JPH1190165A - Treatment of waste water from flue gas desulfurization - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of effectively and sufficiently treating dithionic acid, N-S compounds, heavy metals, and organic COD components present in waste water of a wet flue gas desulfurizer absorbing and removing sulfur oxide in waste gas at heavy oil combustion. SOLUTION: This method of treating waste water from flue gas desulfurization includes a process 1 wherein mineral acid is added to waste water and the mixture is heated under acid condition to decompose dithionic acid and nitrogen-sulfur compounds, a process 2 wherein the waste water is regulated to pH 10-11 to make magnesium in the waste water its oxide and deposit it as flocs thereof and the flocs that catch heavy metals are separated as precipitates, a process 3 wherein a chelating agent and iron compounds are added to the waste water to regulate pH to 6-8, thereby causing formation of heavy metal chelate compounds and deposition of ferric hydroxide flocs to separate a precipitate consisting of the flocs and the chelate compounds, a process 7 wherein the waste water is treated with sand filtration to remove suspended matter, and a process 8 wherein the waste water is brought into contact with active carbon to adsorb and remove organic COD components.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wet type flue gas desulfurization apparatus for cooling and removing dust from combustion exhaust gas such as heavy oil and the like, and for absorbing sulfur oxides by a lime-gypsum method, and particularly for discharging from a soot mixed desulfurization apparatus. The present invention relates to a method for treating flue gas desulfurization wastewater.

[0002]

2. Description of the Related Art Combustion exhaust gas using heavy oil or the like as a fuel is treated by a desulfurization apparatus using the lime-gypsum method, and COD such as dithionic acid and nitrogen-sulfur compound (hereinafter also referred to as "NS compound"). Wastewater containing components (components responsible for chemical oxygen demand) and heavy metal components is discharged. CO in wastewater
As a method for treating the D component, a coagulation sedimentation method, a microbial decomposition method,
An adsorption method or the like is generally used. However, inorganic COD components such as dithionic acid and NS compound in wastewater are extremely difficult to treat, and cannot be sufficiently removed only by these treatment methods.

[0003] Among these inorganic COD components, an acid decomposition method is known as a method for decomposing dithionic acid.
In the acid decomposition method, a mineral acid is added to waste water and maintained at a predetermined temperature to cause the following reaction to decompose dithionic acid into sulfate ions and sulfur dioxide. According to this method, dithionic acid can be removed relatively easily. ^{_{S 2 O 6 2- → SO 4}} 2- + SO 2 acid decomposition method, for example, is described in Japanese or Japanese 64-47493 Patent Publication No. Sho 63-252526.

[0004] As a method for decomposing the NS compound, a sodium nitrite decomposition method and a sodium hypochlorite decomposition method are known. As for the NS compound, there is no report or case in which the acid decomposition treatment is applied. Sodium nitrite decomposition method
Sodium nitrite (NaNO ₂ ) is added to waste water at a ratio of NO ₂ ⁻ −N / NS compound = 1 to 2 (molar ratio), and is decomposed under conditions of pH 2 or less and temperature of 45 ° C. or more. . However, sodium nitrite is expensive. Further, the desulfurization effluent discharged from the soot mixing type flue gas desulfurization device is usually weakly acidic, so a large amount of acid is required to adjust the pH to 2 or less. A large amount of alkaline agent is required to return.

Next, in the sodium hypochlorite decomposition method, sodium hypochlorite (NaClO) is added at a ratio of NaClO / NS compound = 3.0 to 5.0 (molar ratio), and the temperature is reduced to 40%. The reaction is carried out at a temperature of not less than 2 ° C. and a residence time of not less than 2 hours. For example, among the NS compounds, hydroxyamine trisulfonate decomposes as follows. 6ON (SO ₃ ) ₃ ^3- + 18ClO ⁻ + 10H ₂ O →
4NO + 2NO ₃ ⁻ + 18HSO ₄ + 18Cl ⁻ + H ⁺
+ 3O ₂ For example, when ammonium ions are contained in an amount of about 6000 mg / L, sodium hypochlorite is consumed in a large amount, so that the cost of chemicals becomes high and the treatment efficiency is greatly reduced. The sodium hypochlorite decomposition method is described in, for example, JP-A-4-59026. In a conventional treatment method, when dithionic acid and an NS compound coexist, such as in desulfurization wastewater, these components must be treated separately, complicating the process and increasing equipment costs. There was a problem.

