MXPA99007827A - Aeration diffuser - Google Patents

Abstract

A diffuser (1) for mixing and oxygenating water or other liquid with an airstream employs a self supporting microporous tubular membrane (11), arranged in a spiral or grid configuration, with openings which are at least equal to the diameter of the membrane (11), extending both horizontally and vertically between the circuits or grids of the diffuser (1). Gas, when forced through the tubular membrane (11), forms fine bubbles which agitate, oxygenate and entrain the surrounding liquid as it slowly rises through the openings. The tubular membrane (11) is flexible and is to be mounted on a manifold (14, 15) which connects it to a source of air or gas, and which may also impart buoyancy or serve as an anchor in the liquid.

Description

FUSER FOR AERATION This application is a part in continuation of the Provisional Application of E. U., S. N. 60 / 043,378, filed on April 4, 1997.

ICO TECHNICAL FIELD This invention relates to a new and improved diffused gas system for treating aqueous medium with fine bubbles of air or other gas, and to the method for conducting such treatment.

BACKGROUND TO THE ICA TECHNIQUE For many years, it has been known that oxygenation results in the biological and chemical decomposition of organic pollutants in effluents or wastewater. The surface of a body of liquid provides some absorption or intake of oxygen, due to its exposure to the atmosphere. However, when using diffused gas systems of the prior art in order to accelerate oxygenation, they require the use of additional devices to promote proper mixing. It is well known that it is important for reasons of cost, to minimize the time and energy required for such treatment. The unique design of the diffuser of this invention makes it possible to efficiently achieve both of these requirements from a simple energy source. Similar considerations apply to the newer trade area, often referred to as aquaculture or "fish farming". The medium in which the fish will grow must be rich in oxygen and well mixed. The supply of adequate quantities of oxygen, and its dispersion uniformly throughout the tank is of paramount importance for the success of such companies. The diffuser of this invention achieves both functions economically. In the treatment of effluents, there have been a number of methods used in the prior art to expose a larger surface area of the effluent for contact with the atmosphere, including devices such as sources for spraying the liquid in the air. Others, such as the Bearden Patent of E. U., No. 3,852,384, have devised submerged vertical columns with means for intermixing liquid and air passing therethrough. Kober, U.S. Patent No. 3, 133,878 describes an arrangement for creating a circular flow of the liquid and treating gas. Like many others, both of these Patents employ a perforated tube to supply the gas. The Morgan Patent, of E. U., No. 3,232,866 is of interest because it refers to the separation of diffusers in the container of the liquid being treated. Morgan describes a critical relationship between the oxygen taken and the arrangement of the diffuser heads. U. U. Patent of Goudy et al. No. 4,597,530 discusses several prior art patents in the field and covers a diffuser in the form of a disc that is designed in such a way as to prevent clogging of its orifices. Some of the prior art use coarse aerators or "sprinklers" which have the advantage of moving the liquid upwards, or stirring it, as a result of relatively large air bubbles to the surface. Current diffusers that produce fine bubbles, on the other hand, are less effective in mixing or stirring the liquid as the bubbles rise to the surface, but are more effective than coarse diffusers in their aeration effectiveness, due to the larger surface area of the fine bubbles exposed to the liquid. The design of the present invention is effective in both mixing and aeration. Some diffusers of the prior art employ a membrane through which air is passed to produce fine bubbles, while others employ a porous stone. They are of a simpler construction than those of the present invention, and like conventional coarse air diffusers, they simply inject air into the liquid which forms large bubbles without improving oxygenation. The membranes of the prior art are, however, very flexible and not self-supporting, requiring assembly on a type of mandrel or internal support. In addition, they are so easily distended when subjected to air pressure that air is not emitted from their entire circumference. For example, a tubular-shaped diffuser emits air mostly from its upper surface.

