JPS59127690A - Optimum driving method for filtering desalinator for condensed water - Google Patents

Abstract

PURPOSE:To reduce the amount of radioactive waste, while prolonging the filtering life of the titled filtering desalinator for condensed water, by making the amount of water flowing through a column in the step of inner filtering larger than the simple average value and the amount of water flowing through a column in the step of surface filtering smaller than said simple average value. CONSTITUTION:Condensed water is parallelly sent into a plurality of filtering desalination columns 14 by a pump 13 for condensed water. Each column contains many elements in it, and the condensed water is circulated after said elements are precoated with powdery ion exchange resin. The amount of water flowing through the filtering desalination column existing in the step of inner filtering is made larger than the simple average value per one column to perform LV driving with high water circulation, while the amount of water flowing through the filtering desalination column existing in the step of surface filtering is made smaller to perform LV driving with low water circulation. Thus, the elongation of filtering life is contrived under the fixed amount of water circulated as a whole. To adjust the amount of water flowing through the filtering desalination column, a discharge regulator valve 15 provided at the downstream side of each column is used.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to an optimal operating method for a condensate p superdemineralizer, and in particular to a condensate filtration demineralizer suitable for use in a condensate purification system of a nuclear power plant. It concerns the optimal method of operating salt vessels.

[Prior art]

As the oil situation has worsened in recent years, it is thought that electricity will become increasingly dependent on nuclear power generation in the future. There are already 23 nuclear power plants in operation in Japan, and a considerable number are under construction or in the planning stages. However, since nuclear power generation involves the handling of radioactive materials, extremely high levels of safety and reliability are required for its operation.

One of the important systems for the safe operation of a nuclear power plant is the condensate purification system. A typical example of this system is shown in Figure 1, and the purpose of the system is to remove impurities such as iron, cobalt, and chlorine ions that cause pipe dose rates and equipment corrosion from condensate. Steam 2 generated in the nuclear reactor 1 drives a steam turbine 3 to generate electricity, and then passes through a condenser 4 to become condensed water 5. Condensate contains solid and ionic impurities (mainly iron), which must be removed to improve the safety and reliability of power plants. The filtration demineralizer 6 and the demineralizer 7 are devices for removing impurities, and the filtration demineralizer 6 pre-coats the surfaces of multiple elements containing powdered ion exchange resin to remove especially solid ion exchange resin. Remove impurities. The demineralizer 7 is filled with granular ion exchange resin and is intended to remove ionic impurities. A filtration demineralizer 6 and a demineralizer 7 are installed in the condensate purification system, and water is passed through them in parallel. In addition, each tower is operated so that the amount of water flowing through each tower is equal. In the case of a filtration demineralizer, a water flow LV (linear velocity) of 6 m/h to 3 m/b is adopted in Japan.

In this system, the effect of reducing the pipe dose rate is particularly high due to the purification performance of the filtration demineralizer 6, which greatly contributes to lowering the radioactivity of the plant.

However, the powdered ion exchange resin used in the filtration demineralizer 6 is discarded and is backwashed and precoated 9 times over a cycle of about 10 to 15 days, resulting in a large amount of waste resin. . Moreover, since waste resin is radioactive waste, it is extremely difficult to process and dispose of it, and we are struggling to find countermeasures. Various solutions have been considered, one of which is to extend the filtration life of the filtration demineralizer.

[Object of the Invention] An object of the present invention is to provide a method of operating a filtration demineralizer with a long filtration life in order to reduce the amount of radioactive waste.

[Summary of the invention]

There are two main mechanisms by which solid matter is captured by the precoat resin layer of the filtration and demineralizer. These are internal filtration and surface filtration. As shown in FIG. 2, internal filtration refers to a mechanism in which solids are captured inside the precoat resin layer, and even solids smaller than the voids in the precoat resin layer can be captured. On the other hand, surface filtration refers to a mechanism in which solids are captured by a layer of solids deposited on the surface of the precoat resin layer.

XMA (X-ray microanalyzer) of a cross section of the precoat resin layer has revealed that the mechanism for trapping solids in the precoat resin layer is primarily internal filtration, and then gradually shifts to surface filtration.

