JP7307567B2 - Degassing method and degassing device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a deaeration method and a deaeration device for removing dissolved gas from raw water such as industrial water.

In Patent Document 1, a membrane decarboxylation is performed by separating a liquid distribution side and a gas distribution side by a degassing membrane, passing raw water through the liquid distribution side, and passing air through the gas distribution side. An apparatus is disclosed. Carbonic acid contained in the raw water can be removed to the carbonic acid concentration in the air by circulating the air on the side opposite to the raw water side.

In Patent Document 2, in a water treatment device, by adding a disinfectant such as hypochlorous acid (NaClO) to raw water upstream from the degassing membrane, biological contamination (slime) of the degassing membrane can be suppressed. disclosed.

Japanese Patent Application Laid-Open No. 2001-205297 WO2017/141717

By adding hypochlorous acid to the raw water, the degassing membrane can be sterilized and the generation of slime on the degassing membrane can be suppressed. However, the addition of hypochlorous acid can cause deterioration of the degassing membrane. Specifically, when a degassing device that is partitioned into a liquid circulation area and a gas circulation area by a degassing membrane is used, chlorine gas is generated from raw water containing hypochlorous acid in the liquid circulation area. Chlorine gas passes through the degassing membrane together with other gas components and moves to the gas flow area. Even when the concentration of hypochlorous acid in the liquid is low, the chlorine gas concentration of the gas passing through the degassing membrane is considerably high, so it is considered that the degassing membrane is deteriorated by the chlorine gas. When using an oxidizing agent to sterilize the degassing membrane, not only hypochlorous acid, the degassing membrane may deteriorate when gas derived from the oxidizing agent passes through the degassing membrane.

An object of the present invention is to provide a degassing method and a degassing apparatus capable of preventing the generation of slime while suppressing deterioration of the degassing membrane.

According to one aspect of the invention,
A degassing method for degassing using a degassing device including a liquid circulation area and a gas circulation area partitioned by a degassing membrane,
a sweep gas circulating step of circulating the sweep gas through the gas circulating region;
a first raw water circulating step of circulating raw water having a lower concentration of an oxidant having an effect of sterilizing the degassing membrane through the liquid circulating region;
a second raw water circulating step of circulating raw water having a higher concentration of the oxidant through the liquid circulating region;
Switching between a first operation mode in which the sweep gas circulation step and the first raw water circulation step are performed simultaneously, and a second operation mode in which the second raw water circulation step is performed without performing the sweep gas circulation step. and
performing the second operation mode intermittently while repeating the first operation mode;
There is provided a degassing method characterized by adding the oxidizing agent to the raw water in the second raw water circulation step .

According to another aspect of the invention,
A degassing device comprising a liquid flow area and a gas flow area separated by a degassing membrane,
sweep gas circulation means for circulating the sweep gas through the gas circulation area;
a first raw water circulating means for circulating raw water having a lower concentration of an oxidant having a function of sterilizing the degassing membrane into the liquid circulating region;
a second raw water circulating means for circulating raw water having a higher concentration of the oxidant through the liquid circulating region;
A first operation mode in which the sweep gas circulation means and the first raw water circulation means are operated simultaneously, and a second operation mode in which the second raw water circulation means is operated without operating the sweep gas circulation means. and a control means for intermittently performing the second operation mode while repeatedly executing the first operation mode,
The degassing device is provided , wherein the second raw water circulation means comprises oxidant addition means for adding the oxidant to the raw water .

ADVANTAGE OF THE INVENTION According to this invention, the deaeration method and deaeration apparatus which can prevent slime generation are provided, suppressing deterioration of a deaeration film|membrane.

1 is a schematic configuration diagram showing an example of a degassing device according to an embodiment of the present invention; FIG. FIG. 4 is a schematic configuration diagram showing another example of the degassing device according to the embodiment of the present invention;

The embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited thereto.

The degassing device includes a liquid flow area 12 and a gas flow area 13 separated by a degassing membrane 11, as shown in FIG. The degassing membrane 11, the liquid circulation area 12 and the gas circulation area 13 are accommodated in the container 10 to form a so-called degassing membrane module.

