JP3223311B2 - Treatment method of condensate and desalinated reclaimed water - Google Patents

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 condensate and desalinated reclaimed water in a thermal power plant and the like. More specifically, the present invention relates to a method for efficiently removing ammonium ions contained in condensed and desalinated reclaimed water and separating it as desalinated water. In addition, the present invention relates to a processing method capable of separating and recovering ammonia and other contained impurities.

[0002]

2. Description of the Related Art Condensation in thermal power plants
Usually, it is desalinated by a desalination unit and used in circulation. On the other hand, in the desalination apparatus, the ion exchange resin is periodically regenerated with an acid and an alkali. The wastewater at the time of this regeneration is called condensate demineralized regenerated water. The regenerated water generally contains ammonia nitrogen in an amount exceeding the environmental standard, and a part or most of the ammonia nitrogen is present in the liquid as ammonium ions. Conventionally, biological denitrification, ammonia emission, chlorination, evaporative concentration, and the like have been known as methods for reducing the amount of ammonia nitrogen in such condensate, desalinated and reclaimed water below environmental standards.

[0003]

However, it has been difficult for these methods to efficiently separate and recover ammonium ions as ammonia. Furthermore, the condensed demineralized regenerated water contains impurities such as SO ₄ ^2- ions, Na ⁺ ions, and Cl ⁻ ions as other components, and these impurities, ammonia, and reusable demineralized water are separately separated. Was difficult to separate. Therefore, an object of the present invention is to provide a method for treating condensed, desalinated, and reclaimed water that solves such a problem.

[0004]

According to the present invention, there is provided a method for treating condensate and desalinated regenerated water, which comprises subjecting condensed and desalinated regenerated water containing ammonium ions to electrodialysis, and separating a dilute solution containing reduced ammonium ions as desalinated water. In addition, the concentrated solution in which ammonium ions are concentrated is distilled under alkaline pH conditions to distill and separate ammonia, and the distillation residue is dried to separate solids.

[0005] In a preferred embodiment of the present invention, an acid is added to the condensed demineralized regenerated water to obtain an acidic condensed demineralized regenerated water, and the acid condensed demineralized regenerated water is subjected to electrodialysis. At that time, an acid is preferably added so that the pH of the condensed water and the regenerated water is 2 to 4. In another preferred embodiment of the present invention, in the electrodialysis of the condensed demineralized regenerated water containing ammonium ions from a thermal power plant, fixed particles having a particle diameter of 0.1 μm or more are previously obtained from the condensed demineralized regenerated water. Is removed. In still another preferred embodiment of the present invention, the liquid component discharged during drying is returned to the condensed demineralized regenerated water before electrodialysis. In still another preferred embodiment of the present invention, the ammonia separated by distillation is reacted with sulfuric acid and recovered as ammonium sulfate.

Next, the method for treating condensed, desalinated, and regenerated water of the present invention will be described in more detail. FIG. 1 is an example of a flow sheet for carrying out the treatment method of the present invention, wherein 1 is a pH adjustment tank, 1a is its agitator, 3 is a filter, 4 is a first electrodialysis device, and 5 is a second Electrodialysis machine, 6 is distillation machine, 7
Denotes a drying device, 8 denotes a cooling device, 9 denotes a reaction device, and 10 denotes a drying device. The number of electrodialyzers may be one depending on the case. The condensate and desalinated regenerated water a from a condensate and desalination regenerator (not shown) is mixed with the acid b added by the stirrer 1a in the pH adjustment tank 1 to adjust the pH to 4 or less, preferably about 2 to 4. Adjusted. Then, ammonium ions (NH ₄ ⁺ ions) which do not precipitate and other inorganic ions remain in the liquid. As the acid to be added, a mineral acid such as hydrochloric acid or sulfuric acid is preferable. It is preferable to remove the precipitate so that the concentration of the solid content remaining in the liquid is about 0.2 mg / liter.

