KR100262689B1 - Treatment of stack gas desulfurization waste water - Google Patents

Abstract

The flue gas desulfurization wastewater treatment method of the present invention comprises: a COD component decomposition step 1 of decomposing and removing an excess oxidant with a reducing agent by adding an oxidizing agent to the waste water to decompose the nitrogen-sulfur-containing compound, a chelating agent for collecting heavy metals, Agglomeration sedimentation step A2 which adds an aluminum compound, an alkali chemicals for pH adjustment, and precipitates and isolates solids containing fluorine and heavy metals, and adds sodium carbonate and an alkali chemicals for pH adjustment, precipitates and separates solids containing calcium and fluorine. After contacting the flocculation sedimentation step B3 with activated carbon, the activated carbon adsorption step 7 which adsorbs and removes the organic COD component and the fluorine adsorption resin are contacted to remove the remaining fluorine, and then adjusted to pH 5.8 to 8.6 with an alkaline agent. Fluorine adsorption step 8. According to the treatment method of the present invention, COD components, fluorine, heavy metals, and the like can be efficiently and sufficiently removed from the wastewater of the wet flue gas desulfurization apparatus that absorbs and removes sulfur compounds in lime combustion exhaust gas.

Description

Treatment method of flue gas desulfurization drainage

The present invention is directed to a method for treating flue gas desulfurization which is discharged from a desulfurization apparatus, in particular a soot mixed desulfurization apparatus, which desulfurizes sulfur oxide gas in combustion exhaust gas such as coal by an alkali absorption liquid by a lime-gypsum method. It is about.

The combustion exhaust gas which uses coal etc. as fuel is processed by the desulfurization apparatus by the lime-gypsum method, and the waste water containing fluorine-decomposable COD component (component which causes chemical oxygen demand) and fluorine is discharged | emitted.

At this time, the hardly decomposable COD component contained in the desulfurization wastewater includes an inorganic COD component and an organic COD component. Among these, the inorganic COD component is composed of a nitrogen-sulfur compound (hereinafter also referred to as an "NS compound") produced by reacting a part of SO ₂ and NO x absorbed in the absorbent liquid in the desulfurization apparatus and is organic. The COD component mainly consists of the organic component in industrial water used as replenishment water of a desulfurization apparatus.

Such COD components are difficult to remove by a coagulation precipitation method using a conventional flocculant or an activated sludge removal method using microorganisms, and it is very difficult to achieve a discharge standard value (for example, 20 mg / L or less) of the COD component.

In addition, among these COD components, a method of decomposing an NS compound is known to decompose an acetate salt (NO ₂ −). This method, sodium acetate,

NO ₂ ^-- N / NS Compound = 1-2 (molar ratio)

It is added in the ratio of and decomposes on the conditions of pH2 or less and the temperature of 45 degreeC or more. However, since the desulfurization drainage discharged from the soot-mixed flue gas desulfurization apparatus is usually weakly acidic and has a pH of 2 or less, a large amount of acid is required, and a large amount of alkaline agent is required to neutralize to neutral to weak alkaline after completion of the reaction. It is a waste of money and a lot of hands.

As described in Japanese Patent Laid-Open Publication No. Hei 4-59026, the present applicant first takes out a part of the absorption slurry of the desulfurization apparatus to separate the solid and liquid, and then adjusts the separation liquid (filtrate) to pH 3 to 4 to hypochlorite. By adding, a method of removing the NS compound has been proposed. In this treatment method, the N-S compound in the treated water can be removed to 5 m mol / L or less.

However, this publication discloses a method for treating N-S compounds in desulfurization drainage, but does not mention a method for treating other organic COD, fluorine, heavy metals, and the like.

In addition, the organic COD component contained in the desulfurization drainage is also very difficult to decompose. As a treatment method of this hardly decomposable organic COD component, the activated carbon adsorption method is common. However, the organic component in the desulfurization waste water is derived from industrial water, and has less adsorption to activated carbon than general organic matter. Therefore, in order to sufficiently adsorb and remove the organic components, there is a problem that the adsorption facility must be enlarged.

On the other hand, as a treatment method of wastewater containing fluorine, a calcium coagulation sedimentation method in which 2 to 3 times the amount of calcium ions is added to fluorine ions and removed as calcium fluoride is common. However, with this method, it is not possible to sufficiently remove fluorine, and it is quite difficult to achieve a uniform emission standard (15 mg / L or less) nationwide.

