Highly efficient airlift pump

Abstract

This document describes a gas inlet device used between an injection port and a mixing chamber in an airlift pump, and an airlift pump having the gas inlet device. The gas inlet device includes a flat plate with a plurality of holes extending therethrough. The holes are sized to separate the gas into multiple fine streams for air to flow from the injection port into the mixing chamber. An airlift pump combined with such a gas inlet device is useful for removing abnormally high concentrations of dissolved gas in a liquid. The improved efficiency of the present invention may make this type of pump economical in other applications where the elevation or induction of a flow of a liquid is desired. [Selection diagram] 1

Description

[Technical field]

[0001] The present invention relates generally to air lift pumps, and more specifically to vertically oriented lift pumps for recirculating fluids in aquaculture systems. [Background technology]

[0002] An air lift pump is a self-contained liquid transport device capable of moving large volumes of water. An air lift pump is a mechanical device, usually in the form of a vertically oriented cylinder or tube, the lower portion of which is submerged in the liquid medium. The submerged tube is fitted with an air injection source near the submerged lower end.

[0003] As water enters the tube from the bottom, it simultaneously forces gas into the liquid. The gas may be injected through a commercial product known as an air stone. This gas injection decreases the density of the water, causing it to rise in the tube. This allows water to enter the tube from the bottom, or draws water into the tube from the bottom. In other words, the specific gravity of the gas / water mixture decreases, causing it to rise in the tube. Before gas is also injected into the tube, the "heavier" water is at the bottom of the tube. As the less dense water rises in the tube, above the water line level of the tank on the outside of the vertically oriented tube, it reaches one or more ports where the liquid and gas are released.

[0004] There are many parameters that affect the performance of such airlifts, and even small variations can significantly change efficiency.

[0005] One use of lift pumps is in fish farming. When fish are housed in tanks, the concentration of dissolved CO2 in the water tends to become excessive compared to the normal concentration of CO2 in the air. In this situation, when air is pumped into the water by an air lift pump, the water rises through the pump toward a discharge port that opens above the water line. As the water is discharged, it tends to release its excess CO2 and reach equilibrium with the surrounding air. At equilibrium, the surrounding air and the total dissolved gases in the water have approximately the same percentage of CO2.

[0006] Known air lift pumps are notoriously inefficient. It is not uncommon for an air lift pump to require three or more volumes of gas to move one volume of water. Due to their inefficiency, known air lift pumps are (relatively) rarely used in applications where there is a need to lift or otherwise facilitate the flow of liquid. As a result, their most common use is as a means to adjust the relative concentration of dissolved gas in a liquid. Summary of the Invention [Means for solving the problem]

[0007] The present disclosure describes a device for use between an injection port and a mixing chamber in an airlift pump, the device comprising a flat plate having a plurality of holes extending therethrough, the holes being sized to separate the gas into a plurality of fine streams for allowing air from the injection port to enter the mixing chamber.

[0008] The present disclosure also describes an air lift pump. an injection port for injecting compressed air into the airlift pump; a mixing chamber having a plurality of perforations, the mixing chamber coupled to the inlet port for receiving air from the inlet port and receiving water through the plurality of perforations; a lift tube fluidly connected to and extending from the mixing chamber; a discharge port fluidly connected to and extending from the lift barrel, the discharge port having an exhaust port and a drain port; a gas inflow device positioned between the injection port and the mixing chamber, the gas inflow device having a flat body with a plurality of holes extending therethrough, the holes being sized to separate the gas into a plurality of fine streams for allowing air from the injection port to flow into the mixing chamber; Equipped with. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] US Patent Application Publication No. 62 / 610,675 [Patent Document 2] U.S. Patent No. 7,537,200

[0010] Advantages and features of the present invention will become apparent upon consideration of the following detailed description and the accompanying drawings, which are briefly described below.