Regenerated water from the pH adjusting tank 1 is sent by a pump 2 through a pipe c to a filter 3 provided as required. Generally, the dialysis performance of the dialysis membrane of the electrodialysis apparatus is reduced in proportion to the amount of iron oxide or solid particles present in the processing solution. According to the study of the present inventors, the solid particles in the condensate and desalinated reclaimed water from the thermal power plant are almost distributed in the range of 0.1 to 1.0 μm, and substantially 0.1 μm or less is present. Turned out not to be. 0.1 μm
By using a filter having a characteristic of effectively separating solid particles having the above particle diameter, it is possible to greatly extend the effective treatment time of the electrodialysis membrane while maintaining a high dialysis efficiency. In particular, thermal power plants are used for a long time, for example, once a year.
Since the operation can be stopped only once, it is extremely important to extend the effective treatment time of the condensed demineralized regenerated water including the electrodialysis membrane. A filter having such performance is preferably a middle-fiber membrane filter formed by bundling a large number of hollow fibers. The hollow fiber membrane filter is suitable as a filter used for the above purpose because the membrane area per unit volume can be extremely large, and the pore size of the membrane can be controlled precisely, and the membrane can be easily cleaned. .

FIG. 2 is a flow sheet showing an example of a hollow fiber membrane filter 11 as a filter 3 used in the present invention and a peripheral device for cleaning the same. The hollow fiber membrane filter 11 includes a container 12, a partition plate 13 provided therein, and a hollow fiber module 14 supported by the partition plate 13. The lower side of the partition plate 13 is the primary side of the filter, and the upper side is the secondary side of the filter. The regenerated water introduced from the pipe c is filtered from the outside to the inside of the hollow fiber membrane and discharged from the pipe d. The pressure difference between the inside and outside of the hollow fiber membrane during the filtration of the regenerated water is monitored by the differential pressure gauge 15. AO, MO in the figure
And DO are on-off valves such as solenoid valves, air-driven valves, and manual valves, and are used for cleaning the hollow fiber module 14, etc., and these are opened and closed by a signal from a control device (not shown) or manually. Is done. A during reclaimed water filtration
Close O, DO and open MO. Close MO and AO for cleaning
Is opened, the pressurized air supplied by the pipe 1 is supplied into the container 12 through the air filter 16, the pipe m, and the pipe n.

[0009] The air from the pipe m passes from the inside to the outside of the hollow fiber membrane, and blows off solid particles attached to the membrane holes to the primary side of the filter to be washed off. At this time, the hollow fiber module 14 is vibrated by the air from the pipe n to promote the cleaning. The air in the container 12 is discharged from the pipe o to the outside. The on-off valve DO is for discharging the reclaimed water in the container 12 from the pipe q, and can be operated prior to washing. At this time, the discharge can be performed more smoothly by opening the on-off valve of the AO on the right side in the drawing. Usually, two or more hollow fiber membrane filters 11 are provided in parallel, and one of the hollow fiber membrane filters 11 is configured to continue the treatment of regenerated water by another hollow fiber membrane filter 11 during washing.

In FIG. 1, regenerated water from which solid particles have been removed by a filter 3 flows into a dilution side 4 a of a first electrodialysis apparatus 4 through a pipe d. First electrodialysis device 4
The regenerated water from which a certain amount of ammonium ions and other inorganic ions have been reduced by the electrodialysis treatment flows into the dilution side 5a of the second electrodialysis device 5 through the pipe e, and the ammonium ions and the other ions are reduced by the electrodialysis treatment. Other inorganic ions are further reduced. Regenerated water from the second electrodialysis device 5 is discharged through a pipe i,
Reused or released out of the system. Second electrodialysis device 5
Supply water is supplied to the concentration side 5b of the first electrodialysis apparatus 4 by a pipe g, and concentrated water of ammonium ions and other inorganic ions flowing out therefrom is supplied to the concentration side 4b of the first electrodialysis apparatus 4 by a pipe g. Is flowed in.

