JPS6251146B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing corrosion products mainly consisting of iron compounds such as iron oxide, that is, crud adhering to ion exchange resins.

When crud adheres to the ion exchange resin, not only does its exchange capacity decrease, but iron content constantly leaks out and the quality of treated water deteriorates. To avoid this situation, for example, in condensate desalination equipment at thermal power plants, crud removal treatment (hereinafter referred to as ``iron removal regeneration treatment'') is performed when the amount of crud adhesion exceeds approximately 500 mg/-RasFe. ing.

Conventionally, various iron removal and regeneration agents have been proposed and put into practical use for iron removal and regeneration treatment, but they have the following major problems.

That is, as explained below using a condensate desalination apparatus as an example, for example, a reducing agent such as hydrosulfite, sulfite, bisulfite, hydrazine salt, etc. is brought into contact with an ion exchange resin to reduce the crud adhering to the resin. By doing so, it is removed as a soluble substance. At this time, in addition to these reducing agents, we also adjust the resin ion type, adjust the processing liquid PH,
Add salt or other substances to remove organic matter, etc.
Since salts, alkalis, and acids containing Na, K, CL, SO ₄ , etc. are used together, the cation exchange resin may be Na type or anion exchange resin after iron removal regeneration treatment, depending on the salts contained in the iron removal regeneration agent used. The resin turns into a salt type such as Cl type.

In condensate desalination equipment, the resin that has been converted into salt type is a major obstacle to carrying out the ammonia cycle, so almost 100% of the resin must be removed.
In the near future, cation exchange resins will need to be converted to H type or _NH4 type, and anion exchange resins will need to be converted to OH type.
A large amount of regenerating agent is required to regenerate these salt type resins.

For example, cation exchange resin (porous strong acid cation exchange resin) with 80% converted to Na type
Even when regenerated with 10 eq/-R of H ₂ SO ₄ , 1% Na type remains, and it is almost impossible to reduce the Na type to less than 0.1%, which is necessary to carry out an ammonia cycle. In addition, it is more difficult to convert anion exchange resins (porous type, I-type strongly basic anion exchange resins) to OH type, and converting 100% Cl type resin to 10 eq/-R of NaOH
Even if it is regenerated, about 25% remains, and it is impossible to reduce the amount of Cl leakage to below 3%, which is required to reduce the amount of leakage to below 1.5 ppb.

As described above, in the conventional iron removal regeneration treatment method, a large amount of salt remains after regeneration, and when the ammonia cycle that is currently used in thermal power plants is implemented, a large amount of Na and Cl leaks. Therefore, the resin after iron removal regeneration treatment cannot be subjected to an ammonia cycle immediately, but is subjected to an H-OH cycle for 5 cycles or more, and for about 1 month or more, and then an ammonia cycle is carried out after the salt content has decreased. The reality is that the situation is shifting.

The present invention eliminates the drawbacks of such conventional methods,
It is an object of the present invention to provide a method that can extremely effectively perform iron removal regeneration treatment and also smoothly perform the subsequent regeneration process and water sampling process.

The present invention provides iron removal and regeneration of ion exchange resins, which is characterized in that when iron is removed and regenerated from ion exchange resins with crud attached, the resins are treated with a solution containing oxalic acid and/or oxalate, and then passed through with an inorganic acid. It's a method.

Hereinafter, the present invention will be explained in detail using a condensate desalination device as an example. Clads attached to the ion exchange resin of the condensate desalination device are composed of approximately magnetic iron oxides (Fe ₃ O ₄ and γ-Fe ₂ O ₃ ), α−Fe ₂ O ₃ , γ−
It is divided into FeOOH, α-FeOOH and amorphous. In thermal power plants, magnetic iron oxide, γ-FeOOH,
It is said that the three main types are amorphous. Furthermore, the morphology of the cladding attached to the resin is said to be different between cationic and anionic resins, but the details are currently unknown.

However, as a result of intensive research into iron removal regeneration methods using resin chemicals actually used in thermal power plants, the present inventors found that oxalic acid and oxalate have a great effect on iron removal regeneration from cation exchange resins. The present invention has been completed by discovering that

In other words, when a cation exchange resin is treated with oxalic acid (salt), the clad becomes ferrous oxalate, and since this compound has low solubility, only a small amount of iron is eluted into the treated supernatant, but oxalic acid (salt) After treatment, the ferrous oxalate that has precipitated or adhered to the resin is completely removed by passing an inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid through the resin.
70%, and more than 90% with hydrochloric acid, which is significantly more effective than conventional methods. In addition, treatment with a mixture of oxalic acid (salt) and an inorganic acid, rather than using oxalic acid (salt) alone, and then passing through the inorganic acid has an even greater iron removal effect. Even if the mixed waste liquid with acid is reused, there is a sufficient effect.

