JPH0140672B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method and apparatus for purifying condensate.

This type of product is used in various plants that perform condensation. For example, it is used to purify condensate in turbines of power plants.

Among power plants, nuclear power plants,
Particularly in power plants using boiling water reactors, such condensate purification technology is important. Corrosion products leached from the plant's structural materials are brought into the reactor and activated by neutron irradiation, so if purification is not sufficient, some of these radioactive corrosion products will increase the number of years the reactor has been in operation. This is because it is deposited on the piping around the furnace, increasing the radioactivity level within the plant. The accumulation of such radioactivity leads to an increase in radiation exposure during periodic inspections and when the reactor is shut down, which in turn leads to a decrease in availability and an increase in operating costs.From the standpoint of safety and economy, it is important to suppress corrosion products. and removal measures are essential.

Corrosion products leached from plant structural materials include suspended iron (hereinafter referred to as cladding; mostly iron, but also various other iron oxides, iron hydroxides, etc.) and various metals in iron alloys. There are metal ions. Therefore, conventionally, ion exchange resins have been used to remove such corrosion products and purify condensate.

A system outline of a conventional boiling water nuclear reactor equipped with such condensate purification technology will be explained with reference to FIG. 1a. Steam generated when cooling water passes through a reactor core 2 in which fuel rods are arranged in a reactor vessel 1 is sent to a high-pressure turbine 4 and a low-pressure turbine 5 through a main steam pipe 3. Steam discharged from the low pressure turbine 5 is condensed into water in a condenser 6. This water returns to the reactor vessel 1 through the condensate demineralizer 7, the low pressure feed water heater 8 and the high pressure feed water heater 9.
On the other hand, steam extracted from the high-pressure turbine 4 is guided to the high-pressure water heater 9 through a high-pressure extraction pipe 10. The drain of the high pressure water heater 9 is the drain pipe 11
The steam extracted from the low pressure turbine 5 is guided to the low pressure water heater 8 by the low pressure extraction piping 12. Drain from the low-pressure water heater 8 is led to the condenser 6 through a drain pipe 13. In such a system, corrosion products (ions, and crud) are generated and become impurities in the condensate, but both are returned to the condenser 6 and removed by the condensate demineralizer 7. However, impurities that are not removed by the condensate desalter 7 are brought into the nuclear reactor and are activated.

Recently, however, it has become clear that the dose rate of a plant can be reduced by reducing the amount of iron cladding carried into the water supply. For this reason, there is a growing demand to reduce the amount of iron crud carried into the water supply as much as possible. However, since the conventional example shown in FIG. 1a described above uses the condensate demineralizer 7 filled with ion exchange resin, the ion removal performance is good, but the crud removal performance is not necessarily excellent.

For example, as the condensate salt enhancer 7 in Fig. 1a, a cation exchange resin and an anion exchange resin are mixed and the depth is increased.
A case will be explained in which the resin is placed in a deep bed of about 90 cm and the particle size of each resin is about 0.8 mm. Impurities in the condensate are removed by the ion exchange resin in the condensate demineralizer 7. At this time, ions are removed by an ion exchange reaction, and cruds are removed by adhesion to the resin surface. The iron removal mechanism (crud removal mechanism) using the ion exchange resin in the condensate demineralizer 7 is complex, and (1) sieving effect, (2) sedimentation effect, (3) adsorption effect, etc. interact with each other, resulting in crud removal. is happening. Resins that have lost their desalting performance are chemically or non-chemically regenerated and recycled. However, the impurities in condensate from nuclear power generation usually include more cruds than ions. However, as mentioned above, although ion exchange resins have excellent elemental ion exchange removal ability, their crud removal ability is as low as about 70%.
For this reason, the method of purifying condensate using only a demineralizer filled with granular ion-exchange resin does not remove crud as well as remove ions, and some of the crud is carried into the reactor, which is undesirable.

