JP2015150521A - Exhaust gas purification method and system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a purification method and a system, which can reduce emission of NO contained in NOx.SOLUTION: The exhaust gas purification system 11 includes: a purification cylinder 3 that has a forced mixer 19 for mixing oxygen and/or air with an exhaust gas containing NOx and an underwater foam maker 35 foaming a nitric acid gas mixed with oxygen underwater to cause the water to absorb the gas and obtaining a nitric acid aqueous solution.

Description

  The present invention relates to a purification method and apparatus for waste gas containing nitrate gas, and more particularly, to a purification method and apparatus for waste gas containing nitrate nitrogen oxide (NOx).

  In small-scale smelting and refining for the recovery of valuable and useful metals, nitric acid is used for dissolution, where a gas containing NOx called nitrate gas is generated. In the following description, nitrate gas is abbreviated as NOx.

  In addition, even in the business of recovering reusable metals from electronic devices and parts, also known as “urban mines,” the generated NOx has become a concern for air pollution, greenhouse effect, ozone layer destruction, and health hazards. ing.

  Furthermore, NOx is also contained in exhaust gas discharged from power plants, various factories, and automobiles.

In the following description, NOx generated when recovering valuable, useful metals and renewable metals and exhaust gas from a power plant are collectively referred to as waste gas containing NOx. Such NOx is often a mixture of nitric oxide (NO) and nitrogen dioxide (NO ₂ ), and also contains other nitrogen oxides. In addition, PM2.5, pollen, etc. are further contained in waste gas.

Waste gas containing NOx is released into the atmosphere after being converted into nitrogen gas (N ₂ ) using a chemical or a catalyst in a waste gas purification device for purifying the waste gas.

  Examples of the waste gas purification device or the waste gas purification method for purifying waste gas containing NOx include those shown in the following Patent Documents 1 to 3.

The apparatus of Patent Document 1 performs an ammonia exhaust gas purification method for denitrating carbon monoxide (CO) and NOx to N ₂ or the like using an ammonia (NH ₃ ) reduction method, and further a catalyst therefor Also disclosed.

Patent Document 2 discloses a method for controlling the concentrations of nitrogen oxides, hydrocarbons, and carbon monoxide together with purification of exhaust gas. More specifically, the exhaust gas purification method according to Patent Document 2 uses two types of catalysts to reduce NOx with carbon monoxide (CO), while the remaining CO is converted to carbon dioxide (carbon dioxide; CO ₂ ). This is done by oxidizing.

Further, Patent Document 3 discloses an apparatus for purifying waste gas that generates N ₂ by catalytic reduction of NOx in the presence of hydrocarbons using a carrier material having a special catalytic action.

On the other hand, in Patent Document 4, an activated carbon bed is arranged in a hollow tower, NOx is introduced from above the activated carbon bed, and water or a weakly acidic aqueous solution (nitric acid aqueous solution) is sprayed from above the tower. , as well as oxidize NO to NO _2, the NO ₂ is absorbed in water, a method for recovering has been proposed as a nitrate aqueous solution.

JP-A-10-5591 JP-T-2004-508158 JP-A-10-28842 Japanese Patent Publication No. 1-17734

However, all of the waste gas purification methods and apparatuses described in Patent Documents 1 to 3 reduce NOx to N ₂ for purification. As a result of this purification, N ₂ is discharged. All of the discharged N ₂ contains some nitric oxide (NO). For this reason, NO is naturally oxidized in the atmosphere and NO ₂ is generated, so it cannot be said that the NOx waste gas purification device is perfect.

  Moreover, in patent documents 1 thru | or 3, the gas phase reaction made to contact a catalyst in a gaseous phase state is main. Even if a liquid phase reaction is performed, nitric oxide (NO) is generated in NOx. Since NO hardly dissolves in water, nitric oxide (NO) is not removed simply by passing water.

  Furthermore, the waste gas purification methods and apparatuses disclosed in Patent Documents 1 to 3 have a problem in terms of purification costs because they use expensive catalysts that reduce NOx and the like.

On the other hand, in the NOx recovery method disclosed in Patent Document 4, NO in the waste gas is insoluble in water and has a lower specific gravity than NO _2, so that it collects in the upper part of the tower. For this reason, NO remains in the space above the activated carbon bed in the tower. Activated carbon adsorbs organic matter and carbon monoxide (CO), but does not adsorb water and NO. For this reason, the oxidation reaction from NO to NO ₂ hardly occurs on the surface of the bed of activated carbon. Therefore, the apparatus described in Patent Document 4 is not suitable because the efficiency for recovering NO as a nitric acid aqueous solution is not good.

