Gas dissolving 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

Gas dissolution method

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

[0002] It has been attempted to dissolve useful gases such as carbon dioxide into a water flow to increase its concentration. For example, Patent Document 1 discloses a gas dissolution device in which carbon dioxide gas stored in a gas cylinder is supplied to a collision part that generates fine bubbles. Patent Document 2 discloses a method of pressurizing and dissolving gas in water. In all of the gas dissolution methods described in these prior 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, paragraphs 2 and 3).

[0004] Patent No. 6182715 Patent No. 5762210 Patent No. 6279179, paragraphs 0040 and 0041 Patent No. 6978793

[0005] There is a growing demand for forcibly dissolving useful gases into water to enhance its functionality. For example, it is known that increasing the amount of oxygen dissolved in the water in the fish tanks of trucks transporting live fish can help keep the fish alive for a longer period of time. Meanwhile, in the past, forcibly dissolving gases such as oxygen into water required pressurization of the gas, which required the preparation of, for example, oxygen tanks. This resulted in complex equipment, high costs, and laborious maintenance.

[0006] The present invention has been made to solve the above-mentioned problems, and its first aspect is defined as follows: A method for dissolving gas in a water flow, which comprises creating a negative pressure region in a part of the water constituting the water flow, sucking the gas by the negative pressure in the negative pressure region, entraining the gas in the water flow, and generating fine bubbles.

[0007] According to the gas dissolution method of the first aspect defined above, the negative pressure in the negative pressure region draws in gas from the gas supply source, entraining it in the water flow. In other words, a sufficient amount of gas is drawn into the negative pressure region without pressurizing the introduced gas. Pressurizing the introduced gas improves the gas suction efficiency. A portion of the water in the negative pressure region of the water flow 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 escaping the negative pressure region increases, the water vapor condenses and returns to water. At this time, the gas is absorbed into the water and dissolved therein. Even if the water in the negative pressure region is not gasified, its vapor pressure decreases, weakening the bonds between water molecules, making it easier for the introduced gas to penetrate between the water molecules. Furthermore, because 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 sucked into the negative pressure region at atmospheric pressure. To produce oxygen industrially and inexpensively, an adsorption separation method is generally employed, and the oxygen produced by such a method is not pressurized. In other words, even unpressurized oxygen extracted from an adsorption separation device serving as an oxygen source can be dissolved directly in water, i.e., at atmospheric pressure, according to the second aspect.

[0010] A third aspect of the present invention is defined as follows. That is, in the gas dissolution method of the first aspect, the water flow flows through a tube, which is provided with a vertical downstream wall facing downstream of the water flow, and the water flow wraps around the downstream wall to form the negative pressure region. According to the gas dissolution method of the third aspect defined in this way, the water flow that wraps around the downstream wall moves away from the center of the tube, forming a negative pressure region on the outer periphery of the tube. It becomes easier to supply gas to this negative pressure region from outside the tube. Patent Document 4 explains that passing water through a tube with a vertical downstream wall generates fine bubbles containing nano-sized microbubbles in the water (see Figures 4 and 5). It is preferable that a small diameter portion (orifice) is provided inside the tube, 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 portion of the water flow that has detoured into 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' investigations, the pressure in the recess changes (oscillates), and at the maximum negative pressure, the water is almost vaporized.

[0012] When the gas supplied to the negative pressure area 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 inside the recess. When the negative pressure inside the vibrating recess decreases (when it returns to water), the gas is drawn into the water along with the water vapor. The gas can be supplied directly to the recess. The pressure oscillation in the recess also has the stirring effect of the water flow, which also improves the gas dissolution effect.

[0013] A fifth aspect of the present invention is defined as follows. That is, in the gas dissolving device defined in the fourth aspect, the recess extends to the peripheral wall of the cylinder, and the gas is supplied through a gas supply path that penetrates from the peripheral wall of the cylinder to the recess. In the gas dissolving device of the fourth aspect defined in this manner, the recess extends to the peripheral wall of the cylinder, resulting in a state in which a lid is placed over a portion of the recess. According to studies by the present inventors, evaporation of water is promoted in the recess in the portion that is covered with the lid.

[0014] A seventh aspect of the present invention is defined as follows: An apparatus for dissolving gas into a water flow from a water flow source, comprising: a gas supply source; and a dissolving unit, the dissolving unit comprising: 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 within the tube, the water flow wrapping around the downstream wall to form a negative pressure region; and a gas supply path extending from the peripheral wall of the tube to the negative pressure region, the gas supply path being connected to the gas supply source; wherein gas from the gas supply source is supplied to the negative pressure region via the gas supply path by the negative pressure of the negative pressure region.

