U.S. patent application number 16/630454 was filed with the patent office on 2021-05-20 for sensor for measuring hydraulic fluid pressure of a diaphragm compressor.
The applicant listed for this patent is Nel Hydrogen A/S. Invention is credited to Joshua Andrew ADAMS, Alexander George MURASHKO, JR..
Application Number | 20210148353 16/630454 |
Document ID | / |
Family ID | 1000005382347 |
Filed Date | 2021-05-20 |
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United States Patent
Application |
20210148353 |
Kind Code |
A1 |
ADAMS; Joshua Andrew ; et
al. |
May 20, 2021 |
SENSOR FOR MEASURING HYDRAULIC FLUID PRESSURE OF A DIAPHRAGM
COMPRESSOR
Abstract
A pressure sensor having a housing connected to a compressor
head, the housing including a piston movably mounted in a cylinder,
the cylinder is fluidly connected to a high-pressure part of a
hydraulic system of the compressor, where the piston is adapted to
be moved in a first direction away from the compressor head by the
pressure of the hydraulic fluid in the high-pressure part, thereby
moving a displacement member which is movably attached to the
housing by one or more flexible suspensions, and the piston is
adapted to be moved in a second direction towards the compressor
head by the flexible suspension via the displacement member.
Inventors: |
ADAMS; Joshua Andrew;
(Herning, DK) ; MURASHKO, JR.; Alexander George;
(Webster, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nel Hydrogen A/S |
Herning |
|
DK |
|
|
Family ID: |
1000005382347 |
Appl. No.: |
16/630454 |
Filed: |
June 27, 2018 |
PCT Filed: |
June 27, 2018 |
PCT NO: |
PCT/DK2018/050171 |
371 Date: |
January 12, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F04B 43/0081 20130101;
F04B 45/0533 20130101; F04B 49/002 20130101; F17C 2227/0157
20130101; F17C 7/00 20130101; F04B 2205/18 20130101; F05B 2270/301
20130101; F04B 43/067 20130101; F17C 2221/012 20130101 |
International
Class: |
F04B 43/067 20060101
F04B043/067; F04B 45/053 20060101 F04B045/053 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 13, 2017 |
DK |
PA 2017 70570 |
Claims
1. A pressure sensor comprising a housing connected to a compressor
head, the housing comprising a piston movably mounted in a
cylinder, the cylinder is fluidly connected to a high-pressure part
of a hydraulic system of the compressor, wherein the piston is
adapted to be moved in a first direction away from the compressor
head by the pressure of the hydraulic fluid in the high-pressure
part, the piston is thereby adapted to move a displacement member
which is movably attached to the housing by one or more flexible
suspensions, and wherein the piston is adapted to be moved in a
second direction towards the compressor head by the flexible
suspension via the displacement member.
2. A pressure sensor according to claim 1, wherein the flexible
suspensions are implemented as an array of bolts and springs.
3. A pressure sensor according to claim 1, wherein the pressure
sensor further comprise a displacement sensor adapted to detect the
distance of the movement of the displacement member.
4. A pressure sensor according to claim 1, wherein the displacement
member and the piston is made of aluminium.
5. A pressure sensor according to claim 1, wherein the center part
of the displacement member which is in physical contact with the
head of the piston is made of steel.
6. A pressure sensor according to claim 1, wherein the shape of the
head of the piston is spherical and wherein the contact point of
the displacement member to the piston is concave.
7. A pressure sensor according to claim 1, wherein the pressure
sensor is connected to the hydraulic fluid distribution plate or
the lower compressor head.
8. A pressure sensor according to claim 1, wherein the cylinder end
towards the displacement member is closed only leaving an opening
through which the piston can obtain mechanical contact with the
displacement member.
9. A pressure sensor according to claim 1, wherein the array of
flexible suspensions is fastening the displacement member to the
housing so that movement of the displacement member requires a
hydraulic fluid pressure above a displacement pressure.
10. A pressure sensor according to claim 1, wherein the
displacement sensor is a distance sensor.
11. A pressure sensor according to claim 1, wherein the compressor
is a diaphragm compressor compressing hydrogen gas to a pressure of
at least 65 Mpa.
12. A hydrogen fueling station comprising a first hydrogen storage
and a second hydrogen storage and a compressor having an oblong
shaped chamber moving hydrogen in a first pressure of the first
hydrogen storage to a second pressure in the second hydrogen
storage, wherein the compressor comprising a pressure sensor
according to claim 1.
13. A method of controlling the peak pressure of the high-pressure
part of a hydraulic system of a diaphragm compressor pressurising a
gas, the diaphragm compressor comprising: an injection assembly
forming part of a hydraulic fluid path between a low-pressure part
of the hydraulic system and the high-pressure part, the injection
assembly comprising: an output valve, a valve, and an injection
pump establishing a flow of hydraulic fluid from the low-pressure
part to the high-pressure part when the output valve is open, and a
pressure sensor establishing a feedback signal representing the
pressure in the high-pressure part, wherein the injection pump
establishing a pressure potential of injection of hydraulic fluid
when the valve is closed and when the output valve is closed, and
wherein a controller is controlling the pressure potential of
injection of hydraulic fluid into the high-pressure part, by
control of the injection assembly based on the feedback signal and
a hydraulic fluid peak pressure target value of a desired pressure
of hydraulic fluid in the high-pressure part.
14. A method according to claim 13, wherein the pressure potential
of injection of hydraulic fluid is established in the injection
assembly.
15. A method according to claim 13, wherein the amount of hydraulic
fluid injected into the high-pressure part in a compression cycle
is determined by the established potential of injection of
hydraulic fluid, wherein the potential of injection of hydraulic
fluid is controlled by controlling the valve based on the pressure
difference between the pressure represented by the feedback signal
and the peak pressure target value.
16. A method according to claim 13, wherein the pressure is
increased during a plurality of compression cycles following the
compression cycle during which the feedback signal representing the
pressure of the high-pressure part was below the peak pressure
target value.
17. A method according to claim 13, wherein the feedback signal
representing the pressure in the high-pressure part is measured in
each compression cycle.
18. A method according to claim 13, wherein the controller is
controlling the potential of injection of hydraulic fluid so that
the pressure in the high-pressure part is always above a reference
potential which is equal to or higher than the inlet pressure of
the gas.
19. A method according to claim 13, wherein the feedback signal is
established by a pressure sensor comprise a housing mounted to the
high-pressure part in which a cylinder with a piston in fluidly
connection with the hydraulic fluid of the high-pressure part is
located, a displacement member and a displacement sensor, wherein
the pressure of the hydraulic fluid in the high-pressure part is
physically displacing a displacement member and wherein the size of
the displacement is measured by a displacement sensor.
20. A method according to claim 1, wherein the compressor is used
for pressurizing hydrogen gas in a high-pressure storage of a
hydrogen refueling station or of a fuel cell vehicle to a pressure
above 35 Mpa.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to diaphragm compressor
having a sensor for measuring the hydraulic pressure of the
diaphragm compressor and a method of controlling the diaphragm
compressor based on said pressure measurements.
BACKGROUND
[0002] In a diaphragm compressor for pressurizing a fluid the
diaphragm is separating a lower hydraulic fluid chamber and an
upper fluid chamber. The hydraulic fluid chamber is part of a
hydraulic fluid system establishing a pressure in the hydraulic
fluid chamber by moving a piston. The pressure makes the diaphragm
moving towards the fluid chamber thereby pressurizing the fluid
hereof. To ensure full displacement of the diaphragm and to
compensate e.g. for leakage at the piston, hydraulic fluid is
injected each cycle. When the diaphragm reaches full displacement
and the piston has still not finished its discharge stroke, the
excess hydraulic fluid in the hydraulic fluid chamber exits the
hydraulic fluid chamber and via a passage conducted to a hydraulic
fluid reservoir of the hydraulic fluid system.
[0003] The known systems have the drawback that the exit of the
excess hydraulic fluid leads to loss in efficiency of the
compressor.
BRIEF SUMMARY
[0004] The present disclosure solves the problem with controlling
the maximum hydraulic fluid pressure by a compressor and control
hereof according to the inventive method described below.
[0005] The disclosure relates to a pressure sensor comprising a
housing connected to a compressor head, the housing comprising a
piston movably mounted in a cylinder, the cylinder is fluidly
connected to a high-pressure part of a hydraulic system of the
compressor, wherein the piston is adapted to be moved in a first
direction away from the compressor head by the pressure of the
hydraulic fluid in the high-pressure part, the piston is thereby
adapted to move a displacement member which is movably attached to
the housing by one or more flexible suspensions, and wherein the
piston is adapted to be moved in a second direction towards the
compressor head by the flexible suspension via the displacement
member.
