KR102085614B1 - Wastewater treatment method and treatment device - Google Patents

Abstract

The present invention relates to a method for treating wastewater, which comprises the following steps: pretreating wastewater including methyldiethanolamine by adding iron salt and hydrogen peroxide to the wastewater; and mixing the pretreated wastewater with wastewater including cyanide. According to the present invention, the method is capable of efficiently treating wastewater including methyldiethanolamine and wastewater including cyanide and can be performed in linkage with a biological treatment process. In addition, as compared to a conventional method for treating wastewater including cyanide, the method can reduce a usage of acids and iron salt. Furthermore, through minimum modification of a conventional wastewater treatment process, the method can be performed in linkage with a COG refining process using methyldiethanolamine. Moreover, the method is able to stably treat wastewater through increased biodegradability according to oxidation by OH radicals of methyldiethanolamine.

Description

Wastewater Treatment Method and Apparatus {WASTEWATER TREATMENT METHOD AND TREATMENT DEVICE}

The present invention relates to a wastewater treatment method and apparatus.

Conventional chemical conversion process for coke production is to collect hydrogen sulfide (H ₂ S) in the coke oven gas (COG) using ammonia water, to remove ammonia by distilling ammonia water collected hydrogen sulfide Traces remaining in the wastewater are discharged after biological water treatment. Recently, in order to improve the H ₂ S capture efficiency of the H ₂ S capture process using the existing ammonia water, H ₂ S capture technology using a new absorbent solution is applied to replace the ammonia water. Among these techniques, a technology for purifying coke oven gas using methyldiethanolamine (MDEA, N -methyldiethanolamine) capable of removing ammonia at the same time with high selectivity for H ₂ S has been proposed (Patent Registration No. 1839225).

In the COG purification process using MDEA, an electrodialysis (ED, electrodialysis) is used to remove the heat stable salt (HSS) generated by reacting the components present in the COG itself or the COG component with MDEA from the MDEA solution. Wastewater containing high concentrations of HSS is generated. This waste liquid contains high concentrations of HSS and may contain MDEA used for H ₂ S absorption, so that if these wastewaters enter existing biological treatment processes, the effects on microorganisms or the introduction of new substances Problems such as low bioavailability, long adaptation periods for the decomposition of new materials, and discharge of pollutants by undegradation can occur. Accordingly, wastewater generated from hydrogen sulfide purification process using MDEA should be treated in conjunction with biological treatment after appropriate treatment.

Various types of contaminants are included in the wastewater generated from the existing coke oven, and an anoxic tank and an aerobic tank are disposed to effectively remove the wastewater, thereby meeting effluent standards using nitrification, denitrification, and carbon oxidation. At this time, the wastewater generated from the coke oven has a cyanide compound which may affect the activity of microorganisms, and thus a physicochemical treatment reactor is operated to deplete cyanide in the form of an iron-cyanide compound. (iron based coagulant). Then, for example, the denitrification-carbon oxidation / nitrification reaction is induced in the order of anoxic tank, aerobic tank, anoxic tank, and aerobic tank to meet the effluent standard.

The present invention is to provide an apparatus for effectively treating the electrodialyzer waste liquid containing methyl diethanolamine and cyanide compounds that can occur in the COG purification process using the MDEA as described above.

According to an aspect of the invention, the step of pre-treating the iron salt and hydrogen peroxide in the wastewater containing methyl diethanolamine; And it provides a wastewater treatment method comprising the step of mixing the pretreated wastewater with wastewater containing a cyan compound.

Hydrogen peroxide may be added in an amount of 1.0 to 5.0 g per 1 g of COD _Cr of the waste liquid containing methyl diethanolamine, and the iron salt may be added in an amount of 3.0 to 5.0 g per 1 g of the hydrogen peroxide added.

The pH of the pretreated wastewater may be 2 to 5.

PH of the wastewater containing the cyanide compound may be 7 or more.