In addition, a two-stage flocculation sedimentation method is known as an improved treatment method. This method removes the precipitate composed of heavy metal hydroxide, gypsum and calcium fluoride, which is formed in the neutral vicinity when slaked lime is added to the desulfurization drainage, and then adds an alkali chemicals such as sodium hydroxide to give an alkaline region of pH 10 or more. It is a method of precipitating magnesium ions derived from a gas component as a precipitate of magnesium hydroxide, and simultaneously precipitating and separating the remaining fluorine ions.

According to this method, the concentration of fluorine ions in the treated waste water can be made equal to or less than the above discharge standard value. However, when stricter regulations are required by the added standards or the like, for example, when it is required to reduce the fluorine in the discharged water to 2 mg / L or less, it is difficult to achieve the regulation value by this method.

An object of the present invention is to provide a method for efficiently and sufficiently removing components such as inorganic COD components, organic COD components, fluorine, heavy metals, etc. from the desulfurization drainage of the wet flue gas desulfurization apparatus of lime combustion exhaust gas.

In the first flue gas desulfurization wastewater treatment method of the present invention, in the flue gas desulfurization wastewater treatment method discharged from a wet flue gas desulfurization apparatus that absorbs and removes sulfur compounds in coal combustion exhaust gas,

(a) a COD component decomposition step of adding an oxidizing agent to the wastewater to decompose the nitrogen-sulfur compound as a COD component in the drainage, and then adding a reducing agent to decompose and remove the excess oxidizing agent;

(b) a coagulation sedimentation step A for adding a heavy metal chelating agent, an aluminum compound, and a pH adjusting alkali agent to precipitates separated from solids containing fluorine and heavy metals to the waste water treated by the COD component decomposition step;

(c) a coagulation precipitation step B which adds sodium carbonate and a pH adjusting alkali agent to the waste water treated by the coagulation precipitation step A, and precipitates and separates solids containing calcium and fluorine.

That way, also,

(d) an activated carbon adsorption step of bringing the wastewater treated in the flocculation precipitation step B into contact with activated carbon to adsorb and remove the organic COD component;

(e) The fluorine adsorption process may be included in which the wastewater treated in the activated carbon adsorption process is brought into contact with the fluorine adsorption resin to adsorb and remove the remaining fluorine, and then adjusted to pH 5.8 to 8.6 with an alkaline agent.

The second flue gas desulfurization wastewater treatment method of the present invention is the flue gas desulfurization wastewater treatment method discharged from a wet flue gas desulfurization apparatus that absorbs and removes sulfur compounds of coal combustion exhaust gas.

(a) a COD component decomposition step of adding an oxidizing agent to the wastewater to decompose the nitrogen-sulfur compound as a COD component in the drainage, and then adding a reducing agent to decompose and remove the excess oxidizing agent;

(b) a coagulation precipitation step C for adding a pH adjusting alkali agent to the wastewater treated in the COD component decomposition step and depositing and separating solids containing magnesium and fluorine under alkalinity;

(c) a coagulation sedimentation step A for depositing and separating solids containing fluorine and heavy metals by adding a chelating agent for heavy metal collection, an aluminum compound, and an alkali chemicals for pH adjustment to the wastewater treated in the COD decomposition step. It is characterized by.

That way, also

(d) an activated carbon adsorption step of adsorbing and removing organic COD components by bringing the wastewater treated in the flocculation settling step A into contact with activated carbon;

(e) A fluorine adsorption step of adjusting the pH of the activated carbon adsorption step by contacting the fluorine adsorption resin with the fluorine adsorption resin to remove the remaining fluorine and adjusting the pH to 5.8 to 8.6 with an alkaline agent.

In the first or second flue gas desulfurization wastewater treatment method of the present invention, during the decomposition of the COD component, using sodium hypochlorite as an oxidizing agent, the wastewater is adjusted to pH 4 or less by hydrochloric acid, and nitrogen-sulfur in the wastewater. Compounds can be decomposed and removed.

In the first or second flue gas desulfurization and wastewater treatment method of the present invention, as the chelating agent for heavy metal capture in the flocculation sedimentation step A, for example, one having a dithiocarbamic acid group or a thiol group can be used.

In the first or the second flue gas desulfurization wastewater treatment method of the present invention, during the fluorine adsorption step, the wastewater is adjusted to pH 2 to 4 by hydrochloric acid, and then the pH-adjusted wastewater is passed through the fluorine adsorption resin layer. Can be adsorbed and removed.

