U.S. patent application number 12/738028 was filed with the patent office on 2010-10-21 for cascaded organic rankine cycle (orc) system using waste heat from a reciprocating engine.
This patent application is currently assigned to UNITED TECHNOLOGIES CORPORATION. Invention is credited to Bruce P. Biederman, Joost Brasz, Frederick J. Cogswell, Jarso Mulugeta, Lili Zhang.
Application Number | 20100263380 12/738028 |
Document ID | / |
Family ID | 40526480 |
Filed Date | 2010-10-21 |
United States Patent
Application |
20100263380 |
Kind Code |
A1 |
Biederman; Bruce P. ; et
al. |
October 21, 2010 |
CASCADED ORGANIC RANKINE CYCLE (ORC) SYSTEM USING WASTE HEAT FROM A
RECIPROCATING ENGINE
Abstract
A method and system for operating a cascaded organic Rankine
cycle (ORC) system (100) utilizes two waste heat sources from a
positive-displacement engine (106), resulting in increased
efficiency of the engine (106) and the cascaded ORC system (100). A
high temperature waste heat source from the positive-displacement
engine (106) is used in a first ORC system (102) to vaporize a
first working fluid (118). A low temperature waste heat source from
the positive-displacement engine (106) is used in a second ORC
system (104) to heat a second working fluid (130) to a temperature
less than the vaporization temperature. The second working fluid
(130) is then vaporized using heat from the first working fluid
(118). In an exemplary embodiment, the positive-displacement engine
(106) is a reciprocating engine. The high temperature waste heat
source may be exhaust gas and the low temperature waste heat source
may be jacket cooling water.
Inventors: |
Biederman; Bruce P.; (Old
Greenwich, CT) ; Brasz; Joost; (Fayetteville, NY)
; Cogswell; Frederick J.; (Glastonbury, CT) ;
Mulugeta; Jarso; (West Hartford, CT) ; Zhang;
Lili; (West Hartford, CT) |
Correspondence
Address: |
KINNEY & LANGE, P.A.
THE KINNEY & LANGE BUILDING, 312 SOUTH THIRD STREET
MINNEAPOLIS
MN
55415-1002
US
|
Assignee: |
UNITED TECHNOLOGIES
CORPORATION
Hartford
CT
|
Family ID: |
40526480 |
Appl. No.: |
12/738028 |
Filed: |
October 4, 2007 |
PCT Filed: |
October 4, 2007 |
PCT NO: |
PCT/US07/21318 |
371 Date: |
April 14, 2010 |
Current U.S.
Class: |
60/651 |
Current CPC
Class: |
F01K 25/08 20130101;
F02G 5/04 20130101; F01K 23/065 20130101; Y02E 20/14 20130101; F02G
2262/00 20130101; Y02T 10/166 20130101; Y02T 10/12 20130101 |
Class at
Publication: |
60/651 |
International
Class: |
F01K 25/08 20060101
F01K025/08 |
Claims
1. A method of operating a cascaded organic Rankine cycle (ORC)
system, the method comprising: vaporizing a first organic working
fluid in a first ORC system using a high temperature heat source
from a positive-displacement engine; heating a second organic
working fluid in a second ORC system using a low temperature heat
source from the positive-displacement engine; and vaporizing the
second organic working fluid using heat from the first organic
working fluid, wherein the first organic working fluid has a higher
critical temperature than the second organic working fluid.
2. The method of claim 1 wherein the positive-displacement engine
is a reciprocating engine.
3. The method of claim 1 wherein the high temperature heat source
is exhaust gas, and the low temperature heat source is jacket
cooling water.
4. The method of claim 1 wherein a temperature of the high
temperature heat source is between approximately 475 and 540
degrees Celsius, and a temperature of the low temperature heat
source is between approximately 100 and 110 degrees Celsius.
5. The method of claim 1 wherein vaporizing the second organic
working fluid is performed by a heat exchanger configured to
condense the first organic working fluid and to vaporize the second
organic working fluid.