As a method for treating heavy metal components in wastewater, a coagulation sedimentation method in which slaked lime or bansulfate is added to wastewater to separate precipitates is generally used. However, when this processing method is used, although heavy metals can be almost removed, it is inevitable that heavy metals remain to some extent. Therefore, in order to satisfy the strict emission standard value, some subsequent means is required.

Further, a method has also been used in which a chelating agent (polymer heavy metal collecting agent) is added together with ordinary coagulated sedimentation to generate microflocs that have collected heavy metals and are separated together with coagulated sediment sludge. However, in order to obtain the required processing performance, it has to be added in a large amount, and since the chelating agent is expensive, the cost of the chemical is considerably high.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide an inorganic COD component, dithionic acid and N-S, from waste water of a wet flue gas desulfurization unit that absorbs and removes sulfur oxides in heavy oil combustion exhaust gas. It is an object of the present invention to provide a method for efficiently and sufficiently removing a compound, a heavy metal such as manganese and cadmium, and an organic COD component without having the drawbacks of the conventional treatment methods for these components. .

[0009]

The first method of treating flue gas desulfurization effluent of the present invention is a method of treating flue gas desulfurization effluent discharged from a wet type flue gas desulfurization unit for absorbing and removing sulfur oxides in heavy oil combustion exhaust gas. In the treatment method, (a) an acid decomposition step of adding a mineral acid to the wastewater and raising the temperature under acidity to decompose dithionic acid and a nitrogen-sulfur compound in the wastewater; and (b) the acid decomposition step The wastewater treated in the above is adjusted to pH 10 to 11, and magnesium in the wastewater is used as hydroxide to precipitate flocs,
A flocculating sedimentation step A in which the floc captures heavy metal components to separate a precipitate formed; and (c) adding a chelating agent and an iron compound to the wastewater treated in the flocculating sedimentation step A and adjusting the pH to 6 to 8. By adjusting, to generate a heavy metal chelate compound and precipitate the flocs of ferric hydroxide,
A flocculating and sedimentation step B in which the ferric hydroxide floc captures the heavy metal chelate compound to separate a precipitate formed (claim 1). The method further comprises: (d) sand filtration of the wastewater treated in the coagulation / sedimentation step B to remove suspended matter; and (e) wastewater treated in the sand filtration step. Activated carbon adsorbing step of adsorbing and removing organic COD components by contacting with activated carbon (claim 2).

[0010] The second method of treating flue gas desulfurization wastewater according to the present invention is a method of treating flue gas desulfurization wastewater discharged from a wet flue gas desulfurization unit that absorbs and removes sulfur oxides in heavy oil combustion exhaust gas. A) an acid decomposition step of adding a mineral acid to the wastewater and raising the temperature under acidity to decompose dithionic acid and a nitrogen-sulfur compound in the wastewater; and (b) treating the wastewater treated in the acid decomposition step. After adding a chelating agent and adjusting the pH to 8 to 10 to generate a heavy metal chelate compound, adding an iron compound and maintaining the pH at 8 to 10 to precipitate flocs of ferric hydroxide, A flocculant-precipitation step C in which the ferric hydroxide floc captures the heavy metal chelate compound and separates a precipitate formed (claim 3). The method further comprises (c) the coagulation and precipitation step C
And (d) contacting the wastewater treated in the sand filtration step with activated carbon to remove organic COD components by adsorption. Activated carbon adsorption step (claim 4).

In the first or second method for treating flue gas desulfurization waste water according to the present invention, the acid decomposition step is carried out by adding hydrochloric acid to the flue gas desulfurization waste water so that the concentration thereof becomes 0.2 to 2.0% by weight. A step of adding and raising the temperature to 95 to 130 ° C can be adopted (claim 5). In the first or second method for treating flue gas desulfurization wastewater of the present invention, a chelating agent having a chelating group of a dithiocarbamic acid group or a thiol group can be used (claim 6).

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Each step of the method for treating flue gas desulfurization wastewater of the present invention will be described in order. Note that steps common to the first processing method and the second processing method of the present invention will be described together.

