PISTON COMPRESSOR AND METHOD FOR COMPRESSING A CRYOGENIC GASEOUS MEDIUM, IN PARTICULAR HYDROGEN
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.
The invention pertains to a piston compressor according to claim 1, as well as to a method for compressing a fluid medium, particularly a cryogenic gaseous medium in the form of hydrogen, according to claim 8.
In the context of the present invention, a cryogenic fluid medium particularly refers to a fluid medium that has a temperature in the range between 0 K and 130 K. In this case, the fluid medium respectively is a gaseous or liquid medium or a mixed phase of a gaseous and a liquid phase. However, the inventive piston compressor can also be operated with higher input temperatures, in particular, up to 320 K, i.e. in a range between 0 K and 320 K.
Under standard conditions, gases have a very low density in comparison with other energy carriers. In order to efficiently store a gas, it is necessary to increase the mass of the gas in the available storage space.
An effective storage of gases is in most cases realized by increasing the gas pressure. The most popular methods and devices currently used for compressing a gaseous medium involve compressor systems such as reciprocating piston compressors, ionic liquid piston compressors, rotary screw compressors or diaphragm-type compressors. Furthermore, known methods for conveying and compressing liquid cryogenic mediums are in most cases realized with piston compressor systems.
Methods and devices of the initially cited type are used, for example, in natural gas and hydrogen compressor stations of the type realized in natural gas fueling stations.
For example, DE-B 102006060147 discloses a fluid processing machine that is driven by a linear motor, in which, e.g., the stator and the armature are separated by a can and static seals.
The aforementioned compressors typically operate with gas input temperatures that lie in the range of the ambient temperature at the operating site. In compressor systems that are supplied with liquid gas, it is therefore necessary to transform the liquid into the gaseous state. The adaptation of the gas input temperature into the compressor is realized with evaporator systems. The energy required for the temperature increase of the medium in the evaporator systems is obtained, for example, by means of heat extraction from the surroundings or with an electrical preheating device.
High-capacity cryopumps, in contrast, have to be supplied with a liquid medium. The liquid tanks required for the supply are extremely uneconomical due to the limited insulating options and the associated losses of liquid hydrogen occurring over long storage times as a result of unusable boil-off gases.
Due to the temperature differences occurring in compressors, it is a constructive necessity, for example in piston compressors, to provide length tolerances that are associated with an increase of the clearance volume. The increased gas re-expansion caused by the relatively large clearance volume results in a reduced capacity.
In a compressor without clearance volume (e.g. an ionic liquid piston compressor)f the crystallization temperature of the ionic fluid limits the use at low temperatures. In addition, ionic liquid piston compressors require a horizontal installation position in order to maintain the liquid column.
Furthermore, piston compressors known from the prior art frequently cannot be constructed in a pressure-encapsulated fashion such that a certain leakage of the medium to be compressed into the surroundings has to be accepted. Even static seals only make it possible to realize a leakage-free seal under certain conditions. If hydrogen is conveyed and compressed as it is the case in the system disclosed in DE-B 102006060147, a person skilled in the art furthermore faces the problem of hydrogenation of the permanent magnets by the leakage gas.
Based on these circumstances, the objective of the present invention can be seen in disclosing an improved piston compressor, as well as a corresponding method for compressing a fluid (e.g. gaseous) and, in particular, cryogenic medium, especially hydrogen.
This objective is attained by means of a piston compressor with the characteristics of claim 1. Advantageous embodiments of the inventive piston compressor are disclosed in the corresponding dependent claims and described in greater detail below.
