JPH04371239A - Method for regenerating cation-exchanger resin in condensate desalter - Google Patents

Abstract

PURPOSE:To reduce the amt. of the oxidative decomposition product to be eluted in passing water through a cation-exchange resin as the source of the SO4 ion, etc., harmful to the member constituting the high-temp. and pressure line of the boiler and atomic reactor, etc., by preventing the oxidative decomposition of the resin used in a condensate desalter when the resin is scrubbed with air. CONSTITUTION:A mixed ion-exchange resin used in a desalting tower is transferred to a regeneration tower, and then immediately separated into the anion- exchange resin and cation-exchange resin by a water current without being air-scrubbed. A regenerant such as hydrochloric acid is passed through the separated cation-exchange resin to regenerate the resin, and the resin is scrubbed with air, if necessary, after the regenerant is passed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for regenerating ion exchange resins used in condensate desalination equipment in thermal power plants or nuclear power plants, and in particular to an improvement in the method for regenerating cation exchange resins.

0002

[Prior Art] Condensate in thermal power plants and nuclear power plants needs to be highly purified from the viewpoint of preventing corrosion damage to steam generating means such as boilers, steam generators, and nuclear reactors and reducing radioactivity. Therefore, purification devices such as condensate desalination equipment equipped with a mixed-bed condensate desalination tower, powdered ion exchange resin filters, and hollow fiber membrane filters are used singly or in combination.

[0003] Among these, the above-mentioned condensate demineralization equipment usually has a water flow system consisting of a plurality of condensate demineralization towers (hereinafter referred to as demineralization towers) and a system for regenerating the ion exchange resin used in the demineralization towers. The demineralization tower is filled with a mixed ion exchange resin consisting of a strongly acidic cation exchange resin in the H form or NH4 form and a strongly basic anion exchange resin in the OH form. It is.

[0004] In the condensate desalination apparatus, condensate is treated as follows. In other words, condensate is passed through multiple desalination towers in parallel, and the Na contained in the condensate is removed.
ion, Fe ion, Cu ion, Cl ion, SO4
Impurity ions such as ions are removed by ion exchange, and suspended solids (generally called crud) mainly composed of metal oxides such as iron oxide contained in condensate are removed by filtration or physical adsorption. to obtain purified treated water.

[0005] If such water flow continues and one of the desalination towers causes an increase in pressure loss due to accumulation of crud, or reaches a constant volume throughput, or the demineralization tower in question When the ion exchange resin in the demineralization tower becomes saturated with impurity ions, or when the so-called water flow end point is reached, the demineralization tower is disconnected from the water flow system and the used mixed ion exchange resin in the demineralization tower is regenerated. Transfer to the regeneration tower within the system. After the resin transfer is completed, the already regenerated cation exchange resin and anion exchange resin are transferred from the regeneration system to the demineralization tower to form a mixed ion exchange resin layer, and the flow of condensate water is started again.

On the other hand, the used mixed ion exchange resin transferred to the regeneration tower is first immersed in water, and then air is blown into the regeneration tower from the bottom to agitate it with air. (called scrubbing cleaning),
This performs an operation to physically peel off the metal oxides and the like adhering to the resin surface.

Next, cleaning water is introduced from the lower part of the regeneration tower (this is called backwashing) to remove suspended solids such as metal oxides that have been removed by the air scrubbing (hereinafter simply referred to as air scrubbing) to the outside of the tower. After that, it is backwashed and settled by a conventional method, and separated into a lower cation exchange resin layer and an upper anion exchange resin layer. After the separation, an acid regenerant such as hydrochloric acid or sulfuric acid is passed through the cation exchange resin layer, and an alkaline regenerant such as sodium hydroxide solution is passed through the anion exchange resin layer to desorb impurity ions and perform both ion exchange. Regenerate resin.

