Title: Power cycle and system for utilizing moderate temperature heat sources
Abstract: A new thermodynamic cycle is disclosed for converting energy from a moderate temperature stream, external source into useable energy using a working fluid comprising of a mixture of a low boiling component and a higher boiling component and including a higher pressure circuit and a lower pressure circuit. The cycle is designed to improve the efficiency of the energy extraction process by recirculating a portion of a liquid stream prior to further cooling. The new thermodynamic process and system for accomplishing the improved efficiency is especially well-suited for streams from moderate-temperature geothermal sources.
Patent Number: 7,021,060 Issued on 04/04/2006 to Kalina
| Inventors:
|
Kalina; Alexander I. (Hillsborough, CA)
|
| Assignee:
|
Kaley, LLC (Belmont, CA)
|
| Appl. No.:
|
069937 |
| Filed:
|
March 1, 2005 |
| Current U.S. Class: |
60/649; 60/651; 60/671 |
| Current Intern'l Class: |
F01K 25/06 (20060101) |
| Field of Search: |
60/649,651,653,671
|
References Cited [Referenced By]
U.S. Patent Documents
Primary Examiner: Nguyen; Hoang
Attorney, Agent or Firm: Strozier; Robert W.
Claims
The invention claimed is:
1. A method comprising the steps of:
transforming a portion of thermal energy in a superheated vapor stream into usable
energy to produce a spent stream;
transferring thermal energy from an external heat source stream to a first vapor
stream to form the superheated vapor stream and a first cooled external heat source stream;
transferring thermal energy from the first cooled external heat source stream
to a first mixed stream to form the first vapor stream and a second cooled external
heat source stream;
transferring thermal energy from the spent stream to a first pre-heated higher
pressure, basic working fluid substream to form a partially condensed spent stream
and a first heated, higher pressure, basic working fluid substream;
transferring thermal energy from a third cooled external heat source substream
to a second pre-heated higher pressure, basic working fluid substream to form a
second heated, higher pressure, basic working fluid substream and a first cooled
external heat source substream;
combining the first and second heated, higher pressure basic working fluid substreams
to form a combined heated, higher pressure basic working fluid stream;
transferring thermal energy from a first portion of the second cooled external
heat source stream to the combined heated, higher pressure basic working fluid
stream to form a higher temperature, higher pressure, basic working fluid stream
and the third cooled external heat source substream;
separating the partially condensed spent stream into a separated vapor stream
and a separated liquid stream;
pressurizing a first portion of the separated liquid stream to a pressure equal
to a pressure of the combined higher temperature, higher pressure basic working
fluid stream to form a pressurized liquid stream;
transferring thermal energy from a second portion of the second cooled external
heat source stream to the pressurized liquid stream to form a second mixed stream
and a fourth cooled external heat source substream;
combining the second mixed stream with the combined higher temperature, higher
pressure basic working fluid stream to form the first mixed stream;
combining a second portion of the separated liquid stream with the separated
vapor stream to from a lower pressure, basic working fluid stream;
transferring thermal energy from the lower pressure, basic working fluid stream
to a higher pressure, basic working fluid stream to form a pre-heated, higher pressure,
basic working fluid stream and a cooled, lower pressure, basic working fluid stream;
transferring thermal energy from the cooled, lower pressure, basic working fluid
stream to an external coolant stream to from a spent external coolant stream and
a fully condensed, lower pressure, basic working fluid stream; and
pressurizing the fully condensed, lower pressure, basic working fluid stream
to the higher pressure, basic working fluid stream.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thermodynamic cycle and an apparatus for implementing
the thermodynamic cycle for converting a portion of thermal energy associated with
superheated stream of a multi-component fluid in a high efficient manner.
More particularly, the present invention relates to a thermodynamic cycle and
an apparatus for implementing the thermodynamic cycle for converting a portion
of thermal energy associated with superheated stream of a multi-component fluid
in a high efficient manner, where the cycle utilizes four different compositions
of the multi-component fluid and heats, vaporizes three of the compositional streams
and superheats one of the compositional streams to form the superheated stream
from which useable energy is produced. The cycle is designed to use with moderate
temperature heat source stream.
