Gas dissolution method

Abstract

Conventionally, it is necessary to pressurize gas in order to forcibly dissolve gas such as oxygen into water; for example, it is necessary to prepare an oxygen cylinder or the like. This results in a complicated device, which not only is high in cost but also requires troublesome maintenance.　The gas dissolving device according to the present invention is configured as follows. The device dissolves gas into a water flow, and comprises a gas supply source, a water flow source, and a dissolution part. The dissolution part includes: a cylinder for passing a water flow from the water flow source; a vertical downstream wall located in the cylinder and facing the downstream side of the water flow, the water flow forming a negative pressure region by turning along the downstream wall; and a gas supply passage penetrating from a circumferential wall of the cylinder to the negative pressure region, the gas supply passage being connected to the gas supply source. The gas of the gas supply source is supplied to the negative pressure region through the supply passage of the gas by negative pressure in the negative pressure region.

Description

[Technical Field]

[0001] The present invention relates to a method for dissolving a gas into a water stream. [Background technology]

[0002] Useful gases such as carbon dioxide are dissolved in the water stream to increase its concentration. For example, Patent Document 1 discloses a gas dissolving device in which carbon dioxide gas stored in a gas cylinder is supplied to a collision section that generates fine bubbles. Patent Document 2 discloses a method of dissolving a gas in water under pressure. In all of the gas dissolving methods described in these prior art documents, pressurized gas is supplied to a water flow.

[0003] In the gas dissolution device described in Patent Document 1, mixing with water progresses significantly in the strong stirring region downstream of the collision section, and gas dissolution is carried out efficiently (see Patent Document 1, page 21, columns 2 and 3). See also Patent Documents 3 and 4. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6182715 [Patent Document 2] Patent No. 5762210 [Patent Document 3] Patent No. 6279179, paragraph 0040, paragraph 0041 [Patent Document 4] Patent No. 6978793 Summary of the Invention [Problem to be solved by the invention]

[0005] There is a growing demand for water that can be forcibly dissolved with useful gases to enhance its functionality. For example, it is known that increasing the amount of dissolved oxygen in the water of fish tanks in trucks that transport live fish can help the fish survive for a longer period of time. On the other hand, conventionally, to forcibly dissolve gases such as oxygen in water, the gas had to be pressurized, which required the preparation of an oxygen cylinder, etc. This not only made the equipment complicated and costly, but also required time and effort for maintenance. [Means for solving the problem]

[0006] The present invention has been made to solve the above problems, and its first aspect is defined as follows: 1. A method for dissolving a gas in a water stream, comprising: A gas dissolution method in which a portion of the water constituting the water flow is made into a negative pressure region, the gas is sucked in by the negative pressure of the negative pressure region, the gas is entrained in the water flow, and fine bubbles are generated.

[0007] According to the gas dissolving method of the first aspect defined as above, the negative pressure in the negative pressure region draws in gas from the gas supply source, and the gas is entrained in the water flow. In other words, a sufficient amount of gas is drawn into the negative pressure region without pressurizing the introduced gas. If the introduced gas is pressurized, the gas suction efficiency is improved. In the negative pressure region of the water flow, a portion of the water is gasified (vaporized). When gas is introduced into this negative pressure region, the water vapor in the negative pressure region and the gas mix. Then, as the pressure of the portion of the water flow that escapes from the negative pressure region increases, the water vapor condenses and returns to water. At this time, the gas is taken in and dissolved in the water. Even if the water in the negative pressure region is not gasified, its vapor pressure decreases and the bonds between the water molecules become weaker, making it easier for the introduced gas to penetrate between the water molecules. In addition, since fine bubbles are generated, gas is also present in the fine bubbles, preventing a decrease in the dissolved gas concentration in the water.

[0008] In this invention, the gas is sucked by the negative pressure of the negative pressure region, so there is no need for an external pressure device to pump the gas.

[0009] A second aspect of the present invention is defined as follows: That is, in the method of the first aspect, The gas is drawn into the negative pressure region at atmospheric pressure. In order to produce oxygen industrially and inexpensively, an adsorption separation method is generally adopted, and the oxygen produced by such a method is not pressurized. In other words, even if the oxygen is not pressurized and is extracted from an adsorption separation device as an oxygen source, it can be dissolved in water as is, i.e., at atmospheric pressure, according to the second aspect.

