Process swivel fluid barrier system

Abstract

A rotary interface (30) comprising inner (20) and outer (25) housings, a process fluid channel (18) at a rotary interface between the housings, first and second seals in a rotary gap (31) between the housings, a barrier fluid pump (80A), a gas supply system (70), a differential accumulator (40) having process fluid (46), barrier fluid (41) and gas (51) chambers and primary and secondary differential pistons operative between the process and barrier fluid chambers and between the gas and barrier fluid chambers, respectively, and a pneumatic secondary differential feedback system (85A) operatively configured to regulate the barrier fluid pump as a function of a parameter of the secondary differential piston (44), whereby barrier fluid is operatively provided to a barrier fluid gap (135) between the first (33) and second (34) seals at a barrier pressure greater than a process pressure of a process fluid in the process fluid channel.

Description

PROCESS SWIVEL FLUID BARRIER SYSTEMTECHNICAL FIELD

[0001] The presently disclosed subject matter relates generally to high pressure process swivels, and more particularly to a high pressure process swivel fluid barrier system.BACKGROUND

[0002] A process swivel assembly generally provides fluid or gas transfer across a rotating interface. Process swivel assemblies and swivel stack systems are used, for example, in floating or marine production systems in which one or more fixed production risers are connected to a surface vessel.

[0003] These systems require swivel assemblies because the riser remains in a fixed position while the vessel is free to rotate relative to the riser due to wind and current effects. Such production systems may include offshore oil and gas industry systems in which large floating vessels, such as a floating production storage and offloading (FPSO) vessel, are used to receive produced hydrocarbons from subsea wells or other subsea equipment. The floating vessel may be moored to a single point mooring (SPM) system via a mooring turret, which permits the vessel to weathervane and rotate 360 degrees about a single mooring point. The vessels use swivel assemblies to allow for the transfer of fluids across the rotary interface when the vessel weathervanes or rotates around the mooring site.

[0004] Production fluids can contain hy drocarbon liquids and gasses, water, solids, and other materials. Barrier fluid systems are generally used in conjunction with process swivels when hydrocarbon gas is present to prevent flammable gas escaping, which could create an explosive atmosphere around the turret. A barrier fluid system may be used to create an over pressured liquid barrier between the process fluid in the swivel and the environment. The over pressured barrier fluid, generally an oil, will leak into the process stream rather than allowing the process stream to leak in the other direction.BRIEF SUMMARY

[0005] With parenthetical reference to corresponding parts, portions, or surfaces of the disclosed embodiment, merely for the purposes of illustration and not by way of limitation, the present disclosure provides a rotary interface comprising: an inner housing (20, 220); at least one outer housing (25, 225) rotatably supported relative to the inner housing so that the outer housing is free to rotate about a center axis (x-x) relative to the inner housing at a rotaryinterface (30, 230) between the inner housing and the outer housing; a process fluid exchange channel (18, 218) extending across the rotary’ interface between the outer housing and the inner housing; the rotary interface comprising an annular rotary' gap (31, 131, 231) between an inner-facing surface (27, 127, 227) of the outer housing and an outer-facing surface (22, 122, 222) of the inner housing; an annular first seal (33, 133, 233) disposed in the rotary gap between the inner-facing surface of the outer housing and the outer-facing surface of the inner housing; an annular second seal (34. 134, 234) disposed in the rotary gap between the inner- facing surface of the outer housing and the outer-facing surface of the inner housing; the rotary' interface comprising an annular barrier fluid gap (35, 135, 235) disposed in the rotary’ gap between the inner-facing surface of the outer housing and the outer-facing surface of the inner housing and between the first seal and the second seal; a differential accumulator (40) comprising a process fluid chamber (46), a barrier fluid chamber (41), a gas chamber (51), a primary' differential piston (42, 44, 49, 47) operative between the process fluid chamber and the barrier fluid chamber, and a secondary differential piston (42, 44, 52) operative between the gas chamber and the barrier fluid chamber; a barrier fluid passage (63, 63A, 63B) extending between the barrier fluid chamber of the differential accumulator and the barrier fluid gap of the rotary gap of the rotary’ interface; a barrier fluid pump (80A) connected to the barrier fluid passage; a process fluid passage (66) extending between the process fluid chamber of the differential accumulator and the process fluid exchange channel; a gas passage (75) extending between the gas chamber of the differential accumulator and a gas supply system (70); and a pneumatic secondary differential feedback system (85A, 85B, 82) operatively configured to regulate the barrier fluid pump as a function of a parameter of the secondary' differential piston; whereby a barrier fluid is operatively provided to the barrier fluid gap between the first and second seals at a barrier pressure greater than a process pressure of a process fluid in the process fluid exchange channel.

[0006] The gas supply system may comprise: a gas tank (78) connected to the gas passage; a gas supply input (73) connected to the gas tank; and a valve (79) between the gas tank and the gas supply input; whereby the gas tank is operatively charged to a regulated pressure via the gas supply input. The gas supply system may comprise a gas supply input (73); the barrier fluid pump may comprise a gas driven pump (80A) connected to the gas supply input; the secondary' differential feedback system may comprise a first pneumatic limit switch (85 A, 185) operatively configured to sense the secondary differential piston translating beyond a first threshold position; the secondary differential feedback system may comprise apneumatic valve (82) between the gas supply input and the gas driven pump; and the first pneumatic limit switch may be connected (77A) to the pneumatic valve.

