Note: Descriptions are shown in the official language in which they were submitted.
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EFFICIENT CONVERSION OF HEAT TO USEFUL ENERGY
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates to systems, methods and apparatus configured to
implement a thermodynamic cycle via countercurrent heat exchange. In
particular,
the present invention relates to generating electricity by heating a multi-
component
stream with a heat source stream at one or more points in a thermodynamic
cycle.
2. Background and Relevant Art
Some conventional heat transfer systems allow heat that would otherwise be
wasted to be turned into useful energy. One example of a conventional heat
transfer
system is one which converts thermal energy from a geothermal hot water or
industrial waste heat source into electricity using a counter current heat
exchange
technology. For example, the heat from relatively hot liquids in a geothermal
vent
(e.g., "brine") can be used to heat a multi-component fluid in a closed system
(a "fluid
stream"), using one or more heat exchangers. The multi-component fluid is
heated
from a low energy and low temperature fluid state into a relatively high-
pressure gas
("working stream"). The high-pressure gas, or working stream, can then be
passed
through one or more turbines, causing the one or more turbines to spin and
generate
electricity.
Accordingly, conventional heat transfer systems operate on the general
counter current heat exchange principles to heat the multi-component working
fluid
through a variety of temperature ranges, from relatively cold to relatively
hot. A
conventional fluid stream for such a system comprises different fluid
components that
each have a different boiling point. Thus, one component of the fluid stream
may
become a gas at one temperature point, while another fluid stream component
may
remain in a relatively hot liquid state at the same temperature. This can be
useful for
separating the different components at different points in the closed system.
Nevertheless, all, or nearly all, of the components of the fluid stream can be
raised to
a temperature such that all components of the fluid stream collectively
comprise a
"working stream", or high pressure gas.
To accomplish heating of the fluid between the fluid stream and the working
stream, the heat transfer system comprises apparatus configured primarily to
cool the
working, stream to a cooler temperature, or heat the fluid stream to a hotter
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temperature. For example, the fluid stream passes through one or more heat
exchangers that couple the fluid stream to the heat source stream as the fluid
stream
progresses toward a high temperature state, which is then passed through the
one or
more turbines. By contrast, the working stream that has already passed through
the
turbines is typically referred to as a spent stream. The spent stream is
cooled by
transferring heat to the fluid stream in a heat exchanger, since the spent
stream is
relatively hotter than the fluid stream at one or more stages in the system.
In order to achieve the temperature requirements for expansion in the
turbines,
countercurrent heat exchange systems heat the fluid stream from lower
temperature
1o points to the higher temperature points. This results in a number of system
variables
that conventional, heat exchange systems will take into account. For example,
if the
optimal expansion temperature of an ambient temperature multi-component stream
is
a vapor working, stream of a very high temperature, a very hot heat source
that is.
typically much hotter than the desired temperature of the working stream will
be
utilized. Alternatively, if the heat source is only somewhat hotter than the
ultimate
desired temperature of the multi-component stream, the fluid stream will
likely need
to be warmer than ambient temperature, so that the multi-component fluid can
be
heated to the desired working stream temperature.
At least in part, due to this distinction in fluid stream starting
temperatures,
temperatures of the heat source, desired temperature of the working stream,
and
efficiencies of the system the heat source brine is usually discarded at a
temperature
that is, much hotter than desired. For example, in some illustrative systems
as
conventional heat transfer systems pass the brine through one or more heat
exchangers, the brine is cooled from an average temperature of about 600 F to
a
throw-away temperature of about 170-200 F. While 200 F is still a relatively
hot
temperature to perform meaningful heat transfers on conventional fluid
streams, the
conventional fluid stream is considered relatively cool, or lukewarm, at a
similar
temperature of about 170-200 F. In particular, the coolest point of a
conventional
fluid stream is usually too warm to be heated in any efficient way by the low
temperature portion (i.e., the "low temperature tail") of the brine. As such,
conventional heat systems tend to be more efficient by discarding the brine at
approximately 170-200 F.
