U.S. patent application number 12/916191 was filed with the patent office on 2012-05-03 for rankine cycle integrated with absorption chiller.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Sebastian Walter Freund.
Application Number | 20120102996 12/916191 |
Document ID | / |
Family ID | 45033746 |
Filed Date | 2012-05-03 |
United States Patent
Application |
20120102996 |
Kind Code |
A1 |
Freund; Sebastian Walter |
May 3, 2012 |
RANKINE CYCLE INTEGRATED WITH ABSORPTION CHILLER
Abstract
A power generation system is provided. The system includes a
carbon-dioxide waste heat recovery Rankine cycle, integrated with
an absorption chiller cycle. The Rankine cycle includes a condenser
and a desorber. The condenser of the Rankine cycle is combined with
the evaporator of the absorption chiller cycle. The Rankine cycle
and the absorption chiller cycle can be integrated at the
desorber.
Inventors: |
Freund; Sebastian Walter;
(Unterfoehring, DE) |
Assignee: |
GENERAL ELECTRIC COMPANY
SCHENECTADY
NY
|
Family ID: |
45033746 |
Appl. No.: |
12/916191 |
Filed: |
October 29, 2010 |
Current U.S.
Class: |
62/238.4 ;
62/476 |
Current CPC
Class: |
F01K 25/00 20130101;
Y02P 80/152 20151101; F01K 23/08 20130101; Y02P 80/15 20151101;
F01K 23/04 20130101 |
Class at
Publication: |
62/238.4 ;
62/476 |
International
Class: |
F25B 27/00 20060101
F25B027/00; F25B 15/00 20060101 F25B015/00 |
Claims
1. A power generation system, comprising: a carbon-dioxide waste
heat recovery Rankine cycle integrated with an absorption chiller
cycle; wherein the Rankine cycle comprises a condenser and a
desorber; wherein the condenser of the Rankine cycle functions as
an evaporator for the absorption chiller cycle; and wherein the
Rankine cycle and the absorption chiller cycle are integrated at
the desorber.
2. A power generation system, comprising: a Rankine cycle-first
working fluid circulation loop, comprising a heater, an expander, a
recuperator, a first working fluid condenser, a desorber, a first
working fluid pump, and a first working fluid comprising CO.sub.2;
integrated with an absorption chiller cycle comprising a second
working fluid circulation loop, which itself comprises an
evaporator, an absorber, a second working fluid pump, a desorber, a
second working fluid condenser, and a second working fluid
comprising a refrigerant; wherein the Rankine cycle and the
absorption chiller cycle are integrated at the desorber; and
wherein the condenser of the Rankine cycle functions as the
evaporator of the absorption chiller cycle.
3. The system of claim 2, wherein the Rankine cycle-first working
fluid circulation loop further comprises a cooler.
4. The system of claim 2, wherein the absorption chiller cycle
further comprises at least one heat exchanger.
5. The system of claim 2, wherein the absorption chiller cycle
further comprises an additional fluid loop to transport a solution
of the refrigerant in a solvent between the desorber and the
absorber.
6. A power generation system, comprising: a first loop comprising a
single expansion recuperated carbon-dioxide waste heat recovery
Rankine cycle, integrated with a second loop comprising an
absorption chiller cycle, wherein the first loop comprises: a
recuperator configured to receive a liquid CO.sub.2 stream, and to
produce a heat-enhanced liquid CO.sub.2 stream; a waste heat
recovery boiler configured to receive the heat-enhanced liquid
CO.sub.2 stream, and to produce a vaporized CO.sub.2 stream; a
first expander configured to receive the vaporized CO.sub.2 stream
and to produce an expanded CO.sub.2 stream; wherein the recuperator
is also configured to receive the expanded CO.sub.2 stream and to
produce a cooler CO.sub.2 stream; a desorber configured to receive
the cooler CO.sub.2 stream, and to further reduce its temperature;
a cooler configured to receive the cooled CO.sub.2 stream, and to
produce an even cooler CO.sub.2 stream, having a temperature in the
range of about 35 degrees Celsius to about 55 degrees Celsius; and
a CO.sub.2 condenser configured to receive the cooled CO.sub.2
stream, and to produce a liquid CO.sub.2 stream which is capable of
being pumped back to the recuperator, using a CO.sub.2 pump,
wherein the condenser is integrated with an evaporator of an
absorption chiller cycle; wherein the second loop comprises: the
evaporator of the absorption chiller cycle configured to receive a
substantially liquid refrigerant and to produce a vaporized
refrigerant; an absorber configured to receive the vaporized
refrigerant and to produce a first solution of the refrigerant and
a solvent, wherein a second solution of the refrigerant and the
solvent is contained in the absorber; a refrigerant pump configured
to receive the first solution and to increase its pressure; wherein
the desorber is also configured to receive the first solution,
having an increased pressure, and to produce a vaporized
refrigerant and the second solution; wherein the concentration of
the refrigerant in the first solution is greater than the
concentration of the refrigerant in the second solution; a
refrigerant condenser configured to receive the vaporized
refrigerant and to produce a liquid refrigerant; and a
pressure-reducing device configured to receive the liquid
refrigerant and lower its pressure, so that it can be received by
the evaporator; and wherein the evaporator of the absorption
chiller cycle is capable of directing the vaporized refrigerant
back to the absorber.
7. The system of claim 6, wherein the absorption chiller cycle
further comprises a heat exchanger configured to receive the
vaporized refrigerant from the evaporator and provide a
heat-enhanced vaporized refrigerant to the absorber.