[0006] The pressure sensor is advantageous in that it functions as
an overpressure protection at the same time as a pressure sensor.
This is because the flexible suspension is able to at least
temporary absorb pressure increase from the high-pressure part of
the hydraulic system of the compressor.
[0007] According to an embodiment of the disclosure, the flexible
suspensions are implemented as an array of bolts and springs. This
implementation is advantageous in that the springs temporary
absorbs the pressure from the hydraulic system in one part of the
compression cycle and in another part of the compression cycle
returns the absorbed pressure to the hydraulic system.
[0008] According to an embodiment of the disclosure, the pressure
sensor further comprise a displacement sensor adapted to detect the
distance of the movement of the displacement member. The compressor
comprises a hydraulic system creating a hydraulic pressure which
via the diaphragm is pressurizing the gas. The part of the
hydraulic systems creating the high-pressure moving the diaphragm
is referred to as high-pressure part and is located between the
valve and the pressure sensor. In the ideal scenario, the peak
pressure of the hydraulic fluid is just enough to move the
diaphragm to a position where all of the gas is leaving the gas
chamber.
[0009] The pressure sensor is adapted to measure the pressure in
the high-pressure part. This can be done in various ways hence the
pressure sensor may at least be adapted to measure a displacement
caused by the pressure and/or a flow of excess hydraulic fluid from
the high-pressure part. Accordingly, the feedback signal is either
by the pressure sensor or a controller converted to a pressure
which is comparable to the peak pressure value.
[0010] The housing is preferably connected to the high-pressure
part of the hydraulic system of the compressor. It is advantageous
in that its connection point to the compressor is not limited to a
specific location of the compressor head as long as it is able to
fluidly communicate with the hydraulic fluid of the high-pressure
part.
[0011] The fluid connection/communication path between the
high-pressure part and the cylinder is preferably a straight
conduit to ensure straight flow of the hydraulic fluid to be able
to obtain the most accurate measurement of the pressure.
[0012] The displacement member is preferably mounted to the housing
by flexible suspensions the load of which is equal to or less than
the pressure of the hydraulic fluid when the piston is just before
the so-called top dead center of a pressure curve of a compression
cycle. This ensures displacement of the displacement member before
the compression reaches its top dead center.
[0013] The displacement member is preferably a massive block of a
metal suitable to withstand the pressure from the piston in one
direction and from the suspensions in the opposite direction.
Preferably the housing is made of the same material and of a
thickness of the cylinder walls that can withstand the pressure
from the hydraulic fluid.
[0014] By movable mounted should be understood that the piston is
"floating" in the cylinder i.e. it is preferably not fastened in
any of its ends. At the second end the piston is simply pushing to
the displacement member with a pressure equal to the pressure by
which the hydraulic fluid is pushing to the first end of the
piston. The friction between the piston seal(s) and cylinder walls
can be neglected.
[0015] According to an embodiment of the disclosure, the
displacement member and the piston is made of aluminum, preferably
an aluminum alloy. This is advantageous in that weight of the
movable piston and displacement member is low in mass to
accommodate high frequency cyclic movement. This is in contrary to
more heavy masses which may disturb the dynamics between movement
and pressure ending up in a delayed feedback signal. Low weight is
preferably less than 350 grams for a displacement member having a
diameter of about 10 centimeters.
[0016] According to an embodiment of the disclosure, the center
part of the displacement member which is in physical contact with
the head of the piston is made of steel, preferably a steel alloy.
This is advantageous in that at the contact point between the
piston and displacement member a material is used which is more
resistant to wear than the aluminum.
[0017] According to an embodiment of the disclosure, the shape of
the head of the piston is spherical and wherein the contact point
of the displacement member to the piston is concave. This is
advantageous in that hereby is obtained an equal pressure to and
from the displacement member on the piston. Hence, it is not a
problem if the suspensions are not completely evenly loaded.
[0018] According to an embodiment of the disclosure, the pressure
sensor is connected to the hydraulic fluid distribution plate or
the lower compressor head. This location is advantageous in that
here it is possible to obtain a short and direct fluid path between
the hydraulic fluid and the cylinder of the pressure sensor.
[0019] Further, this location is advantageous in that the oil
distribution plate and the lower compressor head are large rigid
parts to which the pressure sensor can be securely mounted or
connected e.g. by means of an array of bolts.
[0020] According to an embodiment of the disclosure, the cylinder
end towards the displacement member is closed only leaving an
opening through which the piston can obtain mechanical contact with
the displacement member. This is advantageous in that then the
piston so to speak is closing the conduit in which the hydraulic
fluid is able to leave the high-pressure part and at the same time
the pressure of the hydraulic fluid can be transmitted to the
displacement member.
[0021] According to an embodiment of the disclosure, the array of
flexible suspensions is fastening the displacement member to the
housing so that movement of the displacement member requires a
hydraulic fluid pressure above a displacement pressure. The
flexibility of the suspensions can be adjusted either by the choice
of springs and/or by the torque with which they are held in place
between the bolt head and the displacement member. Preferably each
of the suspensions (in a preferred embodiment bolts with springs
around the threaded part between displacement member and the bolt
head) are all tightened with the same torque ensure equal load of
the piston.
[0022] The displacement pressure is preferably less than or equal
to the pressure of the hydraulic fluid at the top dead center.
[0023] According to an embodiment of the disclosure, the
displacement sensor is a distance sensor, preferably an optic
distance sensor. An optic distance sensor is advantageous in that
it is very fast i.e. it facilitates performing at least one
distance measurement per compression cycle i.e. up to 7-800
measurements per second. The optic sensor is connected to the
controller and the distance measurement is transmitted to the
controller. The distance measurement is referred to as feedback
signal. The displacement of the displacement member i.e. the
measured distance is directly linked to pressure of hydraulic fluid
in the high-pressure part.
[0024] According to an embodiment of the disclosure, the
displacement sensor provides the displacement measurements to a
controller. Preferably the displacement sensor is sending or the
controller is scanning the output of the displacement sensor so
that the controller is receiving a signal which represents a
distance moved by the displacement member.
[0025] This distance is by knowledge of a known reference distance
linked to a known pressure and thereby it can be converted to a
pressure of the hydraulic fluid. If this pressure is below the
pressure peak target value, then the controller controls the
injection pump and valve to establish an injection pressure
potential allow an amount of hydraulic fluid to enter the
high-pressure part. The amount is determined by size of gas inlet
pressure, established injection pressure potential and time the gas
inlet pressure is lower than the established injection pressure
potential. The latter will according to an embodiment of the
disclosure facilitate opening an output valve allowing flow from
the low-pressure part to the high-pressure part.
[0026] According to an embodiment of the disclosure, the compressor
is diaphragm compressor compressing hydrogen gas to a pressure of
at least 65 Mpa.
[0027] Moreover, the disclosure relates to a hydrogen fueling
station comprising a compressor.
[0028] Moreover, the disclosure relates to a method of controlling
the peak pressure of the high-pressure part of the hydraulic system
of the diaphragm compressor pressurizing a gas, the diaphragm
compressor comprising: an injection assembly forming part of the
hydraulic fluid path between a low-pressure part of the hydraulic
system and the high-pressure part, the injection assembly
comprising: an output valve, a valve and an injection pump
establishing a flow of hydraulic fluid from the low-pressure part
to the high-pressure part when the output valve is open, and a
pressure sensor establishing a feedback signal representing the
pressure in the high-pressure part, wherein the injection pump
establishing a pressure potential of injection of hydraulic fluid
when the valve is closed and when the output valve is closed, and
wherein a controller is controlling the pressure potential of
injection of hydraulic fluid into the high-pressure part, by
control of the injection assembly based on the feedback signal and
a hydraulic fluid peak pressure target value of a desired pressure
of hydraulic fluid in the high-pressure part.
[0029] According to an embodiment of the disclosure, the pressure
potential of injection of hydraulic fluid is established in the
injection assembly.
[0030] According to an embodiment of the disclosure, the amount of
hydraulic fluid injected into the high-pressure part in a
compression cycle is determined by the established potential of
injection of hydraulic fluid, wherein the potential of injection of
hydraulic fluid is controlled by controlling the valve based on the
pressure difference between the pressure represented by the
feedback signal and the peak pressure target value. Alternatively,
the injected amount is simply the amount of hydraulic fluid that
can be injected during a period of time where the pressure in the
high-pressure part is below the established injection pressure
potential.
