U.S. patent application number 13/350032 was filed with the patent office on 2012-05-03 for compression/expansion process that allows temperature to vary independent of pressure.
This patent application is currently assigned to GENERAL COMPRESSION, INC.. Invention is credited to Justin A. Aborn, Matthew Blieske, Eric D. Ingersoll.
Application Number | 20120102954 13/350032 |
Document ID | / |
Family ID | 45554844 |
Filed Date | 2012-05-03 |
United States Patent
Application |
20120102954 |
Kind Code |
A1 |
Ingersoll; Eric D. ; et
al. |
May 3, 2012 |
COMPRESSION/EXPANSION PROCESS THAT ALLOWS TEMPERATURE TO VARY
INDEPENDENT OF PRESSURE
Abstract
Systems and methods are described herein to operate an air
compression and/or expansion system in its most efficient regime,
at a desired efficiency, and/or achieve a desired pressure ratio
independent of discharge temperature, with little to no impact on
thermal efficiency. For example, systems and methods are provided
for controlling and operating hydraulic pumps/motors used within a
hydraulically actuated device/system, such as, for example, a gas
compression and/or expansion energy system, in its most efficient
regime, continuously, substantially continuously, intermittently,
or varied throughout an operating cycle or stroke of the system to
achieve any desired pressure and temperature profile. Such systems
and methods can achieve any desired pressure ratio independent of
input or discharge temperature, and can also achieve any desired
discharge temperature independent of pressure ratio, without
altering any of the structural components of the device or
system.
Inventors: |
Ingersoll; Eric D.;
(Cambridge, MA) ; Aborn; Justin A.; (Hingham,
MA) ; Blieske; Matthew; (Francestown, NH) |
Assignee: |
GENERAL COMPRESSION, INC.
Newton
MA
|
Family ID: |
45554844 |
Appl. No.: |
13/350032 |
Filed: |
January 13, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61432945 |
Jan 14, 2011 |
|
|
|
Current U.S.
Class: |
60/650 ; 417/438;
60/682 |
Current CPC
Class: |
F04B 35/008 20130101;
F15B 11/072 20130101; F04B 9/109 20130101 |
Class at
Publication: |
60/650 ; 417/438;
60/682 |
International
Class: |
F04B 39/06 20060101
F04B039/06 |
Claims
1. An apparatus, comprising: a hydraulic pump operable to deliver
hydraulic fluid over at least a hydraulic pressure range that
includes a predetermined lower pressure and a predetermined upper
pressure, greater than said lower pressure; a hydraulic actuator
arrangement including a first hydraulic piston and a second
hydraulic piston, each of said hydraulic pistons having a first
side and a second side; and a working actuator operably coupled to
said hydraulic actuator arrangement, said working actuator having a
working cylinder and a working piston disposed for reciprocating
movement in the working cylinder, the working piston defining at
least in part between a first side thereof and the working cylinder
a working chamber configured to contain a quantity of gas, said
hydraulic actuator arrangement being operably coupled to said
hydraulic pump to enable selective delivery of pressurized
hydraulic fluid from said hydraulic pump to one or both of said
first side and said second side of each of said first and second
hydraulic pistons to yield an output force in a first force range
corresponding to a first combination, and to yield an output force
in a second force range, different than said first force range,
corresponding to a second combination; a hydraulic controller
operable to cause the hydraulic actuator arrangement to move the
working piston: a) at a first average speed over a first distance,
and b) at a second average speed over a second distance different
than the first average speed, wherein the hydraulic controller is
operable to compress the quantity of gas contained therein at an
approximately constant rate as the working piston is moved over the
first distance at the first stroke speed and the second distance at
the second stroke speed.
2. The apparatus of claim 1, further comprising: a heat transfer
element disposed within the working chamber, the heat transfer
element configured to receive heat energy from the gas being
compressed to reduce the temperature of the compressed gas.
3. The apparatus of claim 2, wherein the heat transfer element is
configured to transfer heat energy received from the compressed gas
to the exterior of the working chamber.
4. The apparatus of claim 2, wherein the heat transfer element is
configured to transfer heat energy received from the compressed gas
to a volume of liquid contained in the working chamber.
5. The apparatus of claim 4, wherein the volume of liquid is not in
contact with the heat transfer element during movement of the
working piston over the first distance.
6. The apparatus of claim 5, wherein at least a portion of the
volume of liquid is in contact with at least a portion of the heat
transfer element during movement of the working piston over the
second distance.
7. The apparatus of claim 1, wherein the first stroke speed
corresponds to the first force range and the second stroke speed
corresponds to the second force range.
8. An apparatus, comprising: a hydraulic pump operable to deliver
hydraulic fluid over at least a hydraulic pressure range that
includes a predetermined lower pressure and a predetermined upper
pressure, greater than said lower pressure; a hydraulic actuator
arrangement including a first hydraulic piston and a second
hydraulic piston, each of said hydraulic pistons having a first
side and a second side; and a working actuator operably coupled to
said hydraulic actuator arrangement, said working actuator having a
working cylinder and a working piston disposed for reciprocating
movement in the working cylinder, the working piston defining at
least in part between a first side thereof and the working cylinder
a working chamber configured to contain a quantity of gas, said
hydraulic actuator arrangement being operably coupled to said
hydraulic pump to enable selective delivery of pressurized
hydraulic fluid from said hydraulic pump to one or both of said
first side and said second side of each of said first and second
hydraulic pistons to yield an output force in a first force range
corresponding to a first combination, and to yield an output force
in a second force range, different than said first force range,
corresponding to a second combination; a hydraulic controller
operable to cause the hydraulic actuator arrangement to move the
working piston: a) at a first average speed over a first distance,
and b) at a second average speed over a second distance different
than the first average speed, wherein the hydraulic controller is
operable to compress the quantity of gas contained therein such
that heat energy produced by compression of the quantity of gas is
transferred from the quantity of gas to the exterior of the working
chamber at a substantially constant rate as the working piston is
moved over the first distance at the first stroke speed and the
second distance at the second stroke speed.
9. The apparatus of claim 8, further comprising: a heat transfer
element disposed within the working chamber, the heat transfer
element configured to receive heat energy from the gas being
compressed to reduce the temperature of the compressed gas.
10. The apparatus of claim 9, wherein the heat transfer element is
configured to transfer heat energy received from the compressed gas
to the exterior of the working chamber.
11. The apparatus of claim 9, wherein the heat transfer element is
configured to transfer heat energy received from the compressed gas
to a volume of liquid contained in the working chamber.
12. The apparatus of claim 8, wherein the heat energy produced by
compression of the quantity of gas is transferred from the quantity
of gas to the exterior of the working chamber to maintain a
substantially constant temperature during compression of the
quantity of gas.
13. A method of compressing gas in a pressure vessel, the pressure
vessel having a working piston disposed therein for reciprocating
movement in the pressure vessel, the working piston defining at
least in part between a first side thereof and the pressure vessel
a working chamber configured to contain at least one of a liquid or
a gas, the method comprising: moving the working piston at a
predetermined velocity profile to compress a quantity of gas
contained therein so that the time rate of change of pressure is
approximately constant over substantially the entire stroke.
14. The method of claim 13, wherein the working chamber includes a
heat transfer element disposed therein, and wherein the
predetermined velocity profile is determined by taking into account
the portion of the cross-sectional area occupied by the heat
transfer element.
15. The method of claim 13, further comprising: moving a volume of
liquid into the working chamber during at least a portion of a
compression stroke, wherein the predetermined velocity profile is
determined by taking into account the volume of liquid being
received in the working chamber.
16. The method of claim 13, wherein the working chamber includes a
heat transfer element disposed therein, the method further
comprising: moving a volume of liquid into the working chamber
during at least a portion of a compression stroke, wherein the
predetermined velocity profile is determined by taking into account
the portion of the cross-sectional area occupied by the heat
transfer element and the volume of liquid being received in the
working chamber.
17. The method of claim 13, further comprising: causing heat energy
produced by the compression of the quantity of gas to be
transferred from the quantity of gas to the exterior of the working
chamber so that a predetermined temperature profile during
compression of the quantity of gas is maintained.
18. The method of claim 17, wherein the rate of temperature change
is approximately constant over substantially the entire stroke.
19. The method of claim 13, wherein the working chamber includes a
heat transfer element disposed therein, the method further
comprising: causing the temperature of the quantity of gas to
increase to a temperature above a temperature of the heat transfer
element, and causing heat energy produced by the compression of the
quantity of gas to be transferred from the quantity of gas to the
heat transfer element.
20. The method of claim 19, wherein the predetermined velocity
profile is determined by taking into account a rate at which heat
energy produced by compression of the quantity of gas is
transferred from the quantity of gas to the heat transfer element
so that a predetermined temperature profile of the gas is
maintained.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to and the benefit of U.S.
Provisional Patent Application Ser. No. 61/432,945, entitled
"Compression/Expansion Process That Allows Temperature to Vary
Independent of Pressure," filed Jan. 14, 2011, the disclosure of
which is hereby incorporated by reference herein in its
entirety.
BACKGROUND
[0002] The invention relates generally to devices, systems and
methods for the compression and/or expansion of a gas, such as air,
and particularly to such a device that allows the temperature of
the gas to be varied independently of its pressure during
compression and/or expansion.
[0003] Devices and systems used to compress and/or expand a gas,
such as air, and/or to pressurize and/or pump a liquid, such as
water, can generate heat during, for example, a compression
process. Adiabatic compression assumes that no energy (heat) is
transferred to or from the gas during the compression, and all
supplied work is added to the internal energy of the gas, resulting
in increases of temperature and pressure. The increase in
temperature means compression does not follow a simple pressure to
volume ratio. Although adiabatic compression is less efficient, it
is a very fast process for compressing a gas. An air compressor can
achieve near adiabatic compression and expansion when the
compressor has good insulation, a large gas volume, and/or a
relatively fast compression stroke. In practice, there will always
be a certain amount of heat flow out of the compressed gas to the
compressor itself Thus, making a perfect adiabatic compressor would
require perfect heat insulation of all parts of the machine.
[0004] In contrast to adiabatic compression, isothermal compression
assumes that the compressed gas remains at a constant temperature
throughout the compression or expansion process. During the
compression cycle, energy is removed from the system at the same
rate as heat is added by the mechanical work of compression. An air
compressor can achieve near isothermal compression when the
compressor has a large heat exchanging surface, a small gas volume,
and/or a relatively slow compression stroke. In practice, there
will always be a certain amount of heat flow into the compressed
gas, resulting in an increased temperature of the gas.
[0005] Since perfect isothermal compression is generally not
attainable with conventional compression technologies, known
compressor systems have a multi-stage compressor that may include
intercoolers that cool air between stages of compression and/or
after-coolers that cool air after compression. In such a system,
however, the air may still achieve substantial temperatures during
each stage of compression, prior to being cooled, which will
introduce inefficiencies in the system. For example, unless an
infinite number of compression stages with corresponding
intercoolers are used, perfect isothermal compression cannot be
achieved.
[0006] Since perfect adiabatic and isothermal compression are not
practical, a polytropic model is used to measure real-world
results. This model takes into account both a rise in temperature
in the gas as well as some loss of energy (heat) to the
compressor's components. This assumes that heat may enter or leave
the system, and that input shaft work can appear as both increased
pressure (usually useful work) and increased temperature above
adiabatic (usually losses due to cycle efficiency). Compression
efficiency is then the ratio of the actual temperature rise
(polytropic) vs. theoretical 100 percent (adiabatic).
[0007] For a given gas volume reduction (i.e., ratio of final
volume to initial volume), an adiabatic compression process results
in the highest final gas pressure, the highest final gas
temperature, and the highest work consumption. In contrast, for the
same volume reduction, an isothermal compression process results in
the lowest final pressure, lowest final gas temperature (i.e. the
same as the starting temperature), and lowest work consumption.
