FROTH HANDLING PUMP
A froth handling pump includes a pump casing, an impeller mounted within the casing, and a de-aeration chamber mounted to the rear side of the pump casing. The impeller comprises multiple pumping vanes, each of the vanes having an inlet angle and an outlet angle, wherein the outlet angle is greater than the inlet angle, the outlet angles terminating at a rear shroud. The rear shroud includes multiple vent holes for the passage of gases therethrough. The de-aeration chamber, which comprises an inner volume, includes an inlet formed on the inner side for receiving gases passing through the plurality of vent holes. At least one vent outlet is provided for the discharge of gases from the de-aeration chamber.
This is a continuation-in-part of application Ser. No. 12/208,747, filed Sep. 11, 2008, the content of which is incorporated herein in its entirety.
FIELD OF THE INVENTIONThe present invention relates to the field of centrifugal slurry pumps, and particularly, to froth pumps for mining applications where flotation methods are utilized.
BACKGROUND OF THE INVENTIONCentrifugal pumps, as the name implies, employ centrifugal force to lift liquids from a lower to a higher level or to produce a pressure. This type of pump, in its is simplest form, comprises an impeller consisting of a connecting hub with a number of vanes and shrouds, rotating in a volute collector or casing. Liquid drawn into the center, or eye, of the impeller is picked up by the vanes and accelerated to a high velocity by rotation of the impeller. It is then discharged by centrifugal force into the casing and out the discharge branch of the casing. When liquid is forced away from the center of the impeller, a vacuum is created and more liquid flows into the center of the impeller. Consequently, there is a flow through the pump. There are many forms of centrifugal pumps, including the type used to pass solid and liquid mixtures. These are known as slurry pumps.
Froth handling pumps are a special application of centrifugal slurry pumps. The need to pump froth occurs in many mining applications where flotation methods are utilized. These pumps take advantage of the surface tension effects between pulverized ore and fine bubbles to separate the ore from the waste rock by floating one away from the other. The various mining applications include mining for metallic ores such as copper, iron, etc., and in the oil sand industry, where the components of froth include bitumen, water, and air. In the process of mining oil sands, for example, a mixture of approximately 10% bitumen and 90% sand is mined directly from the ground and the bitumen is separated from the sand for conversion to synthetic crude oil. As the separation takes place, gas develops, creating a bitumen froth with approximately a 15 percent to 30 percent gas/air content.
While froth is widely pumped in mining applications and much is known about the process, a number of problems exist with froth pumps themselves and the pumping process. First, froth handling pumps often “air lock.” This occurs when gases accumulate in the suction of the pump under the action of the centrifugal forces operating on the fluid in the passages of a rotating impeller to form an air/gas bubble, which partially blocks the suction and significantly degrades pump performance (as much as 40 percent to 70 percent loss in both flow and head). With viscous flows like bitumen, for example, this air lock can be particularly difficult to remedy due to the laminar, or near laminar, nature of the high viscosity flow. Even if the pump is stopped, the bubble can remain within the pump casing or connecting piping and may be drawn back into the pump suction upon restart. Second, froth pumps cannot typically produce as much head as non-froth applications, being limited by the presence of air (which cannot be effectively energized by the centrifugal pump), by the blockage which occurs as the air lock begins to form, and by the maximum speed at which the pump can be run before net positive suction head available (NPSHA) to the pump suction falls below the minimum required to prevent cavitation in the pump impeller. The head may be limited to as little as 30 meters to 40 meters in viscous froth applications, due to the additional viscous friction losses. This often necessitates that a number of pumps be placed in service to provide the necessary capacity for the mining and pumping process.
SUMMARY OF THE INVENTIONThe present invention is directed to a froth handling pump, which significantly minimizes or eliminates the problems described herein during ore or bitumen froth pumping. As used herein, “ore” refers to any of the many minerals and metals, which may be extracted through mining. Also, as used herein, “bitumen” refers to any of various flammable mixtures of hydrocarbons and other substances, occurring naturally or obtained by distillation from coal or petroleum.
