U.S. patent application number 13/512689 was filed with the patent office on 2013-05-30 for direct evaporator system and method for organic rankine cycle systems.
The applicant listed for this patent is Sebastian Walter Freund, Matthew Alexander Lehar, Giacomo Seghi, Giulio De Simon. Invention is credited to Sebastian Walter Freund, Matthew Alexander Lehar, Giacomo Seghi, Giulio De Simon.
Application Number | 20130133868 13/512689 |
Document ID | / |
Family ID | 42312094 |
Filed Date | 2013-05-30 |
United States Patent
Application |
20130133868 |
Kind Code |
A1 |
Lehar; Matthew Alexander ;
et al. |
May 30, 2013 |
DIRECT EVAPORATOR SYSTEM AND METHOD FOR ORGANIC RANKINE CYCLE
SYSTEMS
Abstract
Systems and methods include heat exchangers using Organic
Rankine Cycle (ORC) fluids in power generation systems. A system
for power generation using an ORC comprises: a heat exchanger
configured to be mounted entirely inside a duct, the heat exchanger
comprising a single inlet which traverses from an outer side of the
duct to an inner side of the duct, a single outlet which traverses
from the inner side of the duct to the outer side of the duct, and
a conduit connecting the single inlet to the single outlet, the
conduit being provided entirely inside the duct.
Inventors: |
Lehar; Matthew Alexander;
(Munich, DE) ; Freund; Sebastian Walter;
(Unterfoehring, DE) ; Simon; Giulio De; (Firenze,
IT) ; Seghi; Giacomo; (Firenze, IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lehar; Matthew Alexander
Freund; Sebastian Walter
Simon; Giulio De
Seghi; Giacomo |
Munich
Unterfoehring
Firenze
Firenze |
|
DE
DE
IT
IT |
|
|
Family ID: |
42312094 |
Appl. No.: |
13/512689 |
Filed: |
November 8, 2010 |
PCT Filed: |
November 8, 2010 |
PCT NO: |
PCT/US10/55786 |
371 Date: |
July 25, 2012 |
Current U.S.
Class: |
165/168 |
Current CPC
Class: |
F22B 29/067 20130101;
F28F 9/00 20130101; F01K 25/08 20130101 |
Class at
Publication: |
165/168 |
International
Class: |
F28F 9/00 20060101
F28F009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 30, 2009 |
IT |
CO2009A000057 |
Claims
1. A system for power generation using an Organic Rankine Cycle
(ORC), the system comprising: a heat exchanger configured to be
mounted entirely inside a duct, the heat exchanger comprising: a
single inlet which traverses from an outer side of the duct to an
inner side of the duct; a single outlet which traverses from the
inner side of the duct to the outer side of the duct; and a conduit
between the single inlet and the single outlet, the conduit being
provided entirely inside the duct, wherein the heat exchanger is
configured to receive an ORC fluid at the single inlet as a
pressurized liquid at a pressure greater than or equal to a
critical pressure of the ORC fluid, to heat the ORC fluid to a
temperature greater than or equal to a critical temperature of the
ORC fluid, and to exit the ORC fluid through the single outlet as a
supercritical fluid, and wherein the supercritical fluid is defined
by the temperature being greater than the critical temperature and
the pressure being greater than the critical pressure.
2. The system of claim 1, wherein the critical pressure and
critical temperature for the ORC fluid define a point at which the
ORC fluid becomes supercritical.
3. The system of claim 1, wherein the ORC fluid is selected from a
group comprising pentane, propane, cyclohexane, butane, a
fluorohydrocarbon, a ketone, an aromatic, or a combination
thereof.
4. The system of claim 1, wherein the ORC fluid is heated to a
temperature greater than or equal to the critical temperature of
the ORC fluid inside of the conduit without leaving the exhaust
duct.
5. The system of claim 1, wherein the heat exchanger is one of a
plate or plate-and-fin heat exchanger.
6. A system for power generation using an Organic Rankine Cycle
(ORC), the system comprising: a heat exchanger configured to be
mounted inside a duct, the heat exchanger comprising: an inlet
which traverses from an outer side of the duct to an inner side of
the duct and is configured to receive an ORC fluid; an outlet which
traverses from the inner side of the duct to the outer side of the
duct and is configured to exit the ORC fluid; and a conduit
connecting the inlet to the outlet and configured to heat the ORC
fluid, wherein the heat exchanger is configured to operate in a
near-critical region of the ORC fluid, and wherein the
near-critical region of the ORC fluid being is described by an
upper half of a curve linking a triple point and a critical point
for the ORC fluid, and the curve is defined by pressure values and
temperature values which define boiling points for the ORC
fluid.
