KR20160069539A - Wet gas cleaning system using oxidizing agent produced from the wastewater - Google Patents

Abstract

The present invention relates to a wet gas cleaning system using an oxidizing agent produced from wastewater. The purpose of the present invention is to provide a wet gas cleaning system in which persulfate as a non-chloride-based oxidizing agent is self-produced by an oxidizing agent raw material substance being obtained from ammonia-containing wastewater for wet cleaning of pollutants contained in nitrogen oxide-containing exhaust gas so that nitrogen oxide in the exhaust gas is wet-removed after oxidation at a low cost and in a safe and environment-friendly manner. The system of the present invention includes: an absorption tower (1) which performs wet cleaning after nitrogen oxide oxidation based on gas-liquid contact between nitrogen oxide-containing exhaust gas and a persulfate-containing cleaning solution; a cleaning solution tank (2) which supplies the absorption tower with the stored persulfate-containing cleaning solution; persulfate production means (3) for performing ammonia gas degassing from ammonia-containing wastewater or industrial byproducts, producing persulfate by including sulfuric acid solution injection and electrolysis processes, and then supplying the persulfate to the cleaning solution tank; and wastewater treatment means (4) for purifying and discharging the wastewater discharged from the absorption tower.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a wet gas cleaning system using an oxidizing agent produced from wastewater,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wet gas cleaning system using an oxidant produced from wastewater, and more particularly, to a wet gas cleaning system using an oxidant produced from wastewater, The present invention relates to a technique for wet-cleaning an exhaust gas using a chlorine-based radical generated by wet cleaning of an exhaust gas using a non-chlorine-based oxidizing agent alone or by injecting sodium chloride.

 Nitrogen oxides (NOx) contained in exhaust gas from ships and onshore plants cause optical smog, acid rain, global warming, and are subject to strong emission regulations.

For reference, it is known that most of NOx generated from stationary pollutants accounts for 90 ~ 95 vol.% Of extremely low solubility NO, while the remaining 4 ~ 9 vol.% Exists as NO ₂ which is 20 times higher than solubility. Therefore, in recent years, a technology for converting NO having a low solubility into NO ₂ having a high solubility to remove NO x has been extensively studied.

Hereinafter, various conventional technologies for removing NOx will be described.

First, a NOx removing technique using an ammonia-based reducing agent and a reducing catalyst is disclosed in Korean Patent Registration No. 10-0549778 (catalyst for removing vanadium / titania-based nitrogen oxide having low-temperature denitrification property, its using method and its denitration method) The main content is that in case of selective catalytic reduction, it is necessary to satisfy a high temperature condition of 250 ° C or more to achieve NO x removal efficiency, and there is a weakness such as poisoning of catalyst, use of vanadium designated as harmful substance, Urea water or ammonia in the atmosphere and secondary pollution problems such as generating strong greenhouse gases such as nitrous oxide (N ₂ O).

Also, a NOx removal technique using a wet cleaning technique is disclosed in Korean Patent Registration No. 10-0456912 (a device for simultaneously removing nitrogen oxides, sulfur oxides, and noxious gases in a combustion gas using electrolysis of water and a method for removing the same) (NO ₂ ) which is easily wet-absorbed by primary oxidation of non-water-soluble nitrogen monoxide (NO) with a chlorine-based oxidizing agent. However, this technique is always exposed to the risk of chlorine (Cl ₂ ) gas due to the use of chlorinated oxidizers, and there are additional problems such as power cost / corrosion / secondary treatment of wastewater.

The prior art in which persulfuric acid is introduced into the flue gas treatment is disclosed in Korean Patent Registration No. 10-1307089 (exhaust gas treatment method), and the main contents are sulfuric acid and iodine It is difficult to judge that the oxidizing power of persulfuric acid is properly used or that it is used as the main chemical liquid.

In the conventional cleaning technique for removing exhaust gas as described above, chlorine-based oxidizing agents such as NaClO and NaClO ₂ are used for the purpose of oxidizing NO to NO ₂ , so that chlorine gas generation, excessive power consumption, corrosion of apparatus, And there are problems such as the generation and the treatment facility problems. Therefore, measures are urgently needed.