At this time, as the fluorine adsorption resin, for example, at least one or more selected from phosphomethyl amino group chelate resins, zirconium-supported resins, and cerium-supported resins can be used.

In the first or second flue gas desulfurization wastewater treatment method of the present invention, the method further includes a step of returning a regeneration waste liquid generated upon regeneration of the fluorine adsorption resin to the flue gas desulfurization apparatus after the adsorption of fluorine in the fluorine adsorption step. You may also do it.

1 is a process diagram of a first treatment method of the present invention.

2 is a process chart of the second treatment method of the present invention.

3 is an explanatory diagram of a COD component decomposition step in the first and second treatment methods of the present invention.

4 is an explanatory diagram of a coagulation precipitation step A in the first and second treatment methods of the present invention;

5 is an explanatory diagram of a coagulation sedimentation step B in the first treatment method of the present invention.

6 is an explanatory diagram of a coagulation precipitation step C in a second treatment method of the present invention;

The method of the present invention will be described in the order of process. In addition, the process common to the processing method of this invention and a 2nd processing method is demonstrated together.

(1) COD component decomposition process

The COD component decomposition step is a step of adding an oxidant to the wastewater, decomposing the nitrogen-sulfur compound as the COD component in the wastewater, and then adding a reducing agent to decompose and remove the excess oxidant.

The desulfurization wastewater discharged from the desulfurization apparatus for treating coal combustion exhaust gas is introduced into a COD component decomposition step. This wastewater contains an NS compound (inorganic COD component) mainly having the following composition produced by the reaction of SO ₂ and NOx as a desulfurization apparatus.

Hydroxy amine monosulfonate HONHSO _3-

Hydroxyamine disulfonate HON (SO ₃ ) ₂ ^2-

Hydroxyamine trisulfonate ON (SO ₃ ) ₃ ^3-

In this wastewater, the acid content of NS compound is adjusted to pH3 to 4 in order to eliminate unnecessary portions of the pH 4 or less, preferably in the chemical usage, and then the content of the NS compound based on the redox potential (ORP) of the wastewater. A corresponding amount of an oxidizing agent such as sodium hypochlorite (NaOCl) or the like is added to decompose the NS compound. When sulfuric acid is used as the photonic acid at this time, since scale easily occurs, it is preferable to use hydrochloric acid. Moreover, hypochlorite is mentioned as an oxidizing agent, Especially, sodium hypochlorite is preferable from a processability and economical viewpoint.

As a result of the experiment, the addition amount of sodium hypochlorite was set to NaOCl / NS compound = 3.0 to 5.0 (molar ratio), and it was confirmed that the decomposition rate of COD component reached 95% or more by reacting at a temperature of 40 ° C or more and a residence time of 2 hours or more. It became. Among the N-S compounds, as a representative example, hydroxy amine trisulfonate decomposition reaction is described below. In this reaction, some of the heavy metals are also oxidized.

^{_{6ON (SO 3) 3 3- +}} 18ClO - + 10H 2 O

^{_{→ 4NO + 2NO 3 - + 18HSO}} 4 - + 18Cl - + H + + 3O 2

After decomposing the NS compound, the residual amount of the oxidizing agent is determined based on the redox potential of the drainage, and almost the same amount of sodium sulfite (Na ₂ SO ₃ ), acidic sodium sulfite (NaHSO ₃ ), and sodium thiosulfate (Na ₂ S) are obtained. ₂ O ₃ ) or the like is added as a reducing agent to decompose excess oxidant such as sodium hypochlorite.

The wastewater from which the COD component has been decomposed after completion of the redox reaction is treated in the next step (coagulation sedimentation step A in the first method or coagulation sedimentation step C in the second method).

(2) Coagulation Sedimentation Process A

In the flocculation sedimentation step A, a chelating agent for collecting heavy metals, an aluminum compound, and an alkali chemicals for adjusting pH are added to the waste water to precipitate and separate solids containing fluorine and heavy metals.

Examples of the chelating agent for heavy metal collection include liquid high molecular heavy metal collecting agents having chelate forming groups such as dithiocarbamic acid groups (-NH-CS ₂ Na) and thiol groups (-SNa). The microfloc which collected the heavy metal is produced by adding 10-100 mg / L of chelating agents for heavy metal collection normally.

An aluminum compound acts as a flocculant, Specifically, poly aluminum chloride (PAC), aluminum chloride, alumina sulfate (aluminum sulfate), etc. can be used. The addition amount depends on the fluorine concentration in the wastewater or is usually about A1 / F = 0.1 to 0.5.

