U.S. patent application number 12/438945 was filed with the patent office on 2010-11-18 for heat engine system.
Invention is credited to Colin Buckland, Patrick Joseph Glynn.
Application Number | 20100287934 12/438945 |
Document ID | / |
Family ID | 39106404 |
Filed Date | 2010-11-18 |
United States Patent
Application |
20100287934 |
Kind Code |
A1 |
Glynn; Patrick Joseph ; et
al. |
November 18, 2010 |
Heat Engine System
Abstract
A heat engine system for producing work by expanding a working
fluid comprising first and second components, the system
comprising, an apparatus for combining the second component of the
working fluid as a liquid with the first component, the first
component being a gas throughout the system, a compressor for
compressing the first component, a pump for compressing at least
most of the second component, a heater for heating the first and
second components, an expander for expanding the first and second
components to produce the work, and a recuperator for transferring
at least some of the energy of the working fluid from the outlet of
the expander, to the working fluid from the outlet of the
apparatus, wherein a substantial portion of the energy transferred
in the recuperator is at least a portion of the latent heat of the
second component from the outlet of the expander.
Inventors: |
Glynn; Patrick Joseph;
(Queensland, AU) ; Buckland; Colin; (Queensland,
AU) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER, EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Family ID: |
39106404 |
Appl. No.: |
12/438945 |
Filed: |
August 24, 2007 |
PCT Filed: |
August 24, 2007 |
PCT NO: |
PCT/AU07/01226 |
371 Date: |
May 6, 2010 |
Current U.S.
Class: |
60/645 ;
60/643 |
Current CPC
Class: |
F28D 20/026 20130101;
F01K 17/06 20130101; Y02E 60/145 20130101; F01K 21/04 20130101;
Y02E 60/14 20130101 |
Class at
Publication: |
60/645 ;
60/643 |
International
Class: |
F01K 27/00 20060101
F01K027/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 25, 2006 |
AU |
2006904633 |
Aug 25, 2006 |
AU |
2006904634 |
Claims
1. A heat engine system for producing work by expanding a working
fluid comprising first and second components, the system
comprising, an apparatus for combining the second component of the
working fluid as a liquid with the first component, the first
component being a gas throughout the system, a compressor for
compressing the first component, a pump for compressing at least
most of the second component, a heater for heating the first and
second components, an expander for expanding the first and second
components to produce the work, and a recuperator for transferring
at least some of the energy of the working fluid from the outlet of
the expander, to the working fluid from the outlet of the
apparatus, wherein a substantial portion of the energy transferred
in the recuperator is at least a portion of the latent heat of the
second component from the outlet of the expander.
2. A heat engine system as claimed in claim 1, wherein the
apparatus is arranged to spray the liquid second component into a
space having the first component therein.
3. A heat engine system as claimed in claim 1, wherein the
apparatus is arranged to diffuse the first component into the
liquid second component.
4. A heat engine system as claimed in any one of the preceding
claims, wherein the recuperator is in the form of a shell and tube
heat exchanger.
5. A heat engine system as claimed in any one of the preceding
claims, wherein the recuperator is in the form of a falling film
condenser.
6. A heat engine system as claimed in any one of the preceding
claims, wherein the recuperator is arranged to provide separation
of a liquid fraction of the working fluid from a gaseous fraction
upon cooling of the working fluid from the outlet of the
expander.
7. A heat engine system as claimed in any one of the preceding
claims, wherein the system also comprises at least one cooler for
cooling the first and/or second components prior to combining them
in the apparatus.
8. A heat engine system as claimed in claim 7, wherein at least one
of the cooler comprises an intercooler in the compressor to provide
interstage cooling of the first component.
9. A heat engine system as claimed in either one of claim 7 or
claim 8, wherein the or at least one of at least one cooler
comprises a post compressor cooler for cooling the first component
after it has been compressed.
10. A heat engine system as claimed in any one of claims 7 to 9,
wherein the or at least one of at least one cooler comprises a
pre-compressor cooler for cooling the first component prior to
being compressed in the compressor.
11. A heat engine system as claimed in any one of claims 7 to 10,
wherein the or at least one of at least one cooler comprises a
liquid cooler for cooling the liquid second component.
12. A heat engine system as claimed in any one of the preceding
claims, wherein the pump compresses at least most of the liquid
second component to a pressure above the ambient pressure.
13. A heat engine system as claimed in any one of the preceding
claims, wherein the pump compresses the liquid second component to
at or about the pressure to which the compressor compresses the
first component.
14. A heat engine system as claimed in any one of the preceding
claims, wherein the system also comprises a condenser for cooling
the working fluid from the expander after it exits the
recuperator.
15. A heat engine system as claimed in claim 14, wherein the
condenser is arranged to substantially condense the second
component of the working fluid from the expander to a liquid.
16. A heat engine system as claimed in either one of claim 14 or
claim 15, wherein the condenser is a separator for separating the
second component as it condenses from the first component.
17. A heat engine system as claimed in any one of the preceding
claims, wherein the system is a closed system having substantially
no mass inputs or outputs during operation of the system, other
than replacement of incidental losses.
18. A heat engine system as claimed in any one of the preceding
claims, the system also comprising an energy transfer controller
for controlling the energy transfer in the recuperator during
operation of the system.
19. A heat engine system as claimed in any one of the preceding
claims, wherein the system also comprises a mass flow controller
for controlling the mass flow rate of the second component relative
to the mass flow rate of the first component.
20. A heat engine system as claimed in any one of the preceding
claims, wherein the first and second components of the working
fluid are substances which are substantially inert with respect to
each other.
21. A heat engine system as claimed in any one of the preceding
claims, wherein the second component is a substance which has a
high volumetric expansion ratio from liquid to gas.
22. A heat engine system as claimed in any one of the preceding
claims, wherein the first component is a substance which is highly
compressible as a gas.
23. A heat engine system as claimed in any one of the preceding
claims, wherein the first component is nitrogen and the second
component is water.
24. A heat engine system as claimed in any one of the preceding
claims, wherein the heater comprises at least one volume of
material arranged to be heated to at or above the melting
temperature of the material, the heater also comprising passages
through the at least one volume of material for the flow
therethrough of the working fluid.
25. A heat engine system as claimed in claim 24, wherein the at
least one volume of material is heated using a heating fluid
flowing through space through the at least one volume of
material.
26. A heat engine system as claimed in either one of claim 24 or
25, wherein the heater comprises at least two volumes of material,
the materials in the volumes being different and having different
melting temperatures.
27. A heat engine system as claimed in claim 26, wherein the
materials are of progressively decreasing melting temperatures from
the first volume to the last volume, the passages being arranged
for the flow of the working fluid through the last volume first and
the first volume last.
28. A heat engine system as claimed in claim 25, wherein the
working fluid is arranged to flow through the at least one volume
of material countercurrently to the flow of the heating fluid.
29. A heat engine system as claimed in any one of claims 24 to 28,
wherein at least one of the volumes of material contains a mixture
of two or more different materials.
30. A heat engine system as claimed in claim 29, wherein one of the
materials in the mixture of materials of the or each volume is for
improving the heat transfer of the or each volume of material.
31. A heat engine system as claimed in either one of claim 29 or
30, wherein one of the materials in the mixture of materials of the
or each volume is for effecting the melting temperature of the or
each volume of material.