7. The system of claim 6, wherein the heat exchanger further
comprises: a preheater section connected to the inlet and located
towards a cooler end of the duct; an evaporator section connected
to the preheater section and located towards a warmer end of the
duct, the evaporator section being configured to evaporate a
pressurized liquid; and a superheater section connected to the
evaporator section and connected to the outlet, the superheater
section being located between the preheater section and the
evaporator section and the superheater section being configured to
superheat a vapor from the evaporator section.
8. The system of claim 6, wherein the near-critical region of the
ORC fluid is described by an upper twenty percent of the curve
linking the triple point and the critical point for the ORC
fluid.
9. A method for performing a heat exchange in a power generation
system using an Organic Rankine Cycle (ORC) fluid, the method
comprising: receiving at a heat exchanger heat from a source,
wherein the heat exchanger is configured to be mounted entirely
inside a duct, the heat exchanger having a single inlet, a conduit
and a single outlet; receiving the ORC fluid as a pressurized
liquid at a pressure greater than or equal to a critical pressure
of the ORC fluid at the single inlet which traverses from an outer
side of the duct to an inner side of the duct; exiting the ORC
fluid in a supercritical phase at the single outlet which traverses
from the inner side of the duct to the outer side of the duct; and
passing the ORC fluid through the conduit between the single inlet
and the single outlet, the conduit being provided entirely inside
the duct, while heating the ORC fluid to change from the
pressurized liquid to the supercritical fluid, wherein the heat
exchanger is configured to heat the ORC fluid to a temperature
greater than or equal to a critical temperature of the ORC fluid,
and to exit the ORC fluid through the single outlet as a
supercritical fluid, and wherein the supercritical fluid is defined
by the temperature being greater than the critical temperature and
the pressure being greater than the critical pressure.
10. A method for heating an Organic Rankine Cycle (ORC) fluid in a
heat exchanger, the method comprising: receiving at a heat
exchanger heat from a source, wherein the heat exchanger is
configured to be mounted inside a duct and has an inlet, a conduit
and an outlet; receiving the ORC fluid as a pressurized liquid at
the inlet which traverses from an outer side of the duct to an
inner side of the duct; exiting the ORC fluid in a near-critical
region at the outlet which traverses from the inner side of the
duct to the outer side of the duct, and passing the ORC fluid
through the conduit between the inlet and the outlet, the conduit
being provided inside the duct, while heating the ORC fluid to
change from the pressurized liquid to the near-critical region,
wherein the near-critical region of the ORC fluid is described by
an upper half of a curve linking a triple point and a critical
point for the ORC fluid, and wherein the curve is defined by
pressure values and temperature values which define boiling points
for the ORC fluid.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a national stage application under 35 U.S.C.
.sctn.371(c) of prior-filed, co-pending PCT patent application
serial number PCT/US2010/055786, filed on Nov. 8, 2010, which
claims priority to Italian Patent Application Serial No.
CO2009A000057, filed on Nov. 30, 2009, the entire contents of which
are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] Embodiments of the subject matter disclosed herein generally
relate to power generation systems and more particularly to Organic
Rankine Cycle (ORC) systems.
[0004] 2. Description of the Related Art
[0005] Rankine cycles use a working fluid in a closed cycle to
gather heat from a heating source or a hot reservoir by generating
a hot gaseous stream that expands through a turbine to generate
power. The expanded stream is condensed in a condenser by
transferring heat to a cold reservoir and pumped up to a heating
pressure again to complete the cycle. Power generation systems such
as gas turbines or reciprocating engines (primary system) produce
hot exhaust gases that are either used in a subsequent power
production process (by a secondary system) or lost as waste heat to
the ambient. For example, the exhaust of a large engine may be
recovered in a waste heat recovery system used for production of
additional power, thus improving the overall system efficiency. A
common waste heat power generation system is a Rankine cycle as
shown in FIG. 1.
[0006] The power generation system 100 includes a heat exchanger 2,
also known as a boiler, a turbine 4, a condenser 6 and a pump 8.
Walking through this closed loop system, beginning with the heat
exchanger 2, an external heat source 10, e.g., hot flue gases,
heats the heat exchanger 2. This causes the received pressurized
liquid medium 12 to turn into a pressurized vapor 14, which flows
to the turbine 4. The turbine 4 receives the pressurized vapor
stream 14 and can generate power 16 as the pressurized vapor
expands. The expanded lower pressure vapor stream 18 released by
the turbine 4 enters the condenser 6, which condenses the expanded
lower pressure vapor stream 18 into a lower pressure liquid stream
20. The lower pressure liquid stream 20 then enters the pump 8,
which both generates the higher pressure liquid stream 22 and keeps
the closed loop system flowing. The higher pressure liquid stream
12 then is pumped to the heat exchanger 2 to continue this
process.