[0007] The pneumatic valve may comprise a pilot operated spool valve (82) having an open state and a closed state; and the first pneumatic limit switch may comprise a first plunger (90A, 190) operatively configured to translate relative to a first housing (91 A, 191) and having a first pilot open state and a first pilot closed state. The first housing of the first pneumatic limit switch may comprise a first pressure inlet port (86, 186) and a first pilot outlet port (88A, 188); and the pneumatic valve may comprise a first pilot input port (83 A) connected to the first pilot outlet port of the first pneumatic limit switch. Operative translation of the secondary differential piston beyond the first threshold position may actuate the first plunger to the first pilot open state; and actuation of the first plunger to the first pilot open state may actuate the spool valve to the open state; whereby the gas driven pump is operatively driven by the gas supply input to pump the barrier fluid to the barrier fluid gap. The secondary differential feedback system may comprise a second pneumatic limit switch (85B, 185) operatively configured to sense the secondary differential piston translating beyond a second threshold position; and the second pneumatic limit switch may be connected to the pneumatic valve. The second pneumatic limit switch may comprise a second plunger (90B, 190) operatively configured to translate relative to a second housing (91B, 191) and having a second pilot open state and a second pilot closed state. The second housing of the second pneumatic limit switch may comprise a second pressure inlet port (86, 186) and a second pilot outlet port (88B, 188); and the pneumatic valve may comprise a second pilot input port (83B) connected (77B) to the second pilot outlet port of the second pneumatic limit switch. Operative translation of the secondary differential piston beyond the second threshold position may actuate the second plunger to the second pilot open state; and actuation of the second plunger to the second pilot open state may actuate the spool valve to the closed state; whereby the gas driven pump is not operatively driven by the gas supply input to pump the barrier fluid to the barrier fluid gap. The first pneumatic limit switch may comprise a first spring (192) biasing the first plunger to the first pilot closed state and the second pneumatic limit switch may comprise a second spring (192) biasing the second plunger to the second pilot closed state. The first pressure inlet port (86) and the first plunger (90A) may be configured such that the first pressure inlet port provides a biasing of the first plunger to the first pilot closed state and the second pressure inlet port (86) and the second plunger (90B) may be configured such that the second pressure inlet port provides a biasing of the second plunger to the second pilot closed state.

[0008] The rotary' interface may comprise a secondary gas driven pump (80B) connected to the gas supply input and a valve (104) between the secondary gas driven pump and the gas supply input operatively configured to regulate flow from the gas supply input to the gas driven pump and the secondary gas driven pump. The gas supply input may be operatively configured to connect to a gas supply pump (71). The primary' differential piston may comprise a barrier surface area (43) exposed to the barrier fluid chamber and a process surface area (48) exposed to the process fluid chamber. The barrier surface area may be equal to or less than the process surface area. The secondary differential piston may comprise the barrier surface area exposed to the barrier fluid chamber and a gas surface area (53) exposed to the gas fluid chamber. The gas surface area may be greater than the barrier surface area. The primary’ differential piston may comprise a first primary piston head (42) having the barrier surface area, a second primary piston head (47) having the process surface area, and a rod (44, 49) extending betyveen the first primary- piston head and the second primary piston head. The secondary differential piston may comprise a secondary' piston head (52) having the gas surface area and the rod may comprise a first portion (44) extending betyveen the first primary piston head and the secondary piston head and a second portion (49) extending between the secondary piston head and the second primary piston head such that each of the first and second primary' piston heads translate with translation of the secondary’ piston head.

[0009] The rotary' interface may comprise a failsafe valve (101) between the barrier fluid passage and the process fluid passage, whereby in an open state the failsafe valve alloyvs the process fluid to bypass the first seal and floyv to the barrier fluid gap via the barrier fluid passage and such that the barrier fluid passage and the process fluid passage are pressure balanced. The rotary interface may comprise a backflow valve (102) in the barrier fluid passage between the failsafe valve and the differential accumulator, whereby in a closed state the backflow valve blocks the process fluid from flowing to the barrier fluid chamber of the differential accumulator when the failsafe valve is in an open state. The rotary interface may' comprise a bleed-off valve (100) betyveen the barrier fluid passage and the process fluid passage, whereby in an open state the bleed-off valve alloyvs the barrier fluid to bypass the first seal and flow to the process fluid exchange channel via the process fluid passage.

[0010] The rotary interface may comprise a barrier fluid input (62) connected to the barrier fluid pump and the barrier fluid passage. The barrier fluid input may be operatively configured to connect to a barrier fluid source (61). The gas may comprise air and the gas supply input may be operatively configured to connect to an air supply pump (71) of a vessel (HO).BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanying drawings are incorporated herein as part of the specification. The drawings described herein illustrate embodiments of the presently disclosed subj ect matter and are illustrative of selected principles and teachings of the present disclosure. However, the drawings do not illustrate all possible implementations of the presently disclosed subject matter and are not intended to limit the scope of the present disclosure in any way.

[0012] FIG. 1A is a schematic view' of an embodiment of an offshore system employing an embodiment of a high pressure process swivel with an embodiment of an improved barrier fluid system.

[0013] FIG. IB is a front and partial enlarged cross-sectional view of the high pressure process swivel shown in FIG. 1A.

[0014] FIG. 2 is an enlarged partial cross-sectional and schematic view of the rotary interface and barrier fluid system shown in FIG. IB.

[0015] FIG. 3 is an enlarged schematic view of the barrier fluid system shown in FIG. 2.

[0016] FIG. 4 is a cross-sectional view of a first embodiment of the pneumatic switch shown in FIG. 3 in a closed position.

[0017] FIG. 5 is a cross-sectional view of the pneumatic switch shown in FIG. 4 in an open position.