Due to the above-mentioned circumstances, recently, in order to further reduce crud, a configuration has been developed in which an overflow condensate purifier 14 for the purpose of removing crud is installed upstream of the condensate demineralizer 7 of the conventional condensate purification system. are increasingly being adopted. A conventional example of such a configuration is shown in FIG. 1b. As the material for the overflow condensate purifier 14, powdered ion exchange resin, electromagnetic filter, etc. can be used. According to this configuration, since the crud removal capacity of the overflow condensate purifier 14 is about 80%, effective crud removal is performed together with the crud removal in the subsequent condensate desalination device 7.

However, in this configuration in which the overflow condensate purifier 14 is installed before the condensate desalinator 7, the overall crud removal capacity is certainly increased compared to the case where the condensate demineralizer 7 is used alone. There is a problem in that the inherent ability of the condensate demineralizer 7 to remove crud is reduced. As will be explained in detail later, if the condenser demineralizer 7 was used alone, the iron removal rate due to crud removal was about 70%, but if the overflow condensate purifier 14 is installed in front of it, ,
The iron removal rate of condenser demineralizer 7 drops to 50%.
Ideally, after the crud is removed in the overflow condensate purifier 14 according to its performance, it is expected that about 70% of the iron will be removed from the condensate in the condensate demineralizer 7. However, in reality it cannot function like this. In addition, the conventional example shown in FIG. 1b has problems such as a large amount of radioactive waste such as decommissioned reactor material generated from the overflow condensate purifier 14.

An object of the present invention is to enable efficient removal of crud in the condensate demineralizer even when using the overfill condensate purifier and the condensate demineralizer together,
It is an object of the present invention to provide an advantageous method and apparatus for purifying condensate that can improve the overall crud removal performance and reduce the amount of radioactive waste produced in an overflow condensate purifier.

In order to achieve this objective, in the present invention,
When purifying condensate water through ion exchange resin after evaporation, the condensate water is added to the ion exchange resin after evaporation, and the ion exchange resin is passed through. In addition to optimizing the ion exchange resin, the crud removal ability of the ion exchange resin is thereby activated and increased.

The present invention is based on the following considerations, which the present inventors have diligently investigated in order to achieve the above-mentioned problems. In other words, the crud removal ability of the condensate demineralizer is
It is greatly affected by the cladding particle size and cladding composition. The larger the crud particle size and the broader the particle size distribution, the higher the iron removal ability in the condensate demineralizer. Regarding the composition, the iron removal ability increases in the order of triiron tetroxide (Fe ₃ O ₄ ) > iron sesquioxide (Fe ₂ O ₃ ) > iron oxyoxide (FeOOH). In addition, iron removal ability is higher when the cladding composition is a mixed system. These results were confirmed through experiments and are based on actually obtained data.

Based on the above knowledge, even in a condensate purification system in which an overflow condensate purifier is installed before a condensate demineralizer, in order to increase the iron removal efficiency of the condensate demineralizer, it is necessary to The cladding particle size in the inlet condensate flowing into desalination may be increased, the particle size distribution may be widened, and the cladding composition may be mixed. In order to achieve this with a simple configuration, the present invention adds condensate before overtreatment to condensate at the inlet of a condensate demineralizer. This is because condensate from the past naturally contains particles with large diameters, has a wide particle diameter distribution, and is expected to form a mixed system containing multiple components. For example, the drain of a feedwater heater system contains several ppb of iron cladding.
A part of this is added to the condensate water at the inlet of the condenser demineralizer. In this way, the previous condensate has a certain amount of crud, which has the effect of increasing the crud removal efficiency of the condenser desalter, resulting in an increase in the overall crud removal rate.

As mentioned earlier, the upstream overflow purifier 14 as shown in FIG. 1b removes about 80% of the crud, but all conventional purifiers This acts to reduce the removal capacity of the condensate demineralizer 7. In other words, the conventional purifier 14
is undesirable in view of the above findings, since it serves to reduce the particle size, narrow the particle size distribution, and narrow the composition distribution. For example, the filter-type condensate purifier 14 may be filled with a pre-coated powder ion exchange resin, but since the crud is removed by the filter mechanism, the treated condensate and condensate demineralizer Naturally, the crud remaining in the condensate at the inlet to 7 becomes smaller in particle size. (~10 μm before treatment, reduced to ~3 μm after treatment). Naturally, the particle size distribution is also narrow. On the other hand, an electromagnetic filter or the like may be used as the overflow condensate purifier 14. In this conventional example, magnetic Fe ₃ O ₄ is preferentially removed, and cladding is partially removed due to overaction in the matrix. For this reason, the composition of the crud remaining in the treated condensate changes and Fe ₂ O ₃ and FeOOH become the main components.
In addition, uniformity of the crud is unavoidable as the particle size becomes smaller and the powder size distribution becomes narrower.