[0007] One working fluid that can be used in a Rankine cycle is an
organic working fluid. Such an organic working fluid is referred to
as an organic Rankine cycle (ORC) fluid. ORC systems have been
deployed as retrofits for engines as well as for small-scale and
medium-scale gas turbines, to capture waste heat from the hot flue
gas stream. This waste heat may be used in a secondary power
generation system to generate up to an additional 20% power on top
of the power delivered by the engine producing the hot flue gases
alone.
[0008] A conventional boiler 2, which is often used to heat fluids
under subcritical conditions, is now described with respect to FIG.
2. Initially, a pressurized ORC liquid 204 enters a heat exchanger
202 in a preheating section 206, which is typically located towards
the cooler end of a gas flow 218, inside exhaust duct 216. From a
preheating section 206 the ORC fluid moves into an evaporator
section 208 for evaporation. Because during transient operation not
all the ORC fluid may have evaporated, the ORC fluid exits from the
evaporator section 208 and enters into a separating drum 210, which
separates out any liquid that did not evaporate. The multiple
piercings of the duct 216, four in this example, are shown by the
"X"s 220. The vapor then reenters duct 216 to enter a superheating
section 212 of the heat exchanger 202 for superheating. The vapor
then exits as superheated ORC vapor 214 en route to the expansion
stage of the ORC cycle. FIG. 2 shows a simplified ORC heating
system. However, an ORC system includes other elements between
evaporator section 208 and superheating section 212, traditionally
placed outside duct 216, which are not shown.
[0009] ORC systems often operate below the critical pressure of the
working fluid. When a fluid is below its critical point, but above
its triple point (a point at which the fluid can coexist as a
liquid, vapor, and solid) along a curve connecting the triple point
and the critical point on a pressure versus temperature diagram,
the fluid can be a gas, a liquid or performing the phase change
between the two, e.g., evaporating. At temperature and pressure
combinations above the critical point, i.e., where the pressure and
temperature are both above the critical point, the fluid is
considered to be a supercritical fluid. A graphical representation
of these regions is shown in FIG. 3 and is now described. Some
media, including ORC fluids, can be described using a pressure (P)
versus temperature (T) diagram 300 to illustrate certain
characteristics of the medium under various pressures and
temperatures. Point A represents the triple point. Point B
represents the critical point for which the pressure and
temperature are both at their respective Pc and Tc values and
beyond this point there is no clear distinction between the liquid
phase and the gas phase, i.e., there is no phase transition. The
curve 302 linking A and B represents those points having various
temperatures and pressure combinations where the medium can boil,
with the gas phase being the region 304 below the curve 302 and the
liquid phase being the region 306 above the curve 302.
[0010] A subcritical region is defined by those points on curve
302, along a lower 50% of curve 302. ORC systems generally operate
in the subcritical region using various types of heat exchanger
designs. One such heat exchanger is a plate-fin system, which is
generally considered to be a compact heat exchanger. However,
compact heat exchangers are not generally used to heat a working
fluid in a near-critical or supercritical region in an ORC system
because the relatively low pressure vapor generated during boiling
creates impractically large pressure drops through the narrow
channels within the heat exchanger. For this reason, the plate-fin
system is used in the subcritical region. Operating ORC systems in
the supercritical region can generate an efficiency improvement in
the power generation system. However the exchangers for such a
region are expensive to build.
[0011] Accordingly, systems and methods for reducing cost and
improving the efficiency for using ORC systems in power generation
systems are desirable.
BRIEF SUMMARY OF THE INVENTION
[0012] According to an exemplary embodiment a system for power
generation using an Organic Rankine Cycle (ORC) is provided. The
system comprises: a heat exchanger configured to be mounted
entirely inside a duct, the heat exchanger being configured to
include, a single inlet which traverses from an outer side of the
exhaust duct to an inner side of the duct, a single outlet which
traverses from the inner side of the duct to the outer side of the
duct, and a conduit between the single inlet and the single outlet,
the conduit being provided entirely inside the duct. The heat
exchanger is configured to receive an ORC fluid at the single inlet
as a pressurized liquid at a pressure greater than or equal to the
critical pressure of the ORC fluid, to heat the ORC fluid to a
temperature greater than or equal to the critical temperature of
the ORC fluid, and to exit the ORC fluid through the single outlet
as a supercritical fluid. The supercritical fluid is defined as
having a temperature greater than the critical temperature and a
pressure greater than the critical pressure.
