BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to the dissolution of gases in liquids and more specifically to a device for introducing large numbers of microbubbles of the gas into the liquid to greatly increase the gas/liquid contact, facilitating rapid dissolution.

2. Description of the Prior Art.

The ability to rapidly and efficiently dissolve gases and liquids is required in several different fields in several different applications. Soluble gases are relatively easily and rapidly dissolved in liquids, especially under the application of elevated pressure. However, less soluble the gases are more difficult to dissolve in liquid economically and efficiently.

Additional difficulties are encountered when attempting to dissolve one gas of a gas mixture, such as dissolving oxygen in water from an air mixture that is approximately 20% oxygen and 80% nitrogen. It is well known that the rate of solubility of the gases in the liquid is directly proportional to the concentration of the gases in the mixture. Thus, it will take oxygen in air about five times as long to dissolve in water than it would take a 100% oxygen gas to dissolve in water. However, many times it is desirable to dissolve oxygen in a fluid and typically air is the desired source of oxygen due to the availability.

Frequently, it is desirable to dissolve oxygen in water. Oxygen, however, is relatively insoluble in water. For example, at 32°C the solubility of oxygen in water in contact with air at one atmosphere of pressure is only 7.3 mg./liter or 7.3 parts per million (p.p.m) . Solubility increases with the decrease in temperature - at 0°C the solubility is approximately 14.6 p.p.m.

Many applications exist which require the dissolution of large amounts of oxygen into a large volume of liquid. For example, it is necessary to oxygenate commercial fish ponds to enhance production and to oxygenate treated sewage or process water from industrial plants and mills to purify the liquid.

Oxygenation of commercial fish ponds is necessary for the following reasons. For example, aquatic organisms, including both animals and plants require at least a minimum amount of dissolved oxygen in water to survive. The amount of required dissolved oxygen varies between different aquatic organisms. For example, cold water fish such as trout and salmon require much more dissolved oxygen than warm water organisms, such as catfish or crawfish. Currently, aquatic animals such as crawfish, shrimp, catfish, trout, salmon, and abalone are being raised in horticultural ponds. In order to sustain maximum production in these ponds, a minimum amount of dissolved oxygen is required. The more oxygen dissolved in the pond water, the more animals that can be raised.

Oxygen is introduced into commercial fish ponds by a variety of mechanisms where the natural air-to-water contact is insufficient to reach the desired oxygen level. As previously stated, when water is in contact with air, the maximum concentration or saturation point of oxygen in water at 32°C and one atmosphere of pressure is approximately 7.3 p.p.m. Typically, it is desirable to maintain the oxygen concentration in the fish pond as close to saturation point as possible to enhance production. The rate of solution increases as wind and wave action increase because of

increased air-to-water contact. However, even on wind days the rate of solution is slow.

One source of oxygen in the outdoor commercial ponds is green plants. Any green plant that engages in photosynthesis utilizes some of the dissolved oxygen, but normally produces significantly more photosynthetic oxygen than it uses. However, in darkness no photosynthetic oxygen is produced, yet the plant organism is using some of the dissolved oxygen. Therefore, typically in a fish pond the dissolved oxygen decreases during the night to its lowest value at daybreak, unless there is considerable night wave action. On the other hand, many commercial fish ponds are inside, requiring photosynthesis producing light sources.

Many attempts have been made at trying to raise the oxygen content of the water in commercial fish ponds. Most techniques are targeted at improving the gas-to-water contact, including: pumping pond water over rocky waterfalls; squirting water from fountains in the air; turning paddle wheels on surface of the ponds; and pumping water/air mixtures at very high pressures and velocities into the pond surfaces at various angles. All of these techniques require large amounts of energy primarily because of the large amount of energy required to lift 8.3 lb./gallon of water above the pond surface. An alternate means of introducing more oxygen into the water is the use of a simple stack of wire screens placed in the water with the screen mesh fines decreasing from bottom to top. A stream of air is then pumped into the water below the screen stack. This technique requires little energy, but the bubbles coming through the screens are still relatively large and at shallow depths, the efficiency is very poor.

Another oxygen introducing means is the use of spinning air nozzles beneath the water. The nozzles are somewhat more efficient than the other schemes. Venturi tubes and porous

diffuser stones are also used, but are not efficient, particularly at shallow depths.