8. The system of claim 6, wherein the absorption chiller cycle
further comprises an additional fluid loop, including a recuperator
and a pump to cool and transport the second solution of the
refrigerant and the solvent between the desorber and the
absorber.
9. The system of claim 6, wherein the refrigerant comprises lithium
bromide or water.
10. The system of claim 6, wherein the refrigerant pump in the
absorption chiller cycle provides a refrigerant having an enhanced
pressure in the range of about 0.1 bar to about 10 bar.
11. A power generation system comprising: a first loop comprising a
double expansion recuperated carbon-dioxide waste heat recovery
Rankine cycle integrated with a second loop comprising an
absorption chiller cycle, wherein the first loop comprises: a waste
heat recovery boiler configured to receive a first portion of a
liquid CO.sub.2 stream and to produce a heated first portion of the
CO.sub.2 stream; a first expander configured to receive the heated
first portion of the CO.sub.2 stream and to produce an expanded
first portion of the CO.sub.2 stream; a recuperator configured to
receive the expanded first portion of the CO.sub.2 stream and to
produce a cooler first portion of the CO.sub.2 stream; wherein the
recuperator is also configured to receive a second portion of
liquid CO.sub.2 stream, and to produce a heat-enhanced second
portion of the CO.sub.2 stream; a second expander configured to
receive the heat-enhanced second portion of the CO.sub.2 stream and
to produce an expanded second portion of the CO.sub.2 stream; a
desorber configured to receive the expanded second portion of the
CO.sub.2 stream and to produce a cooler second portion of the
CO.sub.2 stream; a cooler configured to receive the cooled first
portion of the CO.sub.2 stream and the cooled second portion of the
CO.sub.2 stream, and to produce an even cooler CO.sub.2 stream
having a temperature in the range of about 35 degrees Celsius to
about 55 degrees Celsius; a first working fluid condenser,
configured to receive the cooled CO.sub.2 stream, integrated with
an evaporator of an absorption chiller cycle; and capable of
producing a liquid CO.sub.2 stream; which can be pumped back as the
first portion and the second portion of the liquid CO.sub.2 stream,
using a CO.sub.2 pump; wherein the second loop comprises: the
evaporator of the absorption chiller cycle configured to receive a
substantially liquid refrigerant, and to produce a vaporized
refrigerant; an absorber configured to receive the vaporized
refrigerant, and to produce a first solution of the refrigerant and
a solvent; wherein a second solution of a refrigerant and a solvent
is contained in the absorber; a second working fluid pump
configured to receive the first solution and to increase its
pressure; wherein the desorber is also configured to receive the
first solution with an increased pressure, and to produce a
vaporized refrigerant and the second solution; wherein the
concentration of the refrigerant in the first solution is greater
than the concentration of the refrigerant in the second solution; a
refrigerant condenser configured to receive the vaporized
refrigerant and to produce a liquid refrigerant; a pressure
reducing device configured to receive the liquid refrigerant and
lower its pressure, so that it can be received by the evaporator;
and wherein the evaporator of the absorption chiller cycle is
capable of directing the vaporized refrigerant back to the
absorber.
12. The system of claim 11, wherein the absorption chiller cycle
further comprises a heat exchanger configured to receive the
vaporized refrigerant from the evaporator, and to provide a heated
vaporized refrigerant to the absorber.
13. The system of claim 11, wherein the absorption chiller cycle
further comprises an additional fluid loop, including a recuperator
and a pump to cool and transport the second solution of the
refrigerant and the solvent between the desorber and the
absorber.
14. The system of claim 11, wherein a conduit or container captures
the heat of the CO.sub.2 left over after expansion, and is capable
of directing the heat to the desorber.
15. The system of claim 11, further comprising an external heating
mechanism to heat the desorber.
16. The system of claim 11, wherein the refrigerant comprises
lithium bromide or water.
17. The system of claim 11, wherein the refrigerant comprises
lithium bromide, and the solvent comprises water.
18. A power generation system that includes a carbon-dioxide, waste
heat recovery Rankine cycle, integrated with an absorption chiller
cycle; wherein the system comprises a combined Rankine cycle
condenser and chiller cycle evaporator.
Description
BACKGROUND
[0001] The systems and techniques described include embodiments
that relate to power generation using waste heat. More particularly
the disclosure relates to power generation systems that employ a
closed-loop, integrated carbon-dioxide (CO.sub.2) Rankine cycle.
They also include embodiments that relate to a closed-loop
absorption chiller cycle integrated with the Rankine cycle. The
invention also includes embodiments that relate to the use of waste
heat to improve the efficiency of the power generation systems.
[0002] CO.sub.2 as a supercritical working fluid for Rankine cycles
is known to have advantages over organic fluids. The advantages
include high stability, along with reduced or minimized
flammability, and environmentally acceptable characteristics, e.g.,
generally non-toxic attributes. However, a CO.sub.2 Rankine cycle
for power generation may suffer performance penalties when the
ambient temperature approaches the critical temperature of 30
degrees Celsius, especially during summertime. CO.sub.2 is not used
commonly because it cannot be readily condensed at the cold end of
the cycle, like alternative fluids. This is due to the fact that
the critical temperature of CO.sub.2 is too high to allow
condensation under warm ambient conditions, i.e., at a temperature
of about 15 degrees Celsius to about 25 degrees Celsius. A cooling
medium with a temperature significantly below 30 degrees Celsius
may be needed to cool the condenser below 30 degrees Celsius. This
attribute can be important because cooling below 30 degrees Celsius
may facilitate condensation and subsequent pumping of CO.sub.2 in a
liquid state, to a high pressure.
