JPH0775778A - Treatment of flue gas desulfurizing waste water - Google Patents

Abstract

PURPOSE:To efficiently remove peroxysulfuric acid in advance and to efficiently remove the COD component by adsorption to obtain high-quality treated water by firstly regulating the pH of the flue gas desulfurizing waste water contg. peroxysulfuric acid and CCD component and bringing the water into contact with activated carbon and then with COD adsorbing resin. CONSTITUTION:The heavy metal and fluorine contained in stack gas desulfurizing waste water are separated and removed, the filtrate water is sent to a pH regulating tank 3 from a pipeline 13, and an acid such as hydrochloric acid is added to regulate the pH of the water to <=pH5 or preferably to pH3 to 5. The water is then sent to an activated-carbon adsorption tower 4 to remove peroxysulfuric acid and oxidative harmful matter. The water is then sent to a COD adsorption tower 5 to adsorptively remove the COD component with a COD adsorbing resin. High-quality treated water is obtained in this way.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating flue gas desulfurization wastewater, and more particularly to a method for efficiently treating flue gas desulfurization wastewater containing peroxosulfuric acid and COD components to obtain high quality treated water.

[0002]

2. Description of the Related Art Exhaust gas discharged from a desulfurization device for exhaust gas generated when coal or oil is burned in a thermal power plant, so-called flue gas desulfurization waste water is fluorine, heavy metals, COD
Since it contains the components, it is necessary to remove them.

Conventionally, as a method for treating such flue gas desulfurization wastewater, first, calcium salt is added to treat heavy metals and fluorine to adjust the alkalinity, and after precipitation separation, pH adjustment is performed to adjust COD. A method of adsorbing and removing components has been adopted (Japanese Patent Publication Nos. 55-43732 and 55-1).
2312).

More specifically, flue gas desulfurization effluent contains calcium salts such as slaked lime and calcium chloride and caustic soda,
After removing most of the harmful substances such as heavy metals and fluorine by a treatment method such as coagulation sedimentation and filtration by adding an alkaline chemical such as sodium carbonate, the pH is adjusted to remove the COD component, preferably pH 7 to In the neutral or weakly acidic region of 3, the COD component (thionic acid) was selectively adsorbed and separated by bringing it into contact with the adsorption resin of the weakly basic or neutrally basic anion exchange resin.

[0005]

Recently, the quality of flue gas desulfurization wastewater has changed due to the efficiency of coal and petroleum fuels and the improvement of flue gas desulfurization systems in thermal power plants. And
Due to the change in the water quality of the flue gas desulfurization wastewater, the harmful substances cannot be sufficiently removed by the conventional treatment method, and the performance of the COD adsorbing resin suddenly deteriorates or deteriorates. , The total exchange capacity of the COD adsorption resin came to be reduced to about 50%.

As a result of various investigations to investigate the cause of the performance deterioration or deterioration of the COD adsorbing resin, the present inventors have adopted the soot mixing type oxidation system by aeration of air in the absorption tower. It has been found that peroxosulfuric acid is produced as an oxidizing harmful substance which cannot be removed by the technique, and this peroxosulfuric acid causes oxidative deterioration of the COD adsorption resin.

The present invention has been made on the basis of the above findings, and prior to the adsorption treatment of the COD component of the flue gas desulfurization wastewater, the COD component, which is an oxidative harmful substance, is efficiently removed in advance to obtain COD. An object is to provide a method for efficiently adsorbing and removing components to obtain high-quality treated water.

[0008]

According to the method for treating flue gas desulfurization wastewater of the present invention, a pH adjusting agent is added to flue gas desulfurization wastewater containing peroxosulfuric acid and a COD component to adjust the pH to 5 or less,
It is characterized in that it is brought into contact with activated carbon and then with a COD adsorbing resin.

The peroxosulfuric acid contained in the flue gas desulfurization wastewater to be treated in the present invention is also called peroxysulfuric acid, persulfuric acid or peroxosulfuric acid, and specifically, peroxodisulfuric acid: H ₂ S ₂ O ₈ ,
Peroxosulfuric acid: H ₂ SO ₅
Etc. are illustrated.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of a method for treating flue gas desulfurization wastewater according to the present invention.

In FIG. 1, 1 is a flocculation sedimentation separation tank, 2 is a filter, 3 is a pH adjusting tank, 4 is an activated carbon adsorption tower, and 5 is CO.
The D adsorption tower, 6 is a treated water tank, and the symbols 11 to 16 are pipes.

In the method of this embodiment, first, a calcium salt, for example, slaked lime is added to the flue gas desulfurization wastewater to treat fluorine, and the pH is adjusted and heavy metal ions are converted into hydroxides as a coagulating sedimentation separation tank 1. And precipitate and separate. In this treatment, a scavenger may be additionally added in order to reduce the residual amount of heavy metals, if necessary. In this case, examples of the scavenger include high molecular weight heavy metal chelating agents such as dithiocarbamic acid.

