Cryopump

Abstract

A piston pump (1) suitable for pumping a fluid at very low temperatures, such as hydrogen, has a suction side (A) and a compression side (B), the suction side (A) comprising: an inlet (4) provided for a liquid and intended to be connected to a liquid supply reservoir external to the pump (1), a suction chamber (3) provided for the liquid supply reservoir, and a first fluid degassing conduit (5) provided for the suction chamber (3) and intended to be connected to the pump (1); the invention relates to a device for compressing and conveying a fluid, comprising a suction chamber (3) for receiving the fluid, a first fluid degassing conduit in communication with the suction chamber (3), a compression side (B) comprising a pump cylinder (2) carrying an assembly (8) for compressing and conveying the fluid, the cylinder (2) comprising a second chamber (6) in communication with the suction chamber (3), and the fluid at a very low temperature circulates in the second chamber in order to cool the compression and delivery assembly (8).

Description

Technical Field

[0001] The present invention belongs to the technical field of cryogenic pumps, which are suitable for gases liquefied at very low temperatures, such as hydrogen. Background Art

[0002] A cryogenic pump generally comprises a cylinder carrying an assembly for compression and delivery, the assembly comprising a cylinder liner in which a piston moves axially to form a compression chamber. As the piston moves, the fluid is alternately drawn from the suction side toward the compression chamber and then compressed to be discharged through a dedicated opening.

[0003] The frictional movement of the piston in the cylinder liner by the piston ring generates heat which can be transferred to the compression chamber, thereby heating the fluid and changing part of the fluid from an incompressible liquid to a compressible gas. This can lead to reduced pump efficiency and accelerated wear due to hydraulic shock and / or cavitation. It is therefore necessary to ensure that the hot areas are adequately cooled.

[0004] Most piston pumps are cooled and degassed only on the suction side. However, on the one hand, the cooling effect of the compression and delivery components is poor, because part of the accumulated heat cannot be discharged on the compression side; on the other hand, the heat generated in the cylinder is guided to the suction chamber for discharge through a single degassing pipeline, which causes the liquid in the suction chamber to warm up. For standard cryogenic fluids (such as nitrogen) with a temperature as low as -196°C, this process usually has no adverse effects, but for cryogenic fluids with a liquefaction temperature of about -255°C (such as hydrogen), the pump may cavitate or fail due to lack of cooling.

[0005] The purpose of the present invention is to propose a solution to the above problems. Summary of the invention

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

[0007] The suction side comprises: an inlet, a suction chamber, and a first fluid degassing conduit, the inlet being provided for liquid and intended to be connected to a liquid supply reservoir outside the pump, the suction chamber being used to receive the fluid, the first fluid degassing conduit being in communication with the suction chamber,

[0008] The compression side includes a pump cylinder including components for compressing and delivering liquid,

[0009] The cylinder comprises a second chamber communicating with the suction chamber and in which a fluid circulates in order to cool the compression and delivery assembly.

[0010] The second chamber can have a length covering at least a portion of the compression and delivery assembly. For example, the second chamber can surround the compression and delivery assembly.

[0011] The compression and delivery components generate heat which may be transferred into the compression chamber. The second chamber allows the fluid at a very low temperature to cool the compression and delivery components and thus avoids that the fluid reaching the compression chamber is heated and thus limits gas formation.

[0012] According to one embodiment, the cylinder may include a first shell and an inner cylinder body carrying the compression and delivery assembly, the first shell being attached to the cylinder body to at least partially form a second chamber with the body, and the body having a concave shape allowing fluid to flow into the second chamber.

[0013] A concave shape means that the body has openings along its length that allow the movement of cooling fluid.

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

[0015] The heat generated by the compression and delivery components is partially discharged via the second degassing duct, which prevents the hot gases from flowing back towards the suction chamber, thus limiting the heating of the fluid and the risk of cavitation.

[0016] According to one embodiment, the compression and delivery assembly may include:

[0017] - a pump bushing and a cylinder head integral with each other, and the cylinder head may be coaxial with the bushing,

[0018] - a piston that is axially movable in the bushing, the piston forming a fluid compression chamber with the cylinder head, the cylinder head connecting the bushing to the suction chamber, and

[0019] - A delivery opening arranged in the sleeve.

[0020] Advantageously, the cylinder head may comprise a pre-compression chamber communicating with the suction chamber.

[0021] For example, the pre-compression chamber may comprise a volume formed by the wall of the cylinder head, in which a movable valve mounted on a rod coaxial with the piston is arranged. For example, the rod is attached to the piston so that movement of the piston causes the valve to move.

