U.S. patent application number 13/663793 was filed with the patent office on 2013-10-10 for reciprocating expander valve operating apparatus, system and method.
The applicant listed for this patent is DELTATREC INC.. Invention is credited to David P. Anderson, John G. Brisson, Nalin Walpita.
Application Number | 20130263803 13/663793 |
Document ID | / |
Family ID | 49291303 |
Filed Date | 2013-10-10 |
United States Patent
Application |
20130263803 |
Kind Code |
A1 |
Walpita; Nalin ; et
al. |
October 10, 2013 |
RECIPROCATING EXPANDER VALVE OPERATING APPARATUS, SYSTEM AND
METHOD
Abstract
The disclosure describes a method to operate a conventional 4
cylinder engine as an expander for any pressurized fluid (e.g.,
liquid, vapor, or gas). A poppet valve system is disclosed enabling
upward lift of the inlet valve, with assist from cylinder
compression pressure, together with downward lift from an exhaust
valve, resulting in especially efficient expansion of fluid or gas
in a thermodynamic power cycle. Further, it is described that a
desmodromic valve operation system may be employed and provides
essential guidance and opening closing actions for proper operation
of the expander system.
Inventors: |
Walpita; Nalin; (Somerville,
MA) ; Brisson; John G.; (Rockport, MA) ;
Anderson; David P.; (Wellesley, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DELTATREC INC. |
Somerville |
MA |
US |
|
|
Family ID: |
49291303 |
Appl. No.: |
13/663793 |
Filed: |
October 30, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61553666 |
Oct 31, 2011 |
|
|
|
Current U.S.
Class: |
123/90.15 ;
123/90.1 |
Current CPC
Class: |
F01L 1/30 20130101; F01L
9/026 20130101; F01B 1/00 20130101; F02G 1/043 20130101; F01K 7/34
20130101; F01L 1/34 20130101; F01K 25/10 20130101 |
Class at
Publication: |
123/90.15 ;
123/90.1 |
International
Class: |
F01L 1/34 20060101
F01L001/34 |
Claims
1. A method of operating a reciprocating expansion device, the
expansion device comprising at least one expansion chamber with a
reciprocating element, a inlet to the expansion chamber with at
least one outward opening inlet valve, and an exhaust from the
expansion chamber having at least one inward opening outlet valve,
the method comprising: providing pressurized working fluid to the
inlet; opening the inlet valve in the outward directed to deliverer
pressurized working fluid to the expansion chamber to expand and to
drive a motion of the reciprocating element; and opening the outlet
valve in the inward direction to allow expanded working fluid to
escape the expansion chamber to the exhaust.
2. The method of claim 1, further comprising: opening and closing
the inlet and outlet valves using a desmodromic cam device, said
cam device applying force during both opening and closing movements
of the inlet and outlet valves.
3. The method of claim 2, wherein each of the inlet and outlet
valves is opened and closed without the use of a spring closure
mechanism.
4. The method of claim 1, comprising: using an exhaust stroke of
the reciprocating element to drive expanded working fluid out
through the outlet valve; and using pressure generated in the
expansion chamber during the exhaust stroke to apply an outward
force to the inlet valve to assist in opening the inlet valve;
wherein the pressure generated in the expansion chamber during the
exhaust is greater than the pressure at the inlet on a side
external to the expansion chamber.
5. The method of claim 4, wherein the applied outward force on the
inlet valve reduces an inlet valve cam opening force on a cam used
to open the inlet valve.
6. The method of claim 5, comprising generating pressure in the
cylinder to a required value by controlling of the point of closure
of the exhaust valve.
7. The method of claim 4, wherein the opening of the inlet valve is
accomplished using only the outward force to the inlet valve,
generated by a recompression pressure in the cylinder.
8. The method of claim 7, wherein the inlet valve does not have an
associated opening cam.
9. The method of claim 1, wherein the inlet valve comprises one or
more mechanical latches, the method comprising: using at least one
mechanical latch to hold the inlet valve in a stable open or a
stable closed position during at least a portion of an operating
cycle of the expansion chamber.
10. The method of claim 9, comprising: during a first portion of
the operating cycle, using the internal pressure of the expansion
chamber to move the inlet valve outward towards a fully open
position; using at least one mechanical opening latch to hold the
in the fully open position.
11. The method of claim 10, comprising: using the operation of the
opening latch to provide a force which assists in moving the inlet
valve towards the fully open position.
12. The method of claim 1, wherein: the inlet valve comprises a
mechanical latch and a spring mechanism, and wherein the method
comprises: during a first portion of an operating cycle of the
expansion chamber, using the mechanical latch to maintain the inlet
valve in a closed position; during a second portion of the
operating cycle, releasing the latch, and using pressure inside the
expansion chamber to open the inlet valve; and using the spring
mechanism to return the inlet valve from the open position to the
closed position.
13. The method of claim 10, wherein the inlet valve is opened using
the pressure inside the expansion chamber without the assistance of
a force from an opening mechanism located external to the expansion
chamber.
14. The method of claim 1, wherein the inlet valve comprises at
least one electromagnet, the method comprising: controlling the
electromagnet to actuate the inlet valve between a substantially
stable open position and a substantially stable open position.
15. The method of claim 14, wherein the at least one electromagnet
comprises at least a first and a second electromagnets, the method
comprising: switching the first electromagnet to an on state and
the second electromagnet to an off state to maintain the inlet
valve in the stable open position; and switching the first
electromagnet to an off state and the second electromagnet to an on
state to maintain the inlet valve in the stable closed
position.
16. The method of claim 1, wherein the inlet valve comprises an
over-center toggle mechanism having a stable closed and a stable
open position, wherein the method comprises: during a first portion
of the operating cycle of the expansion chamber, using the internal
pressure of the expansion chamber to toggle the inlet valve from
the stable closed position to the stable open position.
17. The method of claim 16, further comprising: during a second
portion of the operating cycle, using a mechanism external to the
expansion chamber to toggle the inlet valve into the stable closed
position.
18. The method of claim 1, wherein the inlet valve comprises a
spring loaded cam driven toggle mechanism, the method comprising:
placing the valve in a closed position by seating a valve body
against a seal, thereby causing a build up of pressure in the inlet
to the expansion chamber; and rotating a cam to drive the toggle
mechanism to apply an opening force on the valve body to unseat it
from the seal, thereby placing the expansion chamber in fluid
communication with the inlet and causing a reduction in inlet
pressure.
19. The method of claim 1, wherein the reciprocating expansion
device comprises: a primary expansion chamber with a primary
reciprocating element, and a secondary expansion chamber with a
secondary reciprocation element, the method comprising: using fluid
exhausted from the primary expansion chamber to drive the operation
of the secondary expansion chamber.
20. An apparatus comprising a reciprocating expansion device
comprising: at least one expansion chamber with a reciprocating
element, an inlet to the expansion chamber with at least one
outward opening inlet valve and configured to receive a pressurized
working fluid, and an exhaust from the expansion chamber having at
least one inward opening outlet valve; and a valve drive system
configured to: open the inlet valve in the outward directed to
deliver pressurized working fluid to the expansion chamber to
expand and to drive a motion of the reciprocating element; and open
the outlet valve to allow expanded working fluid to escape the
expansion chamber to the exhaust.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 61/553,666, entitled "RECIPROCATING EXPANDER
VALVE OPERATING APPARATUS, SYSTEM AND METHOD", filed Oct. 31, 2011,
the entire contents of which are herein incorporated by reference
in their entirety.
[0002] This application is also related to U.S. application Ser.
No. 12/773,431, entitled "HEAT ENGINE WITH CASCADED CYCLES", filed
May 4, 2010, U.S. Provisional Application Ser. No, 60/719,327,
entitled "PIEZOELECTRIC SELECTABLY ROTATABLE BEARING," filed on
Sep. 21, 2005, U.S. Provisional Application Ser. No. 60/719,328,
entitled "SOLAR HEAT ENGINE SYSTEM," filed on Sep. 21, 2005, U.S.
application Ser. No. 11/512,568, entitled "SOLAR HEAT ENGINE
SYSTEM," filed on Aug. 30, 2006, and U.S. application Ser. No.
12/246,127, entitled "HEAT ENGINE IMPROVEMENTS," filed on Oct. 6,
2008, U.S. application Ser. No. 12/773,431, the entire contents of
each of which are herein incorporated by reference in their
entirety.
BACKGROUND
[0003] This disclosure relates to the conversion of heat energy to
another form of energy, e.g. mechanical energy. The disclosure
further relates to such conversion where the heat energy source is
concentrated solar energy or a low grade or waste heat source.
[0004] Several different types of heat engines have been used in
practice to convert concentrated solar radiation to mechanical
power, notably Stirling cycle engines and Rankine cycle engines,
trilateral flash cycle engines, and engines of the type described
in the patent applications incorporated by reference above.
[0005] Heat engines of various types type typically employ one or
more expanders. Expanders are devices (e.g. turbine or piston
devices) through which a high pressure gas is expanded to produce
work. Because work is extracted from the expanding high pressure
gas, for may expanders the expansion is approximated by an
isentropic process (i.e., a constant entropy process). For example,
in theoretical, conventional Rankine cycles, expansion of working
fluid takes place under reversible adiabatic conditions.