From the above, in the configuration in which the overflow condensate purifier 14 shown in FIG. 1b is installed upstream, the subsequent condensate demineralizer 7 itself has an iron removal rate of about 50%. Compared to the removal rate of about 70% in the condensate demineralizer 7 (FIG. 1a) when the overflow condensate purifier 14 is not installed, the iron removal rate is much lower. The reason why the iron removal rate in the condensate demineralizer 7 is higher when the overflow condensate purifier 14 is not installed is understandable from the above-mentioned findings. Compared to the case where the condensate moves forward, the crud particle size in the condensate at the inlet of the condensate demineralizer 7 is larger, the particle size distribution width is also wider, and the crud composition is also a mixed system, so the crud becomes non-uniform. In the ion-exchange resin layer filled in the condensate demineralizer 7, various crud removal reactions such as the sieving effect, precipitation effect, and adsorption effect described above proceed, making it easier for crud to adhere to the resin, causing the resin layer to deteriorate. This is because the crud trapping ability is increased.

The present invention can be said to have been achieved based on the above knowledge and the above background.

Some embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows a first embodiment of the present invention, in which pre-condensed water is added to post-condensed water through a bypass pipe 15, and this is passed through an ion exchange resin.

This device consists of a condenser 6 and an overflow condensate purifier 1.
4 and a condensate demineralizer 7 filled with ion exchange resin
The overflow condensate purifier 14 is installed upstream of the condensate salt enhancer 7, and the previous condensate is is added to the condensate after passing through the condensate demineralizer 7.

More specifically, in this embodiment, a condensate demineralizer return drain piping 15 is provided in the feedwater heater drain piping 13, and this is used as a bypass piping, so that a part of the feedwater heater drain is routed downstream of the overflow condensate purifier 14. The condensate is returned to the condensate at a position before the condensate demineralizer 7.

FIG. 3 shows a second embodiment of the present invention, which includes a bypass pipe 1 from the front stage of the overflow condensate purifier 14.
Add the previous condensate to the subsequent condensate using Step 6,
This is configured to pass through a condensate demineralizer 7. (The crud concentration is different between the drain from the drain pipe 13 and the condensate from the condenser 6 in the example of FIG. 2). As shown in the figure, an overflow purifier bypass piping 16 is provided as a bypass piping from the front stage of the purifier 14 to bypass the purifier 14, and is connected to the front stage of the condensate demineralizer 7. (In Figures 2 and 3, the same components as in the conventional example are designated by the same reference numerals.
(Detailed explanation is omitted).

In both examples, as the overflow purifier 14,
An electromagnetic filter or a filter filled with a pre-coated powdered ion exchange resin can be used. In addition, even when using ion exchange resin, when using it as the overflow purifier 14, the diameter is 10 mm.
In many cases, the structure is such that condensate passes through a relatively thin layer, and the passage speed is high, so the desalination function as ion exchange usually does not contribute much.

According to these configurations, the overflow condensate purifier 14
The crud-containing water before being treated in the condensate demineralizer 7
Because it is added at the front stage of the condensate demineralizer inlet condensate, the crud particle size is larger and the particle size distribution is wider than that of the condensate treated by the filter clarifier, and the crud composition is mixed, making the crud non-uniform. Therefore, the iron removal capacity of the condensate demineralizer increases, and the iron removal rate is about 70%, which is the same as when no overflow demineralizer is installed.

As a result, the overall removal of crud is enhanced, and the iron removal effect is also superior to that of the conventional method. The effects of this embodiment will be specifically described below.

