EP2331227A1

EP2331227A1 - Froth handling pump

Info

Publication number: EP2331227A1
Application number: EP09813648A
Authority: EP
Inventors: Robert J. Visintainer; Peter Hergt; Thillainatarajan Ravisundar; Christoph Jaeger
Original assignee: GIW Industries Inc
Current assignee: GIW Industries Inc
Priority date: 2008-09-11
Filing date: 2009-09-11
Publication date: 2011-06-15
Also published as: CL2011000316A1; BRPI0918015A2; MX2011002615A; US20100061841A1; AU2009291679A1; CA2732683A1; RU2011113962A; ZA201101013B; EP2331227A4; PE20110790A1; WO2010030841A1

Abstract

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.

Description

FROTH HANDLING PUMP

Related Applications

This is a continuation-in-part of application Serial No. 12/208,747, filed September 11 , 2008, the content of which is incorporated herein in its entirety.

Field of the Invention

The 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 Invention

Centrifugal 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 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 Invention

The 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.

Brief Description of the Drawings Figure 1 is a perspective view of an embodiment of the froth handling pump of the present invention.

Figure 2 is a side elevational cross-sectional view of the froth handling pump of Figure 1. Figure 3 is a perspective view of one embodiment of the impeller of the froth handling pump of Figure 1.

Figure 4 is a front view of the impeller of Figure 3 with the front shroud removed to show the vanes. Figure 5 is a schematic illustration of the gaseous venting scheme of the froth handling pump of Figure 1.

Figure 6 is a side rear view of the shroud of the impeller of Figure 3, illustrating the arrangement and geometry of the clearing vanes.

Figure 7 is a rear perspective view illustrating the optional auxiliary impeller on the rear shroud of the impeller of Figure 3.

Figure 8 is a perspective view of the de-aeration chamber of the froth handling pump of Figure 1.

Figure 9 is a side rear view of the de-aeration chamber of Figure 8.

Figure 10 is a perspective view of an alternative embodiment of the impeller of the froth handling pump of Figure 1.

Figure 11 is a front view of the impeller of Figure 10.

Figure 12 graphically demonstrates the head loss performance of the froth handling pump of the present invention with the closed-shroud configuration pumping a water-soap froth. Figure 13 graphically demonstrates the flow loss performance of the froth handling pump of the present invention with the open-shroud configuration pumping a water-soap froth.

Detailed Description of the Preferred Embodiments Referring to the Figures in general, and to Figures 1 and 2 in particular, the froth handling pump of the present invention is shown generally as 100. In its simplest embodiment, the froth handling pump 100 comprises a centrifugal pump casing 120, a novel impeller 140 mounted in the casing, and a de-aeration chamber 160 mounted to the rear side 124 of the pump casing 120. A conventional pump shaft 170 passes through the de-aeration chamber 160 and attaches to the hub 141 of the impeller 140. The shaft 170 is then mounted on a conventional pedestal 190 via a conventional bearing and bearing housing arrangement (not shown).

As shown in Figure 2, the pump casing 120 of the froth handling pump of the present invention is a conventional design for centrifugal slurry pumps; however, a modified, or more open inlet side may be contemplated for a particular froth handling application, or for alternative impeller configurations, as described below. Alternatively, as described in detail below, the front shroud may be eliminated in its entirety. Referring to Figures 2 through 5, the novel impeller 140 of the froth handling pump 100 is illustrated in detail. As best shown in Figure 3, one embodiment of the impeller 140 comprises a front shroud 142, a rear shroud 144, and a plurality of pumping vanes 146. As shown in Figure 3, the front shroud 142 is conventional for a centrifugal slurry pump; however, in an alternative embodiment, the front shroud 142 also may be modified for a particular froth handling application and could include a more open configuration, having a larger suction inlet diameter. As shown in Figure 4, the impeller 140 of this illustrated embodiment comprises a novel pumping vane 146 arrangement. To maximize the number of pumping vanes 146, as shown in Figure 4, full size vanes 146a and splitter vanes 146b are arranged in an alternating fashion about the circumference of the impeller 140. Splitter vanes 146b, as used herein and as shown in the Figures, are shorter, thus not extending radially inwardly as far toward the suction eye 147 as the fuller size pumping vanes 146a. As will be appreciated by those skilled in the pump art, the number of pumping vanes 146a, 146b is maximized within the constraints of vane thickness and minimum required passage size. It has been found, however, that the use of splitter vanes 146b helps to increase the effective number of pumping vanes 146 without "choking" the suction eye 147 of the impeller.