[0006] Because expanders are employed in a wide variety of heat
engine systems, it would be advantageous to provide an expander
that operates with high efficiency (e.g. extracting work with an
efficiency approaching the thermodynamic limit), while maintaining
desirable features such as low manufacturing cost, robust
performance, etc. Moreover, it would be advantageous to provide an
expander design that can be adapted for use under a variety of
input conditions, e.g., over a broad range of working fluid input
pressures.
SUMMARY OF THE INVENTION
[0007] The inventors have realized that devices, systems, and
methods may be provided for the execution of thermodynamic cycles
or the generation of power using pressurized heated or unheated
fluids of any description, in a manner wherein most of the
available energy in the fluid under a strict thermodynamic
definition of same may be converted to mechanical work in a manner
approaching 100% conversion efficiency.
[0008] In some embodiments, an expander is provided which includes
facilities for input of working fluid into an expansion chamber
(e.g., cylinder) and egress of same, whilst reducing or minimizing
fluid friction losses and also reducing or minimizing mechanical
loading on valves, cam trains and other mechanical components used
to regulate the flow of working fluid through the expander.
[0009] In one aspect, the present disclosure relates to using a
reciprocating or piston and cylinder type engine to expand any
pressurized gas or liquid which converts to gas or mixture of vapor
and liquid, utilizing poppet type valves and with mechanisms which
enable valve opening and closing to be carried out. Various
embodiments may be adapted for operation at essentially any
suitable inlet pressure value.
[0010] In one aspect, the system may include a set of valves which
work in different directions, the inlet valve always opening
outward away from the cylinder and piston contained therein, the
other, the exhaust valve, opening inward or towards the piston. In
various embodiments, this motion of the inlet valve in the opposite
direction to the exhaust valve applies for multiple valve
combinations, as well as single valves
[0011] In another aspect, a desmodromic (also knows as a "positive
in both directions") valve operating system may be used that
enables mechanically operated inward and outward or up and down
motion of both types of valves, inlet and exhaust. In some
embodiments, the desmodromic system is free of the spring closure
mechanisms present in many conventional internal combustion engine
inlet and exhaust valves systems and as, will be described, reduces
or minimizes valve train loading forces, in this particular
context.
[0012] In another aspect, devices and techniques are described
which partially or wholly utilize a cylinder compression pressure
after exhaust stroke, higher then or equal to the inlet pressure,
by design to partially or wholly carry out inlet valve lifting or
upward opening action, thereby minimizing forces on cam trains
and/or eliminating opening cams altogether.
[0013] In various embodiments, the devices and techniques described
herein have the capability to provide an expander of high
isentropic efficiency in the case of expansion of fluids, including
supercritical fluids. This is in contrast to conventional rotating
turbomachines, which typically do not cope well due to greater
fluid friction losses and leakage losses. Various embodiments of
the presently described expansion device may have the higher
isentropic efficiency that available gas expanders, e.g., those
below 1 MW in capacity.
[0014] In another aspect, the devices and techniques described
herein may provide the capability, e.g., in a four cylinder
configuration and with the same valve train but differences in
timing, to act as a two or more stage expander where one or several
high pressure cylinders exhaust into one or more low pressure
cylinders, leading to a highly efficient gas expansion process.
[0015] In one aspect, a method is disclosed of operating a
reciprocating expansion device, the expansion device including at
least one expansion chamber with a reciprocating element, a inlet
to the expansion chamber with at least one outward opening inlet
valve, and an exhaust from the expansion chamber having at least
one inward opening outlet valve, the method including: providing
pressurized working fluid to the inlet; opening the inlet valve in
the outward directed to deliverer pressurized working fluid to the
expansion chamber to expand and to drive a motion of the
reciprocating element; and opening the outlet valve in the inward
direction to allow expanded working fluid to escape the expansion
chamber to the exhaust.
[0016] Some embodiments include opening and closing the inlet and
outlet valves using a desmodromic cam device, said cam device
applying force during both opening and closing movements of the
inlet and outlet valves.
[0017] In some embodiments, each of the inlet and outlet valves is
opened and closed without the use of a spring closure
mechanism.
[0018] Some embodiments include: using an exhaust stroke of the
reciprocating element to drive expanded working fluid out through
the outlet valve; and using pressure generated in the expansion
chamber during the exhaust stroke to apply an outward force to the
inlet valve to assist in opening the inlet valve. In some
embodiments, the pressure generated in the expansion chamber during
the exhaust is greater than the pressure at the inlet on a side
external to the expansion chamber.
[0019] In some embodiments, the applied outward force on the inlet
valve reduces an inlet valve cam opening force on a cam used to
open the inlet valve.
[0020] Some embodiments include providing pressure in the cylinder
to a required value by controlling of the point of closure of the
exhaust valve.
[0021] In some embodiments the opening of the inlet valve is
accomplished using only the outward force to the inlet valve,
generated by a recompression pressure in the cylinder.
[0022] In some embodiments, the inlet valve does not have an
associated opening cam.
[0023] In some embodiments, the inlet valve includes one or more
mechanical latches. In some embodiments, the method includes: using
at least one mechanical latch to hold the inlet valve in a stable
open or a stable closed position during at least a portion of an
operating cycle of the expansion chamber.
[0024] Some embodiments include, during a first portion of the
operating cycle, using the internal pressure of the expansion
chamber to move the inlet valve outward towards a fully open
position; and using at least one mechanical opening latch to hold
the in the fully open position.
[0025] Some embodiments include using the operation of the opening
latch to provide a force which assists in moving the inlet valve
towards the fully open position.
[0026] In some embodiments, the inlet valve includes a mechanical
latch and a spring mechanism. In some embodiments, the method
includes: during a first portion of an operating cycle of the
expansion chamber, using the mechanical latch to maintain the inlet
valve in a closed position; during a second portion of the
operating cycle, releasing the latch, and using pressure inside the
expansion chamber to open the inlet valve; and using the spring
mechanism to return the inlet valve from the open position to the
closed position.
[0027] In some embodiments, the inlet valve is opened using the
pressure inside the expansion chamber without the assistance of a
force from an opening mechanism located external to the expansion
chamber.
[0028] In some embodiments, the inlet valve includes at least one
electromagnet. In some embodiments, the method includes:
controlling the electromagnet to actuate the inlet valve between a
substantially stable open position and a substantially stable open
position.
[0029] In some embodiments, the at least one electromagnet includes
at least a first and a second electromagnets. In some embodiments,
the method includes: switching the first electromagnet to an on
state and the second electromagnet to an off state to maintain the
inlet valve in the stable open position; and switching the first
electromagnet to an off state and the second electromagnet to an on
state to maintain the inlet valve in the stable closed
position.
[0030] In some embodiments, the inlet valve includes an over-center
toggle mechanism having a stable closed and a stable open position.
In some embodiments, the method includes: during a first portion of
the operating cycle of the expansion chamber, using the internal
pressure of the expansion chamber to toggle the inlet valve from
the stable closed position to the stable open position.
[0031] Some embodiments include: during a second portion of the
operating cycle, using a mechanism external to the expansion
chamber to toggle the inlet valve into the stable closed
position.
[0032] In some embodiments, the mechanism external to the expansion
chamber includes at least one selected from the list consisting of:
a cam, a mechanical actuator, a hydraulic actuator, and an
electromechanical actuator.
[0033] In some embodiments, the inlet valve includes a spring
loaded cam driven toggle mechanism. In some embodiments, the method
includes: placing the valve in a closed position by seating a valve
body against a seal, thereby causing a build up of pressure in the
inlet to the expansion chamber; and rotating a cam to drive the
toggle mechanism to apply an opening force on the valve body to
unseat it from the seal, thereby placing the expansion chamber in
fluid communication with the inlet and causing a reduction in inlet
pressure.
[0034] In some embodiments, the force applied on the cam by the
toggle mechanism is less than 20%, 10%, 5%, 1%, or less (e.g., in
the range of 0-30%, or any subrange thereof) of the opening force
applied to the valve body by the toggle mechanism.
[0035] In some embodiments, the reciprocating expansion device
includes: a primary expansion chamber with a primary reciprocating
element, and a secondary expansion chamber with a secondary
reciprocation element. In some embodiments, the method includes:
using fluid exhausted from the primary expansion chamber to drive
the operation of the secondary expansion chamber.
[0036] In some embodiments, the expansion chamber and reciprocating
element include a cylinder with a piston.
[0037] In some embodiments, the reciprocating expansion device
includes at least four piston cylinders.
[0038] Some embodiments include providing a supercritical working
fluid to the inlet of the expansion chamber.
[0039] Some embodiments include implementing at least one
thermodynamic trilateral flash cycle at least in part using the
reciprocating expansion device.
[0040] Some embodiments include implementing at least two cascaded
thermodynamic cycles at least in part using the reciprocating
expansion device.
[0041] Some embodiments include using the reciprocating expansion
device to extract mechanical work from expansion of the working
fluid with an efficiency of at least 90%, 95%, 97%, or more (e.g.
in the range of about 75% to about 100%, or any subrange thereof)
of the thermodynamic limit.