[0010] The third aspect of the present invention is defined as follows: In the gas dissolution method of the first aspect, the water flow flows through a tube, and the tube is provided with a vertical downstream wall facing the downstream side of the water flow, and the water flow flows around the downstream wall to form the negative pressure region. According to the gas dissolving method of the third aspect defined above, the water flow that has detoured along the downstream wall moves away from the center of the cylinder and forms a negative pressure region on the outer periphery of the cylinder, making it easier to supply gas to this negative pressure region from outside the cylinder. Patent Document 4 explains that fine bubbles containing nano-sized microbubbles are formed in water by passing the water through a tube with a vertical downstream wall (see Figures 4 and 5). Preferably, a small diameter portion (orifice) is provided in the cylinder, and a vertical downstream wall is formed at the outlet of the small diameter portion.

[0011] A fourth aspect of the present invention is defined as follows: In the gas dissolving method of the third aspect, a recess is formed in the downstream wall, and a part of the water flow that has reached the recess is vaporized by the negative pressure of the recess. The negative pressure becomes extremely large in the recess formed in the downstream wall. According to the inventors' investigation, the pressure in this recess changes (oscillates), and at the maximum negative pressure, the water is almost vaporized.

[0012] When the gas supplied to the negative pressure region is guided by the water flow and reaches the recess, it is drawn into the recess by the large negative pressure and mixes with the water vapor in the recess. When the negative pressure in the vibrating recess decreases (when it returns to water), gas is absorbed into the water along with the water vapor. The gas can be supplied directly to the recess. The pressure oscillation in the recessed portion also has the effect of stirring the water flow, which also improves the gas dissolution effect.

[0013] The fifth aspect of the present invention is defined as follows: In the gas dissolving device according to the fourth aspect, the recess extends to a peripheral wall of the cylinder, The gas is supplied through a gas supply passage that penetrates from the peripheral wall of the cylinder to the recess. In the gas dissolving device of the fourth aspect thus defined, the recess extends into the peripheral wall of the cylinder, so that a lid is placed over a portion of the recess. According to the study by the inventors, evaporation of water is promoted in the recess in the portion covered with the lid.

[0014] The seventh aspect of the present invention is defined as follows: 1. An apparatus for dissolving a gas into a water flow from a water flow source, comprising: a gas supply source and a dissolving unit, The dissolving part is a tube through which the water flow from the water flow source passes; a vertical downstream wall facing the downstream side of the water flow in the tube, the water flow wrapping around the downstream wall to form a negative pressure region; and a gas supply passage extending from the peripheral wall of the cylinder to the negative pressure region, the gas supply passage being connected to a gas supply source; Here, the gas from the gas supply source is supplied to the negative pressure region through the gas supply path by the negative pressure of the negative pressure region.

[0015] According to the gas dissolving device of the seventh aspect defined as above, the gas from the gas supply source is supplied to the negative pressure region through the gas supply path by the negative pressure of the negative pressure region, so that no gas pressurizing device (including a pump) is required. Therefore, the number of parts in the entire device is reduced, resulting in an inexpensive device. Furthermore, according to the gas dissolving device including the dissolving unit, fine bubbles are also generated in the dissolving unit. When the target gas is the atmosphere, a tank or the like is not required as a gas supply source, and the atmosphere itself serves as the gas supply source. Therefore, the end of the gas supply path on the gas supply source side is open to the atmosphere. The water flow that has passed through this gas dissolving device can be fed back to the water flow source. That is, the water in the tank is circulated, and the circulating water flow is passed through the dissolving section. It has been found that when this gas dissolving device is applied to such a circulation system, the temperature of the circulating water does not increase at all. This is thought to be because there is no need to pressurize the gas when dissolving it, and also because no mechanical external force such as stirring is applied to the water flow.

[0016] In order to generate a higher negative pressure in the negative pressure region, a recess can be formed in the downstream wall, and a part of the water flow that has flowed around the recess is vaporized by the negative pressure of the recess (ninth aspect). In a ninth aspect of the present invention, a gas supply channel opens into the recess. A high negative pressure is generated in the recess, allowing gas to be efficiently drawn in from the outside. Furthermore, the high negative pressure promotes the conversion of water into water vapor, which entrains gas into the water when the water vapor returns to water, resulting in a high concentration of dissolved gas. The gas supply path preferably opens at a position facing the recess (ninth aspect).