BRIEF DESCRIPTION OF THE INVENTION The present invention consists of a flexible microporous continuous tubular membrane arranged in the form of a spiral or grid configuration. When connected to an air source, the membrane provides fine bubbles that are emitted around its entire circumference, to a bottom. Because the resistance of the membrane is low, this is achieved with less than 5.08 centimeters of water column pressure difference between the top and bottom of the membrane. In both configurations, the loop! and the grid, substantial openings between adjacent elements of the tubular membrane must be provided. The fine bubbles generated by the membrane entrain the liquid that is treated to move it through such openings. This is a critical aspect of the structure of the present invention, which results in the liquid being stirred or inverted on a horizontal axis, such as thick bubble diffusers, but, due to the fine bubbles emitted, it is far superior to them in oxygenation effectiveness. It has been observed in the spiral diffuser of this invention that the volume of liquid that is raised by the fine bubbles, is also rotated about a vertical axis as it rises this further contributes to the mixing and absorption of oxygen, due to the time Increased retention of fine bubbles emitted. The rotation of liquid from the top to the bottom increases the natural effectiveness of this invention. As is well known, there is a natural cleansing process that occurs twice annually in lakes, rivers, and streams. The present invention simulates that natural inversion, with the advantage that it can be repeated as often as necessary. The efficiency of the present invention is so substantial that the energy requirements are dramatically reduced allowing the use of a much smaller motor to drive the fan. This is confirmed by the much higher Standard Oxygen Transfer Efficiency levels of the present invention compared to the prior art, resulting in reductions of 25% to 45% in the requirement for horsepower and corresponding reductions in the cost of both, energy and equipment. This accompanies the greatly improved natural mixing process, fine bubble aeration, and surface absorption of oxygen. The open structural design also minimizes the contamination of the liquid that is treated, a particularly important advantage in wastewater applications. Preliminary tests indicate that a fine air grid of 55.9 centimeters has more than four times the revolving movement or inversion of liquid that is treated compared to all known fine air diffusers of the prior art, when the same amount of flow is used. air. Such tests also show a better movement of total liquid compared to coarse air diffusers when the same amount of air flow is used. This is because the present design provides at least four times the active membrane surface area, and emits "fine point" bubbles in that area having a vertical interface about 10 times as long as more conventional diffusers. The "vertical interface" refers to the vertical edges of the exposed membrane. As to effectiveness, independent tests have shown that the diffusers of the present invention have superior oxygen absorption performance which is more than twice as great as the best conventional aerator previously employed, a membrane tube. No comparison was made with rubber dome or ceramic diffusers of the prior art, which are known to be even less effective than such membrane tubes. Oxygen transfer, also called Standard Aerator Efficiency (SAE) is measured using a test procedure called the "non-stable clean water status" test, and the results are given as the number of kilograms of oxygen per hour per horsepower (O2 / Hr / HP) . All test results were calculated using the ASCE (American Society Engineers) method. , that is, the accepted non-linear regression method. The typical diffusers of the prior art have SAE values of 0.908 to 3.178 kilograms of O2 / Hr / HP, when the air flow rate fluctuates from 0.0283726 to 0.283726 Cubic Meters of Air per Minute Standard (MCAME). Many diffusers of the prior art have a very low oxygen transfer rate when the air flow rate is greater than 0.0567 or 0.0851 MCAME, and some can not be operated above 0.1418 MCAME. The diffusers of the present invention have, however, SAE values even at 0.283726 MCAME, ranging from about 2.27 to 4.54 kilograms O2 / Hr / HP. Independent comparative tests also show loss of air pressure or "Head Loss" (H), values of diffusers of the present invention are much lower and much higher than the prior art. Pressure losses of the prior art range from 15.24 cm to 88.9 cm of water column pressure over a range of 0.0283726 to 0.283726 MCAME per diffuser. The majority of the diffuser pressure loss is so inefficient at 0.1 135-0.1418 MCAME that they can not be used. The diffusers of the present invention have a low pressure loss even at 0.283726 MCAME ranging from 6.35 to 68.6 centimeters. Furthermore, such tests show that the percent of Standard Oxygen Transfer Efficiency (SOTE) per submersion meter is frequently one and one-half to two times better than diffusers of the prior art. Typical SOTE diffuser values range from 0.5 to 2.2 percent over a range of 0.0283726 to 0.283726 MCAME per diffuser. Most diffusers are very inefficient at more than 0.1 135 to 0.1418 MCAME, with some being inoperable at levels above 0.1418 MCAME. The diffusers of the present invention have SOT's of 2.4% to 2.9% even when operated as high as 0.283726 MCAM E. An ideal spiral structure according to this invention uses a floating manifold frame that allows the spiral to be anchored in a Generally horizontal position at any desired depth in the liquid that is treated. By placing the diffuser close to the bottom of the liquid, further cleaning and detoxification of the bottom is achieved, due to the boiling or revolving action described above. The manifold for the present invention provides air to both ends of the membrane, providing a more balanced air distribution across the entire membrane than if it were only connected to one end. The ideal grid structure, the preferred embodiment for use in large aquaculture tanks, has a different structure because it is designed to rest on the bottoms of the tanks. However, the principles employed are the same. In the grid shown in the drawings and described below, the various sections of pipe membrane are not arranged in a horizontal plane. They are arranged in a manner that produce the required openings between adjacent sections of tubular membrane. Like the spiral design, the membranes in the grid are supplied with air at each end in order to balance the flow of air more evenly between them.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a top elevation view of the scroll diffuser of the present invention; Figure 2 is a lateral elevation of said diffuser; Figure 3 is a perspective view showing a pair of said spiral diffusers anchored in a liquid body; Figure 4 is a top elevation view of the grid diffuser of the present invention; Figure 5 is a side elevation of said grid diffuser; and Figure 6 is an end elevation thereof.

