WO2018101699A2

WO2018101699A2 - Method for treating flue gas-desulfurization wastewater using electrolysis device

Info

Publication number: WO2018101699A2
Application number: PCT/KR2017/013664
Authority: WO
Inventors: 박규원; 김성태; 이해돈; 김대원; 권재형
Original assignee: (주) 테크로스
Priority date: 2016-11-30
Filing date: 2017-11-28
Publication date: 2018-06-07
Also published as: KR20180062121A; KR101910635B1; WO2018101699A3

Abstract

The present invention relates to a method for treating flue gas-desulfurization wastewater using an electrolysis device, and specifically, provides a method for treating flue gas-desulfurization wastewater, wherein the method is characterized in that ions needed in a reaction are supplied by electrolyzing raw water without using hazardous chemical substances.

Description

Treatment method of flue gas desulfurization wastewater using electrolysis device

The present invention relates to a method for treating flue gas desulfurized wastewater using an electrolysis device, and specifically, to treating effluent desulfurized waste water, wherein the raw water is electrolyzed to supply ions required for the reaction without using harmful chemicals. It is about a method.

As the demand for environmental protection increases around the world, the importance of desulfurization wastewater treatment in thermal power plants is emerging. Flue gas emitted from coal or petroleum-fired power plants includes nitrogen oxides and sulfur oxides, and various methods are used to remove them. In general, nitrogen oxides are removed using a selective catalytic reduction device, and sulfur oxides are removed using a wet absorption tower, which is called a wet desulfurization process. In the wet desulfurization process, waste water containing a large amount of inorganic N-S COD component and ammonia nitrogen is discharged.

The chemical oxygen demand (COD) component generated in the desulfurization process is largely composed of NS-based COD component composed of NO ₂ and SO ₂ compounds, COD component by dithio acid ion (S ₂ O ₈ ^-2 ), and limestone as a desulfurization absorber. It is classified as COD and COD components due to organic substances ^- which is generated CaCO _3. Among the COD components contained in the wastewater generated in the desulfurization process, most of the NS-based COD components produced by the NS-based components are used. These are generated by the reaction of NO ₂ and SO ₂ in the exhaust gas of the desulfurization process under acidic conditions and aqueous solutions in the absorption tower.

In order to remove the NS-based COD components, there is a method of injecting and treating NaNO ₂ under a water temperature of 55 to 60 ° C. and a pH of 2, and a method of treating chemicals by injecting NaOCl under a water temperature of 45 ° C. and a pH of 4. This method has a disadvantage in that the drug must be transported and stored every time because a large amount of the drug is used. In the case of NaOCl, the concentration is easily reduced according to the ambient temperature and the risk of a safety accident is included because a human must operate it directly. .

Various documents have been published regarding the method for treating the desulfurized wastewater discharged from the desulfurization process.

Korean Laid-Open Patent Publication No. 2006-0026510 describes an apparatus and method for removing nitrogen components such as nitrate and nitrogen at the same time by removing sludge from desulfurized wastewater and directly electrolyzing to remove the bonds of the hardly decomposable NS compounds. .

In addition, in Korean Patent Laid-Open Publication No. 2003-0478206, in order to remove a hardly-treated COD component, after contacting a palladium-based bimetallic catalyst with a large amount of nitrate ions present in the desulfurized wastewater, the bimetal is activated by active hydrogen ions present in the wastewater. The use of nitric acid adsorbed on to a nitrate discloses a process of reducing to nitrite and reacting with a hardly-treated COD component.

It is an object of the present invention to provide a method for treating flue gas desulfurization waste water safely without using harmful chemicals.

The above task is to remove the NS-based COD component in the flue gas desulfurization waste water; And a method for treating flue gas desulfurization wastewater comprising the step of removing heavy metals and fluorine, wherein an aqueous solution containing chlorine ions is passed through an electrolysis device including an anode portion and a cathode portion, thereby generating hydrogen ions (H ⁺ ) and hypochlorous acid at the anode portion. It is achieved by the method for treating flue gas desulfurization waste water, wherein the ion (OCl ⁻ ) is added to the NS-based COD component removal step to remove the NS COD component.

Preferably, the pH of the flue gas desulfurization waste water may be neutralized to 6.5 to 8.0 by adding hydroxide ions (OH ⁻ ) generated at the cathode part to a heavy metal and fluorine removal step.

Also preferably, the pH in the N-S-based COD component removal step may be 4 to 4.5.

Also preferably, the chlorine ion-containing aqueous solution may include final discharged water or seawater of flue gas desulfurization waste water.

Preferably, the electrolysis device may be a diaphragm type or a diaphragm type.

Also preferably, the chlorine ion-containing aqueous solution may have a chloride concentration of 10,000 to 15,000 mg / L.