In addition, in the regeneration system in this case, both ion exchange resins are separated to form a cation exchange resin layer in the lower layer and an anion exchange resin layer in the upper layer, and the cation exchange resin layer is formed while maintaining the separated layer. One method is a one-tower regeneration method in which an acid regenerant is passed through the anion exchange resin layer and an alkali regenerant is passed through the anion exchange resin layer, and the other is a one-tower regeneration method in which both ion exchange resins are separated and the anion exchange resin in the upper layer is transferred to another regeneration tower. There is a separate tower regeneration method in which ion exchange resin is regenerated in separate towers. Both ion exchange resins that have been regenerated are kept on standby until the next desalination tower reaches the end point of water flow.

[0009] In this way, the condensate desalination equipment used for condensate purification staggers the water flow times of the plurality of desalination towers so that each desalination tower reaches the end point of water flow at approximately regular intervals. The used mixed ion exchange resin of each demineralization tower is sequentially regenerated in the regeneration system at approximately equal water flow intervals.

[0010] The quality of treated water required for the above-mentioned condensate desalination equipment has tended to be increasingly purified in recent years from the viewpoint of preventing corrosion damage and scaling damage to steam generators, nuclear reactors, boilers, etc. For example, the target for Na ions and Cl ions is 0.01 μg/L (0.01 ppb) or less. Various improvements have been made to condensate desalination equipment in order to obtain treated water of such high purity, and as a result, we are currently at a stage where the above goals can be fully achieved.

[0011]

[Problem to be solved by the invention] However, Na
Even with condensate desalination equipment that can sufficiently achieve the target of removing inorganic ions such as ions and Cl- ions, there are problems as described below. That is, when the used ion exchange resin is transferred from the demineralization tower to the regeneration system, the already regenerated ion exchange resin is transferred from the regeneration system to the demineralization tower, and the flow of condensate water is started again. Particularly in the early stages of water flow, a very small amount of organic matter leaks into the treated water.

[0012] According to recent research, it has been found that the organic substances include styrene sulfonic acid oligomers and relatively low-molecular polymers, and these are commonly used in condensate desalination equipment. It has been found that this substance is eluted from a strongly acidic cation exchange resin made by sulfonating a copolymer of styrene and divinylbenzene.

As mentioned above, the treated water of the condensate desalination equipment is supplied to a steam generating means such as a steam generator, a nuclear reactor, or a boiler. If it contains polymers,
It is decomposed under high temperature and high pressure inside the steam generation means, and as a result, SO4 ions and the like are generated, which causes adverse effects such as corrosion on the steam generation means and the like.

The inventors of the present invention have conducted various studies regarding the causes of elution of organic substances from cation exchange resins as described above, and have come to the following conclusion. That is, in the condensate desalination equipment, before the mixed ion exchange resin transferred from the desalination tower to the regeneration tower is separated into a cation exchange resin and an anion exchange resin based on the difference in specific gravity, the resins adhere to the surface of each resin. Air scrubbing is performed by blowing air to remove metal oxides such as iron oxide.

On the other hand, the used cation exchange resin transferred to the regeneration tower adsorbs relatively large amounts of Fe ions and Cu ions contained in the condensate in addition to Na ions. As is well known, these Fe ions and Cu ions are excellent oxidation catalysts, and cation exchange resins that have relatively large amounts of these heavy metal ions adsorbed can absorb dissolved oxygen in water and air due to the catalytic action of the heavy metal ions. When it comes into contact with oxygen, it undergoes oxidative decomposition, albeit to a very small extent. As a result, decomposition products consisting of oligomers and low-molecular polymers of styrene sulfonic acid, which are part of the base structure of the cation exchange resin, are generated, and these decomposition products leak out during the water passage process after regeneration, especially in the initial stage. I assumed that it would.

Therefore, for cation exchange resins in which relatively large amounts of Fe ions and Cu ions are adsorbed,
Carrying out air scrubbing as described above is exactly the kind that promotes the oxidative decomposition of the cation exchange resin, and is not preferable in terms of elution of decomposition products and deterioration of the cation exchange resin.