As the alkali agent for pH adjustment, sodium hydroxide etc. are used. By the addition of an alkaline agent for pH adjustment and adjustment to near neutral (pH 6 to 8), the following reaction occurs, resulting in the fluorine-aluminum complex [Al (OH) ₃ ... F] is formed and at the same time, a floc of aluminum hydroxide is formed. The complex is adsorbed and contained in the formed floc to precipitate.

^{Al 3+ + 3OH - + F →} Al (OH) 3 ... F

At this time, a part (20 to 30%) of the microfloc or organic COD component in which the heavy metal is collected is also removed by adsorption.

Anionic polymer coagulants, such as polyacrylamide, can be added suitably, and coarse floc can be formed and separability can be improved.

The solid liquid in the suspension containing such flocs is separated in the settling tank. The supernatant is treated in the next step (agglomeration sedimentation step B in the first treatment method or activated carbon adsorption step in the second treatment method).

(3) Coagulation sedimentation process B

The flocculation sedimentation step B is a step of adding sodium carbonate and an alkali chemicals for pH adjustment to the wastewater treated in the flocculation sedimentation step A to precipitate and separate solids containing calcium and fluorine.

The amount of sodium carbonate added depends on the concentration of calcium in the wastewater, or is usually an amount that is reduced by 10 to 50%, that is, an amount slightly larger than 0.1 to 0.5 mol relative to the amount of calcium (Ca).

In the flocculation sedimentation step B, by adding sodium carbonate and adjusting it to pH 9 to 10 as the alkali agent for pH adjustment, the following reaction occurs, and calcium ions in the drainage become calcium carbonate and are adjusted to pH 10 or more. As a result, magnesium ions become magnesium hydroxide. Calcium carbonate and magnesium hydroxide each form a floc. At this time, fluorine ions are adsorbed and contained in the flocs thus formed and precipitated.

_{^{Ca 2+ + CO 3 2+ F -}} → CaCO 3 ... F

^{Mg 2+ + 2OH - + F _} → Mg (OH) 2 ... F

At this time, as described above, the anionic polymer flocculant may be appropriately added, and coarse flocs are formed again to improve the separability.

Solids in suspension containing these flocs are separated in the settling bath. The supernatant water is treated in the next step (activated carbon adsorption step in the first treatment method).

(4) Coagulation sedimentation process C

The flocculation sedimentation step C is a step of adding a pH-adjusting alkali agent to the waste water, and depositing and separating a solid containing magnesium and fluorine under alkaline conditions.

In the flocculation sedimentation step C, by adjusting the pH to 10 to 11 with a pH adjusting alkali agent such as sodium hydroxide and slaked lime (calcium hydroxide), the magnesium ions in the wastewater become magnesium hydroxide to form flocs. At this time, the floc ions are adsorbed on the floc formed and precipitated.

Solids in suspension containing such flocs are separated in the settling tank. The symbol water is treated in the next step (coagulation sedimentation step A in the second treatment method).

(5) concentration process

The concentration step is carried out in a flocculation sedimentation step A and B of the first treatment method, or in the flocculation sedimentation steps C and A of the second treatment method, the contaminated sludge separated and discharged as a solid is concentrated by a concentration device. It is a process to do it.

The concentration of each contaminated sludge is usually about 1 to 2% by weight, but is about 5% by weight after concentration. The separated water is returned to the front end step (coagulation sedimentation step A in the first treatment method, or coagulation sedimentation step C in the second treatment method), and reprocessed together with the waste water from which the COD component is decomposed. Contaminated sludge from the concentrate is sent to the dehydration process.

(6) dehydration process

The dewatering process is a process of dewatering the concentrated contaminated sludge again, converting it into cake, and discharging it. As the dehydrator, a filter press, a belt press, a screw decanter or the like can be used. For example, in the case of a filter press, the moisture content of contaminated sludge can be 70 weight% or less.

(7) Activated Carbon Adsorption Process

The activated carbon adsorption step is a step of adsorbing and removing organic COD components by bringing drainage into contact with activated carbon.

The wastewater discharged in the front-end process (coagulation sedimentation step B in the first treatment method or coagulation sedimentation step A in the second treatment method) is introduced into the activated carbon adsorption step after removing the suspended matter by sand filtration or the like as necessary. . In the case of alkaline drainage, after adjusting the drainage to pH 6-8 with a mineral acid such as hydrochloric acid, the pH-adjusted drainage is passed through the granular activated carbon layer in the packed column, and the organic COD component mainly derived from industrial water. Adsorption removes.