[0031] In practice this amount is determined by the size of
established potential of injection of hydraulic fluid i.e. the
pressure established in the injection assembly (i.e. between valve,
output valve and injection pump) and the inlet gas pressure
determining the lowest pressure in the hydraulic fluid chamber and
thereby if and for how long time (in a compression cycle) the
output valve is open.
[0032] Hence a control loop exists where injection pressure
potential is controlled based on injection of hydraulic fluid and
the amount of hydraulic fluid injected is determined based on the
difference between the pressure represented by the feedback signal
and the peak pressure target value.
[0033] Preferably the hydraulic fluid is an incompressible fluid or
a fluid having an as low compressibility as possible. Oil is
preferred in that sealing's of the compressor piston is lubricated
by oil leaking from the high-pressure part to the reservoir.
[0034] Using the feedback signal representing the pressure in the
high-pressure part to control the amount of hydraulic fluid to
inject, is advantageous in that the otherwise non-detectable
leakage of hydraulic fluid at the piston is also compensate
for.
[0035] According to an embodiment of the disclosure, the pressure
is increased during a plurality of compression cycles following the
compression cycle during which the feedback signal representing the
pressure of the high-pressure part was below the peak pressure
target value This is advantageous in that adjusting the pressure in
just one compression cycle following the compression cycle in which
the feedback signal was obtained would require a sophisticated
injection assembly. However, in case the pressure is adjusted in
the subsequent compression cycle, the wear of the compressor would
be reduced.
[0036] According to an embodiment of the disclosure, the feedback
signal representing the pressure in the high-pressure part is
measured in each compression cycle.
[0037] According to an embodiment of the disclosure, the controller
is controlling the potential of injection of hydraulic fluid so
that the pressure in the high-pressure part is always above a
reference potential which is equal to or higher than the inlet
pressure of the gas. This is advantageous in that this prevents the
diaphragm from getting in contact with the bottom of the hydraulic
fluid chamber and thereby avoiding cavitation.
[0038] The control of the lower pressure is preferably made based
on a reference pressure measurement obtained from a pressure sensor
measuring the pressure of the gas entering the gas chamber and/or
the signal from the pressure sensor.
[0039] According to an embodiment of the disclosure, the feedback
signal is established by a pressure sensor comprise a housing
mounted to the high-pressure part in which a cylinder with a piston
in fluidly connection with the hydraulic fluid of the high-pressure
part is located, a displacement member and a displacement sensor,
wherein the pressure of the hydraulic fluid in the high-pressure
part is physically displacing a displacement member and wherein the
size of the displacement is measured by a displacement sensor. This
is advantageous in that it has the effect, that the displacement is
equal to the excess of hydraulic fluid in the chamber and thereby a
measure for the amount of hydraulic fluid which need to be added
(if any).
[0040] According to an embodiment of the disclosure, the compressor
is used for pressurizing hydrogen gas in a high-pressure storage of
a hydrogen refueling station or of a fuel cell vehicle to a
pressure above 35 Mpa. This is advantageous in that refueling of a
vehicle tank can be made directly from the high-pressure storage or
directly from the compressor.
[0041] Moreover, the disclosure related to a method of controlling
the injection of hydraulic fluid into a high pressure diaphragm
compressor comprising a hydraulic system, the method comprising:
measuring a representation of pressure in a high-pressure part of
the hydraulic system of the diaphragm compressor, and maintaining a
desired pressure in the high-pressure part of the hydraulic system
by adding hydraulic fluid to the high-pressure part of the
hydraulic system under the control of a controller on the basis of
said measuring of pressure.
[0042] The representation of pressure can in an advantageous
embodiment of the disclosure be made based on a measurement of
volume of hydraulic fluid in the high-pressure part of the
hydraulic system.
[0043] High pressure is preferably understood as a pressure above
10 MPa, i.e. a reference to a high pressure compressor (or simply a
compressor) in this document is to a compressor facilitating
pressurizing a gaseous fluid to a pressure of 10 MPA or above.
[0044] The high-pressure part of the hydraulic system is preferably
referred to as the part of the hydraulic system downstream the
injection assembly hereof more specifically downstream the output
valve. In the same way, the low-pressure part of the hydraulic
system is preferably referred to as the part of the hydraulic
system upstream the injection assembly hereof more specifically
upstream the output valve.
[0045] According to an embodiment of the disclosure, the amount of
the added hydraulic fluid to the high-pressure part substantially
corresponds to the amount of leaked hydraulic fluid from the
high-pressure part to a low-pressure part of the hydraulic system.
This is advantageous in that then only a very small amount of
hydraulic fluid needs to be added. This leads to a more efficient
compressor in that energy is only used on pressurizing the needed
amount of hydraulic fluid to pressurize the medium such as gaseous
fluid. This is in contrast to known systems where energy is also
used on the amount of hydraulic fluid which exits the hydraulic
fluid chamber.
[0046] Furthermore, it is advantageous in that since the present
disclosure only injects hydraulic fluid corresponding to what is
leaked stress (e.g. related to heat and flow of the excess
hydraulic fluid) is reduced on compressor components in that no
excess hydraulic fluid have to return to the low-pressure part.
[0047] In a situation with similar properties of the inlet medium
(in its gaseous or liquid state) to be pressurized such as a
gaseous fluid and no other losses to maintain a given outlet
pressure of the gaseous fluid the injected amount should be the
same as the leaked amount of hydraulic fluid. If outlet pressure
should be increased the injected amount should be higher than the
leaked amount and in the same way less if the pressure should be
reduced.
[0048] The amount (volume) injected to increase pressure is small
even one or a few drops of hydraulic fluid more than what is leaked
is enough to increase the hydraulic peak pressure. The hydraulic
peak pressure is preferably required to be higher than the pressure
of the medium such as a gaseous fluid.
[0049] According to an embodiment of the disclosure, the amount of
the added hydraulic fluid to the high-pressure part is added to the
high-pressure part in discontinued periods of time under the
control of the controller 8 on the basis of said measured pressure.
The discontinued periods of time are determined by the controller
based on the measured pressure in the high-pressure part and
knowledge of a desired peak pressure target value. Accordingly,
hydraulic fluid is not necessarily injected in each compression
cycle. Examples of compression cycles in which injection does not
happen could be if desired outlet pressure of the pressurized
medium is reduced, if properties of the inlet medium such as inlet
pressure change, etc.
[0050] It should be mentioned, that the pressure of the hydraulic
fluid in the high-pressure part is measured continuously. With this
said the measurement may be "0" value at least during some of the
compression cycle. Preferably, towards the peak pressure of a
compression cycle measurements are made to be able to determine if
in the following compression cycle injection of hydraulic fluid is
necessary or not.
[0051] According to an embodiment of the disclosure, the diaphragm
compressor comprising: an injection assembly forming part of a
hydraulic fluid path between the low-pressure part of the hydraulic
system and the high-pressure part, and a pressure sensor
establishing a feedback signal representing the pressure in the
high-pressure part, wherein the controller is controlling the
pressure potential of injection of hydraulic fluid into the
high-pressure part, by control of the injection assembly based on
the feedback signal and a hydraulic fluid peak pressure target
value of a desired pressure of hydraulic fluid in the high-pressure
part.
[0052] According to an embodiment of the disclosure, the injection
assembly comprising: an output valve, an injection pump
establishing a flow of hydraulic fluid from the low-pressure part
to the high-pressure part when the output valve is open, and an
injection pump establishing a pressure potential in the injection
assembly when a valve is closed and the output valve is closed. The
injection assembly comprising components (valve, pumps, etc.)
facilitating a controlled injection of hydraulic from the
low-pressure part to the high-pressure part of the hydraulic
system.
[0053] According to an embodiment of the disclosure, the peak
pressure of the high-pressure part of the hydraulic system of the
diaphragm compressor pressurizing a gas, the diaphragm compressor
comprising: the injection assembly forming part of the hydraulic
fluid path between the low-pressure part of the hydraulic system
and the high-pressure part, the injection assembly comprising: the
output valve, the valve, and the injection pump establishing a flow
of hydraulic fluid from the low-pressure part to the high-pressure
part when the output valve is open, and a pressure sensor
establishing a feedback signal representing the pressure in the
high-pressure part, wherein the injection pump establishing a
pressure potential of injection of hydraulic fluid in the injection
assembly when the valve is closed and when the output valve is
closed, and wherein a controller is controlling the pressure
potential of injection of hydraulic fluid into the high-pressure
part, by control of the injection assembly based on the feedback
signal and a hydraulic fluid peak pressure target value of a
desired pressure of hydraulic fluid in the high-pressure part.