[0017] Conventionally, in order to reduce the above-mentioned leakage of organic matter as much as possible, the cation exchange resin after regeneration is sufficiently washed in the regeneration system, and then transferred to the demineralization tower and the condensate water is passed therethrough. A method of starting the cleaning process has also been implemented, but this method requires a large amount of purified water for cleaning and also takes a long time.

The present invention has been made based on the above-mentioned assumption, and provides a method for regenerating a cation exchange resin in a condensate desalination apparatus that can prevent the above-mentioned oxidative decomposition of the cation exchange resin in the regeneration system. The purpose is to provide the following.

[0019]

[Means for Solving the Problems] The regeneration method of the present invention, which has been made to achieve the above object, is a method for regenerating a cation exchange resin used in a condensate demineralization tower with an acid. This is a method for regenerating a cation exchange resin, which is characterized by passing an acid regenerant through the resin without performing air scrubbing.

[0020]

[Operation] The regeneration method of the present invention will be explained in detail below. The used mixed ion exchange resin in the demineralization tower, which has reached the end point of the water flow through the condensate, is transferred to the regeneration tower in the regeneration system.

Conventionally, as mentioned above, air was blown into the regeneration tower immediately after transferring the resin to perform air scrubbing, which caused the problem that the oxygen in the air accelerated the oxidative decomposition of the cation exchange resin. There was, but
In the present invention, in order to prevent such oxidative decomposition, air scrubbing at this stage is eliminated, and water (pure water) is first introduced from the lower part of the regeneration tower in an upward flow, and the mixed ion exchange resin is anion exchanged by the water flow. An operation is performed to separate the resin and cation exchange resin.

[0022] Thereafter, the inflow of water is stopped to allow both ion exchange resins to settle down, thereby forming an anion exchange resin layer in the upper layer and a cation exchange resin layer in the lower layer. During the above-described separation operation, suspended substances such as metal oxides accumulated in the mixed ion exchange resin layer or attached to the resin surface are partially discharged to the outside of the column.

Next, the process moves to the step of passing a regenerant through both ion exchange resins. Here, the regeneration system of the condensate desalination equipment includes the one-column regeneration system and the separate-column regeneration system as described above, but first, the separation layer between the cation exchange resin layer and the anion exchange resin layer is maintained in the regeneration tower. In the case of a one-tower regeneration method in which each regenerant is passed through the cation exchange resin layer, an acid regenerant such as hydrochloric acid or sulfuric acid is first passed through the lower cation exchange resin layer, and the Na ions adsorbed on the cation exchange resin are removed. and Fe ions,
The cation exchange resin is regenerated by desorbing heavy metal ions such as Cu ions.

[0024] The used cation exchange resin contains heavy metal ions such as Na ions and Fe ions, as well as
Metal oxides mainly composed of fine particles of iron oxide are physically adsorbed or attached, but most of these metal oxides are dissolved and removed by the passage of the acid regenerant. After passing the acid regenerant, an extrusion step using pure water and a washing step are performed in a conventional manner to complete the cation exchange resin regeneration step.

After the above-mentioned regeneration of the cation exchange resin is completed, the anion exchange resin is regenerated, but the surface of the anion exchange resin contains metal oxides etc. as in the case of the cation exchange resin. Since the particles are attached, it is recommended to perform air scrubbing by blowing air into the regeneration tower before regeneration.

[0026] The air scrubbing cleaning removes the metal oxides adhering to the surface of the anion exchange resin, and since the cation exchange resin is also subjected to air scrubbing at the same time, it was not completely dissolved by the passage of the acid regenerant. If metal oxide remains on the surface of the cation exchange resin, this metal oxide can also be peeled off. Note that the scrubbing cleaning is performed after almost completely desorbing Fe ions and Cu ions adsorbed on the cation exchange resin, so the oxidative decomposition of the cation exchange resin as described above hardly occurs. . In addition, in the case of anion exchange resin, since Fe ions and Cu ions are not adsorbed to begin with, there is almost no fear of oxidative decomposition even if air scrubbing is performed.

