U.S. patent application number 14/763674 was filed with the patent office on 2015-12-17 for gas compressor.
This patent application is currently assigned to Parker-Hannifin Corporation ("Parker"). The applicant listed for this patent is PARKER-HANNIFIN CORPORATION. Invention is credited to Tim Beck, Thomas Biagi, Blake Carl, Raymond E. Collett, James Howland, Christopher Parafinczuk, Nicholas N. White, Hao Zhang.
Application Number | 20150361970 14/763674 |
Document ID | / |
Family ID | 50151384 |
Filed Date | 2015-12-17 |
United States Patent
Application |
20150361970 |
Kind Code |
A1 |
White; Nicholas N. ; et
al. |
December 17, 2015 |
GAS COMPRESSOR
Abstract
A compressor is provided suitable for compressing natural gas
from a pressure associated with a residential gas supply to a
pressure suitable for an automotive gas tank. The compressor
utilizes a par of pneumatic cylinders driven by a hydraulic
cylinder to compress the gas in a multi-stage process. Various
embodiments are provided with respect to the gas compressor portion
and the drive portion. A pressure boost system is also provided
which utilizes an internal control valve and internal orifice
through the piston of one of the pneumatic cylinders.
Inventors: |
White; Nicholas N.; (Shaker
Heights, OH) ; Carl; Blake; (University Heights,
OH) ; Beck; Tim; (Marysville, OH) ; Collett;
Raymond E.; (Put-in-Bay, OH) ; Parafinczuk;
Christopher; (Park Ridge, IL) ; Biagi; Thomas;
(Algonquin, IL) ; Howland; James; (Mayfield Hts.,
OH) ; Zhang; Hao; (Twinsburg, OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PARKER-HANNIFIN CORPORATION |
Cleveland |
OH |
US |
|
|
Assignee: |
Parker-Hannifin Corporation
("Parker")
Cleveland
OH
|
Family ID: |
50151384 |
Appl. No.: |
14/763674 |
Filed: |
February 4, 2014 |
PCT Filed: |
February 4, 2014 |
PCT NO: |
PCT/US2014/014575 |
371 Date: |
July 27, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61760390 |
Feb 4, 2013 |
|
|
|
61820688 |
May 7, 2013 |
|
|
|
61820670 |
May 7, 2013 |
|
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Current U.S.
Class: |
417/53 ;
417/320 |
Current CPC
Class: |
F04B 27/005 20130101;
F04B 49/22 20130101; F04B 53/143 20130101; F04B 39/10 20130101;
F04B 41/04 20130101; F04B 53/16 20130101; F04B 39/0016 20130101;
F04B 35/04 20130101; F04B 25/00 20130101; F04B 35/002 20130101 |
International
Class: |
F04B 27/00 20060101
F04B027/00; F04B 39/00 20060101 F04B039/00; F04B 53/14 20060101
F04B053/14; F04B 49/22 20060101 F04B049/22; F04B 53/16 20060101
F04B053/16; F04B 35/04 20060101 F04B035/04; F04B 39/10 20060101
F04B039/10 |
Claims
1. A gas compressor comprising: a first pneumatic cylinder having a
piston separating a first pneumatic cylinder chamber and a second
pneumatic cylinder chamber; a second pneumatic cylinder having a
piston separating a third pneumatic cylinder chamber and a fourth
pneumatic cylinder chamber; a drive mechanism operatively coupled
to each piston to move the piston of each pneumatic cylinder; a gas
conduit circuit selectively connecting a gas compressor inlet to
the first pneumatic cylinder chamber, selectively connecting the
first pneumatic cylinder chamber to the fourth pneumatic cylinder
chamber, and selectively connecting the fourth pneumatic cylinder
chamber to the gas compressor outlet.
2. The compressor of claim 2, wherein the gas conduit circuit
includes a plurality of check valves to control the flow of gas
within the gas conduit circuit.
3. The compressor of any of claims 1-2, wherein the gas conduit
connects the inlet of the first pneumatic cylinder to a source of
residential gas.
4. The compressor of any of claims 1-3, wherein the gas conduit
connects the gas compressor outlet of the second pneumatic cylinder
to a gas storage tank.
5. The compressor of any of claims 1-4 further comprising one or
more additional pneumatic cylinders.
6. The compressor as in any one of claims 1-5, wherein the drive
mechanism comprises a hydraulic cylinder selectively driven by a
hydraulic pump through a directional control valve.
7. The compressor as in claim 6, wherein the hydraulic pump
comprises a first hydraulic pump and a second hydraulic pump driven
by an electric motor.
8. The compressor as in any of claims 6-7 wherein the drive
cylinder has an axis of the drive cylinder which is substantially
coaxial with an axis of one of the first and second cylinders.
9. The compressor of any of claims 1-8, wherein the gas conduit
circuit selectively connects the gas compressor inlet to the second
pneumatic cylinder chamber, and the piston in the first pneumatic
cylinder includes a check valve in series with an orifice formed
through the piston and selectively connecting the second pneumatic
cylinder chamber to the first pneumatic cylinder chamber.
10. The compressor as in any of claims 1-8, wherein the gas conduit
circuit selectively connects the gas compressor inlet to the third
pneumatic cylinder chamber, and the piston in the second pneumatic
cylinder includes a check valve in series with an orifice formed
through the piston and selectively connecting the third pneumatic
cylinder chamber to the fourth pneumatic cylinder chamber.
11. The compressor as in any of claims 1-10, wherein the first
pneumatic cylinder is connected to the second pneumatic cylinder by
an end cap, the end cap including a check valve in series with an
orifice formed through the end cap and selectively connecting third
pneumatic cylinder chamber to the second pneumatic cylinder.
12. The compressor as in any of claims 1-8, wherein the gas conduit
circuit selectively connects the gas compressor inlet to the second
pneumatic cylinder chamber, the first cylinder including an
internal inner diameter flow passage formed by a portion of an
inner cylindrical wall being formed at a radius larger that the
radius of the inner diameter of the cylinder.
13. The compressor as in any of claims 1-8, the compressor further
comprising: the gas conduit circuit selectively connects the
compressor inlet to the second pneumatic cylinder chamber and the
third pneumatic cylinder chamber, and selectively connects the
second pneumatic cylinder chamber to the first pneumatic cylinder
chamber, and selectively connects the third pneumatic cylinder
chamber to the first pneumatic cylinder chamber, a shut off valve
selectively enabling and disabling flow for the second and third
pneumatic cylinder chamber to the first pneumatic cylinder chamber;
and a gas reservoir.
14. A method of compressing gas utilizing the compressor of claim
10 comprising the steps of: activating the drive mechanism to
extend the cylinder pistons from a fully retracted position causing
the gas to flow from the gas supply into the first pneumatic
cylinder and into the third pneumatic cylinder chamber and from the
second pneumatic cylinder chamber to the gas reservoir and from the
fourth pneumatic cylinder chamber to the gas storage tank;
disengaging the shut off valve to allow gas to flow from the gas
reservoir to the first pneumatic cylinder chamber when the pistons
are fully extended; engaging the shut off valve while the pistons
are retracted to allow gas to flow from the first pneumatic
cylinder chamber to the fourth pneumatic cylinder chamber and from
the third pneumatic cylinder chamber to the gas reservoir and from
the gas source to the second pneumatic cylinder chamber.
15. A method of compressing gas utilizing the compressor of claim 9
comprising the steps of: activating the drive mechanism to extend
the cylinder pistons from a fully retracted position to a fully
extended position causing the gas to flow from the gas supply into
the first pneumatic cylinder chamber and from the second pneumatic
cylinder chamber to the first pneumatic cylinder chamber and from
the fourth pneumatic cylinder chamber to the gas storage tank;
activating the drive mechanism to retract the cylinder pistons from
a fully extended position to a fully retracted position causing the
gas to flow from the gas supply into the second pneumatic cylinder
chamber and from the first pneumatic cylinder chamber to the fourth
pneumatic cylinder chamber.
16. A gas compressor connectable to a supply of gas and to a gas
storage tank, the compressor comprising: a first pneumatic cylinder
having a piston separating a first pneumatic cylinder chamber and a
second pneumatic cylinder chamber; a second pneumatic cylinder
having a piston separating a third pneumatic cylinder chamber and a
fourth pneumatic cylinder chamber; an end cap connecting the first
pneumatic cylinder and the second pneumatic cylinder; a drive
mechanism operatively coupled to move the piston of each pneumatic
cylinder; a gas conduit circuit selectively connecting the supply
of gas to the first pneumatic cylinder chamber, selectively
connecting the supply of gas to the second pneumatic cylinder
chamber, selectively connecting the supply of gas to the third
pneumatic cylinder chamber, and selectively connecting the fourth
pneumatic cylinder chamber to the gas storage tank; the piston in
the first pneumatic cylinder includes a check valve in series with
an orifice formed through the piston and selectively connecting the
first pneumatic cylinder chamber to the second pneumatic cylinder
chamber; the end cap including a check valve in series with an
orifice formed through the end cap and selectively connecting the
second pneumatic cylinder chamber to the third pneumatic cylinder;
the piston in the second pneumatic cylinder includes a check valve
in series with an orifice formed through the piston and selectively
connecting the third pneumatic cylinder chamber to the fourth
pneumatic cylinder chamber.
17. A gas compressor comprising: a cylinder; a piston moveably
positioned within the cylinder and forming an internal chamber on
either side of the piston within the cylinder, the piston having a
check valve in series with an orifice formed through the piston and
selectively connecting the internal chambers of the cylinders; a
gas inlet connected to each chamber of the cylinder; and a
compressed gas outlet connected to one chamber of the cylinder.
18. A method of compressing gas using a cylinder having a piston
moveably positioned within the cylinder and forming a boost chamber
on one side of the piston and a boosted chamber on the other side
of the piston, the method comprising the steps of: extending the
piston to compress a volume of gas in the boost chamber and
allowing gas provided by a source of gas to enter the boosted
chamber; allowing a portion of the gas in the boost chamber to pass
through a piston check valve and orifice through the piston when
the pressure in the boost chamber surpasses the check valve
activation pressure; retracting the piston to compress a volume of
gas in the boosted chamber, and allowing gas provided by the source
of gas to enter the boost chamber; allowing a portion of the gas in
the boosted chamber to pass through a check valve of a cylinder
exit line when the pressure in the boosted chamber surpasses the
check valve activation pressure.
19. A method of compressing gas using a gas compressor comprising a
first cylinder having a piston separating a first cylinder chamber
and a second cylinder chamber, a second cylinder having a piston
separating a third cylinder chamber and a fourth cylinder chamber,
each piston having a check valve in series with an orifice formed
through the piston and selectively connecting the chambers of the
respective cylinders; a means for moving the piston of each
cylinder, a gas reservoir, and a gas storage tank, the method
comprising the steps of: moving the pistons of each cylinder from a
retracted position to an extended position forcing gas to flow from
a source of gas into the first cylinder chamber and the third
cylinder chamber, and forcing gas to flow from the second cylinder
chamber to the gas reservoir, and forcing gas to flow from the
fourth cylinder chamber to the storage tank; opening a valve to
allow gas flow from the gas reservoir to the first cylinder chamber
when the pistons are in a fully extended position; closing the
valve and retracting the pistons until they are fully retracted
which forces gas flow from the first cylinder chamber to the fourth
cylinder chamber, and from the third cylinder chamber into the
reservoir, and from the gas source into the second cylinder
chamber.