A deaeration method using this deaeration device includes the following steps.
a sweep gas distribution step of distributing the sweep gas through the gas distribution area 13;
A first raw water distribution step of distributing raw water having a lower oxidizing agent concentration through the liquid distribution region 12 . This oxidant has the effect of sterilizing the degassing membrane 11 .
A second raw water distribution step of distributing raw water having a higher oxidizing agent concentration through the liquid distribution region 12 .
Here, the terms "lower" and "higher" refer to the raw water circulated through the liquid circulation region 12 in the first raw water circulation step, the raw water circulated through the liquid circulation region 12 in the second raw water circulation step, Based on mutual comparison between That is, these terms refer to the concentration of oxidant in the raw water dispensed into the liquid distribution region 12 in the first raw water distribution step compared to the oxidant concentration in the raw water distributed in the liquid distribution region 12 in the second raw water distribution step. means low.

This degassing method is performed by switching between a first operation mode and a second operation mode described below. At this time, the second operation mode is performed intermittently while the first operation mode is repeatedly performed.
First operation mode: The sweep gas flow process and the first raw water flow process are performed simultaneously.
Second operation mode: The second raw water circulation process is performed without performing the sweep gas circulation process.

That is, during normal operation, the first operation mode is performed to produce degassed water. Then, during the sterilization operation for sterilizing the degassing membrane, the second operation mode is performed. Furthermore, after the second operation mode, the first raw water supply step is performed again. In this way, by intermittently performing the second operation mode (sterilization operation) while repeatedly performing the first operation mode (normal operation), the oxidant concentration is relatively high only during the sterilization. Raw water is circulated in the liquid circulating area. In this case, by not using the sweep gas, it is possible to suppress the movement of the gas from the liquid circulation area to the gas circulation area through the degassing membrane, thereby suppressing the deterioration of the degassing membrane. As a result, shortening of the life of the degassing membrane can be suppressed.

[First form]
In this embodiment, when the deaeration membrane is sterilized, an oxidizing agent having a function of sterilizing the deaeration membrane 11 is added to the raw water. When performing sterilization, the supply of the sweep gas to the gas circulation area 13 is stopped. In this embodiment, the raw water supplied from the line L1 to the degassing device contains a relatively low concentration of oxidizing agent, or the raw water contains substantially no oxidizing agent, and the oxidizing agent is added to the raw water during sterilization. can be suitably used when desired. For example, the raw water (line L1) may be well water, industrial water, or waste water for washing semiconductor devices in a semiconductor manufacturing factory.

・First operation mode (normal operation)
A sweep gas is supplied to the gas circulation area 13 from a line L5 connected to the inlet of the gas circulation area 13 . The used sweep gas is taken out from the line L6 connected to the outlet of the gas circulation area 13. As shown in FIG. This used sweep gas can be appropriately discharged to the outside.

During normal operation, it is preferable to reduce the pressure in the gas flow area 13 from the viewpoint of promoting degassing. The sweep gas can be circulated in the gas circulation area 13 by pulling the sweep gas while reducing the pressure in the gas circulation area 13 using the exhaust pump 14 provided in the line L6 as a decompression means for that purpose. If the gas circulation area 13 is not decompressed, for example, a blower can be provided in the line L5 to push the sweep gas into the gas circulation area 13 .

The sweep gas distribution means includes line L5 and line L6 and exhaust pump 14 .

Line L1 is connected to the inlet of liquid flow area 12 via line L2. Raw water is supplied to liquid flow area 12 via lines L1 and L2. A line L4 is connected to the outlet of the liquid flow area 12 . The deaerated water that has been deaerated is taken out from the liquid circulation area 12 to the line L4. In addition, in the first raw water circulation process performed during normal operation, no oxidizing agent is added to the raw water. Therefore, the fluid flowing through line L1 and the fluid flowing through line L2 are the same. A pump (not shown) for supplying raw water can be provided on the line L1 as required.

The first raw water circulation means includes lines L1, L2, L4. The first raw water circulation means does not include the oxidant addition means, that is, does not include the line L3 provided with the oxidant addition pump 21 .