Flue gas desulfurization treatment method of the present invention can effectively remove the N-S-based COD components without injecting HCl or NaOCl used in the existing chemical treatment process, it can significantly reduce the injection amount of the neutralizing chemical in the subsequent process. The present invention can significantly reduce the use of strong acids or strong alkaline chemicals, and can reduce the risk of safety accidents.

1 schematically illustrates a method for treating flue gas desulfurization wastewater according to the present invention.

All technical terms used in the present invention, unless defined otherwise, have the following definitions and conform to the meanings commonly understood by those skilled in the art in the relevant field of the present invention. In addition, although a preferred method or sample is described herein, similar or equivalent things are included in the scope of the present invention.

The term "about" means 30, 25, 20, 15, 10, 9, 8, 7, 6, 5, by reference quantity, level, value, number, frequency, percentage, dimension, size, amount, weight, or length. By amount, level, value, number, frequency, percentage, dimension, size, amount, weight or length, varying by 4, 3, 2 or 1%.

Throughout this specification, the terms “comprises” and “comprising”, unless otherwise indicated in the context, include a given step or component, or group of steps or components, but any other step or component, or It is to be understood that it does not exclude a step or group of components.

As used herein, the term "N-S-based COD component" refers to an inorganic or organic compound comprising nitrogen (N) and sulfur (S).

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention.

Flue gas desulfurization wastewater is discharged through an N-S-based COD component removal step, heavy metal and fluorine removal step, calcium removal step, residual COD removal and biological denitrification step and third advanced treatment step.

Waste water discharged from a flue gas desulfurization process, NS-based COD components, TN type component _{^{_{^{(NH 4 +, NO 3 -}}}} ) are and the like, heavy metals, fluorine, calcium. First, the wastewater is introduced into a first reactor for removing the NS-based COD component. In the first reactor, NaOCl and HCl are added and pH 4 to 4.5 is maintained while removing NS-based COD components present in the flue gas desulfurization wastewater as shown in Scheme 1 below.

Scheme 1

_{_{^{NO (SO 3) 3 -3 +}}} HOCl -> NO, NO 3 -

Next, the wastewater discharged from the first reactor is sent to the second reactor to remove heavy metals and fluorine. Alum hydrate is added to the second reactor to coprecipitate and remove fluorine ions, and a chelating agent is added to form a metal complex to remove heavy metals. In this reaction, the pH of the reactor should be maintained at 6.5-8.0, for which NaOH is added.

The present invention is characterized by generating and supplying materials used in the N-S-based COD component removal step and heavy metal and fluorine removal step using an electrolysis device. That is, raw water is electrolyzed to separate anode water and cathode water, and the anode water is added to the first reactor to participate in the removal reaction of ions contained in the anode water, and the cathode water is added to the second reactor to pH Neutralize

The electrolytic apparatus according to the present invention may be a diaphragm-type or non-diaphragm-type including an anode portion and a cathode portion, and preferably may be a membrane-free electrolysis apparatus. When the electrolysis device is a diaphragm type, since there is a diaphragm between the anode and the cathode, the diaphragm acts as an electrical resistance, thereby increasing power consumption, and periodic cleaning or maintenance is required due to the scale problem of the diaphragm. In the case of the non-diaphragm type electrolysis device, the power consumption is lower than that of the diaphragm type. However, it is important to maintain the laminar flow between the anode and the cathode.

Both the anode portion and the cathode portion may use an insoluble electrode, or only an anode may use an insoluble electrode. The insoluble electrode is prepared by mixing one or more platinum groups (Pt, Ir, Ru, Pd) by plating or by thermal decomposition at high temperature. Alternatively, the anode may be manufactured using CVD (chemical vapor deposition) or PVD. The electrolytic apparatus arranges the positive and negative electrode portions 1: 1, and separates the positive and negative water by passing an aqueous solution containing chlorine ions therebetween.

The raw water used in the electrolysis device may be the final effluent or seawater after treatment of the aqueous solution containing chlorine ions, flue gas desulfurization wastewater in the treatment steps. Preferably, the final effluent may be recycled and added to the electrolysis device. The final effluent all the waste water of flue gas desulfurization waste water treatment process via a chlorine ion (Cl ^{^-) -} it is possible to smoothly generate the ion OCl using the electrolysis because the concentration is very high. In addition, since the process of treating flue gas desulfurization waste water includes a process of removing calcium contained in the waste water, there is an advantage that scale is not generated at the cathode during electrolysis. Therefore, it is more preferable to recycle and use the final discharged water.

In the anode part of the electrolysis device, OCl ⁻ ions and H ⁺ ions are generated as shown in Scheme 2 below.

