Submerged pumping system with multi-strand cable

Abstract

 A submersible pumping system is disclosed for pumping cryogenic liquid from a reservoir (1) in which an electrically powered motor /pump unit (34/32) is located in an operative position at the bottom of a fluid transmitting casing (14) in the reservoir (1). The motor/pump unit (34/32) is electrically connected to a power source and to ground by means of flexible electrical and ground conduits (62/64), and is raised and lowered through the casing by means of support (56) and lift cables (76). The flexible conduits (62/64) and support cable (56) are arranged within a flexible sheath (60) to thereby provide a multi-strand cable which is separated from the lift cable (76) by detachable brackets (80).

Description

[0001] This invention relates generally to a submersible pumping system for discharging a reservoir such as the hull of a cargo ship or a land based storage vessel containing liquids, particularly cryogenic liquids such as liquified gases.

[0002] An example of one such pumping system is disclosed in U. S. Patent No. Re 31,445 (Carter). In this type of system, a fluid transmitting casing extends downwardly into the reservoir. The casing is closed at its upper end by a removable head plate which includes a sealing gland with a vertically shiftable lift element. The casing has a discharge outlet in an upper portion thereof leading to the exterior of the reservoir, and a foot valve at the lower end thereof which is yieldably biased to a normally closed position to isolate the casing from the reservoir. An integral unit consisting of a pump driven by an electrically powered motor is suitably configured and dimensioned to be passed through the upper casing end and to be raised and lowered through the casing to and from an operative position at the lower casing end where the unit exerts a force on the foot valve to open the same and thereby permit fluid to be pumped by the pump from the reservoir through the casing and out through the discharge outlet.

[0003] The motor is electrically connected to a junction point located beneath the head plate by means of flexible electrical conduits extending upwardly through the casing. Ground conduits similarly extends from the motor upwardly through the casing to a ground connection on the underside of the head plate. A flexible support cable extends from the unit up through the casing to the vertically shiftable lift element in the sealing gland, and a separate lift cable also extends from the unit up through the casing to the upper portion thereof for connection to an exterior lift mechanism.

[0004] When the motor/pump unit requires servicing, it is removed from the casing in the following manner: the unit is initially lifted off of the foot valve, by pulling up on the shiftable element of the sealing gland, which is turn is connected to the unit by the support cable. This allows the foot valve to close. Thereafter, a purge gas is introduced into the casing to force any residual fluid out of the casing through the foot valve back into the reservoir. The head plate is then disconnected from the upper casing end and raised to provide access to the casing interior. Once this has been accomplished, the lift cable is attached to a winch, the electrical and ground conduits are freed from their respective uppermost connections, and the support cable is detached from the vertically shiftable element of the sealing gland. The winch is then employed to extract the unit. During extraction, the electrical and ground cables and the support cable are either coiled on the top of the reservoir, or wound onto storage reels. Essentially the reverse procedure (except for the introduction of purge gas) is followed when introducing a pump/motor unit into the casing.

[0005] The above-described pumping system has been installed and is operating successfully in many locations throughout the world. There are, however, certain difficulties associated with this type of system. For example, during operation the upward liquid flow through the casing may cause the separate conduits and cables to undulate and to come into contact with each other. This can abrade the electrical conduits, thereby presenting a risk of an electrical short circuit. In extreme cases, the cables and conduits may become intertwined, making it difficult to remove the unit. Also, during removal, the several separate conduits and cables are awkward to handle and difficult to store on the top of the reservoir during pump removal.

[0006] Other pumping systems, which for-various reasons have fallen short of satisfactorily dealing with the above- noted difficulties, ad developed in U. S. Patent Nos. 3,876,126 (Haesloop et al); 4,080,106 (Haesloop); and 4,435,132 (Haesloop et al).

[0007] The objective of the present invention is to provide an improved arrangement for the electrical and ground conduits and the support and lift cables which obviates, or at least substantially minimizes, the above- noted difficulties.