The drained water from which the organic COD component has been adsorbed is led to a fluorine adsorption step for treatment.

In addition, the activated carbon filled with waste by passing the waste water for a certain period of time is returned to the step (agglomeration sedimentation step A in the first treatment method or the coagulation sedimentation step C in the second treatment method) by backwashing with water. The COD component is then reprocessed with the decomposed drain.

(8) Fluorine adsorption process

The fluorine adsorption step is a step of adjusting the wastewater treated by the activated carbon adsorption step into contact with the fluorine adsorption resin to adsorb and remove the remaining fluorine to pH 5.8 to 8.6 with an alkaline agent.

In the fluorine adsorption step, after the wastewater is adjusted to pH 2 to 4 with a mineral acid such as hydrochloric acid, the pH-adjusted wastewater is passed through the fluorine adsorption resin layer in the fluorine adsorption column to adsorb and remove a small amount of fluorine ions remaining in the liquid. . The fluorine adsorption resin may have various forms as functional groups or supported metals, and specific examples thereof include phosphotyl amino group chelate resins, zirconium-supported resins, and cerium-supported resins. Among them, for example, the cerium-supported resin reacts with fluorine ions as follows.

[Adsorption reaction] Ce. OH ^- + F ^_ → Ce ... F ^- + OH ^-

In addition, the adsorptive resin whose fluorine adsorption capacity is lowered by passing drainage for a certain period of time can be regenerated by reacting with an alkali agent such as sodium hydroxide as follows, and then washed with mineral acid such as hydrochloric acid and water, to impart activity.

Play ^{reaction] Ce - F - + NaOH →} Ce ... OH ^_ + NaF

The recycled waste liquid discharged at this time is returned to the front end process (agglomeration sedimentation step A in the first treatment method, or the coagulation sedimentation step C in the second treatment method), and is again treated with the waste water in which the COD component is decomposed. Or, it can return to a flue gas desulfurization apparatus, and can utilize effectively as replenishment water at the time of cooling and absorbing combustion exhaust gas.

When the regenerated waste liquid is returned to the flue gas desulfurization apparatus, the following reaction occurs, and fluorine ions in the regenerated waste liquid are captured by a large amount of calcium ions in the desulfurization apparatus.

Ca ²⁺ + 2NaF → CaF ₂ + 2Na ⁺

In this way, the fluorine ions are fixed as calcium fluoride and included in the gypsum (CaSO ₄ ) produced at the same time and discharged. For this reason, the fluorine ion in desulfurization waste water does not increase. In addition, since the quantity of calcium fluoride produced | generated at this time is overwhelmingly small compared with the quantity of gypsum, it does not cause the quality fall of collect | recovered gypsum. Calcium fluoride can be used as a valuable material, for example as a cement material.

The wastewater from which fluorine ions have been adsorbed is adjusted to pH 5.8 to 8.6 with an alkaline agent such as sodium hydroxide and discharged or reused.

Example

Hereinafter, the processing method of this invention is demonstrated based on an Example.

Example 1 (First Treatment Method)

In FIG. 1, the present embodiment includes a COD component decomposition step 1, an aggregation precipitation step A 2, an aggregation precipitation step B 3, an activated carbon adsorption step 7, and a fluorine adsorption step 8. Desulfurization wastewater 10 was sequentially processed by this step. In addition to this process, the concentration step 5 and the dehydration step 6 were additionally installed, and contaminated sludge generated in the coagulation sedimentation step A 2 and the coagulation sedimentation step B 3 was treated. Hereinafter, the present embodiment will be described in detail.

First, the desulfurization wastewater 10 discharged from the desulfurization apparatus for treating the lime combustion exhaust gas was introduced into the COD component decomposition step 1. COD component decomposition | disassembly process 1 is comprised from oxidation tank 1a and reduction tank 1b shown in FIG. As the oxidant 21, sodium hypochlorite was added to decompose the inorganic COD component. The addition amount of the oxidizing agent 21 confirmed the content of N-S compound under redox potential (ORP) and made it NaOCl / N-S compound = 3.0 (molar ratio). At this time, as the reaction conditions, the temperature was about 40 ° C. and the residence time was 3 hours. Under these conditions, N-S compounds decomposed over 95%. The excess oxidant (sodium hypochlorite) 22 remained in the waste water after the N-S compound was decomposed, so it was led to a reducing tank 1b and decomposed by the addition of a reducing agent 23. As the reducing agent 23, acidic sodium sulfite was used. The addition amount of the reducing agent confirmed the amount of remaining oxides under the redox potential, and was almost equivalent to the oxidizing agent. The wastewater 11 in which the COD component was decomposed was led to the coagulation sedimentation step A2.

