JPH08948A - Treatment of exhaust gas desulfurized drainage and device therefor - Google Patents

Abstract

PURPOSE:To provide a compact treatment device for exhaust gas desulfurized drainage, for which the addition of a flocculant is not required, by filtering drainage from a wet exhaust gas desulfurizing device by means of hollow fiber mebranes. CONSTITUTION:Membrane modules 10 are disposed in a membrane separation tank 19 having a slurry collecting section 15 and an outlet 20 on a lower section of a desulfurization drainage treatment device 5. Pipings 21 for discharging permeation liquid 6 through hollow fiber membranes are connected with respective membrane modules 10, and an air dispersion tube 11 for vibrating the hollow fiber membranes is installed. When desulfurized drainage 4 is fed to the membrane separation tank 19 and the pressure of the membrane modules 10 is reduced by a filter pump 13, the solution part of the desulfurized drainage 4 as permeation liquid 6 is extracted, and a solid component is separated on the outer surfaces of the membrane modules 10. The permeation liquid 6 is transferred to the following process by the filter pump 13, and concentrated slurry containing the solid component is passed through a slurry collecting section 15 and a discharge outlet 20 and discharged in the form of condensed slurry 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for decontaminating wastewater discharged when sulfur oxide gas in combustion exhaust gas is desulfurized by a wet lime-gypsum method.

[0002]

2. Description of the Related Art An example of a conventional wet lime-gypsum flue gas desulfurization wastewater treatment method will be described with reference to FIG. Combustion exhaust gas such as petroleum and coal is released as clean gas after removing soot dust and sulfur oxides by a wet lime-gypsum desulfurization device, but desulfurization gypsum slurry 1 which is a cooling / absorbing liquid is dehydrator 2 It is separated into desulfurization gypsum 3 and desulfurization drainage 4.
The desulfurization effluent 4 contains combustion ash in combustion exhaust gas, solid contents such as gypsum produced by reaction, dissolved metal, and nitrogen / sulfur compound produced by desulfurization reaction. Therefore, this property cannot be discharged into public water bodies without any treatment, and it is necessary to treat it to make it pollution-free. Therefore, first desulfurization drainage 4 is neutralized tank 2
4, the flocculant 25 and the alkali agent 26 are mixed, and then the polymer flocculant 27 is added to cause the flocculated sludge to be generated.
To precipitate. This removes heavy metals and the like. The coagulation / sedimentation-treated water 29 separated in the sedimentation tank 28 is further treated in the post-treatment device 8 and then discharged as the discharge water 9. On the other hand, the coagulation sludge 30 in the settling tank 28 is carried out of the system as a dehydrated cake 32 by the dehydrator 31. The post-treatment device 8 is provided when it is necessary to perform a neutralization treatment for removing contaminants (for example, CO compounds and F originating from NS compounds and organic substances) that cannot be removed by the coagulation-sedimentation treatment and adjusting the pH.

[0003]

The solid content of the desulfurization effluent in the conventional method is separated and removed in the settling tank 28. The solid content concentration in the coagulation-treated water 29 in the settling tank 28 is determined by the post-treatment device 8. Strict control is required in view of the model and the regulation value of the discharged water 9. For this reason, the settling tank 28 has a settling area in consideration of the variation of the solid content particle size in the desulfurization drainage 4 and the amount of drainage. Therefore, the settling tank 28 originally has a large occupied area, and in addition, considering the fluctuation of the drainage property, the apparatus becomes larger.

In view of the above-mentioned state of the art, the present invention is to provide a method and an apparatus for treating flue gas desulfurization wastewater which is compact and does not require addition of a flocculating precipitant.

[0005]

The present invention provides (1) a method for treating wastewater discharged from a wet flue gas desulfurization apparatus for absorbing and separating sulfur oxide in combustion exhaust gas by a wet lime-gypsum method, A method for treating flue gas desulfurization effluent, which comprises: (2) a membrane module formed of a hollow fiber membrane; an air diffuser provided below the membrane module for ejecting air; It is provided with a collecting slurry part for collecting concentrated slurry having a high solid content concentration provided under the air diffuser, an outlet for discharging concentrated slurry from the collecting slurry part, and a pipe for taking out permeated liquid filtered from the membrane module. (3) Inside the hollow fiber membrane of the flue gas desulfurization wastewater discharged from the wet flue gas desulfurization equipment, and (3) inside the hollow fiber membrane of the membrane module, a permeated liquid of the hollow fiber membrane or a solution having a solid concentration equivalent to that. Supply Wherein characterized by comprising providing a pipe is a processing apparatus waste water of flue gas desulfurization of (2).