[0013] According to another exemplary embodiment, a system for
power generation using an Organic Rankine Cycle (ORC) is provided.
The system comprises a heat exchanger configured to be mounted
inside a duct. The heat exchanger is configured to include an inlet
which traverses from an outer side of the duct to an inner side of
the duct and is configured to receive an ORC fluid, an outlet which
traverses from the inner side of the duct to the outer side of the
duct and is configured to discharge the ORC fluid, and a conduit
connecting the inlet and the outlet and configured to heat the ORC
fluid. The heat exchanger is configured to operate in a
near-critical region of the ORC fluid. The near-critical region of
the ORC fluid is described by an upper half of a curve linking a
triple point and a critical point for the ORC fluid, and the curve
is defined by pressure values and temperature values which define
boiling points for the ORC fluid.
[0014] According to another exemplary embodiment, a method for
performing a heat exchange in a power generation system using an
Organic Rankine Cycle (ORC) fluid is provided. The method
comprises: receiving at a heat exchanger heat from a source,
wherein the heat exchanger is configured to be mounted entirely
inside a duct, the heat exchanger having a single inlet, a conduit
and a single outlet; receiving said ORC fluid as a pressurized
liquid at a pressure greater than or equal to a critical pressure
of the ORC fluid at the single inlet which traverses from an outer
side of the duct to an inner side of the duct; exiting the ORC
fluid in a supercritical phase at the single outlet which traverses
from the inner side of the duct to the outer side of the duct; and
passing the ORC fluid through the conduit between the single inlet
and the single outlet. The conduit is provided entirely inside the
duct. The ORC fluid is heated to change from the pressurized liquid
to a supercritical fluid. The heat exchanger is configured to heat
the ORC fluid to a temperature greater than or equal to a critical
temperature of the ORC fluid, and to exit the ORC fluid through the
single outlet as a supercritical fluid. The supercritical fluid is
defined by the temperature being greater than the critical
temperature and the pressure being greater than the critical
pressure.
[0015] According to another exemplary embodiment, a method for
heating an Organic Rankine Cycle (ORC) fluid in a heat exchanger is
provided. The method comprises: receiving at a heat exchanger heat
from a source, wherein the heat exchanger is configured to be
mounted inside a duct and has an inlet, a conduit and an outlet;
receiving the ORC fluid as a pressurized liquid at the inlet which
traverses from an outer side of the duct to an inner side of the
duct; exiting the ORC fluid in a near-critical region at the outlet
which traverses from the inner side of the duct to the outer side
of the duct, and passing the ORC fluid through the conduit between
the inlet and the outlet, the conduit being provided inside the
duct. The ORC fluid is heated to change from the pressurized liquid
to the near-critical region. The near-critical region of the ORC
fluid is described by an upper half of a curve linking a triple
point and a critical point for the ORC fluid, and the curve is
defined by pressure values and temperature values which define
boiling points for the ORC fluid.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Other objects, features and advantages of the embodiments of
the present invention will appear on reading the following
description, given only as a non-limiting example, and made with
reference to the appended drawings in which:
[0017] FIG. 1 depicts a conventional Rankine Cycle;
[0018] FIG. 2 illustrates a heat exchanger which uses an organic
fluid disposed within an exhaust duct;
[0019] FIG. 3 shows a generic phase change diagram;
[0020] FIG. 4 illustrates a once-through heat exchanger according
to exemplary embodiments;
[0021] FIG. 5 shows a once-through heat exchanger for subcritical
and near-critical operations according to exemplary
embodiments;
[0022] FIG. 6 shows a once-through heat exchanger for subcritical
and near-critical operations according to other exemplary
embodiments;
[0023] FIG. 7 illustrates an ORC cycle for a near-critical
operation according to exemplary embodiments;
[0024] FIG. 8 shows a vertical tube heat exchanger according to
exemplary embodiments;
[0025] FIG. 9 shows a plate-and-fin heat exchanger to be used in a
near-critical or supercritical operation according to exemplary
embodiments;
[0026] FIG. 10 is a flowchart illustrating steps for operating a
heat exchanger in a supercritical region according to exemplary
embodiments; and
[0027] FIG. 11 is a flowchart illustrating steps for operating a
heat exchanger in a near-critical region according to exemplary
embodiments.
