JPH04349902A - Deoxygenating method and apparatus using high purity gas - Google Patents

Abstract

PURPOSE:To reduce the conc. of dissolved oxygen to a low level of several ppb in a low cost by simple apparatus constitution. CONSTITUTION:A high purity gas supply line (4) and a vacuum discharge line (6) are connected to a deoxygenating module equipped with a gas permeable membrane (11) and raw water is brought into contact with high purity gas through permeable membrane and the gas is discharged on the high purity gas contact side of the gas permeable membrane.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a vacuum deoxidation method and apparatus using a gas permeable membrane.

0002

[Prior Art] As is well known, methods for removing dissolved oxygen in water that cause corrosion of metal materials include aeration method (gas replacement method), thermal deaeration method, vacuum deaeration method, chemical There are various degassing methods. The aeration method (gas replacement method) includes, for example, the nitrogen gas aeration method using high-purity nitrogen gas. As shown in Figure 5, nitrogen gas is blown into the water in the tank (20), and the nitrogen gas and water are mixed. Dissolved oxygen is physically removed by bringing it into direct contact and lowering the oxygen partial pressure in the water. (21) indicates a raw water supply line, (22) a treated water discharge line, and (23) a nitrogen gas supply line. When using this nitrogen gas aeration method, in order to reduce the dissolved oxygen concentration in water to a low level, it is necessary to use highly purified nitrogen gas or to reduce the size of the nitrogen gas bubbles blown into the water. It is necessary to take measures such as increasing the contact area. However, high-purity nitrogen gas is expensive, and in order to reduce the size of nitrogen gas bubbles, the shape of the gas outlet must be devised, resulting in a complicated structure. There was a point. Due to constraints on the equipment configuration, aeration is performed under positive pressure, but there is also the problem that dissolved oxygen is difficult to escape if the atmospheric pressure is high.

[0003] Some thermal degassing methods involve bringing water and steam into contact to heat the water and release and remove dissolved oxygen. However, since deaeration is performed in an open system, oxygen may be released due to operational negligence or equipment malfunction. may be re-dissolved. The vacuum degassing method uses a degassing tower to reduce the gas partial pressure by creating a vacuum in the atmosphere in contact with the liquid, thereby degassing dissolved gases in the liquid.
In order to increase the degree of vacuum, it is necessary to increase the height of the degassing tower, which poses the problem of a large equipment configuration. Chemical deaeration methods use chemicals (oxygen scavengers) and have problems in terms of safety, and have disadvantages such as not being able to be used in applications where contamination with impurities is averse.

0004

[Problem to be solved by the invention] Therefore, in recent years, as one of the vacuum degassing methods, a gas permeable membrane (hydrophobic polymer membrane) that allows only gas to pass through without passing water has been used. A membrane deaeration method has been put into practical use, in which dissolved oxygen in water is precipitated into a gas phase under reduced pressure. Membrane deaerators have features such as a compact device configuration, low running costs, and high safety. However, in order to reduce the dissolved oxygen concentration in water to a low level (several ppb level), it is necessary to increase the degree of vacuum on the gas phase side (oxygen partial pressure 0.1 Torr or less), and for this purpose An expensive vacuum pump is required due to its performance. Naturally, this will increase the cost of the entire device.

The present invention solves the problems of the above-mentioned membrane type deaerator, and uses a low cost and simple device configuration to produce several ppb
The purpose is to remove dissolved oxygen to low levels.

[0006]

[Means for Solving the Problems] That is, the present invention combines a vacuum deaeration method and a gas replacement method, and injects a small amount of high-purity gas other than oxygen into the vacuum exhaust side of a membrane deaeration device. , an attempt is made to remove oxygen using an inexpensive vacuum pump with relatively low vacuum performance, without using a particularly high-performance vacuum pump. Specifically, a raw water supply line is connected to one end of a deoxidation module equipped with a gas permeable membrane, and a treated water discharge line is connected to the other end, and one side of the gas permeable membrane is connected to the raw water contact side, and the other side is evacuated. It is characterized in that a high purity gas supply line and an evacuation line into which a vacuum pump is inserted are connected to the evacuation side of this gas permeable membrane.

[0007]

[Operation] According to the above configuration, raw water and high purity gas are brought into contact through the gas permeable membrane, and are discharged under reduced pressure from the high purity gas contact side of the gas permeable membrane, reducing the oxygen partial pressure on the exhaust side. By doing so, dissolved oxygen in raw water can be removed to very low levels.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. In the figure (1) is a gas permeable membrane (11)
A deoxidation module with a raw water supply line (
2) and the treated water discharge line (3) is connected to the other end. As the gas permeable membrane (11), for example, a hollow fiber type or a flat membrane type is used. (7)
is a water supply pump, which is inserted into the raw water supply line (2). In the gas permeable membrane (11), one side is set as the raw water contact side and the other side is set as the vacuum exhaust side, and a high purity gas supply line (4) is connected to the space on the vacuum exhaust side.
and the vacuum exhaust line (6). In the example shown in Fig. 1, a hollow fiber-shaped gas permeable membrane is used, and the inside of the permeable membrane is set as a raw water flow path, and the outside is set as a vacuum exhaust part. It is also possible to set the inside of the tube as a vacuum exhaust section. (5) is a vacuum pump,
It is inserted into the vacuum exhaust line (6). (8) is a cylinder filled with high-purity gas, and nitrogen gas, carbon dioxide gas, etc. are used as the high-purity gas. (9) is a pressure reducing valve, and (10) is a high-purity gas supply solenoid valve, which is inserted into the high-purity gas supply line (4).