2. Description of the Related Art
In U.S. Pat. No. 6,769,256, issued Aug. 31, 2004, a system is disclosed which
utilizes heat from moderate and low temperature heat sources. This system is presented
in three variants ranging from a highest efficiency and highest complexity variant,
to a moderate variant, and finally to a lowest efficiency and lowest complexity
variant. A detailed calculation of this system demonstrates than when the initial
temperature of the heat source exceeds 325-330° F., the high complexity and
moderate variants of the system (in which the working fluid is not fully vaporized,
and the remaining liquid is recycled) degenerate and are thus in effect converted
into the lowest complexity, lowest efficiency variant (in which all working fluid
is vaporized).
Although prior systems for improving energy extraction from moderate temperature
geothermal or other heat sources have been disclosed, there is still a need in
the art for an improved and simplified system for energy extraction from moderate
temperature sources.
SUMMARY OF THE INVENTION
The present invention provides an energy extraction apparatus comprising eight
heat exchangers, at least three mixers, at least three splitters, two pumps, a
separator and a turbine, where the heat exchangers are designed to produce a fully
condensed basic working fluid stream and a superheated working fluid stream utilizing
an external coolant stream, an external heat source stream and two working fluid streams.
The present invention also provides a method for energy extraction including
the steps of
DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts a flow diagram of a preferred embodiment of a power cycle and
system for utilizing moderate temperature heat sources of this invention.
DETAILED DESCRIPTION OF THE INVENTION
The inventors have found that an improved power cycle and system for utilizing
moderate temperature heat sources can be designed. The system has been developed
for the purpose of producing useful power from heat sources, such as geothermal
fluids, waste heat sources and other similar sources, with a moderate initial temperature,
i.e., a temperature between about 325° F. and about 500° F. The inventor
has found that the system of this invention has higher efficiency than the systems
described in the prior art with heat sources whose initial temperatures are greater
than or equal to 325° F.
The proposed system uses, as a working fluid, a multi-component mixture of at
least two components with different normal boiling temperatures. In the preferred
embodiment of the system, this mixture consists of water and ammonia, but other
working fluids, such as a mixture of hydrocarbons, freons or other substances can
be used as well.
Referring now to FIG. 1, the power cycle and system, generally
1,
is shown. A fully condensed working fluid stream
3 having a high concentration
of a low boiling component of a multi-component fluid, hereafter referred to as
a basic solution, and having parameters as at a point
1 enters into a pump,
P
1. The stream
102 is pressurized to a desired higher pressure and
becomes a higher pressure stream
5 having parameters as at a point
2.
The stream
104 having the parameters as at the point
2 then passes
through a recuperative pre-heater or a second heat exchanger HE
2, where
the stream
104 is heated in counterflow by a returning stream
7 having
parameters as at a point
26 of condensing basic solution in a first heat
exchange process
26-
27 or
2-
3 described below. The
first heat exchange process
26-
27 produces a pre-heated stream
9
having parameters as at a point
3 and a condensed stream
11 having
parameters as at a point
27. The parameters of the pre-heated stream
108
correspond to a state of saturated or slightly subcooled liquid.
The pre-heated stream
108 having the parameters as at the point
3
is then divided into two substreams
13 and
15 having parameters as
at points
4 and
5, respectively. The basic solution substream
112
having the parameters as at the point
4 passes through a fourth heat exchanger
HE
4, where it is heated and partially vaporized in counterflow with a fifth
heat source fluid stream
17 having parameters as at a point
42 in
a second heat exchange process
42-
43 or
4-
6 as described
below. The second heat exchange process
42-
43 produces a stream
19
having parameters as at a point
6 and a sixth cooled heat source stream
21 having parameters as at a point
43. The basic solution substream
114 having the parameters as at the point
5 passes through a recuperative
boiled-condenser or third heat exchanger HE
3, where it is heated and partially
vaporized in counterflow with a condensing working fluid stream
23 having
parameters as at a point
20 in a third heat exchange process
20-
21
or
5-
7 as described below. The third heat exchange process
20-
21
produces a stream
25 having obtains parameters as at a point
7 and
a partially condensed working fluid stream
27 having parameters as at a
point
21. In the preferred embodiment of this system, the parameters of
the streams
118 and
124 having the parameters as at the points
6
and
7, respectively, are identical or close to identical, where close to
identical means that the parameters of each of the stream
118 and
124
are with about 5% of each other.