(1) Acid Decomposition Step In the acid decomposition step, a mineral acid is added to waste water, and the temperature is raised under acidic conditions.
This is a step of decomposing dithionic acid and nitrogen-sulfur compounds in the wastewater. During desulfurization effluent which is processed by the method of the present invention, dithionite produced during the oxidation of SO ₂ in the desulfurization apparatus (S ^₂ O ₆ ^2-), and reacts with SO ₂ and NO _X And mainly contains an NS compound having the following composition. (a) hydroxylamine mono sulfonates: HONHSO ₃ ^- (b) hydroxylamine THIS Gandolfo ^{_{sulfonate: HON (SO 3) 2 2-}} (c) hydroxylamine tris Gandolfo sulfonate: ON (SO _{3) 3} ^3-

As the mineral acid (inorganic acid), for example, hydrochloric acid,
Sulfuric acid and the like can be mentioned. For example, in the case of hydrochloric acid, the concentration is about 0.2 to 2.0% by weight in the waste water. It is expected that the addition of a mineral acid will result in an acidity of pH 2 or less. When hydrochloric acid and sulfuric acid are added at the same concentration, respectively, there is no significant difference in COD value of the acid-decomposed wastewater. However, in terms of reduction of sludge generation and suppression of scale generation, hydrochloric acid is used. Is preferred.

The temperature is raised at 95 to 130 ° C. by steam.
Until it reaches. After raising the temperature, the temperature is
The dithioic acid and N
The -S compound decomposes as follows. (a) dithionite ^{_{(S 2 O 6 2-) →}} SO 4 2- + SO 2 (b) N-S compounds ^{_{→ N 2 O + mSO 4 2-}} + nH + acidolysis treated waste water after completion of the reaction, the following Step (Aggregative precipitation step A in the first processing method, or aggregative precipitation step C in the second processing method).

(2) Coagulation and Precipitation Step A In the coagulation and precipitation step A, pH of the wastewater treated in the acid decomposition step is adjusted to pH.
This step is a step in which magnesium is contained in the wastewater as hydroxide to precipitate flocs, and the flocs capture heavy metal components to separate precipitates formed. pH
Is adjusted using an alkali agent such as sodium hydroxide.

By adjusting the pH to 10 to 11, magnesium ions and heavy metals (manganese, cadmium, etc.) originally contained in the wastewater react as follows to form magnesium hydroxide and heavy metal hydroxides. . The hydroxide of the heavy metal is adsorbed and included in the magnesium hydroxide flocs to form a precipitate. ^{(a) Mg 2+ + 2OH -} → Mg (OH) 2 (b) Mn 2+ + 2OH - → Mn (OH) 2 (c) Cd 2+ + 2OH - → Cd (OH) 2 suspension containing these flocs The solids therein are separated in a sedimentation tank, and the supernatant water is treated in the next step (coagulation / sedimentation step B in the first treatment method).

(3) Coagulation and Precipitation Step B In the coagulation and precipitation step B, a chelating agent and an iron compound are added to the wastewater treated in the coagulation and precipitation step A, and the pH is adjusted to pH 6.
To 8 to form a heavy metal chelate compound and precipitate flocs of ferric hydroxide, and the floc of ferric hydroxide captures the heavy metal chelate compound to separate a precipitate formed. It is. As the chelating agent, a liquid polymer heavy metal collecting agent having a chelating group such as a dithiocarbamic acid group (—NH—CS ₂ Na) or a thiol group (—SNa) can be used. By adding a chelating agent in an amount of usually 10 to 1,000 mg / L, a microfloc capturing heavy metals is generated.

As the iron compound, ferric chloride, ferric sulfate and the like, which are coagulants, can be used. For example, in the case of ferric chloride, it reacts as follows near neutrality to become ferric hydroxide. The ferric hydroxide becomes flocs, and the flocs adsorb and include the microflocs that have collected the heavy metals, thereby producing precipitates. FeCl ₃ + OH ⁻ → Fe (OH) _{3 The} amount of the iron compound added is 100 to 500 mg / Fe as Fe.
It is about L.

At this time, by adding an anionic polymer flocculant such as polyacrylamide as appropriate, a coarser floc can be formed and the separability can be improved. The solids in the suspension containing these flocs are:
Separated in the precipitation tank and the supernatant water is treated in the next step (sand filtration step in the first treatment method). By using a chelating agent and an iron compound in combination, heavy metal ions can be removed to a high degree, and the amount of the chelating agent used can be significantly reduced.