6. The method of claim 1 wherein heating the second organic working
fluid in the second ORC system is performed by a heat exchanger
configured to extract heat from the low temperature heat source and
to preheat the second organic working fluid.
7. The method of claim 1 wherein the first organic working fluid is
selected from a group consisting of siloxanes, toluene, isobutene,
isopentane, n-pentane and
4-trifluoromethyl-1,1,1,3,5,5,5-heptafluoro-2-pentene
((CF.sub.3).sub.2CHCF.dbd.CHCF.sub.3).
8. The method of claim 1 wherein the second organic working fluid
is selected from a group consisting of R123, R134a, R236fa and
R245fa.
9. The method of claim 1 further comprising: heating an external
source using heat from the second organic working fluid.
10. (canceled)
11. A waste heat recovery system comprising: a first organic
Rankine cycle (ORC) system configured to vaporize a first organic
working fluid using a high temperature waste heat source from a
reciprocating engine, and to generate power using the first organic
working fluid; a second organic Rankine cycle (ORC) system
configured to receive heat from the first organic working fluid to
vaporize a second organic working fluid, and to generate power
using the second organic working fluid; and a heat exchanger
configured to increase a temperature of the second organic working
fluid using a low temperature waste heat source from the
reciprocating engine and prior to vaporizing the second organic
working fluid, wherein a critical temperature of the first organic
working fluid is greater than a critical temperature of the second
organic working fluid.
12. The waste heat recovery system of claim 11 wherein the high
temperature waste heat source passes through an evaporator of the
first ORC system to vaporize the first organic working fluid.
13. The waste heat recovery system of claim 12 wherein the first
organic working fluid passes through a condenser located downstream
of the evaporator of the first ORC system to condense the first
organic working fluid and vaporize the second organic working
fluid.
14. The waste heat recovery system of claim 11 wherein the heat
exchanger is located downstream of a condenser of the second ORC
system and upstream of an evaporator of the second ORC system.
15. The waste heat recovery system of claim 11 wherein the high
temperature waste heat source is exhaust gas from the reciprocating
engine, and the low temperature waste heat source is jacket cooling
water from the reciprocating engine.
16. (canceled)
17. The waste heat recovery system of claim 11 further comprising:
a heat sink configured to receive heat from the second organic
working fluid and to provide heating to an external source.
18. A method of operating a cascaded organic Rankine cycle (ORC)
system having a first ORC system configured to circulate a first
working fluid and a second ORC system configured to circulate a
second working fluid, the method comprising: vaporizing the first
working fluid in an evaporator of the first ORC system using
exhaust gas from a reciprocating engine; heating the second working
fluid upstream of an evaporator of the second ORC system using
cooling water from the reciprocating engine; and vaporizing the
second working fluid in the evaporator of the second ORC system
using heat from the first working fluid of the first ORC system,
wherein a critical temperature of the first working fluid is
greater than a critical temperature of the second working
fluid.
19. The method of claim 18 wherein the evaporator of the second ORC
system is configured as a condenser of the first ORC system.
20. The method of claim 18 wherein the first working fluid is
selected from a group consisting of siloxanes, toluene, isobutene,
isopentane, n-pentane and
4-trifluoromethyl-1,1,1,3,5,5,5-heptafluoro-2-pentene
((CF.sub.3).sub.2CHCF.dbd.CHCF.sub.3), and the second working fluid
is selected from a group consisting of R123, R134a, R236fa and
R245fa.
21. The method of claim 18 wherein a temperature of the exhaust gas
exiting the reciprocating engine is between approximately 475 and
540 degrees Celsius, and a temperature of the cooling water exiting
the reciprocating engine is between approximately 100 and 110
degrees Celsius.
22. The method of claim 18 further comprising: heating an external
source using heat from the second working fluid in the second ORC
system.
Description
BACKGROUND
[0001] The present disclosure relates to an organic Rankine cycle
(ORC) system. More particularly, the present disclosure relates to
operating a cascaded ORC system using two waste heat sources from a
reciprocating engine.
