CRYOGENIC PUMP

Description

TECHNICAL FIELD OF THE INVENTION

The invention belongs to the technical field of cryogenic pumps applicable to gases liquefied at very low temperatures, such as hydrogen.

TECHNOLOGICAL BACKGROUND OF THE INVENTION

Cryogenic pumps generally comprise a cylinder carrying an assembly for compression and delivery comprising a cylinder liner wherein a piston moves axially to form a compression chamber. As this piston moves, the fluid is alternately drawn from the suction side towards the compression chamber, then compressed in order to be evacuated via a dedicated opening.

The movement of the piston through the friction of the piston rings thereof in the cylinder liner generates heat which can propagate into the compression chamber, causing the fluid to heat up, transforming part of it from an incompressible liquid state into a compressible gas state. The efficiency of the pump is reduced and the wear thereof accelerated as a result of hydraulic shock and/or cavitation. It is therefore necessary to ensure that heat-generating areas are adequately cooled.

Most piston pumps feature cooling and degassing on the suction side only. But on the one hand, cooling of the compression and delivery assembly is not optimal as part of the accumulated heat is not evacuated on the compression side, and on the other hand, the heat created in the cylinder is routed to the suction chamber in order to be evacuated via the single degassing duct, resulting in heating of the liquid in the suction chamber. This process is generally not a disadvantage for use with standard cryogenic fluids down to −196° C., such as nitrogen for example, but with a cryogenic fluid, such as hydrogen having a liquefaction temperature of around −255° C., the pump may cavitate or defuse due to lack of cooling.

The aim of the present invention is to propose a solution to the problems described above.

SUMMARY OF THE INVENTION

For this purpose, 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,

• • the suction side comprising an inlet provided for the liquid and intended to be connected to a liquid supply reservoir external to the pump, a suction chamber for receiving the fluid and a first fluid degassing duct communicating with the suction chamber,
  • the compression side comprising a pump cylinder comprising an assembly for compression and delivery of the liquid,
  • said cylinder comprising a second chamber which communicates with the suction chamber, and wherein the fluid circulates in order to cool the compression and delivery assembly.

The second chamber may have a length covering at least part of the compression and delivery assembly. For example, the second chamber may surround the compression and delivery assembly.

The compression and delivery assembly generates heat which may propagate into the compression chamber. The second chamber allows the fluid at very low temperature to cool said compression and delivery assembly and thus avoids the fluid arriving at the compression chamber from being heated and therefore limits gas formation.

According to one embodiment, the cylinder may comprise a first casing and an inner cylinder body carrying the compression and delivery assembly, said first casing being attached to the cylinder body to at least partially form the second chamber with said body and the body having a recessed shape allowing fluid to flow into said second chamber.

By recessed shape, we mean that the body has openings along the length thereof allowing the movement of the cooling fluid.

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

The heat created by the compression and delivery assembly is partly evacuated via this second degassing duct, which prevents these hot gases from flowing back towards the suction chamber, thus limiting the heating of this fluid and the risk of cavitation.

According to one embodiment, the compression and delivery assembly may comprise:

• • a pump liner and a cylinder head which are integral with each other and may be coaxial with the liner,
  • a piston that is axially movable in the liner forming a fluid compression chamber with the cylinder head, the cylinder head connecting the liner to the suction chamber, and
  • a delivery opening arranged in the liner.

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

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

This pre-compression chamber supplies the compression chamber with fluid from the suction chamber. As the volume of the pre-compression chamber is greater than that of the compression chamber, the compression chamber is perfectly supplied with super-cooled liquid from the suction chamber.

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

Advantageously, the pump comprises a second casing external to the first casing and forming therewith a space intended to be evacuated.

This thermally insulates the pump from the exterior, limiting heat exchange and thus heating of the fluid.

Advantageously, an insulating material is arranged between the first casing and the second casing.

Preferably, the insulating material may be multi-layer insulation. This provides even better thermal insulation for the pump.