Processes that involve levels of heat flow intermediate to those in
adiabatic (zero heat flow) and isothermal (maximum heat flow),
result in intermediate values of gas pressure, gas temperature, and
work consumption. Those skilled in the art will recognize that a
perfectly isothermal air compression process is a theoretical
extreme that can only be achieved in reality by involving a
relatively cold heat sink; regardless it is a useful metric for air
compression/expansion discussion and analysis. While it is possible
to provide cooling or heating to have a discharge temperature lower
than the inlet during a compression process (or vice versa for an
expansion process), the theoretical extremes discussed here assume
no heat removal or addition using a separate cycle (such as a
Rankine or heat engine cycle) is employed to increase heat transfer
to or from the process.
[0008] Compression and/or expansion systems and related
thermodynamic processes are usually designed to have a target
temperature and pressure at the input or output of the system,
whether that process involves expansion or compression. Generally,
a design output pressure is achieved using a compressor/expander
device and the desired temperature is adjusted with an after
treatment such as, for example, a cooler or a heater. Processes
that use a series of compressor/expander devices (stages) with
intercoolers between each stage that cool the gas between stages of
compression and/or after coolers that cool the gas after the final
compression stage come closest to achieving isothermal compression.
These multi-stage systems are really no different than a single
compression/expansion device except that several are placed in
series to achieve a higher output pressure or accept a higher input
pressure (depending on the desired function of the system) at a
different discharge temperature than would have been achieved with
a single stage. The temperature achieved after the compression or
expansion process is a function solely of the pressure ratio and
isentropic/polytropic efficiency for adiabatic compression, and
cannot be optimized independently from the pressure ratio.
[0009] Other processes, such as oil flooded screw compressors, can
achieve a lower discharge temperature by cooling during the
compression process, however this result is secondary to the
primary function of the oil as a lubricant for the rotors. Such
devices cannot independently tailor the discharge temperature and
pressure, and are specified primarily based upon delivery pressure.
After treatments such as, for example, a cooler or a heater, are
still required to deliver the process fluid at the required
temperature.
[0010] Having to deal separately with temperature and pressure
requirements of a process fluid is a product of the fact that, for
a given pressure ratio, temperature is a function purely of the
isentropic efficiency of the device. No heat transfer is built into
the process as a specific function of the device (in contrast to
devices such as screw compressors described above, where the
reduced discharge temperature is a byproduct of the sealing the oil
provides). Popular design methodology suggests reducing the
discharge temperature (for compression or expansion) is a desired
goal insofar as it indicates an increase in isentropic efficiency.
The reason for this design methodology is that conventional
compression systems and processes are not capable of decoupling
temperature from pressure.
[0011] A compression/expansion process that can achieve a desired
pressure ratio independent of discharge temperature, with little to
no impact on thermal efficiency would be very valuable to modern
industry and represents a novel and unparalleled approach to
compression and expansion.
SUMMARY OF THE INVENTION
[0012] Systems and methods are described herein to operate an air
compression and/or expansion system in its most efficient regime,
at a desired efficiency, and/or achieve a desired pressure ratio
independent of discharge temperature, with little to no impact on
thermal efficiency. For example, systems and methods are provided
for controlling and operating hydraulic pumps/motors used within a
hydraulically actuated device/system, such as, for example, a gas
compression and/or expansion energy system, in its most efficient
regime, continuously, substantially continuously, intermittently,
or varied throughout an operating cycle or stroke of the system to
achieve any desired pressure and temperature profile. In such a
system, a variety of different operating regimes can be used
depending on the desired output gas pressure and the desired stored
pressure of the compressed gas. Hydraulic cylinders used to drive
working pistons within the system can be selectively actuated
and/or can be actuated to achieve varying force outputs to
incrementally increase the gas pressure, within the system for a
given cycle. Such systems and methods can achieve any desired
pressure ratio independent of input or discharge temperature, and
can also achieve any desired discharge temperature independent of
pressure ratio, without altering any of the structural components
of the device or system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic illustration of a compression and/or
expansion device according to an embodiment.
[0014] FIG. 2 shows a single stage of one embodiment of an air
compression and expansion system.
[0015] FIG. 3A is a schematic illustration of a portion of another
embodiment of an air compression and expansion system.
[0016] FIG. 3B is a schematic illustration of a portion of the air
compression and expansion system of FIG. 3A illustrating a system
controller and hydraulic pump.
[0017] FIGS. 4A and 4B are each a schematic illustration of a
portion of an actuator of the air compression and expansion system
of FIG. 3.
[0018] FIG. 4C is a side view of a portion of an actuator of the
system of FIG. 3.
[0019] FIG. 4D is a cross sectional view taken along line 4D-4D in
FIG. 4C.
[0020] FIG. 4E is an end view taken along line 4E-4E in FIG.
4C.
[0021] FIG. 4F is a cross sectional view taken along line 4F-4F in
FIG. 4C.
[0022] FIGS. 5-11 are each an example graph illustrating the
operation of a compression and/or expansion device according to an
embodiment.
[0023] FIG. 12 is a schematic illustration of a compression and/or
expansion device, according to another embodiment.
DETAILED DESCRIPTION
[0024] Systems, methods and devices used to compress and/or expand
a gas, such as air, and/or to pressurize and/or pump a liquid, such
as water, are described herein. Such devices and systems can be
used, for example, within a compressed air energy storage (CAES)
system. In some compression and/or expansion devices and systems, a
hydraulic actuator can be used to move or compress a gas within a
pressure vessel. For example, an actuator can move a liquid within
a pressure vessel such that the liquid compresses the gas in the
pressure vessel. Such compression devices and systems are described
in U.S. patent application Ser. No. 12/785,086; U.S. patent
application Ser. No. 12/785,093; and U.S. patent application Ser.
No. 12/785,100, each titled "Compressor and/or Expander Device"
(collectively referred to as "the Compressor and/or Expander Device
applications"), incorporated herein by reference in their entirety.
The Compressor and/or Expander Device applications describe a CAES
system that can include multiple stages of compression and/or
expansion. Other examples of devices and systems for expanding
and/or compressing as gas are described in U.S. Provisional patent
application Ser. No. 12/977,724, to Ingersoll et. al. ("the
Ingersoll I application"), entitled "System and Methods for
Optimizing efficiency of a Hydraulically Actuated System," the
disclosure of which is incorporated herein by reference in its
entirety.
[0025] In some compression and/or expansion devices and systems,
one or more hydraulic pumps/motors can be used to move (or be moved
by) gas and liquid within the system, and systems and methods are
described herein to operate the hydraulic pump/motor in its most
efficient regime, continuously, substantially continuously,
intermittently, or varied throughout an operating cycle or stroke
of the system to achieve any desired pressure and temperature
profile. Compression and/or expansion devices and systems can have
efficient or optimal operating ranges that can vary as a function
of, for example, mass flow rate, pressure, temperature, overall
system efficiency, among other parameters. Systems and methods are
provided that allow the hydraulic pumps/motors to be operated as a
function of any given parameter (e.g. gas inlet temperature, gas
outlet temperature, inlet pressure, outlet pressure, pressure
ratio, system efficiency, etc.) throughout the stroke or cycle of
the gas compression and/or expansion system to achieve any desired
pressure and temperature profile.
[0026] As described herein, devices and systems used to compress
and/or expand a gas, such as air, and/or to pressurize and/or pump
a liquid, such as water, can release and/or absorb heat during, for
example, a compression or expansion process, using one or more heat
transfer mechanisms. Such systems and methods as described herein,
can be used to operate a gas compression and/or expansion system in
its most efficient regime, at a desired efficiency, and/or to
achieve a desired pressure ratio independent of discharge
temperature, with little to no impact on thermal efficiency.
[0027] In some embodiments, the devices and systems described
herein can be configured for use only as a compressor. For example,
in some embodiments, a compressor device described herein can be
used as a compressor in a natural gas pipeline, a natural gas
storage compressor, or any other industrial application that
requires compression of a gas. In another example, a compressor
device described herein can be used for compressing carbon dioxide.
For example, carbon dioxide can be compressed in a process for use
in enhanced oil recovery or for use in carbon sequestration.
[0028] In some embodiments, the devices and systems described
herein can be configured for use only as an expansion device. For
example, an expansion device as described herein can be used to
generate electricity. In some embodiments, an expansion device as
described herein can be used in a natural gas transmission and
distribution system. For example, at the intersection of a high
pressure (e.g., 500 psi) transmission system and a low pressure
(e.g., 50 psi) distribution system, energy can be released where
the pressure is stepped down from the high pressure to a low
pressure. An expansion device as described herein can use the
pressure drop to generate electricity. In other embodiments, an
expansion device as described herein can be used in other gas
systems to harness the energy from high to low pressure
regulation.
[0029] In some embodiments, a compression and/or expansion device
as described herein can be used in an air separation unit. In one
example application, in an air separator, a compression and/or
expansion device can be used in a process to liquefy a gas. For
example, air can be compressed until it liquefies and the various
constituents of the air can be separated based on their differing
boiling points. In another example application, a compression
and/or expansion device can be used in an air separator co-located
with in a steel mill where oxygen separated from the other
components of air is added to a blast furnace to increase the burn
temperature.
[0030] In some embodiments, a compression and/or expansion device
as described herein can be used in a chemical reaction process. In
one example application, the compressor and/or expansion device can
be the reaction vessel in a chemical reaction process. Some
chemical reactions only take place at a certain temperature,
pressure, range of temperatures, or range of temperatures. For
example, gas and/or liquid reactants in the compression and/or
expansion device can be maintained at a certain temperature or with
in a certain temperature range by changing the pressure in the
compression and/or expansion device. The temperature of the gas
and/or liquid reactants can be changed over time by changing the
pressure in the compression and/or expansion device as the reaction
proceeds. In another example application, the rate of a reaction
can also be a function of temperature and/or pressure. Thus, the
reaction rate can be maximized, minimized, or optimized for other
factors (e.g., selectivity or efficiency) by changing the
temperature and/or pressure in the compression and/or expansion
device.
[0031] A compression and/or expansion system as described herein
can include one or multiple stages of compression and/or expansion.
For example, a system can include a single stage
compression/expansion device, two stages, three stages, etc. Each
stage of compression/expansion can have a variety of different
configurations and can include one or more actuators that are used
to compress/expand a gas (e.g. air) within a compression/expansion
device. In some embodiments, an actuator can include one or more
pump/motor systems, such as for example, one or more hydraulic
pumps/motors and/or one or more pneumatic pumps/motors that can be
use to move, or be moved by, one or more fluids within the system
between various water pumps/motors and pressure vessels. As used
herein, "fluid" can mean a liquid, gas, vapor, suspension, aerosol,
or any combination thereof. The Compressor and/or Expander Device
applications incorporated by reference above describe various
compression and expansion systems in which the systems and methods
described herein can be employed.
[0032] As described herein, in some embodiments of a gas
compression and/or expansion system, hydraulic pumps/motors can be
used to drive (or be driven by) one or more hydraulic actuators,
which in turn can drive (or be driven by) a working piston. The
working piston can act on (or be acted on by) a gas contained in a
working chamber to compress or expand the gas, directly, or
indirectly through a liquid disposed between the working piston and
the gas in the working chamber. As used herein the term "piston" is
not limited to pistons of circular cross-section, but can include
pistons with a cross-section of a triangular, rectangular, or other
multi-sided shape.