Korean Patent Registration No. 10-0549778 (Jan. 31, 2006) Korean Patent Registration No. 10-0456912 (Nov. 3, 2004) Korean Registered Patent Publication No. 10-1307089 (2013.09.04.) Korean Unexamined Patent Publication No. 10-2003-0053331 (Jun. 28, 2003)

In order to solve the above problems, an object of the present invention is to provide a method for producing a non-chlorine-based oxidizing agent from an oxidizing agent raw material from wastewater containing ammonia for wet cleaning pollutants contained in an exhaust gas containing nitrogen oxides, In which the nitrogen oxide is oxidized and removed.

Another object of the present invention is to provide a wet gas cleaning system in which a chlorine-based oxidizing agent is produced from wastewater containing ammonia as a raw material, and further reacted with sodium chloride to produce chlorine-based radicals.

According to the present invention, there is provided an exhaust gas purifying apparatus for purifying nitrogen oxides by contacting a cleaning liquid containing a persulfate with a flue gas containing nitrogen oxide, and;

A cleaning liquid tank for supplying a cleaning liquid containing stored persulfate to the absorption tower;

A persulfate production means for supplying a persulfate to the cleaning liquid tank after production of the persulfate, including the step of supplying sulfuric acid solution and electrolysis after deaeration of ammonia gas from wastewater containing ammonia or industrial byproduct;

And a wastewater treatment means for purifying and discharging the wastewater discharged from the absorption tower. BRIEF DESCRIPTION OF THE DRAWINGS FIG.

According to a preferred embodiment, the persulfate production means comprises: a degassing means for generating ammonia gas by vaporizing dissolved ammonia components in wastewater; a gas-liquid contacting means for producing ammonium sulfate by vapor-contacting a sulfuric acid solution with ammonia gas; Electrochemical conversion means for producing ammonium persulfate, which is a primary persulfate, by electrolysis; and ammonium persulfate, which is a primary persulfate, with sodium hydroxide or potassium hydroxide to produce a secondary persulfate, sodium persulfate or potassium persulfate, The reactor can be composed of:

In a preferred embodiment, the apparatus may further comprise a second reactor for circulating the ammonia gas generated in the process of generating the secondary persulfate salt to the gas-liquid contacting means or converting a portion of the ammonia gas into nitrogen gas.

In a preferred embodiment, the deaeration unit may be configured to remove deaeration after adjusting the pH to 9 to 13 by introducing an aqueous solution of NaOH into the introduced wastewater.

In a preferred embodiment, the gas-liquid contacting means can be configured to react with ammonia gas and a sulfuric acid solution diluted from 5 to 50 wt% to concentrate in the form of 5 to 45 wt% ammonium sulfate.

In a preferred embodiment, the electrochemical conversion means converts the stored ammonium sulfate into an ammonium persulfate form by ion exchange membrane while reacting the stored ammonium sulfate at an electric current density of 0.001 to 0.4 A / cm ² for 10 to 600 minutes .

In a preferred embodiment, the electrochemical conversion means may be composed of a plurality of metal cathodes and cathodes arranged alternately, and an ion exchange membrane capable of selectively moving ions between the cathodes and the cathodes.

In a preferred embodiment, the electrochemical conversion means comprises at least one selected from the group consisting of platinum (Pt), iridium (Ir), ruthenium (Ru), tantalum (Ta), tin (Sn), and boron- And the negative electrode is composed of the positive electrode or at least one selected from the group consisting of titanium (Ti), nickel (Ni), graphite, lead (Pb) and zirconium (Zr) Mesh-type or plate-type electrodes can be used.

In a preferred embodiment, the absorption tower is a structure in which a cleaning liquid is sprayed into an exhaust gas, a form in which the exhaust gas is aerated in a cleaning liquid, a state in which the cleaning liquid is atomized by ultrasonic vibration or the like and brought into contact with the exhaust gas, And a method of inserting the cleaning liquid into the shape absorption tower, so that the cleaning liquid can be brought into contact with the exhaust gas to be treated.

In a preferred embodiment, the cleaning liquid stored in the cleaning liquid tank may further comprise a chlorine-based radical generated by supplying sodium chloride in addition to the primary or secondary persulfate.

In a preferred embodiment, the exhaust gas supplied to the absorption tower may be supplied through the gas pretreatment means.

In a preferred embodiment, an additional absorber may be connected in series or parallel to the absorption tower, and a rinse liquid containing persulfate or sodium hydroxide may be supplied from the rinse liquid tank, respectively, have.

