JPH0972993A - Scrubbing method for filter tower using hollow fiber membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the surface roughness of membrane to the utmost extent and effectively peel off and remove trapped fine particles by setting an optical flow rate of cleaning air and cleaning time. SOLUTION: Hollow fiber membranes 2A and 2B of 100 to 50000 pieces are housed in a protective cylinder 3A. Raw water including fine particles mainly comprised of iron oxide as impurities is allowed to pass through a filter tower provided with a hollow fiber membrane module 1 from the outside to inside of the fiber membranes 2A and 2B for filtration. Then, after forming a gas-liquid mixing state in the cylinder 3A, the membranes 2A and 2B are vibrated so as to peel of the fine particles adhered to the outside thereof. At this time, the flow rate of a gas to be introduced into the cylinder 3A is set to 290 to 700m/h. Thus, a decrease in permeability due to roughed outer surface of the membranes 2A and 2B can be suppressed and the fine particles of iron oxide adhered to the surface thereof be also removed effectively by setting a scrubbing air flow rate or processing time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for scrubbing a filtration tower using a hollow fiber membrane module, which is used in condensate treatment of nuclear power plants and thermal power plants, industrial wastewater treatment and the like.

[0002]

2. Description of the Related Art In a filtration tower using a hollow fiber membrane, a plurality of hollow fiber membranes having a large number of fine holes are bundled to form a hollow fiber membrane module, and a large number of the hollow fiber membrane modules are horizontally installed in the filtration tower. In the filtration step, the raw water is supplied to the lower chamber partitioned by the partition plate, so that the raw water is passed from the outside to the inside of the hollow fiber membrane in the filtration step. Fine particles of impurities in the raw water are captured on the outer side, and the filtered water obtained from the inner side of the hollow fiber membrane is collected in the upper chamber partitioned by a partition plate and discharged from the filtration tower.

When such a filtration process is continuously carried out for a long period of time, fine particles are accumulated on the outer surface of the hollow fiber membrane, so that the differential pressure in the filtration tower is increased. Therefore, conventionally, a gas is supplied to water in the vicinity of each hollow fiber membrane existing in water to vibrate each hollow fiber membrane, and a scrubbing step of peeling the fine particles captured outside each hollow fiber membrane is performed, and then peeling is performed. The blow process of discharging the cleaning waste liquid containing the fine particles from the lower chamber is performed, and the filtration process, the scrubbing process, and the blow process are sequentially repeated to perform the treatment. In addition, before or after the scrubbing step or during the scrubbing step, a backwashing step may be performed in which wash water is backflowed from the inside to the outside of the hollow fiber membrane.

Since the filtration tower using the hollow fiber membrane is basically operated by repeating the filtration step, the scrubbing step and the blowing step, the fine particles trapped in the hollow fiber membrane in the filtration step are accumulated. Then the differential pressure of the filtration tower rises,
It is necessary to give sufficient consideration so that the filtration cannot be continued. Therefore, in order to prevent the accumulation of fine particles, studies, tests, and developments have been made on the hollow fiber membrane module structure, tower structure, hollow fiber membrane cleaning method including scrubbing method, and the like.

[0005]

As described above, the present inventors have made efforts to develop a more effective method for cleaning a hollow fiber membrane. However, when raw water is mainly condensate (primary cooling water) of a boiling water nuclear power plant that contains iron oxide as fine particles as raw water impurities, the hollow fiber membrane module whose differential pressure has increased due to the filtration process On the other hand, even if the scrubbing step or the backwashing step is performed, the differential pressure does not return to the original value, and even if the hollow fiber membrane is washed with an acid to dissolve and remove the iron oxide adhering to the outer surface of the membrane, the difference in pressure remains. It turned out that there are cases where the pressure does not return to the original level.

The following has been clarified as the cause of this. That is, the reason why the differential pressure does not return to the original is that the water permeability of the membrane itself is reduced, and the membrane is neither consolidated nor crushed due to the differential pressure between the inside and outside of the membrane, Only the surface of the outer surface of the membrane is rough,
This is because the fine pores that were originally present in the rough skin area were blocked, and as a result, the fine pores in the entire hollow fiber membrane were reduced, and the condition was to use a cleaning agent such as an acid, an oxidizing agent, or a reducing agent. It was found that there was no change even after washing with water, and it was not a physical property deterioration that appears as a decrease in mechanical strength such as tensile strength, tensile elongation and burst strength of the hollow fiber membrane.