Broadly, one aspect of the present invention is directed to a froth handling pump, which comprises either a conventional, or modified, pump casing having an inlet side and a rear (hub) side. A novel impeller has been invented, which can produce a head equal to or greater than existing froth slurry pumps, but without the application of some of the conventional methods for reducing the NPSH required, such as an enlarged suction diameter, an inducer or auxiliary impeller, etc., or by increasing the NPSHA beyond what is normally present. This, in effect, keeps the size of the froth handling pump smaller and more economical.
The pump achieves heads of 50 meters or higher at viscosities up to 3,000 cP and with NPSHA less than 10 meters by application of a very high vane outlet angle. While typical centrifugal pump outlet angles range from between about 15 degrees and 40 degrees, with 20 degrees to 25 degrees considered optimal, the impeller of the present invention has a vane outlet angle of between about 80 degrees and 100 degrees, with 90 degrees being optimal. Unexpectedly, the resulting efficiency is at least about 73 percent peak efficiency (with clear water).
The rear shroud of the impeller includes an inner face and an outer face, with a plurality of vent holes formed through the shroud for the passage of gases to an attached de-aeration chamber. A plurality of generally radially oriented clearing vanes are formed on the outer face of the rear shroud. The clearing vanes are configured to create a pressure at the back side of the vent holes that is less than the fluid side so that vented gases are drawn into the de-aeration chamber. An outlet vent is provided proximate the top of the de-aeration chamber for venting the gases to the atmosphere or to a connected vent line.
Further, while front shrouds are generally used in froth pump impellers, including one embodiment described herein, it has been found that removal of the front shroud of the impeller further serves to reduce the occurrence of air locks and to maintain maximum pump head and flow.
These and other aspects of the present invention will become apparent to those skilled in the art after a reading of the following description of exemplary embodiments when considered in conjunction with the drawings. It should be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.
Referring to the Figures in general, and to
As shown in
Referring to
For froth handling applications, it has been found that a minimum passage size of about two inches is sufficient. As used herein, “passage size” refers to the minimum mid-channel clearance between two adjacent pumping vanes 146. As best shown in
While the exemplary embodiments shown herein comprise an arrangement of 12 alternating full size 146a and splitter 146b pumping vanes, other pumping vane configurations also may provide suitable head and pumping efficiencies. For the pumping vane 146 configuration, as shown, having outlet angles of about 90 degrees, the inventors have found unexpectedly that a relative efficiency of at least about 73 percent may be achieved when pumping clear water.
As further shown in
Turning now to
By providing vent holes 148, as shown in
Although the vent holes 148 provide outlets for the gaseous phase to escape, the passage of the gases may be facilitated by creating a differential pressure between the main impeller passages and the outer face 144a of the rear shroud 144. Accordingly, and as shown in
In one embodiment, as shown in
Turning now to
As shown the Figures, the de-aeration chamber 160 comprises a housing 163 having an inner volume. As shown, the de-aeration chamber 160 is a passive component of the froth handling pump 100 construction; i.e., the chamber 160 has no moving or movable parts. As best shown in
Turning now to
It is believed that the open-shroud configuration creates greater shear and turbulence between the pumping vanes and the suction liner of the pump, which breaks up air bubbles and further delays the formation of an air lock bubble. The inventors have found that this effectively increases the suction diameter, which reduces the velocity at the inlet edge of the impeller, and thereby increases the static pressure at the inlet edge. Optionally, the diameter of the suction inlet of the pump casing 120 may be increased for the open-shroud impeller to provide more open suction, which is less subject to air blockage. This effectively reduces the velocity at the inlet edge of the impeller, and thereby increases the static pressure there, which delays vapor formation (cavitation).
Turning lastly to
Although the present invention has been described with exemplary embodiments, it is to be understood that modifications and variations may be utilized without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the appended claims and their equivalents.