After performing the air scrubbing cleaning as described above, pure water is flowed upward from the lower part of the regeneration tower, and the metal oxides separated by the air scrubbing cleaning are discharged to the outside of the tower. Thereafter, the above-described separation operation is performed to separate the cation exchange resin and anion exchange resin again, and then an alkali regenerant is passed through the anion exchange resin layer, and the anion exchange resin is regenerated by a conventional method. The regenerated both ion exchange resins are transferred to a resin storage tank or the like and stored, and are kept on standby until the next desalination tower reaches the end point of water flow.

Next, in the case of a separate column regeneration method in which both ion exchange resins are regenerated in separate columns, after the above-mentioned separation operation of both ion exchange resins is completed, the upper layer anion exchange resin is transferred to another regeneration column. After the cation exchange resin is transferred, an acid regenerant is immediately passed through the regeneration tower where the cation exchange resin remains to regenerate the cation exchange resin. On the other hand, the transferred anion exchange resin is first subjected to air scrubbing cleaning and then water cleaning to peel off and remove metal oxides adhering to the surface of the anion exchange resin, and then passed through an alkali regenerant. Medicine and regeneration.

[0029] In the regeneration of the cation exchange resin, if the metal oxide adhering to the surface of the cation exchange resin is insufficiently dissolved and removed by passing the acid regenerant, It is best to perform air scrubbing after the treatment to remove residual metal oxides. In this case, as in the case described above, since Fe ions, Cu ions, etc. adsorbed on the cation exchange resin have been desorbed, the cation exchange resin The oxidative decomposition of is hardly promoted.

As the acid regenerating agent in the present invention, acids such as hydrochloric acid or nitric acid, which are commonly used for regenerating the cation exchange resin of condensate desalination equipment, can be used. It is particularly preferable to use hydrochloric acid because it has an excellent ability to dissolve adsorbed metal oxides such as iron oxide. When using hydrochloric acid, air scrubbing after passing the acid regenerant is often unnecessary.

On the other hand, when sulfuric acid, for example, is used as an acid regenerating agent, its ability to dissolve metal oxides is slightly inferior to that of hydrochloric acid, so there are cases where the metal oxides are not sufficiently dissolved or removed. There is still. Therefore, in such a case, after passing the acid regenerant, it is necessary to perform air scrubbing on the cation exchange resin to physically remove residual metal oxides.

[0032]

[Examples] Examples of the present invention will be described below.

(Reference example) (Cation exchange resin scrubbing test) A column was packed with Amberlite (registered trademark, the same applies hereinafter) 200CP, a strongly acidic cation exchange resin made by sulfonating a copolymer of styrene and divinylbenzene. Synthetic water in which commercially available ferrous sulfate and copper sulfate reagents were dissolved was passed through the column to collect approximately 600 mg/L of Fe2+ ions.
A cation exchange resin (this is referred to as a metal ion adsorption resin) in which R and Cu2+ ions are adsorbed at a ratio of about 300 mg/LR was prepared.

Separately, two glass containers containing 300 mL of pure water were prepared, and 100 mL of the metal ion adsorption resin and commercially available Fe2 O3 powder were added to each container at a concentration of 1,000 mg/L. These containers were placed in a constant temperature shaker at 50°C, and while stirring constantly, air was continuously introduced into the water in one container, and N2 gas was continuously introduced into the water in the other container at a flow rate of 10 mL/sec. I blew it.

In the experiment described above, the water in each container was sampled at regular intervals and its T. O. Measure the C concentration,
We looked at the elution of organic matter from the cation exchange resin. Further, an experiment similar to the above was also conducted on Amberlite 200CP to which Fe2+ and Cu2+ were not adsorbed (this is referred to as metal ion non-adsorbed resin).

Elapsed time (hr) and T. of water in the container. O.
The relationship with C concentration (mgC/L) is shown in FIG. Note that RUN1 to RUN4 in FIG. 1 correspond to the experimental conditions shown in Table 1, respectively.

