JPS6260931B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for evaluating the precoat state of powdered ion exchange resin in, for example, a filtration and desalination apparatus. Conventionally, a combination of a precoat type microfilter and a mixed bed demineralizer filled with granular ion exchange resin has been used to remove trace amounts of ions and suspended solids in water. In recent years, higher purity water quality has been required in various fields such as nuclear power generation, and filtration and desalination equipment that simultaneously performs precision filtration and ion exchange has been adopted as an alternative treatment equipment. This filtration desalination equipment is a very fine powder (approximately
Specially recycled cation exchange resin and anion exchange resin (60 to 400 mesh) are mixed in water, and this mixed resin is pre-coated on the outer peripheral surface of the filtration element. Therefore, ●Ion exchange and precision filtration can be performed at the same time, so the equipment can be simplified. ●Since the resin is fine particles, the ion exchange rate is fast and the exchange capacity of the resin can be utilized to the maximum. ●Since the resin is non-recyclable, there is almost no effect from aging or radiation. Furthermore, it has the advantage that chemical regeneration waste liquid is not produced. This filtration and demineralization apparatus is comprised of a filtration and demineralization tower, backwash precoat equipment, and their control equipment. As shown in Fig. 1, the filtration and demineralization tower 1 has a large number of filtration elements 2 installed inside a shell 3 (only one of them is shown in Fig. 1), and resin is coated on the outer peripheral surface of the filtration elements 2. precoat and perform filtration and desalting. Furthermore, the filtration and demineralization tower 1 has a structure that allows backwashing and precoating of the filtration element 2. That is, a top plate 3a is flanged to the upper part of the body 3, a vent nozzle 4 is connected to the top plate 3a, and an outlet nozzle 5 is provided on the bottom plate 3b of the body 3. The interior of the body 3 is vertically separated by a partition wall 7, and is divided into a lower chamber 8 and an upper chamber 9. A condensate inlet nozzle 6 is connected to the partition wall 7 through the bottom plate 3b. The lower part of the filtration element 2 is watertightly supported by the partition wall 7, and the lower end is connected to the lower chamber 8.
The upper end is supported by a lifting plate 10. A backwash air inlet nozzle 11 is provided on the side wall of the lower chamber 8, and a side drain nozzle 12 is provided on the side wall of the upper chamber 9. Outlet nozzle 5
And rectifying plates 13 and 14 are provided to cover the opening end of the inlet nozzle 6. The filtration element 2 is a cylindrical body made of stainless steel or nylon, for example, and has a number of mesh-like holes provided on its side surface. And stainless steel elements are used for high temperature or high radiation systems. The ion exchange resin pre-coated on the outer peripheral surface of the filtration element 2 is, for example, a cation exchange resin of approx.
120℃, anion exchange resin is stable up to about 60℃. However, in the case of anionic resin, 2~
After three weeks of operation, the ion exchange capacity decreases by 20 to 30% compared to a new product, and at temperatures above 90°C, the capacity decreases rapidly. Therefore, the limit on the temperature of granular ion exchange resin is due to the heat resistance of anion exchange resin.
Most are operated at around 40℃. Powdered ion exchange resin (trade name: Powdex Resin) has the characteristics shown in the table.

