JPH1157415A - Operating method of membrane deaerator and apparatus for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recover performance of a membrane by effectively cleaning the membrane face of the gas permeation membrane of a membrane deaerator. SOLUTION: In the operating method of the membrane deaerator, one side of a gas permeation membrane 3A in the inside of a membrane module 3 is held as a liquid phase side 3a and liquid to be treated is permeated. The other side thereof is held as a gas phase side 3b and decompression is performed. Thereby, gas dissolved in liquid to be treated is permeated on the gas phase side and removed. In the case of cleaning the membrane face of the gas permeation membrane 3A, supply of liquid to be treated into the membrane module 3 is stopped and liquid in the membrane module 3 is discharged and also gas is introduced into the liquid phase side 3a in the inside of the membrane module 3. Thereafter, liquid to be treated is flowed to the liquid phase side 3a. Further, the membrane deaerator is equipped with the membrane module 3 in which the inside is partitioned into the liquid phase side 3a and the gas phase side 3b by the gas permeation membrane 3A, a decompression means 4 for decompressing the gas phase side in the inside of the membrane module 3 and a means for flowing liquid to be treated to the liquid phase side in the inside of the membrane module. The membrane deaerator is provided with such a means that the liquid phase side 3a in the membrane module 3 is communicated with the outside air and liquid in the membrane module is discharged and gas is introduced into the liquid phase.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for operating a membrane deaerator for removing dissolved gas in a liquid to be treated and a membrane deaerator, and more particularly to a method for removing a gas permeable membrane of a membrane deaerator. The present invention relates to a method for operating a membrane degassing apparatus and a membrane degassing apparatus that can effectively clean and restore membrane performance.

[0002]

2. Description of the Related Art Oxygen dissolved in a liquid causes various obstacles due to its oxidizing power. For example, in the case where the liquid is a beverage, the liquid causes a deterioration in flavor such as deterioration of flavor and discoloration. Further, when the liquid is water in the building piping, the steel material as the piping material is corroded and causes red water. Further, when the liquid is supplied to the boiler, it causes corrosion in the boiler and in the steam line.

[0003] In order to prevent such an obstacle, oxygen in a liquid is removed.

Conventionally, as a method for removing oxygen from a liquid, there are a vacuum degassing method, an aeration method (gas replacement method), a chemical method using chemicals, a heating degassing method, and the like. Are often adopted.

[0005] The membrane degassing method is a kind of vacuum degassing method, in which a gas-permeable membrane that allows only gas to pass without passing a liquid is used, and a liquid to be treated is supplied to one side (liquid phase side) of the membrane. Then, by reducing the pressure on the other side (gas phase side), dissolved oxygen in the liquid to be treated is permeated to the gas phase side and removed. In this case, a gas other than oxygen, such as nitrogen, is blown into the liquid to be treated to reduce the oxygen partial pressure in the liquid to increase the effect of removing oxygen, or a gas other than oxygen, such as nitrogen, is supplied to the gas phase. There is also known a method in which the oxygen partial pressure on the gaseous phase side is reduced by flowing to increase the oxygen removing effect.

Conventionally, a gas-permeable membrane used in a membrane deaerator is a tubular, hollow fiber or spiral membrane module so that a large permeation area per unit volume can be secured. By adopting a cross-flow method in which the liquid to be treated is circulated in parallel with the membrane surface of such a membrane module, clogging of the membrane surface is suppressed, the membrane performance is maintained stably, and the membrane life is shortened. Is being extended.

However, even when the cross-flow method is employed, clogging of the film occurs due to long-term use, and the film performance is reduced. That is, fine particles such as dust and corrosion products contained in the liquid to be treated gradually accumulate as dirt on the film surface, and this impairs the gas permeability of the film. The rate of decrease in the membrane performance is not uniform due to the quality of the liquid to be treated and the characteristics of the membrane deaerator. For example, when tap water is subjected to membrane deaeration, the treated water volume decreases by about 20% in two months of treatment. . Therefore, before the amount of treated water drops to 80% or less of the operation start time, the operation of the membrane deaerator is stopped to remove dirt and the like adhered to the membrane surface and perform an operation to restore the membrane performance, Thereafter, a method of restarting operation is adopted.

Conventionally, as a method of restoring the membrane performance by stopping the operation of the membrane deaerator, as shown in Comparative Example 2 described below,
A method has been proposed in which pressurized air is introduced into the gas phase while flowing a liquid such as washing water through the liquid phase.

Further, as shown in Comparative Example 1 described later, a method has been proposed in which the flow direction of the liquid to be treated in the membrane module is switched from a forward flow to a backward flow to remove dirt on the membrane surface.