Thereafter, the basic solution streams
118 and
124 having
parameters as at the points
6 and
7, respectively, are combined forming
a stream
29 having parameters as at a point
8. The parameters of
the stream
128 are such that the stream
128 is generally in a state
of a liquid-vapor mixture. The stream
128 having the parameters as at the
point
8 is then sent through a seventh heat exchanger HE
7, where
it is further heated and vaporized in counterflow with a third cooled heat source
fluid steam
31 having parameters as at a point
46 in a fourth heat
exchange process
46-
42 or
8-
14 as described below.
The fourth heat exchange process
46-
42 produces a first mixed stream
33 having parameters as at a point
14 and a fifth cooled heat source
stream
116 having parameters as at a point
42. In the preferred embodiment
of this system, the parameters of the basic working fluid stream
132 is
such that the stream
132 is either in a state of saturated vapor, i.e.,
fully vaporized, or has some very small amount wetness generally less than about
5% wetness.
Thereafter, the stream
132 having the parameters as at the point
14 is combined with a liquid stream
37 having parameters as at a
point
29, forming a working solution stream
39 having parameters
as at a point
10. The stream
136 having the parameters as at the
point
29 is referred to herein as a recirculating solution. The parameters
of the stream
136 at the point
29 is such that the stream
136
is in a state of saturated or slightly subcooled liquid as described below. The
working solution stream
138 having the parameters as at the point
10
then passes though a fifth heat exchanger HE
5, where it is heated and vaporized
in counterflow with a first cooled heat source fluid stream
41 having parameters
as at a point
41 in a fifth heat exchange process
41-
44 or
10-
11 as described below. The fifth heat exchange process
41-
44
produces a second mixed stream
43 having parameters as at a point
11
and a second cooled heat source stream
45 having the parameters as at a
point
44.
In the preferred embodiment of this system, the parameters of the stream
142
at the point
11 is such that the stream
142 is in a state of a saturated
vapor. The stream
142 having the parameters as at the point
11 is
sent into a sixth heat exchanger HE
6, where it is superheated in counterflow
with a heat source fluid stream
47 having parameters as at a point
40
in a sixth heat exchange process
40-
41 or
11-
17 as
described below. The sixth heat exchange process
40-
41 produces a
fully vaporized and superheated stream
49 having obtains parameters as at
a point
17 and the first cooled heat source stream
140 having the
parameters as at the point
41. The stream
148 having the parameters
as at the point
17 then enters a turbine T
1, where it is expanded,
producing power, and the spent stream
122 having parameters as at a point
20.
The spent stream
122 having the parameters as at the point
20 is
then sent into the third heat exchanger HE
3, where it is cooled and partially
condensed, releasing heat for the third heat exchange process
20-
21
as described above forming the stream
126 having the parameters as at the
point
21. The parameters of the stream
126 at the point
21
is in a state of a vapor-liquid mixture. The stream
126 with parameters
as at point
21 then enters into a separator S
1, where it is separated
into a saturated vapor stream
51 having parameters as at a point
22,
and a saturated liquid stream
53 having parameters as at a point
23.
The concentration of a low boiling component in the vapor stream
150 having
the parameters as at the point
22 must be higher or equal to the concentration
of the low boiling component in the basic working solution as described above.
The liquid stream
152 having the parameters as at the point
23
is divided into two substreams
55 and
57 having parameters as at
points
24 and
25, respectively. The liquid stream
156 having
the parameters as at the point
25 is then combined with the vapor stream
150 having the parameters as at the point
22, forming a basic working
solution stream
106 having the parameters as at the point
26. The
stream
106 of basic working solution having the parameters as at the point
26 then passes through the recuperative pre-heater or second heat exchanger
HE
2, where it is cooled and partially condensed, releasing heat for process
2-
3 or
26-
27 as described above becoming the stream
110 having parameters as at point
27.