20. A method of compressing gas using a gas compressor comprising a
first cylinder having a piston separating a first cylinder chamber
and a second cylinder chamber, a second cylinder having a piston
separating a third cylinder chamber and a fourth cylinder chamber,
a means for moving the piston of each cylinder, a gas reservoir,
and a gas storage tank, the method comprising the steps of: moving
the pistons of each cylinder from a retracted position to an
extended position forcing gas to flow from a source of gas into the
first cylinder chamber and the third cylinder chamber, and forcing
gas to flow from the second cylinder chamber and from the fourth
cylinder chamber to the storage tank; retracting the pistons from
the extended position until they are fully retracted forcing gas
flow from the first cylinder chamber and the third cylinder chamber
into the gas storage tank, and forcing gas flow from the source of
gas into the second cylinder chamber and the fourth cylinder
chamber.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of the filing date of
U.S. Provisional Patent Application Ser. No. 61/760,390, filed Feb.
4, 2013; US Provisional Patent Application Ser. No. 61/820,670
filed May 7, 2013; US Provisional Patent Application Ser. No.
61/820,688 filed May 7, 2013, the disclosures of which are
incorporated herein by reference in their entirety.
TECHNICAL FIELD
[0002] This invention relates to gas compressors, and more
particularly to a compressor suitable for residential compression
of natural gas with particular use in automotive applications.
BACKGROUND OF INVENTION
[0003] Natural gas powered vehicles are becoming more common, but
the prevalence of commercial filling stations poses an issue to
ensure reliable operation of the vehicle. In certain areas of the
United States, nearly every home has access to a supply of natural
gas from their local provider and this can be compressed for use in
a natural gas vehicle. The typical supply of natural gas available
to a home is around 200 millibar. A vehicle natural gas tank is
generally pressurized to 248 bar at a temperature of 25.degree. C.;
this is a compression ratio of 1240 with respect to the home supply
pressure--while adding nearly no temperature to the system. Due to
the high degree that the force changes over a compression cycle, a
hydraulically powered drive unit appears to offer a good tradeoff
of cost, both initial and variable, and functionality, but
mechanically driven systems also offer their own benefits of
simplicity and efficiency. Achieving this level of compression
while minimizing leaks, energy, power consumption, and maximizing
fill rate poses a challenge while maintaining an affordable cost to
the end user.
[0004] There are a few prior art commercial systems available. The
fill rate on these products varies significantly from 0.5 gallon of
gas equivalent (GGE) per hour up to a fill rate of 6 GGE per
hour.
SUMMARY OF THE INVENTION
[0005] At least one embodiment of the present invention
provides
[0006] At least one embodiment of the present invention
provides
[0007] At least one embodiment of the present invention
provides
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a schematic view of an embodiment of a compressor
system of the present invention which uses internally routed check
valves and orifices to boost the pressure in the pressure boosted
chamber of the first stage cylinder;
[0009] FIG. 2 is a schematic view of another embodiment of a
compressor system of the present invention which utilizes a two
stage filling process and a single pump;
[0010] FIG. 3 is a schematic view of an embodiment of a compressor
system of the present invention which is similar to the embodiment
shown in FIG. 1, except the passive hydraulically piloted unloading
valve is replaced by a solenoid piloted unloading valve;
[0011] FIG. 4 is a schematic view of an embodiment of a compressor
system of the present invention which is similar to the embodiment
shown in FIG. 1, except the fixed relief valve is replaced with a
variable relief valve;
[0012] FIG. 5 is a schematic view of a compressor section of an
embodiment of a compressor system of the present invention wherein
the compressor section which utilizes internally routed pressure
boost in the second stage cylinder as well as the first stage
cylinder;
[0013] FIG. 6 is a schematic view of another compressor section
embodiment where the second stage pressure boosting chamber is
connected to the pressure boosting chamber via check valves and
orifices through a mutual end cap;
[0014] FIG. 7 is a schematic view of another compressor section
embodiment which is a combination of FIGS. 5 and 6 which enables
high pressure gas flow internally through the pistons and end
caps;
[0015] FIG. 8 is a schematic view of a two cylinder pressure boost
system utilizing internal orifices and check valves between the
cylinders via the mutual end cap;
[0016] FIG. 9A is a cross-sectional view of a cylinder illustrating
an embodiment of the invention that implements variable sized
internally muted orifices and check valves that when the piston
travels past an orifice a flow passage opens between the two
chambers of the cylinder; and FIG. 9B is a detail cross-sectional
view of this area of FIG. 9A;
[0017] FIG. 10 is a detail cross-sectional view of a cylinder of
the present invention which utilizes inner diameter flow passages
which selectively connect the two chambers of the cylinder based on
the position of the piston;
[0018] FIG. 11 is a detail cross-section view of a piston used in
an embodiment of the invention showing the check valves and
internally routed orifice;
[0019] FIG. 12 is a top view of the piston of FIG. 11;
[0020] FIG. 13 is a schematic view of an embodiment of a compressor
system of the present invention which utilizes a three stage
filling circuit without pressure boost;
[0021] FIG. 14 is a schematic view of an embodiment of a three
stage filling circuit without pressure boost similar to FIG. 13 but
including a low pressure filling configuration;
[0022] FIG. 15 is a schematic view of an embodiment of a compressor
system of the present invention which utilizes a five stage filling
circuit;
[0023] FIG. 16 is a schematic view of an embodiment of a compressor
system of the present invention which utilizes a three stage
filling circuit with a high-low pump system;
[0024] FIG. 17 is a schematic view of an embodiment of a compressor
system of the present invention which utilizes a two stage filling
circuit with the drive system positioned between the cylinders;
[0025] FIG. 18 is a schematic view of an embodiment of a compressor
system of the present invention which utilizes a two stage filling
circuit with a mechanically driven system with cylinders arranged
generally in parallel;
[0026] FIG. 19 is a schematic view of an embodiment of a compressor
system of the present invention which utilizes a two stage filling
circuit with a mechanically driven system with the cylinders
arranged in series;
[0027] FIG. 20 is a schematic view of an embodiment of a compressor
system of the present invention which utilizes a two stage filling
circuit with a mechanically driven system driven by a connecting
rod in a reciprocating fashion.
[0028] FIG. 21 is a schematic view of the embodiment shown in FIG.
3 depicting an initial stage of the compression cycle wherein the
compression pistons are fully retracted;
[0029] FIG. 22 is a schematic view of the embodiment shown in FIG.
3 depicting a secondary stage of the compression cycle;
[0030] FIG. 23 is a schematic view of the embodiment shown in FIG.
3 depicting a third stage of the compression cycle;
[0031] FIG. 24 is a schematic view of the embodiment shown in FIG.
3 depicting a fourth stage of the compression cycle;
[0032] FIG. 25 is a schematic view of the embodiment shown in FIG.
3 depicting a fifth stage of the compression cycle;
[0033] FIG. 26 is a schematic view of the embodiment shown in FIG.
3 depicting a sixth stage of the compression cycle wherein the
compression pistons are fully extended;
[0034] FIG. 27 is a schematic view of the embodiment shown in FIG.
3 depicting a seventh stage of the compression cycle where the
compression pistons have started retracting;
[0035] FIG. 28 is a schematic view of the embodiment shown in FIG.
3 depicting a eighth stage of the compression cycle;
[0036] FIG. 29 is a schematic view of the embodiment shown in FIG.
3 depicting a ninth stage of the compression cycle;
[0037] FIG. 30 is a schematic view of the embodiment shown in FIG.
3 depicting a tenth stage of the compression cycle wherein the
compression pistons are fully retracted and the gas is moving
toward the state shown in FIG. 21;
[0038] FIG. 31 is a cross-sectional view of the compression piston
within a cylinder depicting gas coming through the check valve and
orifice in the compression piston to the pressure boosted side of
the cylinder;
[0039] FIG. 32 is a cross-sectional view of the compression piston
within a cylinder similar to FIG. 31 where the piston has extended
further allowing gas to move around the piston through the cylinder
inner diameter flow passages which connect to the two chambers of
the cylinder;
[0040] FIG. 33 is a cross-sectional view of the compression piston
within a cylinder similar to FIG. 32 where the piston has now fully
extended;
[0041] FIG. 34 is a cross-sectional view of the compression piston
within a cylinder similar to FIG. 33 where the piston begins to
retract allowing gas to move around the piston through the cylinder
inner diameter flow passages which connect to the two chambers of
the cylinder;
[0042] FIG. 35 is a cross-sectional view of the compression piston
within a cylinder similar to FIG. 31 where the piston has retracted
to close the cylinder inner diameter flow passages;
[0043] FIG. 36 is a schematic view of another embodiment of a
compressor system of the present invention which utilizes a three
stage filling process and a high low pump system shown with the
pistons beginning to extend within the cylinders;
[0044] FIG. 37 is a schematic view of the system of FIG. 36 shown
with the pistons continuing to extend within the cylinders causing
gas flow through the circuit;
[0045] FIG. 38 is a schematic view of the system of FIG. 37 shown
with the pistons fully extended within the cylinders;
[0046] FIG. 39 is a schematic view of the system of FIG. 38 shown
with the pistons beginning to retract within the cylinders;
[0047] FIG. 40 is a schematic view of the system of FIG. 39 shown
with the pistons continuing to retract within the cylinders;
[0048] FIG. 41 is a schematic view of the system of FIG. 40 shown
with the pistons fully retracted within the cylinders;
[0049] FIG. 42 is a schematic view of another embodiment of a
compressor system of the present invention which utilizes a three
stage filling process and a single pump system shown with the
pistons extending within the cylinders;
[0050] FIG. 43 is a schematic view of the system of FIG. 42 shown
with the pistons retracting within the cylinders;
[0051] FIG. 44A is a plan view of an end cap in accordance with an
embodiment of the invention; and FIG. 44B is a perspective view of
the end cap shown in FIG. 44A; and
[0052] FIG. 45 is a schematic view of a compressor system immersed
in a liquid cooling tank in accordance with an embodiment of the
invention.
DETAILED DESCRIPTION
[0053] A compressor system is provided comprising a drive section
and a compression section. There are a number of different
embodiments for each of the compressor and drive sections that can
be can be combined into the full system resulting in additional
system combinations. The compressor is discussed below primarily
for use in compressing natural gas, however, the invention is not
limited to use with a particular gas.