The wastewater containing methyldiethanolamine absorbs hydrogen sulfide and ammonia contained in coke oven gas (COG) using an aqueous solution containing methyldiethanolamine, and absorbs the absorbed liquid containing hydrogen sulfide and ammonia. Discharging; Separating hydrogen sulfide and ammonia contained in the absorbent liquid into a gaseous phase and discharging the regenerated absorbent liquid; And removing the heat stable salt (HSS; Heat Stable Salt) contained in the regenerated absorbent liquid using an electrodialysis apparatus, and collecting wastewater containing methyldiethanolamine discharged from the electrodialysis apparatus. have.

After the step of mixing the pre-treated waste water with the waste water containing the cyan compound may further comprise the step of adding a neutralizing agent.

The neutralizing agent may be at least one selected from sulfuric acid, hydrochloric acid, and caustic soda.

The mixed wastewater may further comprise the step of treating with a bardenpho method.

According to another aspect of the invention, the first treatment unit for the iron salt and hydrogen peroxide is added to the wastewater containing methyl diethanolamine; And a wastewater treatment apparatus comprising a second treatment unit is mixed with the wastewater pre-treated from the first treatment unit and the wastewater containing the cyan compound.

The hydrogen peroxide may be added in an amount of 1.0 to 5.0 g per 1 g of COD _Cr of the waste liquid containing methyl diethanolamine, and the iron salt may be added in an amount of 3.0 to 5.0 g per 1 g of the hydrogen peroxide added.

The wastewater containing methyl diethanolamine may include: an absorption tower that absorbs hydrogen sulfide and ammonia contained in the coke oven gas with an aqueous methyldiethanolamine solution and discharges it to a regeneration tower; A regeneration tower connected to the absorption tower and separating hydrogen sulfide and ammonia contained in the absorption liquid discharged from the absorption tower in a gas phase; And an electrodialysis apparatus provided between the absorption tower and the regeneration tower and removing the heat stable salt contained in the absorption liquid discharged from the regeneration tower.

The wastewater treated in the second treatment unit may further include a third treatment tank for treating by a bardenpho method.

According to the present invention, it is possible to efficiently treat wastewater containing methyl diethanolamine and wastewater containing cyanide compounds, and furthermore, it is possible to link with biological treatment processes.

In addition, it is possible to reduce the amount of acid and iron salt used compared to the conventional wastewater treatment method containing a cyan compound.

In addition, through minimal modification of the existing wastewater treatment process, it is possible to link with the COG purification process using methyldiethanolamine.

Furthermore, according to the oxidation of MDEA by OH radicals, there is an advantage in that stable wastewater treatment through biodegradability is increased.

Figure 1 schematically shows a COG purification apparatus.
Figure 2 schematically shows a wastewater treatment method containing a conventional cyan compound.
Figure 3 schematically shows a wastewater treatment method according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described with reference to various examples. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

The present invention relates to a wastewater treatment method and apparatus. According to an aspect of the invention, the step of pre-treating the iron salt and hydrogen peroxide in the wastewater containing methyl diethanolamine; And a wastewater treatment method comprising the step of mixing the pretreated wastewater with the wastewater containing the cyan compound generated in the coke oven.

The pretreatment step of the present invention may be applied without limitation as long as it is wastewater containing methyldiethanolamine. For example, the wastewater containing methyldiethanolamine may be a waste solution generated from an electrodialysis apparatus of a COG purification process using methyldiethanolamine, or an acid gas (H ₂ S, CO ₂₎ using methyldiethanolamine. Wastewater generated in the separation and purification process.

FIG. 1 schematically shows a COG refining apparatus using methyldiethanolamine. Referring to FIG. 1, the refining apparatus absorbs hydrogen sulfide and ammonia contained in a coke oven gas as an aqueous methyldiethanolamine solution. Absorption tower 201 for discharging to the regeneration tower; A regeneration tower 202 connected to the absorption tower and separating hydrogen sulfide and ammonia contained in the absorption liquid discharged from the absorption tower in a gas phase; And an electrodialysis apparatus 203 provided between the absorption tower and the regeneration tower to remove thermally stable salts contained in the absorption liquid discharged from the regeneration tower.