[0042] Some embodiments include using the reciprocating expansion
device to do work at the rate of at least 0.1, 0.5. 1.0, or 10.0
megawatts (e.g. in the range of 0.01-100 megawatts or any subrange
thereof).
[0043] In another aspect, an apparatus including a reciprocating
expansion device is disclosed, the apparatus including: at least
one expansion chamber with a reciprocating element, an inlet to the
expansion chamber with at least one outward opening inlet valve and
configured to receive a pressurized working fluid, an exhaust from
the expansion chamber having at least one inward opening outlet
valve; and a valve drive system. In some embodiments, the valve
drive system is configured to: open the inlet valve in the outward
directed to deliver pressurized working fluid to the expansion
chamber to expand and to drive a motion of the reciprocating
element; and open the outlet valve to allow expanded working fluid
to escape the expansion chamber to the exhaust.
[0044] In some embodiments, the valve drive system includes a
desmodromic cam device, said cam device applying force during both
opening and closing movements of the inlet and outlet valves.
[0045] In some embodiments, during operation, each of the inlet and
outlet valves is opened and closed without the use of a spring
closure mechanism.
[0046] In some embodiments, where the expansion device is
configured to: use an exhaust stroke of the reciprocating element
to drive working fluid out through the outlet valve; and use
pressure generated in the expansion chamber during the exhaust
stroke, after closure of the exhaust valve at a point in the
exhaust stroke, to apply an outward force to the inlet valve to
assist in opening the inlet valve. In some embodiments, the
pressure generated in the expansion chamber during the exhaust
stroke is greater than the pressure at the inlet on a side external
to the expansion chamber.
[0047] In some embodiments, the valve operating system includes an
inlet cam that facilitates opening of the inlet valve, and, during
operation, the applied outward force on the inlet valve reduces the
opening force on the inlet cam.
[0048] In some embodiments, the applied outward force reduces the
opening force on the inlet cam to less than 50%, 75%, 90%, or 95%
(e.g., in the range of about 50% to about 100%, or any subrange
thereof) of the force that would be required for opening in the
absence of the applied outward force.
[0049] In some embodiments, during operation, the opening of the
inlet valve is accomplished using only the outward force to the
inlet valve.
[0050] In some embodiments, the inlet valve does not have an
associated opening cam.
[0051] In some embodiments, where the inlet valve includes one or
more mechanical latches, where: at least one mechanical latch is
configured to hold the inlet valve in a stable open or a stable
closed position during at least a portion of an operating cycle of
the expansion device.
[0052] In some embodiments, during operation, the expansion device
is configured to: during a first portion of the operating cycle,
use the internal pressure of the expansion chamber to move the
inlet valve outward towards a fully open position; and use at least
one mechanical opening latch to hold the in the fully open
position.
[0053] In some embodiments, during operation, the expansion device
is configured to: use the operation of the opening latch to provide
a force which assists in moving the inlet valve towards the fully
open position.
[0054] In some embodiments, the inlet valve includes a mechanical
latch and a spring mechanism, configured such that: during a first
portion of an operating cycle of the expansion device, the
mechanical latch maintains the inlet valve in a closed position;
and during a second portion of the operating cycle, the latch is
released and pressure inside the expansion chamber opens the inlet
valve.
[0055] Some embodiments include: a spring mechanism configured to
return the inlet valve from the open position to the closed
position.
[0056] In some embodiments, the inlet valve is configured to be
opened using the pressure inside the expansion chamber without the
assistance of a force from an opening mechanism located external to
the expansion chamber.
[0057] In some embodiments, the inlet valve includes at least one
electromagnet, and the valve drive system is configured to: control
the electromagnet to actuate the inlet valve between a
substantially stable open position and a substantially stable open
position.
[0058] In some embodiments, at least one electromagnet includes at
least at least a first and a second electromagnets, and the valve
drive system is configured to:: switch the first electromagnet to
an on state and the second electromagnet to an off state to
maintain the inlet valve in the stable open position; and switch
the first electromagnet to an off state and the second
electromagnet to an on state to maintain the inlet valve in the
stable closed position.
[0059] In some embodiments, the inlet valve includes an over-center
toggle mechanism having a stable closed and a stable open position,
and the expansion device is configured to: during a first portion
of the operating cycle of the expansion device, use the internal
pressure of the expansion chamber to toggle the inlet valve from
the stable closed position to the stable open position.
[0060] In some embodiments, the expansion device is configured to:
during a second portion of the operating cycle, using a mechanism
external to the expansion chamber to toggle the inlet valve into
the stable closed position.
[0061] In some embodiments, the mechanism external to the expansion
chamber includes at least one selected from the list consisting of:
a cam, a mechanical actuator, a hydraulic actuator, and an
electromechanically actuator.
[0062] In some embodiments, the inlet valve includes a spring
loaded cam driven toggle mechanism, and where the valve drive
system is configured to: place the valve in a closed position by
seating a valve body against a seal, thereby causing a build up of
pressure in the inlet to the expansion chamber; and rotate a cam to
drive the toggle mechanism to apply an opening force on the valve
body to unseat it from the seal, thereby placing the expansion
chamber in fluid communication with the inlet and causing a
reduction in inlet pressure.
[0063] In some embodiments, the force applied on the cam by the
toggle mechanism is less than 20%, 10%, 5%, 1%, or less (e.g., in
the range of 0-30%, or any subrange thereof) of the opening force
applied to the valve body by the toggle mechanism.
[0064] In some embodiments, the reciprocating expansion device
includes: a primary expansion chamber with a primary reciprocating
element, and a secondary expansion chamber with a secondary
reciprocation element, and is configured to use fluid exhausted
from the primary expansion chamber to drive the operation of the
secondary expansion chamber.
[0065] In some embodiments, the expansion chamber and reciprocating
element include a cylinder with a piston.
[0066] In some embodiments, the reciprocating expansion device
includes at least four piston cylinders.
[0067] In some embodiments, the working fluid at the inlet includes
a supercritical working fluid.
[0068] Some embodiments include a system for implementing at least
one thermodynamic trilateral flash cycle at least in part using the
reciprocating expansion device.
[0069] Some embodiments include a system for implementing at least
two cascaded thermodynamic cycles at least in part using the
reciprocating expansion device.
[0070] In some embodiments, the expansion device is configured to
extract mechanical work from expansion of the working fluid with an
efficiency of at least 90%, 95%, 97%, or more (e.g. in the range of
about 75% to about 100%, or any subrange thereof) of the
thermodynamic limit.
[0071] In some embodiments, the expansion device is configured to
extract mechanical work from expansion of the working fluid with an
efficiency of at least 95% of the thermodynamic limit.
[0072] In some embodiments, the expansion device is configured to
do work at the at least 0.1, 0.5. 1.0, or 10.0 megawatts (e.g. in
the range of 0.01-100 megawatts or any subrange thereof).
[0073] In some embodiments, at least one inlet valve includes a
poppet valve.
[0074] Various embodiments may include an of the above features,
elements, steps, or techniques, either alone or in any suitable
combination.
DESCRIPTION OF THE DRAWINGS
[0075] FIG. 1A and FIG. 1B show views of a desmodromic or positive
opening positive opening cam and valve train. In each figured the
left pane is a head on view, while in FIG. 1A the right pane is a
top down view, and in FIG. 1B the right pane is a side view.
[0076] FIG. 2 illustrates lifting or upward opening twin inlet
valve.
[0077] FIG. 3 illustrates upward opening inlet valve positioned in
cylinder block.
[0078] FIG. 4 is a pressure-volume diagram illustrating the
operation of a cylinder using overcompression to assist or
accomplish inlet valve opening.
[0079] FIG. 5 illustrates a mechanical latch pressure opened inlet
valve.
[0080] FIG. 6 illustrates a mechanical profiled latch pressure
opened inlet valve.
[0081] FIG. 7 illustrates an electromagnetic latching and valve
assist system.
[0082] FIG. 8 illustrates an over-centre spring and toggle pressure
operated inlet valve.
[0083] FIG. 9 illustrates a cam actuated toggle lifter.
[0084] FIG. 10 is an illustration of a heat engine device featuring
cascaded cycles.
[0085] FIG. 11 depicts the upper thermodynamic cycle of the heat
engine of FIG. 10 laid out on a steam T s diagram.
[0086] FIG. 12 depicts the upper thermodynamic cycle of the heat
engine of FIG. 10 laid out on an organic fluid Pressure-Enthalpy
diagram.
[0087] FIG. 13 is a schematic of an exemplary embodiment of a heat
engine device featuring cascaded thermodynamic cycles as depicted
in FIGS. 11 and 12.
[0088] FIG. 14 depicts a thermodynamic cycle featuring feed
preheating laid out on a steam T s diagram.
[0089] FIG. 15 illustrates an exemplary heat engine corresponding
to the thermodynamic cycle of FIG. 12.
[0090] FIG. 16 is a plot of efficiency versus temperature for the
heat engine of FIG. 15.
[0091] FIG. 17 is an illustration of an exemplary heat engine
suitable for use with a low grade heat source.
