JP2941551B2 - Electrodialysis equipment for desulfurization wastewater treatment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flue gas desulfurization facility for absorbing and separating sulfur oxide gas (hereinafter referred to as SOx gas) in combustion exhaust gas from a viewpoint of preventing environmental pollution by using an alkali agent such as limestone as an absorbent. The present invention relates to an electrodialysis apparatus for treating wastewater discharged from the desulfurization facility (hereinafter simply referred to as wastewater).

[0002]

2. Description of the Related Art Waste water from flue gas desulfurization equipment is mainly composed of calcium chloride, magnesium chloride, and dissolved gypsum. It contains nitrogen-sulfur compounds (hereinafter simply referred to as NS compounds) produced by the reaction in the smoke desulfurization facility, so it cannot be discharged into public waters with the same properties, and the emission standards specified by law Requires processing that conforms to

[0003] In recent years, wastewater treatment equipment incorporating an electrodialysis device has become promising, with the aim of reducing the treatment cost and the installation area of the treatment equipment as a wastewater treatment method.

In this treatment method, the wastewater is concentrated and reduced in volume using an electrodialyzer and an evaporator, and the concentrated wastewater is insolubilized with harmful components such as metals and chemical oxygen (hereinafter simply referred to as COD). It is to perform landfill dumping after treatment, and compared with the conventional treatment method combining treatment such as chemical liquid addition and solid separation by precipitation from the viewpoint of treatment cost and reduction of the installation area of treatment equipment as described above. It has great advantages.

FIG. 3 is a diagram showing an embodiment of a conventional processing facility incorporating an electrodialysis apparatus, and the conventional processing method will be described with reference to FIG. Note that FIG. 3 shows only the wastewater concentration step, and does not show the step of insolubilizing the concentrated wastewater from the concentration step. However, the concentrated wastewater is already mixed and kneaded with cement, gypsum, combustion ash, limestone, and the like. And the like have been proposed.

In FIG. 3, reference numeral 101 denotes a storage tank for storing waste water from a flue gas desulfurization facility (not shown), and reference numeral 102 denotes a solid for removing a solid content in order to prevent a decrease in performance due to solid content in the waste water in an electrodialyzer 103 described later. Filtration device 103 is a concentrated wastewater (hereinafter referred to as primary concentration) containing a large amount of dissolved salts such as calcium chloride and magnesium chloride (excluding sulfate ions (hereinafter referred to as SO ₄ ^2- ions)) by a dialysis membrane. An electrodialyzer that separates the concentrated wastewater generated by the electrodialyzer 103 into an evaporator and an evaporator that further concentrates the primary concentrated wastewater generated by the electrodialyzer 103 by an evaporation method. A storage tank for storing the concentrated wastewater generated in 104 (hereinafter referred to as secondary concentrated wastewater). A storage tank 106 cools and concentrates the steam generated during the evaporation of the wastewater in the evaporator 104 and collects the collected water as recovered water. Capacitors, and 107 storage tank 1
A pump for supplying wastewater to the filtration device 102 from 01, a pump 108 for supplying wastewater after removing solids in the wastewater by the filtration device 102 to the electrodialysis device 103, and a pump 109 for supplying the secondary concentrated wastewater in the storage tank 105 A pump 110 for supplying to a downstream insolubilization step (not shown) maintains a negative pressure in the evaporator 104 in order to promote the evaporation of the primary concentrated waste water in the evaporator 104, and the evaporator 104.
This is an evacuation device for moving the steam generated inside to the condenser 106.

[0007] Wastewater from a desulfurizer (not shown) is stored in a storage tank 101 by a line aa, and then sent to a filter 102 via a line bb and a pump 107. Here, from the line cc, a filter aid such as a flocculant necessary for removing the solid content by the filtration device 102 is added to the line bb, but may be unnecessary depending on the drainage property. The filtration device 102 removes solids in the wastewater so that the concentration of the solids in the wastewater is such that the performance of the electrodialysis device 103 can be stably maintained over a long period of time. The concentration of the solid content in the waste water at the outlet of the normal filtration device 102 is 0.2 to 0.1.
It is required to be 3 mg / liter or less. The wastewater from the filtration device 102 is supplied to the electrodialysis device 103 via the line dd, the pump 108 and the line ee. The solid content removed from the wastewater by the filtration device 102 is a line s
It is discharged out of the system through s.