[0018] FIG. 6 is a cross-sectional view of an alternative embodiment of the pneumatic switch shown in FIG. 4.

[0019] FIG. 7 is a cross-sectional view of an alternative embodiment of the rotary interface shown in FIG. 2.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] At the outset, it should be clearly understood that like reference numerals are intended to identify the same structural elements, portions or surfaces consistently throughout the several drawing figures, as such elements, portions or surfaces may be further described or explained by the entire written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this invention. As used in the following description, the terms "horizontal", "vertical", "left", "right", "up" and "down", as well as adjectival and adverbial derivatives thereof (e g., "horizontally", "rightwardly"."upwardly", etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms "inwardly" and "outwardly" generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate.

[0021] It is to be understood that the specific assemblies and systems illustrated in the attached drawings and described in the following specification are simply exemplary- embodiments of the inventive concepts defined herein. Hence, specific dimensions, directions, or other physical characteristics relating to the embodiments disclosed are not to be considered as limiting, unless expressly stated otherwise. Also, although they may not be, like elements in various embodiments described herein may be commonly referred to with like reference numerals within this section of the application.

[0022] It is to be appreciated that the present teaching is by way of example only, not by limitation. The concepts herein are not limited to use or application with a specific system or method. Thus, although the instrumentalities described herein are for the convenience of explanation, shown and described yvith respect to exemplary embodiments, it will be appreciated that the principles herein may be applied equally in other types of systems and methods involving high pressure process swivels.

[0023] Where they are used herein, the terms “first,” “second,” and so forth, do not necessarily denote any ordinal, sequential or priority relation, but are simply used to distinguish one element or set of elements more clearly from another element or set of elements, unless specified otherwise. The term “pneumatic” is intended to include containing or operated by air or gas under pressure and the term “gas” is intended to include air.

[0024] An improved fluid barrier system for a high pressure process swivel is provided, a first embodiment of which is generally indicated at 15. As shown in FIG. 1, in an exemplary- embodiment, swivel 150 may be employed in offshore system 100. In system 100, floating production storage and offloading (FPSO) vessel 110 is moored to the ocean floor via anchoring lines 111 and mooring turret 112. Vessel 110 can w eathervane around geostationary turret 112 having various swivels or rotary j oints for providing fluid, power, and communications across the rotary joint when vessel 110 weathervanes or rotates around the mooring site and turret 112. Thus, for example, one or more risers (not shown) of a production system (not shoyvn) moored to the ocean floor may extend up to process or fluid swivel 150 on turret 112. Swivel 150 may be used in various alternative ty pes of floating production storage and offloading, in various types of subsea production systems and installations, and in various alternative applications to an offshore production or power system.

[0025] As shown in FIG. 1, in this embodiment process swivel 150 is a three pass swivel stack having inner shaft or housing segments 20, 20A and 20B supporting three separate stacked swivel outer housings or components 25, 25A and 25B, respectively. In this embodiment, base or mounting flange 20C of the inner housings 20, 20A and 20B is operatively attached to the riser of a production system moored to the ocean floor and the swivel outer housings 25, 25A and 25B are each attached to a floating vessel via torque arms 113, 113A and 113B. Outer housings 25, 25A and 25B are each rotatably supported on inner housings 20, 20A and 20B so that they are each operatively free to rotate about center axis x- x relative to inner housing segments 20, 20 A, 20B and 20C at rotary interfaces between inner housings 20, 20A and 20B and outer housings 25, 25A and 25B, respectively. As each of outer housings 25, 25A and 25B are operatively the same, this disclosure describes the fluid barrier system between inner housing 20 and outer housing 25 with the understanding that each of outer housings 25A and 25B have a similar structure and rotary interface fluid barrier system with inner housings 20A and 20B. While three stacked outer housings are shown, the number of outer housings in rotary engagement with an inner housing may be varied depending on the desired application. Also, the system may be used in alternative applications to an offshore production system.

[0026] As shown, outer housing 25 is rotatably supported on inner housing 20 so that outer housing 25 is free to rotate about center axis x-x relative to inner housing 20 at rotary interface 30 between inner housing 20 and outer housing 25. Annular fluid exchange cavity, passage, chamber, or channel 18 is formed at rotary interface 30 between outer housing 25 and inner housing 20. Rotary interface 30 between inner housing 20 and outer housing 25 is defined by upper annular rotary gap 31, which is above annular channel 18 and between upper inner- facing surface 27 of outer housing 25 and upper outer-facing surface 22 of inner housing 20, and lower annular rotary gap 131, which is below' annular channel 18 and between lower inner- facing surface 127 of outer housing 25 and low er outer-facing surface 122 of inner housing 20. Upper annular rotary' gap 31 is in limited fluid communication with annular process fluid channel 18 via an upper annular entrance or throat and lower annular rotary gap 131 is in limited fluid communication with annular process fluid channel 18 via a lower annular entrance or throat.

[0027] With reference now' to upper rotary gap 31 shown in FIG. 2, annular seals 33 and 34 are disposed in annular rotary gap 31 between inner-facing surface 27 of outer housing 25 and outer-facing surface 22 of inner housing 20. Thus, annular seals 33 and 34 are disposed in annular rotary gap 31 above the throat between inner-facing surface 27 of outer housing 25and outer-facing surface 22 of inner housing 20 to dynamically seal rotary gap 31. Seals 33 and 34 are thereby located in gap 31 between stationary inner housing 20 and rotating outer housing 25 to contain process fluids within annular channel 18 therebetween and prevent fluid from leaking past the two radially opposed surfaces 22 and 27 when high pressure process fluid is present in annular channel 18.