In a preferred embodiment, the wastewater treatment means comprises a wastewater treatment and regeneration means comprising at least one of electrochemical treatment means, solid-liquid separation means, and chemical treatment means, and the persulfate contained in the wastewater, To the washing liquid tank and the remaining wastewater to be discharged.

The present invention having such characteristics as described above is characterized in that an oxidizing agent necessary for removing nitrogen oxides (NOx) contained in exhaust gas generated in various industrial fields including ships and onshore plants is removed from wastewater containing ammonia components Which is a non-chlorine-based oxidizing agent, to produce NO _2, which is low in solubility, from NO ₂ contained in the exhaust gas, is oxidized to NO ₂ or NO ₃ having high solubility and then removed. It also has the advantage of recycling resources while removing ammonia from wastewater.

In addition, waste water containing an ammonia component is used to produce persulfate, which is a non-chlorine-based oxidizer, to remove the exhaust gas. Thus, the second pollution problem caused by the greenhouse gas generation occurring in the wet cleaning of the exhaust gas using the ammonia- , The risk of exposure to chlorine (Cl ₂ ) gas generated by the conventional chlorine oxidizing agent, the increase of the electric power cost, the corrosion problem and the secondary treatment of the wastewater,

It also has the advantage of increasing the wet cleaning power by producing chlorine-based radicals by reacting it with sodium chloride after producing persulfate, which is a non-chlorine-based oxidizer, by using wastewater containing ammonia component and then using it for flue gas cleaning together with persulfate Which is a useful invention of the present invention.

FIG. 1 is a process diagram showing a process of treating an exhaust gas by wet cleaning according to an embodiment of the present invention,
FIG. 2 is a specific configuration diagram of the persulfate production facility of FIG. 1,
3 is a process diagram showing an exhaust gas treatment process including a flue gas pretreatment means by wet scrubbing according to another embodiment of the present invention,
FIG. 4 is a process diagram showing a multi-exhaust gas treatment process by wet cleaning according to another embodiment of the present invention,
FIG. 5 is a process diagram showing a method for recovering wastewater in accordance with another embodiment of the present invention; FIG.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

FIG. 1 is a process diagram showing an exhaust gas treatment process by wet cleaning according to an embodiment of the present invention, and FIG. 2 is a specific configuration diagram of the persulfate production facility of FIG.

As shown in the drawings, the apparatus for wet-cleaning an exhaust gas containing nitrogen oxide according to the present invention includes a nitrogen oxide-containing exhaust gas supply unit for supplying an exhaust gas containing NOx to a cleaning liquid containing a persulfate to contact the exhaust gas to oxidize the nitrogen oxide contained in the exhaust gas An absorption tower (1) for wet-cleaning by gas-liquid contact; A cleaning liquid tank (2) for storing a cleaning liquid containing persulfate and supplying the cleaning liquid to the absorption tower; A persulfate production means (3) for removing ammonia gas from wastewater containing ammonia or industrial byproducts, electrolyzing the ammonia gas, and supplying the persulfate to a cleaning liquid tank after production; And a wastewater treatment means 4 for purifying and discharging the wastewater discharged from the absorption tower.

Specifically, when flue gas containing nitrogen oxides generated from power plant boilers, industrial boilers, municipal waste incinerators and designated waste incinerators, ship engines, generators and boilers, generators of onshore plants, and boilers is introduced, persulfate supplied from the rinse tank And a chlorine-based radical generated by storing sodium chloride together with a persulfate and a persulfate together with NOx in the exhaust gas is contacted with the exhaust gas to oxidize low solubility NO to NO2 in the nitrogen oxides contained in the exhaust gas And an absorber (1) for wet-cleaning by gas-liquid contact.

In the absorption tower, an exhaust gas containing nitrogen oxide and a non-chlorine-based oxidant produced by using wastewater as a raw material, that is, a cleaning liquid containing persulfate, are brought into contact with the exhaust gas or the persulfate and persulfate produced from the wastewater as raw materials The cleaning liquid containing the chlorine radicals generated by the reaction of sodium chloride is contacted with the exhaust gas to fix the nitrogen oxide contained in the exhaust gas in the cleaning liquid to be removed from the exhaust gas to be treated. In the present invention, the term 'fixed' means to keep unchanged, meaning that it is not re-released but dissolved and removed in the washing liquid and does not chemically change.

