U.S. patent application number 13/345330 was filed with the patent office on 2013-07-11 for non-azeotropic working fluid mixtures for rankine cycle systems.
This patent application is currently assigned to UNITED TECHNOLOGIES CORPORATION. The applicant listed for this patent is Frederick J. Cogswell, Jaeseon Lee, Dong Luo, Ahmad M. Mahmoud, Thomas D. Radcliff. Invention is credited to Frederick J. Cogswell, Jaeseon Lee, Dong Luo, Ahmad M. Mahmoud, Thomas D. Radcliff.
Application Number | 20130174552 13/345330 |
Document ID | / |
Family ID | 47115596 |
Filed Date | 2013-07-11 |
United States Patent
Application |
20130174552 |
Kind Code |
A1 |
Mahmoud; Ahmad M. ; et
al. |
July 11, 2013 |
NON-AZEOTROPIC WORKING FLUID MIXTURES FOR RANKINE CYCLE SYSTEMS
Abstract
A power generation system includes a non-azeotropic working
fluid mixture and a Rankine cycle system. The Rankine cycle system
includes a turbine generator that is driven by vapor of the first
working fluid mixture, and a condenser that exchanges thermal
energy between the vapor received from the turbine generator and a
cooling medium. The working fluid mixture is characterized by a
condenser temperature glide during phase change between
approximately five degrees and thirty degrees Kelvin, a condensing
pressure between approximately one tenth of one percent and eleven
percent of a critical pressure of the working fluid mixture, and a
condenser bubble point temperature between approximately one degree
and nine degrees Kelvin greater than a temperature at which the
cooling medium is received by the condenser.
Inventors: |
Mahmoud; Ahmad M.; (Bolton,
CT) ; Radcliff; Thomas D.; (Vernon, CT) ; Lee;
Jaeseon; (Glastonbury, CT) ; Luo; Dong; (South
Windsor, CT) ; Cogswell; Frederick J.; (Glastonbury,
CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mahmoud; Ahmad M.
Radcliff; Thomas D.
Lee; Jaeseon
Luo; Dong
Cogswell; Frederick J. |
Bolton
Vernon
Glastonbury
South Windsor
Glastonbury |
CT
CT
CT
CT
CT |
US
US
US
US
US |
|
|
Assignee: |
UNITED TECHNOLOGIES
CORPORATION
Hartford
CT
|
Family ID: |
47115596 |
Appl. No.: |
13/345330 |
Filed: |
January 6, 2012 |
Current U.S.
Class: |
60/671 |
Current CPC
Class: |
F01K 23/02 20130101;
F01K 25/08 20130101 |
Class at
Publication: |
60/671 |
International
Class: |
F01K 25/06 20060101
F01K025/06; F01K 25/00 20060101 F01K025/00 |
Goverment Interests
[0001] This invention was made with government support under
Contract No. DE-EE0002770 awarded by the United States Department
of Energy. The government may have certain rights in the invention.
Claims
1. A power generation system, comprising: a non-azeotropic working
fluid mixture; and a Rankine cycle system comprising a turbine
generator that is driven by vapor of the working fluid mixture, and
a condenser that exchanges thermal energy between the vapor
received from the turbine generator and a cooling medium; wherein
the working fluid mixture exhibits a condenser temperature glide
during phase change between approximately five degrees and thirty
degrees Kelvin, a condensing pressure between approximately one
tenth of one percent and eleven percent of a critical pressure of
the working fluid mixture, and a condenser bubble point temperature
between approximately one degree and nine degrees Kelvin greater
than a temperature at which the cooling medium is received by the
condenser.
2. The system of claim 1, wherein the working fluid mixture
comprises a first chemical component and a second chemical
component, and the first chemical component and the second chemical
component each comprise at least one of a hydrocarbon, a
fluorocarbon, an ether, a hydrochlorofluorocarbon, a
hydrofluorocarbon, a fluorinated ketone, a hydrofluoro ether, a
hydrochlorofluoro olefin, a bromofluoro olefin, a fluoro olefin, a
hydrofluoro olefin, a cyclic siloxane and a linear siloxane.
3. The system of claim 2, wherein the first chemical component
comprises at least one of R134a, R245fa, R236ea,
1,1,1,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)-3-pentanone,
HFE-7000, R1234ze, R1234yf, R1233zd and R1243zf.
4. The system of claim 3, wherein the second chemical component
comprises at least one of pentane, hexane, isohexane, cyclopentane,
cyclohexane, R245fa, R1234ze, isopentane, R161, R30, R134a,
R1233zd, C7FK, isobutene,
1,1,1,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)-3-pentanone,
R236ea, HFE-7000, CF3I and R1243zf.