The supernatant water of the coagulating sedimentation separation tank 1 is sent to a filter 2 through a pipe 12 and filtered to separate and remove heavy metals and fluorine contained in flue gas desulfurization wastewater.
The filtered water is fed to the pH adjusting tank 3 through the pipe 13, and an acid such as hydrochloric acid is added to the solution to adjust the pH to 5 or less, preferably pH 3.0 to 5.
Adjust to 0.

The pH-adjusted water is supplied from the pipe 14 to the activated carbon adsorption tower 4
To remove the oxidative harmful substance peroxosulfuric acid contained therein.

In the present invention, the activated carbon may be in the form of powder or particles, and the treatment with activated carbon may be treatment in a reaction tank, but the particle size is preferably 0.1.
The column packed with ~ 1 mm of granular activated carbon is brought into water contact.
The water flow condition of this activated carbon adsorption tower is preferably about SV = 5 to 20 hr ⁻¹ .

The effluent of the activated carbon adsorption tower 4 is then fed to the pipe 1
5 to the COD adsorption tower 5 to adsorb and remove COD components. The COD adsorption tower 5 is a COD adsorption resin filled with a weakly basic or medium basic anion exchange resin. The adsorption treatment with the COD adsorption resin may be treatment with a reaction tank, but it is desirable to bring the column filled with the COD adsorption resin into contact with water.

Since the peroxosulfuric acid, which is an oxidizing harmful substance, has been removed from the inflow water of the COD adsorption tower 5 in advance,
OD adsorption resin does not cause deterioration with time and COD
The components can be efficiently adsorbed and removed. The water flow conditions of the COD adsorption tower 5 are preferably SV = 5 to 20 hr ⁻¹ .

Outflow water from the COD adsorption tower 5 is sent to the treated water tank 6 through the pipe 16 and discharged out of the system through the pipe 17.

In the case of flue gas desulfurization effluent, since a small amount of fluorine usually remains in the effluent of the COD adsorption tower,
It is preferable that the outflow water of the COD adsorption tower is adjusted to a pH of about 3 to 7 by adding a pH adjuster, if necessary, and then contacted with a fluorine adsorption resin to remove fluorine to a higher degree.

In this case, as the fluorine adsorbing resin, for example, cerium, hafnium, titanium, zirconium,
Examples thereof include resins that adsorb metal ions forming complex compounds with fluorine ions such as iron, aluminum, and lanthanides, activated carbon, activated alumina, hydrous titanium oxide, zeolite, and magnesia adsorbents. In addition, such a treatment with a fluorine-adsorbing resin is performed by adding S
It is preferably carried out by passing water at a V of about 0.5 to 30 hr ^-1 .

[0022]

In the present invention, the CO
The COD component can be efficiently removed by the COD adsorption resin after the peroxosulfuric acid, which is an oxidizing harmful substance that deteriorates the D adsorption resin, is decomposed and removed by activated carbon in advance.

For example, of the peroxodisulfuric acid, peroxodisulfuric acid undergoes the following reduction reaction due to the catalytic action of activated carbon under acidic conditions of pH 5 or lower,
Efficiently decomposed and removed.

Na ₂ S ₂ O ₈ + H ₂ O → Na ₂ SO ₄ + H ₂ SO ₅ H ₂ SO ₅ + H ₂ O → H ₂ SO ₄ + H ₂ O ₂ (or H ₂
O + 1 / 2O ₂ )

[0025]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples below.

Example 1 Flue gas desulfurization wastewater was treated by the method shown in FIG.

First, slaked lime 1500 mg was added to the flue gas desulfurization wastewater.
/ L and polyacrylamide polymer flocculant 1mg / l
Was injected and coagulated and sedimented in the coagulation-separation separation tank 1, and the supernatant water was subjected to a two-layer filtration of sand-anthracite by the filter 2. Table 1 shows the water quality of the filtered water.

Next, 75 mg / l of hydrochloric acid (HCl) was injected into the filtered water in the pH adjusting tank 3 to adjust the pH to 3, and then the activated carbon packed column (activated carbon: "Kuraray Coal KW" (2
(0/40 mesh) 20 ml filled with Kuraray Co., Ltd.) 4
Water was passed through at a water flow rate of SV = 10 hr ⁻¹ . Table 1 shows the quality of runoff water.

As is clear from Table 1, S ₂ O ₈ ²⁻ which causes oxidative deterioration of the anion exchange resin was removed to 0.5 mg / l or less.

Next, the effluent water of the activated carbon packed tower 4 is changed to CO
A COD adsorption tower (weak (medium) basic anion exchange resin: "Diaion WA-30" manufactured by Mitsubishi Kasei Co., Ltd., filled with 20 ml) 5 for the purpose of adsorbing the component D has a water flow rate SV = 1.
When water was passed through at ⁰ hr ⁻¹ , effluent having the water quality shown in Table 1 was obtained (at the time of BV = 200).

