JPH0938648A - Treatment of blow water of power plant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To assure a differential pressure restoring property by washing using gas-liquid mixed water and to easily, inexpensively and stably treat blow water while suppressing the degradation in the strength of hollow fiber filter membranes by an oxidizing agent by intermittently eexecuting the addition of the oxidizing agent to blow water. SOLUTION: The blow water or the water mixture composed of this blow water and city water, etc., is admitted from an inflow pipe 9 for the water to be treated into a filter column 1. The water to be treated is risen in this filter column 1 and is admitted into a hollow fiber module 3, where the water is passed through the hollow fiber filter membranes 4 to have iron oxide filtered. In the meantime, the filtrate is collected above a partition plate 2 and is discharged from an outflow pipe 8. Air is thereafter admitted from an air inflow pipe 11A into the filter column A to stir the water and to peel the iron oxide. The waste washing water is removed from a drain pipe 20. Incidentally, the oxidizing agent is intermittently added to the water to be treated. Namely, an injecting pump 16 is driven at every cycle of a prescribed number of times to inject the oxidizing agent in an oxidizing agent soln. tank 15 into the inflow pipe 9 for the water to be treated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of treating blow water discharged from a circulation system of turbine driving steam and condensate in a power plant using a hollow fiber filtration membrane.

[0002]

2. Description of the Related Art In thermal power plants and nuclear power plants,
Basically, condensate is heated by a boiler to generate steam,
After the turbine is driven by the steam, the steam is cooled by a condenser to be condensed water, and the condensed water is supplied to the boiler again to generate electricity. In such a circulation cycle, blow water is discharged from the circulation system of turbine driving steam and condensed water.

Blow water is drain water produced by condensation of steam in pipes and equipment, such as heater drain water and turbine drain water. Blow water includes those that are constantly discharged from the power plant and those that are discharged particularly when the power generation turbine is started. Both are at relatively high temperatures and are caused by corrosion of metal surfaces such as equipment and piping. The content of iron oxide is considerably large, 100 to 1000 ppb or more, but almost no salt or the like is contained.

Therefore, in the power plant, the above-mentioned blow water is collected in a tank, iron oxide is removed from the blow water, and the blow water after the iron oxide is removed is supplied to the front stage of the makeup water treatment system to the condensate circulation system. It is supplied and reused. As a method for treating such blow water, conventionally known is a method of adding an oxidizing agent to the blow water and then filtering with a hollow fiber filtration membrane. 63-80896).

The processing method disclosed in JP-A-63-80896 is as follows.
Iron oxide is removed from the filtration membrane surface of the hollow fiber filtration membrane, and when the filtration pressure difference rises, gas-liquid mixed water is brought into contact with the hollow fiber filtration membrane to remove the iron oxide from the filtration membrane surface and filter again. Is to do. In this case, in the conventional hollow fiber filtration membrane treatment performed without adding an oxidizing agent to the blow water, iron oxide adhering to the hollow fiber filtration membrane surface at the time of increasing the differential pressure was washed with only the gas-liquid mixed water by a conventional method. However, the pressure difference was not restored to the original state. On the other hand, JP-A-63-8089
In the treatment method of No. 6, by adding an oxidizing agent to blow water and then filtering with a hollow fiber filtration membrane, if the hollow fiber filtration membrane is washed with only gas-liquid mixed water by a conventional method at the time of increasing the differential pressure,
The differential pressure is restored to the original state, and stable treatment of blow water becomes possible.

[0006]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention
When an oxidant is continuously added to blow water and filtration is performed using a hollow fiber filtration membrane, the recovery of the differential pressure by washing is improved, but the oxidative deterioration of the material of the hollow fiber filtration membrane is promoted and its physical strength is increased. It was found that the hollow fiber membrane significantly shortens the life of the hollow fiber filtration membrane. Therefore, after a certain period of time, the physical strength of the hollow fiber filtration membrane decreases to a certain limit value and the hollow fiber filtration membrane is damaged by vibration and pressure during water passage or washing with gas-liquid mixed water. In order to prevent this, the hollow fiber filtration membrane must be replaced with a new one before the strength of the hollow fiber filtration membrane falls below a certain value, which complicates the operation and increases the running cost. .

