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(11) | EP 3 739 210 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | APPARATUS FOR PUMPING CRYOGENIC FLUIDS |
| (57) Apparatus for pumping a cryogenic fluid (22), comprising a pump (32) located inside
a sump, the sump having a sump body (4) and a heat-insulated lid (6). The corresponding
use of the apparatus and method for pumping a cryogenic fluid are also disclosed.
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[0002] More precisely, the present invention relates to an apparatus for pumping cryogenic fluids comprising a sump for a submerged cryogenic pump. The term cryogenic fluids is understood to mean liquid or gaseous fluids at cryogenic temperatures, cryogenic temperatures being defined as temperatures below -50°C and preferably below -150°. The term cryogenic pump is understood to mean any kind of pumps suitable for pumping operation at cryogenic temperature.
[0003] It is well known in the field of pumping fluids to use submerged cryogenic pumps to deliver a cryogenic fluid, for example but not limited to, liquid carbon dioxide, liquid oxygen, liquid nitrogen, liquefied natural gas, from a storage vessel. Submerged cryogenic pump are usually of centrifugal type and can be located outside the storage vessel
[0004] Submerged cryogenic pumps are generally installed inside sumps, where they are partially or totally submerged by the cryogenic fluid to be pumped in order to avoid gas ingress inside the pump. Gas ingress can trigger a loss of the pump priming, and cavitation, ultimately leading in mechanical damage to the pump.
[0005] Typically, sumps have a cylindrical shape and are vertically oriented. They comprise a lower elongated part, called the sump body, and an upper part, called the lid. Both parts are manufactured in a material suitable for cryogenic temperatures, such as stainless steel or aluminum. During operation of the pumping apparatus, the lid is a demountably affixed on top of the sump body by suitable means, like flanges and gasket, as to form a leak-proof assembly. For the maintenance of the pumping apparatus, the sump can be opened by separating the lid from the sump body, and therefore removing the pump located inside the sump body.
[0006] Because of the high thermal conductivity of the materials used for the realization of the sump body and the lid, thermal bridges are formed between the inside of the sump and the outside environment. The upper section of the sump, including the lid, become very cold and the water moisture from the ambient air can solidify and form a block of ice on the upper section of the sump, hampering the accessibility to the pumping apparatus for maintenance or for service.
[0007] Therefore, it appears desirable to provide a pumping apparatus for cryogenic fluids minimizing the formation of ice on top of the sump containing the submerged pump.
[0008] The sump containing the submerged pump are usually installed in an industrial environment and are exposed to the elements. Therefore, it is also desirable to provide a pumping apparatus able to durably withstand the rigors of industrial service, notably by having a high durability and a by high mechanical strength.
[0009] According to the first aspect of the present invention there is provided an apparatus for pumping a cryogenic fluid, comprising a sump body, a lid affixed on top of a sump body, a centrifugal pump provided within the sump body wherein in use the pump is totally or partially submerged in the cryogenic fluid. To minimize the heat ingress toward the low temperature parts of the apparatus, the lid is heat-insulated.
[0010] In a further embodiment, to facilitate accessing the pump for installation and maintenance, the lid is demountably affixed on top of the sump body.
[0011] In another embodiment, the centrifugal pump may be demountably suspended under the lid, thus the pump can be removed from the sump by lifting the demountable lid with the pump suspended underneath, and then reversibly separating the pump from the lid.
[0012] In another embodiment, during normal operation of the apparatus for pumping cryogenic fluids, the pump may be totally or partially submerged in the cryogenic fluid to be pumped.
[0013] In a further embodiment, one or more layers of insulation material may be located underside the lid, to limit any heat-transfer by conduction through the lid between the ambient air and the inside of the lid, at cryogenic temperatures. One or more layers of heat insulating material may be located underside the lid and around an outlet of the pump to limit any heat-transfer by conduction through the lid between the ambient air and the inside of the lid, at cryogenic temperatures.