5. The system of claim 1, wherein the condenser temperature glide
is between approximately six degrees and twenty-five degrees
Kelvin.
6. The system of claim 5, wherein the condenser temperature glide
is between approximately eight degrees and twenty degrees
Kelvin.
7. The system of claim 1, wherein the condensing pressure is
between approximately one percent and eight percent of the critical
pressure of the working fluid mixture.
8. The system of claim 7, wherein the condensing pressure is
between approximately two and one half percent and seven and one
half percent of the critical pressure of the working fluid
mixture.
9. The system of claim 1, wherein the condenser bubble point
temperature is between approximately one degree and five degrees
Kelvin greater than the temperature at which the cooling medium is
received by the condenser.
10. The system of claim 1, wherein the working fluid mixture
exhibits a global warming potential less than approximately
675.
11. The system of claim 10, wherein the global warming potential is
less than approximately 150.
12. The system of claim 1, wherein the condenser comprises one of a
plate-frame counter-flow heat exchanger, a one pass direct
expansion shell and tube counter-flow heat exchanger, and a
plate-shell counter-flow heat exchanger.
13. A power generation system, comprising: an intermediate heat
exchanger comprising a condenser passage that receives a first
working fluid, and an evaporator passage that receives an organic,
non-azeotropic second working fluid mixture, wherein the heat
exchanger transfers thermal energy from the first working fluid to
the second working fluid mixture; a first Rankine cycle system
comprising a first pump that directs the first working fluid
through an evaporator and the condenser passage; and a second
Rankine cycle system comprising a second pump that directs the
second working fluid mixture through the evaporator passage, a
second turbine generator that is driven by vapor of the second
working fluid mixture, and a condenser that exchanges thermal
energy between the vapor received from the second turbine generator
and a cooling medium; wherein the second working fluid mixture is
characterized by a condenser temperature glide between
approximately five degrees and thirty degrees Kelvin, a condensing
pressure between approximately one tenth of one percent and eleven
percent of a critical pressure of the second working fluid mixture,
and a condenser bubble point temperature between approximately one
degree and nine degrees Kelvin greater than a temperature at which
the cooling medium is received by the condenser.
14. The system of claim 13, wherein the second working fluid
mixture comprises a first chemical component and a second chemical
component, and the first chemical component and the second chemical
component each comprise at least one of a hydrocarbon, a
fluorocarbon, an ether, a hydrochlorofluorocarbon, a
hydrofluorocarbon, a fluorinated ketone, a hydrofluoro ether, a
hydrochlorofluoro olefin, a bromofluoro olefin, a fluoro olefin, a
hydrofluoro olefin, a cyclic siloxane and a linear siloxane.
15. The system of claim 14, wherein the first chemical component
comprises at least one of R134a, R245fa, R236ea,
1,1,1,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)-3-pentanone,
HFE-7000, R1234ze, R1234yf, R1233zd and R1243zf.
16. The system of claim 15, wherein the second chemical component
comprises at least one of pentane, hexane, isohexane, cyclopentane,
cyclohexane, R245fa, R1234ze, isopentane, R161, R30, R134a,
R1233zd, C7FK, isobutene,
1,1,1,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)-3-pentanone,
R236ea, HFE-7000, CF3I and R1243zf.
17. The system of claim 13, wherein the evaporator transfers
thermal energy into the first working fluid from a thermal source
fluid received from one of a geothermal reservoir, a combustion
engine, a solar-thermal system, an incinerator and an industrial
system, and the cooling medium comprises at least one of a liquid
and a gas.
18. The system of claim 13, wherein the evaporator comprises a
solar-thermal system.
19. The system of claim 13, wherein the first working fluid
comprises a first chemical component and a second chemical
component, and the first chemical component and the second chemical
component each comprise at least one of a hydrocarbon, a
fluorocarbon, an ether, a hydrochlorofluorocarbon, a
hydrofluorocarbon, a fluorinated ketone, a hydrofluoro ether, a
hydrochlorofluoro olefin, a bromofluoro olefin, a fluoro olefin, a
hydrofluoro olefin, a cyclic siloxane and a linear siloxane.
