MAGNETICALLY COUPLED EXPANDER PUMP WITH AXIAL FLOW PATH

FIELD OF THE INVENTION

[0001] The following disclosure relates to a pump arrangement and in particular, to a magnetically coupled expander pump with an axial flow path.

DESCRIPTION OF THE RELATED ART

[0002] Magnetic couplings have been used in various applications related to pumping fluids, particularly when isolation of the pumped fluid is desired.

Typical magnetic coupling arrangements include disc ("face-to-face") magnetic drive arrangements, such as those described in U.S. Patent No. 5,332,374 (Kricker et al.), and coaxial canister-type coupling arrangements with axially aligned drive shafts, such as those described in U.S. Patent 5,464,333 (Okada et al.), which can be used to transfer torque to a completely isolated fluid path. In such typical arrangements, the fluid flow is necessarily redirected in a perpendicular direction between inlet and outlet as it passes through the pump. However, there are some applications in which such a redirection of the fluid flow is not desirable.

[0003] Some pumps with magnetic couplings are driven by a motor. However, it is possible for the driving torque to be provided by an expansion turbine. Such an arrangement is disclosed in International Patent Application No.

PCT/US 12/61165 (Fryrear et al.), to be published, which is incorporated by reference herein. In that International patent application, a working fluid is fed into one annulus of a set of concentric pipes and allowed to build pressure as it flows down a geothermal power wellbore. Within the wellbore, heat is added to the working fluid, and the hot, high pressure fluid then flows through an expander before returning to the surface in a lower density condition. The expansion of the working fluid provides torque that is used to drive the geothermal fluid pump. Fryrear et al. describes at least one embodiment of a canister-type cylindrical magnetic coupling that is used to transfer torque from the expander, which is positioned vertically above the pump. The geothermal fluid in the well feeds the inlet of the pump in the center of the well, but the geothermal fluid is discharged at the outlet of the pump in an essentially perpendicular direction with respect to the inlet direction, subsequently flowing up the well in the outer annulus.

SUMMARY

[0004] A need exists for a magnetically coupled, expander-driven pump, wherein the pumped fluid is able to flow through the center of the magnetic coupling.

[0005] In a first aspect of the present inventor's work, an expander pump unit is described in which an expander is located surrounding the pump. A pressurized working fluid provided in the annulus surrounding a center pipe flows through an expansion turbine (hereinafter referred to as an expander), causing it to rotate around the center pipe. The torque generated by the expander is transferred to a rotating drive shaft, which is coupled to the pump, in the middle of the center pipe via the use of an open-ended magnetic coupling. The pump increases the pressure of a pumped fluid contained within the center pipe to move the pumped fluid axially through the pipe.

[0006] The magnetic coupling described herein is comprised of outer and inner magnet-bearing cylinders, separated by a non-magnetic cylindrical wall that can be formed as a single unit or attached to the center pipe. The non-magnetic cylindrical wall provides separation of the two fluid streams. The outer magnet-bearing cylinder is integrated with the expander. The inner

magnet-bearing cylinder is connected to the pump shaft by rigid spokes around which fluid can pass.

[0007] This arrangement is applicable to a system in which a pressurized working fluid is being used to drive a pump, and in which the allowable apparatus diameter may be limited. More specifically, the pumped stream flow path is maintained in an axial direction, such as in a section of straight pipe, particularly as may be found in a wellbore for geothermal or oil and gas production.

[0008] In a second aspect of the present inventor's work, an expander pump unit is described, in which the pump is disposed in a pipe, and the pump is constructed to pump a first fluid. The pump unit includes an expander disposed in an annular space surrounding the pipe. The expander is driven by a second fluid flowing in the annular space. The expander pump unit further includes a magnetic coupling comprising an inner magnetic cylinder connected to the pump within the pipe and an outer magnetic cylinder connected to the expander surrounding the pipe. The inner magnetic cylinder has open ends in fluid communication with the pump.

[0009] In a third aspect of the present inventor's work, a pump unit is described, in which the pump unit includes a pump disposed in a pipe, and the pump is constructed to pump a first fluid. The pump unit also includes a pump driver constructed to drive the pump. The pump unit further includes a magnetic coupling comprising an inner magnetic cylinder connected to the pump within the pipe, and an outer magnetic cylinder connected to the pump driver surrounding the pipe. The inner magnetic cylinder has open ends in fluid communication with the pump.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The structures, articles, and methods claimed and/or described herein may be better understood by considering the non-limiting example embodiments presented below, in conjunction with the attached drawings, wherein:

[0011] Fig. 1 shows an example of a canister-type magnetic coupling described in International Patent Application No. PCT/US 12/61 165 (Fryrear et al.); [0012] Fig. 2a shows a sectional view of an expander pump unit in accordance with an example embodiment of the invention;

[0013] Fig. 2b shows an exploded sectional view of a portion of the expander pump unit shown in Fig. 2a; and

[0014] Fig. 2c shows an exploded sectional view of another portion of the expander pump unit shown in Fig. 2a.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENT(S)

[0015] In Fig. 2a an expander pump unit 100 is shown, which can be located below ground in a cased wellbore, such as may be used in a geothermal or oil and gas production well. A well casing 105 separates the surrounding geologic formation from fluid 101 contained within the well.