DETAILED DESCRIPTION OF THE INVENTION
[0028] The following detailed description of the exemplary
embodiments refers to the accompanying drawings. The same reference
numbers in different drawings identify the same or similar
elements. Additionally, the drawings are not necessarily drawn to
scale. Also, the following detailed description does not limit the
invention. Instead, the scope of the invention is defined by the
appended claims. For simplicity, the following description refers
to a heat exchanger being placed in a duct in which flue gases are
passing. However, the heat source may be different, for example,
geothermal water and the heat exchanger may not be placed in a
duct.
[0029] Reference throughout the specification to "one embodiment"
or "an embodiment" means that a particular feature, structure, or
characteristic described in connection with an embodiment is
included in at least one embodiment of the subject matter
disclosed. Thus, the appearance of the phrases "in one embodiment"
or "in an embodiment" in various places throughout the
specification is not necessarily referring to the same embodiment.
Further, the particular features, structures or characteristics may
be combined in any suitable manner in one or more embodiments.
[0030] As described in the Background, and shown in FIG. 1, a
Rankine cycle can be used in secondary power generation systems to
reuse some of the wasted energy from the hot exhaust gases of the
primary power generation system. A primary system produces the bulk
of the energy while also wasting energy. A secondary system can be
used to capture a portion of the wasted energy from the primary
system. An ORC system can be used in these power generation systems
depending upon system temperatures and other specifics of the power
generation systems. According to exemplary embodiments, ORC systems
can be used for small to mid-sized gas turbine power generation
systems to capture additional heat/energy from the hot flue gas.
Examples of ORC fluids include, but are not limited to, pentane,
propane, cyclohexane, cyclopentane, butane, a fluorohydrocarbon
such as R-245fa, a ketone such as acetone or an aromatic such as
toluene or thiophene.
[0031] According to exemplary embodiments, a once-through direct
heat exchanger may be used to reduce size, cost and improve
efficiency as illustrated in FIG. 4. According to an exemplary
embodiment, a heat exchanger 402 can have a single inlet 404
traversing an exhaust duct 406 and a single outlet 408 traversing
the exhaust duct 406 and no other parts of the heat exchanger 402
traversing a wall of the exhaust duct 406. This is in contrast to
the traditional heat exchanger shown in FIG. 1 in which different
portions of the heat exchanger communicate through the wall of the
exhaust duct with other elements placed outside the exhaust duct.
The hot exhaust 410 may first contact the heat exchanger 402 near
the working fluid outlet 408 and the cold (or relatively cooler)
exhaust gas 412 may leave the heat exchanger 402 near the working
fluid inlet 404. This exemplary heat exchanger can be used with
various working fluids in various pressure and temperature ranges.
Additionally, while showing the hot exhaust 410 as the heat source
in FIG. 1, other heat sources may be used in exemplary embodiments
described herein, such as, other hot gases and hot liquids, e.g.,
geothermal brine.
[0032] Additionally, according to exemplary embodiments, the heat
source fluid, e.g., an exhaust gas or a liquid such as a geothermal
brine flow, may operate in a counter flow path relative to a flow
of the ORC working fluid within the piping of the heat exchanger
402. Also, according to exemplary embodiments, using this
once-through heat exchanger the ORC fluid is brought to a gaseous
state (or supercritical fluid state) without the ORC fluid being
taken out of the duct 406, which is in contrast to the conventional
system shown in FIG. 1. For this reason, the novel heat exchanger
of this exemplary embodiment is called a once-through heat
exchanger. For such a once-through heat exchanger to produce the
ORC fluid in the supercritical fluid state, dimensions of the heat
exchanger are calculated based on the mass flow and properties of
the specific ORC fluid passing through it as well as the mass flow
and temperature of the heat source medium used in the heat
exchanger.
[0033] According to an exemplary embodiment, the heat exchanger 402
can be operated in a supercritical region. In this exemplary case,
the ORC fluid 414 enters the heat exchanger as a liquid or as a
quasi liquid at or above the critical pressure (Pc) for the type of
ORC fluid used. It may be desirable that the pressure of the
working ORC fluid when entering the heat exchanger 402 be higher
than the critical pressure of the ORC fluid to compensate for the
relatively small decreases in pressure that can occur due to, for
example, flow obstructions. The ORC fluid is heated as it travels
through the piping in the heat exchanger 402. Prior to exiting the
heat exchanger 402, the ORC fluid reaches a temperature at or
greater than the ORC fluid critical temperature (Tc). Therefore,
the exiting ORC fluid 416 is, in this exemplary case, a
supercritical ORC fluid. Depending upon the ORC fluid used, the
critical temperature can be approximately 240.degree. C. and the
critical pressure can be approximately 45 bar.
