KR910010242B1 - Exit gas treating method - Google Patents

Abstract

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Description

Exhaust gas treatment method

1 is a block diagram of an exhaust gas treatment system implementing the method of the present invention.

2 is a block diagram of a conventional off-gas treatment system.

* Explanation of symbols for the main parts of the drawings

1: absorption tower 2: circulation tank

3: neutralization tank 4: concentration tank

5: solid-liquid separator (filter press) 6: hopper

7: untreated gas 8: absorbent liquid

9: water 10: caustic soda

11: sulfuric acid 12: hydrogen peroxide

13 ferrous sulfate 14 treated exhaust gas

15: absorbent liquid after absorption treatment 16: eluent

17: absorbing liquid after neutralization 18: supernatant

19: concentrate 20: residue

21: filtrate

In other words, 4, 5 and 6 denote secondary processing units.

The present invention cleans and removes reducing substances such as phenol and formaldehyde in the exhaust gas with an absorbent liquid containing hydrogen peroxide and ferrous ions, and does not require an apparatus for treating iron sludge in the waste liquid. It relates to a gas treatment method.

In general, odorous components such as phenol and formaldehyde, which are reducing substances, are contained in the exhaust gas discharged from a casting process or the like. Thus, it is necessary to remove such odor components from the exhaust gas before releasing this exhaust gas into the atmosphere.

Reducing substances such as phenol and formaldehyde are aqueous solutions, and the equilibrium partial pressure of the aqueous phase is low thereon. Therefore, when these substances are washed and removed, the substances may be appropriately oxidized and decomposed so as not to increase the concentration of these substances in the absorbent liquid.

In order to oxidatively decompose the substance in the absorbent liquid, it is known to add hydrogen peroxide and ferrous ions (usually using ferrous sulfate). As an exhaust gas treatment method of this kind, as disclosed in Japanese Unexamined Patent Application Publication No. 51-44898,

There was a way to use.

Ferrous ions are also required in this exhaust gas treatment, and ferrous sulfate is actually added. By the way, the ferrous ions become ferric ions in the process of oxidative decomposition of phenol and the like and in the process of gas-liquid contact. Therefore, in order to maintain ferrous ions at a predetermined concentration, ferrous sulfate must always be added in an equivalent amount, and as a result, unnecessary iron powder is appropriately removed from the system and secondary treatment is performed. You must do it.

Moreover, when the operation result of the practical apparatus to which the said prior art was applied is seen, unnecessary iron becomes sludge and it accumulates in the system. As a result, ″ always high supply of ferrous sulphate ″, ″ disposal and secondary processing of unnecessary iron ″ and ″ removal of iron sludge deposited in the system ″ are problems in terms of maintenance and economics. have.

In order to solve this problem, the present inventors have disclosed the pH, the hydrogen peroxide concentration and the ferric iron concentration of the absorbent liquid, as disclosed in Japanese Patent Application Laid-Open No. 62-237926, at least 2-4, 0.8 mg-mol / l and 1, respectively. Regeneration of ferrous ions is promoted by holding at least 2 minutes in a circulation tank within a range of mg-mol / l and the amount of ferrous ions supplied is 30 mg-mol / hr or less per 1m 3 / hr of absorbent circulation flow rate. As a result, the supply amount of ferrous ions was reduced, and as a result, a technique for reducing the amount of iron sludge and preventing deposition of iron sludge in the system was developed.

However, in the conventional method, the reduction of the amount of iron sludge is insufficient, so that iron sludge (ferric hydroxide) produced as a secondary treatment after the neutralization treatment is removed in order to properly remove and discard unnecessary iron in the system. As shown in FIG. 1, the supernatant 18 is discharged to a terminal treatment plant and the concentrate 19 is treated with a solid-liquid separator (filter press) 5 or the like. There was a problem that must be done.