[0014] In another embodiment, the lid is provided with a cavity, said cavity defining a hollow and gas tight enclosure within the lid. The cavity may be vacuum insulated. The inner horizontal diameter of the cavity may be at least equal to the largest horizontal dimension of the pump.
[0015] In a further embodiment, the cavity can be delimited by a lid flange and a lid jacket affixed on top of the flange, the lid flange and the lid jacket being parts of the lid. The lid flange and the lid jacket may be affixed together as to form a gas-tight enclosure by demountable means, like nuts and bolts, or by non-demountable means like for example welding the flange and the upper concave part together.
[0016] In a further embodiment, the lid jacket comprises a cylindrical section and an ellipsoidal section, the ellipsoidal section being located on top of the cylindrical section.
[0018] In another embodiment, the lid comprises at least one duct passing through both the lid jacket and the lid flange and fluidly connecting the inside of the sump with the outside of the apparatus. In a further embodiment, to minimize the heat ingress through the lid,
the inward-looking surfaces of the cavity and the upward facing side of the lid flange, and the outward facing walls of the ducts passing through the lid jacket and the lid flange are, altogether or not, heat insulated with heat-insulating material, like for example polyurethane foam, or any other material suitable for low-temperature heat insulation with a thermal conductivity as per ASTM C518 below 0.025 W/mK, and preferably below 0.015 W/mK. The thickness of one of the one or more layers can be from 0.5 to 30 cm, and preferably from 2 to 5 cm.
[0019] In another embodiment, still to minimize the heat-transfer between the cryogenic parts and the outside environment, the cavity may be insulated with multi-layer vacuum-evacuated heat insulation material. The air trapped inside the cavity during its assembly has been evacuated by vacuum, to form a low pressure, gas tight enclosure in order to minimize the heat transfer inside the cavity. The pressure inside the cavity can be between 0.001 and 100 mbar, preferably between 0.001 and 10 mbar and more preferably between 0.001 and 2mbar.
[0020] In another embodiment, the lid comprises a duct for vacuum evacuation of the cavity comprised within the lid.
[0021] According to a further aspect of the invention, there is provided a method for pumping a cryogenic fluid by using the above-mentioned apparatus.
[0022] According to an another aspect of the invention, there is provided a method for pumping a cryogenic fluid comprising the of
- a. Filling a sump a sump with the cryogenic fluid
- b. Aspiring the cryogenic fluid with a pump located in the sump, the pump being totally or partially submerged in the cryogenic fluid
- c. Delivering the cryogenic fluid through a sump lid,
- d. Providing insulation within the sump lid
[0023] Whilst the invention has been described above, it extends to any inventive combination of features set out above or in the following description or drawings.
[0025] Specific embodiment of the invention will now be described in detail by way of example only and with reference to the accompanying drawing in which:
2: sump
4: sump body
6: lid
8: inner jacket
10: outer jacket
12: flange of the outer jacket
14: hollow gas tight enclosure of the sump
16: bottom plate
18: sump inlet
20: flange of the sump inlet
22: cryogenic fluid
24: gas
26: degassing outlet
28: flange of the degassing outlet
30: lid flange
32: pump
34: means of affixing
36: gasket
38: insulating material
40: pump inlet
42 pump outlet
44: upper bearing of the pump motor
46: expansion bellow
48: first duct
50: sump outlet
52: third duct
54: fourth duct
56: pump impeller
58: pump motor
60: lid jacket
62: fifth duct
64: cavity
66: horizontally elongated cylinder
[0026] In FIG. 1 schematically shows an embodiment of an apparatus according to the present invention. The apparatus comprises sump (2) with a sump body (4) having the shape of a vertically oriented cylindrical enclosure with an upper opening. A lid (6) is affixed on top of the sump body (4), and a pump (32) is vertically suspended under the lid (6), inside the sump (2).
