GB2124929A

GB2124929A - Liquid gas separator

Info

Publication number: GB2124929A
Application number: GB08221263A
Authority: GB
Inventors: Lee Lawrence Che-Keung; Lee Stanley Kobylinski; Tyagi Mukul Kumar; Michael Wesley Furnas; Francis Theodore Traylor
Original assignee: TRW Inc
Current assignee: Northrop Grumman Space and Mission Systems Corp
Priority date: 1982-07-22
Filing date: 1982-07-22
Publication date: 1984-02-29
Also published as: GB2124929B

Abstract

A centrifugal liquid-gas separator apparatus which is particularly adapted for use downhole with a submergible pump in oil-producing wells comprises an elongated hub (30) having disposed on its periphery helical blades (60,62) defining a screw-type inducer (48) for pressurizing a liquid-gas fluid mixture entering the apparatus, axially extending vanes (62',70',72') defining a centrifugal separator (50) for separating the liquid and gas components of the fluid mixture, and smoothly curved blade segments (62'',70'',72'') which connect each blade with an associated vane and which are shaped to provide a smooth transition for the fluid mixture flowing between the inducer and the centrifugal separator. The apparatus is capable of providing a high relatively constant flow rate, even for large volumetric ratios of gas to liquid. <IMAGE>

Description

SPECIFICATION Liquid-gas separator apparatus Background of the invention This invention relates to separator apparatus and more particularly to downhole liquid-gas separators used in conjunction with submergible pumps.

Liquid-gas separators are used downhole in oilproducing wells to separate gas from crude oil before the oil enters the downhole pump. Any gas present in the oil supplied to the pump tends to reduce the volumetric efficiency of the pump. If excessive quantities of gas are present in the oil, "gas lock" can occur which completely restricts the flow of the oil through the pump. When "gas lock" occurs, the pump must be shut down for later restart. An effective liquid-gas separator reduces the occurrence of "gas-lock" and enables the pump to operate continuously and efficiently to pump more oil.

The prior art is replete with liquid-gas separators for downhole use. U.S. Patent No. 3,887,342 to Bunnelle, issued June 3, 1975, and U.S. Patent No.

4,088,459 to Tuzson, issued May 9, 1978 disclose centrifugal-type liquid-gas separators. U.S. Patent No. 2,969,742 to Arutunoff, issued January 1961, and assigned to the same assignee as the present invention, discloses a reverse flow-type liquid-gas separator. U.S. Patent No. 4,231,767 to Acker, issued November 4, 1980, also assigned to the same assignee as the present invention, discloses a screen-type liquid-gas separator. Although known centrifugal-type separators perform satisfactorily at low to moderate flow rates, they do not operate well at high flow rates, particularly as the volumetric ratio of gas to liquid increases, and they are unable to match the requirements of many high-capacity submergible pumps, resulting in the pump being "starved" and its output being reduced.Reverse flow-type separators also suffer from the same disadvantages. Screen-type separators perform well at high flow rates. However, over a period of time, their screens tend to become clogged, which re ducts the capacity of the separator.

It is desirable to provide liquid-gas separators which overcome these and other disadvantages of known separators, and it is to this end that the present invention is directed.

Summary of the invention The present invention provides liquid-gas separ ators which are capable of operating at high flow rates, even with a relatively large volumetric ratio of gas to liquid, and which are exceptionally effective to separate the liquid and the gas components of a downhole well fluid. In addition, the separators are smaller, less complicated, and less expensive to produce than known separator apparatus.

Briefly stated, a liquid-gas separator apparatus in accordance with the invention may comprise an elongated hub having means for connecting the hub to a rotary shaft, helical blade means defining a screw-type inducer disposed on a first longitudinal portion of the hub, vane means defining a centrifugal separator disposed on a second longitudinal portion of the hub, and curved blade segment means connecting the blade means and the vane means and shaped to provide a smoothly curved transition between the blade means and the vane means.