[0037]

[Table 1]
Experimental conditions ────
──────────────────────
RUN1 Blow air into metal ion adsorption resin RUN
2 〃
N2 blowing RUN3
Air is blown into the resin that has not adsorbed metal ions.
RUN4
〃 N2 blowing
────────────────────
────────

In the above experiment, R.U.
N2 and RUN4 correspond to scrubbing the cation exchange resin with substantially oxygen-free N2 gas, in which case no oxidative decomposition of the cation exchange resin occurs. Therefore, RUN2 and RUN4
T. O. C is due to the leakage of organic matter originally present in the cation exchange resin, and R
Although there are some differences between UN2 and RUN4, these can be regarded as so-called blank values.

On the other hand, in the case of RUN1 in which air was blown into the metal ion adsorption resin, the T.V. was much higher than that of the blank. O. Therefore, in this case, it is considered that the oxidative decomposition of the cation exchange resin was promoted by air blowing, and organic substances as decomposition products were eluted into the water.

[0040] Note that the metal ion-unadsorbed resin and Fe2O
3 RUN3 in which air was blown into the container containing the powder.
In this case, even though air was blown, the T. O.
C concentration and therefore suspended metal oxide (
It can be seen that Fe2O3 powder) hardly promotes the oxidation reaction of the cation exchange resin. From the above results, it can be seen that the factor that promotes the oxidation reaction of the cation exchange resin is metal ions such as Fe ions and Cu ions adsorbed on the cation exchange resin.

(Example) The regeneration method of the present invention was actually applied to a condensate desalination apparatus using a separate column regeneration method, and a comparison was made with a conventional method. The cation exchange resin used was Amberlite 200CP, and the anion exchange resin used was Amberlite IRA900CP.

The regeneration method of the present invention was carried out according to the procedure shown in FIG. First, the used mixed ion exchange resin is transferred from the demineralization tower that has reached the water flow end point to the regeneration tower (this is referred to as the K regeneration tower), and then the anion exchange resin is immediately recycled by water flow without air scrubbing. (upper layer) and cation exchange resin (lower layer). Next, the anion exchange resin in the upper layer was transferred to another regeneration tower (this is referred to as regeneration tower A).

A prescribed amount of 5% hydrochloric acid (HCL) solution was passed through the cation exchange resin left in the K regeneration tower, followed by washing with pure water to regenerate the cation exchange resin. After the cleaning was completed, air was blown into the K regeneration tower to perform air scrubbing of the cation exchange resin, and then pure water was introduced to perform backwashing. Note that such air scrubbing and backwashing were repeated five times in total.

On the other hand, the anion exchange resin transferred to the A regeneration tower is first subjected to the above-mentioned air scrubbing and backwashing five times in total to remove metal oxides attached to the surface of the anion exchange resin. After peeling off and removing suspended substances such as, a specified amount of 4% sodium hydroxide (NaOH) solution was passed through the resin, and the anion exchange resin was further washed with pure water to regenerate the anion exchange resin.

[0045] Next, the regenerated anion exchange resin is
Transferred to the regeneration tower, and further within the K regeneration tower, the regenerated cation exchange resin originally contained in the K regeneration tower,
The transported recycled anion exchange resin was thoroughly mixed. After the mixing was completed, the mixed ion exchange resin was finally washed with pure water, and then the mixed ion exchange resin was transferred from the K regeneration tower to the demineralization tower, and the flow of condensate water was started.

[0046] Three hours after the start of water flow, the treated water of the demineralization tower was sampled, and the conductivity and T. O. In addition to measuring the C concentration, the organic matter contained in the sample was decomposed by irradiating the sample with ultraviolet rays, and the SO4 ion concentration in the decomposed solution was measured. The measurement results are shown in Table 2.