However, in the case where filtration is carried out using a hollow fiber filtration membrane without addition of an oxidizing agent, the differential pressure does not recover to the original differential pressure even after washing with gas-liquid mixed water as described above, The pressure rises gradually. Therefore, it is necessary to clean the hollow fiber filtration membrane with a chemical agent such as alkali and acid at regular intervals to remove fine particles such as iron oxide remaining on the membrane surface and impurities with high adhesion such as organic substances. However, the operation was complicated and the running cost was increased.

The present invention has been made in view of the above circumstances, and in a treatment method in which an oxidizing agent is added to blown water in a power plant and then filtration is performed using the hollow fiber filtering membrane, the strength of the hollow fiber filtering membrane using the oxidizing agent is increased. While suppressing the decrease, it is possible to secure the recoverability of the differential pressure by washing with gas-liquid mixed water, and therefore it is possible to perform stable blow water treatment at low running cost without performing a complicated operation. It is an object to provide a method for treating power plant blow water.

[0009]

In order to achieve the above object, the present invention is to add an oxidizer to blow water discharged from a turbine drive steam and condensate circulation system in a power plant, and then add the blow water. A method for treating blow water of a power plant, wherein the oxidant is intermittently added to the blow water in a treatment method of filtering the water with a hollow fiber filtration membrane (claim 1).

In the present invention, the reason why the recovery of the differential pressure by washing with gas-liquid mixed water can be ensured while suppressing the strength reduction of the hollow fiber filtration membrane due to the oxidizing agent is as follows. Guessed. That is, at the time of filtration without addition of an oxidizing agent, a trace amount of organic matter in the water to be treated adheres to the membrane surface of the hollow fiber filtration membrane to promote bacteria generation, and slime is formed and adheres on the membrane surface. Amorphous iron oxide contained in the water to be treated also adheres to the film surface, but this is iron oxide that is difficult to peel off by cleaning with gas-liquid mixed water. Therefore, during filtration without addition of an oxidizing agent, the slime or amorphous iron oxide adheres to the membrane surface to increase the differential pressure. On the other hand, when the filtration with the addition of the oxidant is carried out after the filtration without the addition of the oxidant as in the present invention, the slime adhering to the film surface during the filtration without the addition of the oxidant is oxidized and removed by the oxidant. At the same time, the oxidizing agent changes the amorphous iron oxide into crystalline iron oxide with good releasability, which allows the slime and iron oxide to be easily peeled off by washing at the end of filtration with the addition of the oxidant. It is considered that the pressure recovers to the initial differential pressure.

Further, according to the present invention, the time during which the hollow fiber filtration membrane is in contact with the oxidizing agent can be greatly shortened by intermittently adding the oxidizing agent, so that the physical properties of the hollow fiber filtration membrane due to oxidative deterioration can be reduced. It is possible to greatly suppress the decrease in strength and extend the service life of the hollow fiber filtration membrane.

In the present invention, the kind of the oxidizing agent intermittently added to the blow water is not limited, and for example, a chlorine-based oxidizing agent such as sodium hypochlorite, an arbitrary oxidizing agent such as hydrogen peroxide, ozone and the like can be used. Can be used. In this case, using a chlorine-based oxidizing agent such as sodium hypochlorite is advantageous in terms of running cost, and using hydrogen peroxide or ozone is advantageous in that the amount of ions in the filtered water is not increased.

The amount of the oxidizing agent added during the intermittent addition is preferably such that a small amount of the oxidizing agent remains in the filtered water of the hollow fiber filtration membrane. For example, when sodium hypochlorite is used, it is appropriate to add it so that the residual chlorine concentration in the filtered water is about 1 ppm.