[0017] The recess can be recessed to the peripheral wall of the tube (tenth aspect). When the recess extends to the peripheral wall of the tube, a lid is placed over a portion of the recess. According to the inventors' investigations, evaporation of water is promoted in the recess where the lid is placed.

[0018] Incidentally, by providing such recesses, fine bubbles are efficiently generated in the water flow, as described in Patent Document 4. In this specification, fine bubbles include minute bubbles on the nano-order. The gas may be one or more selected from inorganic gases such as air, oxygen, ozone, ammonia, and nitrogen, and organic gases such as carbon dioxide and ethane. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic diagram showing a gas dissolving device according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a front view of the bubble generating device employed in the gas dissolving device of FIG. [Figure 3] FIG. 3 is a schematic diagram showing a gas dissolving device according to another embodiment. [Figure 4] FIG. 4 is a schematic diagram showing a gas dissolving device according to another embodiment. [Figure 5] FIG. 5 is a schematic diagram showing a gas dissolving device according to another embodiment. [Figure 6] FIG. 6 is a graph showing the characteristics of the gas dissolving device of the example. [Figure 7] FIG. 7 shows the change in oxygen concentration over time. [Figure 8] FIG. 8 is a graph showing the results of another example. DETAILED DESCRIPTION OF THE INVENTION

[0020] (Embodiment 1) A gas dissolving device 1 according to a first embodiment of the present invention will be described. The gas dissolving device 1 comprises a gas supply source 10 , a water flow source 100 and a dissolving section 500 . An adsorption separation type oxygen generator was used as the gas supply source 10. The oxygen output from this oxygen generator was at atmospheric pressure. Any gas to be dissolved in the water flow can be selected as the type of gas supplied by the gas supply source 10. A tank or cylinder of such a gas can be used as the gas supply source 10. The atmosphere can also be used as the gas source.

[0021] A general-purpose pump can be used as the water flow source 100. The pressure and amount of water delivered by the pump can be set as desired. A water faucet can also be used as the water source.

[0022] The dissolving section 500 includes a cylindrical section 600 and a bubble generator 1000. The bubble generator 1000 is described in Patent Document 3 (Japanese Patent No. 6279179), the disclosure of which is incorporated herein by reference. The cylindrical portion 600 is divided in the axial direction (water flow direction). The upstream portion 610 is connected to the water flow source 100 via a conduit 200. The water flow inlet comprises a funnel-shaped portion 611 whose diameter decreases in the water flow direction, and an inlet orifice 612. An outlet orifice 632 is formed in the downstream portion 630. The two orifices 612, 632 have the same diameter.

[0023] The bubble generator 1000 is sandwiched and built in between the upstream portion 610 and the downstream portion 630. Fig. 2 is a side view of the bubble generator 1000. Fig. 1 is a cross section indicated by the AA cross section indication line in Fig. 2. The bubble generating device 1000 comprises a main body 1100 and a bubble generating unit 1200 .

[0024] The main body 1100 is formed in a cylindrical shape. A part of the outer surface of the main body 1100 is notched to form a flat portion 1110. This flat portion prevents unnecessary rotation and is used for positioning. The main body 1100 does not have to be cylindrical, and any shape can be adopted. For example, it can be a rectangular tube. It can also be divided in the radial direction. It can also be tapered, with the diameter decreasing downstream in the water flow direction.

[0025] The bubble generating part 1200 includes pillar parts 1210 that bulge out from the inner peripheral surface of the main body part 1100 and are formed integrally with the main body part 1100. In this example, there are six pillar parts 1210. Slits 1300 are formed between each pillar part 1210.