・Second operation mode (sterilization operation)
The oxidizing agent as a disinfectant is used in a liquid state such as an aqueous solution. Raw water is supplied from the line L1 to the deaerator. A line L3 is connected between the lines L1 and L2. The line L3 is provided with a pump 21 for adding an oxidant. A liquid oxidant is added to the raw water from line L3. Raw water added with an oxidant is supplied from the line L2 to the liquid distribution area 12, and the degassing membrane 11 is sterilized by the oxidant. Water used for sterilization is taken out from the liquid distribution area 12 to the line L4. Water from the line L4 can be appropriately discharged to the outside.

The second raw water communication means includes lines L1, L2, L3 and L4 and pump 21 for addition of oxidant. The oxidant addition means for adding the oxidant to the raw water includes the line L3 and the oxidant addition pump 21 . A storage means (not shown) such as a tank for storing the oxidant can be appropriately provided. If the oxidant supplied to the deaerator has a sufficient pressure, the oxidant addition pump 21 may not be used. In this case, instead of the oxidant addition pump 21, a valve (on/off valve) can be used to switch between execution and stop of addition of the additive.

In the second operation mode, no sweep gas is allowed to flow through the gas flow area 13 . Also, the pressure in the gas circulation area 13 is not reduced.

- Control of operation mode The control device 22 is used as control means for switching between the first and second operation modes and intermittently performing the second operation mode while the first operation mode is repeatedly performed. Specifically, the controller 22 controls the oxidant addition pump 21 and the exhaust pump 14 as follows.
First operation mode: The oxidant addition pump 21 is stopped and the exhaust pump 14 is operated.
Second operation mode: The oxidant addition pump 21 is operated and the exhaust pump 14 is stopped.
The control device has a timer function, and can alternately perform the first and second operation modes for predetermined periods.

[Second form]
This form is suitably used when the raw water contains an amount of oxidizing agent sufficient to sterilize the degassing membrane, such as when the raw water supplied to the deaerator is city water (for example, tap water). be done. In this embodiment, the oxidizing agent is removed from raw water during normal operation, and the oxidizing agent is not removed during sterilization.

This embodiment differs from the first embodiment in the method of supplying raw water to the liquid circulation area 12 or the configuration of the device upstream of the liquid circulation area 12 . Other configurations can be the same as those of the first embodiment. In the following description of the second embodiment, the differences from the first embodiment will be detailed.

・First operation mode (normal operation)
As shown in FIG. 2, raw water is supplied to the deaerator from line L11. Line L11 branches into line L12 and line L13. The line L12 is provided with a valve (on-off valve) 23 and an activated carbon packed tower 25 as oxidant removing means. Line L13 bypasses activated carbon packed tower 25 . Downstream of the activated carbon packed tower 25, the line L12 and the line L13 merge to form a line L14. Line L14 is connected to the inlet of liquid flow area 12 . The valve 23 is opened, and the valve (on/off valve) 24 provided on the line L13 is closed. The raw water from the line L11 has the oxidant removed by activated carbon while flowing through the line L12, and is supplied to the liquid distribution area 12 through the line L14.

The first raw water communication means includes lines L11, L12, L14 and L4, valve 23, and oxidant removal means (activated carbon packed tower 25). A pump (not shown) for supplying raw water can be provided on the line L11 as required.

・Second operation mode (sterilization operation)
Valve 24 is opened and valve 23 is closed. The raw water supplied to the deaerator from line L11 is supplied to liquid flow area 12 via lines L13 and L14.

The second raw water communication means includes lines L11, L13, L14 and L4, and valve 24. Note that the oxidizing agent is not removed during the sterilization operation. Therefore, the second raw water circulation means does not include the oxidant removing means and does not include the line L12.

- Control of operation mode The control device 26 is used as control means for switching between the first and second operation modes and intermittently performing the second operation mode while the first operation mode is repeatedly performed. Specifically, controller 26 controls valves 23 and 24 and exhaust pump 14 as follows.
First mode of operation: valve 23 is opened, valve 24 is closed, and exhaust pump 14 is activated.
Second mode of operation: valve 23 is closed, valve 24 is open, and exhaust pump 14 is stopped.
The control device has a timer function, and can alternately perform the first and second operation modes for predetermined periods.