Next, FIG. 3 is a schematic view for explaining the principle of electrodialysis. For example, an anode plate 17 formed by platinum plating a titanium plate and a cathode plate 1 formed of a stainless steel plate
8, anion exchange membranes A and cation exchange membranes C are alternately arranged. As the anion exchange membrane A, for example, a quaternary ammonium salt as an ion exchange group is 1.5 to 3.0.
A styrene / divinylbenzene copolymer-based membrane containing (meq / g dry resin) is used. As the cation exchange membrane C, for example, a sulfonic acid group as an ion exchange group is 1.5 to 1.5%.
A styrene / divinylbenzene copolymer film containing 3.0 (meq / g dry resin) is used.

The logarithm of these ion-exchange membranes varies depending on the concentration of ammonia contained in the condensate water, but is generally 20
About 0 to 600 pairs are used. When sulfuric acid is used as the acid as described above, for example, as shown in FIG. 3, ammonium ion (NH ₄ ⁺ ion) and sulfate ion (SO ₄ ^2- ion) are generated by an electric field formed between the negative electrode and the positive electrode. Electrophoresis. Cations such as ammonium migrate toward the cathode plate 18, pass through the cation exchange membrane C and enter the concentration side, and then try to migrate toward the cathode plate 18, but are blocked by the anion exchange membrane A. Remains in the concentrate. On the other hand, sulfate ions migrate toward the anode plate 17, pass through the anion exchange membrane A, enter the concentration side, and then try to migrate toward the anode plate 17, but are blocked by the cation exchange membrane C, and concentrate. Remains inside. Thus, ammonium ions and sulfate ions in the concentrate are removed from the electrodialysis apparatus by the concentrate, which is a moving medium. An anolyte solution and a catholyte solution are allowed to flow near the anode 17 and the cathode 18, respectively.

Referring again to FIG. 1, the first electrodialysis device 4
The concentrated water flowing out of the enrichment side 4b flows into the distillation apparatus 6 through the pipe f. As the distillation device 6, for example, a distillation column or a stripper device can be used. The concentrated water that has flowed into the distillation device 6 is subjected to pH adjustment by an alkali source, for example, caustic soda (NaOH) supplied by a pipe j.
Is made alkaline, especially highly alkaline, and a part thereof is distilled (or stripped). By distilling the pH under alkaline conditions, ammonium ions present in the liquid can be efficiently separated as high-concentration ammonia. This was confirmed by the following experiment. That is, first, a predetermined amount of a solution containing ammonium ions was placed in a flask, and the pH was adjusted as shown in Table 1.
Caustic soda (NaOH) was added to obtain a value as shown in FIG. Next, the pipe was led out from the mouth of the flask, connected to the distillate reservoir through a cooler, and the flask was heated by an electric heater. At predetermined intervals, the ammonium ion concentration in the flask and the amount of liquid accumulated in the distillate reservoir were determined. The amount of ammonium ions is calculated from the above, and the amount of distillate is calculated as the ammonium ion removal rate (%) based on the amount of ammonium in the flask at the beginning (the ratio of the amount of distillate with the initial amount of liquid in the flask being 100 is expressed as%). Each time was measured. The results are shown in Table 1 below.

[0014]

[Table 1]

FIG. 4 is a curve showing, based on the results in Table 1, the removal rate of ammonium ions from the liquid by distillation separation, using the pH value as a parameter. From the experimental data, the distillation conditions in the distillation apparatus 6 were pH 10 or more,
In particular, it is understood that the pH is preferably about 11 to 13. The component distilled from the distillation apparatus 6 through the pipe 1 can be cooled by a cooling device (not shown) and recovered as ammonia water. In this example, the component is introduced into the reaction apparatus 9, where sulfuric acid supplied from the pipe k is added. The reaction is made into an ammonium sulfate solution. The ammonium sulfate solution flowing out of the reaction device 9 is introduced by a pipe r into a drying device 10 such as a centrifugal thin film dryer using steam as an energy source. The ammonium sulfate solution introduced into the drying device 10 is dried here, and the evaporated component flows out of the pipe s connected to the pipe i and becomes a part of demineralized water,
Ammonium sulfate, which is a solid content, is discharged out of the system from the pipe t and is used as fertilizer. In order to more efficiently liquefy the evaporated components flowing out of the pipe 1, a cooling device may be provided in the middle of the pipe 1. Since the structure and operation of the above-described centrifugal thin film dryer are well known, a detailed description thereof will be omitted.