[0016] The expander pump unit 100 includes a down-hole expander 120 coupled to a fluid pump 110 via a magnetic coupling 114. The pump 110 is located within an inner pipe 107 and is connected to the magnetic coupling 114 via a pump shaft 112 and a plurality of spokes 117 around which the fluid 101 can freely flow. The expander 120 is located circumferentially around the inner pipe 107 and axially aligned with the magnetic coupling 114. An outer pipe 106 is located concentrically surrounding the inner pipe 107 and the expander 120, but extending to a lower end below the expander 120 and magnetic coupling 114.

[0017] A pressurized working fluid 102 flows in a downward direction in an annular space between the well casing 105 and the outer pipe 106. The working fluid 102 is prevented from flowing down the well further by a packer 108 which seals the space between the inner pipe 107 and the well casing 105 at some distance below the lower end of the outer pipe 106. Upon reaching the lower end of the outer pipe 106, the working fluid 102 reverses direction and begins flowing upward in an annular space between the inner pipe 107 and the outer pipe 106.

[0018] The upward flowing working fluid 103 is directed into the expander 120, which is located between the inner pipe 107 and outer pipe 106. As the upward flowing working fluid 103 flows through the expander 120, its pressure is reduced as it provides rotating torque to the rotating expander 120. Upon exiting the expander 120, the lower pressure working fluid 103 subsequently flows up the well between the outer pipe 106 and the inner pipe 107.

[0019] Attached to the rotating expander 120 is an outer magnetic cylinder 122, which is magnetically coupled to an inner magnetic cylinder 115. The two magnetic cylinders, 122 and 115, are separated by a non-magnetic section of the inner pipe 107. As the outer magnetic cylinder 122 rotates with the expander 120, the inner magnetic cylinder 115 also rotates, thereby transferring torque to the pump shaft 112 via the spokes 117.

[0020] When arranged in a well, the pump 110 can deliver produced fluids 101 upwardly from the producing formation to the surface. The produced fluids 101 flow through the rotating spokes 117 internal to the inner magnetic cylinder 115 before flowing into the pump 110. As the produced fluid 101 flows into the pump 110 it is directed into the first of several pump impellers 111 which increase the pressure of the produced fluid 101. Now at a higher pressure, the produced fluid 101 is able to flow to the surface inside the inner pipe 107.

[0021] Axial support for the pump shaft 112 is provided by a pump pressure balance chamber 113, as shown in greater detail in Fig. 2b.

[0022] As shown in Fig. 2b pressure balance chamber 113 is formed between a pump housing 140 and a disc 135 attached to an upper end of the pump shaft 112. A labyrinth seal 141 is interposed between the shaft 112 and the pump housing 140 to control the flow of fluid 101 into the pump pressure balance chamber 113. The disc 135 includes an upper seal 137, which is constructed to seal against a sealing surface 138 attached to the pump housing 140. The upper seal 137 is constructed, for example, from a low friction material that can also withstand high temperatures. One suitable material for the seal includes polyether ether ketone (PEEK). Of course, other suitable materials exist and are within the scope of the invention. A pump chamber valve 136 is comprised of the upper seal 137 and the sealing surface 138.

[0023] At startup and when the pump 110 is not operating, the pump chamber valve 136 is closed. During operation of the pump 110, the pump impellers 111 and pump shaft 112 experience a thrust in a downward direction, opposite the direction of produced fluid 101 flow. The pump pressure balance chamber 113 provides a means to offset the downward thrust so as to axially support the pump shaft 112. A portion of the pressurized produced fluid 101, shown by small solid arrows in Fig. 2b, flows past the pump chamber labyrinth seal 141 into the pump pressure balance chamber 113. The pressure of fluid 101 in the pump pressure balance chamber 113 increases, exerting increased pressure between the pump housing 140 and the disc 135 tending to open the pump chamber valve 136 by moving the pump shaft 112 in an upward direction. Fluid 101 flowing from the pump pressure balance chamber 113 through the open pump chamber valve 136 subsequently proceeds to flow around the disc 135 into a hollow bore 139 formed in the pump shaft 112, whereupon the fluid 101 flows to the relatively low pressure pump suction below the spokes 117, as shown in Fig. 2c.