[0033] In some embodiments, a hydraulic actuator as described
herein can be used to drive, or be driven by, a working piston
within, for example, a water pump/motor, to move water (or other
liquid) in and out of the working chamber of a pressure vessel used
to compress and/or expand a gas, such as air, contained in the
working chamber. Although particular embodiments of an actuator are
described herein to drive, or be driven by, a water pump/motor
and/or a compression and/or expansion device, it should be
understood that the various embodiments and configurations of an
actuator can be used to drive, or be driven by, a working piston
within a water pump, a compression and expansion device, a
compression device, an expansion device, any other device in which
a working piston is used to move a fluid, and/or any device to
which motive force can be applied or from which motive force can be
received.
[0034] The loads applied to the working piston(s) can be varied
during a given cycle of the system. For example, selectively
establishing fluid communication between the hydraulic
pump/motor(s) and different hydraulic pistons, and/or different
surfaces of the hydraulic piston(s), in the hydraulic actuator(s),
the ratio of the net working surface area of the hydraulic
actuator(s) to the working surface area of the working piston
acting on the gas in the working chamber can be varied. Thus, the
ratio of the pressure of the hydraulic fluid provided by (or
received by) the hydraulic pump/motor to the pressure of the gas in
the working chamber can be varied during a given cycle or stroke of
the system. A state in which a hydraulic actuator has a particular
piston area ratio (e.g., the ratio of the net working surface area
of the hydraulic actuator to the working surface area of the
working piston acting on, or being acted on by, the gas in a
working chamber) at a given time period can be referred to herein
as a "gear," and a change in from one state to another state can be
referred to herein as a "gear change." In addition, the number of
working pistons/working chambers and hydraulic actuators can be
varied as well as the number of piston area ratio changes within a
given cycle.
[0035] As described herein, heat energy can be removed from a gas
during a compression process (or can be added to a gas during an
expansion process) via a liquid that is present in one or more
pressure vessels of a compressor/expander device to control the gas
temperature throughout the process. The heat energy can be
transferred between the gas and the liquid, the compressor/expander
device, and/or a heat transfer element disposed within the working
chamber. This allows an operator to modify the amount of energy
that is added or removed throughout the process (depending on
whether the process is compressing or expanding), thereby achieving
a desired pressure ratio independent of temperature. This can be
done in a manner that has very little impact on thermal efficiency,
in order to make the temperature control capability of the process
transparent to the performance and cost of the device.
[0036] In some embodiments, a heat transfer element can be
positioned within the interior of a working chamber of a
compressor/expander device that can provide sufficient gas/liquid
interface and/or sufficient thermal capacity to efficiently
intermediate in, and enhance, the transfer of heat between the gas
and the liquid. The heat transfer element can provide for an
increased heat transfer area both with gas that is being compressed
and with gas that is being expanded (either through an gas/liquid
interface area or gas/heat transfer element interface), while
allowing the exterior structure and overall shape and size of a
working chamber/pressure vessel to be optimized for other
considerations, such as pressure limits and/or shipping size
limitations. The heat transfer element can be a variety of
different configurations, shapes, sizes, structures, etc. to
provide a relatively high surface area per unit volume or mass with
the gas as it is being compressed/expanded and/or at an end of the
stroke of a compression/expansion cycle. The heat transfer element
can be formed from one or more of a variety of different materials
that provide a relatively high volumetric specific heat as compared
to the gas. The combined effects of density, volume and specific
heat, and how these parameters behave per unit volume, can
contribute to the absorption performance of a particular heat
transfer element. For example, both water and various metals
provide a relatively high volumetric specific heat as compared to
air, particularly at atmospheric air density. Thus, when the metal
or water absorbs the heat from the air as it is begin compressed,
the air and/or water temperature increases only moderately. Such
heat transfer elements are described in U.S. patent application
Ser. No. 12/977,679; titled "Methods and Devices for Optimizing
Heat Transfer within a Compression and/or Expansion Device," ("the
Ingersoll II application"), the disclosure of which is incorporated
herein by reference in its entirety.
[0037] The use of a liquid (such as water) as a medium through
which heat passes during compression and/or expansion may allow for
a continuous cooling process during compression and may provide a
mechanism by which heat may be moved in and/or out of the
compression vessel. It can provide the reverse during expansion. A
liquid can have a relatively high thermal capacity as compared to a
gas (such as air) such that a transfer of an amount of heat energy
from the gas to the liquid produces a significant decrease in the
temperature of the gas but only a modest increase in the
temperature of the liquid. This allows buffering of the system from
substantial temperature changes.
[0038] Heat that is transferred between the gas and liquid or
components of the compressor/expander device itself may be moved
from or to the working chamber through one or more heat exchangers
that are in contact with the liquid or components of the
compressor/expander device. That is, during compression the liquid
may receive heat from gas that is being compressed, and pass this
heat to the external environment continuously, both while gas is
being compressed and while gas is being received by the working
chamber for later compression. Similarly, heat addition may occur
when a compressor/expander device is operating in an expansion mode
both during expansion and as expanded gas is passed from a pressure
vessel. Thus, the liquid within a working chamber can be used to
transfer heat from gas that is compressed (or to gas that is
expanded) and can also act in combination with a heat exchanger to
transfer heat to an external environment (or from an external
environment).
[0039] As described herein, a gas compression and/or expansion
system can have a heat removal process that can be varied
independent of process conditions. For example, different pressure
ratios (i.e., ratio of initial pressure to final pressure in a
compression cycle) will result in different heat energy fluxes
within the device. Therefore, the device can include a heat
transfer system or methods that allow heat to be transferred out of
the process fluid regardless of the heat energy flux and fluid
pressure. One type of heat exchanger that can be used to accomplish
this is a heat pipe as described in the Compressor and/or Expander
Device applications and the Ingersoll I application incorporated by
reference above.
[0040] In some embodiments, as a liquid (such as water) is moved
into a working chamber to compress a gas (such as air), if there is
relatively little vertical mixing of the liquid, a temperature
gradient can be established in the liquid, with the highest (during
compression, or lowest, during expansion, of the gas) temperature
at the gas/liquid interface. Thus, the layer of liquid at the top
of the liquid column (closest to the gas/liquid interface) will
contain a higher proportion of the heat energy received from the
gas during compression (or has given up a higher proportion of the
heat energy to the gas during expansion) than the remainder of the
liquid. A portion of this top layer of liquid can be removed from
the working chamber after the compression or expansion cycle has
been completed, and transferred to another stage of the system
and/or out of the system entirely.
[0041] In some embodiments, a gas compression/expansion system can
have variable displacement capability. As a liquid (such as water)
is moved into a pressure vessel, a gas (such as air) is compressed
at a rate proportional to the displacement of the liquid. The flow
of liquid into the pressure vessel can be stopped at any time
during the compression stroke once a predetermined pressure is
achieved. In this manner, the pressure ratio can be modified
quickly and easily, while the discharge temperature can be
maintained at a desired value by changing the heat transfer
characteristics within the system. During subsequent compression
cycles, the flow of liquid into the pressure vessel can be stopped
at the same time to achieve the same displacement or can be changed
to increase or decrease the displacement depending on any of a
number of variables such as, for example, pressure vessel
parameters including pressure, temperature and thermal efficiency,
system parameters including pressures upstream or downstream of the
pressure vessel (i.e., earlier or later compression stages of the
system), overall system efficiency and electricity generation, and
power grid parameters including electricity price, electricity
supply/demand and grid stability. Thus, in addition to the
compression and expansion system being capably of varying
temperature independent of pressure, the reverse is also true and
the system is capable of varying pressure independent of
temperature. When such systems are paired in series to achieve
higher pressures (called a staged process), the pressure ratio
within each system can be changed by varying the stroke and amount
of water displaced to not only change the discharge pressure, but
also change the distribution of work and heat transfer in each. In
this manner, not only is the pressure and temperature of the whole
process independently variable, but the pressure and temperature
within each stage can be varied as well.
[0042] FIG. 1 schematically illustrates a portion of a compression
and/or expansion device (also referred to herein as
"compression/expansion device") according to an embodiment. A
compression/expansion device 100 can include one or more pressure
vessels 120 (also referred to herein as "cylinder") having a
working chamber 140, an actuator 122 by which the volume of working
chamber 140, and/or the portion of the volume of the working
chamber 140 that can be occupied by gas, can be changed (decreased
to compress the gas, increased to expand the gas), and one or more
heat transfer elements 124 disposed within the working chamber 140.
The compression/expansion device 100 can be used, for example, to
compress or expand a gas, such as air, within the working chamber
140. The device provides the flexibility of being able to vary
temperature independent of pressure and pressure independent of
temperature without introducing significant penalties to efficiency
and performance. The device 100 integrates thermal management with
pressure ratio management such that separate devices are not
required to vary either parameter.
[0043] The pressure vessel 120 can include one or more gas
inlet/outlet conduits 130 in fluid communication with the working
chamber 140. Optionally, the pressure vessel 120 can include one or
more liquid inlet/outlet conduits 128 in fluid communication with
the working chamber 140. The working chamber 140 can contain at
various time periods during a compression and/or expansion cycle, a
quantity of gas (e.g., air) that can be communicated to and from
working chamber 140 via the inlet/outlet conduits 130, and
optionally can also contain a quantity of liquid (e.g., water) that
can be communicated to and from working chamber 140 via the
inlet/outlet conduits 128. The compression/expansion device 100 can
also include multiple valves (not shown in FIG. 1) coupled to the
inlet/outlet conduits 128, 130 and/or to the pressure vessel 120.
The valves can be configured to operatively open and close the
fluid communication to and from the working chamber 140. Examples
of use of such valves are described in more detail in the
Compressor and/or Expander Device applications incorporated by
reference above.
[0044] The actuator 122 can be any suitable mechanism for
selectively changing the volume of the working chamber 140 and/or
the portion of the volume of the working chamber that can be
occupied by gas. For example, the working chamber 140 can be
defined by a cylinder and the face of a piston (not shown in FIG.
1) disposed for reciprocal movement within the cylinder. Movement
of the piston in one direction would reduce the volume of the
working chamber 140, thus compressing gas contained in the working
chamber 140, while movement of the piston in the other direction
would increase the volume of the working chamber 140, thus
expanding gas contained in the working chamber 140. The actuator
can thus be the piston and a suitable device for moving the piston
within the cylinder, such as a pneumatic or hydraulic actuator such
as, for example, the hydraulic actuators described in the Ingersoll
I application incorporated by reference above.
[0045] In some embodiments, the working chamber can have a fixed
volume, i.e. a volume defined by a chamber with fixed boundaries,
and the portion of the volume of the working chamber 140 that can
be occupied by gas can be changed by introducing a liquid into, or
removing a liquid from, the working chamber 140. Thus, the working
chamber 140 has a volume with a first portion containing a volume
of liquid, and a second portion that can contain gas, which volume
is the total volume of the working chamber 140 less the volume of
the first portion (the volume of the liquid). In such embodiments,
the actuator 122 can be any suitable device for introducing liquid
into, or removing liquid from, the working chamber, such as a
hydraulic actuator that can move a liquid in and out of the working
chamber 140 via liquid inlet/outlet conduit 128. In such an
embodiment, the actuator 122 can include a water pump (not shown)
that drives a hydraulically driven piston (not shown) disposed
within a housing (not shown) and can be driven with one or more
hydraulic pumps (not shown) to move a volume of liquid in and out
of the working chamber 140. An example of such a hydraulic actuator
is described in the Compressor and/or Expander Device applications
incorporated by reference above.