Sodium hydroxide (NaO
H) was added for neutralization to obtain treated water having the water quality shown in Table 1. NaOH required for this neutralization is 80 mg /
It was l.

Under the above water flow conditions, the COD adsorption tower 5
After passing about 4000 BV of water, the total exchange capacity of the anion exchange resin was measured and found to be 1.33 meq / ml-resin. Since the new resin is 1.4 meq / ml-resin, it can be seen that in this example, the decrease in the total exchange capacity is about 5%, which is extremely small.

Comparative Example 1 By the method shown in FIG. 2, the same flue gas desulfurization wastewater as that used in Example 1 was treated.

In FIG. 2, members having the same functions as those shown in FIG. 1 are designated by the same reference numerals. That is,
The method shown in FIG. 2 is different from the method of Example 1 in that the pH adjusting tank 3 is not provided and the pH of the inflow water of the activated carbon adsorption tower 4 is not adjusted, and other processing operations are performed in the same manner as in Example 1. It was

Activated carbon adsorption tower 4 obtained by this method
Table 1 shows the water quality of the effluent water and the water quality of the effluent water of the COD adsorption tower 5. In addition, the COD adsorption tower outflow water is treated with NaOH.
Table 1 shows the water quality of the treated water obtained by neutralization with. The NaOH required for neutralization was 20 mg / l.

Further, as in Example 1, the COD adsorption tower 5
After passing about 4000 BV of water, the total exchange capacity of the anion exchange resin was measured and found to be 0.98 meq / ml-resin. As described above, since the new resin is 1.4 meq / ml-resin, the reduction rate of the total exchange capacity in this comparative example was about 30%.

[0037]

[Table 1]

As is clear from the above results, according to the method of the present invention, S ₂ O ₈ ²⁻ , which is a harmful substance that deteriorates the anion exchange resin of the COD adsorption tower, can be efficiently used in the activated carbon adsorption tower. Can be removed. Therefore, the COD component can be removed to an extremely low concentration without causing deterioration of the COD adsorption removal efficiency of the COD adsorption tower with time.

On the other hand, even when the activated carbon adsorption tower is installed before the COD adsorption tower, according to the method of Comparative Example 1 in which the pH is not adjusted to 5 or less prior to the activated carbon adsorption treatment, S ₂ O is adsorbed in the activated carbon adsorption tower. ₈ ^2- cannot be removed efficiently (S ₂ O ₈ ^2-
mg / l remains. ), Therefore, the COD adsorption removal efficiency in the COD adsorption tower is poor, and 10 mg / l of COD remains in the treated water. Moreover, due to the deterioration of the anion exchange resin, this COD adsorption / removal efficiency significantly decreases with time.

Examples 2 and 3 The same treatment as in Example 1 was carried out except that the amount of hydrochloric acid added to the filtered water was changed to adjust the pH of the activated carbon adsorption tower inflow water to 5.0 or 4.0. Was done.

The concentration of S ₂ O ₈ ^{2− in the} effluent of the activated carbon adsorption tower was
The results are shown in Table 2 together with the results in Example 1 and Comparative Example 1.

[0042]

[Table 2]

From Table 2, it can be seen that S ₂ O ₈ ²⁻ can be sufficiently removed if the pH of the inflowing water of activated carbon is 5 or less.
This pH may be less than 3, but there is no great difference in the effect of removing S ₂ O ₈ ^2- , and since the amount of the alkaline agent required for adjusting the pH of the final treated water is large, the pH is 3.0 to 3.0.
It is preferable to adjust to 5.0.

[0044]

As described in detail above, according to the method for treating flue gas desulfurization wastewater according to the present invention, in the treatment of flue gas desulfurization wastewater containing peroxosulfuric acid and a COD component,
Prior to the adsorption treatment of the OD component, CO 2 is removed by efficiently removing peroxosulfuric acid, which is an oxidizing harmful substance, in advance.
Highly treated water can be obtained by efficiently adsorbing and removing the D component. According to the present invention, the COD adsorption efficiency is enhanced, and the COD adsorption resin is prevented from deterioration over time.
The D adsorption removal efficiency can be kept high for a long period of time.

[Brief description of drawings]

FIG. 1 is a system diagram showing a method of an embodiment of a method for treating flue gas desulfurization wastewater according to the present invention.

2 is a system diagram showing a method in Comparative Example 1. FIG.

[Explanation of symbols]

 1 Coagulation sedimentation separation tank 2 Filtration tank 3 pH adjustment tank 4 Activated carbon adsorption tower 5 COD adsorption tower 6 Treated water tank

Claims (1)

[Claims] 1. A flue gas characterized by adding a pH adjuster to flue gas desulfurization wastewater containing peroxosulfuric acid and a COD component to adjust the pH to 5 or less, contacting with activated carbon, and then contacting with a COD adsorbing resin. Desulfurization wastewater treatment method.