Oxygen is also used in water treatment applications. For example, government regulation requires sewage treatment plants to dissolve oxygen in effluent prior to releasing the effluent into rivers, lakes, or oceans. The spillage of any organic substance into a body of water causes the fairly rapid loss of dissolved oxygen, because of the oxidative destruction of the organic material. The amount of dissolved oxygen required to decompose the organic sewage by bacteria oxidation is greatly in excess of the amount of dissolved oxygen that must be added to the effluent prior to release. Reduction of oxygen causes death in fish and aquatic plants. The devices used in the sewage treatment plants are very costly and require a great deal of power to run, just as those described above.

Oxygen can also be used to clean process water from industrial plants, such as chemical plants, paper mills, and many other similar operations. However, again the dissolution process is very costly.

Just as oxygen is used to remove undesirable products in water, so too is ozone. Ozone is a form of oxygen having three oxygen atoms per molecule rather than two. Ozone is a much better oxidizing agent than oxygen because ozone is a much more energetic molecule. The ozone is used for oxidatively destroying organic compounds in the liquid. Organic destruction using ozone requires only seconds to minutes, as opposed to the hours to days required to destroy the organic compound using oxygen. An aqueous solution of ozone decomposes within about 15 minutes, leaving no undesirable product. Ozone is very fast acting at very low concentration which makes it invaluable for removing undesirable bacteria, viruses, and contaminating organic matter from drinking water, spas, swimming pool water, and

industrial water. However, there are very few efficient means for producing ozone.

The problems of producing ozone from oxygen and the inefficient methods currently available for dissolving it make the ozone purification of water more expensive than chlorine treatment. Even so, it is now being recognized as superior because any excess ozone decomposes within about 25 minutes, leaving no bad taste, bad odor or toxic products, as is true for chlorine. Chlorine does not destroy organic contaminants but does react with them to produce substances that are now recognized as carcinogens. In spite of the current greater cost of the ozone purification of water, the drinking water in at least one major United States city is purified with ozone, as is virtually all the drinking water in Europe. The water in virtually all European swimming pools and spas and increasing number of pools and spas in the United States is purified with ozone. Yet, the available methods for dissolving ozone in a liquid are relatively inefficient.

The dissolution of gases in liquids is required in other areas as well. A gas-to-liquid reaction can be used in any chemical process which requires the dissolution of a slightly soluble gas. For example, cleaning and disinfecting agents, like bleach and related products, are produced by dissolving the slightly soluble chlorine gas in a water slurry of lime. Carbon monoxide is a valuable gas for reacting with many organic liquids for producing products of great value such as different types of polymers and pharmaceuticals.

Therefore, it is a feature of the present invention to provide an improved apparatus for inexpensively and efficiently dissolving a gas in a liquid.

It is another feature of the present invention to provide an improved process for oxygenating horticulture ponds to enhance the productions of the ponds.

It is yet another feature of the present invention to provide an improved mechanism for oxygenating sewage water.

It is another feature of the present invention to provide an improved process for removing impurities from liquid.

SUMMARY

These and other features and advantages are accomplished by an apparatus including a hollow frustum having a closed top and a bottom opening with the closed top being larger than the bottom opening. A plurality of side openings are located around the circumference of the frustum and preferably nearer to the closed top rather than the bottom opening. The frustum is rotated at sufficient speed to create a pumping action to draw water up through the bottom opening and out through the plurality of openings.

Preferably, the total surface area of the plurality of openings is greater than 20% of surface area of the bottom opening. The hollow frustum is either conical or pyramidal.

This apparatus is used in the processes of oxygenating of horticultural ponds, waste water treatment, and impurity removal from water and an application that requires dissolution of a gas in a liquid.

BRIEF DESCRIPTION OF

THE DRAWINGS

So that the manner in which the above-cited features, advantages and objects of the invention, as well as others which will become apparent, are obtained and can be understood in detail, more particularly a description of the invention briefing summarized above may be had by reference to the embodiments thereof that are illustrated in the drawings, which drawings form a part of the specification. It is to be noted, however, that the impended drawings illustrate only preferred embodiments of the invention and are, therefore, not to be considered limiting of its scope for the invention may admit to other equally effective embodiments.

In the Drawings:

FIG. 1 is a side view of a diffuser illustrating a preferred embodiment of the invention.

FIG. 2 is a perspective view of a system used to dissolve gases in a liquid in accordance with this invention.

FIG. 3 is a side view of a diffuser illustrating an alternate embodiment of the invention.