The liquid component substantially free of ammonium ions discharged from the distillation device 6 through the pipe u is introduced into the drying device 7 and dried. As the drying device 7, a centrifugal thin film dryer similar to the drying device 10 can be used.
The moisture in the liquid is evaporated to about several% by the drying device 7,
The evaporating component flowing out of the pipe v is cooled and liquefied by the cooling device 8 and returned to the pipe d to the first electrodialysis apparatus 4 by the pipe w. The liquid introduced into the drying device 7 is neutralized with a mineral acid, preferably sulfuric acid, supplied through a pipe m. On the other hand, solids discharged from the drying device 7 through the pipe x are discharged to the outside of the system, and components such as Na ₂ SO ₄ and NaCl useful as raw materials for glass production, for example, are contained in the solids. It is included and can be used effectively.

[0017]

Next, an embodiment of the present invention implemented by a process configured as shown in the flow sheet of FIG. 1 will be described. Condensate and desalinated reclaimed water from a thermal power plant at 140 T / day from pipe a
The solution was supplied to the H adjusting tank 1 and the pH was adjusted to 3 by adding sulfuric acid. SS (suspended solid matter) in reclaimed water whose pH has been adjusted
Was contained at 20 ppm. In the reclaimed water, NH ₄ ⁺ ions are contained as other components at 1,130 ppm and SO ₄
2,050 ppm of ^2- ion, 2,440 p of Na ⁺ ion
pm, Cl ^- contains ions 40 ppm, TDS was 11,660Ppm.

The pH-adjusted regenerated water is then introduced into a filter 3 constructed as shown in FIG. 2 to remove solid particles having a particle size of 0.1 μm or more to reduce SS to 0.2 ppm.
The electrodialysis treatment was performed by sequentially passing through the first electrodialysis device 4 and the second electrodialysis device 5. The effective membrane areas of these electrodialysis treatment devices 4 and 5 are 36.8 dm / pair, the number of incorporated membranes is 200, the membrane surface flow rate is 14 cm / s, and the current densities are 2.9 A / dm ² and 0.8 A, respectively. / Dm ² . Also, 7.3 m ³ / day of makeup water was supplied from the pipe p. The regenerated water discharged from the pipe i after the electrodialysis treatment was 137 m ³ / day, and its NH ₄ ion was 5 pp.
m and TDS were 150 ppm.

On the other hand, the concentrated water from the pipe f is 10 m ³ / day, its NH ₄ ion is 15,700 ppm, and TD
S was 161,200 ppm. PH of this concentrated water
After setting to 11, it was introduced into the distillation apparatus 6 and distilled. The distillate from the distillation apparatus 6 was 2 t / day, and the content of ammonium ions was about 98% of the amount of ammonium ions in the concentrate. This distillate component was introduced into the reactor 9 to react with sulfuric acid, and was introduced into the drying device 10 as an ammonium sulfate solution. Then, it was dried by the drying device 10 to obtain a steam component of 3.9 T / day and an ammonium sulfate powder of approximately 600 kg / day. The residual liquid discharged from the distillation device 6 to the drying device 7 is 8 T / day. After neutralization treatment in sulfuric acid, the remaining liquid is dried by the drying device 7 to obtain a vapor component of 7 T / day and approximately 1100 kg / day of Na _2.
It was isolated as a solid consisting of 99.5% SO _{4 and} 0.5% NaCl. In this example, 150
Although the continuous operation was performed for a long time, there was no trouble on the apparatus including the electrodialysis apparatus, and the effectiveness was proved.

