Piston compressor and method for compressing a cryogenic gaseous medium, in particular hydrogen

Abstract

A piston compressor for compressing a cryogenic fluid medium, in particular in the form of hydrogen is described. It is provided according that an encircling first gap between a first piston and an inner side, facing towards the first piston, of a first cylinder is sealed off by means of at least one seal, which is provided on the first piston, in such a way that leakage medium from the first cylinder interior space passes through the first gap into the interior space of the housing and flows around the rotor and in particular also the stator, wherein the permanent magnets are provided with a coating in order to protect against the medium, in particular in order to protect against hydrogenation in the case of a medium in the form of hydrogen. A method for compressing a cryogenic fluid medium, in particular hydrogen is also disclosed.

1 . A piston compressor for compressing a cryogenic fluid medium comprising:
 a linear motor that comprises a stator and an armature with permanent magnets, wherein the stator is designed for driving the armature by generating a magnetic field in order to move the armature relative to the stator in a reciprocating fashion along a longitudinal axis, along which the armature extends,   a housing of the linear motor that defines an interior, in which the armature and the stator are arranged,   a first cylinder that is connected to the housing and defines a first cylinder chamber that originates at said interior,   a first cylinder head of the first cylinder with an inlet, through which the medium can be introduced into the first cylinder chamber, and with an outlet, through which the compressed medium can be discharged from this first cylinder chamber,   a first piston that protrudes into the first cylinder chamber and extends along the longitudinal axis, wherein this first piston is coupled to the armature such that the first piston is driven by the armature and moved in a reciprocating fashion along the longitudinal axis, wherein the first piston is designed for compressing medium located in the first cylinder chamber during a motion of the first piston toward the first cylinder head,   characterized in that an encircling first gap between the first piston and an inner side of the first cylinder facing the first piston is sealed with at least one seal provided on the first piston in such a way that medium is transferred from the first cylinder chamber into the interior of the housing through this first gap and flows around the armature, wherein the permanent magnets are provided with a coating as protection from this medium.   
     
     
         2 . The piston compressor according to  claim 1 , characterized in that the permanent magnets feature an alloy comprising neodymium, iron and boron with the composition Nd 2 Fe 14 B. 
     
     
         3 . The piston compressor according to  claim 1 , characterized in that the coating is selected from the group consisting of the following coatings:
 a nickel-copper-nickel coating, wherein the coating is produced by initially applying at least one layer of nickel, then a layer of copper and ultimately another layer of nickel, and wherein the overall layer thickness of the coating lies in the range between 3 μm and 500 μm,   a coating that is selected from the group consisting of aluminum oxide, tungsten, molybdenum, gold, platinum, chromium, cadmium, tin, aluminum, silicates of tungsten and molybdenum or nickel-aluminum alloys, and   a coating that comprises at least one oxide of the permanent magnet material, wherein this coating is produced by bringing the permanent magnets in contact with oxygen.   
     
     
         4 . The piston compressor according to  claim 1 , characterized in that the interior is fluidically connected to a supply line leading to the inlet on the first cylinder head by means of a first leakage return line such that the interior is acted upon with a pressure corresponding to the pressure in said supply line, wherein this first leakage return line branches off a first end section of the interior, and wherein the first cylinder chamber originates at this first end section of the interior. 
     
     
         5 . The piston compressor according to  claim 1 , characterized in that the piston compressor furthermore comprises:
 a second cylinder that is connected to the housing and defines a second cylinder chamber that originates at the interior, as well as   a second cylinder head of the second cylinder, wherein the second cylinder head has an inlet, through which the medium can be introduced into the second cylinder chamber, and an outlet, through which the compressed medium can be discharged from this second cylinder chamber, and   a second piston that protrudes into the second cylinder chamber and extends along the longitudinal axis, wherein this second piston is coupled to the armature such that the second piston is driven by the armature and moved in a reciprocating fashion along the longitudinal axis, wherein the second piston is designed for compressing medium located in the second cylinder chamber during a motion of the second piston toward the second cylinder head, and wherein an encircling second gap between the second piston and an inner side of the second cylinder facing the second piston is sealed with the least one seal provided on the second piston in such a way that medium is transferred from the second cylinder chamber into the interior of the housing through this second gap and flows around the armature.   
     