Brief description of the drawings Figure 1 is a longitudinal sectional view illustrating a liquid-gas separator apparatus in accordance with the invention; Figure 2 is a perspective view of a separator unit of the apparatus of Figure 1; Figure 3 is a top view of the separator unit of Figure 2; Figure 4 is a bottom view of the separator unit of Figure 2; Figure 5 is a diagram illustrating the operation of a known reverse flow-type separator at different volumetric ratios; and Figure 6 is a diagram illustrating the operation of a liquid-gas separator apparatus in accordance with the invention at different volumetric ratios.

Detailed description of the preferred embodiment Figure 1 illustrates a liquid-gas separator apparatus 10 in accordance with the invention. The apparatus comprises a tubular (preferably cylindrical) housing 12 adapted to extend longitudinally within and spaced from a well casing (not illustrated). The upper end of the housing is threaded onto a discharge head 14, which may be connected to the housing of a submergible pump 16 (illustrated diagramatically), and the lower end of the housing may be threaded onto an intake head 18, which may be connected to the housing of an electric motor 20 (also illustrated diagrammatically).Pump 16 and motor 20 may be a conventional submergible centrigugal pump and drive motor adapted for operation downhole in an oil well. A drive shaft 22 extends from the motor to the pump along the axis of the housing and through the intake head and the discharge head. Shaft 22 may be supported within the housing by sleeves 24 mounted in the discharge head and the intake head, and by a bearing assembly 26 mounted in the intake head.

The invention employs a separator unit 28 (shown in more detail in Figures 2-4) located within the housing between the intake head 18 and the discharge head 14. Separator unit 28 comprises an elongated tubular hub 30 having an axial bore 32 to enable the hub to be mounted coaxially on shaft 22 for rotation therewith. The hub may be connected to the shaft by a key (not illustrated) received in a keyway 34 (see Figures 2 and 4) within bore 32 and a corresponding keyway (not illustrated) in the shaft.

As shown in Figure 1,the hub may be located axially on the shaft by bushings 36 at opposite ends of the hub and by sleeves 38,40 mounted on the shaft by snap rings 42 received in circumferential grooves 44 in the shaft. Sleeve 40, at the upper end of the hub, may be the inner sleeve portion of a flow divider 46, to be described hereinafter.

As shown in Figures 1 and 2, disposed at different longitudinal positions on the periphery of hub 30 are pluralities of vanes and blades having different shapes. The vanes and blades are shaped to perform different functions, and they divide the separator unit into three distinct regions or stages. As will be described in detail hereinafter, the lower portion of the separator unit comprises a screw-type inducer 48; the upper portion of the separator unit comprises a centrifugal separator 50; and the portion between the inducer and the centrifugal separator comprises a transition region 52. The inducer pressurizes the liquid-gas fluid mixture entering intake ports 54 of intake head 18 sufficiently to force the fluid mixture through the separator apparatus.The centrifugal separator 50 communicates with the inducer via transition region 52 and imparts rotary or circular motion to the fluid mixture to separate the liquid and gas components thereof through centrifuge action.

The transition region 52 provides a smooth transition between the inducer and the centrifugal separator and is shaped to minimize losses.

As shown in Figures 1 and 2, inducer 48 of separator unit 28 comprises a pair of helical blades 60,62 disposed symmetrically about the lower portion of hub 30 to define a double helix screw-type inducer. Each blade has a radially extending leading edge 64, 66, respectively, located near the lower end of the hub adjacent to the intake head. As shown in Figure 2, blades 60, 62 are tapered (circumferentially) toward their leading edges so that the leading edges form sharp cutting blades. This reduces turbulence and cavitation in the fluid mixture entering the inducer. As shown in Figure 4, leading edges 64,66 are symmetrically disposed 180 apart on opposite sides of hub 30 and they lie in an axially extending plane indicated by the line A-A.

