JPH0236286B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of operating a condensate over-desalination equipment,
In particular, the present invention relates to an optimal operating method for extending the life of a condensate over-desalination device suitable for use in condensate purification in nuclear power plants. [Background of the Invention] Figure 1 shows a typical example of a condensate purification system for a BWR type nuclear power plant. vapor generated by atom 1 2
rotates the steam turbine 3 to generate electricity, and then becomes condensed water 5 in the condenser 4. This condensate contains solid and ionic impurities due to corrosion of equipment and seawater leaks, and in order to improve the safety and reliability of power plants, it is necessary to reduce the amount of these impurities brought into the atom 1. There is a need to. The over-demineralizer 6 and the demineralizer 7 are devices for removing the above-mentioned impurities for this purpose. The over-desalination device 6 is made of fiber or stainless steel pre-coated with powdered ion exchange resin (a mixture of cationic and anionic exchange resins), as shown in the schematic cross-sectional view of FIG. 2. Over element 8 with a diameter of 50 mm and a height of 1500 to 1800 mm
The tower contains 200 to 300 of these per tower, and its main purpose is to excessively separate solid impurities. The demineralizer 7 is a tower filled with granular ion exchange resin (mixed bed type), and its main purpose is to remove ionic impurities. This condensate purification system is called a dual system, and because it has extremely high removal performance, it has a remarkable effect on reducing the dose rate of the plant, making a major contribution to reducing the radiation exposure of workers during periodic inspections. However, the powdered ion exchange resin used in the over-demineralizer 6 is difficult to regenerate, so currently it is discarded after one use. The period of one cycle is determined by the upper limit set value of the differential pressure (1.75Kg/cm ² in the actual device), and the rate of increase in the differential pressure due to the capture of impurities called iron crud (corrosion products of piping) If the size is large, the powdered ion exchange resin must be replaced frequently. According to actual plant results, one cycle takes about 10 days, and about 10 towers of super desalination unit 6 are operated in parallel, so waste resin (dry weight 50 to 100 kg) is generated per tower per day. . Because waste resin is radioactive waste, it is difficult to process and dispose of it, so currently it is packed in drums and stored in storage facilities. Therefore, their number continues to increase, and reducing the amount of waste generated has become an urgent issue. To reduce the amount of waste, it is necessary to extend the overlife of the over-desalination equipment, and the typical factors that influence overlife are the resin material, equipment structure, operating method, and water quality. Needs consideration.
Of these, resins are currently the most studied, and various improved resins are beginning to be developed. However, the equipment and operating methods are the same as before, and have hardly been studied.
Furthermore, since it is currently difficult to arbitrarily change water quality, the amount of iron cladding has only been reduced, and the quality (for example, the chemical form of iron cladding, particle size, etc.) has not been improved. . [Purpose of the Invention] The present invention has been made in view of the above-mentioned circumstances, and its purpose is to focus on the operating method of a condensate over-desalinator in a condensate purification system of a BWR type nuclear power plant, and to develop the method. The object of the present invention is to provide an optimal operating method for a condensate over-desalination device that can increase the overlife and minimize the amount of radioactive waste generated from waste resin. [Summary of the Invention] The present invention is characterized by the operation of a condensate over-desalination device which is constructed by paralleling a plurality of condensate over-desalination devices that have a built-in over-element pre-coated with a super-aid agent and remove impurities from the liquid. In the first stage of water flow, each condensate over-desalinator performs volumetric filtration by making the overflow velocity smaller than the average flow velocity of the entire water flow period, and conversely, in the latter half of water flow, the overflow velocity is reduced. Surface