Gas and liquid contact apparatus – Contact devices – Rotating
Reexamination Certificate
2003-04-30
2004-10-26
Bushey, Scott (Department: 1724)
Gas and liquid contact apparatus
Contact devices
Rotating
C261S120000, C261S122100
Reexamination Certificate
active
06808165
ABSTRACT:
FIELD OF THE INVENTION
The disclosed device herein relates to the field of aeration and mixing of large bodies of fluid. More particularly, the present invention is an improved apparatus for the introduction of gas and dissolved gases into a large body of liquid and for concurrently providing the ability to mix the liquid in a large body of liquid.
BACKGROUND OF THE INVENTION
Aeration and mixing have been used for treating water and other liquids for more than one hundred years. During that time various devices and methods have been employed for the mixing and aeration of such large bodies of fluid. Such aeration devices include compressor/diffusers, surface aerators, turbine/spargers, jet aerators, blade diffusers, with each having its own utility when it comes to the task at hand.
Compressor/diffuser type aerators employ a compressor suitable to the task to force gas through a diffuser located below the liquid surface. As the bubbles naturally rise to the surface of the liquid being aerated, gas is imparted from the bubbles into the liquid. Resulting mixing of the liquid is provided by the hydraulic resistance of the bubbles as they travel to the liquid surface.
Diffuser type aereators range from coarse bubble to fine bubble diffusers. Coarse bubble systems as the name implies employ larger bubbles and are more reliable but less energy-efficient to operate, when compared to fine bubble systems. Fine bubble diffusing systems, while at first more energy-efficient, frequently become fouled or clogged due to the small apertures required to produce the small bubbles clogging thereby resulting in decreased reliability. Such fine-bubble diffusers, in particular, are limited in low volume capability, due to increased fouling problems at lower gas flow rates.
Compressor diffuser type devices employ a rotating gas diffuser in the form of a large flat horizontal disk-shaped component. Compressed gas is therein discharged from porous plates arranged completely around the circumference of the disk. This type of gas deployment into the liquid tends to produce gas flow where many of the bubbles tend naturally to follow in the path of preceding bubbles which limits the efficiency of the transfer of gas into the surrounding body of liquid. Such a bubble pattern also tends to interrupt the effective inflow of liquid into the reactor column and therefor further limits mixing efficiency. Such a device is shown in U.S. Pat. No. 3,630,498 (Belinski) which teaches the use of a small, high-speed rotating mixing and an aerating element comprising a pair of horizontal radially extending blades or foils. In operation of Belinski, a partial vacuum is formed in a zone of cavitation behind the foils. Gas bubbles which emerge from the blades enter this zone of cavitation and expand due to the reduced pressure around the bubbles. While expanded, the bubbles are shattered by hydraulic forces into smaller bubbles. These smaller bubbles then exit the reduced pressure zone of cavitation and are further reduced in size as they are subjected to ambient pressure. Critical to the Belinski patent is the creation of the zone of cavitation. To create this zone of cavitation in a practical device, the foils must be short (such as 24 inches) and rotated at very high speeds (such as 450 RPM). Consequently, such a device is best suited for a smaller area. If the foils are made appreciably longer, the energy cost and physical loads of high-speed rotation quickly become prohibitive.
Surface aerators employ an engine or motor to rotate impellers or blades near the surface of the liquid body. Such devices conventionally either lift the water into the air above the surface, or aspirate air and inject it just below the surface of the liquid body. Surface aerators in general possess a poor gas transfer efficiency when compared to fine bubble diffused aeration systems since they consume more horsepower hours of energy for each pound of dissolved oxygen they produce. Mixing from surface aerators is generally limited to liquid at or near the surface of the body of fluid being aerated. Further, mixing energy tends to be point limited to positions at or near the impeller. Consequently, localized zones of high shearing forces tend to damage delicate floc structures necessary for proper liquid clarification. Further, surface aerators are generally limited in the length of the shaft overhang, and shaft bearing life tends to be problematic.
Turbine/Spargers aerators use compressors to force and distribute gas below the surface of the liquid body. They also employ a submerged impeller positioned just above the diffuser(sparger), to shear the bubbles and provide bulk mixing of the liquid body in which they reside. Disadvantages of turbine spargers are similar to those for surface aerators with the additional disadvantage caused by the turbine sparger requiring an independent source of compressed gas such as a compressor.
Jet Aerators employ a liquid pump and an eductor to impart gas into the liquid body surrounding them using the Venturi principle. Such a system is taught in U.S. Pat. No. 4,101,286 (Nagao). Such jet aeration systems may also be equipped to mix additional gas, liquid, or solid chemicals into the liquid body into which they are engaged. While such systems are generally reliable and have good low volume capability, they tend to be inefficient aerators.
Blade diffusers as taught in U.S. Pat. No. 1,383,881 (Ingram) use a flotation apparatus having rotating blades which dispense gas bubbles into the surrounding body of liquid. The design of these blades is dictated, however, by the requirement that they also act as impellers to rotate the blades as well as discharging the gas bubbles. Such blades are pitched so that the leading edges are elevated about 45 degrees and as a result, the emerging gas is formed into elongated and then enlarged bubbles, which result in a less efficient introduction of the gas into the liquid. In addition, examination of the patent and our research indicates that the blades would rotate in the opposite direction than is indicated in the Ingram Patent. This would result from the upward flow of fluid caused by the fluid lift pump effect of the released gas moving upward toward the liquid surface. Such a vertical water flow across the pitched blades would appear to in fact cause rotation opposite that which is taught in Ingram.
Another excellent example of a device for aeration and mixing of large bodies of liquid is taught in U. S. Pat. No. 5,681,509 (Bailey). Bailey teaches an apparatus and method for mixing and introducing gas into a large body of liquid by rotating a plurality of permanently mounted spoke-like discharge members which are below the surface of the liquid body. These members have upwardly facing perforated discharge surfaces through which compressed gas is released up into the liquid. Upward lift is countered by angling the members which are tilted with their leading edges lower than their trailing edges and balancing the rotation speed to achieve substantially zero lift. A control system is provided to change the depth of submergence of the discharge members to regulate dissolved gas infusion rate and speed of member rotation to maintain angle of attack. Bailey, while a leader in this field, teaches the use of permanantly mounted blade members which are self supporting for the load forces encountered and which can prove labor intensive to change if needed. Bailey also teaches the use of a vertically inclining main shaft which, while providing valuable utility in the ability to raise the blade members from the liquid in which they rotate, does require a substantial frame and mechanical structure to support the components allowing for the inclining main shaft.
As such, there exists a need for a device for mixing and for introducing gas into a large body of liquid which is easily servicable and energy efficient. Such a device should provide maximum aeration and mixing to the water to which it is immersed and also provide easy ingress and egress of the diffuser blades from the water or li
Avers Fredric H.
Dashew Stephen
Downs Ernest W
Gorby Jack
Sperber, Jr. David O.
Bushey Scott
Smith & Loveless, Inc.
Wood Phillips Katz Clark & Mortimer
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