  The waste gas includes PM2.5 and pollen in the atmosphere. In order to remove these, a filter cloth is used. However, in many cases, PM2.5 and pollen cannot be removed because the filter cloth often passes through the filter cloth.

  Therefore, a technical problem of the present invention is to provide a method and apparatus for purifying waste gas containing nitrate gas that can reduce NO emissions.

  According to one aspect of the present invention, oxygen and / or air is forcibly mixed with waste gas containing NOx to obtain a waste gas obtained by mixing the oxygen and / or air, and the oxygen and / or air. And a submerged foaming step in which a nitric acid aqueous solution is obtained by causing the waste gas mixed with water to be foamed into water to be absorbed in water.

  According to another aspect of the present invention, a forced mixer for forcibly mixing waste gas containing NOx and oxygen and / or air, and foaming the waste gas mixed with oxygen and / or air into water. By doing so, a waste gas purification device having a purification cylinder provided with an underwater foamer that is absorbed in water to obtain an aqueous nitric acid solution is obtained.

  The purification method and apparatus according to the present invention can reduce NO emissions when purifying waste gas.

It is a schematic sectional drawing which shows the whole structure of the purification system 11 by embodiment of this invention. FIG. 2 is a schematic partial cross-sectional view showing a purification cylinder 3 in FIG. 1.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic sectional view showing an overall configuration of a purification system 11 according to an embodiment of the present invention. FIG. 2 is a schematic partial sectional view showing the purification cylinder 3 of FIG.

  The purification system 11 shown in FIG. 1 includes a purification device 9, a gas purification device 5 in which activated carbon 29 is stored in an activated carbon container 30, and a filtration device 7 having a filter cloth 33.

  The purification device 9 has a water tank 1 and a plurality of purification cylinders 3 immersed in water 2 in the water tank 1. Since the lower end of the purification cylinder 3 is opened, the water 4 in the water tank and the water 2 in the purification cylinder 3 communicate with each other and have a water surface having substantially the same height.

  As shown in FIG. 2, the purification cylinder 3 includes a purification container 13, a water sprayer 41 disposed near the upper end in the purification container 13, and a foaming foam disposed on the lower end side in the purification container 13. It has an underwater foaming device 35 having pores, a foam diffusion plate 37 disposed immediately above the underwater foaming device 35, and a multi-surface resin portion 39 disposed between the water sprayer 41 and the foam diffusion plate 37. doing. The water sprayer 41 is connected to a water supply pipe 23 that supplies water from the outside. In addition, an oxygen forced mixer 19 is provided outside the purification container 13.

Air or oxygen (O ₂ ) 16 is supplied to an oxygen forced mixer 19 via a pipe 17. On the other hand, the waste gas 15 is supplied to the oxygen forced mixer 19 via the waste gas pipe 18.

The air or oxygen (O ₂ ) 16 and the waste gas 15 supplied to the oxygen forced mixer 19 are forcibly mixed and supplied to the underwater foamer 35 via the pipe 21 as an oxygen mixed gas. The oxygen mixed gas of the waste gas 15 that is forcibly mixed with air or oxygen (O ₂ ) 16 is foamed into the water 2 from the pores of the underwater foamer 35. The foamed air or oxygen (O ₂ ) 16 and the oxygen mixed gas foam 36 of the waste gas 15 are further converted into a foamed foam 36 by a foam diffusion plate 37 made of a perforated plate disposed immediately above the underwater foamer 35. A finely divided bubble 38 is formed to increase contact with water. Thereby, NO ₂ in the waste gas 15 forcedly mixed with air or oxygen (O ₂ ) 16 is absorbed by the water 2.

  The multi-surface resin part 39 has a multi-surface resin made of porous polyvinyl chloride filled in order to further increase the mutual contact area between the mixed gas bubbles 38 and water on the surface.

  On the other hand, water 40 is sprayed onto the multi-surface resin part 39 from the water sprayer 41 disposed above the multi-surface resin part 39.

  Referring again to FIG. 1, the water 4 in the water tank 1 and the water 2 in the purification cylinder 3 communicate with each other through an opening at the lower end of the purification cylinder 3. Therefore, the water 2 and the water 4 are always mixed.

  The gas component of the water 4 in the water tank 1 is separated from the liquid component (nitric acid aqueous solution) and sent to the clean container 5 through the pipe 25. In the clean container 5, the separated gas components pass through the layer of activated carbon 29, organic matter, PM2.5, carbon monoxide CO, and the like are removed, and are discharged into the atmosphere as exhaust 28 from the exhaust port 27. .