BEST MODE FOR CARRYING OUT THE INVENTION Figure 1 represents an embodiment of the present invention, wherein a tubular microporous membrane 11 is arranged in a spiral configuration. The spiral diffuser is generally shown at 7 in Figure 1 of the drawings. As shown in Figure 2, said diffuser consists of a tubular membrane 11 interwoven around vanes or blades 12, of which three are shown extending radially from the center of the structure, in such form to create large openings between the windings of said membrane 11. The tubular membrane 11 is self-supporting in the sense that it does not require any internal structure to maintain its integrity. It is not stretched measurably by the air pressure that passes through it, by the depth at which it is operated, or by some combination of these two factors. It has been found that the tubular membrane 11 should preferably have a maximum internal diameter of approximately 2.54 centimeters and a maximum external diameter of approximately 3.81 centimeters, and a pore size in the range of 50-500 microns, preferably at the lower end of such a range. Optimal minimum membrane diameters would be approximately 0.95 cm ID and approximately 1.27 cm OD, and the optimum pore size would be approximately 50 to 100 microns. Pores smaller than about 50 μ will produce the fine bubbles desired by this invention, but are less suitable due to the higher air pressure and higher resulting operating costs. A preferred membrane is one that is made in accordance with the method described in U.S. Patent No. 4,958,770. As shown in Figure 3, the spiral diffuser 7, when in use, is generally arranged horizontally, but rests in multiple planes due to the inter-woven around the blades 12. A spiral diffuser, which was found to be very effective, it uses approximately 5,185 m of such a pipe, and has a total diameter of approximately 55.88 centimeters. A critical element of the present invention is that there are wide openings between the proximal arcs of pipe 1 1 of the spiral diffuser 7, and between adjacent sections of pipe 11 in the grid diffuser 8. Such openings should be at least as large as the outer diameter of pipe 1 1, to provide optimum performance in agitating or stirring the liquid to be treated, to aerate the same and to collect debris from the lower levels of said liquid. The manifold 14 of the spiral diffuser 7 is connected to the pump 30 by means of non-porous pipe 20, as shown in Figure 3. It will be obvious that a similar connection can be made to the grid diffuser 8. The cylinder 15 and the tube 14 in the spiral diffuser 7 comprise a manifold of distribution which provides buoyancy to the diffuser. Figure 1 shows the diffuser 7 having three blades 12 extending radially from the cylinder 15, but a larger number could be employed without departing from this invention. The tube 14 is connected at both ends to an air source, namely at the bottom of the cylinder 15 and at the end of its radius. This arrangement helps to equalize the air pressure along the entire length of the tubular membrane 1 1. As best seen in Figure 3, the anchor lines 31 position one or more spiral diffusers 7 in the desired depth and placement in a pond of liquid to be treated., where the hose 20 connects the manifold to the pump 30. One skilled in the art will recognize that the cylinder 15 can be placed elsewhere, or even removed from the diffuser, depending on the desired buoyancy. The feed air at both ends of tube 14 must still be arranged, however, because the tubular membrane causes so little counter-pressure that the more remote portions are almost devoid of air. The blades 12, shown in Figures 1 and 2, consist of polyvinyl chloride, but any other plastic can be substituted as long as it has required structural characteristics and is inert with respect to the liquid being treated. It is also possible to use stainless steel instead of PVC, and the spiral diffusers of the present invention have been constructed using stainless steel wire to form the vanes. The grid diffuser 8 has operating characteristics similar to the spiral diffuser 7. However, it has a different configuration to adapt it for use in large pond tanks used in aquaculture. In such use, it is desirable that the diffuser be placed at the bottom of the tank, which requires that it be provided with support legs or legs. The spiral diffuser 7, on the other hand, is better suited for waste water treatment, where it is usually more effective when placed above the bottom where it will be less subject to clogging by sediments that are usually found in that medium. The grid diffuser 8 is provided with multiple lengths of porous pipe 1 1, three pipes being shown in Figures 4, 5 and 6, each of which is attached at each end to the pipe 14. Figure 4 shows the pipe 14 forming a rectangular shaped manifold, although one skilled in the art would appreciate a square configuration for certain uses may be desirable. It also shows the three sections of porous tube 1 1 which are parallel to each other, parallel to the main axis of the rectangular manifold, and appear to be of equal length and equidistant from one another. The diffuser 8 is shown in its operative position in Figures 5 and 6, supported by a pair of equilateral trapezoidal legs 24, one of which is mounted on each end of the weight 25. The weight 25 preferably has a cylindrical shape and it extends between the legs 24 with its major axis perpendicular to it and parallel to the base of the legs 24. The sections of the porous tube 11 in the grid diffuser 8 extend over the weight 25 between the two ends of the manifold 14, as best seen in Figures 5 and 6. Said manifold is shown in Figure 6 mounted at a different level on each of the legs 24, such that its minor axis is not parallel to the base of either of the legs 24. The result of this design is that the sections of the porous tube 11 are not of equal length, and are not equidistant from one another at all points, when they pass over the cylindrical weight 25. They are equidistant where they join the manifold 14, and in the portion that passes over the weight 25, co It can be seen better in Figure 5. Such an arrangement is necessary in order to help equalize the air pressure in the entire manifold, with the elevated section of the pipe 1 1 receiving more air simply because of its higher elevation. The structure also has the benefit of enlarging the openings between adjacent sections of the tubular membrane, so that the separation between them is greater than if they were completely parallel. Preferably, such openings are at least as large as the external diameter of said pipe.INDUSTRIAL VIABILITY The product and process of this invention can be used for the low cost and effective treatment of aqueous medium with gas in all forms of commerce.