FIG. 4 is a perspective view of an system used to dissolve gases in a liquid in accordance with an alternate embodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now referring to the drawings and first to FIG. 1, a typical preferred embodiment of the present invention is illustrated. Diffuser 10 includes a hollow frustum 12 and attached to hollow cylindrical member 18. Frustum 12 includes bottom opening 14 and top opening 16. Cylindrical member 18 is of the same diameter as top opening 16 and has closed top 19 and a bottom opening 21 that aligns with top opening 16, such that when frustum 12 and cylindrical member 18 are attached, one homogeneous unit is created. A plurality of side openings are spaced about the top of the perimeter or circumference of cylindrical member 18. Rotating shaft 22 is positioned in the middle of the closed top 19 of the cylindrical member 18 for rotating diffuser 10 when submerged in a liquid to create a centrifuge-pump.

In the preferred embodiment of this invention, the diameter of cylindrical member 18 and top opening 16 is 2-3/4". The overall vertical dimension of diffuser 10 is 3- 15/32", with the vertical dimension of cylindrical member being 2-3/32". The diameter of bottom opening 14 is 1", and internal cone angle 24 is 147.5°. Frustum 12 is conical.

Figure 2 shows a diffuser, such as the one shown in FIG. 1, submerged in reservoir 28 containing liquid 30. Diffuser

10 is suspended by rotating shaft 22 of motor 34. Motor 34 spins rotating shaft 22, and thus diffuser 10 at high velocities, at which point the diffuser becomes a centrifuge- pump, wherein liquid is drawn up through bottom opening 14, thrown in an upward direction and out plurality of openings 20.

Pump 36 injects a stream of gas through tubing 38 into bottom opening 14, forming a liquid-gas-mixture that is drawn into the diffuser 10 and ejected through plurality of openings 20. The injections of the gas into diffuser 10 is typically only required when diffuser 10 is submerged substantially below the surface of liquid 30.

When oxygenating a liquid, no gas injection is required if diffuser 10 is submerged in liquid only a small distance below the surface. Preliminary results have shown that the rate of oxygen dissolution into the liquid is much higher when diffuser 10 is located near the surface of the water without the injection of the gas, as opposed to the diffuser being located well below the surface of the liquid with the injection of the gas. When a diffuser of the dimensions described above is placed within three inches of the surface of the liquid in a 40 gallon reservoir containing approximately 35 gallons of liquid and rotated at approximately 3,450 revolutions per minute (r.p.m.) , a violent surface action is created generating significant cavitation and a concentrated water-air-mixture. The diffuser operating under these conditions produces a greater rate of gas dissolution than when the diffuser is places within 12 inches of the surface with air being introduced into the bottom opening at rates from 200-2000 milliliters per minute. The lower rates produce high percentage oxygen solution, while the higher rates produce poorer percentage oxygen solution, but achieve a greater total rate of solution.

The slower rates might be ideal for dissolving gases like ozone, where the high percentage oxygen solution would be

desirable, but large quantities are not required. For oxygenating a fish pond or sewage plant effluent, rotating a diffuser near the surface without introducing additional gases is a more efficient means of oxygenating, primarily, because the energy required to pump the gases from an external source is not required.

FIG. 4 shows an alternate embodiment of the present invention. Diffuser 200 is constructed of PVC plastic water pipe fittings, including a top cap and a reducing adapter glued together with PVC cement. The top cap is approximately 66 millimeters (mm.) in diameter. The bottom opening is approximately 34 mm. in diameter and approximately 94 mm. in height. The internal cone angle of the reducing adapter is approximately 143° and the overall height diffuser 200 is approximately 94 mm. , creating an internal volume of approximately 226 ml.

Diffuser 200 is connected to hollow shaft 222, which is constructed of 1 inch (in.) PVC hollow water pipe and is approximately a 16.5 in. in length, with pvc cement. A metal fitting is attached to the top of hollow shaft 222 to allow for connection to motor 34. Four 3/16 in. holes were drilled two inches below the top of hollow shaft 222 as air holes. Forty 3/8 in. holes were drilled into the top cap of diffuser 200. Tests have shown that submerging diffuser 200 into reservoir 28 to a depth of 12 3/8 in. below the surface of the water and turning the diffuser at approximately 3500 r.p.m. pulls air down into the hollow shaft and expels it at high velocities into diffuser 200, producing violent gas-water mixing. When diffuser 200 is rotated at high speed, it acts like a centrifuge-pump and pumps water through the side holes creating a vacuum inside the cone that pulls air down through the hollow shaft. The air-water mixture inside the spinning cone is thrown out through the side holes. Thus, this

embodiment of the invention pumps its own air into the cone without requiring an external air or gas source.