[0011] Reference will now be made, by way of example, to the accompanying drawings which illustrate an example of the present application. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a side cross-sectional view of an air lift pump according to an example of the present invention. [Diagram 2] FIG. 2 is an isolated plan view of a gas inlet device used in the lift pump of FIG. 1. [Diagram 3] FIG. 3 is an enlarged view of a portion A of the disk in FIG. 2. [Figure 4] FIG. 1 is a sample table explaining the terms and units in the following figures. [Diagram 5] 1 shows test data when the air lift pump of FIG. 1 was used according to Test Method 1. [Figure 6] 1 shows test data when the air lift pump of FIG. 1 was used according to Test Method 1. [Figure 7] 1 shows test data when the air lift pump of FIG. 1 was used according to Test Method 1. [Figure 8] 1 shows test data when the air lift pump of FIG. 1 was used according to Test Method 1. [Figure 9] 1 shows test data when the air lift pump of FIG. 1 was used according to Test Method 1. [Figure 10] 1 shows test data when the air lift pump of FIG. 1 was used according to Test Method 1. [Figure 11] 1 shows test data when the air lift pump of FIG. 1 was used according to Test Method 1. [Figure 12] 1 shows test data when the air lift pump of FIG. 1 was used according to Test Method 1. [Figure 13] 1 shows test data when the air lift pump of FIG. 1 was used according to Test Method 1. [Figure 14] 1 shows test data when the air lift pump of FIG. 1 was used according to Test Method 1. [Figure 15] 1 shows test data when the air lift pump of FIG. 1 was used according to Test Method 1. [Figure 16] 1 shows test data when the air lift pump of FIG. 1 was used according to Test Method 1. [Figure 17] 1 shows test data when the air lift pump of FIG. 1 was used according to Test Method 1. [Figure 18] 1 shows test data when the air lift pump of FIG. 1 was used according to Test Method 1. [Figure 19] 1 shows test data when the air lift pump of FIG. 1 was used according to Test Method 1. [Figure 20] 1 shows test data when the air lift pump of FIG. 1 was used according to Test Method 1. [Figure 21] 1 shows test data when the air lift pump of FIG. 1 was used according to Test Method 1. [Figure 22]1 shows test data when the air lift pump of FIG. 1 was used according to Test Method 1. [Diagram 23] 1 shows test data when the air lift pump of FIG. 1 was used according to Test Method 2. [Figure 24] 1 shows test data when the air lift pump of FIG. 1 was used according to Test Method 2. [Diagram 25] 1 shows test data when the air lift pump of FIG. 1 was used according to Test Method 2. [Figure 26] 1 shows test data when the air lift pump of FIG. 1 was used according to Test Method 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] An exemplary embodiment of the air lift pump 10, the gas inlet device 50 for inletting air into the air lift pump 10, and their uses will now be described. First, the air lift pump 10 will be described.

[0014] Air Lift Pump As shown in FIG. 1, the air lift pump 10 generally includes an injection port 12, an injection chamber 14, a mixing chamber 16, a lift barrel 18, a discharge port 20, and a gas inlet device 50 disposed between the injection port 12 and the mixing chamber 16.

[0015] The injection port 12 is located at one end of the air lift pump 10 and is fluidly coupled to the air supply 22 and connected to the injection chamber 14. As will be appreciated by those skilled in the art, the location and size of the injection port 12 may vary. For example, a 6 inch diameter air lift pump may have a 2 inch diameter injection port to allow a sufficient volume of water to enter the air lift pump 10 without a significant pressure drop. In another example, a 1 inch diameter air lift pump may have a 1 / 8 inch diameter injection port. Additionally, the injection port 12 may be located at the bottom of the air lift pump 10 or to one side of one end, as long as the injection port 12 is located near the bottom of the tank to maximize the pumping capacity.

[0016] The injection chamber 14 is fluidly connected to the mixing chamber 16 with a gas inlet device 50 located therebetween. As shown, the gas inlet device 50 is sealed from the surrounding liquid and oriented horizontally or laterally between the injection chamber 14 and the mixing chamber 16. The height of the gas inlet device 50 is as low as the prefabricated parts will allow to avoid large air pockets being placed near the bottom of the tank that could cause the unit to float. The diameter of the injection chamber 14 will approximately correspond to the diameter of its corresponding air lift pump. For example, an air lift pump with a 6 inch diameter will have an injection chamber with a 6 inch diameter. As shown, the mixing chamber 16 is a cylindrical tube with multiple perforations in its wall 17. The height of the mixing chamber 16 can vary but is typically between 8 and 12 inches. The ratio of the mixing chamber height to the air lift pump height will be approximately 6:1. However, in alternative embodiments, this ratio may be different, particularly for shorter or longer lifts. Since the mixing chamber 12 is where the surrounding water / liquid is drawn into the airlift pump 10, the mixing chamber 12 is typically located as close to the bottom of the tank as possible to maximize circulation.