[0002] Rankine cycle systems are commonly used for generating
electrical power. The Rankine cycle system includes an evaporator
or a boiler for evaporation of a motive fluid, a turbine that
receives the vapor from the evaporator to drive a generator, a
condenser for condensing the vapor, and a pump or other means for
recycling the condensed fluid to the evaporator. The motive fluid
in Rankine cycle systems is often water, and the turbine is thus
driven by steam. An organic Rankine cycle (ORC) system operates
similarly to a traditional Rankine cycle, except that an ORC system
uses an organic fluid, instead of water, as the motive fluid.
[0003] The ORC system uses a waste heat source to provide heat to
vaporize the organic fluid in the evaporator. A reciprocating
engine is a common source of waste heat for an ORC system. Usable
waste heat from the reciprocating engine may include exhaust gas at
temperatures near approximately 540 degrees Celsius (approximately
1000 degrees Fahrenheit), as well as cooling water at approximately
105 degrees Celsius (approximately 220 degrees Fahrenheit).
Challenges arise in trying to use both of the waste heat sources
from the reciprocating engine, particularly given the temperature
difference between them. As such, the exhaust gas is typically
preferred over the cooling water, given the potential for greater
heat transfer.
[0004] To effectively utilize the high-temperature exhaust heat
from the reciprocating engine, the ORC system typically uses an
organic fluid with a high critical temperature, allowing boiling at
elevated temperatures. However, expanding an organic fluid with a
single turbine over a large pressure ratio causes the vapor exiting
the turbine to be more superheated, thus limiting the amount of
power captured by the turbine. The highly superheated fluid exiting
the turbine may also require special condensation equipment.
[0005] There is a need for an improved method and system of
recovering waste heat from a reciprocating engine in order to
increase efficiency of the reciprocating engine and the ORC
system.
SUMMARY
[0006] A method and system for operating a cascaded organic Rankine
cycle (ORC) system utilizes two waste heat sources from a
positive-displacement engine, resulting in increased efficiency of
the engine and the cascaded ORC system. A high temperature waste
heat source from the positive-displacement engine is used in a
first ORC system to vaporize a first working fluid. A low
temperature waste heat source from the positive-displacement engine
is used in a second ORC system to heat a second working fluid to a
temperature less than the vaporization temperature. The second
working fluid is then vaporized using heat from the first working
fluid. The first working fluid has a higher critical temperature
than the second working fluid. In an exemplary embodiment, the
positive-displacement engine is a reciprocating engine and the
waste heat sources are exhaust gas and jacket cooling water.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a schematic of an organic Rankine cycle (ORC)
system designed to produce electrical power using waste heat.
[0008] FIG. 2 is a schematic of a cascaded ORC system with a first
ORC system and a second ORC system, designed to utilize two waste
heat sources from a reciprocating engine.
[0009] FIG. 3 is a T-s diagram for the cascaded ORC system of FIG.
2.
DETAILED DESCRIPTION
[0010] A waste heat recovery system, such as an organic Rankine
cycle (ORC) system, may be used to capture heat from a prime mover,
such as a reciprocating engine. The ORC system may then be used to
generate electrical power. A reciprocating engine has two sources
of waste heat that may be recoverable by the ORC system--exhaust
gas (high temperature) and cooling water (low temperature).
However, given the large temperature difference between the waste
heat sources, it is difficult to effectively utilize both of these
waste heat sources in a single ORC system. As described herein, in
a cascaded ORC system, a first ORC system utilizes a high
temperature working fluid to power a generator and a second ORC
system utilizes a low temperature working fluid to power a second
generator. The first ORC system recovers heat from the exhaust gas
of the reciprocating engine. The second ORC system recovers heat
from the cooling water of the reciprocating engine, as well as the
heat of condensation from the high temperature working fluid of the
first ORC system. The cascaded ORC system and method described
herein utilizes more of the waste heat from the reciprocating
engine, and thus generates a greater amount of power per unit of
waste heat from the reciprocating engine.