[0020]

According to the present invention, when treating condensed demineralized regenerated water containing ammonium ions in a thermal power plant or the like, the condensed demineralized regenerated water is first subjected to electrodialysis to efficiently use reusable demineralized water as a diluent. Then, the concentrated solution is distilled under alkaline conditions to efficiently separate ammonium ions as a high ammonia concentration component, and the distillate residue is dried to separate other impurities as solids. Therefore, the reusable demineralized water, ammonia component, and other impurities present in the condensed demineralized regenerated water can be separated efficiently and with low energy consumption. According to the treatment method of the present invention, ammonium ions are separated and recovered from the condensed demineralized regenerated water to be processed, reusable demineralized water is separated and recovered, and other impurities are separated and recovered as solids. By doing so, it is possible to achieve no drainage and no waste. Further, when the ammonium component is reacted with sulfuric acid to form an ammonium sulfate solution, which is dried and recovered as ammonium sulfate powder, the concentration of ammonia obtained as a distillation component is high, so that the energy required for drying can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a flow sheet for implementing the processing method of the present invention.

FIG. 2 is a flow sheet showing an example of a filter that can be used in the present invention.

FIG. 3 is a schematic diagram shown for explaining the principle of electrodialysis in the present invention.

FIG. 4 is a curve showing the removal rate of ammonium ions from a liquid by distillation separation, using alkaline values as parameters.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 pH adjustment tank 1a Stirrer 2 Pump 3 Filter 4 First electrodialysis device 5 Second electrodialysis device 6 Distillation device 7 Drying device 8 Cooling device 9 Reaction device 10 Drying device 11 Hollow fiber membrane filter 12 Container 13 Partition plate 14 Hollow fiber module 15 Differential pressure gauge 16 Air filter 17 Anode 18 Cathode A Anion exchange membrane C Cation exchange membrane AO On-off valve MO On-off valve DO On-off valve

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI C01C 1/24 C01C 1/24 H C02F 1/04 C02F 1/04 C 1/469 1/46 103 (72) Inventor Yasuo Murayoshi Tokyo 3-7-1, Nishishinbashi, Minato-ku Toshiba Plant Construction Co., Ltd. (72) Inventor Hiroshi Kobayashi 2-1-2, Marunouchi, Chiyoda-ku, Tokyo Asahi Glass Co., Ltd. (72) Inventor Shiro Fukui Marunouchi, Chiyoda-ku, Tokyo 2-1-2 1-2 Asahi Glass Co., Ltd. (56) References JP-A-7-80254 (JP, A) JP-A-2-169090 (JP, A) JP-A-7-88477 (JP, A) JP 54-119757 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C02F 9/00, 1/46 B01D 61/44

Claims (6)

(57) [Claims] 1. A method for electrodialyzing condensed and demineralized regenerated water containing ammonium ions to separate a dilute solution containing reduced ammonium ions as demineralized water and to convert a concentrated solution containing ammonium ions into alkaline pH conditions. A method for treating condensed, desalinated, and reclaimed water, comprising distilling off ammonia by distillation under reduced pressure, drying the distillation residue, and separating solids. 2. The method for treating condensed and desalinated regenerated water according to claim 1, wherein an acid is added to the condensed and desalinated regenerated water to obtain an acidic condensed and desalinated regenerated water, and the acidic condensed and desalinated regenerated water is subjected to electrodialysis. 3. The method according to claim 2, wherein an acid is added so that the pH of the condensed demineralized regenerated water becomes 2 to 4. 4. The electrodialysis of condensed demineralized regenerated water containing ammonium ions from a thermal power plant,
3. The method for treating condensed and desalinated regenerated water according to claim 1 or 2, wherein solid particles having a particle size of 0.1 μm or more are removed from the condensed and desalinated regenerated water in advance. 5. The method according to claim 1, wherein the liquid component discharged during drying is returned to the condensed water and desalinated regenerated water before electrodialysis.
Or 2) a method for treating condensed and desalinated regenerated water. 6. The method for treating condensed demineralized regenerated water according to claim 1, wherein the ammonia separated by distillation is reacted with sulfuric acid and recovered as ammonium sulfate.