The oxidant removing means is not limited to the activated carbon packed tower 25, and any device capable of removing the oxidant can be used as appropriate. For example, the oxidizing agent can be removed by adding a reducing agent such as sodium sulfite or sodium bisulfite to the raw water to reduce the oxidizing agent. In this case, the reducing agent is added to the raw water in the first operation mode, and the reducing agent is not added in the second operation mode. For this purpose, reducing agent adding means for adding a reducing agent to the raw water can be used as the oxidizing agent removing means. In this case, the reducing agent addition means is operated in the first operation mode, and the reducing agent addition means is not operated in the second operation mode.

In either of the first and second forms, following the second operation mode, the following third operation mode can be performed.
Third operation mode: no sweep gas flow process is performed, flow of raw water in the liquid flow area 12 is stopped, and raw water with a higher concentration of oxidant is retained in the liquid flow area 12 .

After the third mode of operation, the first mode of operation can be performed. That is, the first, second and third operation modes can also be switched. In the third operation mode, the raw water (raw water with a relatively high oxidant concentration) supplied to the liquid circulation area 12 in the second operation mode is retained in the liquid circulation area 12 . The raw water retained in the liquid flow area 12 sterilizes the degassing membrane. After performing the third operation mode for an appropriate time, the operation mode is shifted to the first operation mode.

It should be noted that water can be sampled from the deaerator during the first operation mode, that is, deaerated water obtained from the deaerator can be sent to equipment downstream of the deaerator. When the first operation mode is performed after the second or third operation mode, an appropriate amount of time is required after starting the first operation mode in order to push out raw water having a relatively high oxidant concentration from the deaerator. It is not necessary to sample water from the deaerator until the time elapses. By sampling water from the deaerator in the first operation mode after the appropriate time has passed, it is possible to avoid sending raw water with a relatively high oxidant concentration to downstream equipment. Discarding the water discharged from the deaerator in the second operation mode and the water discharged from the deaerator during the time from the start of the first operation mode to the elapse of the appropriate time. can be done.

[Timing for performing the second operation mode]
The timing at which the second operation mode (sterilization operation) is performed can be determined according to the quality of the raw water and the like, and can be, for example, about 1 to 10 times per day. The time for one operation in the second operation mode can also be determined according to the quality of the raw water, and can be, for example, 10 minutes to 1 hour.

〔Oxidant〕
The oxidizing agent has the effect of sterilizing the degassing membrane. The oxidizing agent is particularly an oxidizing agent that can generate chlorine gas or bromine gas, and specific examples thereof include hypochlorous acid, hypochlorite, hypobromous acid, hypobromite, and chlorine-based oxidizing agents. and a sulfamic acid compound, and a stabilized hypobromous acid composition containing a brominated oxidizing agent and a sulfamic acid compound. Examples of these salts include alkali metal salts such as sodium and potassium, and alkaline earth metal salts such as calcium and barium.

In the first embodiment, as the oxidizing agent (line L3) added to the raw water, particularly as a liquid oxidizing agent, for example, a 6% by mass hypochlorous acid aqueous solution can be used.

In the first operation mode (normal operation), the oxidant concentration of the raw water (raw water with a lower oxidant concentration) supplied to the liquid circulation region 12 is preferably low from the viewpoint of suppressing deterioration of the degassing membrane. For example, in a first mode of operation, raw water that is substantially oxidant-free can be supplied to liquid flow area 12 . In the first form, raw water substantially free of oxidant can be used as the raw water supplied to the deaerator from line L1. In the second mode, the raw water after removing the oxidant (downstream of the activated carbon packed tower 25 in line L12) can be substantially free of the oxidant.

In the second operation mode (sterilization operation), the oxidant concentration of raw water (raw water with a higher oxidant concentration) supplied to the liquid distribution area 12 is, for example, about 0.01 mg/liter to 10 mg/liter. In the first form, the oxidant concentration of the raw water (line L2) to which the oxidant has been added can be within this range. In the second form, raw water having an oxidant concentration within this range can be used as the raw water supplied to the deaerator from line L11.