  On the other hand, the aqueous nitric acid solution, which is a liquid component of the water 4 in the water tank 1, is introduced into the filtration device 7 through the pipe 31, passes through the filter cloth 33, and is collected as the wastewater 43 of the aqueous nitric acid solution.

  Next, with reference to FIG.1 and FIG.2, operation | movement of the purification system by embodiment of this invention is demonstrated.

In FIG. 1 and FIG. 2, first, at point (A), the waste gas containing NOx is forcibly mixed by air or oxygen forcible mixer 15 by 2 to 3 times. The oxygen mixing amount is preferably as much as possible, but is preferably ³ m ³ / min or more, more preferably in the range of ³ m ³ / min to 30 m ³ / min in terms of the oxygen mixing amount. Here, at the point (A), most of the low-valence nitrogen oxides NO in the waste gas react with oxygen as shown by the following formula (1a) to produce a tetravalent or higher nitrogen oxide ( It is oxidized to NO ₂ ). Here, NO ₂ and N ₂ O ₄ (a dimer of NO ₂ ) are in an equilibrium state at room temperature, as shown in Formula (1b).

Next, the oxygen mixed gas of the waste gas 15 forcibly mixed with air or oxygen (O ₂ ) 16 is sent to the underwater foamer 35 through the pipe 21, and from the pores of the underwater foamer 35, Foam in water 2 as indicated by reference numeral 36. The foam 36 is refined by a foam diffusion plate 37 made of a perforated plate disposed immediately above the underwater foaming device 35 to increase contact with the water 2 as indicated by reference numeral 38.

  Further, the finely divided bubbles 38 are increased in mutual contact between the oxygen mixed gas and the water 2 by the multi-surface area resin 39 disposed on the upper part of the bubble diffusion plate 37. Water 40 is sprayed onto the multi-surface area resin 39 by a water sprayer 41 from above. Here, on the surface of the multi-surface resin layer 39, reactions of the following formulas (2), (3), and (4) occur.

At point (B), NO generated from the water 2 or unreacted NO in the waste gas 15 forcibly mixed with the oxygen 16 exists. Unreacted NO is oxidized into NO ₂ by oxygen supplied by bubbles floating on the liquid surface, as shown in the formula (1a) or (1b), and the water 40 sprayed from the water sprayer 41 Contact with water vapor. As a result, as shown in the above formula (4), NO ₂ is dissolved (hydrolyzed) in water 2 to generate an aqueous nitric acid solution.

Further, a part of the unreacted NO comes into contact with oxygen (O ₂ ) in the space and water 2, 40 or water vapor, so that as shown in the above formulas (2) to (3), Dissolved (hydrolyzed) to produce nitrous acid, and nitric acid is produced in water 2.

  In the illustrated example, there is also a space indicated by a point (C) in the upper part of the water 4 in the water tank 1 other than the purification cylinder 3. Even when NO remains in the water 4 stored below the space (C), it moves to the space (C) and therefore does not remain in the water 4. Note that a minute amount of NO in the space (C) generates an aqueous nitric acid solution in the water 4 by a reaction similar to that in the purification cylinder.

  The gas component of the water 4 in the water tank 1 is exhausted as the exhaust 28 via the gas purification device 5 including the activated carbon layer 29 inside the container 30. Note that organic matter, PM2.5, and carbon monoxide (CO) contained as gas components in the water 4 are absorbed by the activated carbon layer and are not contained in the exhaust 28.

  On the other hand, the liquid component of the water 4 in the water tank 1 is a nitric acid aqueous solution, which is filtered through the filter cloth 33 and taken out as drainage 43 made of the nitric acid aqueous solution.

  Examples will be described below, but the present invention is not limited thereto.

Example 1
As shown in FIG. 1, a waste gas purification device 9 is used, and two washing towers 3 shown in FIG. 2 are set up in a water tank 1 filled with water at about 80 cm and connected to a clean container 5 and a filtration device 7, respectively. The following experiment was conducted.

The oxygen concentration of the oxygen forced mixer 19 shown in FIG. 1 and FIG. 2 is 3 m ³ / min, and after 15 minutes and 60 minutes have elapsed, the NO concentration at each point (A) to (D) shown in FIG. 1 is measured. did. The results are shown in Table 1 below.

  As shown in Table 1, as the operation time increases from 15 minutes to 60 minutes, the NO concentration decreases from 250 ppm to 100 ppm at point (B), but at point (C), any operation Also in time, it is 20 ppm which is below the emission standard value (60 ppm to 100 ppm) of the gas-fired boiler of the Ministry of the Environment. In the exhaust of (D), it is less than 1 ppm at any operating time.