32. A method for producing work, the method comprising the steps
of: compressing a first component of a working fluid in a
compressor, the first component being a gas at all times during the
method; at least most of compressing a second component of the
working fluid as a liquid in a pump; combining the second component
as a liquid with the first component in an apparatus; heating the
combined first and second components in a heater; expanding the
heated first and second components to produce the work in an
expander; and transferring in a recuperator at least some of the
energy of the working fluid after it has been expanded to the
working fluid prior to it being heated in the heater, wherein a
substantial portion of the energy transferred is at least a portion
of the latent heat of the second component after the working fluid
has been expanded in the expander.
33. A method as claimed in claim 32, wherein the step of
transferring at least some of the energy in the recuperator
converts at least some of the second component from liquid to gas
prior to it being heated in the heater.
34. A method as claimed in either one of claim 32 or 33, wherein
the step of transferring at least some of the energy in the
recuperator converts at least some of the second component from gas
to liquid after it has been expanded in the expander.
35. A method as claimed in any one of claims 32 to 34, wherein the
method is a closed cycle method also comprising the step of
repeating the steps of the method performed on the working fluid
after at least some of its energy has been transferred in the
recuperator to the working fluid which is yet to be heated in the
heater.
36. A method as claimed in any one of claims 32 to 35, the method
also comprising the step of returning the first component to the
compressor.
37. A method as claimed in any one of claims 32 to 36 the method
also comprising the step of returning at least most of the second
component to the pump.
38. A method as claimed in any one of claims 32 to 37, the method
also comprising the step of cooling the first and/or second
components prior to the step of combining them.
39. A method as claimed in claim 38, wherein the cooling step
comprises cooling the first component between at least two stages
of the compressor using an intercooler.
40. A method as claimed in either one of claim 38 or 39, wherein
the cooling step comprises cooling the first component after the
step of compressing the first component.
41. A method as claimed in any one of claims 38 to 40, wherein the
cooling step comprises cooling the first component prior to the
step of compressing the first component.
42. A method as claimed in any one of claims 38 to 41, wherein the
cooling step comprises cooling the second component prior to
combining the second component with the first component.
43. A method as claimed in any one of claims 32 to 42, wherein the
method comprises the step of maintaining the temperature of the
first component, prior to the step of combining it with the second
component, to a temperature which is less than one which would
cause vaporisation of the second component during the combining
step.
44. A method as claimed in any one of claims 32 to 43, wherein the
method also comprises a step of separating a liquid fraction of the
working fluid from a gaseous fraction after the working fluid has
been expanded.
45. A method as claimed in claim 44, wherein the step of separating
occurs at least partially in the recuperator.
46. A method as claimed in either one of claim 44 or 45, wherein
the step of separating comprises separating at least most of the
second component as a liquid from the first component as a gas.
47. A method as claimed in claim 46, wherein the step of separating
the first component from the second component comprises cooling the
working fluid to condense most of the second component.
48. A method as claimed in any one of claims 32 to 47, wherein the
method also comprises the step of controlling the energy
transferred in the recuperator.
49. A method as claimed in claim 48, wherein the step of
controlling the energy transferred in the recuperator comprises
changing the conditions of the working fluid prior to expanding it
in the expander.
50. A method as claimed in either one of claim 48 or 49, wherein
the step of controlling the energy transferred in the recuperator
comprises changing the amount of the second component which is
combined with the first component in the apparatus.
51. A method as claimed in any one of claims 32 to 50, wherein the
method also comprises the step of controlling the mass flow rate of
the second component relative to the mass flow rate of the first
component.
52. A method as claimed in any one of claims 32 to 51, wherein the
step of heating comprises flowing the combined first and second
components through at least one volume of material which is heated
to at or above the melting temperature of the material.
53. A method as claimed in claim 52, wherein the step of heating
also comprises heating the at least one volume of material using a
heating fluid.
54. A method as claimed in claim 53, wherein the step of heating
comprises flowing the heating fluid through the at least one volume
material in a counter current direction to the flow of the combined
first and second components.
55. A method as claimed in any one of claims 32 to 54, wherein the
step of heating comprises heating the working fluid to a
super-critical gas.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a heat engine system and to
a method for producing work.
BACKGROUND OF THE INVENTION
[0002] A heat engine is a system arranged to convert thermal energy
to mechanical work. The heat engine does this by transferring
energy from a high temperature heat source (T.sub.H) to a low
temperature heat sink (T.sub.L). The efficiency of any heat engine
is understood to be determined by, amongst other factors, the
difference in temperature between the heat source and the heat
sink. The efficiency of various heat engines currently in use range
from 3% to about 60%. Most automotive engines have an efficiency of
approximately 25% and supercritical coal-fired power stations have
an efficiency of approximately 35-41%.
[0003] Because the efficiency of any heat engine is understood to
be dependent on the temperature gradient between the heat source
and heat sink, many attempts have been made to increase heat engine
efficiencies by increasing this temperature gradient. It is
generally understood that in order to increase the temperature
gradient in a heat engine, then the temperature of the heat source
has to be raised, because the temperature of the heat sink is
limited by the atmospheric temperature of the Earth.
[0004] Theoretically, the most efficient heat engine is defined by
the Carnot cycle and comprises a boiler, a turbine, a condenser and
a pump. Under the Carnot cycle, the working fluid undergoes
reversible isothermal heating from the high temperature reservoir
in the boiler, reversible adiabatic expansion of the working fluid
with a reduction in temperature from the high temperature (T.sub.H)
to the low temperature (T.sub.L), reversible isothermal cooling of
the working fluid to the low temperature reservoir in the
condenser, and reversible adiabatic compression of the working
fluid with an increase in temperature from T.sub.L to T.sub.H in
the pump. The thermal efficiency (.eta..sub.TH) of a heat engine
operating according to the Carnot cycle is defined by the
equation:
.eta..sub.TH=1-T.sub.L/T.sub.H.
[0005] In practice, however, it is not possible to operate a heat
engine according to the ideal Carnot cycle because none of the
process steps are truly "reversible". A reversible process is an
ideal process that once having taken place can be reversed and in
doing so leave no change in either the system or its surroundings.
A number of factors are responsible for the processes in the Carnot
cycle being irreversible, including friction losses in the
system.
[0006] An alternative, but not as efficient, cycle for operating a
heat engine is the Rankine cycle. The ideal Rankine cycle involves
reversible adiabatic compression from a low pressure to a high
pressure by the pump, constant pressure (isobaric) heat transfer
from the high temperature heat source in the boiler, reversible
adiabatic expansion from the high pressure to the low pressure in
the turbine, and a constant pressure (isobaric) transfer of heat
from the working fluid to the low temperature heat sink in the
condenser.
[0007] The Rankine cycle differs from the Carnot cycle primarily in
that complete condensation of the working fluid from a vapour to a
liquid in the condenser occurs in the Rankine cycle. The reason for
doing this is that whilst it reduces the efficiency of the heat
engine, in practice, it is difficult for a pump to handle a mixture
of liquid and vapour as is the case in the Carnot cycle. A further
difference is that if the working fluid is heated to a superheated
vapour in the boiler, in the Carnot cycle all the heat transfer is
at a constant temperature and hence during this process the
pressure must be reduced. This means that the heat must be
transferred to the vapour as it undergoes an expansion process
(which is difficult to carry out in practice), as opposed to the
Rankine cycle in which the vapour is superheated at a constant
pressure. The isobaric heat transfer process in the Rankine cycle
is easier to achieve in practice than the isothermal process in the
Carnot cycle.