[0054] For reference, the most basic form of the compressor system
(110) of this invention comprises two pneumatic cylinders (7), (8)
used to compress the natural gas, the cylinders driven by a
hydraulic cylinder (4) connected to an electrically driven
hydraulic power unit as shown in FIG. 2. One or more of the sides
of the pneumatic cylinders are connected to the home supply of
natural gas (6) and connections between the pneumatic cylinders in
the form of a gas circuit are plumbed differently and varying
components to achieve varying functionality and efficiency. The
compressor system has an inlet (60) which connects the gas conduit
to the supply of gas (6) and an outlet (61) which connects the gas
conduit to the gas storage tank (9). For clarity, the left side of
the first pneumatic cylinder (7) is generally referred to as the
first pneumatic cylinder chamber and the right side of the first
pneumatic cylinder (7) is generally referred to as the second
pneumatic cylinder chamber while the left side of the second
pneumatic cylinder (8) is generally referred to as the third
pneumatic cylinder chamber and the right side of the second
pneumatic cylinder (8) is generally referred to as the fourth
pneumatic cylinder chamber. In specific embodiments, the compressor
systems compress the gas in stages and these cylinder chambers may
be designated by the stage sequence. Check valve (5), (8) are
utilized in the circuit to help control the flow of the gas. By
plumbing the system differently, varying numbers of stages of
compression can be obtained to increase the flow rate and decrease
the energy and power consumption.
[0055] One aspect that is illustrated in FIG. 2, but could be
present in several other embodiments are the cylinder standoffs
(51) which are used to separate the hydraulic cylinder (2) from the
CNG Cylinders (7), (8). This feature helps prevent contamination of
the natural gas which harmful to the vehicles that will be filled.
Besides separating the natural gas, the cylinder standoffs (51) are
used as structural support and cost reduction as the same function
could be achieved by some sort of empty cylinder body. The open
nature of the standoffs (51) will allow technicians to service the
device more easily as it is more accessible and the standoffs allow
for easily assembly and disassembly. From an integration
perspective the cylinder standoffs (51) can also be used to
transport hydraulic fluid (which could be used as coolant) from the
hydraulic pump or reservoir to where it is needed such as on the
line connecting the First Stage CNG Cylinder (7) and the Second
Stage CNG Cylinder or the final compression chamber, among other
locations.
[0056] Also illustrated in FIG. 2 is an inlet capacitance (52),
which could be included on any of the embodiments, and is used as
volume chamber before the first stage cylinder (7) to ensure there
is ample gas available when filling any of the chambers with gas
from the natural gas supply (6). The inlet capacitance (52) present
is expected to maintain the pressure of the natural gas supply at a
more consistent level as well as preventing the functioning of this
invention from affect the natural gas service of others in the area
due to a rapid demand in gas. The inlet capacitance (52) could take
a number of forms including a volume chamber, a large or long pipe,
a small low pressure accumulator, or any other device that
increases the effective line volume and/or mass of gas near the
inlet (60) to the compressor system (110).
[0057] Another embodiment of the compressor (111) shown
schematically in FIG. 1, compresses gas in a pseudo three stage
process in a method to increase the number of moles of gas in a
constant volume chamber or dwelling cylinder chamber, above that
allowed by the ideal gas law when said chamber is connected to a
constant pressure. The double rod first stage pneumatic cylinder
(7) is connected to the second stage pneumatic cylinder (8) where
the two chambers of the first stage cylinder (7) are both connected
through inlet (60) to the natural gas supply (6) via CNG supply
check valves (5) and connected to each other through the first
stage piston (30) via internal check valve(s) (32) and orifice(s)
(31); the drive cylinder (4) is connected to the first stage
pneumatic cylinder (7) and the second stage pneumatic cylinder (8)
and is actuated via the hi-low hydraulic pump circuit. The first
stage pneumatic cylinder utilizes the second pneumatic cylinder
chamber as the pressure boosting chamber (28) to increase the mass
of natural gas in the first pneumatic cylinder chamber as the
pressure boosted chamber (29), which then compresses the gas and
passes it to the second stage pneumatic cylinder (8) via a series
of high pressure CNG check valves (34) where it is passed to the
fourth pneumatic cylinder chamber as the final compression chamber
(43), compressed again, and then passed through outlet (61) to the
CNG storage tank (9). The hi-low circuit is composed of an electric
motor (23) to drive both the high flow pump (14) and low flow pump
(13), which are constant volume units, where a hydraulically
piloted unloading valve (17) is used to control the power when both
pumps are in use and the relief valve (35) is used to control the
maximum power when only the low flow pump (13) is in use. The high
flow pump (14) is connected to the low the flow pump (13) via a
hydraulic check valve (15) and the two pumps are connected to the
drive cylinder (4) via another hydraulic check valve (15) and the
directional control valve (3); the directional control valve (3) is
used to determine the direction of motion for the drive cylinder
(4). The hydraulically piloted unloading valve (17) is set to open
at some pressure below that of the relief valve (35). The
hydraulically piloted unloading valve (17) is used to ensure that
the flow power from the hydraulic pumps do not exceed the maximum
rating of the electric motor (23) by reducing the pressure, and
therefore power, of the high flow pump (14) to nearly zero and only
allowing the low flow pump (13) to generate pressure. The relief
valve (35) is used to limit the pressure, and therefore flow power,
from the low flow pump (13) so as to ensure the maximum rated power
of the electric motor (23) is not exceeded.
[0058] In the embodiment of FIG. 1, the high flow pump (14)
actually produces less flow than the low flow pump (13), but to
maintain the assumption that the high flow device is unloaded the
present nomenclature is selected. Further, the hydraulically
piloted unloading valve (17) is set to the open at the pressure
when the flow power (pressure.times.flow of both pumps) exceeds the
electric motor (23) maximum rated power. The maximum size of the
low flow pump (13) is determined by solving for the flow that will
equal the maximum rated power of the electric motor (23) at the
pressure setting of the relief valve (35). The size of the high
flow pump (14) is simply determined by taking the difference
between the total flow required and the low flow pump (13) flow.
The total flow required and the relief valve setting is a function
of the size of the pneumatic cylinders and the desired fill
rate.
[0059] Another embodiment of the compressor system (112),
illustrated in FIG. 3, differs from the system shown in FIG. 1 in
that it replaces the hydraulically piloted unloading valve (17)
with a solenoid operated pilot valve (36) which is actuated by the
signal from the hydraulic pressure transducer (37) connected to the
hydraulic line directly preceding the directional control valve
(3). The benefit of this embodiment is that the pressure required
to actuate the solenoid operated pilot valve (36) can be changed
over the course of the filling cycle. Another embodiment of the
compressor system (113) is shown in FIG. 4, which is also a
derivative of the circuit in FIG. 1, replaces the relief valve (35)
with a variable relief valve (38) where the relief pressure is set
based on the direction of motion and the pressure in the CNG
storage tank (9) as reported by the pneumatic pressure transducer
(39). The pressure setting on the variable relief valve (38) can be
changed over the filling cycle as the pressure required to dwell at
either end is a function of the pressure in the CNG storage tank
(9) and therefore increases during the filling cycle. The purpose
of the embodiment depicted in FIG. 4 is to reduce the flow power
that is wasted over the variable relief valve (38) when the system
is dwelling at either end; this reduces the average power required
from the electric motor (23) and the energy required over a fill
cycle. Another embodiment, not shown in this document, combines the
additional components utilized in FIGS. 3 and 4 to obtain
functionality where both the relief valve and unloading valve
pressures can be adjusted depending on the current pressure in the
CNG tank or other parameters such as environmental temperature, CNG
storage tank (9) temperature, etc. which leads to reducing the
average power required and the cost of energy to complete a fill
cycle. An embodiment exists for driving the compression section
using a variable displacement pump, or a horsepower limiting
variable displacement pump. Another option for providing flow to
the drive cylinder (4) is using a fixed displacement pump connected
to a variable frequency drive. The variable frequency drive can be
used to limit the power of the electric motor and the hydraulic
pump, so as the pressure increases the speed can be decreased. This
is an advantage over the hi-lo pump circuit as there is a discreet
step change in the power output when the high flow pump (14) is
unloaded to tank. Other benefits include reducing the wasted power
when dwelling as the required pressure can continue to be provided
by the flow can be minimized by slowing the electric motor to near
its stall speed. There are a number of different methods not
mentioned in this document to achieve the desired result and are
considered within the scope of the present invention.
[0060] Another embodiment of the compression system (114), shown in
FIG. 5, uses a pressure boost concept described in both the first
stage pneumatic cylinder (7) and the second stage pneumatic
cylinder (8). This will increase the mass of gas in the final
compression chamber (43) before the gas is propagated from the
pressure boosted chamber (29) as gas is also delivered from the
natural gas supply (6) through a CNG supply check valve (5) and the
second stage pressure boosting chamber (40). Notice that in FIG. 5
the orientation of the check valve (32) in the second stage piston
(33) is reversed compared to the internal check valve (32) in the
first stage piston (30). The internal check valve (32) is reversed
as the stroke direction when the gas should propagate from the
boosting chamber (28) to the boosted chamber (29) is the opposite
between the first stage pneumatic cylinder (7) and the second stage
pneumatic cylinder (8). If using the system (114) described in FIG.
5 the mass of gas delivered to the CNG storage tank (9) per cycle
and therefore the fill rate is increased when compared to an
equally sized system using the compression system (112) depicted in
FIG. 3. It is possible also to use a system where the final
compression chamber (43) is not connected to the natural gas supply
(6).
[0061] Another embodiment of the compressor system (115), shown in
FIG. 6, uses the pressure boost concept, but a slightly modified
version as gas is propagated from the second stage boosting chamber
(40) to the pressure boosting chamber (28) in the first stage
pneumatic cylinder (7). Pressure boost is not used in the piston
(33) of the second stage pneumatic cylinder (8). This will increase
the mass of gas in the pressure boosting chamber (28) so more mass
of gas can be passed to the pressure boosted chamber (29) and
therefore more gas pumped per cycle. One benefit of this
modification is that the gas is passed internal to the cylinders
(7), (8), so as to minimize the leak points. This embodiment
alternatively can be used to the decrease the cycle time as the
same mass of gas can be filled in the pressure boosted chamber (29)
in a shorter amount of time.
