Cryogenic pump

Abstract

Piston pump (1) suitable for pumping a fluid at very low temperature, for example hydrogen, said pump (1) having a suction side (A) and a compression side (B), the suction side (A) comprising an inlet (4) provided for the liquid and intended to be connected to a liquid supply reservoir external to the pump (1), a suction chamber (3) for receiving the fluid, and a first fluid degassing duct (5) communicating with the suction chamber (3), the compression side (B) comprising a pump cylinder (2) carrying an assembly (8) for compression and delivery of the liquid, said cylinder (2) comprising a second chamber (6) which communicates with the suction chamber (3) and in which the fluid at very low temperature circulates in order to cool the compression and delivery assembly (8).

Description

Cryogenic pump TECHNICAL FIELD OF THE INVENTION

[0001] The invention belongs to the technical field of cryogenic pumps applicable to liquefied gases at very low temperatures, such as hydrogen. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] Cryogenic pumps generally comprise a cylinder carrying a compression and discharge assembly comprising a cylinder liner in which a piston moves axially so as to form a compression chamber. As this piston moves, the fluid is alternately drawn from the suction side towards the compression chamber, then compressed to be discharged via a dedicated opening.

[0003] The movement of the piston via the friction of its segments in the cylinder liner generates heat that can propagate into the compression chamber, causing the fluid to heat up, part of which changes from an incompressible liquid state to a compressible gaseous state. The pump's efficiency is reduced and its wear accelerated as a result of hydraulic shocks and / or cavitation. It is therefore necessary to ensure adequate cooling of the heat-producing areas.

[0004] Most piston pumps have cooling and degassing only on the suction side. But on the one hand, the cooling of the compression and discharge assembly is not optimal because some of the accumulated heat is not evacuated on the compression side, and on the other hand, the heat created in the cylinder is conveyed to the suction chamber to be evacuated through the single degassing duct, which causes the liquid in the suction chamber to heat up. This process is generally not a disadvantage for use with common cryogenic fluids down to -196°C, such as Nitrogen for example, but with a cryogenic fluid, such as hydrogen, having a liquefaction temperature around -255°C, the pump can cavitate or lose its prime due to lack of cooling.

[0005] The present invention aims to provide a solution to the problems described above.

[0006] To this end, the invention relates to a piston pump suitable for pumping a cryogenic fluid, such as hydrogen, said pump having a suction side and a compression side,

[0007] the suction side comprising an inlet for the liquid intended to be connected to a fluid supply reservoir external to the pump, a suction chamber for receiving the liquid and a first fluid degassing conduit communicating with the suction chamber,

[0008] the compression side comprising a pump cylinder comprising a liquid compression and discharge assembly,

[0009] said cylinder comprising a second chamber, communicating with the suction chamber, and in which the liquid circulates to cool the compression and discharge assembly.

[0010] The second chamber may have a length spanning at least a portion of the compression and discharge assembly. For example, the second chamber may surround the compression and discharge assembly.

[0011] The compression and discharge assembly generates heat that can propagate into the compression chamber. The second chamber allows the very low temperature fluid to cool the said compression and discharge assembly and thus avoids heating the fluid arriving at the compression chamber and therefore limits the formation of gas.

[0012] According to an exemplary embodiment, the cylinder may comprise a first casing and an internal cylinder body carrying the compression and discharge assembly, said first casing being fixed to the cylinder body to at least partially form the second chamber with said body and the body having a hollow shape allowing the circulation of the fluid in said second chamber.

[0013] By hollow shape we mean the fact that the body has openings along its length allowing the movement of the cooling fluid.

[0014] Advantageously, the pump may further comprise a second degassing conduit to the outside, communicating with the second chamber, and configured to allow degassing of the fluid circulating in the second chamber.

[0015] The heat created by the compression and discharge assembly is partly evacuated via this second degassing duct, which prevents these hot gases from returning to the suction chamber, thus limiting the heating of this fluid and the risk of cavitation.

[0016] According to an exemplary embodiment, the compression and discharge assembly may comprise: a pump sleeve and a cylinder head which are integral and may be coaxial with the sleeve, a piston which is axially movable in the sleeve forming a fluid compression chamber with the cylinder head, the cylinder head connecting the sleeve to the suction chamber, and a discharge opening arranged in the sleeve.

[0017] Advantageously, the cylinder head may comprise a pre-compression chamber communicating with the suction chamber.