20. The system of claim 19, wherein the first chemical component
comprises at least one of R134a, R245fa, R236ea,
1,1,1,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)-3-pentanone,
HFE-7000, R1234ze, R1234yf, R1233zd and R1243zf; and the second
chemical component comprises at least one of pentane, hexane,
isohexane, cyclopentane, cyclohexane, R245fa, R1234ze, isopentane,
R161, R30, R134a, R1233zd, C7FK, isobutene,
1,1,1,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)-3-pentanone,
R236ea, HFE-7000, CF3I and R1243zf.
Description
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] The present invention relates to Rankine cycle systems and,
in particular, to a non-azeotropic working fluid mixture that may
circulate through an organic Rankine cycle system to generate
power.
[0004] 2. Background Information
[0005] An organic Rankine cycle (ORC) system may be used for
generating electrical power within, for example, a geothermal power
generation system. A typical organic Rankine cycle system may
include an organic working fluid that is circulated through a pump,
an evaporator, a turbine generator and a condenser. A recuperator
may be also used if the technical and economical merits warrant.
During operation, the evaporator transfers thermal energy from a
relatively warm thermal source fluid into the working fluid in
order to form working fluid vapor, which drives the turbine
generator as the vapor expands. The condenser transfers thermal
(e.g., heat) energy from the expanded working fluid vapor into a
relatively cool thermal sink fluid in order to condense the working
fluid vapor before it is resupplied to the evaporator through the
pump.
[0006] A typical organic working fluid may include a single (pure)
chemical component, or an azeotropic mixture of different chemical
components. Pinch points associated with single component organic
working fluids in heat exchangers, however, typically reduce
overall efficiencies of the organic Rankine cycle systems in which
they are implemented. The term "pinch point" may describe a point
in a working fluid temperature profile where a minimum (smallest)
temperature difference exists between the temperature of the
working fluid and that of the thermal source or sink fluid.
SUMMARY OF THE DISCLOSURE
[0007] According to a first aspect of the invention, a power
generation system includes a non-azeotropic working fluid mixture
and a Rankine cycle system. The Rankine cycle system includes a
turbine generator that is driven by vapor of the working fluid
mixture, and a condenser that exchanges thermal energy between the
vapor received from the turbine generator and a cooling medium. The
working fluid mixture exhibits a condenser temperature glide
between approximately five degrees and thirty degrees Kelvin, a
condensing pressure between approximately one tenth of one percent
and eleven percent of a critical pressure of the working fluid
mixture, and a condenser bubble point temperature between
approximately one degree and nine degrees Kelvin greater than a
temperature at which the cooling medium is received by the
condenser.
[0008] According to a second aspect of the invention, a power
generation system includes an intermediate heat exchanger, a first
Rankine cycle system and a second Rankine cycle system. The heat
exchanger includes a condenser passage that receives a first
working fluid, and an evaporator passage that receives an organic,
non-azeotropic second working fluid mixture. The heat exchanger
transfers thermal energy from the first working fluid to the second
working fluid mixture. The first Rankine cycle system includes a
first pump that directs the first working fluid through an
evaporator and the condenser passage. The second Rankine cycle
system includes a second pump that directs the second working fluid
mixture through the evaporator passage, a turbine generator that is
driven by vapor of the second working fluid mixture, and a
condenser that exchanges thermal energy between the vapor received
from the turbine generator and a cooling medium. The second working
fluid mixture is characterized by a condenser temperature glide
between approximately five degrees and thirty degrees Kelvin, a
condensing pressure between approximately one tenth of one percent
and eleven percent of a critical pressure of the second working
fluid mixture, and a condenser bubble point temperature between
approximately one degree and nine degrees Kelvin greater than a
temperature at which the cooling medium is received by the
condenser.
[0009] The foregoing features and the operation of the invention
will become more apparent in light of the following description and
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic illustration of a power generation
system that includes a Rankine cycle system;
[0011] FIG. 2 is a temperature-entropy phase diagram for an
organic, non-azeotropic working fluid mixture circulating through
the Rankine cycle system illustrated in FIG. 1; and
[0012] FIG. 3 is a schematic illustration of an alternate
embodiment power generation system that includes a plurality of
Rankine cycle systems.
DETAILED DESCRIPTION OF THE INVENTION
[0013] FIG. 1 is a schematic illustration of a power generation
system 10 that includes a working fluid mixture (e.g., an organic,
non-azeotropic working fluid mixture) that circulates through a
Rankine cycle system 12 (e.g., an organic Rankine cycle system).
The Rankine cycle system 12 may include a turbine generator 14, a
condenser 16 (e.g., a counterflow heat exchanger), a pump 18 and an
evaporator 20 (e.g., a counterflow heat exchanger). The condenser
16 may include a first heat exchange passage 22 and a second heat
exchange passage 24. The evaporator 20 may include a first heat
exchange passage 26 and a second heat exchange passage 28.