[0003] At common ambient temperatures, (about 20 degrees Celsius to
about 25 degrees Celsius), it may be nearly impossible to use air
or water to cool the CO.sub.2 to below 30 degrees Celsius.
Alternately, a refrigeration system may be employed to cool the
condenser and discharge the heat of condensation at a temperature
above ambient temperature. Mechanical vapor compression
refrigeration systems can be employed. These refrigeration systems
would operate at relatively high efficiencies, at expected
temperature conditions. However, a chiller, for example, a water
chiller, may be needed to cool the condenser. The chiller may
require power on the order of about 10 kilowatts to about 20
kilowatts per kilogram of CO.sub.2, per second, to provide the
necessary cooling and condensation. Given the high mass flow of
CO.sub.2 in the cycle per unit power generated, this parasitic load
would amount to a severe performance penalty, potentially rendering
the whole system too inefficient to be cost effective.
[0004] To commercialize a Rankine cycle system for waste heat
recovery that benefits from the specific advantages of CO.sub.2, a
condenser cooling system is required for operation above 20 degrees
Celsius ambient temperature. Unlike alternative systems, this
system, in using an absorption cycle, would not significantly
impact the performance. The system would enable the generation of
more electricity during times of higher temperatures, which may
coincide with peak demand, when electricity can be sold at a
premium.
[0005] In view of these considerations, new processes for cooling
and condensing the CO.sub.2 would be welcome in the art. The new
processes should also be capable of economic implementation, and
should be compatible with other power generation systems.
BRIEF DESCRIPTION
[0006] One embodiment of the invention provides a power generation
system. The system comprises a carbon-dioxide waste heat recovery
Rankine cycle, integrated with an absorption chiller cycle. The
Rankine cycle comprises a condenser and a desorber. The condenser
of the Rankine cycle functions as an evaporator for the absorption
chiller cycle. The Rankine cycle and the absorption chiller cycle
can be integrated at the desorber.
[0007] Another embodiment of the invention relates to a power
generation system. The system comprises a Rankine cycle-first
working fluid circulation loop, comprising a heater, an expander, a
recuperator, a first working fluid condenser, a desorber, a first
working fluid pump, and a first working fluid comprising CO.sub.2.
The Rankine cycle is integrated with an absorption chiller cycle,
comprising a second working fluid circulation loop. The absorption
chiller cycle comprises an evaporator, an absorber, a second
working fluid pump, a desorber, a second working fluid condenser,
and a second working fluid, which comprises a refrigerant. The
Rankine cycle and the absorption chiller cycle are integrated at
the desorber. The condenser of the Rankine cycle can function as
the evaporator of the absorption chiller cycle.
[0008] Yet another embodiment of the invention relates to a power
generation system. The system comprises a first loop comprising a
single expansion recuperated carbon-dioxide waste heat recovery
Rankine cycle, integrated with a second loop comprising an
absorption chiller cycle. The first loop comprises a recuperator
configured to receive a liquid CO.sub.2 stream and to produce a
heated liquid CO.sub.2 stream, a waste heat recovery boiler
configured to receive the heated liquid CO.sub.2 stream and to
produce a vaporized CO.sub.2 stream, and a first expander
configured to receive the vaporized CO.sub.2 stream and to produce
an expanded CO.sub.2 stream. The recuperator is also configured to
receive the expanded CO.sub.2 stream, and to produce a cooler
CO.sub.2 stream. The system also comprises a desorber configured to
receive the cooler CO.sub.2 stream, and to produce a CO.sub.2
stream that is even cooler. A cooler is configured to receive the
cooled CO.sub.2 stream, and to produce a CO.sub.2 stream that is
even cooler, having a temperature in the range of about 35 degrees
Celsius to about 55 degrees Celsius. An associated CO.sub.2
condenser is configured to receive the cooled CO.sub.2 stream,
which is capable of being pumped back to the recuperator, using a
CO.sub.2 pump. The condenser is integrated with an evaporator of
the absorption chiller cycle. The second loop comprises the
evaporator of the absorption chiller cycle, configured to receive a
substantially liquid refrigerant and to produce a vaporized
refrigerant, an absorber configured to receive the vaporized
refrigerant and to produce a first solution of the refrigerant and
a solvent; wherein a second solution of the refrigerant and the
solvent are contained in the absorber. The system also comprises a
refrigerant pump configured to receive the first solution and to
increase its pressure, wherein the desorber is also configured to
receive the first solution at the higher pressure, and to produce a
vaporized refrigerant and the second solution. The concentration of
the refrigerant in the first solution is greater than the
concentration of the refrigerant in the second solution. An
associated refrigerant condenser is configured to receive the
vaporized refrigerant and to produce a liquid refrigerant, and a
pressure-reducing device is configured to receive the liquid
refrigerant and reduce its pressure, for entry into the evaporator.
The evaporator of the absorption chiller cycle is capable of
directing the vaporized refrigerant back to the absorber.