[0092] FIG. 17A is a plot of cycle efficiency as a function of heat
source return temperature for an exemplary heat engine.
[0093] FIG. 17B. is an illustration of an exemplary heat engine
suitable for use with a low grade heat source featuring a heat
recuperator.
[0094] FIG. 17C is an illustration of an exemplary heat engine
suitable for use with a low grade heat source featuring three
expanders and heat recuperator.
[0095] FIG. 18 depicts the thermodynamic cycle of the heat engine
of FIG. 17 laid out on an organic fluid T s diagram.
[0096] FIG. 18A is a schematic of the thermodynamic cycle of the
heat engine of FIG. 17 accounting for imperfectly isentropic
expansion.
[0097] FIG. 19 is an illustration of an exemplary heat engine
suitable for use with a low grade heat source featuring a secondary
cycle.
[0098] FIG. 20 depicts the thermodynamic cycle of the heat engine
of FIG. 19 laid out on an organic fluid T s diagram.
[0099] FIG. 21 is an illustration of the secondary cycle of the
heat engine of FIG. 19.
DETAILED DESCRIPTION
[0100] The examples presented below describe the operation of
expansion chamber (e.g., piston cylinder) inlet and exhaust valves.
For the sake of convenience and as is conventional in the art, in
these example, a valve which opens by movement of a vale body
element in a direction outward from the expansion chamber is
referred to as an upward opening valve. A valve which opens by
movement of a vale body element in a direction inward the expansion
chamber is referred to as a downward opening valve. However, as
will be understood by one skilled in the art, that the embodiments
described herein are not limited to those where the valves must be
oriented on the top side of the expander device (although in may
typical applications, this will be the case). In various
embodiments, any suitable orientation may be used which maintains
the inward/outward orientation of the valves described in the
examples below.
[0101] In some embodiments, the present invention includes
desmodromic valve operating system which operates poppet valves
within the cylinder heads of a piston and cylinder engine, where
total number of pistons may vary from one to 24 or greater. Some
embodiments may feature multiple stage expansion. For example, in
the case of two stages of expansion, in some embodiments, the
expander may include sets of four cylinders (e.g., as shown in
FIGS. 1A and 1B), where there is one high pressure cylinder
followed by three low pressure cylinders, with exhaust from high
pressure cylinder being directs as inlet to the low pressure
cylinders. In various embodiments, any suitable number of stages
with any suitable number of associated cylinders may be used.
[0102] Referring to FIGS. 1A and 1B, in one embodiment, for each
cylinder and piston (labeled Cyl 1 through Cyl 4) the valve
operating system includes an inlet valve 100 which is lifted off
it's seat 105, away from the cylinder and piston by a mechanism
consisting of two cams primary cam 106 and conjugate cam 107. These
cams respectively bear on two over and under rockers 101 and 102
respectively, which in turn act on the valve stem through lifter
108. The task of the primary cam 106 is to lift or open the valve
100 and that of the conjugate cam 107 is to close or place the
valve 100 back on its seat 105.
[0103] A similar action is performed on the exhaust valve 200,
however in the opposite direction. That is a corresponding primary
cam 206 opens the exhaust valve 200 by lowering it towards the
piston within the cylinder and the conjugate cam 207 closes it by
raising it into it's seat, away from the piston. Note that the
valve action described above are quite unlike those occurring in a
conventional internal combustion (IC) engine, where both sets of
valves open into the cylinder. Similarly the valve timing is also
quite different as compared with a conventional IC engine.
[0104] The relative working modes of the inlet and exhaust valves
can be clearly seen in FIG. 1B, where inlet valves 100 open upwards
and the exhausts valves 200 open downwards, in a typical four
cylinder engine valve train.
[0105] Some embodiments include the provision of more than one
valve per cylinder for inlet purposes. FIG. 2 shows an embodiment
where two inlet valves 109 are operated by a single primary cam 110
and conjugate cam 111 pair, through a bridge lifter 112 running in
guides 113. In this manner more than one valve inlet (or,
additionally or alternatively, exhaust) function per cylinder may
be accommodated by a single desmodromic cam train. In the
particular configuration shown twin inlet valves 113 are used in a
high pressure cylinder with a single exhaust valve (not shown). In
the same manner a twin exhaust valve set up 301 may also be fitted,
resulting in a four valve system, e.g., as shown in FIG. 3. In
various embodiments, any suitable number on inlet and exhaust
valves for a given cylinder may be used. In typical embodiments,
the larger the number of valves per intake or exhaust function the
smaller the flow friction loss experienced.
[0106] In various embodiments, the valve drive system is configured
to ensure proper operation of the upward and downward motion
through the use of cams, without either excessive gap between the
upward rocker and valve which would result in delay and impact or
clearances being too close which would result in "binding" and
imperfect closure or insufficient valve opening.
[0107] For example, in a four cylinder engine (e.g., an IC type
engine) converted to expander type operation, the valve train
configuration may be as shown in FIG. 1A and FIG. 1B. An upward
opening inlet valve 100 or valves is accompanied by a downward
opening exhaust valve 200 or valves, as shown. In the case of a
desmodromic system, the opening and closing cams are configured to
push upward on plunger 108, in the case of the inlet valve with the
closing rocker 102 being out of contact and travelling in an upward
direction, enabling the inlet valve 100 to travel upwards. As the
peak point of the cam 106 contacts rocker 101, as shown, plunger
108 is caused to move upward, opening the inlet valve 100.
[0108] In a similar manner, once the peak in the opening cam 103
moves out of contact, the closing cam 107 is moving the closing
rocker 102 in such a manner as to close the inlet valve 100. By
suitably arranging the shapes of the opening cam 106 and closing
cam 107 and the design of the corresponding contacting rockers 101
and 102, the inlet valve 105 is caused to open or lift off the
valves seat and after the appropriate dwell angle, caused to close
on to it's seat.
[0109] In various embodiments, an expander which includes a
negative (outward) or upward opening inlet valve and a positive
(inward) or downward opening exhaust valve is capable of achieving
very high isentropic efficiencies, e.g., as shown in the
pressure-volume (pV) diagram of FIG. 4.
[0110] In the case shown an expander designed for use with an
organic working fluid is instead being operated on pressurized air.
Starting at the right hand end, position 501 corresponds to Bottom
Dead Center (BDC) of the piston, the pressure in the cylinder has
dropped to it's minimum value (atmospheric pressure in this case)
and the exhaust valve 200 is open. The process 501-502 is the
exhaust stroke, where spent gases are expelled by upward movement
of the piston.
[0111] The exhaust valve 200 closes at position 502. Note that in
various designs, the choice of the position of 502 is completely
discretionary. That is, in various embodiments, the point of
exhaust valve closure may be varied, e.g., by adjustment of the
exhaust cams, an opening cam and a closing cam. The portion 502-503
represents a recompression stroke, wherein pressure in the cylinder
increases to equal or exceed the inlet pressure in the chamber
above the inlet valve. Recompression with pressure increase above
inlet pressure provides an advantage in that it can be actively
utilized to open the inlet valve, independent of or in assistance
to a cam and rocker or other external system.
[0112] The inlet valve closes at point 505 and an adiabatic
expansion takes place from point 505 to BDC before the exhaust
valve opens at BDC. By varying the position n of each closing cam
against the opening cam it is possible to precisely vary the
opening and closing positions for each valve.
[0113] In various embodiments, the thermodynamic cycle shown above
may be tailored to the application at hand (e.g., based on a given
inlet pressure). Iv various embodiments the cycle above may be used
to extract work from the working fluid with efficiency approaching
the thermodynamic limit, e.g., 80%, 90%, 95%, or 99% efficiency or
more, e.g., in the range of 80-100% or any subrange thereof. These
efficiencies may be exhibited at any suitable piston reciprocation
speed, and at any suitable power capacity (e.g. 1 kW, 10 kW, 100,
kW, 1 MW, or more, e.g., in the range of 1-100,000 kW or any
subrange thereof).
[0114] Note that, although one particularly advantages example has
been described above, in various embodiments, the thermodynamic
cycle described above may be modified.
[0115] In some embodiments, initiation of opening of the inlet
valve is carried out using a mechanical latch system, e.g., in
which all upward movement of the inlet valve is provided by virtue
of the compression pressure in the cylinder. In such a system a
rotating or other latch is released as shown in FIG. 5, such that
the inlet valve is free to move upward under pressure. There are
several methods to cause the inlet valve to reseat on it's valve
seat. In some embodiments, one may accelerate an opened valve
downward using a spring which contacts the valve only at a certain
point in it's upward movement. In some embodiments, one may move
the valve downward using a rotating cam which has the sole function
of moving the valve down onto it's seat.