[0024] Also, during operation, as pressure in the pump pressure balance chamber 113 decreases, the pump chamber valve 136 tends to close, allowing the disc 135 and the pump shaft 112 to move axially downward.

[0025] Fig. 2c shows a detailed view of the expander 120 and magnetic coupling 114. Inner magnetic cylinder 115 is shown with embedded inner magnets 116, and the outer magnetic cylinder 122 is shown with embedded outer magnets 123. The outer magnetic cylinder 122 functions as the inner wall of the expander 120. The expander is comprised of the outer magnetic cylinder 122, the expander outer wall 124, and a plurality of expander vanes 121, which connect the outer magnetic cylinder 122 to the outer wall 124. The expander vanes 121 convert the reduction of pressure in the working fluid stream 103 into rotating torque.

[0026] An outer labyrinth seal 126 and an inner labyrinth seal 127 are attached, respectively, to the expander outer wall 124 and outer magnetic cylinder 122 to control the flow of working fluid 103 bypassing the expander 120, as discussed in greater detail below. Fluid bearings 125, which can include foil bearings, are interposed between the expander outer wall 124 and the outer pipe 106 to radially support the expander 120. Axial support for the expander 120 is provided by a retaining ring 129, extending radially inwardly from the inner pipe 107, and an expander pressure balance chamber 130.

[0027] The expander pressure balance chamber 130 is formed between labyrinth seal 126, a lower sealing flange 134 extending from an upper edge 135 of the expander outer wall 124, and an upper sealing flange 128 extending inwardly from the outer pipe 106. The upper sealing flange 128 includes an upper seal 132, which is constructed to seal against a lower sealing surface 133 attached to the lower sealing flange 134. The upper seal 132 is constructed, for example, from a low friction material that can also withstand high temperatures. One suitable material for the seal includes polyether ether ketone (PEEK). Of course, other suitable materials exist and are within the scope of the invention.

[0028] An expander chamber valve 131 is comprised of the upper seal 132 and the lower sealing surface 133.

[0029] At startup and when the expander is not operating, the expander chamber valve 131 is open and the labyrinth seal 127 rests on ring 129. During operation of the expander 120, impellers 121 experience a thrust in the direction of the working fluid 103 flow tending to urge the lower sealing flange 134 upward so as to close the expander chamber valve 131. The expander pressure balance chamber 130 provides a means to offset the generated thrust. A portion of the high pressure working fluid 103, shown by small solid arrows in Fig. 2c, flows between the outer labyrinth seal 126 and outer pipe 106, through the fluid bearings 125, towards the expander chamber valve 131. The pressure of working fluid 103 in the expander pressure balance chamber 130 increases, exerting pressure on the upper sealing flange 128 and the lower sealing flange 134 tending to open the expander chamber valve 131 and thus moving the expander 120 in a downward direction opposite the direction of flow of working fluid 103. Fluid flowing from the expander pressure balance chamber 130 through the open expander chamber valve 131 subsequently proceeds into the relatively lower pressure annular space formed between the outer pipe 106 and inner pipe 107, above the expander 120.

[0030] Also, during operation, as pressure in the expander pressure balance chamber 130 decreases, the expander chamber valve 131 tends to close, allowing the expander 120 to move axially upward.

[0031] One skilled in the art will recognize that aspects of the present invention may be applied in numerous different applications, whether downhole or above ground. For example, in an embodiment disclosed herein, torque is provided to the outer portion of the magnetic coupling by a second working fluid stream. Other installations, particularly above ground, may instead provide a similar rotating torque to the outer magnetic cylinder by different mechanical means, such as a gear drive or a belt and pulley system. Such an arrangement would allow for true in-line pumping of a completely isolated fluid.

[0032] In other embodiments, a different type of pump may be selected. The embodiment herein discloses the use of a centrifugal pump. However, other pumps requiring rotating torque may be substituted, such as a twin-screw pump.

[0033] One skilled in the art may also recognize that the relative location of the various key parts may be altered. For example, the expander may be axially offset from the outer magnetic cylinder instead of the integrated design disclosed herein, or the relative axial locations of the pump and the magnetic coupling may be reversed. Also, in another embodiment, the flow direction of the working fluid may be reversed if it becomes advantageous to flow the working fluid downward in the annular space between the inner pipe and outer pipe.

[0034] While the present disclosure has been described with respect to what is presently considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.