JPH11319809A - Treatment of dioxin-containing liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the separation process of an activated carbon unnecessary by adding activated carbon powder to a dioxin-contg. liquid and subjecting the liquid to solid-liquid separation by using a filtering means. SOLUTION: After dust is removed from a waste gas in a dry dust collecting machine 1, the gas is brought into contact with a circulating water 7 in a preliquid contact room 2 to adsorb dioxins. A cleaning tower 4 is equipped with two contact rooms 6, 6', and each contact room 6, 6' is connected with a circulating line 5C, 5'C to circulate the circulating water 8, 8'. A mixture water of active carbon powder in a tank 9 and water is supplied to the circulating water 7 and circulating water 8, 8'. One circulating line 5'C is equipped with a water cooling device 15, where the gas passed through the liquid contact room 6' is cooled to a lower temp. than that of the gas passed through the liquid contact room 6. The gas at a high temp. from the liquid contact room 6 and the gas at a low temp. from the liquid contact room 6' are mixed in a mixing room 12 to produce white fume, which surrounds fine particles in the gas to grow particles. The gas flows into an electric dust collecting machine 13 where most of particles are efficiently removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to organic chlorine compounds such as polychlorinated-p-dibenzodioxins (PCDD) and polychlorinated dibenzofurans (PCDF) (hereinafter, these are referred to as "dioxins"). The present invention relates to a method for treating a dioxin-containing liquid for removing dioxins from a liquid obtained, and more particularly to a method for treating a dioxin-containing liquid using activated carbon.

[0002]

2. Description of the Related Art After exhaust gas from a garbage incineration plant is removed by passing it through an electric dust collector or a bag filter, it is brought into contact with water to absorb gaseous dioxins into water to remove dioxins from the gas. There is. The water that has absorbed the dioxins is added with powdered activated carbon, the dioxins are adsorbed on the powdered activated carbon, and then the powdered activated carbon is separated from the water, whereby the dioxins are removed from the water.

Conventionally, a coagulation sedimentation method has been used as a solid-liquid separation means for separating the activated carbon powder adsorbing dioxins from the water.

[0004]

When powdered activated carbon is subjected to solid-liquid separation by coagulation sedimentation, a small amount of powdered activated carbon may leak to the treated water side, and dioxins may not be captured in a small amount.

The present invention provides a method for treating a dioxin-containing liquid capable of sufficiently removing dioxins from water by reliably solid-liquid separation of the powdered activated carbon in the water adsorbing dioxins from the water. The purpose is to provide.

Another object of the present invention is to provide a method for treating a dioxin-containing liquid, which eliminates the need for a step of separating activated carbon in a method for removing dioxins utilizing the adsorption action of activated carbon.

[0007]

A method for treating a dioxin-containing liquid according to claim 1 is characterized in that powdered activated carbon is added to the dioxin-containing liquid, and then solid-liquid separation is performed using a filtration means. It is.

According to the method for treating a dioxin-containing liquid of the present invention, the activated carbon powder adsorbed with the dioxins can be separated into solid and liquid without substantially leaking to the treated water side. Can be almost completely removed.

As described in claim 2, by using a filtration membrane as the filtration means, it is possible to perform advanced solid-liquid separation.

When a filter medium such as sand or styrofoam is used as the filtration means, solid-liquid separation can be performed with a simpler device than in the case where a filtration membrane is used.

[0013] The method for treating a dioxin-containing liquid according to claim 3 is characterized in that the dioxin-containing liquid is passed through an activated carbon packed column.

By using the activated carbon packed column, a step of separating activated carbon is not required, and the activated carbon after the treatment can be easily incinerated.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the dioxin-containing liquid is a liquid in which dioxins are adsorbed by contacting exhaust gas from various incinerators such as garbage incinerators, for example, garbage provided with a wet smoke washer. Examples include cooling water discharged from various incinerators such as incinerators (hereinafter, referred to as "smoke washing cooling water"), leachate at final disposal sites, and smoke washing drainage from thermal power generation.

The solubility of dioxins in water is extremely low, and usually dioxins on the order of nanograms / L are dissolved in the water.

[0015] In the method of claim 1, the powdered activated carbon to be added to the dioxin-containing liquid includes:
The maximum particle size is 200 μm or less, particularly 100 μm or less,
The average particle size is preferably 10 to 50 μm, particularly preferably about 15 to 25 μm.