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One possible solution could be to cool the fluid stream to temperature that is
much lower than 190-2000 F, so that the fluid stream can be efficiently heated
using
the heat of the low temperature tail. In principle, this might involve the use
of a
Distillation Condensation Sub-system ("DCSS") in conjunction with the above-
described heat transfer system. Unfortunately, while use of a DCSS could
efficiently
cool a spent stream, the temperature to which the conventional DCSS would cool
a
typical spent stream would ordinarily be too low to be efficiently utilized.
That is, the
conventional DCSS would cool the spent stream to a temperature that is so low
that it
could not be efficiently raised to a high enough temperature later on as a
working
stream.
Accordingly, an advantage in the art can be realized with systems and
apparatus that allow efficient use of a low temperature tail. In particular,
an
advantage in the art can be realized with heat transfer systems that are able
to
efficiently use a DCSS, so that a fluid stream can still be raised to an
efficient
working stream temperature.
BRIEF SUMMARY OF THE INVENTION
The present invention solves one or more of the foregoing problems in the
prior art with systems and apparatus configured to efficiently use more waste
heat
than possible in prior heat transfer systems. In particular, the present
invention
provides for the use of a "low temperature tail" of a brine heat source in a
heat
transfer system, at least in part by efficiently incorporating a DCSS along
with
additional heat exchange apparatus.
For example, in one embodiment of the present invention, a DCSS is coupled
to a counter current heat exchange system. The DCSS is used at least in part
to cool a
spent working stream after the working stream has been passed through one or
more
turbines. Due to the relatively cool temperature of the fluid stream provided
by the
DCSS, however, one or more heat exchange apparatus are added to increase the
temperature of the fluid stream to a useful temperature range. At this
temperature
range, the fluid stream can subsequently be coupled to a low temperature tail
as low
3o as 150-200 F via an additional heat exchanger, and still ultimately reach
an
appropriate working stream temperature.
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Accordingly, a heat transfer system in accordance with the present invention
can convert a greater amount of heat from the heat source into useful energy,
and can
do so with significantly more energy efficiency than prior heat transfer
systems.
Additional features and advantages of exemplary embodiments of the
invention will be set forth in the description which follows, and in part will
be
obvious from the description, or may be learned by the practice of such
exemplary
embodiments. The features and advantages of such embodiments may be realized
and
obtained by means of the instruments and combinations particularly pointed out
in the
appended claims. These and other features will become more fully apparent from
the
following description and appended claims, or may be learned by the practice
of such
exemplary implementations as set forth hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
In order to describe the manner in which the above-recited and other
advantages and features of the invention can be obtained, a more particular
description of the invention briefly described above will be rendered by
reference to
specific embodiments thereof which are illustrated in the appended drawings.
Understanding that these drawings depict only typical embodiments of the
invention
and are not therefore to be considered to be limiting of its scope, the
invention will be
described and explained with additional specificity and detail through the use
of the
accompanying drawings in which:
Figure 1 illustrates a heat transfer system in accordance with an embodiment
of the present invention, in which two turbines are used; and
Figure 2 illustrates a heat transfer system in accordance with another
embodiment of the present invention, in which one turbine is used.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention extends to systems and apparatus configured to
efficiently use more waste heat than possible in prior heat transfer systems.
In
particular, the present invention provides for the use of a "low temperature
tail" of a
brine heat source in a heat transfer system, at least in part by efficiently
incorporating
3o a DCSS along with additional heat exchange apparatus.
For example, Figure 1 illustrates one embodiment of the present invention in
which a heat transfer system 100 comprises a power sub-system 101 that is
coupled to
a cooling system, such as Distillation Condensation Sub-system ("DCSS") 103.