[0026] The slits 1300 are formed radially in a planar view. In this example, the radiation center coincides with the central axis of the main body portion 1100. The radiation center does not have to coincide with the central axis of the main body portion 1100. The slits 1300 are formed on one imaginary cross section in the main body portion 1100. In other words, in each pillar portion 1210, the portion that bulges most from the inner peripheral surface of the main body portion 1100 is formed on the imaginary cross section. It is preferable that this most bulging portion coincides with the periphery of the bottom surface 1211 of the pillar portion 1210. It is preferable that the bottom surface 1211 is formed perpendicular to or at an acute angle to the direction of the water flow at the most bulging portion, because this can cause a large change in the flow velocity and generate negative pressure there.

[0027] A recess 1220 is formed in the bottom surface 1211. The water flow that has flowed over the slit 1300 toward the bottom surface is further sucked into this recess 1220, and the generation of negative pressure on the bottom surface 1211 is promoted. In order to generate negative pressure uniformly, it is preferable that the recesses 1220 are arranged radially and uniformly from the center of the slit 1300, that is, from the central axis of the main body 1100.

[0028] This recess 1220 extends to the main body 1100. The portion of the main body 1100 where the recess 1220 exists becomes a gap during use. Water attempting to flow into the recess 1220 will interfere with the water already present in the recess 1220, but this interference is alleviated by this gap. This increases the negative pressure generation effect. In this example, each slit 1300 is formed to have the same width, but the width can be varied. The width variation here means that the width of each slit is different, or that the width of a single slit is varied.

[0029] The cross-sectional area of the column 1210 gradually decreases from its bottom surface 1211 toward the upstream side. The cross-sectional area reaches zero at the upstream side. This reduces the column's resistance to the water flow. Furthermore, by adopting this structure, the mold can be removed without any resistance during molding.

[0030] The pillar portion 1210 in this example has a cone shape with the surface defined by each edge 1310 of the slit 1300 as the bottom surface 1211. The ridge line of the pillar portion 1210 is defined as follows: it is a line connecting the intersection of the edges 1310, 1310 of adjacent slits 1300 and the most upstream point on the inner circumferential surface of the main body portion 1100 where the imaginary bisector plane of these edges 1310, 1310 intersects.

[0031] A gas supply path 700 is disposed between the gas supply source 10 and the orifice 632. The gas supply path 700 is made of a pipe, one end of which is connected to the gas supply source 10 and the other end of which is open to the orifice 632. The other end of the gas supply path 700 can be opened facing the recess 1220. This allows the gas to be efficiently supplied to the water flowing into the recess 1220. Furthermore, as shown in FIG. 3, the other end of the gas supply path 700 can be opened to a recess 1220 (gas dissolver 2).

[0032] The water flow supplied from the water flow source 100 to the dissolving section 500 via the conduit 200 is compressed by the funnel-shaped section 611, increasing the water flow rate. This water flow is further compressed by the column section 1210 of the bubble generation section 1200. After the water flow passes through the slit 1300, a negative pressure region is formed in the downstream orifice 632, generating minute bubbles. This generally results in the formation of fine bubbles in the negative pressure region (cavitation effect). Because a portion of the water flow that passes through the slit 1300 flows along the vertical bottom surface (downstream wall) of the column section 1210, a negative pressure region is also formed in the outer region of the downstream orifice 632 (the region close to the peripheral wall of the cylindrical section) and in the region close to the bottom surface 1211.

[0033] This negative pressure region can suck gas from the gas supply source 10 through the gas supply passage 700 that opens into this region. The gas sucked into the negative pressure region is taken into the water in the negative pressure region. Since the water flows along bottom surface 1211, it also flows into recesses 1220, where the negative pressure is further increased. Therefore, it is preferable that gas supply path 700 opens facing at least one of these recesses 1220. This is to efficiently supply gas to recesses 1220 where the negative pressure is large.

[0034] Fig. 4 shows another embodiment of a gas dissolving device 3. The same elements as those in Fig. 1 are given the same reference numerals and their explanation will be omitted. The dissolving section 2100 of this gas dissolving device 2 has a cylindrical main body 2200, on which an introduction section 2210, an orifice 2220, and an expanded diameter section 2230 are formed in this order from the upstream side. The dissolving section 2100 is described in Japanese Patent No. 6978793 (Patent Document 4), and the description thereof is quoted here.