The amount of the powdered activated carbon added to the dioxin-containing liquid is preferably 300 mg / L or more, particularly 500 to 1500 mg / L, particularly 800 to 1 / L.
It is preferably 000 mg / L.

In particular, in the case of the above-mentioned cooling water for smoke washing, the amount of powdered activated carbon added is 10 g to 20 k per m ³ of cooling water.
g, especially 0.5 to 1 kg.

When the powdered activated carbon is added to the dioxin-containing liquid, the activated carbon may be added as it is to the dioxin-containing liquid, or the powdered activated carbon may be added to a liquid such as water or alcohol (preferably water) or a small amount of dioxin. After dispersing in a dioxin-containing liquid, this dispersion may be added to the dioxin-containing liquid. A dispersant may be used to improve the dispersibility of the powdered activated carbon. By adding powdered activated carbon as a dispersion, powdered activated carbon can be uniformly dispersed in a dioxin-containing liquid in a short time, which is preferable.

As the powdered activated carbon to be added, peat type, coal type, lignite type, coconut hull type and the like can be mentioned.
In particular, peat-based or lignite-based activated carbon having many intermediate pores of 20 to 500 ° is preferred.

The dioxin-containing liquid to which the powdered activated carbon has been added is preferably stirred to sufficiently disperse the powdered activated carbon. As the stirring means, various means such as a stirrer having a rotary stirring blade and a line mixer can be used. Further, even after the powdered activated carbon is dispersed by stirring, the liquid may be stirred so that the powdered activated carbon does not settle, or the liquid may be kept in a fluid state. In this step, dioxins in the liquid are adsorbed on the activated carbon powder. Note that the dioxin-containing liquid may be cooled in the adsorption step or a step before the adsorption step.

In the method of the first aspect, after the dioxins are adsorbed on the activated carbon powder, the dioxin-containing liquid in which the activated carbon powder is dispersed is subjected to a solid-liquid separation treatment using a filtration means. In this case, the liquid may be subjected to a preliminary solid-liquid separation treatment such as natural sedimentation separation treatment, centrifugal separation treatment, coagulation separation, flotation separation, and then subjected to a solid-liquid separation treatment by a filtration treatment means. The treatment may be immediately performed by the filtration means without performing the treatment.

Examples of the filtration means include a method using a filter medium such as sand and styrene foam, and a method using a filtration membrane. If it is a method using a filter medium, it can be implemented by a simple method. When a filtration membrane is used, the accuracy of filtration is improved and the powdered activated carbon is easily reused.

To perform solid-liquid separation using a filtration membrane, various types of membrane modules and membrane separation devices such as a spiral type membrane module, a hollow fiber type membrane module, a flat type membrane module, a tubular type membrane module, and a permeation type membrane separation device are used. Can be used.

As the filtration membrane, a microfiltration (M) made of various materials such as a ceramic membrane, a resin membrane, and a metal precision membrane is used.
F) membranes and ultrafiltration (UF) membranes can be used.

The pore size of the filtration membrane used is 0.1 to 1.0.
μm especially 0.2 to 0.9 μm especially 0.3 to 0.8 μm
It is preferable to use those having a size of about m. However, if the film is a ceramic film or a precision metal film, the film may have a pore diameter smaller than 0.1 μm. With a filter membrane having such a pore diameter, powdered activated carbon in the liquid can be almost completely separated by filtration. If the pore size is too small, the filtration time is unnecessarily long. If the pore diameter is too large, activated carbon may leak.

In the method according to the third aspect, the dioxin-containing liquid is passed through an activated carbon packed column. As a result, dioxins in the dioxin-containing liquid are adsorbed and removed,
Further, a step of separating activated carbon is not required. Examples of the activated carbon used include peat-based, coal-based, lignite-based, and coconut husk-based activated carbons. In particular, peat-based or lignite-based activated carbon having many intermediate pores of 20 to 500 ° is preferable.

The activated carbon packed column may be a fixed bed or a fluidized bed.

When the method of claim 3 is applied to the treatment of cooling water for cleaning smoke, the activated carbon packed tower may be provided either before or after the cooling tower, but from the viewpoint of preventing the cooling tower from being contaminated, it is provided before the cooling tower. Is preferred.

The used activated carbon or the activated carbon concentrated slurry separated by the method of the present invention, or the used activated carbon discharged from the activated carbon packed tower can be incinerated. However, the activated carbon for dioxin removal in a wet smoke cleaning device is used. It can also be reused by re-adding it to the cooling water for smoke washing.