The flocculation sedimentation step A2 consists of the flocculation tank 2a, the reaction tank 2b, and the precipitation tank 2c shown in FIG. The chelating agent 24 and the aluminum compound 25 were added to the wastewater 11 in which the COD component guide | induced to the coagulation tank 2a was decomposed, and it adjusted to pH 6-8 in the alkali chemicals (sodium hydroxide) 26. At this time, 10 mg / L of "Epoploflo L-1" (made by Miyoshi Oil Holding Co., Ltd.) of the liquid chelating agent was added as the chelating agent 24. In addition, as aluminum compound 25, aluminum sulfate (alumina sulfate) was added so that F / A1 = 0.3. By adjusting the pH by adding an alkali agent (sodium hydroxide) 26, a fluorine-aluminum complex [Al (OH) ₃ -F] was formed and a floc of aluminum hydroxide was formed. At this time, the micro-floc which collected the heavy metal by the addition of a chelating agent, a part of organic COD component (about 20-30%), and the fluorine-aluminum complex produced here adsorb | suck to the floc of the formed aluminum hydroxide. Was included.

The flocculant containing this floc was led to Reactor 2b, and the coagulant floc which was more degradable was formed by adding the polymer flocculant 27 suitably. In settling tank 2c, the solid consisting of these floes was separated. The supernatant was coagulated sedimentation treated water A12, which was treated by the next coagulated sedimentation step B3. The coagulated sedimentary contaminated sludge A12s was sent to a concentration step 5 for treatment.

The flocculation sedimentation step B3 consists of the flocculation tank 3a, the reaction tank 3b, and the precipitation tank 3c shown in FIG. 0.3 mol amount of sodium carbonate 28 was added to the flocculation sedimentation-treated water A12 guide | induced in the flocculation tank 3a, and it adjusted to pH 9-10 in the alkali chemicals (sodium hydroxide) 26. At this time, the calcium ions in the liquid became calcium carbonate, and an alkali chemicals 26 was added again to adjust the pH to 10 or higher. As a result, magnesium ions initially present in the wastewater became magnesium hydroxide. Calcium carbonate and magnesium hydroxide each formed flocs, and fluorine ions were adsorbed on the flocs thus formed and precipitated.

The flocculant containing this floc was guide | induced to reaction tank 3b, and the coarse floc with good separability was formed by adding "San Poly 305" (made by Sampo Corporation) 27 of a polymeric flocculant suitably. In settling tank 3C, the solids consisting of these flocs were separated. The supernatant water was treated by coagulation sedimentation treatment water B13 in the following activated carbon adsorption step 7. Agglomerated precipitate contaminated sludge B13S was sent to a concentration step 5 for treatment.

Agglomerated sediment contaminated sludge A12S and Agglomerated sediment contaminated sludge B13S were led to concentration step 5, followed by sedimentation and separation with a concentrator. In actual test results, the concentration of each contaminated sludge was about 1 to 2% by weight, but after concentration, it was concentrated to about 5% by weight. The separated water 15 separated at this time was reprocessed in the coagulation precipitation step A2 together with the wastewater 11 from which the COD component was decomposed. On the other hand, the concentrated contaminated sludge was led to dehydration step 6 to be dewatered again and discharged out of the system as cake 16. When a filter press was used as the dehydrator, a cake having a water content of 70% or less was obtained.

On the other hand, the flocculation sedimentation treatment water B13 is sent to activated carbon adsorption step 7 after removing the suspended matter by sand filtration (not shown), if necessary, and adjusted to pH 6 to 8 with a mineral acid such as hydrochloric acid if it is alkaline. Then, the mixture was passed through a granular activated carbon layer in the packed column, and the organic COD component mainly derived from industrial water was adsorbed and removed. Waste water 17 treated with activated carbon adsorption was sent to fluorine adsorption step 8.

When the activated carbon layer is filled with the residues filtered out by the adsorption treatment, backwash water can be sent to the activated carbon layer to remove these residues. The backwash water 17W discharged at this time is returned to the coagulation sedimentation step A2, and reprocessed together with the COD decomposition treatment water 11.