[0116] In the embodiment shown in FIG. 5, a lower latch 201 holds
the valve 100 in a stable closed position by contacting fixed
spacer 203, as shown in the left hand diagram. Before Top Dead
Center (TDC) of a piston stroke, the latch is withdrawn but valve
remain closed due to pressure in valve chamber 205 being higher
than the pressure in working cylinder 206. At or approaching TDC,
the pressure in the working cylinder 206 is configured to rise
above the pressure in inlet chamber 205, e.g., as shown in step
502-503 in FIG. 4. This may ensured by suitably choosing the
exhaust valve closing point 502 in FIG. 4, in relation to the final
clearance volume along step 503-504. For any given clearance volume
503-504, any desired pressure may be achieved in the clearance
volume 503-654. Once valve 207 has moved upward due to overpressure
in cylinder 206, latch 202 is activated in such a manner as to lock
valve 207 in an upper, stable open position, against compression
force in spring 2051.
[0117] In some embodiments, as shown in FIG. 6, the upper latch 202
in the embodiment in FIG. 4 has a profiled shape and is able to
bear against an upper step 204 on the inlet valve 100, from the
moment of valve opening. In this case the profiled shape of the
latch promotes valve lifting and also holds valve open (left hand
pane) until it is time to reseat (right hand pane).
[0118] Referring to FIG. 7, in some embodiments the opening and/or
closing of the inlet valve 100 is facilitated to operate
electromagnetically using two sets of electromagnets 301 and 302,
which would latch and unlatch, depending on valve position and
operations required. In one embodiment, the manner of operation
would be as follows: Just before piston TDC, electromagnet 301
(holding valve 100 in a stable closed position) will be released
and electromagnet 302 energized, such that magnet rider 303 will be
attracted to the upper magnet disk 302. At the point in time where
upward recompression force in cylinder below the valve reaches or
exceeds pressure within inlet chamber, a net upward pressure force
will act on the inlet valve 100 and it will be forced upward. At
the same time, there will be a further attractive force upward
exerted by the switched on electromagnet 302, further enhancing
valve upward movement, until magnet rider 303 is locked against
upper, energized electromagnet 302 in a stable open position. In
this manner any penetration into the chamber which carries hot
inlet fluid will be reduced or completely eliminated-
[0119] In a further embodiment of the invention, a toggle and off
center spring arrangement (sometimes referred to as an over-centre
toggle mechanism) is provided such that the valve 100 is stable in
two positions, ON the seat and OFF the seat, see FIG. 8 (left pane
is on seat, right pane is off seat). Two swing arms 401 and 402 are
provided, tension spring 403 mounted off center such that its
greatest extension occurs when both arms 401 and 402 are in line,
with the valve slightly lifted off it's seat. Also, it provides a
second stable position with the valve fully open, as shown in the
right hand diagram. As such, the spring provides a positive closing
of the valve onto it's seat, in the closed position in the left
hand diagram. The plunger 404 is actuated through a hydraulic
connection through base 405 and has two positions, a fully extended
position (left hand pane) diagram and a retracted position (right
hand pane) In various embodiments, any other suitable type of
actuator may be used.
[0120] The mode of operation is as follows: When the piston below
the inlet valve 100 reaches TDC, the designed overpressure in the
cylinder (point 503 in FIG. 4) causes inlet valve 100 to lift off
it's seat. The toggle 401, 402 and spring 403 is configured such
that the toggle goes over-center, within a few millimeters of
travel and completely lifts the inlet valve off it's seat, to the
second stability position shown in the right hand diagram. The
small hydraulic plunger of valve 100 is withdrawn to its retracted
position well before TDC, as such free movement of the toggle to
it's upper stability positions is enabled. Before the proper valve
cutoff time, the hydraulic plunger in base 405 is activated to push
down on the valve stem and overcome the upward holding force due to
the off center spring. Once the hydraulic plunger downward movement
pushes the valve 100 past the upper stability position, the spring
403 moves the system to it's second stable point, causing it to
seat. Further seating force is provided by the pressure
differential between inlet chamber pressure and the decreasing
pressure in the cylinder.
[0121] In another embodiment of the valve operating mechanism a cam
actuated toggle may be configured as shown in FIG. 8. The left hand
pane shows the valve 100 in a closed position. The right hand pane
shows the valve 100 in an open position. In this case a short valve
opening of distance X is caused by a cam 1501 bearing on a toggle
1502 having a roller 1505. The valve 100 is kept closed by a spring
1503 applying a force to the roller 1505 of the toggle 1502. As the
cam 1501 rotates, it actuates the toggle 1502, lifting and
unseating the valve 100 by a distance X from its seat. As shown,
the cam effective lift distance Z-Y>>X (e.g. 2, 3, 4, 5, 10,
or more times X, e.g., in the range of 2-100 times X or any
subrange thereof) and as such the total force exerted on the valve
100 is much greater than the force on the cam 1501. A mechanical
advantage is created which enables the inlet valve 100 to be lifted
against very high pressures in the inlet chamber, without relying
on gas over-compression pressure in the cylinder.
[0122] The arrangement of FIG. 9 is advantageous in that it
accommodates a reverse seating valve, and features a single cam
design. In some embodiments, a high inlet pressure will force the
valve onto its seat with large forces, e.g., more than about 1000
lbs. Once the valve is moved off of the seat, the pressure will
drop significantly (e.g., by more than 50%, 60%, 70%, 80%, 90%, or
more). Note that controlled valve closing can then be accomplished
using the spring force from spring 1502 on the roller 1505, or, in
some embodiments, another type of closing actuator may be used.
[0123] Expanders of the type described herein may be used in any
suitable type of heat engine or any other system which includes and
expander. For example, expanders of the type described herein may
be used in conjunction with the devices, systems and methods
described in any of the applications incorporated by reference
above.
[0124] For example, one or more expanders of the type described
herein may be employed in a system featuring cascaded thermodynamic
cycles. Referring to FIG. 10, a heat engine device 4000 includes
multiple cascaded thermodynamic cycles (two are shown). An upper
cycle operating on a first working fluid accepts heat from a heat
source at a first temperature T1, rejects heat at a second lower
temperature T2, and yields work (e.g. mechanical work.) The lower
cycle accepts heat rejected by the upper cycle at a temperature T3
less than or about equal to T2. The lower cycle rejects heat into
the surrounding environment (or yet another lower cycle) at a lower
temperature T4. Accordingly, the lower cycle generates useful work
from rejected heat from the upper cycle that otherwise may have
simply gone to waste.
[0125] In some embodiments, the first working fluid of the upper
cycle has a relatively high boiling point, while the second working
fluid of the lower cycle has a relatively low boiling point. For
example, the first working fluid may be pressurized water/steam,
while the second working fluid is a low boiling point fluid, e.g.
an organic fluid such as HCFC 123 or HCFC 134a. In other
embodiments, the organic working fluid may include organic ammonia,
benzene, butane, isobutane, carbon tetrachloride, propane, R-245fa,
R-245ca, toluene, or any other suitable fluid. Accordingly, the
lower cycle is able to operate efficiently using the relatively low
temperature heat rejected from the upper cycle.
[0126] FIG. 13 shows an exemplary heat engine device 5000 featuring
upper and lower cascaded trilateral flash cycles. The upper cycle
operates on a pressurized water/steam working fluid and is depicted
in the temperature-entropy T-s steam table of FIG. 11. The lower
cycle operates on a an organic HCFC 123 fluid pressure-enthalpy
diagram of FIG. 12.
[0127] Considering first the upper cycle, in process 5-1, a liquid
pump 1500 isentropically compresses the water working fluid to
upper working pressure. In process 1-2, a heat exchanger 135
transfers heat from a primary heat source to the compressed water
working fluid. As shown, the heat source is waste heat from a coal
power station at 140 degrees C., which heats the compressed working
fluid from a temperature of about 32 degrees C. to a temperature of
120 degrees C.
[0128] In process 2-3 the heated working fluid undergoes isentropic
(reversible, adiabatic) expansion in an expander 1360, and is
cooled to a temperature of 102 degrees C. As shown, expander 1360
is a reciprocating piston expander, and may incorporate any of the
devices and techniques described herein. For example, expander 1360
may be of the type shown in FIGS. 1A and 1B.
[0129] In process 3-4 heat is recovered from the expanded water
vapor exhausted from the expander and transferred to the HCFC 123
working fluid of the lower cycle using a heat exchanger 1510. In
process 4-5 the water vapor working fluid exiting the heat
exchanger 1510 is condensed back tot the liquid state using a steam
vapor condenser 1370. Note that, in some embodiments, the heat
rejected during this process may also be transferred to heat the
lower cycle working fluid. The condensed water working fluid is
then recirculated to the pump 1500 to begin the cycle anew.
[0130] Considering the lower cycle, this cycle of the heat engine
operates as a conventional trilateral flash cycle on the HCFC 123
working fluid. In process 6-7 a liquid pump 1500 isentropically
compresses the HCFC 123 working fluid to upper working pressure. In
process, 7-8, the pressurized HCFC 12 working fluid is heated to a
temperature of 82 degrees C. in heat exchanger 1510 using heat
rejected from the upper cycle.
[0131] In process 8-9 the heated HCFC 123 working fluid undergoes
isentropic (reversible, adiabatic) expansion in an expander 1390,
and is cooled to a temperature of about 40 degrees C. As shown,
expander 1390 is a reciprocating piston expander and may
incorporate any of the devices and techniques described herein. For
example, expander 1360 may be of the type shown in FIGS. 1A and
1B.