That is, roughening of the outer surface of the membrane is caused by collision of fine particles such as iron oxide with the surface of the membrane, and the fine particles exist between the hollow fiber membranes while the hollow fiber membrane is vibrating. It was found that this occurs occasionally and is most likely to occur during the scrubbing process of the hollow fiber membrane. It was also found that it is promoted with the gas flow rate during scrubbing and the scrubbing time length.

Therefore, in order to prevent the roughening of the outer surface of the membrane as described above, the gas flow rate at the time of contact between the hollow fiber membrane and the iron oxide fine particles in the scrubbing step is minimized, and the scrubbing time is shortened. As a result, it is considered effective not to perform scrubbing, but if the accumulation of fine particles trapped in the membrane during the filtration process is allowed, the filter will deviate from the original usage and the differential pressure will increase due to the accumulation of fine particles on the outer surface of the membrane. And the filtration process cannot be continued.

The present invention has been made on the basis of such a background, and it is possible to suppress the roughening of the surface of the membrane which causes a decrease in the water permeability of the membrane as much as possible, and to exfoliate the fine particles trapped in the hollow fiber membrane. The purpose is to propose an optimum scrubbing method for a filtration tower using a thread membrane.

[0010]

A method for scrubbing a filtration tower using a hollow fiber membrane according to the present invention, which has been made to achieve the above object, comprises a partition plate for partitioning the inside of the filtration tower into an upper chamber and a lower chamber. Multiple hollow fiber membranes are bundled in a protective cylinder, both ends of the hollow fiber membranes are fixed, and a hollow fiber membrane module in which the hollow fiber membrane and an outer cylinder for protecting the hollow fiber membrane are integrally formed is partitioned. Into the lower chamber of the filtration tower suspended vertically with the plate, raw water containing fine particles mainly composed of iron oxide as impurities is caused to flow, and the raw water is passed from the outside to the inside of each hollow fiber membrane, A filtration step of capturing the fine particles on the outside of each hollow fiber membrane and causing the filtered water obtained on the inside of each hollow fiber membrane to flow out from the upper chamber; and the hollow fiber membrane in a state where the hollow fiber membrane is immersed in a liquid. Gas is introduced into the protective cylinder from the bottom of the module to It includes a scrubbing step of forming a gas-liquid mixed state and separating the fine particles adhering to the outside of the hollow fiber membrane by vibrating the hollow fiber membrane, and a blowing step of discharging the cleaning waste liquid containing the separated fine particles from the lower chamber. In the filtration method using the hollow fiber membrane, the gas flow rate introduced into the hollow fiber membrane module protective cylinder in the above scrubbing step is 290 to 700 m / m with respect to the effective sectional area in the protective cylinder.
The scrubbing operation is optimized by setting it to h.

Here, the effective cross-sectional area refers to a cross-sectional area through which a gas can pass in the region where the effective filtration surface of the hollow fiber membrane in the hollow fiber membrane module protective cylinder exists, and from the inner cross-sectional area of the protective cylinder to the inside of the protective cylinder. The cross-sectional area of the components such as the hollow fiber membrane provided in the above is excluded. In addition, the gas flow rate is 1 effective area
It shows the flow rate of the gas introduced into the hollow fiber membrane module per m ^2, which is, so to speak, an average flow velocity at which the gas rises in the passable space in the hollow fiber membrane module protection cylinder. Since gas has compressibility and its flow rate changes depending on the depth in the liquid, the gas flow rate here is the upper end of the region where the effective filtration surface of the hollow fiber membrane in the hollow fiber membrane module protection tube exists. Indicates the flow rate in the section.

The function of the present invention is to define the optimum cleaning gas flow rate or the optimum cleaning flow rate and cleaning time to minimize the roughening of the film surface during the scrubbing process, and to effectively remove the fine particles trapped on the film surface. It is to be peeled and removed.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing a hollow fiber membrane module used in the present invention, and FIG. 2 is an explanation showing a flow of a filtration tower used in the present invention. It is a figure.