The stream
110 of basic working solution with parameters as at point
27
is then sent through a condenser or first heat exchanger HE
1, where it is
cooled and fully condensed, in counterflow with a stream
59 of coolant (air
or water) stream having parameters as at a point
50 in a seventh heat exchange
process
50-
51 or
27-
1. The seventh heat exchange process
50-
51 produces a spent coolant stream
61 having parameters
as at a point
51 and the stream
102 having parameters as at the point
1 as described above.
The stream
154 of liquid with the parameters as at the point
24
as described above enters into a second pump P
2, where its pressure is increased
to form a higher pressure stream
63 having parameters as at a point
9.
The parameters of the stream
162 are such that the stream
162 correspond
to a state of subcooled liquid. The stream
162 having the parameters as
at point
9 then passes through an eighth heat exchanger HE
8, where
it is heated in counterflow with a fourth cooled heat source fluid stream
65
having parameters as at a point
47 in an eighth heat exchange process
47-
48
or
9-
29 described below. The eighth heat exchange process
47-
48
produces a seventh cooled heat source stream
67 having parameters as at
a point
48 and the stream
136 having the parameters as at the point
29. The parameters of the stream
136 are such that the stream
136
corresponds to a state of saturated or slightly subcooled liquid. Thereafter, the
stream
136 having the parameters as at the point
29 is combined with
the stream
132 having the parameters as at the point
14, forming
the stream
138 having the parameters as at the point
10 as described above.
The heat source fluid stream
146 having the initial parameters as at the
point
40, passes through the sixth heat exchanger HE
6, where it is
cooled, providing heat for process
11-
17 as described above forming
the first cooled heat source stream
140 having the parameters as at the
point
41. Thereafter, the first cooled heat source stream
140 having
the parameters as at the point
41 passes through the fifth heat exchanger
HE
5, where it is cooled, providing the fifth heat exchange process
10-
11
as described above forming the stream
144 having the parameters as at the
point
44. Thereafter, the stream
144 of heat source fluid having
the parameters as at the point
44 is divided into two substreams
130
and
164 having the parameters as at the points
46 and
47, respectively.
The stream
130 having the parameters as at the point
46 passes
through the seventh heat exchanger HE
7, where it is cooled, providing heat
for the fourth heat exchange process
8-
14 as described above to form
the fifth cooled heat source stream
116 having the parameters as at the
point
42. The stream
116 of heat source fluid having the parameters
as at the point
42 then passes through the fourth heat exchanger HE
4,
where it is further cooled, providing heat for the second heat exchange process
4-
6 as described above to form the sixth cooled heat source stream
120 having the parameters as at the point
43.
The stream
164 of heat source fluid having the parameters as at the point
47 passes through the eighth heat exchanger HE
8, where it is cooled,
providing heat for the eighth heat exchange process
9-
29 as described
above to form the seventh cooled heat source stream
166 having the parameters
as at the point
48. Thereafter, the sixth cooled heat source streams
120
and the seventh cooled heat source
166 of heat source fluid having the parameters
as at the points
43 and
48 are combined, forming a spent heat source
stream
69 having parameters as at a point
49 which is sent out of
the system.
The cycle is closed.
The complete vaporization of the basic solution and the preheating of the recirculating
solution prior to the combination of the basic solution with the recirculating
solution reduces the irreversibility in the process of mixing of these two streams
and therefore increases the efficiency of the overall process. Moreover, this approach
increases the heat load in the process cooling the heat source fluid from point
44 down. This, in turn, requires an increase of a flow rate of the heat
source fluid per unit of a flow rate of the basic solution. As a result, a flow
rate of the recirculating solution can also be increased leading to an increase
of a flow rate of the working solution passing through the turbine, and thus an
increase in a power output. At the same time, a flow rate of the basic solution
passing through the final condenser or first heat exchanger HE
1 of the seventh
heat exchange process
27-
1, remains unchanged, and a quantity of
heat rejected in the first heat exchanger HE
1 also remains unchanged. As
a result, the overall efficiency of the system is increased.
A summary of a performance of the system of this invention is presented in Table
1 and the parameters of all key points described above are tabulated in Table 2.