[0008] According to a principle aspect of the present invention, the major lengths of the electrical and ground conduits and the support cable are encased in a common flexible abrasion resistent sheath, thereby providing a unitary multi-strand cable. The sheath is preferably foraminous to allow condensate to evaporate therethrough. Alternatively, however, the sheath can be impervious with its ends sealed to prevent condensate from forming therewithin. The lower ends of the support cable and electrical and ground conduits extend beyond the lower end of the sheath for connection to the motor/pump unit. Similarly, the upper ends of the support cable and electrical and ground conduits extend beyond the upper end of the sheath. The support cable is connected to the shiftable lift element of the sealing gland, the electrical conduits are connected to their junction point, and the ground conduit is connected to a ground connection. Contact between the multi-strand cable and the lift cable is largely prevented by detachable brackets which maintain the two in a laterally spaced relationship. To the extent that any such contact does take place, however, damage to the electrical conduits is prevented by the abrasion resistant sheath.

[0009] The electrical and ground conduits and the support cable are tightly contained within the sheath, thereby preventing abrasive damage which might otherwise result from relative movement between these components. As indicated previously, the foraminous nature of the sheath allows any condensation on the enclosed conduits and support cable to evaporate to the atmosphere following removal of the multi-strand cable from the casing. The support cable is sheathed with an electrical insulating material to protect it in the case of ground fault of the unit.

[0010] The protective sheath is preferably constituted of a metallic mesh, such as for example stainless steel. The detachable brackets loosely surround the multi-strand cable and are tightly secured to the lift cable. Collars are tightly secured to the multi-strand cable at locations adjacent to each bracket. As the lift cable is pulled upwardly to raise the motor/pump unit, the connecting brackets contact the collars to raise the multi-strand cable. The lift cable may be wound onto the rotating drum of a conventional hoisting apparatus, and as the connecting brackets arrive at the upper end of the casing, they are disconnected from the multi-strand cable and are allowed to slide on the lift cable The multi-strand cable then may be conveniently wound onto storage drum, or neatly coiled on the reservoir roof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] 

Figure 1 is a vertical sectional view showing a reservoir with a pump installation in accordance with the present invention, the motor/pump unit being in its lowered operative position;

Figure 2 is a perspective view of adjacent potions of the multi-strand cable and the lift cable separated by a spacer bracket;

Figure 3 is a sectional view of the spacer bracket taken along line 3-3 of Figure 2; and

Figures 4, 5 and 6 are schematic illustrations similar to Figure 1 showing various stages in the removal of the motor/pump unit.

DESCRIPTION OF PREFERRED EMBODIMENT

[0012] Referring initially to Figure 1, a tank 10 provides a reservoir R for any liquid and especially for liquified gas or cryogenic material such as natural gas, methane, butane, propane, ammonia, ethylene or the like. The liquid level L is somewhat below the roof 12 of the reservoir, and the intervening space may be filled with gas boiling off from the liquid, thereby pressurizing the reservoir to the vapor pressure of the liquid at the prevalent temperature. Alternatively, the intervening space may be filled with another preferably inert gas.

[0013] A cylindrical casing 14 extends vertically through the roof 12 and downwardly to a lower region of the tank. The casing is closed at its upper end by a removable head plate 16. A discharge outlet 18 in an upper portion of the casing communicates with the exterior of the tank. A purge gas inlet 20 is connected to the casing,: and the lower end of the casing carries a foot valve 22. The foot valve has a poppet 24 yieldably biased by springs 26 to a normally closed position (as shown in Figures 4 and 5) in sealing engagement with an annular valve seat 28 to thereby isolate the interior of the casing 14 from the reservoir R. An integral unit 30 consisting of a pump 32 driven by an electrically powered motor 34 is suitably dimensioned and configured to be passed through the upper casing end and to be raised and lowered through the casing to and from an operative position resting on a seat 36 herein illustrated as having a conical shape. When thus operatively positioned, as shown in Figure 1, the pump engages the foot valve poppet as at 38. The weight of the unit 30, augmented when necessary by a force exerted by purge gas introduced into the casing, overcomes the biasing action of the springs 26 and the differential pressure acting on the poppet, with the result that the valve poppet is pushed downwardly to provide an inlet opening 40 between the poppet 24 and the valve seat 28. Once the poppet has been opened, it no longer is subjected to a differential pressure between the tank and the casing, and consequently the weight of the unit will be sufficient to hold the poppet open without continued assistance by supplemental means such as the force of purge gas in the casing. During operation, the pump draws liquid from the reservoir R through opening 40 and pumps the liquid out through a pump discharge 42. From here, the liquid is forced up through the casing 14 where it exits through discharge opening 18.