(4) Coagulation and Precipitation Step C In the coagulation and precipitation step C, a chelating agent is added to the wastewater treated in the acid decomposition step and the pH is adjusted to 8 to 10 to generate a heavy metal chelate compound. In the step of adding the compound and maintaining the pH at 8 to 10 to precipitate flocs of ferric hydroxide, the flocs of ferric hydroxide capture the heavy metal chelate compound and separate the precipitate formed. is there. As the chelating agent, the same chelating agent as that used in the coagulation / precipitation step B can be used.
The addition amount of the chelating agent is usually 10 to 1,000 mg /
L.

The pH is adjusted by using an alkali agent such as sodium hydroxide or, if necessary, a mineral acid such as hydrochloric acid. By adjusting the pH to 8 to 10, microfloc mainly collecting cadmium is generated. As the iron compound, the same iron compound as that used in the coagulation / precipitation step B can be used. The amount of iron compound added is
It is about 100 to 500 mg / L as Fe. To maintain the drainage at pH 8 to 10, an alkaline agent such as sodium hydroxide is added.

By maintaining the pH of the waste water at pH 8 to 10, a reaction similar to that in the coagulation / precipitation step B occurs, and flocs of ferric hydroxide precipitate. In addition to the microfloc, manganese and the like not yet trapped are adsorbed and included in the floc, and a precipitate is formed. At this time, by adding a polymer flocculant similar to that in the above-mentioned flocculation / precipitation step B, a coarser floc can be formed and the separability can be improved. The solids in the suspension containing these flocs are separated in a settling tank. The supernatant water is treated in the next step (sand filtration step in the second treatment method).

(5) Concentration Step In the concentration step, in the coagulation precipitation step A and the coagulation precipitation step B in the first treatment method, or in the coagulation precipitation step C in the second treatment method, the solid matter is separated and discharged. The sludge is concentrated by a thickener. The concentration of these sludges is usually about 1 to 2% by weight, but becomes about 5% by weight after concentration. The separated water is returned to the previous step (the coagulation / sedimentation step A in the first treatment method, or the coagulation / sedimentation step C in the second treatment method), and is treated again together with the acid-decomposed wastewater. . Sludge is sent to a dewatering step.

(6) Dehydration Step In the dehydration step, the concentrated sludge is further dehydrated by a dehydrator and discharged as a cake. Here, a filter press, a belt press, a screw decanter, or the like can be used as the dehydrator. For example, when a filter press is used, the water content of the sludge can be reduced to 70% by weight or less.

(7) Sand Filtration Step In the sand filtration step, the coagulation precipitation step B in the first treatment method,
Alternatively, the suspended matter remaining in the supernatant water discharged from the coagulation / sedimentation step C in the second treatment method is separated and removed by a sand filtration treatment. The configuration of the filtration layer at the time of sand filtration is, for example, 300 mm of support gravel, 600 mm of sand, and 60 anthracite.
0 mm. The flow rate (LV) of the filtration is usually
7 to 15 m / h.

(8) Activated carbon adsorption step The sand filtration treatment water discharged from the sand filtration step is introduced into the activated carbon adsorption step, and is passed through the activated carbon layer in the packed tower. In this step, organic COD mainly caused by industrial water is used.
The components are adsorbed and removed. The wastewater subjected to the activated carbon adsorption treatment is discharged or reused as final treated water.

[0028]

Embodiment 1 (First Processing Method) Embodiment 1 is shown in FIG. In FIG. 1, the flue gas desulfurization wastewater treatment method includes an acid decomposition step 1, a coagulation precipitation step A2, a coagulation precipitation step B3, a sand filtration step 7, and an activated carbon adsorption step 8.
Consists of Along these steps, the desulfurization wastewater 10
Were processed sequentially. In addition, together with these steps, a concentration step 5 and a dehydration step 6 are additionally provided, and the coagulation precipitation step A
2 and the sludge generated in the coagulation sedimentation step B3 were treated. The details will be described below.