According to the above configuration, the water supply pump (7)
The raw water is supplied to the deoxidation module (1), the raw water is brought into contact with high-purity gas through the gas permeable membrane (11), and the water is evacuated using the vacuum pump (5) to perform the deoxidation operation. It is now possible to do so. The supply of high purity gas reduces the oxygen partial pressure in the gas layer in contact with the water, increasing the amount of deoxidation and making it possible to remove dissolved oxygen in the water to very low levels. When high-purity gas is supplied, the partial pressure of the gas increases, but the oxygen partial pressure can be relatively lowered. As the high-purity gas to be used, nitrogen gas is optimal because it is inexpensive and has stable properties (does not have any chemical influence on other substances). According to experimental results, when nitrogen gas with a purity of 99.9% is used for a flow rate of 200 liters of water per unit time, the dissolved oxygen concentration in the water can be reduced to approximately 4 ppb at a vacuum pressure of 20 to 30 Torr. be able to.

The embodiment shown in FIG.
1) It has a configuration in which multiple devices are connected in series in a multi-stage configuration.
One vacuum pump (5) is provided for each deoxidation module. In a deoxidizer configured in multiple stages like this, high-purity gas may be supplied to each deoxidizer module, but as shown in the figure, high-purity gas is supplied only to the final stage deoxidizer module. By supplying this gas, the amount of high-purity gas consumed can be reduced, and a very high deoxidizing effect can be obtained with a small amount of high-purity gas. In other words, supplying high-purity gas will increase the displacement of the vacuum pump, but the density of the gas itself decreases under reduced pressure, so the required amount of high-purity gas may be very small, and to some extent ( When deoxygenating water that has been deoxygenated to about 10 ppb), the amount of high-purity gas may be even smaller. The embodiment shown in FIG. 3 also has multiple stages of deoxidizing modules connected in series like the embodiment shown in FIG. By connecting to the upstream position of the vacuum pump in the vacuum exhaust line, the pressure reduction ratio of the vacuum pump on the downstream side can be kept low, and dissolved oxygen can be removed to an extremely low level even with a vacuum pump that has relatively low vacuum performance and is inexpensive. I'm trying to make it possible.

In the embodiment shown in FIG. 4, the vacuum pump (5)
A water-seal type is used, and the water seal is used to cool the water. (12) is a water seal tank, (13) is a cooling device, (14) is a water seal supply line, and (15) is a return line. Cooling the sealed water lowers the steam partial pressure, and the synergistic effect of this in combination with the supply of high-purity gas makes it possible to remove dissolved oxygen to even lower levels.

0012

Effects of the Invention Since the present invention has the above-described structure, it is possible to reduce the oxygen partial pressure by supplying high-purity gas and obtain a very high deoxidizing effect. Furthermore, by using a gas permeable membrane, the contact area between water and high-purity gas per unit amount of water treated can be increased, resulting in high deoxidation efficiency. Since the deoxygenation operation is performed under reduced pressure, the amount of high-purity gas consumed is small, and at the same time, it is possible to promote deoxygenation from water. The vacuum pump used can be a commercially available one with relatively low vacuum capacity, and if the high-purity gas used is about 99.9% pure, the unit price is low, and the entire device is low cost and has a simple configuration. can be made into

[Brief explanation of drawings]

FIG. 1 is a system diagram showing one embodiment of the present invention.

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

FIG. 3 is a system diagram showing another embodiment of the present invention.

FIG. 4 is a system diagram showing another embodiment of the present invention.

FIG. 5 is a system diagram showing a conventional example.

[Explanation of symbols]

1　Oxygen removal module 2 Raw water supply line 3. Treated water discharge line 4 High purity gas supply line 5 Vacuum pump 6 Vacuum exhaust line 11 Gas permeable membrane

Claims (2)

[Claims] [Claim 1] High-purity gas is used, characterized in that raw water and high-purity gas are brought into contact through a gas-permeable membrane (11), and the gas is exhausted under reduced pressure from the high-purity gas contact side of the gas-permeable membrane. Deoxidation method. 2. A deoxidation module (1) equipped with a gas permeable membrane (11) is connected to one end of the raw water supply line (2) and the other end to a treated water discharge line (3), and the gas permeable membrane is connected to the deoxidation module (1). One side is the raw water contact side and the other side is the evacuation side, and a high purity gas supply line (4) and a vacuum pump (5) are inserted into the evacuation line to the evacuation side of the gas permeable membrane. (6) A deoxidizer using high-purity gas, characterized in that the following is connected.