JPH04313308A - Degassing method utilizing molecular diffusion - Google Patents

Abstract

PURPOSE:To reduce the dissolved oxygen amt. of raw water to a specified value with a commercially available (low-capacity) water-sealed vacuum pump by imparting a temp. difference between the sealing water of the pump and raw water to control their vapor pressure difference to a specified value, making the temp. of the sealing water lower than that of the raw water and degassing the raw water. CONSTITUTION:The vapor pressure difference between a working fluid (or sealing water) and raw water is adjusted to >= about 8 Torr in the region where the fluid flows into a water-sealed vacuum pump 2 by making the temp. of the fluid lower than that of the raw water. Consequently, a steam flow is generated, the separated gas is transported from a degassing module 1 toward the pump 2 by the molecular diffusion at this time, and the degassing of the raw water is promoted. Consequently, the dissolved oxygen concn. of the raw water is reduced to <=10 ppb with a commercially available (low-capacity) water-sealed vacuum pump.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a deaeration method for effectively removing dissolved oxygen from raw water.

0002

[Prior Art] Industrial water and other raw water contain several kinds of dissolved gases, including oxygen, carbon dioxide, and nitrogen. It is known that physical causes have a significant impact. One of the aspects of such influence is related to the water permeability of the applied product. For example, when raw water that has not been sufficiently deaerated is used during dyeing processing,
Even if the required amount of dye is dissolved, it cannot effectively act on the object to be dyed. Another aspect related to oxidation is that when applied to the cleaning of electronic components such as LSIs, the surfaces of those components are oxidized by insufficiently degassed raw water, impairing the accuracy of circuits. One example is damage. In addition to the above, various attempts have been made to use deaerated raw water in the food processing field, but in this case as well, several problems have been pointed out regarding the above-mentioned water permeability and oxidation effect. has been done.

[0003] For this reason, in recent years, a higher level of deaeration treatment has been required, but as is well known, the method of heating raw water does not provide sufficient deaeration treatment despite the high heating cost. There are drawbacks. On the other hand, the method of adding a commercially available oxygen scavenger not only increases costs, but also requires the selection of an oxygen scavenger that matches the properties of the raw water, and the need to adequately address problems that may occur if the oxygen scavenger remains in the supplied water. special care must be taken. In view of the above, a vacuum degassing module that can be used at room temperature was proposed as a relatively new method, and as a result, it is now possible to perform degassing at a considerable level industrially (dissolved oxygen concentration of 10 to 1 PPM). It is about to be realized.

FIG. 3 is a system diagram schematically showing one example. The deaeration device shown in the figure consists of a membrane deaeration module (32) and a flow switch (33) installed in a water supply line (31) for raw water, a water supply line (31), and a water ring vacuum pump (31). Water sealing supply line (35) between
A water-sealing solenoid valve (36) provided in the vacuum degassing line (37) between the degassing module (32) and the water-sealing vacuum pump (34) for maintaining vacuum during shutdown. solenoid valve(
38). In this system, when raw water is supplied, a flow switch (33) is activated to drive a water ring vacuum pump (34), and two solenoid valves (36) and (38) are opened to release the vacuum. Air treatment is performed. When the water supply is stopped, the water ring vacuum pump (34) is stopped and the two electromagnetic valves (36) and (38) are closed.

This type of conventional deaerator has the following problems. That is, when using a conventional degassing device, the outside pressure of the hollow fiber membrane in the degassing module is 30 torr.
r (water vapor partial pressure 17.5 torr), the oxygen concentration in the raw water can be reduced from about 10 PPM to about 0.5 PPM (at 20 °C), but this can be reduced to 0.01
To achieve a dissolved oxygen concentration of less than PPM, approximately 1
0PPM oxygen at 18 torr (including water vapor partial pressure)
must be aspirated under a vacuum. At this time, since the volume of the separated gas increases significantly as the partial pressure decreases, a vacuum pump that has a suction volume about 10 times that of conventional pumps and a pressure ratio of about 1000 is required. Such large capacity vacuum pumps have a high power requirement and are inefficient, making it virtually difficult to reduce the dissolved oxygen concentration below 10 PPB using known simple techniques or equipment.

[0006]

[Problems to be Solved by the Invention] This invention uses a commercially available water ring vacuum pump to reduce the dissolved oxygen concentration of raw water to 10%.
The purpose of this method is to obtain a degassing method that can reduce the amount of water to less than PPB by applying a temperature difference between the sealed water of the vacuum pump and the raw water to create the desired vapor pressure difference. The desired purpose is achieved by setting the temperature to a low temperature.