Claims
1. A froth handling pump, comprising
- (a) a pump casing having an inlet side and a rear side;
- (b) an impeller mounted within the casing, the impeller comprising: (i) a rear shroud, comprising: (A) an inner face and an outer face; (B) a plurality of vent holes formed through the rear shroud for the passage of gases therethrough; (ii) a plurality of pumping vanes, each of the pumping vanes comprising: (A) inlet ends affixed to the inner face of the rear shroud and extending radially inwardly from the rear shroud; (B) an inlet angle and an outlet angle, wherein the outlet is angle is greater than the inlet angle, the outlet angles terminating at the rear shroud;
- (c) a de-aeration chamber mounted to the rear side of the pump casing and comprising: (i) an inner volume; (ii) an inner side mounted to the rear side of the pump casing; (iii) an inlet formed on the inner side for receiving gases passing through the plurality of vent holes; and (iv) at least one vent outlet for the discharge of gases therethrough.
2. The pump of claim 1, wherein the plurality of pumping vanes extending radially inwardly from the rear shroud terminate at free ends.
3. The pump of claim 2, wherein the space between the free ends of the pumping vanes and the inlet side of the pump casing being free of a front shroud;
4. The pump of claim 1, wherein the outlet angles of the pumping vanes are between about 80 degrees and about 100 degrees.
5. The pump of claim 4, wherein the outlet angles of the pumping vanes are about 90 degrees.
6. The pump of claim 1, wherein the pumping vanes comprise full size main pumping vanes, and splitter vanes of a lesser radial dimension.
7. The pump of claim 6, wherein the impeller comprises 12 pumping vanes comprising: wherein the pumping vanes and splitter vanes are arranged in an alternating configuration, having passages therebetween.
- (a) 6 main pumping vanes;
- (b) 6 splitter vanes; and
8. The pump of claim 1, wherein the passage size between adjacent pumping vanes is at least about 2 inches.
9. The pump of claim 1, further comprising a plurality of clearing vanes formed on the outer face of the rear shroud.
10. The pump of claim 9, wherein the plurality of clearing vanes are configured to create a pressure on the outer face of the rear shroud less than the pressure created by the pumping vanes.
11. The pump of claim 10, wherein the clearing vanes project outwardly from the outer face of the rear shroud at about a 90 degree angle.
12. The pump of claim 11, wherein the rear shroud has a central hub and wherein the clearing vanes have differing lengths extending radially outwardly relative to the central hub.
13. The pump of claim 9, wherein the clearing vanes are at least about 5 percent larger in diameter than the pumping vanes.
14. The pump of claim 1, wherein the vent holes in the rear shroud each have a minimum area of at least about 3.14 square inches.
15. The pump of claim 1, wherein the at least one vent outlet on the de-aeration chamber is positioned at an angle of less than about 45 degrees with respect to the vertical.
16. The pump of claim 15, wherein the at least one vent outlet is positioned at an angle of about 22.5 degrees with respect to the vertical.
17. The pump of claim 1, wherein the at least one vent outlet has an outlet diameter of at least about 3 inches.
18. The pump of claim 1, where the de-aeration chamber further comprises a drain outlet.
19. The pump of claim 1, further comprising an auxiliary impeller mounted to the outer face of the rear shroud.
20. The pump of claim 19, wherein the auxiliary impeller has an outer radius that is greater than the maximum radial position of the plurality of vent holes.
21. The pump of claim 1, wherein the impeller comprises a front shroud.
Type: Application
Filed: Aug 18, 2009
Publication Date: Mar 11, 2010
Inventors: Robert J. Visintainer (Augusta, GA), Peter Hergt (Ludwigshafen), Thillainatarajan Ravisundar (Clarendon Hills, IL), Christoph Jaeger (Gerolsheim)
Application Number: 12/543,303
International Classification: F04D 29/30 (20060101);