Hollow fiber membrane module used in the present invention (1)
Will be described with reference to the embodiment shown in FIG. 1, but the present invention is not limited to this range. As shown in Figure 1,
Outer diameter 0.2 to 7 mm with fine pores of 0.01 μm to 0.3 μm,
Hollow fiber membranes (2A, 2B) with an inner diameter of 0.2-5 mm are 100-500
Approximately 00 pieces, which are housed in a protective cylinder (3A), are bonded to both ends of the hollow fiber membranes (2A, 2B) at the joints (4A, 4B) without blocking the hollows, and are attached to the lower joints. Is provided with a cap (3B) in a liquid-tight state so as to form a water collecting chamber (5), and gas inlets (6A, 6B) are provided at a lower portion and an upper portion of the protective cylinder (3A), respectively, and a lower joint A gas inlet (7) is provided near the portion (4A), and a skirt portion (8) is further provided below the protective cylinder (3A).

The hollow fiber membranes (2A, 2B) are thin hollow fiber membranes (2A) for exclusively filtering the liquid to be treated and thick hollow fiber membranes (2) for simultaneously filtering the liquid to be treated and also as a water collecting pipe.
B), a part of the permeated water that has been filtered from the outside of the hollow fiber membrane (2A) and has flowed in the hollow fiber is sent to the upper end surface, and the other part from the lower end surface to the water collection chamber (5). And then sent to the upper end surface through the hollow fibers of the hollow fiber membrane (2B) and joins with the permeated water that has flowed to the upper end. In the hollow fiber membrane module, a tubular water intake pipe is used instead of the hollow fiber membrane (2B), a water intake pipe is provided outside the hollow fiber membrane module, or the lower end of the hollow fiber membrane (2A) is installed. There are various types such as closing and taking permeated water only from the upper end surface. Further, the hollow fiber membrane to be used includes various materials such as polyolefin-based material and polysulfone.

When arranging the hollow fiber membrane module (1) in the filtration tower, a partition plate (10) is provided above the filtration tower (9) as shown in FIG. Is divided into an upper chamber F and a lower chamber R, and a large number of hollow fiber membrane modules (1) are vertically suspended below the partition plate (10) on the partition plate (10). Further, a bubble distribution mechanism (11) is arranged in the filtration tower (9). The bubble distribution mechanism (11) includes a bubble receiver (12) and a bubble distribution pipe (1) penetrating the bubble receiver (12).
Hollow fiber membrane module (1)
The bubble distribution pipe (13) is made to correspond directly below the skirt (8).

In addition, one end of the filtered water outflow pipe (14) and one end of the compressed air inflow pipe (15A) are connected to the upper part of the filtration tower (9), and the raw water inflow pipe (16) is connected to the lower part of the filtration tower (9). ), One end of the compressed air inflow pipe (15B), and the drain pipe (1
8) One end of each is connected, and further the partition plate (10)
One end of the air vent pipe (17) communicates with the side body portion immediately below.
In addition, (19)-(24) shows a valve, respectively (25) is a baffle plate.

Using the filtration tower (9), condensate containing iron oxide will be described as an example of the object of the present invention. In the filtration step, raw water flows into the lower chamber R of the filtration tower (9) from the raw water inflow pipe (16) by opening the valves (19) and (23),
The hollow fiber membrane module (1) filters iron oxide fine particles in the raw water, and the filtered water collects in the upper chamber F, and the filtered water outflow pipe (1
4) outflow. By continuing the filtration, the differential pressure of the filtration tower (9) rises, and the scrubbing step is carried out when the specified differential pressure is reached.

That is, in order to remove the iron oxide fine particles adhering to the surface of the hollow fiber membrane, the valves (19) and (23) are closed and the lower chamber R is filled with raw water and the upper chamber F is filled with filtered water. The valves (21) and (22) are opened, and the compressed air flows in from the compressed air inflow pipe (15B). The compressed air is once received by the lower surface of the bubble receiver (12), and then forms air bubbles inside the air distribution pipe (13) through a hole (not shown) provided at the side of the bubble distribution pipe (13). It flows into the skirt (8) of the hollow fiber membrane module (1) and then into each hollow fiber membrane module (1) via the gas inlet (7). As the bubbles rise, the hollow fiber membranes (2A, 2B) vibrate and the water in the hollow fiber membrane module (1) is agitated, so that the hollow fiber membranes (2A, 2B) are stirred.
The iron oxide fine particles captured on the surface of B) are separated and dispersed in the lower chamber R of the filtration tower (9). The bubbles flow out of the hollow fiber membrane module (1) through the flow port (6B) of the hollow fiber membrane module (1), and then are discharged from the air vent pipe (17) to the outside of the filtration tower (9).