[0008] Most common power generation plants, including coal fired
power generation plants operate according to the Rankine cycle. In
practice, however, heat engines operating according to the Rankine
cycle have a lesser efficiency than the maximum theoretical
efficiency (ie. the efficiency of the ideal Rankine cycle) for
similar reasons to those outlined for the Carnot cycle above.
[0009] Another cycle is the Brayton cycle. The Brayton cycle
operates similarly to the Rankine cycle except that the working
fluid exists only in the gaseous phase throughout the cycle (ie.
the Brayton cycle does not involve condensing and boiling of the
working fluid). In a closed Brayton cycle, the system involves
isentropic compression, followed by isobaric heating, before
isentropic expansion of the working fluid occurs to produce work,
followed by isobaric cooling of the working fluid. Gas turbines
generally operate according to an open Brayton cycle, in which a
combustible fuel is added to the working fluid after the
compressor, whereupon combustion of the fuel raises the temperature
of the working fluid prior to it being expanded in the turbine to
produce work. The exhaust from the turbine containing working fluid
mixed with products of the combustion of the fuel is sent to waste
and not returned to the inlet of the compressor.
[0010] Variations on the Rankine cycle, in order to increase the
efficiency of the heat engine, have been considered. Two such
variations include the Rankine cycle with reheat and the
regenerative Rankine cycle. In the Rankine cycle with reheat, the
heat engine comprises two turbines in series. Working fluid as a
vapour from the boiler at high pressure enters the first turbine
where it is expanded to a lower pressure. The reduced pressure
vapour exiting the first turbine re-enters the boiler where it is
reheated before passing through the second turbine which operates
at lower pressures. One advantage of this system is that reheating
of the working fluid between the turbines prevents the working
fluid from condensing from a vapour to a liquid during expansion in
the turbines which could result in significant damage to the
turbine.
[0011] The regenerative Rankine cycle involves preheating of the
working fluid prior to its entry to the boiler by splitting a small
portion of steam from an intermediary stage in the turbine and
mixing it with the liquid working fluid after it has been cooled in
the condenser in a "feed water heater" which is located at an
intermediary pumping stage prior to the inlet of the working fluid
to the boiler.
[0012] Many other attempts have been made to increase the
efficiency of real heat engines, such as the combined
Brayton-Rankine cycle or COGAS cycle, which involves using the hot
exhaust gas from a gas combustion heat engine operating according
to the Brayton cycle as the heat source for the boiler of a second
heat engine operating according to the Rankine cycle.
[0013] However, the efficiencies of all real heat engines remain
significantly limited, and improvements which increase the
efficiency of power and refrigeration production are still
sought.
SUMMARY OF THE INVENTION
[0014] According to a first aspect of the present invention, there
is provided a heat engine system for producing work by expanding a
working fluid comprising first and second components, the system
comprising, an apparatus for combining the second component of the
working fluid as a liquid with the first component, the first
component being a gas throughout the system, a compressor for
compressing the first component, a pump for compressing at least
most of the second component, a heater for heating the first and
second components, an expander for expanding the first and second
components to produce the work, and a recuperator for transferring
at least some of the energy of the working fluid from the outlet of
the expander, to the working fluid from the outlet of the
apparatus, wherein a substantial portion of the energy transferred
in the recuperator is at least a portion of the latent heat of the
second component from the outlet of the expander.
[0015] In an embodiment, the apparatus comprises an injector.
[0016] In another embodiment, the apparatus comprises an
atomiser.
[0017] In an embodiment, the apparatus is arranged to spray the
liquid second component into a space having the first component
therein.
[0018] In another embodiment, the apparatus is a diffuser.
[0019] In an embodiment, the apparatus is arranged to diffuse the
first component into the liquid second component.
[0020] In an embodiment, the apparatus comprises multiple
injectors, atomisers or diffusers.
[0021] In an embodiment, the apparatus is located between the
compressor and the recuperator, to enable the liquid second
component to be combined with the gaseous first component after it
has been compressed.
[0022] Preferably, there is also some sensible heat transferred in
the recuperator.
[0023] Preferably, a substantial portion of the latent heat of the
second component is transferred in the recuperator.
[0024] In an embodiment, the recuperator converts at least some of
second component from the outlet of the apparatus from liquid to
gas.
[0025] In an embodiment, the recuperator converts at least some of
the second component from the outlet of the expander from gas to
liquid.
[0026] In an embodiment, the recuperator is generally in the form
of a shell and tube heat exchanger.
[0027] In an embodiment, the recuperator is generally in the form
of a falling film condensor.
[0028] In an embodiment, the recuperator is arranged to provide
separation of a liquid fraction of the working fluid from a gaseous
fraction upon cooling of the working fluid from the outlet of the
expander.
[0029] In an embodiment, the recuperator comprises a boiling side
and a condensing side.
[0030] In an embodiment, working fluid from the outlet of the
apparatus enters the boiling side of the recuperator where the
second component of the working fluid substantially boils as it
receives energy from the working fluid on the condensing side.
[0031] In an embodiment, working fluid from the outlet of the
expander enters the condensing side of the recuperator where the
second component of the working fluid substantially condenses as it
loses energy to the working fluid on the boiling side.
[0032] In an embodiment, the condensing side of the recuperator
comprises a liquid separator basin that collects the liquid second
component for recycling in the system.
[0033] In an embodiment, the boiling side of the recuperator is the
tubes of a shell and tube heat exchanger, and the condensing side
is the shell of a shell and tube heat exchanger.
[0034] In an embodiment, the system comprises multiple recuperators
connected in parallel and/or series.
[0035] In an embodiment, the pressure at the inlet to the expander
is the pressure to which the first component is compressed in the
compressor, less any losses in the system therebetween. Compression
of the first component of the working fluid also increases its
temperature.
[0036] In an embodiment, the compressor compresses a small portion
of the second component as a gas in addition to the first
component.
[0037] In an embodiment, the compressor is any suitable compressor
such as an axial, centrifugal, reciprocating or scroll compressor
for example.
[0038] In an embodiment, the system comprises multiple compressors
connected in parallel and/or series.
[0039] In an embodiment, the system also comprises at least one
cooler for cooling the first and/or second components prior to
combining them in the apparatus.
[0040] In an embodiment, at least one of the coolers comprises an
inter-cooler in the compressor to provide inter-stage cooling of
the first compressor.
[0041] In an embodiment, at least one of the coolers comprises a
post compressor cooler for cooling the first component after it has
been compressed.
[0042] In another embodiment, at least one of the coolers comprises
a pre-compressor cooler for cooling the first component prior to it
being compressed in the compressor.
[0043] In an embodiment, the at least one cooler has a cooling
source.
[0044] In an embodiment, the cooling source is cooling water,
ambient air or any suitable refrigeration system to which heat may
be rejected.
[0045] In an embodiment, the heat rejected to the at least one
cooler may be used as a heat source for any other suitable process
such as heating hot water, creating low pressure steam,
desalination, as the heat input to a heat pump vapour compression
system or as the heat input for any low temperature power
generation or refrigeration cycle.
[0046] In an embodiment, the at least one cooler comprises a liquid
cooler for cooling the liquid second component.