[0062] Another embodiment of the compressor system (116), shown in
FIG. 7, illustrates a configuration where the high pressure
compressed gas can be entirely routed internally until it must be
passed to the CNG storage tank (9); this embodiment minimizes leak
points in comparison to previous embodiments. The embodiment is
quite similar to that described in FIG. 6, except that the high
pressure CNG check valves (34) have been removed between the first
stage pneumatic cylinder (7) and the second stage pneumatic
cylinder (8), and the check valves (32, 44) in the first stage
piston (30) and the mutual end cap (42) have reversed their
orientation. Further, internal high pressure check valves (44) have
been added to the second stage piston (33) so as to be able to
transfer gas from the second stage boosting chamber (40) to the
final compression chamber (43). It is key to recognize that the
internally routed passage through the second stage piston does not
include an internal orifice, but only a high pressure check valve
(44) because the second stage pressure boosting chamber is
predominantly used as a pass through, and therefore the flow
resistance should be minimized to pass gas as quickly as possible
to the final compression chamber (43) when the system is moving to
the left. It is contemplated that a system could use internal
orifices (31) in series with the internal high pressure check
valves (44) muted through the second stage piston (33) if the
second stage pressure boosting chamber (40) were to be used for
increasing the mass of gas (or pressure). Please note that the
location of the pressure boosting chamber (28) and the pressure
boosted chamber (29) have also been reversed. Also note that
although the second stage pneumatic cylinder (8) is depicted as
being larger in diameter than the first stage pneumatic cylinder
(7), but it is not a requirement for this invention. Another
benefit of this embodiment is that the line diameter between the
chambers can be made very large as the line length will be very
short and this will create a very small dead volume. Previously the
line had to extend from the bottom of the first stage piston (7) to
the top of the second stage piston (8) which is about twice the
stroke length of a single piston; if all the lines are routed
internally the line lengths will simply be the height of the
pistons or end caps. This will reduce the energy consumption of the
system as the pressure build up due to choked flow will be
minimized and potentially the system can operate at a higher
frequency as the time for gas to propagate between chambers will be
reduced.
[0063] The invention can be expanded to a plurality of stages, as
demonstrated by the system (117) in FIG. 8, by combining the
cylinders back to back and routing internal orifices (31) and check
valves (32) internal to the mutual end cap (42). The embodiment
shown in FIG. 8 is composed of two cylinders separated by a mutual
end cap (42) and where the pistons (30, 33) in each cylinder and
mutual end cap (42) have internally routed orifices (31) and check
valves (32). Each of the chambers is connected through inlet (60)
to the constant pressure source (6) through the low pressure check
valves (5). In this configuration, the pneumatic chambers are
generally reversed in comparison to the previous embodiments. The
right most chamber is referred to as the 1.sup.st pressure boosting
chamber (45) the next right most chamber is referred to as the
2.sup.nd pressure boosting chamber (46), the right most chamber in
the left cylinder is referred to as the 3.sup.rd pressure boosting
chamber (47), and finally, the left most chamber in FIG. 8 is
referred to as the pressure boosted chamber (29). At steady state,
as one examines the chambers from right to left, the mass of gas
will be increasing. It is straightforward to recognize that this
concept can be expanded to a plurality of pressure boosting stages
by combing additional cylinder back to back with the mutual end
cap. Also note that this invention can be driven from either end
and the end that is not driven can be modified to be a single ended
cylinder to achieve more surface area and chamber volume.
[0064] Besides routing the flow internally it is also possible to
route the flow externally where a check valve and orifice continue
to separate the flow path between the two chambers. The added
volume of the line segment between the two chambers is detrimental
to the process as more moles will remain in the pressure boosting
stage (28) and the flow path. Further, by routing the flow
externally additional leak points are introduced. Another
embodiment, as shown in FIG. 9, where the externally routed flow
connects via a single path to the pressure boosting chamber (28)
but to multiple locations on the pressure boosted chamber (29)
spaced along the stroke length. A check valve (32) and orifice (31)
can either be placed in each of the flow passages or a single check
valve (32) and orifice (31) in the path out of the pressure
boosting chamber (28). This embodiment results in a variable
orifice size between the chambers depending on the position of the
piston (30). The size of the orifices (31) do not necessarily
require the same flow area.
[0065] To obtain the variable orifice functionality while
maintaining the high pressure fluid internal to the cylinder (7),
low resistance flow passages can connect the chambers near the end
of stroke or route the flow through the end cap. One embodiment to
achieve the described functionality utilizes notches or cylinder ID
flow passages (48) created in the cylinder wall to allow flow to
pass from one chamber to the other, with minimal restriction, once
the piston (2) has passed a certain point, as illustrated in FIG.
10. One issue with this arrangement is that when the piston (30)
begins to move in the other direction there will be free flow
between the two chambers until the piston (30) passes the point
where the cylinder ID flow passages (48) no longer connect the two
chambers. This will be detrimental to the performance as the two
chambers will be attempting to equalize in pressure, but depending
on where the cylinder ID flow passages (48) end, only a minimal
amount of gas will exit the pressure boosted chamber (29). This
embodiment allows gas to propagate very quickly from the pressure
boosting chamber (28) to the pressure boosted chamber (29) once the
piston (30) passes a certain point in its travel, and therefore
will reduce the dwell time required for the fluid to pass through
the internal restriction (31). This concept also reduces the energy
consumption per stroke, because once the two chambers are connected
with large orifices the pressure will balance quickly. On one hand,
the end position of the cylinder ID flow passages (48) should be
located in a position where they will connect the two chambers once
the pressure in the boosted chamber (29) has exceeded the constant
pressure source's (6) pressure (the purpose of the internal
orifices (31) in the piston (30) is to slow down the propagation of
gas between the two chambers to maximize the gas filled from the
constant pressure source (6)). On the other hand, opening the
notches or cylinder ID flow passages (48) too early in the stroke
would result in the notches or cylinder ID flow passages (48)
closing too late when moving in the opposite direction meaning too
much mass may propagate back to the pressure boosting chamber (28)
from the pressure boosted chamber (29). A plurality of cylinder ID
flow passages (48) can also be added around the circumference of
the inner diameter of the cylinder with the same or varying
lengths. If varying lengths of cylinder ID flow passages (48) are
used they will change the flow area based on the position of the
piston (30). This, however, could create the issue of excessive
"leakage" between the two chambers when moving the piston (30) in
the direction that reduces the volume of the pressure boosted
chamber (29).
[0066] In an alternate embodiment, the pressure boosting flow can
be routed through a check valve in the end cap (32) and then to
flow passages into the cylinder (7). In this case, the flow
passages could be machined directly into the ID, but would need to
be in the cylinder wall and then enter the pressure boosted chamber
(29) via a hole to connect the flow passage and the chamber. This
will achieve the same functionality as FIG. 10, but the flow will
not be able to propagate from the pressure boosted chamber (29)
back to the pressure boosting chamber (28) due to the check valve
in the end cap. Both of the concepts above and others similar to
these can be combined with or without the concept of internally
routing an orifice (32) and check valve (31) through the piston
(30).
[0067] The construction of the piston and internally routed orifice
can vary depending on the needs of the system. In one embodiment, a
single internally muted orifice (31) with check valve (32) may be
considered. In a single orifice and check valve design, the orifice
and check valve are located close to the center of the piston and
preferably directly in the center of the piston so as to minimize
any moments applied to the piston due to flow forces or variations
in local static pressure due to the gas flowing between the
chambers (28), (29). In another embodiment, a plurality of orifices
(31) with check valves (32) may be used such as in FIG. 11 showing
two internally routed orifices (31) and check valves (32) placed
circumferentially at 1800 spacing. An alternative embodiment, shown
in FIG. 12, uses three sets of check valves (4) and internally
routed resistances (31) arranged circumferentially around the
piston (30) and spaced 1200 apart. This will achieve the same
benefit as inserting a single set of an internally routed orifice
(31) and a check valve (32) in series through the rod as the flow
forces and variations in local pressure would be distributed
equally around the piston resulting a minimal net moment. It is
further contemplated that other embodiments of the piston design
encompass a plurality of check valves inserted into the piston at
regular or non-regular spacing. The shape of the orifices (31)
affects the flow characteristics between the two chambers. FIGS. 10
and 11 illustrate orifices (32) that resemble a converging nozzle,
but it is also permissible to utilize an orifice (32) with a
constant flow area. The purpose of utilizing an orifice (32) shaped
like a converging nozzle is that it will permit sonic flow at the
throat without shrinking the effective flow area due to the vena
contracta phenomenon. Use of a converging nozzle with the same
throat area as the area of an orifice will result in a higher mass
flow rate; it will also be easier to calculate the mass flow rate
as the flow area will not be reduced by the boundary layer
separation and recirculation.
[0068] Another embodiment of the compressor system (118) is shown
in FIG. 13. The compressor comprises a first pneumatic cylinder (7)
having a piston separating a first cylinder chamber and a second
cylinder chamber. The compressor further comprises a second
pneumatic cylinder (8) having a piston separating a third cylinder
chamber and a fourth cylinder chamber. The compressor includes a
means for moving the piston of each cylinder in this configuration
shown as pump (1) in this case a fixed displacement pump (1) driven
by an electrical motor (not shown) at a constant speed, that
provides flow to the drive cylinder (4). The directional control
valve (3) is used to control the direction of the drive cylinder
(4). When the drive cylinder (4) is dwelling at either end of the
stroke the flow from the pump (1) is dumped over the pump relief
valve (2) to the tank. In this embodiment the position of the
directional control valve (3) is determined by a timer, but it can
also be controlled by an electric signal. The first stage pneumatic
cylinder or CNG cylinder (7) and the second stage pneumatic
cylinder or CNG cylinder (8) are coupled via mechanical shaft to
the drive cylinder (4) and therefore move with the same cadence.
All four chambers of the two CNG cylinders are used to compress the
natural gas; the left chamber of the first stage CNG cylinder (7)
is considered to be the second stage chamber (which is also
designated the first pneumatic cylinder chamber), the right side of
the first stage CNG cylinder (7) and the left side of the second
stage CNG cylinder (8) are considered to be the first stage
chambers (which are also designated the second and third pneumatic
cylinder chambers, respectively), and the right side of the second
stage CNG cylinder (8) is considered to be the third stage (which
is also designated the fourth pneumatic cylinder chamber). As with
all the embodiments, the compressor system (118) has an inlet (60)
which connects the gas conduit to the supply of gas (6) and an
outlet (61) which connects the gas conduit to the gas storage tank
(9). The gas conduit circuit connects the inlet (60) to the first
cylinder chamber, the second cylinder chamber, the third cylinder
chamber, and the fourth cylinder chamber; the gas conduit circuit
connects the first cylinder chamber and the third cylinder chamber
to the outlet (61) when the pistons are retracting and the gas
conduit circuit connecting the second cylinder chamber and the
fourth cylinder chamber to the outlet (61) when the pistons are
extending. The compressed gas moves from the outlet to the gas
storage tank (9).
[0069] All chambers composing the first and second stage
compression are connected through inlet (60) to the natural gas
supply (6) through CNG check valves (5). The two first pneumatic
cylinder chambers are connected in parallel to the CNG reservoir
(11), but through individual CNG check valves (5) connected to each
of the chambers; the CNG reservoir (11) is used to store the
compressed gas from the first stage before passing it to the second
stage. The shutoff valve (10) is used to separate the first stage
chambers and the CNG reservoir (11) from the second stage chamber;
the position of the shutoff valve (10) is controlled via an
electronic signal. The second stage chamber (left side of the first
stage pneumatic cylinder (7)) is connected to the third stage
chamber (right side of second stage pneumatic cylinder (8)) via a
pipe and a series of CNG check valves (5) to control the flow
direction.