According to claim 1, the inventive piston compressor for compressing, in particular, a cryogenic fluid medium, especially in the form of hydrogen, features a linear motor comprising a stator and an armature with permanent magnets, wherein the stator is conventionally designed for 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. The piston compressor also features a housing of the linear motor that defines an interior, in which the armature and the stator are arranged, and a first cylinder of the piston compressor that is connected to the housing and defines a first cylinder chamber originating at said interior, as well as a first cylinder head of the first cylinder with an inlet, through which the medium can be introduced into the first cylinder chamber of the first cylinder, and with an outlet, through which the compressed medium can be discharged from said first cylinder chamber. The piston compressor furthermore features a first piston that protrudes into the first cylinder chamber and extends along the longitudinal axis, wherein this first piston is connected to the armature such that it is driven by the armature and moved along the longitudinal axis in a reciprocating fashion, and wherein the first piston is designed for compressing medium located in the first cylinder chamber when the first piston moves in the direction of the first cylinder head. According to the invention, it is proposed 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 only part of the medium, which is presently referred to as leakage medium, can transfer from the first cylinder chamber into the interior of the housing through this first gap and flow around the armature and, in particular, the stator, wherein the permanent magnets of the armature are provided with a coating that serves as protection from said leakage medium, particularly as protection from hydrogenation and also embrittlement when a medium in the form of hydrogen is processed.
The at least one seal provided on the first piston therefore is intended to seal the first cylinder chamber, but a certain leakage past the seal can typically not be prevented. This also applies to the second piston (see below).
The inventive piston compressor and the method described below are preferably realized or designed for compressing a fluid medium. The medium therefore may be purely gaseous or consist of a mixture of a gaseous and a liquid phase. The medium may furthermore also consist of a liquid.
According to a preferred embodiment of the inventive piston compressor, the aforementioned permanent magnets respectively feature a neodymium-iron-boron alloy or are made of this material.
Suitable materials for the inventive permanent magnets generally are ferrites and their alloys with the zinc and/or nickel and with manganese, as well as strontium-ferrites, cobalt-ferrites, barium-ferrites and also alloys of samarium-cobalt and aluminum-nickel-cobalt.
According to another preferred embodiment of the inventive piston compressor, it is proposed that the coating of the permanent magnet consists of a nickel-copper-nickel coating. In other words, the permanent magnets are initially coated with a layer of nickel, then with a layer of copper and ultimately with another (particularly outermost) layer of nickel. Inventive NiCuNi coatings can be produced, e.g., by means of electroplating.
A coating of the permanent magnets for protecting the permanent magnets may furthermore also feature one of the following materials or alloys: aluminum oxide, tungsten, molybdenum, gold, platinum, chromium, cadmium, tin, aluminum, silicates of tungsten and molybdenum or nickel-aluminum alloys.
The coating may furthermore also consist of an oxidation layer of the base material of the permanent magnets that is produced, in particular, prior to the hydrogenation/embrittlement. Such an oxidation layer can be produced, e.g., by exposing the unprotected permanent magnets to a flow of atmospheric oxygen for a certain time period or preferably by acting upon the permanent magnets with pressure in (particularly high-purity) oxygen.
The overall layer thickness of the respective coating perpendicular to its surface area or perpendicular to the individual layers preferably lies in the range between 3 μm and 500 μm.
It is furthermore preferred that the interior of the housing 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 of the housing is acted upon with a pressure corresponding to the pressure in said supply line, wherein the first leakage return line preferably branches off a first end section of the interior, and wherein the first cylinder chamber preferably originates at this first end section of the interior.
According to another preferred embodiment of the invention, the piston compressor features a second cylinder that is connected to the housing. Such a second cylinder makes it possible to carry out a two-stage compression of the medium to be compressed. The second cylinder preferably features a second cylinder chamber that originates at the interior of the housing of the linear motor, as well as a second cylinder head of the second cylinder, wherein this second cylinder head features an inlet, through which the medium to be compressed can be introduced into the second cylinder chamber of the second cylinder. The second cylinder head furthermore features an outlet, through which the medium compressed in the second cylinder chamber can be discharged from the second cylinder chamber. It is furthermore preferred to provide a second piston that protrudes into the second cylinder chamber and extends along the aforementioned longitudinal axis. The second piston preferably is also connected to the armature such that the second piston is driven by the armature and moved along the longitudinal axis in a reciprocating fashion, wherein the second piston is designed for compressing medium located in the second cylinder chamber when the second piston moves in the direction of the second cylinder head.