The hollow fiber filtration membrane may be made of any material such as polyolefin, polyvinyl alcohol and polysulfone. The properties of the hollow fiber filtration membrane are not limited, but for example, the membrane surface has a pore size of 0.01 to 1 μm.
m, preferably about 0.1 μm, having fine pores with an outer diameter of 0.3 to 2 mm and an inner diameter of 0.2 to 1.5 mm can be suitably used. The hollow fiber filtration membrane may be one that allows the treated water to pass from the outside to the inside of the membrane (external pressure type), or one that allows the treated water to pass from the inside to the outside of the membrane (internal pressure type). It may be. In the present invention, usually, a large number of the hollow fiber filtration membranes are bundled to form a hollow fiber module, and a large number of the hollow fiber modules are mounted in a filtration tower and used as an external pressure type.

Since blow water has a relatively high temperature,
When the heat resistance of the hollow fiber filtration membrane is not so high, the blow water is mixed with room temperature city water, industrial water or its turbidity filtered water for cooling, or the blow water is passed through a heat exchanger for cooling. After this, it is preferable to perform a filtration treatment with a hollow fiber filtration membrane.

The method for intermittently adding the oxidizing agent to the blow water is not particularly limited, but the following methods (a) to (c) can be preferably adopted.

(A) In the filtration treatment of blown water with a hollow fiber filtration membrane, usually, after the filtration is started, the filtration is carried out continuously until the filtration differential pressure reaches a constant value. When the temperature reaches, the filtration is stopped and the hollow fiber filtration membrane is washed with gas-liquid mixed water. That is, the operation of [starting filtration process-increasing differential pressure-washing] is one cycle,
The blow water is treated while repeating this cycle.

Therefore, as one method of intermittently adding the oxidant, a procedure of carrying out one or a plurality of cycles without adding the oxidant and then carrying out one or a plurality of cycles by adding the oxidant. Can be determined in advance, and an oxidant can be intermittently added according to this procedure.

(B) Another method for intermittently adding an oxidant is as follows.
Regardless of the cycle described above, a method of adding an oxidizing agent for a certain period of time can be adopted at the time of filtration by the hollow fiber filtration membrane.

(C) The quality and contents of the blow water of the power plant are
It changes depending on the operating conditions of the power plant. For example, blow water discharged at the time of start-up after periodic inspection of a power plant contains a large amount of iron oxide, and when treating this start-up blow water, the difference between hollow fiber filtration membranes in one cycle is The pressure rise speed becomes extremely fast. Therefore,
Since the filtration time in one cycle of [starting filtration process-increasing differential pressure-washing] is shortened and the time during which the oxidant contacts the deposit on the film surface in the cycle of adding the oxidant is also shortened, In some cases, the effect of removing the deposits is reduced, and the differential pressure may not be restored to the original state by washing after adding an oxidizing agent and performing filtration.

Therefore, as still another method for intermittently adding the oxidant, the interval of the oxidant addition is changed according to the change in the differential pressure increase rate, and the difference in one cycle is treated as in the case of treating the blow water at startup. When the rate of pressure increase is extremely fast, it is possible to adopt a method in which the time during which the oxidizing agent contacts the film surface deposit is lengthened to enhance the effect of removing the film surface deposit by the oxidizing agent. Thus, the intermittent oxidizing agent addition method in which the interval of the intermittent addition of the oxidizing agent to the blow water is changed according to the change in the increasing rate of the filtration differential pressure of the hollow fiber filtration membrane (claim 2).
Is preferably used when treating blow water discharged at the time of start-up after periodic inspection of a power plant. In addition,
The method (c) can be applied not only to the case of treating blow water at startup but also to the treatment of blow water in a steady state.