[0011] FIG. 1 is a schematic of a single ORC system 10, which
includes condenser 12, pump 14, evaporator 16, and turbine 18.
Working fluid 22 circulates through system 10 and is used to
generate electrical power. Liquid working fluid 22a from condenser
12 passes through pump 14, resulting in an increase in pressure.
High pressure liquid fluid 22a enters evaporator 16, which utilizes
heat source 24 to vaporize fluid 22. Heat source 24 may include,
but is not limited to, any type of waste heat resource, including
reciprocating engines, fuel cells, and microturbines, and other
types of heat sources such as solar, geothermal or waste gas.
Working fluid 22 exits evaporator 16 as a vapor (22b), at which
point it passes into turbine 18. Vaporized working fluid 22b is
used to drive turbine 18, which in turn powers generator 28 such
that generator 28 produces electrical power. Vaporized working
fluid 22b exiting turbine 18 is returned to condenser 12, where it
is condensed back to liquid 22a. Heat sink 30 is used to provide
cooling to condenser 12.
[0012] In those cases in which heat source 24 is a high temperature
heat source, working fluid 22 is preferably a high temperature
fluid having a high critical temperature. In that case, heat source
24 is able to transfer sufficient heat to the working fluid, while
maintaining the working fluid below the critical temperature in
evaporator 16. A disadvantage of such a high temperature working
fluid, however, is that when it exits turbine 18, it is highly
superheated. At least a portion of the heat from the superheated
vapor is not converted into power, and thus turbine 18 has a low
efficiency. Moreover, the high temperature working fluid requires
additional cooling in condenser 12, resulting in expensive
equipment and typically a large amount of unrecoverable waste heat
from the working fluid.
[0013] In contrast, if heat source 24 is a low temperature heat
source, a low temperature working fluid may be used within system
10. However, there is a reduced efficiency in power output, as
compared to when system 10 recovers heat from a high temperature
heat source.
[0014] In the scenario in which heat source 24 is waste heat from a
reciprocating engine, ORC system 10 typically uses either the
exhaust gas (i.e. high temperature waste heat) or the jacket
cooling water (i.e. low temperature waste heat), since it is
difficult to use both. As such, some of the waste heat from the
reciprocating engine is unrecoverable by ORC system 10.
[0015] FIG. 2 is a schematic of cascaded ORC system 100 having
first ORC system 102 and second ORC system 104, both of which
recover waste heat from reciprocating engine 106. First ORC system
102 is similar to ORC system 10 of FIG. 1 and includes evaporator
110, turbine 112, condenser 114, and pump 116. First working fluid
118 is circulated through system 102 and used to drive turbine 112,
which enables generator 120 to produce electrical power. Second ORC
system 104 includes turbine 122, condenser 124, pump 126, heat
exchanger 128, and evaporator 114. Second working fluid 130 is used
in second ORC system 104 to drive turbine 122, which powers
generator 132. Condenser 124 of second ORC system 104 uses heat
sink 134 to provide cooling and condense vaporized working fluid
130 from turbine 122. Heat sink 134 may be water or air, and in
some cases, heat sink 134 may be used to provide useful heating to
an external source, as discussed further below. First working fluid
118 and second working fluid 130 are organic working fluids,
examples of which are provided below.
[0016] Condenser 114 of first ORC system 102 also functions as the
evaporator of second ORC system 104. As described further below,
first working fluid 118 is a high temperature working fluid and
second working fluid 130 is a low temperature working fluid. As
such, evaporator/condenser 114 is configured such that vaporized
working fluid 118 from turbine 112 is condensed, thereby
transferring heat to vaporize second working fluid 130.
[0017] Reciprocating engine 106 has two sources of waste heat
recoverable by system 100. The first source is exhaust gas ranging
in temperature from approximately 475 to 540 degrees Celsius
(approximately 885 to 1005 degrees Fahrenheit). The second source
is jacket cooling water with a temperature range of approximately
100 to 110 degrees Celsius (approximately 212 to 230 degrees
Fahrenheit). Heat from the exhaust gas is used by first ORC system
102. More specifically, exhaust gas is used by evaporator 110 to
vaporize working fluid 118.
