JPH0342921B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a precoating method for a precoat filter used for condensate treatment in power plants, etc., and in particular a precoating method that can efficiently form a precoat layer with a long filtration life. It is related to.

[Conventional technology]

For condensate treatment in power plants, precoat filters are used to remove oxidation products (cruds) from condensate. As the precoat material used in this precoat filter, natural or artificial fibrous substances, diatomaceous earth, ion exchange resin powder, etc. are used. Ion-exchange resin powder is used at nuclear power plants, especially from the viewpoint of treated water quality, but since used pre-coat materials contain radioactive materials and must be treated, there is a desire to reduce the amount of waste generated. , it is desirable to extend the filtration life, that is, the operating time.

In order to extend the filtration life of the precoat material, it has been proposed to mix fibrous materials into the ion exchange resin powder, but the effect is not significant, so multi-layered filter layers have been proposed to improve this. Multilayering of filter layers involves forming a fine precoat layer on the lower layer in contact with the filtration element, and forming multiple layers of coarse precoat layers in order toward the upper layer.In the case of a single layer, only surface filtration is performed. By using multiple layers, it becomes close to full-layer filtration and the filtration life is extended.

FIG. 2 is a system diagram showing a conventional precoat filter. In the figure, reference numeral 1 denotes a filter, which contains a filter element 2, and is connected to a stock solution pipe 3 and a processing liquid pipe 4. A circulation path 5 includes a precoat tank 6 and a pump 7, and a bypass path 8 is provided in parallel with the precoat tank 6. V ₁
~V ₆ is a valve.

In the above pre-coated filter, condensate treatment is performed by opening the valves V ₁ and V ₂ , supplying condensate from the stock solution pipe 3 to the filter 1, filtering it through the pre-coated filtration element 2, and processing it from the processing solution pipe 4. Return the condensed water. The conventional precoating method is performed in the following steps.

Stop water flow to filter (close all valves) Peel off precoat layer (perform by backwashing operation, details omitted) Precoat preparation (disperse precoat material in precoat tank 6) Precoat (pump 7 running, valves V ₃ and V ₄ open) ) Precoat (pump 7 running, valves V ₃ , V ₄ , V ₅ , V ₆
Open) Precoat (Pump 7 running, valves V ₁ , V ₂ , V ₃ , V ₄
Open) Water flow (Pump 7 stopped, valves V ₁ and V ₂ opened) In the case of multilayer precoating, in the above process,
, and each time a different precoat material is dissolved in the precoat tank 6 to form a multilayer precoat layer.

[Problem that the invention seeks to solve]

However, in the conventional precoating method as described above, when performing multilayer precoating,
The precoat material is manually dispersed during the process, which is complicated, and for example, a single layer can be precoated in 30 minutes, but two layers can be precoated in 50 minutes, and three layers can be precoated in 70 minutes. In addition to being time consuming, even if multilayer precoating is performed, the particle size of the precoat material is not continuous, so there are problems such as complete all-layer filtration cannot be performed.

This invention is intended to solve the above-mentioned problems. It is possible to perform precoating in a short time with a simple structure and operation, and the precoat layer formed changes continuously from fine to coarse. The purpose of the present invention is to provide a precoating method that enables full-layer filtration and has a long filtration life.

[Means for solving problems]

This invention provides a method for precoating by dispersing a precoat material in a precoat tank, supplying the precoat material in the precoat tank to a filter having a built-in filter element, and circulating a filtrate, in which a fine precoat material is supplied. After precoating for a certain period of time, with the fine precoat material remaining in the precoat tank, continue precoating while injecting the coarse precoat material into the precoat tank to create a precoat layer that changes continuously from a fine layer to a coarse layer. This is a pre-coating method characterized by forming.