An encircling second gap preferably also exists between the second piston and an inner side of the second cylinder facing the second piston, wherein this second gap is sealed with at least one seal provided on the second piston in such a way that only part of the medium, which is presently likewise referred to as leakage medium, can transfer from the second cylinder chamber into the interior of the housing through this second gap and flow around the armature and, in particular, the stator (see above).
It is furthermore preferred that the interior on the side of the second cylinder is fluidically connected to the supply line leading to the inlet on the first cylinder head by means of a second leakage return line, wherein this second leakage return line particularly branches off a second end section of the interior that lies opposite of the first end section referred to the longitudinal axis of the piston compressor, and wherein the second cylinder chamber preferably originates at this second end section of the interior. The two cylinders therefore are arranged to both sides of the linear motor such that medium is taken in by one cylinder chamber while it is discharged from the other cylinder chamber.
In order to influence the motion of the piston and, in particular, to control the stroke of the first and the second piston, it is preferred to provide a position detection means for detecting the position of the first and/or second piston. In this respect, sensorless methods utilizing construction-related and position-specific ratios of the inductances in the longitudinal and lateral direction referred to the center axes of the linear motor may be considered, wherein the position-specific ratios make it possible to deduce the position. It would furthermore be possible to use methods according to EP-B 1746718 or WO-A 1992019038.
According to an embodiment of the invention, the position detection means features a displacement transducer that is coupled to the first or the second piston and generates a first magnetic field (the displacement transducer may be formed, e.g., by a magnet), as well as a measuring element that features, e.g., a compression-proof rod, in which a magnetic, elastically deformable body is respectively arranged or mounted. In this case, the displacement transducer is designed for generating a longitudinal magnetic field in the measuring element. The position detection means is furthermore designed for passing a current signal through the measuring element such that a second magnetic field is created radially around the measuring element. When the two magnetic fields meet, the elastic body is deformed such that a torsional wave passes through the measuring element and is detected by the position detection means. The position of the displacement transducer and therefore the position of the piston or pistons are deduced based on the time difference between the current pulse and the arrival of the torsional wave.
The above-defined objective of the invention is furthermore attained by means of a method for compressing a cryogenic fluid medium, especially in the term of hydrogen, by utilizing an inventive piston compressor, wherein the fluid medium is compressed at least in the first cylinder chamber by means of the first piston, wherein only part of the medium (referred to as leakage medium) is transferred into the interior of the housing through this first gap and flows around the armature and, in particular, the stator, and wherein the permanent magnets are particularly protected from said medium, especially from hydrogenation and also embrittlement, by the coating of the permanent magnets.
According to an advantageous embodiment of the inventive method, it is furthermore proposed 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 only part of the medium, is likewise transferred from the second cylinder chamber into the interior of the housing of the linear motor through the second gap and flows around the armature and, in particular, also the stator therein.
It is furthermore preferred 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. The interior of the housing is therefore acted upon with pressure in the above-described fashion and allows the return of the leakage medium to the inlet on the first cylinder head (first compressor stage of the piston compressor).
As already mentioned above, it is furthermore preferred to detect the position of the armature, the first piston and/or the second piston, particularly with the above-described position detection means. The stroke of the first and/or the second piston is preferably controlled in such a way that the corresponding clearance volume in the first and/or second cylinder chamber is reduced in order to increase the efficiency of the piston compressor. In this context, the respective clearance volume is the volume defined by the end face of the respective piston together with the encircling inner side of the respective cylinder, as well as the inner side of the respective cylinder head facing the piston. As the clearance volume diminishes, the piston or its end face contacts the respective cylinder head.
In the inventive method, it is particularly preferred that the first medium is supplied to the piston compressor in liquid form and generally transferred into the gaseous state shortly before it is introduced into the first cylinder chamber, wherein ambient heat and/or waste heat of the linear motor is preferably used for evaporating the medium.
For compression purposes, it is proposed that the intake temperature of the medium to be compressed lies slightly above that of the point of equilibrium of the corresponding intake pressure. In addition to supplying a liquid medium to be compressed, it is furthermore also possible to supply a cryogenic gaseous medium that is transported into the first cylinder chamber from a source in a cryogenic gaseous state.