[0015] According to the seventh aspect of the gas dissolving device defined in this manner, gas from the gas supply source is supplied to the negative pressure region through the gas supply path due to the negative pressure of the negative pressure region, eliminating the need for any gas pressurization device (including a pump). This reduces the number of parts required for the entire device, resulting in an inexpensive device. Furthermore, a gas dissolving device equipped with the dissolving unit also generates fine bubbles in the dissolving unit. When the target gas is atmospheric air, a tank or other gas supply source is not required, and the atmosphere itself serves as the gas supply source. Therefore, the end of the gas supply path facing the gas supply source is open to the atmosphere. The water flow passing through the gas dissolving device can be fed back to the water flow source. That is, water in the tank is circulated, and the circulating water flow passes through the dissolving unit. 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. This is thought to be due to the fact that no pressurization of the gas is required when dissolving the gas, and no mechanical external force, such as stirring, is applied to the water flow.

[0016] A recess can be formed in the downstream wall to generate a high negative pressure in the negative pressure region. A portion of the water flow that has circumvented 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. Since a high negative pressure is generated in the recess, gas can be efficiently sucked in from the outside. In addition, the high negative pressure promotes the conversion of water into steam, and when this steam returns to water, it entrains gas into the water, resulting in a high concentration of dissolved gas. It is preferable that the gas supply channel opens at a position opposite the recess (ninth aspect).

[0017] The recess can be extended to the peripheral wall of the tube (aspect 10). By extending the recess 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 in the portion covered with the lid.

[0018] Incidentally, the provision of such recesses allows for efficient generation of fine bubbles in the water flow, as described in Patent Document 4. In this specification, fine bubbles include nano-sized microbubbles. The gas can 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.

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

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

[0022] The dissolving section 500 comprises a tubular 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 tubular section 600 is divided in the axial direction (water flow direction). Its upstream section 610 is connected to the water flow source 100 via a conduit 200. The water flow inlet comprises a funnel-shaped section 611 whose diameter decreases in the water flow direction, and an inlet orifice 612. An outlet orifice 632 is formed in the downstream section 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 line A-A in Fig. 2. The bubble generator 1000 comprises a main body portion 1100 and a bubble generator portion 1200.

[0024] The main body 1100 is formed in a cylindrical shape. A portion of the outer periphery 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 center of the radiation coincides with the central axis of the main body 1100. The center of the radiation does not have to coincide with the central axis of the main body 1100. The slits 1300 are formed on one imaginary cross section in the main body 1100. In other words, in each column 1210, the portion that bulges most from the inner peripheral surface of the main body 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 column 1210. It is preferable that this bottom surface 1211 is formed perpendicular or at an acute angle to the water flow direction at the most bulging portion. This is because a large change in flow velocity can be caused, generating negative pressure there.

[0027] Recesses 1220 are formed in bottom surface 1211. The water flow that has flowed over slit 1300 toward the bottom surface is further sucked into recesses 1220, promoting the generation of negative pressure on bottom surface 1211. To generate negative pressure evenly, recesses 1220 are preferably arranged radially and evenly from the center of slit 1300, i.e., the central axis of main body 1100.

[0028] This recess 1220 extends to the main body 1100. The portion of the recess 1220 present in the main body 1100 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 the same width, but the width can be varied. The width variation here refers to making the widths of the slits different from each other, and to varying the width of a single slit.

[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] In this example, the pillar portion 1210 has a cone shape with a 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: that is, 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 the 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 formed of a pipe, one end of which is connected to the gas supply source 10 and the other end of which opens to the orifice 632. The other end of the gas supply path 700 can be opened facing the recess 1220. This allows 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 also be opened to the recess 1220 (gas dissolving device 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. This water flow is further compressed by the column section 1210 of the bubble generation section 1200. After this 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 in gas from the gas supply source 10 through the gas supply channel 700 that opens into this region. The gas sucked into the negative pressure region is taken up into the water in the negative pressure region. As the water flows along the bottom surface 1211, it also flows into the recesses 1220, further strengthening the negative pressure there. Therefore, it is preferable that the gas supply channel 700 opens opposite at least one of the recesses 1220. This is to efficiently supply gas to the recesses 1220 where the negative pressure is large.

[0034] Figure 4 shows another embodiment of a gas dissolver 3. The same elements as those in Figure 1 are designated by the same reference numerals, and their description will be omitted. The dissolver 2100 of this gas dissolver 2 comprises a cylindrical main body 2200, an introduction section 2210, an orifice 2220, and an expanded diameter section 2230, which are formed in this order from the upstream side. The dissolver 2100 is described in Japanese Patent No. 6978793 (Patent Document 4), and that description is hereby incorporated by reference.

[0035] The outlet of the orifice 2220 opens, and the downstream wall 2240 defining 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 has a circumferential recess 2231. 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 grooves can be formed in the peripheral wall within a range that 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 Japanese Patent Application Laid-Open No. 2021-20153. That is, a negative pressure region is formed in the expanded diameter section 2230 and the recessed section 2250. As disclosed in Japanese Patent Application Laid-Open No. 2021-20153, fine bubbles are generated even without the recessed section 2250 in the downstream wall 2240 or the recessed section 2231 in the expanded diameter section 2230. Therefore, if the downstream wall of a cylindrical main body provided with an orifice 2220 is vertically raised, 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 section 2230. As shown in FIG. 5, the gas supply path 700 may open into the recessed section 2250 (gas dissolving device 4).