[0017] The exact size and placement of the perforations can vary to keep particulates and microorganisms out of the airlift pump 10. That said, the perforations generally provide at least 60% open space to allow water or liquid to enter the airlift pump 10.

[0018] A lift tube 18 is fluidly connected to and extends from the mixing chamber 16 .

[0019] The discharge port 20 is fluidly connected to and extends from the lift barrel 18. As such, the discharge port 20 is located at the opposite end of the air lift pump 10 from the inlet port 12. The discharge port 20 has an exhaust port 24 oriented parallel to the lift barrel 18 and a drain port 26 oriented approximately perpendicular to the lift barrel 18. The air lift pump 10 further includes a fluid flow sensor 32 integrated into the discharge port 20.

[0020] In the illustrated embodiment, the air lift pump 10 further includes a bacterial culture 28 suspended within the lift barrel 18 or attached to the interior wall of the lift barrel 18 .

[0021] While a particular embodiment of an air lift pump is shown and described herein, numerous variations are possible. In some instances, for example, for gas inflow devices greater than 6 inches in diameter, the inlet chamber 14 may include a diffuser, baffle, or other mechanical means to promote uniform flow through the face of the gas inflow device 50. The placement of one or more inlet ports 12 may be another mechanical means to promote uniform flow through the gas inflow device 50.

[0022] In other examples, instead of a single gas inlet port and injection chamber, the air lift pump 10 includes multiple gas inlet ports adjacent the bottom of the lift pump 10. The gas inlet ports will be connected to one or more injection chambers.

[0023] In another example, the air lift pump 10 would include multiple gas inlet devices, a gas flow control valve, and a subsequent flow sensor. The gas flow control valve and the flow sensor would be configured to regulate the gas flow to the multiple gas inlet devices.

[0024] In another example, a separate fluid flow sensor would be incorporated into the lift barrel 18.

[0025] In another example, a mechanical device such as a pump is integrated into injection port 12 to allow for regulation and control of the gas pressure introduced into injection chamber 14 .

[0026] In another example, the air lift pump 10, instead of having a circular cross-section throughout, will have multiple components having non-circular cross-sections.

[0027] In still other examples, the height and / or radius of the lift tube 18 may be varied to maximize gas removal from the liquid medium. As will be appreciated by those skilled in the art, the height and radius of the lift tube 18 may be altered to accommodate various tank sizes and air sources.

[0028] The air lift pump 10 may further be enclosed and integrated into a portable tank that contains the liquid medium to be purified by the air lift pump 10 .

[0029] Gas Inflow Device We now provide a detailed description of the gas inflow device 50. The gas inflow device 50 is shown alone in Figures 2 and 3.

[0030] The gas inflow device 50 comprises a body having a plurality of 0.35 mm diameter holes or perforations 52. As shown, the body is a circular plate 54 having a first side, an opposing second side, and a perimeter 56.

[0031] Plate 54 is made of a solid, hydrophobic material that can be washed and sterilized. Plate 54 has a thickness of 12.7 mm.

[0032] A plurality of holes 52 extend from the first surface to the second surface and are evenly spaced across the plate 54. In particular, the plurality of holes 52 are spaced from one another in a grid pattern on 0.55 mm centers. The plurality of holes 52 are further located at least 0.5 mm from the outer perimeter 56 of the plate 54.

[0033] Although not shown in these figures, the plurality of holes 52 in plate 54 include a spiral groove pattern, or rifling. In this embodiment, the rifling is oriented at an angle of 30 degrees relative to the longitudinal axis of each hole.

[0034] Although one particular embodiment of the gas inflow device is shown and described herein, numerous variations are possible. The dimensions of the perforations 52 do not generally scale proportionally with the diameter or height of the air lift pump 10. However, in some instances, the size and shape of the perforations 52 may vary. For example, the holes or perforations 52 may have a diameter of between approximately 0.2 mm and 0.4 mm.

[0035] In other examples, the holes 52 are spaced from one another in a grid pattern with centers between 0.5 mm and 0.6 mm, and the thickness of the plate 54 is between 12 mm and 13 mm.

[0036] Alternatively, the holes 52 are non-equally spaced across the plate 102 .