The electrodialysis apparatus 103 comprises a concentrated liquid chamber, a dilute liquid chamber, and positive and negative electrode plates provided at both ends of the concentrated liquid chamber, which are formed by alternately arranging cation exchange membranes and anion exchange membranes. The cation exchange membrane selectively permeates cations such as calcium and magnesium, and the anion exchange membrane selectively transmits anion such as chlorine.At the same time, the concentrated solution containing a large amount of dissolved salt and the dissolved salt are diluted. This is to take out the diluted liquid that has become used.

FIG. 4 is a schematic diagram showing the structure of the electrodialysis apparatus and the movement of ions. As shown in FIG. 4, calcium ions (CaCl ₂ ) and magnesium ions (MgCl ₂ ), which are the main components in the wastewater, are electrically converted by the electric field formed between the positive electrode and the cathode plate. Electrophoresis is performed, and during this time, it is selectively blocked or permeated by a positive / anion exchange membrane, and consequently becomes a concentrated solution or a dilute solution, and is taken out of the electrodialysis apparatus 103.

[0010] For example, cations such as calcium and magnesium migrate toward the cathode plate, pass through the cation exchange membrane, enter the concentrated solution chamber, and then attempt to migrate toward the cathode plate, but are blocked by the anion exchange membrane and concentrated. It remains in the liquid chamber. on the other hand,
Anions such as chlorine migrate toward the anode plate, pass through the anion exchange membrane and enter the concentrate chamber, and then try to migrate toward the anode plate, but are blocked by the cation exchange membrane and remain in the concentrate chamber. It combines with the cation migrated from the opposite direction, is carried by the concentrated solution as the moving medium, and is taken out of the electrodialysis apparatus 103.

Next, the primary concentrated wastewater from the electrodialyzer 103 is sent to the evaporator 104 via the line ff, while the dilute liquid is taken out of the electrodialyzer 103 via the line gg and is desulfurized (not shown). Re-used as make-up water.

[0012] The primary concentrated wastewater is evaporated and concentrated in the evaporator 104 and decomposed into secondary concentrated wastewater and steam. Normally, the evaporator 104 heats the primary concentrated waste water with a heating medium such as steam in order to promote evaporation in the evaporator,
04 is depressurized. The heating medium enters from the line jj, and after heating the wastewater from the evaporator 104, is discharged from the line kk to the outside of the system.

Wastewater concentrated by evaporation in the evaporator 104, ie, secondary concentrated wastewater, is sent from the evaporator 104 to the storage tank 105 via the line hh. From the storage tank 105, it is sent to the insolubilization step (not shown) by the pump 109 via the line ii.

[0014] The vapor generated in the evaporator 104 is evacuated by a vacuum evacuation device 110 via a line ii to a condenser 106.
, And is cooled and condensed by a cooling medium in the condenser 106 to become a liquid, which is taken out as recovered water by a line pp. The cooling medium enters from the line mm, cools the condenser 106, and is discharged out of the system from the line nn. The recovered water is reused as boiler make-up water and desulfurization equipment make-up water according to the water quality. The non-condensable gas in the condenser 106 is discharged out of the system through the line qq by the vacuum exhaust device 110.

[0015]

In THE INVENTION It is an object of the above described processing for electrodialysis of conventional desulfurization effluent, and contains sulfate ions in the waste water (hereinafter referred to as SO ₄ ^2-ions), the SO ₄ ^{2 -} ions Cl ^- gypsum by Ca ²⁺ and SO ₄ ^2-of both ions in the waste water in the ion-exchange membrane to permeable anion exchange membrane with an anion such as (CaSO
₄ ) to produce a reaction. The gypsum produced has a low solubility and precipitates on the ion-exchange membrane as a solid content, and is fixed, hinders the movement of other ions, and has been confirmed by the experiments of the present inventors to cause a large decrease in membrane performance. I have.

That is, C moving due to the potential gradient
Each ion of a ²⁺ and SO ₄ ²⁻ is formed inside or on the surface of the ion exchange membrane due to the difference in transport number between the ion exchange membrane and the liquid in the electrodialysis tank, diffusion on the ion exchange membrane surface, and potential difference. It is thought that the concentration becomes high in the part and the reaction is generated, and the generated gypsum is deposited and fixed on the ion exchange membrane, thereby obstructing the ion transfer as described above, and also lowering the performance of the ion exchange membrane, such as an increase in electric resistance, and power consumption. The cost increases.

As a countermeasure against this, conventionally, a method has been adopted in which an anion exchange membrane having selective permeability is used, and only Cl ^- ions are selectively transmitted, while SO ₄ ^2- ions which cause gypsum precipitation are not transmitted. .