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 Figure 3, the pumping vane 146 geometry extends between the front 142 shroud (when included) and rear 144 shroud of the impeller 140 in a manner that provides maximum efficiency. The inventors have found that the size of the impeller 140, and thus the overall size of the pump 100, can be minimized by employing pumping vanes 146 that have a combination of high angle outlets, for maximum head, and conventional lower angle inlets for developing sufficient NPSH performance. In the exemplary embodiments shown and described herein, an outlet vane angle may be between about 80 degrees and 100 degrees, with 90 degrees being optimal. As used herein, pumping vane 146 angles are defined relative to the tangent of the impeller circumference; e.g., an outlet angle of 0 degrees would be tangential to the circumference of the impeller, while an outlet angle of 90 degrees is radial with respect to the center of the impeller, or perpendicular to the tangent of the impeller. 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 Figure 4, a plurality of vent holes 148 are formed through the rear shroud 144 of the impeller 140. The vent holes 148 are located for the effective venting of gases therethrough. For the bitumen application, for example, the vent holes 148 must provide a minimum opening of about 2 inches in diameter, or, if not circular, an area of about 3.14 square inches.

Turning now to Figure 5, the principle of operation of the novel froth handling pump 100 is schematically illustrated. As will be appreciated by those skilled in the art, when pumping a two-phase (gas and liquid, such as froth) flow, due to the centrifugal forces within the impeller, the gas (shown as G in Figure 5) separates from the liquid at the inlet of the impeller. This causes the gas to accumulate on the trailing faces of the impeller pumping vanes 146. As will also be appreciated, the continuous accumulation of gas during operation of the pump will eventually create "choking" of the impeller passage, resulting in cavitation and air lock of the impeller. By providing vent holes 148, as shown in Figure 6, at the appropriate circumferential locations through the rear shroud 144 of the impeller 140, the gases have outlets to escape from the impeller main passages. The size, shape, and relative positions of these vent holes 148 are influenced by the quantity and anticipated location for gas accumulation. In the illustrated embodiments shown in the Figures, the positions of the vent holes 148 correspond approximately to the suction diameter of the impeller.

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 Figure 6, the present invention comprises an impeller 140 having a plurality of clearing vanes 149a, 149b formed on the outer face 144a of the rear shroud 144. These clearing vanes serve several purposes: (1) they assist in balancing the axial thrust of the rotating impeller, and (2) they exert a static pressure equal to or greater than the main impeller vanes to restrict the inwardly entry of main (liquid) flow from the impeller outlet. Additionally, the clearing vanes 149a and 149b are formed such that, as the impeller rotates, the clearing vanes 149a, 149b create a pressure at the outer face 144a that is lower than the pressure in the impeller suction eye 147. By creating this differential pressure, the gases are drawn through the impeller vent holes 148 into the attached de-aeration chamber 160. As shown in Figure 6, the clearing vanes 149a, 149b are radially-oriented (90 degrees) and extend substantially perpendicularly outward from the outer face 144a of the rear shroud 144. In the embodiment shown, there are 18 clearing vanes 149a, 149b, comprising 12 short vanes 149a and 6 long vanes 149b; however, the total number of clearing vanes is not critical to the operation of the froth handling pump 100 of the present invention. Rather, the number, geometry, and angles of the clearing vanes are dependent upon the particular froth handling application. By forming the clearing vanes in the manner shown in Figure 6, i.e., with short and long vanes, the number of clearing vanes 149a, 149b may be maximized. In this embodiment, it also has been found that the clearing vanes 149a, 149b may need to be larger in diameter than the pumping vanes 146 by as much as 10 percent to obtain the desired pressure differential between the impeller suction eye 147 and the de-aeration chamber 160. This means that the clearing vanes 149a, 149b extend radially inwardly further than the pumping vanes 146.