[0014] During operation, the working fluid mixture may circulate
sequentially through the turbine generator 14, the first heat
exchange passage 22 of the condenser, the pump 18 and the second
heat exchange passage 28 of the evaporator, which may be connected
together in a closed loop circuit. In some embodiments, the power
generation system 10 may also include a liquid receiver/accumulator
connected, for example, between the first heat exchange passage 22
and the pump 18. A cooling medium (e.g. water, seawater, air), may
be directed through the second heat exchange passage 24 of the
condenser. A thermal source fluid may be directed through the first
heat exchange passage 26 of the evaporator.
[0015] FIG. 2 is a temperature-entropy phase diagram of the working
fluid mixture during operation of the Rankine cycle system 12. The
phase diagram illustrates a first curve 30 for the organic
non-azeotropic working fluid mixture, a second curve 32 for the
cooling medium, and a third curve 34 for the thermal source fluid.
Referring to FIGS. 1 and 2, superheated vapor of the working fluid
mixture is directed into the turbine generator 14 at point 200. The
vapor expands and mechanically drives the turbine generator 14
between the point 200 and point 204, which may thereby generate
power (e.g., electricity). The vapor is directed from the turbine
generator 14 into the first heat exchange passage 22 at point 204.
Thermal energy is transferred from the working fluid mixture into
the cooling medium through the condenser 16 between the point 204
and point 206, which may cause the working fluid mixture to undergo
a phase change from vapor to liquid. The vapor may be, for example,
de-superheated within the first heat exchange passage 22 between
the point 204 and point 208, and condensed into liquid between the
point 208 and point 210. The liquid may also be sub-cooled within
the first heat exchange passage 22 between the points 210 and 206.
The liquid is directed from the first heat exchange passage 22 into
the pump 18 between the point 206 and point 212. The liquid is
pressurized within the pump 18 between the point 212 and point 214,
and is directed into the second heat transfer passage 28 at point
216. Thermal energy is transferred from the thermal source fluid
into the working fluid mixture through the evaporator 20 between
the point 216 and point 200, which may cause the working fluid
mixture to undergo another phase change from the liquid to the
vapor. The liquid may be, for example, preheated within the second
heat exchange passage 28 between the point 216 and point 220, and
evaporated into vapor between the points 220 and 218. The vapor may
also be, for example, superheated beyond point 218 to point 200 to
minimize risk of condensation of the mixture vapor in the turbine
generator 14. The vapor is then directed from the second heat
exchange passage 28 into the turbine generator 14 at point 200.
[0016] The working fluid mixture may exhibit certain properties
such as temperature glide during phase change, pressure, bubble
point temperature in both the condenser passage 22 and the
evaporator passage 28, and a mixture critical pressure that
increases (e.g., maximizes) the power generation potential and
cycle thermal efficiency during the afore-described Rankine cycle.
The term "temperature glide" describes the temperature difference
between the saturated vapor temperature and the saturated liquid
temperature of a working fluid mixture. The term "saturated vapor
temperature" describes a dew point temperature of the working fluid
mixture; e.g., the temperature at the point 208 during
condensation, and the temperature at the point 218 during
evaporation. The term "saturated liquid temperature" describes a
bubble point temperature of the working fluid mixture; e.g., the
temperature at the point 210 during condensation, and the
temperature at the point 220 during evaporation. The condenser
temperature glide may be, for example, between about five and
thirty degrees Kelvin (e.g., between about 6-8.degree. K and
20-25.degree. K). The condenser pressure may be, for example,
between about one tenth of one percent (0.1%) and eleven percent of
the critical pressure (e.g., between about 1-2.5% and 7.5-8% of the
critical pressure) of the working fluid mixture. The condenser
bubble point temperature at the point 210 may be, for example,
between about one and nine degrees Kelvin (e.g., between about
1.degree. K and 5.degree. K) greater than temperature T.sub.5
(e.g., T.sub.5 is between about 280.degree. K and 308.degree. K) at
which the cooling medium is received by the second heat exchange
passage 24. The critical pressure may be, for example, between
about 2 MPa and 6.5 MPa.
[0017] The working fluid mixture may also exhibit other
characteristics during the Rankine cycle such as, for example, low
global warming potential (GWP), low flammability, low ozone
depletion potential, low toxicity, etc. The term "global warming
potential" is a relative measure of how much heat a greenhouse gas
traps in the atmosphere relative to carbon dioxide for the
atmospheric lifetime of the species. The global warming potential
of carbon dioxide is standardized to 1. The global warming
potential of the working fluid mixture may be, for example, less
than about 675 (e.g., less than about 150-250), and the working
fluid mixture may be, for example, non-flammable.