[0014] The structure and operation of the foot valve 22 and motor/pump unit 30 is more fully described in the previously mentioned U.S. Patent No. RE 31,445 (Carter), the disclosure of which is incorporated herein by reference.

[0015] The head plate 16 includes a sealing gland 44 with a vertically shiftable element 46 having a lifting eye 48 at its upper end and a connecting eye 50 at its lower end. The eye 50 is detachably connected-by means of a U-bolt and cross pin assembly 52 to a support eye 54 which in turn is connected to the upper end of a flexible support cable 56. The lower end of the support cable is attached to a connection such as an eye 58 at the top of the motor/pump unit 30.

[0016] As can be best seen in Figure 2, the support cable 56 comprises part of a multi-strand cable 60 which also includes flexible electrical conduits 62 and at least one flexible ground conduit 64. The major lengths of these conduits are surrounded by and tightly enclosed along with flexible fillers indicated typically at 66 in a flexible preferably foraminous protective sheath 68. The upper and lower ends of the electrical conduits 62 and the ground conduit 64 extend respectively beyond the upper and lower ends of the sheath. The upper and lower ends of the electrical conduits are connected respectively to separable connectors 70 located beneath the head plate 16 and a junction box 72 on th,. motor 34. The upper and lower ends of the ground conduit 64 are connected respectively to a ground bracket 74 on the underside of the head plate 16 and the junction box 72.

[0017] A lift cable 76 is connected to the unit at a convenient location such as for example the eye 58 on motor/pump unit 30 and extends upwardly through the casing 14 in generally parallel relationship with the multi-strand cable 60, with the upper end of the lift cable being coiled when not in use on a storage bracket 78 on the underside of the head plate 16.

[0018] The multi-strand cable 60 and the lift cable 76 are laterally separated by a plurality of brackets 80. As can be best seen in Figures 2 and 3, each bracket 80 consists of two halves 80a,80b held together by a connecting bolt 81 or the like which can be loosened to permit lateral separation of the halves. The two halves 80a,80b tightly grip the lift cable 76 therebetween, thus fixing the position of each bracket 80 thereon. However, the two halves 80a,80b define an enlarged opening 82 which loosely receives the multi-strand cable 60. The brackets 80 are thus free to slide along the cable 60. Collars 84 are tightly fixed to the multi-strand cable 60 adjacent to each bracket 80. The collars 84 are too large to pass through the bracket openings 82.

[0019] The collars 84 have centering brackets 86 detachably connected thereto. The brackets 86 carry guide wheels 88 which are arranged to contact and roll along the inside of the casing. During operation of the installation, the support cable 56 is maintained in a taut condition, thereby minimizing undulation of the multi-strand cable 60 and the lift cable 76 (the latter by virtue of its connection to the multi-strand cable by brackets 80) within the casing.