[0034] According to exemplary embodiments, various other heat
exchanger types can be used as a once-through heat exchanger shown
in FIG. 4. For example, exemplary heat exchanger designs can
include, for supercritical ORC applications, but are not limited
to, plate, plate-fin, shell-and-tube, compact fin-tube, and
continuous-plate-fin tube heat exchangers. As these types of heat
exchangers are known in the art, their description is omitted
herein. Also, this exemplary process can be expanded to be
performed in series or parallel to match the desired scale,
capacity and temperature change. Thus, more than one conduit may be
used between the inlet 404 and the outlet 408.
[0035] According to another exemplary embodiment, the once-through
heat exchangers can be used in subcritical and near-critical ORC
applications as shown in FIG. 5. A near-critical ORC application
can be defined by those points on curve 302 in FIG. 3 that are in
the upper 50% of the curve. Additionally, according to exemplary
embodiments, near-critical points can also include those points
having pressures and temperatures which are around the critical
point. With regard to FIG. 5, a pressurized ORC liquid 514 enters
the heat exchanger 502 through an inlet 510 (while not shown each
inlet/outlet corresponds to a piercing of the exhaust duct by
piping) into a preheating section 504 of the heat exchanger 502.
The preheating section 504 is located towards the end of the heat
exchanger 502 where the cooler exhaust gas 520 leaves the heat
exchanger 502. The preheated liquid then moves on to a boiler or
evaporator section 506 for evaporation. After evaporation, the ORC
vapor continues on to a superheating stage 508 in the heat
exchanger. In this exemplary embodiment, the evaporator section 506
is located between the preheating section 504 and the superheating
section 508 of the heat exchanger 502, with the superheating
section 508 being located closest to the entry point of the hot
exhaust gas 518. After superheating, the superheated vapor ORC 516
exits at outlet 512 the heat exchanger 502 and advances to the next
step of the power generation cycle, e.g., expansion.
[0036] According to an alternative exemplary embodiment, the
location of the various heat exchanging stages can occur in
different locations within the heat exchanger 502 as shown in FIG.
6. In this alternative exemplary embodiment, the locations of the
superheating section 508 and the evaporator section 506 are
reversed. This change results in the evaporator section being
located closer to the hot exhaust gas 518 entrance to the heat
exchanger 502. Additionally, this change can alter the relative
exit point 512 from the heat exchanger 502 (and exhaust duct (not
shown)) of the superheated vapor ORC 516 as well as, in some
exemplary cases, mitigate otherwise excessive fluid temperatures
under certain exhaust and ORC fluid conditions. This change in
order within the heat exchanger 502 can be used in both subcritical
and near-critical ORC systems.
[0037] According to other exemplary embodiments, various types of
heat exchangers can implement the once-through design, for
subcritical and near-critical ORC systems, shown in FIGS. 4-6. For
example, exemplary heat exchanger types can include, but are not
limited to, plate, vertical tube (as shown in FIG. 8), plate-fin
(as shown in FIG. 9), shell-and-tube, and compact tube-fin heat
exchangers. Additionally, the once-through design of the heat
exchanger allows for reducing cost (and space requirements)
associated with the heat exchanger by removing various conventional
intermediate stages, e.g., a separator between evaporation and
superheating, other storage stages, etc. Also, reductions in cost
can be realized by a potential reduction in system maintenance and
downtime due to reduction of components when using this exemplary
once-through heat exchanger. According to exemplary embodiments,
this exemplary process can be expanded to be performed in series or
parallel to match the desired scale and capacity.
[0038] As described above, according to exemplary embodiments, a
once-through heat exchanger can be used in subcritical and
near-critical ORC systems. Near-critical ORC systems allow for some
of the efficiency improvements gained from supercritical ORC
systems while still using, as desired, the physical components of
the less expensive subcritical systems. The near-critical ORC
systems are configured to operate at temperatures and pressures
combinations along the upper 10 percent or upper 20 percent or
upper 50 percent of the curve 302 (see FIG. 3) linking the triple
point to the critical point for an ORC fluid and also at points
described in the pressure versus temperature plane as having a
pressure less than the critical pressure. Curve 302 defines the
boiling/condensation point for the ORC fluid at the various
pressure/temperature combinations. Thus, near-critical ORC systems
are configured to operate such that a pressure P of the medium is
less than Pc and a temperature T of the medium is less than Tc, in
the preheating and evaporation stages. However, according to
exemplary embodiments, in some cases the pressure may be above the
critical point value. After evaporation, e.g., during superheating,
T can become greater than Tc to create a superheated vapor as long
as P remains less than Pc. According to alternative exemplary
embodiments, near-critical ORC systems can also operate using
conventional heat exchangers with piping that enters and exits the
exhaust duct two or more times, e.g., the piping exits to
communicate the fluid to a separator and then provides the pure
vapor back into the duct.