[0070] In another embodiment of the compressor system (119), shown
in FIG. 14, the three stage filling process adds low pressure
filling functionality by altering the plumbing as well as adding a
number of CNG check valves (5), a CNG directional valve (12), and
connecting the natural gas supply (6) to all cylinder chambers.
This embodiment has two distinct modes of operation: one when the
CNG storage tank pressure is below a certain valve and a second
when it is above a certain value. When the CNG storage tank
pressure is above a certain value, the functionality of this
embodiment is precisely the same as that described for FIG. 13.
This embodiment is plumbed so that when the pressure in the CNG
storage tank is low, all four chambers have direct access to the
CNG storage tank and this is accomplished by connecting the
previously referenced first and second stages to the CNG
directional valve (12). The CNG directional valve (12) merges the
flow from the first and second stage chambers and plumbs it
directly to the CNG storage tank (9) via a CNG check valve (5). The
CNG directional valve (12) is shown to be an on/off valve that is
pilot operated by the pressure in the CNG storage tank (9), however
it can also be an electronically controlled on/off valve. When the
CNG directional valve (12) is actuated the connections from the
previous embodiment, FIG. 13, are reestablished, the low pressure
filling mode ends, and the system reverts to the previously
described actuation.
[0071] Although the two stage and three stage compression processes
have been highlighted to this point, it is also possible to expand
the invention to any number of compression stages. FIG. 15
highlights an embodiment of the compressor system (120) where there
are three pneumatic cylinders and five compression stages; there
also exists an embodiment composed of three pneumatic cylinders
that utilizes only four or less compression stages. The requirement
for adding additional compression stages is that the maximum volume
of the previous stage must be greater than that of the next stage;
this can be accomplished via either a reduction in bore diameter or
stroke length if the pneumatic cylinders' positions can be
controlled independently. To fulfill the previously stated
requirement, the system (120) illustrated in FIG. 15 must compress
gas in the piston side of the third stage pneumatic cylinder (28)
before it is passed to the rod side of the third CNG stage cylinder
(28). Further, to move the gas from the third stage compression
chamber to the fourth stage compression chamber an additional
shutoff valve (10) and CNG reservoir (11) are needed as the third
stage and the fourth stage compression chambers both compress when
the system is extending. Adding additional compression stages may
increase the total gallons of gas equivalent pumped per hour by
increasing the amount of gas pumped per stroke.
[0072] Besides altering the compression section, the drive section
can also be modified. FIG. 16 illustrates an embodiment of the
compressor system (121) where the basic drive section from FIG. 13
is replaced with a more complex section comprised of a permutation
of a hi-lo pump circuit. The compression section is the same as
that described for FIG. 13, except that there is a pressure sensor
(20) added to the CNG storage tank (9). A typical hi-lo circuit is
generally designed where one pump provides high flow and low
pressure and the other pump provides low flow and high pressure
where the unloading valve is operated by a pressure setting. Like
normal, this hi-lo circuit utilizes a high flow pump (13), a low
flow pump (14) and a hydraulic check valve (16), however, in this
embodiment the hi-lo circuit's unloading valve (17) is controlled
via a signal from the unloading valve controller (18) determined by
the position measured from the position sensor (21). In the
description accompanying FIG. 8 it was noted that when the drive
cylinder (4) dwells at either end the entire flow from the pump
would be dumped over a relief valve, however in this case only a
small amount of flow, that from the low flow pump (14), is dumped
over the variable pump RV (16). Further, the variable pump RV (16)
uses a signal from the relief valve controller (19) based on the
measure pressured from the pressure sensor (20) in the CNG storage
tank (9). The relief valve controller (19) computes the amount of
force, and therefore hydraulic pressure, required to hold the drive
cylinder (4) in place while dwelling and therefore minimizing the
energy wasted over the variable pump RV (16). Although not
explicitly shown, there is also an embodiment where the variable
pump RV (16) can be set to fixed value. The drive cylinder (4) can
also be mounted in the middle of the two pneumatic cylinders as
opposed to at one end as illustrated in FIG. 17. Note that the
drive cylinder is separated from the pneumatic cylinder, and as
such the hydraulic fluid cannot mix with the natural gas and
contaminate the mixture. Further, the drive cylinder (4) is
connected to the first stage pneumatic cylinder (7) in such a way
that the portion of the rod that comes in contact with the
hydraulic fluid will not contact the natural gas; one possible
embodiment of this is where the length of the rod between the drive
cylinder (4) and the first stage cylinder (7) is greater than twice
the stroke length.
[0073] The previous figures have illustrated an arrangement where
the drive cylinder (4) is in series with the first and second stage
pneumatic cylinders, however it is also possible to arrange it in a
manner where the pneumatic cylinders are instead arranged in a
parallel or stacked manner. Further, all of the drive sections
illustrated to this point are hydraulically powered, however it is
also possible to drive the pneumatic cylinders in a purely
mechanical manner in either a series or stacked manner. For
example, FIG. 18 illustrates a design where the pneumatic cylinders
are oriented horizontally and operate parallel to one another and
are driven by an electric motor (23) connected to a gear box (26);
this can also be referred to as a stacked arrangement. The
pneumatic cylinder rods (25) have gear teeth cut into them so they
act as a rack and the gear attached to the output of the gear box
(26) as the pinion (24). Very similar to FIG. 18 there also exists
an embodiment where instead of orienting the system horizontally it
can be oriented vertically. Further, another embodiment, shown in
FIG. 19 can be used where the pneumatic cylinders are connected in
series and are driven from a central electric motor (23) connected
to the previously described gear box (26) and rack (25) and pinion
(24) concept. On both embodiments described in FIGS. 18 and 19,
ample support will need to be applied to the rods with the rack
machined into them. Securing a journal bearing, or other type of
bearing, on each side of the rod where the pinion interacts with
the rack should provide the support required to minimize stress and
deflections. The geared solutions also offers the benefit of being
able to use different stroke lengths for the stacked cylinder
concepts as the gear ratio of the gear box can be altered between
its two outputs to each pinion gear. A more compact embodiment, as
shown in FIG. 20 is composed of vertically or horizontally oriented
pneumatic cylinders where the rods are attached to a centrally
located electric motor (23) via a connecting rod (27) that the
electric motor (23), attached a to a gear box potentially (26), is
able to rotate. The attachment point between the connecting rod
(27) and rods of the cylinders must be able to rotate to facilitate
the required motion. The inventions in FIGS. 18-20 will need a
variable speed electric motor so it can change direction.
[0074] Other embodiments not shown are also contemplated. For
examples one can implement either of the drive sections with any of
the circuit configurations described previously. Further, a two
stage low pressure filling circuit or a three stage filling circuit
where only a single chamber is used as the first stage are examples
of permutation only presented to demonstrate other obvious
solutions but not intended to limit the scope of this document.
Besides the two and three stage compression concepts shown in this
document it is quite obvious how this can be expanded to a
plurality of compression stages. The invention can have a plurality
of stages and is not limited to the compressor sections described
herein.
[0075] Another aspect of the invention is the cooling of the
compressed natural gas as compressing the gas will undoubtedly lead
to a rise in temperature meaning higher pressures and more input
work required for compression. Therefore, ample cooling is required
and there are a number of locations where the cooling can be
performed such as line sections between compression chambers, the
CNG reservoir, or potentially directing the flow through a heat
exchanger between any stage or before entering the CNG storage
tank. Alternatively, cooling can also be accomplished inside the
compression chambers with an in-situ cooler such as using the end
cap as a cooler or a more advanced shape. Besides cooling the fluid
internal to the cylinders it is also feasible to submerge the
cylinders in the coolant via a cooling jacket. The coolant will be
pumped through the cooling jacket removing heat from the gas which
has convected into the cylinder wall and then conducted through the
wall. The cooling flow can be generated by a standalone pump, can
be tapped from the main hydraulic pump, or it can be used in series
from the hydraulic pump. Additionally, the gas leaving the final
stage cylinder can be cooled by an additional heat exchanger before
it travels to the CNG storage tank (9).
[0076] The small volume of gas trapped at very high pressure at the
end of each stroke in either the extend or retract direction can be
used to propel the assembly in the opposite direction for a small
distance. As the pressure in the storage tank increases there would
be more energy available at the end of each stroke to accomplish
this task. Using this high pressure yet low volume gas should not
be an issue because as the volume of the chamber gets larger the
pressure will decrease according to the ideal gas law. To implement
this idea, the directional control valve (3) would need a position
where both the rod side and the drive side of the drive cylinder
(4) are connected to tank. To some extent this phenomenon already
occurs when the directional control valve (3) is changing direction
as the pump pressure decreases rapidly and therefore the pressure
that was holding the drive cylinder (4) is removed and the high
pressure natural gas at the end of stroke rapidly moves the drive
cylinder (4) at a rate which is higher than that provided by the
flow from the pump. This is of benefit as it increases the volumes
of the chambers more rapidly so they begin filling with natural gas
sooner and also lessens the negative impact of the time required
for the directional valve to shift.
[0077] Other hydraulic drive or CNG compression setups can be
utilized. Other drive and compression systems based on similar
principles exist and further that each of the drive systems and CNG
compression systems can be combined with each other to create a
number of permutations of the full invention even though they may
not all be noted in this document.
[0078] The present invention provides a number of advantages over
current systems used for the same purpose by both modifying the
current art while also applying novel concepts resulting in better
performance, reliability, and other key metrics. The present
inventions allow an increase the amount of compressed natural gas
pumped, measured in gallons of gas equivalent (GGE) per hour, as
compared to a similar sized unit using the prior art for linear
compressors, especially by taking advantage of all chambers of a
pumping device. The compression section and drive section are
separated and therefore the natural gas will not be contaminated by
other medium. This is especially a benefit when the drive section
is operated by a hydraulic cylinder so the hydraulic fluid and
natural gas cannot mix. The invention can reduce the number of leak
points by internally routing the high pressure natural gas. The
invention can increase reliability of a residential system by
operating at a lower frequency and decrease the amount of energy
required to pump each GGE of natural gas.
[0079] The benefits of using the pressure boost concept with the
invention include: Increasing the pressure of a chamber connected
to a constant pressure source above the pressure of the constant
pressure source. Increasing the mass of gas in a constant volume
chamber beyond that specified by the ideal gas law when it is
connected to a constant pressure source and result in a required
lower energy output for the linear actuator to move a given mass of
gas.
[0080] FIGS. 21-30 illustrate the operation of the invention,
however a slightly modified system from the preferred embodiment is
used to ease the description of the operation of the invention; the
description mostly closely resembles that of the system
configuration depicted in FIG. 3. Throughout the following
description it is assumed that the temperature in the compressor
section remains constant unless otherwise noted. Realistically this
assumption is not true, but the general principals and operation
described below will still remain true. Further, please note that
the color of the particles and the number of the particles relates
to the pressure and mass or moles of gas in a chamber respectively.