(Example 2)
Next, the NO concentrations at points (A) to (D) shown in FIG. 1 were measured in the same manner as in Example 1 except that the oxygen mixing amount was 10 m ³ / min and 30 m ³ / min.
The results are shown in Table 2 below.

As shown in Table 2 above, as the oxygen mixing amount increases at 10 m ³ / min and 30 m ³ / min, the NO concentration at point (B) decreases from 250 ppm to 100 ppm, respectively (C) In any respect, in any oxygen mixing amount, it is 20 ppm which is below the emission standard value (60 ppm to 100 ppm) or less of the gas-fired boiler of the Ministry of the Environment. In the exhaust of (D), the oxygen mixed amount operating time is less than 1 ppm.

  As described above, in the present invention, nitric acid is used for dissolution in small-scale smelting and refining for the recovery of valuable and useful metals, but the nitrate gas generated there is purified only with water. It is easy and can be released as an aqueous nitric acid solution without releasing NO into the atmosphere.

  Moreover, even in the business of recovering reusable metals from electronic devices and parts, which are also called “urban mines”, NO is not released and it is easy without fear of air pollution, greenhouse effect, ozone layer destruction, and health damage. Recovery becomes possible.

  In the present invention, the recovered nitrate water can be reused or neutralized and drained with an alkaline chemical or the like.

  Furthermore, according to the present invention, airborne particulate matter (equivalent to PM2.5 and cedar pollen) can be taken into water and filtered and removed by underwater foaming and shower purification.

  As described above, according to the present invention, the present invention is most suitable for a waste gas purification device that purifies waste gas containing NOx.

DESCRIPTION OF SYMBOLS 1 Water tank 2,4 Water 3 Purifying cylinder 5 Gas purifier 7 Filtration apparatus 9 Purifying apparatus 11 Purifying system 13 Purifying container 15 Waste gas 16 Oxygen (O ₂ )
17 Piping 18 Waste Gas Piping 19 Oxygen Forced Mixer 21 Piping 23 Water Supply Piping 25 Piping 27 Exhaust Port 28 Exhaust 30 Activated Carbon Container 31 Piping 33 Filter Cloth 35 Submerged Foamer 37 Foam Diffuser 39 Multi-Surface Resin Portion 40 Spray Water 41 Water Sprayer 43 Drainage

Claims (10)

  A mixing step for obtaining a waste gas in which oxygen and / or air is forcibly mixed with a waste gas containing NOx, and a water for obtaining a nitric acid aqueous solution by foaming the waste gas mixed with oxygen or air into water and absorbing it into water. A waste gas purification method comprising: a foaming step.   2. The waste gas purification method according to claim 1, wherein the underwater foaming step further includes foaming using a foamed fine diffusion plate.   The waste gas purification method according to claim 1 or 2, wherein the gaseous component in the aqueous nitric acid solution is released through the activated carbon layer.   The waste gas purification method according to any one of claims 1 to 3, wherein the underwater foaming step oxidizes the waste gas mixed with oxygen or air or nitric oxide (NO) in the aqueous nitric acid solution. And a method for purifying a waste gas, comprising the step of generating a nitric acid aqueous solution by absorbing it in water. The waste gas purification method according to any one of claims 1 to 4, wherein the oxygen mixing step is 3 m ³ / min or more in terms of an oxygen mixing amount. apparatus.   A forced mixer that forcibly mixes oxygen and / or air with waste gas containing NOx, and water that foams the waste gas mixed with oxygen and / or air into water and absorbs it in water to obtain an aqueous nitric acid solution. A waste gas purification device comprising a purification cylinder provided with a foamer.   The waste gas purification apparatus according to claim 6, further comprising a foam refined diffusion plate installed immediately above the underwater foamer of the purification cylinder.   The waste gas purification apparatus according to claim 6 or 7, further comprising a clean container having an activated carbon layer, wherein the clean container discharges a gaseous component of the nitric acid aqueous solution through the activated carbon layer and discharges it as exhaust gas. Exhaust gas purification device.   The exhaust gas purification apparatus according to any one of claims 6 to 8, wherein the purification cylinder oxidizes nitrogen monoxide (NO) in the waste gas mixed with the oxygen or air or the nitric acid aqueous solution, A waste gas purifier comprising absorbing water to produce an aqueous nitric acid solution. 10. The waste gas purification apparatus according to claim 6, wherein the oxygen forced mixer is forcibly mixed at 3 m ³ / min or more in terms of an oxygen mixing amount.

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