Claims (11)

1. CLAIMS 1. An improved diffuser for the oxygenation and mixing of aqueous medium of the type employing a pressurized gas containing oxygen and a pump for pressurizing said gas, said diffuser consisting of a self-supporting flexible microporous tubular membrane with a balanced gas flow , and a manifold connecting said pump to said membrane, said membrane being mounted on said manifold in a manner that provides proximal elements of said membrane, said proximal elements having openings therebetween, said openings being at least equal to the outer diameter of said membrane. The diffuser of claim 1 wherein said membrane has, throughout its entire extent, uniformly fine pores, ranging in size from about 50 to 500 microns, and wherein said gas is uniformly emitted from the entire circumference of said membrane in the form of fine bubbles. The diffuser of claim 2, wherein said diffuser has at least three vanes extending radially from its manifold with said tubular membrane being interwoven about said vanes in a spiral configuration and wherein said proximal elements are separated horizontally and vertically from one another. The diffuser of claim 2, wherein said diffuser has a grid configuration with said tubular membrane being mounted on a rectangular or square manifold, and wherein said proximal elements are separated horizontally and vertically from each other. 5. The diffuser of claim 2, which has a Standard Aerator Efficiency that ranges from 2,179 to 4.54 kilograms of oxygen per horsepower per hour, Head Loss from about 6.35 to 68.58 centimeters of pressure water column, and with Standard Oxygen Transfer Efficiency that fluctuates from 2.4% to 2.9% per meter of submersion over a range of approximately 0.0283726 Cubic Meters of Air per Standard Minute. 6. The diffuser of claim 5 having a spiral configuration. 7. The diffuser of claim 5 having a rectangular or square configuration. 8. The method of simultaneously mixing and oxygenating aqueous medium comprising submerging therein a diffuser consisting of a self-supporting flexible microporous tubular membrane, said membrane being mounted on a manifold connecting said membrane to a source of pressurized gas, forcing said gas uniformly across the entire circumference of said membrane, with the pressure required to eject said gas as fine bubbles, and to cause said bubbles to rise slowly and entrain said aqueous medium. 9. The method of claim 8, wherein said membrane has, throughout its entire extent, fine pores uniformly, ranging in size from about 50 to 500 microns. The method of claim 8, wherein said membrane is configured in a manner which provides openings between the proximal elements of said membrane said openings being at least equal to the outer diameter of said membrane. 11. The method to simultaneously agitate and oxygenate aqueous medium which comprises immersing in it a diffuser having a Standard Aerator Efficiency that ranges from 2,179 to 4,54 kilograms of oxygen per horsepower per hour, Head Loss from approximately 6.35 to 68.58 centimeters of pressure water column, and with Standard Oxygen Transfer Efficiency that fluctuates from approximately 2.4% to 2.9% per immersion meter over a range of approximately 0.0283726 to 0.283726 Cubic Meters of Air per Standard Minute.