[0047] In another embodiment, the liquid second component when
combined with the first component by the apparatus is at ambient
temperature.
[0048] In these embodiments, the second component when combined
with the first component cools the first component.
[0049] Preferably, the at least one cooler acts to ensure that the
temperature of the first component entering the apparatus is less
than a temperature which would cause vaporisation of the second
component upon its combination with the first component by the
apparatus.
[0050] In an embodiment, the pump compresses at least most of the
second liquid component to a pressure above the ambient
pressure.
[0051] In an embodiment, the pump compresses at least most of the
liquid second component to at or about the pressure to which the
compressor compresses the first component.
[0052] In an embodiment, the system comprises multiple pumps
connected in parallel and/or series.
[0053] In an embodiment, the working fluid is a gas-liquid mixture
after the second component (liquid) has been combined with the
first component (gas) by the apparatus.
[0054] In an embodiment, the expander comprises any suitable unit
for producing mechanical work by the expansion of a working
fluid.
[0055] In an embodiment, the expander may be a turbine, a positive
displacement rotary expander, a scroll expander a linear expander
or a reciprocating engine for example.
[0056] The expander may also comprise multiple turbines, rotary
expanders, linear expanders or reciprocating engines, connected in
either parallel or series, with or without inter-stage reheat.
[0057] The expander may or may not be directly coupled to the
compressor to the drive the compressor.
[0058] In an embodiment, the expander is in the form of a
turbine.
[0059] In an embodiment, the turbine has variable pitch blades.
[0060] It is noted that the system may comprise any number of
multiple expanders and/or compressors arranged in parallel or
series.
[0061] The heater provides a heat input to the working fluid from
any suitable heat source.
[0062] In an embodiment, the heater heats the working fluid to a
super-critical gas.
[0063] In an embodiment, the heat source for the heater may be
steam or any other heated medium generated by nuclear power, coal
or another combustible fuel, hot exhaust gasses from a gas turbine,
waste heat from any other process, direct heating from a furnace,
electrical, solar thermal, stored heat or a thermal energy cell(s)
for example.
[0064] In an embodiment, the heat engine system also comprises a
condenser for cooling the working fluid after it exits the
recuperator.
[0065] In an embodiment, the condenser is arranged to substantially
condense the second component of the working fluid to a liquid.
[0066] The condenser may be in the form of a shell and tube heat
exchanger, a radiator, a finned cooling coil with cooling fluid in
serpentine coils, located inside a plenum with condensate recovery
or any other suitable condenser.
[0067] In an embodiment, one side of the condenser receives the
working fluid exiting the condensing side of the recuperator.
[0068] In an embodiment, cooling fluid flows through the other side
of the condenser for cooling the working fluid to condense most of
the second component of the working fluid to liquid.
[0069] The cooling fluid may be air, refrigerant of any composition
or water or brine at or below ambient conditions.
[0070] In an embodiment, the heat removed from the working fluid by
the condenser may be used as the heat input to any other suitable
system, such as an external heat engine, a heat pump, a
refrigeration cycle, desalination or for process heating of water
for example.
[0071] In an embodiment, the condenser is a separator for
separating the second component, as it condenses from the first
component.
[0072] In an embodiment, the separated second component, is
recycled to the apparatus.
[0073] In this embodiment, the remaining working fluid which
comprises the first component and any of the second component
remaining as a gas, flows to the inlet to the compressor.
[0074] In an embodiment, the system comprises multiple condensers
connected in parallel and/or series.
[0075] In an embodiment, the system also comprises a load,
connected to the expander for converting the work produced by the
expander to mechanical or electrical power.
[0076] In an embodiment, the system is a closed system having
substantially no mass inputs or outputs during operation of the
system, other than replacement of incidental losses.
[0077] In an embodiment, the system comprises a top-up feed of the
working fluid for replacing any incidental losses. Incidental
losses may result from leaks, maintenance, or high-pressure or
high-temperature releases for example.
[0078] In an embodiment, the system comprises an energy transfer
controller for controlling the energy transfer in the recuperator
during operation of the system.
[0079] In an embodiment, the energy transfer controller controls
the energy transfer in the recuperator by changing the conditions
at the inlet of the expander and subsequently the expansion done in
the expander and hence the conditions at the outlet of the
expander.
[0080] In an embodiment, the energy transfer controller controls
the energy transfer in the recuperator by changing the amount of
the liquid second component combined with the first component in
the apparatus.
[0081] In an embodiment, the system comprises a mass flow
controller for controlling the mass flow rate of the second
component relative to the mass flow rate of the first
component.
[0082] In an embodiment, the mass flow controller comprises a
variable speed control on the pump.
[0083] In an embodiment, the mass flow controller comprises a pump
diverter, arranged to divert flow of the second component from the
outlet of the pump to the inlet of the pump.
[0084] In an embodiment, the mass flow controller comprises
variable inlet guide vanes in the compressor.
[0085] In an embodiment, the mass flow controller comprises a
variable speed control on the compressor.
[0086] In an embodiment, the mass flow controller comprises a
compressor diverter, arranged to divert flow of the first component
from the outlet of the compressor to the inlet of the
compressor.
[0087] In an embodiment, the mass flow controller comprises
appropriate valving on the apparatus.
[0088] In an embodiment, the system comprises an energy storage
unit upstream of the compressor for storing compressed working
fluid (largely the first component with any gaseous second
component), for use in particular during start-up for example.
[0089] In another embodiment, start-up may be effected by supplying
power to the compressor, pump and expander shafts.
[0090] In an embodiment, the first and second components of the
working fluid are substances which are substantially inert with
respect to each other.
[0091] In an embodiment, the first and second components will not
react with one another, nor substantially dissolve in one another,
nor substantially dissociate at high temperatures.
[0092] In an embodiment, the second component is a substance which
has a high volumetric expansion ratio from liquid to gas.
[0093] In an embodiment, the first component is a substance which
is highly compressible as a gas.
[0094] In an embodiment, the first component may be nitrogen,
argon, helium, hydrogen or methane for example.
[0095] In an embodiment, the second component may be water,
propane, butane, ethanol or carbon dioxide for example.
[0096] A preferred working fluid is nitrogen as the first component
and water as the second component.
[0097] In an embodiment, the working fluid may comprise more
components than the first and second components. These additional
components will generally each follow the flow path of either the
first component (as a gas) or the second component (as a liquid and
a gas) in the system.
[0098] In an embodiment, the heater is a heat exchanger.
[0099] In an embodiment, the heater is a regenerative heater.
[0100] In an embodiment, the regenerative heater comprises at least
one volume of material arranged to be heated to at or above the
melting temperature of the material, the heater also comprising
passages through the at least one volume of material for the flow
therethrough of the working fluid.
[0101] In an embodiment, the regenerative heater comprises at least
two volumes of material, preferably three. The heater may comprise
more than three volumes of material.
[0102] In an embodiment, when the regenerative heater comprises at
least two volumes of material, the passages are arranged for the
working fluid to flow through the volumes of material in
series.
[0103] In other embodiments, however, the passages may be arranged
for the working fluid to flow through the volumes of material in
parallel.
[0104] In an embodiment, the volume(s) of material is heated using
a heating fluid flowing through spaces through the volume(s) of
material.
[0105] The heating fluid may be steam or any other heated medium
generated by nuclear power, coal or other combustible fuel or hot
exhaust gases from a gas turbine for example.