[0009] An additional embodiment of the invention relates to another
power generation system. The system comprises a first loop
comprising a double expansion recuperated carbon-dioxide waste heat
recovery Rankine cycle, integrated with a second loop comprising an
absorption chiller cycle. The first loop comprises a waste heat
recovery boiler configured to receive a first portion of a liquid
CO.sub.2 stream, and to produce a heated first portion of the
CO.sub.2 stream, a first expander configured to receive the heated
first portion of the CO.sub.2 stream and to produce an expanded
first portion of the CO.sub.2 stream, a recuperator configured to
receive the expanded first portion of the CO.sub.2 stream and to
produce a cooler, first portion of the CO.sub.2 stream, wherein the
recuperator is also configured to receive a second portion of
liquid CO.sub.2 stream, and to produce a heat-enhanced (i.e.,
heated), second portion of the CO.sub.2 stream, a second expander
configured to receive the heat-enhanced second portion of the
CO.sub.2 stream, and to produce an expanded second portion of the
CO.sub.2 stream, a desorber configured to receive the expanded
second portion of the CO.sub.2 stream, and to produce a cooler
second portion of the CO.sub.2 stream, a cooler configured to
receive the cooled first and second portion of the CO.sub.2 stream,
and to produce an even cooler CO.sub.2 stream, having a temperature
in the range of about 35 degrees Celsius to about 55 degrees
Celsius, and a first working fluid condenser configured to receive
the cooled CO.sub.2 stream, integrated with an evaporator of an
absorption chiller cycle. The evaporator is capable of producing
the liquid CO.sub.2 stream, which can be pumped back as the first
portion and the second portion of the CO.sub.2 stream, using a
CO.sub.2 pump. The second loop comprises the evaporator of the
absorption chiller cycle, configured to receive a substantially
liquid refrigerant, and to produce a vaporized refrigerant, an
absorber configured to receive the vaporized refrigerant, and to
produce a first solution of the refrigerant and a solvent; wherein
a second solution of a refrigerant and a solvent is contained in
the absorber, a second working fluid pump configured to receive the
first solution of the refrigerant and the solvent, and to produce a
first solution with increased pressure, wherein the desorber is
also configured to receive the first solution with an increased
pressure, and to produce a vaporized refrigerant, and the second
solution, wherein the concentration of the refrigerant in the first
solution is greater than the concentration of the refrigerant in
the second solution, a refrigerant condenser configured to receive
the vaporized refrigerant and to produce a liquid refrigerant, a
pressure reducing device configured to receive the liquid
refrigerant and reduce its pressure, for entry into the evaporator.
The evaporator of the absorption chiller cycle is capable of
directing the vaporized refrigerant back to the absorber.
[0010] Another embodiment of the invention relates to a power
generation system that includes a carbon-dioxide, waste heat
recovery Rankine cycle, integrated with an absorption chiller
cycle. The system comprises a combined Rankine cycle condenser and
chiller cycle evaporator.
BRIEF DESCRIPTION OF THE FIGURES
[0011] These and other features, aspects, and advantages of the
present invention will become better understood when the following
detailed description is read, with reference to the accompanying
drawings, wherein:
[0012] FIG. 1 is a process block flow diagram of the steps in an
illustrative process for cooling and condensing CO.sub.2;
[0013] FIG. 2 is a process block flow diagram of the steps in
another illustrative process for cooling and condensing CO.sub.2;
and
[0014] FIG. 3 is a process block flow diagram of the steps in still
another illustrative process for cooling and condensing
CO.sub.2.
DETAILED DESCRIPTION
[0015] Approximating language, as used herein throughout the
specification and claims, may be applied to modify any quantitative
representation that could permissibly vary without resulting in a
change in the basic function to which it is related. Accordingly, a
value modified by a term such as "about" is not to be limited to
the precise value specified. In some instances, the approximating
language may correspond to the precision of an instrument for
measuring the value. Similarly, "free" may be used in combination
with a term, and may include an insubstantial number, or trace
amounts, while still being considered free of the modified
term.
[0016] As used herein, the terms "may" and "may be" indicate a
possibility of an occurrence within a set of circumstances; a
possession of a specified property, characteristic or function.
These terms may also qualify another verb by expressing one or more
of an ability, capability, or possibility associated with the
qualified verb. Accordingly, usage of "may" and "may be" indicates
that a modified term is apparently appropriate, capable, or
suitable for an indicated capacity, function, or usage, while
taking into account that in some circumstances the modified term
may sometimes not be appropriate, capable, or suitable. For
example, in some circumstances, an event or capacity can be
expected, while in other circumstances the event or capacity cannot
occur--this distinction is captured by the terms "may" and "may
be".
[0017] One or more specific embodiments of the present invention
will be described below. In an effort to provide a concise
description of these embodiments, all features of an actual
implementation may not be described in the specification. It should
be appreciated that in the development of any such actual
implementation, as in any engineering or design project, numerous
implementation-specific decisions must be made to achieve the
developers' specific goals, such as compliance with system-related
and business-related constraints, which may vary from one
implementation to another. Moreover, it should be appreciated that
such a development effort might be complex and time consuming, but
would nevertheless be a routine undertaking of design, fabrication,
and manufacture for those of ordinary skill having the benefit of
this disclosure.
[0018] When introducing elements of various embodiments of the
present invention, the articles "a," "an," and "the," are intended
to mean that there are one or more of the elements. The terms
"comprising," "including," and "having" are intended to be
inclusive, and mean that there may be additional elements other
than the listed elements. Furthermore, the terms "first," "second,"
and the like, herein do not denote any order, quantity, or
importance, but rather are used to distinguish one element from
another.
[0019] All ranges disclosed herein are inclusive of the endpoints,
and the endpoints are combinable with each other. The terms
"first," "second," and the like as used herein do not denote any
order, quantity, or importance, but rather are used to distinguish
one element from another. The use of the terms "a" and "an" and
"the" and similar referents in the context of describing the
invention (especially in the context of the following claims) are
to be construed to cover both the singular and the plural, unless
otherwise indicated herein or contradicted by context.