When the scrubbing air flow rate for separating the iron oxide fine particles is increased, the chances of the separated iron oxide fine particles colliding with the membrane surface of the hollow fiber membrane (2A, 2B) increase, and the outer surface of the membrane becomes rough. When the amount is small, the chances that the peeled iron oxide fine particles collide with the membrane surface of the hollow fiber membrane (2A, 2B) are reduced, and roughening of the outer surface of the membrane is suppressed, but the peeling effect of the iron oxide fine particles is reduced. . By carrying out the optimum cleaning air flow rate scrubbing according to claims 1 to 4 of the present invention, the roughening of the film surface during the scrubbing process is minimized, and further the iron oxide fine particles trapped on the film surface are effectively peeled and removed. It becomes possible.

The iron oxide fine particles separated by the above scrubbing and dispersed in the water in the lower chamber R of the filtration tower (9) are blown out of the filtration tower after the scrubbing step. That is, the valve (21) is closed while the valve (22) is open, and the valve (20) is opened to allow the cleaning waste liquid in which the iron oxide fine particles are dispersed to flow out from the drain pipe (18). Although the process of flowing out the cleaning waste liquid uses a head difference, the air vent pipe (1
7) Alternatively, compressed air can be introduced from the compressed air inflow pipe (15B) for rapid outflow using the air pressure. At the same time as the above-mentioned blow or after the end of the blow, a backwashing step is performed in which compressed air is introduced from the compressed air inflow pipe (15A) and the permeated water existing in the upper chamber F is caused to flow back through the hollow fiber membranes (2A, 2B). Sometimes.

[0022]

INDUSTRIAL APPLICABILITY The present invention increases the differential pressure of the hollow fiber membrane module by optimizing the scrubbing air flow rate in the scrubbing step to prevent deterioration of the water permeability of the hollow fiber membrane and prevention of contamination accumulation of the hollow fiber membrane. The effect of extending the replacement life of the hollow fiber membrane module is minimized.

[0023]

EXAMPLES In order to more clearly explain the effects of the present invention, examples of the present invention will be shown below. Outer diameter with fine pores of around 0.1 μm
Fig. 1 shows 4200 hollow fiber membranes with 1.22mm, inner diameter 0.7mm and length 2200mm and 75 hollow fiber membranes with outer diameter 5.4mm, inner diameter 4mm and length 2200mm bundled in a protective cylinder with inner diameter 123.4mm. One such hollow fiber membrane module was placed in the filtration tower to form a small-scale experimental filtration tower according to the flow shown in FIG. 2, and the following experiment was conducted. The material of the hollow fiber membrane was polyethylene.

First, the scrubbing air flow rate condition for minimizing the roughness of the outer surface of the hollow fiber membrane, that is, the deterioration of the membrane water permeability will be described. Raw water in which iron oxide fine particles having a particle diameter of 10 to 20 μm and containing α-Fe ₂ O ₃ as a main component was adjusted to have an adhesion amount of 10 g per 1 m ² of the hollow fiber membrane was filtered with a hollow fiber membrane module (1). After that, the scrubbing process was performed. Scrubbing was performed at a water temperature of 40 ° C. The reason for using the iron oxide fine particles having a relatively large particle size is that the outer surface of the hollow fiber membrane is surely roughened during the scrubbing process to simulate an actual machine.

FIG. 3 shows the relationship between the scrubbing air flow rate and the membrane water permeability reduction rate. Here, the reduction rate of the membrane water permeability is represented by the measurement result of the hollow fiber membrane having an outer diameter of 1.22 mm that occupies most of the filtration area. The rate of decrease in membrane permeability increases gradually with increasing scrubbing air flow rate up to about 700 m / h, but in the range of air flow rate higher than that, the rate of decrease in membrane permeability increases rapidly with increase in air flow rate.

It was shown that the scrubbing air flow rate of 700 m / h or more accelerates the decrease of the membrane water permeability and is not suitable as the scrubbing condition. From Fig. 3, the scrubbing air flow rate is set to 700 m / h or less.