From their respective leading edges, blades 60,62 extend helically upwardly about hub 30 for a distance approximately equal to one-third the length of the hub. Preferably, each blade makes approximate lytwo complete revolutions (720 degrees) about the hub with a relatively small blade angle, û, with respectto a plane normal to the hub axis. In a preferred form, the blades have a two-inch lead or pitch, i.e., they traverse 360" in two inches of axial length. The blade angle Ovaries as a function of radius, r, in accordance with the equation tan o = p/2wr, where p = pitch, i.e., 2 inches in the above example.

At the inner radius of the blades (at the hub), the blade angle is preferably approximately 29.6 . At the outer radius of the blades, the blade angle is preferably approximately 10.6 . For a given radius, the blade angle of each blade 60, 62 is preferably constant as the blade extends helically upwardly about the hub.

In the transition region 52, the blade angle of each blade 60,62 varies as a linear function of axial length from the constant blade angle in the lower portion of the hub to a blade angle of 90 , i.e., vertical, in a circumferential distance of approximately 90 (one quarterturn about the hub). The blades then extend vertically upwardly for approximately the remaining length of the hub (in the centrifugal separator portion) forming substantially straight radially directed axially extending vanes 60', 62'.

As best shown in Figure 3, vanes 60', 62' are symmetrically disposed 1800 apart on opposite sides of hub 30, and lie in an axially extending plane indicated by the line B-B, which is normal to axial plane A-A. The one-quarter turn blade segments 60", 62" in transition region 52 provide a smoothly curved transition between helical blades 60, 62 and their corresponding axial vanes 60', 62', respectively. (It should be noted that fluid transition regions, in pumps for example, are conventionally shaped to provide a change in fluid velocity which is a linear function of distance, rather than shaped to provide a change in blade angle which is a linear function of distance, as in the invention.Designing transition region 52 in a conventional manner would result in an abrupt change in blade angle, which would produce undesirable losses.) In order to distribute the fluid mixture more evenly in the centrifugal separator portion of the apparatus, it is desirable to form the centrifugal separator 50 with another pair of axially extending vanes 70', 72', symmetrically disposed 180 apart on opposite sides of hub 30 and positioned at right angles to vanes 60', 62'. As shown in Figure 3, vanes 70', 72' are preferably located in axial plane A-A. Each vane 70', 72' is connected to an associated helical blade 70, 72, respectively, by an associated smoothly curved blade segment 70", 72", respectively, in transition region 52.Blade segments 70", 72" preferably have the same shape as blade segments 60", 62", and function in the same manner to provide a smooth transition between vanes 70', 72' and their associated blades.

Unlike blades 60,62, however, blades 70,72 do not extend to the lower end of hub 30. Rather, as shown in Figures 1 and 2, blades 70,72 terminate in tapered leading edges 74,76, respectively, just below the transition region 52. As best illustrated in Figure 1, each associated blade, blade segment and vane 70-70"-70', 72-72"-72' preferably traverses approximately 180 (one-half turn) about hub 30 so that leading edges 74,76 lie in axial plane A-A. Each blade segment 70", 72" may traverse approximately one-quarter turn about the hub and its associated blade 70,72 may traverse another one-quarter turn.

As is also shown in Figures 1 and 2, leading edges 74,76 of blades 70,72, respectively, are located midway between adjacent blades 60, 62. Blades 70, 72 serve to divide the fluid mixture flowing between blades 60,62 into two different paths to distribute the fluid mixture evenly between adjacent vanes of the centrifugal separator. Blades 70,72 do not extend to the lower end of hub 30 since this would unduly restrict the intake to the inducer.

As shown in Figures 14, the vanes, the blades, and the blade segments all have the same radial dimension, and extend to slightly less than the inner surface of tubular housing 12. Representative approximate dimensions for the separator unit may be: outer diameter 3.4 inches, length 1 f inches, inducer length 4 inches, centrifugal separator length 3.75 inches, and transition region length 3.25 inches.