Other characteristics and advantages of the invention are elucidated in the following description of an exemplary embodiment of the invention with reference to the figures.
In these figures:
An inventive piston compressor 1 is illustrated in
A first piston 31 slides in the first cylinder chamber 300, wherein an encircling gap S is formed between the piston 31 and an inner side 300a of the first cylinder 30 facing the first piston 31, and wherein said gap is sealed, in particular, with at least one or preferably several slotted seals 32 that seal in the dynamic mode, but not statically. Such slotted seals 32 are particularly characterized by a transection that may be produced with a cut extending parallel, oblique or three-dimensionally offset to the cylinder axis of the seal. The seal 32 can be manufactured with such a transection or the transection can be produced after the manufacture of the seal 32.
A second piston 70 analogously slides in the second cylinder chamber 700 and once again contacts an inner side 700a of the second cylinder 70, in particular, with at least one or preferably several slotted seals 72 and thereby seals an encircling second gap S′ between the second piston 71 and said inner side 700a of the cylinder 70.
During the operation or the compressor, the two pistons 31, 71 of the thusly designed compressor stages move along the longitudinal axis L in a reciprocating fashion between their reversal points in the two cylinders 30, 70 and are respectively centered and fixed on the piston rod and the armature 20 of the tubular linear motor 10 by means of a corresponding device. In this case, a centering adapter 21, 23 is respectively arranged on the free ends of the armature 20. The centering adapters 21, 23 are respectively provided with a thread. The counter rings 22, 24 are provided with a corresponding mating thread and screwed to the respectively assigned centering adapter 21, 23, wherein the centering adapters 21, 23 are on one side screwed to the armature 20 and the respective piston 31, 71 is clamped between the respective centering adapter 21, 23 and the respective counter ring 22, 24 such that a rigid connection between the armature 20 and the pistons 31, 71 results.
In this case, the second piston 71 is realized in two parts and features two sections 710, 720, wherein the first section 710 is fixed on the armature 20, namely by means of the aforementioned centering adapter 23 and the assigned counter ring 24, and wherein the second section 720 of the second piston 71 protrudes into the second cylinder 700 from the interior 100 and compresses medium M taken in by the second cylinder chamber 700 therein.
The end faces of the two cylinders 31, 71 are respectively closed with a first and a second cylinder head 40, 80, through which the medium hi to be compressed is introduced into the respective cylinder 30, 70 and discharged from the respective cylinder in compressed form.
In addition, a centering surface of a flange 12 respectively centers the cylinders 30, 70 relative to the respective flange 12, wherein said flanges 12 are in turn centered relative to the housing 11 of the linear motor 10 by means of a centering surface. The end faces of both flanges 12 are respectively screwed to the housing 11 and thereby fix the cylinders 30, 70 on the housing 11. The housing 11 and the cylinders 30, 70 are sealed relative to the surroundings by means of static seals in the form of O-rings 101, 102 arranged between the respective flange 12 and the housing 11. The housing 11 is thereby pressure-encapsulated. The linear motor 10 itself is fixed on its respective base by means of a flange mounting 13 on the housing 11.
In addition, each piston 31, 71 features an annular guide band 33, 73 that encircles the respective piston and serves for absorbing radial forces. As already mentioned, parts of the medium M located in the respective cylinder chambers 300, 700 may be transferred into the interior 100 of the housing 11 through the aforementioned gaps S, S′ during the reciprocating motion of the two pistons 31, 71, wherein this seal leakage is returned to the input side of the piston compressor 1 through a first and a second leakage return line 51, 52 in the form of a pipeline. In this case, the first leakage return line 51 branches off the first end section 100a of the interior 100 and is fluidically connected to a supply line 61, through which medium M to be compressed can be supplied to an inlet 41 of the first cylinder head 40. This inlet 41 can be closed by means of a valve in the form of a suction valve 410. Due to the pressure-encapsulated design and the above-described leakage return, the stator and the armature 20 of the linear motor 10 are acted upon with a pressure corresponding to the supply pressure of the piston compressor 1 at the inlet 41. Leakage gas M′ accordingly flows around the stator and the armature 20, which in turn transfer heat to the leakage gas M′ during the operation of the compressor. Medium M compressed in the first cylinder chamber 300 by means of the first piston 31 is discharged through an outlet 42 on the first cylinder head 40 that can be closed with a pressure valve 420.