In the absorption tower 201, the aqueous methyldiethanolamine solution and the coke oven gas are in countercurrent contact, and the absorber absorbs hydrogen sulfide and ammonia contained in the coke oven gas. The absorbing liquid 103 in which the hydrogen sulfide and ammonia are absorbed is discharged to the lower portion of the absorption tower. On the other hand, the gas contained in the coke oven gas, such as hydrogen, methane, carbon monoxide, and the like, which does not react with the aqueous methyldiethanolamine solution, that is, the coke oven gas 102 from which hydrogen sulfide and ammonia are removed is the upper portion of the absorption tower 201. Can be discharged through.

Hydrogen sulfide and ammonia absorbed from the lower portion of the absorption tower 201 are absorbed by the absorption liquid 103 is transferred by the pump 204, it is supplied to the regeneration tower 202 in a preheated state by a heat exchanger. In the regeneration tower, the absorption liquid is regenerated at a temperature of 100 to 130 ° C. Due to such a high temperature, the hydrogen sulfide and ammonia-containing gas 104 may be discharged from the absorbing liquid absorbed by the hydrogen sulfide and ammonia after passing through the reflux drum 205. The discharged gas containing hydrogen sulfide and ammonia may be transferred to a sulfur recovery process or a treatment process and used depending on the purpose.

Absorption process of absorbing hydrogen sulfide and ammonia in absorption tower 201 and regeneration process of separating hydrogen sulfide and ammonia absorbed by applying thermal energy in the form of high-temperature steam in regeneration tower 202 in a gaseous phase are repeated. is the absorption tower 201 and the regeneration tower 202 continuously circulated by the reaction and due to the carbon monoxide (CO), hydrogen cyanide (HCN), hydrogen sulfide contained in the coke oven gas to formate ion (HCOO ^-), thiosulfate ion ( It is create an acidic substance such as a) ^- SCN. This acidic substance is combined with methyldiethanolamine to form a stable salt, that is, a thermally stable salt, thereby lowering the performance of the absorbent liquid.

These thermally stable salts are salts that are not separated in the regeneration tower 202 operated at a temperature of about 100 to 130 ° C., which may cause corrosion of the process equipment or deteriorate the performance of the absorbent liquid, which may eventually cause absorbent liquid replacement. . Such thermostable salts may be, for example, one or more selected from the group consisting of formate, thiocyanate, acetate, sulfate, chloride, thiosulfate, oxalate, glycolate or nitrate.

An electrodialysis apparatus 203 is used to remove the heat stable salts contained in the regenerated absorbent liquid. Due to the electrodialysis method, the anion and the cation of the thermally stable salt may be selectively permeated and then removed to maintain the performance of the aqueous solution of methyldiethanolamine as an absorbent liquid. The methyldiethanolamine aqueous solution, that is, the absorbent liquid from which the heat stable salt has been removed, is passed through the electrodialysis apparatus 203 to remove the hydrogen sulfide and ammonia contained in the coke oven gas.

The waste liquid generated from the electrodialysis apparatus must be continuously discharged, and the waste liquid contains a high concentration of thermal stabilized salts and outflowed methyldiethanolamine, which may have a great adverse effect when the biological wastewater treatment process is performed. The properties of the waste liquid generated from the electrodialysis apparatus are shown below.

ingredient density MDEA 1.5% COD _Mn 17,000 COD _Cr 39,000 T-N (Total Nitrogen Content in Waste) 2,500 T-CN (Total Cyanide Compound Content in Waste) 500 pH 9.5-10.5

As described above, the waste liquid generated from the electrodialysis apparatus contains high concentrations of COD, TN, CN, and methyldiethanolamine flowing out through the electrodialysis apparatus, so that the load is high to link biological treatment and the biodegradation rate of methyldiethanolamine is high. It has a low risk of being finally discharged without being processed by microorganisms.