[0020] Figure 1 illustrates all of the components of the pumping system in their operative positions. 'The motor/ pump unit 30 holds the foot valve poppet 24 in the open position, thereby permitting the pump to receive fluid from the reservoir R and to pump the fluid up through the casing 14 to the discharge port 18. As the fluid flows upwardly through the casing, it will have a tendency to produce undulations in the multi-strand cable 60 and the lift cable 76. The brackets 80 will serve to keep the cables 60 and 76 apart, thereby minimizing any tendency of the two to come into contact with one another. However, should such contact take place, the electrical conduits 62 and the ground conduit 64 will be safeguarded from damaging abrasion by the protective foraminous sheath 68. By virtue of the fact that the electrical and ground conduits 62,64 are tightly confined along with the fillers 66 within the sheath, movement of these conduits and cables in relation to each other will also be substantially inhibited, thereby further decreasing any possibility of damaging abrasion. Thus, the danger of electrical short circuiting resulting from conduit abrasion is substantially obviated.

[0021] With reference to Figure 4, when it becomes necessary to remove the motor/pump unit 30 to perform normal maintenance or to repair of replace worn components, a winch or other like lifting mechanism (not shown) is attached to the lifting eye 48 and the vertically shiftable element 46 is pulled upwardly through the sealing gland 44. The element 46 is connected to the motor/pump unit 30 by the support cable 56, and hence as the unit is raised, the foot valve poppet 24 is biased by the springs 26 into closed sealing engagement with the valve seat 28, thereby effectively isolating the casing interior from the reservoir R. Thereafter, purge gase is introduced through inlet 20. The purge gas forces any fluid in the casing 14 past the motor/pump unit 30 and back out through the foot valve 22 which now effectively acts as a one way check valve.

[0022] As shown in Figure 5, after the casing has been purged, the head plate 16 is detached from the casing and raised sufficiently to permit insertion of a support bar 90 through the support eye 54. The head plate is then lowered slightly until the support bar 90 comes to rest on the upper casing edge. At this point, the entire weight of the motor/pump unit 30 is carried by the support bar via the support cable 56. Thereafter, the electrical conduits 62 are disconnected from the junction point 70, the ground conduit 64 is disconnected from the ground bracket 74, and the U-bolt and crosspin assembly 52 is disconnected from the support eye 54, thereby freeing the head plate for removal to the side of the casing.

[0023] Once this has been accomplished, and as shown in Figure 6, the lift cable 76 is connected to a lifting device, for example a winch 92, which operates to continue lifting the motor/pump unit 30 out of the casing. The brackets 80 engage the collars 84 and thus cause the multi-strand cable 60 to be pulled upwardly along with the lift cable. As each collar 84 arrives at the upper end of the casing, its associated centering bracket may be detached and set aside. This allows the multi-strand cable 60 with its collars 84 either to be conveniently stored on a drum 94, or alternatively coiled on the roof of the tank. As each bracket 80 arrives at the upper end of the casing, it is detached from the multi-strand cable 60 while being allowed to remain loosely attached to the lift cable 76. Thus, the brackets 80 can slide along the lift cable as it is wound onto the winch 92.

[0024] Thus, maintenance personnel need only be concerned with two cables. Any moisture which condehses on the electrical and ground conduits may evaporate through the foraminous sheath 68 of the multi-strand cable, and the sheath will continue to protect the conduits from damage while they are being handled by maintenance personnel.

[0025] The same or a replacement motor/pump unit may be reintroduced into the casing and lowered to its operative position by essentially reversing the foregoing procedure, with the exception that there is no need to reintroduce purge gas into the casing during the installation phase.

[0026] In light of the foregoing, it will be appreciated by those skilled in the art that the present invention has a wide range of applicability to various submerged pumping systems, including for example those of the type disclosed in U. S. Patent Nos. 4,435,132 and 4,080,106, the latter having a rigid segmented lift element in place of the conventional flexible lift cable.