[0018] Some non-azeotropic mixtures may exhibit a lower
condensation heat transfer coefficient due to a reduced interfacial
temperature between the liquid and vapor phases. This reduced
interfacial temperature gives rise to heat and mass transfer
resistances. In order to avoid such implications, the working fluid
mixture may be selected such that the condensing heat transfer
coefficient of the mixture is greater than the (e.g., smallest)
condensing heat transfer coefficient of the components. The least
volatile component refers to the component with the lowest boiling
point at a given temperature.
[0019] The working fluid mixture may be manufactured by mixing
together a plurality of different chemical components (e.g.,
organic chemical components). The working fluid mixture may
include, for example, a plurality of the chemical components listed
in Table 1 below.
TABLE-US-00001 TABLE 1 Chemical Group Representative Chemical
Components (CAS Registry Number) Hydrocarbon Propane (74-98-6),
butane (106-97-8), pentane (109-66-0), hexane (110-54-3), heptanes
(142-82-5), octane (111-65-9), nonane (111-84-2), decane
(124-18-5), ethylene (74-85-1), propylene (115-07-1), propyne
(74-99-7), isobutene (75-28- 5), isobutene (115-11-7), 1butene
(106-98-9), c2butene (590-18-1), cyclepentane (287-92-3),
isopentane (78-78-4), neopentane (463-82-1), isohexane (107-83-5),
cyclohexane (110-82-7) Fluorocarbon R14 (75-73-0), R218 (76-19-7)
Ether RE170 (dimethyl ether 115-10-6) Hydrochlorofluorocarbon R21
(75-43-4), R22 (75-45-6), R30 (75-09-2), R32 (75-10-5), R41
(593-53-3), R123 (306-83-2), R124 (2837-89-0) Hydrofluorocarbon
R134a (811-97-2), R143a (420-46-2), R152a (75-37-6), R161
(353-36-6), R23 (75-46-7), R227ea (431-89-0), R236ea (431-63-0),
R236fa (690-39-1), R245ca (679-86-7), R245fa (460-73-1), R365mfc
(406-58-6), R338mccq (662-35-1) Fluorinated Ketone
1,1,1,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)-3-pentanone (e.g.,
Novec .RTM. 649) (756-13-8), C7FK (C7 fluoroketone) Hydrofluoro
ether RE125 (3822-68-2), RE134, RE143a (421-14-7) RE236fa, RE245cb2
(22410- 44-2), RE245fa2 (1885-48-9), HFE-7000 (C3F7OCH3), HFE-7100
(C4F9OCH3), HFE-7200 (C4F9OC2H5) Hydrochlorofluoro olefin R1233zd
(102687-65-0), 2-chloro-3,3,3-trifluoropropene Bromofluoro olefin
C5F9Cl Fluoro olefin R1216 (116-15-4) Hydrofluoro olefin R1234yf
(754-12-1), R1234ze (1645-83-6), R1243zf (677-21-4), R1225ye
(5595-10-8) Cyclic siloxane D2 (7782-39-0), D4 (556-76-2), D5
(541-02-6), D6 (540-97-6) Linear siloxane MM (107-46-0), MDM
(107-51-7), MD2M (141-62-8), MD3M (141-63-9), MD4M (00107-52-8)
[0020] The aforesaid chemical components may be selected, for
example, in order to tailor the heat exchanger temperature glide,
the heat exchange pressure, the bubble point temperature and/or
other characteristics (e.g., the GWP, the flammability, etc.) of
the working fluid mixture to a particular Rankine cycle system
design and application. The chemical components may also be
selected, for example, to shift the pinch point in order to reduce
a temperature T.sub.6 at which the thermal source fluid exits the
heat exchange passage 26 of the evaporator, which may thereby
increase Rankine cycle efficiency by increasing the amount of power
generated per unit of resource flow. The working fluid mixture
included in the power generation system 10 in FIG. 1, for example,
may include a first chemical component and a second chemical
component. Examples of first and second chemical component
combinations are listed below in Table 2.
TABLE-US-00002 TABLE 2 Concentration Temp. Glide Range
Representative Chemical (% by mass) (.degree. K) Crit. Pressure
Bubble Point Components (A + B) A B Min. Max. (MPa) Temp. (.degree.