[0039] According to exemplary embodiments, an ORC fluid, e.g.,
cyclopentane or isopentane, can be used in near-critical ORC power
generation systems as is described with respect to a power
generation system 700 shown in FIG. 7. In this exemplary
embodiment, the critical point of the ORC fluid is defined by
approximately 45 bar and 240.degree. C. Beginning with a pump 702
in the closed-loop power generation system 700, the ORC fluid is
received as a relatively low pressure and temperature liquid, e.g.,
1 bar at 50.degree. C., and is pressurized to at least 40 bar (by
comparison a standard subcritical ORC system will operate on its
high pressure side at approximately 20 bar). This pressurized ORC
fluid passes through a recuperator 704 and is heated to
approximately 110.degree. C. prior to being received by a preheater
section 708 of the heat exchanger 706. The heat exchanger receives,
for example, an exhaust gas at 500.degree. C., which heats the
various stages of the heat exchanger 706. These stages can include
the preheater 708 and a boiler/superheater section 710.
Alternatively, other styles of heat exchangers can be used, e.g.,
the once-through heat exchangers shown in FIGS. 5 and 6. After
heating the ORC fluid, the exhaust gas exits the heat exchanger 706
at, for example, 120.degree. C.
[0040] As described above, the pressurized ORC fluid enters the
preheater 708 and then is moved on to the boiler/superheater 710.
As the ORC fluid arrives at the heat exchanger at a pressure near,
but below, its critical pressure, it is evaporated (and possibly
superheated) at a temperature near its critical temperature and the
ORC fluid exits the heat exchanger as a high pressure vapor or a
high pressure superheated vapor, e.g., 40 bar and 250.degree. C.,
and travels on to the turbine 712 for power generation and
expansion. The ORC vapor exits the turbine 712 at a lower pressure
then the ORC vapor which entered the turbine 712 and then passes
through the recuperator 704, which cools the vapor. The ORC vapor
then enters a condenser 714, is condensed into a liquid phase, and
is moved on back to the pump 702 as a low pressure liquid.
[0041] While various temperatures and pressures are shown in FIG.
7, there can be some variances to these purely illustrative values
which will not significantly alter the ability of the system to
perform as desired. Additionally, the type of exhaust generator can
vary the inlet exhaust temperature, which can be compensated by,
for example, increasing the length of the piping used in the heat
exchanger 708. Also, various temperature and pressure combinations
can be used for different ORC fluids and/or when at different
points in the near-critical point region.
[0042] According to exemplary embodiments, as described above,
various heat exchanger designs can be used in near-critical ORC
systems. For example, a vertical tube bank heat exchanger 802 as
shown in FIG. 8 can be used. The vertical tube bank heat exchanger
802 can be mounted inside the exhaust duct 804. The vertical tube
bank heat exchanger 802 includes a vertically oriented bank of
tubes in which the working ORC fluid is vaporized, surmounted by a
vessel that redistributes the unboiled liquid evenly among the
tubes.
[0043] According to exemplary embodiments, a system for power
generation using an Organic Rankine Cycle (ORC) in a heat
exchanger, includes: an inlet which traverses from an outer side of
an exhaust duct to an inner side of the exhaust duct; an outlet
which traverses from the inner side of the exhaust duct to the
outer side of the exhaust duct; and a conduit fluidly and directly
connecting the inlet to the outlet and configured to either (i)
receive an ORC fluid at a pressure higher than a critical pressure
of the ORC fluid and increase a temperature of the ORC fluid above
a critical temperature of the ORC fluid while the ORC fluid is
inside the heat exchanger or (ii) receive the ORC fluid and
increase the temperature of the ORC fluid to a subcritical value
before outputting the ORC fluid out of the heat exchanger.
Additionally, the length of the conduit, or piping, used to connect
the inlet to the outlet can be a calculated length. Inputs to
calculating this length can include, but are not limited to,
various parameters, such as, exhaust heat temperature, ORC fluid
selected, piping diameter, type of heat exchanger used, physical
space limitation, inlet fluid pressure, fluid flow rates, operating
range, e.g., subcritical, near-critical or supercritical, and the
like.
[0044] According to another exemplary embodiment, heat exchange in
a power generation system using an ORC fluid can include receiving
at a heat exchanger heat from a source, wherein the heat exchanger
is configured as a relatively inexpensive counter flow or cross
flow compact heat exchanger such as a plate or plate-and-fin heat
exchanger 902 as shown in FIG. 9. As shown in FIG. 9, an exemplary
plate-and-fin heat exchanger 902 includes plate sections 904, a fin
section 906 with the fluid flow direction shown by arrow 908.