[0027] The sump body (4) comprises an inner jacket (8) co-axially disposed inside an outer jacket (10). The outer jacket (10) is formed by a vertically oriented cylindrical part, affixed by welding to a bottom plate (16). The upper part of the outer jacket (10) is terminated by a horizontally disposed flange (12).
[0028] The inner jacket (8) is vertically oriented with a cylindrical upper part and an ellipsoidal bottom. The upper part of the inner jacket (8) is affixed to the horizontally disposed flange (12) of the outer jacket (10) by welding, thus defining a hollow and gas-tight enclosure (14) between the bottom plate (16), the outer jacket (10), the inner jacket (8) and the horizontally disposed flange (12). The hollow gas tight-enclosure (14) is heat insulated. The heat insulating can be performed by layering the outward facing walls of the inner jacket (8), for example but not limited, to with multi-layer insulation, or with polyurethane, or by vacuum evacuation. The vacuum evacuation is performed by aspiring the gas located inside the hollow enclosure (14) with a vacuum pump, through a duct (not shown).
[0029] The pump (32) is disposed vertically inside the sump (2). The pump (32) has a pump inlet (40) and a pump outlet (42). The pump inlet (40) is at the lower end of the pump (32), so that in operation the pump inlet (40) is submerged in the cryogenic liquid (22) contained in the lower part of the inner jacket (8) of the sump body (4). The pump outlet (42) is located at the upper end of the pump (32), in fluid connection with a vertically oriented hole located on the horizontally disposed flange (12) of the outer jacket (10) of the sump body (4).
[0030] In operation, the cryogenic liquid (22) being pumped moves in an essentially vertical direction from the pump inlet (40) toward the pump outlet (42). Typically, the pump (32) is of a centrifugal type, meaning that the cryogenic fluid aspired by the pump (32) is centrifuged by one or more pump impellers (56) connected to a shaft rotated by an electrical motor (58). The electrical motor (58) is located inside the pump (32) and is submerged in the cryogenic fluid (22) passing through the pump so that the electrical motor (58) is cooled down by the cryogenic fluid after said cryogenic fluid has been passed through the one or more impellers (56). The shaft is supported by ball bearings located above (44) and under the motor, the ball bearings are in direct contact with the cryogenic liquid for lubrication and heat dissipation.
[0031] The inner jacket (8) comprises a horizontal inlet (18) disposed on its upper half, above the elevation of the pump inlet (40), to ensure that the pump inlet (40) is always submerged by the cryogenic liquid (22) to be pumped. The horizontal inlet (18) is formed by a duct passing through the hollow gas-tight enclosure (14) and through the outer jacket (10). The proximal part of the horizontal inlet is affixed by welding to a first circular opening of the inner jacket (8). The outer jacket (10) also comprises a first circular opening with a protruding horizontally elongated cylinder (66) disposed around the distal part of the horizontal inlet, defining an horizontal extension of the hollow, gas-tight enclosure (14), said horizontal extension also being insulated.
[0032] A flange (20) is welded to the distal end of the horizontal inlet (18). For connection to an external supply of cryogenic fluid (not shown). During operation of the pumping apparatus, cryogenic fluid to be pumped by the apparatus is supplied to the apparatus through the horizontal inlet (18).
[0033] Before start-up of the pumping apparatus, the inner jacket (8) is filled with air and/or an inert gas like nitrogen. It is therefore necessary to evacuate said gas in order to fill the inner jacket (8) with the cold cryogenic fluid (22) to be pumped. Cold cryogenic fluid (22) will be supplied through the horizontal inlet (18) to evacuate the gas from the pumping apparatus through a horizontal degassing outlet (26).