filtration is carried out at a flow rate higher than the average flow rate during the entire water flow period, thereby increasing the overlife of each condensate demineralizer. Conventionally, condensate demineralizers have been operated with a constant amount of water to be treated, that is, at a constant speed, and the rise characteristics of the differential pressure ΔP are as shown in FIG. That is, it can be understood from the figure that the rate of increase in differential pressure is small at the beginning of water flow, but it rapidly increases after a certain point. The region where the rate of increase in differential pressure is low is considered to be the volume excess region, and the main mechanism is that iron crud in the condensate is trapped inside the resin layer. On the other hand, the region where the rate of increase in differential pressure is high is considered to be a surface excess region, and the main mechanism is that iron cladding is captured on the surface of the resin layer. These iron clad capture mechanisms are summarized in Figure 4. This iron cladding trapping model was derived from the changes in resin layer thickness over time shown in Figure 5 and the results of XMA (X-ray microanalyzer) observation shown in Figure 6. The X-ray intensity in Figure 6 can be regarded as an index of iron concentration, and LV is the linear velocity (Iinear
velocity). Figures 5 and 6 show that at the beginning of water flow, the resin layer is rough and iron crud is trapped inside the resin layer, but as the resin layer gradually becomes denser, the amount of iron crud trapped on the surface of the resin layer decreases. An increase is observed, and it can be seen that the surface irradiation is becoming more dominant. In this way, the filtration mechanism is primarily volume filtration at the initial stage of water flow, but gradually shifts to surface filtration. Extending the overlife is one way to reduce the amount of radioactive waste, but as mentioned above, the increase in differential pressure is closely related to the overload mechanism, and the increase in differential pressure is smaller in the volumetric overload area than in the surface overload area. Therefore, it is presumed that the overlife span can be extended by increasing the volume of the overload mechanism as much as possible. As can be seen from Fig. 3, the rise in differential pressure depends mostly on the surface area, so the following surface area formula (constant speed area) (ΔP - ΔP ₀ ) ¹ is used to quantitatively evaluate the area. ^-n = a×θ a: constant n: cladding compressibility index ΔP: differential pressure ΔP ₀ : initial differential pressure θ: number of days of water flow When we considered the application of A linear relationship was obtained between −ΔP ₀ and the number of days of water flow, indicating that the surface permeability equation can be used to evaluate the permeability characteristics. The slope of this straight line is related to the cladding compressibility index n, and the chemical form of the iron cladding is the main controlling factor. Therefore, if the condensate water quality is constant, the slopes of the straight lines will have approximately the same value.
Furthermore, the run-up section before transitioning to the surface area is the volume area, and application of the surface area method has the effect of separating the volume area and the surface area. From FIG. 7, it can be seen that the overlife can be extended by increasing the volume elapsed time or the surface elapsed time. Since the cladding compressibility index n, which governs the surface time, is almost determined by the water quality of condensate, reducing the n value requires improving the water quality of condensate, which is a very difficult problem in reality. Therefore, an extension of the volume transit time is more likely. What is extremely important here is that the number of water passage days shown in Figure 7 is on a logarithmic scale, so extending the volume elapsed time will increase the overlife by 2.
This means that it has the effect of amplifying up to 3 times. Typical factors that affect volume elapsed time are shown in Table 1. LV in the table means linear velocity. The quality of condensate water and overflow rate (water flow rate) are related to the load on the iron cladding, and the resin physical properties and precoating conditions are related to the density and compressive strength of the resin layer.
The volume elapsed time becomes longer as the cladding load is smaller or the resin layer is coarser and the compressive strength is larger.

