U.S. patent application number 10/258718 was filed with the patent office on 2003-09-11 for mixed working fluid power system with incremental vapor generation.
Invention is credited to Bharathan, Desikan, Hassani, Vahab.
Application Number | 20030167769 10/258718 |
Document ID | / |
Family ID | 27788833 |
Filed Date | 2003-09-11 |
United States Patent
Application |
20030167769 |
Kind Code |
A1 |
Bharathan, Desikan ; et
al. |
September 11, 2003 |
Mixed working fluid power system with incremental vapor
generation
Abstract
A power generating system (110) comprising a heat source (116)
and an incremental vapor generator system (112) operatively
associated with the heat source (116). The incremental vapor
generator system (112) includes a first heating section (136) and a
second heating section (138). The first heating section (136)
receives a mixed working fluid (114) and generates a first heated
working fluid stream comprising a vapor portion (120) and a liquid
portion. The second heating section (138) is operatively associated
with the first heating section (136) and receives the liquid
portion from the first heated working fluid stream. The second
heating section (138) generates a second heated working fluid
stream comprising a vapor portion (122). An energy conversion
device (126) operatively associated with the incremental vapor
generator system (112) converts into useful work heat energy
contained in the vapor portions (120, 122) of the first and second
heated working fluid streams.
Inventors: |
Bharathan, Desikan; (Arvada,
CO) ; Hassani, Vahab; (Denver, CO) |
Correspondence
Address: |
Paul J White
Senior Counsel
National Renewable Energy Laboratory
1617 Cole Boulevard
Golden
CO
80401
US
|
Family ID: |
27788833 |
Appl. No.: |
10/258718 |
Filed: |
March 31, 2003 |
PCT Filed: |
July 19, 2001 |
PCT NO: |
PCT/US01/22773 |
Current U.S.
Class: |
60/676 ;
60/670 |
Current CPC
Class: |
F01K 25/065
20130101 |
Class at
Publication: |
60/676 ;
60/670 |
International
Class: |
F01K 001/00; F01K
013/00 |
Goverment Interests
[0001] The United States Government has rights in this invention
pursuant to Contract No. DEAC36-99GO10337 between the U.S.
Department of Energy, and the National Renewable Energy Laboratory,
a division of the Midwest Research Institute.
Claims
1. A power generating system, comprising: a heat source; an
incremental vapor generator system operatively associated with said
heat source, said incremental vapor generator system comprising: a
first heating section, said first heating section receiving a mixed
working fluid and generating a first heated working fluid stream
comprising a vapor portion and a liquid portion; a second heating
section operatively associated with said first heating section,
said second heating section receiving the liquid portion from said
first heated working fluid stream, said second heating section
generating a second heated working fluid stream comprising a vapor
portion; and an energy conversion device operatively associated
with said incremental vapor generator system, said energy
conversion device converting into useful work heat energy contained
in the vapor portions of the first and second heated working fluid
streams.
2. The power generating system of claim 1, further comprising: a
condensing system operatively associated with said energy
conversion device, said condensing system receiving an exhaust
stream from said energy conversion device and condensing the
exhaust stream to form a condensed mixed working fluid; and a pump
system operatively associated with said condensing system and said
incremental vapor generator system, said pump transferring the
condensed mixed working fluid from said condensing system to said
incremental vapor generator system.
3. The power generating system of claim 1, further comprising a
first separator system having an inlet, a vapor outlet, and a
liquid outlet, the inlet of said first separator system being
operatively associated with said first heating section, the liquid
outlet of said first separator system being operatively associated
with said second heating section, said first separator system
separating the vapor portion and the liquid portion of said first
heated working fluid stream.
4. The power generating system of claim 3, further comprising a
second separator system having an inlet, a vapor outlet, and a
liquid outlet, the inlet of said second separator being operatively
associated with said second heating section.
5. The power generating system of claim 4, further comprising a
vapor mixer having a first inlet, a second inlet, and an outlet,
the first inlet of said vapor mixer being operatively associated
with the vapor outlet of said first separator system, the second
inlet of said vapor mixer being operatively associated with the
vapor outlet of said second separator system, the outlet of said
vapor mixer being operatively associated with said power conversion
system.
6. Tile power generating system of claim 5, further comprising a
third heating section operatively associated with said heat source,
the outlet of said vapor mixer, and said energy conversion device,
said third heating section additionally heating the first and
second vapor streams.
7. The power generating system of claim 4, wherein said first and
second separator systems comprise an integral system wherein the
vapor portion of said first heated working fluid stream from said
first separator system at least partially condenses in said second
separator system the liquid portion from said second heated working
fluid stream.
8. The power generating system of claim 7 further comprising a
third heating section operatively associated with said heat source,
said integral first and second separator systems, and said energy
conversion device, said third heating section additionally heating
the first and second vapor streams.
9. A method for generating power from a mixed working fluid,
comprising: incrementally heating the mixed working fluid to
produce a first vapor stream and a second vapor stream; and
converting into useful work heat energy contained in the first and
second vapor streams.
10. The method of claim 9, wherein said step of incrementally
heating comprises: heating the mixed working fluid to produce a
first heated working fluid stream comprising a vapor portion and a
liquid portion; separating the vapor portion and the liquid
portions of the first heated working fluid stream, the separated
vapor portion forming the first vapor stream; and additionally
heating the liquid portion from the first heated working fluid
stream to produce the second vapor stream.
11. The method of claim 10, further comprising combining the first
and second vapor streams into a combined vapor stream.
12. The method of claim 11, further comprising additionally heating
the combined vapor stream to produce a superheated
vapor-stream.
13. The method of claim 10, further comprising using the vapor
portion from the first heated working fluid stream to condense on
the liquid portion from the second heated working fluid stream and
to produce additional portions of the vapor portion from the first
heated working fluid stream.
14. The method of claim 13, further comprising combining the
additional portions of the vapor portion from the first heated
working fluid stream and the second vapor streams to form a
combined vapor stream.
15. The method of claim 14, further comprising additionally heating
the combined vapor stream to produce a superheated vapor
stream.
16. A power generating system, comprising: a heat source;
incremental vapor generating means operatively associated with said
heat source for incrementally generating a first vapor stream and a
second vapor stream from a mixed working fluid; and power
conversion means operatively associated with said incremental vapor
generating means for converting into useful work heat energy
contained in said first and second vapor streams.
17. The power generating system of claim 16, further comprising
separator means operatively associated with said incremental vapor
generating means for separating the first and second vapor streams
from a heated working fluid stream from said incremental vapor
generating means.
18. The power generating system of claim 17, further comprising
means for combining said first vapor stream and said second vapor
stream to form a combined vapor stream, the combined vapor stream
being directed to said power conversion means.
19. The power generating system of claim 17 wherein said separator
means comprises means for using a portion of the first vapor stream
to condense on a liquid portion from the heated mixed working
fluid.
20. The power generating system of claim 16, further comprising:
condensing means operatively associated with said power conversion
means for condensing a vapor exhaust from said power conversion
means into a condensed mixed working fluid; and recirculating means
operatively associated with said condensing means for recirculating
condensed mixed working fluid to said incremental vapor generating
means.
21. An incremental vapor generator system for vaporizing a mixed
working fluid, comprising: a first heating section operatively
associated with a heat source, said first heating section receiving
the mixed working fluid and generating a first heated working fluid
stream comprising a vapor portion and a liquid portion; a separator
system operatively associated with said first heating section, said
separator system separating the vapor portion and the liquid
portion of the first heated working fluid stream; and a second
heating section operatively associated with the heat source and
said separator system, said second heating section receiving the
liquid portion from the first heated working fluid stream, said
second heating section generating a second heated working fluid
stream comprising a vapor portion.
Description
TECHNICAL FIELD
[0002] This invention relates to power generation systems in
general and more specifically to power generation systems utilizing
mixed working fluids.
BACKGROUND ART
[0003] Power generation systems or power plants are well-known in
the art and are widely used to generate electricity. Most such
power generation systems generate electricity from heat energy
derived from burning fossil fuels (e.g., coal or natural gas) and
are referred to herein as thermal power plants. In addition to
using heat energy derived from burning fossil fuels, thermal power
plants can also be used with a wide variety of other heat sources,
such as solar, geothermal, and nuclear sources.
[0004] Traditionally, thermal power plants have operated in
accordance with the well-known Rankine thermodynamic cycle. In the
Rankine cycle, a so-called "pure" working fluid, such as water, is
heated to produce vapor or steam. The steam is then expanded,
typically through a turbine, in order to convert heat energy
contained therein into mechanical work. In the case of an electric
power generation system, the turbine is operatively connected to an
electrical generator which produces the electricity. While power
plants operating in accordance with the Rankine cycle are
well-known and widely used, certain characteristics of the Rankine
cycle impose fundamental limitations on the thermodynamic
efficiency of the cycle. For example, a Rankine cycle operating
with a pure working fluid suffers some thermodynamic
irreversibilities due to the fact that the pure working fluid
vaporizes at substantially constant temperature. These
irreversibilities can be larger or smaller depending on the
temperature difference between the heating medium and working
fluid.
[0005] Partly in an effort to solve some of the limitations
associated with the use of a pure working fluid in the Rankine
cycle, other types of thermodynamic cycles (e.g., any of the
so-called Kalina cycles) have been developed which utilize mixed
working fluids. Briefly, a mixed component working fluid comprises
two or more vaporizable components which vaporize and condense
progressively over a temperature range rather than at the
relatively constant temperature of a so-called "pure" working fluid
(e.g., water). Accordingly, thermodynamic cycles utilizing mixed
working fluids can, if properly designed, realize increased
efficiencies over similar thermodynamic cycles (e.g., the Rankine
cycle) that utilize pure working fluids, such as water.
[0006] One design consideration for mixed working fluid systems
relates to the boiler or vapor generator that is used to vaporize
the mixed working fluid. That is, since the mixed working fluid
vaporizes over a temperature range, it is generally preferred to
design the vapor generator so that heating function of the mixed
working fluid closely follows the cooling function of the heating
medium. Closely matching the heating and cooling functions of the
working and heating fluids reduces the thermodynamic
irreversibilities during the heating cycle, thus increasing the
overall thermodynamic efficiency of the system. In accordance with
this consideration, thermodynamic cycles utilizing mixed fluids
often make use of countercurrent heat exchangers, in which the
heating medium and mixed working fluid flow in opposite directions.
In this manner, the heating function of the mixed working fluid can
be made to more closely follow the cooling function of the heating
medium.
[0007] While such countercurrent heat exchangers have been used in
mixed working fluid systems to achieve some performance and
efficiency gains, there is still room for improvement, particularly
in light of other requirements or limitations of the particular
type of power generation system in which the heat exchanger is to
be used. For example, a primary consideration of geothermal power
generation systems relates to the so-called "brine effectiveness,"
that is, the amount of useful work that can be extracted or derived
from a given brine flow rate. A desirable geothermal power
generation system will seek to maximize brine effectiveness.
DISCLOSURE OF INVENTION
[0008] A power generating system according to the present invention
may comprise a heat source and an incremental vapor generator
system operatively associated with the heat source. The incremental
vapor generator system includes a first heating section and a
second heating section. The first heating section receives a mixed
working fluid and generates a first heated working fluid stream
comprising a vapor portion and a liquid portion. The second heating
section is operatively associated with the first heating section
and receives the liquid portion from the first heated working fluid
stream. The second heating section generates a second heated
working fluid stream comprising a vapor portion. An energy
conversion device operatively associated with the incremental vapor
generator system converts into useful work heat energy contained in
the vapor portions of the first and second heated working fluid
streams.
[0009] Also disclosed is a method for generating power from a mixed
working fluid that comprises the steps of incrementally heating the
mixed working fluid to produce a first vapor stream and a second
vapor stream; and converting into useful work heat energy contained
in the first and second vapor streams.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Illustrative and presently preferred embodiments of the
invention are shown in the accompanying drawings in which:
[0011] FIG. 1 is a schematic diagram of a power generating system
according to the present invention utilizing parallel flow
incremental vapor generation;
[0012] FIG. 2 is an equilibrium/phase diagram of the mixed working
fluid at the various stations of the power generating system shown
in FIG. 1;
[0013] FIG. 3 is a graphical representation of the heating and
cooling functions of the mixed working fluid and the heating fluid
for the power generating system shown in FIG. 1;
[0014] FIG. 4 is a schematic diagram of a second embodiment of a
power generating system according to the present invention
utilizing serial flow incremental vapor generation;
[0015] FIG. 5 is an equilibrium/phase diagram of the mixed working
fluid at the various stations of the power generating system shown
in FIG. 4; and
[0016] FIG. 6 is a graphical representation of the heating and
cooling functions of the mixed working fluid and the heating fluid
for the power generating system of FIG. 4.
BEST MODES FOR CARRYING OUT THE INVENTION
[0017] A power generating system 110 according to one embodiment of
the present invention is shown in FIG. 1 and may comprise an
incremental vapor generator system 112 for vaporizing a mixed
working fluid 114. The incremental vapor generator system 112
incrementally vaporizes the mixed working fluid 114 with heat
energy extracted from a heat source, such as, for example,
geothermal brine 116. Alternatively, and as will be described in
greater detail below, the present invention may be utilized with
other types of heat sources and/or other types of heating
fluids.
[0018] In the embodiment shown in FIG. 1, the incremental vapor
generator system 112 comprises a parallel flow incremental vapor
generation system 118 in which the mixed working fluid 114 is
incrementally vaporized to form a first vapor portion 120 and a
second vapor portion 122. The first and second vapor portions 120
and 122 thereafter may be combined in a vapor mixer 124 before
being directed to an energy conversion system 126, which converts
energy contained in the first and second vapor portions 120 and 122
into useful work heat. In the embodiment shown in FIG. 1, energy
conversion system 126 comprises a turbine 128 and an electrical
generator 130. Accordingly, heat energy contained in the first and
second vapor portions 120, 122 is converted into electrical energy
by the energy conversion system 126. In an alternate embodiment
described below, the incremental vapor generator system may
comprise a series flow incremental vapor generation system 218
(FIG. 4) in which the mixed working fluid is incrementally
vaporized in a serial manner.
[0019] The parallel flow incremental vapor generating system 118
utilized in the first embodiment 110 of the power generating system
according to the present invention is shown in FIG. 1 and may
comprise a heat exchanger or vaporizer 132 having a primary loop
134 through which is caused to flow the heating fluid, e.g.,
geothermal brine 116. The heat exchanger or vaporizer 132 may also
comprise first and second heating sections 136 and 138 that are in
thermal communication with the primary loop 134 so that heat energy
contained in the heating fluid (e.g., brine 116) is transferred to
the mixed working fluid 114 flowing through the first and second
heating sections 136 and 138, respectively. The heat exchanger 132
may also be provided with a third heating section 140 suitable for
additionally heating the first and second vapor portions 120 and
122 in a manner that will be described in more detail below.
[0020] The first and second heating sections 136 and 138 are
operatively associated with respective first and second separator
systems 142 and 144. The first and second separator systems 142 and
144 separate liquid and vapor portions from the heated mixed
working fluid introduced therein by the first and second heating
sections 136 and 138, respectively. More specifically, a first
inlet 146 of the first separator 142 is connected to the outlet 148
of the first heating section 136, whereas a liquid outlet 150 of
the first separator 142 is connected to the inlet 152 of the second
heating section 138. A second inlet 154 of first separator 142 is
connected to a high temperature recuperator 156. A vapor outlet 158
of first separator 142 is connected to the vapor mixer 124.
[0021] The second separator 144 is provided with an inlet 160 that
is connected to the outlet 162 of the second heating section 138. A
liquid outlet 164 of second separator 144 is connected to the high
temperature recuperator 156, whereas a vapor outlet 166 is
connected to the vapor mixer 124.
[0022] The vapor mixer 124 is provided with a vapor outlet 168
which, in the embodiment shown and described herein, is connected
to the third heating section 140. The third heating section 140 is
used to further heat (e.g., superheat) the vaporized mixed working
fluid 114 exiting the mixer 124. The outlet 170 of the third
heating section 140 is connected to the energy conversion system
126. As mentioned above, the energy conversion system 126 may
comprise a turbine 128 and electrical generator 130. The exhaust
outlet 172 of turbine 128 is connected to a low temperature
recuperator 174. The low temperature recuperator 174 is in turn
connected to a condenser 176 via a mixer 178. The condenser 176 is
operatively connected to the heat exchanger 132 via a pump 180 and
the high and low temperature recuperators 156 and 174,
respectively.
[0023] The power generation system 110 may be operated as follows
to convert into useful work heat energy contained in the heating
fluid (e.g., geothermal brine 116). As was briefly described above,
the mixed working fluid 114 utilized herein vaporizes progressively
over an increasing temperature range. That is, the temperature of
the vapor and liquid comprising the heated mixed working fluid 114
increases with increasing quality. The point at which vaporization
begins (i.e., at 0% quality) is referred to herein as the "bubble
point," whereas the point at which vaporization is complete (i.e.,
at 100% quality) is referred to herein as the "dew point." By way
of example, the mixed working fluid 114 utilized in the preferred
embodiments shown and described herein comprises a mixture of
ammonia and water. Alternatively, other mixed working fluids could
be used as well.
[0024] Referring now to FIGS. 1 and 2 simultaneously, the mixed
working fluid feed stream 114 exits the condenser 176 at about the
bubble point for the mixture. This corresponds to station L.sub.0
in FIG. 1 and the corresponding point L.sub.0 in FIG. 2. Before
proceeding with the description, it should be noted that various
points in the system 110 that are of interest thermodynamically are
referred to herein as "stations" and are indicated in FIGS. 1 and 4
as encircled numbers or encircled letter-number combinations. Such
stations are indicated on the equilibrium/phase diagrams (e.g.,
FIGS. 2 and 5) as points having corresponding numbers or
letter-number combinations. Hence, station L.sub.0 is designated in
FIG. 1 as encircled legend "L.sub.0". The corresponding point in
the equilibrium/phase diagram illustrated in FIG. 2 is also
designated "L.sub.0".
[0025] Continuing now with the description, the pump 180 increases
the pressure of the mixed working fluid 114 to a point suitable for
use in the high pressure side of the power generation system 110.
The flow of the working fluid 114 is then split, with a first
stream 182 being directed through the high temperature recuperator
156 and a second stream 184 being directed to the low temperature
recuperator 174. The heating characteristics of the high
temperature recuperator 156 and the flow rate of the first stream
182 are selected so that the first stream 182 is heated to a point
above its bubble point at the particular pressure involved (e.g.,
about 425 pounds per square inch absolute (psia)). That is, the
first stream 182 is heated to a quality greater than zero. By way
of example, in one preferred embodiment, the first stream 182 is
heated to a quality in the range of about 10% to about 40% (30%
preferred). This quality corresponds to a vapor portion in the
range of about 80% to about 96% (90% preferred) on a volume basis.
The heated first stream 182 is then directed to the inlet 154 of
first separator system 142. This is identified as station 2.sub.1
in FIG. 1 and as point 2.sub.1 in FIG. 2.
[0026] The second stream 184 is heated by the low temperature
recuperator 174 and thereafter is directed to the first heating
section 136 of heat exchanger 132 where it is additionally heated
to a temperature that exceeds the bubble point. This corresponds to
station 2.sub.3 in FIG. 1 and to point 2.sub.3 in FIG. 2. It is
generally preferred that the heating characteristics of the low
temperature recuperator 174 and the first heating section 136, as
well as the flow rate of the second stream 184 be such that the
mixed working fluid 114 comprising the second stream 184 is heated
to about the same quality as the first stream 182. That is, it is
preferred that the points 2.sub.1 and 2.sub.3 on FIG. 2 be
approximately coincident. The heated second stream 148 from the
first heating section 136 is then directed to the first inlet 146
of the first separator 142.
[0027] The first separator system 142 receives the first and second
heated streams 182 and 184 and separates the two streams 182 and
184 into a liquid portion and a vapor portion. The liquid portion
exits the liquid outlet 150 of the separator 142 and is directed to
the inlet 152 of the second heating section 138. The vapor portion
exits the vapor outlet 158 of the first separator 142 as first
vapor stream 120. The first vapor stream 120 is at about the dew
point (i.e., 100% quality) for the particular concentration of the
mixed working fluid 114 comprising the vapor portion stream 120.
This corresponds to station v.sub.1 in FIG. 1 and to point v.sub.1
in FIG. 2.
[0028] Before proceeding with the description it should be noted
that the concentrations of the constituents (e.g., ammonia and
water) comprising the mixed working fluid 114 are different for the
liquid and vapor portions. For example, with reference now to FIG.
2, in one preferred embodiment wherein the mixed working fluid 114
comprises a mixture of ammonia and water, the first vapor portion
stream 120 (corresponding to point v.sub.1 in FIG. 2) of the mixed
working fluid 114 comprises a higher concentration of ammonia
(e.g., slightly greater than about 0.95 on a mass basis) than does
the liquid portion (point 3 in FIG. 2) of the mixed working fluid
114. The liquid portion of the mixed working fluid 114 at point 3
has an ammonia concentration that is slightly less than about 0.55
(on a mass basis). Consequently, any characteristics (e.g.,
quality) specifically recited herein for the mixed working fluid
114 at a particular station refer to the working fluid 114 in the
particular state (e.g., vapor or liquid) and at the corresponding
concentration at the referenced station. For example, at station
v.sub.1, the mixed working fluid 114 comprises a vapor having an
ammonia concentration that is slightly greater than about 0.95 and
is at about the dew point (i.e., a quality of about 100%) for the
mixture at that particular ammonia concentration. At station 3, the
mixed working fluid 114 comprises a liquid having an ammonia
concentration that is slightly less than about 0.55 and is at about
the bubble point (i.e., a quality of about 0%) for the mixture at
the lower ammonia concentration. The ammonia concentrations (i.e.,
mass fractions) for the ammonia/water mixed working fluid 114 that
may be utilized in the preferred embodiments of the present
invention are shown in FIGS. 2 and 4 for the corresponding liquid
and vapor portions of the mixed working fluid at the various
stations.
[0029] With the foregoing points in mind, the liquid portion of the
mixed working fluid 114 from the first separator 142 is at about
the bubble point of the liquid portion of mixed working fluid 114
at the corresponding ammonia concentration. That is, the liquid
portion is at about the bubble point for the lower ammonia
concentration of the liquid portion of the mixed working fluid 114.
This corresponds to station 3 in FIG. 1 and to point 3 in FIG. 2.
The liquid portion is directed into the inlet 152 of the second
heating section 138 whereupon it is heated to a temperature in
excess of the bubble point. It is generally preferred that the
liquid portion be heated in the second heating section 138 to about
the same quality as the mixed working fluid at stations 2.sub.1 and
2.sub.3. That is, the quality of the mixed working fluid stream
exiting the second heating section 138 should be about the same as
the qualities of the working fluid streams exiting the first
heating section 136 and the high temperature recuperator 156. For
example, in the embodiment shown and described herein, the mixed
working fluid stream exits the second heating section 138 at a
quality in the range of about 10% to about 40% (30% preferred),
which corresponds to a vapor portion in the range of about 80% to
about 96% (90% preferred) on a volume basis. This corresponds to
station 4 in FIG. 1 and to point 4 in FIG. 2.
[0030] The second separator system 144 receives the heated mixed
fluid from the second heating section 138 and separates the heated
mixed fluid into a liquid portion and a vapor portion. The liquid
portion exits the liquid outlet 164 of the separator 144 and is
directed to the high temperature recuperator 156 whereupon it
surrenders a portion of its heat to the first working stream 182.
The vapor portion from separator 144 exits the vapor outlet 166 as
the second vapor portion stream 122. The second vapor portion
stream 122 is at about the dew point (i.e., 100% quality) for the
higher ammonia concentration of the mixed working fluid 114 that
comprises the second vapor portion stream 122. See station v.sub.2
in FIG. 1 and point v.sub.2 in FIG. 2.
[0031] The vapor mixer 124 receives the first and second vapor
streams 120 and 122 and combines them into a combined vapor stream
186. The combined vapor stream 186 corresponds to station v.sub.3
in FIG. 1 and to point v.sub.3 in FIG. 2. The combined vapor stream
186 may be additionally heated (e.g., superheated) by the third
heating section 140 to a temperature greater than the dew point
temperature for the combined vapor stream 186. The superheated
stream 188 exiting the third heating section 140 corresponds to
station v.sub.4 in FIG. 1 and to point v.sub.4 in FIG. 2. The
stream 188 is then directed to the energy conversion system
126.
[0032] The energy conversion system 126 extracts heat energy from
the superheated stream 188, converting it into useful work. In the
embodiment shown and described herein, heat energy contained in the
first and second vapor streams 120 and 122 (which comprise combined
stream 186 and superheated stream 188) is converted into electrical
work by the turbine 128 and the electrical generator 130 comprising
the energy conversion system 126.
[0033] The exhaust stream 172 from the turbine 128 corresponds to
station v.sub.5 in FIG. 1 and to point v.sub.5 in FIG. 2 and is at
a temperature that is greater than the dew point temperature for
the mixed working fluid at the reduced pressure on the low pressure
side of the power generating system 110. By way of example, in the
embodiment shown and described herein, the mixed working fluid 114
is at a pressure of about 71 psia on the low pressure side.
Alternatively, the exhaust stream could exit the turbine 128 at a
temperature below the dew point of the mixed working fluid if the
turbine is capable of handling wet mixtures. The exhaust stream 172
from turbine 128 is thereafter directed to the low temperature
recuperator 174 wherein it surrenders a portion of its heat energy
to the second working fluid stream 184. The cooled exhaust stream
172 exits the low temperature recuperator 174 at station v.sub.6 at
a temperature between the bubble and dew points for the mixed
working fluid. By way of example, in one preferred embodiment, the
cooled exhaust stream 172 exits the low temperature recuperator 174
at a quality in the range of about 0% to about 100% (45%
preferred). See also point v.sub.6 in FIG. 2.
[0034] The mixed working fluid exiting the low temperature
recuperator 174 is then mixed with the liquid portion exiting the
high temperature recuperator 156 in the mixer 178. The combined
working fluid stream exits mixer 178 at station v.sub.7 which
corresponds to point v.sub.7 in FIG. 2. The combined working fluid
stream is then condensed to the bubble point (station L.sub.0 in
FIG. 1 and point L.sub.0 in FIG. 2) by the condenser 176. The
condensed stream is then returned to the high pressure side of the
system by pump 180 and the cycle is repeated.
[0035] A significant advantage of the power generating system 110
according to the present invention is that it results in closely
matched heating and cooling curves for the working and heating
fluids, respectively. For example, with reference now to FIG. 3 the
heating curve or function 190 of the mixed working fluid closely
follows the cooling curve or function 192 of the heating fluid
(e.g., brine 116). The closely matched heating and cooling
functions 190 and 192, improves thermodynamic efficiency by
reducing the irreversibilities occurring in the heat exchanger 132.
The closely matched heating and cooling functions also allow the
brine 116 to be cooled to a lower temperature, closer to the bubble
point of the working fluid, than is possible with prior systems.
Consequently, the power generating system 110 of the present
invention substantially reduces the heating fluid (e.g., brine 116)
flow rate required for a given amount of useful work. Accordingly,
the power generating system 110 can be used with considerable
advantage in geothermal power generation systems wherein it is
desired to minimize the brine flow rate per kilowatt of electricity
produced.
[0036] Having briefly described one embodiment of the power
generating system 110, as well as some of its more significant
features and advantages, the various embodiments of the power
generating system according to the present invention will now be
described in detail. However, before proceeding with the
description, it should be noted that while the various embodiments
of the power generating system are shown and described herein as
they could be used in a geothermal electrical generating system
utilizing hot brine 116 as the heating fluid, the present invention
is not limited to use in geothermal electrical generating systems.
In fact, power generating systems according to the present
invention could be used with any of a wide variety of heating
fluids and working fluids that are now known in the art or that may
be developed in the future, as would be obvious to persons having
ordinary skill in the art after having become familiar with the
teachings of the present invention. Consequently, the present
invention should not be regarded as limited to the particular
applications and/or heating and working fluids shown and described
herein.
[0037] With the foregoing considerations in mind, one embodiment of
a power generating system 110 according to the present invention
comprises an incremental vapor generator system 112 for vaporizing
a mixed working fluid 114 utilizing heat obtained from a suitable
heat source. By way of example, in the embodiments shown and
described herein, the heat source may comprise geothermal brine
116. The geothermal brine 116 comprises the heat source or heating
fluid and is used to vaporize the working fluid 114 in the
incremental vapor generator system 112.
[0038] The working fluid 114 used in the power generation system
110 may comprise any of a wide range of mixed, non-azeotropic
fluids now known in the art or that may be developed in the future
suitable for use in the particular application. As used herein, the
term "mixed fluid" refers to any fluid wherein the temperature of
the vapor and liquid components increases with increasing quality.
By way of example, in the embodiment shown and described herein,
the mixed working fluid comprises a mixture of ammonia and
water.
[0039] As was briefly mentioned above, in one embodiment of the
invention the incremental vapor generator system 112 comprises a
parallel flow incremental vapor generation system 118. In the
parallel flow incremental vapor generation system 118, the mixed
working. fluid 114 is incrementally vaporized to form a first vapor
portion 120 and a second vapor portion 122. The first and second
vapor portions 120 and 122 are combined (i.e., in a parallel
manner) before being directed to the energy conversion system 126,
hence the designation parallel flow incremental vapor generation
system 118.
[0040] With reference now primarily to FIG. 1, the parallel flow
incremental vapor generating system 118 utilized in one embodiment
of the power generating system 110 according to the present
invention comprises a heat exchanger or vaporizer 132 having a
primary loop 134 through which is caused to flow the heating fluid.
As mentioned above, in the embodiment shown and described herein,
the heating fluid comprises geothermal brine 116. Alternatively,
other types of heating fluids may be used, as would be obvious to
persons having ordinary skill in the art after having become
familiar with the teachings of the present invention.
[0041] The heat exchanger or vaporizer 132 may also comprise first
and second heating sections 136 and 138 arranged so that they are
in thermal communication with the primary loop 134. Accordingly,
heat energy contained in the brine 116 is transferred to the mixed
working fluid 114 flowing in the first and second heating sections
136 and 138, respectively. The heat exchanger 132 may also be
provided with a third heating section 140 suitable for additionally
heating the first and second vapor portions 120 and 122. For
example, in the embodiment shown and described herein, the third
heating section 140 is used to heat the first and second vapor
portions 120 and 122 above the dew point, a process that is
commonly known as "superheating."
[0042] It is generally preferred that the heat exchanger 132
comprise a counter-current heat exchanger in which the inlet end of
the primary loop 134 is thermally adjacent the "hottest" heating
section (e.g., the third heating section 140) and in which the
outlet end is thermally adjacent the "coolest" heating section
(e.g, the first heating section 136). Such an arrangement makes it
easier to more closely match the heating function 190 of the
working fluid 114 with the cooling function 192 of the heating
fluid (e.g., brine 116). See FIG. 3.
[0043] The exact number of heating sections (e.g., heating sections
136, 138, and 140) comprising the heat exchanger 132 may vary
depending on the particular application, the particular heating and
working fluids used, as well as on the number of stages (e.g.,
vapor separators) used to achieve the incremental heating of the
working fluid in the manner shown and described herein. That is,
the number of heating sections comprising the heat exchanger in any
given application could be readily determined by persons having
ordinary skill in the art after having become familiar with the
teachings of the present invention and by applying the teachings to
the particular application. Consequently, the present invention
should not be regarded as limited to a heat exchanger having any
particular number of heating sections.
[0044] The heat exchanger 132 may be constructed from any of a wide
range of materials and in accordance with any of a wide range of
techniques that are now known in the art or that may be developed
in the future that would be suitable for the particular
application. However, since heat exchangers of the type described
herein could be readily fabricated by persons having ordinary skill
in the art after having become familiar with the teachings of the
present invention, and since the details of such heat exchangers
are not necessary to understand or practice the present invention,
the heat exchangers used in the embodiments shown and described
herein will not be described in further detail herein.
[0045] The first and second heating sections 136 and 138 of the
heat exchanger 132 are operatively associated with first and second
separator systems 142 and 144. As will be described in greater
detail below, the first and second separator systems 142 and 144
separate liquid and vapor portions (not shown) from the heated
mixed working fluid introduced therein by the first and second
heating sections 136 and 138, respectively.
[0046] The first separator system 142 comprises a first inlet 146,
a second inlet 154, a liquid outlet 150, and a vapor outlet 158.
The first inlet 146 is connected to the outlet 148 of the first
heating section 136 so that heated mixed working fluid from the
first heating section 136 enters the separator system 142. The
second inlet 154 of the first separator system 142 is connected to
the high temperature recuperator 156 so that the first mixed
working fluid stream 182 from the high temperature recuperator 156
is also directed into the separator system 142. The liquid outlet
150 of the first separator system 142 is connected to the inlet 152
of the second heating section 138 of heat exchanger 132. The vapor
outlet 158 of the first separator system 142 is connected to the
vapor mixer 124.
[0047] The first separator system 142 may comprise any of a wide
range of separator systems that are well-known in the art that
would be suitable for separating vapor and liquid portions from an
incoming wet mixture stream (e.g., the heated working fluid 114).
Consequently, the present invention should not be regarded as
limited to any particular type of separator system.
[0048] The second separator system 144 may be similar to the first
separator system 142, except that the second separator system 144
is provided with but a single inlet 160 connected to the outlet 162
of the second heating section 138. The arrangement is such that the
second separator system 144 receives the heated mixed working fluid
114 from the second heating section 138 of heat exchanger 132. A
liquid outlet 164 of the second separator 144 is connected to the
high temperature recuperator 156, whereas a vapor outlet 166 is
connected to the vapor mixer 124.
[0049] The high temperature recuperator 156 connected to the liquid
outlet 164 of second separator system 144 is used to recover heat
contained in the liquid portion separated by the second separator
144. The recovered heat is used to pre-heat the first mixed working
fluid stream 182. In the embodiment shown and described herein, the
liquid outlet 164 of the second separator 144 is connected to a
heating loop 155 of the high temperature recuperator 156, whereas a
heated loop 157 of high temperature recuperator 156 is connected
between the pump 180 and the second inlet 154 of first separator
system 142. The separated liquid portion in the heating loop
surrenders heat to the first mixed working fluid stream 182 in the
heated loop 157, thereby pre-heating the first mixed working fluid
stream 182. Thereafter, the separated liquid portion passes through
an expansion valve 194 before entering the low pressure side of the
system 110.
[0050] The vapor mixer 124 is connected to the vapor outlets 158
and 166 of the respective first and second separator systems 142
and 144 and receives the corresponding first and second vapor
portions 120 and 122. A vapor outlet 168 on the mixer 124 is
connected to the third heating section 140. The outlet 170 of the
third heating section 140 is connected to the energy conversion
system 126.
[0051] The vapor mixer 124 may comprise any of a wide range of
devices known in the art or that may be developed in the future
that would be suitable for mixing together the first and second
vapor portions 120 and 122. Consequently, the present invention
should not be regarded as limited to any particular type of vapor
mixer system.
[0052] The energy conversion system 126 may comprise any of a wide
range of systems and devices suitable for converting into useful
work heat energy contained in the heated mixed working fluid 114
exiting the parallel flow vapor generator 118 (or third heating
section 140, if a third heating section is used). By way of
example, in the embodiments shown and described herein, the energy
conversion system 126 comprises a turbine 128 and an electric
generator 130 connected thereto. The turbine 128 and electric
generator 130 may comprise any of a wide range of systems and
devices that are well-known in the art and readily commercially
available. Consequently, the turbine 128 and electric generator 130
utilized in one preferred embodiment of the invention will not be
described in greater detail herein.
[0053] The exhaust outlet 172 of turbine 128 is connected to a low
temperature recuperator 174. The low temperature recuperator 174
recovers heat contained in the turbine exhaust stream and uses it
to pre-heat the second mixed working fluid stream 184. More
specifically, the exhaust outlet 172 of turbine 128 is connected to
a heating loop 173 of the low temperature recuperator 174, whereas
a heated loop 175 of the low temperature recuperator 174 is
connected between the pump 180 and the first heating section 136 of
the heat exchanger 132. The turbine exhaust stream in the heating
loop 173 surrenders heat to the second mixed working fluid stream
184 in the heated loop 175, thereby pre-heating the second mixed
working fluid stream 184 before the same enters the first heating
section 136. Thereafter, the exhaust stream is combined in the
mixer 178 with the separated liquid portion exiting the expansion
valve 194. A condenser 176 connected to the mixer 178 receives the
combined cooled mixed working fluid 114, condenses it, and returns
it to pump 180.
[0054] The condenser 176 may comprise any of a wide range of
condensers that are well-known in the art or that may be developed
in the future that would be suitable for condensing the combined
cooled mixed working fluid 114 from the mixer 178. By way of
example, in the embodiment shown and described herein, the
condenser 176 comprises an air-cooled condenser in which air 196 is
used to condense the mixed working fluid 114 flowing in the
condenser 176. Alternatively, other cooling media besides air may
be used to condense the mixed working fluid 114.
[0055] The power generation system 110 may be operated as follows
to convert into useful work heat energy derived from the heating
fluid. Consider, for example, a geothermal power generation system
which generates electricity from geothermal brine 116 extracted
from the earth. The geothermal brine 116 serves as the heating
fluid and, in the example described herein, enters the primary loop
134 of the heat exchanger 132 at a temperature of about 335.degree.
F., although other temperatures are possible. The mixed working
fluid 114 may comprise a mixture of ammonia and water and is
maintained at a pressure of about 425 pounds per square inch
absolute (psia) on the high pressure side of the power generating
system 110. The low pressure side of the power generating system
110 is maintained at a pressure of about 71 psia. Alternatively,
other mixed fluids may be used at other pressures, as would be
obvious to persons having ordinary skill in the art after having
become familiar with the teachings of the present invention. The
ammonia/water mixture that comprises the mixed working fluid 114
vaporizes progressively over an increasing temperature range. That
is, the temperature of the vapor and liquid comprising the heated
mixed working fluid increases with increasing quality.
[0056] Referring now to FIGS. 1-3, the mixed working fluid feed
stream 114 exits the condenser 176 at station L.sub.0 at about the
bubble point for the mixture 114. This station corresponds to point
L.sub.0 in FIG. 2. The pump 180 increases the pressure of the mixed
working fluid 114 to a pressure suitable for use in the high
pressure side of the power generating system 110. In the embodiment
shown and described herein, the high pressure side of the system
110 is maintained at a pressure of about 425 psia. Therefore, the
pump 180 increases the pressure of the mixed working fluid 114 to a
pressure of about 425 psia. The mixed working fluid stream 114
exiting the pump 180 is then split into a first working fluid
stream 182 and a second working fluid stream 184. The first working
fluid stream 182 is directed through the heated loop 157 of the
high temperature recuperator 156 whereupon it is heated by the
liquid portion from the second separator 144 passing through the
heating loop 155. The heating characteristics of the high
temperature recuperator 156 and the flow rate of the first stream
182 are such that the first stream 182 is heated to a temperature
in excess of its bubble point. This corresponds to station 2.sub.1
in FIG. 1 and to point 2.sub.1 in FIG. 2.
[0057] By way of example, in the embodiment shown and described
herein, the first stream 182 is heated to a quality in the range of
about 10% to about 40% (30% preferred). This quality range
corresponds to a vapor portion range of about 80% to about 96% (90%
preferred) on a volume basis. So heating the first working fluid
stream 182 to a vapor portion in the range specified herein
provides for good heat transfer characteristics in the high
temperature recuperator 156. That is, some loss of efficiency in
the high temperature recuperator 156 will occur if the first
working fluid stream 182 is heated to a vapor portion that is
substantially greater than the vapor portion range specified
herein. After being heated in the high temperature recuperator 156,
the heated first working fluid stream 182 is directed to the inlet
154 of the first separator system 142.
[0058] The second working fluid stream 184 is directed to the
heated loop 175 of the low temperature recuperator 174 whereupon it
is pre-heated by the exhaust stream 172 exiting the turbine 128.
Thereafter, the pre-heated second working fluid stream 184 is
directed to the first heating section 136 of heat exchanger 132
which heats the second working fluid stream 184 to a temperature in
excess of the bubble point. This corresponds to station 2.sub.3 in
FIG. 1 and to point 2.sub.3 in FIG. 2. It is generally preferred
that the flow rate of the second stream 184 be matched to the
heating characteristics of the low temperature recuperator 174 and
the first heating section 136 so that the mixed working fluid 114
comprising the second working fluid stream 184 is heated to about
the same quality as the first stream 182. That is, it is preferred
that the points 2.sub.1 and 2.sub.3 in FIG. 2 be approximately
coincident. Stated another way, the second working fluid stream 184
is heated to a quality in the range of about 10% to about 40% (30%
preferred), which corresponds to a vapor portion in the range of
about 80% to about 96% (90% preferred).
[0059] In the embodiment shown and described herein, the mass ratio
of the first working fluid stream 182 to the second working fluid
stream 184 is about 1:4. That is, most of the working fluid 114 is
directed to the second stream 184, with only a small amount (i.e.,
1/4 on a mass basis) being directed through the high temperature
recuperator 156 as first working fluid stream 182. Of course, the
mixed working fluid stream 114 may be divided in accordance with
other mass ratios depending on the characteristics of the
particular system.
[0060] Referring back now primarily to FIG. 1, the first separator
system 142 receives the first and second heated streams 182 and 184
and separates the two streams 182 and 184 into a liquid portion and
a vapor portion. The liquid portion exits the liquid outlet 150 of
the first separator 142 and is directed to the inlet 152 of the
second heating section 138. The vapor portion exits the vapor
outlet 158 of the first separator 142 as a first vapor portion
stream 120. The first vapor portion stream is at about the dew
point (i.e., 100% quality) for the mixed working fluid 114. This
corresponds to station v.sub.1 in FIG. 1 and to point v.sub.1 in
FIG. 2.
[0061] The liquid portion from the first separator 142 is at about
the bubble point of the mixed working fluid 114. See station 3 in
FIG. 1 and point 3 in FIG. 2. The liquid portion is directed into
the inlet 152 of the second heating section 138 whereupon it is
heated to a temperature in excess of the bubble point. It is
generally preferred that the liquid portion be heated to about the
same quality as the mixed working fluid at stations 2.sub.1 and
2.sub.3. That is, the quality of the mixed working fluid stream
exiting the second heating section 138 should be about the same as
the qualities of the working fluid streams exiting the first
heating section 136 and the high temperature recuperator 156. For
example, in the embodiment shown and described herein, the mixed
working fluid stream exits the second heating section 138 at a
quality in the range of about 10% to about 40% (30% preferred).
This corresponds to a vapor portion in the range of about 80% to
about 96% (90% preferred). See station 4 in FIG. 1 and point 4 in
FIG. 2. As discussed above, heating the mixed working fluid to the
quality ranges specified herein provides a good balance between
temperature rise and heat transfer efficiency in the second heating
section 138.
[0062] The second separator system 144 receives the heated mixed
fluid from the second heating section 138 and separates the heated
mixed fluid into a liquid portion and a vapor portion. The liquid
portion exits the liquid outlet 164 of the separator 144 and is
directed to the high temperature recuperator 156 whereupon it
surrenders a portion of its heat to the first working fluid stream
182. Thereafter, the cooled liquid portion is expanded through the
expansion valve 194 to the low pressure side of the power
generating system 110. See station 5.sub.2 in FIG. 1 and point
5.sub.2 in FIG. 2. The cooled, expanded liquid portion is then
combined with the turbine exhaust stream in mixer 178.
[0063] The vapor portion from the second separator 144 exits the
vapor outlet 166 of separator 144 as the second vapor portion
stream 122. The second vapor portion stream 122 is at about the dew
point (i.e., 100% quality) and corresponds to station v.sub.2 in
FIG. 1 and to point v.sub.2 in FIG. 2.
[0064] The vapor mixer 124 receives the first and second vapor
streams 120 and 122 and combines them into a combined vapor stream
186. The combined vapor stream 186 corresponds to station v.sub.3
in FIG. 1 and to point v.sub.3 in FIG. 2. If desired, the combined
vapor stream 186 may be additionally heated by the third heating
section 140 to a temperature greater than the dew point temperature
for the combined vapor stream 186. That is, the combined vapor
stream 186 may be superheated in the third heating section 140. The
superheated stream 188 exiting the third heating section 140 is
designated as station v.sub.4 in FIG. 1 and corresponds to point
v.sub.4 in FIG. 2. The stream 188 is then directed to the energy
conversion system 126.
[0065] The energy conversion system 126 extracts heat energy from
the superheated stream 188, converting it into useful work. In the
embodiment shown and described herein, heat energy contained in the
first and second vapor streams 120 and 122 (which comprise combined
stream 186 and superheated stream 188) is converted into electrical
work by the turbine 128 and the electrical generator 130 comprising
the energy conversion system 126.
[0066] The superheated stream 188 is expanded in the turbine 128
and exits the turbine 128 as exhaust stream 172. See station
v.sub.5 in FIG. 1 and point v.sub.5 in FIG. 2. It is generally
preferred that the expansion process be terminated before the mixed
working fluid 114 is cooled below the dew point temperature. By way
of example, in the embodiment shown and described herein, the mixed
working fluid 114 is expanded to a pressure of about 71 psia and to
a temperature of about 150.degree. F., which is below the dew
point. That is, the mixed working fluid 114 is cooled to a
temperature below the dew point temperature since, in the
embodiment shown and described herein, the energy conversion device
126 functions effectively with wet mixtures. The exhaust stream 172
is thereafter directed to the low temperature recuperator 174
wherein it surrenders a portion of its heat energy to the second
working fluid stream 184 flowing in the heated loop 175 of low
temperature recuperator 174. The cooled exhaust stream 172 exits
the low temperature recuperator 174 at station v.sub.6 at a
temperature between the bubble and dew points for the mixed working
fluid. See point v.sub.6 in FIG. 2. By way of example, in the
embodiment shown and described herein, the cooled exhaust stream
172 exits the low temperature recuperator 174 at a quality in the
range of about 0% to about 100% (45% preferred).
[0067] The mixed working fluid exiting the low temperature
recuperator 174 is then mixed in mixer 178 with the liquid portion
flowing through the expansion valve 194. The combined working fluid
stream that exits mixer 178 is designated as station v.sub.7 and
corresponds to point v.sub.7 in FIG. 2. The combined working fluid
stream is then condensed by the condenser 176 to about the bubble
point, (i.e., at station L.sub.0 in FIG. 1 and point L.sub.0 in
FIG. 2). The condensed stream is then returned to the high pressure
side of the system by pump 180 and the cycle is repeated.
[0068] The power generating system 110 just described results in
the closely matched heating and cooling functions 190 and 192 shown
in FIG. 3. That is, the heating curve 190 of the mixed working
fluid 114 closely follows the cooling curve 192 of the heating
fluid (e.g., geothermal brine 116).
[0069] As mentioned above, the first embodiment 110 of the power
generating system according to the present invention utilizes a
parallel flow vapor generator system 118 in which the working fluid
is incrementally vaporized to produce first and second vapor
portion streams 120 and 122 which are then combined in a parallel
manner (e.g., by mixer 124) before being superheated (if desired)
and directed to the energy conversion system 126. However, other
incremental vaporization arrangements are possible in accordance
with the teachings of the present invention.
[0070] With reference now to FIGS. 4-6, a second embodiment 210 of
a power generating system according to the present invention
embodies an incremental vapor generator system 212 that comprises a
series flow vapor generator system 218. Briefly, in the series flow
vapor generator system 218, the mixed working fluid 214 is
incrementally vaporized to form a first vapor portion 220 and a
second vapor portion 222. The first vapor portion 220 is then used
to condense or separate a liquid portion from a heated mixed
working fluid stream 221 from which is derived the second vapor
portion 222. Since, in the case of the mixed working fluid 214, the
liquid is "lean" and the first vapor portion 220 is "rich," the
first vapor portion 220 condenses on the lean liquid. The heat of
condensation causes additional vapor to be produced. Accordingly,
the series flow vapor generator system 218 produces the vapor
streams 220 and 222 in a serial manner.
[0071] With reference now primarily to FIG. 4, the serial flow
incremental vapor generating system 218 utilized in the second
embodiment 210 of the power generating system according to the
present invention comprises a heat exchanger or vaporizer 232
having a primary loop 234 through which is caused to flow the
heating fluid. In the embodiment shown and described herein, the
heating fluid comprises geothermal brine 216, although other types
of heating fluids may be used, as would be obvious to persons
having ordinary skill in the art after having become familiar with
the teachings of the present invention. The heat exchanger or
vaporizer 232 may also comprise first and second heating sections
236 and 238 arranged so that they are in thermal communication with
the primary loop 234 so that heat energy contained in the brine 216
is transferred to the mixed working fluid 214 flowing in the first
and second heating sections 236 and 238, respectively. The heat
exchanger 232 may also be provided with a third heating section 240
suitable for additionally heating the combined first and second
vapor portions 220 and 222. For example, and as was the case for
the first embodiment 110, the third heating section 240 of the
second embodiment 210 is used to heat the first and second vapor
portions 220 and 222 above the dew point.
[0072] It is generally preferred that the heat exchanger 232 be of
the counter-current type in which the inlet end of the primary loop
234 is thermally adjacent the "hottest" heating section (e.g., the
third heating section 240) and the outlet end is thermally adjacent
the "coolest" heating section (e.g, the first heating section 236).
Such an arrangement allows the system 210 to more closely match the
heating function 290 of the working fluid 214 with the cooling
function 292 of the heating fluid (e.g., brine 216). See FIG.
6.
[0073] The exact number of heating sections (e.g., heating sections
236, 238, and 240) comprising the heat exchanger 232 may vary
depending on the particular application, the particular heating and
working fluids used, as well as the number of stages used to
achieve the incremental heating of the working fluid 214 in the
serial manner described herein. The number of heating sections
comprising the heat exchanger in any given application could be
readily determined by persons having ordinary skill in the art
after having become familiar with the teachings of the present
invention and by applying the teachings to the particular
application. Consequently, the present invention should not be
regarded as limited to a heat exchanger having any particular
number of heating sections.
[0074] The heat exchanger 232 may be constructed from any of a wide
range of materials and in accordance with any of a wide range of
techniques that are now known in the art or that may be developed
in the future that would be suitable for the particular
application. However, since heat exchangers of the type described
herein could be readily fabricated by persons having ordinary skill
in the art after having become familiar with the teachings of the
present invention, and since the details of such heat exchangers
are not necessary to understand or practice the present invention,
the heat exchangers used in the embodiments shown and described
herein will not be described in further detail herein.
[0075] The first and second heating sections 236 and 238 of the
heat exchanger 232 are operatively associated with an integral
separator system 241 comprising a first separator section 242 and a
second separator section 244. As will be described in greater
detail below, the first and second separator sections 242 and 244
comprising the integral separator system 241 separate liquid and
vapor portions (not shown) from respective first and second heated
mixed working fluid streams 219 and 221.
[0076] The first separator section 242 of integral separator system
241 is provided with an inlet 246 that is connected to the high
temperature recuperator 256 and the first heating section 236 in
the manner best seen in FIG. 4. The arrangement is such that the
first separator section 242 receives the first heated working fluid
stream 219. The liquid outlet 250 of the first separator section
242 is connected to an inlet 252 of the second heating section
238.
[0077] The second separator section 244 of integral separator
system 241 is provided with an inlet 260 connected to the outlet
262 of second heating section 238 so that the second separator
section 244 receives the second heated working fluid stream 221
from the second heating section 238. The second separator section
244 is also provided with a collector 264 for collecting additional
amounts of separated liquid. The collector 264 is connected to a
heating loop 255 of the high temperature recuperator 256. A vapor
outlet 266 provided in the second separator section 244 is
connected to the third heating section 240. The outlet 270 of the
third heating section 240 is connected to the energy conversion
system 226.
[0078] The high temperature recuperator 256 is connected to the
collector 264 of the second separator section 244 of integral
separator 241. The high temperature recuperator 256 recovers heat
contained in the liquid portion separated by the second separator
section 244 of the integral separator 241. The recovered heat is
used to heat the pre-heated second working fluid stream 282. In the
embodiment shown and described herein, the collector 264 is
connected to the heating loop 255 of the high temperature
recuperator 256, whereas a heated loop 257 of high temperature
recuperator 256 is connected in parallel with the first heating
section 236 of the heat exchanger 232. The heating loop 255 is
connected to an expansion valve 294 which returns the cooled liquid
portion to the low pressure side of the power generating system
210.
[0079] As was the case for the first embodiment 110 (FIG. 1) of the
power generating system, the energy conversion system 226 of the
second embodiment 210 of the power generating system may comprise
any of a wide range of systems and devices suitable for converting
into useful work heat energy contained in the heated mixed working
fluid 214 exiting the series flow vapor generator 218 (or third
heating section 240, if a third heating section is used). By way of
example, the energy conversion system 226 comprises a turbine 228
and an electric generator 230 connected thereto. The turbine 228
and electric generator 230 may comprise any of a wide range of
systems and devices that are well-known in the art and readily
commercially available. Consequently, the turbine 228 and electric
generator 230 utilized in one preferred embodiment of the invention
will not be described in greater detail herein.
[0080] The exhaust outlet 272 of turbine 228 is connected to a low
temperature recuperator 274. The low temperature recuperator 274
recovers heat contained in the turbine exhaust stream and uses it
to pre-heat the mixed working fluid stream 214. More specifically,
the exhaust outlet 272 of turbine 228 is connected to a heating
loop 273 of the low temperature recuperator 274, whereas a heated
loop 275 of the low temperature recuperator 274 is connected
between the pump 280 and the parallel arrangement of the heating
loop 257 of the high temperature recuperator 256 and the first
heating section 236 of heat exchanger 232. The turbine exhaust
stream in the heating loop 273 surrenders heat to the mixed working
fluid stream 214 in the heated loop 275, thereby pre-heating the
mixed working fluid stream 214 before the same enters the high
temperature recuperator 256 and the first heating section 236.
Thereafter, the exhaust stream is combined with the separated
liquid portion exiting the expansion valve 294. A condenser 276
connected to the low temperature recuperator 274 and expansion
valve 294 receives the combined cooled mixed working fluid 214,
condenses it, and returns it to pump 280.
[0081] The condenser 276 may comprise any of a wide range of
condensers that are well-known in the art or that may be developed
in the future that would be suitable for condensing the combined
cooled mixed working fluid 214. By way of example, in the
embodiment shown and described herein, the condenser 276 comprises
an air-cooled condenser in which air 296 is used to condense the
mixed working fluid 214 flowing in the condenser 276.
[0082] The second embodiment 210 of the power generation system of
the present invention may be operated as follows to convert into
useful work heat energy derived from the heating fluid, i.e.,
geothermal brine 216 extracted from the earth. As was the case for
the first embodiment, the geothermal brine 216 may enter the
primary loop 234 of the heat exchanger 232 at a temperature of
about 335.degree. F., although other temperatures are possible. The
mixed working fluid 214 may comprise a mixture of ammonia and water
and is maintained at a pressure of about 250 psia on the high
pressure side of the power generating system 210. The low pressure
side is maintained at a pressure of about 43 psia. Alternatively,
other mixed working fluids may be used at other pressures, as would
be obvious to persons having ordinary skill in the art after having
become familiar with the teachings of the present invention.
[0083] With reference now to FIGS. 4-6, the mixed working fluid
stream 214 exits the condenser 276 at station L.sub.0 about the
bubble point for the mixture 214. This station corresponds to point
L.sub.0 in FIG. 5. The pump 280 increases the pressure of the mixed
working fluid 214 to a pressure suitable for use in the high
pressure side of the power generating system 210. In the embodiment
shown and described herein, the high pressure side of the system
210 is maintained at a pressure of about 250 psia. Therefore, the
pump 280 increases the pressure of the mixed working fluid 214 to a
pressure of about 250 psia. The mixed working fluid stream 214
exiting the pump 280 is then directed to the heated loop 275 of the
low temperature recuperator 274 which pre-heats the mixed working
fluid 214. See station 2 of FIG. 4 and corresponding point 2 in
FIG. 5. The pre-heated mixed working fluid stream 214 is then split
or divided into a first stream 282 and a second stream 284. The
first stream 282 is directed through the heated loop 257 of the
high temperature recuperator 256 whereupon it is heated by the
liquid portion extracted from the second separator section 244 by
the collector 264. The heating characteristics of the high
temperature recuperator 256 and the flow rate of the first stream
282 are such that the first stream 282 is heated to a temperature
in excess of its bubble point. This corresponds to station 3.sub.2
in FIG. 4 and to point 3.sub.2 in FIG. 5.
[0084] In the embodiment shown and described herein, the first
stream 282 is heated to a quality in the range of about 10% to
about 40% (30% preferred). This quality range corresponds to a
vapor portion range of about 80% to about 96% (90% preferred) on a
volume basis. So heating the first working fluid stream 282 to a
vapor portion in the specified range provides for good heat
transfer characteristics in the high temperature recuperator 256.
That is, some loss of efficiency in the high temperature
recuperator 256 will be experienced if the first working fluid
stream 282 is heated to a vapor portion that is substantially
greater than the vapor portion range described herein. After being
heated in the high temperature recuperator 256, the heated first
working fluid stream 282 mixed with the heated working fluid stream
284 exiting the first heating section 236 and directed into the
inlet 246 of first separator section 242 as first heated working
fluid stream 219. See station 3 in FIG. 4 and corresponding point 3
in FIG. 5.
[0085] The second stream 284 is directed to the first heating
section 236 of the heat exchanger 232 which heats the second
working fluid stream 284 to a temperature in excess of the bubble
point. This corresponds to station 3.sub.1 in FIG. 4 and to point
3.sub.1 in FIG. 5. It is generally preferred that the flow rate of
the second stream 284 be matched to the heating characteristics of
the first heating section 236 so that the mixed working fluid 214
comprising the second working fluid stream 284 is heated to about
the same quality as the first stream 282. That is, it is preferred
that the points 3.sub.1 and 3.sub.2 in FIG. 5 be approximately
coincident. Stated another way, the second working fluid stream 284
is heated to a quality in the range of about 10% to about 40% (30%
preferred), which corresponds to a vapor portion in the range of
about 80% to about 98% (90% preferred).
[0086] In the embodiment shown and described herein, the mass ratio
of the first working fluid stream 282 to the second working fluid
stream 284 is about 1:4. That is, most of the working fluid 214 is
directed to the second stream 284, with only a small amount (i.e.,
1/4 on a mass basis) being directed through the high temperature
recuperator 256 as first working fluid stream 282. Of course, the
mixed working fluid 214 may be divided in accordance with other
mass ratios depending on the characteristics of the particular
system.
[0087] Still referring primarily to FIG. 4, the first separator
section 242 in integral separator system 241 receives the first and
second heated streams 282 and 284 as combined first heated working
fluid stream 219 and separates the stream 219 into a liquid portion
and a vapor portion 220. The liquid portion exits the liquid outlet
250 of the first separator section 242 and is directed to the inlet
252 of the second heating section 238. The vapor portion 220 is at
about the dew point (i.e., 100% quality) for the mixed working
fluid 214. This corresponds to station v.sub.1 in FIG. 4 and to
point v.sub.1 in FIG. 5.
[0088] The liquid portion from the first separator 242 is at about
the bubble point of the mixed working fluid 214. See station 4 in
FIG. 4 and point 4 in FIG. 5. The liquid portion is directed into
the inlet 252 of the second heating section 238 whereupon it is
heated to a temperature in excess of the bubble point. This
corresponds to station 5 in FIG. 4 and to point 5 in FIG. 5. It is
generally preferred that the liquid portion be heated to about the
same quality as the mixed working fluid at stations 3.sub.1 and
3.sub.2. That is, the quality of the mixed working fluid stream
exiting the second heating section 238 should be about the same as
the qualities of the working fluid streams exiting the first
heating section 236 and the high temperature recuperator 256. For
example, in the embodiment shown and described herein, the mixed
working fluid stream exits the second heating section 238 at a
quality in the range of about 10% to about 40% (30% preferred).
This corresponds to a vapor portion in the range of about 80% to
about 98% (90% preferred). As discussed above, heating the mixed
working fluid to the quality ranges specified herein provides a
good balance between temperature rise and heat transfer efficiency
in the second heating section 238.
[0089] The second separator section 244 of integral separator
system 241 receives the heated mixed fluid from the second heating
section 238 as second heated mixed working fluid stream 221. The
second separator section 244 separates the second heated working
fluid stream 221 into a liquid portion (not shown) and a vapor
portion 222. As mentioned earlier, the first vapor portion 220 from
the first separator section 242 is used to further separate the
vapor portion from the heated mixed working fluid stream 221.
Since, the liquid portion to be separated from the second heated
mixed working fluid stream is "lean" (e.g., lower ammonia
concentration) and since the first vapor portion 220 is "rich"
(e.g., higher ammonia concentration), portions of the first vapor
portion 220 will condense on the lean liquid portion in the second
separator section 244. The heat of condensation causes additional
amounts of vapor portion 222 to be produced.
[0090] The liquid portion drained from separator 244 is collected
by the collector 264 and exits the integral separator system 241.
This corresponds to station 6 in FIG. 4 and to point 6 in FIG. 5.
The collected liquid portion then proceeds to the high temperature
recuperator 256 whereupon it surrenders a portion of its heat to
the first working fluid stream 282. See station 7 in FIG. 4 and
corresponding point 7 in FIG. 5. Thereafter, the cooled liquid
portion is expanded through the expansion valve 294 to the low
pressure side of the power generating system 210. See station 8 in
FIG. 4 and point 8 in FIG. 5. The cooled, expanded liquid portion
is then combined with the turbine exhaust stream at station v.sub.6
and corresponding point v.sub.6 in FIG. 5.
[0091] The vapor portion 222 produced in the second separator
portion 244 combines with residual amounts of the first vapor
portion 220 from the first separator portion 242 and exits the
integral vapor separator system 241 as combined vapor stream 286.
This corresponds to station v.sub.2 in FIG. 4 and to point v.sub.2
in FIG. 5. The combined vapor stream 286 may be additionally heated
by the third heating section 240 to a temperature that is greater
than the dew point temperature for the combined vapor stream 286.
That is, the combined vapor stream 286 is superheated in the third
heating section 240. The superheated stream 288 exiting the third
heating section 240 corresponds to station v.sub.3 in FIG. 4 and to
point v.sub.3 in FIG. 5. The stream 288 is then directed to the
energy conversion system 226.
[0092] As was the case for the first embodiment 110, the energy
conversion system 226 of the second embodiment 210 extracts heat
energy from the superheated stream 288, converting it into useful
work. In the embodiment shown and described herein, heat energy
contained in the first and second vapor streams 220 and 222 (which
comprise combined stream 286 and superheated stream 288) is
converted into electrical work by the turbine 228 and the
electrical generator 230 comprising the energy conversion system
226.
[0093] The superheated stream 288 is expanded in the turbine 228
and exits the turbine 228 as exhaust stream 272. See station
v.sub.4 in FIG. 4 and point v.sub.4 in FIG. 5. It is generally
preferred that the expansion process be terminated before the mixed
working fluid 214 is cooled below the dew point temperature. By way
of example, in the embodiment shown and described herein, the mixed
working fluid 214 is expanded to a pressure of about 43 psia and to
a temperature of about 160.degree. F., which is below the dew point
of the mixed working fluid 214 at the designated pressure. The
mixed working fluid 214 can be cooled to a temperature below the
dew point temperature since the energy conversion device 226 can
function effectively with wet mixtures. The exhaust stream 272 is
thereafter directed to the low temperature recuperator 274 wherein
it surrenders a portion of its heat energy to the working fluid
stream 214 flowing in the heated loop 275 of low temperature
recuperator 274. The cooled exhaust stream 272 exits the low
temperature recuperator 274 at station v.sub.5 at a temperature
between the bubble and dew points for the mixed working fluid. See
point v.sub.5 in FIG. 5. By way of example, in this embodiment, the
cooled exhaust stream 272 exits the low temperature recuperator 274
at a quality in the range of about 0% to about 100% (45%
preferred).
[0094] The mixed working fluid exiting the low temperature
recuperator 274 is then mixed with the liquid portion flowing
through the expansion valve 294. See station v.sub.6 in FIG. 4 and
point v.sub.6 in FIG. 5. The combined working fluid stream is then
condensed by the condenser 276 to about the bubble point (station
L.sub.0 in FIG. 4 and point L.sub.0 in FIG. 5). The condensed
stream is then returned to the high pressure side of the system 210
by pump 280 and the cycle is repeated.
[0095] The second embodiment 210 of the power generating system
just described results in the closely matched heating and cooling
functions 290 and 292 shown in FIG. 6. That is, the heating curve
290 of the mixed working fluid 214 closely follows the cooling
curve 292 of the heating fluid (e.g., geothermal brine 216).
[0096] It is contemplated that the inventive concepts herein
described may be variously otherwise embodied and it is intended
that the appended claims be construed to include alternative
embodiments of the invention except insofar as limited by the prior
art.
* * * * *