In one embodiment, as shown in Figure 7, an auxiliary impeller configuration 180 may be rigidly mounted on the outer face 144a of the rear shroud 144. The inventors have found that this configuration assists in creating a negative pressure relative to the pumping vanes 146. As shown in Figure 7, the outer radius of the auxiliary impeller configuration 180 is greater than the maximum radial position of the vent holes 148 to prevent gases from being trapped on the outer face 144a. Turning now to Figures 8 and 9, the de-aeration chamber 160 is illustrated.

As shown in the Figures, the de-aeration chamber 160 has an inlet opening 162 having a diameter that is dimensioned to extend outwardly beyond the maximum radial position of the vent holes 148 in the rear shroud 144. The de-aeration chamber is thus rigidly coupled to the rear side 124 of the pump casing 120 by bolting or other conventional fastening means. As will be appreciated, pump casing 120 is modified from a conventional centrifugal pump casing, with an opening formed in the rear side 124 of the pump casing 120 corresponding in size to the inlet opening 162 of the de-aeration chamber 160. 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 Figures 2 and 9, an opening 165 is formed on the rear face 164 of the de-aeration chamber 160 for passage of the pump shaft 170 therethrough the chamber 160 for mounting to the impeller hub 142. At least one outlet 166 is formed for discharging the gases from the chamber 160. Depending on the particular froth handling application, the de-aeration chamber 160 may comprise a second outlet 168. For bitumen froth handling, for example, it has been found that the outlets 166, 168 should be at least about 3 inches in diameter to prevent clogging and to adequately vent the anticipated volume of gases. For the bitumen froth handling application, for example, it has been found that the outlet 166 should be located at about 22.5 degrees or less of vertical (in either direction from the vertical) for sufficiently releasing the gases. The outlet 166 may be provided with a flange 167 so that it may be interconnected to a discharge line (not shown) leading to a location suitable for discharging the vented gases. As will be understood, the vented flow may include some liquid discharge that should be diverted to a sump or other drainage location. Further, outlet 168 may be utilized for cleaning and drainage, as necessary.

Turning now to Figures 10 and 11 , an alternative embodiment of the novel impeller 240 of the froth pump 100 of the present invention is shown. As shown in Figure 10, the impeller is an open-shroud configuration, comprising only a rear shroud 244 and a plurality of pumping vanes 246, including full size vanes 146a and splitter vanes 146b. In this embodiment, with elimination of a front shroud, the pumping vanes 246 may be geometrically extrapolated outwardly axially toward the suction liner to compensate for the thickness of a front shroud. The inventors again have found that an outlet vane angle may be between about 80 degrees and 100 degrees, with 90 degrees being optimal. In all other respects, the configuration of the pump 100, including the de-aeration chamber 160, are similar to the closed- shroud configuration of the pump 100. 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 Figures 12 and 13, testing and performance data for both embodiments of the pump 100 are graphically illustrated. The testing was performed under similar conditions for both embodiments. A water-soap froth was formulated for the testing of the novel impellers. Figures 12 and 13 demonstrate the performance of the open-shroud froth handling impeller compared to the closed- shroud embodiment described herein. Data is provided with the venting system open and closed, and at two different flowrates above and below the pump design flowrate. The open-shroud froth impeller resists air lock at a higher percentage of air than the closed-shroud froth impeller. The open-shroud froth impeller also exhibits a lower degree of losses than the closed-shroud design after air lock, with the venting system operational.

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

We claim:

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 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:

(a) 6 main pumping vanes; (b) 6 splitter vanes; and wherein the pumping vanes and splitter vanes are arranged in an alternating configuration, having passages therebetween.

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.