In addition, a method of causing the liquid to be contacted with the cleaning liquid at the absorption tower in the gas-liquid contact may be a mode of spraying the cleaning liquid into the exhaust gas, a mode of aerating the exhaust gas into the cleaning liquid, And a method of inserting a member for increasing the contact area between the cleaning liquid and the cleaning liquid into the tubular absorber may be combined and used.

The washing liquid supplied to the absorption tower 1 is stored in the washing liquid tank 2. The cleaning liquid used in the present invention is a cleaning liquid or a persulfate containing persulfate (such as sodium persulfate, ammonium persulfate unconverted into sodium persulfate, etc.) and a chlorine-based radical generated by the reaction of persulfate and sodium chloride in the cleaning liquid tank It is a cleaning liquid.

In addition, the water constituting the rinsing liquid can be constituted so as to supply water in the form of liquid in the persulfate production means 3 or persulfate in the solid state in accordance with the process constitution to the rinsing liquid tank storing the water. At this time, wasted or depleted water may be supplied to the washing liquid tank (2) by connecting a common fresh water supply line, or may be used by introducing seawater when it is constructed on a ship or a coastal industrial plant. It may be configured not to supply sodium chloride separately when the seawater is introduced.

The reason why the persulfate, especially sodium persulfate, oxidizes NO in the exhaust gas is that the OH radical is generated and reacted. The reaction process can be referred to the following equation.

On the other hand, if the sodium sulphate by the chloride ions present when the OH radical is generated, as shown in the reaction scheme below to produce a chlorine radical, such as ClOH ^and can further promote NO oxidation. In this case, the supply of chlorine ions by sodium chloride can reduce the supply amount of sodium persulfate. However, when comparing the oxidizing power of Table 1 below, it should be noted that when the sodium chloride is added and when the sodium chloride is added alone, the oxidizing power is shown when the chlorinating oxidant is used. Therefore, when the sulfur chloride is used alone, , But it is a different interpretation than what is shown in Table 1. Table 1 below is a table that proves that the reaction is accelerated when sodium sulfate is added to the persulfate salt rather than the oxidizing power of the chlorine-based oxidizer and the sodium persulfate. In other words. Oxidation power can be determined by adding additional conditions such as the amount of oxidizing agent / reaction time / energy input, so that the oxidizing power is lower than that of the chlorinated oxidizing agent because the oxidizing power is 30% when only the sodium persulfate described in Table 1 is used It is meaningless to do.

Specifically, there is a structural disadvantage that toxic chlorine gas and hydrogen gas are generated when the chlorine-based oxidizing agent is produced, and the energy consumed when producing the chlorine-based oxidizing agent is 2000 ppm and the energy consumed when the sodium persulfate is produced is different from each other. Such a problem does not occur when sodium chloride is used.

That is, the chlorine-based oxidizing agent generally used and the chlorine-based radicals included in the present invention have different effects. Since the chlorine-based oxidizing agent usually used is dissolved in water or caustic soda, the chlorine-based oxidizing agent is easily released again according to temperature or pH, and chlorine gas is generated in the course of production. However, the chlorine- The chlorine radical according to the present invention plays a role of a safe oxidizing agent which does not cause problems caused by the conventional chlorine-based oxidizing agent, since the half-life period of the radicals is tens of thousandths of a second because of the characteristics of the radicals .

The wastewater discharged from the absorption tower is discharged through a wastewater treatment means (4) for discharging the wastewater after purification. As the wastewater treatment means, particulate matter may exist in the case of gas introduced without pretreatment, and it may be washed out in the washing liquid in the wet absorption step. Therefore, it is composed of means for performing solid-liquid separation or treating means such as pH control according to the post- .

 The persulfate (particularly, sodium persulfate) which is a non-chlorine oxidizing agent supplied to the washing liquid tank 2 can be produced by removing the ammonia gas from the wastewater containing ammonia or industrial byproducts through the persulfate production means 3, , Which is reacted with a sulfuric acid solution to produce ammonium sulfate, and the ammonium sulfate is firstly converted to ammonium persulfate, which is a persulfate, through electrochemical conversion means. Subsequently, ammonium persulfate is reacted with sodium hydroxide or potassium hydroxide again to make a better oxidizing agent, and is then subjected to secondary conversion into persulfate, that is, sodium persulfate or potassium persulfate.

The persulfate, which is the non-chlorous oxidant produced in this manner, has an oxidizing power equal to or higher than that of the chlorine-based oxidizing agent and is easy to handle, and is supplied to the cleaning liquid of the present invention to oxidize the nitrogen oxides in the exhaust gas.