[0106] In an embodiment, the passages through which the working
fluid flow are separate from the spaces through which the heating
fluid flow.
[0107] In other embodiments, the volume(s) of material may be
heated using any other suitable means, such as waste heat from
another process, direct heating from a furnace, electrical or solar
thermal heat.
[0108] In an embodiment, when the regenerative heater comprises at
least two volumes of material, the materials in the volumes are
different. The different materials preferably have different
melting temperatures.
[0109] In one embodiment, the materials are of progressively
decreasing melting temperatures from the first volume to the last
volume, the passages being arranged for the flow of the working
fluid through the last volume first and the first volume last.
[0110] In an embodiment, working fluid flows counter-currently to
the heating fluid. Thus, the spaces are arranged for the flow of
the heating fluid through the first volume first and the last
volume last.
[0111] In an embodiment, at least one of the volumes of material
contains a mixture of two or more different materials.
[0112] In an embodiment, one of the materials in the mixture of
materials of the or each volume is for improving the heat transfer
of the or each volume of material. Such a material may be
graphite.
[0113] In an embodiment, one of the materials in the mixture of
materials of the or each volume is for affecting the melting
temperature of the or each volume of material.
[0114] In one such embodiment, aluminium is mixed with silicon to
reduce the melting temperature of the volume of material.
[0115] In an embodiment, when the regenerative heater comprises at
least two volumes of material, the material in the volumes are each
mixtures of the same materials but at different ratios.
[0116] The different ratios preferably have different melting
temperatures.
[0117] The materials in the volumes may be referred to as "phase
change materials" or "PCMs". Any suitable phase change materials
may be employed.
[0118] In an embodiment of the invention, when the regenerative
heater comprises three volumes of material the first volume
contains silicon, which has a melting temperature of about
1410.degree. C., the second volume contains lithium fluoride, which
has a melting temperature of about 870.degree. C. and the third
volume contains magnesium oxide or calcite, which have a melting
temperature of about 560.degree. C.
[0119] In an embodiment, the volume(s) of material is held in a
container(s) which is able to withstand the temperatures of the
molten material(s) held therein.
[0120] In an embodiment, the container(s) is manufactured from a
ceramic, preferably silicon carbide.
[0121] In an embodiment, the regenerative heater also comprises a
number of valves on the inlets and outlets to the heater which can
be used to control the flow rate of the working fluid and the
heating fluid through the heater to maintain the temperature of the
material(s) in the volume(s) so as to keep them in a molten phase
and to control the temperature of the working fluid as it leaves
the heater.
[0122] In an embodiment, the system comprises multiple regenerative
heaters. In one such embodiment, the system comprises three
regenerative heaters, whereby while one heater is in operation a
second is on stand-by and the other is shut-down for
maintenance.
[0123] According to a second aspect of the present invention, there
is provided a method for producing work, the method comprising the
steps of:
[0124] compressing a first component of a working fluid in a
compressor, the first component being a gas at all times during the
method;
[0125] compressing at least most of a second component of the
working fluid as a liquid in a pump;
[0126] combining the second component as a liquid with the first
component in an apparatus;
[0127] heating the combined first and second components in a
heater;
[0128] expanding the heated first and second components to produce
the work in an expander; and
[0129] transferring in a recuperator at least some of the energy of
the working fluid after it has been expanded to the working fluid
prior to it being heated in the heater, wherein a substantial
portion of the energy transferred is at least a portion of the
latent heat of the second component after the working fluid has
been expanded in the expander.
[0130] In an embodiment, the step of combining the second component
with the first component comprises spraying the liquid second
component into a space having the first component therein.
[0131] In another embodiment, the step of combining the second
component with the first component comprises diffusing the first
component into the liquid second component.
[0132] In an embodiment, the step of combining the second component
with the first component occurs after the steps of compressing the
first component and compressing at least most of the second
compound.
[0133] Preferably, some of the energy transferred in the
recuperator is sensible heat.
[0134] In an embodiment, the step of transferring at least some of
the energy in the recuperator converts at least some of the second
component from liquid to gas prior to it being heated in the
heater.
[0135] In an embodiment, the step of transferring at least some of
the energy in the recuperator converts at least some of the second
component from gas to liquid after it has been expanded in the
expander.
[0136] In an embodiment, the method also comprises the step of
separating a liquid fraction of the working fluid from a gaseous
fraction after the working fluid has been expanded.
[0137] In an embodiment, the step of separating occurs at least
partially in the recuperator.
[0138] Preferably, the method is a closed cycle method also
comprising the step of repeating the steps of the method after at
least some of the working fluid's energy has been transferred in
the recuperator to the working fluid which is yet to be heated in
the heater.
[0139] In an embodiment, the method also comprises the step of
returning the first component to the compressor.
[0140] In an embodiment, the method also comprises the step of
returning at least most of the second component to the pump.
[0141] In an embodiment, the step of compressing the first
component occurs in at least two stages.
[0142] In another embodiment, the step of compressing the first
component occurs in only one stage.
[0143] In an embodiment, the method also comprises the step of
cooling the first and/or second components prior to the step of
combining them.
[0144] In an embodiment, the cooling step comprises cooling the
first component between at least two of the stages of the
compressor using an intercooler.
[0145] In an embodiment, the cooling step comprises cooling the
first component after the step of compressing the first component,
preferably before the step of combining with the second
component.
[0146] In an embodiment, the cooling step comprises cooling the
first component prior to the step of compressing the first
component.
[0147] In an embodiment, the cooling step comprises cooling the
second component prior to combining the second component with the
first component.
[0148] In an embodiment, the liquid second component when combined
with the first component in the apparatus is at ambient
temperature.
[0149] In an embodiment, the step of compressing at least most of
the second component compresses at least most of the second
component to a pressure above the ambient pressure.
[0150] In an embodiment, the step of compressing at least most of
the second component compresses most of the second component to at
or about the pressure to which the first component is compressed in
the compressor.
[0151] In an embodiment, the method comprises the step of
maintaining the temperature of the first component prior to the
step of combining with the second component to a temperature which
is less than one which would cause vaporisation of the second
component during the combining step.
[0152] In an embodiment, the step of separating the liquid fraction
from the gaseous fraction of the working fluid comprises separating
at least most of the second component as a liquid from the first
component as a gas.
[0153] Typically, the step of separating does not completely
separate all of the second component from the first component. Some
of the second component remains as a gas mixed with the first
component.
[0154] In an embodiment, the step of separating occurs at least in
part in the recuperator.
[0155] In an embodiment, the step of separating the first component
from the second component occurs at least in part in a condenser,
and preferably after at least some of the energy of the working
fluid has been transferred in the recuperator to the working fluid
which is yet to be heated in the heater.
[0156] In an embodiment, the step of separating the first component
from the second component comprises cooling the working fluid to
condense at least most of the second component.
[0157] In an embodiment, the method also comprises the step of
controlling the energy transferred in the recuperator.
[0158] In an embodiment, the step of controlling the energy
transferred in the recuperator comprises changing the conditions of
the working fluid prior to expanding it in the expander.
[0159] In an embodiment, the step of controlling the energy
transferred in the recuperator comprises changing the amount of the
second component which is combined with the first component in the
apparatus.
[0160] In an embodiment, the method also comprises the step of
controlling the mass flow rate of the second component relative to
the mass flow rate of the first component.