[0035] The outlet of the orifice 2220 opens, and the downstream wall 2240 that defines the expanded diameter portion 2230 rises perpendicular to the water flow. Four recesses 2250 are formed in the downstream wall 2240 at 90-degree intervals. The expanded diameter portion 2230 is formed with recesses 2231 in the circumferential direction. Here, the orifice 2220 refers to a portion of the cylindrical main body that has a reduced diameter and is of the same diameter. The diameter can be changed or a groove can be formed in the peripheral wall as long as it does not cause turbulence in the water flow.

[0036] The configuration of the dissolving section 2100 generates fine bubbles as disclosed by the present applicant in JP 2021-20153 A. That is, a negative pressure region is formed in the expanded diameter section 2230 and the recessed section 2250. As disclosed in JP 2021-20153 A, fine bubbles are generated even without the recess 2250 in the downstream wall 2240 or the recess 2231 in the expanded diameter portion 2230. Therefore, if the downstream wall of the cylindrical main body portion equipped with the orifice 2220 stands up vertically, a sufficient negative pressure region is formed, and this negative pressure allows gas to be taken in from the gas supply source 10 via the gas supply path 700. In the example of FIG. 4, the other end of the gas supply path 700 opens into the expanded diameter portion 2230 . As shown in FIG. 5, the gas supply channel 700 may be opened into the recess 2250 (gas dissolver 4). [Example]

[0037] An oxygen gas dissolution test was carried out using the gas dissolution device 1 shown in FIG. Tap water (water temperature 20.0°C) from an open tank was introduced into the gas dissolution device 1 at a rate of 8 L / min and a water pressure of 0.3 MPa. An adsorption separation type oxygen generator (Kinki Oxygen Co., Ltd., Orgenator 601) was used as the oxygen gas supply source 10, and oxygen gas could be supplied to the gas supply line 700 at atmospheric pressure without any pressurization. FIG. 6 shows the relationship between the oxygen gas supply flow rate and the dissolved oxygen concentration when the oxygen gas supply flow rate is changed under the above conditions. From FIG. 6, it can be seen that under the above conditions, the supply flow rate of oxygen gas is preferably set to 1 L / min to 2 L / min. In other words, it is preferable to adjust the oxygen gas supply capacity of the oxygen gas supply source so as to correspond to the inflection point of the oxygen gas supply flow rate-oxygen concentration curve shown in FIG.

[0038] FIG. 7 shows the change over time in the dissolved oxygen concentration in the water thus obtained with dissolved oxygen. The results in Figure 7 show that the oxygen concentration decay behavior is equivalent to that of oxygen-dissolved water produced by a conventional gas dissolution device that involves pressurization. This shows that the oxygen dissolution device of the present invention is suitable for energy conservation because it does not require external energy for pressurization, stirring, etc. when dissolving oxygen (excluding the energy required to pump water).

[0039] Using a 500 L tank of tap water, a circulation device equipped with a pump, piping, and valves was used to circulate the tap water from the tank at a water volume (8 L / min) and a water pressure of 0.3 MPa, and the circulating water flow was passed through the gas dissolution device 1.

[0040] The results are shown in Table 1. [Table 1]

[0041] The dissolved oxygen concentration of the tap water in the tank before circulation was 10.8 mg / L. After 60 minutes of circulation (480 L circulation), the dissolved oxygen concentration of the tap water in the tank was 28.8 mg / L, and after 120 minutes of circulation (960 L circulation), the dissolved oxygen concentration of the tap water in the tank was 37.9 mg / L. This shows that the dissolved oxygen concentration of the tap water before circulation had increased by approximately four times.

[0042] Furthermore, no change in water temperature was observed in the tank before and after 120 minutes of circulation. The tank was left stationary indoors and no temperature control was performed from the outside. In contrast, general-purpose gas dissolving devices dissolve gas under high pressure, which causes the temperature of the water in the tank to rise, so it is common to add ice or other materials to cool it down. The dissolved oxygen concentration was measured using a Hanna model number HI98198.

[0043] 1, the oxygen supply device 10 was removed, the gas supply line 700 was opened to the atmosphere, and the relationship between the water pressure and the dissolved oxygen concentration when the water pressure was changed is shown in Fig. 8. Note that fine bubbles were generated at each water pressure. The amount of air self-supply when the water pressure was changed was as shown in Table 2. [Table 2] The results in FIG. 8 show that the gas dissolving device of the example can increase the oxygen concentration in water by using air.