Next, a specified amount of condensate is passed through the desalination tower filled with the cation exchange resin regenerated by the method of the present invention described above to reach the water flow end point, and then the desalination The used mixed ion exchange resin in the tower was transferred again to the K regeneration tower. The mixed ion exchange resin transferred to the K regeneration tower was then regenerated using the conventional method of first performing air scrubbing. The series of operations consisting of air scrubbing and backwashing was repeated five times in total. Furthermore, the type, concentration, amount, etc. of the acid and alkali regenerant used were the same as in the method of the present invention.

After the regeneration is completed, the cation exchange resin and anion exchange resin are thoroughly mixed, and after a final washing with pure water,
The mixed ion exchange resin was transferred to the demineralization tower, and the flow of condensate water was started. Three hours after the start of water flow, the treated water from the desalination tower was sampled, and the conductivity, T. O. C concentration and SO4 ion concentration after ultraviolet decomposition were measured. The measurement results are shown in Table 2 in comparison with the results of the present invention.

[0048]

[Table 2]
Measurement results ──────────
────────────────────────
Item
Method of the present invention Conventional method ────────────────────
────────────── Conductivity (μ
s/cm) 0.058
0.058 T. O. C(p
pb) 14
22 SO4 ion (ppb
) 0.8
1.5 (after ultraviolet decomposition) ────────────────────────
────────────

As is clear from Table 2, in the case of the method of the present invention, T. The O, C concentration and the SO4 ion concentration after ultraviolet decomposition are reduced to 1/1.5 to 1/2 of those in the conventional method. It can be seen that it is extremely effective in reducing

[0051]

[Effect] As explained above, according to the present invention, it is possible to prevent oxidative decomposition of the cation exchange resin used in condensate desalination equipment during air scrubbing, thereby preventing deterioration of the cation exchange resin and extending its life. In addition, high-temperature, high-pressure applications such as boilers in thermal power plants, nuclear reactors in boiling water (BWR) nuclear power plants, and steam generators (SG) in pressurized water (PWR) nuclear power plants, etc. The elution of oxidative decomposition products from the cation exchange resin, which is a source of SO4 ions, etc. that are harmful to the components of the system, and the leakage of the oxidative decomposition products from the demineralization tower during water flow are significantly reduced compared to conventional methods. can be reduced.

[0052] Furthermore, when the deterioration of the cation exchange resin due to oxidation progresses, relatively high molecular weight decomposition products with a molecular weight of 100,000 or more may be eluted from the cation exchange resin; When the eluate is adsorbed on the anion exchange resin used in the desalting device, it is extremely difficult to desorb it, and if the amount of adsorption is too large, the ion exchange ability of the anion exchange resin will be reduced. As a result, the removal performance of impurity ions such as CL ions and SO4 ions may deteriorate, resulting in problems such as the inability to meet the strict water quality requirements mentioned above. The method of the present invention has the effect of reliably preventing such problems.

[0053] As can be seen from the reference examples mentioned above,
Oxidative decomposition of the cation exchange resin can also be prevented by replacing the air scrubbing in the conventional method with scrubbing using an inert gas such as N2 gas or H2 gas. Considering the cost and the equipment required to recover the gas, this method cannot be called a preferable method.

[Brief explanation of drawings]

FIG. 1: T.I. from a cation exchange resin in a reference example. O
．． It is a graph showing the elution status of C (organic substance).

FIG. 2 is a block diagram showing the procedure of a reproduction method in the embodiment.

Claims (3)

[Claims] Claim 1: A regeneration method characterized in that, when regenerating a cation exchange resin used in a condensate demineralization tower with an acid, an acid regenerating agent is passed through the cation exchange resin without performing air scrubbing. A method for regenerating cation exchange resin in water desalination equipment. 2. The method for regenerating a cation exchange resin in a condensate desalination apparatus according to claim 1, wherein the acid used is hydrochloric acid. 3. The method for regenerating a cation exchange resin in a condensate desalination apparatus according to claim 1 or 2, wherein the cation exchange resin is cleaned by air scrubbing after passing the acid regenerant.