Among the above-mentioned methods, the methods (a) and (c) in which the oxidant is intermittently added in units of the cycle are more than the method (b) in which the oxidant is intermittently added at a constant time interval. It is advantageous in that the effect of recovering the filtration differential pressure by the intermittent addition of the oxidizing agent can be clearly determined.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a flow chart showing an example of a blow water treatment apparatus used for carrying out the present invention. In the figure, 1 indicates a filtration tower. A partition plate 2 is installed above the filtration tower 1, and a large number of hollow fiber modules 3 are suspended on the partition plate 2. The hollow fiber module 3 is an outer cylinder (not shown)
In which a large number of hollow fiber filtration membranes 4 are arranged inside, water is passed from the outside to the inside of each hollow fiber filtration membrane 4 to filter the iron oxide contained in the blown water on the outer surface of the hollow fiber filtration membranes 4, The filtered water is collected above the partition plate 2.

At the lower end of each hollow fiber module 3, a bubble inflow mechanism 5 for introducing bubbles into the hollow fiber module 3 is installed. An inlet pipe 6 is provided at the lower end of the filtration tower 1, an air vent pipe 7A is provided slightly below the partition plate 2, and a filtration tower 1 is provided.
An air vent pipe 7B and a filtered water outflow pipe 8 are connected to the upper part of the. The inflow pipe 6 has a treated water inflow pipe 9,
The drain pipe 10 and the air inflow pipe 11A communicate with each other, and the filtered water outflow pipe 8 communicates with the air inflow pipe 11B.

In the figure, 12 is an air surge tank and 13 is an air storage tank. The air surge tank 12 and the air storage tank 13 are the air pipe 1
These air storage tanks 1 are connected through
3 and the air surge tank 12 have an air inlet pipe 11A, respectively.
And the air inflow pipe 11B is connected. Further, in this apparatus, an oxidant solution tank 15 is installed, and the oxidant solution tank 15 and the treated water inflow pipe 9 are connected by an injection pipe 17 in which an injection pump 16 is interposed. In addition, 18 to 25 in the figure
Are valves, 26 is a differential pressure gauge, and 27 is an air supply pipe.

Next, a preferred embodiment of the processing method of the present invention using the apparatus of FIG. 1 will be described. First, the valves 18 and 24 are opened, and blow water or a mixed water of blow water mixed with city water, industrial water, or turbidity filtered water thereof is passed through the treated water inflow pipe 9 and the inflow pipe 6 in the filtration tower 1. Flow into. The water to be treated rises in the filtration tower 1, flows into each hollow fiber module 3, and passes from the outside to the inside of each hollow fiber filtration membrane 4. At this time, iron oxide is filtered on the outer surface of each hollow fiber filtration membrane 4, and the filtered water is collected above the partition plate 2 and taken out from the filtered water outflow pipe 8. By continuing such filtration, when the differential pressure indicated by the differential pressure gauge 26 rises to a predetermined value, the filtration is terminated and the valve 1
Close valves 8 and 24.

Next, cleaning with gas-liquid mixed water described below is performed. That is, with the filtered water above the partition plate 2 and the water to be treated below the partition plate 2, the valves 20 and 22 are opened, and the air inflow pipe 11A and the inflow pipe 6 are opened.
Through which air is introduced into the filtration tower 1. Air flows as bubbles from the bubble inflow mechanism 5 into each hollow fiber module 3, agitates the water in each hollow fiber module 3, and vibrates each hollow fiber filtration membrane 4 to adhere to its surface. Remove the iron oxide that is present. The air bubbles flow out from a flow port (not shown) provided above each hollow fiber module 3 and are discharged to the outside of the filtration tower 1 through the air vent pipe 7A.

After completion of such air stirring, the valve 22
While the valve is open, the valve 20 is closed, the valve 19 is opened, and the cleaning waste water existing below the partition plate 2 and containing a large amount of iron oxide is drained from the drain pipe 10. Next, the valve 25 is opened to allow the compressed air in the air surge tank 12 to flow into the filtration tower 1 from above, and the filtered water existing above the partition plate 2 is caused to flow back to each hollow fiber filtration membrane 4. This backwash drainage is also drained from the drain pipe 10 to the outside of the filtration tower 1.