[0132] In process, 9-6 the expanded working fluid exhausted from
the expander 1390 is condensed in fluid condenser 1400, rejecting
heat into the surrounding environment. Note that in some
embodiments, the heat rejected by the lower cycle may be used to
drive a tertiary cycle, etc.
[0133] As shown, all of the mechanical output of both types of
expanders, upper water/vapor based expander 1360 and lower low
boiling point organic based expander 1390 is integrated into a
common shaft 1520 which is then used to turn a single alternator
1530 to generate electrical energy.
[0134] In embodiments described herein, two trilateral flash
cycles, the upper one using water and the lower using a working
fluid with a lower boiling point, are cascaded for purposes of
achieving higher efficiency. In a typical example, recovery useful
energy from the waste heat of a coal power plant stack gas, input
and output parameters were as follows:
TABLE-US-00001 Coal fired power station Capacity 1000 MW flue gas
flow 2.40E+06 M.sup.3/hr Flue gas temp 140 Deg C. Energy in flue
gas 89760 kJ/sec Efficiency 10% power output 13.464 MW
[0135] Therefore useful power generation from waste heat may be
carried out using low grade heat sources, utilizing the proposed
cascaded thermodynamic cycle
[0136] While in both exemplary cycles described above the working
fluid was heated into the wet vapor region, in other embodiments,
the working fluid in one or more cycle may be heated to a
supercritical fluid state.
[0137] As will be understood by those skilled in the art, the
described heat engines may be modified to employ and of the devices
or techniques described herein or in the reference incorporated
above. For example, the heating processes may include the injection
of quantity of working fluid into a chamber (e.g. of a piston), and
the introduction of energy (e.g. via concentrated solar energy
directed through a transparent window in the chamber) to the
quantity of working fluid to vaporize the fluid, as described in
detail above. Any of the cycles may include multiple expanders
and/or bypass preheating devices and techniques described in the
applications incorporated by reference above.
[0138] The general class of liquid to vapor expansion cycles in the
wet vapor and supercritical region with bypass constitute a new
class of thermodynamic cycles and provides enhanced efficiency
possibilities in a multitude of applications: fixed bypass ratio
systems may be used in constant output applications such as
geothermal power generation; and, variable bypass ratio systems may
be considered for hybrid vehicle applications, wherein a low bypass
ratio is used during cruising only to charge a battery at a high
efficiency, with a momentary high bypass ratio used to produce
higher power output for overtaking, etc.
[0139] In some embodiment, it is possible to recover heat by
splitting the working fluid into two parts after a first expansion
process, see FIGS. 14 and 15. In such a case, the cycle diagram is
shown in FIG. 14.
[0140] The cycle process steps are as follows. In process 1-2 the
working fluid is preheated by means of extracted working fluid from
an expansion process, in heat exchanger 1310. In process 2-3 heat
is added to the preheated working fluid from outside source in a
heat exchanger. In process 3-4, a primary expansion of all of the
working fluid occurs, e.g. in piston/cylinder expander 1120, which
may include and of the expander devices and techniques described
herein. As shown, the primary expansion is isentropic (i.e.
reversible and adiabatic). In some embodiments, the primary
expansion may take place in any other suitable type of expander,
e.g. a turbine expander. In some embodiments, mechanical work
extracted during the primary expansion process (e.g. from piston
expander 1120) may be used for any suitable application, e.g. to
drive the shaft of a generator (e.g. a linear generator as shown)
to generate electrical energy.
[0141] The working fluid is then exhausted at point 4 and divided
into two parts in the flow splitter 1290. A first portion of the
working fluid, having a fluid fraction k where 0<k<1 is
diverted into heat exchanger 1310, as a heating fluid used to
preheat the working fluid as described above. In process 4-2'-1
heat is transferred in exchanger 1310 from the first portion (i.e.
the diverted portion) of the working fluid to the condensed and
pressurized working fluid moving from condenser 1030 through pump
1040.
[0142] A second portion of the working fluid, having fluid fraction
1-k, is sent to a second expander 1300. As shown expander 1300 is a
piston expander, e.g., of the type described herein, but any other
suitable expander (e.g. a turbine expander) may be used. In process
4-5 the second portion of the working fluid undergoes further
expansion to the condition at the fluid condenser 1030 denoted as
point 5, with production of additional work. In process 5-6 the
second portion of the working fluid is condensed in the condenser
1030.
[0143] In process 6-6' the first (diverted) and second (undiverted)
portions of the working fluid are mixed at the suction entrance to
the pump. In process 6-1 the combined fluid is pressurization by
the pump, and is ready to be recirculated to start new cycle
[0144] By utilizing a fraction k of the working fluid to preheat
all of the working fluid, a significant efficiency gain is achieved
in the thermodynamic cycle. Not wishing to be bound by theory, the
inventors have found that the overall cycle efficiency may be
calculated by the formula:
Efficiency = ( h 3 - ( 1 - k ) h 5 ) - h 4 k ( h 3 - h 2 )
##EQU00001##
[0145] Where h3 is enthalpy at point 3, h5 is enthalpy at point 5,
h2 is the liquid enthalpy at point 2, h4 is the liquid vapor mix
enthalpy at point 4, k is the fraction of working fluid diverted to
be used in preheating, and T4 is the temperature at point 4. This
simple but elegant formula provides a convenient method of
calculating ideal cycle efficiency.
[0146] FIG. 16 shows an efficiency curve as a function of
temperature T4 for a high pressure cycle with fluid extraction. In
this case the temperature T4 is the intermediate temperature after
the first expansion in expander 112, The basic cycle parameters are
as follows:
TABLE-US-00002 Cycle top temperature T3 600 Deg C. Cycle Max
pressure p3 300 bar a Condensing temperature T5 40 Deg C. Base
efficiency w/o extraction 43% (dashed line in graph)
[0147] Notably, as shown in FIG. 16, the efficiency of the cycles
is improved relative to a cycle without extraction for preheating
over a wide range of intermediate temperatures T4.
[0148] A cycle of this type may have it's highest temperature and
pressure point in the supercritical or subcritical region, in FIG.
14, the presentation is given in the subcritical region. As
described in detail below, a similar construction is applicable in
the supercritical region. The cycle is highly advantageous in that
the primary heat exchanger providing "heat input" and the condenser
1030 may both be much smaller than in a comparable Rankine cycle,
also a higher efficiency is achieved with just one stage of
extraction type feedheating. In typical applications, a Rankine
cycle requires six to nine or more stages of extraction
feedheating, to achieve high efficiencies.
[0149] Referring to FIGS. 17, an exemplary heat engine 2000
suitable for use with a low grade heat source (for example at a
temperature of less than 250 degrees C., less than 200 degrees C.,
or even less, e.g. in the range of 150-250 degrees C.) is
illustrated. The corresponding thermodynamic cycle diagram for the
heat engine 2000 is shown in FIG. 18. As with the embodiment shown
in FIGS. 14 and 15, the heat engine 2000 recovers heat for feed
fluid preheating by splitting the working fluid into two parts
after a first expansion process. However, the heat engine 2000
preferably operates on an working fluid (e.g. an organic fluid)
having a relatively low critical point temperature, for example
less than 250 degrees C., less than 200 degrees C., less than 175
degrees C., less than 150 degrees C., or even less. In some
embodiments, the working fluid critical temperature is in the range
of 150 to 200 degrees C. As detailed below, such a low critical
point working fluid may be readily heated to a supercritical state
prior to expansion using heat from a low grade source.
[0150] Referring to FIG. 17, the heat engine includes a heat
exchanger 2010 for transferring sensible heat from an incoming
fluid (e.g. heated water from a collector field) to the pressurized
cycle working fluid (as shown, organic working fluid R-245fa having
a critical temperature of about 154 degrees C.). As shown the
incoming fluid is at a temperature T=190 degrees C. This heat
transfer is represented in FIG. 18 as process 1-2. As shown, the
pressurized fluid is heated from a liquid state to a supercritical
fluid state at a temperature T.sub.2=180 degrees C.
[0151] The heated supercritical working fluid undergoes an
isentropic expansion process 2-3 in the first high pressure
expander 2020 (e.g., of any of the types described herein). As
shown the first expander is a turbine expander, but any suitable
expander (e.g. a reciprocating piston expander of the type
described above) may be used. Work W.sub.hp (e.g. mechanical work)
is extracted during the expansion process. Referring to FIG. 18,
note that the saturated vapor states of the organic working fluid
has a region of positive gradient. Accordingly, the working fluid
R-245fa becomes progressively drier during expansion process 1-2.
As will be understood by those skilled in the art, this is
advantageous, e.g., in that smaller, less costly expanders may be
used to expand a relatively dry vapor than would be required to
expand a wet vapor.
[0152] The working fluid exhausted from the first expander 2020
enters a flow splitter 2030 which directs a first portion of the
working fluid to second low pressure expander 2040, as indicated by
process 3-4. The flow splitter 2030 directs a second portion of the
working fluid to bypass the second expander 2040, as indicated by
process 3-6.