First, the desulfurization effluent 10 discharged from the desulfurization unit for treating heavy oil combustion exhaust gas was introduced into the acid decomposition step 1. In the acid decomposition step 1, as shown in FIG.
a, steam mixing tank 1b, decomposition tank 1c, and neutralization tank 1d
Consists of In the mineral acid mixing tank 1a, a mineral acid (hydrochloric acid) 22 was added to the desulfurization wastewater 10. Hydrochloric acid was added and mixed so that the concentration became 0.2% by weight. The pH after mixing is
It seems to be 2 or less. Next, in the steam mixing tank 1b, the temperature of the wastewater was raised to 95 ° C. by the steam 21. Then, the wastewater was allowed to flow into the decomposition tank 1c having a heat retaining function and reacted for 2 hours. The hydrochloric acid concentration, the reaction temperature, and the reaction time were determined based on a series of experimental results.
This is a value that has been found to be effective in decomposing the D component. The waste water after decomposing the dithionic acid and the NS compound was flowed into the neutralization tank 1d, and the pH was previously adjusted to around neutral (about pH 7) with the alkali agent 23 in the neutralization tank 1d. As the alkaline agent 23, sodium hydroxide which does not generate a solid was used. By preliminarily neutralizing, the material of the apparatus to be used in the next step can be protected, and the pH adjustment in the next step can be made small and easy. Wastewater treated with acid decomposition 1
No. 1 was treated in the coagulation sedimentation step A2.

As shown in FIG. 3, the coagulation / sedimentation step A2 includes a pH adjusting tank 2a, a coagulation tank 2b, and a precipitation tank 2c. In the pH adjusting tank 2a, the wastewater 1 subjected to the acid decomposition is treated.
1 was adjusted to pH 10.3 by injecting sodium hydroxide as the alkaline agent 23, and then the polymer flocculant 25 was added in the flocculation tank 2b to obtain a coarse particle containing magnesium hydroxide and a heavy metal hydroxide. A flock. In addition, as the polymer coagulant 25, an anionic coagulant such as polyacrylamide can be used. The suspension containing these flocs is transferred to the settling tank 2c.
And the supernatant water is coagulated sedimentation treated water A 1
As No. 2, it was treated in the following coagulation / sedimentation step B3, and the coagulation / sedimentation sludge A 12s was sent to the concentration step 5 for treatment.

As shown in FIG. 4, the coagulation / precipitation step B3 includes a coagulation tank 3a, a reaction tank 3b, and a precipitation tank 3c. In the coagulation tank 3a, 60 mg / L of the chelating agent 26 and 100 mg / L of ferric chloride as the iron compound 24 are added to the coagulated sedimentation treated water A12, and then hydrochloric acid and hydroxylic acid are used as the mineral acid 22 and the alkali agent 23. The pH was adjusted to 7.4 using sodium. Next, in the reaction tank 3b, a coarse floc of ferric hydroxide containing a heavy metal component was generated by adding the polymer flocculant 25. In addition, as the chelating agent 26, Epofloc L-1 (manufactured by Miyoshi Oil & Fats Co., Ltd.) was used. As the iron compound 24, ferric sulfate or the like may be used instead of ferric chloride. The suspension containing these flocs is transferred to the settling tank 3c.
And the supernatant water is coagulated sedimentation treated water B 1
As No. 3, treated in the next sand filtration step 7, the coagulated sediment sludge B
13s was sent to the concentration step 5 for processing.

The coagulated sediment sludge A 12 s and the coagulated sediment sludge B 13 s were led to a concentration step 5, and were collectively settled and separated by a thickener. As a result, the concentration of these sludges was concentrated from about 1 to 2% by weight to about 5% by weight. The separated water 15w after the concentration was returned to the coagulation / sedimentation step A2, and the concentrated sludge 15s was further dehydrated in the dehydration step 6, and discharged out of the system as a cake 16s. When dewatered using a filter press as a dehydrator, the water content was 70%.
A cake of less than or equal to% by weight was obtained. The desorbed water 16w was returned to the coagulation sedimentation step A2.

In the sand filtration step 7, the supernatant water discharged from the coagulation / sedimentation step B3, that is, the coagulation / sedimentation treated water B13
Was passed through a single-layer sand filter layer using sand as a filter layer to separate and remove remaining suspended matter. The method of sand filtration is
The present invention is not limited to this, and a commonly used pressure type rapid filtration type may be used. At that time, taking into account the state of suspended matter such as particle size, filter layer (single layer or multiple layers)
Decide. The filter medium can be appropriately selected from sand, gravel, anthracite and the like. The sand filtration treatment water 17 after passing through the filter layer was sent to the next activated carbon adsorption step 8 for treatment.

If the filtration layer is clogged by the suspended matter while the filtration is continued, water is fed into the tank and backwashed to remove solid matter composed of the accumulated suspended matter.
The backwash water 17w discharged at this time is subjected to the coagulation and precipitation step A.
2 for processing. In the activated carbon adsorption step 8, the sand filtration treatment water 17 was passed through a granular activated carbon layer in a packed tower (not shown) to adsorb and remove organic COD components mainly caused by industrial water. The activated carbon can be used in any of a granular form and a powder form.