In the fluorine adsorption step 8, the activated activated carbon adsorption treatment water 17 was adjusted to pH 2 to 4 in a mine such as hydrochloric acid, and then passed through a fluorine adsorption resin layer to adsorb and remove fluorine remaining in the liquid. As a fluorine adsorption resin, hydrous cerium (CeO ₂ nH ₂ O) supported resin (manufactured by Asahi Engineering Co., Ltd.) was used.

The activated carbon adsorption treatment water 17 contains only a small amount of residual fluorine, which is not removed in each flocculation settling step at the front end, so that the load on the resin can be minimized and the fluorine adsorption capacity can be maintained for a long time. However, it is ruptured eventually while continuing this adsorption treatment, and therefore it is necessary to regularly regenerate with an alkaline agent such as sodium hydroxide. After activating the resin, the resin is washed with mineral acid 21 such as hydrochloric acid and water, and the recycled waste liquid 18W discharged is returned to the coagulation sedimentation step A2, and retreated with COD decomposition water 11, or flue gas desulfurization. It can be conveyed to an apparatus and can be used as replenishment water at the time of cooling and absorption of combustion exhaust gas.

The final treated water 19 from which fluorine ions were adsorbed was adjusted to pH5.8 to 8.6 with an alkalizing agent (sodium hydroxide) 26 and discharged or reused.

Example 2 (second treatment method)

In FIG. 2, this embodiment includes a COD component decomposition step 1, an aggregation precipitation step C4, an aggregation precipitation step A2, an activated carbon adsorption step 7, and a fluorine adsorption step 8. Desulfurization drainage 10 was sequentially treated in this process. In addition to this process, a concentration step 5 and a dehydration step 6 were additionally installed to treat the contaminated sludge generated in the coagulation sedimentation step C 4 and the coagulation sedimentation step A 2.

This embodiment differs from Example 1 (first processing method) in that the coagulation sedimentation step C4 is provided at the front end of the coagulation sedimentation step A2, and the coagulation sedimentation step B3 at the next stage is omitted.

In the same manner as in Example 1, the desulfurization discharged water 10 discharged from the desulfurization apparatus for treating the lime combustion exhaust gas was introduced into the COD component removal step 1, and the N-S compound was decomposed in the oxidizing agent (sodium hypochlorite) 22. After the reaction, the excess oxidant (sodium hypochlorite) 22 was decomposed in a reducing agent (sodium sulphite) 23, and the drainage 11 obtained by decomposing the COD component was led to the coagulation sedimentation step C4.

In FIG. 6, the flocculation settling process C4 is comprised by the flocculation tank 4a, the reaction tank 4b, and the precipitation tank 4c. Magnesium ions in the wastewater became magnesium hydroxide by adjusting the COD decomposition treatment water 11 induced in the coagulation tank 4a to pH 10 to 11 with an alkaline agent 26 such as sodium hydroxide or slaked lime. At this time, fluorine ions are adsorbed into this product and included.

The flocculant containing this floc was led to reaction tank 4b, and the coagulant floc which was more separable was formed by adding the polymer flocculant 27 suitably. In the following settling tank 4c, the solids consisting of these floes were separated. The supernatant was coagulated sedimentation treated water C 14, which was treated in the next coagulated sedimentation step A2. The coagulated sedimentary contaminated sludge C 14s was sent to a concentration step 5 for treatment.

The flocculation sedimentation treated water C14 introduced in the flocculation sedimentation step A 2 was treated in the same manner as in Example 1. The flocculation sedimentation treated water A12 generated at this time was guided to the activated carbon adsorption step again. Hereinafter, it processed similarly to Example 1 and obtained the final process water 19.

Table 1 summarizes the results of the desulfurization wastewater treatment according to the first and second embodiments.

Water Quality of Desulfurization Wastewater Water quality of treated water Example 1 Example 2 Temperature ℃ 49 40 40 pH - (Weakly acidic) 7.2 7.1 Magnesium (Mg) mg / L 11800 11700 6000 T-COD mg / L 170 〈15 〈15 NS-COD mg / L 50 〈10 〈10 Fluoride mg / L 38 <2 <2

T-COD: Total amount of COD component

NS-COD: Amount of N-S Compound

The method of this invention demonstrated above has the following effects.

By organically combining the treatment processes for each component in the desulfurization drainage and processing in multiple stages, a plurality of components can be treated highly efficiently and highly, and any component among COD components, heavy metals, and fluorine is always kept at a predetermined value based on emission standards. Can satisfy.

Each equipment required for the desulfurization wastewater treatment process can be miniaturized, and the equipment cost and the amount of chemicals used can be greatly reduced.