Thus, in the present invention, wastewater containing methyldiethanolamine by pretreatment of wastewater containing methyldiethanolamine, in connection with the treatment of wastewater containing cyan compounds, in particular, wastewater containing cyan compounds. And it is to provide a wastewater treatment method that can efficiently treat all of the wastewater containing the cyan compound and can be linked to the biological treatment process.

Accordingly, iron salt and hydrogen peroxide are added to the wastewater containing methyldiethanolamine to perform pretreatment. By the step of radical (OH and, HO ^and ₂₎ produced by the reaction represented by the following general formula 1, methyl diethanolamine, etc., decomposition reaction of the organic matter occurs, and H ₂ O ₂ is Fe ^{2 +} with H ₂ O is It is converted to Fe ^{+ 3.}

[Equation 1]

^{_{Fe 2 + + H 2 O 2}} ↔ Fe 3 + + OH + OH and ^-

Fe ^{3 +} + H ₂ O ₂ ↔ Fe ^{2 +} + HO ^ㆍ ₂ + H ⁺

OH ・ + H ₂ O ₂ ↔ HO ^ㆍ ₂ + H ₂ O

OH · + Fe ^{2 +} ↔ Fe ^{3 +} + OH-

Fe ^{+ 3} + HO ^{and _{2 ↔ Fe 2 + + O 2}} H +

Fe ^{+ 2} + ^and HO _{^{2 + H + ↔ Fe 3 +}} + H 2 O 2

2 HO ^ㆍ ₂ ↔ H ₂ O ₂ + O ₂

The hydrogen peroxide water is preferably added in an amount of 1.0 to 5.0 g per 1 g of COD _Cr of the wastewater containing methyldiethanolamine _, that is, chemical oxygen demand (COD _Cr ) according to the chromium method. When a smaller amount of iron salt is supplied, the amount of radicals formed by the Fenton reaction is less, which may lower the decomposition rate of methyldiethanolamine, and when a larger amount of hydrogen peroxide is added, the economic efficiency may deteriorate. Hydrogen peroxide may enter the post process and affect microorganisms.

The iron salt is preferably added in an amount of 3.0 to 5.0 g per 1 g of hydrogen peroxide added. Than a small amount of ferrous salt in this case is supplied, the Fe ^{2 +} that the catalyst of the Fenton reaction not sufficiently supplied, and the decomposition rate of methyl diethanolamine by the Fenton reaction can be lowered, than a large amount of when the iron salt is supplied, Excessive sludge generation by iron salt and economics due to iron salt supply may deteriorate.

Since the pH of the pretreated wastewater shows acidity of 2 to 5, neutralizing the wastewater containing the cyanide compound having a pH of 7 or more described later, forming an iron-cyanide compound, for example, prussian blue, to decompose cyanide, Fe (OH) ₃ floc is also formed, and can be used to remove organic matter and suspended solids by coprecipitation.

Next, the step of mixing the pretreated wastewater with the wastewater containing the cyan compound. Wherein when the pre-treatment the waste water mixture of cyan compound occurs in the coke oven and the waste water, according to the reaction according to the following formula 2, Fe ^{3 +} and CN ^- can be precipitated and removed to form a cyanide salt-iron by the reaction of. In this case, since the pH of the pretreated wastewater is 2 to 5, the neutralization of the wastewater containing the cyan compound having a pH of 9 or more is also performed, so that the use of the neutralizing agent may be omitted or at least reduced. In addition, the amount of FeCl ₃ injected to remove the cyan compound contained in the wastewater can be omitted or at least reduced.

The weight ratio of the pretreated wastewater and the wastewater containing the cyan compound is not particularly limited. For example, if the wastewater containing methyl diethanolamine is wastewater generated from the electrodialysis apparatus of the coke oven gas refiner, the amount of waste liquid generated also varies depending on the coke production, so that the wastewater can be properly mixed. have.