In contrast to the conventional method, in which the cladding is removed as a soluble compound at once by the action of a reducing agent, in the method of the present invention, a compound with low solubility such as ferrous oxalate is removed, and then an inorganic acid is used to regenerate the cladding. , is characterized by the removal of these. The precipitated ferrous oxalate is treated with an inorganic acid (regenerating agent), for example, sulfuric acid and the concentration adjusted to 4-8%, at SV2-4 for 1 part cation exchange resin.
It can be completely dissolved and removed by passing 200 to 400 times, and after passing sulfuric acid, ferrous oxalate does not precipitate and remain, causing no problems with subsequent water sampling.

As mentioned above, it is very preferable that the ion type of the resin is maintained in the H type or OH type even after iron removal regeneration treatment, but in the present invention, by using oxalic acid and inorganic acid, the cation exchange resin can be changed to the salt type. The conversion of iron is completely avoided, and the iron removal effect is also greater than that of conventional methods.
Oxalates such as sodium oxalate and potassium oxalate have the same iron removal effect as oxalic acid. The oxalic acid (salt) used in the present invention does not generate harmful sulfur dioxide gas during treatment, unlike hydrosulfite, sulfite, etc. used as conventional iron removal and regeneration agents.
Extremely easy to handle.

On the other hand, for anion exchange resins, the effect of iron removal by oxalic acid (salt) is not as great as that for cation exchange resins. This is probably due to the fact that the morphology of the attached crud is different between the two. Therefore, conventional iron removal and regeneration agents may be used for the anion exchange resin, if desired.
In this case, the anion exchange resin is usually in the Cl type after treatment because common salt is used to remove organic matter and adjust the ionic type. Even if regeneration is performed in the Cl type, it is difficult to reduce the Cl type to 3% or less, which is required for ammonia cycle operation, as described above. Therefore, an inorganic acid (especially sulfuric acid in this case) is used to remove iron and regenerate the cation exchange resin.
The anion exchange resin is converted to the easily regenerated SO ₄ type by passing it through a cation exchange resin and an anion exchange resin in that order, and then OH with caustic soda.
It is preferable to make it into a mold. In this case, the regeneration level of caustic soda is sufficient at 2 to 3 times the normal amount.
Although some SO ₄ type remains, SO ₄ remains even during the ammonia cycle.
Because it is difficult to leak, it can be transferred directly to the ammonia cycle.

Next, an embodiment of the present invention will be described with reference to FIG.

(1) After transferring the resin from the demineralization tower (not shown) to the cation regeneration tower/separation tower (hereinafter abbreviated as "CRT") 1, a normal backwash separation operation is performed and the anion exchange resin is transferred to the anion regeneration tower. (hereinafter abbreviated as "ART") 2, open the valve 3 of the transfer line and transfer.

(2) After completion of transfer, transfer oxalic acid saturated solution tank 4 to CRT1
Then, 1 to 20 g of oxalic acid is injected to 1 part of the cation exchange resin using the ejector, and the concentration is 0.5 to 1.
Adjust the dilution to 8%. Additionally, if necessary, inorganic acid with a concentration of 0.5 to 15% is injected from the normal regeneration line. Then, valve 7 is opened to introduce air, and air scrubbing is performed for 5 to 10 minutes to mix the resin. Then air scrub for 1 to 2 minutes every 30 minutes and leave it for 30 minutes to 5 hours. The ionic type of the cation exchange resin at this time is H
It does not matter if it is a type or _NH4 type. The higher the concentration of oxalic acid, the more appropriate it is 1-4%, and the iron removal effect will be greater if the concentration of inorganic acid is also set higher, 4-10%.

(3) Regarding ART2, the conventional iron removal regeneration agent will be used for treatment. Normal table salt and iron removal regeneration agent are added.

(4) Extrude both CRT1 and ART2 after leaving them for a certain period of time, then add 4 to 10% inorganic acid (in the case of sulfuric acid, 2 to 3 times the normal regeneration level) to CRT1.
200 to 400 g/-Ras66°Be'H ₂ SO ₄ ) is passed through a normal regeneration line at SV3 to 4. The regenerated waste liquid at this time is
Open valve 8 to allow the medicine to pass through ART2, and open valve 8 to discharge the medicine. Next, extrusion and washing are performed. With the operations up to this point, iron removal and regeneration of the cation exchange resin of CRT1 is completed. The anion exchange resin of ART2 becomes Cl type once due to iron removal regeneration treatment.
By passing the H ₂ SO ₄ regenerated waste liquid from CRT1, it is converted to SO ₄ type.

(5) ART2 is further regenerated by passing 2 to 3 times the amount of caustic soda at the normal regeneration level.

In this way, in the illustrated example, by passing the regenerated waste liquid from CRT1 through the conventional regenerator to ART2, there is no generation of salt types such as Na type in the cation exchange resin after iron removal and regeneration, and anion exchange The resin is also converted to the OH type, and although some SO ₄ type remains, it has no effect and can be transferred to the ammonia cycle as is.

Next, examples of the present invention will be described.

EXAMPLE When the iron removal regeneration treatment of the present invention was applied to a cation exchange resin that had been used for five years at a thermal power plant, the results shown in FIGS. 2 and 3 were obtained. FIG. 4 shows the results of treatment with inorganic acid only.