[0046] In some embodiments, the working chamber can be configured
to combine the techniques described above, i.e. the working chamber
can have a variable volume, e.g. using a cylinder and piston as
described above, and the portion of the variable volume that can be
occupied by gas can be changed by introducing liquid into, or
removing a liquid from, the working chamber. In another embodiment,
a constant volume of liquid can be maintained in the variable
volume working chamber throughout all, or a portion, of the
compression cycle. As described above, in some embodiments, the
working chamber 140 can contain a liquid, and/or the actuator 122
can be used to change the portion of the working chamber 140 that
is available to contain gas, by moving a liquid (such as water)
into and out of the working chamber, such that gas (such as air)
within the working chamber 140 is compressed by the liquid. In such
embodiments, depending on the rate at which the working chamber 140
is filled with liquid, and the heat transfer properties of the heat
transfer element 124, the gas and the heat transfer element 124
will be relatively closer or farther from thermal equilibrium, and
thus, during some or all of the compression cycle, the liquid in
the working chamber 140 can be caused to contact the heat transfer
element 124 to receive from the heat transfer element 124 heat
energy it received from the compressed gas. Optionally, the volume
may be decreased by a mechanical piston directly such as in a
reciprocating compressor with a reduced volume of water disposed
within the chamber for the purpose of effecting heat transfer.
Optionally, at the end of the compression cycle, any pressurized
gas remaining in the working chamber 140 can be released from the
working chamber 140, and transferred to the next step or stage in
the compression process or to a storage facility. Liquid can then
be moved into the working chamber 140, to substantially fill the
volume occupied by gas that was released from the working chamber
140 after compression (which volume is now filled with gas at a
lower pressure) by introducing more liquid and/or by reducing the
volume of the working chamber (e.g. by moving a piston). The heat
energy stored in the heat transfer element 124 can then be
transferred (again, by conductive and/or convective transfer) to
the water in the working chamber 140.
[0047] In some embodiments, the working chamber 140 can be
partially filled with a liquid (e.g. water) that can be
communicated to and from the working chamber 140 via the inlet
conduit 128 and the outlet conduit 130, respectively, or via other
conduits (not shown). During the compression cycle, heat energy
generated during the compression process can be transferred from
the gas, to the heat transfer element 124, and then to the liquid.
A volume of the heated liquid can then be discharged from the
pressure vessel 120 via the outlet conduit 130 or via a separate
liquid discharge conduit (not shown). As described above with
respect to the heat transfer element 124, the volume of liquid that
occupies a portion of working chamber 140 reduces the remaining
volume of the working chamber 140 available for a mass of gas to be
compressed. In other words, although the liquid in the working
chamber 140 provides a mechanism by which the heat energy generated
by the compression of the gas can be removed from the pressure
vessel 120 (i.e. by first quenching the heat transfer element 124
to transfer the heat energy to the liquid, and then discharging the
heated liquid out of the pressure vessel 120), both the liquid and
the heat transfer element occupy a portion of the working chamber
140, thereby reducing the mass of gas that can be compressed. In
some embodiments, the heat transfer element and the volume of
liquid in the working chamber 140 can be designed to remove a
sufficient amount of heat energy generated during the compression
process, while maximizing the amount of gas in the working chamber
140 to be compressed. For example, having multiple heat transfer
elements 124 that are movable with respect to each other such that
the density of the heat transfer element 124 disposed in the
portion of the working chamber containing gas can be varied
throughout a compression cycle can reduce the volume of liquid for
quenching the heat transfer element 124.
[0048] Heat energy transferred from the gas to the heat transfer
element 124 can in turn be transferred out of the pressure vessel
120 by any suitable means, include a heat pipe, circulating fluid,
etc., to a location where it can be dissipated, used in other
processes, and/or stored for future use in the
compression/expansion device (e.g. in an expansion cycle). In
addition, or alternatively, heat energy transferred from the gas to
the heat transfer element 124 can be transferred from the heat
transfer element 124 to fluid contained in the working chamber 140.
The heat energy can then be transferred from the fluid out of the
pressure vessel. Similar techniques can be used to transfer heat
energy from outside the pressure vessel to the heat transfer
element 124 and thence to the gas in the working chamber, e.g.
during an expansion cycle.
[0049] The heat transfer element 124 can be a variety of different
configurations, shapes, sizes, structures, etc. to provide a
relatively high surface area per unit volume or mass that can be in
contact with the gas (e.g., air) as it is being compressed or
expanded within the working chamber 140. In some embodiments, it
may be desirable to include a heat transfer element 124 that can be
formed with a material that can provide high thermal conductivity
in a transverse and a longitudinal direction within the working
chamber 140. The heat transfer element 124 can be formed from one
or more of a variety of different materials. For example, the heat
transfer element 124 can be formed with metals (e.g. stainless
steel), metal wires, hybrid wires, carbon fiber, nano-materials,
and composite materials (e.g. carbon polymer compounds) which have
anti-corrosion properties, are lighter weight, and are less
expensive than some metallic materials.
[0050] The heat transfer element 124 can be disposed at various
locations within the working chamber 140 so as to optimize the heat
transfer within the pressure vessel 120. For example, in some
embodiments, the heat transfer element 124 can be disposed within
the working chamber 140 near an end portion of the working chamber
140 in a portion occupied by the gas (e.g., air) near the end of a
compression cycle. As the gas is compressed during the compression
cycle, the work done on the gas adds heat energy to the gas. The
heat energy is continuously transferred (primarily by conductive
and/or convective, rather than radiant, heat transfer) to the heat
transfer element 124. This transfer maintains the gas temperature
at a lower value than would be the case without the heat transfer
element 124, and moderately increases the temperature of the heat
transfer element 124. Other examples of heat transfer elements and
systems that can be used to optimize heat transfer are described in
the Ingersoll II application incorporated by reference above.
[0051] FIG. 2 illustrates a portion of a compressed gas storage
system 200 that includes a compressor/expander device 220 and an
actuator 212. The compressor/expander device 220 illustrates a
single stage of a compressed gas storage system. The
compressor/expander device 220 includes a first pressure vessel 224
and a second pressure vessel 226. The first and second pressure
vessels 224, 226 are each coupled fluidly to the actuator 212 by a
conduit or housing 228 and 230, respectively. The actuator 212 can
include a water pump that includes a hydraulically driven piston
232. The piston 232 is disposed within a housing or reservoir 240
and can be driven with one or more hydraulic pumps (not shown in
FIG. 2) to move toward and away from the conduit 228 of first
pressure vessel 224 to alternately reduce and then increase the
portion of the internal volume of the first pressure vessel 224
available to contain gas (with an equivalent, but opposite increase
and reduction of the portion of the volume of the second pressure
vessel 226 available to contain gas). Each of the first and second
pressure vessels 224, 226 are at least partially filled with a
liquid, such as water, that is moved by the actuator 212 to
alternately compress and drive gas from the volume of each of the
first and second pressure vessels 224, 226, when operated in a
compression mode, or to be moved by compressed gas received in
either of the first and second pressure vessels 224, 226 when
operated in an expansion mode.
[0052] Each pressure vessel 224, 226 can be considered to define a
working chamber for compressing and/or expanding a gas. The working
chamber has a volume that is defined by the volume of the pressure
vessel. The working chamber has a portion of this volume that can
contain gas and a portion that contains liquid--the portion of the
volume that contains gas is equal to the total volume of the
working chamber less the volume of the portion containing liquid.
Operation of the water pump to urge liquid from the pump cylinder
into the pressure vessel reduces the volume of the portion of the
working chamber that can contain gas, thus compressing the gas
contained in that portion (e.g. during a compression cycle).
Similarly, operation of the water pump to allow liquid to be
transferred from the pressure vessel to the water pump increases
the volume of the portion of the working chamber that can contain
gas, allowing the gas to expand. Alternatively, a working chamber
can be considered to be defined by the pressure vessel and the
portion of the water pump in fluidic communication with the
pressure vessel (i.e. on one side of the working piston), and any
conduit or other volume connecting the pressure vessel and the
water pump. So defined, the working chamber has a variable volume,
which volume can be changed by movement of the working piston. A
portion of the variable volume can be occupied by liquid (e.g.
water), while the remaining portion can be occupied by gas (e.g.
air). The pressure of the gas contained in the working chamber is
essentially equal to the pressure of any liquid contained in the
working chamber, and to the pressure acting on the corresponding
side or face of the working piston.
[0053] The compressor/expander device 220 may also include fins,
dividers and/or trays 234 that can be positioned within the
interior of the first and second pressure vessels 224, 226. The
dividers 234 can increase the overall area within a pressure vessel
that is in direct or indirect contact with gas, which can improve
heat transfer. The dividers 234 can provide for an increased heat
transfer area with both gas that is being compressed and gas that
is being expanded (either through an gas/liquid interface area or
gas/divider interface), while allowing the exterior structure and
overall shape and size of a pressure vessel to be optimized for
other considerations, such as pressure limits and/or shipping size
limitations.
[0054] In this embodiment, the dividers 234 are arranged in a stack
configuration within the first and second pressure vessels 224 and
226. Each divider 234 can be configured to retain a pocket of gas.
In one illustrative embodiment, each of the dividers 234 can
include an upper wall, a downwardly extending side wall that may
conform in shape and substantially in size to the inner wall of the
pressure vessel, and an open bottom. The open bottom of each of the
dividers 234 face in a common, substantially downward direction
when the pressure vessel is oriented for operation. It is to be
appreciated that although the figures show dividers that conform in
size and shape to the interior of the pressure vessels 224, 226,
and are generally shaped similarly to one another, other
configurations are also possible and contemplated, including
embodiments that include dividers that are substantially smaller in
width than the interior of a pressure vessel and/or that are shaped
and sized differently than one another, among other configurations.
Various other shapes and configurations of dividers can be used,
such as, for example, the dividers that are shown and described in
U.S. Provisional App. No. 61/216,942 and the Compressor and/or
Expander Device applications incorporated by reference above.
[0055] As shown in FIG. 2, a manifold 236 can extend centrally
through the stack of dividers 234 and fluidly couple each of the
dividers 234 to an inlet/outlet port 238 of the pressure vessels
224, 226. In other embodiments, the manifold may include multiple
tubes and/or may be located peripherally about the stack of
dividers or in other positions. Gas may enter and/or exit the
pressure vessels 224, 226 through the ports 238, and can provide a
conduit for fluid communication between pockets of gas associated
with each divider 234. In other embodiments, such as those in which
dividers do not retain a pocket of gas, the manifold may not be
included.
[0056] As discussed above, heat can be transferred from and/or to
gas that is compressed and/or expanded by liquid (e.g., water)
within a pressure vessel. A gas/liquid or gas/divider interface
(e.g., provided in part by dividers discussed above) may move
and/or change shape during a compression and/or expansion process
in a pressure vessel. This movement and/or shape change may provide
a compressor/expander device with a heat transfer surface that can
accommodate the changing shape of the internal areas of a pressure
vessel through which heat is transferred during compression and/or
expansion. In some embodiments, the liquid may allow the volume of
gas remaining in a pressure vessel after compression to be nearly
eliminated or completely eliminated (i.e., zero clearance
volume).
[0057] A liquid (such as water) can have a relatively high thermal
capacity as compared to a gas (such as air) such that a transfer of
heat energy from the gas to the liquid significantly decreases the
temperature rise of the gas but incurs only a modest increase in
the temperature of the liquid. This allows buffering of the system
from substantial temperature changes. Heat that is transferred
between the gas and liquid or components of the vessel itself may
be moved from or to the pressure vessel through one or more heat
exchangers that are in contact with the liquid or components of the
vessel. One type of heat exchanger that can be used to accomplish
this is a heat pipe, as discussed in greater detail below.