From lowest to highest pressure the colors are light blue, blue,
green, light purple, light orange, and red; the color blue
indicates a pressure close to or at the supply pressure. Further,
the colors red and blue are used in the drive section to indicate
the relative pressure between the hydraulic lines. These colors
have no relation to the colors used in the compressor section.
[0081] FIG. 21 illustrates the system when it is dwelling in the
fully retracted position. To ensure force on the pistons (30, 33),
due to the compressed gas in the pressured boosted chamber (29),
does not move the drive cylinder (4), it is held in place by
pressure from the low flow pump (13). To limit the holding force,
and therefore the low flow pump pressure, a relief valve (35) is
used to direct the flow back to tank. The high flow pump (14) is
sending its flow through an unloading valve (17) at a very low
pressure back to tank. After a long time dwelling the compressor
section has come to steady state where the natural gas supply (6)
has equalized in pressure with the pressure boosting chamber (28)
and the pressure boosted chamber (29) has ceased propagating gas to
the final compression chamber (43). The pressure in the pressure
boosted chamber (29) is quite high as there is some mass of gas
left in the chamber but a very small volume. It is important to
note that dwelling in this position until steady state has been
achieved is not vital to the operation of the invention.
[0082] FIG. 22 illustrates the situation where the system has begun
to extend due to the shifting of the directional control valve (3).
When the directional control valve (3) shifts, the high pressure in
the pressure boosted chamber (29) will rapidly move the system and
this is a benefit as the volume in the chamber increases more
rapidly. Concurrently, the pressure in the hydraulic system drops
so both the unloading valve (17) and the pressure relief valve (35)
close so both pumps are providing flow to the drive cylinder (4)
for the extend operation. The volume of the pressure boosted
chamber (29) increases resulting in a large pressure drop, below
that of the natural gas supply (6), so the natural gas supply (6)
begins filling the chamber through the CNG supply check valve (5).
At the same time the final compression chamber (43) and pressure
boosting chamber (29) are reducing in volume which raises their
pressures; in the depicted state the pressure in the chambers have
not gone high enough to begin propagating gas to its next
destination so at this point the chambers undergo a constant mass
process.
[0083] FIG. 23 depicts a state in which the system is continuing to
extend, but both the final compression chamber (43) and the
pressure boosting chamber (28) are sending gas to the CNG storage
tank (9) and the pressure boosted chamber (28) respectively. The
pressure in the pressure boosted chamber (29) continues to be below
that of the natural gas supply (6), so both the natural gas supply
(6) and the pressure boosting chamber (28) are filling the pressure
boosted chamber (29) with gas. The hydraulic circuit continues to
operate as described in FIG. 22's state.
[0084] The pressure boosting concept uses the properties of
compressible fluids and the tendency for gas to move from a higher
pressure volume to a lower pressure chamber. The effect of the
pressure boost concept increases the mass of gas beyond that
specified by the ideal gas law for a given volume connected to a
constant pressure source at a given temperature. It accomplishes
this by connecting both chambers of a cylinder (first stage
pneumatic cylinder (7) in the current example) to a constant
pressure source (6) and connecting the two chambers via an internal
orifice (31) and check valve (32) to restrict the flow rate and
direction of flow. As the piston is extended quickly, for example,
the chamber that is getting larger will begin to fill with gas from
the constant pressure source and the chamber that is getting
smaller will rise in pressure. However, due to the orifice (31)
between the two chambers, gas will propagate from the higher
pressure to lower pressure side at a rate highly dependent on the
orifice size; the smaller the orifice the longer the time it will
take for the two sides to balance and conversely the larger the
orifice the shorter the time it will tank for the pressure to
balance in pressure. Gas will continue flowing from the higher
pressure side to the lower pressure side until the pressures have
balanced. The key to this concept is that the low pressure volume
is continuing to fill with gas from the constant pressure source
while also receiving gas from the high pressure chamber. Selecting
the proper sized internal orifice (31) and proper closing pressure
on the internal check valve (32) is the key to optimizing this
process as those two factors determine the boost in mass, but also
the time constant for the pressure to balance, and also the
required energy to perform the operation. If the cylinder moves in
the other direction, the check valves prevent the same operation
from occurring, but instead allow the pressure boosting chamber to
fill with gas from the constant pressure source while the pressure
boosted chamber is compressed and potentially passes its gas to the
next element in the work path.
[0085] The system is continuing to extend in FIG. 24, but the
pressure in the pressure boosted chamber (29) has increased to or
above the natural gas supply pressure (6) and therefore the CNG
supply check valve (5) closes so the chamber is only being supplied
gas from the pressure boosting chamber (28). The mass of gas in the
final compression chamber (43) and the pressure boosting chamber
(28) continue to decrease as the system extends. At some point, as
depicted in FIG. 25, the hydraulic system pressure will exceed that
of the setting on the unloading valve (17) and it will open which
dumps the flow from the high flow pump (14) at a very small
pressure back to the tank. Please note that the unloading valve
(17) may open before the pressure boosted chamber (29) reaches the
pressure of the natural gas supply (6) or potentially not until the
system is dwelling in the fully extended position. The point in the
stroke at which the unloading valve opens is highly dependent on
the location in the fill cycle which relates to the pressure in the
CNG storage tank (9). The effect of unloading the high flow pump
(14) reduces the flow rate and therefore the extend speed of the
drive cylinder (4), but it also reduces the power demand on the
electric motor (23). This will eventually allow the low flow pump
(13) to generate a higher pressure to finish the extend cycle as
the total power is limited by the maximum rated power of the
electric motor (23).
[0086] Finally, the drive cylinder (4) reaches the fully extended
position and may or may not dwell in this position as shown in FIG.
26. To hold the drive cylinder (4) in place a large force/pressure
is required and therefore the directional control valve (3) remains
shifted to its current position and the low flow pump (13) provides
the necessary pressure to hold the drive cylinder (4) in place
while the balance of the flow is dumped over the relief valve (35).
While the system is dwelling gas will continue propagating from the
pressure boosting chamber (28) to the pressure boosted chamber (29)
until the pressures equalize. At this point the mass of gas will
have exceeded that specified by the ideal gas law for a chamber of
a given volume at some temperature and connected to a constant
pressure source, such as the natural gas supply (6). The final
compression chamber (43) may continue to propagate gas to the CNG
storage tank (9), but it will more than likely have equalized in
pressure already as the high pressure in the final compression
chamber (43) results in a high density and therefore a higher mass
flow rate for a given volumetric flow rate.
[0087] Eventually, the directional control valve (3) will shift
which allows the compressed gas in the final compression chamber
(43) and the pressure boosting chamber (28) to expand and rapidly
begin retracting the system as illustrated in FIG. 29. Further, due
to the hydraulic fluid pressure drop during the directional control
valve shift the unloading valve (17) and the pressure relief valve
(35) close so both pumps can supply flow to the drive cylinder (4)
for the retract operation. The pressure in the pressure boosting
chamber (28) has decreased below that of the natural gas source
(6), so the natural gas source (6) begins filling the pressure
boosting chamber (28) with gas through the CNG supply check valve
(5). The pressure in the pressure boosted chamber (29) is
increasing and the pressure in the final compression chamber (43)
is decreasing as their volumes are decreasing and increasing
respectively, but the high pressure CNG check valves (34) have not
opened yet so it is a constant mass process for those chambers
during this state. It is important to note that gas will not
propagate from the pressure boosted chamber (29) to the pressure
boosting chamber (28) due to the orientation of the internal check
valves (32) in the first stage piston (30).
[0088] As the system continues to retract, as shown in FIG. 28, gas
will begin to propagate from the pressure boosted chamber (29) to
the final compression chamber (43) while the pressure boosting
chamber (28) continues to receive gas from the natural gas supply
(6). At some point during the retracting process, depending on the
point in the fill cycle and the pressure in the CNG storage tank
(9), the pressure of the hydraulic circuit will exceed the
specified pressure for the unloading valve (17). At this point the
state depicted in FIG. 29 will occur where the high flow pump (14)
is directing its flow to tank through the shifted unloading valve
(17) at a very low pressure while the low flow pump (17) continues
to provide flow to the drive cylinder (4). The pressure of the gas
in the final compression chamber (43) may or may not be rising
depending on the mass flow rate and the rate at which the system is
retracting; a similar relationship exists for the gas in the
pressure boosted chamber (29) due to the unknown parameterization
of the system.
[0089] Eventually the cylinders will be fully retracted as shown in
the state depicted by FIG. 30 and the system may or may not dwell
in this position. While dwelling in the fully retracted position,
the low flow pump (13) will provide pressure to the drive cylinder
(4) to hold the system in this position, but the balance of the
flow will be directed through the pressure relief valve (35). Gas
will continue to flow into the pressure boosting chamber (28) from
the natural gas supply (6) until they become equal in pressure when
the CNG supply check valve (5) will close. Depending on the
parameterization of the system, gas may continue to propagate from
the pressure boosted chamber (29) to the final compression chamber
(43) until the pressure has equalized, but it is likely this
process is complete or will finish quickly due to the increased
density discussed earlier. If the system dwells in this state long
enough it will be same as the state depicted in FIG. 21.
[0090] Up to this point it has simply been noted that the
directional valve (3) shifts position, but there are a number of
methodologies to determine when the valve should shift. One method
is simply based on a constant time before the valve shifts, such as
2.5 seconds retracting and 1.7 seconds extending, or potentially
equal times. Another method may use a position sensor that when the
cylinder reaches the full extended or retracted position it dwells
for a certain amount of time and then shifts the valve. Another
means to decide when to actuate the directional control valve could
be a measure of the pressure in the hydraulic circuit, the CNG
Storage tank, or some combination dependent on the current state
both. Alternatively some means of measuring the mass of gas in a
cylinder chamber may be invented and that could be used to
determine when to shift the valve. The point trying to be
illustrated is that there are an infinite number of methods to
determine when to shift the directional control valve (3) and
should not be limited to the methods described above.
[0091] The operation described above is very closely related to the
operation of the systems depicted in FIGS. 1, 3, and 4; however the
difference in operation of the system depicted in FIG. 4 will be
highlighted. In the described operation above it was assumed that
the relief valve (35) was set to a constant relief pressure,
however it is possible to reduce the power and energy consumption
by utilizing a variable relief valve (38) as depicted in FIG. 4.
The required pressure to hold the drive cylinder in either dwell
position can be computed by knowing the area for the rod and piston
sides of the drive cylinder (4) and each of the compression
cylinders along with the current pressure in the CNG storage tank.
The pressures in the pressure boosted chamber (29) and the pressure
boosting chamber (28) will positively vary with the current
pressure in the CNG storage tank (9) and therefore the required
variable relief valve pressure (38) can start low and increase as
the required holding pressure at the dwell locations increases with
a rising pressure in the CNG storage tank (9). It is interesting to
note that depending on the parameterization of the system the
required dwell pressure can vary drastically.