The method of the present invention is a method for treating flue gas desulfurization wastewater in which wastewater discharged from a wet flue gas desulfurization apparatus is filtered by a hollow fiber membrane in place of conventional wastewater treatment equipment. Further, in the device of the present invention, a hollow fiber membrane in which hollow fibers having a diameter of about 300 μm are bundled is immersed in the liquid to be filtered, and a pressure difference is provided between the inner hollow part of the hollow fiber membrane and the liquid to be filtered. The filtrate is allowed to permeate into the hollow portion while removing solids on the surface of the hollow fiber membrane. Further, an air diffuser is installed below the hollow fiber membrane, and the hollow fiber membrane is constantly vibrated by air bubbles to prevent the solid content concentration on the surface of the hollow fiber membrane from rising.
Furthermore, the pressure difference between the hollow part of the hollow fiber membrane and the outside liquid to be filtered,
In other words, when the filtration pressure loss is increased, the hollow fiber membrane is equipped with a membrane cleaning means that causes the filtrate of the hollow fiber membrane to flow from the inside of the hollow fiber membrane to the side of the liquid to be filtered, and to remove the adhered solids. It is a device for treating flue gas desulfurization wastewater.

[0007]

According to the present invention, a hollow fiber membrane module in which fibrous hollow fiber membranes such as polyethylene porous hollow fiber membranes having a diameter of about 300 μm are bundled is directly immersed in a liquid to be filtered having a high solid content to extract only liquid components. Thus, the filtrate can have an extremely low concentration of 0.2 mg / liter or less in solid content. Further, the filtration area of the device of the present invention is much larger than the filtration device conventionally used for the treatment of flue gas desulfurization wastewater in view of the size of the device, for example, 70 to 8 per 1 m ^{3 of the} filtration tank.
It is possible to secure a filtration area of 0 m ² . As described above, the hollow fiber membrane filtration device of the present invention can obtain high filtration performance, can be made extremely compact, and has a great advantage economically as compared with the conventional device.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a diagram showing an embodiment of a desulfurization wastewater treatment process using the device of the present invention. In FIG. 1, the desulfurization gypsum slurry 1 is separated into a desulfurization gypsum 3 and a desulfurization wastewater 4 by a dehydrator 2 and then desulfurization wastewater. 4 is supplied to the membrane separation device 5 of the present invention. As the dehydrator 2, a basket type centrifuge, a vacuum belt filter or the like can be used. The membrane separator 5 separates and discharges the concentrated slurry 7. The concentrated slurry 7 is returned to the dehydrator 2, and the solid matter contained therein is finally discharged out of the system as desulfurized gypsum 3. On the other hand, the permeated water 6 from which the solid matter has been removed is subjected to necessary post-treatment in the post-treatment device 8 and then discharged as discharged water 9 out of the system. The post-treatment device 8 is a pollutant that cannot be removed by the membrane separation device 5 (for example, an N—S compound, and COD and F derived from organic substances).
Etc.) or a neutralization treatment for pH adjustment is required. When the desulfurization wastewater is not discharged as wastewater to public water bodies, a series of devices including an electrodialysis device, an evaporator and a solidification device can be used as the post-treatment device 8.

FIG. 2 shows an example of a basic structural diagram of a filtration device using a hollow fiber membrane module, which is a flue gas desulfurization wastewater treatment device according to the present invention. In the desulfurization wastewater treatment device 5 of FIG. 2, one or more sets of membrane modules 10 are arranged in a membrane separation tank 19 having a collecting slurry part 15 for collecting concentrated slurry and a discharge port 20 for discharging the concentrated slurry 7 in the lower part. It has been configured. A pipe 21 for taking out the permeated liquid 6 that has permeated the hollow fiber membrane is connected to each membrane module 10, and the membrane module 10
An air diffuser 11 for ejecting air 12 to vibrate the hollow fiber membranes that constitute the membrane module 10 is installed below. A filtration pump 13 for extracting the permeated liquid and a backwash pump 14 for sending the permeated liquid 6 in the reverse direction (from the inside to the outside of the hollow fiber membrane) are connected to the pipe 21 when necessary. Note that the desulfurization wastewater treatment device shown in FIG. 2 is an example, and basically, the hollow fiber membrane may be immersed in the desulfurization wastewater. As for the driving force for filtration, the pressure reducing method is used in FIG. 2, but basically, it is sufficient if there is a pressure difference between the desulfurization wastewater and the permeate side of the hollow fiber membrane, and therefore there is also a method of pressurizing the desulfurization wastewater. .

The desulfurization wastewater 4 is supplied to the membrane separation tank 19, and the inner hollow portion of the membrane module 10 is depressurized by the filtration pump 13 so that the desulfurization wastewater 4 is passed through the membrane module 10.
Solution portion, that is, the permeated liquid 6 is extracted. At this time, solids are separated on the outer surface of the membrane module 10. The permeate 6 is sent to the next step by the filtration pump 13,
The concentrated slurry containing the solid content removed on the outer surface of the membrane module 10 is collected in the collecting slurry portion 15 provided at the lower part of the membrane separation tank 19 and discharged from the membrane separation tank 19 through the discharge port 20 as the concentrated slurry 7. To be done. A predetermined amount of air 12 is ejected from the air diffuser 11 to vibrate the hollow fiber membrane of the membrane module 10 located above the air diffuser 11. When the pressure difference between the inside and the outside of the hollow fiber membrane of the membrane module 10 increases, the permeate 6 is caused to flow backward from the backwash pump 14,
The solid content deposited on the outer surface of the hollow fiber membrane is peeled off.