FIG. 1 shows an example of a wet flue gas cleaning apparatus for exhaust gas.

The exhaust gas containing dioxin is supplied to the dry dust collector 1
After the dust is removed by the above, circulating water (dispersed water of the powdered activated carbon) by the pump 3 and the circulating line 3c in the pre-stage liquid contact chamber 2
And dioxin is absorbed. (Water containing powdered activated carbon also has the effect of rubbing off dioxin adhering to the inner wall surface of the pre-stage liquid contact chamber 2.) This gas flows into the washing tower 4 in a saturated state of steam.

In the washing tower 4, two liquid contact chambers 6, 6 'are provided so that the gas passes in parallel. Circulating water (dispersed water of powdered activated carbon) 8,
Circulation lines 5C and 5'C having circulating water pumps 5 and 5 'are connected to circulate 8'.

The circulating water 7 and the circulating water 8, 8 ′ in the pre-stage liquid contact chamber 2 are supplied with a mixed liquid (dispersed water) of activated carbon and water in the tank 9 by a supply pump 10.

One circulation line 5'C has a water cooler 15
Is provided, and the circulating water is cooled. For this reason, the gas passing through the liquid contact chamber 6 ′ has a lower temperature than the gas passing through the liquid contact chamber 6. Since the gas passing through the liquid contact chambers 6 and 6 'is saturated with water vapor, the relatively high temperature gas from the liquid contact chamber 6 and the relatively low temperature gas from the liquid contact chamber 6' are mixed. A large amount of white smoke is generated by mixing inside. The white smoke (fine water droplets) wraps the fine particles in the gas, and the apparent particle diameter increases, or the particles combine to grow the particles. When the gas containing the particles thus grown flows into the electrostatic precipitator 13, most of the particles are efficiently removed. This significantly reduces the amount of dioxin released into the atmosphere.

Reference numeral 14 in the figure denotes a cleaning circuit for periodically cleaning the electrode plates of the electric dust collector 13. Water is supplied from the water cooler 15 to the dust collector 13 by opening the valve 14V.

The larger the temperature difference between the liquids 8 and 8 'circulating in the circulation lines 5C and 5'C at the start of gas contact, the greater the amount of white smoke generated, but if a cooling tower is used as the water cooler 15, It is easy to make the temperature of the liquid 8 '35 to 40 ° C, and the temperature difference at the start of gas contact between the liquids 8 and 8' can be made 25 to 30 ° C.

For the generation of white smoke, there is also a suitable range for the mixing ratio of a relatively high-temperature gas and a relatively low-temperature gas. In the range of 0.25-0.
It is desirable to use about 5 parts by volume.

The amount of circulating water with respect to the gas in the first stage liquid contacting chamber is determined by the heat balance, mass balance and absorption capacity of the target gas and liquid, and is usually 5% by weight with respect to the dry gas amount of the target gas.
It is preferable to set it to about 15.

As the circulating water 7, 8, 8 ', 0.0
5% or more, desirably 0.05 to 0.3%, especially 0.1
% Of the powdered activated carbon is suitable, and the dioxin absorbed in the water is effectively adsorbed on the activated carbon. The circulating water 7, 8, 8 ′ is continuously or intermittently discharged little by little through the drain line 11. The dioxin is efficiently removed from the wastewater by filtering the wastewater with a filtration means such as a membrane module provided at the position shown in FIG. These filtration means may be provided alone or at a plurality of locations.

[0040]

[Example] Example 1 Scrubber flow water at a waste incineration plant (SS 60 mg / L,
Peat powdered activated carbon (average particle diameter: 20 μm) was added at a ratio of 500 mg / L to dioxin concentration of 51 ng / L, and dispersed by stirring with a stirrer, and then gently stirred for 30 minutes so that the powdered activated carbon did not settle. Continued.

Hereinafter, the liquid after the lapse of 30 minutes is simply referred to as "powdered activated carbon dispersion raw water".

This powdered activated carbon dispersion raw water was supplied with a pore diameter of 0.5 μm.
Then, the mixture was filtered through a UF membrane of m, and the concentration of dioxins in the filtrate was measured. As a result, no dioxins were detected from this filtrate.

Comparative Example 1 The above-mentioned raw water of the activated carbon powder was subjected to coagulation sedimentation. That is, 1000 mg /
L, 2 mg / L of a polymer flocculant (polyacrylamide partial hydrolyzate) was added to perform flocculation treatment. When the supernatant water of this aggregation treatment liquid was collected and the dioxin concentration was fractionated, dioxins of 0.66 ng-TEQ / L were detected.