K) C2butene + hexane 5-90 95-10 10-17 .sup. 25-31.2 3.1-4.1 289-291
Cyclopentane + Octane 55-95 45-5 9-15.4 27.6-36.2 3.6-4.4 289-291
Isohexane + t2butene 15-95 85-5 10.5 23.8-27.2 3.1-3.9 289-291
Cyclohexane + isopentane 10-95 90-5 7.5 21.5 3.4-4.1 289-291
Pentane + propyne 10-95 90-5 5.9 22.2-31.7 3.5-5.6 289-291 Pentane
+ R245fa 30-95 70-5 4.8 8.2 3.4-4.1 289-291 Octane + R30 5-25 95-75
13.8 27.6-35.4 4.8-5.8 289-291 Heptane + R30 5-95 95-5 5.6-9.7
13.2-24.6 2.8-5.8 289-291 Isobutane + Pentane 5-90 95-10 5.3 17.7
3.4-3.8 289-291 Cyclohexane + R245ca 10-95 90-5 8.9-9.3 19.1-28.9
4.1-4.7 289-291 Hexane + R245fa 30-95 70-5 8.2 17.8-27.sup.
3.1-3.85 289-291 Isohexane + R245fa 30-95 70-5 6.5 18.2-21.9
3.1-3.9 289-291 Cyclopentane + R236ea 45-90 55-10 6.5-9.sup. 19.2
4.5-4.65 289-291 Cyclopentane + R152a 10-30 90-70 14.7 21.2-34.4
4.6-4.8 289-291 Heptane + R365mfc 25-80 75-20 13.7 17.7-23.1
2.7-3.1 289-291 Pentane + 1butene 15-95 85-5 5.2-7.4 14.8 3.5-4.0
289-291 Hexane + R1233zd 5-90 95-10 5.5-7.8 18.4 3.0-3.6 289-291
R245fa + R1234ze 25-70 75-30 5.2 11 3.7-3.9 289-291 Isopentane +
R1234ze 5-85 95-15 6.2 16.4-18.sup. 3.3-3.6 289-291 Pentane +
R1234ze 5-90 95-10 6.6 16.4-23.9 3.3-3.6 289-291 Cyclopentane +
R245fa 30-90 70-10 5.1 14.1 4.5-4.75 289-291 Cyclohexane + HFE-7000
5-80 95-20 5.7-8.5 16.1 2.7-4.0 289-291 R152a + R245fa 35-75 65-25
6.7 12.8 4.1-4.5 289-291 R30 + R152a 5-95 95-5 5.6-10.9 22.6-33.8
4.6-6.0 289-291 R236ea + R161 25-55 75-45 5.5-9.9 11.9 4.4-4.9
289-291 R30 + R1234ze 5-90 95-10 8.9 22.5-27.2 3.7-5.85 289-291
Pentane + MM 5-90 95-10 7.2 20.9-31.sup. 2.0-3.3 289-291 C7FK +
R245fa 30-90 70-10 10.2 19.1-29.8 2.8-3.4 289-291 R30 + MM 5-90
95-10 6.4-9.1 22.3-28.sup. 2.1-5.6 289-291 Novec .RTM.649 +
isobutene 25-95 75-5 8.8 15.4-26.1 2.9-4.0 289-291 Novec .RTM.649 +
R245fa 45-95 55-5 5.2 12.6 2.0-3.2 289-291 Novec .RTM.649 + R236ea
45-65 55-35 10.6 16.1 2.7-3.1 289-291 R245ca + MM 65-90 35-10 11.2
23.3-34.4 3.4-3.9 289-291 R365mfc + MM 10-75 90-25 13.3 23.1-25.1
2.0-3.0 289-291 HFE-7000 + R1234ze 10-95 90-5 6.5 .sup. 16-23.8
2.6-3.6 289-291 R30 + R245fa 30-45 70-55 5.1 5.8 4.4-4.9 289-291
Isobutane + r365mfc 25-85 75-15 5.8-9.5 .sup. 17-20.7 3.3-3.6
289-291 R152a + R365mfc 30-90 70-10 6.7-9.8 20.0-32.8 3.9-4.5
289-291 R245fa + CF3I 25-65 75-35 5.6-10.3 16.4-17.8 4.3-4.55
289-291 HFE-7000 + R1243zf 10-40 90-60 6.2-11.7 20.8 3.2-3.5
289-291 R236ea + HFE-7000 15-35 85-65 5 7.4 2.6-2.85 289-291
[0021] The thermodynamic and transport properties for the
refrigerant mixtures provided in Table 2 were generated using the
National Institute of Standards and Technology's REFPROP 8.0
database. The equations of state for these refrigerant mixtures are
generated using empirical estimation schemes (e.g. mixing rules)
contained within the database. The present invention, however, is
not limited to the aforesaid mixing rules.