[Effect]

In the precoat method of the present invention, finely granular precoat materials such as ion exchange resin powder and diatomaceous earth are dispersed in a precoat tank and supplied to the filter through a circulation path to form a precoat layer on the filtration element. Circulate through circuits and bypasses. After a certain period of time, fine pre-coat material remains in the pre-coat tank.
If you continue precoating while injecting the coarse precoat material made of natural or artificial fibrous materials such as cellulose filter media dispersed in the auxiliary precoat tank into the precoat tank, the fine granular precoat material remaining in the precoat tank will be mixed with the injected coarse precoat material. The fibrous coarse precoat material is mixed and precoated, and the ratio of the two is reversed as the precoating continues, and finally only the fibrous coarse precoat material is precoated. Therefore, the precoat layer formed is fine on the filtration element side and becomes coarser toward the upper layer, and the change is continuous, making it possible to perform complete full-layer filtration.

〔Example〕

Hereinafter, the present invention will be described with reference to embodiments shown in the drawings. FIG. 1 is a system diagram showing a precoat filter according to an embodiment of the present invention, and the same reference numerals as in FIG. 2 indicate the same or corresponding parts. Reference numeral 9 denotes an auxiliary precoat tank, which is filled with a coarse precoat material in which fibrous materials such as cellulose filter media are dispersed in water, and is connected to the precoat tank 6 through a valve V ₇ so that it can be injected. . The pre-coat tank 6 is filled with a fine pre-coat material in which granular materials such as ion exchange resin powder and diatomaceous earth are dispersed in water. After pre-coating with this pre-coat material for a certain period of time, an auxiliary pre-coat tank 9 is filled with a fine pre-coat material consisting of fibrous materials. The rough precoat material is poured into the precoat tank 6 and precoating is continued.

In the above configuration, the precoating method is performed in the following steps.

Filter water flow stops (all valves closed) Peeling and removal of pre-coat layer (same as conventional method) Pre-coating preparation (dispersing pre-coating material in pre-coating tanks 6 and 9) Pre-coating (pump 7 running, valves V ₃ and V ₄ open) ) Precoat (pump 7 running, valves V ₃ , V ₄ , V ₅ , V ₆
Open) Precoat (Pump 7 running, valves V ₃ , V ₄ , V ₅ , V ₆ ,
V ₇ open) Precoat (pump 7 running, valves V ₁ , V ₂ , V ₃ , V ₄
Open) Water flow (Valves V ₁ and V ₂ open) In the above operation, the liquid circulates through the bypass path 8 in the precoat, and a uniform flow through the filter element 2 is generated. In the precoating process, fine granular precoat material from the precoat tank 6 is supplied to the filter 1, and a fine precoat layer is formed on the filter element 2. When entering the precoat after precoating for a certain period of time, the fine granular precoat material remaining in the precoat tank 6 and the coarse fibrous precoat material injected from the auxiliary precoat tank 9 are mixed and supplied to the filter 1, where they are mixed. A precoat layer is formed. Since the fine precoat material remaining in the precoat tank 6 gradually decreases, the ratio of the coarse fibrous precoat material increases, and the precoat layer formed on the filter element 2 changes continuously from fine to coarse.

Therefore, in the water passing step, suspended matter (crud) in condensate is captured sequentially from the fine precoat layer, and the entire precoat layer is effectively used to perform full-layer filtration, thereby extending the filtration life.

The steps and the timing of the steps and the flow rate of the valve V ₇ in the steps are important factors,
Although it varies depending on the properties of the condensate to be filtered, it is desirable that the following conditions be satisfied.

Amount of fine precoat material used in precoat tank 6: 60 to 90% of the total Amount of coarse precoat material used in auxiliary precoat tank 9: 10 to 40% of the total Timing of transition from precoat to precoat: Set the capacity of precoat tank 6 to Va (m ³ ),valve
If the flow rate of V ₆ is Qa (m ³ /h), then 0.1 to 3 Va / Qa (h) after the start of precoating. Flow rate of valve V ₇ : Capacity of auxiliary precoat tank 9 is Vb (m ³ ), flow rate of valve V _7. If is Qb (m ³ /h) and the time required for precoating is T (h), then 0.1T≦Vb/Qb≦
1/2T range Due to the above, the auxiliary precoat tank 9 has a small capacity.
The valve V ₇ may have a small diameter, and the precoating of the present invention can be performed simply by adding it to a conventional device. Precoating can be performed in approximately the same time as in the case of a conventional single precoat layer, and the filtration life is approximately 1.2 to 2.5 times longer.

Test examples will be explained below.