[0028] A similar barrier fluid system and sealing arrangement is employ ed below annular exchange channel 18 to seal leakage of high pressure fluid out of annular exchange channel 18 through gap 131 between inner housing 20 and outer housing 25. Annular seals 133 and 134 are disposed in annular rotary gap 131 between inner- facing surface 127 of outer housing 25 and outer-facing surface 122 of inner housing 20. Thus, annular seals 133 and 134 are disposed in annular rotary gap 131 below the throat between inner-facing surface 127 of outer housing 25 and outer-facing surface 122 of inner housing 20 to dynamically seal rotary gap 131. Seals 133 and 134 are thereby located in gap 131 between stationary inner housing 20 and rotating outer housing 25 to contain process fluids within annular channel 18 therebetween and prevent fluid from leaking past the two radially opposed surfaces 122 and 127 when high pressure process fluid is present in annular channel 18.

[0029] In a representative embodiment, seals 33, 34, 133 and 134 may comprise an annular primary seal and a stiffer or more rigid annular back-up ring and the annular primary seal may comprise a seal jacket and a seal spring energizer. The back-up ring may provide additional extrusion resistance to the high pressures acting on the seal. In this embodiment, seals 33, 34, 133 and 134 operate as dynamic seals across rotary gaps 31 and 131, respectively, at the rotational interface between inner housing 20 and outer housing 25.

[0030] To aid in the axial pressure balance between the top and bottom of seals 33 and 133, hydraulic barrier system 15 is provided. With hydraulic barrier system 15, seals 33 and 133 may be operatively configured such that a separate axial barrier fluid is provided at a high pressure to gaps 35 and 135, respectively, to provide axial pressure balance or an axial counter load to the opposed process fluid pressure acting axially on seal 33 from process fluids below seal 33 and acting axially on seal 133 from process fluids above seal 133. As shown, annular barrier fluid gap 35 is formed radially between outer-facing surface 22 of inner housing 20 and inner- facing surface 27 of outer housing 25 and axially between seal 33 and seal 34. Barrier fluid system 15 is connected to barrier fluid gap or chamber 35 via barrier fluid passage 63 and branch 63 A in housing 20. With this hydraulic and pneumatic circuit, swivel 150 may be operative configured such that a separate balancing barrier fluid is provided at a high pressure to chamber 35 as described below. Similarly, annular barn er fluid gap 135 is formed radially between outer-facing surface 122 of inner housing 20 and inner-facing surface 127 of outer housing 25 and axially between seal 133 and seal 134. Barrier fluid system 15 is connected to barrier fluid gap or chamber 135 via barrier fluid passage 63 and branch 63B in housing 20. With this hydraulic and pneumatic circuit, swivel 150 may also be operative configured such that the separate balancing barrier fluid is also provided at a high pressure to chamber 135.

[0031] As shown in FIGS. 2 and 3, in this embodiment fluid barrier system 15 generally comprises hydraulic barrier fluid subsystem 60, hydraulic process fluid subsystem 65, pneumatic air subsystem 70, differential accumulator 40, pneumatic limit switches 85A and 85B, pneumatic spool valve 82, and air-driven barrier fluid pumps 80A and 80B.

[0032] Hydraulic barrier fluid subsystem 60 is operatively configured to extend between barrier fluid source 61, barrier fluid cavities 35 and 135, and barrier fluid chamber 41 of accumulator 40 and to operatively and selectively hydraulically link pump 80A or 80B, barrier fluid cavities 35 and 135, and barrier fluid chamber 62. In this embodiment, subsystem 60 includes barrier fluid input line 62 linking barrier fluid source 61 and barrier fluid charge pumps 80A and 80B, barrier pump line 63 linking pumps 80A and 80B and barrier fluid cavities 35 and 135, and barrier fluid chamber line 64 linking fluid cavities 35 and 135 and barrier fluid chamber 41 via pump line 63. One-way check valve 102 is provided in pump line 63 to block barrier fluid flow from barrier fluid cavity 35 or 135 to either pumps 80A and 80B or barrier fluid chamber 41 of accumulator 40.

[0033] Hydraulic process fluid subsystem 65 is operatively configured to extend between process fluid channel 18 and process fluid chamber 46 of accumulator 40 and to operatively hydraulically link fluid channel 18 and process fluid chamber 46. In this embodiment, subsystem 66 includes process fluid line 66 directly linking process channel 18 and process fluid chamber 46.

[0034] As shown in FIG. 3, system 15 includes bypass line 67 extending between pump line 63 and process fluid line 66, with the junction to pump line 63 being between valve 102 and barrier fluid cavities 35 and 135. One-way check valve 101 is provided in bypass line 67 to block barrier fluid flow from barrier fluid cavity' 35 or 135 to process fluid line 66 in a closed state and to open when pressure on the line 66 side of valve 101 exceeds pressure on the opposite line 63 side of valve 101. Thus, in an open state failsafe valve 101 allows the process fluid to bypass seals 33 and 133 and flow to barrier fluid cavities 35 and 135 via barrier fluid line 63 and such that barrier fluid passage 63 and the process fluid passage 66 are pressure balanced.

