KR800001304B1 - Process for removing nox and so2 from waste gas - Google Patents

Abstract

Radiation or electron beams are used for removing NOx and SO2 from a waste gas. The waste gas is transferred into a reactor and radiated at more than 105 rad/sec., and the resulting mist or solid materials, formed from NOx and SO2, are removed by filters or electric dust collectors. Thus, electron beam was used for treating a waste gas contg. 1000ppm SO2 and 310 ppm NOx at 106 rad/sec to remove 38% of SO2 and approximately 100% of NOx.

Description

New method for removing nitrogen oxides and sulfur dioxide from flue gas

FIG. 1 shows the relationship between the dose rate, the desulfurization rate of the effluent gas, and the denitrification rate in Examples and Comparative Examples of the present invention.

The present invention relates to a novel process for removing contaminants, in particular sulfur dioxide and nitrogen oxides, from effluent gases generated by various chemical processes and combustion of carbonaceous fuels. More specifically, the present invention treats the effluent gas by ionizing radiation or ultraviolet rays, and changes these pollutants into particles or spray forms, thereby allowing particles or spray forms by conventional collecting devices such as electrostatic precipitators, filters, and cyclones. The present invention relates to a method for treating pollutants of the present invention.

Today, various industrial plants, such as metallurgical processes, iron mills, sulfuric acid, nitric acid and other acid manufacturing plants, paper mills, nuclear plants, etc., generate large amounts of effluent gases from various sources. Effluent gas sources also include various combustion devices, research institutes and laboratories, and automobile engines. The total amount of these effluents generated throughout the country and released into the atmosphere is immense.

These effluent gases are usually sulfur dioxide, various types of nitrogen oxides (hereinafter referred to as NOX), harmful gases such as ozone, carbon monoxide, carbon dioxide, hydrogen fluoride and hydrogen chloride and fly ashes generated from coal minerals. Iii) particulates derived from, for example, aluminum silicate, coal dust or grains, coke dust, dust from post- or roasted concentrates from metallurgical fine powders, sulfuric acid and other acids in the form of sprays, etc. It consists of one or more pollutants selected from among the streams.

Many efforts have now been made to remove these pollutants from the effluent streams before they are released to the atmosphere, and many useful methods and devices have been developed. However, it is not easy to satisfactorily remove sulfur dioxide (SO ₂ ) and nitrogen oxides (NOX), especially nitrogen oxides, among the contaminants described above, any method that has proven to be practical in practice to this day. There was no. In addition, sulfur dioxide and nitrogen oxides are particularly harmful to humans and toxic. In addition, these pollutants are considered to be the most important factor in the photochemical smog phenomenon, which is one of the most serious problems for people living in the city today.

Therefore, the present inventors have concentrated their research on a method for removing sulfur dioxide and nitrogen oxides generated from the effluent gas. Therefore, in particular, the method for removing the nitric acid compounds and sulfur dioxide will be described below.

However, the improved process of the present invention is particularly useful for the removal of sulfur dioxide and nitrogen oxides, but this method is also useful for the removal of other contaminants as described above, and the main purpose of the present invention is to release effluent gas into the atmosphere. Prior to this, it is to provide an effective and efficient method for purifying these effluent gases to a satisfactory degree.

The gaseous NOX and SO ₂ can be converted into spray and SO ₂ or solid particles by ionizing radiation or by irradiating ultraviolet light to the effluent gas containing NOX and SO ₂ . The term "radiation" refers to ionization radiation and ultraviolet rays, and the term "ionization radiation" refers to any α-ray, β-ray, γ-ray, X-ray, accelerated electron beam, accelerated particle beam, and the like. With the above irradiation treatment method, NOx in the effluent gas furnace can be almost completely removed. Although there are many useful methods for satisfactorily removing SO ₂ and other contaminants from the effluent gas, considering that only the irradiation treatment method is effective for the removal of NOX, the irradiation treatment method is most important for NOx removal. You will see that this is a valid method. However, this method has not yet been implemented on an industrial scale because of deficiencies such as cost problems.