[0054] The compressor comprises a hydraulic system creating a
hydraulic pressure which via the diaphragm is pressurizing the gas.
The part of the hydraulic systems creating the high-pressure moving
the diaphragm is referred to as high-pressure part and is located
between the injection assembly and the pressure sensor. In the
ideal scenario, the peak pressure of the hydraulic fluid is just
enough to move the diaphragm to a position where all of the gas is
leaving the gas chamber. It should be mentioned that the pressure
in the high-pressure part is substantially the same in all parts
hereof i.e. a feedback signal from the pressure in the hydraulic
fluid distribution plate or hydraulic distribution chamber should
be understood as a signal representing the pressure in the
high-pressure part.
[0055] The injection assembly is controlling the injection of
hydraulic fluid. To reduce requirements to the injection assembly,
the hydraulic fluid is injected when the pressure in the
high-pressure part is lowest. Even small (measured in milliliter)
quantities of injected hydraulic fluid can make relatively large
pressure increase. The controlled amount of hydraulic fluid is
preferably added as one amount for fast pressure adaption or in
portions for a less fast pressure adaption.
[0056] The pressure sensor is adapted to measure the pressure in
the high-pressure part. This can be done in various ways hence the
pressure sensor may at least be adapted to measure a displacement
caused by the pressure and/or a flow of excess hydraulic fluid from
the high-pressure part. Accordingly, the feedback signal is either
by the pressure sensor or a controller converted to a pressure
which is comparable to the peak pressure value.
[0057] The controller may be any suitable data processor but
preferably it is a standard industrial computer such as a
programmable logic controller. Preferably the controller determines
the peak pressure target value and a bottom pressure value by
calculation, lookup tables or via communication to a data storage
where predetermined values may be stored. Preferably, the
controller determines the pressure reference (minimum pressure) by
sensor input. Based on the pressure represented by the feedback
signal and the peak pressure target value, the controller is then
able to adjust the injection of hydraulic fluid to obtain a desired
pressure of the gas. Control of the injection assembly is control
of the components hereof which in an embodiment is output valve,
valve and injection pump.
[0058] The injection is preferably adjusted by creating a potential
of injection. The potential of injection of hydraulic fluid into
the high-pressure part is preferably created by running the
injection pump which when the valve is closed will create an
increase of the potential lowest pressure in the high-pressure
part. When this pressure increases to above the lowest pressure in
the high-pressure part during a compression cycle injection of
hydraulic fluid into the high-pressure part eventually happens.
Hence, the pressure created by the pump is now the new lowest
pressure in the high-pressure part. If the valve continues to be
closed and the injection pump continues to run, the pressure
continues to increase and the lowest pressure in the high-pressure
part will again in the following compression cycle be increased to
the pressure established by the running pump by the amount of
hydraulic fluid injected into the high-pressure part during the
compression cycle.
[0059] The amount of hydraulic fluid and thereby the potential
injected of hydraulic fluid into the high-pressure part can be
controlled between the capacity of the pump during one compression
cycle and nothing by control of the valve between completely closed
and completely opened. Hence, the pressure potential is equal to
the pressure in the low-pressure part when the valve is fully
opened (injection pump is simply circulating oil) and fully closed
where pressure potential is continuing to increase until maximum
capacity of the injection pump is reached.
[0060] Preferably, the injection potential is created between the
injection assembly/injection pump hereof and the output valve
located in the hydraulic flow path downstream the injection
pump.
[0061] The compression cycle refers to one cycle of the piston of
the hydraulic system i.e. one intake stroke bringing gas into the
gas chamber and one discharge stroke discharging pressurized
gas.
[0062] Controlling the injection assembly includes controlling the
components hereof which in a preferred embodiment includes
controlling the injection pump located in the hydraulic fluid path
and the valve located in the return path (the output valve is
preferably pressure regulated such as a check valve).
[0063] Determining the hydraulic fluid peak pressure target value
of a desired pressure of hydraulic fluid in the high-pressure part
may be dynamic or predetermined. The adaptive or dynamic
determination may be made during operation by the controller by
look-up tables or calculations e.g. based on measurements of inlet
pressure, outlet pressure, pressure of hydraulic fluid in the
high-pressure part, etc. Alternatively, it may be predetermined
i.e. independent from the control of the compressor e.g. by an
engineer designing the control of the compressor.
[0064] The disclosure is advantageous in that injecting an amount
of hydraulic fluid determined by an established potential to
increase the pressure just as much as needed to reach a peak
pressure target value reduces the amount of excess hydraulic fluid
leaving the hydraulic fluid chamber. Thereby wear of the system is
reduce leading to a compressor having less failures and needs fewer
service visits compared to similar high-pressure compressors.
[0065] Further, the efficiency of the compressor is increased in
that no energy is lost in getting rid of excess hydraulic fluid of
the hydraulic fluid chamber due to the non-controlled hydraulic
fluid injection used in known compressor systems.
[0066] Further, when the compressor is in normal operation there is
no need for a hydraulic fluid return path from the high to the
low-pressure parts of the compressor in that only the hydraulic
fluid needed to establish a desired pressure is in the hydraulic
fluid chamber. The return path however is needed for emergency
situations where hydraulic fluid for some reason have to exit the
hydraulic fluid chamber.
[0067] Further, the injected hydraulic fluid pressure is also
sometimes referred to as injection pressure and by controlling the
amount of hydraulic fluid so that only the required amount is
injected leads at least to the above-mentioned advantages.
[0068] According to an embodiment of the disclosure, the hydraulic
flow path is separated in the high-pressure part and the
low-pressure part by an output valve. Preferably this valve is a
check valve and will be referred to as such. However, other types
of valves such as electronic controllable valve, pneumatic or
hydraulic controllable valve, etc. can be used.
[0069] The output valve is advantageous in that the pressure
potential can be established between the output valve and the
injection pump which is released into the high-pressure part when
the inlet gas pressure and thereby the pressure of the
high-pressure part is below the established potential.
[0070] The output valve is furthermore advantageous in that it
protects the injection assembly from the high pressure created by
the compressor piston. In a situation, the compressor piston may
establish a pressure of 100 MPa and the injection pump a pressure
of 70 MPa. Accordingly, without the protection of the output valve,
due to this difference, the pressure potential would, each time the
compressor piston establishes a pressure above 70 MPa, be equal to
the pressure established by the compressor piston.
[0071] In addition, with reference to the above example, the output
valve also prevents hydraulic fluid from passing back through the
injection assembly.
[0072] According to an embodiment of the disclosure, the hydraulic
fluid path between the low-pressure part and the high-pressure part
in the low-pressure part includes a forward path and a return path,
wherein the valve is located in the return path for controlling
flow of hydraulic fluid from the injection pump to a hydraulic
fluid reservoir. The location of the valve in the return path is
advantageous in that by control of the valve facilitates control of
the increase of potential of injection of hydraulic fluid by
closing for the flow of hydraulic fluid in the return path.
[0073] According to an embodiment of the disclosure, the forward
path fluidly connects the injection pump to a hydraulic fluid
supply station at least one inner wall positioned between the
hydrogen fluid inlet from the hydraulic fluid reservoir and the
forward path and wherein a hydraulic fluid storage volume is
located beneath the at least one inner wall. Although it is
possible within the scope of the disclosure to connect the
injection pump to the hydraulic fluid reservoir (housing the crank
shaft) it is advantageous not to do so. This is because of the
movement of the crank shaft, the hydraulic fluid is mixed with air
in the reservoir. Accordingly, due to the small amounts of
hydraulic fluid which is injected per compression cycle even minor
air bubbles may lead to difficulties in reaching the desired
pressure in the high-pressure part.
[0074] According to an embodiment of the disclosure, the hydraulic
supply station is fluidly connected to the hydraulic fluid
reservoir. This is advantageous in that when the level (e.g.
measured by a level sensor) of hydraulic fluid in the hydraulic
fluid reservoir is too high a pump is preferably used to pump
hydraulic fluid from the hydraulic fluid reservoir to the hydraulic
supply station.
[0075] According to an embodiment of the disclosure, the at least
one inner wall is a net with holes between 50.mu. [mu] and 150.mu.
[mu], preferably 100.mu. [mu].