Figure 2 shows a mixture of oxalic acid with a concentration of 4% and sulfuric acid with a concentration of 8% so that the amount of treated liquid for cation exchange resin 1 is 100 g of oxalic acid and 200 g of H ₂ SO ₄ .
After treatment for a period of time, each inorganic acid (4 types) at a concentration of 8% was added.
The results are shown when administering the drug using SV3. H ₂ SO ₄ (1) shows the effect when treated with a new mixed solution, and H ₂ SO ₄ (2) shows the effect when the mixed solution is recovered and reused. The conventional method is said to be the most effective method, in which H ₂ SO ₄ is passed through treatment after treatment with a conventional iron removal regeneration agent, that is, one mainly composed of sulfur oxides.

Figure 3 shows the case where the sample was treated with a 4% oxalic acid solution for 5 hours and then passed through with an inorganic acid. It can be seen from FIGS. 2 and 3 that the method of the present invention has a 20 to 30% greater iron removal effect than the conventional method. The broken lines in Figures 2 and 3 indicate oxalic acid.
The iron removal effect by sulfuric acid mixture and the iron removal effect by oxalic acid are shown respectively. In the conventional method, the iron removal regeneration agent dissolves the crud and turns it into an ionic form, and this ionic iron is ion-exchanged with a cation exchange resin, and this ion-exchanged iron can be desorbed using an inorganic acid. It is considered that the effect of the conventional method is small because it is quite difficult. In the method of the present invention, the cladding is attached to the resin as a precipitate such as ferrous oxalate due to the action of oxalic acid, so the proportion of the clad in ionic form is lower than in the conventional method, and therefore the cladding is strongly ion-exchanged with the cation exchange resin. It is thought that the iron removal effect is greater than that of the conventional method because there is less iron removal.

In the method of the present invention, when hydrochloric acid is used, an iron removal effect of 90% or more can be obtained. The same effect as shown in FIG. 2 was also obtained when sodium oxalate was used as the oxalate. Furthermore, from FIG. 2, it was found that repeated use of a mixed solution of oxalic acid and H ₂ SO ₄ was sufficiently effective. FIG. 3 shows the case of treatment with oxalic acid alone, which is slightly inferior to the case of treatment with the mixed solution shown in FIG. 2, but the iron removal effect is greater by 5 to 10% in the case of H ₂ SO ₄ than in the conventional method.

The exchange capacity was measured for both the cation exchange resin treated with sulfuric acid shown in Figure 2 and the anion exchange resin immersed in the same mixed solution for 7 days and regenerated with caustic soda, and no decrease was found at all. In addition, when condensate was treated in a mixed bed of both resins, the treated water had an electrical conductivity of 0.055 to 0.06.
μS/cm was obtained, and it was confirmed that the resin was not deteriorated by the method of the present invention.

As mentioned above, according to the method of the present invention, the iron removal regeneration effect is significantly greater than that of the conventional method, and when sulfuric acid is used as a regenerating agent, the regeneration level is twice the normal amount (approximately 300 g/- Although it is less than 50% even when Ras CaCO ₃ ) is used, the method of the present invention has a reduction of 70%.
% removal rate can be obtained. In this way, the method of the present invention is not only highly effective in terms of regenerating iron removal, but also does not become salt-type after treatment operations, unlike conventional methods.
This iron removal regeneration method is very convenient for subsequent regeneration and water sampling, and the benefits are great. The present invention is not only useful for condensate desalination equipment, but can also be effectively applied to cleaning crud-adhered pure water equipment, powdered ion exchange resins, and other crud-adhered fillers.

[Brief explanation of the drawing]

Fig. 1 is a flow sheet showing an embodiment of the present invention, and Figs. 2 to 4 are graphs showing the results of an embodiment of the present invention, which show the correspondence between iron removal regeneration conditions and iron removal efficiency. be. 1...Cation regeneration tower/separation tower (CRT), 2...
...Anion regeneration tower (ART), 3, 5, 7, 8...
Valve, 4... Oxalic acid saturated solution tank, 6... Medication line.

Claims (1)

[Scope of Claims] 1. An ion-exchange resin that is characterized in that, when regenerating iron removal from an ion-exchange resin to which crud is attached, the resin is treated with a solution containing oxalic acid and/or oxalate, and then passed through with an inorganic acid. Iron removal regeneration method. 2. The liquid containing oxalic acid or oxalate contains oxalic acid and/or oxalate.
Or the method according to claim 1, which is a mixed solution of oxalate and an inorganic acid. 3. When the ion exchange resin to which the crud is attached is a mixed resin of a cation exchange resin and an anion exchange resin, a patent claim in which the mixed resin is separated into individual columns and then an iron removal regeneration operation is performed on the cation exchange resin. The method according to item 1 or 2 of the scope. 4. The method according to claim 3, wherein the inorganic acid discharged liquid after being passed through the anion exchange resin in the iron removal regeneration operation for the cation exchange resin is passed through the anion exchange resin.