[0044] The present invention is not limited to the above-described embodiments and examples. The present invention also includes various modifications within the scope of the claims that can be easily conceived by a person skilled in the art. Disclose the following: (1) A method for dissolving a gas in a water stream, comprising: A gas dissolution method in which a portion of the water constituting the water flow is made into a negative pressure region, the gas is sucked in by the negative pressure of the negative pressure region, the gas is entrained in the water flow, and fine bubbles are generated. (2) The method according to (1), wherein the gas is drawn into the negative pressure region at atmospheric pressure. (3) The method according to (1), wherein the water flow flows through a tube having a vertical downstream wall facing the downstream side of the water flow, and the water flow flows around the downstream wall to form the negative pressure region. (4) The method according to (3), wherein a recess is formed in the downstream wall, and a portion of the water flow that has flowed around the recess is vaporized by the negative pressure of the recess. (5) The recess extends to the peripheral wall of the cylinder, The gas is supplied through a gas supply path that penetrates from the peripheral wall of the cylinder to the recess. (4) The method described in (4). (6) The method according to (1), wherein the gas is one or more selected from inorganic gases such as air, oxygen, ozone, ammonia, nitrogen, hydrogen, and argon, and organic gases such as carbon dioxide and ethane. [Explanation of symbols]

[0045] 1, 2, 3, 4 Gas dissolving device 10 Gas supply source 100 Water source 500, 2100 Melting part Gas supply line 700 1211, 2240 Downstream wall 1220, 2250 recess

Claims

1. 1. An apparatus for dissolving a gas into a water flow from a water flow source, comprising: a gas supply source and a dissolving unit, The dissolving part is a tube through which the water flow from the water flow source passes; a vertical downstream wall facing the downstream side of the water flow in the tube, the water flow wrapping around the downstream wall to form a negative pressure region; and a gas supply passage extending from the peripheral wall of the cylinder to the negative pressure region, the gas supply passage being connected to a gas supply source; Here, the gas from the gas supply source is supplied to the negative pressure region through the gas supply path by the negative pressure of the negative pressure region.

2. 2. The device according to claim 1, wherein a recess is formed in the downstream wall, and a portion of the water flow that has flowed around the recess is vaporized by the negative pressure of the recess.

3. The apparatus according to claim 2 , wherein the gas supply passage opens into the recess.

4. The device of claim 3 , wherein the recess extends to the peripheral wall of the barrel.

5. The apparatus according to claim 1 , wherein the gas supply passage opens facing the recess.

6. 2. The gas dissolving device according to claim 1, wherein the gas supply source is an adsorbent-type oxygen gas generator, and the oxygen gas supplied from the gas generator is supplied to the gas supply path without being pressurized.

7. An apparatus for dissolving atmospheric gases into a water flow from a water flow source, comprising: a dissolving unit for the atmospheric gas, The dissolving part is a tube through which the water flow from the water flow source passes; a vertical downstream wall facing the downstream side of the water flow in the tube, the water flow wrapping around the downstream wall to form a negative pressure region; and a gas supply passage extending from the peripheral wall of the cylinder to the negative pressure region, the gas supply passage being connected to atmospheric gas; Here, the atmospheric gas is supplied to the negative pressure region through the gas supply path by the negative pressure of the negative pressure region.

8. The gas dissolving device according to claim 1 , wherein the dissolving section generates fine bubbles in the water flow.

9. A device for dissolving gas into water in a tank, comprising: a gas supply source, the tank, a dissolving unit, and a water circulation device for circulating water in the tank; The dissolving part is a tube through which the water flow from the tank by the circulation device passes; a vertical downstream wall facing the downstream side of the water flow in the tube, the water flow wrapping around the downstream wall to form a negative pressure region; and a gas supply passage extending from the peripheral wall of the cylinder to the negative pressure region, the gas supply passage being connected to a gas supply source; Here, the gas from the gas supply source is supplied to the negative pressure region through the gas supply path by the negative pressure of the negative pressure region, and fine bubbles are generated in the gas dissolving device.

10. 10. A gas dissolving method using a gas dissolving apparatus according to claim 9, wherein the water in the tank is not cooled.

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