[0076] According to an embodiment of the disclosure, the at least
one inner wall is positioned with an angle of inclination relative
to a horizontal bottom plane between 1 and 20 degrees preferably
between 2 and 10 degrees and most preferably between 3 and 5
degrees. This inner wall is advantageous in that the perforations
are so small that they are functioning as air filter for the air
bubbles of the received hydraulic fluid. Hence, when the received
hydraulic fluid fills up the hydraulic supply station the air
bubbles travels up the inclined perforated wall(s) whereas the
hydraulic fluid penetrates the perforated wall(s). Preferably, the
hydraulic supply station comprises two or more perforated inner
walls forming a triangle or funnel through which the hydraulic
fluid enters on its way from inlet to outlet of the hydraulic
supply station.
[0077] The angle of inclination, diameter and density of holes
together with the storage volume is advantageous in that it allows
filtered (including filtering air bubbles) hydraulic fluid to be
collected in the storage volume over time from where it can be
sucked up by the injection pump.
[0078] According to an embodiment of the disclosure, the diaphragm
is in physical contact with the inner surface of the gas chamber
prior to the pressure of the high-pressure reaches the pressure
peak value. This is advantageous in that then the diaphragm is
discharging all of the gas in the gas chamber in each compression
cycle. It should be mentioned that the gas chamber may comprise
voids from where minor quantities of the gas cannot escape.
[0079] The contact between the diaphragm and the inner surface of
the gas chamber is preferably at least made between the inlet port
and the outlet port.
[0080] According to an embodiment of the disclosure, the peak
pressure target value is between 20% and 15%, preferably between
15% and 10%, most preferably between 10% and 5% above the desired
pressure of the gas leaving the chamber 14.
[0081] It is advantageous to control the pressure of the gas
leaving the gas chamber by controlling the pressure of the
hydraulic fluid in the high-pressure part. This is because the
pressure of the pressurized gas is less stable compared to the
pressure of the hydraulic fluid. Hence to avoid calculations,
compensations etc. to obtain a precise and reliable control loop it
is preferred to use the pressure of the hydraulic fluid in the
high-pressure part as feedback in the control loop. To be able to
do so sufficient movement of the displacement member to create a
resolution of the measurements which is sufficient to use in the
control requires a pressure peak target value some percentage above
the desired outlet gas pressure.
[0082] Further, to be sure to obtain a feedback signal, the
pressure peak target value is higher than the desired pressure of
the gas leaving the gas chamber.
[0083] According to an embodiment of the disclosure, the controller
is controlling the injection of hydraulic fluid into the
high-pressure part so that injection is possible during the intake
stroke of a compression cycle where the pressure of the hydraulic
fluid in the high-pressure part is being reduced. Injecting
hydraulic fluid in the beginning of the compression cycle following
the compression cycle where the feedback signal indicated a
pressure increase was needed is advantageous in that the
requirements to the injection pump is reduce. This is because at
the beginning of a compression cycle the pressure in the
high-pressure part is low. It should be mentioned that the
injection of hydraulic fluid requires that the output valve opens
and which according to an embodiment of the disclosure is the case
when the established potential upstream the output valve is higher
that the pressure downstream the output valve.
[0084] According to an embodiment of the disclosure, the pressure
sensor comprise a housing mounted to the high-pressure part 1 in
which a cylinder with a piston in fluidly connection with the
hydraulic fluid of the high-pressure part is located, a
displacement member and a displacement sensor, wherein the pressure
of the hydraulic fluid in the high-pressure part 1 is physically
displacing a displacement member and wherein the size of the
displacement is measured by a displacement sensor.
[0085] The displacement based pressure sensor is advantageous when
used on a compressor controlled according to the present
disclosure. This is because the inventive control only injects a
very small amount of hydraulic fluid leading to only a very small
amount of excess hydraulic fluid. Hence because the amount is so
small, a flow is difficult to measure. Instead since the excess
amount is so small it is possible to guide it to a cylinder of the
pressure sensor where it activates a piston, where it again
activates the displacement member according to the pressure of the
hydraulic fluid.
[0086] According to an embodiment of the disclosure, the
displacement member is movably mounted to the housing by means of
an arrangement of springs and bolts. The electromagnetic force is
advantageous in that this enables electrically adjustable of the
force (and thereby hydraulic fluid pressure) which is needed to
displace the displacement member.
[0087] The mechanical arrangement with bolts holding springs
between the bolt head and the displacement member is advantageous
in that it does not require any control i.e. the force needed from
the hydraulic fluid pressure to displace the displacement member is
constant. Accordingly, the processing of the size of the
displacement is less complicated.
[0088] According to an embodiment of the disclosure, the pressure
sensor is a pressure control valve connected to the high-pressure
part comprising a flow sensor for measuring an amount of hydraulic
fluid leaving the high-pressure part. The pressure control valve
could be a spring-loaded valve opening for flow of hydraulic fluid
at a pressure determined by safety margins of the compressor
design.
[0089] Even though this is possible Feedback may also come from
measurement of pressure of the gas, however it is preferred to
obtain feedback from the expansion chamber in that this is more
precise to the amount of excess hydraulic fluid and thereby the
control of the amount of injected hydraulic fluid can be controlled
more precisely.
[0090] According to an embodiment of the disclosure, the pressure
sensor is connected to the hydraulic fluid distribution plate or to
the hydraulic fluid chamber. Due to the high working pressure of
the compressor the pressure sensor needs to be securely connected
to the compressor. The easiest way of doing so is by means of bolts
to either the hydraulic fluid chamber or the hydraulic fluid
distribution.
[0091] According to an embodiment of the disclosure, the
displacement sensor is a distance sensor, preferably an optic
distance sensor. An optic distance sensor is advantageous in that
it is very fast i.e. it facilitates performing at least one
distance measurement per compression cycle i.e. up to 7-800
measurements per second. Furthermore, an optic sensor is accurate
in its measurements.
[0092] The optic sensor is connected to the controller and the
distance measurement is transmitted to the controller. The distance
measurement is referred to as feedback signal. The displacement of
the displacement member i.e. the measured distance is directly
linked to pressure of hydraulic fluid in the high-pressure
part.
[0093] Alternative sensor types which may be used includes
inductive and ultrasonic sensors.
[0094] According to an embodiment of the disclosure, the
displacement sensor certified to be located in an explosive
atmosphere. Since the preferred gas to compress is hydrogen, the
atmosphere in which the compressor is located is explosive.
Accordingly, the displacement sensor should be safe to use in such
area. This can be obtained by sealing the sensor housing, using low
power measurement module and communication module, etc.
[0095] According to an embodiment of the disclosure, the feedback
signal is at least received when the diaphragm is in the upper half
of its movement towards the inner surface of the gas chamber.
Preferably there is no feedback signal from the pressure sensor
when the pressure of the high-pressure part is a certain level
below the peak pressure target value. Preferably, only when the
diaphragm is on the last part of its way to the top position
(referred to as top dead center) and cannot increase the pressure
of the gas in the gas chamber anymore, the pressure increase in the
high-pressure part is measured by the pressure sensor.
[0096] Together with the controlled injection of hydraulic fluid,
according to an embodiment of the disclosure this is advantageous
in that then no return path for the hydraulic fluid to the
low-pressure part of the hydraulic system is needed during normal
operation.
[0097] According to an embodiment of the disclosure, the gas is
hydrogen.
[0098] According to an embodiment of the disclosure, the hydraulic
fluid is a hydraulic oil.
[0099] Moreover, the disclosure relates to a diaphragm compressor
for pressurizing a gas to a pressure above 10 MPa, the diaphragm
compressor comprising: an injection assembly forming part of a
hydraulic fluid path between the low-pressure part of the hydraulic
system and the high-pressure part, a pressure sensor adapted to
establish a feedback signal representing the pressure in the
high-pressure part, and a controller adapted to control the
injection assembly so as to establish a pressure potential of
injection of hydraulic fluid based on the feedback signal and a
hydraulic fluid peak pressure target value of a desired pressure of
hydraulic fluid in the high-pressure part.
[0100] According to an embodiment of the disclosure, the injection
assembly comprising: [0101] an output valve, a valve, and an
injection pump adapted to establish a flow of hydraulic fluid from
the low-pressure part to the high-pressure part when the output
valve is open, wherein the injection pump is furthermore adapted to
establish a pressure potential in the injection assembly when the
valve is closed and the output valve is closed.
[0102] According to an embodiment of the disclosure, the pressure
potential of injection of hydraulic fluid is established in the
injection assembly.
[0103] Moreover, the disclosure relates to a hydrogen fueling
station comprising a first hydrogen storage and a second hydrogen
storage and a compressor having an oblong shaped chamber moving
hydrogen in a first pressure of the first hydrogen storage to a
second pressure in the second hydrogen storage, wherein the
compressor is controlled.