The
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power sub-system 101 can be thought of generally as heating the multi-
component
stream to a point at which the fluid multi-component stream becomes an at
least
partially a vapor working. stream. By contrast, the DCSS 103 can be thought of
generally as cooling a post expansion spent stream to a cooled fluid stream,
as well as
5 heating the fluid stream where appropriate for later use as a multi-
component stream
in the power sub-system 101. Figure 1 also shows the direction of a multi-
component
stream (both for the fluid stream and for the heat source stream) throughout
the heat
transfer system 100, as the fluid is condensed and heated in heat exchangers
in the
system.
Accordingly, the following description outlines the stream of a heat source
stream (e.g., "brine") as it streams through the heat transfer system 100 (and
system
200), and then the flow of spent and intermediate fluid streams, which are
distinct and
separate from the heat source stream, through the power sub-system 101 and the
DCSS 103. With reference to the heat source stream, it will be understood that
there
can be many types of heat source streams that can be implemented with the
present
invention. For example, a heat source stream that is suitable for use with the
present
invention can comprise any suitably hot liquid or vapor, or mixture thereof,
such as
naturally or synthetically produced liquids, steams, oils, and so forth.
Accordingly,
implementations of the systems described herein can be particularly, useful
for
converting heat from geothermal fluids, such as "brine", into electric power,
as well
as converting other synthetic fluid waste heat in a factory environment into
electric
power.
Referring again to Figure 1, the heat source stream enters the heat transfer
system 100 at point 50 (anywhere from 250 F to 800 F), whereupon the heat
source
splits into two streams 51 and 151, which are used to add heat to a working
stream
just before the working stream passes to a turbine or other expansion
component. For
example, stream 51 passes through heat exchanger 304, which transfers heat to
the
working stream at point 30 just before passing into a first turbine 501. As
described
herein, the splitting of streams can be carried out by any suitable means,
such as a
conventional splitting component that splits the multi-component stream into
two
separate streams.
After the working stream passes the first turbine, the working stream cools
somewhat to a point 32. Accordingly, stream 151 heats the working stream from
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point 32 to point 35 when it passes through heat exchanger 305, which is
adjacent a
second turbine 502, such that the working stream can be heated just before it
passes
into the second turbine 502. As used herein, a "heat exchanger" may be any
conventional type of heat exchanger, such as conventional shell and tube, or
plate-
s type heat exchangers, or variations or combinations thereof. Accordingly,
the heat
source stream at point 151 cools to parameters at point 150, having
transferred an
amount of its heat in heat exchanger 305.
Streams 150 (original stream 151) and 152 (original, stream 51) are then
combined at point 153 prior to entering heat exchanger 303, wherein the
combined
stream at point 153 is an amount cooler than at point 50. The mixing or
combining of
any working, intermediate, spent, or otherwise fluid stream may, be carried
out by any
suitable mixing device to combine the streams. to form a single stream.
Having passed heat exchangers at point 153, the combined heat source stream
is still at a relatively high temperature, and so still has a significant
amount of heat
that can be transferred to the working stream. As such, the combined stream at
point
153 is passed through heat exchanger 303, thereby transferring the heat from
the heat
source stream to the working stream, causing the working stream to heat from
points
66 to 67. The heat source stream, having somewhat cooler parameters at point
53, is
still at a relatively high temperature, and so is passed through heat
exchanger 301.
This heats the working stream from point 161 to 61, and cools the heat source
stream
further from point 53 to point 54.
In one embodiment, at point 54, these parameters of the heat source stream are
associated with a temperature range of about 170-200 F, depending in part on
other
operating conditions of the relevant heat source and system 101. In another
embodiment, the parameters of the heat source stream at point 54 are
associated with
a temperature ranges of about 130-250 F. At point 54, the heat source stream
is now
at parameters of the conventional "low temperature tail", and would ordinarily
be
discarded. As will be understood more fully from the following description,
however,
system 100 can efficiently use this low temperature tail, such that the heat
source
stream is passed from point 54 through heat exchanger 405 to point 55. Since
heat
exchanger 405 transfers heat from the low temperature tail, the heat exchanger
405
can be termed a "residual heat exchanger".