[0022] The pre-compression chamber supplies the compression chamber with fluid from the suction chamber. Since the volume of the pre-compression chamber is greater than the volume of the compression chamber, the compression chamber is preferably supplied with supercooled liquid from the suction chamber.

[0023] Advantageously, the cylinder head and / or the cylinder may comprise a calibrated exhaust port to allow the pressure in the compression chamber to be adjusted. This therefore produces advantageous properties for the fluid away from the saturation curve.

[0024] Advantageously, the pump comprises a second housing, which is located outside the first housing and which forms, together with the first housing, a space intended to be evacuated.

[0025] This thermally isolates the pump from the outside, limiting the heat exchange and therefore the temperature rise of the fluid.

[0026] Advantageously, the thermal insulation material is arranged between the first shell and the second shell.

[0027] Preferably, the insulation material may be a multi-layer insulation material. This provides even better insulation for the pump.

[0028] In one embodiment, the multilayer insulation material may comprise layers of aluminium and glass fibres alternately, preferably overlapping each other. Advantageously, the number of layers may be between 10 and 100. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Other characteristics and advantages of the invention will become apparent from the following description with reference to the accompanying drawings given as non-limiting examples, in which:

[0030] [ Figure 1 ] is a schematic diagram of a pump according to one embodiment of the present invention.

[0031] [ Figure 2 ]yes[ Figure 1 ] is an enlarged cross-sectional view of zone Z shown in FIG.

[0032] [ Figure 3 ] is along Figure 1 A partial cross-sectional view taken along line III-III.

[0033] Unless otherwise indicated, identical elements appearing in different drawings have unique reference numbers. DETAILED DESCRIPTION

[0034] An example of a pump 1 according to the invention is shown in [ Figure 1 ] is shown as a whole viewed from the outside. The pump 1 includes a suction side A and a compression side B. The suction side A includes a suction chamber 3 formed by a first housing 31 and has a first opening 4 as a liquid inlet of the suction chamber 3. The opening 4 is designed to be connected to an external reservoir (not shown) containing a fluid at a very low temperature, such as hydrogen. The suction chamber 3 also includes a second opening 5 for degassing the fluid entering the suction chamber 3. The second opening 5 is also designed to be connected to the external reservoir.

[0035] Optionally, the suction side A may further include a second housing 32 located outside the first housing 31. The two housings form a space that can be evacuated in order to thermally isolate the suction side A.

[0036] The compression side B includes a pump cylinder 2, which includes [ Figure 2 ] The cylinder body 21 shown in FIG. The cylinder body 21 carries a compression and delivery assembly 8, which will be described later.

[0037] The cylinder 2 also includes a first housing 22 located outside the cylinder body 21. It may also include a second housing 23 located outside the first housing 22. Figure 2 ] it can be seen that the first shell 22 and the second shell 23 form a certain space, which can be evacuated to form thermal insulation of the cylinder 2 relative to the outside.

[0038] Advantageously, insulating material 10 , in particular multiple layers of insulating material, may be arranged between the first shell 22 and the second shell 23 to increase the thermal insulation of the cylinder 2 .

[0039] A first housing 22 of the cylinder 2 is attached to the cylinder body 21 and forms with the cylinder body a second chamber 6 which is connected to the suction chamber 3 via an opening 24 so that fluid at a very low temperature enters the second chamber 6 to cool the compression and delivery assembly 8 .

[0040] In order to allow the liquid to circulate in the second chamber 6, the cylinder body 21 has a hollow shape. In the example shown, the rear portion of the body is hollowed out to form the rear portion 62 of the second chamber 6 together with the first housing 22. The front portion of the body is also hollowed out to form the front portion 61 of the second chamber 6. The middle portion of the cylinder body 21 is also hollow to allow the fluid to flow from the front portion 61 to the rear portion 62, but also has a contact point 64 with the first housing 22. [ Figure 3 ] is along[ Figure 1 ] is a partial cross-sectional view along line III-III of FIG. 1 , showing an example of the hollow shape of the middle portion of the main body 21.

[0041] Advantageously, the cylinder 2 may comprise a second degassing duct 9 communicating with the second chamber 6 so as to allow degassing of the fluid circulating in the second chamber 6 .

[0042] The compression and delivery assembly 8 comprises:

[0043] - One-piece coaxial pump bushing 81 and cylinder head 84,

[0044] a piston 82 capable of axial movement in the bushing 81, which forms a fluid compression chamber with a cylinder head 84, which connects the bushing 81 to the suction chamber 3, and

[0045] - a delivery opening 85 arranged in the bushing 81, such as [ Figure 2 ] as shown.