[0020] Embodiments of the invention described herein address the
noted shortcomings of the state of the art. These embodiments
advantageously provide an improved system of cooling and condensing
CO.sub.2. The system of cooling described herein fills the needs
described above, by employing a Rankine cycle integrated with an
absorption chiller cycle. The system comprises a combined Rankine
cycle condenser and chiller cycle evaporator. This invention
describes a system based on an absorption refrigeration technology
that allows cooling and condensing CO.sub.2, driven mainly by
low-grade waste heat from a CO.sub.2 Rankine Cycle after expansion.
Employing the power generation system described herein enables
minimizing or even removing the performance penalty associated with
operating at high ambient temperatures. The CO.sub.2 Rankine cycle
may provide enough heat at the right temperature to seamlessly
integrate a suitable absorption chiller.
[0021] One embodiment of the invention provides a power generation
system. The system comprises a carbon-dioxide waste heat recovery
Rankine cycle integrated with an absorption chiller cycle. The
Rankine cycle comprises a condenser and a desorber. The condenser
of the Rankine cycle functions as an evaporator of the absorption
chiller cycle. The Rankine cycle and the absorption chiller cycle
are integrated at the desorber. As used herein, the term
"integrated" refers to certain elements of a power generation
system that are combined or common to both the Rankine cycle and
the absorption chiller cycle. As described herein both the loops
use a common desorber. A single device or unit functions as the
condenser of the Rankine cycle, and as the evaporator of the
absorption chiller cycle. In other words, the second working fluid,
comprising the refrigerant of the absorption chiller cycle,
evaporates at the cost of condensing the first working fluid of the
Rankine cycle, as part of the single device.
[0022] A condenser is a device or unit used to condense a substance
from its gaseous state to its liquid state, typically by cooling
it. The condenser of the Rankine cycle as described herein is
employed to condense the first working fluid, for example,
carbon-dioxide to liquid carbon-dioxide. In so doing, the resulting
heat is given up by carbon-dioxide, and transferred to a
refrigerant used in the condenser for cooling the carbon-dioxide.
The refrigerant used in the condenser for cooling the
carbon-dioxide is the working fluid of the absorption chiller
cycle. The refrigerant absorbs the latent heat from the
carbon-dioxide being cooled in the condenser, and the refrigerant
is vaporized. Thus, as mentioned above, the condenser of the
Rankine cycle also functions as the evaporator of the absorption
chiller cycle.
[0023] As used herein, "Rankine cycle" is a cycle that converts
heat into work. The heat is supplied externally to a closed loop,
which usually uses water. This cycle generates most of the electric
power used throughout the world. Typically, there are four
processes in the Rankine cycle. In the first step, the working
fluid is pumped from low pressure to high pressure. The fluid is a
liquid at this stage, and the pump requires little input energy. In
the second step, the high-pressure liquid enters a boiler where it
is heated at constant pressure by an external heat source, so as to
become a vapor. In the third step, the vapor expands through a
turbine, generating power. This decreases the temperature and
pressure of the vapor. In the fourth step, the vapor then enters a
condenser, where it is condensed at a constant pressure, to become
a saturated liquid. The process then starts again with the first
step.
[0024] A recuperator is generally a counter-flow energy recovery
heat exchanger that serves to recuperate, or reclaim heat from
similar streams in a closed process in order to recycle it.
Recuperators are used, for instance, in chemical and process
industries, in various thermodynamic cycles including Rankine
cycles with certain fluids, and in absorption refrigeration cycles.
Suitable types of recuperators include shell and tube heat
exchangers, and plate heat exchangers.
[0025] A desorber is used to remove the refrigerant from a
solution, without thermally degrading the refrigerant. Suitable
types of desorbers that may be employed include shell and tube heat
exchangers and reboilers that may be coupled to a rectifier
column.
[0026] A condenser is a heat transfer device or unit used to
condense vapor into liquid. In one embodiment, the condenser
employed includes shell and tube heat exchangers.
[0027] A cooler is a heat transfer device or unit used to decrease
the temperature of a liquid or a vapor. In one embodiment, the
cooler employed is an air-cooled heat exchanger with finned
tubes.
[0028] One skilled in the art will appreciate that the recuperator,
condenser, cooler, and desorber described herein may, individually
or collectively include heat exchangers.
[0029] As used herein the phrase "substantially liquid refrigerant"
usually refers to a two-phase mixture of liquid and vapor-phase
refrigerant, with a relatively large mass fraction of liquid. For
example, the mass fraction of the vapor component might be about 20
weight percent, based on the total mass.
[0030] Referring to FIG. 1, a power generation system 100 is
provided, based on some embodiments of the invention. The system
100 comprises a first cycle or "loop" 102. The first loop 102 is an
example of a single expansion recuperated carbon-dioxide cycle for
waste heat recovery. The first loop 102 is integrated with a second
cycle or loop 104. The second loop 104 is an absorption chiller
cycle. The first loop 102 can be viewed as beginning with a pump
110. A liquid CO.sub.2 stream 112, usually having a temperature of
about 10 degrees Celsius to about 30 degrees Celsius, is pumped
through the pump 110 to an intermediate temperature recuperator
114, to produce a heat-enhanced liquid CO.sub.2 stream 116, having
a temperature in a range of about 100 degrees Celsius to about 200
degrees Celsius. As used herein the term "heat-enhanced" refers to
a stream or liquid having a temperature greater than the
temperature of the stream or liquid when it entered the particular
system element or stage.