[0037] In other examples, the body is constructed of a fiber packing rather than a solid circular plate. The fibers can be oriented vertically and / or horizontally to allow gas to flow around the fibers. The fibers are hydrophobic and will pack into the interior of the perforated plate.

[0038] 1, the arrows indicate the movement of fluids using the air lift pump 10. The movement of gas is indicated by dashed arrows and the movement of water is indicated by solid arrows. As shown, the air lift pump 10 is placed in water 100 in a tank 102 such that the injection chamber 14 and the mixing chamber 16 are submerged while the discharge port 20 is above the water line.

[0039] Compressed air is injected into the injection chamber 14 at the injection port 12 by the air supply 22. From there, the air is directed into the mixing chamber 16 through a gas inlet device 50. The gas inlet device 50 forces the gas or air into multiple streams as it enters the mixing chamber 16.

[0040] The diameter and spacing of the holes 52 in the plate 54 are set to produce a uniform small gas stream as vertical as possible at the bottom of the pump to provide uniform lift. The spiral groove pattern, or rifling, of the holes 52 also helps to gyroscopically stabilize the gas streams as they leave the plate 54. These features help minimize merging of multiple gas streams and minimize gas leakage through the porous wall 17 of the mixing chamber 16.

[0041] The plate 54 is also oriented horizontally within the air lift pump 10, such that the orientation of the holes 52 is generally parallel to the longitudinal orientation of the air lift pump 10. This is useful to help ensure the narrowest vertical path possible for each gas stream as it leaves the plate 54. The uniformity of these gas streams helps the gas rise more uniformly through the liquid. The vertical flow is also advantageous to help prevent the formation of larger bubbles due to the merging of multiple air streams, which would result in uneven rise.

[0042] As the air streams enter the mixing chamber 16, they mix with the water within the mixing chamber 16. This mixing creates a water / air mixture. The density of this mixture is lower than the density of the water surrounding the mixing chamber 16. Because of its lower density, the water / air mixture rises within the lift tube 18 toward the discharge port 20.

[0043] As the water / air mixture rises within the lift canister 18, it creates a vacuum or suction force within the mixing chamber 16. This suction force simultaneously draws water from the tank 102 into the mixing chamber 16 through the porous wall 17. This new water mixes with the incoming airflow from the gas inlet device 50 and is forced up within the lift canister 17.

[0044] As the water / air mixture travels upward within the lift tube 18, it will also pass through the bacterial culture 28. The bacterial culture 28 may react with other particles within the water / air mixture. The bacterial culture 28 allows for the use of bacteria for purification of targeted impurities, such as ammonia, in the liquid.

[0045] When the water / air mixture reaches the discharge port 20 above the water line, if the water / air mixture has a high concentration of gas, such as CO2, it will tend to release its excess CO2 or other gas through the exhaust port 24 (and possibly through the drain 26) in an attempt to reach equilibrium with the surrounding air by osmosis. The water component will then be discharged through the drain 26 back to the tank 102 or directed elsewhere.

[0046] As discussed above, the height and / or radius of the lift tube 18 is adjusted to accommodate the depth of the surrounding liquid media and the desired lift of the liquid media above the water line by the pump.

[0047] Use in combination The airlift pump 10 may be used in water simultaneously with one or more saturator systems configured to provide gas exchange with the aqueous phase liquid in-line with the same water.

[0048] In particular, the saturator systems are adapted to dissolve oxygen in water and remove carbon dioxide such that the total gas pressure within the fluid remains relatively constant. An example of such a saturator system is disclosed in US Pat. No. 5,399,633. Each saturator system uses one or more gas injection devices to dissolve oxygen in the water.

[0049] Each gas injection device has a fiber module array disposed between its ends, the fiber module array being constructed from a microporous fibrous material coated with a polymer. An example of such a gas injection device is found in U.S. Pat. No. 5,393,323 to Glassford, dated Oct. 31, 2003.

[0050] When used in this combination, the saturator system pumps oxygen into the water and removes carbon dioxide, while the one or more air lift pumps 10 also remove dissolved CO2 and purify ammonia to form nitrates.

[0051] Such a combined system may further include one or more oxygen tanks connected to the saturator system to supply oxygen to the saturator system, and a compressor connected to the airlift pump 10 to supply ambient air to cause the lift.