[0046] Optionally, the cylinder head 84 includes a pre-compression chamber 840 communicating with the suction chamber 3. For example, the pre-compression chamber 840 is formed by a wall 841 that forms a part of the cylinder head 84 and forms a space in which a movable valve 843 mounted on a rod 842 coaxial with the piston 82 is arranged.

[0047] Advantageously, cylinder head 84 may include calibrated exhaust ports 846 to regulate the pressure in the compression chamber.

[0048] Possible pump operations :

[0049] Before the pump 1 is started, the fluid reaches 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, passing through the filter 33 and then through the opening in the valve 843. As long as the pre-compression chamber 840 has not yet completely cooled, the fluid returning to the external reservoir includes a portion of the gas generated by contact with the element to be cooled.

[0050] The fluid may also enter the second chamber 6 to cool the compression and delivery assembly 8. The fluid rises to a certain level in the second degassing conduit 9. Degassing is performed via conduit 9 until the second chamber 6 has been cooled to the saturation temperature of the fluid.

[0051] Once the suction chamber 3 and the components have cooled down completely, the pump 1 can be started.

[0052] When the rod 83 of the piston 82 is pulled by the drive system (in [ Figure 2 ] from left to right), which causes rod 842 to move, plate 844 to press against valve 843, thereby pushing the fluid present in pre-compression chamber 840 toward the compression chamber formed by bushing 81, piston 82 and cylinder head 84. The passage is through opening 845, and when piston 82 returns (in [ Figure 2 ] from right to left direction), these openings are then closed so that the fluid is compressed by the piston 82 in the compression chamber and then discharged through the opening 85. The valve (not shown) closing the opening 85 is opened to allow the pressurized fluid to flow out of the pump 1.

[0053] The movement of the piston assembly 82 and its rings (not numbered) in the bushing 81 generates heat which vaporizes a portion of the cryogenic fluid. By means of the second degassing conduit 9, this gaseous portion present in the second chamber 6 can be discharged without returning it to the suction chamber 3 as in the case of known pumps.

Claims

1. A piston pump (1) suitable for pumping fluids at very low temperatures, such as hydrogen, the pump (1) having a suction side (A) and a compression side (B), The suction side (A) comprises: an inlet (4) provided for a 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 conduit (5) communicating with the suction chamber (3), The compression side (B) comprises a pump cylinder (2) carrying an assembly (8) for compressing and delivering the liquid, the cylinder (2) comprising a second chamber (6) communicating with the suction chamber (3) and in which the fluid at a very low temperature circulates in order to cool the compression and delivery assembly (8).

2. A pump (1) according to claim 1, wherein the cylinder (2) comprises a first housing (22) and an internal cylinder body (21) carrying the compression and delivery assembly (8), the first housing (22) being attached to the cylinder body (21), the cylinder body (21) having a concave shape allowing the fluid to circulate in the second chamber (6).

3. Pump (1) according to one of the preceding claims, further comprising a second degassing duct (9) communicating with the second chamber (6) and configured to allow degassing of the fluid circulating in the second chamber (6).

4. Pump (1) according to one of the preceding claims, wherein the compression and delivery assembly (8) comprises: - an integral coaxial pump bushing (81) and cylinder head (84), - a piston (82) axially movable in the bushing (81), the piston forming a fluid compression chamber with the cylinder head (84), the cylinder head (84) connecting the bushing (81) to the suction chamber (3), and - a delivery opening (85) arranged in the bushing.

5. Pump (1) according to the preceding claim, wherein the cylinder head (84) comprises a pre-compression chamber (840) communicating with the suction chamber (3).

6. Pump (1) according to one of claims 4 or 5, wherein the cylinder head (84) comprises an exhaust port (846) configured to allow the pressure in the compression chamber to be adjusted.

7. Pump (1) according to one of claims 2 to 6, wherein the cylinder (2) comprises a second housing (23) which is located outside with respect to the first housing (22) and which forms together with the first housing a space intended to be evacuated.

8. Pump (1) according to the preceding claim, wherein a thermally insulating material (10) is arranged between the first housing (22) and the second housing (23).

9. Pump (1) according to the preceding claim, wherein the thermal insulation material (10) is a multi-layer thermal insulation material.

10. Pump (1) according to the preceding claim, wherein the multilayer thermal insulation material comprises alternating layers of aluminium and glass fibre.

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