Comparing these results with the results of the system presented in the
prior art shows that the system of this invention within a temperatures range between
about 325° F., and about 500° F. has a net thermal efficiency that is
from 7% to 10% higher than the efficiency of the system presented in the prior art.
| TABLE 1 |
|
| Plant Performance Summary |
|
| Heat in |
30,470.49 |
kW |
538.65 |
Btu/lb |
| Heat rejected |
24,800.44 |
kW |
438.41 |
Btu/lb |
| Turbine enthalpy Drops |
5,803.26 |
kW |
102.59 |
Btu/lb |
| Gross Generator Power |
5,533.70 |
kW |
97.82 |
Btu/lb |
| Process Pumps (-2.35) |
-144.79 |
kW |
-2.56 |
Btu/lb |
| Cycle Output |
5,388.91 |
kW |
95.26 |
Btu/lb |
| Other Pumps and Fans (-2.25) |
-136.61 |
kW |
-2.41 |
Btu/lb |
| Net Output |
5,252.30 |
kW |
92.85 |
Btu/lb |
| Gross Generator Power |
5,533.70 |
kW |
97.82 |
Btu/lb |
| Cycle Output |
5,388.91 |
kW |
95.26 |
Btu/lb |
| Net Output |
5,252.30 |
kW |
92.85 |
Btu/lb |
| Net thermal efficiency |
17.24% |
| Second Law Limit |
29.50% |
| Second Law Efficiency |
58.43% |
| Specific Brine Consumption |
95.20 |
lb/kW-hr |
| Specific Power Output |
10.50 |
W-hr/lb |
|
| Overall Heat Balance Btu/lb |
|
| Heat In: |
Source + pumps = 538.65 + 2.35 = 541.00 |
| Heat Out: |
Turbines + condenser = 102.59 + 438.41 = 541.00 |
|
| TABLE 2 |
|
| Parameters of Key Points |
|
| Working Fluid |
| |
X |
T |
P |
H |
S |
Ex |
G rel |
Ph. |
Wetness |
| Pt. |
lb/lb |
° F. |
psia |
Btu/lb |
Btu/lb-R |
Btu/lb |
G/G = 1 |
lb/lb |
or T ° F. |
|
| 1 |
0.9000 |
69.81 |
115.587 |
8.7511 |
0.0717 |
53.6564 |
1.00000 |
Mix |
1 |
| 2 |
0.9000 |
71.09 |
474.724 |
10.8310 |
0.0725 |
55.3018 |
1.00000 |
Liq |
-95.67° F. |
| 3 |
0.9000 |
165.00 |
464.724 |
121.8394 |
0.2649 |
67.9204 |
1.00000 |
Mix |
1 |
| 4 |
0.9000 |
165.00 |
464.724 |
121.8394 |
0.2649 |
67.9204 |
0.39329 |
Mix |
1 |
| 5 |
0.9000 |
165.00 |
464.724 |
121.8394 |
0.2649 |
67.9204 |
0.60671 |
Mix |
1 |
| 6 |
0.9000 |
227.47 |
462.724 |
533.3776 |
0.9076 |
150.7830 |
0.39329 |
Mix |
0.1799 |
| 7 |
0.9000 |
227.47 |
462.724 |
533.3776 |
0.9076 |
150.7830 |
0.60671 |
Mix |
0.1799 |
| 8 |
0.9000 |
227.47 |
462.724 |
533.3778 |
0.9076 |
150.7830 |
1.00000 |
Mix |
0.1799 |
| 9 |
0.3811 |
170.79 |
464.724 |
48.6950 |
0.2189 |
15.9998 |
0.17026 |
Liq |
-114.35° F. |
| 10 |
0.8245 |
284.57 |
462.224 |
606.6533 |
1.0093 |
171.7561 |
1.17026 |
Mix |
0.1686 |
| 11 |
0.8245 |
322.52 |
460.724 |
757.8078 |
1.2073 |
221.6375 |
1.17026 |
Vap |
-0.1° F. |
| 14 |
0.9000 |
284.57 |
462.224 |
679.1791 |
1.1111 |
192.5432 |
1.00000 |
Mix |
0.0271 |
| 17 |
0.8245 |
361.00 |
460.224 |
784.8355 |
1.2411 |
231.3555 |
1.17026 |
Vap |
38.6° F. |
| 20 |
0.8245 |
232.47 |
121.587 |
697.1728 |
1.2635 |
132.2385 |
1.17026 |
Mix |
0.0442 |
| 21 |
0.8245 |
170.00 |
119.587 |
483.8153 |
0.9440 |
82.2867 |
1.17026 |
Mix |
0.2499 |
| 22 |
0.9722 |
170.00 |
119.587 |
629.3327 |
1.1858 |
104.8123 |
0.87779 |
Mix |
0 |
| 23 |
0.3811 |
170.00 |
119.587 |
47.0820 |
0.2183 |
14.6817 |
0.29247 |
Mix |
1 |
| 24 |
0.3811 |
170.00 |
119.587 |
47.0820 |
0.2183 |
14.6817 |
0.17026 |
Mix |
1 |
| 25 |
0.3811 |
170.00 |
119.587 |
47.0820 |
0.2183 |
14.6817 |
0.12221 |
Mix |
1 |
| 26 |
0.9000 |
170.00 |
119.587 |
558.1742 |
1.0676 |
93.7972 |
1.00000 |
Mix |
0.1222 |
| 27 |
0.9000 |
112.84 |
117.587 |
447.1658 |
0.8843 |
76.5215 |
1.00000 |
Mix |
0.2273 |
| 29 |
0.3811 |
284.57 |
462.224 |
180.6858 |
0.4111 |
49.6667 |
0.17026 |
Mix |
1 |
|
| |
X |
T |
P |
H |
S |
Ex |
G rel |
Ph. |
| Pt. |
lb/lb |
° F. |
psia |
Btu/lb |
Btu/lb-R |
Btu/lb |
G/G = 1 |
lb/lb |
|
| 40 |
BRINE |
370.00 |
14.693 |
352.5340 |
0.5047 |
94.4232 |
2.58868 |
Liq |
| 41 |
BRINE |
358.29 |
14.693 |
340.3156 |
0.4899 |
89.7893 |
2.58868 |
Liq |
| 42 |
BRINE |
234.59 |
14.693 |
211.2994 |
0.3189 |
48.2247 |
2.40263 |
Liq |
| 43 |
BRINE |
170.00 |
14.693 |
143.9340 |
0.2171 |
32.9407 |
2.40263 |
Liq |
| 44 |
BRINE |
292.77 |
14.693 |
271.9834 |
0.4028 |
65.9851 |
2.58868 |
Liq |
| 46 |
BRINE |
292.77 |
14.693 |
271.9834 |
0.4028 |
65.9851 |
2.40263 |
Liq |
| 47 |
BRINE |
292.77 |
14.693 |
271.9834 |
0.4028 |
65.9851 |
0.18605 |
Liq |
| 48 |
BRINE |
176.96 |
14.693 |
151.1910 |
0.2285 |
34.3364 |
0.18605 |
Liq |
| 49 |
BRINE |
170.50 |
14.693 |
144.4556 |
0.2179 |
33.0388 |
2.58868 |
Liq |
|
| |
X |
T |
P |
H |
S |
Ex |
G rel |
Ph. |
T |
| Pt. |
lb/lb |
° F. |
psia |
Btu/lb |
Btu/lb-R |
Btu/lb |
G/G = 1 |
lb/lb |
° F. |
|
| 50 |
water |
51.70 |
54.693 |
19.9395 |
0.0394 |
0.1617 |
15.6119 |
Liq |
-235 |
| 51 |
water |
51.81 |
64.693 |
20.0833 |
0.0397 |
0.1914 |
15.6119 |
Liq |
-245.84 |
| 52 |
water |
79.92 |
54.693 |
48.1655 |
0.0932 |
0.9127 |
15.6119 |
Liq |
-206.78 |
|
All references cited herein are incorporated by reference. While this invention
has been described fully and completely, it should be understood that, within the
scope of the appended claims, the invention may be practiced otherwise than as
specifically described. Although the invention has been disclosed with reference
to its preferred embodiments, from reading this description those of skill in the
art may appreciate changes and modification that may be made which do not depart
from the scope and spirit of the invention as described above and claimed hereafter.
*