[Embodiments of the invention]

An embodiment of the present invention will be described in detail below with reference to FIG. In FIG. 11, the condensate sent by the condensate pump 9 is branched to each super-demineralizer 6 via the condensate main pipe 10, but a flow rate adjustment valve 11 is installed on the upstream side of the super-demineralizer 6. has been done. Super desalination device 6
A flow meter 12 is provided on the downstream side of the flow rate, and the amount of treated water, that is, the overflow velocity (LV) can be monitored. The control device 13 controls the overflow rate in response to the overflow rate signal detected by the flow meter 12 so that the overflow rate of each overdemineralizer 6 follows the set pattern. The regulating valves 11 are automatically driven to adjust the respective overflow speeds. The setting of the overflow rate pattern needs to be determined to the optimum value depending on the plant, but in general, it is desirable that the variation width of the overflow rate be ±12.5% from the average value. The water flow rate should be lower than the average value for the entire water flow area, and be higher in the later stages of water flow, that is, the surface flow area. The timing to change the excess flow rate is determined from the time from the start of water flow or the excess pressure differential. An experimental device similar to that shown in FIG. 11 was manufactured and an experiment was conducted to confirm the effect. The over-desalination device used in this experiment was the over-element (diameter
50mm, height 1500mm, made of nylon). As shown in Figure 12, the experimental conditions were a conventional example where the overflow velocity (LV) was constant at 7 m/h;
As an example of the present invention, initial water flow LV7m/h, late water flow LV8.5
m/h was selected, and the time to change the overflow rate was set at the time of transition from volume flow to surface flow. The experimental results are shown in FIG. In the case of the example of the present invention, the overlife was extended by 43% compared to the conventional example. Table 2 summarizes the life extension effects in each area of volume overload and surface overload. It was confirmed that the effect of low flow rate operation at the initial stage of water flow was noticeable on the surface overtime, and it was also confirmed that high flow rate operation in the surface overflow area had little effect within the scope of this experiment. From this experiment, we found that operating the over-desalinator according to an over-flow rate pattern of low flow rate operation in the early stage of water flow and high flow rate operation in the later stages, with the same over-flow rate as before on average, has a great effect on extending the over-life. It was confirmed that there is.

【table】

[Table] Time ratio [Effects of the invention] According to the operating method of the present invention, it is possible to extend the overlife of the condensate demineralizer to a greater extent than in the past. If used for condensate purification at power plants, the amount of radioactive waste produced by waste resin from condensate over-desalination equipment can be minimized, and the operating method of the present invention can maintain the same overflow rate as conventional methods on average. This has the advantage of not placing any restrictions on plant operation.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing an example of condensate purification equipment for a BWR type nuclear power plant, Figure 2 is a vertical cross-sectional view explaining the structure of a condensate over-desalinator, and Figure 3 is a condensate over-desalinator. Fig. 4 is a diagram showing the iron clad capture mechanism, Fig. 5 is a diagram showing the change in resin layer thickness over time, and Fig. 6 is an XMA of the cross section of the resin layer. Figure 7 is a diagram showing the observation results, Figure 7 is a diagram showing the results of arranging excess pressure data using the surface flow equation, Figure 8 is a diagram showing the relationship between excess flow velocity (LV) and volume transit time, and Figure 9 is the conventional Figure 10 is a diagram illustrating the operation method (overflow rate) of the condensate super-demineralizer, and Figure 10 is a diagram showing the relationship between overflow velocity (LV) and surface time.
Figure 1 is a schematic diagram illustrating one embodiment of the present invention.
FIG. 2 is a diagram illustrating the operating conditions of one embodiment of the present invention in comparison with a conventional example, and FIG. 13 is a diagram showing the effects of one embodiment of the present invention. 1...Atom, 2...Steam, 3...Steam turbine, 4
...Condensate channel, 5...Condensate, 6...Condensate over-desalinator, 7...
Condensate demineralizer, 8... Passing element, 9... Condensate pump, 10... Condensate main pipe, 11... Flow rate adjustment valve, 12...
Flow meter, 13...control device.

Claims (1)

[Scope of Claims] 1. A method of operating a condensate over-desalination device in which a plurality of condensate over-desalination devices are installed in parallel and each includes a built-in per-element pre-coated with a super-aid and removes impurities from the liquid. Therefore, each condensate over-desalination device performs volumetric overflow by reducing the overflow rate to a value lower than the average flow rate during the entire water flow period during the first period of water flow, and conversely lowers the overflow speed to the total flow rate during the latter half of water flow. An optimal operating method for a condensate over-desalination equipment characterized by performing surface filtration at a flow rate higher than the average flow rate for the period. 2. The condensate over-desalination apparatus according to claim 1, characterized in that the range of change in the overflow velocity between the early period of the water flow and the latter half of the water flow is set to ±12.5% with respect to the average flow velocity. Optimal driving method.