KR20020050991A - Method for wet scrubbing of nitrogen oxides from flue gas - Google Patents

Abstract

PURPOSE: To remove nitrogen oxides from flue gas, a method for wet scrubbing is provided. It is possible to remove nitrogen oxides effectively by using the mixed solution of NaClO2, Na2SO3, NaOH with absorbent. CONSTITUTION: The process of wet scrubbing comprises the steps of (i) the producing stage of absorbent by mixing NaClO2, Na2SO3, NaOH; (ii) the contact stage of flue gas with the absorbent.

Description

Wet removal method of nitrogen oxide contained in exhaust gas {METHOD FOR WET SCRUBBING OF NITROGEN OXIDES FROM FLUE GAS}

[Industrial use]

The present invention relates to a method for the wet removal of nitrogen oxides (NO _x ) contained in the exhaust gas, in particular using a solution of NaClO ₂ , Na ₂ SO ₃ , and NaOH as a absorbent in the wet cleaning process of nitrogen oxides. It relates to a removal method for removing an oxide.

[Prior art]

Nitrogen oxides (NO _x ) produced during incineration or combustion processes are known to be the cause of acid rain and environmental degradation. Therefore, it is important to remove nitrogen oxides from the exhaust gas before it is released into the atmosphere.

In general, the method of removing the nitrogen oxide contained in the exhaust gas is largely divided into a dry process and a wet process. Double wet process is used to remove nitrogen oxides in exhaust gas from nitric acid manufacturing facilities and metal pickling processes, because the nitrogen oxides generated in these processes contain a lot of NO ₂ which is easily dissolved in water and easily removed. to be.

In such a wet cleaning process, an alkali solution such as NaOH or Na ₂ S is mainly used to remove nitrogen oxides in the exhaust gas. In this case, the reaction is shown in Scheme 1 below.

Scheme 1

However, nitrogen monoxide (NO), which occupies a large portion of nitrogen oxides, has low solubility in water, so that it is not soluble in water, and oxidation of NO ₂ is very low due to oxidation with oxygen. If the content is high, the removal efficiency is reduced.

Therefore, methods have been devised to solve the problems of the wet cleaning process. For example, the publication "Industrial & Engineering Chemistry: Process Design and Development, Col. 22, No. 2, pp.323-329, 1983" uses KMnO ₄ as an oxidant in NaOH solution to dissolve NO in water. By oxidizing to NO ₂ or NO _{3 which} is good, it shows that nitrogen oxide (NO _x ) removal efficiency can be improved. However, this method has a problem in that solid MnO ₂ is generated during the reaction and the washing tower is blocked.

In addition, a method of improving NO removal efficiency by using an oxidizing agent, NaClO ₂ , is known. In the well-known document "Chem.Eng.Comm., Col.174, pp.21-51, 1999", an absorbent liquid in which NaClO ₂ and NaOH are mixed is used. Discloses a method for removing NO. In this method, NO can be effectively removed, but there is a problem that a part of NO is oxidized to NO ₂ and is discharged without being removed from the absorbent liquid.

The present invention has been made in view of the problems of the prior art, and an object thereof is to provide an absorbent having a high removal efficiency of nitrogen oxide contained in exhaust gas.

Another object of the present invention is to provide a wet removal method for removing nitrogen oxides contained in exhaust gas using the absorbent.

[Means for solving the problem]

In order to achieve the above object, the present invention provides an absorbent having high removal efficiency of nitrogen oxide (NO _x ) contained in exhaust gas.

In addition, the present invention in the wet cleaning process of the nitrogen oxide contained in the exhaust gas,

a) mixing NaClO ₂ , Na ₂ SO ₃ , and NaOH to provide an absorbent; And

b) contacting the absorbent exhaust gas containing nitrogen oxides

It provides a wet removal method of nitrogen oxide comprising a.

Hereinafter, the present invention will be described in detail.