[0031] The heat-enhanced liquid CO.sub.2 stream 116 is then passed
through a waste heat recovery boiler 118, to produce a vaporized
CO.sub.2 stream 120 having a temperature in a range of about 350
degrees Celsius to about 500 degrees Celsius. In certain
embodiments, the waste heat recovery boiler may be provided with an
external source of heat, for example, heat originating in a gas
turbine. In that instance, the heat source may enter the waste heat
recovery boiler 118 at a higher temperature (designated by element
117), and may then exit the waste heat recovery boiler 118 at a
lower temperature (designated by element 119). The vaporized
CO.sub.2 stream 120 is then passed through an expander 122. The
temperature and pressure of the vaporized CO.sub.2 stream is
lowered in the expansion process to form a CO.sub.2 stream 124,
typically having a pressure in a range of about 60 bar to about 100
bar, and a temperature which is typically in a range of about 250
degrees Celsius to about 350 degrees Celsius.
[0032] The expander 122 may be connected to a generator via a shaft
(not shown in figure). The cooler CO.sub.2 stream 124 is then
passed through the intermediate temperature recuperator 114. The
CO.sub.2 stream 124 is further cooled in the recuperator, to form a
cooled CO.sub.2 stream 126, usually having a temperature in a range
of about 150 degrees Celsius to about 250 degrees Celsius. The
liquid CO.sub.2 stream 112 (pumped to the recuperator 114) absorbs
the sensible heat from the CO.sub.2 stream 124, as it passes
through the recuperator 114. In doing so, the temperature of liquid
CO.sub.2 stream 112 increases to form the heat-enhanced CO.sub.2
stream 116, i.e., a CO.sub.2 stream having a higher temperature
than the CO.sub.2 stream 112.
[0033] The CO.sub.2 stream 126 is then usually passed through a
desorber 128, to form a cooler CO.sub.2 stream 130, typically
having a temperature in a range of about 70 degrees Celsius to
about 120 degrees Celsius. The CO.sub.2 stream 130 can then be
passed through a cooler 132, to form an even cooler CO.sub.2 stream
134. Stream 134 usually (but not always) has a temperature of about
35 degrees Celsius to about 55 degrees Celsius. In certain
embodiments, the cooler 132 may be provided with an external
cooling means, such as water or ambient air. The cooling source
enters the cooler 132 at a lower temperature (designated by element
131) and exits the cooler 132 at a higher temperature (designated
by element 133). The cooled CO.sub.2 stream 134 can then be passed
through a condenser 136, to form a liquid CO.sub.2 stream 138,
which can then be pumped (e.g., using the pump 110) back to the
recuperator 114. In this manner, the first loop 102 of the CO.sub.2
Rankine cycle is closed.
[0034] As mentioned above, an absorption chiller cycle 104 is
integrated with the first loop 102. The condenser 136 of the first
loop is cooled, using a substantially liquid refrigerant stream 160
(for example, water or ammonia). In doing so, the refrigerant
stream 160 evaporates in the condenser 136, to form a vaporized
refrigerant stream 140. Thus, in one embodiment, the condenser 136
of the first loop 102 functions as the evaporator 136 of the second
loop 104. The vaporized refrigerant stream 140 can then be passed
into an absorber 142.
[0035] A second solution of the refrigerant in a solvent (not shown
in FIG. 1) is typically contained in the absorber 142. (In certain
embodiments, the absorber is brought to a lower temperature by
conventional cooling means e.g., air or water. The temperature of
the absorber is mantianed at a level sufficient to keep the second
solution in a liquid state.) The vaporized refrigerant stream 140
is usually dissolved in the second solution, to form a first
solution of the refrigerant in the solvent 144, having a relatively
low pressure, e.g., about 0.1 bar to about 10 bar, depending on the
selection of the particular refrigerant. The temperature of the
first solution is usually in a range from about 20 degrees Celsius
to about 25 degrees Celsius, and depends, for example, on the
pressure of the first solution (the pressure can be adjusted so as
to obtain a desired temperature for a selected solution). The heat
absorbed by the vaporized refrigerant stream 140, when dissolving
into the solvent in the absorber 142, may be rejected to the
ambient atmosphere by means used to maintain the absorber at a
lower temperature, as discussed above.
[0036] The first solution 144 is then usually passed thorough a
refrigerant pump 146, to produce a first solution with an increased
pressure 148. The pressure is in a range of about 11 bar to about
20 bar. The first solution 148 can then be passed to the desorber
128. Heat from the CO.sub.2 stream 126 is transferred to the first
solution 148, in the desorber. In doing so, the CO.sub.2 stream 126
exits the desorber 128 as a relatively cooler CO.sub.2 stream 130.
In this process, the refrigerant in the first solution 148 is
vaporized and mostly separated from the solvent, to form the second
solution. The vaporized refrigerant 154 can then be passed from the
desorber 128 to the refrigerant condenser 150. The second solution
of the refrigerant in the solvent is usually retained in the
desorber 128. (The second solution is formed when the refrigerant
is vaporized from the first solution 148).
[0037] An additional loop (sometimes referred to as a "solution
loop", shown in FIG. 3 described below), can be used to convey the
second solution from the desorber to the absorber. The additional
loop may further comprise additional heat exchangers and valves to
maintain the temperature and pressure of the second solution, as it
is conveyed from the desorber to the absorber. The refrigerant
condenser 150 provides a condensed liquid refrigerant 156. In
certain embodiments, the refrigerant condenser 150 may be provided
with an external cooling mechanism, for example, the use of water
or ambient air. This type of coolant stream would enter the
refrigerant condenser 150 at a lower temperature 149, and exit the
refrigerant condenser 150 at a higher temperature 151. (Again, the
figure elements represent the streams at different temperature
levels.)