Next, the scrubbing air flow rate condition for effectively peeling and removing the fine particles mainly composed of iron oxide captured on the surface of the hollow fiber membrane will be described. Raw water in which iron oxide fine particles containing α-Fe ₂ O ₃ having a particle diameter of 1 to ₃ μm as a main component were adjusted so that the adhered amount was 50 g per 1 m ² of the hollow fiber membrane was filtered by the hollow fiber membrane module (1). Then, the differential pressure rise was set to about 0.3 kg / cm ² , and then the scrubbing process was performed. Scrubbing was performed at a water temperature of 40 ° C. 1-3
The reason why iron oxide having a particle diameter of μm is used is to select a particle diameter that does not easily cause roughening of the outer surface of the membrane during scrubbing and to recognize the differential pressure recovery rate after scrubbing cleaning as the iron oxide fine particle peeling effect.

FIG. 4 shows the relationship between the iron oxide fine particle removal rate and the differential pressure recovery rate. FIG. 4 shows that it is sufficient to secure the iron oxide fine particle removal rate of 70% in order to obtain the differential pressure recovery rate of 80% or more, which is generally considered to be good in the conventional differential pressure recovery rate.

FIG. 5 shows the relationship between the scrubbing air flow rate and the scrubbing time for obtaining an iron oxide removal rate of 70% (shown by the line B in FIG. 5), which is shown below by the empirical formula (2).

Empirical Formula (2) Y = Scrubbing time (min) X = Scrubbing air flow rate (m / h) Y = 600 / (X-265) +3.5

From the empirical formula (2) and FIG. 5, it was shown that the required scrubbing time is remarkably increased when the scrubbing air flow rate is reduced to around 265 m / h. For this reason, it is necessary to set the scrubbing air flow rate, which has practical significance, to 290 m / h or more with a margin. Therefore, the minimum scrubbing air flow rate was set to 290 m / h and is shown by line C in FIG. The scrubbing air flow rate is 290m /
70% of iron oxide fine particles removal rate between h and 700 m / h (the upper limit flow rate setting value in FIG. 3 and shown by line A in FIG. 5)
The area where the above can be secured is indicated by hatching in the figure.

FIG. 6 shows a conventional scrubbing condition: an air flow rate of 940 m / h, a time of 5 minutes and a range in which the permeation performance is reduced to the same level or less. First, conventional scrubbing conditions: air flow rate 940m / h,
The relationship between the scrubbing time and the scrubbing air flow rate, which has the same value as the membrane water permeability reduction rate at time 5 minutes, is shown by the following empirical formula (3), and is shown by line D in FIG.

Empirical formula (3) Y = scrubbing time (min) X = scrubbing air flow rate (m / h) Y = 2292.9X ^-0.7541

The range in which the rate of decrease in membrane water permeability is suppressed more than in the prior art is the range surrounded by lines A, C and D in FIG.

FIG. 7 was drawn under the conditions of FIG. 5 and FIG. Region E shown in FIG. 7 is a scrubbing air flow rate at which the iron oxide removal rate is 70% or more, that is, the differential pressure recovery rate is 80% or more.
It is in the range of 290 to 700 m / h, and in the range in which the reduction rate of the membrane permeability is suppressed as compared with the prior art, lines A, B,
It is a range surrounded by C and D.

According to the above-mentioned embodiment, the air flow rate in the scrubbing process is set to 290 to 700 m / h, the set scrubbing air flow rate, the difficulty of peeling iron oxide fine particles in the treated water, and the stoppage in operation of the apparatus. By setting the scrubbing process time in association with time constraints and the like, it becomes possible to obtain the effect of suppressing deterioration of water permeability due to roughening of the outer surface of the hollow fiber membrane and removing iron oxide fine particles adhering to the membrane surface.

<Comparative example> Using the same filtration tower as the above-mentioned example of the present invention, α-Fe ₂ O ₃ having a particle size of 10 to 20 μm was adjusted so that the adhered amount was 10 g per 1 m ² of the hollow fiber membrane. Raw water was filtered by the hollow fiber membrane module (1), and then the scrubbing step was performed. Scrubbing was performed at a water temperature of 40 ° C. One scrubbing air flow rate is 560 m / h within the optimal scrubbing flow rate range, and the other is outside the optimal scrubbing flow rate range.
Changes in the differential pressure of the hollow fiber membrane modules after scrubbing for 10 minutes at 40 m / h for 10 times were compared. A comparison of the differential pressure rise widths is shown in FIG. It can be seen that the increase in differential pressure is suppressed when scrubbing is performed within the optimum scrubbing air flow rate range.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a hollow fiber membrane module used in the present invention.