[0035] As shown in FIG. 3. system 15 also includes bypass line 68 extending between pump line 63 and process fluid line 66, with the junction to pump line 63 being between valve 102 andbarrier fluid cavities 35 and 135. One-way check valve 100 is provided in bypass line 68 to block barrier fluid flow from process fluid line 66 to barrier fluid cavities 35 and 135 in a closed state and to open when pressure on the line 63 side of valve 100 exceeds pressure on the opposite line 66 side of valve 100. Thus, in an open state bleed-off valve 100 allows the barrier fluid to bypass first seals 33 and 133 and flow to process fluid channel 18 via process fluid line 66 and such that barrier fluid passage 63 and the process fluid passage 66 are pressure balanced.

[0036] Accordingly, valve 101 in passage 67 acts as a failsafe valve if air supply is lost allow ing process fluid to bypass seals 33 and 133 and press against the inside of seal 33 via cavity 35 and the inside of seal 133 via cavity 135. This protects the seals from potential damage due to back pressure. V alve 100 allows barrier fluid to bleed off into the process fluid when process fluid pressure is reduced. And valve 102 prevents fluid from being forced back into accumulator 40 if failsafe valve 101 opens.

[0037] Pneumatic subsystem 70 is operatively configured to extend between air pump 71, air driven pump 80A or 80B, air switches 85 A and 85B, air tank 78 and air chamber 51 of accumulator 40 and to operatively and selectively pneumatically link air pump 71, air driven fluid pump 80A or 80B, switches 85A and 85B, air tank 78 and air chamber 51 of accumulator 40. In this embodiment, subsystem 70 includes air input line 72 linking air pump 71 and air driven pumps 80A and 80B, air switch line 76 linking air pump 71 and pneumatic switches 85 A and 85B via input line 72, and air chamber line 74 linking air pump 71 , air tank 78 and air chamber 51 via input line 72 and chamber input line 75.

[0038] In this embodiment, air pump 71 may comprise the air supply system of vessel 110, which may for example and without limitation supply air at about 100 PSI and 10 CFM. Air conditioning unit 73 conditions the air from pump 71 for use in system 15. For example, unit 73 may include an air regulator configured to maintain lines 72 and 74 at a constant air pressure, such as about 80 PSI for example and without limitation.

[0039] Air tank 78 is operatively configured to be filled with air from pump 71 to a desired operating pressure and communicates directly with air chamber 51 of accumulator 40 via input line 75 so as to charge chamber 51 to such desired air pressure. Air regulator 79 in charge line 74 between input line 72 and tank 78 and air chamber 51 is configured to maintain tank 78 at a desired air pressure range, such as for example and without limitation a maximum of 75 PSI and a minimum of 22 PSI. Check valve 102 is provided in charge line 74 to block air flow back out from tank 78 and air chamber 51 of accumulator 40.

[0040] Directional valve 104 is provided between conditioner 73 and air driven barrier fluid pumps 80A and 80B to direct air from air supply 71 to either pump 80A or pump 80B. In thisembodiment, pump 80A is the primary barrier fluid pump and pump 80B is a redundant or backup pump that is only operated in the event of a failure at primary pump 80A. In the event of such a failure, valve 104 switches from being open betw een input line 72 and pump line 72A and closed between input line 72 and pump line 72B so as to only operate pump 80A, to being open between input line 72 and pump line 72B so as to only operate pump 80B.

[0041] As shown in FIGS. 2, 3 and 7, accumulator 40 generally comprises piston heads 42, 47 and 52 orientated about axis 55A and slidably disposed within dual-diameter cylindrical housing 55 orientated about axis 55 A such that piston heads 42, 47 and 52 may be driven together in both directions along axis 55A relative to housing 55. As shown, cylinder housing 55 has first and second end portions 56 and 57 of a first diameter and center portion 58 between end portions 56 and 57 of a greater second diameter. Thus, piston 42 is slidably disposed within cylindrical housing portion 56 such that piston 42 may be driven in both directions relative to housing portion 56, piston 47 is slidably disposed -within cylindrical housing portion 57 such that piston 47 may be driven in both directions relative to housing portion 57, and piston 53 is slidably disposed within cylindrical housing portion 58 such that piston 53 may be driven in both directions relative to housing portion 58. Piston 42 is connected to one side of piston 52 by actuating rod 44 and piston 47 is connected to the other side of piston 52 by actuating rod 49 such that pistons 42, 47 and 52 move together relative to housing 55 along axis 55 A. In this embodiment, pistons 42 and 47 have the same outside diameter and piston 52 has an outside diameter greater than the outside diameter of each of pistons 42 and 47.

[0042] Pistons 42 and 47, connected by rods 44 and 49, sealingly separate left chamber 41 from right chamber 46. In this embodiment, the leftwardly -facing annular vertical end surface 43 of piston 42 faces into left chamber 41 and the rightwardly -facing annular vertical end surface 48 of piston 47 faces into right chamber 46, creating an equal piston area configuration with respect to primary piston pairings 42 and 47. As shown, one side or port of barrier fluid pump 80A communicates with chamber 41 via fluid line 64 and the opposite side or port of barrier fluid pump 80A communicates with fluid supply line 62. Process channel 18 communicates with chamber 46 via process fluid line 66.

[0043] Pistons 42 and 47, connected by rods 44 and 52, sealingly separate left chamber 41 from center chamber 51. Leftwardly -facing annular vertical end surface 43 of piston 42 faces into left chamber 41 and rightwardly -facing annular vertical end surface 53 of piston 52 faces into right chamber 51. In this embodiment, end surface 53 of piston 52 has a greater surface area than end face 43 of piston 42. creating an unequal piston area configuration with respect to secondary piston pairings 42 and 52. Air tank 78 communicates with chamber 51 via air line 75.