[0038] The liquid refrigerant stream 156 can then be passed through
a pressure-reduction device 158, where its pressure is lowered,
e.g., to a range of about 7 bar to about 9 bar. The
pressure-reduction device 158 may constitute a variety of devices,
e.g., a throttle valve or an expander. By passing through the
pressure reduction device 158, stream 156 becomes a relatively cold
refrigerant stream 160. The refrigerant stream 160 is then used to
condense the CO.sub.2 stream 134 entering the evaporator 136, to
form the liquid CO.sub.2 stream 138. In doing so, the refrigerant
stream 160 is evaporated in the heat exchanger 136, to form the
vaporized refrigerant stream 140. Stream 140 can then be passed
again through the absorber 142, to form the first solution 144,
thus closing the loop 104. The concentration of the refrigerant in
the first solution is usually greater than the concentration of the
refrigerant in the second solution.
[0039] In certain embodiments, additional heat exchangers may be
provided to heat the CO.sub.2 streams to the required temperature.
One skilled in the art will appreciate that the heat exchangers may
be provided at required positions in the second loop to maintain
the heat balance of the loop. In one embodiment, an additional heat
exchanger may be provided between the condenser/evaporator 136 and
the absorber 142. The heat exchanger placed in this position may
serve to adjust (e.g., increase) the temperature of the vaporized
refrigerant 140.
[0040] In one embodiment, the system uses the heat of the working
fluid, left over after expansion in the expander, to heat the
desorber. However, in embodiments where the Rankine cycle
configuration does not provide sufficient heat, or where the
temperature level is below the required temperature level,
additional heat sources may also be employed. Suitable, additional
heat sources include, for example, the remaining waste heat
generated from the CO.sub.2 boiler; or the heat provided by an
auxiliary, fired boiler.
[0041] In certain embodiments, the high-pressure refrigerant vapor
and solution mixture 154 exiting the desorber may be passed through
a rectifier in which most of the remaining refrigerant is separated
from the solution. The refrigerant vapor exiting the rectifier can
then be passed through the refrigerant condenser 150.
[0042] The refrigerant is usually water or ammonia. Unless
otherwise indicated, the pressure values (e.g., about 7 bar to
about 9 bar) are provided for the case of ammonia. (It should be
understood that the pressure values may be lower for other types of
refrigerants, such as water). The solvent is either water for the
ammonia, or a lithium bromide-water solution.
[0043] Referring to FIG. 2, a power generation system 200 is
provided, based on some embodiments of the invention. The system
200 comprises a first loop 202. The first loop 202 is an example of
a double expansion recuperated carbon-dioxide cycle for waste heat
recovery. The first loop 202 is integrated with a second loop 204.
The second loop 204 is an absorption chiller cycle. The first loop
202 usually begins with a pump 210. A liquid CO.sub.2 stream 212,
having a temperature of about 10 degrees Celsius to about 30
degrees Celsius, can be pumped through the pump 210 to a waste heat
recovery boiler 214. In certain embodiments, the waste heat
recovery boiler 214 may be provided with an external source of
heat, for example, heat originating in a gas turbine. The heat
source enters the waste heat recovery boiler 214 at a higher
temperature 217, and exits the waste heat recovery boiler 214 at a
lower temperature 216 (as designated by reference numerals).
[0044] The CO.sub.2 stream 212 is heated to provide a vaporized
CO.sub.2 stream 218, usually having a temperature in a range of
about 350 degrees Celsius to about 500 degrees Celsius. The
vaporized CO.sub.2 stream 218 is then passed through a first
expander 220, to form a cooler CO.sub.2 stream 226. The temperature
and pressure of the vaporized CO.sub.2 stream 218 are often lowered
in the expansion process, to a pressure in a range of about 60 bar
to about 100 bar, and a temperature in a range of about 250 degrees
Celsius to about 350 degrees Celsius, to produce the cooler
CO.sub.2 stream 226. The first expander 220 may be connected to a
generator 224, via a shaft 222. The cooler CO.sub.2 stream 226 can
then be passed through an intermediate temperature recuperator 228.
The CO.sub.2 stream 226 is further cooled, on passing through the
recuperator 228, to form an even cooler CO.sub.2 stream 230,
usually having a temperature in a range of about 50 degrees Celsius
to about 100 degrees Celsius. The cooled CO.sub.2 stream 230 can
then be passed through a mixing junction 232.
[0045] In parallel with the passage of the first portion of the
liquid CO.sub.2 stream 212 (and sometimes, simultaneously
therewith) a second portion of the liquid CO.sub.2 stream 234 is
pumped through the pump 210, to the recuperator 228. Heat from the
CO.sub.2 stream 226 passing through the recuperator is transferred
to the second portion of the liquid CO.sub.2 stream 234, to produce
a heat vaporized CO.sub.2 stream 236, having a temperature which is
usually in the range of about 240 degrees Celsius to about 340
degrees Celsius. The vaporized CO.sub.2 stream 236 can then be
passed through a second expander 238. The expander 238 is usually
connected to the generator 224 through a portion of a shaft 240. A
cooler CO.sub.2 stream 242, (i.e., cooler than the vaporized
CO.sub.2 stream 236), usually having a temperature in a range of
about 150 degrees Celsius to about 200 degrees Celsius, exits from
the second expander 238, and is then passed through the desorber
244, to form a relatively cool CO.sub.2 stream 246. The CO.sub.2
stream 246 may have a temperature in a range of about 70 degrees
Celsius to about 120 degrees Celsius. The CO.sub.2 stream 246 can
then be passed through the mixing junction 232. The two CO.sub.2
streams 230 and 246 can be mixed at the junction 232, and then
passed through a cooler 248. In certain embodiments, the cooler 248
may be provided with an external cooling mechanism, as described
for other embodiments. As an example, the cooling source can enter
the cooler 248 at a lower temperature 250, and exit the cooler 248
at a higher temperature 251. The cooled CO.sub.2 stream 252,
usually having a temperature in a range of about 30 degrees Celsius
to about 55 degrees Celsius, can then be passed through a condenser
254, to form a liquid CO.sub.2 stream 256, which usually has a
temperature in a range of about 20 degrees Celsius to about 30
degrees Celsius, thus closing the first loop 202.
