JPS5824170B2 - High gas stew - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for efficiently removing NOx, which consists mostly of nitrogen monoxide (NO), such as nitrogen oxides (NOx) in combustion furnace exhaust gas, by a wet method. .

Absorbing liquids that can absorb and remove NO in the wet method include aqueous solutions of ferrous sulfate and sodium sulfite, which form complex salts with NO, and sodium sulfite has the effect of reducing NO to harmless nitrogen. It is known that there are

However, ferrous sulfate is easily oxidized to ferric sulfate by oxygen, which normally coexists at a concentration 100 times higher than that of No, such as combustion furnace exhaust gas, and thus loses its No absorption ability.

Furthermore, in the NO absorption method using sodium sulfite or the reduction method of NO to N2, the reaction rate is extremely slow as almost no NOx in the exhaust gas is removed.

Therefore, the present inventors conducted research on eliminating the drawbacks of the conventional method as described above, and found that by adding a water-soluble catalyst to the absorption liquid, the reaction rate between the above-mentioned No and sodium sulfite can be significantly accelerated. I found out.

Also, as an absorption tower, a bubble tower has higher N than a packed tower.
It was clarified that the Ox removal rate could be obtained.

That is, iron chelate compounds selected as the highest performance catalysts from among a large number of inorganic metal salts, organic metal salts, metal complex salts, and metal chelate compounds, such as ethylenediaminetetraacetic acid, dihydroxyethylglycine, and ethylenediaminediorthohydroxyphenylacetic acid. Ferrous chelates such as 0.001 to 11 per 11 aqueous sulfite
This is a method in which a gas containing mainly NOx and S02, such as combustion furnace exhaust gas, is passed through the absorption liquid to which 0.02 mole is added.

According to this method, N
Ox and SO□ can be removed efficiently.

For example, in a glass tube with an inner diameter of 4crI'L and a length of 150cm, a 10% aqueous sodium sulfite solution adjusted to pH 6.5 to 70 is poured to a liquid column height of 100Cr/L, and the liquid temperature is adjusted to 50cm.
Warm it to °C and insert a glass filter from below (40~
NO265p through gas vent pipe with 50 micron)
A mixed gas of NO, SO2 and N2 containing 500 ppm of SO2 was fed at a rate of 1.51 per minute.

Then, the gas became bubbles with an inner diameter of 8 mm and came into contact with the absorption liquid.

Since the rise in the liquid column due to ventilation was approximately 20CT,
The appropriate time for bubbles to pass through the liquid column was about 8 seconds.

Table 1 shows a comparison of the No removal rates after adding various chemicals.

As is clear from this table, ferrous and ferric chelate compounds, inorganic and organic ferrous salts, etc. are good, but when 1 to 5% oxygen gas is added to the mixed gas, as shown in Table 2, It can be seen that, except for chelate compounds of ferrous and ferric iron, the No removal rate decreases when the oxygen concentration becomes 3% or more.

The present invention was made based on the discovery that when a surfactant is added to the absorption liquid used in the method proposed by the present inventors as described above, the NOx removal rate can be further significantly improved. By adding a small amount (0,0001 to 0.002%) of a surfactant to the absorption liquid to slightly lower the surface tension of the solution, the size of the exhaust gas bubbles flowing in the bubble column can be reduced. and NOx
and to significantly improve the SO2 removal rate.

Examples of the surfactant to be added in the present invention include commercially available anionic surfactants such as sodium alkylbenzene sulfonate, sodium higher alcohol sulfate, sodium alkyl sulfate, hexadecyltrimethylammonium chloride, alkyltrimethylammonium chloride, and alkylpyridinium chloride. Cationic surfactants such as chloride, diciamin-cyamine mixtures, dimethylalkylbetaine, alkylbetaine,
Amphoteric surfactants such as alkylimidacillin and H
Nonionic surfactants such as polyoxyethylene alkylphenyl ethers having an LBL of 4 or more can be used, but
Among these, those that are water-soluble and have low foaming properties are preferred.

Addition of surfactant reduces the diameter of bubbles flowing in the column and increases the NOx removal effect, but the effect is 0.0
It is preferably within the range of 0.001% to 0.002%.

On the other hand, if the amount of surfactant added is increased to 0.002% or more, foaming properties may be increased and bubbles may be blown out of the tower together with gas.

As mentioned above, the amount of surfactant added to enhance the Noχ removal effect and minimize the generation of bubbles is 0.0001.
A range of 0.002% is preferable.

The above surfactants are organized by system as follows.

Anionic surfactant: Sodium alkynebenzene sulfonate, sodium higher alcohol sulfate, sodium alkyl sulfate Cationic surfactant: Hexadodecyl I-IJ methylammonium chloride, alkyltrimethylammonium chloride, diciamine-cyamine mixture , alkylbequin amphoteric surfactant; dimethylalkylbetaine, alkylimidacillin nonionic surfactant; polyoxyethylene alkyl ether The present invention will be specifically explained with reference to Examples.

In a glass tube with an inner diameter of 4 CrIL and a length of 150 cm, 10
% sodium sulfite aqueous solution to which 0.01 mol/l of ferrous ethylenediaminetetraacetate was added, and the liquid column height was 2.
5C'rI'L was added to warm the liquid temperature to 50°C, and it was passed through a gas ventilation tube with a glass filter (40 to 50 microns) inserted from below to produce NO265ppm and 5O250.
When a mixed gas of No 2 , SO 2 and N 2 containing 0p impediment is passed at a rate of 1.51 per minute, N.

The removal rate was 75%.

However, by adding a small amount of surfactant to this absorption liquid, NOχ
A comparison of the removal effects is as shown in Table 3, which shows that the surfactant has the effect of significantly improving the No removal rate.

Claims (1)

[Claims] 1. A trace amount of a surfactant, that is, 0.0001 to 0.00, is added to an absorption liquid in which 0.001 to 0.02 mole of an iron chelate compound is added per 11 of the aqueous solution to an aqueous solution of alkali sulfite.
A method for removing nitrogen oxides and sulfur dioxide gas from exhaust gas, which comprises circulating post-combustion furnace exhaust gas containing 2% additive.