Example 2 The same procedure as in Example 1 was carried out except that a UF membrane having a pore diameter of 2 μm was used as the filtration membrane. The dioxin concentration in the filtrate was 0.05 ng-TEQ / L.
Which was inferior to the result of Example 1,
A remarkably superior removal effect was obtained as compared with the result of Comparative Example 1.

Example 3 The same treatment as in Example 1 was carried out except that a UF membrane having a pore diameter of 0.05 μm was used as the filtration membrane, and no dioxins were detected from the filtrate at all. Filtration took four times as long as in Example 1.

Example 4 The same procedure as in Example 1 was carried out except that a ceramic membrane having a pore size of 0.05 μm was used as the filtration membrane, and no dioxins were detected in the filtrate at all.

The relationship between the filtration time, the permeation flux and the concentration ratio at this time is as shown in FIG. 2, and a practical filtration treatment was possible.

Example 5 The same treatment as in Example 1 was carried out except that a ceramic membrane having a pore size of 0.02 μm was used as the filtration membrane. As a result, no dioxins were detected in the filtrate.

The relationship between the filtration time, the permeation flux and the concentration ratio at this time is as shown in FIG. 3, and a practical filtration treatment was possible.

Example 6 To 10 L of cooling water collected from a cooling tower of a refuse incinerator equipped with a wet smoke washer was added 1 g / L of peat type powdered activated carbon from Norit (average particle size: 10 μm). Stirred. After 30 minutes, the mixture was filtered through a 1 mm glass filter, and the concentration of dioxins in the filtrate was measured.
0.8 pg-TEQ / L.

Comparative Example 2 A treatment was carried out in the same manner as in Example 6 except that no activated carbon was added, and the concentration of dioxins in the treated product was measured. The concentration of dioxins was 1.2 ng-T.
EQ / L.

As is clear from the results of Example 6 and Comparative Example 2, the dioxin removal rate of Example 6 was 99.93%. The dioxin was removed by adding powdered activated carbon to cooling water and filtering. It is clear that the concentration can be significantly reduced.

Example 7 10 L of cooling water collected from a cooling tower of a refuse incinerator equipped with a wet smoke washer was passed through a glass column filled with peat-based granular activated carbon (average particle size: 10 μm) of Norit Co., Ltd. and passed through. When the dioxin concentration of the liquid was measured,
1.3 pg-TEQ / L.

Comparative Example 3 A treatment was carried out in the same manner as in Example 7 except that cooling water was passed through a glass column to which no activated carbon was added, and the concentration of dioxins in the obtained permeate was measured. .
It was 2 ng-TEQ / L.

As is clear from the results of Example 7 and Comparative Example 3, the dioxin removal rate of Example 7 was 99.89%, and the dioxin concentration was reduced by passing cooling water through an activated carbon column. It is clear that this can be significantly reduced.

[0056]

As described above, according to the method for treating a dioxin-containing liquid of the present invention, dioxins are almost completely removed from a dioxin-containing liquid such as cooling water of a refuse incinerator equipped with a wet smoke washer. be able to. The method of the present invention can be easily carried out with relatively simple equipment without making major modifications to existing equipment, and the processing cost is low.

[Brief description of the drawings]

FIG. 1 is a system diagram of a wet-type smoke cleaning apparatus.

FIG. 2 is a graph showing a relationship between a filtration time, a permeation flux and a concentration ratio in Example 4.

FIG. 3 is a graph showing a relationship between a filtration time, a permeation flux and a concentration ratio in Example 5.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Dry-type dust collector 2 Pre-stage liquid contact chamber 4 Washing tower 12 Mixing chamber 13 Electric dust collector 15 Water cooler

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Noboru Fujiwara 3-4-7 Nishishinjuku, Shinjuku-ku, Tokyo Kurita Water Industries Ltd.

Claims (3)

[Claims] 1. A method for treating a dioxin-containing liquid, comprising adding powdered activated carbon to the dioxin-containing liquid and then separating the mixture into solid and liquid using a filtration means. 2. The method for treating a dioxin-containing liquid according to claim 1, wherein a filtration membrane is used as the filtration means. 3. A method for treating a dioxin-containing liquid, comprising passing the dioxin-containing liquid through an activated carbon packed column.