It is therefore an object of the present invention to provide an improved method for removing NOx and SO ₂ from effluent gas by means of an irradiated treatment method which can be economically implemented and industrially used.

In devising and establishing the method, the present inventors have conducted a lot of research in various aspects.

In one of the studies, the inventors focused their attention on the relationship between irradiation conditions and pollutant removal rates. That is, the present inventors continued to study the effect of the irradiation treatment of the electron beam on the removal rate of the gas pollutant by using the electron beam accelerator and the effluent gas generated during Class B heavy oil combustion. As a result of irradiating the effluent gas with the electron beam emitted from the accelerator, as a result of the irradiation of the electron beam, a specific specific dose effect effective for removing contaminants in the effluent gas, mainly NOX and NO ₂ , is effective. The inventors have discovered that there is. In other words, the present inventors found that sulfur dioxide and nitrogen oxides can be more effectively removed in the process of purifying the effluent gas by the electron beam irradiation treatment when high dose rate irradiation is used rather than low dose rate irradiation. Found. That is, even if the total dose given to the effluent gas is the same, the irradiation treatment at a higher dose rate is more effective than the irradiation treatment at a lower dose rate.

When irradiating gaseous substances by radiation, such as when polymerizing ethylene by radiation, low dose rates are usually more effective than high dose rates in generating effective reactions between radicals and ions normally produced. In addition, the above results were unpredictable because they were extinguished before reacting with monomers of high yields of radicals and ions generated by high dose irradiation.

Based on the unexpected finding described above, the present inventors have completed an improved method of removing gaseous pollutants, mainly NOX and SO ₂ , from industrial effluent gases.

In carrying out this improved method, it is possible to perform irradiation treatment satisfactorily using electron beam of high energy from a source such as a full-length line accelerator or the like.

And the dose rate that can be used is 10 ⁵ rads / sec in the range 10 to ¹⁵ rads / sec, 10 ⁵ Rad / sec, and a 10 ¹⁰ rads / sec preferably at, and most preferably from 10 ⁵ rads / sec 10 ⁸ rads / sec Do. The total dose required to satisfactorily remove contaminants is in the range of 1 × 10 ⁶ to 1 × 10 ⁷ rads.

In carrying out this improved method, the residence time of the outflow gas in the reaction chamber is usually between 1 and 20 seconds. However, if necessary, a high dose rate irradiation treatment can be carried out, so a very short residence time such as less than 1 second can be used.

The excellence of this improved method described above by the peculiar "non-dose effect" will now be described by way of examples.

Example 1

A heavy oil combustion gas containing 10 ppm SO ₂ and 310 ppm NO x 10 nm ³ / hour (standard cubic meters per hour) was transferred to the reaction chamber where the dose rate was 6.45 × 10 ⁵ rads / sec. Irradiation was carried out at 150 ° as the dose of the rad. The irradiated gas was then transferred to an electrostatic precipitator to collect hardened and bulky contaminants. Sample gas was collected from the airflow coming out of the electrostatic precipitator, and NOx and SO ₂ contents were measured. The contents of SO ₂ and NOX were 610 ppm and nearly 0 ppm, respectively.

That is, the desulfurization ratio was 39%, and the denitrification ratio was almost 100%.

Example 2-4

Similar experiments were conducted under the same conditions as in Example 1 except that the dose rates were 2.15 × 10 ⁵ rads / sec, 4.3 × 10 ⁵ rads / sec and 8.6 × 10 ⁵ rads / sec, respectively. In each case, the investigations were all carried out with 0.97 sheets of electron beams. The results obtained in Example 1 together with the results obtained in Example 1 are shown in FIG.

Example 5-6 (Comparative Example)

Similar experiments were conducted under the same conditions as in Example 1, except that CO-60 was used as the irradiator and the dose rates were 200 rad / sec and 270 rad / sec, respectively. In each example, the total dose rate was 0.97 metrade. The desulfurization rate was less than 20% in each example, and the results are shown in FIG. 1 along with the results of other experiments.

