Cryogenic Pump

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

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.

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 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:

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.

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

An example of pumpaccording to the invention is shown inas seen overall from the outside. The pumpcomprises a suction side A and a compression side B. The suction side A comprises a suction chamberformed by a first casingand having a first openingserving as a liquid inlet to the suction chamber. The openingis designed to be connected to an external reservoir, not shown, comprising the fluid at very low temperature, which is for example hydrogen. The suction chamberfurther comprises a second openingfor degassing the fluid entering the suction chamber. This second openingis also designed to be connected to said external reservoir.

Optionally, the suction side A may also comprise a second casingwhich is external with respect to the first casing. 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 cylindercomprising a cylinder bodyshown in. The cylinder bodycarries the compression and delivery assemblywhich will be described later.

The cylinderalso comprises a first casingwhich is external with respect to the cylinder body. It may also comprise a second casingwhich is external with respect to the first casing. As can be seen in, the first casingand the second casingform a space that can be evacuated to create thermal insulation for the cylinderwith respect to the outside.

Advantageously, an insulating material, in particular a multi-layer insulation, may be arranged between the first casingand the second casingto increase the thermal insulation of the cylinder.

The first casingof the cylinderis attached to the cylinder bodyand forms a second chambertherewith which is connected to the suction chambervia openings, so that the fluid at very low temperature enters the second chamberto cool the compression and delivery assembly.

To allow the circulation of liquid in the second chamber, the cylinder bodyhas a hollow shape. In the example shown, the rear part of the body is hollowed out to form the rear partof the second chamberwith the first casing. The front part of the body is also hollowed out to form the front partof the second chamber. The intermediate part of the cylinder bodyis also hollow to allow fluid to pass from the front partto the rear part, but also has contact pointswith the first casing.shows a partial section along line III-III ofshowing an example of the hollow shape of the intermediate part of the body.

Advantageously, the cylindermay comprise a second degassing ductcommunicating with the second chamberto allow the degassing of the fluid circulating in the second chamber.

The compression and delivery assemblycomprises:

Optionally, the cylinder headcomprises a pre-compression chamberwhich communicates with the suction chamber. For example, the pre-compression chamberis formed by a wallforming part of the cylinder headand forming a space wherein a movable valvemounted on a rodcoaxial with the pistonis arranged.

Advantageously, the cylinder headmay comprise a calibrated exhaust portto adjust the pressure in the compression chamber.

Prior to the start-up of pump, the fluid arrives in the suction chambervia the inletand returns to the reservoir via the openingto cool the suction chamberand the pre-compression chamber, passing through the filterand then the openings in the valve. As long as the pre-compression chamberhas 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 chamberto cool the compression and delivery assembly. The fluid rises in the second degassing ductup to a certain level. Degassing takes place via the ductuntil the second chamberhas cooled to the saturation temperature of the fluid.

Once the suction chamberand the parts have cooled down completely, the pumpcan be started.

When the rodof the pistonis pulled by a drive system (from left to right in), it causes the rodto move, with the platepressing against the valvewhich thus pushes the fluid present in the pre-compression chambertowards the compression chamber formed by the liner, the pistonand the cylinder head. Passage is via the openings, which are then closed when the pistonreturns (right to left direction in), so that the fluid is compressed by the pistonin the compression chamber and then discharged via the opening. The valve (not shown) closing this openingopens to allow pressurized fluid to flow out of the pump.

The movements of the piston assemblyand the rings thereof (not marked) in the linergenerate heat which vaporizes a fraction of the cryogenic fluid. By virtue of the second degassing duct, it is possible to evacuate this gaseous fraction present in the second chamberwithout returning it to the suction chamberas is often the case with known pumps.