[0161] In an embodiment, the step of heating comprises transferring
heat from a high temperature source to the working fluid in the
heater, such as for example by using a heating medium in a heat
exchanger.
[0162] In an embodiment, the step of heating comprises flowing the
combined first and second components through at least one volume of
material which is heated to at or above the melting temperature of
the material.
[0163] In an embodiment, the step of heating comprises flowing the
combined first and second components through at least two volumes
of material, preferably three.
[0164] In an embodiment, the step of heating also comprises heating
the at least one volume of material using a heating fluid.
[0165] In an embodiment, heating the at least one volume of
material comprises flowing the heating fluid through spaces through
the volume(s) of material.
[0166] In an embodiment, the step of heating comprises flowing the
heating fluid through the at least one volume of material in a
counter current direction to the flow of the combined first and
second components.
[0167] In an embodiment, the step of heating comprises heating the
working fluid to a super-critical gas.
BRIEF DESCRIPTION OF THE DRAWINGS
[0168] Embodiments of the present invention will now be described,
by way of example only, with reference to the accompanying
drawings, in which:
[0169] FIG. 1 is a schematic view of a heat engine system according
to embodiments of the present invention;
[0170] FIG. 2 is a schematic view of the heat engine regenerative
heater for heating the working fluid of the heat engine system
according to an embodiment of the present invention; and
[0171] FIG. 3 is a schematic view of a HYSYS.RTM. model of a system
heat engine according to an embodiment of the present
invention.
DETAILED DESCRIPTION OF EMBODIMENTS
[0172] Referring firstly to FIG. 1, a heat engine system 10
according to embodiments of the present invention is shown. The
heat engine system 10 produces work by expanding a working fluid.
The working fluid comprises first and second components, the first
component being a gas throughout the system 10. The system 10
comprises an apparatus 11 for combining the second component of the
working fluid as a liquid with the first component. The apparatus
11 may comprise an injector or atomiser arranged to spray the
liquid second component as a mist into a space of sufficient volume
having the first component therein. The apparatus 11 may
alternatively comprise a diffuser, which is arranged to diffuse the
first component into the liquid second component.
[0173] The system 10 also comprises a compressor 12 for compressing
the first component of the working fluid, a pump 19 for compressing
at least most of the second component, a heater 13 for heating the
first and second components and an expander 14 for expanding the
first and second components to produce the work. The apparatus 11
is located after the compressor 12 and the pump 19, to enable the
liquid second component to be combined with the gaseous first
component after they have been compressed.
[0174] The system 10 also comprises a recuperator 15 for
transferring some of the energy of the working fluid from the
outlet of the expander 14, to the working fluid from the outlet of
the apparatus 11. A substantial portion of the energy transferred
in the recuperator 15 is at least some of the latent heat of the
second component of the working fluid (ie. the energy associated
with the phase change of a material such as between liquid and
gaseous states). There is typically also some sensible heat of the
working fluid transferred in the recuperator 15. In the recuperator
15 at least some of second component from the outlet of the
apparatus 11, which is liquid, is converted to gas and at least
some of the second component from the outlet of the expander 14,
which is gas, is converted to liquid.
[0175] The change of phase for the second component of the working
fluid produces a large expansion in the volume of the working
fluid, thus substantially increasing the volumetric flow through
and hence the work produced by the expander 14 compared to a gas
turbine in a conventional Brayton cycle for the same mass flow
rate. Furthermore, the recycling of energy, particularly the latent
heat, in the recuperator 15, reduces the load on the heater 13 and
hence the energy input to the system 10. These factors enable the
system 10 to operate with greater comparative power, improved
efficiency and less net energy consumption to produce the same work
(in the expander 14) as for an equivalently sized conventional
system.
[0176] The compressor 12 has interstaged cooling provided by an
intercooler 18. The primary purpose of this is to ensure that the
temperature of the first component entering the apparatus 11, is
less than a temperature which would cause vaporisation of the
second component upon its combination with the first component in
the apparatus 11. This enables the recuperator 15 to provide
efficient transfer of the substantial portion of the latent heat of
the second component of the working fluid as described above.
Ensuring that the temperature of the first component exiting the
compressor 12 is at this temperature may alternatively (or in
combination with the intercooler 18) be provided by post
compression cooling of the first component, pre-compression cooling
of the first component or by pre-cooling the second component prior
to it being combined with the first component in the apparatus 11
as outlined in FIG. 1.
[0177] The intercooler 18 has a cooling source (as do any of the
other coolers described above) for cooling the first component
between stages of the compressor 12. The cooling source may be
cooling water, ambient air or any suitable refrigeration system to
which heat from the first component may be rejected. It is noted
that the heat rejected from the compressor 12 by cooling of the
first component (either using the intercooler 18, or by pre or post
compression cooling) may be used as a heat input to any other
suitable process such as for heating hot water, creating low
pressure steam, desalination, as the heat input to a heat pump
vapour compression system or for any low temperature power
generation or refrigeration cycle.
[0178] The compressor 12 is any suitable compressor such as an
axial, centrifugal, reciprocating or scroll compressor for
example.
[0179] The expander 14 comprises any suitable unit for producing
mechanical work by the expansion of a working fluid. The expander
14 may or may not be directly coupled to the compressor 12. The
expander 14 may be a turbine, a positive displacement rotary
expander, a linear expander, a scroll expander or a reciprocating
engine for example. The expander 14 may also comprises multiple
turbines, rotary expanders, linear expanders or reciprocating
engines, connected in either parallel or series, with or without
inter-stage reheat. In the embodiment of FIG. 1, the expander 14 is
in the form of a turbine which may or may not have variable pitch
blades. In this embodiment, all the working fluid at the outlet of
the expander 14 is in the gas phase. Of course, it is to be
understood that the system 10 may comprise any number of multiple
expanders and/or compressors arranged in parallel or in series.
[0180] The heater 13 provides a heat input to the working fluid
from any suitable heat source, which heats the working fluid to a
super-critical gas (ensuring that all of the second component is
vaporised). The heat source for the heater 13 may be steam or any
other heated medium generated by nuclear power, coal or another
combustible fuel, hot exhaust gasses from a gas turbine, waste heat
from any other process, direct heating from a furnace, solar
thermal, electrical, stored heat or a thermal energy cell(s) for
example. One suitable heater 13 which provides a heat input from
stored heat source is shown in FIG. 2, and will be described in
more detail further on in the specification.
[0181] The heat engine system 10 also comprises a condenser 16 for
cooling the working fluid after it exits the expander 14 (and also
the recuperator 15) to substantially condense the second component
of the working fluid to a liquid. This enables the majority of the
second component to be readily separated from the first component
(which is a gas) prior to the first component (and any residual
gaseous second component) being compressed in the compressor 12.
The separated second component is recycled to the pump 19.
[0182] The system 10 also comprises a load 17, connected to the
expander 14 for converting the work produced by the expander 14 to
mechanical or electrical power.
[0183] The system 10 is a closed system, with theoretically no mass
inputs or outputs during operation of the system 10, other than
replacement of incidental losses. However, a top-up of either of
the components of the working fluid may need to be provided due to
some incidental losses such as those resulting from leaks,
maintenance, or high-pressure or high-temperature releases for
example.