[Table] As mentioned above, the above ion exchange resin has a particle size of 60~
Since it is as fine as 400 meshes, if only one type of resin is precoated on the filtration element 2, the pressure loss will be extremely large even if the amount is small.
However, when cationic resin and anionic resin are mixed, they coagulate electrostatically and increase the porosity.
Pressure loss becomes extremely small. Although the state of aggregation changes depending on the ratio of cationic resin to anionic resin, it is usually highly agglomerated and cannot be uniformly precoated onto the filtration element 2 as it is. For this reason, a polyelectrolyte solution is added to the mixed slurry to adjust the aggregation state so that it can be precoated on the outer peripheral surface of the filter element 2 with an appropriate porosity. However, in order to judge whether the outer circumferential surface of the filtration element 2 is uniformly precoated, that is, to evaluate the precoat state, the quality of the outlet water of the filtration and demineralization tower 1 is measured, and it is determined whether ultrapure water is obtained. This was the only criterion for judgment. However, the impurity concentration in the outlet water of a filtration desalination device is generally extremely low and falls below the detection limit of ordinary chemical analysis methods, making quantitative evaluation impossible. For this purpose, we measured the electrical conductivity of the outlet water of the filtration and demineralization tower, confirmed that it showed electrical conductivity equivalent to pure water, and evaluated the precoat state of the powdered ion exchange resin (hereinafter simply referred to as resin). There is. Even with this method, when reactor water is actually passed through the reactor water after confirming the pre-coating state of the resin in the filtration and demineralization tower, sometimes the ion exchange capacity of the pre-coated resin is not fully consumed. The electrical conductivity at the outlet of the filtration and demineralization tower continues to rise, reaching a so-called electrical conductivity break state, and it becomes necessary to backwash and discard the resin that has been used so far and pre-coat with a new resin. The causes of conductivity break without consuming sufficient ion exchange capacity are as follows:
The reason is that the resin is not uniformly pre-coated on the filter element in the filtration and demineralization tower, and that there is a thin part of the pre-coated layer (thin layer part), which causes the conductivity to break quickly in this thin pre-coated layer part. It is considered. Especially when filtering and desalting cooling water containing radioactive materials in nuclear power generation facilities,
It is an important issue to keep the amount of radioactively contaminated resin, which is excess secondary waste, generated as low as possible.
It is necessary to provide the filtration and demineralization tower with sufficient ion exchange capacity. The present invention has been made in view of the above points,
An object of the present invention is to provide a method for evaluating the precoat state of a powdered ion exchange resin that can suppress the amount of secondary waste generated in the treatment of liquids containing radioactive substances as low as possible and exhibit sufficient water treatment performance. . That is, the present invention is a method for evaluating and confirming the precoating state of ion exchange resin on the filtration and demineralization tower 1, using a solution (electrolyte solution) with a known ion concentration that has been artificially adjusted. A water flow test was conducted, and the outlet conductivity of the filtration and demineralization tower was 0.1.
Calculating the flow-through exchange ion capacity corresponding to the ion exchange capacity consumed to exceed μν/cm and comparing it with the design requirement value is a method of determining the quality of precoating of powdered resin using an actual machine. The details of the present invention will be explained below with reference to the illustrated embodiments. FIG. 2 is a flow diagram showing a filtration and desalination apparatus used to explain an example of the present invention. During normal operation, water to be filtered and demineralized is led from system 40 to upper chamber 9 through pipe 21, valve 22, pipe 23, and inlet nozzle 6, respectively. The water to be filtered and demineralized led to the upper chamber 9 passes through the resin layer 2 pre-coated on the outer surface of the filtration element 2.
a, and is led to the lower chamber 8, and the outlet nozzle 5,
It passes through piping 24, valve 25, and piping 26 and is returned to the appropriate system 41. When the resin layer 2a pre-coated on the filtration element 2 consumes its ion exchange capacity through water passing through the filtration and demineralization tower 1 and reaches a break state, it is backwashed and regenerated from the opposite direction of the above-mentioned normal water treatment route. By flowing water or air, the resin that has been precoated is peeled off and transferred to the waste treatment system 27 for backwashing. When precoating the filtration element 2 in the filtration and demineralization tower 1 with resin, put the resin in the precoat tank 28, add water, and stir it with the stirrer 42 to make a uniform slurry. 30, Piping 2
3. The resin is sent into the upper chamber 9 through the inlet nozzle 6 in order, and the water is passed through the filtration element 2. The flowed water flows through the lower chamber 8, the outlet nozzle 5, and the pipe 2.
4. The liquid passes through the valves 31 in turn and is returned to the precoat tank 28. As a result, a resin layer 2a is formed on the filtration element 2. Figure 3 is a simulated diagram of the state in which the resin is pre-coated on the filtration element 2. In order to ensure uniform pre-coating and to achieve the performance required in the design, the resin should be pre-coated on the filtration element 2 as shown in The resin layer 2a needs to have a certain thickness. On the other hand, in the so-called non-uniform pre-coating state, when the lower part of the filtration element 2 is thick and the upper part is thinly pre-coated as shown in (B), or when the lower part is thin and the upper part is thickly pre-coated as shown in (C), The thin layer portion consumes the ion exchange capacity, and sufficient ion exchange cannot be performed, and the quality of the water at the outlet of the filtration and demineralization tower 1 deteriorates, reaching a so-called ion break state. However, the areas where the resin is thickly precoated still have sufficient ion exchange capacity. When the ion break state occurs, the resin layer 2a that has been precoated will be discarded without completely consuming its ion exchange capacity. One method of the present invention for determining the quality of the precoated state of the precoated resin is to artificially create a solution with a known ion concentration, pass water through the filtration and demineralization tower 1, and remove the ions collected in the resin layer. Evaluation is based on the amount of ions. The purpose of this evaluation is to determine the completeness of the precoat and determine the operating conditions for the precoat (flow rate, valve opening/closing timing, etc.). Therefore, in the present invention, carbonate ions are used to evaluate the precoat state of the resin. In FIG. 2, carbon dioxide gas is dissolved in a precoat tank 28 from a carbon dioxide gas cylinder 31 via a valve 32 and a pipe 33, and this dissolved solution is introduced into the resin layer 2a to continuously remove carbonate ions. The amount of carbonate ions sent to the filtration and demineralization tower 1 is determined by the conductivity meter 34 on the filtration and demineralization tower 1 and the piping 23.
The water quality of the water treated in the filtration and demineralization tower 1 is similarly continuously monitored using the conductivity meter 35 on the piping 24 of the filtration and demineralization tower 1. By continuously monitoring the electrical conductivity of the water at the inlet and outlet of the filtration and demineralization tower in this way, the amount of carbonate ions removed in the resin layer 2a pre-coated on the filtration element 2 can be integrated. Figure 4 shows the readings (unit: This shows an example of the time change of μν/cm). The reading on the conductivity meter 34 at the entrance of the filtration and demineralization tower is A.
The figure shows the saturated conductivity of carbon dioxide gas.
When the water flow process to the filtration and demineralization tower is started at point C, the indication of the conductivity meter 35 at the outlet of the filtration and demineralization tower changes as shown in characteristic B as the water flow time elapses. At point D, the electrical conductivity indication at the outlet of the filtration and demineralization tower becomes 0.1μν/cm or more. By this point, the resin layer 2 on the filtration element
The amount of carbonate ions collected by ion exchange in a is determined by the electrical conductivity at the outlet of the filtration and demineralization tower from point C where water flow treatment started.
It can be determined as the flow-through exchange ion capacity, which is the ion exchange capacity consumed up to point D, which is 0.1μν/cm. In order to calculate the flow-through exchange ion capacity, it can be easily calculated by multiplying the difference in conductivity between the inlet and outlet of the filtration and demineralization tower by the amount of treated water, and it is proportional to the area of the shaded area in Figure 4. In addition, if the resin is pre-coated non-uniformly on the filtration element 2 of the filtration and demineralization tower, the electrical conductivity at the outlet of the filtration and demineralization tower 1 deteriorates more rapidly than in characteristic B, as shown in characteristic E. is commonly seen. Therefore, it is possible to determine the precoat operating conditions under which characteristic B is obtained by this method. Thus, the problem with conventional precoating is that the resin layer 2a of the filtration element 2 is slightly affected by the flow rate during precoating, the timing of valve opening/closing, the length of the system piping, etc. Even if the uniformity of the ion exchange is confirmed and pre-coat conditions are set, sufficient ion exchange performance may not always be achieved in actual equipment.Furthermore, in actual equipment, valves, pumps, etc. may change over time. Although the precoating was done to a uniform thickness at the beginning of the plant's operation, after a few years, the precoating may no longer be uniform and sufficient water treatment effects may not be achieved. However, as mentioned above, by accurately evaluating the state of resin pre-coating on the filtration and demineralization tower and using the filtration and demineralization tower with the designed ion exchange capacity for water treatment, the generation of excess resin waste can be reduced. At the same time, sufficient treatment effects can be exhibited. Furthermore, by using the method of the present invention, the validity of the precoating status of the resin can be easily confirmed and evaluated at any time, making it possible to operate the filtration and demineralization tower in a healthy state at all times. Note that the present invention relates to a fuel pool purification system filtration desalination tower,
It can be applied to all types of filtration and demineralization towers that pre-coat powdered resin, such as reactor coolant purification system filtration and demineralization towers and condensate filters.Also, by using any chemical species other than carbon dioxide, the quality is closer to the actual treated water quality. The precoat condition can be evaluated by creating simulated water quality and passing water through it.