[0058] Thus, the liquid within a pressure vessel can be used to
transfer heat from air that is compressed (or to air that is
expanded) and can also act in combination with a heat exchanger to
transfer heat to an external environment (or from an external
environment). By way of example, as shown in FIG. 2, a heat
exchanger that includes a circular array of heat pipes 242 that
extend through a wall of the pressure vessels 224 and 226 and can
contact both the liquid within the vessels and the external
environment. The heat pipes 242 are just one example embodiment of
a type of heat exchanger that can be used to transfer heat to or
from liquid of a pressure vessel. It should be understood that
other types of heat exchangers and other heat pipe configurations
can alternatively be used. For example, other heat management
devices can be used (alternatively or in addition to) such as, for
example, fins, pins, convection-inducing shapes, and/or
swirl-inducing shapes, etc.
[0059] The embodiment of FIG. 2 is one example of an arrangement of
pressure vessels and an actuator that can be used within a gas
compression and storage system. It should be understood, that other
arrangements are also possible and contemplated. By way of example,
although the actuator is shown as including a single, double acting
piston that is oriented vertically, other embodiments may include
housings with actuators that include horizontally oriented pistons
and/or multiple hydraulic pistons that operate in parallel to move
fluid within working chambers. According to some embodiments,
actuators may lack pistons altogether and instead comprise pumps
that move fluid into and out of the pressure vessels. Multiple
pumps and/or pistons can additionally, or alternatively, be used in
parallel to move fluid into and out of the pressure vessels,
according to some embodiments. Still, according to other
embodiments, an actuator, such as a hydraulic piston, may have a
direct mechanical connection to the motor/generator of the system,
as embodiments of the system are not limited to that shown in the
figures. Another embodiment can combine the water pump 212 with the
pressure vessel 220 such that the mechanical piston moves within
the pressure vessel.
[0060] FIGS. 3A-3B illustrate schematically an example of a
two-stage gas energy compression and expansion system 300. FIG. 3A
is a schematic illustration of a portion of the system 300. Stage
one includes a pair of pressure vessels 324, 326 connected in fluid
communication to an actuator 312. For example, various types of
conduit or housing (as shown in FIG. 3A) can be used to fluidically
couple various components of the actuator 312 to the pressure
vessels. The pressure vessels 324, 326 can each include dividers or
tray (not shown in FIG. 3A) as described above for previous
embodiments. The actuator 312 includes liquid pumps driven by
hydraulic actuators or cylinders as described below. As shown in
FIG. 3A, the actuator 312 includes liquid pumps 344A, 344B and 346.
In this embodiment, liquid pumps 344A and 344B are constructed in
two portions to reduce the height of the pumping equipment, and in
this embodiment liquid pumps 344A and 344B act in concert as a
single pump. Each of the liquid pumps 344A, 344B and 346 include a
liquid piston, or working piston, that is hydraulically driven with
a pair of hydraulic cylinders. Liquid pump 344A is coupled to and
driven by hydraulic cylinders 352 and 354; liquid pump 344B is
coupled to and driven by hydraulic cylinders 356 and 358; and
liquid pump 346 is coupled to and driven by hydraulic cylinders 348
and 350. A common drive rod couples the liquid pistons to their
respective hydraulic cylinders. The hydraulic cylinders for stage
one can all be controlled by a first high efficiency hydraulic pump
314 as shown in FIG. 3B. A hydraulic pump/motor, such as, for
example, an Artemis Digital Displacement hydraulic pump
manufactured by Artemis Intelligent Power Ltd. can be used. Other
examples of hydraulic pumps that can be used are described in U.S.
Pat. No. 7,001,158, entitled "Digital Fluid Pump," and in U.S. Pat.
No. 5,259,738, entitled "Fluid-Working Machine," the entire
disclosures of which are hereby incorporated by reference.
[0061] As shown in FIG. 3B, a system controller or hydraulic
controller 316 can be used to operate and control the hydraulic
pump/motor 314. The hydraulic pump/motor 314 can be connected to
each end of the hydraulic cylinders associated with the various
liquid pumps (or working actuators) of the system. A valve is
coupled between each end (i.e. each hydraulic chamber) of the
hydraulic cylinders and the hydraulic pump, which can be
selectively opened and closed, e.g. under control of the hydraulic
controller 316, to fluidically couple or fluidically isolate,
respectively, the output of the hydraulic pump 314 and each
hydraulic chamber of each hydraulic cylinder to selectively actuate
a specific hydraulic cylinder and, more particularly, a particular
side (e.g., blind side and/or rod side, as described in more detail
below) of the hydraulic piston in the specific hydraulic cylinder.
Each valve is designated by 318 in FIG. 3B.
[0062] As shown in FIG. 3A, stage two of the system 300 includes a
pair of pressure vessels 362 and 364 connected in fluid
communication to an actuator 313 that includes liquid pumps 366 and
368. As with the stage one configuration, each of the pressure
vessels 362 and 364 can include dividers and each of the liquid
pumps 366 and 368 include a liquid piston that is hydraulically
driven by (or, in expansion mode, drives) a pair of hydraulic
cylinders, also shown in FIG. 3A. Liquid pump 366 is coupled to and
driven by hydraulic cylinders 370 and 372 and liquid pump 368 is
coupled to and driven by hydraulic cylinders 374 and 376. The
hydraulic cylinders for stage two can all be driven by, or drive a
second high efficiency hydraulic pump/motor (not shown) in a
similar fashion as stage one, using the same hydraulic controller
316, or a second hydraulic controller (not shown). It is to be
appreciated that the stage two hydraulic cylinders can be driven
by, or drive various configurations of hydraulic pump/motor, and
that the system 300 can have, for example, one, two, three, four,
or more hydraulic pump/motors.
[0063] Each of the first and second pressure vessels 324 and 326 of
the first stage are fluidly coupled to the pressure vessels 362 and
364 of the second stage by a conduit that may include one or more
valves (not shown in FIG. 3A) to selectively open and close fluid
communication between the volumes of the corresponding pressure
vessels. The first and second pressure vessels 324 and 326 of stage
one can also each include a valve (not shown) that opens to allow
the receipt of air from the environment (e.g., at atmospheric
pressure) or air that has been optionally pre-compressed from
atmospheric pressure to a desired pressure, for example, 1-3 bar.
Additional valves can be used between the pressure vessels of stage
two and a storage structure or cavern (not shown) in which the
compressed air from the system may be stored. Valves can be coupled
to and disposed at locations along the conduit connecting the
various components or directly to the components.
[0064] FIGS. 4A-4F illustrate an example of a portion of an
actuator of a gas compression and expansion system 300. FIG. 4A
schematically illustrates the various components of a portion of
actuator 312 including the liquid pump 346, and its corresponding
hydraulic cylinders 348 and 350; and FIG. 4B schematically
illustrates the various components of the hydraulic cylinder 348.
It should be understood, however, that each of the liquid pumps and
hydraulic cylinders in both the first stage and the second stage of
the system 300 can be similarly constructed and function in the
same manner as liquid pump 346 and hydraulic cylinder 348. As shown
in FIG. 4A, the liquid pump 346 includes a cylindrical liquid
reservoir or housing 382 that can contain liquid, such as, for
example, water W (though other working liquids could be used), a
liquid piston, or working piston, 374 and a drive rod 376 coupled
to the piston 374. The drive rod 376 is also coupled to hydraulic
drive pistons 378 and 380 of the hydraulic cylinders 348 and 350,
respectively. Thus, the hydraulic cylinders 348 and 350 can be used
to operate or drive the piston 374 back and forth within the
housing 382, pressurizing and moving the liquid W contained
therein. The liquid housing 382 is divided into two portions, one
on each side of piston 374. Each portion is in fluid communication
with a pressure vessel, such as the pressure vessels described
above (not shown in FIG. 4A). As described above, each side of
working piston 374 bears the same pressure as that of the gas
contained in the pressure vessel with which that side of working
piston 374 bounds a working chamber containing the air.
[0065] FIG. 4B schematically illustrates the hydraulic cylinder
348. As shown in FIG. 4B, the hydraulic cylinder 348 includes a
cylindrical housing 384 in which a hydraulic drive piston 378 is
movably disposed. As stated above, the drive piston 378 is coupled
to the drive rod 376. Within the housing 384 of the hydraulic
cylinder 348, hydraulic fluid Hf can be pumped in and out, as will
be described in more detail below.
[0066] The housing 384 of the hydraulic cylinder 348 defines an
interior volume that is divided into two portions at any given time
during a stroke of the hydraulic cylinder by the drive piston or
hydraulic piston 378. As shown in FIG. 4B, the portion of the
interior volume within the housing 384 above the drive piston 378
(or on the opposite side of the piston 378 from the rod 376) is
referred to herein as the "blind side" or "bore side" Bs, and the
portion of the interior volume within the housing 384 shown below
the drive piston 378 (or on the same side as the rod 376) is
referred to herein as the rod side Rs. To drive the hydraulic
cylinders, hydraulic fluid Hf can be pumped into each hydraulic
cylinder on either (or both) sides of the drive piston to achieve
varying pressures and flow rates within the system. For example, at
various steps in the process of compressing air for energy storage,
the pressurized hydraulic fluid Hf can be pumped into the housing
384 only on the blind side Bs, only on the rod side Rs, or on both
sides, depending on the desired output pressure, flow rate and/or
direction of force desired at the various steps of a compression or
expansion cycle.
[0067] For example, referring to the liquid pump 346 and its
associated hydraulic cylinders 348 and 350, to move the working
piston 374 within the housing 382 to change the volume of the
working chamber bounded in part by the working piston, one or both
of the hydraulic cylinders 348 and 350 can be actuated at a given
time period to provide the desired force to move the piston. For
example, to move the piston 374 upward, hydraulic fluid can be
pumped into the blind side, or both the blind side and the rod side
of the hydraulic cylinder 350, or hydraulic fluid can be pumped
into the rod side of the hydraulic cylinder 348, or a combination
thereof To move the piston 374 downward, hydraulic fluid can be
pumped into the blind side of hydraulic cylinder 348, both the
blind side and the rod side of the hydraulic cylinder 348, or the
rod side of the hydraulic cylinder 350, or a combination thereof
Each of these modes has a different total area of hydraulic piston
bearing the pressure of the hydraulic fluid, and thus will exert a
different force on the working piston 374. It is to be appreciated
that varying the pressure of the hydraulic fluid can act in concert
with the varying combinations of reservoir pressurization to
provide a wide range of force to move the piston.
[0068] The system 300 can be configured to operate within a desired
energy efficiency range of the hydraulic pump(s). The operating
pressure range of the hydraulic pump(s) and the ratio of surface
areas of the liquid pistons to the hydraulic drive pistons (also
referred to herein as "piston ratio") can be used to determine an
optimal operating sequence for the compression process. In
addition, by varying which hydraulic pump(s) is actuated to move a
liquid piston at a particular point in the cycle, the pressure in
the system can be further varied. The pump has a preferred range of
pressure and flow, within which it can be continuously operated as
the air piston strokes.
[0069] As shown, for example, in FIGS. 4C-4F, the liquid piston 374
has an operating surface 390 that has a surface area SA.sub.w that
is the same on both sides of the liquid piston (i.e. the annular
area bounded by the outer perimeter of the liquid piston 374 and
the outer perimeter of the rod 376), and the hydraulic drive piston
378 has an operating surface 392 on the blind side with surface
area SA.sub.b (i.e. the circular surface area bounded only by the
outer perimeter of the hydraulic drive piston) and an operating
surface 394 on the rod side with a surface area SA.sub.r (i.e. the
annular area bounded by the outer perimeter of the hydraulic drive
piston and the outer perimeter of the rod). The operating surface
area of a piston is the surface area of the piston on which force
is exerted by hydraulic fluid pressure. Thus, when a hydraulic
cylinder is actuated by communicating pressurized hydraulic fluid
to the blind side, the effective surface area of the hydraulic
piston is greater than when the same pressure is communicated to
the rod side (i.e., SA.sub.b>SA.sub.r). Thus, for a given
hydraulic fluid pressure, more force is applied to the rod 376
(albeit in different directions) when the hydraulic fluid pressure
is applied to the blind side than when it is applied to the rod
side. It is also possible to generate yet a different amount of
force for a given hydraulic pressure by applying the hydraulic
fluid pressure to both sides of a piston. In this mode of
operation, referred to as a regenerative mode, the net piston area
is equal to the difference between the blind side area SA.sub.b and
the rod side area SA.sub.r. This net area corresponds to the
cross-sectional area of the rod, and is referred to as
SA.sub.(b-r).