Additionally, side bars can be used, as well as a series of plate
and fin sections. However, various types of plate-and-fin heat
exchangers 902 can be used in the exemplary embodiments described
herein.
[0045] According to another exemplary embodiment, the heat
exchanger 902 receives the ORC fluid as a pressurized liquid at a
pressure greater than or equal to a critical pressure of the ORC
fluid at one inlet, discharging the ORC fluid in a supercritical
phase at an outlet on the other end of the heat exchanger conduit.
Alternatively, the heat exchanger 902 can receive and discharge the
ORC fluid at a near critical pressure. In a respective other
conduit, e.g., an exhaust duct, the heating medium flows from an
inlet to a respective opposite outlet as a liquid or gaseous
heating medium from which heat is transferred across a wall of the
other conduit to the ORC fluid, thereby cooling the heating medium.
In these exemplary embodiments, when the heating occurs in the
near-critical or supercritical region, the volume occupied by the
now relatively high-pressure vapor results in a far lower pressure
drop through the constricted passages of compact heat exchangers
like the plate or plate-fin varieties, which makes the plate or
plate-fin heat exchangers viable for these specific regions.
[0046] Utilizing the above-described exemplary systems according to
exemplary embodiments, a method for heat exchange is shown in the
flowchart of FIG. 10. Initially a method for performing a heat
exchange in a power generation system using an Organic Rankine
Cycle (ORC) fluid includes: receiving at a heat exchanger heat from
a source in step 1002, wherein the heat exchanger is configured to
be mounted entirely inside an exhaust duct, the heat exchanger
having a single inlet, a conduit and a single outlet; receiving the
ORC fluid as a pressurized liquid in step 1004 at a pressure
greater than or equal to a critical pressure of the ORC fluid at
the single inlet which traverses from an outer side of the exhaust
duct to an inner side of the exhaust duct; exiting the ORC fluid in
a supercritical phase in step 1006 at the single outlet which
traverses from the inner side of the exhaust duct to the outer side
of the exhaust duct; and passing the ORC fluid through the conduit
between the single inlet and the single outlet in step 1008, while
heating the ORC fluid to change a phase from the pressurized liquid
to the supercritical phase. The heat exchanger is configured to
heat the ORC fluid to a temperature greater than or equal to a
critical temperature of the ORC fluid, and to exit the ORC fluid
through the single outlet as a supercritical fluid, and the
supercritical fluid is defined by the temperature being greater
than the critical temperature and the pressure being greater than
the critical pressure.
[0047] Utilizing the above-described exemplary systems according to
exemplary embodiments, a method for heating an ORC fluid is shown
in the flowchart of FIG. 11. A method for heating an Organic
Rankine Cycle (ORC) fluid in a heat exchanger includes: receiving
at a heat exchanger heat from a source in step 1102, where the heat
exchanger is configured to be mounted inside a duct and has an
inlet, a conduit and an outlet; receiving the ORC fluid as a
pressurized liquid in step 1104 at the inlet which traverses from
an outer side of the duct to an inner side of the duct; exiting the
ORC fluid in a near-critical region in step 1106 at the outlet
which traverses from the inner side of the duct to the outer side
of the duct, and passing the ORC fluid through the conduit between
the inlet and the outlet in step 1108. The ORC fluid is heated to
change from the pressurized liquid to the near-critical region,
wherein the near-critical region of the ORC fluid is described by
an upper half of a curve linking a triple point and a critical
point for the ORC fluid. The subcritical region of the ORC fluid is
described by a lower half of the curve, and the curve is defined by
pressure values and temperature values which define boiling points
for the ORC fluid.
[0048] The above-described exemplary embodiments are intended to be
illustrative in all respects, rather than restrictive, of the
present invention. Thus the present invention is capable of many
variations in detailed implementation that can be derived from the
description contained herein by a person skilled in the art. All
such variations and modifications are considered to be within the
scope and spirit of the present invention as defined by the
following claims. No element, act, or instruction used in the
description of the present application should be construed as
critical or essential to the invention unless explicitly described
as such. Also, as used herein, the article "a" is intended to
include one or more items.
[0049] This written description uses examples of the subject matter
disclosed to enable any person skilled in the art to practice the
same, including making and using any devices or systems and
performing any incorporated methods. The patentable scope of the
subject matter is defined by the claims, and may include other
examples that occur to those skilled in the art. Such other
examples are intended to be within the scope of the claims.
* * * * *