Test example 1 (conventional method) In the apparatus shown in Fig. 2, a wedge wire element with a filtration area of 700 cm ² was installed as the filtration element 2,
Assuming the capacity of the pre-coat tank 6 to be 7, 23.3 g (dry weight) of cation exchange resin powder DIAION DFK-10 (manufactured by Mitsubishi Chemical Industries KK, registered trademark), 11.7 g of anion exchange resin powder DIAION DFA-10.
(dry weight) and 35 g (dry weight) of a fibrous pre-coat material, Crysorb L-10 (manufactured by Kurita Kogyo KK, registered trademark), were dissolved and pre-coated (pre-coat amount used: 1 kg/cm ² filter surface). When the precoating was carried out through the circulation path 5 at a flow rate of 210/h, the circulating water became clear in about 10 minutes, but the precoating was completed by continuing the circulation for 15 minutes as is generally done.

After precoating, simulated condensate containing 2 mg of hydrated iron oxide/Fe was applied at a flow rate of 350/h (flow velocity to the filtration surface 5 m/h),
When water was passed through the filter and filtration was continued until the differential pressure reached 1.2 kg/cm ² , the amount of iron captured was 33 g - Fe/Kg - filter medium, and the iron removal rate was 98%.

Test Example ₂ (Example) As shown in FIG.
10, 11.7 g of Diaion DFA-10, and 5 g of Chrysove L-10 were dispersed, and 30 g of Chrysove was dispersed in the auxiliary pre-coat tank 9 (the total amount of pre-coat material used was the same as in Test Example 1). .

The precoat is circulated through the circulation path 5 with the valve V ₇ closed at a flow rate of 210/h, and after 2 minutes, the valve V ₇ is opened and the precoat material is transferred from the auxiliary precoat tank 9 at a flow rate of 30/h to the precoat tank in about 2 minutes. 6 was injected. When the circulation was continued further, the circulating water became clear in about 10 minutes, and precoating was completed after 5 minutes.

Then, in the same manner as in Test Example 1, 2 mg of hydrated iron oxide
Condensate of Fe/ is passed at a rate of 350/h, and the differential pressure is 1.2Kg/
When filtration was carried out until it reached cm ² , the amount of iron captured was 64g.
-Fe/Kg-filter medium, iron removal rate was 98%.

From the above results, by extending the precoating time by about 5 minutes compared to the conventional single-layer precoat (15 minutes), the filtration life can be extended and the amount of iron captured can be increased.
The amount of radioactive waste can be reduced.

In the above explanation, the coarse precoat material in the auxiliary precoat tank 9 is injected into the precoat tank 6 rather than directly into the circulation path 5 (including the filter 1) to continuously change the precoat layer. I can do it. Further, although the present invention is suitable for condensate treatment in a nuclear power plant, it can also be applied to other precoated filters.

〔Effect of the invention〕

According to this invention, precoating is performed while injecting coarse precoat material while fine precoat material remains in the precoat tank, so precoating can be performed in a short time with a simple structure and operation, and formation The precoat layer changes continuously from thin to coarse, allowing full-layer filtration and long filtration life, making it possible to reduce the amount of radioactive waste even when processing radioactive materials.

[Brief explanation of drawings]

FIG. 1 is a system diagram of an embodiment, and FIG. 2 is a system diagram of a conventional precoat filter. In each figure, the same reference numerals indicate the same or corresponding parts, 1 is a filter, 2 is a filter element, 5 is a circulation path, and 6 is a filter.
is a precoat tank, 7 is a pump, 8 is a bypass path, 9 is an auxiliary precoat tank, and V ₁ to V ₇ are valves.

Claims (1)

[Claims] 1. A method for precoating by dispersing precoat material in a precoat tank, supplying the precoat material in the precoat tank to a filter having a built-in filtration element, and circulating the filtrate. After supplying and precoating for a certain period of time, with the fine precoat material remaining in the precoat tank, precoating continues while coarse precoat material is injected into the precoat tank, changing continuously from a fine layer to a coarse layer. A precoating method characterized by forming a precoat layer. 2. The precoat method according to claim 1, wherein the fine precoat material is a granular material and the coarse precoat material is a fibrous material.