The first cylinder head 40 with the suction and pressure valves 410, 420 is positioned on an end of the first cylinder 30 and screwed to the first cylinder 30 by means of a coupling ring. The second cylinder head 80 is analogously fixed on the opposite end of the second cylinder 70 by means of a coupling ring, wherein the second cylinder head 80 also features an inlet 81 and an outlet 82 that can be respectively closed with a suction valve 810 and a pressure valve 820. A (not-shown) connecting line leads from the outlet 42 of the first cylinder head 40 to the inlet 41 of the second cylinder 80, wherein it is preferred that the supply line 61 and said connecting line are respectively realized in a thermally insulated fashion.
During the compression of a hydrogenous medium M, the permanent magnets P of the linear motor 10 need to be protected from the hydrogen molecules. The high-performance magnets used in heavy-duty linear motors 10 preferably consist of alloys of the elements neodymium-iron-boron. Neodymium is a rear-earth metal. Rare earths are used in metal hydride reservoirs for storing hydrogen. In this case, the effect of adsorption and subsequent dispersion of the hydrogen atoms in the metal matrix is utilized, but this effect is extremely undesirable in the linear motor 10 and would destroy she permanent magnets P over time. The protection of the permanent magnets P from this hydrogen accumulation is preferably realized in the form of a nickel-copper-nickel coating of the permanent magnets P.
The positioning of the two pistons 31, 71 in the corresponding cylinder chambers 300, 700 is preferably realized with a position detection system 90 that may consist of a suitable displacement transducer system or of a sensorless control system. In this way, the drive concept by means of the tubular linear motor 10 allows highly dynamic interventions in the motion sequences of the piston compressor 1 during the compression process. This makes it possible to design the reciprocating piston compressor variably and to react to length changes resulting from thermal expansions by adapting the stroke. Consequently, the adaptation of the piston stroke of both pistons 31, 71 minimizes the clearance volume and thereby positively affects the capacity of the piston compressor 1.
The compression of a cryogenic gaseous medium M, particularly in the form of hydrogen, by means of the inventive piston compressor 1 is preferably realized in that said hydrogen M is taken in by the first compression chamber or the first cylinder chamber 300 from a hydrogen reservoir through the supply line 61 that preferably is thermally insulated and through the suction valve 410 of the first cylinder head 40, wherein the hydrogen M being taken in is in the next cycle compressed by the first piston 31 (in that the first piston 31 moves toward the first cylinder head 40) and discharged through the pressure valve 410 on the first cylinder head 40. The compressed gas M being discharged is taken in by the second cylinder chamber 700 through the aforementioned connecting line, which preferably is likewise thermally insulated, and through the suction valve 810 of the second cylinder head 80 of the second compressor stage, as well as subsequently compressed in the second cylinder chamber due to a corresponding motion of the second piston 71 and discharged through the pressure valve 820. The density of the hydrogen has been increased as a result of the pressure increase. Due to the structural shape, the compression by the first stage and the intake by the section stage sake place reciprocally simultaneous.
The inventive compression at low temperature levels likewise results in a lower enthalpy difference of the medium M between the intake state and the final compressed state than in a process carried out with the same pressure potentials, but at a higher temperature (e.g. gas at room temperature). In this way, the effort required for the compression is reduced, which in turn manifests itself in reduced power consumption.
The inventive compression at a low temperature level particularly makes it possible to forgo an intermediate circuit heat exchanger because the intermediate circuit temperature after the first compressor stage still remains below the typical ambient temperature encountered at the operating sites due to a temperature increase caused by the compression process.
The inventive compression at a low temperature level is furthermore associated with high specific densities of the mediums M such that a relatively high capacity is achieved, particularly for mere gas compressors.
Due to the preferred fully hermetic design of the compressor system 1, a dynamic seal of moving parts relative to the surroundings is eliminated such that the known technical advantages of a static seal can be utilized.