[0092] The system depicted in FIG. 5 operates similarly to the
system described via FIGS. 21-30, but it differs in the fact that
it increases the mass of gas in the final compression chamber (43)
by using the pressure boosting concept on the left most chamber of
the second stage cylinder (8), which is referred to as the second
stage pressure boosting chamber.
[0093] FIG. 6 also operates in a similar fashion to the system
described via FIGS. 21-30. While it is retracting it supplies gas
to the pressure boosting chamber (28) via the natural gas supply
(6) as well as the second stage pressure boosting chamber (40). The
second stage pressure boosting chamber is connected via internal
check valves (32) and orifices (31) routed through the mutual end
cap (42) of the first stage pneumatic cylinder (7) and the second
stage pneumatic cylinder (8).
[0094] FIG. 10 illustrates a device where the restricted fluid
passage is external and where there are multiple connection points
along the stroke length of the pressure boosted chamber (28). If
the piston (30) is dwelling in a position where the pressure
boosted chamber (28) volume is very small the pressure boosting
chamber (29) will equalize with the constant pressure source (6)
after a long time. As the piston (30) begins to extend, which
reduces the volume of the pressure boosting chamber (29), the
pressure of that gas will increase, but gas cannot travel between
the two chambers until the piston (30) passes the first orifice
(31) and check valve (32). FIG. 10 illustrates an instance when the
piston (30) has extended far enough so as to connect the boosted
chamber (28) to both the constant pressure source (6) and a single
connection to the boosting chamber (29). At this point both the
constant pressure source (6) and the pressure boosting chamber (29)
will both provide mass flow to pressure boosted chamber (28) as
long as its pressure remains lower than the constant pressure
source (6). Eventually, the piston (30) will pass the next
combination of a check valve (32) and orifice (31) along the stroke
length which will increase the flow area and therefore the mass
flow rate between the chambers.
[0095] FIG. 8 illustrates an embodiment where two cylinders are
connected back to back and there is a fluid passage composed of
check valves (32) and internal orifices (31) routed through the
mutual end cap (42). This embodiment operates in a very similar
fashion to other embodiments using pressure boost, except that
there are additional pressure boost chambers. When the pistons
(30,33) are moving to the left the 1st pressure boosting chamber
(45) will be filling with gas from the constant pressure source
(46) and the 3rd pressure boosting chamber (47) will be increasing
the mass of gas in it via the 2nd pressure boosting chamber (46)
and the constant pressure source (6); the principle of moving gas
from the 2nd pressure boosting chamber to the 3rd pressure boosting
chamber is the same as described in FIGS. 21-30, except instead of
being routed through a piston it is routed through a mutual end
cap. At the same time the pressure in the pressure boosted chamber
(28) is rising and will eventually pass its compressed gas to the
next element through the check valve (32). When the pistons (30,
33) are moving to the right the constant pressure source (6) will
be increasing the mass of gas in the pressure boosted chamber (29)
and the 2nd pressure boosting chamber (46). The pressure boosted
chamber will also be receiving gas from the 3rd pressure boosted
chamber (47) via the check valves (32) and internally routed
orifices (31) through the first stage piston (30) while at the same
time the 2nd pressure boosting chamber (46) will be receiving gas
also from the 1st pressure boosting chamber (45) with the orifices
(31) and check valves (32) routed through its respective piston
(33).
[0096] FIG. 31 illustrates the embodiment shown in FIG. 9 when the
cylinder (30) is moving in the upward position which is reducing
the volume of the pressure boosting chamber (28); this motion will
be referred to as extending. At this point the gas is only
traveling to the pressure boosted chamber (29) through the check
valves (32) and internally routed orifices (31) as the pressure
boosted chamber (29) has surpassed the pressure of the constant
pressure source (6) and the piston (30) has not extended enough
where the cylinder ID flow passages (48) connect the two chambers.
The pressure of the gas in the pressure boosted chamber (29) is at
or above the supply pressure (6) and the pressure in the pressure
boosting chamber (28) is at a pressure well above that of the
constant pressure source as the volume has been reduced and the
internally routed orifices (31) are restricting the mass flow and
therefore the rate at which the pressures can balance.
[0097] As the piston (30) continues to extend the cylinder ID flow
passages (48) will eventually connect the pressure boosting stage
(28) and the pressure boosted stage (29) as shown in FIG. 32.
Because the cylinder ID flow passages (48) are large, a larger mass
of gas can quickly transfer from the pressure boosting chamber (28)
to the pressure boosted chamber (29) through the cylinder ID flow
passes (48) than if solely flowing through the internal orifices
(31). Once the pressure between the two chambers has equalized, gas
will cease propagating through the internally routed orifice (31)
and check valve (32) as there is a path of less resistance, namely
the cylinder ID flow passage (48). Also, at this point the amount
of force required to continue extending the piston (30) will
dramatically decrease, because the pressure on the pressure
boosting chamber (28) side of the piston (30).
[0098] As the piston (30) continues extending the volume of the
boosting chamber (28) will continue decreasing and therefore the
gas will propagate over to the pressure boosted chamber (29). When
at end of stroke, as shown in FIG. 33, if the piston (30) can
"bottom out" all of the gas will be in the pressure boosted chamber
(29) as there is zero volume in the pressure boosting chamber (28).
Having zero volume at the end of stroke is not necessary for the
operation of this invention. One of the benefits of this invention
is that it will take less time for the gas to propagate from the
boosting chamber (28) to the boosted chamber (29).
[0099] As the piston (30) begins to retract, as shown in FIG. 34,
gas from the pressure boosted chamber (29) will actually propagate
back to the pressure boosting chamber (28) as there are not check
valves to prevent the back flow. However, the theoretical
distribution of gas is equal to the percent volume of each chamber
immediately after the piston (30) travels far enough as to
disconnect the chambers via the cylinder ID flow passage (48). So
for example, if the piston (30) has traveled far enough that the
pressure boosting chamber (28) takes up 10% of the volume it is
expected 10% of the mass of gas is in the pressure boosting chamber
(28) and 90% in the pressure boosted chamber (29). Even though some
gas propagated back to the pressure boosting chamber (29), there is
still more gas in the pressure boosted chamber (8) than if it had
only been connected to the constant pressure source (6).
[0100] Finally, as mentioned before, once the piston (30) retracts
far enough so the chambers are no longer connected the gas will not
propagate from chamber to chamber due to the flow direction
restriction of the check valve (32) in the piston (30); FIG. 35
illustrates this state. However, as the volume of the pressure
boosting chamber (28) is increasing, the pressure will decrease
rapidly and the constant pressure source (6) will begin filling it
with gas. At the same time, the volume of the pressure boosted
chamber (29) is shrinking and therefore the pressure will
increase.
[0101] The principles of operation for the system depicted in FIG.
8 are very similar to those depicted in the systems discussed so
far, but it differs in that all the high pressure flow is routed
internally which requires the rearrangement of the chambers. As the
system retracts from the fully extended position the natural gas
supply (6) and the pressure boosting chamber (28) will supply gas
to the pressure boosted chamber (29) which is now the right most
chamber of the first stage pneumatic cylinder (7). At the same time
the second stage pressure boosting chamber (40) will pass gas from
it to the final compression chamber (43) through check valves (44)
internally routed through the second stage piston (33). The
pressure build up in the second stage pressure boosting chamber
(40) is expected to be very low as the orifice through the second
stage piston is either non-existent or very large; the second stage
pressure boosting chamber (40) is primarily used as a holding
chamber to pass the gas to the final compression chamber (43), but
is necessary due to the desire to internally route the flow; the
second stage pressure boosting chamber (40) can potentially be used
to increase the mass of gas depending of the parameterization of
the system and the components. After the system has attained the
fully retracted position there should be gas in the pressure
boosted chamber (29) above that allowed by the ideal gas law based
on the pressure of the natural gas supply (6). Further the gas will
have fully propagated to final compression chamber from the second
stage pressure boosting chamber (40) especially if the dead volume
in the chambers is minimized. As the system extends from the fully
retracted position, gas in the final compression chamber (43) will
travel to the CNG storage tank (9) and gas from the pressure
boosted chamber (29) will travel to the second stage pressure
boosting chamber (40) via the check valves (44) and orifices (31)
internally routed through the mutual end cap (42). Maximizing the
orifice (31) size will minimize the required energy expenditure to
extend the cylinder, but it will also minimize and entirely cancel
out any chance of using the pressure boost concept in the second
stage pressure boosting chamber (40) as gas will propagate between
the two chambers very quickly.
[0102] FIGS. 36-41 describe the operation of the hi-low pump
circuit using a three stage compression as shown schematically in
FIG. 13. FIG. 36 illustrates one embodiment of the invention when
the pistons are beginning to move to the right, i.e. the drive
cylinder (4) is extending. As the embodiment begins to extend the
piston side chamber of the first stage pneumatic cylinder (7),
referred to as the second stage compression chamber, and the left
side of the second stage pneumatic cylinder (8), part of the first
stage compression chamber, have some, but very little working fluid
in them at a relatively high pressure; this high pressure fluid is
left over from the last cycle and is the part that could not be
extracted. As such more gas cannot enter these chambers until the
pressure decreases by expanding their volume. The right side of the
first stage cylinder (7), the other piece of the first stage
compression chamber, has been pressurized by the natural gas supply
(6) and achieved or nearly achieved the supply pressure. The piston
side of the second stage pneumatic cylinder (8), referred to as the
third stage compression chamber, is at a pressure significantly
above that of the natural gas supply (6) as it has already
undergone compression by the first and second stage chambers.
Finally the CNG reservoir (11) is at some pressure elevated from
that of the natural gas supply (6) because pressurized gas is
present from the previous cycle where the first stage chamber of
the second stage pneumatic cylinder (8) compressed gas into it and
it is contained there due to the closed shutoff valve (10) and a
CNG check valve (5).
[0103] As the cylinders are extending the pressure is decreasing in
the second stage compression chamber and the first stage
compression chamber on the second stage pneumatic cylinder (8),
because the volume is increasing. Eventually the natural gas supply
(6) pressure will be greater than that in either of the previously
mentioned chambers and at this point the CNG check valves (5) will
open and the previously mentioned chambers will begin filling with
gas; the number of moles of gas in the chambers will be increasing.
At the same time, pressure in the third stage chamber will rise as
the volume of the chamber will be decreasing. Eventually the
pressure inside the third stage compression chamber will surpass
that of the pressure in the CNG storage tank (9) and the gas will
flow into the tank. The number of moles in the third stage
compressions chamber will be decreasing and the moles in the CNG
storage tank (9) will be increasing. The volume of the CNG storage
tank (9) is constant so as more moles of gas enter both the
pressure and the temperature will increase according to the ideal
gas law. Concurrently to the previously described events, the first
stage compression chamber of the first stage pneumatic cylinder (7)
will see a pressure rise and eventually the gas inside the chamber
will rise beyond that of the CNG reservoir (11) causing the CNG
check valve (5) to open. The first stage chamber volume will
continue to decrease while storing gas at increasingly higher
pressures in the CNG reservoir (11). FIG. 37 is illustrating a time
when the previously described events have occurred, but the shutoff
valve (10), has not opened.