[Degassing membrane]
Gases to be degassed may be those known to be treated by degassing membranes, examples of which include carbonic acid and oxygen. Therefore, the deaeration film can be used as a decarbonation film or an oxygen removal film. As the material of the degassing membrane, a hydrophobic polymer known as a degassing membrane material in water treatment can be appropriately used. can be used. The shape of the degassing membrane is typically a hollow fiber membrane.

[Sweep gas]
The sweep gas used in the first operation mode can be a gas known as a sweep gas for degassing membranes, such as air or nitrogen gas. The flow rate of the sweep gas can also be in a known range, for example, preferably 0.5 to 500 N liters/minute per unit area of the inner surface area of the gas flow region, and 5 to 50 N liters/minute m ^{2 .} is more preferable (“N” in the gas flow unit means a value converted to 20° C. and 1 atmosphere).

[Use of deaerator and further treatment]
A degassing device can be used, for example, in the pretreatment stage of a reverse osmosis device. For example, downstream of the degassing device, a reverse osmosis membrane device and an ion exchange device can be connected in series in this order to form a pure water production device. In that case, the degassed water obtained from the deaerator during the first mode of operation is sent to the reverse osmosis membrane device.

A pretreatment filter (not shown), also called a prefilter, is provided in the raw water supply line (line L1 or L11) to the deaerator to remove coarse suspended solids from the raw water supplied to the deaerator. , the degassing process described above can be performed. As this pre-filter, a pre-filter known in the field of degassing membranes can be appropriately used.

In the degassing method described above, unless otherwise specified, the temperature and pressure of the fluid (raw water, degassed water, sweep gas, oxidizing agent) may be about normal temperature and normal pressure (20° C., 1 atm).

10 Vessel 11 Degassing membrane 12 Liquid distribution area 13 Gas distribution area 14 Exhaust pump 21 Pump 22 for adding oxidant Controllers 23, 24 Valve 25 Activated carbon packed tower 26 Controller

Claims (6)

A degassing method for degassing using a degassing device including a liquid circulation area and a gas circulation area partitioned by a degassing membrane,
a sweep gas circulating step of circulating the sweep gas through the gas circulating region;
a first raw water circulating step of circulating raw water having a lower concentration of an oxidant having an effect of sterilizing the degassing membrane through the liquid circulating region;
a second raw water circulating step of circulating raw water having a higher concentration of the oxidant through the liquid circulating region;
Switching between a first operation mode in which the sweep gas circulation step and the first raw water circulation step are performed simultaneously, and a second operation mode in which the second raw water circulation step is performed without performing the sweep gas circulation step. and
performing the second operation mode intermittently while repeating the first operation mode;
The degassing method , wherein the oxidizing agent is added to the raw water in the second raw water circulation step . 2. The degassing method according to claim 1, wherein said oxidizing agent is removed from said raw water in said first raw water circulation step. 3. The degassing method according to claim 1 , wherein in said sweep gas circulating step, said gas circulating region is decompressed. A degassing device comprising a liquid flow area and a gas flow area separated by a degassing membrane,
sweep gas circulation means for circulating the sweep gas through the gas circulation area;
a first raw water circulating means for circulating raw water having a lower concentration of an oxidant having a function of sterilizing the degassing membrane into the liquid circulating region;
a second raw water circulating means for circulating raw water having a higher concentration of the oxidant through the liquid circulating region;
A first operation mode in which the sweep gas circulation means and the first raw water circulation means are operated simultaneously, and a second operation mode in which the second raw water circulation means is operated without operating the sweep gas circulation means. and a control means for intermittently performing the second operation mode while repeatedly executing the first operation mode,
The degassing device, wherein the second raw water circulation means comprises oxidant addition means for adding the oxidant to the raw water. 5. The degassing device according to claim 4 , wherein said first raw water circulation means comprises oxidant removal means for removing said oxidant from raw water. 6. A degassing device according to claim 4 or 5 , wherein said sweep gas distribution means comprises decompression means for decompressing said gas distribution area.

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