[0070] In some embodiments, a combination of surface areas
associated with hydraulic drive piston 378 and hydraulic drive
piston 380 are pressurized to achieve a desired output force on rod
376, which may correspond to a second pressure of liquid W. The
effective or net operating surface area A.sub.net being pressurized
for a given gear is then equal to the sum of the surface areas
associated with the various portions of the hydraulic cylinders 348
and 350 being pressurized with hydraulic fluid. The sum of the
surface areas can also be referred to as the surface area of the
hydraulic piston(s) SA.sub.h. It is to be appreciated that other
embodiments include those in which the hydraulic fluid pressure
communicated to the various surface areas in actuator 312 may be
different from each other.
[0071] The ratio of the surface area of the working piston or
liquid piston SA.sub.w to the surface area of the hydraulic
piston(s) SA.sub.h dictates the hydraulic pressure needed to
achieve a desired liquid pressure, and thus gas pressure, at a
given point in the cycle. By varying the surface area ratio for a
given liquid pump/hydraulic cylinder set, varying levels of liquid
pressure can be achieved at different points within the compression
cycle for the same levels of hydraulic pressure. The pressure of
the hydraulic fluid needed to achieve a particular liquid pressure
(and/or gas pressure) can be calculated as follows.
F.sub.h (force of hydraulic fluid)=P.sub.h (hydraulic
pressure).times.SA.sub.h (SA.sub.r or SA.sub.b or SA.sub.(b-r)
F.sub.w (force applied to liquid)=P.sub.w (liquid
pressure).times.SA.sub.w
F.sub.h=F.sub.w
P.sub.w.times.SA.sub.w=P.sub.h.times.SA.sub.h
P.sub.w=P.sub.h.times.(SA.sub.h/SA.sub.w) and
P.sub.h=P.sub.w.times.(SA.sub.w/SA.sub.h)
[0072] A maximum and minimum operating pressure for each hydraulic
pump can be established, e.g. as the limits of a range of operating
pressure within which the hydraulic pump operates at or above a
desired energy efficiency. This pressure range can be used to
determine the piston ratio (e.g., (SA.sub.h/SA.sub.w)) needed at
various points during a compression cycle to operate the system so
as to approach or achieve operation within the maximum efficiency
range of the hydraulic pump. For example, for a hydraulic pump
having a maximum efficient operating pressure of 300 bar and a
desired maximum output pressure of the air (and therefore the
liquid) is 30 bar, the piston ratio (i.e., (SA.sub.w/SA.sub.h))
required at the end of the pressurization cycle, when the liquid
and gas pressure reaches 30 bar, is 10:1. Correspondingly, if the
hydraulic pump has a minimum efficient operating pressure of 120
bar, and the air enters the system at 3 bar, then the piston ratio
(i.e., (SA.sub.w/SA.sub.h)) required at the start of the
pressurization cycle, when the liquid and gas pressure is 3 bar, is
40:1. The number of liquid pumps and hydraulic pumps needed, and
the piston ratios (and corresponding size of the hydraulic
cylinders and liquid pumps) for the various liquid pump/hydraulic
sets can then be determined such that the system can operate within
the desired efficiency range for the entire compression cycle
(i.e., compressing the gas from 3 bar to 30 bar). There are a
variety of different operating sequences that can be used to
incrementally increase the pressure in the system and to achieve
this output. It is understood that the approach can be applied
using hydraulic pumps with maximum operating pressures higher or
lower than 300 bar, and minimum operating pressures higher or lower
than 120 bar.
[0073] At a given time during a compression or expansion cycle, the
actuator 312 can be referred to as being in a particular "state" or
gear that is associated with the piston area ratios being
pressurized within the actuator at that time. As described above,
when the system makes a change in the ratio of the pressure of the
hydraulic fluid in the hydraulic actuator to the pressure of the
liquid in the liquid pump(s) actuated by the hydraulic actuator
(i.e., the ratio of the pressurized surface area of the liquid
piston to the net operating pressurized surface area(s) of the
hydraulic piston(s) actuating the liquid piston) this is referred
to as a "gear shift" or "gear change." There is a variety of
different combinations or sequences of gear changes (changes in
piston area ratios) that can be incorporated into a particular
operating sequence of the system.
[0074] In the example of system 300, where each liquid pump has two
identical associated hydraulic cylinders to actuate the liquid
pump, there are sixteen possible states for the two actuators, i.e.
every combination of each chamber being pressurized or not
pressurized (two states for four chambers gives 2.sup.4
combinations). For identical hydraulic cylinders (i.e. in which the
blind side area of each cylinder is the same and the rod side area
of each cylinder is the same), there are four different possible
gears (with associated piston area ratios) that can be used to
actuate each working or liquid piston in each direction. For
example, to move a liquid piston upward in one liquid pump,
hydraulic fluid can be pumped into (1) the rod side of the upper
hydraulic cylinder (or the rod side of the upper hydraulic cylinder
and the blind side of both cylinders, which cancel each other out),
(2) the blind side of the lower hydraulic cylinder (or the blind
side of the lower cylinder and the rod side of both cylinders,
which cancel each other out), (3) both the blind side and the rod
side of the lower hydraulic cylinder, or (4) both the rod side of
the upper hydraulic cylinder and the blind side of the lower
hydraulic cylinder. The state in which none of the chambers is
pressurized does not produce any force on the working piston, nor
(for identical cylinders) does the state in which all chambers are
pressurized. In the embodiment depicted in FIG. 3A, each stage is
configured with two liquid pumps that actuate one after the other,
and because each liquid pump in this embodiment has four possible
gears, the compression process has eight possible gears. It is to
be appreciated that other embodiments include those in which the
hydraulic fluid pressure communicated to the various surface areas
in actuator 312 may be different from each other and may create
more than four possible gears in each liquid pump. It is
appreciated that given an actuator that can achieve four possible
gears, it may be preferable to use fewer gears than four gears, for
example three gears. The reasons for such a preference may involve
the dynamic response of the fluid and/or mechanical components to
the gear shift events. Correspondingly, an embodiment configured
with two liquid pumps may be operated using five, six, or seven of
the possible eight gears. Moreover, the compression process may
also vary according to the current pressure of the compressed air
storage vessel, e.g. when the storage vessel is at relatively low
pressure, the preferred compression process may use one, two,
three, four, five, six, or seven of the possible eight gears.
[0075] In other embodiments, an actuator can be configured to have
a different number of possible different gears and gear changes
based on, for example, the number of hydraulic cylinders, the size
(e.g., diameter) of the housing of a hydraulic cylinder in which a
hydraulic piston is movably disposed, the size (e.g., diameter) of
the hydraulic pistons disposed within the housing of the hydraulic
cylinders, the number and size of drive rods coupled to the
hydraulic pistons, and/or the size of the working piston to be
actuated. Other examples of actuators are described in the
Ingersoll I application incorporated by reference above.
[0076] Thus, the hydraulic pressure time profile can be varied as
needed to achieve a particular output gas pressure. The efficiency
range of the hydraulic pump system can determine the number of
gears and gear shifts that may be needed for a desired gas pressure
range (difference between input or start pressure and output or end
pressure). For example, if the hydraulic pump's efficiency range is
narrower, then more gears may be needed for a given gas pressure
range. The size and number of gears can also depend on the
particular operating speed (RPM) of the system.
[0077] As discussed above, heat can be transferred from air (or
other gas) that is compressed in the working chamber to reduce the
work consumed by the compression process. Heat can be transferred
from gas to a liquid, and/or gas to dividers within the working
chamber, and/or from the liquid out of the working chamber. In some
embodiments, to increase the total amount of heat energy
transferred during each cycle, the system can be operated at a
relatively slow speed. For example, in some embodiments, a complete
compression or expansion cycle may be slow enough to provide
sufficient time for enough heat energy to be transferred between
the gas and the liquid to approximate an isothermal compression
and/or expansion process, achieving work reduction or extraction
and the efficiencies associated therewith. Additionally or
alternatively, faster speeds may allow larger power levels to be
achieved during expansion, isothermally or with temperature
changes, which may be desirable at particular times during the
system operation.
[0078] The use of a liquid (e.g. water) as a medium through which
heat passes during compression and/or expansion may allow for a
continuous temperature moderation process and may provide a
mechanism by which heat energy may be moved in and/or out of the
working chamber. That is, during compression the liquid may receive
heat energy from gas that is being compressed, and pass this heat
energy to the external environment continuously, or in batches,
both while gas is being compressed and while gas is being received
by the working chamber for later compression. Similarly, heat
energy addition may occur when a compressor/expander device is
operating in an expansion mode both during expansion and as
expanded gas is passed from a pressure vessel.
[0079] As discussed above, the liquid within a pressure vessel can
be in contact with the gas at one or more gas/liquid interfaces and
gas/divider interfaces, across which heat energy is transferred
from gas that is compressed and/or to gas that is expanded. The
pressure vessel/working chamber can also include a heat exchanger,
such as one or more heat pipes as discussed above, that transfers
heat energy between the liquid and an environment that is external
to the device. Heat energy may be moved from gas that is compressed
and/or to gas that is expanded to achieve isothermal or near
isothermal compression and/or expansion processes.
[0080] As described above, adiabatic compression assumes that no
energy (heat) is transferred to or from the gas during the
compression process, and all applied work is added to the internal
energy of the gas, resulting in increases of both temperature and
pressure. In contrast, isothermal compression assumes that the
compressed gas remains at a constant temperature throughout the
compression process, and energy is removed from the system at the
same rate as heat is added by the mechanical work of compression.
For a given gas volume reduction (i.e., ratio of final volume to
initial volume), an adiabatic compression process results in the
highest final gas pressure, the highest final gas temperature, and
the highest work consumption. For the same volume reduction, an
isothermal compression process results in the lowest final pressure
and consumes half of the work as the adiabatic compression process.
The difference in the amount of mechanical work required is
reflected in the heat energy that is retained in the compressed
gas. This due to the fact that if there is no temperature
difference throughout the process, the internal energy (U) remains
invariant. The equation below is a simplified version of the
conservation of energy or the first law of thermodynamics. If dU is
zero, then the amount of heat transferred (dQ) equals the work
input (dW).
dU=dQ-dW
for dU=0, dQ=dW
[0081] The use of adiabatic compression (or near adiabatic
compression) may be desirable in some applications since
approximately twice as much energy is stored at the end of the
compression process. However, since approximately half of this
stored energy is heat energy, and perfect insulation is not
practical, the heat energy will flow out of the compressed gas over
time. In applications where the compressed gas is going to be
stored for a period of time, isothermal compression (or near
isothermal compression) may be desirable to prevent work from being
lost in the form of heat energy flow out of the compressed gas over
time. For example, in compressed gas energy storage, where a
compressed gas is moved out of a compression device to a storage
structure for potentially longer term storage, minimizing the work
lost due to heat flow out of the compressed gas/system may be
desirable.