After the washing process as described above is completed, the filtration is performed again. At this time, first, the valves 18 and 22 are opened, the water to be treated is allowed to flow into the filtration tower 1, and the air below the partition plate 2 is extruded by the water to be treated and withdrawn from the air vent pipe 7A. Next, the valve 22 is closed and the valve 23 is opened, and the air above the partition plate 2 is extruded by the filtered water and withdrawn from the air vent pipe 7B. After that, the valve 23 is closed and the valve 24 is opened to perform filtration.

In this embodiment, the oxidizing agent is intermittently added by the method (a). That is, [Filtration process start ~
Increase of differential pressure-cleaning] is set as one cycle, and the injection pump 16 is driven every predetermined number of cycles, so that the oxidant solution in the oxidant solution tank 15 (Sodium chlorate solution) is added to the water to be treated which flows through the treated water inflow pipe 9.

For example, after carrying out 4 cycles of the oxidizing agent-free cycle for filtering without adding an oxidizing agent to the water to be treated, the injection pump 16 is driven from the start of the 5th cycle filtration and the 5th cycle filtration. Continue adding oxidant until the end. Then, the process proceeds to the 5th cycle of washing, and the oxidant-free cycle from the start of the 6th cycle is continued until the 9th cycle, and then the 10th cycle is taken as the oxidant addition cycle. repeat. In this case, in the oxidizing agent addition cycle, the sodium hypochlorite solution is added to the water to be treated so that the residual chlorine concentration in the filtered water flowing out from the filtered water outflow pipe 8 becomes about 1 ppm.

[0032]

EXAMPLES Next, the present invention will be illustrated concretely by examples, but the present invention is not limited to the following examples. Power plant blow water was treated using the apparatus shown in FIG. In this case, the hollow fiber filtration membrane 4 has an outer diameter of 1.2 m.
m, an inner diameter of 0.7 mm, and a polyolefin-based hollow fiber filtration membrane having a large number of fine pores with a pore diameter of 0.1 μm on the membrane surface. The hollow fiber module 3 has about 40 hollow fiber membranes.
An outer diameter of 5 inches and a length of 2 m were prepared by bundling 00 pieces, and 18 hollow fiber modules 3 were attached to the partition plate 2.

[Example 1] Using the above-mentioned apparatus, the blow water of the power plant was treated by three kinds of operating methods, that is, no oxidant addition, continuous oxidant addition and intermittent oxidant addition. FIG. 2 shows the relationship between the differential pressure of the hollow fiber filtration membrane and the treatment time in each operating method. Figure 2 (a) shows the results of operation without addition of oxidant.
2B shows the operation result of the continuous addition of the oxidizing agent, and FIG. 2C shows the operation result of the intermittent addition of the oxidizing agent. In the figure, A is the initial differential pressure, B
Is a set differential pressure, and in each operation example, one cycle is set to about 200 hours in advance so that cleaning with the gas-liquid mixed water is performed before the differential pressure reaches the set differential pressure B. Further, when the differential pressure reaches the set differential pressure B before the preset cycle time (about 200 hours) elapses, the filtration is terminated and the cleaning is performed at that time. Each operation example will be described below.

[0034] When performing the operation of the oxidizing agent additive-free oxidizing agent not added, as shown in FIG. 2 (a), although initial operation of the differential pressure was A, the differential pressure after washing with gas-liquid mixed water Did not recover to the initial differential pressure A, and the differential pressure after cleaning increased with each cycle. Then, finally, the set differential pressure B is reached before the preset cycle time (about 200 hours) is completed. That is, the differential pressure after cleaning approaches the set differential pressure B each time the cycle is increased,
The interval between washes gradually became shorter and finally filtration was impossible. The hollow fiber filtration membrane which cannot be filtered in this way cannot recover the differential pressure unless it is washed with a chemical such as an alkali, an acid, a reducing agent or an oxidizing agent.

