Abstract:
An apparatus for introducing gas into a large body of liquid, including a horizontal frame on ballast adjustable floats, a pressurized gas source, a vertical shaft rotatable about its axis, and a plurality of blades submerged in the liquid and extending radially from a hub on the lower end of the shaft. The blades each have an elastomeric membrane around a longitudinal member, where the longitudinal member is hollow with a closed end and in communication with the pressurized gas source through the shaft on the other end, with openings through its lower side, and the elastomeric membrane has perforations which are spaced from the longitudinal member openings. A drive on the platform rotates the shaft via a ring gear around the shaft with a key connection thereto allowing axial movement therethrough, and an inwardly facing surface supported on bearings. A selectively driven and smaller pinion gear directly engages the ring gear.

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     REFERENCE TO A MICROFICHE APPENDIX 
     Not applicable. 
     TECHNICAL FIELD 
     The present invention relates to aerating and mixing large bodies of fluid, and more particularly to an apparatus for introducing gas and dissolved gases into a large body of liquid and mixing the fluid of such a body. 
     BACKGROUND OF THE INVENTION AND TECHNICAL PROBLEMS POSED BY THE PRIOR ART 
     Aeration and mixing have been used for treating water and other liquids for over a century. During that time various methods, including the following, have been employed: 
     Compressor/diffusers use a suitable compressor to force gas below the liquid surface and through a diffuser. As the bubbles rise to the surface, gas is transferred from the bubbles to the liquid. Mixing is accomplished via the change in liquid density created by the air and the hydraulic resistance of the bubbles as they travel to the liquid surface. Diffuser types range from coarse bubble to fine bubble diffusers. Coarse bubble systems do not transfer oxygen as efficiently and can be energy-inefficient to operate, when compared to fine bubble systems. Fine bubble diffusers are at first more energy-efficient, but they can become fouled, clogged, or damaged, resulting in decreased air transfer. The fine-bubble diffusers, in particular, are limited in turn-down capability, due to increased fouling problems at lower gas flow rates. 
     U.S. Pat. No. 3,630,498 to Belinski shows the use of a small, high-speed rotating mixing and aerating element comprised of a pair of horizontal radially extending blades or foils. In operation, a partial vacuum is created in a zone of cavitation, which is formed behind the foils. Gas bubbles which emerge from the blades enter the 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. The shattered 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 a 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). 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 becomes prohibitive. 
     Surface Aerators use motors to drive impellers or blades near the surface. They either lift the water into the air, or aspirate air and inject it just below the surface. Surface aerators generally have a poor air transfer efficiency when compared to fine bubble diffused aeration systems. In other words they consume more horsepower hours of energy for each pound of dissolved oxygen they produce. In addition, mixing from surface aerators is generally limited to liquid near the surface. Also, mixing energy tends to be point loaded at or near the impeller. Localized zones of high shearing forces tend to damage delicate floc structures necessary for proper liquid clarification. Further, they are limited in the length of the shaft overhang, and have a limited shaft bearing life. 
     Turbine/Spargers aerators use compressors to force and distribute a gas under the liquid surface. They also use a submerged impeller located just above the diffuser (sparger) to shear the bubbles and provide bulk mixing. Disadvantages of turbine spargers are similar to those for surface aerators with the additional disadvantage that the turbine sparger needs a source of compressed gas such as a compressor. 
     Jet Aerators use a liquid pump and an eductor to entrain gas into the liquid using the Venturi principle, as in U.S. Pat. No. 4,101,286. Jet aerators may be equipped to mix additional gas, liquid, or solid chemicals into the bulk liquid. They are reliable, have good turn down capability, and tend to be good mixers; however, they are inefficient aerators. 
     Blade Diffusers as taught in Ingram U.S. Pat. No. 1,383,881 (issued Jul. 5, 1921) use a flotation apparatus having rotating blades that dispense gas bubbles into a 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. The blades are pitched so that the leading edges are elevated about 45 degrees. As a result, the emerging gas is formed into elongated and then enlarged bubbles, which provide less efficient introduction of the gas into the liquid. In addition, examination of the patent and some 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 vertical water flow across the pitched blades would appear to in fact cause rotation opposite that which is indicated in the patent. 
     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, which 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. U.S. Pat. No. 5,681,509 teaches the use of permanently mounted blade members which are self supporting for the load forces encountered and which can prove labor intensive to change if needed, and 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. 
     Of course, the discharge members which have surfaces through which compressed gas may be discharged can face the risk of damage should the air pressure in those members be interrupted. In that case, the higher liquid pressure outside the members could force the liquid into the discharge members, potentially carrying undesirable particulates with it and thereby damaging/clogging the discharge members. U.S. Pat. No. 6,808,165 B1 discloses one advantageous structure for preventing such damage, in which the discharge members (diffuser blades) are attached to a hub mounted on a main shaft that automatically cantilevers out of the fluid should compressed gas supplied to the diffuser blades through the main shaft cease. 
     The present invention is directed toward overcoming one or more of the problems set forth above. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention, a blade is provided for an apparatus for introducing gas into a large body of liquid, where the apparatus includes a submergible hub on a rotatable shaft, radially directed connectors on the hub, and a pressurized gas source in communication with the connectors. The blade includes a longitudinal member and a membrane around the longitudinal member. The longitudinal member includes a mount adapted to secure the longitudinal member to one of the connectors of the hub in a radial direction relative to the rotatable shaft, a passage inside the member closed on one end and in communication with the pressurized gas source when secured to one of the connectors, and openings between the passage and the lower side of the longitudinal member. The membrane has perforations which are spaced from the longitudinal member openings whereby the membrane substantially blocks the longitudinal member openings when pressure in the longitudinal member passage is no greater than the pressure outside the membrane. 
     In one form of this aspect of the present invention, the membrane is elastomeric and its elasticity biases the membrane toward the outer surface of the longitudinal member along substantially the length of the longitudinal member, and clamps rigidly secure the membrane against the longitudinal member around opposite ends of the longitudinal member. 
     In another form of this aspect of the present invention, the perforations comprise lines of slits in the membrane, wherein no lines of slits are disposed over the longitudinal member openings. 
     In still another form of this aspect of the present invention, the longitudinal member is tubular with a selected diameter. In a further form, the membrane is an elastomeric sleeve having an unstretched diameter larger than the selected diameter, and clamps secure opposite ends of the sleeve to the longitudinal member. In another further form, the tube is stainless steel. 
     In yet another form of this aspect of the present invention, the membrane is elastically stretched by a selected pressure differential of the pressurized gas source in the longitudinal member passage over liquid pressure outside the membrane when submerged. 
     In another aspect of the present invention, an apparatus for introducing gas into a large body of liquid is provided, including a platform supported above the body of liquid, a pressurized gas source, a vertical shaft rotatable about its axis, and a plurality of blades submerged in the liquid and extending radially from the lower end of the shaft. At least one of the blades comprises a longitudinal member and an elastomeric membrane around the longitudinal member. The longitudinal member includes a passage inside the member closed on one end and in communication with the pressurized gas source through the vertical shaft, and openings between the passage and the lower side of the longitudinal member. The elastomeric membrane has perforations which are spaced from the longitudinal member openings whereby the membrane substantially blocks the longitudinal member openings when pressure in the longitudinal member passage is no greater than the pressure outside the membrane. 
     In one form of this aspect of the present invention, the pressurized gas source is an inlet pipe connectable to a supply of pressurized gas, with the inlet pipe including a vertical portion with a joint therein. A rotation joint secures a downwardly open end of the inlet pipe to the upper end of the vertical shaft to provide a gas passage from the inlet pipe to the vertical shaft, whereby pipe lengths may be added to or removed from the vertical portion of the inlet shaft at the pipe joint to increase or decrease the depth of the blades in the body of liquid. 
     In a further form, a drive on the platform engages the vertical shaft for rotating the vertical shaft about its axis, with the drive being keyed to selectively allow axial movement of the vertical shaft therethrough and, in a still further form, the drive includes a ring gear around the vertical shaft with a key connection thereto, there being an inwardly facing ring gear surface supported on bearings, and a selectively driven pinion gear directly and drivably engaging the ring gear, the pinion gear being substantially smaller in diameter than the ring gear, and in a still further form, the ring gear includes a drive sleeve having the key connection to the vertical shaft. 
     In another further form, a cord and pulley lift mechanism is between the vertical shaft and a support frame above the drive, which the lift mechanism provides a mechanical advantage in lifting the vertical shaft. In a still further form, the cord comprises a wire rope. 
     In still another further form, all of the blades include a longitudinal member and elastomeric membrane as recited. 
     In yet another aspect of the present invention, an apparatus for introducing gas into a large body of liquid is provided, including a platform supported above the body of liquid, a pressurized gas source, a vertical shaft rotatable about its axis, the shaft being supported on the platform and having its lower end extending into the body of liquid, a plurality of blades submerged in the liquid and extending radially from the lower end of the shaft, and a drive on the platform engaging the upper end of the vertical shaft for rotating the vertical shaft. The blades communicate with the pressurized gas source through the vertical shaft whereby pressurized gas is ejected from the blades to the body of liquid. The drive is keyed to selectively allow axial movement of the vertical shaft therethrough, and includes a ring gear around the upper end of the vertical shaft with a key connection thereto, the ring gear having an inwardly facing surface supported on bearings, and a selectively driven pinion gear directly and drivably engaging the ring gear, the pinion gear being substantially smaller in diameter than the ring gear. 
     In one form of this aspect of the present invention, the pressurized gas source is an inlet pipe connectable to a supply of pressurized gas, where the inlet pipe includes a vertical portion with a joint therein. A rotation joint secures a downwardly open end of the inlet pipe to the upper end of the vertical shaft and provides a gas passage from the inlet pipe to the vertical shaft, whereby pipe lengths may be added to or removed from the vertical portion of the inlet shaft at the pipe joint to raise or lower the vertical shaft. 
     In another form of this aspect of the present invention, a plurality of floats support the platform, and the floats comprise buoyant containers having a removable cap thereon allowing access to adjust the ballast in the containers. 
     In still another form of this aspect of the present invention, the platform is supported on one end by a first float and on its opposite end by an intermediate portion of a longitudinal structural member supported on its opposite ends by second and third floats, wherein the platform and the structural member are configured in a “T” disposed in a substantially horizontal plane. 
     In yet another form of this aspect of the present invention, a plurality of floats on which the platform is supported, the floats comprising buoyant containers having a removable cap thereon allowing access to adjust the ballast in the containers. 
     In another form of this aspect of the present invention, the ring gear includes a drive sleeve having the key connection to the upper pipe length. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an aerating and mixing apparatus according to the present invention; 
         FIG. 2  is a partial perspective view of  FIG. 1 , illustrating the pressurized air connection; 
         FIG. 3  is a top broken view of a blade incorporating one feature of the present invention; 
         FIG. 3   a  is a cross-sectional view taken along line  3   a - 3   a  of  FIG. 3  (wherein the slits in the membrane sleeve are not shown); and 
         FIG. 4  is a cross-sectional view showing the drive for rotating the vertical shaft according to one feature of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An apparatus  10  for introducing gas and dissolved gases into a large body of liquid and mixing the fluid of such a body in accordance with the present invention is shown in  FIG. 1 . The apparatus  10  may, for example, be advantageously used with large bodies of fluid such as in wastewater treatment to aerate and mix the wastewater to increase available oxygen to promote the growth of aerobic bacteria such as disclosed in U.S. Pat. Nos. 5,681,509 and 6,808,165 B1, the full disclosures of which are hereby incorporated by reference. 
     The apparatus  10  is supported between three floats  14  by a frame  18  which includes a first structural member  20  extending between two of the floats  14 , with a platform  22  secured on one end to the structural member  20  and on the other to the third float  14  in a generally T configuration. The platform  22  and first structural member  20  are disposed in a substantially horizontal plane. 
     The structural member  20  may be a metal rectangular box beam of suitable dimension to support anticipated loading, and the platform  22  may similarly be formed of suitable supporting structural frame members (e.g., tube and C-channel members such as structural member  24 ). As contrasted with parallel truss supports used for similar apparatuses in the prior art, this frame  18  eliminates the need for expensive, multiple piece trusses which require fabricating, fitting and welding together. Moreover, this frame  18  is substantially stronger in withstanding horizontal forces (e.g., at  26 ) than were the truss supports of the prior art. 
     As described in greater detail below, the platform  22  supports a shaft  30  rotatable about a vertical axis which advantageously may be centrally located between the three floats  14 , and effectively mounted to the supporting frame members. A hub  34  is disposed at the bottom of the shaft  30  and a plurality of blades  40  are secured to the hub  34  in a generally radial orientation. 
     As will be appreciated by those skilled in this art, the shaft  30  may advantageously be cylindrical so as to define a central passage through which air under pressure may be supplied to the hub  34 , and then from the hub  34  to the blades  40 . In operation, the shaft  30  supports the blades  40  so that they are horizontally oriented beneath the surface of the body of liquid on which the floats  14  are disposed and, as the shaft  30  is rotated, the blades  40  will sweep through the liquid and disperse the pressurized air into the liquid as described in greater detail below. 
     The three floats  14  may be advantageously provided with a removable cap  42  to facilitate easy adjustment of the float ballast (e.g., by adding metal shot, or drawing out metal shot) whereby the supported frame  18  may be readily supported in a level configuration, to thereby similarly support the shaft  30  in the desired vertical orientation (so that the blades  40  will sweep through a generally horizontal plane beneath the surface of the body of liquid). Difficult to use and expensive adjustable bracket connections to the floats such as used in the prior art are therefore not required. 
     Referring now specifically to  FIG. 2 , the previously referenced pressurized air may be advantageously supplied via a pipe  44  supported on the platform  22  and having an inlet pipe  46  which may be suitably connected to a compressor or other suitable source of pressurized air (not shown). The pipe  44  includes a vertical section  48  spaced from the vertical shaft  30  and extending upwardly from the inlet pipe  46 , with a U-section  50  connected between the upper end of the vertical section  48  and a suitable rotation joint  54 . The rotation joint  54  is disposed above, and connected to, the vertical shaft  30 , whereby the vertical shaft  30  may rotate relative to the stationary pipe  44  while remaining connected to the pipe  44  so that pressurized air from the pipe  44  passes into the central passage in the shaft  30 . This advantageous pipe  44  configuration for supplying pressurized air is easy to assemble and install, and thus may result in cost savings over prior pressurized air supplies for similar apparatuses requiring more crane time and expensive flexible duct connectors, hose clamps and flanges. 
     It should be appreciated that the length of the vertical section  48  may be adjusted by adding or removing pipe lengths, thereby raising or lowering the U-section  50 , the rotation joint  54 , and the attached vertical shaft  30 , hub  34 , and blades  40  as well. A suitable lifting structure  60  is provided to facilitate such operation, with an advantageous lifting structure being shown in  FIG. 1  as including a vertical support frame  62  and a pair of cables or cords, such as wire ropes  64 ,  66 . (It should be understood that, as used herein, cable and cord is intended to refer to any longitudinal member sufficiently flexible to be usable with a pulley and having tensile strength sufficient to support the structure intended to be lifted by the lifting structure  60 .) 
     A first one of the ropes  64  (e.g., a ⅜ inch wire rope) is looped over a guide  68  on the top of the frame  62  and connected on one end to a suspended pulley  70  and on the other end to a bracket  72  (see  FIGS. 1 and 2 ) which is suitably secured to the U-section  50  of the pressurized air supply. A pivoting connection  74  (see  FIG. 1 ) may advantageously be provided in the connection of the one wire rope  64  to the pulley  70  to prevent twisting of the ropes  64 ,  66 . Opposite ends of the other rope  66  (e.g., a 5/16 inch wire rope) are secured to a suitable winch  76  (see  FIG. 2 ) which may be manually or power driven. It should thus be appreciated that operating the winch  76  to pull on the second cable  66  will provide a two to one mechanical advantage in the first cable  64  lifting the bracket  72  and attached structure. As a result, the U-section  50  and attached shaft  30  (and blades  40 ) can be easily raised for maintenance and/or adjustment (e.g., when adding or removing pipe sections to the vertical section  48  to adjust the depth of the blades  40 , or when servicing the blades  40  which requires raising the blades  40  out of the body of liquid for access). 
     The vertical shaft  30  may also be advantageously rotatably driven as illustrated in  FIG. 4 . Specifically, a housing mount  80  is supported on the platform  22 , and supports a bearing structure  82  about which a ring gear  84  is rotatably mounted. The bearing structure  82  may advantageously be a large rotational ball bearing integral to the ring gear  84 , providing reduced friction and thereby decreasing the torque required to rotate the shaft  30  (and attached blades  40 ). 
     The ring gear  84  is suitably secured to a drive sleeve  86  which is itself rotatably supported in a tubular portion  88  of the housing mount  80 . A gear reducer pinion gear  90  is driven by a suitable motor  92 . Such an assembly is the PISTA® Gear drive available from Smith &amp; Loveless, Inc. of Lenexa, Kans., U.S.A., and directly engages the ring gear  84  to rotate the ring gear  84  and drive sleeve  86  secured thereto. By omitting the use of drive chains such as have heretofore been used to rotatably drive the shaft of apparatuses of this type, chain wear and resulting premature failure may be avoided. Further, the cost of the required frequent maintenance of such chains may also be avoided. Moreover, the high overhung load created by the tension in such prior art chain drives may be avoided, thereby also avoiding failure resulting from such load, and avoiding the need for increased size gear reducers to minimize such failures. 
     A key guide block  94  is provided on the interior of the drive sleeve  86 , and a drive spline on the vertical shaft  30  (not shown in  FIG. 4 ) is slidably secured within the drive sleeve  86  to engage with the key guide block  94 . As a result, the shaft  30  will be rotatably driven with the drive sleeve  86  when the tube  86  is rotated by the motor driven pinion gear  90 . Moreover, when it is desired to raise or lower the shaft  30 , the shaft  30  can be raised and lowered through the drive sleeve  86  by use of the lifting structure  60  as previously described. 
     One highly advantageous embodiment of the blades  40  of the present invention is illustrated in  FIGS. 3 and 3   a.    
     Each blade  40  may advantageously consist of a suitable tube  100 , such as a stainless steel pipe  100  which is closed on its outer radial end  102  and has a mount  104  on the inner radial end adapted to secure to the hub  34  on the vertical shaft  30 . Of course, the blade tube  100  could also be advantageously made of materials other than stainless steel which are sufficiently strong to withstand the expected loading over long periods of use. Moreover, the tube  100  includes a suitable interior passage  106  which receives pressurized air from the shaft  30 , through the hub  34 , and via an associated blade opening in the mount  104 . Simply put, pressurized air input through pipe  44  passes through rotation joint  54 , vertical shaft  30 , and hub  34  to reach the interior of the blades  40 . Air holes  108  are spaced along the bottom of the blade tube  40  and allow air to pass through the tube  100  from the interior passage  106 . The air holes  108  may advantageously be sized to create a pressure drop which forces the air to exit the holes fairly evenly. 
     A membrane sleeve  110  is disposed around a substantial portion of the length of the blade tube  100 , with clamps  114  securing opposite ends of the sleeve  110  to the outer surface of the blade tube  100 . Depending upon the length of the blade tube  100 , additional clamps may be provided along the sleeve  110 , including in the middle of the sleeve  110 . The sleeve  110  may advantageously be elastomeric with perforations  120  therethrough allowing passage of air through the sleeve  110 . In one preferred form, perforations  120  are not provided in the portions of the sleeve  110  overlying the tube air holes  108 . 
     In one configuration found to have been suitable for this blade structure, the tubes  100  are four inch diameter stainless steel tubes having ⅜ inch diameter air holes  108  at approximately four inch centerline spacing along the bottom of the tube  100  when mounted to the hub  34 . The membrane sleeve  110  is an elastomeric material such as EPDM having about 2 mm (0.080 inch) thickness, and nominally about ⅛ inch larger in diameter than the tube  100  to facilitate sliding of the sleeve  110  on the tube  100  during assembly. The sleeve perforations  120  are lines of slits spaced apart about 1.5 mm, with the slits themselves being about 1.5 mm in length, and the lines of slits laterally spaced apart about 2 to 3 mm. About ⅝ inch circumferential sections extending longitudinally along the top and bottom of the membrane sleeve  110  do not have slits. Of course, it should be understood that many different configurations and sizes consistent with the blades of the present invention may be used, both within comparable applications and in different applications. 
     It should be appreciated that operation of the apparatus  10  of the present invention will allow the blades  40  to be rotated through the body of liquid at a desired depth, with the blades  40  making air bubbles in the submerged liquid. The air which exits the tube holes  108  fairly evenly will cause the membrane sleeve  110  to swell to a slightly larger diameter with the air evenly distribute under the membrane sleeve  110 , and then exiting through the perforations (slits)  120 , which create fine bubbles that are advantageously diffused into the body of liquid (e.g., wastewater). 
     Further, it should be appreciated that, in the event that air pressure in the blades  40  is lost while the blades are submerged, the pressure of the liquid outside the blades  40  will press the membrane sleeve  110  against the outer surface of the tube  100 , and the unperforated portions of the sleeve  110  will function like a check valve to seal the tube air holes  108  and prevent the liquid from undesirably entering the blade tubes  100  and further will block undesirable particulates carried in the liquid from damaging/clogging the tubes  100  and tube air holes  108 . Accordingly, when suitable air pressure is later reestablished in the blade tubes  100 , that air will be able to flow under pressure out of the air holes  108  and then from the membrane perforations  120  to continue to generate the air bubbles desired for aeration. Moreover, it should be appreciated that this check valve function of the membrane sleeve  110  allows the depth of the blades  40  to be readily adjusted (as may be desired, e.g., seasonally) without requiring removal of the blades  40  from the liquid (since air pressure will intentionally be disconnected during such depth changes). 
     It should further be appreciated that the present invention provides improved blades  40  which are inexpensive, and easy to install and maintain. The membrane sleeve  110  serves both to facilitate aeration and to protect the blade tube  100 . Moreover, even if the membrane sleeve  110  should be damaged in some manner, the blade  40  may be repaired by simply replacing the inexpensive membrane sleeve  110  and not the entire blade  40 . 
     It should still further be appreciated that the lifting structure  60 , and the direct drive of the ring gear  84  and pinion gear  90 , the key guide block  94  and spline connection of the vertical shaft  30  to that drive, the pressurized air pipe  44  secured to the vertical shaft  30  by the rotation joint  54 , and the secure support frame  18  with readily adjustable float  14 , all combine to provide an inexpensive, reliable, and easy to maintain apparatus  10 . 
     Still other aspects, objects, and advantages of the present invention can be obtained from a study of the specification, the drawings, and the appended claims. It should be understood, however, that the present invention could be used in alternate forms where less than all of the objects and advantages of the present invention and preferred embodiment as described above would be obtained.