[0044] Thus, differential accumulator 40 is connected to both the process fluid, via process fluid subsystem 65. and the barrier fluid, via barrier fluid subsystem 60. The two pistons 42 and 48, which are a continuous rod in the present embodiment, are equally sized in the present embodiment creating a balanced pressure component. As air supply 71 is activated, air chamber 51 and air tank 78 are charged to a predetermined regulated pressure. The compressed air acts as an air spring that pushes air piston 52 toward barrier fluid end 56. The air pressure, which can be adj usted, determines how much additional pressure is created in the barrier fluid than in the process fluid.

[0045] As shown in FIG. 3, activation limit switch 85A is mounted on the barrier side of center portion 58 and is operatively configured to sense when air piston 52 translates to the left beyond a low barrier pressure threshold by contact with air piston 52. Completion limit switch 85B is mounted on the process side of center portion 58 and is operatively configured to sense when air piston 52 translates to the right beyond a high barrier pressure threshold by contact with air piston 52.

[0046] As shown in FIGS. 4 and 5, each of switches 85A and 85B are specially configured three way, two position, normally closed, monostable, direct controlled pneumatic valves having supply pressure inlet port 86 connected to air supply 71 via air switch pressure line 76, pilot outlet port 88 connected to valve 82, and vent port 89 to the environment. Switches 85A and 85B each generally comprise plunger 90 slidably disposed within housing 91 such that plunger 90 and poppet 93 may translate relative to housing 91 and valve sleeve 94 between a closed position, shown in FIG. 4, and an open position, shown in FIG. 5. In the closed position shown in FIG. 4, the connection between supply port 86 and pilot outlet port 88 in sleeve 94 is blocked and pilot outlet port 88 is instead air flow connected to vent port 89 and the environment. In the open position shown in FIG. 5, supply port 86 is air flow connected to pilot outlet port 88 and the connections between supply port 86 and pilot outlet port 88 and vent port 89 are blocked such that air flows from supply port 86 to pilot port 88. Spring 92 operates between plunger 90 and poppet 93 such that poppet 93 is biased to move to the open position with movement of plunger 90 to the open position shown in FIG. 5. The end of plunger 90 is open to pressure inlet port 86 such that air pressure biases plunger 90 to the closed position shown in FIG. 4.

[0047] In this embodiment, valve 82 is a three way, two position, latching, pilot-activated, spool valve. As shown in FIG. 3, spool valve 82 is in line 72 between conditioner 73 and pumps 80A and 80B and comprises a spool slidably disposed within a housing such that the spool translates relative to the housing between a closed position blocking the ports connected to air supply 71 via line 72 and pumps 80A and 80B via directional valve 104 and lines 72A and 72B,respectively, and an open position connecting air supply 71 to pumps 80A and 80B. As shown in FIG. 3, pilot outlet port 88A of activation switch 85A is connected to first pilot input port 83A of spool valve 82 via line 77A and pilot outlet port 88B of completion switch 85B is connected to second pilot input port 83B of spool valve 82 via line 77B. When plunger 90A of activation switch 85A is actuated by surface 54 of piston 52 to an open position, air supply port 86 of activation switch 85A is connected to pilot outlet port 88A of switch 85A and in turn to pilot input port 83A of spool valve 82 to thereby pressure the spool of spool valve 82 to an open position connecting air supply 71 to pump 80A or 80B. On the other side, w hen plunger 90B of completion switch 85B is actuated by surface 53 of piston 52 to an open position, air supply port 86 of switch 85B is connected to pilot outlet port 88B of switch 85B and in turn pilot input port 83B of spool valve 82 to thereby pressure the spool of spool valve 82 to a closed position blocking air supply to pump 80A or 80B.

[0048] Accordingly, piston face 54 of air piston 52 will contact plunger 90A and will activate activation air switch 85A when air piston 52 moves beyond a threshold at the barrier side 56 of accumulator 40 due to, for example and without limitation, leakage past process swivel seals 33, 133, 34 and / or 134. Once air switch 85 A is activated or triggered by air piston 52, pilot line 77A shuttles valve 82 to an open position and opens air supply to air driven pumps 80A and 80B to drive pump 80A or 80B. Air driven pump 80A or 80B, depending on the position of valve 104, thereby charges barrier fluid lines 63 and 64 and, at a certain pressure, forces air piston 52 back towards the process side 57 of accumulator 40 until piston face 53 of air piston 52 contacts plunger 90B and activates completion air switch 85B. Once completion air switch 85B is activated or triggered, pilot line 77B shuttles valve 82 back to a closed and blocked position, thereby shutting off air driven pumps 80A and 80B. Thus, switches 85A and 85B and valve 82 provide an automated pneumatic secondary differential feedback system that is operatively configured to regulate barrier fluid pump 80A or 80B as a function of the position of air piston 52 and the relative pressure of fluid and air in chambers 41, 46 and 51, respectively.

[0049] Figure 6 shows an alternate embodiment 185 to air switch valve 85. In this embodiment, switch 185 has supply pressure inlet port 186 connected to air supply 71 via air switch pressure line 76, pilot outlet port 188 connected to valve 82, and vent port 189 to the environment. Switch 185 generally comprise plunger 190 slidably disposed within housing 191 such that plunger 190 may translate relative to housing 191 and valve sleeve 194 between a closed position, shown in FIG. 6, and an open position (not shown). In the closed position shown in FIG. 6, plunger 190 is biased by spring 192 to the right and the connection between supply port 186 and pilot outlet port 188 in sleeve 194 is blocked and pilot outlet port 188 is instead air flowconnected to vent port 189 and the environment via sleeve 195 and groove 193 in plunger 190. In the open position, when plunger 190 has been forced to the left by piston 52 for example, supply port 186 is air flow connected to pilot outlet port 188 via sleeve 195 and groove 193 in plunger 190, and the connection between pilot outlet port 188 and vent port 189 is blocked by plunger 190 such that air flows from supply port 186 to pilot port 188. Spring 192 operates between plunger 190 and housing 191 such that plunger 190 is biased to the closed position shown in FIG. 6.