In the case of performing the operation of the oxidizing agent continuously added oxidant continuous addition, as shown in FIG. 2 (b), the differential pressure after washing by gas-liquid mixed water in each cycle was restored to the initial pressure difference A. However, in the present operating method, the continuous addition of the oxidizing agent promotes the oxidative deterioration of the hollow fiber filtration membrane, resulting in a significant decrease in its physical strength. That is, when the initial value of the elongation retention rate, which is an index of the physical strength of the hollow fiber filtration membrane, was 100%, the elongation retention rate of 98% was retained even after 100 days in the operation without adding the oxidizing agent. On the other hand, in the operation in which the oxidizing agent was continuously added, the elongation retention rate after 100 days was reduced to 30%.

In the case of performing the operation of the oxidizing agent intermittent addition oxidant intermittent addition, as shown in FIG. 2 (c), the differential pressure after washing the oxidizing agent without addition cycle (first 4 cycles) gradually increases However, in the oxidizing agent addition cycle (fifth cycle), the differential pressure after cleaning is the initial differential pressure A.
Recovered. Further, in the present operating method, the decrease in physical strength of the hollow fiber filtration membrane due to the oxidizing agent was greatly suppressed. That is, the elongation retention rate was 80% even after 100 days.

As described above, the oxidizing agent is intermittently added to the blow water to carry out filtration through the hollow fiber filtration membrane, so that the gas-liquid mixed water can be used while suppressing the decrease in strength of the hollow fiber filtration membrane due to the oxidizing agent. It was confirmed that the recovery of the differential pressure due to the washing was secured.

[Embodiment 2] As described above, the blow water discharged at the time of start-up after the periodical inspection of the power plant contains a large amount of iron oxide. The differential pressure rising speed of the hollow fiber filtration membrane in the cycle becomes extremely fast. Therefore, the start-up blow water was treated using the intermittent addition method (c). The results are shown in FIG.

During normal blow water treatment, the differential pressure does not reach the set value B within a preset cycle time (about 200 hours), and the cleaning is performed every preset cycle time. However, since the differential pressure rises very quickly when the blow water is started, the differential pressure reaches the set value B before the preset cycle time elapses.
Washing is performed. As a result, the time required for one cycle was shortened when the blow-off water at the time of startup was passed, and in the example of FIG. As a result of shortening the water passage time for one cycle, the time during which the oxidant contacts the deposits on the film surface during the oxidant addition cycle becomes shorter, and the differential pressure recovers to the initial value A after cleaning in the oxidant addition cycle. lost.

Therefore, in the example of FIG. 3, the interval of addition of the oxidant is changed according to the change in the differential pressure increase rate. That is,
Normally, the oxidizer addition cycle is performed once after repeating the oxidizer non-addition cycle four times. However, if the differential pressure increase rate changes due to the flow of blow water at startup, depending on the change. By reducing the number of non-addition cycles and shortening the oxidant addition interval, the oxidant addition cycle was increased, and further the oxidant addition cycle was continued for several cycles. As a result, the differential pressure after cleaning in the oxidant addition cycle was restored to the initial differential pressure A. Also,
Even when such an operation was performed, the decrease in physical strength of the hollow fiber filtration membrane due to the oxidizing agent was suppressed. That is, the elongation retention rate described above was 75% even after 50 days.

Any method may be used to detect the differential pressure increase rate. In this example, the time required for one cycle is monitored, and the difference per water passage time is calculated from the differential pressure increase curve at that time. The method of detecting the pressure rise rate was used. By changing the oxidant addition interval using this method, even if the water quality of the blow water changes, for example, even if the blow water at the startup has a high differential pressure rising speed, the differential pressure after sufficient washing is sufficient. It was found that the recoverability can be maintained. As a method of detecting the differential pressure increase rate, other than the method described above,
For example, the flow rate of blow water may be monitored to detect the differential pressure increase rate per flow rate.

