U.S. patent application number 15/034564 was filed with the patent office on 2016-09-29 for piston compressor and method for compressing a cryogenic gaseous medium, in particular hydrogen.
The applicant listed for this patent is LINDE AKTIENGESELLSCHAFT. Invention is credited to Robert Adler, Christoph Nagl.
Application Number | 20160281705 15/034564 |
Document ID | / |
Family ID | 51900838 |
Filed Date | 2016-09-29 |
United States Patent
Application |
20160281705 |
Kind Code |
A1 |
Adler; Robert ; et
al. |
September 29, 2016 |
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.
Inventors: |
Adler; Robert; (Gerasdorf,
AT) ; Nagl; Christoph; (Windhaag 1, AT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LINDE AKTIENGESELLSCHAFT |
Munchen |
|
DE |
|
|
Family ID: |
51900838 |
Appl. No.: |
15/034564 |
Filed: |
November 5, 2014 |
PCT Filed: |
November 5, 2014 |
PCT NO: |
PCT/EP2014/002960 |
371 Date: |
May 5, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F04B 39/121 20130101;
F04B 25/005 20130101; F04B 35/04 20130101; F04B 37/18 20130101;
F04B 49/12 20130101; F04B 39/123 20130101; F04B 53/143 20130101;
F04B 17/04 20130101; F04B 35/045 20130101; F04B 39/0005
20130101 |
International
Class: |
F04B 49/12 20060101
F04B049/12; F04B 37/18 20060101 F04B037/18; F04B 53/14 20060101
F04B053/14; F04B 39/12 20060101 F04B039/12; F04B 35/04 20060101
F04B035/04; F04B 25/00 20060101 F04B025/00; F04B 39/00 20060101
F04B039/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 21, 2013 |
DE |
10 2013 019 499.7 |
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 Nd.sub.2Fe.sub.14B.
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 .mu.m and 500 .mu.m, 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.
Description
[0001] 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.
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] 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).
[0016] 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.
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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 .mu.m and
500 .mu.m.
[0023] 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.
[0024] 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.
[0025] 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).
[0026] 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.
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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.
[0031] 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).
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] In these figures:
[0037] FIG. 1 shows a partially sectioned view of an inventive
piston compressor; and
[0038] FIG. 2 shows another partially sectioned view of the
inventive piston compressor according to FIG. 1.
[0039] An inventive piston compressor 1 is illustrated in FIG. 1
and FIG. 2. The piston compressor 1 features a linear motor 10 with
a stator and with an armature 20 that can be moved along a
longitudinal axis L in a reciprocating fashion by means of the
stator. In this case, the stator generates a magnetic field that
cooperates with the permanent magnets P of the armature 20 such
that this armature is moved along the longitudinal axis L in a
reciprocating fashion. In this case, the stator and the armature 20
of the linear motor 10, which is presently realized in the form of
a tubular linear motor 10, are arranged in a housing 11 of the
linear motor 10 that defines an interior 100 of the linear motor
10. Along the longitudinal axis L, the piston compressor 1 features
a first cylinder 30 and a second cylinder 70 to both sides of the
housing 11, wherein said cylinders respectively enclose a first
cylinder chamber 300 and a second cylinder chamber 700. These two
cylinder chambers 300, 700 respectively extend along the
longitudinal axis L from a first end section 100a and a second end
section 100b of the interior 100 of the housing 11. The two end
sections 100a, 100b of the interior 100 of the housing 11 lie
opposite of one another along the longitudinal axis L.
[0040] 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.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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.
[0052] 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.
[0053] 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.
[0054] 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.
[0055] 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.
[0056] 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.
[0057] 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.
[0058] 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.
[0059] The above-described compressor system 1 can be
advantageously operated horizontally, as well as vertically.
[0060] 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.times.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.
[0061] 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
[0062] 1 Piston compressor [0063] 10 Linear motor [0064] 11 Housing
[0065] 12 Flange [0066] 13 Flange [0067] 20 Armature [0068] 21
Centering adapter [0069] 22 Counter ring [0070] 23 Centering
adapter [0071] 24 Counter ring [0072] 30 First cylinder [0073] 31
First piston [0074] 32 Seal [0075] 33 Guide band [0076] 40 First
cylinder head [0077] 41 Inlet [0078] 42 Outlet [0079] 51 First
leakage return line [0080] 52 Second leakage return line [0081] 61
Supply line [0082] 70 Second cylinder [0083] 71 Second piston
[0084] 72 Seal [0085] 73 Guide band [0086] 80 Second cylinder head
[0087] 81 Inlet [0088] 82 Outlet [0089] 90 Position detection means
[0090] 91 Displacement transducer [0091] 92 Measuring element
[0092] 100 Interior [0093] 100a First end section [0094] 100b
Second end section [0095] 101, 102 O-rings (static seals) [0096]
300 First cylinder chamber [0097] 300a Inner side [0098] 400
Housing [0099] 410 valve (suction valve) [0100] 420 Valve (pressure
valve) [0101] 700 Second cylinder chamber [0102] 700a Inner side
[0103] 810 Valve (suction valve) [0104] 820 valve (pressure valve)
[0105] M Medium (e.g. hydrogen) [0106] M' Leakage medium [0107] P
Permanent magnets (armature) [0108] B Coating [0109] L Longitudinal
axis [0110] S First gap [0111] S' Second gap
* * * * *