[0104] Moreover, the disclosure relates to a compressor comprising
a pressure sensor.
BRIEF DESCRIPTION OF THE FIGURES
[0105] In the following, a few exemplary embodiments of the
disclosure are described with reference to the figures, of
which
[0106] FIG. 1 illustrates an example of a prior art compressor
[0107] FIG. 2 illustrates an example of a compressor according to
an embodiment of the present disclosure
[0108] FIG. 3 illustrates a pressure sensor according to an
embodiment of the present disclosure, and
[0109] FIG. 4 illustrates a pressure curve of a compression cycle
according to an embodiment of the present disclosure.
DETAILED DESCRIPTION
[0110] FIG. 1 illustrates an example of a prior art type of control
of the hydraulic pressure in a diaphragm compressor. A pump is
simply pumping oil from the hydraulic fluid reservoir into the oil
chamber and as explained, when the diaphragm reaches its maximum,
the excess oil exits the oil chamber via a return path to the
reservoir. The amount of oil pumped into the oil chamber is the
same for each compression cycle and "enough" to ensure that some
quantity exist the oil chamber and thereby maximum pressure have
been reached.
[0111] FIG. 2 (and the other figures) illustrates a preferred
embodiment of the present disclosure, hence the description in
relation to the figures should only be understood as such leaving
room for changes to the description still being within the scope of
the disclosure.
[0112] A compressor 2 having an upper compressor head 24 in which a
gas chamber 14 is present and a lower compressor head 25 in which a
hydraulic fluid chamber 26 is present.
[0113] The upper compressor head 24 has a gas inlet port 27 and a
gas outlet port 28. The pressure of the gas inlet may be measured
by a pressure sensor 29.
[0114] The lower compressor head 25 is part of a high-pressure part
1 illustrated above the dot/dash line. Hence, the high-pressure
part 1 is found downstream the injection assembly 3 including part
of a hydraulic fluid flow path, hydraulic distribution plate 22,
hydraulic chamber 26 and part of the compressor cylinder 31 above
the compressor piston 32 and a pressure sensor 7.
[0115] Illustrated is also an emergency vent line 33 from the
high-pressure part 1 to the hydraulic fluid reservoir 11 (referred
to as reservoir). Flow in the emergency vent line 33 is controlled
by an emergency valve 34. The emergency valve 34 is preferably
controlled mechanically so that if the pressure of the exceeds a
predetermined value the emergency valve 34 opens and pressure is
reduced in the high-pressure part 1 a hydraulic fluid exits to the
reservoir 11. Accordingly, this emergency vent line is not part of
control of the hydraulic pressure in the high-pressure part 1 but
is only used in case of emergency as a so-called second stage
overprotection.
[0116] Below the dot/dash line dividing the hydraulic system at the
output valve 38 and compressor piston 32 is the low-pressure part
4. Hence the low-pressure part 4 is found upstream the injection
assembly 3 including part of a flow path, reservoir 11, hydraulic
fluid supply station 12 (referred to as supply station) and
connection hereto illustrated by a pump 35. The pump 35 facilitates
pumping hydraulic fluid from the reservoir 11 to the supply station
12. In addition, the connection may comprise not illustrated
filters or venting components.
[0117] It should be mentioned, that the pressure in the part of the
hydraulic flow path downstream the injection assembly 3 is normally
higher that the pressure of the part upstream the injection
assembly 3. Normally, the pressure in the injection assembly 3
(between the injection pump 5, valve 6 and output valve 38) is
close the to the gas inlet pressure so that an increased pressure
(pressure potential) above this pressure can be established
fast.
[0118] The output valve 38 is preferably a check valve or another
kind of mechanically controlled pressure valve but could also be an
electrically controlled valve.
[0119] The pump 35 is controlled by a level sensor 36. When the
level of hydraulic fluid in the reservoir 11 is above a predefined
level, the hydraulic fluid is pumped to the supply station 12. As
illustrated, the supply station 12 comprise diagonal like walls 37
through which the hydraulic fluid has to travel. Therefore, the
walls 37 are perforated or designed as a net having meshes between
50.mu. [mu] and 150.mu. [mu], preferably 100.mu. [mu]. The walls 37
may be implemented as forming a basket in which the hydraulic fluid
from the reservoir 11 enters mixed with air and when leaving the
basket through the walls 37 ending in a reservoir without the air.
Due to this small size of the holes and surface tension air bubbles
mixed into the hydraulic fluid is filtered away traveling towards
to the top of the supply station 12 leaving air free hydraulic
fluid to be ready to be sucked up into the forward path 9 by the
injection pump 5.
[0120] As illustrated the injection assembly 3 is located in the
flow path between the high and low-pressure parts 1, 4. Besides the
injection pump 5, the injection assembly 3 comprise a valve 6 which
is preferably located in the return path 10 and the output valve
located in the flow path to the high-pressure part 1.
[0121] Preferably, the injection pump is continuously pumping
hydraulic fluid from the supply station 12 to compensate for
leakages at the compressor piston 32. In addition, the continuous
pumping is used to create an injection pressure potential which is
at a level controlled by how much of the hydraulic fluid is allowed
to circulate back to the reservoir 11.
[0122] It should be mentioned, that the forward path 9 could also
simply be connecting the reservoir 11 and the injection pump 5.
However, due to the movement of the compressor piston 32 the
hydraulic fluid in the reservoir 11 is mixed with air which is then
sucked up into the injection pump 5 and further into the
high-pressure part 1. Air is not desired in the high-pressure part
in that it air is compressible i.e. opposite of desired property of
the hydraulic fluid hence with air in the hydraulic fluid the
compressed less effective as without. Accordingly, to avoid this
the supply station 12 is developed to filter air.
[0123] It should be mentioned that the valve 6 could also be
located downstream the injection pump 5, however this location is
not preferred in that it will lead to less flexibility in control
of the injection pump and pressure potential. One reason for this
is that the pump then needs to be stopped when a given pressure
potential is reached in order not to exceed it.
[0124] A controller 8 is controlling the operation of the
compressor. The controller 8 is communicating at least with the
injection assembly and the pressure sensor 7. The same or other
controllers may facilitate control of the pump 35, operation of the
piston 32, control of the gas in/outlet and other not illustrated
elements in relation to operation of the controller.
[0125] The hydraulic fluid is preferably an incompressible oil
which when leaking around the piston sealing is used for
lubrication hereof. Any fluid having limited compression properties
which at the same time may facilitate lubrication may in principle
be used as hydraulic fluid.
[0126] The pressure sensor 7 is on FIG. 2 illustrated as attached
to the lower compressor head 25 including the hydraulic
distribution plate 22 and hydraulic fluid chamber 23. In relation
to location of the pressure sensor 7 it should be mentioned that it
in principle can be located anywhere in the high-pressure part 1.
Only real limiting factor for its location is that it should be
able to be firmly attached to comply with the pressures created by
the compressor which may be up to and above 100 MPa. This makes the
lower compressor head 25 the obvious choice.
[0127] At FIG. 2 the hydraulic fluid distribution 22 plate has a
fluid path fluidly connecting it to the pressure sensor 7. As
mentioned a similar fluid path could connect the pressure sensor 7
to the hydraulic fluid chamber 23 or the hydraulic fluid flow path
from the injection assembly 3 to the lower compressor head 25.
[0128] FIG. 3 illustrates the pressure sensor 7 according to an
embodiment of the disclosure. As mentioned, it is not important to
which part of the high-pressure part 1 of the compressor 2 the
pressure sensor 7 is attached.
[0129] At FIG. 3 the housing 15 of the pressure sensor 7 is
illustrated as attached to the lower compressor head 25 by means of
bolts 21. Preferably the lower compressor head 25 comprise a
threated part and the housing 15 comprise not illustrated ducts
through which bolts 21 can reach the threated part and thereby
fastening the housing 15 to the compressor 2. Other ways of
fastening depending on where the housing is connected to the
high-pressure part 1 could also be used.
[0130] At the opposite end of the housing 15 a displacement member
18 is movably attached to the housing 15 by means of flexible
suspensions such as an array of bolt 21/spring 20 arrangements. The
torque with which the bolts 21 is tightened and the tension of the
springs 20 are determining for the movement of the displacement
member 18 at a giver pressure. Hence, by adjusting this the
movement can be adjusted.
[0131] The pressure sensor 7 comprise a cylinder 16 in which a
piston 17 is movable. In one direction, away from the compressor 2
the movement is determined by the pressure of the hydraulic fluid
and in a second direction, towards the compressor 2 the movement is
determined by the displacement member 18.