[0052] Such a system may further include a gas regulator operatively coupled between the oxygen tank and the saturator system for regulating a gas flow rate into the saturator system, a dissolved oxygen sensor disposed in the water, a saturator feed pump in fluid communication with the water adapted to draw and direct water from the tank into the saturator system, and an ammonia sensor disposed in the water.

[0053] A control and monitoring system may be provided in communication with, and to control and coordinate each of the above components. For example, when an ammonia concentration is detected rising above a maximum level, the compressor may be activated to operate the air lift pump 10. Thereafter, when an ammonia concentration is detected falling below a minimum level, the compressor may be deactivated to shut down the air lift pump 10. Similarly, when an oxygen concentration is detected falling below a minimum level, the gas regulator and saturator feed pump may be activated and controlled. The gas regulator and saturator feed pump may be shut down as appropriate.

[0054] One advantage of using the present gas inlet device 50 in an air lift pump 10 is that it allows three or more units of liquid to be lifted the same distance as a conventional lift pump using only one unit of gas. This increased efficiency may also make the air lift pump 10 economical in other applications where lifting or directing the flow of liquid is desirable.

[0055] To demonstrate this advantage, the following test was performed.

[0056] Test method 1 The following were used in conducting these studies: Water tank Air source (pressure dependent) ·CO2 source ·CO2 dissolution method Air lift pump 10 -Measuring equipment (CO2, temperature, salinity, pressure, air flow, water flow)

[0057] First, CO2 was dissolved in the water in the tank to the desired level using any method known in the art. The air lift pump 10 was attached to a measurable air source and then inserted into the water in the tank, making sure that the discharge port 20 was above the water line. It was noted that the exact location was dependent on the air lift pump unit.

[0058] Air was then supplied to the air lift pump 10 and the air pressure in the injection chamber 14 below the gas inflow device 10 was measured to determine the actual air flow rate.

[0059] The CO2 level in the tank was recorded throughout the experiment. Since the CO2 level in the tank would obviously not be uniform, it was assumed that the highest CO2 level in the tank was at the vacuum or suction area in the mixing chamber 16 and the lowest CO2 level was at the drain 26. The average of these two values ​​was used as a representative value for the entire tank.

[0060] The temperature and salinity of the water in the tank were measured, along with the flow rate of the water from the drain 26. These measurements were used to generate a profile over time of the CO2 concentration in the tank as well as the efficiency of the airlift pump 10 (using the known volume of water leaving the drain 26 and the concentration in the tank). The instantaneous rate of change of CO2 (the amount removed at any given concentration) was determined by taking the derivative of the concentration over time.

[0061] Test method 2 The second test method (Test Method 2) was similar to Test Method 1, but was used in situations where it was not possible to measure the water flow rate out of the air lift pump 10. This method required adding a known amount of CO2 to the tank while the air lift pump 10 was running until an equilibrium condition was reached (i.e., the point where the CO2 added equals the CO2 removed). The water flow rate was calculated by determining the concentrations at the top and bottom of the air lift pump 10.

[0062] The overall results are shown in Figures 4-26.

[0063] FIG. 4 is a sample table explaining the terms and units of measurement in the tables of FIGS.

[0064] In Figures 5-14, the first graph in each figure shows the drop in CO2 levels throughout the trial (using Test Method 1). The second graph in each figure shows the calculated CO2 rate of change versus concentration when using an air lift pump with the parameters specified in the corresponding table. Each corresponding table shows all the set points specified for the particular trial, as well as the calculated liquid to gas ratio and calculated percent removal.

[0065] In Figures 15-17, the first graph in each figure shows the drop in CO2 levels over the trial measurements. Measurements were taken at both the top and bottom of the lift (using Test Method 1). The second graph in each figure shows the calculated CO2 rate of change versus concentration when using the lift with the parameters specified in the corresponding table. Each table shows all the set points determined for each trial, as well as the calculated liquid to gas ratio and calculated percent removal.

[0066] In Figure 18, the first graph shows the drop in CO2 levels over the course of the trial (using Test Method 1). The second graph shows the calculated CO2 percentage change versus concentration when using the lift with the parameters specified in the table. The table shows all the settings specified for the trial, as well as the calculated liquid to gas ratio and the calculated percent removal.

[0067] In Figure 19, the first graph shows the drop in CO2 levels over the course of the trial (using Test Method 1). This is a comparison of the old and new disc (or gas inflow device) styles, showing little difference in performance at the given levels.