     
         6 . The piston compressor according to  claim 4 , characterized in that the interior is fluidically connected to the supply line leading to the inlet of the first cylinder head by means of a second leakage return line, wherein this second leakage return line branches off a second end section of the interior, and wherein the second cylinder chamber originates at this second end section of the interior. 
     
     
         7 . The piston compressor according to  claim 1 , characterized in that a position detection means is provided for detecting the position of the first and/or the second piston, wherein said position detection means comprises a displacement transducer that is coupled to the first or the second piston and designed for generating a first magnetic field, as well as for being moved along a measuring element, which extends in the interior along the longitudinal axis and comprises a magnetic, elastically deformable body, during each reciprocating motion of the armature, wherein the position detection means is designed for generating a second magnetic field around the measuring element by applying a current signal to the second measuring element such that a torsional wave is generated in the elastically deformable body due to the interaction of the two magnetic fields, and wherein the position detection means is furthermore designed for detecting said torsional wave and for determining said position based on the time difference between the application of the current signal and the detection of the torsional wave. 
     
     
         8 . A method for compressing a cryogenic fluid medium by utilizing a piston compressor comprising:
 a linear motor, that comprises a stator and an armature with permanent magnet, wherein the stator is designed for driving for driving the armature by generating a magnetic field in order to move the armature relative to the stator in a reciprocating fashion along a longitudinal axis, along which the armature extends,   a housing of the linear motor that defines an interior, in which the armature and the stator are arranged,   a first cylinder that is connected to the housing and defines a first cylinder chamber that originates at said interior,   a first cylinder head of the first cylinder with an inlet through which the medium can be introduced info the first cylinder chamber, and with an outlet, through which the compressed medium can be discharged from this first cylinder chamber,   a first piston that protrudes into the first cylinder chamber and extends along the longitudinal axis, wherein this first piston is coupled to the armature such that the first piston is driven by the armature and moved in a reciprocating fashion along the longitudinal axis, wherein the first piston is designed for compressing medium located in the first cylinder chamber during a motion of the first piston toward the first cylinder head,   characterized in that an encircling first gap between the first piston and an inner side of the first cylinder facing the first piston is sealed with at least one seal provided on the first piston in such a way that medium is transferred from the first cylinder chamber into the interior of the housing through this first gap and flows around the armature, wherein the permanent magnets are provided with a coating as protection from this medium, wherein the medium is compressed at least in the first cylinder chamber by means of the first piston, wherein part of the medium is transferred into the interior of the housing through the first gap and flows around the armature, and wherein the permanent magnets are protected from said medium.   
     
     
         9 . The method according to  claim 8 , characterized in that medium compressed in the first cylinder chamber is discharged from the first cylinder chamber and compressed once again in the second cylinder chamber by means of the second piston, wherein part of the medium transferred from the second cylinder chamber into the interior of the housing through the second gap and flows around the armature. 
     
     
         10 . The method according to  claim 8 , characterized in that medium transferred into the interior is returned to the inlet on the first cylinder head through the first leakage return line and/or the second leakage return line. 
     
     
         11 . The method according to  claim 8 , characterized in that the position of the armature, the first piston and/or the second piston is detected, and that the stroke of the first and/or the second piston is controlled in such a way that the clearance volume in the first and/or the second cylinder chamber is reduced. 
     
     
         12 . The method according to  claim 8 , characterized in that the medium is supplied to the piston compressor in liquid form and transferred into the gaseous state before it is introduced into the first cylinder chamber wherein ambient heat and/or waste heat of the linear motor is used for evaporating the medium. 
     
     
         13 . The piston compressor according to  claim 1 , characterized in that the cryogenic fluid medium is in the form of hydrogen. 
     
     
         14 . The piston compressor according to  claim 1 , characterized in that the protection is against hydrogenation when a hydrogen medium is being processed. 
     
     
         15 . The method according to  claim 8 , characterized in that the cryogenic fluid medium is in the form of hydrogen. 
     
     
         16 . The method according to  claim 8 , characterized in that the protection is against hydrogenation when a hydrogen medium is being processed.