FIG. 2 is an explanatory diagram showing a flow of a filtration tower used in the present invention.

FIG. 3 is a diagram showing the relationship between the scrubbing air flow rate and the membrane water permeability reduction rate.

FIG. 4 is a diagram showing the relationship between the differential pressure recovery rate and the iron oxide fine particle removal rate.

FIG. 5 is a diagram showing an effective range of iron oxide removal rate.

FIG. 6 is a diagram showing a range in which deterioration of water permeability is suppressed.

FIG. 7 is a diagram showing an optimum cleaning condition range.

FIG. 8 is a diagram showing a comparative example of the hollow fiber membrane module differential pressure increase due to scrubbing air flow rate setting.

[Explanation of symbols]

 1 Hollow Fiber Membrane Module 2A Thin Hollow Fiber Membrane 2B Thick Hollow Fiber Membrane 3A Protective Tube 3B Cap 4A Upper Joint 4B Lower Joint 5 Water Collection Chamber 6A Upper Flow Port 6B Lower Flow Port 7 Gas Inlet 8 Skirt 9 Filter Tower 10 Partition plate 11 Bubble distribution mechanism 12 Bubble receiver 13 Bubble distribution pipe 14 Filtered water outflow pipe 15 Compressed air inflow pipe 16 Raw water inflow pipe 17 Air vent pipe 18 Drain pipe 19 to 24 Valve 25 Baffle plate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshio Morita 1-4-9 Kawagishi, Toda City, Saitama Prefecture Organo Corporation

Claims (4)

[Claims] 1. A plurality of hollow fiber membranes are bundled in a protective cylinder in a partition plate that divides the inside of a filtration tower into an upper chamber and a lower chamber, and both ends of the hollow fiber membranes are fixed, and the hollow fiber membranes and the hollow fibers are hollow. In the lower chamber of the filtration tower in which a hollow fiber membrane module in which an outer cylinder for protecting the fiber membrane is integrally configured is suspended in a vertical direction with a partition plate, raw water containing fine particles mainly composed of iron oxide as impurities. By flowing raw water from the outer side to the inner side of each hollow fiber membrane to capture the fine particles on the outer side of each hollow fiber membrane, and to obtain the filtered water obtained inside the hollow fiber membrane from the upper chamber. From the filtration step of flowing out from the hollow fiber membrane, the gas is introduced into the protective cylinder from the lower part of the hollow fiber membrane module in the state where the hollow fiber membrane is immersed in the liquid, and a gas-liquid mixed state is formed in the protective cylinder to form the hollow fiber membrane. A scrubber that separates the fine particles adhering to the outside of the hollow fiber membrane by vibrating In the filtration method using a hollow fiber membrane including a bubbling step, the gas flow rate introduced into the hollow fiber membrane module protective tube in the scrubbing step is set to 290 to 700 m / h with respect to the effective cross-sectional area in the protective tube. A method for scrubbing a filtration tower using a hollow fiber membrane. 2. The scrubbing air flow rate (m / h) is X,
When the scrubbing time (min) is Y, the attached FIG.
The values of X and Y are set within the range of the diagonal line above the curve B indicating the region where the iron oxide fine particle removal rate is 70% or more represented by Y = 600 / (X-265) +3.5 (Formula I). The scrubbing method according to claim 1. 3. A scrubbing air flow rate (m / h) is X,
When the scrubbing time (min) is Y, the attached FIG.
2. In, the values of X and Y are each set within the range of the diagonal line below the curve D indicating the region in which the decrease in membrane permeability represented by Y = 2292.9X ^-0.7541 (Formula II) is suppressed. Scrubbing method. 4. The scrubbing air flow rate (m / h) is X,
When the scrubbing time (min) is Y, the attached FIG.
In X, the values of X and Y are respectively a straight line A (X = 700), a straight line C (X = 290), a curve B (equation I ... X = 600 / (X-265) +3.
5) The scrubbing method according to claim 1, wherein the scrubbing method is set in a substantially shaded area E surrounded by the curve D (formula II ... Y = 2292.9X ^-0.7541 ).