[0034] The horizontal degassing outlet (26) is disposed near the upper end of the inner jacket (8), slightly above the elevation of the upper bearing (44) located above the motor of the pump, in order to maintain the level of the cryogenic fluid (22) inside the sump (4) above the upper bearing (44) of the pump (32). The horizontal degassing outlet (26) is formed by a duct passing through the hollow gas-tight enclosure (14) and through the outer jacket (10). The proximal part of the horizontal degassing outlet (26) is affixed by welding to a second circular opening of the inner jacket (8). The horizontally elongated cylinder (66) protruding out of the outer jacket also extends around the horizontal degassing outlet (26). To compensate for the thermal dilatation and contraction that happens during the cooling-down or warming-up of the pumping apparatus, an expansion bellow (46) is provided on the horizontally elongated cylinder (66) protruding out of the outer jacket (10).
[0035] A flange (28) is welded to the distal end of the horizontal degassing outlet (26) for connection to an external vent (not represented).
[0036] A lid (6) is affixed on top of the sump body (4). The lid (6) comprises a bottom flange (30), which during operation of the pumping apparatus is demountably affixed, typically by means of nuts and bolts (34), to the upper flange (12) of the sump body (4). One or more concentrically arranged gaskets (36) are disposed in between the lid flange (30) and the sump body upper flange (12) thus making the sump (2) gas tight and leakage proof.
[0037] A pump (32) is demountably affixed below the bottom flange of the lid (12). Typically, the upper end (42) of the pump comprises a flange (30) of a smaller diameter than the internal diameter of the inner jacket (8). The pump (32) is demountably affixed to the flange (30) of the lid (6) by means of nuts and bolts. In order to lower the heat ingress through the lid (6) towards the pump (32) and the inner jacket (8), one or more layers of an insulating material (38) such as, for example but not limited to : polyurethane foam or vetronite or any other heat insulating material suitable for cryogenic service with a thermal conductivity as per ASTM C518 below 0.025 W/mK, and preferably below 0.015 W/mK , are affixed on the underside of the bottom flange (30) of the lid (6), around the upper end, or outlet (42), of the pump (32).
[0038] A lid jacket (60) is disposed on top of the flange (30) of the lid (6), thus defining a cavity (64) between the lid jacket (60) and the lid flange (30). Typically, the lid jacket (60) is composed of a lower cylindrical part with an upper ellipsoidal part. The upper ellipsoidal part is more precisely an oblate spheroid, which is an ellipsoid defined around two axes of the same length and a third, perpendicular axis that is shorter than the two other axes. The lid jacket (60) and the lid flange (30) are traversed by one or more ducts (50, 52, 48, 54), connecting the inside of the sump (2) to the outside.
[0039] A first duct (48) is used to pass one of more electrical wires to supply electrical power to the motor (58) of the pump (32), and optionally to transfer measurement signals from the pump (32) to a control system located outside of the pump (32), so the pump operator can access information related to the pump status, like for example but not limited to the temperature of the cryogenic fluid (22) inside the inner jacket (8) of the sump body (4).
[0040] A cavity in the form of a hollow enclosure is defined by the inner surface of the lid jacket (60) and the upper surface of lid flange (30). A second duct (50) is located on the vertical axis of the sump body (4), the sump lid (6) and the pump (32), and is used to exit the pumped cryogenic fluid from the sump (22), therefore constituting the sump outlet. The second duct (50) is in fluid communication with the pump outlet through an opening in the lid flange (30) and the upper flange (12) of the external jacket (10) of the sump body (4). A third duct (52) is provided on top or on the side of the lid jacket (60) for connection to a vacuum pump, to vacuumize the hollow enclosure for heat insulation. A fourth duct (54) is provided for connecting the inside of the sump to a pressure relief valve. An optional fifth duct (62) is also passing through the lid jacket (60) and the lid flange (30) and is extended in connection with a duct located inside the inner jacket of the sump body, alongside the pump (32), down below the pump inlet (40). Said fifth duct (62) is used for purging of the cryogenic liquid and / or vapors thereof before dismantling of the sump
[0041] To limit heat ingress from the ambient air to the inside of the sump (2) and formation of ice on top of the lid one or more of the following can provided with heat insulation: the inward facing walls of the lid jacket (60), the upward facing side of the lid flange (30), the outward facing walls of the ducts (48, 54, 50, 52, 62) passing through the lid jacket (60) and the lid flange (30). , The heat insulation can be one or more layers of a heat insulating material, like for example polyurethane foam, or any other material suitable for low-temperature heat insulation with a thermal conductivity as per ASTM C518 below 0.025 W/mK, and preferably below 0.015 W/mK. The thickness of one of the one or more layers can be from 0.5 to 30 cm, and preferably from 2 to 5 cm.