The fully hermetic design of the piston compressor system 1 prevents the contamination of the housing 11 with ambient air. This is realized in that the housing 11 is constantly acted upon with an overpressure that corresponds to the supply pressure of the first compressor stage. This allows the return of the gas leakage M′ of the dynamic piston seals 32, 72 into the respective intake section or cylinder chamber 300, 700.
The above-described device for respectively fixing the pistons on the linear motor piston rod and on the so-called armature 20 allows an uncomplicated exchange of both pistons 31, 71 if servicing is required. If the cylinder diameters are adapted simultaneously, the piston diameters can furthermore be varied in such a way that either higher final compression pressures are achieved or the capacity is increased.
In compressor stations 1 that are supplied with a liquid, it is still possible to take in the boil-off gas created due to a heat input into the tank and to utilize this gas for the compression.
Despite the fact that a high process-related capacity of the compressor system 1 can be realized, the space requirement remains small in comparison with conventional gas compression systems.
The above-described compressor system 1 can be advantageously operated horizontally, as well as vertically.
In an embodiment of the piston compressor 1 for compressing hydrogen, it is proposed that the first piston 31 has a diameter of 42 mm and the second piston 71 has a diameter of 16 mm. The frequency of the piston motion preferably lies at 10 Hz, the mass flow of the medium M preferably amounts to 10 kg/h and the oscillating inertia forces (composed of the individual oscillating inertia forces of the oscillating components: armature 20, centering adapter 21, 23, counter ring 22, 24, piston 31, 37, seal 32, 72 and guide band. 33, 73) preferably amounts to 50 kg. The stroke of the pistons 31, 71 preferably amounts to 120 mm. The piston motion preferably has a harmonic function. The resulting compression force amounts to 10 kN and the footprint of the compressor 1, i.e. the surface projected in a top view, measures approximately 2.5 m×1 m. The attainable maximum force of the linear motor 10 lies at 13.8 kN and the attainable maximum speed of the linear motor 10 lies at 4.1 m/s. In this case, the rated power of the linear motor 10 amounts to 26.6 kW.
The hydrogen is preferably introduced into the first cylinder chamber with a temperature of 60 K and a pressure of 6 bara, compressed and discharged with a temperature of 184K and a pressure 133 bara, wherein the hydrogen is then pressed into the second cylinder chamber 100, in which it is compressed once again, and ultimately discharged with a temperature of 288 K and a pressure of 600 bara.
LIST OF REFERENCE NUMERALS
- 1 Piston compressor
- 10 Linear motor
- 11 Housing
- 12 Flange
- 13 Flange
- 20 Armature
- 21 Centering adapter
- 22 Counter ring
- 23 Centering adapter
- 24 Counter ring
- 30 First cylinder
- 31 First piston
- 32 Seal
- 33 Guide band
- 40 First cylinder head
- 41 Inlet
- 42 Outlet
- 51 First leakage return line
- 52 Second leakage return line
- 61 Supply line
- 70 Second cylinder
- 71 Second piston
- 72 Seal
- 73 Guide band
- 80 Second cylinder head
- 81 Inlet
- 82 Outlet
- 90 Position detection means
- 91 Displacement transducer
- 92 Measuring element
- 100 Interior
- 100a First end section
- 100b Second end section
- 101, 102 O-rings (static seals)
- 300 First cylinder chamber
- 300a Inner side
- 400 Housing
- 410 valve (suction valve)
- 420 Valve (pressure valve)
- 700 Second cylinder chamber
- 700a Inner side
- 810 Valve (suction valve)
- 820 valve (pressure valve)
- M Medium (e.g. hydrogen)
- M′ Leakage medium
- P Permanent magnets (armature)
- B Coating
- L Longitudinal axis
- S First gap
- S′ Second gap
Claims
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 Nd2Fe14B.
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.
Type: Application
Filed: Nov 5, 2014
Publication Date: Sep 29, 2016
Inventors: Robert Adler (Gerasdorf), Christoph Nagl (Windhaag 1)
Application Number: 15/034,564