FIG. 2 shows the means and process for recovering the raw material of the oxidizing agent from the waste water or industrial by-products containing the ammonia component and producing the oxidizing agent.

Specifically, the persulfuric acid production means 3 includes: a degassing means 31 for generating ammonia gas by vaporizing dissolved ammonia components in the wastewater; and a gas-liquid contacting means 31 for spraying the sulfuric acid solution diluted in the ammonia gas, Liquid contact means 32 for producing ammonium sulfate; electrochemical switching means 33 for electrolyzing ammonium sulfate to produce ammonium persulfate; and ammonium persulfate supplied with sodium hydroxide or potassium hydroxide to produce persulfate And a reactor (34) for producing the catalyst.

The gas-liquid contact means 32 has the same structure as the absorption tower, and is configured to inject ammonia gas and inject sulfuric acid solution. In this case, the proportion of ammonia to sulfuric acid can be adjusted in various proportions according to the concentration of the gas to be introduced and ammonium sulfate to be produced.

And a second reactor 35 for circulating the ammonia gas generated in the course of producing the persulfate in the reactor to the gas-liquid contact means 32 or converting a part of the ammonia gas into nitrogen gas, Liquid contact reaction, or a part thereof is converted into nitrogen gas to be discharged.

Needless to say, the supply flow rate and the persulfate concentration of the washing liquid supplied to the absorption tower include control means for controlling the concentration of the nitrogen oxides in the treatment flue gas, the temperature, and the flow rate conditions.

More specifically, the persulfate production means 3 configured as described above recovers the ammonium sulfate by bringing the ammonia gas generated through the degassing means capable of vaporizing the dissolved ammonia component into the wastewater into contact with the diluted sulfuric acid solution.

In this case, it is preferable to inject the sulfuric acid solution diluted to 30 to 40 wt%, and finally to concentrate the ammonium sulfate to 5 to 45 wt%, preferably 20 to 40 wt% Respectively.

As the degassing means 31, a method of raising the pH, a method of raising the temperature, and a method of treating them in combination may be used by using any one or more of an apparatus for liquid fractionation, an agitator type degassing apparatus and a heating or low temperature degassing apparatus Remove it. Of course, if there is a method capable of degassing by using a means capable of degassing, the present invention is not limited thereto.

The pH of the wastewater introduced at the time of degassing is adjusted to 9 to 13 by using an aqueous solution of NaOH or the like and then degassed using the degassing means (31). Under such conditions, most of the ammonia gas dissolved in the water is vaporized.

The recovered ammonium sulfate is converted to ammonium persulfate through a diaphragm electrochemical conversion means (electrolytic apparatus) having an ion exchange membrane capable of selectively transferring ions and a plurality of electrodes, and finally sodium hydroxide or sodium hydroxide Through the reaction with potassium hydroxide, sodium persulfate or potassium persulfate, which is more oxidizing than ammonium persulfate, which is a primary persulfate, is produced in a second order.

Here, the diaphragm type electrolytic cell used as the electrochemical conversion means (electrolytic apparatus) is made of an electrode material and is made of platinum (Pt) or iridium (Ir), ruthenium (Ru), tantalum (Ta), tin (Sn) (BDD), or a mixture of one or more of these materials is coated on a conductive substrate, and the negative electrode is formed of the above-mentioned positive electrode or a combination of nickel (Ni), graphite, lead (Pb ), Zirconium (Zr), or the like is preferably used.

In addition, the shape of the electrode surface may be an electrode of a mesh type or a plate type.

The interval of the electrodes can be set within 3 to 100 mm, but it is preferably 5 to 50 mm considering the applied voltage.

The current applied to the electrode for electrolysis is such that the current density is 0.001 to 1.0 A / cm ² , preferably 0.2 to 0.6 A / cm ² , and ammonium persulfate is produced by an electrochemical reaction.

The electrode for electrolysis is formed by using an electrode coated with a main component of any one or more of iridium (Ir), ruthenium (Ru), tantalum (Ta), and tin (Sn) on a titanium (Ti) (Ti) electrode can be used. The electrolysis conditions are such that the current density applied according to the electric conductivity of the wastewater and the concentration of the contaminant is 0.001 to 1.0 A / cm ² , and the reaction time is 10 to 600 minutes Respectively.