[0132] At FIG. 3, the piston has moved the displacement member 18
away from the compressor 2 accordingly, the pressure in the
high-pressure part 1 has reached or is close to its maximum
pressure.
[0133] Attached to or in relation to the pressure sensor 7 is
illustrated a displacement sensor 19 the purpose of which is to
measure the length or size of the movement of the displacement
member 18 caused by the piston 17. The displacement sensor 19 is
communicating with the controller 8 hence a control loop is
established where the control of the injection assembly 3 is made
based on feedback from the pressure sensor 7.
[0134] Typically, the displacement member 18 is moved less than 1
millimeter. The adjustment of the size of the movement is aligned
with a given pressure during a test phase. Prior to the test phase,
an estimate of the needed load (spring load, in the embodiment
where springs are used as flexible suspensions) is calculated based
on expected pressure of the hydraulic fluid and area of the
cylinder 16. Then the springs 20 are adjusted to counter act this
load which is also referred to as displacement pressure.
Accordingly, the pressure acting on the piston 17 from the
hydraulic fluid have to be higher than the displacement pressure to
move the displace member 18.
[0135] During the test phase the displacement pressure is
fine-tuned e.g. by mechanically adjusting the displacement pressure
until a desired displacement is found at a desired pressure. The
desired pressure is referred to as pressure peak target value
whereas the actual measured pressure is referred to as pressure
peak value. One non-limiting example is that at a pressure peak
value of 100 MPa, the size of the displacement is adjusted to be
0.05 mm [millimeter].
[0136] The relation between the size of the measured displacement
and the pressure in the high-pressure part 1 is according to a
non-limiting embodiment as follows. The springs 20 holding the
displacement member 18 is fixed so that at a pressure of e.g.
[0137] 100 MPa the displacement member is moving e.g. 0.05 mm.
Accordingly, if only 50 MPa is needed the measured displacement
should only be 0.025 mm. Therefore, no establishing of injection
potential of hydraulic fluid above inlet pressure is initiated if a
displacement of more than 0.025 mm is measured.
[0138] The pressure drops in the high-pressure part 1 due to
leakage at the compressor piston 32 hence when the measured
displacement as consequence hereof drops below 0.025 mm e.g. to
0.020 mm the valve 6 is closed facilitating establishing potential
of injection of hydraulic fluid into the high-pressure part 1.
[0139] The establishing of the potential of injection is simply
made by closing the valve 6 during one or more preferably
successive compression cycles. During a compression cycle where the
inlet gas pressure is lower than whatever pressure established
upstream the output valve 38 this will lead to an injection of
hydraulic fluid in the high-pressure part. The injection happens
due to pressure equalization between the part of the hydraulic flow
path in which the potential is established (i.e. the part from the
injection pump 5/(preferably completely closed) valve 6) to the
output valve 38. This will in the following compression cycle lead
to an increase in the pressure in the hydraulic pressure chamber
and thereby to an increased displacement of the displacement member
18 (at least if the injected amount is higher than what is leaking
via the compressor piston 32). Hence when the measured displacement
again is 0.025 mm or above the establishing of pressure potential
is stopped again by opening the valve 6.
[0140] The injection pressure potential is in the ideal scenario
established as follows. The gas inlet pressure measured by sensor
29 is used as reference pressure (also referred to as reference 0)
for the pressure potential. Accordingly, an injection pressure
potential is increased by closing valve 6 thereby allowing the
injection pump 5 to increase the pressure between valve 6, output
valve 38 and injection pump 5. The pressure here continues to
increase until it is above the reference pressure which will open
output valve 38 allowing an injection of hydraulic fluid into the
high-pressure part 1. Even the small amount/volume of hydraulic
fluid that can be injected in a compression cycle is enough to
increase the peak pressure value in the following compression
cycle.
[0141] If not injection pressure potential is desired the valve 6
is kept open thereby the injection pump 5 only pumps hydraulic
fluid from the supply station 12 to the reservoir 11 without
establishing an injection pressure potential.
[0142] Accordingly, in the ideal scenario, the valve 6 is
controlling the pressure between valve 6, output valve 38 and
injection pump 5 to be just above or just below the reference
pressure.
[0143] The simplest way of implementing flexible suspension is the
illustrated bolt/spring arrangement. Alternative to the arrangement
of bolts 21, one threaded rod can be used about which the
displacement member 18 can be turned thereby moving towards or away
from the housing 15 changing the tension on the springs 20. Yet
another alternative is to use an electromagnetic controllable
displacement member 18 using the electricity to control tension
from the displacement member 18 on the springs 20. In the two
alternatives one spring may be used at the center of the
displacement member 18.
[0144] It should be mentioned that it may be possible to implement
an electronic controllable gearing facilitating an adjustment of
the spring load of the flexible suspension.
[0145] In addition to establishing a feedback signal representing
the pressure in the hydraulic fluid chamber 23, the pressure sensor
7 furthermore has a function of overpressure protection. This is
because when the diaphragm 13 is in its top position and pressure
is still increasing e.g. due to compressor piston 32 has not
reached its top position, then this additional volume of hydraulic
fluid is pushed into the pressure sensor 7. Here this volume is
pushing the piston 17 which again is pushing the displacement
member 18 and thereby expanding/increasing the volume in the
cylinder 16. By this additional volume, the pressure sensor 7 is
able to absorb the additional volume of hydraulic fluid (pressure
is absorbed) and a first state overpressure protection is
provided.
[0146] The principle of this first stage overpressure protection is
the same as the principle leading to establishing the feedback
signal representing the pressure in the hydraulic fluid chamber 23
during normal operation of the compressor. Hence, during an
abnormal operation of the compressor the displacement of the
displacement member 18 is still measured and provided to the
controller, but now the displacement represents a pressure which is
above normal operation pressure.
[0147] As mentioned, in addition to the first stage overpressure
protection a second stage overpressure protection is also included
in the compressor design. The first stage overpressure protection
is limited to absorb a fixed amount of hydraulic fluid/pressure
which is sufficient to protect the compressor during normal
operation. The fixed amount is equal to a pressure which the
flexible suspension can absorb.
[0148] However, in the unlikely event of failure of the compressor
control or part, the second state overpressure protection
(emergency line 33 and valve 34) is used to relief pressure from
the hydraulic fluid chamber 32 by leading the hydraulic fluid to
the reservoir 11.
[0149] FIG. 4 illustrates the principles of a compression cycle
according to an embodiment of the disclosure. One compression cycle
exists between T1 and T6 including one movement up and down of the
diaphragm 13. The movement of the compressor piston 32 is
illustrated as the dotted line.
[0150] Between T1 and T3 the diaphragm 13 is moving up towards the
gas chamber 14 thereby pressurizing the gas therein. From T2 the
pressure is kept constant by opening the gas outlet 28 thereby
discharging the now pressurized gas.
[0151] At T3, the gas chamber 14 is empty (at least close to, there
might be some gas left in the gas chamber in small voids e.g. in
relation the inlet port, etc.) and the pressure continues to
increase until the compressor piston 32 is in its top position at
T4. As illustrated, the compressor piston 32 moves up from T1 to
T4.
[0152] In an embodiment, the pressure sensor 7 comprises a
displacement member 18 which is moving according to the initial
load adjustment of the flexible suspension holding it. In an
embodiment, the displacement member 18 is starting to move at a
pressure of e.g. 35 MPa and as the pressure increases towards a
pressure peak value of e.g. 80 MPa the size of the displacement of
the displacement member 18 increases with the pressure
increase.
[0153] The pressure increase and the displacement of the
displacement member is not necessarily linear in that. In the
situation of non-linearity, the calculations of pressure of a given
displacement is more complex than in the situation of linearity. In
practice this may result in the following, if an outlet pressure of
the gaseous fluid of 100 MPa is desired, the pressure peak target
value may be 110 MPa to ensure measurable displacement of the
movement of the displacement member 18. If the desired outlet
pressure instead is 50 MPa, the pressure peak target value may be
70 MPa.
[0154] At T3 where there is no more gas in the gas chamber 14, the
pressure increases again which is measurable as a displacement of
the displacement member 18.
[0155] Typically, the load adjustment of the flexible suspension
first enables measurement of displacement of the displacement
member 18 when the pressure in the high-pressure part 1 is more
than 50% of the peak pressure target value. At FIG. 4, an example
of a desired interval of pressure measured by the pressure sensor 7
is illustrated.
[0156] At T4 (referred to as top dead center of the piston 32), the
pressure starts to decrease in that the piston 32 starts to move
towards the hydraulic fluid chamber 23. The remaining gas in the
gas chamber 14 expands, gas is introduced into the gas chamber 14
via the gas inlet 27 until the compression cycle ends at T6 to
start over again as described from T1.