If the activated carbon layer is clogged with foreign substances while continuing the adsorption treatment, water is fed into the tank and backwashed to remove these foreign substances. Was returned to the coagulation sedimentation step A2. In this manner, the activated carbon adsorption-treated wastewater discharged from the activated carbon adsorption step 8 is adjusted to pH 7.0 to obtain the final treated water 18.
was gotten.

Second Embodiment (Second Processing Method) FIG. 5 shows the steps of a second embodiment (second processing method). In FIG. 5, the method of Example 2 comprises an acid decomposition step 1, a coagulation and precipitation step C4, a sand filtration step 7, and an activated carbon adsorption step 8
including. The desulfurization effluent 10 was sequentially processed according to these steps. In addition, a concentration step 5 and a dehydration step 6 were additionally provided along with this step, and sludge generated in the coagulation / sedimentation step C4 was treated.

In Example 2, the coagulation / sedimentation step A of Example 1
2 and the coagulation / precipitation step B3 instead of the coagulation / precipitation step B3. As in the case of Example 1, the desulfurization effluent 10 discharged from the desulfurization device that treats the heavy oil combustion exhaust gas is introduced into the acid decomposition step 1 to decompose dithionic acid and NS compounds in the effluent, The discharged acid-decomposed water 11 was introduced into the coagulation / precipitation step C4. In FIG. 5, the coagulation / sedimentation step C4 includes a reaction tank 4a and a pH adjustment tank 4
b, a coagulation tank 4c and a precipitation tank 4d.

In the reaction tank 4a, a chelating agent (trade name "EpoFloc L-1"; manufactured by Miyoshi Oil & Fats Co., Ltd.) 26 is added to the acid-decomposed water 11 at a concentration of 60 mg / L. By adjusting to 8, microfloc containing heavy metal was deposited. Next, in the pH adjusting tank 4b, ferric chloride as the iron compound 24 was added at 100 mg / L, and the pH was maintained with the alkaline agent 23, thereby adsorbing and containing the heavy metal microfloc. Iron flocs precipitated. In the flocculation tank 4c, a polymer flocculant 25 was added to the suspension containing these flocs to further coarsen the flocs and the like, followed by solid-liquid separation in the precipitation tank 4c. The supernatant water was treated in the next sand filtration step 7 as coagulated sedimentation treated water C14. The coagulated sediment sludge C14s was sent to the concentration step 5 for treatment.

The coagulated sedimented water C14 is sequentially treated in the sand filtration step 7 and the activated carbon adsorption step 8 in the same manner as in Example 1 to adjust the pH to 7.0, so that the final treated water 18 is obtained. Was done. The results of processing based on Example 1 and Example 2 are shown in the table.

[0040]

[Table 1] (Note) T-COD: total amount of COD component S ₂ O ₆ -COD: amount of dithionic acid NS-COD: amount of NS compound

[0041]

The method of the present invention has the following effects. In the acid decomposition step, not only the hardly decomposable dithionic acid,
COD components caused by the NS compound can also be decomposed and removed with high efficiency. Heavy metals such as manganese and cadmium, which could not be sufficiently removed by conventional coagulation sedimentation, can be almost completely removed. By organically combining the processing steps corresponding to each component in the desulfurization effluent and treating in multiple stages, it is possible to treat a plurality of components extremely efficiently,
With respect to the COD component and various heavy metals, the values defined in the emission standards can be completely satisfied. Equipment required for a series of processes can be reduced in size, and equipment costs can be significantly reduced. The waste of medicine consumption can be eliminated, and the cost of medicine can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a process chart of a first processing method of the present invention.

FIG. 2 is an explanatory diagram of an acid decomposition step in the first or second treatment method of the present invention.

FIG. 3 is an explanatory view of a coagulation / precipitation step A in the first treatment method of the present invention.

FIG. 4 is an explanatory diagram of a coagulation / precipitation step B in the first treatment method of the present invention.

FIG. 5 is a process chart of a second processing method of the present invention.