[0153] The first portion of the working fluid undergoes an
isentropic expansion process 4-5 in the second low pressure
expander 2050. As shown the first expander is a turbine expander,
but any suitable expander (e.g. a reciprocating piston expander of
the type described above) may be used. Work W.sub.lp (e.g.
mechanical work) is extracted during the expansion process. As in
the first expansion process, the working fluid becomes
progressively drier, which, in some embodiments, may advantageously
allow for the use of smaller, less costly expanders.
[0154] In some embodiments, mechanical work extracted from the
first and second expanders 2020 and 2040 may be used to drive a
common shaft, e.g., which may in turn drive a generator to produce
electrical energy. In other embodiments, the work generated by each
of the expanders may be directed to separate applications.
[0155] Each of the first and second expanders may have expansion
ratios greater than 1:1, 2:1:4:1, 8:1; 12:1 or more, e.g. in the
range of 4:1 to 8:1 or 4:1 to 12:1 or any other suitable value. In
some embodiments the expansion ration of the first expander may be
greater than less than or equal to that of the second expander.
[0156] The first portion of the working fluid exhausted from the
second expander 2040 is directed to condenser 2050. The condenser
condenses the expanded vapor back to a liquid or substantially
liquid state in process 5-7. The condenser rejects heat to the
surrounding environment (as shown at temperature T.sub.7=45 degrees
C.).
[0157] The condensed first portion of the working fluid is directed
to the first low pressure pump 2060, which isentropically
pressurized the condensed fluid. The pressurized fluid is them
mixed with the second portion of working fluid that was diverted to
bypass the second low pressure expander 2040. The first and second
portions of the working fluid are mixed in direct contact heat
exchanger 2070 (point 6 in FIGS. 17 and 18). The second portion of
the working fluid is at a higher temperature than the first
portion, and thus operates to preheat the first portion, as shown
in process 8-9.
[0158] In process 9-10 the combined fluid is pressurization by the
second high pressure pump 2080. In process 10-1, the mixed,
preheated, pressurized working fluid is recirculated to start new
cycle.
[0159] A cyclic power generation process of this type with heat
acceptance at a higher temperature and heat rejection at a lower
temperature is governed by the Second Law of Thermodynamics and the
maximum possible efficiency is the Carnot efficiency which is
1-T2/T1 where T1 and T2 are absolute temperatures of the heat
source (e.g. the temperature of incoming water) and heat sink (i.e.
the temperature in the condensing process 5-7) respectively. For
the general conditions given in FIG. 18, Carnot efficiency is
31.3%. The other performance values for this exemplary embodiment
are shown in the chart below.
TABLE-US-00003 Temperature of Source 190 C. Cycle Maximum
temperature 180 C. Cycle heat rejection temperature 45 C. Bypass
ratio 0.5 Ambient temperature 30 Deg C. (average) Isentropic
efficiency 80% Net Cycle Efficiency 17% Specific Net work output 23
kJ/Kg
[0160] An isentropic or expander efficiencies of 80% or more are
achievable for organic fluids such as R-245fa. Because these fluids
become drier as expansion proceeds, the expansion process can
proceed to temperatures near ambient without the fluid becoming
two-phase. This avoids the complications of and the reductions in
expander efficiency of operation in the two phase region. Therefore
utilizing this type of fluid leads to a high cycle efficiency.
Suitable fluids include organic ammonia, benzene, butane,
isobutane, carbon tetrachloride, HCFC 123, HCFC 134a, propane,
R-245fa, R-245ca, toluene, or any other suitable fluid.
[0161] Not wishing to be bound by theory, the inventors have found
that a formula for the theoretical efficiency .eta. for this type
of cycle may be derived, as:
.eta. = 1 - T c T i n - T out ln ( T i n T out ) ##EQU00002##
[0162] Where T.sub.c is the temperature at which the cycle rejects
heat (i.e. T.sub.7 as shown in FIG. 17), T.sub.in is the
temperature of the heat source (T.sub.A as shown in FIG. 17), and
T.sub.out is the temperature at which fluid is returned to the heat
source (T.sub.B as shown in FIG. 17). FIG. 17A shows a plot of
ideal efficiency .eta. for the cycle shown in FIG. 17 as a function
of T.sub.out. As T.sub.out increases from a value of
T.sub.out=T.sub.c=45 degrees C. to a value of
T.sub.out=T.sub.in=190 degrees C., the ideal efficiency is seen to
increase approximately linearly from about 17% to about to Carnot
efficiency of 31%. In general, the ideal efficiency .eta. may be
used as a figure of merit to evaluate the performance of a given
thermodynamic cycle.
[0163] The above formula for cycle efficiency assumes a perfectly
isentropic (i.e., reversible) expansion process (i.e. process 2-5
as shown in FIG. 18) However, a modified formula may be used to
calculate the efficiency of a cycle where the expansion process is
not perfectly isentropic.
[0164] The isentropic efficiency .eta..sub.isent for any gas
expansion process, may be defined as the actual enthalpy change
divided by ideal enthalpy change possible in the process and
applies to reversible, adiabatic processes. FIG. 18A shows a
modification of a thermodynamic cycle of the type shown in FIG. 18
to include some irreversibility in the expansion process. On the
T-s diagram as shown, the vertical solid line T.sub.in-T.sub.c is
an isentropic expansion line, and the dashed line is an imperfect
expansion line, such that the ratio of the enthalpy differences is
the isentropic efficiency. The temperature after irreversible
expansion is Tout' and temperature after partial heat recovery is
T.sub.out''.
[0165] Ideally, the total amount of heat available for recovery,
represented as a temperature difference, is (T.sub.out'-T.sub.out).
However, this whole amount may not available due to imperfect heat
exchanger efficiencies. In such cases, the actual heat recovered is
may represented by the difference between T.sub.out'' and
T.sub.out, given by (T.sub.out''-T.sub.out) where
k = ( T out '' - T out ) ( T out ' - T out ) ##EQU00003##
[0166] Therefore k is a proportionality factor, where 0<k<1,
which accounts for less-than-perfect heat recovery in an actual
heat exchanger.
[0167] Taking into account the isentropic expansion efficiency
.eta..sub.isent and the heat recovery factor k, the cycle
efficiency .eta. may be calculated as:
.eta. = 1 - T c F ( T i n - T out ) ln ( T i n T out ) - ( 1 -
.eta. isent ) ( 1 - k ) ##EQU00004## where ##EQU00004.2## F = ( ( 1
- k ) + k .eta. isent ) . ##EQU00004.3##
[0168] Note that for the special case k=1 and n.sub.isent=1, the
above efficiency formula reduces to that derived in the case of
perfect expansion efficiency and heat recovery.
[0169] As will be understood by those skilled in the art, the above
described heat engines may be modified to employ and of the devices
or techniques described herein. For example, the heating process
1-2 may include the injection of quantity of working fluid into a
chamber (e.g. of a piston), and the introduction of energy (e.g.
via concentrated solar energy directed through a transparent window
in the chamber) to the quantity of working fluid to vaporize the
fluid, as described in detail above.
[0170] Although in the examples above, 50% of the working fluid was
diverted to bypass the second expander 2040, any other suitable
bypass ratio may be used. In some embodiments, the bypass ratio may
be adjust to improve or maximize one or more operating parameters
of the cycle (e.g. net cycle efficiency, work output, etc.). In
various embodiments, one or more of these operating parameters may
be monitored via a suitable sensor, and the bypass ratio adjusted
based on the sensor measurement (e.g. using a servo loop in real
time).
[0171] In some embodiments, heat engine 2000 may be modified to
include one or more additional components. For example, referring
to FIG. 17B, in one embodiment a further modification of the cycle
of FIG. 17 as described above incorporates another heat exchanger,
called a recuperator 2090, to recover additional heat after the end
of the expansion process in the second expander 2040. The heat
engine cycle is identical to that shown in FIG. 17, except that the
fluid at point 5, instead of being sent directly to the condenser
2050, is first diverted through recuperator 209, for transfer of
residual heat to the fluid stream after condensation and prior to
direct contact heat exchanger 207 (processes 5-5A and 8-8A). The
temperature at point 5 is higher than condensing temperature at 5A
and hence heat may be usefully recovered. In this manner additional
heat recovery is facilitated, leading to increase in cycle
efficiency over and above cycle in FIG. 17.
[0172] The calculated efficiency the heat engine 2000 depicted in
FIG. 17B for a variety of exemplary operating parameters is given
in the table below (all temperatures are in degrees C.). The table
shows cycle efficiencies for various values of the efficiency of
the following cycle components: the recuperator 2090, the pumps
2060 and 2080, and the expanders 2020 and 2040.