[0022] The working fluid mixture may also include one or more
additional chemical components and/or compounds selected to, for
example, enhance system performance, enhance heat transfer between
the Rankine cycle fluids, enhance diagnostics, provide fire
suppression, provide lubrication, provide fluid stabilization,
provide corrosion resistance, etc. The working fluid mixture may
include, for example, flammability inhibitors, oils, lubricants,
heat transfer enhancement agents, tracers, etc.
[0023] The cooling medium may be water, air or a combination
thereof. The water may be received from an underground reservoir, a
lake, a stream or the sea. The cooling medium may also be a process
stream that may condense the working fluid mixture. The cooling
medium may be received from a heat sink having a sink temperature
between, for example, about 280.degree. K and 308.degree. K. In
other embodiments, the cooling medium may be a working fluid
mixture received from another Rankine cycle system, which will be
discussed below in further detail.
[0024] The thermal source fluid may be, for example, liquid and/or
gas received from a geothermal reservoir, a combustion engine
(e.g., a gas turbine engine, an internal combustion engine, etc.),
a solar-thermal system, an incinerator or other waste to energy
devices, or an industrial system or process. The thermal source
fluid may be received from a heat source having a source
temperature between, for example, about 360.degree. K and
623.degree. K. In other embodiments, the thermal source fluid may
be a working fluid mixture received from another Rankine cycle
system, which will be discussed below in further detail.
Alternatively, the thermal source fluid may be omitted from the
power generation system 10 where, for example, the evaporator 20 is
configured as a solar-thermal heating system (e.g., a system that
heats the working fluid mixture directly via solar energy).
[0025] In some embodiments, the turbine generator 14 may be one of
a plurality of turbine generators that are, for example, connected
in series or parallel together in the Rankine cycle system. In
other embodiments, the evaporator 20 may be one of a plurality of
evaporators that are, for example, connected in series or parallel
together in the Rankine cycle system. In still other embodiments,
the condenser 16 may be one of a plurality of condensers that are,
for example, connected in series or parallel together in the
Rankine cycle system.
[0026] According to another aspect of the invention, a power
generation system may include an intermediate heat exchanger, a
topping cycle (e.g., a first Rankine cycle system that operates at
a relatively high temperature), and a bottoming cycle (e.g., a
second Rankine cycle system that operates at a relatively low
temperature). The intermediate heat exchanger may include a
condenser passage that receives a first organic working fluid
mixture from the topping cycle, and an evaporator passage that
receives a second working fluid from the bottoming cycle. The
intermediate heat exchanger transfers thermal energy from the first
working fluid to the second working fluid. In this cascaded ORC
arrangement, the topping cycle (e.g., the high temperature ORC
system) may extract heat, either sensible such as from a hot gas or
hot liquid, or latent such as from a condensing fluid such as steam
in a refrigerant boiler/evaporator, and create a high temperature
and a high pressure vapor. The bottoming cycle (e.g., the low
cost/low temperature ORC system) may be used efficiently and cost
effectively to convert the lower temperature thermal energy to
power.
[0027] FIG. 3 is a schematic illustration of a power generation
system 36. The power generation system 36 includes an intermediate
heat exchanger 38 (e.g., a counterflow heat exchanger), a first
working fluid (e.g., an organic, non-azeotropic working fluid
mixture) that circulates through a topping cycle 40 (e.g., an
organic Rankine cycle system), and a second working fluid (e.g., an
organic, non-azeotropic working fluid mixture) that circulates
through a bottoming cycle 42 (e.g., an organic Rankine cycle
system). The intermediate heat exchanger 38 includes a first heat
exchange passage 44 and a second heat exchange passage 46. The
first heat exchange passage 44 forms a condenser passage 48 where
the first working fluid is condensed. The second heat exchange
passage 46 forms an evaporator passage 50 where the second working
fluid is evaporated. The topping cycle 40 may include a first
turbine generator 52, the condenser passage 48, a first pump 56, an
evaporator 58 (e.g., a counterflow evaporator), and a liquid
receiver/accumulator 54. The evaporator 58 may include a first heat
exchange passage 60 and a second heat exchange passage 62. The
bottoming cycle 42 may include a second turbine generator 64 a
condenser 68 (e.g., a counterflow condenser), a second liquid
receiver/accumulator 66, a second pump 70 and the evaporator
passage 50. The condenser 68 may include a first heat exchange
passage 72 and a second heat exchange passage 74.