The regeneration drainage at the time of regeneration of the fluorine adsorption resin can be effectively used as the replenishment water of the desulfurization apparatus. As a result, the amount of industrial water used as replenishment water can be reduced.

When the regeneration wastewater of the fluorine adsorption resin is treated in a desulfurization apparatus, the amount of chemicals used can be significantly reduced as compared with the case where the fluorine adsorption resin is treated in a desulfurization system.

Since the recycled wastewater of the fluorine adsorption resin has an excess of alkali (NaOH), it has the effect of alleviating the acidity of the combustion exhaust gas, contributing to the improvement of the desulfurization apparatus performance.

Claims (9)

In the method for treating flue gas desulfurization discharged from a wet flue gas desulfurization apparatus that absorbs and removes sulfur compounds in coal combustion exhaust gas, (a) a COD component decomposition step of adding an oxidizing agent to the wastewater to decompose the nitrogen-sulfur compound as a COD component in the drainage, and then adding a reducing agent to decompose and remove the excess oxidizing agent; (b) a coagulation sedimentation step A for depositing and separating solids containing fluorine and heavy metals by adding a chelating agent for heavy metal collection, an aluminum compound, and an alkaline compound for pH adjustment to the wastewater treated in the COD component decomposition step; (c) Flue gas desulfurization and drainage treatment comprising a flocculation sedimentation step B which adds sodium carbonate and a pH-adjusting alkali agent to the waste water treated in the flocculation sedimentation step A, and precipitates and separates solids containing calcium and fluorine. Way. The method of claim 1, (d) an activated carbon adsorption step of adsorbing and removing organic COD components by bringing the wastewater treated in the flocculation sedimentation step B into contact with a fluorine adsorption resin; (e) further comprising a fluorine adsorption step in which the wastewater treated in the activated carbon adsorption step is brought into contact with the fluorine adsorption resin to adsorb and remove the remaining fluorine, and then adjusted to pH 5.8 to 8.6 with an alkaline agent. Desulfurization drainage method. In the treatment method of flue gas desulfurization drainage discharged from a wet flue gas desulfurization apparatus that absorbs and removes sulfur compounds in coal combustion exhaust gas, (a) a COD component decomposition step of adding an oxidant to the wastewater to decompose the nitrogen-sulfur compound as a COD component in the wastewater, and then adding a reducing agent to decompose and remove the excess oxidant; (b) a coagulation sedimentation step C for adding a pH adjusting alkali agent to the wastewater treated in the COD component decomposition step and depositing and separating solids containing magnesium and fluorine under alkaline conditions; (c) a coagulation sedimentation step A for adding a heavy metal chelating agent, an aluminum compound and an pH adjusting alkali agent to precipitates separated from the wastewater treated by the coagulation sedimentation step C to separate solids containing fluorine and heavy metals; Flue gas desulfurization wastewater treatment method characterized in that. The method of claim 1, (d) an activated carbon adsorption step of bringing the wastewater treated in the flocculation sedimentation step A into contact with activated carbon to adsorb and remove organic COD components; (e) further comprising a fluorine adsorption step in which the wastewater treated by the activated carbon adsorption step is brought into contact with a fluorine adsorption resin to adsorb and remove residual fluorine, and then adjusted to pH 5.8 to 8.6 with an alkaline agent. Desulfurization drainage method. The method according to any one of claims 1 to 4, The flue gas desulfurization wastewater treatment method characterized in that during the COD decomposition step, the oxidant is sodium hypochlorite, and the wastewater is adjusted to pH 4 or less by hydrochloric acid to decompose and remove the nitrogen-sulfur compound in the wastewater. The method according to any one of claims 1 to 4, The method for treating flue gas desulfurization, wherein the chelating agent for collecting heavy metals has a dithiocarbamic acid group or a thiol group. The method according to claim 2 or 4, And the fluorine adsorption step adjusts the wastewater to pH 2 to 4 by hydrochloric acid, and then passes the pH-adjusted wastewater through the fluorine adsorption resin layer to adsorb and remove fluorine. The method according to claim 2 or 4, And said fluorine adsorption resin is at least one or more selected from phosphomethylamino group chelate resins, zirconium-supported resins, and cerium-supported resins. The method according to claim 2 or 4, In the fluorine adsorption step, further comprising the step of returning the regeneration waste liquid generated at the time of regeneration of the fluorine adsorption resin to the flue gas desulfurization apparatus after the adsorption of fluorine.