TABLE-US-00004 Working Fluid R245fa Pump C. Cycle Recuperator effi-
Expander C. C. Ambient effi- efficiency ciency efficiency T.sub.2
T.sub.7 Temp. ciency 0.9 0.8 0.6 200 45 35 0.1491 0.9 0.8 0.7 200
45 35 0.1755 0.9 0.8 0.8 200 45 35 0.2008 0.9 0.8 0.9 200 45 35
0.2249 0.95 0.8 0.6 200 45 35 0.151 0.95 0.8 0.7 200 45 35 0.1776
0.95 0.8 0.8 200 45 35 0.2029 0.95 0.8 0.9 200 45 35 0.2271 0.95
0.8 0.6 200 40 35 0.1582 0.95 0.8 0.7 200 40 35 0.1854 0.95 0.8 0.8
200 40 35 0.2113 0.95 0.8 0.9 200 40 35 0.2359 0.9 0.8 0.6 200 40
35 0.1561 0.9 0.8 0.7 200 40 35 0.1832 0.9 0.8 0.8 200 40 35 0.209
0.9 0.8 0.9 200 40 35 0.2337
[0173] Generally the incorporation of both feed water heating and
recuperation after final expansion has result in a significant
practical cycle efficiency improvement. Note that cycle
efficiencies of greater than 17%, e.g., up to about 24% or more may
be achieved. In some embodiments, the efficiency may approach the
theoretical Carnot efficiency (equal to 1-T.sub.2/T.sub.7). In some
embodiments, the cycle efficiency may be in the range of about 15%
to about 25%.
[0174] Referring to FIG. 15C, in one embodiment, heat engine 2000
includes a third, still lower pressure expander 2100 (e.g., of any
of the types described herein) positioned after low pressure
expander 2040. A second flow splitter 2030A is positioned between
expanders 2040 and 2100. Flow splitter 2030A directs a portion of
the working fluid exiting the second expander 2040 to bypass the
third expander 2100. This portion of the working fluid is directed
to feed water heater 2070A, to direct contact heat exchanger 2070A,
which is paired with pump 2080A.
[0175] As will be evident to one skilled in the art, any number of
additional heat expanders may be included in a similar fashion,
each capable of extracting mechanical work Flow splitters
positioned between some or all of the expanders to allow extraction
of working fluid to be used for feed fluid heating.
[0176] The calculated efficiency the heat engine 2000 depicted in
FIG. 17C for a variety of exemplary operating parameters is given
in the table below (all temperatures are in degrees C.). The table
shows cycle efficiencies for various values of the efficiency of
the following cycle components: the recuperator 2090, the pumps
2060, 2080 and 2080A, and the expanders 2020, 2040, and 2100.
[0177] Generally the incorporation of both feed water heating and
recuperation after final expansion has resulted in a significant
practical cycle efficiency improvement. Note that cycle
efficiencies of greater than 17%, e.g., up to about 24% or more may
be achieved. In some embodiments, the efficiency may approach the
theoretical Carnot efficiency (equal to 1-T.sub.2/T.sub.7). In some
embodiments, the cycle efficiency may be in the range of about 15%
to about 25%.
TABLE-US-00005 recup Pump T2 T7 T eff eff Exp eff cycle cycle
ambient Cyc eff 0.9 0.8 0.6 200 45 35 0.1514 0.9 0.8 0.7 200 45 35
0.1774 0.9 0.8 0.8 200 45 35 0.2024 0.9 0.8 0.9 200 45 35 0.2266
0.95 0.8 0.6 200 45 35 0.1533 0.95 0.8 0.7 200 45 35 0.1793 0.95
0.8 0.8 200 45 35 0.2044 0.95 0.8 0.9 200 45 35 0.2283 0.95 0.8 0.6
200 40 35 0.1606 0.95 0.8 0.7 200 40 35 0.1875 0.95 0.8 0.8 200 40
35 0.2133 0.95 0.8 0.9 200 40 35 0.2381 0.9 0.8 0.6 200 40 35
0.1587 0.9 0.8 0.7 200 40 35 0.1856 0.9 0.8 0.8 200 40 35 0.2114
0.9 0.8 0.9 200 40 35 0.2362
[0178] Referring to FIGS. 19 and 20, in some embodiments the heat
engine 2000 may be modified to include a secondary thermodynamic
cycle heat engine (labeled C) which converts the thermal energy
from the diverted second portion of the working fluid to other form
of energy (e.g. mechanical work). As shown, heat exchanger 3010
transfers heat at a first temperature (e.g. about 100 deg C.) from
the diverted fluid to drive cycle C to generate mechanical work
W.sub.C. Cycle C rejects heat to the surrounding environment at a
lower temperature (e.g. 45 degrees C.).
[0179] As will be understood by one skilled in the art, an
increased amount of mechanical work extracted from the diverted
fluid will lead to a decreased cycle efficiency for heat engine
2000. Referring to FIG. 20, the dashed arrows indicate the
operation of the cycle of heat engine 2000 at different values of
work extracted. As more work is extracted, less feed fluid
preheating is provided by the diverted fluid, leading to a decrease
in cycle efficiency. Suitable values for the amount of extracted
work can be selected based on the application at hand.
[0180] FIG. 21 shows a more detailed view of an exemplary
embodiment of secondary cycle C. As shown, cycle C is a single
expander trilateral flash cycle. In process 1-2, the second portion
of working fluid from the primary cycle transfers heat to the
working fluid of secondary cycle C. In the example shown, the
incoming fluid is at a temperature of 130 degrees C., and heats the
working fluid to a temperature of 120 degrees C. In process 2-3,
the heated working fluid is directed to an expander (a piston or
turbine expander). In process 3-4, the heated working fluid
undergoes isentropic expansion in the expander to yield mechanical
work. In process 4-5, the expanded working fluid is condensed,
rejecting heat to the surrounding environment at a temperature of
45 degrees C. In process 5-6, the condensed working fluid is
repressurized, and in process 6-1 the repressurized fluid is
recirculated to start the cycle anew.
[0181] Although FIG. 21 shows a trilateral flash cycle, any
suitable thermodynamic cycle may be used to extract mechanical work
from the second portion of the working fluid of heat engine 2000.
Other heat engine types include a Stirling cycle, a Rankine cycles,
or any of the cycles described herein. The cycles may use any
suitable organic or inorganic fluid, including any of the working
fluids described herein. In various embodiments the working fluid
can be heated to a state in the liquid-vapor region, or in the
supercritical region.
[0182] Various example have been presented of expanders and
thermodynamic cycles which operate without combustion or other
substantial energy generating chemical reaction involving the
working fluid. However, it is to be understood that in some
embodiments, combustion or other chemical reactions may be
used.
[0183] Although a number of particularly advantageous examples have
been given above featuring piston cylinder type reciprocating
expanders, it will be understood that other expanders, e.g., other
types of reciprocating expanders may be used. Some embodiments may
use scroll type expanders, or other expander types known in the
art.
[0184] The scope of the present invention is not limited by what
has been specifically shown and described hereinabove. Those
skilled in the art will recognize that there are suitable
alternatives to the depicted examples of materials, configurations,
constructions and dimensions. Numerous references, including
patents and various publications, are cited and discussed in the
description of this invention. The citation and discussion of such
references is provided merely to clarify the description of the
present invention and is not an admission that any reference is
prior art to the invention described herein. All references cited
and discussed in this specification are incorporated herein by
reference in their entirety.
[0185] While various inventive embodiments have been described and
illustrated herein, those of ordinary skill in the art will readily
envision a variety of other means and/or structures for performing
the function and/or obtaining the results and/or one or more of the
advantages described herein, and each of such variations and/or
modifications is deemed to be within the scope of the inventive
embodiments described herein. More generally, those skilled in the
art will readily appreciate that all parameters, dimensions,
materials, and configurations described herein are meant to be
exemplary and that the actual parameters, dimensions, materials,
and/or configurations will depend upon the specific application or
applications for which the inventive teachings is/are used. Those
skilled in the art will recognize, or be able to ascertain using no
more than routine experimentation, many equivalents to the specific
inventive embodiments described herein. It is, therefore, to be
understood that the foregoing embodiments are presented by way of
example only and that, within the scope of the appended claims and
equivalents thereto, inventive embodiments may be practiced
otherwise than as specifically described and claimed. Inventive
embodiments of the present disclosure are directed to each
individual feature, system, article, material, kit, and/or method
described herein. In addition, any combination of two or more such
features, systems, articles, materials, kits, and/or methods, if
such features, systems, articles, materials, kits, and/or methods
are not mutually inconsistent, is included within the inventive
scope of the present disclosure.
[0186] The above-described embodiments can be implemented in any of
numerous ways. For example, the embodiments may be implemented
using hardware, software or a combination thereof.
[0187] Also, various inventive concepts may be embodied as one or
more methods, of which an example has been provided. The acts
performed as part of the method may be ordered in any suitable way.
Accordingly, embodiments may be constructed in which acts are
performed in an order different than illustrated, which may include
performing some acts simultaneously, even though shown as
sequential acts in illustrative embodiments.
[0188] All definitions, as defined and used herein, should be
understood to control over dictionary definitions, definitions in
documents incorporated by reference, and/or ordinary meanings of
the defined terms.
[0189] Variations, modifications and other implementations of what
is described herein will occur to those of ordinary skill in the
art without departing from the spirit and scope of the invention.
While certain embodiments of the present invention have been shown
and described, it will be obvious to those skilled in the art that
changes and modifications may be made without departing from the
spirit and scope of the invention. The matter set forth in the
foregoing description and accompanying drawings is offered by way
of illustration only and not as a limitation.
* * * * *