[0184] A general description of the operation of the system 10 will
now be provided:
[0185] The gaseous first component of the working fluid enters the
compressor 12 through inlet 20, where it is compressed. Compression
of the first component of the working fluid tends to increase its
temperature, however, the interstage cooler 18 ensures that this
rise is not significant enough to cause the temperature of the
first component to be above a temperature at which combination with
the second component would cause vaporisation of the second
component.
[0186] The first component flows from the outlet 21 of the
compressor 12 to the apparatus 11, where the liquid second
component is combined with the first component through second
component inlet 22 having been compressed in the pump 19. The
liquid second component may be at ambient temperature (or lower)
and may cool the working fluid. The liquid second component is
compressed in the pump 19 to a pressure greater than ambient, and
preferably to at or about the pressure of the first component at
the outlet of the compressor 12, prior to being combined with the
first component. Because there are gas and liquid components of the
working fluid compressed separately in the compressor 12 and pump
19 respectively, the compressor 12 can be smaller than a compressor
which is compressing an equivalent mass flowrate of working fluid
which is all gas. This is advantageous to the system because
compressing a gas requires much more work than compressing (in a
pump) an equivalent mass flowrate of liquid. Therefore, the overall
efficiency of the system(s) is improved by this arrangement of the
pump 19 and the compressor 12. The working fluid as a gas-vapour
mixture exits the apparatus 11 through outlet 23.
[0187] The recuperator 15 is generally in the form of a shell and
tube heat exchanger, preferably a falling film condenser and
comprises a boiling side 24 (shell) and a condensing side 25
(tubes). Working fluid from the outlet 23 of the apparatus 11
enters the boiling side 24 of the recuperator 15 where the second
component of the working fluid substantially boils as it receives
energy from the working fluid on the condensing side 25.
[0188] The working fluid exiting the boiling side 24 of the
recuperator flows to the inlet 26 of the heater 13, where it is
heated. From the heater 13, the working fluid flows to the inlet 27
of the expander 14. The working fluid is expanded in the expander
14 to produce the work. The working fluid at the outlet 28 of the
expander 14 is consequently lower in pressure and temperature. In
the embodiment shown in FIG. 1, the conditions of the working fluid
at the outlet 28 of the expander 14 are such that both the first
and second components are a gas. The working fluid from the outlet
28 of the expander 14 is received by the condensing side 25 of the
recuperator 15 where the second component of the working fluid
substantially condenses as it loses energy to the working fluid on
the boiling side 24.
[0189] The recuperator 15 is also arranged to act as a separator on
the condensing side to provide a separation of a liquid fraction of
the working fluid (the second component) from a gaseous fraction
(primarily the first component).
[0190] The gaseous fraction of the working fluid exiting the
condensing side 25 of the recuperator 15 enters one side of the
condenser 16. The condenser 16 may be a shell and tube heat
exchanger but alternatively may be a radiator, a finned cooling
coil with cooling fluid in serpentine coils, located inside a
plenum with condensate recovery or any other suitable condenser.
Cooling fluid 29 (possibly air, water or refrigerant of any
composition at or below ambient conditions) flows through the other
side of the condenser 16, cooling the working fluid so that most of
the (remaining) second component of the working fluid is condensed
into a liquid. The liquid second component is separated from the
first component in the condenser 16, which is thus acting as a
separator. The separated second component 30, is recycled to the
pump 19. The remaining working fluid which comprises the first
component and any of the second component remaining as a gas flows
to the inlet 20 to the compressor 12.
[0191] The liquid fraction of the working fluid exiting the
condensing side 25 of the recuperator 15 may bypass the condenser
16 and flow to the pump 19 as shown in FIG. 1. However, in an
alternative arrangement, the liquid fraction of the working fluid
exiting the condensing side 25 of the recuperator 15 may also be
sent to the condenser 16. The pump 19 pumps the liquid second
component from the condenser 16 and the recuperator 15 back to the
apparatus 11. Notably, during operation of the system 10, the
energy transfer in the recuperator 15 is controlled to maintain the
optimum system efficiency using an energy transfer controller. This
is compared to conventional heat engines in which it is the
conditions across the expander 14 that are controlled. Temperature
and pressure sensors at the inlets and outlets of both the
condensing and boiling sides 24, 25 of the recuperator 15 monitor
the conditions across the recuperator 15. The energy transfer in
the recuperator 15 is subsequently controlled by changing the
conditions at the inlet of the expander and subsequently the
expansion done in the expander 14 and hence the conditions at the
outlet 28 of the expander 14. The conditions at the inlet of the
expander may be changed by, for example, changing the amount of
compression carried out in the compressor 12 and/or pump 19 as well
as changing the amount of heat transfer to the working fluid in the
heater 13. The energy transfer controller may also control the
energy transferred in the recuperator 15 by changing the amount of
the liquid second component combined with the first component in
the apparatus 11.
[0192] The system 10 may also comprise a mass flow controller for
controlling the mass flowrate of the second component relative to
the mass flowrate of the first component. If the mass flow rate of
the second component relative to the first component becomes too
high, then the second component may not completely evaporate which
could cause problems, particularly in the expander 14 if it is in
the form of a turbine. The mass flow controller may comprise
variable speed controllers on the compressor 12 and pump 19,
respectively. For the compressor 12, alternatively, the mass flow
controller may comprise variable inlet guide vanes. The mass flow
controller may in addition to or alternatively comprise diverters
on the compressor 12 and/or the pump 19 which divert flow from the
outlet of the compressor and/or pump to their respective inlets.
The mass flow controller may also comprise appropriate valving on
the apparatus 11.
[0193] The system may also comprise an energy storage unit located
upstream from the compressor 12 for storing compressed working
fluid from the compressor. The energy storage unit may be used in
particular during start-up of the system 10, during which the
expander 14 is gradually increased from zero to full capacity.
Rather than wasting the energy of the compressed working fluid from
the compressor during this time, by bypassing the expander 14, some
of the working fluid is diverted to the energy storage unit. The
working fluid held in the energy storage unit can be reintroduced
to the system cycle once the expander 14 has reached full capacity.
Alternatively, the system 10 may be started up by supplying power
to the compressor, pump and expander shafts.
[0194] These system controllers provide the system 10 with a high
degree of operational flexibility, thus enabling the system 10 (in
particular the expander 14) to closely follow the load 17 should it
vary. For example, the mass flow controller enables the pump 19 and
the compressor 12 to each be turned down to 30-50% of their full
load.
[0195] The first and second components of the working fluid should
be substances which are substantially inert with respect to each
other, both chemically and physically, ie. they will not react with
one another nor substantially dissolve in one another nor
substantially dissociate at high temperatures. It is also desirable
if the second component is a substance which has a high volumetric
expansion ratio from liquid to gas. Further, it is also desirable
if the first component is a substance which is highly compressible
as a gas. The first component may be nitrogen, argon, helium,
hydrogen or methane for example. The second component may be water,
propane, butane, ethanol or carbon dioxide for example. A preferred
working fluid is nitrogen as the first component and water as the
second component. It is noted that the working fluid may comprise
more components than the first and second components, ie. different
substances. However, these additional components will each
generally follow the flow path of either the first component (as a
gas) or the second component (as a liquid and a gas) in the system
10 as described above.