The present invention has been completed to solve the above-mentioned conventional problems, and its object is to further reduce the amount of ferrous ions supplied, and as a result, to significantly reduce the amount of iron sludge, thereby allowing the secondary treatment apparatus (solid-liquid separation). It is possible to provide an exhaust gas treatment method capable of eliminating an apparatus or the like and preventing deposition of iron sludge in the system, facilitating maintenance of the exhaust gas treatment system, and increasing economic efficiency.

However, when absorbing and removing phenol or the like, the consumption and regeneration of ferrous ions can be considered as follows. That is, ferrous ions become ferrous ions in the process of oxidative decomposition such as phenol and in the process of gas-liquid contact. On the other hand, ferric ions return to ferrous ions by the following reaction.

Provided that C ₆ H ₄ (OH ₂ ) represents hydroquinone or catechol, both of which are decomposition products of phenol. Since the reaction of (2) is slow among the above reactions, it is considered that only the reaction of (1) contributes to the regeneration of ferrous ions.

MEANS TO SOLVE THE PROBLEM As a result of earnestly researching, it discovered that the reaction of said (1) can be accelerated | stimulated by setting the state of an absorption liquid as follows. Furthermore, the concentration of ferrous ions was found to be sufficient for oxidative decomposition of phenol and the like when the concentration of ferrous ions was 0.02 mg-mol / l or more under the following absorbing liquid conditions, thereby making it possible to significantly reduce the amount of ferrous ions supplied.

As a result, the secondary processing apparatus of waste liquid became unnecessary. That is, the present invention is to maintain the pH, hydrogen peroxide concentration and the ferric iron concentration of the absorbent liquid in the purifying tank for at least 2 minutes in the range of 2 ~ 4, 0.5 mg-mol / L or more and 0.5 ~ 1.0 mg-mol / L, respectively Regeneration of ferrous ions is promoted, so that the amount of ferrous ions supplied is in the range of 0.9 to 3.0 mg-mol / hr per 1 m 3 / hr of absorption liquid circulation flow rate. As a result, the amount of iron sludge in the waste liquid is greatly reduced, thereby eliminating the need for a secondary treatment device such as a solid-liquid separation device.

EMBODIMENT OF THE INVENTION Hereinafter, the exhaust gas processing system which implements the method of this invention is described in detail, referring drawings.

FIG. 1 shows the exhaust gas treatment system in the case where the supply amount of ferrous ions is in the range of 0.9 to 3.0 mg-mol / hr per 1 m 3 / hr of the absorption liquid purifying flow rate. For example, the absorbent liquid 8 is brought into contact with the untreated exhaust gas 7 discharged from the casting process, so that the absorbent liquid 8 absorbs reducing substances such as phenol and formaldehyde. Reference numeral 2 denotes a circulation tank, in which the water 9, the caustic element 10 and the sulfuric acid 11 are supplied while being adjusted to maintain the liquid amount and pH value of the absorbing liquid at a predetermined value. Moreover, hydrogen peroxide 12 and ferrous sulfate 13 are also supplied to this circulation tank 2.

Since the treatment system of the present embodiment is constituted as described above, the untreated gas 7 is first washed by the absorbent liquid 8 in the absorption tower 1 so that reducing substances such as phenol and formaldehyde are absorbed in the absorbent liquid 8. ) Is discharged as the discharge gas 14 which is absorbed, decomposed and processed. The absorbent liquid 8 before the exhaust gas cleaning is sent to the absorption tower 1 from the circulation tank 2 by a pump (not shown) to absorb a reducing substance such as phenol and formaldehyde as described above, and then the absorbent liquid. Return to circulation tank 2 as (15). A part of the absorbent liquid 8 is separated from the absorption system as the eluent 16, enters the neutralization tank 3, and is neutralized with caustic soda 10 or sulfuric acid 11. After the neutralization, the absorbing liquid 17 is sent directly to the terminal treatment plant and treated with other wastewater.

However, embodiments of the operating conditions and performance of the system are as follows.