[0010]

However, in the method of removing the dirt on the membrane surface by stopping the operation of the membrane deaerator and introducing washing water into the liquid phase and pressurized air into the gas phase, Although the removal effect is great, there is a problem that a separate means for introducing pressurized air is required.

In the method of switching the flow direction of the liquid to be treated, the effect of removing dirt is small, and the amount of treated water cannot be recovered sufficiently.

The present invention solves the above-mentioned conventional problems and provides a membrane degassing apparatus and a membrane degassing apparatus capable of effectively removing dirt on the membrane surface without requiring special equipment such as pressurized air introduction means. It is intended to provide a driving method thereof.

[0013]

According to a method of operating a membrane degassing apparatus of the present invention, one side of a gas permeable membrane in a membrane module is made to flow through a liquid to be treated, and the other side is made into a gas phase. In the operation method of the membrane deaerator for removing the dissolved gas in the liquid to be treated by passing it to the gas phase side by reducing the pressure as the side, in cleaning the membrane surface of the gas permeable membrane, the gas is introduced into the membrane module. Is characterized in that the supply of the liquid to be treated is stopped, the liquid in the membrane module is discharged, and a gas is introduced into the liquid phase side in the membrane module to wash the membrane surface.

[0014] The membrane deaerator of the present invention comprises a membrane module having an interior partitioned into a liquid phase side and a gas phase side by a gas permeable membrane;
A membrane degassing apparatus comprising: a decompression means for decompressing a gas phase side in the membrane module; and a means for flowing a liquid to be treated to a liquid phase side in the membrane module. Is connected to the atmosphere to discharge liquid from the liquid phase side, and a means for introducing gas to the liquid phase side is provided.

According to the present invention, by displacing the liquid phase side in the membrane module with a gas such as air and then flowing the liquid, the liquid flow is disturbed on the membrane surface of the gas permeable membrane. Dirt adhering to the film surface due to turbulence can be effectively removed.

The cleaning of the membrane surface according to the present invention does not require any special equipment such as pressurized air introduction means, and can be easily carried out by operating a valve.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIGS. 1 and 2 are system diagrams showing an embodiment of the membrane deaerator of the present invention. In FIGS. 1 and 2, 1 is a liquid sending pump, 2 is a security filter, and 3 is a gas permeable membrane 3A. The membrane module 4 provided is a vacuum pump.

In the membrane deaerator shown in FIGS. 1 and 2, the membrane deaerator shown in FIG. 1 uses on-off valves (solenoid valve or electric valve) V ₁ , V ₃ and V ₂ , V _4. contrast, only membrane degasifier three-way valve V _a shown in FIG. 2, the point with V _B different driving operation and principles of membrane degassing treatment and membrane cleaning are equivalent.

In the following, a method of operating the membrane deaerator of FIG. 1 will be described. However, the same operation is performed in the membrane deaerator of FIG.

In the membrane deaerator shown in FIGS. 1 and 2, the inlet is located at the lower part and the outlet is located at the upper part.
The membrane module 3 is placed vertically, but may be placed horizontally. However, from the viewpoint of the cleaning effect of the film, it is preferable that the film is placed vertically.

In the membrane deaerator of FIG. 1, during the membrane deaeration process, the valves V ₁ and V ₂ are opened, the valves V ₃ and V ₄ are closed, and the liquid supply pump 1 and the vacuum pump 4 are operated. The liquid to be treated (raw water) flows into the liquid-phase side 3a of the membrane module 3, removes the membrane-permeable gas from the gas-phase side 3b, performs degassing treatment, and discharges the treated water out of the system.

In cleaning the membrane, the pump 1 and the vacuum pump 4 are stopped, the valves V ₁ and V ₂ are closed, and the valves V ₃ and V ₄ are opened. Thus, it enters the air in the system the valve V ₄ side, most of the liquid in the system is discharged to the outside of the system from the valve V ₃ side.

[0024] After draining the liquid, close the valve V _3, open the valve V _1, is discharged out of the system from the valve V ₄ side through the liquid-phase side 3a of the membrane module 3 raw water by operating the liquid feed pump 1 .

Thus, the liquid side 3a of the membrane module 3
A turbulent flow of gas-liquid mixture is generated on the film surface of the gas permeable film 3A, and the turbulence of the liquid removes dirt on the film surface.

The liquid sending speed at the time of this washing may be equal to that at the time of the membrane degassing treatment. However, the washing time can be shortened by increasing the liquid sending speed at the time of the membrane degassing treatment to enhance the washing effect. Can also.