[Action]

In the present invention, in order to remove nitrogen oxides (NO _x ) contained in the exhaust gas, the exhaust gas containing nitrogen oxides is contacted using a solution containing NaClO ₂ , Na ₂ SO ₃ , and NaOH as an absorbent in a wet cleaning process. In this way, the nitrogen oxide contained in the exhaust gas can be effectively removed.

In the present invention, in the conventional method for removing nitrogen oxides contained in the exhaust gas by using an absorption liquid mixed with NaClO ₂ and NaOH, to improve the disadvantage that the NO ₂ generated by the oxidation of NO is not removed. , A solution of NaClO ₂ , Na ₂ SO ₃ , and NaOH is used as an absorbent.

Absorbent for removing nitrogen oxide gas of the present invention NO and NO to be removed₂It includes in an amount greater than the equivalence ratio according to the quantity, and ratio It is preferable. In addition, in actual use, it is used while continuing to replenish as much as the amount of the gas removal absorbing agent by the reaction with nitrogen oxides. Therefore, the use ratio of absorbent for degassing is NO, and NO₂It is preferable to adjust according to the ratio of.

In the cleaning method of the present invention, NaClO ₂ reacts with NO as a strong oxidant to produce nitric acid, or oxidize NO to NO ₂ . It reacts as in Scheme 2 below.

Scheme 2

Na ₂ SO ₃ in the oxidizing agent for removing the nitrogen oxide of the present invention serves to remove NO ₂ by the reaction shown in Scheme 3 below.

Scheme 3

NaOH used in the absorbent liquid in the present invention is used to maintain the pH of the absorbent liquid, which prevents NaClO ₂ from being degraded when the pH is lowered by nitric acid produced while being absorbed and removed by the nitrogen oxide.

The present invention will be described in more detail with reference to the following examples. However, the examples are not intended to limit the present invention to illustrate the invention.

EXAMPLE

Example 1

In order to measure the removal effect of nitrogen oxides, the removal efficiency was measured by passing a mixed gas mixed with 1600 ppm of NO in air at a flow rate of 2 L / min while bubbling a column containing 1 L of absorbent liquid. The concentrations of NaClO ₂ , Na ₂ SO ₃ , and NaOH used as the absorbent liquid were 5% by weight, respectively. One hour after the start of the reaction, the concentrations of NO and NO ₂ at the outlet of the absorption column are shown in Table 1 below.

Comparative Example 1

In order to measure the removal effect of nitrogen oxides, the removal efficiency was measured by passing a mixed gas mixed with 1600 ppm of NO in air at a flow rate of 2 L / min while bubbling a column containing 1 L of absorbent liquid. Only NaClO ₂ and NaOH were used as the absorbing liquid, and each concentration was 5% by weight. One hour after the start of the reaction, the concentrations of NO and NO ₂ at the outlet of the absorption column are shown in Table 1 below.

Absorbent Outlet concentration (ppm) Total NO _x removal rate (%) NO NO ₂ Nitrogen oxides (NO _x ) NaClO ₂ + Na ₂ SO ₃ + NaOH 0 25 25 98.4 NaClO ₂ + NaOH 0 182 182 88.6

According to Table 1, when only NaClO ₂ and NaOH was used, a lot of NO ₂ was discharged. However, the absorbents using NaClO ₂ , Na ₂ SO ₃ , and NaOH showed a large reduction in NO ₂ emissions, resulting in high NOx removal rates. .

As described above, the method of the present invention can effectively remove nitrogen oxides in the exhaust gas by using a mixture of NaClO ₂ , Na ₂ SO ₃ , and NaOH as an absorbent.

Claims (2)

Absorbent composition for removing nitrogen oxide gas comprising a mixed solution of NaClO ₂ and Na ₂ SO ₃ , and NaOH. In the wet cleaning process of nitrogen oxide contained in the exhaust gas, a) mixing NaClO ₂ , Na ₂ SO ₃ , and NaOH to provide an absorbent; And b) contacting the absorbent exhaust gas containing nitrogen oxides Wet removal method of nitrogen oxide comprising a.