First, as a reference example for comparison, a case will be described in which condensate purification is performed using the conventional configuration shown in FIG. 1b. In this reference example, an overflow purifier 14 pre-coated with powdered ion exchange resin and a condensate demineralizer 7 are used. This results in 15ppb of cladding.
condensate (in addition to the discharge condensate from the turbine 5,
(31% including feed water heater drain through drain piping)
When processed, the iron removal rate in the overflow purifier 14 was
The iron removal rate in condensate demineralizer 7 was 50%, and the crud concentration in the treated water was 1.5 ppb.

Next, the results obtained when the embodiment of the present invention is adopted will be described. Here, using the configuration shown in FIG. 2 and modifying the reference example, 10% of the feed water heater drain (crud concentration 5 ppb) was returned to condensate at the inlet of the condensate demineralizer 7. Other conditions are the same as in the reference example, but as a result of bypassing 10% of the condensate, the crud concentration of the condensate flowing from the condenser 6 into the overflow clarifier 14 is slightly lower than in the reference example, and 14~ It is thought to be around 13ppb. As a result, the iron removal rate in the overflow washer 14 was 80%, and the iron removal rate in the condensate demineralizer 7 was 70%. The cladding concentration of the treated water was 0.94 ppb, and it was possible to obtain a much more significant cleaning effect than in the above-mentioned reference example.

Furthermore, if such a configuration is used, the cladding load on the overflow desalination purifier 14 will naturally be reduced by the amount of bypass compared to the reference example. (in this case
Since 10% is bypassed, the load is reduced to 90%. ) It is easy to understand that this load reduction lengthens the overlife. This will also reduce the amount of radioactive waste.

In the same way as above, 100% of the feed water heater drain amount
%, 50%, 5%, and 1% were bypassed and returned to condensate at the inlet of condensate demineralizer 7, and the crud concentrations in the treated water were 1.3 ppb, 1.1 ppb, and 1.1 ppb, respectively.
They were 0.92ppb and 1.4ppb. According to this, the amount of feed water heater drain returned to the condensate demineralizer inlet condensate is about 5 to 50% of the heater drain amount to be effective for removing crud, especially about 10% (or 5%
However, it can be seen that desired effects can be obtained within a wide range.

Although it may be thought that there is a risk of the heat balance being disrupted by returning the feed water heater drain by bypass, the condensate temperature at the condenser outlet is 30 to 35 degrees Celsius, and the temperature of the low pressure heater drain is Since the temperature is 35 to 40°C, there is no problem, and if the amount of drain returned is small, the effect is small and no practical problem occurs.

As described above, in the present invention, when purifying condensate through the ion exchange resin after passing through the ion exchange resin, the ion exchange resin Also in the condensate desalination process, crud removal can be carried out with high efficiency, and the overall crud removal performance can be improved.
In addition, as a result of bypassing the previous condensate, the crud load on the overflow condensate purifier can be reduced, and the life of the material can be extended, and as a result, the overflow condensate purifier can be This has the effect of reducing the amount of radioactive waste.

It should be noted that, as a matter of course, the present invention is not limited to the illustrated embodiment.

[Brief explanation of drawings]

FIGS. 1a and 1b each show a conventional example in a system diagram. 2 and 3 are system diagrams of embodiments of the present invention, respectively. 6... Condenser, 7... Condensate demineralizer, 14...
Overflow type condensate purifier, 15... Bypass piping (condensate salt increaser return drain piping), 16... Bypass piping (
bypass piping).

Claims (1)

[Claims] 1. A method for purifying condensate in which the condensate is purified through an ion exchange resin after filtration, characterized in that the water before the filtration is added to the water after the filtration and the water is purified through the ion exchange resin. How to purify condensate. 2. Equipped with a condenser, an overflow condensate purifier, and a condensate demineralizer filled with ion exchange resin. In a condensate purification device that purifies water, the pre-condensed water is added to the post-condensed water through bypass piping from the front stage of the condenser or the stage of the over-type condensate purifier, and is then passed through the condensate demineralizer. A condensate purification device characterized by: