US20090035150A1

US20090035150A1 - Surface aerator impeller design including stabilizer cylinder

Info

Publication number: US20090035150A1
Application number: US12/220,957
Authority: US
Inventors: John R. McWhirter; Prakash G. Balan; James Stanton
Original assignee: Mixing and Mass Transfer Technologies LLC
Current assignee: Mixing and Mass Transfer Technologies LLC
Priority date: 2007-07-31
Filing date: 2008-07-30
Publication date: 2009-02-05
Also published as: WO2009017744A9; WO2009017744A3; WO2009017744A2

Abstract

A surface aeration impeller incorporating a stabilizer cylinder that damps out and eliminates any sustained oscillatory or vibratory displacements normal to the axis of rotation when the impeller is in operation. The surface aeration design operates in a mechanically stable fashion under diverse loading conditions and at any static liquid level submergence of the impeller.

Description

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No. 60/962,694, filed Jul. 31, 2007.

INTRODUCTION

The present teachings are directed to systems for achieving mechanical stabilization in the operation of rotating surface aeration impellers. The present teachings are further directed to a stabilizer cylinder affixed to a surface aeration impeller that damps out and eliminates any sustained oscillatory or vibratory displacements normal to the axis of rotation when in operation under specific loading conditions.
Surface aeration is a well known approach for dissolution of gas into liquid in gas-liquid contacting operations. Surface aeration uses an impeller located at or near the surface of the liquid to agitate, pump and spray the liquid into the gas. A surface aerator system typically comprises an electric motor coupled to a speed reducing gear reducer, which is coupled to the surface aeration impeller by means of a cylindrical shaft.
The discharge from the surface aerator has two flow components. One component is turbulent flow that is pumped along the liquid surface, and the other is a stream that is discharged as a dense spray that impinges on the liquid surface at a distance from the surface aerator. The combination of the impinging spray and the turbulent surface flow results in a region of dense turbulence downstream of the spray impingement point. This surface turbulence causes a large amount of gas bubbles to be entrained into the liquid surface. The surface turbulence and the entrained gas produce high rates of gas dissolution into the liquid.
The HI-FLO II surface aerator design disclosed in U.S. Pat. Nos. 6,715,912 and 6,860,631 has been shown to be a superior impeller design for surface aeration purposes, with a substantial documented increase in liquid pumping and gas-liquid mass transfer efficiency over pre-existing art. The impeller designs disclosed therein pump more liquid per unit of horsepower input through the liquid spray mass transfer zone and into the surrounding surface reaeration zone and thereby maximize the total gas-liquid mass transfer efficiency of the overall surface aeration system.
Infrequently, under certain loading conditions, surface aeration impellers may exhibit mechanically unstable performance characteristics. In such operating conditions, the surface aeration impeller may exhibit a vibrating or oscillatory motion normal to the axis of rotation which exerts very large mechanical bending forces on the impeller shaft. These forces may, in turn, be transmitted to the gear reducer. This can result in excessive forces on the gearbox bearings and mechanical seals which, when excessive, cannot be tolerated even for short periods of operation. If not prevented, such forces for prolonged periods can cause mechanical damage and eventually mechanical failure in the system. Accordingly, there is a need to reduce the vibrating and/or oscillatory motion of the impeller shaft, thereby minimizing the detrimental forces on the gear reducer, mechanical seal, etc.
Apparatus for reducing impeller shaft oscillatory motion are known in the art. U.S. Pat. No. 6,089,748 discloses flexural members attached to an impeller shaft near the shaft's base; U.S. Pat. No. 5,931,051 discloses a dampener using a liquid-filled housing. U.S. Pat. No. 5,326,168 discloses the attachment of fins to the impeller blades to reduce such motion. However, using an oscillatory motion dampening apparatus that is made up of multiple parts is both costly and burdensome. A further disadvantage of such apparatus is that it causes the surface aeration impeller to be difficult to store when not in use. Therefore, there is a need for an apparatus that is capable of eliminating any vibrating or irregular oscillatory motion of the impeller shaft that is also inexpensive to produce, easy to use, durable, and easy to store.

SUMMARY

The present teachings disclose surface aeration impellers with improved vibration and oscillatory motion dampening, stability and performance, for use in a liquid filled tank that has a free liquid surface and an enclosed or open gas space above the liquid surface in the tank. The improved surface aeration impeller design includes a stabilizing cylinder. The stabilizer cylinder can be positioned below the upper mounting member of the surface aeration impeller. The stabilizer cylinder provides significantly increased resistance to vibration and irregular oscillatory motion in a direction that is perpendicular to the axis of rotation. The stabilizer cylinder also dampens the effects of the fluid forces that cause the impeller shaft to vibrate and oscillate, and effectively eliminates both periodic and random motions of the impeller shaft, thereby stabilizing the overall assembly and eliminating the unwanted forces on the gear reducer.
These and other features of the present teachings are set forth herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The skilled artisan will understand that the drawings described below are for illustration purposes only. The drawings are not intended to limit the scope of the present teachings in any way.

FIG. 1 is a perspective drawing of the surface aeration impeller with the stabilizer cylinder attached to the underside of a disc-shaped mounting member.

FIG. 2 is a graph of the oxygen transfer efficiency of the present teachings.

FIG. 3 is a series of illustrations depicting the present teachings from different perspectives. Impeller blades are shown with an endcap on the trailing edge in accordance with the present teachings.