[0042]

As described above, according to the method for treating blow water of a power plant according to the present invention, it is possible to suppress the decrease in strength of the hollow fiber filtration membrane due to the oxidant while maintaining the difference due to the cleaning using the gas-liquid mixed water. The pressure recoverability can be ensured, and therefore stable blow water treatment can be performed at low running cost without performing complicated operations such as chemical cleaning.

[Brief description of drawings]

FIG. 1 is a flow chart showing an example of a blow water treatment apparatus used for carrying out the present invention.

FIG. 2 is a graph showing an increasing tendency of the differential pressure of the hollow fiber filtration membrane and a recovering tendency of the differential pressure after washing in the filtration treatment of Example 1, in which (a) is the operation result without addition of an oxidizing agent, and (b) is ) Shows the operation result of the continuous addition of the oxidizing agent, and (c) shows the operation result of the intermittent addition of the oxidizing agent.

FIG. 3 shows the increasing tendency of the differential pressure of the hollow fiber filtration membrane and the recovering tendency of the differential pressure during washing when the interval of intermittent addition of the oxidizing agent to the blow water is changed according to the change of the increasing rate of the differential pressure. It is a graph.

[Explanation of symbols]

 1 Filtration Tower 3 Hollow Fiber Module 4 Hollow Fiber Filtration Membrane 5 Bubble Inflow Mechanism 8 Filtered Water Outflow Pipe 9 Treated Water Inflow Pipe 15 Oxidant Solution Tank 16 Injection Pump 17 Injection Pipe 26 Differential Pressure Meter

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] August 5, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction contents]

In the present invention, it is possible to secure the differential pressure recoverability by washing with gas-liquid mixed water while suppressing the strength reduction of the hollow fiber filtration membrane due to the oxidizing agent, for the following reason. Guessed. That is, at the time of filtration without addition of an oxidizing agent, a trace amount of organic matter in the water to be treated adheres to the membrane surface of the hollow fiber filtration membrane to promote bacteria generation, and slime is formed and adheres on the membrane surface. Amorphous iron oxide contained in the water to be treated also adheres to the film surface, but this is iron oxide that is difficult to peel off by cleaning with gas-liquid mixed water. Therefore, during filtration without addition of an oxidizing agent, the slime or amorphous iron oxide adheres to the membrane surface to increase the differential pressure. In contrast, when carrying out the filtration of the oxidizing agent added after filtration of the oxidizing agent additive-free as in the present invention, the scan lime deposited on the film surface in the filtration of the oxidation agent additive-free oxidizing agent oxidizes Along with facilitating exfoliation, the oxidizing agent changes the amorphous iron oxide into crystalline iron oxide with good exfoliation property, whereby the slime and iron oxide are easily exfoliated by washing at the end of filtration of addition of the oxidizing agent, It is considered that the differential pressure recovers to the initial differential pressure.

[Procedure amendment 2]

[Document name to be amended] Drawing

[Correction target item name] Fig. 1

[Correction method] Change

[Correction contents]

[Fig. 1]

[Procedure 3]

[Document name to be amended] Drawing

[Correction target item name] Figure 3

[Correction method] Change

[Correction contents]

[Fig. 3]

Claims (2)

[Claims] 1. A treatment method in which an oxidant is added to blow water discharged from a circulation system of turbine driving steam and condensate in a power plant, and the blow water is filtered by a hollow fiber filtration membrane. A method for treating blow water of a power plant, which comprises intermittently adding an oxidizing agent to the power plant. 2. The treatment method according to claim 1, wherein the interval of intermittent addition of the oxidizing agent to the blown water is changed according to the change in the rising speed of the filtration differential pressure of the hollow fiber filtration membrane.