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Having described the path of the heat source stream, the following description
illustrates the path and changes to the fluid stream of the system 100, as it
is heated
and cooled in various stages through the power sub-system 101 from point 60-
to
point 36, and then as it travels through the DCSS 103 from point 38 to point
29\ By
way of explanation, in one embodiment the fluid stream can comprise a water-
ammonia mixture that has a boiling point of approximately 196 F, and a dew
point at
approximately 338 F. As will be understood from the present description,
therefore,
the fluid stream is at or near its boiling point at point 60, at or near its
dew point at
point 30, and at or near liquid forms at points 18, and 102. These differences
between
boiling point, dew point, and liquid form occur since the working fluid
comprises a
mixture of components, rather than one pure substance.
With reference to Figure 1 at point 60, the heat transfer system 100 splits
the
working stream into two multi-component streams at points 161 and 162. The
working stream at point 161 is heated by the heat source stream to parameters
at point
61 in heat exchanger 301, while the working stream at point 162 is heated to
parameters of point 62 by the spent stream 36 at heat exchanger 302. After
passing
through the relevant heat exchangers, the working streams at points 61 and 62
are
then combined into a working stream that has parameters at point 66. Since
part of the
working stream at point 60 is heated by the heat source stream, while another
part of
the working stream is heated by the spent stream, the power sub-system 101 can
make efficient use of a number of potential heat sources.
The working stream at point 66 is heated by the heat source stream from point
153 to parameters at point 67 via heat exchanger 303. In one embodiment, at
point 67
the working stream begins to be converted toward a superheated vapor.
Thereafter,
the working stream is heated by the heat source stream at point 51, such that
the
working stream heats from point 67 to point 30 via heat exchanger 304. This
optimizes the conventional working stream so that it can pass through the
turbine 501
at a desired high energy state. In one embodiment, the desired high energy
state is a
superheated vapor.
As the working stream passes through the turbine 501, from points 30 to 32,
the working stream becomes at least "partially spent", such that it loses an
amount of
energy in the form of lost pressure and temperature. The partially spent
stream at
point 32 is heated through a heat exchanger 305 to obtain parameters of point
35. As
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such, one will appreciate that the system 100 may find additional incremental
energy.
gains by continuing to split the heat source stream at point 50 to heat still
subsequent
iterations of a partially spent working stream through still further numbers
of heat
exchangers and turbines, and so on. As such, the use of one or two turbines of
the
present disclosure are merely exemplary of one suitable embodiment.
After passing the working stream through the one or more turbines 501, 502,
the now spent stream at point 36 is passed through a heat exchanger 30-2. This
cools
the spent stream to the parameters of point 38, while at the same time heating
a part of
the working stream from point 162 to 62. (In at least some cases, the spent
stream at
point 36 may be at a lower pressure than the high pressure working stream at
points
162 and 62, even though the spent working stream at point 36 is hotter.) In
conventional systems, the spent stream at point 38 would ordinarily be passed
to. point
60 for recuperative reheating. In the present system 100, however, the spent
stream at
point 38 is cooled further using a DCSS 103.
For example, the spent stream at point 38 is passed through heat exchanger
401, such that the spent stream is cooled from point 38 to parameters at
points 16, and
then 17. This cooling of the spent stream from point 38 to point 17 in heat
exchanger
401 transfers heat to the relatively cooler intermediate "lean stream"' from
point 102
to point 5. The lean stream passes from relatively cooler parameters of point
102 to.
relatively hotter parameters at point 3 (typically a boiling point), and
ultimately to
parameters at point 5. In general, a "lean stream" refers. to a fluid stream
having less
of a lower boiling point component than a higher boiling point component (e.g.
ammonia versus water), while a "rich stream" refers to a fluid stream having
more of
a lower boiling point component than a higher boiling point component.