Claims

1. In a pumping system of the type having a fluid transmitting casing which is closed at its upper end by a removable head plate and which extends downwardly into a reservoir beneath the level of a fluid contained under pressure therein, the casing having a discharge outlet in an upper portion thereof leading to the exterior of the reservoir; and an integral unit consisting of a pump driven by an electrically powered motor, said unit being suitably dimensioned and configured to be passed through the upper casing end and to be raised and lowered through the casing to and from an operative position at the lower casing end at which position the pump operates- to withdraw fluid from the reservoir and to deliver said fluid through the casino and out through the discharge outlet, the improvement comprising: flexible electrical and ground conduits leading from the electrically powered motor to connectors at the upper casing end; a lift cable and a flexible support cable, each of said cables leading from the unit to the upper casing end for detachable connection to lifting means; a flexible sheath enclosing the major lengths of said support cable and said electrical and ground conduits to form a unitary flexible multi-strand cable, with the lower ends of said support cable and electrical and ground conduits extending beyond the lower end of said sheath for connection to said unit, and with the upper ends of said support cable and electrical and ground conduits extending beyond the upper end of said sheath for connection respectively to said lifting means and said connectors; and bracket means for laterally separating and detachably interconnecting said multi-strand cable and said lift cable, said bracket means being arranged at spaced locations along the respective lengths of said multi-strand cable and said lift cable.

2. The pumping system of claim 1 wherein said sheath is foraminous.

3. The pumping system of claim 2 wherein said sheath comprises a metallic mesh.

4. The pumping system of claim 1 wherein said bracket means loosely surrounds said multi-strand cable and is tightly clamped onto said lift cable.

5. The pumping system of claim 4 further comprising collars tightly clamped onto said multi-strand cable at locations closely adjacent to said bracket means, the segments of said multi-strand cable between said collars being movable longitudinally through said bracket means, and said collars being dimensioned to be engaged by said bracket means.

6. In a submersible pumping system for pumping cryogenic liquids from a reservoir in which an electrically powered motor/pump unit is located at an operative position submerged beneath the liquid surface at the bottom of a fluid transmitting casing extending downwardly into the reservoir, with flexible electrical and ground conduits leading from the operatively positioned pump/motor unit to the upper casing end for connection to a power source and to ground, and with an elongate flexible support element and an elongate lift element also extending from the operatively positioned pump/ motor unit to the upper casing end for detachable connection to lifting means, the improvement comprising: said flexible conduits and said support element being arranged within a flexible sheath to thereby provide a multi-strand cable; and bracket means detachably connected to said multi-strand cable for laterally separating the same from said lift element.

7. In a pumping system of the type having a fluid transmitting casing which is closed at its upper end by a removable head plate, and which extends downwardly into a reservoir adapted to contain fluid under pressure, the casing having a discharge outlet in an upper portion thereof leading to the exterior of the reservoir and a foot valve at the lower end thereof which is yieldingly biased to a normally closed position to isolate the casing from the reservoir, with an integral unit consisting of a pump driven by an electrically powered motor, said unit being suitably dimensioned and configured to be passed through the upper casing end and to be raised and- lowered through the casing to and from an operative position at which the unit exerts a force on the foot valve to open the same and thereby permit fluid to be pumped by the pump from the reservoir through the casing and out through the discharge outlet, the improvement comprising: flexible electrical and ground conduits leading from the electrically powered motor to connectors at the upper casing end; a flexible support cable leading from the unit to a vertically shiftable element in a sealing gland extending through the headplate; a flexible lift cable leading from the unit to the upper casing end for connection to a lifting mechanism for raising and lowering the unit after the unit has been elevated by means of the shiftable sealing gland element and support cable to accommodate closure of the foot valve followed by purging of fluid from the casing and removal of the head plate; a flexible foraminous sheath enclosing the major lengths of said support cable and said electrical and ground conduits to form a unitary multi-strand cable, with the lower ends of said support cable and electrical and ground conduits extending beyond the lower end of said sheath for connection to said unit, and with the upper , ends of said support cable and electrical and ground conduits extending beyond the upper end of said sheath for connection respectively to said shiftable sealing gland element and said connectors; and bracket means for laterally separating and detachably interconnecting said multi-strand cable and said lift cable, said bracket means being arranged at spaced locations along the respective lengths of said multi-strand cable and said lift cable.

Drawing