DESCRIPTION OF VARIOUS EMBODIMENTS

As described above, incorporating a stabilizer cylinder into the design of a surface aeration impeller essentially dampens and eliminates any tendency of the surface aeration impeller to exhibit unwanted vibrations, oscillatory motions or displacements normal to the axis of rotation under any operating conditions and at any static liquid level height on the surface aeration impeller blades. Thus, the extensive bending forces on the impeller shaft and gearbox that occur infrequently, but unpredictably, are completely eliminated or are greatly reduced to have no negative impact on mechanical integrity. The fact that this new surface aeration impeller design can operate in a mechanically stable fashion at any static liquid level submergence of the impeller is unique in the industry. The stabilizer cylinder also has the unexpected and additional benefit of improving the gas-liquid mass transfer efficiency of surface aeration impellers, including the HI-FLO II aerator.
As referred to in this application, the term “stabilizer cylinder” refers to a substantially circular band of material that is positioned beneath the surface aeration impeller's mounting member. As referred to in this application, the “mounting member” is the solid object to which the surface aerator impeller blades are attached. The mounting member can be made of any rigid material (e.g., steel, plastic, aluminum, graphite composites) and is typically disc-shaped.
Referring to the Figures, there is shown in FIG. 1 a bottom perspective view of the improved surface aeration impeller 4 according to the present teachings. The surface aeration impeller 4 has a plurality of vertically extending blades 2 affixed to the underside of the mounting member 1. The blades 2 can be affixed to the mounting member 1 via any semi-permanent or permanent means (e.g., bolting, welding). The stabilizer cylinder 3 is positioned below the bottom surface of the mounting member 1.
The stabilizer cylinder 3 can be constructed of any rigid material (e.g., steel, aluminum, plastic, graphite composites and polymer composites). The type of stabilizer cylinder 3 material that is selected will depend on the type of liquid to be aerated by the surface aeration impeller. For example, certain liquids may undergo an unwanted chemical reaction when brought into contact with a steel stabilizer cylinder 3.
The stabilizer cylinder 3 can be any diameter compatible with the overall diameter of the surface aerator impeller 4. The stabilizer cylinder 3 diameter can be approximately less than or equal to the interior diameter of the blades 2 or less than the exterior diameter of the blades 2. As used in this application, “interior diameter of the blades” refers to the diameter of the inwardly-facing vertical edges of the blades 2, and the phrase “exterior diameter of the blades” refers to the diameter of the outwardly-facing vertical edges of the blades 2. In addition, the diameter of the stabilizer cylinder 3 can intersect the horizontal surfaces of the blades 2. In some embodiments of the present teachings, the diameter of the stabilizer cylinder 3 will depend on the nature of the liquid to be aerated and the type of aeration tank being used. For example, a stabilizer cylinder 3 diameter that is greater than the exterior diameter of the blades 2 will provide the greatest amount of surface aerator impeller 4 stabilization. However, a stabilizer cylinder 3 diameter that is greater than the exterior diameter of the blades 2 may reduce the efficiency of the surface aeration system by preventing the liquid from coming into contact with the full surface area of the blades 2.
FIG. 3 illustrates various embodiments of the present teachings. Referring to FIG. 3, the stabilizer cylinder 3 can be connected to the mounting member 1 by a plurality of rods 5, brackets, bolts, nuts, pins or other available hardware that allows for firm attachment. Preferably threaded rods 5, for example, can be constructed of any rigid material such as steel or plastic. In some embodiments, the rods 5 can be attached to the stabilizer cylinder 3 via fasteners that are affixed to the vertical surface of the stabilizer cylinder 3. The preferably threaded fasteners can be standard hardware nuts that have been affixed to the stabilizer cylinder 3 in such a way as to cause threaded holes of the hardware nuts to face towards the bottom surface of the mounting member 1. This arrangement allows for the stabilizer cylinder 3 to be repositioned along the rods 5, while also allowing complete removal of the rods 5 from the stabilizer cylinder 3 for ease of storage.
In various embodiments, the rods 5 can be permanently attached to the stabilizer cylinder 3 by welding or bolting them to the vertical surface of the stabilizer cylinder 3.
In some embodiments of the present teachings, and as shown in FIG. 3, the threaded rods 5 pierce the mounting member 1 and extend through the upper surface of the mounting member 1. A plurality of standard hex nuts and associated hardware can then be positioned along the threaded rods 5 above and below the mounting member 1 to firmly hold the stabilizer cylinder 3 below the mounting member 1. The hex nuts can be adjusted along the length of the threaded rods 5 to raise or lower the stabilizer cylinder 3 to the desired distance below the mounting member 1. It also enables the threaded rods 5 to be removed from the mounting member 1 for easy storage. In some embodiments, the threaded rods 5 are permanently attached (e.g., welded, riveted) to the bottom surface of the mounting member 1, extending downward therefrom.
The stabilizer cylinder 3 can be positioned up against the bottom surface of the mounting member 1, as shown in FIG. 1. In various embodiments, the stabilizer cylinder 3 can be positioned below the mounting member 2 so that it does not come into contact with the mounting member 1, as shown in FIG. 3. The location of the stabilizer cylinder 3 that is selected will depend on the nature of the liquid being aerated and the type of aeration tank being used. The further away from the mounting member 1 the stabilizer cylinder 3 is positioned, the greater the stabilization of the surface aeration impeller 4. However, positioning the stabilizer cylinder 3 further down into the liquid being aerated increases the risk of the stabilizer cylinder 3 encountering material known in the industry as “rags,” and other stringy materials that can become entangled in the surface aeration impeller 4 and reduce its performance. As used herein, the term “rags” generally refers to solid and semi-solid materials that are present in certain liquids undergoing aeration (especially wastewater in treatment plants).
In various embodiments of the present teachings, the space between the inside vertical edge of the blade 1 and the stabilizing cylinder 3 is filled in with metal. In some embodiments, the outer tip of the blade 1 is trimmed with an angled cut, thereby eliminating the usual point of contact that occurs at such outer tip. The stabilizer ring 3 can also be directly welded to the inside vertical edge of the blades 1, avoiding the need to suspend the ring 3 from mounting member 1. In these embodiments, the possibility of “rags” getting entangled in the supporting rods is eliminated.
The stabilizer cylinder 3 can be of varying heights that are compatible overall with the diameter of the surface aeration impeller 4. Determinations relative to height may take into account the nature of the liquid being aerated and the type of aeration tank being used. A general principle is that the greater the height of the stabilizer cylinder 3, the greater the stabilization of the surface aeration impeller 4. Referring to FIG. 2, the stabilizer cylinder 3 also provides an improvement in the oxygen mass transfer efficiency of the surface aeration impeller 4 as shown in the graph of FIG. 2.
The blades 2 of the present teachings have an optional additional segment known as an endcap. The endcap 6 is shown, for example, in FIG. 3. The endcap is a relatively flat geometric piece positioned essentially perpendicular to a vertical section 7 of the blade and connects the outer or trailing edges of both the vertical section 8 and a lower section 7 of the blade. While the exact shape of the endcap can vary widely, the critical feature of the endcap 6 is that it prevents liquid from flowing or “sliding” off the trailing edge of the blades 2 below the vertical section 8 and simultaneously enhances the uplifting or up-pumping capability of the surface aeration impeller 4. The inventors have found that an endcap 6 can significantly increase the power delivered, and simultaneously increase the standard aeration efficiency.
The section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described in any way.
While the present teachings are described in conjunction with various embodiments, it is not intended that the present teachings be limited to such embodiments. On the contrary, the present teachings encompass various alternatives, modifications, and equivalents, as will be appreciated by those of skill in the art.

