JPS6255898B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for removing crud adhering to ion exchange resins, that is, corrosion products mainly composed of iron compounds such as iron oxide. The purpose of this is to provide a removal method suitable for operation (hereinafter referred to as "iron removal regeneration method"). When crud adheres to the ion exchange resin, not only does the exchange capacity decrease, but the crud permanently leaks out, deteriorating the quality of treated water. A particular problem arises when crud adhesion occurs in condensate desalination equipment for purification systems used in thermal power plants and nuclear power plants. The crud that adheres to the ion exchange resin of the condensate desalination equipment is magnetic iron oxide (Fe ₃ O ₄ +γ−
Fe ₂ O ₃ ), α−Fe ₂ O ₃ , γ−FeOOH, α−FeOOH
It is roughly divided into amorphous and amorphous. It is said that the three main materials used in thermal power plants are magnetic iron oxide, γ-FeOOH, and amorphous. Since the cation exchange resin is regenerated with H ₂ SO ₄ , HCl, etc. each time it is regenerated, the amount of attached crud is often less than 500 mg/-RasFe. However, in anion exchange resin,
Adhering crud is difficult to remove with regenerant (caustic soda) and gradually accumulates to 1000-1500mg/
−RasFe may be reached in some cases. The form of the attached cladding is said to differ depending on the cation exchange resin and anion exchange resin, but the details are unknown. In boiling water nuclear power plants, the proportion of α-Fe ₂ O ₃ is large, and most of the crud is removed by cation exchange resin, and the amount of crud deposited by the cation exchange resin is 10,000 to 30,000 mg/-RasFe.
In some cases, it can reach . Although the proportion of crud adhering to anion exchange resin is extremely small, it gradually accumulates as in the case of thermal power plants. As the amount of crud adhesion increases as described above, the leakage of crud into the treated water also increases constantly. Even if backwashing or air scrubbing is performed frequently, only a small percentage of these deposited crud can be removed. Currently, at thermal power plants, when the amount of crud deposits exceeds 500 mg/-RasFe, iron removal regeneration treatment is performed using chemicals (iron removal regeneration agents), and substances mainly composed of sulfur oxides, such as hydrosulfite, Na ₂ SO ₃ , NaHSO ₃ or the like is brought into contact with an ion exchange resin to reduce the adhering crud and remove it as soluble iron. The conventional general iron removal regeneration treatment process is as follows. (1) Otion exchange resin for resin ion type adjustment,
NaCl is added to the anion exchange resin in the same column to form Na-type and Cl-type, respectively. (2) A solid reducing agent is introduced through the manhole and the reduction process is carried out for several hours. At this time, the pH is strictly adjusted using caustic soda, H ₂ SO ₄ , or HCl.
This is to prevent a large amount of sulfur dioxide gas from being generated if the method goes to the acidic side, and also to prevent the iron removal effect from becoming quite small if the method goes to the alkaline side. After the ion exchange resin and the reducing agent are brought into contact for several hours, extrusion and washing are performed. In this step, the crud is eluted from the resin into the liquid as soluble iron and removed. (3) Backwash the mixed resin and separate the cation exchange resin.
Anion exchange resins are regenerated with H ₂ SO ₄ and HCl at two to three times the normal regeneration level, respectively. However, this iron removal regeneration method has the following drawbacks. (a) Reducing agents mainly composed of sulfur oxides are unstable and cannot be stored as a solution and are handled in solid form, which requires opening and closing of the manholes in the regeneration tower, resulting in poor workability. In addition, a large amount of sulfur dioxide gas is generated especially during dissolution or pH adjustment, which poses a considerable problem during work. (b) If the cation exchange resin and anion exchange resin are treated at the same time, the iron ions peeled off and reduced from the anion exchange resin in step (2) above will undergo ion exchange with the cation exchange resin, and will be subjected to the reduction treatment instead. The amount of iron in the cation exchange resin increases compared to before, and a large amount of inorganic acid is required to remove it, and the iron removal effect becomes smaller. (c) Because the NaCl treatment is carried out to specifically convert Na and Cl types, Na
A large amount of type and Cl type remains, and when an ammonia cycle is performed in subsequent water sampling, a large amount of
Na and Cl leaks occur. To avoid this, H
- After operating on the -OH cycle and seeing a decrease in Na type and Cl type, the system was shifted to the ammonia cycle. In other words, subsequent operation is severely restricted by the iron removal regeneration process. In boiling water nuclear power plants, iron removal regeneration agents containing reducing agents, which are used in thermal power plants, are not used for treatment. This is because ions such as Na, K, Cl, and SO ₄ contained in the iron removal regenerating agent form salt types such as Na type and Cl type, so a large amount of regenerating agent is required to regenerate the salt type, resulting in a large amount of recycled waste liquid. This is because it is difficult to achieve treated water quality that is stricter than that at thermal power plants due to the amount of Cl leaking. Currently, cladding removal by ultrasonication is being experimentally performed, but its effectiveness is small, and further long-term research is required before it can be put to practical use. The present inventors conducted intensive research on an effective iron removal regenerating agent that eliminates the above drawbacks, mainly targeting ion exchange resins used in actual condensate desalination equipment at thermal power plants.As a result, oxalic acid, It has been discovered that iron removal regeneration can be effectively achieved by using a reducing agent and an inorganic acid. In other words, (1) Oxalic acid alone has no effect on cation exchange resins.
An iron removal rate of 30 to 40% can be obtained, but the iron removal rate is small and less than 10% for anion exchange resins. (2) A mixed solution of oxalic acid and inorganic acid is more effective than oxalic acid alone, showing an iron removal rate of 40 to 50% compared to cation exchange resin. However, like (1), it has little effect on anion exchange resins. (3) After treatment with oxalic acid or a mixture of oxalic acid and an inorganic acid, the cation exchange resin is treated with 70 to 80% H ₂ SO ₄ by passing with an inorganic acid.