[0037] An oxygen gas dissolution test was conducted using the gas dissolution device 1 shown in Figure 1. Tap water (water temperature 20.0°C) from an open tank was introduced into the gas dissolution device 1 at a water rate (8 L / min) and a water pressure of 0.3 MPa. An adsorption / separation oxygen generator (Kinki Oxygen Co., Ltd., Orgenator 601) was used as the oxygen gas supply source 10, and oxygen gas was supplied to the gas supply line 700 at atmospheric pressure without any pressurization. Figure 6 shows the relationship between the oxygen gas supply flow rate and the dissolved oxygen concentration when the oxygen gas supply flow rate was changed under the above conditions. Figure 6 indicates that, under the above conditions, the oxygen gas supply flow rate 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 vs. dissolved oxygen concentration curve shown in Figure 6.

[0038] The change in dissolved oxygen concentration over time in the oxygen-dissolved water obtained in this manner is shown in Figure 7. 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 requires pressurization. This shows that the oxygen dissolution device of the present invention is suitable for energy conservation because it does not require external energy such as pressurization or stirring when dissolving oxygen (excluding the energy required to pump water).

[0039] Using a 500 L tank of tap water as the target, 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.

[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 increased by about four times.

[0042] No change in water temperature was observed in the tank before and after 120 minutes of circulation. The tank was left stationary indoors, with no external temperature control. In contrast, general-purpose gas dissolution devices dissolve gas under high pressure, which causes the water temperature in the tank to rise. Therefore, it is common to add ice or other materials to cool the water. Dissolved oxygen concentration was measured using a Hanna model HI98198.

[0043] In the apparatus shown in Figure 1, the oxygen supply device 10 was removed, the gas supply line 700 was opened to the atmosphere, and the relationship between water pressure and dissolved oxygen concentration was shown in Figure 8. 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. From the results in FIG. 8, it can be seen 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, and various modifications within the scope of the claims and within the scope that can be easily conceived by a person skilled in the art are also included in the present invention.

[0045] 1, 2, 3, 4 Gas dissolving device 10 Gas supply source 100 Water flow source 500, 2100 Dissolving section Gas supply path 700 1211, 2240 Downstream wall 1220, 2250 Recess

Claims

1. A method for dissolving a gas into a water flow, comprising the steps of: making a portion of the water constituting the water flow a negative pressure region; sucking in the gas by the negative pressure of the negative pressure region; entraining the gas in the water flow; and generating fine bubbles.

2. The method of claim 1, wherein said gas is drawn into said negative pressure region at atmospheric pressure.

3. The method of claim 1, wherein the water flow flows through a tube having a vertical downstream wall facing downstream of the water flow, and the water flow wraps around the downstream wall to form the negative pressure region.

4. The method according to claim 3, wherein a recess is formed in the downstream wall, and a portion of the water flow that has turned around into the recess is vaporized by the negative pressure of the recess.

5. The method according to claim 4, wherein the recess extends to a peripheral wall of the cylinder, and the gas is supplied through a gas supply path that penetrates from the peripheral wall of the cylinder to the recess.

6. The method according to claim 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.

7. A gas dissolving device for dissolving gas into a water flow from a water flow source, comprising: a gas supply source; and a dissolving section, the dissolving section comprising: 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 within the tube, the water flow wrapping around the downstream wall to form a negative pressure region; and a gas supply path extending from the peripheral wall of the tube to the negative pressure region, the gas supply path being connected to the gas supply source, wherein gas from the gas supply source is supplied to the negative pressure region via the gas supply path by the negative pressure of the negative pressure region.

8. The device according to claim 7, 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.

9. The apparatus according to claim 8, wherein the gas supply passage opens into the recess.

10. The device according to claim 9, wherein said recess extends to the peripheral wall of said barrel.

11. The apparatus according to claim 7, wherein the gas supply passage opens opposite the recess.

12. A gas dissolving device as described in claim 7, 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 in any way.

13. A gas dissolving apparatus according to claim 7, wherein said gas supply source is the atmosphere, and said gas supply path is open to said atmosphere.

14. The gas dissolving device according to claim 7, wherein the dissolving section generates fine bubbles in the water flow.

15. A gas dissolving device for dissolving gas into water in a tank, comprising: a gas supply source, the tank, a dissolving section, and a device for circulating water in the tank, the dissolving section comprising: a tube through which the water flow from the tank by the circulation device passes; a vertical downstream wall inside the tube facing downstream of the water flow, the water flow flows around the downstream wall to form a negative pressure region; and a gas supply path extending from the peripheral wall of the tube to the negative pressure region, the gas supply path being connected to the gas supply source, wherein gas from the gas supply source is supplied to the negative pressure region via the gas supply path by the negative pressure of the negative pressure region, and fine bubbles are generated.

16. A method for dissolving gas using the gas dissolving apparatus according to claim 15, wherein the water in the tank is not cooled.

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