[0082] In the gas compression/expansion devices and systems
described herein, the heat transfer characteristics can be varied
to approximate near adiabatic compression and/or expansion or near
isothermal compression and/or expansion, and anywhere in between
those two theoretical limits. For example, as described above, heat
energy can be removed from a gas during a compression process (or
can be added to a gas during an expansion process) via a liquid
that is present in one or more pressure vessels of a
compressor/expander device to control the gas temperature
throughout the process. In other examples, a heat transfer element
can be positioned within the interior of a working chamber of a
compressor/expander device to provide sufficient gas/liquid
interface and/or sufficient thermal capacity to efficiently
intermediate in, and enhance, the transfer of heat between the gas
and the liquid.
[0083] As described above, the rate at which heat energy is added
to the gas as it is being compressed (or released from the gas
during an expansion process) can also be varied to approximate near
adiabatic compression and/or expansion or near isothermal
compression and/or expansion, and anywhere in between those to
theoretical limits, by changing the rate at which mechanical work
is being done on the gas (i.e., changing the speed of the
compression/expansion stroke, or the rate of change of volume of
the working chamber).
[0084] The following discussion compares the operation of a
compression/expansion device as described herein. In each case, it
is assumed that the same quantity of gas is compressed (or
expanded) over the same pressure ratio, the initial temperature of
the gas is the same for compression cycles, but the temperature of
the gas is allowed to vary over the course of the compression
cycle. Since the pressure ratio is held constant and only the
temperature is allowed to vary, the ratio of the mechanical work
done on the gas to the heat flow out of the system is relatively
constant in these examples. Typically the pressure will vary when
the temperature is caused to change through the stroke, however
these graphs keep pressure fixed to best illustrate the flexibility
such a system can have by isolating a single variable for
discussion purposes. That being said, it is possible to change the
discharge temperature while maintaining the same pressure profile
by changing the volumetric compression/expansion ratio. This is
possible with the system described above by changing stroke length,
and/or changing the volume of water in the system. As will be
apparent from the discussion below, one or more of the system
variables can be changed to achieve any desired temperature and
pressure profile.
[0085] Each of FIGS. 5-11 is an example graph illustrating the
operation of a compression and/or expansion device as described
herein. The values shown in FIGS. 5-11 are exemplary and for
comparisons purposes only and the systems and methods described
herein are not limited to the data disclosed in these figures. FIG.
5 illustrates one example of a compressor/expander device designed
and operated to achieve essentially isothermal compression. The
pressure of a quantity of gas is raised from an initial pressure of
1 bar to a final pressure of 7 bar (i.e., 7:1 pressure ratio) over
a six second compression stroke. In this example, during the
compression stroke, energy is continuously being transferred to a
heat transfer element positioned within the interior of a working
chamber of a compressor/expander device. The energy is then
transferred from the heat transfer element to a liquid (such as
water) present in the compressor/expander device. A portion of the
liquid is then removed from the working chamber after the
compression cycle has been completed, and transferred to another
stage of the system and/or out of the system entirely. Heat energy
is removed from the system at the same rate as heat energy is added
by the mechanical work of compression, so the temperature of the
gas remains constant throughout the compression stroke.
[0086] FIG. 6 illustrates another example of the operation of a
compression and/or expansion device where the pressure of a
quantity of gas is raised from an initial pressure of 1 bar to a
final pressure of 7 bar (i.e., 7:1 pressure ratio) over a six
second compression stroke. In this example, less liquid is removed
from the working chamber after the compression cycle has been
completed, thus the heat transfer element is not "reset" to the
initial temperature of the incoming gas. The heat transfer rate is
a function of the temperature differential between the gas being
compressed and the heat transfer element, therefore the heat
transfer rate will be lower in this example than in the isothermal
example shown in FIG. 5. Since the heat transfer rate is lower, and
less heat energy is being removed from the system (i.e., less
heated liquid) than is being added by the mechanical work of
compression, the temperature of the gas rises, in this example at a
relatively linear rate throughout the compression stroke. The rate
at which the temperature of the gas rises related to the volume of
liquid removed from the working chamber after the compression cycle
has been completed.
[0087] FIG. 7 illustrates another example of the operation of a
compression and/or expansion device where the pressure of a
quantity of gas is raised from an initial pressure of 1 bar to a
final pressure of 7 bar (i.e., 7:1 pressure ratio) over a six
second compression stroke. As described above, the configuration
(size, shape, structure, etc.) of the heat transfer element can be
changed to vary the surface area per unit volume or mass within the
gas as it is being compressed/expanded during a
compression/expansion cycle. In this example, the heat transfer
element has multiple components that are movable with respect to
each other such that the volumetric density of the heat transfer
element can be varied as a function of stroke throughout the
compression cycle. The varying density at different times during
the compression cycle changes the heat transfer rates throughout
the compression cycle. As shown, the temperature profile resembles
a polynomial function, which may be desirable for processes where
the temperature profile is of interest (e.g., a chemical reaction
process), and not just the initial and final temperature.
[0088] FIG. 8 illustrates another example of the operation of a
compression and/or expansion device where the pressure of a
quantity of gas is raised from an initial pressure of 1 bar to a
final pressure of 7 bar (i.e., 7:1 pressure ratio). In this
example, the liquid removal rate and the heat transfer element
configuration are the same as the example shown in FIG. 5, however
the compression stroke has been shortened to 3 seconds. As
described above, the rate at which heat energy is added to the gas
as it is being compressed (or released from the gas during an
expansion process) can be varied by changing the rate at which
mechanical work is being done on the gas (i.e., changing the speed
of the compression/expansion stroke). By doubling the speed of the
compression stroke, approximately the same amount of work is being
done on the gas in half the time, thus increasing the rate at which
heat energy is added to the gas as it is being compressed. Since
the heat transfer element geometry and materials have not changed,
the maximum rate at which heat is transferred to or from the gas
has not changed. Therefore the increased rate of heat transfer
necessary with a shorter stroke is not adequately met by the same
geometry as was used in FIG. 5. This results in the rise in
temperature seen in FIG.8 that was not seen in FIG. 5.
[0089] FIG. 9 illustrates another example of the operation of a
compression and/or expansion device where the pressure of a
quantity of gas is raised from an initial pressure of 1 bar to a
final pressure of 7 bar (i.e., 7:1 pressure ratio) over a six
second compression stroke. In this example, the effects of
decreasing the amount of liquid (FIG. 6) that is removed from the
working chamber after the compression cycle and of changing the
configuration of the heat transfer element (FIG. 7) can be combined
or superimposed, allowing a different temperature profile to be
achieved than can be achieved with either effect separately. In
reality the effects are not a simple summation of two separate
effects, however it is a good first approximation and serves to
illustrate the phenomenon.
[0090] FIG. 10 illustrates an example of the operation of a
compression and/or expansion device where the pressure of a
quantity of gas is raised from an initial pressure of 1 bar to
several final pressures isothermally at 300 K. It is possible to
size a heat transfer element such that several different pressure
profiles all result in a near-isothermal process as shown in FIG.
10. Such a change can be effected in process without modification
to the geometry and without shutting down the system. It can be
appreciated that the temperature profile can be simultaneously
altered in the manners shown in FIG. 5-9 at the same time the
pressure profile is customized as shown in FIG. 10.
[0091] FIG. 11 illustrates another example of the operation of a
compression and/or expansion device where the pressure of a
quantity of gas is lowered from an initial pressure of 7 bars to a
final pressure of 1 bar (i.e., 7:1 pressure ratio) over a three
second compression stroke. In this example, the liquid removal rate
and the heat transfer element configuration are the same as the
example shown in FIG. 8, however the compressor/expander device is
operating in an expansion cycle. It is to be appreciated that
although FIGS. 5-10 illustrate the operation of a compression
and/or expansion device during a compression cycle, the changes to
the system variables illustrated in those examples are equally
applicable to an expansion cycle.
[0092] FIG. 12 schematically illustrates a portion of a
compressor/expander device according to another embodiment. A
compressor/expander device 400 can include one or more pressure
vessels (cylinders) 420 having a first working chamber 462 and a
second working chamber 464, an actuator 421 connected to a piston
466 via a piston rod 427, and first heat transfer element 423 and a
second heat transfer element 425 disposed within the pressure
vessel 420. The compression/expansion device 400 can be used in the
same or similar manner as described above for previous embodiments,
to compress and/or expand a gas (e.g., air). In this embodiment,
the piston 466 is used to move a liquid within the pressure vessel
420 to compress and/or expand a gas within the pressure vessel
420.
[0093] More specifically, the first heat transfer element 423 is
disposed within the first working chamber 462 and the second heat
transfer element 425 is disposed within the second working chamber
464. The compressor/expander device 400 can be used, for example,
to compress and/or expand a gas, such as air, within the first
working chamber 462 or the second working chamber 464. The
compressor/expander device 400 can be used, for example, in a CAES
system. The pressure vessel 420 can include an inlet conduit 428
and an outlet conduit 429 in fluid communication with the first
working chamber 462 and an inlet conduit 430 and an outlet conduit
431 in fluid communication with the second working chamber 464. The
first working chamber 462 and the second working chamber 464 can
contain, at various time periods during a compression and/or
expansion cycle, a quantity of the gas (e.g., air) and a quantity
of the liquid (e.g., water) that can be communicated to and from
the working chambers via the inlet/outlet conduits. Optionally, the
pressure vessel 420 can include one or more additional conduits in
fluid communication with the first working chamber 462 or the
second working chamber 464 specifically dedicated to communicating
gas or liquid to or from the first and second working chambers 462,
464. The compressor/expander device 400 can also include multiple
valves (not shown in FIG. 12) coupled to the inlet/outlet conduits
428, 429, 430, and 431 and/or to the pressure vessel 420. The
valves can be configured to operatively open and close the fluid
communication to and from the working chambers 462 and 464.
Examples of use of such valves are described in more detail in the
Compressor and/or Expander Device applications incorporated by
reference above.
[0094] The actuator 465 can be any suitable mechanism for causing
reciprocal movement of the piston 466 within the pressure vessel
420. As the piston 466 is moved back and forth within the pressure
vessel 420, the volume of the first working chamber 462 and the
second working chamber 464 and/or the portion of the volume of the
first working chamber 462 and the second working chamber 464 that
can be occupied by gas can be selectively changed. The actuator 465
can be for example, an electric motor or a hydraulically driven
actuator such as, for example, the hydraulic actuators described in
the Ingersoll I application incorporated herein by reference above.
The actuator 465 can be coupled to the piston 466 via the piston
rod 427 and used to move the piston 466 back and forth within the
interior region of the pressure vessel 420. For example, the
working chamber 462 can be defined by the cylinder 420 and the
bottom face of piston 466. Similarly, the working chamber 464 can
be defined by the cylinder 420 and the top face of the piston 466.
In this manner, the piston 466 is movably disposed within the
interior region of the cylinder 420 and can divide the interior
region between a first interior region (working chamber 462) and a
second interior region (working chamber 464).
[0095] As the piston 466 moves back and forth within the interior
region of the cylinder 420, a volume of the first working chamber
462 and a volume of the second working chamber 464 will each
change. For example, the piston 466 can be moved between a first
position (e.g., top dead center) in which the first working chamber
462 includes a volume of fluid greater than a volume of fluid in
the second working chamber 464, and a second position (e.g., bottom
dead center) in which the second working chamber 464 includes a
volume of fluid greater than a volume of fluid in the first working
chamber 462. As used herein, "fluid" means a liquid, gas, vapor,
suspension, aerosol, or any combination of thereof. At least one
seal member (not shown), such as, for example, a rolling seal
member can be disposed within the first working chamber 462 and the
second working chamber 464 of the cylinder 420 and can be attached
to the piston 466. The arrangement of the rolling seal member(s)
can fluidically seal the first working chamber 462 and the second
working chamber 464 as the piston 466 moves between the first
position (i.e., top dead center) and the second position (i.e.,
bottom dead center). Examples and use of a rolling seal member are
described in more detail U.S. patent application Ser. No.