More than 90% can be removed with HCl and HNO ₃ . However, similar to (1) and (2), the effect on anion exchange resins is small. The reason why the iron removal effect of the anion exchange resin is insufficient is that the cation exchange resin and the anion exchange resin have considerably different forms of the cruds attached to them. The present inventors conducted further experiments to find an anion exchange resin that has an iron removal effect, and obtained the following results. (4) Using L-ascorbic acid or erythorbic acid as a reducing agent, the anion exchange resin is treated with a mixture of this reducing agent, oxalic acid, and an inorganic acid for 10 hours to several days, and then passed through the inorganic acid. The iron removal rate is over 90%. (5) Using even stronger reducing agents Na ₂ SO ₃ and NaHSO ₃ and treating with a mixture of these reducing agents and oxalic acid or a mixture of these and an inorganic acid for several hours, and then passing the inorganic acid through. , the iron removal rate of anion exchange resin is over 90%. (6) Cation exchange resins can also be treated with a mixture of oxalic acid and a reducing agent or a mixture of oxalic acid, a reducing agent, and an inorganic acid, and then passed through with an inorganic acid to improve the iron removal rate. Even if the acid is H ₂ SO ₄
It will be 80-90%. (7) In the above treatment, the effect remains the same even if oxalate is used instead of oxalic acid and L-ascorbate or erythorbate is used as the reducing agent. The present invention was completed based on the above basic findings. That is, in the present invention, a mixture of at least one of oxalic acid and oxalate and a reducing agent, or a mixture of at least one of oxalic acid and oxalate, a reducing agent, and an inorganic acid is used for several tens of minutes to several days. After the treatment, the adhering crud is removed by passing an inorganic acid through the treatment. In contrast to the conventional method, in which the soluble crud is removed at once by the action of a reducing agent, the present invention converts the crud into a compound with low solubility, such as ferrous oxalate, and then removes the crud with an inorganic acid. It dissolves and removes compounds. When the ion exchange resin of the condensate desalination apparatus is subjected to iron removal regeneration treatment using the present invention, it is carried out as follows. If the resin to be treated is a cation exchange resin,
It is preferable to use a reducing agent that is not in a salt form, for example, an acid form such as L-ascorbic acid or erythorbic acid, so that it does not become a salt form during the iron removal regeneration process. After treatment with a mixed solution of acid and H ₂ SO ₄ (H ₂ SO ₄ is preferred as the inorganic acid when operating an ammonia cycle) for more than ten hours to several days, H ₂ SO ₄ is passed through. In this way, the cation exchange resin is regenerated to remove iron without turning into salt form at all. On the other hand, when treating an anion exchange resin, it is impossible to prevent it from turning into a salt form, so it is limited to at least one of oxalic acid and oxalate, an inorganic acid, and the above acid form as a reducing agent. Salt forms such as Na ₂ SO ₃ , NaHSO ₃ , L-ascorbate, and erythorbate may also be used. When Na ₂ SO ₃ or NaHSO ₃ is used, an iron removal rate of 90% or more can be obtained by controlling the pH of the mixed solution to 2 or less, treating it for several tens of minutes to several hours, and then passing it through with an inorganic acid. However, sulfur dioxide gas is generated during processing, so care must be taken when handling it. In addition, in the conventional method, Na ₂ SO ₃ , NaHSO ₃
Even when using iron, the iron removal rate is low, less than 50%. When using L-ascorbic acid or its salts, or erythorbic acid or its salts, their reducing power is weak, so
It is preferable to perform the treatment with the mixed solution for several hours to several days. The mixed solution of both cation exchange resin and anion exchange resin contains at least one of oxalic acid and oxalate.
0.1-8% (1-160g/-R), reducing agent 0.1-8%
10% (1-200g/-R), 0.5-15% inorganic acid
The mixture is mixed and dissolved so that the reducing agent is mixed and dissolved, and the mixture is stirred and left for an appropriate time depending on the type of reducing agent as described above. In this mixture, depending on the inorganic acid used, the cladding is e.g.
In the case of H ₂ SO ₄ , some of it dissolves in the form of ferrous sulfate, etc., but the dissolved amount is only about 30% of the total, and the rest is compounds with low solubility in the form of ferrous oxalate, etc. It adheres to the resin layer as a. Next, drain this mixed solution, adjust the concentration of inorganic acid to 1-10%, and increase the concentration of 200-400%.
By passing ₃ g/-RasCaCO, the compounds with low solubility become ferrous sulfate, ferric sulfate, etc. and are completely removed. At this time, the anion exchange resin changes into SO ₄ type, Cl type, etc. depending on the inorganic acid used. In condensate desalination equipment, it is necessary to reduce leakage of not only Na but also anions as much as possible during operation of an ammonia cycle, etc., and anion exchange resins are more effective than Cl type.
H ₂ SO ₄ is used as the inorganic acid because the SO 4 type has less leakage during the ammonia cycle and the SO ₄ type is much easier to regenerate with caustic soda than _the Cl type. It is convenient. In the present invention, when the ion exchange resin is a mixed resin, it is preferable to use H ₂ SO ₄ as the inorganic acid and conduct the drug passage as described below. The mixed resin is backwashed and separated, and each resin is transferred to a separate regeneration tower. Each resin is treated separately with the mixture. Next, H ₂ SO ₄ is passed through the cation exchange resin to regenerate it into H-type and to remove the low-solubility compound. The regenerated waste liquid after passing through the solution is passed through an anion exchange resin to convert it into SO ₄ type, and at the same time, remove the low-solubility compounds. Next, examples of the present invention will be described. Example 1 Iron removal regeneration treatment was performed on an anion exchange resin currently in use in an actual condensate desalination device. The amount of iron deposited on anion exchange resin before treatment is
650mg/-R (OH type). The types of mixed liquids for treatment are as shown in Table 1. In all treatment methods, the ratio of each single chemical as a component of each mixed liquid to resin is 100g to 1 resin, and The total volume was set to 2.
In addition, in either treatment method, the resin is
H ₂ SO ₄ was added to make it into SO ₄ form and then other chemicals were added.