[0007]

[Means for Solving the Problems] Specifically, the present invention provides that in the inflow side region of the working fluid (or sealed water) flowing into the vacuum pump, the difference in vapor pressure between the fluid and raw water is approximately 8.
By setting the temperature of the former lower than that of the latter so that the temperature of the former reaches a value of torr or higher, a flow of water vapor is generated, and the molecular diffusion effect is used to transfer the water vapor from the degassing module to the vacuum pump. It is characterized by transporting and compressing the separated gas toward the degassing process.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings. In Figure 1, (1) is a degassing module, (2) is a water ring vacuum pump, and these are connected to a raw water supply line (3), a deaerated water supply line (4), and a water ring vacuum pump. A seal water supply line (5) for the vacuum pump, and a vacuum deaeration line (6) that communicates the module with the pump.
) are connected and arranged. In addition, (7) shows a solenoid valve that opens and closes the line for supplying degassed water, and (8) shows a similar type of valve that opens and closes the line for vacuum degassing.

According to this system, valves (7), (8
) is opened and the vacuum pump (2) is operated, the raw water is degassed in the process of passing through the degassing module (1) from the line (3), becoming degassed water and flowing into the line (4).
) to the desired supply point.

[0010] The present invention effectively promotes the degassing process in the degassing system as described above by using the following configuration. In FIG. 1, (10) is a unit for cooling sealed water, which is the main part of the present invention, and is the middle part of the line (5) for supplying sealed water, that is, the pump (2).
heat exchanger (11
) and a cooler (12) connected thereto.

[0011] Preferably a heat exchanger (11
) is provided with a temperature sensor (13) on the upstream side.
The output signal from this sensor is sent to the control box (
16). A temperature sensor as described above for providing an output signal relating to temperature to the box is connected to the heat exchanger (11), shown as (14).
These sensors are also installed downstream of the pump (2) and in the raw water supply line (3) shown as (15), and these sensors can be used in appropriate combinations to adjust the temperature of the sealed water of the pump (2) to the raw water. On the other hand, it is used to set a low temperature.

FIG. 2 shows the raw water temperature on the horizontal axis and the saturated steam pressure on the vertical axis, and the solid line shows the saturated steam pressure of the raw water and the steam partial pressure around the module. If the sealed water of the vacuum pump is at the same temperature as the raw water, the steam partial pressure at the vacuum pump inlet is equal to this pressure. The dotted line represents the steam partial pressure at the vacuum pump inlet when the sealed water temperature is 5°C, and the dashed line represents the steam partial pressure at the vacuum pump inlet when both of these are 10°C lower than the raw water temperature. The partial pressure difference causes a molecular flow from the degassing module toward the vacuum pump, providing the power source that drives the degassed gas toward the pump. When the raw water temperature is high, even if the temperature difference between the raw water and sealed water is small, the difference in steam partial pressure is large, so the partial pressure of the gas in the module part becomes sufficiently low. If the temperature difference with the water is less than 10℃, the vapor partial pressure difference will not be sufficient, and the dissolved oxygen concentration in the water will decrease by 1.
It cannot be lower than PPB.

Next, an example of operation of a system embodying the present invention will be explained. For example, when the raw water temperature is 15°C, if raw water cooled to approximately 5°C is used as seal water, this raw water is supplied to the water ring vacuum pump (2) via the seal water supply line (5). ), but this causes the water vapor partial pressure inside the pump to be about 8.5
torr decreases. Therefore, the flow of water vapor molecules due to the difference in vapor pressure that occurs between the module part and the pump inlet transports and compresses the separated gas from the degassing module (1) toward the vacuum pump (2), and the gas in the pump inlet area is compressed. As a result of increasing the partial pressure and facilitating the action of the vacuum pump, the partial pressure of the separation gas in the module section is reduced and the degassing process is accelerated.

[0014]

[Effects of the Invention] As described above, the present invention uses a water-ring single-stage vacuum pump with a simple structure that is capable of degassing at room temperature and does not require a pump device with exceptionally high vacuum performance. It is possible to reduce the dissolved oxygen concentration to a low level (1 PPB). Further, by implementing the present invention, not only remarkable effects can be obtained in terms of energy saving, but also great industrial effects such as the ability to make the entire device compact can be achieved.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing a deaeration treatment system according to the present invention.

FIG. 2 is a graph showing the saturated vapor pressure of raw water and the sealed water vapor pressure depending on the temperature difference (Δt) between the sealed water and the raw water.

FIG. 3 is a system diagram showing a conventional deaeration processing system.

[Explanation of symbols]

1　Oxygen removal module 2 Water ring vacuum pump

Claims (1)

[Claims] Claim 1: In the inflow side region of the working fluid (or sealed water) flowing into the vacuum pump (2), the former is heated so that the difference in vapor pressure between the fluid and raw water is approximately 8 torr or more. By setting the temperature of the latter lower than that of the latter, a flow of water vapor is generated, and the molecular diffusion effect at that time is used to transport the separated gas from the degassing module (1) toward the vacuum pump (2). A deaeration method that utilizes the molecular diffusion effect, which is characterized by compressing and promoting deaeration processing.