Furthermore, as shown in FIG. 3, it has been found from our experimental results that when surface filtration becomes dominant, the rate of increase in filtration differential pressure becomes remarkable. Therefore, it is relatively easy to distinguish between the internal filtration process and the surface filtration process based on the rising characteristics of the filtration differential pressure. Based on these findings, we conducted the following experiment. That is, this is an experiment in which the amount of iron captured per unit amount of resin in internal filtration and surface filtration is determined using water passing LV as a parameter. A filter tower with a built-in nylon element with a length of 1,500 mm and a diameter of 50 mm was used as the experimental device, and iron oxide (α-F, 203, average particle size of 1 μμm) was used to simulate impurities in condensate. I tried it. The pre-coat resin includes powdered cation exchange resin and anion exchange resin (both manufactured by Graeba, Inc. in the United States, product name: powder).
x) in a dry weight ratio of 2:1. The amount of precoat resin is 1 - per filtration area! 1ll
It is IK7. The experimental results are shown in Figure 4. In the case of internal filtration process, the amount of iron captured per unit amount of resin is LV4 to 12.
In the m/h range, it is almost constant regardless of the water flow LV. However, in the case of the surface filtration process, the amount of iron trapped decreases as the water flow LV increases. Since the amount of iron trapped per unit amount of resin is related to the filtration life, naturally the longer the filtration life, the greater the amount of iron trapped. Therefore, it can be seen from FIG. 4 that in the surface filtration process, the service life can be extended by making the water flow LV as small as possible. In addition, in the internal filtration process, the amount of iron trapped does not change even if the water flow LV is large, so the water flow LV, which was conventionally constant during the water flow time, was changed appropriately between the internal filtration process and the surface filtration process. It can be easily inferred that the amount of iron captured per unit amount of resin during the entire water flow time can be increased. We devised a solution based on the above ideas.

[Embodiments of the invention]

An embodiment of the present invention will be described based on FIG.

Several filtration and demineralization towers 14 and a condensate pump 13! 17 condensate is fed in parallel. A large number of elements are built into each chamber, and after the elements are precoated with powdered ion exchange resin, water is passed through them.

Since each group is operated independently, the filtration pressure difference is different. That is, the mechanism by which the precoat resin layer captures solid matter is different. By determining the filtration differential pressure increase characteristics shown in FIG. 3, it is possible to infer whether the filtration mechanism at that time is internal filtration or surface filtration.

Therefore, from the idea that led to the present invention described above, the water flow rate of the filtration and demineralization tower in the internal filtration process is increased by a simple average value per tower, and high water flow LV operation is carried out, and the water flow rate in the surface filtration tower is increased. The water flow rate of a certain filtration and demineralization tower is reduced and low water flow LV operation is performed in order to extend the filtration life under a constant total water flow rate. To adjust the amount of water flowing through the filtration and demineralization tower, a flow rate adjustment valve 15 provided on the downstream side of each unit is used. If these operations were performed manually, it would be complicated to balance the amount of water flowing through each unit, so it is desirable to automate them. For this purpose, as shown in FIG. 6, a P differential pressure detector 16 is installed in each unit of the filtration and demineralization tower to detect the filtration differential pressure. It is sufficient to calculate the differential pressure increase rate and compare it with a set value to determine whether the filtration mechanism at that time is internal filtration or surface flow. Then, a signal is given to the self-exciting valve 17 for adjusting the water flow rate provided downstream of each unit, and automatic control is performed so that the opening degree of the automatic valve 170 is optimal for extending the filtration life.

Table 1 shows the effects of the present invention.

Table 1 shows the results of an experiment in which three test filtration towers each containing one nylon element with a diameter of 50+u+ and a length of 1500 yn were simultaneously operated in parallel. The experimental conditions were the conventional operation method where the water flow LV was constant at 8 m/h for each group, and the internal p-filtration process according to the present invention at 10 m/hX and the surface filtration process at 6 m/h.
The filtration life was compared when the filter was changed to h. A sample of simulated condensate was prepared by dissolving iron oxide α-F, 2O3 in pure water. The concentration was adjusted to 50 p p d asF. It has been confirmed that the operating method according to the present invention has the effect of increasing each collection filtration life by 25 to 33% compared to the conventional method.

〔Effect of the invention〕

According to the present invention, the filtration life of the condensate filtration demineralizer can be extended, and the amount of radioactive waste mainly composed of waste resin can be reduced.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional nuclear power plant condensate purification system, and Figure 2 shows the filtration mechanism of the filtration demineralizer shown in Figure 1. (a) shows internal flow, (b) shows surface filtration. The respective schematic diagrams are as follows: Fig. 3 is an explanatory diagram of the filtration differential pressure increase characteristics of the filtration demineralizer shown in Fig. 2, and Fig. 4 is an illustration of the filtration characteristics, which is the principle of the optimal operation method of the condensate filtration demineralizer of the present invention. An explanatory diagram, FIG. 5 is a schematic diagram of an apparatus for carrying out the operation method shown in FIG. be. 13... Condensate pot, 14... Filtration and desalination tower, 15.
...Flow rate adjustment valve. Agent Patent Attorney Akio Takahashi / (2) Condolences 20 (Ino (Lori Condolence 3 Zukeiton Time f14-Figure Tosui LV (7n/h)

Claims (1)

[Claims] 1. In the method of operating a condensate filtration demineralizer that operates several filtration and demineralization towers in parallel, the filtration mechanism of each unit is judged from the P differential pressure increase characteristics, and the flow rate of the tower during the internal filtration process is determined. An optimal operating method for a condensate filtration demineralizer characterized by making the amount of water greater than the simple average value and making the amount of water flowing through the tower in the surface filtration process less than the simple average value.