3 is a process diagram showing an exhaust gas treatment process including a flue gas pretreatment means by wet scrubbing according to another embodiment of the present invention. As shown in the figure, the basic structure is the same as that of the apparatus shown in Figs. 1 and 2, and further comprises a gas pretreatment unit 5 for pretreating the exhaust gas supplied to the absorption tower. The reason for including such means is that, when particulate contaminants or dusts are contained in the exhaust gas to be treated, it can act as a factor that interferes with the gas-liquid reaction in the absorption tower. Examples of the gas pretreatment means capable of effectively separating the solid and the gas include a cyclone, a venturi scrubber, a filter, and the like.

FIG. 4 is a process diagram showing a multi-exhaust gas treatment process by wet cleaning according to another embodiment of the present invention. As shown in the drawings, the basic structure is the same as that of the apparatuses of Figs. 1 and 2, except that the second absorption tower 1a for wet-cleaning the exhaust gas through the absorption tower and the second absorption tower 1a for supplying the cleaning liquid to the second absorption tower 2 cleaning liquid tank 2a.

It is also a matter of course that a supply piping is connected between the absorption tower and the second absorption tower to supply the primary treatment flue gas, which is firstly wet-cleaned and discharged by the cleaning liquid containing the oxidizing agent in the absorption tower, to the second absorption tower.

At this time, the cleaning liquid stored in the second cleaning liquid tank 2a may be cleaned by using a cleaning liquid containing persulfate, which is a non-chlorinated oxidizing agent produced from the wastewater as a raw material in the persulfate production means 3 as in the conventional cleaning liquid tank 2, Instead, only a cleaning liquid containing sodium hydroxide may be used. If sodium hydroxide is included, sodium hydroxide added to the nitrogen oxide mixed with NO and NO ₂ re-oxidizes NO.

In the illustrated example, the structure in which the absorber and the second absorber are connected in series is shown. However, the present invention can be applied to an additional multi-stage serial configuration or a parallel application, or a combination of a serial and a parallel have.

FIG. 5 is a process diagram showing a method for recovering wastewater in accordance with another embodiment of the present invention; FIG.

1 and 2, the wastewater treatment device 4 for treating wastewater discharged from the absorption tower 1 is provided with a regeneration function and a wastewater treatment and regeneration means (4a) so that the non-chlorine-based oxidizing agent can be recovered and recycled. To this end, a recovery pipe is provided between the wastewater treatment and regeneration means 4a and the cleaning liquid tank 2.

In this case, various means can be applied as means for recovering and recycling the components necessary for persulfate or other gas cleaning from the wastewater generated in the absorption tower. For example, an electrochemical treatment means, a solid-liquid separation means, It is preferable to include a chemical treatment means.

On the other hand, the absorption tower 1, the second absorption tower 1a, the cleaning liquid tank 2, the second cleaning liquid tank 2a, the persulfate production means 3, the wastewater treatment means 3, The gas-liquid contact means 32, the electrochemical switching means 33, the gas-liquid separating means 4, the waste water treatment and regeneration means 4a, the gas pretreatment means 5 and the persulfate production means 3, A variety of liquid or gas transfer pipes are connected between the reactor 34 and the second reactor 35 between the front and rear means or necessary means as shown in the drawing. And it is also a natural constitution that a valve is provided in a portion where the flow flow needs to be adjusted or interrupted.

Hereinafter, preferred embodiments and comparative examples of the present invention will be described.

(Examples 1 and 2 and Comparative Example 1)

In Example 1, a cleaning liquid containing persulfate (mainly including ammonium persulfate containing sodium persulfate and unreacted ammonium persulfate) produced from wastewater was used. In Example 2, a non-chlorine-based oxidizing agent The phosphorus persulfate (mainly containing unreacted ammonium persulfate containing sodium persulfate) and sodium chloride were used to introduce a chlorine-based cleaning solution.

In Comparative Example 1, a gaseous nitrogen oxide removal experiment through gas-liquid contact in an absorption tower was carried out using a representative sodium hypochlorite among chlorinated oxidizers.

The experimental conditions were the same temperature, gas / liquid flow rate and time. That is, 100 g of the oxidizing agent of the concentration shown in Table 1 was put into a 4 L absorption tower (reactor) and tested in a semi-batch mode while bubbling 800 ppm of NO gas at 3 LPM flow rate. Then, the oxidation rate was calculated while analyzing the NO concentration at the outlet side. In Example 2, 130 g of sodium chloride was further added. The sodium hypochlorite of Comparative Example 1 was tested by adding about 60 mL of a 12% sodium hypochlorite solution to 4 L of distilled water.