[0104] Sometime later, the shutoff valve (10) will open and connect
the CNG reservoir (11) to the second stage chamber which is filled
with gas at a pressure equal to the supply pressure; the shutoff
valve (10) then closes sometime later before the cylinders begins
to retract. The pressure between the CNG reservoir (11) and the
second stage chamber will nearly equalize; the moles of gas present
in each chamber will be proportional to approximately the inverse
of their volume ratios. Eventually, the cylinders will reach their
fully extended position where they will dwell for a moment to allow
the chambers open to the natural gas supply (6) to equilibrate to
its pressure as is shown in FIG. 38.
[0105] Just before the system begins to retract, there are very few
moles of gas, at a high pressure, in the third stage compression
chamber and the first stage compression chamber on the first stage
pneumatic cylinder (7). The first stage compression chamber on the
second stage pneumatic cylinder (8) has gas present in it equal to
or less than that of the supply pressure. The second stage
compression chamber will have pressurized gas in it at a pressure
above that of the natural gas supply (6), but less than the CNG
storage tank (9). The compression chambers are still pressurized
from the previous cycle and they will not begin filling with gas
from the natural gas supply (6) even though it is retracting as
shown in FIG. 39.
[0106] As the system is retracting the pressure in the first stage
compression chamber on the first stage pneumatic cylinder (7) will
be decreasing as the volume increases and eventually the supply
pressure will surpass the pressure in the chamber and it will begin
filling with gas. At the same time, the volume of the first stage
compression chamber on the second stage pneumatic cylinder (8) will
begin decreasing and eventually its pressure will surpass that of
the CNG reservoir (11) and gas will begin flowing through the CNG
check valve (5) from the first stage compression chamber to the CNG
reservoir (11) and remain there as the shutoff valve (10) is
closed. Concurrently to all of this the volume of the third stage
compression chamber is increasing, hence a decrease in pressure,
and the volume of the second stage compression chamber is
decreasing, hence a rise in pressure. Eventually the second stage
cylinder compression chamber will open the CNG check valve (5)
between it and the pipe connecting to the CNG check valve (5)
directly preceding the third stage compression chamber. The rising
number of moles of gas in the intermediate line will increase the
pressure according to the ideal gas law where eventually the CNG
check valve (5) directly proceeding the third stage compression
chamber will open and connect the second stage compression chamber
to the third stage compression chamber. FIG. 40 illustrates the
previously described situation, but the invention has reached such
a position that the check valves have opened. Finally, when the
piston is fully retracted and dwelled for a short time the same
conditions will exist as described just as the system begins to
extend as shown in FIG. 41.
[0107] FIG. 14 illustrated a compressor system 119 that had a
circuit using both three stage filling and low pressure filling.
This circuit operates in the same manner as the one just described
when it is above the pressure required to actuate the CNG
directional valve (12). However, when it is below the pressure
required to actuate the CNG directional valve (12) all of the
chambers have access to the supply pressure and the CNG storage
tank (9). So therefore when the cylinder is extending the second
stage chamber will be filling with gas at the natural gas supplies'
(6) pressure while the third stage cylinder and the first stage
chamber part of the first stage pneumatic cylinder (7) will be
directing pressurized gas directly to the CNG storage tank (9) as
illustrated in FIG. 42. Although not shown, when the cylinder is
retracting, the second stage compression chamber and the first
stage compression chamber part of the second stage pneumatic
cylinder (8) will be directing pressurized gas directly to the CNG
storage tank (9) while the natural gas supply is pressurizing the
third stage compression chamber and the first stage compression
chamber attached to the first stage pneumatic cylinder (4). This
cycle will continue until the CNG storage tank (9) reaches a
certain pressure and the CNG directional control valve (12) will
shift connecting the two first stage compression chambers to the
CNG reservoir (11) and the second stage chamber, the second stage
compression chamber to the third stage compressions chamber, and
solely connecting the third stage compression chamber to the CNG
storage tank (9).
[0108] The drive section as illustrated in FIG. 17 uses a fixed
displacement pump to control cylinder speed and a directional
control valve to control the direction. The pump (1) is turned at a
constant speed by an electric motor which is not illustrated in any
of the figures. In an alternate embodiment the pump (1) can be
turned by a variable displacement electric motor. The directional
control valve (3) is electronically actuated and controlled by a
timer where it will extend plus dwell for some time and then dwell
plus retract for some time; this pattern is repeated until the CNG
storage tank (9) is full. When the system is dwelling at either the
retract or extend position all of the flow is directed over the
pump RV (2) at a high pressure; drive cylinder (4) is held in the
dwell position by this high pressure fluid.
[0109] The drive section illustrated in FIG. 5 uses a modified
hi-lo circuit where the unloading valve (17) is controlled by the
position of the drive cylinder (4). When the drive cylinder (4)
moving either extending or retracting but is not at or near the
dwell position both the unloading valve (17) will be closed and
both the high flow (13) and low flow pump (14) will be contributing
flow to move the drive cylinder (4) as illustrated in FIG. 10 when
the cylinder is extending and FIG. 13 when retracting. However,
when the drive cylinder (4) is nearing or at the dwell position, as
reported by the position sensor (21), the unloading valve
controller (18) will signal the unloading valve (17) to open so the
high flow pump (13) can direct its flow at a low pressure to tank
as illustrated in FIG. 12 when dwelling in the extend position and
FIG. 15 when dwelling in the retracted position. The low flow pump
(14) will continue to provide flow to either hold the drive
cylinder (4) at the dwell position or finish the stroke. If the low
flow pump (14) is holding the drive cylinder (4) at either of the
dwell position then its flow will go to tank through the variable
pump relief valve (16). The hydraulic check valve (15) ensures the
low flow pump's (14) flow directed to the variable pump RV (16) or
the drive cylinder (4) as opposed to traveling to tank through the
unloading valve (17). The relief setting on the variable pump RV
(16) can be adjusted by using the signal from the pressure sensor
attached to the CNG storage tank (9) to compute, via the relief
valve controller (19), the required force and therefore pressure to
hold the drive cylinder (4) at the dwell position. The present
invention provides a number of advantages over current systems used
for the same purpose by both modifying the current art while also
applying novel concepts resulting in better performance,
reliability, and other key metrics namely: (i) Increase the amount
of compressed natural gas pumped, measured in gallons of gas
equivalent (GGE) per hour, as compared to a similar sized unit
using the prior art for linear compressors; (ii) the compression
section and drive section are separated and therefore the natural
gas will not be contaminated by other medium. This is especially a
benefit when the drive section is operated by a hydraulic cylinder
so the hydraulic fluid and natural gas cannot mix; (iii) increase
reliability of a residential system by operating at a lower
frequency; (iv) decrease the amount of energy required to pump each
GGE of natural gas.
[0110] This invention--a multi stage natural gas compression unit
is composed of two distinct pieces: the drive section and the
compression section. There are a number of different embodiments
for each of the compressor and drive sections that can be can be
combined into the full system resulting in additional system
combinations. For reference, the most basic form of the invention
is composed of two pneumatic cylinders used to compress the natural
gas driven by a hydraulic cylinder connected to an electrically
driven hydraulic power unit as shown in FIG. 17. One or more of the
sides of the pneumatic cylinders are connected to the home supply
of natural gas and connections between the pneumatic cylinders are
plumbed differently and varying components to achieve varying
functionality and efficiency. By plumbing the system differently,
varying numbers of stages of compression can be obtained to
increase the flow rate and decrease the energy and power
consumption.
[0111] The construction and arrangement of cylinders in this device
is quite novel for this application as previous products have
utilized small compression chamber arranged in a circular fashion
that operate at a high frequency. This device operates in a linear
fashion, generally at a low frequency, where the drive cylinder (4)
moves the pistons of the two attached cylinders to move the gas
between chambers, progressively compressing the natural gas, and
eventually storing it in the CNG storage tank (9). As opposed to
small volume chambers on a rotary compressor the linear nature of
this present invention allows the use of large cylinders with large
volume allowing more mass of gas per stroke. More gas per stroke
means to compress the same amount of gas less strokes are required.
This reduces the component fatigue and heat generated from friction
due to the lower speeds.
[0112] The construction of the preferred embodiment is also quite
novel as tie rod cylinders are used both for the drive cylinder (4)
as well as the first and second stage pneumatic cylinders (7, 8).
Using tie rod cylinders allows for higher pressures inside the
chambers as well as connecting, securing, and using a mutual end
cap for the first stage pneumatic cylinder (7) and the second stage
pneumatic cylinder (8). Tie rod cylinder construction is used in
the design because it has a significant pressure cycle fatigue life
advantage over welded construction. The inlets and outlets for
natural gas are integrated in the end caps of the cylinder and then
channeled into the cylinder itself. In the end cap (63) of final
compression chamber (43) a single internal orifice (64), which
communicates with both the inlet port (65) and outlet port (66),
improves efficiency by minimizing the volume of high pressure gas
that does not flow to CNG Storage Tank (9) at end of stroke as
shown in FIG. 44A and FIG. 44B. The pistons in the pneumatic
cylinders use internally lubricated seals and therefore will not
discharge particulate into the natural gas. This is a benefit as
the lubrication does not need to be replenished, particulate will
not clog or damage the cylinders or orifices, but most importantly
it will ensure clean and uncontaminated gas being provided to the
CNG storage tank (9). Clean gas supply to the vehicle will increase
the service life of on board CNG filters.
[0113] Cooling the compressor system may be accomplished by any of
a variety of methods. One possible way to cool the required
components is to submerge part or the entire device in a liquid as
shown in FIG. 45 where system 111 is shown submerged in a cooling
tank 50. It is contemplated that the cooling liquid could be the
same fluid used through the pumps and to drive the hydraulic
cylinder. By submerging the device in liquid all of the device
would be convecting its heat to a liquid rather than the air and
this is beneficial due to the higher convective heat transfer
coefficient of liquids than air. Further, by submerging the entire
device there would be a large amount of volume and therefore a
large heat sink where a lot of heat can be rejected. A further
benefit of submerging the pump, electric motor, and other
components in the fluid is the fluid will dampen and lessen the
sound from these components.
[0114] Alternatively only part of the system need be submerged in
the enclosure/tank (200). For example, cooling the 1st and 2nd
stage cylinders (7), (8) is very important as the temperature of
their output gas is important and therefore could be submerged in
the liquid. However, a component such as the relief valve or the
unloading valve will generate a lot of heat and instead of adding
it to the cooling fluid it could be rejected to the
environment.
[0115] Although the principles, embodiments and operation of the
present invention have been described in detail herein, this is not
to be construed as being limited to the particular illustrative
forms disclosed. They will thus become apparent to those skilled in
the art that various modifications of the embodiments herein can be
made without departing from the spirit or scope of the
invention.
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