As previously mentioned, inducer 48 pressurizes the fluid mixture sufficiently to force it through the separator apparatus 10, and the centrifugal separator 50 acts as a centrifuge to separate the liquid and the gas components of the fluid mixture. The centrifugal separator is designed to impart the maximum tangential velocity to the liquid-gas mixture. Because of its greater density, the liquid is centrifuged away from shaft 22 due to the rotary motion imparted to the fluid mixture by the vanes of the centrifugal separator, while the lower density gas tends to conform itself to the region about the shaft. Discharge head 14 may be formed with a plurality of channels 80 symmetrically disposed about its periphery (only one channel being illustrated in Figure 1) which in cooperation with a tubular sleeve 82 lining the interior surface of housing 12 form passageways for the liquid.Each channel may be connected to an upper chamber 84 in the discharge head, which comunicates with the pump impeller intake, by an upwardly angled passageway 86. Discharge head 14 may also have a lower chamber 88 formed about shaft 22 for receiving the gas, and may have a plurality of gas vents 90 symmetrically disposed about the discharge head (only one such gas vent being illustrated in Figure 1) which communicate with chamber 88.

Flow divider 46, which in the form illustrated comprises a spider assembly connected to shaft 22 for rotation therewith, aids in directing the separated liquid into channels 80 and in directing the separated gas into chamber 88. As shown, flow divider 46 may comprise an inner sleeve 40 having a bore through which shaft 22 passes, and an outer concentric cylindrical member 92 connected to sleeve 40 by spokes 94. The openings 96 between cylindrical member 92 and sleeve 40 provide passageways to chamber 88 for the gas, and the inner surface of the lower end of cylindrical member 92 is curved, as shown, to aid in collecting the gas leaving the centrifugal separator. The flow divider is spaced slightly above the centrifugal separator, as opposed to being formed on the centrifugal separator itself, to provide a settling time for the fluids leaving the centrifugal separator.This enables better separation of the liquid and the gas. Although, in the form shown, the flow divider is a separate member which is connected to the shaft 22 and which rotates with the shaft, if desired, the lower end of discharge head 14 may be configured to perform flow division.

In operation, pump 16, separator apparatus 10, and motor 20 are submerged down hole within the liquid-gas well fluid mixture. The liquid-gas mixture enters the intake ports 54 of intake head 18 through a perforated or slotted member 100 which assists in filtering debris from the fluid mixture. From the intake ports, the fluid mixture enters inducer 48 which pressurizes the fluid mixture and supplies it to the centrifugal separator 50 via transition region 52.

As previously described, the centrifugal separator separates the liquid from the gas and supplies the liquid to the impeller intake of the pump. The separated gas is vented via gas vents 90 into the space between the well casing (not illustrated) and the outer surface of the housings of the discharge head and pump.

Although a screw-type inducer has a smaller suction than a standard pump impeller and does not provide as high an output as a pump, a screw-type inducer has a number of advantages. To prevent pump cavitation and possible "gas lock", it is desirable to gradually increase the pressure of the fluid mixture entering the inducer. This is accomplished by maintaining the blade angle of the screw relatively small, as previously described. In addition, the tapered leading edges of the blades reduce turbulence in the fluid mixture and provide a smoother flow through the inducer. The smoothly curved transition region between the inducer and the centrifugal separator also contributes to a smooth fluid flow through the apparatus and minimizes undesirable losses. The flow rate through the separator apparatus is primarily a function of the blade angle and the length of the inducer.Since it is desirable to maintain a relatively small blade angle to prevent pump cavitation, the length of the inducer may be selected appropriately to provide a desired output flow and pressure.

Figures 5 and 6 contrast the performance of a liquid-gas separator apparatus in accordance with the invention (Figure 6) with the performance of a conventional reverse flow liquid-gas separator (Figure 5). As shown in Figure 5, the flow rate through the reverse flow separator decreases dramatically as the volumetric ratio of vapor (gas) to liquid increases. For example, at V/L = 0.20, the flow rate is approximately one-half of the flow rate of V/L = 0.In contrast, the curves of Figure 6, which were derived from tests performed on a liquid-gas separator apparatus in accordance with the invention, show that the flow rate through the separator apparatus of the invention changes very little with changes in volumetric ratio, and that even with a relatively large volumetric ratio ViL = 0.60, the flow rate is not substantially different from the flow rate at V/L = 0.