In the cleaning operation in this embodiment, basically, after the liquid to be processed and the depressurization are stopped, the liquid in the membrane module is discharged and the gas is introduced into the liquid phase. Although the two steps of the circulation of the liquid to be treated are performed, a higher cleaning effect can be obtained by repeating the above steps and the step than by continuously circulating the liquid to be treated.

Generally, after the liquid is discharged and the gas is introduced,
Of the liquid to be treated, the water retained in the membrane deaerator is 2 to 5
After the liquid to be treated is circulated about twice, for example, about three times, the liquid is discharged and the gas is introduced again, and then the liquid to be treated is circulated, and the process is preferably repeated about 2 to 10 times. By performing such repetitive cleaning, dirt on the film surface can be efficiently removed, and the cleaning time can be reduced.

The end time of the washing step can be determined from the appearance of the discharged liquid at the time of washing. Normally, when no colored matter or turbidity is observed in the discharged liquid, the washing is terminated.

After the cleaning, the valves V ₁ and V ₂ are opened, the valves V ₃ and V ₄ are closed, and the liquid supply pump 1 and the vacuum pump 4 are operated to restart the membrane deaeration process.

In such a cleaning process, by continuing the membrane degassing process, the progress of contamination on the membrane surface is predicted due to a decrease in the amount of treated water (flow rate) or an increase in the concentration of the gas to be treated in the treated water. When it is done. Although there is no particular limitation on the criteria for determining the cleaning start time, in the normal case, when the amount of treated water is reduced by about 20% from that at the start of operation, or when the concentration of the gas to be treated in the treated water is 20% lower than at the start of operation. %.

Of course, the cleaning treatment may be carried out before such phenomena as the decrease in the amount of treated water due to the fouling of the film surface and the increase in the concentration of the gas to be treated in the treated water become noticeable. For example, based on the operating experience of the membrane deaerator, cleaning is performed at regular intervals, such as once a day, to prevent the deposition of dirt on the membrane surface for a long time, and to reduce the amount of treated water due to dirt on the membrane surface. Also, it is possible to prevent an increase in the concentration of the gas to be treated.

The switching from the membrane degassing process to the washing operation and the switching from the washing operation to the membrane degassing process can be performed by automatic control or manually.

The membrane deaerator shown in FIGS. 1 and 2 is an example of an embodiment of the membrane deaerator of the present invention, and the present invention is not limited to the illustrated embodiment unless the gist of the invention is exceeded. It is not limited to one. For example, the gas introduction path and the liquid discharge path can be directly connected to the membrane module. Further, the liquid circulated at the time of cleaning the film surface may be a liquid other than the liquid to be treated.

[0035]

The present invention will be described more specifically below with reference to examples and comparative examples.

Example 1 A film deaeration process and a cleaning process were performed by the film deaerator shown in FIG.

As the gas permeable membrane 3A, a hollow fiber membrane made of polypropylene was used, and four modules each having the gas permeable membrane 3A mounted on an external flow-through tube having an inner diameter of 4 inches and a length of 28 inches were placed vertically to remove the membrane. The air device was assembled.

Using Atsugi-shi water as raw water, membrane deaeration is performed,
In three months of continuous operation, treated water volume is 20m ³ / h at the beginning of operation
The cleaning treatment was performed at the time when the temperature decreased from r to 15 m ³ / hr.

First, the valves V ₁ and V ₂ are closed, the valves V ₃ and V ₄ are opened, the liquid supply pump 1 and the vacuum pump 4 are stopped, and air is introduced into the system and the liquid in the system is opened. Was discharged. Thereafter, the valve V ₁ open, the valve V ₃ is closed and the liquid supply pump 1, the raw water was circulated for 1 minute at a flow rate of 15 m ³ / hr (1 single flow 250L). The operation of introducing air, discharging the liquid, and circulating raw water was repeated 10 times (the time required for each operation was about 5 minutes).

The amount of dirt removed from the film surface by this washing operation was examined by determining the amount of iron removed by the following method.

That is, the washing wastewater 25 discharged in each washing cycle
0 L was received in each 500 L tank, and this was mixed well to collect 200 mL each, and a total of 2 mL of these was mixed.
The iron (Fe) concentration M (mg / L) was measured for the L sample water. Total washing drainage is 2500L (250 × 10)
Therefore, the amount of iron removed by washing is calculated by the following equation. The amount of iron removed (g) = M (mg / L) × 2500 × 10 ⁻³ = M × 2.5 As a result, the amount of iron removed was 4.1 g.

When the membrane deaeration treatment was resumed after the above washing, the amount of treated water was changed from 15 m ³ / hr before washing to 20 m
³ / hr.

Comparative Example 1 A film deaeration process and a cleaning process were performed by the film deaerator shown in FIG.