[0046] An absorption chiller system 204 is integrated with the
first loop 202. The condenser 254 of the first loop is usually
cooled, using a substantially liquid refrigerant stream 278 (for
example, water or ammonia). In doing so, the refrigerant stream 278
usually evaporates in the condenser 254, to form a vaporized
refrigerant stream 258. Thus, in one embodiment, the condenser 254
of the first loop 202, functions as the evaporator 254 of the
second loop 204.
[0047] The vaporized refrigerant stream 258 can be passed into an
absorber 260. A second solution of the refrigerant in a solvent
(not shown in figure) is usually present in the absorber 260. The
vaporized refrigerant stream 258 can be dissolved in the second
solution to form a first solution of the refrigerant in a solvent
262, having a pressure in a range of about 7 bar to about 9 bar,
and temperature in a range of about 20 degrees Celsius to about 25
degrees Celsius. (As described for previous embodiments, the
temperature and pressure can vary for a given situation and a given
refrigerant, and are usually interdependent on each other). The
heat absorbed from the vaporized refrigerant stream 258 by the
absorber 260 may be rejected to the ambient atmosphere, as
discussed above in the description for FIG. 1.
[0048] The first solution 262 can then be passed thorough a
refrigerant pump 264, to increase its pressure. The
higher-pressure, first solution 266 can then be passed through the
desorber 244. Heat from the CO.sub.2 stream 242 is transferred to
the first solution 266 in the desorber 244. In doing so, the
CO.sub.2 stream 242 can then be transformed into the cooler
CO.sub.2 stream 246 that exits the desorber 244. In the process,
the refrigerant in the first solution 266 is vaporized, and the
vaporized refrigerant 272 passes from the desorber 244 to the
refrigerant condenser 268. The second solution of the refrigerant
in the solvent (not shown in figure) is retained in the desorber
244. (The second solution is usually formed when the refrigerant is
vaporized from the first solution 266). An additional loop,
discussed in FIG. 3 below, can be used to convey the second
solution from the desorber to the absorber. The additional loop may
further comprise additional heat exchangers and valves to maintain
the temperature and pressure of the second refrigerant solution, as
it is conveyed from the desorber to the absorber. The refrigerant
condenser 268 provides a condensed liquid refrigerant 274. In
certain embodiments, the refrigerant condenser 268 may be provided
with an external cooling mechanism, as described previously. Thus
the cooling source would typically enter the refrigerant condenser
268 at a lower temperature 269, and exit the refrigerant condenser
267 at a higher temperature 270.
[0049] The liquid refrigerant stream 274 can then be passed through
a pressure reducing device 276 where its pressure is lowered,
usually, to a range of about 7 bar to about 9 bar, at a temperature
in the range of about 15 degrees Celsius to about 20 degrees
Celsius. By passing through the pressure reducing device 276, the
stream is formed into a relatively cool, two-phase mixture of
liquid and vapor refrigerant stream 278. The refrigerant stream 278
can then be used to condense the CO.sub.2 stream 252 entering the
condenser 254, to form the liquid CO.sub.2 stream 256. In doing so,
the refrigerant stream 278 is evaporated in the evaporator 254, to
form the vaporized refrigerant stream 258. The evaporator 254 is
capable of directing the vaporized refrigerant back to the absorber
260. As mentioned above, the concentration of the refrigerant in
the first refrigerant solution is usually greater than the
concentration of the refrigerant in the second refrigerant
solution, based on the amount of solvent which is present.
[0050] Referring to FIG. 3, a power generation system 300 is
provided, according to some embodiments. The system 300 comprises a
first loop 102 and a second loop 104, as generally described above
with reference to FIG. 1 (where appropriate, the same reference
numerals have been used). The system 300 may further comprise an
additional loop 306. The additional loop 306, as described
previously, conveys the second solution 362 from the desorber 128
to the absorber 142. The additional loop 306 may further comprise
additional heat exchangers 364 and pressure reducing devices 366,
to maintain the temperature and pressure of the second solution
362, as it is conveyed from the desorber 128 to the absorber
142.
[0051] In one embodiment, the present invention provides a net
power benefit to a CO.sub.2 Rankine Cycle of about 10 percent, as
compared to a cycle without an integrated absorption chiller, under
similar or identical environmental conditions. For higher ambient
temperatures, this benefit may increase, while the benefit may be
lower at cold ambient temperatures where condensation could be
possible without an absorption chiller. This condensing system may
provide considerable benefits to new CO.sub.2 Rankine cycles for
waste heat recovery, and can enable operation at ambient
temperatures above approximately 20 degrees Celsius, with high
efficiency.
[0052] While the invention has been described in detail in
connection with a number of embodiments, the invention is not
limited to such disclosed embodiments. Rather, the invention can be
modified to incorporate any number of variations, alterations,
substitutions or equivalent arrangements not heretofore described,
but which are commensurate with the scope of the invention.
Additionally, while various embodiments of the invention have been
described, it is to be understood that aspects of the invention may
include only some of the described embodiments. Accordingly, the
invention is not to be seen as limited by the foregoing
description, but is only limited by the scope of the appended
claims.
* * * * *