Tests have shown that relatively large internal volumes are required for good results using this embodiment of the invention, primarily because the water in the hollow shaft must be displaced by air, before the air can mix with the water inside the diffuser. The greater the height of water in the hollow shaft, the greater the vacuum must be to displace the water. For example, for the shaft length described above, a diffuser of approximate volume of 182 ml. with twenty 5/16 in. holes in the top cap is not capable of pumping air down the shaft. A larger volume inside the cone appears to produce a greater vacuum for displacing the water in the cone in the shaft. It also appears that if the total number and/or size of holes on the parallel portion of the cone is decreased, the solution efficiency is reduced.

Variations of the parameters of the embodiments described above produce very similar results without departing from the heart of the invention. For example, FIG. 3 shows an alternate embodiment of the diffuser, a single hollow frustum 100 with bottom opening 114 and closed top 119 to which rotating shaft 22 is attached. Plurality of openings 120 are positioned near the top of frustum 100. Thus, cylindrical member 18 of FIG. 1 is not necessary. Preliminary test results have shown that the only essential parameter of the diffuser is that it must be conical in nature and have a closed top. The smoothness of the frustum wall is not critical. For example, the frustum can be pyramidal. Also, it is not critical that the diffuser be hollow. For example, deflecting flanges may be included, but they reduce the efficiency of the diffuser.

Other parameters, such as the size, shape, number, and location of openings are not critical.

The area of the plurality of openings relative to the area of the bottom opening is an influential factor, but not

a critical factor. A diffuser having opening area of at least 20% or less than the area of the bottom opening, produces better results than other commercial devices, but the results are much poorer than when the area of the plurality of the openings is more than 20% or greater than that of the bottom opening. Good results are achieved when the area of the plurality of openings is 100 - 450% larger than the area of the bottom opening.

Since the ratio of plurality of opening area to bottom opening area appear to be the influential parameter, the number and size of the holes can vary. Good results have been achieved with both small and large openings, with the number of openings depending on the size. For a diffuser of the dimensions described above the maximum whole size that will produce good results is in the range from 9/32 of an inch to 1/2 an inch. The maximum whole size dimension varies with the size of the diffuser.

In the preferred embodiment of the invention, round openings were used. However, there is no indication that the opening must be limited to a round shape.

The location of the holes on the vertical dimension of the diffuser is not critical. However, better results are obtained when the openings are concentrated at the closed top. Also the direction that the holes are drilled into the diffuser influences the results, but only slightly.

The selection of diffuser material is not critical. The diffuser of the preferred embodiment is aluminum; however, any substantially rigid material can be used, including hard plastic. Diffusers made of only tough plastic are good for dissolving relatively unreactive oxygen in water. For dissolving the more reactive gases, such as ozone, the diffuser should be made of certain stainless steel alloys, unreactive plastics, or possibly aluminum. The diffuser can also be made of two materials including plastic and aluminum.

The exact rotational speed of the diffuser is not critical. It is, however, a major factor in the efficiency with which the gas is dissolved in the liquid. The higher the turning speed of the diffuser, the higher the speed of the peripheral holes, and thus, the higher the rate of dissolution. There is however a practical upper limit, above which additional speed requires additional power, thus decreasing the overall advantage of using the rotating diffuser. A diffuser in FIG. 1 is rotated at 1000 r.p.m., does not produce as good results as when rotated at higher speeds. The speed of 3450 r.p.m. was chosen to run the diffuser, because good results are obtained, and this speed motor is commercially available in many different power requirements. The size of the diffuser has an impact on the size of the motor.

In order to treat waste water in a sewage plant, one of ordinary skill in the art can easily determine the applicable size of diffuser for a given volume of waste water and of desired efficiency rate. The same is true for determining the size of the diffuser for removing contaminants from a liquid, oxygenating a horticultural pond, and oxygenating treated sewage water.

Although the illustrated and described embodiments are to actual tested embodiments, operable embodiments of the invention can be made utilizing alternative materials, different fabrication techniques, and different dimensions.

From the foregoing it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the apparatus.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.