[Table] Regarding the processing steps, each of the above mixture samples was
After stirring and mixing for 5 minutes, let it stand for 5 hours, and then
% _H2SO4 to SV3, regeneration level ₍ RL) to 300g/
− It was regenerated by passing the drug as RasCaCO ₃ . The processing results are shown in Table 2.

[Table] Example 2 A similar experiment was carried out using the same resin as in Example 1 by changing the reducing agent and inorganic acid. The components of each mixture are shown in Table 3, and the differences in the experimental conditions compared to Example 1 are that the stirring and mixing steps were omitted, and instead the standing time was extended to 24 hours. As shown in Table 3, a substance other than H ₂ SO ₄ was used as a regenerating agent.

【table】

[Table] Note that the concentrations and regeneration levels of each of the above-mentioned regenerants are also the same as in Example 1. The processing results are shown in Table 4.

[Table] Example 3 An experiment similar to Example 2 was conducted on a cation exchange resin currently in use in an actual condensate desalination device. The amount of iron attached to the cationic resin before treatment is 410
mg/−RasFe. The types of the mixed liquid for treatment are as shown in Table 5. The procedure for preparing a mixture sample of resin and this mixed liquid is the same as in Example 1, and the treatment process is the same as in Example 2, including standing for 24 hours and subsequent treatment. H ₂ SO ₄
It consists of playback processing by The experimental results are shown in Table 6.

【table】

[Table] Example 4 An anion exchange resin and a cation exchange resin were prepared by mixing equal amounts of the resins after the iron removal regeneration treatment obtained by the treatment method (11) of Example 2 and the treatment method (22) of Example 3. When condensate was ion-exchanged using this mixed resin in an actual machine, the quality of the treated water decreased in both electrical conductivity and total iron as shown in Table 7, confirming the effectiveness of the iron removal regeneration treatment of the resin. Ta. Next, water was passed through an ammonia cycle, but the Na and Cl leaks in the treated water were both below 0.3 ppb.

[Table] As described above, the present invention has great effects on condensate desalination equipment for thermal power plants.
In addition, it has great advantages for condensate desalination equipment at nuclear power plants, such as being able to remove crud without turning the cation exchange resin into salt form, and making it possible to perform the subsequent regeneration process and water sampling process smoothly. are doing. Furthermore, the present invention can be effectively applied to clean water purifiers with cruds, powdered ion exchange resins, and other fillers with cruds, making a significant contribution to industrial technology.

Claims (1)

[Scope of Claims] 1. The ion exchange resin to which the cladding is attached is treated with a mixed solution of at least one of oxalic acid and oxalate and a reducing agent, or a mixed solution of at least one of oxalic acid and oxalate, a reducing agent, and an inorganic acid. A method for regenerating iron removal from an ion exchange resin, which comprises treating the resin with an inorganic acid and then passing it through an inorganic acid. 2. When the ion exchange resin to which the cladding is attached is a cation exchange resin, claim 1 in which the reducing agent is not in the form of a salt.
The method described in section. 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, after separating the mixed resin into individual columns, iron removal regeneration operation is performed for each of these ion exchange resins. A method according to claim 1 or 2. 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.