mm. (3) A claim characterized in that the superficial velocity of the exhaust gas when introduced into the reactor is adjusted to a range of 0.5 to 10 meters/second (S.T.P). The method described in (1) or (2).