Claims

1. A surface aeration impeller designed to rotate about an axis perpendicular to a liquid surface, said impeller comprising:

(a) a plurality of blades attached to a mounting member wherein said blades each have an inside vertical edge forming an interior diameter and an outside vertical edge forming an exterior diameter;

(b) said mounting member having a top surface and a bottom surface; and

(c) a stabilizer cylinder positioned below the bottom surface of said mounting member.

2. A surface aeration impeller designed to rotate about an axis perpendicular to a liquid surface, said impeller comprising:

(b) said mounting member having a top surface and a bottom surface; and

(c) a stabilizer cylinder positioned below the bottom surface of said mounting member, said stabilizer cylinder being physically attached to the bottom surface of said mounting member.

3. The surface aeration impeller according to claim 1 or 2, further comprising:

a plurality of essentially vertical blades attached to the underside of a horizontal mounting member wherein said blades each have an inside vertical edge forming an interior diameter and an outside vertical edge forming an exterior diameter.

4. The surface aeration impeller according to claim 1 or 2, wherein said blades additionally contain an endcap.

5. The surface aeration impeller according to claim 1 or 2, wherein the diameter of said stabilizer cylinder is less than or equal to the interior diameter of said blades.

6. The surface aeration impeller according to claim 1 or 2, wherein the diameter of said stabilizer cylinder is greater than or equal to the exterior diameter of said blades.

7. The surface aeration impeller according to claim 1 or 2, wherein the height of said stabilizer cylinder is less than the height of said blades.

8. The surface aeration impeller according to claim 1 or 2, wherein the height of said stabilizer cylinder is greater than the height of said blades.

9. The surface aeration impeller according to claim 1 or 2, wherein the height of said stabilizer cylinder is equal to the height of said blades.

10. The surface aeration impeller according to claim 1 or 2, wherein said stabilizer cylinder is attached to the mounting member with threaded rods and fasteners.

11. The surface aeration impeller according to claim 1 or 2, wherein said stabilizer cylinder is smaller than the interior diameter of said blades, and the outer surface of said stabilizer cylinder is directly attached to the inside vertical edge of each blade.

12. The surface aeration impeller according to claim 1 or 2, wherein the diameter of said stabilizer cylinder intersects the horizontal surface of said blades.

13. The surface aeration impeller according to claim 1 or 2, wherein said stabilizer cylinder is directly attached to the axis perpendicular to said liquid surface.