Table 1 shows the results of comparing the performance of each of the oxidative cleaning liquids in Examples 1 and 2 and Comparative Example 1. Table 1 shows that NO removal reaction can be promoted when NaCl is added, and it can be judged that NO removal ability is equal to or higher than that of sodium hypochlorite.

The sodium hypochlorite used as a comparative example is bulky in liquid phase and may be deteriorated by exposure to light or air while being stored. Various disadvantages such as power consumption, chlorine and hydrogen gas generation and corrosion in the field production through electrolysis Lt; / RTI >

On the other hand, the persulfate according to the present invention has many merits in that it can be stored in a solid state as needed, has no risk of deterioration, and can recover the raw material from the ammonia wastewater. For reference, in Table 1, for the sake of convenience, the sulfate was described in the form of persulfate ion, When sodium persulfate (or potassium persulfate) dissolves in water, it forms a persulfate ion form. Therefore, it does not matter because the molar concentration does not change even if it is expressed by the ion.

Cleaning liquid unit density Reaction temperature De-NOx Remarks Example 1 S ₂ O ₈ ^2- mol / L 0.1 333 K 99.0% with NaCl Example 2 S ₂ O ₈ ^2- mol / L 0.1 333 K 30.0% without NaCl Comparative Example 1 NaOCl mg Cl ₂ / L 1,000 333 K 75.0%

(De-NOx removal rate)

The persulfate dissolves in water to form an OH radical, which is a powerful oxidant, through the reaction schemes 1 and 2. OH radicals oxidize NO to fix it in the cleaning liquid.

In addition, when NaCl is added, the reaction with persulfate in the reaction tank without electrolysis reaction generates hypochlorite radical and chlorine radical, and the oxidation / absorption of NO is further progressed, thereby improving the overall removal rate (see reaction formulas 4 to 9). The hypochlorite radicals and the chlorine radicals generated by the reaction of persulfate at this time do not cause problems such as the danger due to the chlorine gas or the secondary treatment of the corrosion and the wastewater when the chlorine-based oxidizing agent is directly used in the wet reaction.

S ₂ O ₈ ^{2 -} ? ² SO ₄ ^- Scheme 1

^And SO _{4 ^{- + H 2 O → HSO 4}} - + OH ^and Scheme 2

^And OH ^{+ NO → H + + NO 2} - Scheme 3

^And OH + Cl ^- → OH ^- + Cl ^and Scheme 4

OH < + > + Cl < ^- > ^{- &}

ClOH ^{- -} + NO ^- & gt ^; H ⁺ + NO ₂ ^- + Cl ^- Scheme 6

Cl ^and Cl- → Cl ₂ + ^{and -} Scheme 7

Cl ₂ ^{and - and} + OH → HOCl + Cl ^- Scheme 8

NO ₂ ^- + HOCl ^- > H ⁺ + NO ₃ ^- + Cl ^- Scheme 9

The persulfate (sodium persulfate) used in Examples 1 and 2 was produced by using ammonia recovered from wastewater containing ammonia nitrogen as a raw material and adjusted to pH 9-13 from wastewater containing ammonia nitrogen , Ammonia gas is obtained through a degassing means configured to contain the pH-adjusted wastewater into a container and to inject air at a flow rate of 20 LPM by placing an acid tube on the bottom of the vessel. Subsequently, a sulfuric acid solution (30% 3 L / m < ³ >) was supplied and reacted to recover ammonium sulfate. Ammonium sulfate recovered at a concentration of 25% was electrolyzed for 60 minutes at an electric current of 0.4 A / cm 2 using a diaphragm type electrolytic apparatus as an electrochemical conversion means to convert it into ammonium persulfate, mol / L injection to finally produce sodium persulfate. At this time, the reaction solution contains an unconverted trace amount of ammonium persulfate.

The non-chlorine-based oxidant produced through the invention of this combined treatment process oxidizes nitrogen monoxide to nitrogen dioxide in a form that is soluble in water and removes ammonia from the wastewater that is a fixed source of pollution by removing ammonia from the wastewater.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims and their equivalents. Of course, such modifications are within the scope of the claims.