[0018] For example, the pre-compression chamber may comprise a volume formed by walls of the cylinder head in which is arranged a movable valve mounted on a rod coaxial with the piston. For example, the rod is fixed to the piston so that the movement of the piston causes the movement of the valve.

[0019] This pre-compression chamber allows the compression chamber to be supplied with fluid from the suction chamber. Since the volume of the pre-compression chamber is greater than the compression chamber, the compression chamber is perfectly supplied with supercooled liquid from the suction chamber.

[0020] Advantageously, the cylinder head and / or cylinder may include a calibrated exhaust port to allow the pressure in the compression chamber to be adjusted. This therefore makes it possible to create advantageous characteristics for the fluid by moving away from the saturation curve.

[0021] Advantageously, the pump comprises a second casing external to the first casing and forming with it a space intended to be placed under vacuum.

[0022] This creates thermal insulation of the pump from the outside, limiting heat exchange and thus heating of the fluid.

[0023] Advantageously, an insulating material is arranged between the first envelope and the second envelope.

[0024] Preferably, the insulating material can be a multi-layer insulator. This allows for even better thermal insulation of the pump.

[0025] In an exemplary embodiment, the multi-layer insulation may alternately comprise layers of aluminum and layers of fiberglass veil, preferably superimposed on each other. Advantageously, this number of layers may be between 10 and 100. BRIEF DESCRIPTION OF THE FIGURES

[0026] Other features and advantages of the invention will appear in the description below in relation to the appended drawings, given as non-limiting examples, in which:

[0027] is an overall view of a pump according to an exemplary embodiment of the invention.

[0028] is an enlarged sectional view of the zone Z indicated on the.

[0029] is a partial section following line III-III of the.

[0030] Unless otherwise specified, the same element appearing in different figures has a single reference. DETAILED DESCRIPTION

[0031] An example of a pump 1 according to the invention is shown in the figure as seen overall from the outside. The pump 1 comprises a suction side A and a compression side B. The suction side A comprises a suction chamber 3 formed by a first casing 31 and having a first opening 4 serving as a liquid inlet to the suction chamber 3. The opening 4 is intended to be connected to an external reservoir, not shown, comprising the fluid at very low temperature, which is for example Hydrogen. The suction chamber 3 further comprises a second opening 5 serving for degassing the fluid arriving in the suction chamber 3. This second opening 5 is also intended to be connected to said external reservoir.

[0032] Optionally, the suction side A may also comprise a second envelope 32 external to the first envelope 31. The two envelopes form a space which can be placed under vacuum to thermally insulate this suction side A.

[0033] The compression side B comprises a pump cylinder 2 comprising a cylinder body 21 visible on the. The cylinder body 21 carries the compression and discharge assembly 8 which will be described later.

[0034] The cylinder 2 also comprises a first outer casing 22 relative to the cylinder body 21. It may also comprise a second outer casing 23 relative to the first casing 22. As can be seen in the, the first casing 22 and the second casing 23 form a space which can be evacuated to create thermal insulation of the cylinder 2 relative to the exterior.

[0035] Advantageously, an insulating material 10, in particular a multi-layer insulator, can be arranged between the first envelope 22 and the second envelope 23 to increase the thermal insulation of the cylinder 2.

[0036] The first casing 22 of the cylinder 2 is fixed to the cylinder body 21 and forms with it a second chamber 6 which is connected to the suction chamber 3, via openings 24, so that the fluid at very low temperature arrives in the second chamber 6 to serve for cooling the compression and discharge assembly 8.

[0037] To allow the circulation of the liquid in the second chamber 6, the cylinder body 21 has a hollow shape. In the example shown, the rear part of the body is hollowed out to form the rear part 62 of the second chamber 6 with the first casing 22. The front part of the body is also hollowed out to form the front part 61 of the second chamber 6. The intermediate part of the cylinder body 21 is also hollow to allow the passage of the fluid from the front part 61 to the rear part 62, but also has contact points 64 with the first casing 22. The shows a partial section along the line III-III of the showing an example of a hollow shape of the intermediate part of the body 21.

[0038] Advantageously, the cylinder 2 may comprise a second degassing conduit 9 communicating with the second chamber 6 to allow the degassing of the fluid circulating in the second chamber 6.

[0039] The compression and discharge assembly 8 comprises: a pump jacket 81 and a cylinder head 84, integral and coaxial, a piston 82 axially movable in the jacket 81 forming a fluid compression chamber with the cylinder head 84, the cylinder head 84 connecting the jacket 81 to the suction chamber 3, and a discharge opening 85 arranged in the jacket 81, as shown by the.