Furthermore,
an "intermediate lean" stream has more of a lower boiling point component
(e.g.,
ammonia, in an ammonia / water composition) than a "lean" or "very lean"
stream
(i.e., least amount of ammonia, in an ammonia / water composition), but less
lower
boiling point component than a "rich" stream.
The spent stream at point 17 then combines with a very lean stream that has
parameters of point 12, to produce a combined fluid stream (or "intermediate
lean
stream") that has parameters of point 18. The combined, intermediate lean
stream is
then cooled at heat exchanger 402, which transfers heat from the intermediate
lean
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stream at point 18 to a cooling medium. Apparatus 402 and 404 may comprise any
suitable heat exchange condensers, such as water or air-cooled heat
exchangers.
The cooling medium can be any number or combination of media sufficient to
condense the intermediate lean stream from point 18 to point 1 through the
heat
exchanger 402. Such media can include air, water, a chemical coolant, and so
forth, and
are simply cycled in and out of the system 100, as appropriate. As such, the
cooling
medium is introduced to the system 100 relatively cool, such of point 23,
heated by
heat exchangers 402 and 404 to points 59 and 58, and then cycled out of the
system 100
relatively warm at point 24. Since the cooling medium is cycled in and out of
the
system, the cooling medium maintains a relatively constant, cool temperature
that can
absorb heat from the multi-component stream.
After the intermediate lean stream has been condensed to parameters at point
1,
pump 504 elevates the pressure of the stream, causing the intermediate lean
stream to
be elevated to parameters of point 2. Thereafter, the elevated pressure
intermediate lean
stream is then split into two parts. One part, which will be discussed in
further detail
subsequently, has parameters of point 8, and is mixed with a rich stream
having
parameters of point 6. The other part of the elevated pressure intermediate
lean stream,
having parameters of point 102, is heated in apparatus 401 by the spent stream
of point
16, such that the intermediate lean stream gains parameters of point 5.
At point 5, the intermediate lean stream is separated in apparatus 503 into
primarily vapor and liquid components, such that the vapor component has
parameters
of point 7, and the liquid component has parameters of point 9. One will
appreciate,
however, that neither the vapor nor the liquid components are purely one
component or
another. Nevertheless, the vapor stream will be richer in the lower boiling
component
(i.e., a "rich" stream); while the liquid stream have a greater amount of
higher boiling
point component (i.e., a "lean" stream). Apparatus 503 can comprise any
suitable
separator or distilling device that is known in the art, such as a gravity
separator (e.g., a
conventional flash tank).
In one embodiment, the vapor and liquid components of the streams at points 7
and 9 are separated so that they can be selectively mixed (or not mixed) to
heat (or
maintain) the amount of temperature provided at an intermediate heat exchanger
403.
For example, a portion of the vapor at point 7 can be selectively split into
one stream at
point 6, and another stream at point 15. If the liquid component at point 9 is
not hot
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enough to heat the multi-component stream from point 21 to point 29 in the
heat
exchanger 403, a greater portion of the hotter vapor component stream from
point 15
may, be added to the liquid component stream at point 9, to produce a hotter
stream
having parameters at point 10. Alternatively, if the liquid component at point
9 is hot
5 enough for what is needed in heat exchanger 403, then no mixing with the
vapor at
point 15 will be needed. Such mixing, therefore, is optional and depends on
the
relevant operating conditions.
Regardless of whether such mixing is done, the stream at point 10 is generally
a "very lean" stream, or a stream with a relatively low amount of low boiling
point
1o component. This very lean stream at point 10 passes through the
intermediate heat
exchanger 403, heats the fluid stream of point 21, and cools the very lean
stream from
point 10 to point 11. In some cases, if necessary, the fluid stream at point
11 may
further be throttled to a lower pressure. Nevertheless, the fluid stream of
point 11
passes to parameters of point 12, and then mixes with the spent stream at
point 17
before passing through heat exchanger 402.