The curves of Figure 6 demonstrate that a liquid-gas separator apparatus in accordance with the invention is able to maintain a relatively constant flow rate over widely varying volumetric ratios, thereby ensuring that the submergible pump operates at close to its maximum efficiency. Remarkably, the invention achieves such improved results with a relatively simple and inexpensive construction.

While a preferred embodiment of the invention has been shown and described, it will be apparent to those skilled in the art that changes can be made in this embodiment without departing from the principle and spirit of the invention, the scope of which is defined in the appended claims.

Claims

1. A liquid-gas separator apparatus comprising an elongated hub having means for connecting the hub to a rotary shaft, helical blade means defining a screw-type inducer disposed on a first longitudinal portion of the hub, vane means defining a centrifugal separator disposed on a second longitudinal portion of the hub, and curved blade segment means connecting the blade means and the vane means, the curved blade segment means being shaped to provide a smoothly curved transition between the blade means and the vane means.

2. The apparatus of Claim 1, wherein the blade means comprises a pair of symmetrically disposed blades extending helically about the hub and longitudinally from a first end region of the hub towards the second portion.

3. The apparatus of Claim 2, wherein each blade makes approximately two revolutions about the hub and at a given radius has a substantially constant blade angle with respect to the axis of the hub.

4. The apparatus of Claim 3, wherein the blade angle with respect to a plane normal to the axis of the hub varies from approximately 30 at the hub to approximately 10 at the outer radius of the blade.

5. The apparatus of Claim 2, wherein each blade has a leading radial edge located in said first end region, and each blade is tapered toward its leading edge.

6. The apparatus of Claim 2, wherein the vane means comprises a pair of symmetrically disposed substantially straight radial vanes extending axially from a second end region of the hub towards the first portion.

7. The apparatus of Claim 6, wherein the blade segment means comprises a pair of curved blade segments connecting each vane to an associated blade.

8. The apparatus of Claim 7, wherein the blade angle between each blade segment and the axis of the hub varies as a linear function of axial distance.

9. The apparatus of Claim 6, wherein the vane means comprises another pair of substantially straight radial vanes symmetrically disposed on the second portion of the hub and extending axially from the second end region towards the first portion ofthe hub.

10. The apparatus of Claim 9, wherein the blade segment means comprises another pair of curved blade segments connected to the vanes of said other pair, the blade segments of said other pair being symmetrically disposed on opposite sides of the hub and positioned between the blade segments of the first-mentioned pair.

11. The apparatus of Claim 10, wherein the blade means comprises another pair of blades symmetrically disposed about the hub and connected to the blade segments of said other pair, and wherein each blade of said other pair makes approximately onequarter revolution about the hub and terminates in a leading edge located within said first portion and positioned between the blades ofthefirst- mentioned pair.

12. TheapparatusofClaim 11, wherein each blade segment extends approximately one-quarter revolution about the hub.

13. The apparatus of Claim 11, wherein the leading edges of the blade segments of said other pair are tapered.

14. The apparatus of Claim 1, wherein the elongated hub has an axial bore for receiving the shaft.

15. A liquid-gas separator apparatus for use with a submergible pump connected to a motor by a shaft, comprising a housing,the housing having inlet means for a liquid-gas fluid mixture and having first and second outlet means for separated liquid and gas, respectively, the shaft passing longitudinally through the housing, a screw-type inducer connected to the shaft within the housing adjacent to the inlet means for pressurizing the fluid mixture entering the housing, the inducer comprising helical blade means disposed about the shaft, a centrifugal separator for receiving the pressurized fluid from the inducer, the centrifugal separator comprising longitudinally extending vane means connected to the shaft for imparting rotary motion to the fluid mixture to separate the liquid from the gas, the vane means being connected to the blade means by blade segment means shaped to provide a smooth transition between the vane means and the blade means, and means for directing the separated liquid and gas to respective outlet means.