[0040] Optionally, the cylinder head 84 comprises a pre-compression chamber 840 which communicates with the suction chamber 3. For example, the pre-compression chamber 840 is formed of a wall 841 forming part of the cylinder head 84 and forming a space in which a movable valve 843 is arranged mounted on a rod 842 coaxial with the piston 82.

[0041] Advantageously, the cylinder head 84 may include an exhaust orifice 846 calibrated to allow the pressure in the compression chamber to be adjusted.

[0042] Possible operation of the pump:

[0043] Before starting the pump 1, the fluid arrives at the suction chamber 3 via the inlet 4 and returns to the reservoir via the opening 5 to cool the suction chamber 3 and the pre-compression chamber 840 by passing through the filter 33, then the openings in the valve 843. As long as the pre-compression chamber 840 is not completely cooled, the fluid returning to the external reservoir includes a fraction of gas generated by contact with the elements to be cooled.

[0044] The fluid can also arrive in the second chamber 6 to cool the compression and discharge assembly 8. The fluid rises in the second degassing conduit 9 up to a certain level. Degassing takes place via conduit 9 as long as the second chamber 6 is not cooled to the saturation temperature of the fluid.

[0045] Once the suction chamber 3 and parts have completely cooled, pump 1 can be started.

[0046] When the rod 83 of the piston 82 is pulled by a drive system (left to right direction on the), it causes the rod 842 to move, the plate 844 sticks against the valve 843 which thus pushes the fluid present in the pre-compression chamber 840 towards the compression chamber formed by the sleeve 81, the piston 82 and the cylinder head 84. The passage is via the openings 845, which are then closed when the piston 82 returns (right to left direction on the) so that the fluid is compressed by the piston 82 in the compression chamber and then discharged via the opening 85. The valve (not shown) closing this opening 85 opens to allow the discharge of the pressurized fluid outside the pump 1.

[0047] The movements of the piston assembly 82 and its segments (not marked) in the jacket 81 generate heat which vaporizes a fraction of the cryogenic fluid. Thanks to the second degassing conduit 9, it is possible to evacuate this gaseous fraction present in the second chamber 6 without returning it to the suction chamber 3 as is often practiced in known pumps.

Claims

Piston pump (1) adapted for pumping a very low temperature fluid, such as hydrogen, said pump (1) having a suction side (A) and a compression side (B), the suction side (A) comprising an inlet (4) for the fluid intended to be connected to a liquid supply tank external to the pump (1), a suction chamber (3) for receiving the fluid and a first degassing conduit (5) for the fluid communicating with the suction chamber (3), the compression side (B) comprising a pump cylinder (2) carrying a fluid compression and discharge assembly (8), said cylinder (2) comprising a second chamber (6) communicating with the suction chamber (3) and through which the very low temperature fluid circulates to cool the compression and discharge assembly (8). Pump (1) according to claim 1, in which the cylinder (2) comprises a first casing (22) and an internal cylinder body (21) carrying the compression and discharge assembly (8), said first casing (22) being fixed to the cylinder body (21), said cylinder body (21) having a hollowed shape allowing the circulation of the fluid into the second chamber (6). Pump (1) according to any one of the preceding claims, further comprising a second degassing conduit (9) communicating with the second chamber (6) and configured to permit degassing of the fluid circulating in the second chamber (6). Pump (1) according to any one of the preceding claims in which the compression and discharge assembly (8) comprises: a pump casing (81) and a cylinder head (84) that are integral and coaxial, a piston (82) that is axially movable in the casing (81) forming a fluid compression chamber with the cylinder head (84), said cylinder head (84) connecting the casing (81) to the suction chamber (3), and a discharge opening (85) arranged in the casing. Pump (1) according to the preceding claim, in which the cylinder head (84) includes a pre-compression chamber (840) communicating with the suction chamber (3). Pump (1) according to any one of claims 4 or 5 wherein the cylinder head (84) includes an exhaust port (846) configured to allow adjustment of the pressure in the compression chamber. Pump (1) according to any one of claims 2 to 6 in which the cylinder (2) comprises a second outer casing (23) relative to the first casing (22) and forming with it a space intended to be evacuated. Pump (1) according to the preceding claim in which an insulating material (10) is arranged between the first jacket (22) and the second jacket (23). Pump (1) according to the preceding claim in which the insulating material (10) is a multilayer insulator. Pump (1) according to the preceding claim in which the multilayer insulation comprises alternately layers of aluminium and layers of fibreglass veil.

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