Referring back to the stream at point 5, the vapor component at point 7 that
is
split apart from the liquid component of point 9, differs from the vapor
components of
points 6 and 15 primarily with respect to stream rate. In practice, however,
the vapor
components, of points 6, 7, and 15 may also have slightly different pressures.
Regardless, the vapor component (i.e., the component at point 7, or component
streams 6, or 15), is a "rich"- stream, having a relatively high amount of low-
boiling-
point component. This "rich" stream at point 6 is subsequently mixed with the
portion of the intermediate lean stream at point 8, to produce the multi-
component
stream at point 13. The intermediate stream at point 13 is approximately the
same
proportion of low and high baling point components (e.g., proportion of
ammonia to
water) as the working stream used subsequently in the heat transfer process,
such of
points 60 and higher.
This intermediate stream at point 13 is then condensed at the heat exchanger
404 by the afore-described cooling medium and becomes a condensed stream. As
such, this fluid stream at point 13 cools from parameters of point 13 to
parameters of
point 14. The fluid stream at point 14 is then pumped through pump 5.05, such
that
the fluid stream becomes a high-pressure working stream that has parameters of
point
21. The working stream at point 21 is then heated to point 29 through the heat
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exchanger 403, causing the intermediate stream to cool from point 10 to point
11. At
point 29, the working stream is heated by the "low temperature tail" of the
heat source
stream at heat exchanger 405, such that the heat source stream cools from
points 54 to
55.
In view of the foregoing, one will appreciate that the working stream at point
29 should be at an appropriate temperature that it can make efficient use
(i.e., be
heated by) of the low temperature tail in heat exchanger 405. This can help
ensure
that the working stream at point 30 passes through the turbine 501 at the
highest
available energy for the system 100. Accordingly, whether the working stream
at
point 30 reaches its most efficient energy output can depend in part on the
temperature of the intermediate stream is at point 10. For example, if the
working
stream at point 29 is at too high of a temperature, there is little or no
efficiency added
transferring heat from the low temperature tail at points 54 to 55. By
contrast, if the
working stream at point 29 is too cool after passing through the DCSS 103, the
low
temperature tail from points 54-55 will not be able to heat the working stream
from
point 29 all the way to the desired temperature at point 60.
According to one embodiment of the present invention, the DCSS 103 can
help ensure the appropriate temperature of the working stream at point 29 by
allowing
for the variable addition of heat to the intermediate stream at point 10. As
previously
described, this, can be accomplished by variably adding (or not adding) vapor
component 15 with liquid component 9. In other words, the more of vapor 15
that is
added to stream 9, the hotter the mixed fluid stream is at point 10, and the
more heat
that can be added to the working stream at point 21. Therefore, the provisions
for
separating. and mixing of the fluid stream in the DCSS 103 allows the system
100 to
make efficient use of the low temperature tail (i.e., points 54-55) in the
working
stream. Furthermore, implementations of the present invention make effective
use of
the low heat source stream for additional power at turbines 501 and 502, and
so on.
Figure 2 shows an alternative heat transfer system 200, which implements
only a single turbine 502. In particular, system 100 can be modified, as shown
in
Figure 2, so that streams 32, 150, and 151, and heat exchanger 305 are
omitted. This
results in only the working stream at point 30 passing through turbine 502 to
produce
a spent stream 36, which is then processed in heat exchanger 302, as described
above.
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As mentioned above, however, the number of turbines that can be used for
incremental energy, gains may be varied within the context of the present
invention.
In alternative embodiments of the present invention, whether system 100 or
200, heat exchanger 303 may be dispensed with, in lieu of heat exchanger 304.
In
another alternative embodiment, heat exchanger 302 may be dispensed with in
lieu of
heat exchanger 301.
The present invention may be embodied in other specific forms without
departing from its spirit or essential characteristics. The described
embodiments are
to be considered in all respects only as illustrative and not restrictive. The
scope of
to the invention is, therefore, indicated by the appended claims rather than
by the
foregoing description. All changes that come within the meaning and range of
equivalency of the claims are to be embraced within their scope.