However, in the above method, the monovalent
SO of permselective anion exchange membrane_Four ^2-Ion impermeability
However, conventional monovalent anion exchange membranes require
Performance is not enough, and in long-term operation, SO_Four ^2-Ion transmission
Gypsum precipitation was a problem.

The present invention has been made in view of the above-mentioned state of the art, and is intended to provide an electrodialysis apparatus capable of preventing performance deterioration due to the gypsum deposition in an ion exchange membrane, particularly an anion exchange membrane, and maintaining a stable performance for a long period of time. is there.

[0020]

SUMMARY OF THE INVENTION The present invention is in the electrodialysis apparatus for processing waste water discharged from a wet flue gas desulfurization, the interlabial Anode, in order from the cathode side to the anode side, 1
The dianion permselective membrane (A1) / 1 dianion permselective membrane (A2) / cation-exchange membrane (C1) 1 set
A plurality of ion exchange membrane groups are provided, and a chloride solution chamber is provided between two adjacent monovalent anion selective permeable membranes (A1, A2).
Selectively permeable anion membrane (A2) and cation exchange membrane (C
1) During the concentrate chamber, the cation exchange membrane and (C1) 1 dianion permselective membrane between (A1) and diluate chamber, a high solubility and reacts with sulfate ion in the chloride solution chamber A cation chloride solution that becomes a salt, a concentrate in the concentrate chamber,
An electrodialysis apparatus for desulfurization wastewater treatment, wherein wastewater is allowed to flow through the dilute solution chamber.

[0021]

According to the present invention, stable performance can be maintained for a long period of time without causing deterioration of the membrane performance due to gypsum scale generated in the conventional ion exchange membrane.

That is, as shown in FIG. 1, the membrane arrangement of the present invention and the movement of ions, a monovalent anion selectively permeable membrane (A1) / monovalent anion between an anion and an anode plate from a cathode to an anode. Permselective membrane (A2) / cation exchange membrane (C1) ...
This set is repeatedly provided as a plurality. Then, a chloride solution chamber is provided between the two monovalent anion selective permeable membranes (A1) and (A2) and concentrated between the monovalent anion selective permeable membrane (A2) and the cation exchange membrane (C1). The liquid chamber, the space between the cation exchange membrane (C1) and the monovalent anion selective permeable membrane (A1) is a diluted liquid chamber. In the chloride solution chamber, a cation chloride solution which reacts with sulfate ions to form a salt having high solubility is passed, a concentrated solution is passed in the concentrated solution chamber, and a wastewater is passed in the dilute solution chamber.

In FIG. 1, a monovalent anion selectively permeable membrane (A) is provided adjacent to the cathode as the beginning and end portions.
And an extra cation exchange membrane (C) is provided adjacent to the anode, and cations and anions are formed as a dilute liquid chamber between (A) and (A1) and between (C1) and (C). Electrodialysis is performed in a stable and current efficient manner without direct contact with the cathode or anode. However, when a large amount of the supply solution is supplied, the ion exchange membrane described in (A) and (C) above is used. Is not necessary.

Cl in wastewater^-, SO_Four ^2-Ion is the anode
Move more electrically in the direction ^-Is A (1) and
The monovalent anion selective permeation exchange membrane (2) (hereinafter referred to as monovalent anion)
(Abbreviated as ion exchange membrane) and reaches the concentrate chamber
You. SO_Four ^2-Is based on the monovalent anion exchange membrane of A (1)
Although it does not transmit light, its performance is not enough and
Permeate the monovalent anion exchange membrane of (1) and enter the chloride solution chamber
enter. However, this chloride solution chamber contains SO_Four ^2-When
Cationic salt that forms a highly soluble salt when reacted
Gypsum precipitation does not occur
No.

Further, some SO ₄ ²⁻ ions permeating through the monovalent anion exchange membrane of A (1) and entering the chloride solution chamber move toward the anode by electric force. Migration is blocked by the monovalent anion exchange membrane. However, for the above-mentioned reason, although it slightly permeates the monovalent anion exchange membrane of A (2), the concentration is no longer such that gypsum or the like is deposited. Does not occur.

[0026]

EXAMPLES To demonstrate the utility of the present invention, a continuous experiment was conducted for 500 hours using a laboratory-scale electroosmotic apparatus.
FIG. 2 shows a flow chart of the apparatus, and the embodiment of the present embodiment will be described in detail with reference to FIG.

The arrangement of the ion exchange membrane and the arrangement of the liquid chambers in the electrodialyzer of FIG. 2 are the same as those of the embodiment shown in FIG. 1, and the chloride of the chloride solution is determined in consideration of the properties of the raw waste water. Sodium chloride was used at a concentration of 3.1 mol / liter.