Additionally, the heat insulation of cavity (64) of the lid can be improved by vacuum insulation. The air trapped inside the cavity during its assembly has been evacuated by vacuum, to form a low pressure, gas tight enclosure in order to minimize the heat transfer inside the cavity. The pressure inside the cavity can be between 0.001 and 100 mbar, preferably between 0.001 and 10 mbar and more preferably between 0.001 and 2mbar.
1. Apparatus for pumping a cryogenic fluid (22), comprising:
A sump body (4);
A lid (6) affixed on top of the sump body (4);
A centrifugal pump (32) provided within the sump body (4) wherein in use the pump (32) is totally or partially submerged in the cryogenic fluid (22).
Characterized in that the lid (6) is heat-insulated.
2. Apparatus according to claim 1, wherein the lid (6) is demountably affixed on top
of the sump body (4).
3. Apparatus according to claim 1 or 2, wherein the centrifugal pump (32) is demountably
suspended under the lid (6).
4. Apparatus according to claim 3, wherein one or more layers of heat insulating material
(38) is located underside the lid (6) and around an outlet (42) of the pump (32).
5. Apparatus according to any of claims 1 to 4, wherein the lid (6) is provided with
a cavity (64).
6. Apparatus according to claim 5, wherein the cavity (64) is vacuum-insulated.
7. Apparatus according to claim 5 or 6, wherein the inner horizontal diameter of the
cavity (64) is at least equal to largest horizontal dimension of the pump (32).
8. Apparatus according to any of claims 5 to 7, wherein the cavity (64) is delimited
by a lid flange (30) and a lid jacket (60) affixed on top of the flange.
9. Apparatus according to claim 8, wherein the lid jacket (60) is formed by a cylindrical
section and an ellipsoidal section, the ellipsoidal section being located on top of
the cylindrical section.
10. Apparatus according to claim 9, wherein the ellipsoidal section is an oblate spheroid.
11. Apparatus according to claim 10, wherein the lid (6) comprises at least one duct (48,
50, 52, 54, 65) passing through both the lid jacket (60) and the lid flange (30) and
fluidly connecting the inside of the sump (2) with the outside of the apparatus.
12. Apparatus according to claim 11, wherein one or more of the following are heat insulated
with heat-insulating material: the interior surfaces of the cavity (64), the upward
facing side of the lid flange (30), the outward facing walls of the at least one duct
(48, 54, 50, 52, 54, 62) passing through the lid jacket (60); and the lid flange (30).
13. Apparatus according to claim 12, wherein the one or more of the following are heat
insulated with multi-layer vacuum-evacuated heat insulation material: the interior
surfaces of the cavity (64); the upward facing side of the lid flange (30), the outward
facing walls of the ducts (48, 54, 50, 52, 62) passing through the lid jacket (60)
and the lid flange (30).
14. Use of the apparatus of any of claims 1 to 13 for pumping a cryogenic fluid.
15. Method for pumping a cryogenic fluid, comprising the steps of
a. Filling a sump with the cryogenic fluid
b. Aspiring the cryogenic fluid with a pump located in the sump, the pump being totally or partially submerged in the cryogenic fluid
c. Delivering the cryogenic fluid through a sump lid,
d. Providing insulation within the sump lid