FIGS. 3 and 4 show an example of the correlation between the structure and position of the membrane module 10 and the diffuser pipe 11 which constitute the desulfurization wastewater treatment apparatus of the present invention. These figures are examples and any structure and position can be used so that the air ejected from the air diffusing tube 11 can efficiently vibrate the hollow fiber membrane. Further, regarding the air ejection holes of the air diffuser 11, any structure may be used as long as it can secure a necessary amount of ejected air and can prevent clogging due to solid contents in the drainage (for example, a structure with the ejection port facing downward). In FIG. 3, the hollow fiber membrane module structure has 6 ends after filtration after filtration.
Is provided with a water collecting pipe 16 through which a hollow fiber membrane 18 is attached so as to have a bend capable of vibrating. As shown in FIG. 4, one or more sets of such membrane modules 10 are provided, and an air diffusing tube 11 is provided below the membrane module 10. Figure 3
L and H indicating the distance between each of the middle membrane modules 10 and the air diffusing tube 11 are set so that the hollow fiber membrane 17 vibrates efficiently by the air bubbles generated in the air diffusing tube 11.

FIG. 5 shows a cross-sectional view (FIG. 5A) and a perspective view (FIG. 5B) of an example of the air diffusing tube 11.
The air diffusing pipe 11 has an air blowing hole 18 having an area and a number capable of ensuring a required jet air amount, and further has a structure capable of preventing blockage due to solid content in drainage. In the present embodiment, the air diffusing pipe 11 has air blowing holes. A set of two 18 directed downward 45 ° was provided, and a plurality of these 18 were provided in the longitudinal direction of the air diffuser 11.

1 to 5 (a set of 5 membrane modules, a combination of 5 air diffusers, a polyethylene porous hollow fiber membrane is used as the hollow fiber membrane, and the length 750 of each hollow fiber membrane)
mm, the diameter of the water collection pipe was 20 mm), and a desulfurization wastewater treatment test was performed by the wet lime-gypsum method. As a result, 30
After operating for a day, it was confirmed that the concentration of solids in the filtered water at the outlet of the membrane separation device was always 0.1 mg / liter or less. The composition of the desulfurization wastewater is shown in Table 1, and the conditions of the wastewater treatment test are shown in Table 2.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

【The invention's effect】

(1) Unlike the conventional method, it is not necessary to add a coagulant for separating and separating fine solid matter, and the amount of waste generated thereby can be reduced. (2) Since a settling tank having a large installation area as in the past is not necessary, the apparatus becomes compact and the installation area can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic flow chart showing one embodiment of a desulfurization wastewater treatment process using the apparatus of the present invention.

FIG. 2 is a schematic structural diagram of a flue gas desulfurization wastewater treatment device of the present invention.

FIG. 3 is a structural explanatory view of a membrane module.

FIG. 4 is an explanatory view showing a positional relationship between a membrane module and an air diffusing tube.

5A and 5B are a schematic cross-sectional view and a perspective view showing a structural example of an air diffusing tube.

FIG. 6 is a schematic flow chart showing an example of a conventional desulfurization wastewater treatment method.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location B01D 63/02 9538-4D B01D 53/34 125 E (72) Inventor Hideyoshi Kamiyoshi Kobe City, Hyogo Prefecture 5-16 Komatsudori, Hyogo-ku Shinbishi High-Tech Co., Ltd. (72) Inventor Kazuo Komitsu-dori 5-chome 1-16 Komatsudori, Hyogo-ku, Hyogo Prefecture

Claims (3)

[Claims] 1. A method of treating wastewater discharged from a wet flue gas desulfurization apparatus that absorbs and separates sulfur oxide in combustion exhaust gas by a wet lime-gypsum method, wherein the wastewater is filtered through a hollow fiber membrane. Flue gas desulfurization wastewater treatment method. 2. A membrane module formed of a hollow fiber membrane, a diffusing tube provided below the membrane module for ejecting air, and a concentrated slurry having a high solid content concentration provided below the diffusing tube for collecting concentrated slurry. Flue gas desulfurization wastewater discharged from a wet flue gas desulfurization apparatus comprising a slurry part, an outlet for discharging concentrated slurry from the slurry collecting part, and a pipe for taking out permeated liquid filtered from the membrane module. Processing equipment. 3. The flue gas desulfurization according to claim 2, wherein a pipe for supplying a permeate of the hollow fiber membrane or a solution having a solid content equivalent to the permeate of the hollow fiber membrane is provided inside the hollow fiber membrane of the membrane module. Wastewater treatment equipment.