(1): absorption tower (2): cleaning liquid tank
(3): Sulfate production means (4): Wastewater treatment means
(5): gas pretreatment means (31): degassing means
(32): gas-liquid contact means (33): electrochemical switching means
(34): reactor (35): second reactor

Claims (13)

An absorption tower for subjecting a flue gas containing nitrogen oxides to a gas-liquid contact with a cleaning liquid containing a persulfate to oxidize the nitrogen oxides, followed by wet cleaning;
A cleaning liquid tank for supplying a cleaning liquid containing stored persulfate to the absorption tower;
A persulfate production means for supplying a persulfate to the cleaning liquid tank after production of the persulfate, including the step of supplying sulfuric acid solution and electrolysis after deaeration of ammonia gas from wastewater containing ammonia or industrial byproduct;
And a wastewater treatment means for purifying and discharging the wastewater discharged from the absorption tower.
The method according to claim 1,
The persulfate production means comprises: a degassing means for generating ammonia gas by vaporizing the dissolved ammonia component in the wastewater;
Liquid contact means for bringing a sulfuric acid solution into vapor-liquid contact with an ammonia gas to produce ammonium sulfate;
An electrochemical conversion means for electrolyzing ammonium sulfate to produce ammonium persulfate, the first persulfate salt, and
And a reactor which reacts ammonium persulfate, which is a primary persulfate, with sodium hydroxide or potassium hydroxide to produce a secondary persulfate, sodium persulfate or potassium persulfate. Cleaning system.
The method of claim 2,
And a second reactor for circulating the ammonia gas generated in the process of generating the secondary persulfate to the gas-liquid contacting means or converting a portion of the ammonia gas into nitrogen gas. Gas cleaning system.
The method of claim 2,
Wherein the degassing means is configured to remove water after the NaOH aqueous solution is introduced into the introduced wastewater to adjust the pH to 9 to 13, and then to degas the wastewater.
The method of claim 2,
Wherein the gas-liquid contacting means is configured to react the ammonia gas with a sulfuric acid solution diluted with 5 to 50 wt% to concentrate the ammonia gas in the form of 5 to 45 wt% ammonium sulfate.
The method of claim 2,
The electrochemical conversion means is characterized in that the stored ammonium sulfate is applied to the positive electrode and the negative electrode at a current density of 0.001 to 1.0 A / cm ² and reacted for 10 to 600 minutes to convert it into an ammonium persulfate form by electrolysis while being electrolyzed A wet gas cleaning system using an oxidant produced from wastewater.
The method of claim 6,
Wherein the electrochemical conversion means comprises an ion exchange membrane in which a plurality of metal anodes and cathodes are arranged alternately and ions are selectively transferred between the anode and the cathode.
The method of claim 6,
Wherein the electrochemical conversion means comprises at least one selected from the group consisting of platinum (Pt), iridium (Ir), ruthenium (Ru), tantalum (Ta), tin (Sn), and boron- The negative electrode may be formed of at least one selected from the group consisting of the positive electrode and the positive electrode or the positive electrode or the negative electrode in the form of a mesh, Or an electrode in the form of a plate is used as the oxidizing agent.
The method according to claim 1,
The absorption tower may be configured to inject a cleaning liquid into the flue-gas, or to form a flue-gas into the flue-gas, or to contact the flue-gas by atomizing the cleaning liquid by ultrasonic vibration or the like, or to insert a member for increasing the contact area between the flue- And the cleaning liquid is brought into contact with the flue gas to be treated. The wet gas cleaning system using the oxidant produced from the wastewater.
The method according to claim 1,
Wherein the cleaning liquid stored in the cleaning liquid tank further comprises a chlorine-based radical generated by supplying sodium chloride in addition to the primary or secondary persulfate generated in the washing liquid tank.
The method according to claim 1,
And the exhaust gas supplied to the absorption tower is supplied through the gas pretreatment means.
The method according to claim 1,
Characterized in that an additional absorber is connected in series or in parallel to the absorption tower and a cleaning liquid containing persulfate or a sodium hydroxide is supplied from the cleaning liquid tank so that the exhaust gas is treated in a multi- Wet gas cleaning system using oxidizing agent.
The method according to claim 1,
The wastewater treatment means comprises wastewater treatment and regeneration means including at least one of electrochemical treatment means, solid-liquid separation means, and chemical treatment means, and the recovered persulfate is returned to the cleaning liquid tank And the remaining wastewater is discharged. The wet gas cleaning system according to claim 1,

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