Table 1 shows the specifications of the electrodialysis apparatus and the conditions of the experiment, and Table 2 shows the properties of the raw wastewater used in the experiment. In addition, this raw wastewater was prepared as a reagent product by simulating the properties of desulfurization wastewater which is the main object of the present invention and setting its composition.

[0029]

[Table 1]

[0030]

[Table 2]

In FIG. 2, 1 is a raw wastewater tank, 2 is a pump for supplying raw wastewater to an electrodialyzer 3 described later, 3 is an electrodialyzer that concentrates the raw wastewater, and 4 is generated by the electrodialyzer 3. The concentrated solution tank 5 and the concentrated solution 5
Pump 6 to supply sodium chloride solution tank, 7
Is a pump for supplying a sodium chloride solution to the electrodialysis apparatus 3.

The raw waste water is supplied to the tank 1 by the line a, and then supplied to the electrodialyzer 3 by the pump 2. In the electrodialysis device 3, the raw waste water is calcium chloride, sodium chloride, magnesium chloride (each of which is hereinafter referred to as CaC
l ₂ , NaCl, and MgCl ₂ ) and a concentrated liquid containing the salt diluted, and the concentrated liquid is supplied to the tank 1 and the tank 1 via the line c. 4 and then the electrodialysis device 3 by a pump 2 and a pump 5 respectively attached to the tank.
Circulated.

Line d is an overflow line for the mixture of the dilute liquid from line c into tank 1 and raw waste water from line a, and line g is an overflow line for the concentrated liquid in tank 4.

On the other hand, the NaCl solution in the tank 6 was circulated to the electrodialyzer 3 by the pump 7.

Such an experiment was continued for 500 hours, and thereafter, the ion exchange membrane incorporated in the electrodialyzer 3 was visually observed and observed with a microscope to confirm that no gypsum was deposited.

Needless to say, the salt concentration in the concentrated solution and the dialysis voltage during this period were very stable and the operation was good.

As a result of the above operation, the composition of the diluent discharged from the diluent chamber was as follows. CaCl ₂ : 7800 [ppm] MgCl ₂ : 4000 [ppm] NaCl: 3300 [ppm] CaSO ₄ : 1400 [ppm]

[0038]

According to the electrodialysis apparatus for desulfurization wastewater treatment of the present invention, stable operation is possible without deterioration of membrane performance due to gypsum deposition for a long period of time.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an ion exchange membrane arrangement and a liquid chamber arrangement in an electrodialysis apparatus according to an example of the present invention.

FIG. 2 is a diagram showing a flow of an experiment performed to demonstrate the usefulness of the present invention.

FIG. 3 is an embodiment diagram of a conventional wastewater treatment facility incorporating an electrodialysis device.

FIG. 4 is an explanatory view showing an ion exchange membrane arrangement and a liquid chamber arrangement in a conventional electrodialysis apparatus.

Continued on the front page (72) Inventor Shinichiro Kotake 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Heavy Industries, Ltd. Headquarters (72) Inventor Naohiko Unagawa 4--22 Kanon Shinmachi, Nishi-ku, Hiroshima, Hiroshima, Japan Mitsubishi Heavy Industries, Ltd. In Hiroshima Laboratory Co., Ltd. (72) Inventor Ryosuke Aoki 10 Goi Kaigan, Ichihara-shi, Chiba Asahi Glass Co., Ltd. Chiba Plant (56) References JP-A-51-52984 (JP, A) JP-A-62-244427 ( JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) B01F 1/46-1/48 B01D 53/50 B01D 53/77 B01D 61/48

Claims (1)

(57) [Claims] 1. A electrodialysis apparatus for treating waste water discharged from a wet flue gas desulfurization, the interlabial Anode, in order from the cathode side toward the anode side, 1 dianion permselective membrane (A1) / Multiple sets of ion exchange membranes with one set of / monovalent anion selective permeable membrane (A2) / cation exchange membrane (C1)
And two adjacent monovalent anion selective permeable membranes (A
1, A2) between the chloride solution chamber, the monovalent anion selective permeable membrane (A2) and the cation exchange membrane (C1) between the concentrated solution chamber, the cation exchange membrane (C1) and the monovalent anion selective permeation Membrane (A
1) a dilute solution chamber, a chloride solution chamber containing a cation chloride solution that reacts with sulfate ions to form a highly soluble salt, a concentrate solution, and a dilute solution chamber. An electrodialysis device for desulfurization wastewater treatment, characterized in that wastewater is circulated in each case.