[0050] The proximity switches may be supported by the housing for detection relative to piston 52 as shown and described or alternatively may be supported by the piston 52 for detection relative to the chamber sidew alls. It is contemplated that other types of switches, such as contact or contactless proximity sensors, contact stop switches, and other detectors, may be used as alternatives.

[0051] An alternative rotary connection is shown in FIG. 7. As shown, this rotary connection generally comprises stator assembly 220 and rotor assembly 225. Inner assembly 220 and outer assembly 225 are rotatable about longitudinal axis x-x relative to each other at sealed rotaiy bearing interface 230. As shown, housing 225 is rotatably supported relative to housing 220 so that housing 225 is free to rotate about center axis x-x relative to housing 220 at the rotary interface between housing 220 and housing 225. Cylindrical fluid exchange channel 218 is formed at the rotary interface between housings 225 and 220. The rotary interface between housing 220 and housing 225 is defined by annular rotary gap 231 between inner- facing surface 227 of outer housing 225 and outer-facing surface 222 of inner housing 220. Annular seals 233 and 234 are disposed in annular rotary gap 231 between inner-facing surface 227 of outer housing 225 and outer-facing surface 222 of inner housing 220. Seals 233 and 234 are thereby located in gap 231 between stationary inner housing 220 and rotating outer housing 225 to contain process fluids within cylindrical channel 218 and prevent fluid from leaking past the two radially opposed surfaces 222 and 227 wdien high pressure process fluid is present in channel 218. In this embodiment, seals 233 and 234 operate as dynamic seals across rotaiy7gap 231 at the rotational interface between housing 220 and housing 225. To aid in the axial pressure balance between the top and bottom of seal 233, hydraulic barrier system 15 is provided. With hydraulic barrier system 15, seal 233 may be operatively configured such that a separate axial barrier fluid is provided at a high pressure to gap 235 to provide pressure balance or a counter load to the opposed process fluid pressure acting on the other side of seal 233. As shown, annular barrier fluid gap 235 is formed radially between outer-facing surface 222 of inner housing 220 and inner-facing surface 227 of outer housing 225 and axially between seal 233 and seal 234. Barrier fluid system 15 is connected to barrier fluid gap or chamber 235via barrier fluid passage 63 in housing 225 and process fluid line 66 in housing 225 directly links process channel 218 and process fluid chamber 46. With system 15, a separate balancing barrier fluid is thereby provided at a high pressure to chamber 235 as described above with respect to interface 30.

[0052] It should be appreciated that certain features of the system, which are, for clarity7, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features, which are. for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable combination. While various embodiments have been described in detail above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant arts that the disclosed subject matter may be embodied in other specific forms, variations, and modifications without departing from the scope, spirit, or essential characteristics thereof. The embodiments described above are therefore to be considered in all respects as illustrative, and not restrictive. The scope of the invention is indicated by the appended claims, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein.

Claims

CLAIMSWhat is claimed is:

1. A rotary' interface comprising: an inner housing; at least one outer housing rotatably supported relative to the inner housing so that the outer housing is free to rotate about a center axis relative to the inner housing at a rotary interface between the inner housing and the outer housing; a process fluid exchange channel extending across the rotary’ interface between the outer housing and the inner housing; the rotary interface comprising an annular rotary' gap between an inner-facing surface of the outer housing and an outer-facing surface of the inner housing; an annular first seal disposed in the rotary gap between the inner-facing surface of the outer housing and the outer-facing surface of the inner housing; an annular second seal disposed in the rotary’ gap between the inner-facing surface of the outer housing and the outer-facing surface of the inner housing; the rotary interface comprising an annular barrier fluid gap disposed in the rotary gap between the inner-facing surface of the outer housing and the outer-facing surface of the inner housing and between the first seal and the second seal; a differential accumulator comprising a process fluid chamber, a barrier fluid chamber, a gas chamber, a primary differential piston operative between the process fluid chamber and the barrier fluid chamber, and a secondary differential piston operative between the gas chamber and the barrier fluid chamber; a barrier fluid passage extending between the barrier fluid chamber of the differential accumulator and the barrier fluid gap of the rotary' gap of the rotary' interface; a barrier fluid pump connected to the barrier fluid passage; a process fluid passage extending between the process fluid chamber of the differential accumulator and the process fluid exchange channel; a gas passage extending between the gas chamber of the differential accumulator and a gas supply system; and a pneumatic secondary differential feedback system operatively configured to regulate the barrier fluid pump as a function of a parameter of the secondary differential piston;whereby a barrier fluid is operatively provided to the barrier fluid gap between the first and second seals at a barrier pressure greater than a process pressure of a process fluid in the process fluid exchange channel.

2. The rotary interface set forth in claim 1, wherein the gas supply system comprises: a gas tank connected to the gas passage; a gas supply input connected to the gas tank; and a valve between the gas tank and the gas supply input; whereby the gas tank is operatively charged to a regulated pressure via the gas supply input.