Example 1

(i) exhaust gas

(ii) absorption tower

Type: charging tower

Filling Material: Flower Type Filling Material

Filling height m: 2.0

Gas flow rate m / sec: 2.5

Liquid gas ratio ℓ / ㎥: 2

(iii) Absorption liquid (circulation tank)

pH: 3

Hydrogen peroxide concentration mg-mol / ℓ: 1

Ferrous ion concentration mg-mol / l: 0.02

Ferric Concentration mg-mol / l: 0.5

Circulation tank residence time min: 3

(iv) ferrous sulfate

Absorption amount Circulation amount mg-mol / hr: 1.4 for 1㎥ / hr

Total supply g-mol / hr: 0.25

(v) emissions

Discharge liquid flow rate ㎥ / hr: 0.5

(vi) discharge after neutralization

SS concentration mg / ℓ: 82

Example 2

(i) exhaust gas

(ii) absorption tower

Type: charging tower

Filling Material: Flower Type Filling Material

Filling height m: 2.0

Gas flow rate m / sec: 2.5

Liquid gas ratio ℓ / ㎥: 2

(iii) Absorption liquid (circulation tank)

pH: 3

Hydrogen peroxide concentration mg-mol / ℓ: 1.8

Ferrous ion concentration mg-mol / l: 0.04

Ferric Concentration mg-mol / l: 0.7

Circulation tank residence time min: 3

(iv) ferrous sulfate

Absorption amount Circulation amount mg-mol / hr: 2.0 for 1㎥ / hr

Total supply g-mol / hr: 0.36

(v) emissions

Discharge liquid flow rate ㎥ / hr: 0.5

(vi) discharge after neutralization

SS concentration mg / ℓ: 104

Example 3

(i) exhaust gas

(ii) absorption tower

Type: charging tower

Filling Material: Flower Type Filling Material

Filling height m: 2.0

Gas flow rate m / sec: 2.5

Liquid gas ratio ℓ / ㎥: 2

(iii) Absorption liquid (circulation tank)

pH: 3

Hydrogen peroxide concentration mg-mol / ℓ: 1.2

Ferrous ion concentration mg-mol / l: 0.02

Ferric Concentration mg-mol / l: 1.0

Circulation tank residence time min: 3

(iv) ferrous sulfate

Absorption amount Circulation amount mg-1g / hr: 2.8

Total supply amount g-mol / hr: 0.5

(v) emissions

Discharge liquid flow rate ㎥ / hr: 0.5

(vi) discharge after neutralization

SS concentration mg / ℓ: 140

After the pH, the hydrogen peroxide concentration and the ferric iron concentration in the absorbent liquid were maintained in the circulation tank for at least 2 minutes in the range of 2-4, 0.5 mg-mol / l or more and 0.5-1.0 mg-mol / l, respectively, the absorbent liquid The amount of ferrous ions supplied per 1 m 3 / hr of absorbent circulating flow rate was set to be in the range of 0.9 to 3.0 mg-mol / hr by using the gas for washing the exhaust gas. As a result, the amount of ferrous sulfate supplied can be extremely reduced. Therefore, the amount of iron sludge in the waste liquid can be greatly reduced, and a secondary treatment device such as a solid-liquid separation device can be eliminated. In addition, iron is not sludge deposited in the system, and maintenance is easy and economical.

Claims (1)

A method of washing and removing a reducing substance containing phenol in exhaust gas with an absorbent liquid containing hydrogen peroxide and ferrous ions, wherein the pH, hydrogen peroxide concentration and ferric iron concentration of the absorbent liquid are 2 to 4 and 0.5, respectively. Ferrous ions per 1 m 3 / hr of absorbed liquid circulating flow rate by holding the absorbed liquid for at least 2 minutes in a purification tank in the range of mg-mol / l and in the range of 0.5-1.0 mg-mol / l and then using the absorbent liquid for washing the exhaust gas. An exhaust gas treatment method, wherein the supply amount is in the range of 0.9 to 3.0 mg-mol / hr.

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