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

[Explanation of symbols]

 1 Acid Decomposition Step 1a Mineral Acid Mixing Tank 1b Steam Mixer 1c Decomposition Tank 1d Neutralization Tank 2 Coagulation Precipitation Step A 2a pH Adjustment Tank 2b Coagulation Tank 2c Precipitation Tank 3 Coagulation Precipitation Step B 3a Coagulation Tank 3b Reaction Tank 3c Precipitation Tank 4 Coagulation sedimentation step C 4a Reaction tank 4b pH adjustment tank 4c Coagulation tank 4d Precipitation tank 5 Concentration step 6 Dehydration step 7 Sand filtration step 8 Activated carbon adsorption step 10 Desulfurization wastewater 11 Acid decomposition treatment water 12 Coagulation precipitation treatment water A 12s Coagulation precipitation sludge A 13 Coagulated sedimentation treated water B 13s Coagulated sedimented sludge B 14 Coagulated sedimentation treated water C 14s Coagulated sedimentation sludge C 15s Condensed sludge 15w Separated water 16s Cake 16w Desorption water 17 Sand filtration treatment water 17w Backwash wastewater 18 Treatment water 18w Wash wastewater 21 Steam 22 Mineral acid 23 Alkali agent 24 Iron compound 25 Polymer flocculant 26 Chelating agent

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tetsuya Ito 5-1-1-16 Komatsu-dori, Hyogo-ku, Kobe-shi, Hyogo Prefecture Inside Shinryo High-Tech Co., Ltd. (72) Hideki Kamiyoshi Komatsu-dori, Hyogo-ku, Hyogo Prefecture 5-1-1-16 Shinryo High-Tech Co., Ltd. (72) Inventor Morishita Nishida 5-1-1-16 Komatsu-dori, Hyogo-ku, Kobe-shi, Hyogo Pref.

Claims (6)

[Claims] 1. A method for treating flue gas desulfurization effluent discharged from a wet flue gas desulfurization apparatus for absorbing and removing sulfur oxides in heavy oil combustion exhaust gas, comprising: An acid decomposition step of raising the temperature and decomposing dithionic acid and a nitrogen-sulfur compound in the wastewater; and (b) treating the wastewater treated in the acid decomposition step with a pH of 10 to 11.
(C) coagulation and precipitation step A in which magnesium in the wastewater is precipitated as hydroxide to precipitate floc, and the floc captures heavy metal components to separate a precipitate formed; To the treated waste water, a chelating agent and an iron compound are added and the pH is adjusted to 6 to 8 to generate a heavy metal chelate compound and precipitate flocs of ferric hydroxide. A coagulation sedimentation step B for separating the precipitate formed by capturing the heavy metal chelate compound. (D) a sand filtration step of removing the suspended matter by subjecting the wastewater treated in the coagulation and precipitation step B to sand filtration, and (e) a wastewater treated in the sand filtration step. The method for treating flue gas desulfurization effluent according to claim 1, further comprising an activated carbon adsorption step of contacting with activated carbon to adsorb and remove organic COD components. 3. A method for treating flue gas desulfurization effluent discharged from a wet flue gas desulfurization device for absorbing and removing sulfur oxides in heavy oil combustion exhaust gas, comprising the steps of: (a) adding a mineral acid to the effluent under acidic conditions; An acid decomposition step of raising the temperature to decompose dithionic acid and nitrogen-sulfur compounds in the wastewater; and (b) adding a chelating agent to the wastewater treated in the acid decomposition step and adjusting the pH to 8 to 10. To form a heavy metal chelate compound, add an iron compound and
Agglomerated sedimentation step C in which the ferric hydroxide floc is precipitated while maintaining the pH at H8-10, and the ferric hydroxide floc captures the heavy metal chelate compound to separate a precipitate formed. A method for treating flue gas desulfurization wastewater, comprising: (C) a sand filtration step of subjecting the wastewater treated in the coagulation and sedimentation step C to sand filtration to remove suspended matter; and (d) a wastewater treated in the sand filtration step. The method for treating flue gas desulfurization effluent according to claim 3, further comprising an activated carbon adsorption step of adsorbing and removing an organic COD component by bringing the organic COD component into contact with activated carbon. 5. The acid decomposition step in which hydrochloric acid is added to flue gas desulfurization effluent so that the concentration thereof becomes 0.2 to 2.0% by weight, and the temperature is raised to 95 to 130 ° C. Items 1-4
The method for treating flue gas desulfurization effluent according to any one of the above. 6. The method according to claim 1, wherein the chelating agent has a dithiocarbamic acid group or a thiol group as a chelating group.