In one embodiment, the multi-layer insulation may alternately comprise layers of aluminum and layers of fiberglass, preferably superimposed on each other. Advantageously, this number of layers may be between 10 and 100.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will become apparent from the following description in relation to the appended drawings, given as non-limiting examples, wherein:

FIG. 1 is an overview of a pump according to one embodiment of the invention.

FIG. 2 is an enlarged cross-sectional view of the Z-zone shown in FIG. 1.

FIG. 3 is a partial section along line III-III of FIG. 1.

Unless otherwise specified, the same element appearing on different figures has a unique reference.

DETAILED DESCRIPTION

An example of pump 1 according to the invention is shown in FIG. 1 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 designed 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 for degassing the fluid entering the suction chamber 3. This second opening 5 is also designed to be connected to said external reservoir.

Optionally, the suction side A may also comprise a second casing 32 which is external with respect to the first casing 31. The two casings forming a space that can be evacuated in order to thermally insulate this suction side A.

The compression side B comprises a pump cylinder 2 comprising a cylinder body 21 shown in FIG. 2. The cylinder body 21 carries the compression and delivery assembly 8 which will be described later.

The cylinder 2 also comprises a first casing 22 which is external with respect to the cylinder body 21. It may also comprise a second casing 23 which is external with respect to the first casing 22. As can be seen in FIG. 2, the first casing 22 and the second casing 23 form a space that can be evacuated to create thermal insulation for the cylinder 2 with respect to the outside.

Advantageously, an insulating material 10, in particular a multi-layer insulation, may be arranged between the first casing 22 and the second casing 23 to increase the thermal insulation of the cylinder 2.

The first casing 22 of the cylinder 2 is attached to the cylinder body 21 and forms a second chamber 6 therewith which is connected to the suction chamber 3 via openings 24, so that the fluid at very low temperature enters the second chamber 6 to cool the compression and delivery assembly 8.

To allow the circulation of 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 fluid to pass from the front part 61 to the rear part 62, but also has contact points 64 with the first casing 22. FIG. 3 shows a partial section along line III-III of FIG. 1 showing an example of the hollow shape of the intermediate part of the body 21.

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

The compression and delivery assembly 8 comprises:

• • a pump liner 81 and a cylinder head 84 that are integral and coaxial,
  • a piston 82 that is axially movable in the liner 81 forming a fluid compression chamber with the cylinder head 84, the cylinder head 84 connecting the liner 81 to the suction chamber 3, and
  • a delivery opening 85 arranged in the liner 81, as shown in FIG. 2.

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 by a wall 841 forming part of the cylinder head 84 and forming a space wherein a movable valve 843 mounted on a rod 842 coaxial with the piston 82 is arranged.

Advantageously, the cylinder head 84 may comprise a calibrated exhaust port 846 to adjust the pressure in the compression chamber.

Possible Pump Operation

Prior to the start-up of pump 1, the fluid arrives in 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 the openings in the valve 843. As long as the pre-compression chamber 840 has not cooled down completely, the fluid returning to the external reservoir comprises a fraction of gas generated by contact with the elements to be cooled.

The fluid can also enter the second chamber 6 to cool the compression and delivery assembly 8. The fluid rises in the second degassing duct 9 up to a certain level. Degassing takes place via the duct 9 until the second chamber 6 has cooled to the saturation temperature of the fluid.

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

When the rod 83 of the piston 82 is pulled by a drive system (from left to right in FIG. 2), it causes the rod 842 to move, with the plate 844 pressing against the valve 843 which thus pushes the fluid present in the pre-compression chamber 840 towards the compression chamber formed by the liner 81, the piston 82 and the cylinder head 84. Passage is via the openings 845, which are then closed when the piston 82 returns (right to left direction in FIG. 2), 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 pressurized fluid to flow out of the pump 1.

The movements of the piston assembly 82 and the rings thereof (not marked) in the liner 81 generate heat which vaporizes a fraction of the cryogenic fluid. By virtue of the second degassing duct 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 the case with known pumps.