[0196] Referring now to FIG. 2, the heater 13 is shown in an
embodiment, as a regenerative heater. It is noted that in other
embodiments, the heater 13 may be a heat exchanger or another type
of suitable heater. The heater 13 of FIG. 2 comprises first, second
and third volumes 40, 41, and 42 respectively, of material. It is
readily understood that the heater 13 may comprise less or more
volumes of material to that shown in FIG. 2. The volumes 40, 41, 42
are arranged to be heated to at or above the melting temperature of
the material. The heater 13 also comprises passages through the
volumes 40, 41, 42 of material for the flow therethrough of the
working fluid. The working fluid, is thus heated by the volumes 40,
41, 42 of material. In the embodiment shown in FIG. 2, the passages
are arranged for the working fluid to flow through the volumes 40,
41, 42 of material in series. However, in other embodiments the
passages may be arranged for the working fluid to flow through the
volumes 40, 41, 42 of material in parallel.
[0197] In the embodiment shown in FIG. 2 the volumes of material
40, 41, 42 are heated using a heating fluid flowing through spaces
through the volumes of material 40, 41, 42. The heating fluid may
be steam or any other heated medium generated by nuclear power,
coal or other combustible fuel or hot exhaust gasses from a gas
turbine. The volumes 40, 41, 42 of material may be heated using any
other suitable means, such as waste heat from another process,
direct heating from a furnace, electrical or solar thermal heat.
The passages through which the working fluid flow are separate from
the spaces through which the heating fluid flow. This enables
continuous operation of the heater 13 as well as preventing any
mixing of the two fluids, which avoids problems such as
contamination, particularly dust contamination, oxygenation and
carbonation of the working fluid.
[0198] The materials in the volumes 40, 41, 42 may be different and
in one embodiment are of progressively decreasing melting
temperatures from the first volume 40 to the third volume 42. The
materials used may be referred to as "phase change materials" or
"PCMs". Any suitable phase change materials may be employed. In an
embodiment of the invention, however, the first volume 40 contains
silicon, which has a melting temperature of about 1410.degree. C.,
the second volume 41 contains lithium fluoride, which has a melting
temperature of about 870.degree. C. and the third volume 42
contains magnesium oxide or calcite, which have a melting
temperature of about 560.degree. C. The volumes of material 40, 41,
42 are all held in containers, which are of a material which is
able to withstand the temperatures of the molten materials held
therein. A particularly suitable material in this regard is a
ceramic material, preferably silicon carbide.
[0199] In another arrangement, the volumes of material 40, 41, 42
may contain a mixture of two or more different materials. In one
form, each volume of material 40, 41, 42 comprises the mixture of
the same materials but at different ratios. The different ratios
preferably have different melting temperatures, thus providing the
graduated heating of the working fluid flowing through the volumes
of material 40, 41, 42. In this respect, at least one of the
materials in the mixture of materials of each volume is for
affecting the melting temperature of the volumes of material. For
example, aluminium may be mixed with silicon to reduce the melting
temperature of the silicon. Alternatively, or in addition to this,
one of the materials in the mixture of materials may be for
improving the heat transfer of the volume of material. Such a
material for example is graphite, which may be added to salts for
example such as lithium fluoride, magnesium oxide, calcite or
sodium chloride to improve the heat transfer of these materials.
This, advantageously, enables the volumes of material 40, 41, 42 to
reach their melting temperatures more rapidly as well as improving
the heat transfer from the volumes of material 40, 41, 42 to the
working fluid. This in turn enables faster start-up and shut down
of the system 10.
[0200] The working fluid flows counter-currently to the heating
fluid, entering the heater 13 through the inlet 26 to be heated
firstly by the lowest temperature volume of material, in this case
the third volume 42, and finally by the highest temperature volume
of material, in this case the first volume 40 before exiting to the
inlet 27 of the expander 14. The heating fluid heats the volumes
40, 41, 42 in reverse order, that is, it enters the heater 13
through inlet 43 to heat the first volume 40, which is required to
be at the highest temperature, first and heats the third volume 42
last.
[0201] In another embodiment, the material in each or two of the
volumes 40, 41, 42 is the same. In this embodiment, the volumes may
not be as readily heated to at or above the melting temperature of
the material using the heating fluid in series because as the
heating fluid flows through the heater 13, it loses energy and heat
as it flows through the volumes 40, 41, 42. Thus, the volumes 40,
41, 42 in this embodiment may need to be heated in parallel or
alternatively by a different source of heat.
[0202] The heater 13 also comprises a number of valves 45 on the
inlets and outlets to the heater 13 which can be used to control
the flow rate of the working fluid and the heating fluid through
the heater 13 to maintain the temperature of the phase change
materials in the volumes 40, 41, 42 so as to keep them in a molten
phase and to control the temperature of the working fluid as it
leaves the heater.
[0203] The flowrate of the working fluid is also controlled with
respect to its temperature at the outlet of the heater 13 (ie. the
inlet 27 to the expander 14). The temperature of the working fluid
required at the inlet 27 of the expander is much less than the
melting temperature of silicon (and hence the temperature of the
first volume 40). If the working fluid at the inlet 27 of the
expander was at this temperature (approximately 1410.degree. C.)
then this could cause damage to the expander 14. Because of this
large temperature difference, the heater 13 advantageously enables
quick start-up of the heat engine system 10.
[0204] The expander inlet temperatures can be varied and controlled
by a modulating bypass control valve that diverts flow around the
regenerative heater 13. This will allow the precise setting of
expander inlet temperatures with variable output. This level of
temperature control cannot be achieved with conventional gas
turbines that rely on internal combustion. Also, when this control
is used with the other control elements as described previously,
good efficiency is attained when the system is turned down.
EXAMPLE
[0205] A model of a heat engine system according to embodiments of
the present invention was constructed in HYSYS.RTM.. FIG. 3
provides a schematic view of the model. The model was prepared on
the basis of an approximately 1:1 mass flow ratio of nitrogen as
the first component and water as the second component. Other
parameters assumed for the model include: [0206] an ambient
temperature of 35.degree. C. (for Queensland ambient temperature
conditions) [0207] compression ratio for the compressor of 6.2:1
[0208] Compressor efficiency of 85% [0209] Expander efficiency of
85% [0210] Pressure drops of 5 kPa for the apparatus, 30 kPa for
the boiling side of the recuperator, 20 kPa for the heater, 300 Pa
for the condensing side of the recuperator. [0211] Exit temperature
for the recuperator condensing side of 60.degree. C.
[0212] Table 1 below sets out the conditions at points A-I in the
system as indicated on FIG. 3.
TABLE-US-00001 TABLE 1 A B (Nitrogen) (Water) C D E F G H I
Temperature 35.00 35.00 273.5 45.91 617.6 1100 742.9 60.00 35.00
(.degree. C.) Pressure 100.0 620.0 620.0 620.0 590.0 570.0 103.0
100.00 100.0 (kPa) Total Mass 1.000 0.9256 1.000 1.926 1.926 Flow
(kg/s) Total Volume 3.332 963.3 540.5 Flow (m.sup.3/h) Vapour
Fraction 0.3979 0.4910 Mass Fraction 0.5005 (H.sub.2O)
[0213] The model system was calculated to produce a net shaft power
output of 0.9736 MW at 58.95% efficiency.
[0214] In the claims which follow and in the preceding description
of the invention, except where the context requires otherwise due
to express language or necessary implication, the word "comprise"
or variations such as "comprises" or "comprising" is used in an
inclusive sense, ie. to specify the presence of the stated features
but not to preclude the presence or addition of further features in
various embodiments of the invention.
* * * * *