3. The rotary interface set forth in claim 1, wherein: the gas supply system comprises a gas supply input; the barrier fluid pump comprises a gas driven pump connected to the gas supply input; the secondary differential feedback system comprises a first pneumatic limit switch operatively configured to sense the secondary differential piston translating beyond a first threshold position; the secondary differential feedback system comprises a pneumatic valve between the gas supply input and the gas driven pump; and the first pneumatic limit switch is connected to the pneumatic valve.

4. The rotary' interface set forth in claim 3, wherein the pneumatic valve comprises a pilot operated spool valve having an open state and a closed state; and the first pneumatic limit switch comprises a first plunger operatively configured to translate relative to a first housing and having a first pilot open state and a first pilot closed state.

5. The rotary interface set forth in claim 4, wherein: the first housing of the first pneumatic limit switch comprises a first pressure inlet port and a first pilot outlet port; and the pneumatic valve comprises a first pilot input port connected to the first pilot outlet port of the first pneumatic limit switch.

6. The rotary' interface set forth in claim 5, wherein:operative translation of the secondary differential piston beyond the first threshold position actuates the first plunger to the first pilot open state; and actuation of the first plunger to the first pilot open state actuates the spool valve to the open state; whereby the gas driven pump is operatively driven by the gas supply input to pump the barrier fluid to the barrier fluid gap.

7. The rotary interface set forth in claim 6, wherein: the secondary differential feedback system comprises a second pneumatic limit switch operatively configured to sense the secondary differential piston translating beyond a second threshold position; and the second pneumatic limit switch is connected to the pneumatic valve.

8. The rotary' interface set forth in claim 7, wherein the second pneumatic limit switch comprises a second plunger operatively configured to translate relative to a second housing and having a second pilot open state and a second pilot closed state.

9. The rotary interface set forth in claim 8, wherein: the second housing of the second pneumatic limit switch comprises a second pressure inlet port and a second pilot outlet port; and the pneumatic valve comprises a second pilot input port connected to the second pilot outlet port of the second pneumatic limit switch.

10. The rotary interface set forth in claim 9, wherein: operative translation of the secondary differential piston beyond the second threshold position actuates the second plunger to the second pilot open state; and actuation of the second plunger to the second pilot open state actuates the spool valve to the closed state; whereby the gas driven pump is not operatively driven by the gas supply input to pump the barrier fluid to the barrier fluid gap.

11. The rotary interface set forth in claim 10, wherein: the first pneumatic limit switch comprises a first spring biasing the first plunger to the first pilot closed state; andthe second pneumatic limit switch comprises a second spring biasing the second plunger to the second pilot closed state.

12. The rotary interface set forth in claim 10, wherein: the first pressure inlet port and the first plunger are configured such that the first pressure inlet port provides a biasing of the first plunger to the first pilot closed state: and the second pressure inlet port and the second plunger are configured such that the second pressure inlet port provides a biasing of the second plunger to the second pilot closed state.

13. The rotary interface set forth in claim 3, compnsing a secondary gas driven pump connected to the gas supply input and a valve between the secondary gas driven pump and the gas supply input operatively configured to regulate flow from the gas supply input to the gas driven pump and the secondary' gas driven pump.

14. The rotary interface set forth in claim 3, wherein said gas supply input is operatively configured to connect to a gas supply pump.

15. The rotary interface set forth in claim 1, wherein the primary differential piston comprises a barrier surface area exposed to the barrier fluid chamber and a process surface area exposed to the process fluid chamber.

16. The rotary interface set forth in claim 15, wherein the barrier surface area is equal to or less than the process surface area.

17. The rotary' interface set forth in claim 15, wherein the secondary' differential piston comprises the barrier surface area exposed to the barrier fluid chamber and a gas surface area exposed to the gas fluid chamber.

18. The rotary' interface set forth in claim 17, wherein the gas surface area is greater than the barrier surface area.

19. The rotary interface set forth in claim 17, yvherein the primary7differential piston comprises a first primary piston head having the barrier surface area, a second primary piston head having the process surface area, and a rod extending between the first primary' piston head and the second primary piston head.

20. The rotary interface set forth in claim 19, wherein the secondary' differential piston comprises a secondary piston head having the gas surface area and the rod comprises a first portion extending between the first primary piston head and the secondary piston head and a second portion extending between the secondary piston head and the second primary piston head such that each of the first and second primary' piston heads translate with translation of the secondary piston head.

21. The rotary interface set forth in claim 1 , comprising a failsafe valve between the barrier fluid passage and the process fluid passage, whereby in an open state the failsafe valve allows the process fluid to bypass the first seal and flow to the barrier fluid gap via the barrier fluid passage and such that the barrier fluid passage and the process fluid passage are pressure balanced.

22. The rotary' interface set forth in claim 21, comprising a backflow valve in the barrier fluid passage between the failsafe valve and the differential accumulator, whereby in a closed state the backflow valve blocks the process fluid from flowing to the barrier fluid chamber of the differential accumulator when the failsafe valve is in an open state.

23. The rotary interface set forth in claim 1, comprising a bleed-off valve between the barrier fluid passage and the process fluid passage, whereby in an open state the bleed-off valve allows the barrier fluid to bypass the first seal and flow to the process fluid exchange channel via the process fluid passage.

24. The rotary interface set forth in claim 1, comprising a barrier fluid input connected to the barrier fluid pump and the barrier fluid passage.

25. The rotary interface set forth in claim 24, wherein said barrier fluid input is operatively configured to connect to a barrier fluid source.

26. The rotary' interface set forth in claim 1, wherein said gas comprises air and the gas supply input is operatively configured to connect to an air supply pump of a vessel.

Images