If necessary, the mixed wastewater may be treated by a bardenpho process. The Badenpo method is a method used for biological treatment of wastewater, and is composed of anaerobic tank, anaerobic tank, aerobic tank, anoxic tank, and aerobic tank. In the latter anoxic tank, untreated nitric oxide is removed through endogenous denitrification. In the final aerobic tank, the reaction removes residual nitrogen gas from the wastewater and prevents the elution of phosphorus from the final sedimentation basin.

Since the OH radical, which is a major oxide produced in the pretreatment step, has no selectivity, the nitrogen component contained in the wastewater containing methyldiethanolamine can be converted into NO ₂ ^- or NO ₃ ^- form, and at the same time, methyldi It is also possible to improve the bioavailability (bioavailabilty) through the decomposition of ethanolamine. Therefore, in connection with the Badenpo process, NO ₂ ⁻ , NO ₃ ⁻ generated in the pretreatment step may be converted to N ₂ by the denitrification microorganism in the anaerobic tank, which is also helpful in the denitrification reaction.

On the other hand, the step of adding a neutralizing agent to satisfy the 7.5 ~ 8.5 level of the optimum pH for biological treatment according to the Badenpo method. Acids (sulfuric acid, hydrochloric acid) and alkalis (caustic soda) can be injected as the pretreated wastewater can be neutral pH when mixed with wastewater containing cyanide compounds, or in some cases acidic or alkaline. However, since nitric acid is present in the waste water in the form of NO ₃ ⁻ , it may affect denitrification and nitrification, so it is not preferable to use it.

As such, according to the present invention, by treating the wastewater containing methyldiethanolamine with pretreatment with the wastewater treatment containing the cyanide compound, the neutralizing agent used for pH control of the wastewater containing the cyanide compound, for example, H ₂ The amount of SO ₄ used can be reduced, and the amount of iron salt used to remove cyanide can be reduced, thereby reducing the load of methyl diethanolamine wastewater, and reducing the amount of H ₂ SO ₄ used for pH control and removing cyanide. It is possible to drastically lower the amount of iron salt injected.

On the other hand, according to another aspect of the invention, the first treatment unit for introducing iron salt and hydrogen peroxide into the wastewater containing methyl diethanolamine; And a second treatment unit in which the wastewater treated by the first treatment unit and the wastewater containing the cyan compound are mixed.

The wastewater treatment apparatus may further include a third treatment tank for treating the wastewater treated by the second treatment unit by a bardenpho method.

In the first treatment unit, pretreatment is performed by introducing iron salt and hydrogen peroxide into the wastewater containing methyl diethanolamine, and the second treatment unit is a mixture of the pretreated wastewater and cyanide wastewater, and the third treatment unit Anaerobic tank, anaerobic tank, aerobic tank, anaerobic tank and aerobic tank is composed of the biological treatment of the waste water is already described in detail above, the detailed description will be omitted here.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples. The following examples are intended to illustrate the present invention in more detail, and the present invention is not limited thereto.

In order to confirm the efficiency of removing methyl diethanolamine during wastewater pretreatment including methyldiethanolamine according to the present invention, the following experiment was conducted.

Iron salts of H ₂ O ₂ and FeSO ₄ .7H ₂ O were added to the wastewater having the same properties as those of Table 1 in the same ratio as in Table 2 below. At this time, H ₂ SO ₄ was injected to adjust the pH to 3.0, and an aqueous solution of FeSO ₄ was injected, followed by H ₂ O ₂ .

H ₂ O ₂ / COD _Cr (g / g) H ₂ O ₂ / FeSO _{4 ·} 7H ₂ O (mol / mol) Example 1 4.22 10 Comparative Example 1 1.27 58.33 Comparative Example 2 2 2

After the reaction as described above, the concentration of methyl diethanolamine and the removal rate of COD _Cr were confirmed and shown in Table 3. Referring to Table 3, in Example 1, it can be seen that methyl diethanolamine can be completely removed.

[Mg / L] before reaction [Mg / L] after reaction Removal rate (%) MDEA COD _Cr MDEA COD _Cr MDEA COD _Cr Example 1 18,384 40,158 N.D 7,115 100 82.3 Comparative Example 1 6,671 29,469 62.6 26.6 Comparative Example 2 3,169 26,281 79.4 34.6

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and variations can be made without departing from the technical spirit of the present invention described in the claims. It will be obvious to those of ordinary skill in the field.