[0018] Second ORC system 104 receives heat from the jacket cooling
water. Heat exchanger 128 of system 104 is located between pump 126
and evaporator 114, and is designed to transfer heat from the
jacket cooling water to liquid working fluid 130. Because jacket
cooling water is a lower temperature waste heat source, as compared
to the exhaust gas, the jacket cooling water is used to heat
working fluid 130 to a temperature that is less than its
vaporization temperature. Thus, working fluid 130 has a higher
temperature at an outlet of heat exchanger 128 compared to its
temperature at an inlet of heat exchanger 128. The jacket cooling
water may be recycled back to reciprocating engine 106 after
exiting heat exchanger 128.
[0019] After passing through heat exchanger 128, second working
fluid 130 passes through condenser/evaporator 114, which is
designed to transfer heat between first working fluid 118 and
second working fluid 130, such that first working fluid 118
condenses to a liquid and second working fluid 130 is vaporized.
First working fluid 118 preferably has a condensation temperature
that is suitable to boil second working fluid 130.
[0020] Second working fluid 130 passes from evaporator 114 to
turbine 122, and then to condenser 124, which may be a water-cooled
condenser or an air-cooled condenser (i.e. heat sink 134 is water
or air). In some embodiments, after water in heat sink 134 exits
condenser 124, the heated water may be used to provide heating to a
source external to cascaded ORC system 100. For example, heat sink
134 may be used to heat district heating water and/or provide
environmental heating, for example, to agricultural crops or
greenhouses.
[0021] Using cascaded ORC system 100, it is possible to utilize
essentially all of the waste heat from reciprocating engine 106.
The high temperature waste heat source (the exhaust gas) is
recovered by ORC system 102 which utilizes a high temperature
working fluid. The low temperature waste heat source (the jacket
cooling water) is recovered by ORC system 104, which utilizes a low
temperature working fluid. Moreover, the design of cascaded ORC
system 100 results in greater efficiency overall since the heat
from first working fluid 118 exiting turbine 112 may be transferred
to second working fluid 130. An efficiency of second ORC system 104
is increased by preheating second working fluid 130 in heat
exchanger 128. Moreover, the heat utilization efficiency of ORC
system 100 may be further increased by using heat sink 134 to heat
a source external to cascaded ORC system 100.
[0022] First working fluid 118 has a higher critical temperature
than second working fluid 130. Because exhaust gas from
reciprocating engine 106 is used in evaporator 110 to vaporize
first working fluid 118, working fluid 118 preferably has a high
critical temperature such that it is able to boil at a high
temperature inside evaporator 110. Operating with the working fluid
in the supercritical phase presents technical challenges that are
preferably avoided by remaining below the critical temperature.
[0023] On the other hand, since second ORC system 104 uses lower
temperature heat sources (i.e. cooling water and lower-temperature
condensation heat of working fluid 118) to vaporize second working
fluid 130, working fluid 130 preferably has a low critical
temperature compared to working fluid 118. If a working fluid with
a high critical temperature were used in second ORC system 104, the
pressures inside system 104 may become too low, resulting in low
fluid densities and requiring larger equipment.
[0024] First working fluid 118 may include, but is not limited to,
siloxanes, toluene, isobutene, isopentane, n-pentane and
4-trifluoromethy1-1,1,1,3,5,5,5-heptafluoro-2-pentene
((CF.sub.3).sub.2CHCF.dbd.CHCF.sub.3). Examples of siloxanes that
are suitable for first working fluid 118 include, but are not
limited to, MM hexamethyldisiloxane (C.sub.6H.sub.18OSi.sub.2), MDM
octamethyltrisiloxane (C.sub.8H.sub.24O.sub.2Si.sub.3), and MD2M
decamethyltetrasiloxane (C.sub.10H.sub.30O.sub.3Si.sub.4). In some
embodiments, siloxanes may be preferred over toluene, isobutene,
isopentane, and n-pentene, which are flammable.