In FIG. 3, reference numerals 1, 2, 3, 3A, 3
a, 3b and 4 are the same as those shown in FIG. V
_C, the V _D three-way valve, V ₅ is the on-off valve.

At the time of membrane deaeration, raw water (Atsugi City water) is
And the same process as in Example 1 was performed.

As in the first embodiment, when a decrease in the amount of treated water is recognized, the three-way valves V _C and V _D are switched, and the on-off valve V ₅ is opened. flow 1 hour path and discharged through the on-off valve V _3. The flow rate at this time was 15 m ³ / hr.

The amount of dirt removed from the film surface in this washing operation was examined by determining the amount of iron removed by the following method.

That is, the washing wastewater is received in a 500 L tank,
While overflowing, 200 mL of water was collected at a time, 6 times each time when the tank was full and about every 10 minutes thereafter, and the iron content (Fe) concentration M (mg / L) was measured. Since the total drainage is 15000 L (15 m ³ / hr × 1 hr),
The amount of iron removed by washing is calculated by the following equation. The amount of iron removed (g) = M (mg / L) × 15000 × 10 ⁻³ = M × 15 As a result, the amount of iron removed was 0.22 g.

When the membrane deaeration treatment was resumed after the above washing, the amount of treated water was changed from 15 m ³ / hr before washing to 16 m ³ / hr.
^It recovered only to ³ / hr.

Comparative Example 2 A film deaeration process and a cleaning process were performed by the film deaerator shown in FIG.

In FIG. 4, reference numerals 1, 2, 3, 3A, 3
a, 3b and 4 are the same as those shown in FIG. 5
Is a compressor, and V ₆ , V ₇ and V ₈ are on-off valves.

At the time of the membrane deaeration treatment, the valves V ₆ and V ₇ were closed and the valve V ₈ was opened to flow raw water (Atsugi City water).

[0053] When the reduction was observed in similarly treated water as in Example 1, the valve V ₈ closed, the valve V _6, V ₇ is opened and 1
During this time, raw water was circulated at 15 m ³ / hr, air was injected into the gas phase by a compressor 5 at a pressure of 3 kg / cm ² (air amount 1 Nm ³ / hr), and the washing wastewater was discharged via the on-off valve V ₇ .

The amount of iron removed from this washing waste water was determined in the same manner as in Comparative Example 1, and the amount of iron removed was 3.20 g.

After the washing, the membrane deaeration was restarted. The treated water amount was changed from 15 m ³ / hr before washing to 18 m ³ / hr.
It recovered only up to m ³ / hr.

From the results of Example 1 and Comparative Examples 1 and 2, it can be seen that according to the present invention, dirt on the film surface can be easily removed and the film performance can be recovered more effectively than the conventional method. .

[0057]

As described above in detail, according to the operation method of the membrane deaerator and the membrane deaerator of the present invention, the gas permeable membrane can be efficiently formed in a short time without requiring any special equipment. It is possible to recover the membrane performance by washing and removing dirt on the membrane surface. Therefore, according to the present invention, the continuous operation of the membrane deaerator can be stably performed over a long period of time.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an example of an embodiment of a membrane deaerator of the present invention.

FIG. 2 is a system diagram showing another example of the embodiment of the membrane deaerator of the present invention.

FIG. 3 is a system diagram showing a membrane deaerator used in Comparative Example 1.

FIG. 4 is a system diagram showing a membrane deaerator used in Comparative Example 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid-feeding pump 2 Security filter 3 Membrane module 3A Gas permeable membrane 4 Vacuum pump

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Nobuyuki Kobayashi Samson Co., Ltd.

Claims (2)

[Claims] 1. Dissolving gas in a liquid to be treated is reduced by flowing the liquid to be treated with one side of a gas permeable membrane in a membrane module as a liquid phase side and reducing the pressure with the other side as a gas phase side. In the method of operating the membrane degassing apparatus for removing the gas-permeable membrane by permeating the gas-phase side, when cleaning the membrane surface of the gas-permeable membrane, the supply of the liquid to be treated into the membrane module is stopped, Discharging the gas and introducing a gas into the liquid phase side, and then circulating the liquid through the liquid phase side to wash the membrane surface. 2. A membrane module whose interior is partitioned into a liquid phase side and a gas phase side by a gas permeable membrane, pressure reducing means for depressurizing a gas phase side in the membrane module, and a liquid phase side in the membrane module. A membrane degassing apparatus comprising means for flowing a liquid to be treated through the membrane module, wherein the liquid phase side in the membrane module is communicated with the atmosphere to discharge the liquid from the liquid phase side, and gas is supplied to the liquid phase side. A membrane degassing device, characterized in that a means for introducing gas is provided.