101: coke oven gas
102: Coke oven gas with hydrogen sulfide and carbon dioxide removed
103: absorbing liquid in which hydrogen sulfide and carbon dioxide are absorbed
104: gas containing hydrogen sulfide and carbon dioxide
105: regenerated absorbent liquid
106: Absorption liquid without thermally stable salts
201: absorption tower
202: regeneration tower
203: electrodialysis apparatus
204: pump
205: reflux drum
206: filter
207: heat exchanger
302: chemical treatment tank
304: biological treatment tank
402: first treatment tank
404: second treatment tank
406: third treatment tank

Claims (12)

Pretreatment by adding iron salt and hydrogen peroxide to the wastewater containing methyl diethanolamine; And
The wastewater treatment method comprising the step of mixing the pretreated wastewater with the wastewater containing the cyan compound.
The method of claim 1,
The hydrogen peroxide is introduced in an amount of 1.0 to 5.0 g per 1 g of COD _Cr of the waste liquid containing methyl diethanolamine, and the iron salt is introduced in an amount of 3.0 to 5.0 g per 1 g of the hydrogen peroxide injected. .
The method of claim 1,
Wastewater treatment method characterized in that the pH of the pretreated wastewater is 2 to 5.
The method of claim 1,
Wastewater treatment method characterized in that the pH of the wastewater containing the cyan compound is 7 or more.
The method of claim 1,
Wastewater containing the methyl diethanol amine,
Absorbing hydrogen sulfide and ammonia contained in a coke oven gas (COG) using an aqueous solution containing methyldiethanolamine, and discharging the absorbing liquid containing hydrogen sulfide and ammonia;
Separating hydrogen sulfide and ammonia contained in the absorbent liquid into a gaseous phase and discharging the regenerated absorbent liquid; And
Removing the heat stable salt (HSS) contained in the regenerated absorbent liquid by using an electrodialysis apparatus, and collecting wastewater containing methyldiethanolamine discharged from the electrodialysis apparatus. Wastewater treatment method.
The method of claim 1,
After the step of mixing the pre-treated waste water and the waste water containing the cyan compound, a wastewater treatment method comprising the step of adding a neutralizing agent.
The method of claim 6,
Waste treatment method characterized in that the neutralizing agent is at least one selected from sulfuric acid, hydrochloric acid and caustic soda.
The method of claim 1,
Wastewater treatment method comprising the step of treating the mixed wastewater by a bardenpho method.
A first treatment part in which iron salt and hydrogen peroxide are introduced into the wastewater containing methyl diethanolamine; And
Wastewater treatment apparatus comprising a second treatment unit is mixed with the wastewater pre-treated from the first treatment unit and the wastewater containing the cyan compound.
The method of claim 9,
The hydrogen peroxide is introduced in an amount of 1.0 to 5.0 g per 1 g of COD _Cr of the waste liquid containing methyl diethanolamine, and the iron salt is introduced in an amount of 3.0 to 5.0 g per 1 g of the hydrogen peroxide injected. .
The method of claim 9,
Wastewater containing the methyl diethanol amine,
An absorption tower for absorbing hydrogen sulfide and ammonia contained in the coke oven gas with an aqueous methyldiethanolamine solution and discharging it to a regeneration tower;
A regeneration tower connected to the absorption tower and separating hydrogen sulfide and ammonia contained in the absorption liquid discharged from the absorption tower in a gas phase; And
An electrodialysis apparatus provided between the absorption tower and the regeneration tower and removing thermally stable salts contained in the absorption liquid discharged from the regeneration tower; and the wastewater obtained from the electrodialysis apparatus of the coke oven gas purification apparatus comprising a. Processing unit.
The method of claim 9,
And a third treatment tank for treating the wastewater treated by the second treatment unit by a bardenpho process.

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