[0025] Second working fluid 130 may include, but is not limited to,
R123, R134a, R236fa and R245fa. In preferred embodiments, R134a or
R245fa is used in ORC system 104. If an ambient air temperature is
cooler, thereby reducing a temperature of heat sink 34, then R134
may be preferred; if the ambient air temperature is warmer, then
R245fa may be preferred.
[0026] It is recognized that first working fluid 118 and second
working fluid 130 may include organic working fluids not listed
above. Numerous combinations of first working fluid 118 and second
working fluid 130 may be used. As stated above, cascaded ORC system
100 is preferably operated with first working fluid 118 having a
higher critical temperature than second working fluid 130.
[0027] FIG. 3 is a T-s diagram for cascaded ORC system 100 of FIG.
2. For both first working fluid 118 and second working fluid 130,
temperature T is plotted as a function of entropy S. As described
in more detail below, FIG. 3 illustrates the thermal energy
transfer from the exhaust gas of reciprocating engine 106 to first
working fluid 118, and from the jacket cooling water of engine 106
to second working fluid 130. As also shown in FIG. 3, first working
fluid 118 transfers heat to second working fluid 130, and second
working fluid 130 then transfers heat to heat sink 134.
[0028] Heat from the exhaust gas of reciprocating engine 106 is
transferred to first working fluid 118, which increases a
temperature of working fluid 118 until fluid 118 reaches its
vaporization temperature, as shown in FIG. 3. Fluid 118 remains
below the critical temperature T.sub.1 critical. As vaporized fluid
118 expands in turbine 112, its temperature decreases, however
fluid 118 remains in the vapor phase. In condenser 114, which also
functions as an evaporator for second ORC system 104, fluid 118 is
desuperheated until it reaches its condensation temperature. The
heat from fluid 118 is transferred to second working fluid 130 in
condenser/evaporator 114. The temperature of fluid 130 remains
below the critical temperature T.sub.2 critical.
[0029] Heat from first working fluid 118 is sufficient to vaporize
second working fluid 130 inside condenser/evaporator 114. This is
due, in part, to preheating of second working fluid 130 upstream of
condenser/evaporator 114. As shown in FIG. 3, jacket cooling water
from reciprocating engine 106 is used to increase a temperature of
working fluid 130 to a temperature below the vaporization
temperature.
[0030] As similarly described for fluid 118, second working fluid
130 shows a decrease in temperature after passing through turbine
122. At that point, superheated fluid 130 is condensed inside
condenser/heater 124 using ambient air or cooling water from heat
sink 134. In other words, heat from second working fluid 130 is
transferred to heat sink 34, as shown in FIG. 3. As described
above, heat sink 34, in some embodiments, may be used to provide
heating to an external source, such as, for example, a
greenhouse.
[0031] In the exemplary embodiment of FIG. 2, cascaded ORC system
100 uses two waste heat sources from a reciprocating engine. The
low temperature heat source is jacket cooling water. It is
recognized that other types of positive-displacement engines, in
addition to reciprocating engines, that require cooling water
during engine operation may also be used to supply waste heat to
system 100. This may include, but is not limited to, rotary
engines, such as, for example, the Wankel engine.
[0032] The cascaded ORC system described herein uses two distinct
waste heat sources from a reciprocating engine. Since two ORC
systems are used, the cascaded ORC system generates additional
power. Because there is no change in the emission levels of the
reciprocating engine, the cascaded ORC system results in a
reduction in emissions from the reciprocating engine per unit of
power generated. Moreover, the cascaded ORC system described herein
reduces any waste heat from the first and second ORC systems. Thus,
the method and system described herein results in improved
efficiency of the reciprocating engine and each of the ORC
systems.
[0033] Although the present invention has been described with
reference to preferred embodiments, workers skilled in the art will
recognize that changes may be made in form and detail without
departing from the spirit and scope of the invention.
* * * * *