Example 7-9

Example 1 except that the dose rates were 2.15 × 10 ⁵ rads / sec, 6.45 × 10 ⁵ rads / sec and 8.6 × 10 ⁵ rads, respectively, and the dose of the total electron beam was 2.5 metrade in each of the embodiments. Similar experiments were conducted under the same conditions as in. The results are shown in FIG. 1 along with the results of other experiments.

From the results shown in Example 1 and 9 and the above-described results, it was found that a higher dose rate than a lower dose rate is more effective in removing contaminants, subcontaminated SO ₂ and NOX by the irradiation treatment method. I can tell.

The results and numerical values also show that the dose rate required to carry out this process effectively and efficiently is 10 ⁵ rad / sec and the total dose requires about 1 metrade.

The most important irradiation source that can be best used in practicing the present invention is an electron beam accelerator. The reason why the electron beam accelerator is the most important irradiation source is for the following reason.

As is known, the "absorbed dose rate" obtained when using a radioisotope as an investigator has a maximum of 1 metrade / hour, or 300 rad / sec, at the current level of technology. It is difficult to achieve higher absorbed dose rates because of the problem of “self-absorption”, ie radiation absorption by the radioisotope itself and the heat generated as a result of the melting of the radiation. Therefore, radioactive isotopes are used for a large amount of effluent gas, and isotope irradiation treatment mainly for desulfurization and denitrification is almost impossible, such as obtaining a total dose of more than 1 kilorad. When CO-60 is used as a surveyor, a large amount of CO-60 and irradiation time are required to satisfactorily treat the effluent gas at a dose of 1 metrade / hour. However, it is almost impossible to remain in the reactor for several hours in order to perform irradiation treatment for industrial effluent gas, which is usually contained in a very large amount.

In the practice of the industrial method for irradiating the effluent gas, the maximum allowable residence time of the gas in the reactor is about 20 seconds. And the total dose required to remove this contaminant from the effluent gas is preferably 2 to 3 metrade, but the minimum required dose is 10 ⁵ rad / sec. to be.

There is an electron beam accelerator as one of the commercially available irradiation sources that can provide the above high dose. Since there are several high output accelerators that can easily provide high dose rates of about 10 ⁷ rad / sec, the improved method described above can be used to carry out irradiation treatment of effluent gas in a short time and economically. You can do it.

Another advantage of using electron beam accelerators is that they are more stable to operate and the radiation is extinguished when the switch is interrupted. In addition, it is possible to create various energy levels for emitting radiation while using an electron beam accelerator. Therefore, this process can be carried out most economically by rapidly changing the dose rate and the total dose according to the change of the amount of effluent gas to be treated or the amount of pollutant in the effluent gas.

However, another important advantage of using an electron beam accelerator is that the light shielding device is quite satisfactory because the average range of the electron beam (ie the average length of the track) is short.

From the above description, it can be understood that the method of irradiating industrial effluent gas to remove contaminants is industrially easy only by using an electron beam accelerator in view of feasibility, stability and economy. will be.

It should be noted that it is a known fact in the radiation chemistry field that the irradiation effect of electron beams is completely different from the irradiation effects of γ-rays, α rays and the like. For example, in the polymerization of ethylenically unsaturated monomers or cross-linking polymerization for curing prepolymers of unsaturated polyester resins, 1-method gamma-ray irradiation at a dose rate of about 10 ⁴ rad / hour by irradiation treatment The effect of the treatment is almost the same as the effect of irradiation of 10 sheets of 10 electron beams at a dose rate of about 10 ⁵ rad / hour. Therefore, in the present invention, the fact that the irradiation effect of more than about 10 ⁵ rads / sec electron beam 1 metrade was significantly more effective than the low dose rate 1 metrade irradiation effect was an unexpected method.

Claims (1)

The exhaust gas is transferred to the reaction chamber inlet to allow the exhaust gas to pass through the reaction chamber, and at the same time, irradiation treatment is performed at a dose rate of about 10 ⁵ rad / sec or more to the exhaust gas by an electron beam from an accelerator installed near the reaction chamber. Nitrogen in flue gas, characterized by converting the gaseous contaminants, NOX and SO ₂ into spray and solid particles, and then collecting the produced particles with a spray and dust collector. New method of removing oxides and sulfur dioxide.

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