[Brief explanation of the drawing]

The drawings are for explaining the method according to the present invention, and FIG. 1 is a cross-sectional view of the filtration and demineralization tower, FIG. 2 is a system diagram for precoating the filtration element with ion exchange resin in the filtration and demineralization tower, and FIG. Figure 3 is a schematic cross-sectional view showing the state in which the ion exchange resin is pre-coated on the filtration element, A shows the ideal state, B and C show the unfavorable state, and Figure 4 shows the confirmation of the pre-coated state of the filtration and demineralization tower. It is a characteristic diagram of electrical conductivity which shows an example. 1...filtration demineralization tower, 2...filtration element, 2
a... Resin layer, 5... Outlet nozzle, 6... Inlet nozzle, 27... Waste treatment system, 29... Precoat pump, 31... Carbon dioxide gas cylinder, 34... Conductivity meter, 35... Electric conductivity Total.

Claims (1)

[Scope of Claims] 1 A filtration element is precoated with a powdered ion exchange resin, and a saturated solution of electrolyte is passed through the filtration element to continuously monitor the conductivity of the inlet and outlet water of the filtration element, and the conductivity of the monitored outlet water is A method for evaluating the precoat state of a powdered ion exchange resin, comprising evaluating the precoat state based on the time when the rate starts to increase and the rate of increase. 2. The method for evaluating the precoat state of a powdered ion exchange resin according to claim 1, wherein the saturated electrolyte solution is a carbon dioxide solution.