[0028] During operation, the first working fluid may circulate
sequentially through the first turbine generator 52, the first heat
exchange passage 44 (i.e., the condenser passage 84 of heat
exchanger 38), the first liquid receiver/accumulator 54, the first
pump 56 and the second heat exchange passage 62, which may be
connected together in a closed loop circuit. The second working
fluid may circulate sequentially through the second turbine
generator 64, the first heat exchange passage 72 (i.e. the
condenser 68), the second liquid receiver/accumulator 66, the
second pump 70 and the second heat exchange passage 46 (i.e., the
evaporator passage 50 of heat exchanger 38), which may be connected
together in a closed loop circuit. A heat source fluid may be
received from a heat source 76, and directed through the first heat
exchange passage 60 (i.e., the evaporator 58). A cooling medium may
be received from a heat sink 78, and directed through the second
heat exchange passage 74 (i.e., the condenser 68).
[0029] In some embodiments, the working fluids (e.g., the
non-azeotropic working fluid mixtures) for the topping and
bottoming cycles may be selected such that the condensation
temperature of the first, higher temperature, cycle is useable for
evaporation of the second, lower temperature, cycle. In this way,
the thermal efficiencies of the organic Rankine cycle may be
increased through increased utilization of the available thermal
energy.
[0030] In some embodiments, a relatively high temperature
non-azeotropic mixture may be directed through the topping cycle
and a relatively low temperature non-azeotropic mixture may be
directed through the bottoming cycle. The use of the non-azeotropic
mixture in the topping cycle may enable increased utilization of
the thermal source fluid through glide matching. The use of a
non-azeotropic mixture in the bottoming cycle may reduce (e.g.,
minimize) irreversibilities realized in the intermediate heat
exchanger where the fluid's evaporating glide is equal to the
condensing glide of the topping cycle's working fluid mixture. FIG.
4 illustrates a temperature-entropy (T-s) phase diagram of the
aforesaid working fluid mixtures during operation of such a power
generation system. The phase diagram illustrates a first curve 400
for the non-azeotropic mixture directed through the topping cycle,
and a second curve 402 for the non-azeotropic mixture directed
through the bottoming cycle.
[0031] The difference of working temperature between the components
of the working fluid mixture may become greater as the temperature
glide increases. This difference may increase the thermal cycle
efficiency of the system. However, high temperature glide working
fluid mixtures may require condensers that include a relatively
large surface area to provide the desired heat transfer necessary
to condense the vapor into liquid. In some embodiments, therefore,
one or more of the heat exchangers (e.g., the condenser and the
evaporator) may be configured as a plate-frame counter-flow heat
exchanger, a one pass direct expansion shell and tube counter-flow
heat exchanger, or a plate-shell counter-flow heat exchanger.
[0032] In some embodiments, a non-azeotropic first working fluid
mixture may be directed through the topping cycle and a second
working fluid that exhibits relatively no temperature glide may be
directed through the bottoming cycle. The working fluid in the
bottoming cycle may include a pure substance or an azeotropic
mixture of one or more known substances (i.e., chemical
components). The non-azeotropic mixture in the topping cycle may
enable increased utilization of the thermal source fluid through
glide matching. Although the use of an azeotropic fluid or pure
substance in the bottoming cycle may increase the irreversibilities
in the intermediate heat exchanger, the negative impact associated
with glide in the bottoming cycle's condenser are reduced (e.g.,
minimized). FIG. 5 illustrates a temperature-entropy (T-s) phase
diagram of the aforesaid working fluids during operation of such a
power generation system. The phase diagram illustrates a first
curve 500 for the non-azeotropic first working fluid mixture
directed through the topping cycle, and a second curve 502 for the
second working fluid directed through the bottoming cycle.
Alternatively, in other embodiments, a first working fluid that
exhibits relatively no temperature glide may be directed through
the topping cycle, and a non-azeotropic second working fluid
mixture may be directed through the bottoming cycle.
[0033] While various embodiments of the present invention have been
disclosed, it will be apparent to those of ordinary skill in the
art that many more embodiments and implementations are possible
within the scope of the invention. The chemical components included
in the organic, non-azeotropic working fluid mixture, for example,
are not intended to be limited to the chemical groups and
components listed in Tables 1 and 2. Accordingly, the present
invention is not to be restricted except in light of the attached
claims and their equivalents.
* * * * *