Scheme 2

^{_{2Cl - -> Cl 2 + 2e}} -

_{_{Cl 2 + H 2 O ->}} H + + Cl - + HOCl -

^{^{HOCl - <-> H + +}} OCl -

_{_{H 2 O -> 1/2 O 2}} + 2H + + 2e -

The OCl ⁻ ions and H ⁺ ions prepared in the anode part may be introduced into the removal step of the NS-based COD component (first reaction tank) without mixing with the OH ⁻ ions generated in the cathode part. At this time, the pH is maintained at 4 to 4.5, and removes the NS-based COD components as shown in Scheme 3 below.

Scheme 3

_{_{^{6 NO (SO 3) 3 -3}}} + 18 OCl - + 10 H 2 O → 4 NO + 2 NO 3 - + 18 HSO 4 - + 18 Cl - + 2 H + + 3 O 2

The injection amount of anode water generated at the anode part and the current applied to the electrolysis device can be controlled by measuring the flow rate of raw water and oxidation-reduction potential (ORP) installed in the NS-based COD removal process. Is measured at the outlet of the first reactor. If the ORP is measured with a negative number, it is determined that the N-S-based COD component is remaining to increase the current applied to the electrolysis device, and if the ORP is measured with a positive number, it is determined that most of the N-S-based COD component is removed.

Injecting excessive amounts of OCl ^- ions in the NS-based COD component removal step may affect the microorganisms in the biological denitrification step during the wastewater treatment step, thus neutralizing agents such as sodium thiosulfate (Na ₂ S ₂ O ₃ ) Sodium bisulfate (NaHSO ₄ ), sulfur dioxide (SO ₂ ), C, etc. are added to remove the excessively injected OCl ^- ions. In this case also, the redox potential (ORP) can be measured to control the dose of the neutralizing agent, and the ORP measurement can be controlled to be a negative number. The reaction upon neutralization is shown in Scheme 4 below.

Scheme 4

^{^{_{OCl - + H + + NaHSO 3}}} → NaHSO 4 ↓ + HCl

According to one embodiment of the present invention, periodic polarity inversion may be performed to remove scale formed on the cathode portion. This allows Mg (OH) ₂ , the scale attached to the cathode. Alternatively, the scale may be cleaned by anodizing and dissolving CaCO ₃ and anodizing again.

In the cathode portion of the electrolysis device, OH ⁻ ions are generated as in Scheme 5 below.

Scheme 5

_{^{2H 2 O + 2e - ->}} H 2 + 2OH -

The OH ^- ions generated in the cathode portion are introduced into the second reactor of the heavy metal and fluorine removal step to serve as a neutral pH. This reaction can be represented as in Scheme 6 below.

Scheme 6

Metal ²⁺ + OH ^-- > M (OH) ₂ ↓

In the existing NS-based COD component removal process, a large amount of HCl and NaOCl are injected. HCl was injected to maintain the pH of the reactor at 4 ~ 4.5 for effective reaction in the NS-based COD removal process. However, commercially available NaOCl has a strong alkali pH above 12. Therefore, the conventional drug treatment method has a disadvantage in that the amount of HCl injection increases. The present invention also has the advantage of significantly reducing the HCl injection amount by H ⁺ , OCl ^- is injected in the positive water. In addition, since OH ^- ions required for neutralization are also manufactured and injected by using an electrolysis device in the field, there is an advantage that the amount of conventional caustic soda (NaOH) can be significantly reduced.

Having described the specific part of the present invention in detail, it is apparent to those skilled in the art that such a specific technology is only a preferred embodiment, and the scope of the present invention is not limited thereto. Thus, the substantial scope of the present invention will be defined by the appended claims and equivalents thereof.

Claims

Removing the N-S-based COD component in the flue gas desulfurization waste water; And a method for treating flue gas desulfurization wastewater comprising the step of removing heavy metals and fluorine,

Pass the aqueous solution containing chlorine ions through an electrolysis device including an anode part and a cathode part, and introduce hydrogen ions (H + ) and hypochlorite ions (OCl − ) generated at the anode part into the NS-based COD component removal step. A method for treating flue gas desulfurization waste, characterized by removing the system COD component.
The method for treating flue gas desulfurized wastewater according to claim 1, wherein the hydroxide ion (OH − ) generated in the cathode portion is added to the heavy metal and fluorine removing step to neutralize the pH of the flue gas desulfurized waste water to 6.5 to 8.0.
The method of claim 1, wherein the pH of the N-S-based COD component removal step is 4 to 4.5, characterized in that the treatment of flue gas desulfurization waste water.
The method of claim 1, wherein the aqueous solution containing chlorine ions comprises final effluent or seawater of flue gas desulfurization waste water.
The method of claim 1, wherein the electrolysis device is a diaphragm type or a diaphragm type.
The method according to claim 1, wherein the aqueous solution containing chlorine ions has a chloride concentration of 10,000 to 15,000 mg / L.