13/312,467 to Ingersoll et al. ("the Ingersoll III application"),
entitled "Compressor and/or Expander Device with Rolling Piston
Seal," the disclosure of which is incorporated herein by reference
in its entirety
[0096] In some embodiments, the piston 466 is moved within the
pressure vessel 420 to compress a gas, such as air, within the
pressure vessel 420. In some embodiments, the piston 466 can be
configured to be single-acting (e.g., actuated in a single
direction to compress and/or expand gas). As shown in FIG. 12, the
compressor/expander device 400 is configured to be double-acting in
that the piston 466 can be actuated in two directions. In other
words, the piston 466 can be actuated to compress and/or expand gas
(e.g., air) in two directions. For example, in some embodiments, as
the piston 466 is moved in a first direction, a first volume of a
fluid (e.g., water, air, and/or any combination thereof) having a
first pressure can enter the first working chamber 462 of the
cylinder 420 on the bottom side of the piston 466. In addition, a
second volume of the fluid having a second pressure can be
compressed by the top side of the piston 466 in the second working
chamber 464. The gas portion of the second volume of fluid can then
exit the second working chamber 464. When the piston 466 is moved
in a second direction opposite the first direction, the gas portion
of the first volume of fluid within the first working chamber 462
can be compressed by the piston 466. The gas portion of the first
volume of fluid can then exit the first working chamber 462 having
a third pressure greater than the first pressure, and
simultaneously a third volume of fluid can enter the second working
chamber 464.
[0097] The heat transfer element 423 disposed within the first
working chamber 462 and the heat transfer element 425 disposed
within the second working chamber 464 can be a variety of different
configurations, shapes, sizes, structures, etc. to provide a
relatively high surface area per unit volume or mass that can be in
contact with the gas (e.g., air) as it is being compressed or
expanded. In this embodiment, as shown in FIG. 8, the heat transfer
element 423 is disposed near the bottom surface of the piston 466
and the heat transfer element 425 is disposed at a top portion of
the second working chamber 464. In some embodiments, the heat
transfer element 423 disposed within the first working chamber 462
can be attached to the bottom face of the piston 466. Similarly, in
some embodiments, the heat transfer element 425 disposed within the
second working chamber 464 can be attached to the top face of the
piston 466, as described in further detail herein. In such
embodiments, the heat transfer elements 423, 425 can move with the
piston 466 as it is actuated.
[0098] In some embodiments, it may be desirable to form the heat
transfer elements 424 with a material that can provide high thermal
conductivity. For example, the heat transfer elements 424 (i.e.,
the heat transfer element 423 and the heat transfer element 424)
can be formed with metals (e.g. stainless steel) in the form of,
for example, sheet or wire, carbon fiber, nano-materials, and
hybrid or composite materials (e.g. carbon polymer compounds) which
have anti-corrosion properties, are lighter weight, and are less
expensive than some metallic materials.
[0099] The compressor/expander device 400 also includes an actuator
421 and an actuator 422 that can each be configured the same as, or
similar to, actuator 122 a described above. The actuators 421 and
422 can each include a piston (not shown) disposed within a housing
(not shown). The actuator 422 can be actuated to move liquid
between the housing and the first working chamber 462 via a liquid
inlet/outlet 433, and the actuator 421 can be actuated to move
liquid between the housing and the second working chamber 464 via a
liquid inlet/outlet 435. The pistons of the actuators 421 and 422
can each be coupled to, for example, an electric motor or hydraulic
actuator configured to actuate the pistons.
[0100] The compression/expansion device 400 can also include a
first liquid outlet 468 coupled to, and in fluid communication
with, a liquid purge system 438 and the first working chamber 462,
and a second liquid outlet 470 coupled to, and in fluid
communication with, the liquid purge system 438 and the second
working chamber 464. The liquid purge system 438 can be configured
the same as or similar to, and function the same as or similar to,
the liquid purge systems 238 and 338 described above. The first
liquid outlet 468 can be opened to evacuate a volume of the liquid
from the first working chamber 462, and the second liquid outlet
470 can be opened to evacuate a volume of the liquid from the
second working chamber 464, as described above for previous
embodiments.
[0101] The liquid purge system 438 can include a first pump (not
shown) coupled to, and in fluid communication with, the first
liquid outlet 468, and a first conduit (not shown) coupled to, and
in fluid communication with, a thermal management facility (not
shown). The liquid purge system 438 can also include a second pump
(not shown) coupled to, and in fluid communication with, the second
liquid outlet 470, and a second conduit (not shown) coupled to, and
in fluid communication with, the thermal management facility. The
pumps can each be actuated to move liquid from the first working
chamber 462 and the second working chamber 464 to the thermal
management facility. The thermal management facility can include a
pump (not shown) configured to pump cooled liquid to the actuator
421 and 422. In some embodiments, the liquid purge system 438 and
actuators 421 and 422 can be subsystems of a liquid management
system that includes a thermal management facility.
[0102] In use, when the piston 466 is actuated to compress a gas
within the pressure vessel 420, the actuator 465 can be controlled
to maintain a relatively constant pressure change profile
throughout the stroke of the piston 466. For example, when the
piston 466 is actuated to compress a quantity of gas within the
second working chamber 464, the piston 466 can be actuated over a
first distance at a first stroke speed and over a second distance
at a second stroke speed. The first distance and the second
distance can be the same or different and the first stroke speed
and the second stroke speed can be the same or different depending
on any of a variety of factors including, for example, the presence
or absence of a liquid in the second working chamber 464, the
presence or absence of a heat transfer element 425 in the second
working chamber 464, the interaction between a volume of liquid and
a heat transfer element 425 in the second working chamber, or the
change in density of the heat transfer element 425 over the
vertical distance of the pressure vessel. Said another way, as the
piston 466 is actuated at the beginning of a compression stroke, a
volume of liquid contained in the second working chamber 464 may
not be in contact with the heat transfer element 425 and the piston
can be actuated over the first distance at the first stroke speed
to maintain a relatively constant compression rate of the quantity
of the because the surface are of the liquid acting on the gas is
substantially equal to the surface area of the piston 466. As the
liquid in the second working chamber 464 contacts and moves into
the heat transfer element 425, the surface area of the liquid
acting on the gas is reduced because the heat transfer element 425
occupies a portion of the cross-sectional area of the pressure
vessel. Thus, in order to maintain a relatively constant
compression rate of the quantity of gas, the piston 466 can be
actuated at a second stroke speed slower than the first stroke
speed. As the compression stroke progresses, the stroke speed can
be modified to maintain a relatively constant compression rate
depending on the structure (e.g., density) of the heat transfer
element 425 or to change the rate of compression. Similarly, the
stroke speed can be modified to maintain a relatively constant heat
transfer rate out of the quantity of gas as it is being compressed
or to manage the temperature of the gas throughout the compression
stroke to any desired profile as described herein.
[0103] While various embodiments of the invention have been
described above, it should be understood that they have been
presented by way of example only, and not limitation. Where methods
and steps described above indicate certain events occurring in
certain order, those of ordinary skill in the art having the
benefit of this disclosure would recognize that the ordering of
certain steps may be modified and that such modifications are in
accordance with the variations of the invention. Additionally,
certain of the steps may be performed concurrently in a parallel
process when possible, as well as performed sequentially as
described above. The embodiments have been particularly shown and
described, but it will be understood that various changes in form
and details may be made.
[0104] For example, although various embodiments have been
described as having particular features and/or combinations of
components, other embodiments are possible having any combination
or sub-combination of any features and/or components from any of
the embodiments described herein. For example, although certain
embodiments of a heat transfer element were shown and described
with respect to a particular embodiment of a compression/expansion
device, it should be understood that the various embodiments of a
heat transfer element including, for example, rods, tubes, fins,
fibers, filaments, coils, plates, mesh, etc. can be used in any of
he various embodiments of a compression and/or expansion device
described herein and in other embodiments of a compress and/or
expansion device not described herein. Additionally, the specific
configurations of the various components of a compression and/or
expansion device can also be varied. For example, the size and
specific shape of the various components can be different than the
embodiments shown, while still providing the functions as described
herein.
[0105] Although the liquid in the compressor/expander devices was
described above as including water, other liquids can be used,
additionally or alternatively. As is to be appreciated, water may
naturally condense out of air that is being compressed by the
system, and in this respect, may combine with the liquid without
adverse impact. Additionally, when used in embodiments of the
expander/compressor devices, water may evaporate into air during
expansion without having an adverse impact. Other types of liquids,
however, may be used in addition to or in place of water. Some
examples of such liquids may include additives or entire liquids
formulated to prevent freezing, such as glycol, liquids that
prevent evaporation, such as glycerin, and/or liquids to prevent
foaming. Similarly, although the gas in the compressor/expander
device was described above as being air (which is a convenient
choice, so that ambient air can be used), other gases can be used,
additionally or alternatively.
[0106] In addition, although the system 300 was described as having
two stages each with two liquid pumps, and the liquid pumps are
each actuated by two hydraulic actuators (an upper and a lower
hydraulic actuator), in alternative embodiments, more hydraulic
actuators can be coupled to the top and bottom of a liquid pump,
which can provide additional possible gear modes. In addition, in
other embodiments, a system can be configured with a different
number of liquid pumps and/or a different number of stages, which
can provide additional possible gear modes. In addition, the
systems and methods described herein can be controlled using known
computer systems and control system used for such purposes.
[0107] The system controller (e.g., 316) can include, for example,
a processor-readable medium storing code representing instructions
to cause a processor to perform a process. The processor can be,
for example, a commercially available personal computer, or other
computing or processing device that is dedicated to performing one
or more specific tasks. For example, the processor can be a
terminal dedicated to providing an interactive graphical user
interface (GUI). The processor, according to one or more
embodiments, can be a commercially available microprocessor.
Alternatively, the processor can be an application-specific
integrated circuit (ASIC) or a combination of ASICs, which are
designed to achieve one or more specific functions, or enable one
or more specific devices or applications. In yet another
embodiment, the processor can be an analog or digital circuit, or a
combination of multiple circuits.
[0108] The processor can include a memory component. The memory
component can include one or more types of memory. For example, the
memory component can include a read only memory (ROM) component and
a random access memory (RAM) component. The memory component can
also include other types of memory that are suitable for storing
data in a form retrievable by the processor. For example,
electronically programmable read only memory (EPROM), erasable
electronically programmable read only memory (EEPROM), flash
memory, magnetic disk memory, as well as other suitable forms of
memory can be included within the memory component. It is
recognized than any and all of these memory components can be
accessed by means of any form of communication network. The
processor can also include a variety of other components, such as
for example, co-processors, graphic processors, etc., depending
upon the desired functionality of the code.
[0109] The processor can be in communication with the memory
component, and can store data in the memory component or retrieve
data previously stored in the memory component. The components of
the processor can be configured to communicate with devices
external to the processor by way of an input/output (I/O)
component. According to one or more embodiments, the I/O component
can include a variety of suitable communication interfaces. For
example, the I/O component can include, for example, wired
connections, such as standard serial ports, parallel ports,
universal serial bus (USB) ports, S-video ports, local area network
(LAN) ports, small computer system interface (SCCI) ports, analog
to digital interface input devices, digital to analog interface
output devices, and so forth. Additionally, the I/O component can
include, for example, wireless connections, such as infrared ports,
optical ports, Bluetooth.RTM. wireless ports, wireless LAN ports,
or the like. The processor can also be connected to a network,
which may be any form of interconnecting network including an
intranet, such as a local or wide area network, or an extranet,
such as the World Wide Web or the Internet. The network can be
physically implemented on a wireless or wired network, on leased or
dedicated lines, including a virtual private network (VPN).
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