[0157] As described, the disclosure is advantageous in that it is
able to reduce the top dead center pressure and thereby the load
and thereby increase the efficiency of the compressor in that no
excess hydraulic fluid has to exit the hydraulic distribution plate
22/hydraulic fluid chamber 23. This is obtained by using the
feedback from the pressure sensor 7 in the control of the pressure
potential established by the injection assembly 3.
[0158] The pressure in the high-pressure part 1 is extremely
difficult to predict in that it depends on the how much hydraulic
fluid is leaking via the compressor piston 32 and the inlet
pressure of the gas entering the gas chamber 14, properties with
the gas, etc.
[0159] Therefore, the peak pressure target value is chosen to be
above the desired pressure of the pressurized gas leaving the
outlet port 28. The peak pressure target value should be high
enough to facilitate movement of the displacement member 18, but
still not higher than the hydraulic fluid causing the extra
pressure from T3 to T4 can be absorbed by the flexible suspensions.
Preferably the peak pressure target value is therefore about 10%
higher than the desired pressure of the pressurized gas leaving the
outlet port 28. The percentage is of course determined by the
dimensions of the pressure sensor 7, cylinder 16 and flexible
suspensions. An example of difference between outlet pressure of
gaseous fluid and pressure peak target value is illustrated on FIG.
3.
[0160] The solution invented to balance the load/efficiency
optimization and still be sure to establish the peak pressure is to
control the injection assembly 3 based on feedback from the
pressure sensor 7. One example for illustration of the control will
now be described.
[0161] As mentioned, the minimum pressure in the high-pressure part
1 is controlled so that it is equal to or just above the inlet
pressure of the gas entering the gas chamber 14. The gas inlet
pressure is preferably measure by the pressure sensor 29 and
communicated to and used by the controller 8 to establish a
pressure reference based on which the injection assembly 3 controls
the injection pressure potential. This is to avoid the gas pressure
moving the diaphragm towards the bottom of the hydraulic fluid
chamber.
[0162] It should be mentioned that if for some reason there is too
much hydraulic fluid in the hydraulic chamber (and thereby too high
gas outlet pressure), then to facilitate a pressure decrease
(reduce volume of hydraulic fluid in hydraulic chamber), the valve
6 is controlled (opened) so that the pressure established by the
injection pump 5 is just below the reference pressure. Thereby no
injection pressure potential is established and thereby no
hydraulic fluid is injected into the high-pressure part 1. The
pressure in the high-pressure part will then drop by the leakage at
the piston 32.
[0163] Just as long as the pressure established by/in the injection
assembly 3 is below the reference pressure no hydraulic fluid is
injected into the high-pressure part 1. How much below doesn't
matter.
[0164] In an example the gas inlet pressure is 20 MPa and used as
pressure reference (0 reference) for the injection potential
controlled via the injection assembly 3. Hence a first purpose of
the injection assembly 3 is ensuring that the diaphragm do not
contact the bottom of the hydraulic fluid chamber 23.
[0165] The pressure reference of 20 MPa is in the controller 8
linked to a size of displacement of the displacement member 18
which in this example could be 1/100 of a millimeter. Accordingly,
if the size of displacement measured by the pressure sensor 7 at
T1/T6 is less than 1/100 of a millimeter the controller 8 via the
injection assembly 3 increases the potential of injection of
hydraulic fluid.
[0166] A second purpose of the injection assembly 3 is the inject
hydraulic fluid in the high-pressure part 1 to increase/control the
pressure peak value.
[0167] The maximum pressure in the high-pressure part 1 is
controlled as close as possible to peak at a peak pressure target
value. The peak pressure target value is determined to be e.g.
5%45% higher than the pressure of the gas leaving the gas chamber.
The pressure in the high-pressure part 1 is controlled as
follows.
[0168] The injection pump 5 is preferably running continuously in
each compression cycle to compensate for the leaking hydraulic
fluid at the compressor piston 32 and for changes in the gas inlet
pressure or outlet pressure. The amount of hydraulic fluid needed
is however as mentioned very difficult to predict. The present
disclosure suggests to use movement of the displacement member 18
to solve this problem.
[0169] Hence, as an example if a displacement of 0.1 mm is measured
at a pressure of 100 MPa, then a measurement of 0.05 mm represents
a pressure of 50 MPa, etc. If the pressure peak target value is
determined to be 50 MPa and a measurement of less than 0.05 mm is
measured, then the injection assembly 3 is controlled to increase
the injection pressure potential.
[0170] Accordingly, during the part of the compression cycle where
the output valve 38 is closed and the valve 6 is controlled
(preferably closed or at least partly closed) to reduce the amount
of hydraulic fluid which is possible to flow through the return
path 10. Thereby, an injection pressure potential is established in
the hydraulic flow path between the valve 6, injection pump 5 and
output valve 38 (i.e. in the injection assembly 3). In this part of
the hydraulic flow path, a pressure higher than the inlet pressure
is then established which eventually will open the output valve 38
and via pressure equalization hydraulic fluid will be injected to
the high-pressure part 1. The volume of the amount of injected
hydraulic fluid will then increase the pressure peak value, if not
enough to displace the displacement member at least 0.05 mm the
valve 6 is kept closed for one more cycle and so on until the
measurement of 0.05 mm representing a pressure of 50 Mpa has been
measured.
[0171] As understood the inventive control is dynamic and is
preferably adjusting the amount of hydraulic fluid in each
compression cycle to optimize the peak pressure in the
high-pressure part of the hydraulic system of the diaphragm
compressor.
[0172] In the same way if e.g. gas inlet pressure decreases, to
ensure the diaphragm continues to allow as much gas in the gas
chamber as desired, the injection assembly 3 may be controlled to
reduce pressure/amount of hydraulic fluid in the high-pressure part
1 by opening (or at least partly opening) the valve 6.
[0173] Preferably, the piston 17 and displacement member 18 are two
independent components, however with this said it should be
mentioned, that they may be made from one piece of material.
[0174] As is now clear from the above description that the peak
pressure value of the hydraulic fluid is measured by displacement
of the displacement member 18 of a pressure sensor 7. In relation
to a desired peak pressure target value, if the peak pressure value
is insufficient, this is measured by an insufficient displacement
of the displacement member 18 and the injection potential is
increased i.e. the injection pressure established by the injection
assembly 3 is increased. In the same way in relation to the desired
peak pressure target value, if peak pressure value is too high,
this is measured by an excessive displacement of the displacement
member 18 and the injection potential is reduced i.e. the injection
pressure established by the injection assembly 3 is reduced.
[0175] As understood from the above description, the disclosure
enables a control of the peak pressure in the hydraulic system by
only adding a small amount of hydraulic fluid to the hydraulic
system more specific to the high-pressure part 1 hereof. As
mentioned in the ideal high-pressure compressor 2 only leakage
between low and high-pressure part 1, 4 is via the compressor
piston 32. Accordingly, the amount (also referred to as volume) of
leaked hydraulic fluid is very small hence to maintain balance
between desired pressure and leaked hydraulic fluid only an equal
amount of hydraulic fluid requires to be added. If on the other
hand the pressure needs to be increased, only a small amount
(measured in milliliters or drops) more than the leaked amount
needs to be added.
[0176] The pressure sensor 7 preferably does not measure pressure
of the hydraulic fluid directly but instead measures volume of the
hydraulic fluid. Since the hydraulic fluid is incompressible when
exposed to a pressure, the volume stays the same. This leads to
displacement of the displacement member 18 of the pressure sensor 7
since it is in fluidly communication with the high-pressure part 1.
During test and calibration, a given displacement is linked to a
given pressure and in this way by observing the displacement the
pressure of the hydraulic fluid is established.
[0177] A further advantage of the present disclosure is that
because the amount of injected hydraulic fluid is controlled, it is
possible to determine the amount of hydraulic fluid leaking via the
compressor piston 32. This information may be used to determine
state of health of at least the piston and piston seals. When the
injected amount of hydraulic fluid (compensated for change in
inlet/output pressure) is monitored over time, at least a tendency
of increase injection of maintain a giver pressure can be
established. Such increase may indicate that the seals maybe are
damaged or defect. The latte may be observed if the tendency of the
amount of hydraulic fluid injected starts to increase with a
steeper slope.
[0178] The above described method of controlling the peak pressure
of the hydraulic fluid enables a wider range of operation speeds
compared to know injection systems for compressor.
* * * * *