Gas and liquid contact apparatus – Contact devices – Injector type
Reexamination Certificate
1999-09-21
2001-07-24
Chiesa, Richard L. (Department: 1724)
Gas and liquid contact apparatus
Contact devices
Injector type
C210S221200, C210S758000, C261S120000, C261S122100, C261S124000
Reexamination Certificate
active
06264176
ABSTRACT:
TECHNICAL FIELD
This invention relates to a new and improved diffused gas system for treating aqueous media with fine bubbles of air or other gas, and to the method of conducting such treatment.
BACKGROUND ART
For many years, it has been known that oxygenation results in the biological and chemical breakdown of organic contaminants in effluent or wastewater. The surface of a body of liquid provides some oxygen uptake or absorption, because of its exposure to the atmosphere. However, when prior art diffused gas systems are used in order to accelerate the oxygenation, they require the use of additional devices to promote proper mixing. It is well-known to be important for cost reasons, to Ionize the time and energy required for such treatment. The unique design of the diffuser of this invention enables it to efficiently achieve both of these requirements from a single power source.
Similar considerations apply to the newer area of commerce, often referred to as aquaculture or “fish farming”. The medium in which fish will thrive must be rich in oxygen and well mixed. Supplying adequate amounts of oxygen, and dispersing it uniformly throughout the tank is of primary importance to the success of such enterprises. The diffuser of this invention accomplishes both functions economically.
In the treatment of effluent, there have been a number of methods used in the prior art to expose a greater surface area of effluent for contact with the atmosphere, including devices such as fountains to spray the liquid into the air. Others, such as the Bearden patent, U.S. Pat. No. 3,852,384 have devised submerged vertical columns with means to intermix liquid and air passing therethrough. Kober, U.S. Pat. No. 3,133,878 discloses an arrangement to create a circular flow of the liquid and treating gas. Like many others, both of these patents employ a perforated pipe to dispense the gas.
The Morgan patent, U.S. Pat. No. 3,232,866 is of interest because it relates to the spacing of diffusers in the container of liquid being treated. Morgan discloses a critical relationship between oxygen uptake and the arrangement of the diffuser heads. The Goudy et. al. patent, U.S. Pat. No. 4,597,530 discusses several prior art patents in the field and covers a diffuser in the shape of a disc which is designed in such a manner as to prevent dogging of its orifices.
Some prior art employs coarse aerators or “spargers” which have the advantage of moving the liquid upward, or rolling it, as a result of relatively large bubbles of air boiling to the surface. Current diffusers which produce fine bubbles, on the other hand, are less effective in mixing or rolling the liquid as the bubbles rise to the surface, but are more effective than the coarse diffusers in their aeration effectiveness, because of the greater surface area of the fine bubbles exposed to the liquid. The design of the present invention is effective both in 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 that of the present invention, and like conventional coarse air diffusers, they merely inject air into the liquid which forms large bubbles without enhancing oxygenation. The membranes of the prior art, however, are so flexible and not self supporting, that they require mounting on a kind of mandrel or internal support. Moreover, 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.
SUMMARY OF THE INVENTION
The present invention consists of a flexible microporous continuous tubular membrane arranged in a variety of forms including a spiral or grid configuration. When connected to a source of air, the membrane provides fine bubbles which are emitted around its entire circumference, even at the bottom. Because the resistance of the membrane is low, this is accomplished with less than two (2) inches of water column pressure difference between the top and bottom of the membrane. In both the spiral and grid configurations, substantial openings must be provided between adjacent elements of the tubular membrane. The fine bubbles generated by the membrane entrain the liquid being treated to move it through such openings. This is a critical feature of the structure of the present invention, resulting in the liquid being rolled over or inverted on a horizontal axis, like the coarse bubble diffusers, but, because of 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 being raised by the fine bubbles, is also rotated around a vertical axis as it rises. This further contributes to mixing and oxygen absorption, due to increased retention time of the fine bubbles emitted The continuous turnover of the liquid from top to bottom, increases the natural effectiveness of this invention. As is well known, there is a natural deansing process which occurs twice annually in lakes, rivers and streams. The present invention mimics that natural inversion, with the advantage that it can be repeated as often as needed.
The efficiency of the present invention is so substantial that the energy requirements are dramatically reduced by permitting the use of a much smaller motor to drive the blower. This is confirmed by the much higher Standard Oxygen Transfer Efficiency levels of the present invention as compared to the prior art resulting in 25% to 45% reductions in the horsepower requirement and corresponding reductions in the cost of both energy and equipment. This accompanies the greatly enhanced natural process of mixing, fine bubble aeration, and surface absorption of oxygen. The open structural design also minimizes fouling from debris in the liquid being treated, an advantage especially important in wastewater applications.
Preliminary testing indicates than a 22 inch fine air grid of the present invention has more than four times the rolling movement or inversion of the liquid being treated, as compared to all known prior art fine air diffusers, when the same amount of air flow is used. Such tests also show a better total liquid movement as 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 ten times as large as most conventional diffusers. The “vertical interface” refers to the vertical edges of exposed membrane.
As for effectiveness, independent testing has shown that the diffusers of present invention have superior oxygen uptake 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 by using a test procedure called the “clean water non-steady state” test, and results are given as the number of pounds of oxygen per hour per horsepower (O
2
/Hr./HP). All test results were calculated using the standard ASCE (American Society of Civil Engineers) method, i.e. the accepted non-linear regression method.
Typical diffusers of the prior art have SAE values of 2 to 7 pounds of O
2
/Hr./HP, when the air flow rate ranges from 1 to 10 Standard Cubic Feet of Air per Minute (SCFM). Many prior art diffusers have a very low oxygen transfer rate when the air flow rate is greater than 2 or 3 SCFM, and some cannot be operated above 5 SCFM. The diffusers of the present invention, however, have a SAE values even at 10 SCFM, ranging from nearly 5 to 10 pounds O
2
/Hr./HP.
The independent comparative tests also show loss of air pressure or “Head Loss” (H
L
) values of diffusers of the present invention are much lower
Dickman Daniel H.
Vollmer Ted K
Brockman Ronald
Chiesa Richard L.
Kivlin Joseph
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