16. TheapparatusofClaim 15, wherein the blade means, the vane means, and the blade segment means are located on an elongated hub to form a unitary assembly that is coaxial with the shaft.

17. TheapparatusofClaim 16, further compris- ing means for connecting the hub to the shaft.

18. TheapparatusofClaim 15, wherein The blade means comprises a pair of helical blades symmetrically disposed about a first portion of the hub, the vane means comprises a pair of substantially straight vanes symmetrically disposed on a second portion of the hub, and the blade segment means comprises a pair of curved blade segments connecting each vane to an associated blade.

19. The apparatus of Claim 18, wherein each blade makes more than one revolution about the hub and has a leading edge adjacent to the inlet means.

20. TheapparatusofClaim 19, wherein the vane means comprises another pair of substantially straight vanes symmetrically disposed on the second portion of the hub, and the blade segment.

means comprises another pair of curved blade segments connected to the vanes of said other pair.

21. The apparatus of Claim 20, wherein the blade means comprises another pair of blades symmetrically disposed about the hub and connected to the blade segments of said other pair, said blades of the other pair terminating in leading edges axially positioned between the blades of the firstmentioned pair and axially displaced from the leading edges of the blades of the first-mentioned pair.

22. The apparatus of Claim 15, wherein the first and second outlet means are located within a discharge head at one end of the housing, the discharge head defining a chamber adjacent to the shaft and a plurality of channels spaced radially from and circumferentially about said chamber, the first outlet means for liquid comprising openings connecting said channels with an impeller intake of said pump, and said second outlet means for gas comprising a plurality of openings connecting said chamber with the exterior of the discharge head.

23. The apparatus of Claim 22, wherein the directing means comprises a flow divider connected to the shaft axially spaced from the centrifugal separator for directing the gas into the chamber and for directing the liquid into the plurality of channels.

24. The apparatus of Claim 23, wherein the flow divider comprises a sleeve coaxial with the shaft and a concentric cylindrical member spaced radially from the sleeve and connected thereto by spokes to define a plurality of openings therebetween that surround the shaft and communicate with the chamber.

25. The apparatus of Claim 24, wherein the cylindrical member is shaped to direct separated gas into said openings surrounding the shaft and to direct separated liquid into a space between an outer surface of the cylindrical member and in inner surface of the housing.

New claims filed on 11 April 1983 Superseded claims 1 and 15 New claims:

1. A liquid-gas separator impeller apparatus comprising an elongated hub having means for connecting the hub to a rotary shaft, helical blade means defining a screw-type inducer disposed on a first longitudinal portion of the hub for pressurizing a liquid-gas mixture entering the apparatus sufficiently to force the liquid-gas mixture through the apparatus, vane means defining a centrifugal separator disposed on a second longitudinal portion of the hub for separating the liquid and the gas components of the liquid-gas-mixture, and curved blade segment means disposed intermediate the blade means and the vane means, the curved blade segment means being shaped to provide a smoothly curved transition for smooth fluid flow between the blade means and the vane means.

15. A liquid-gas separator apparatus for use with a submergible pump connected to a motor by a shaft, comprising a housing, the housing having inlet means for a liquid-gas fluid mixture and having first and second outlet means for separated liquid and gas, respectively, the shaft passing longitudinally through the housing, a screw-type inducer connected to the shaft within the housing adjacent to the inlet means for pressurizing the fluid mixture entering the housing sufficiently to force the fluid mixture through the housing, the inducer comprising helical blade means disposed about the shaft, a centrifugal separator for receiving the pressurized fluid from the inducer, the centrifugal separator comprising longitudinally extending vane means connected to the shaft for imparting rotary motion to the fluid mixture to separate the liquid from the gas, blade segment means disposed intermediate the vane means and the blade means and being shaped to provide a smooth transition for smooth fluid flow between the blade means and the vane means, and means for directing the separated liquid and gas to respective outlet means.

26. Apparatus substantially as herein described with reference to Figures 1 - 4 and Figure 6 of the accompanying drawings.