[0068] The old disc style was a "disc" made up of many hydrophobic hollow fibers held in place by epoxy resin to produce a similar effect as gas inflow device 50. However, the holes in the old discs were not always uniform or narrow and were not always open, which of course reduced the efficiency and quality of gas diffusion.

[0069] The second graph shows the calculated CO2 rate of change versus concentration when using an airlift pump with the parameters specified in the table. The table shows all the settings specified for the trial, as well as the calculated liquid to gas ratio and calculated percent removal.

[0070] In Figures 20-22, the first graph in each figure shows the drop in CO2 levels throughout the trial (using Test Method 1). The second graph in each figure shows the calculated CO2 percentage change versus concentration when using the lift with the parameters specified in the table. The table shows all the set points specified for the trial, as well as the calculated liquid to gas ratios and calculated percent removal.

[0071] In Figures 23-26, each table represents a representative trial (using Test Method 2) and shows all set points specified, as well as the calculated water flow rate, calculated liquid to gas ratio, and calculated percent removal.

[0072] The data generally demonstrates that the airlift pump 10 operates in a variety of conditions and setups, as shown in Figures 5-14 and 18 using disc type 1. Disc type 1 is a gas inlet device 50 comprised of a fiber packing. The fibers can be oriented vertically and / or horizontally to force gas to flow around the fibers.

[0073] As shown in Figures 15-17 and 19-22 using Disc Type 2, the data is similar to the results for Disc Type 1, but with slightly improved efficiency at low pressures. Disc Type 2 is the first printing disc with the same nominal dimensions and spacing as the Disc Type 1 fiber discs.

[0074] Figures 23-26 show data generated when using disc types 3, 4, and 5. The hole and spacing sizes for disc types 3-5 are smaller than those for disc type 2. Specifically, for disc type 3, the holes were between 0.3 and 0.4 mm and the pinches were between 0.45 and 0.55 mm. For disc type 4, the holes were between 0.15 and 0.25 mm and the pinches were between 0.35 and 0.45 mm. For disc type 5, the holes were between 0.175 and 0.225 mm and the pinches were between 0.25 and 0.35 mm.

[0075] The data shows that smaller holes and spacing perform better at lower pressures because smaller bubbles are produced and the total area of ​​open space increases.

[0076] Thus, the present invention has been demonstrated to be able to lift over three unit volumes of liquid the same distance as a conventional lift pump with only one unit volume of gas.

[0077] While one particular embodiment of the method has been illustrated and described herein, numerous variations are possible.

[0078] Therefore, it is intended that the invention be limited only by the scope of the appended claims as interpreted pursuant to the present invention.

Claims

1. An air lift pump, an injection port for injecting compressed gas into said airlift pump; a mixing chamber having a plurality of perforations, the mixing chamber coupled to the inlet port for receiving the gas from the inlet port and for receiving water through the perforations; a lift tube fluidly connected to and extending from the mixing chamber and configured to move liquid in a lift direction; an outlet port fluidly connected to and extending from the lift barrel, the outlet port having an exhaust port and a drain port; a gas inlet device disposed between the injection port and the mixing chamber, the gas inlet device having a flat body with a plurality of holes extending therethrough between the injection port and the mixing chamber in the lift direction, the holes formed in the flat body having a spiral groove pattern to gyroscopically stabilize the gas flow as it leaves the flat body, and the holes having a diameter of 0.15 mm to 0.4 mm and sized to break the gas into a plurality of fine streams for flowing from the injection port into the mixing chamber.

2. An air lift pump as described in claim 1, wherein the multiple holes of the gas inflow device are evenly spaced throughout.

3. An air lift pump as described in claim 2, wherein the gas inflow device is a plate having a first surface and a second surface, and the hole extends from the first surface to the second surface.

4. An air lift pump as described in claim 3, wherein the plurality of holes have a diameter of approximately between 0.3 mm and 0.4 mm.

5. An air lift pump as described in claim 3, wherein the plurality of holes have a diameter of approximately between 0.15 mm and 0.25 mm.

6. An air lift pump as described in claim 4, wherein the holes in the gas inflow device are spaced from each other in a grid pattern with a center-to-center distance of 0.5 mm to 0.6 mm.

7. The method of claim 6, wherein the holes are located at least 0.5 mm from the outer periphery of the body. Air lift pump.

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