U.S. patent application number 12/104797 was filed with the patent office on 2008-10-30 for isothermal power.
Invention is credited to Melvin L. Prueitt.
Application Number | 20080264062 12/104797 |
Document ID | / |
Family ID | 39885383 |
Filed Date | 2008-10-30 |
United States Patent
Application |
20080264062 |
Kind Code |
A1 |
Prueitt; Melvin L. |
October 30, 2008 |
Isothermal power
Abstract
This invention provides means for producing power by using
isothermal compressors and isothermal expanders. One embodiment has
an isothermal compressor that compresses air (or other gas), passes
the air through a counter-flow heat exchanger, which heats the air,
uses the heated air to drive an isothermal expander for power
generation, and transfers the expander exhaust back through the
counter-flow heat exchanger to heat the input air to the expander.
Another embodiment has a boiler that produces vapor that flows
through a counter-flow heat exchanger to superheat the vapor. The
vapor then flows through an isothermal expander for power
generation. The exhaust from the isothermal expander flows back
through the counter-flow heat exchanger to supply heat to the vapor
coming from the boiler and then flows through another heat
exchanger that preheats the feed liquid flowing to the boiler.
Inventors: |
Prueitt; Melvin L.; (Los
Alamos, NM) |
Correspondence
Address: |
Melvin Prueitt
161 Cascabel St.
Los Alamos
NM
87544
US
|
Family ID: |
39885383 |
Appl. No.: |
12/104797 |
Filed: |
April 17, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60914036 |
Apr 26, 2007 |
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Current U.S.
Class: |
60/670 ;
60/671 |
Current CPC
Class: |
F01K 27/00 20130101 |
Class at
Publication: |
60/670 ;
60/671 |
International
Class: |
F01K 25/00 20060101
F01K025/00; F01K 27/00 20060101 F01K027/00 |
Claims
1. An isothermal power generating system comprising: means for
adding energy to a working fluid; a cooler for cooling the fluid; a
counter-flow heat exchanger for heating the fluid; an isothermal
expander for expanding the heated fluid to produce mechanical
power; a heater for supplying hot fluid to the isothermal expander
to keep hot the working fluid; and a means for conducting the
expanded working fluid back through the counter-flow heat exchanger
to heat the fluid; wherein the working fluid from the heating means
flows through the counter-flow heat exchanger, where the working
fluid vapor is heated, and wherein the working fluid vapor flows
into the isothermal expander to extract mechanical energy from the
expanding working fluid vapor, and the working fluid vapor flows
back through the counter-flow heat exchanger to heat the working
fluid from the heating means.
2. An isothermal power generating system according to claim 1
wherein the working fluid is a gas, and further wherein: the means
for adding energy comprises an isothermal compressor for
compressing gas therein; the cooler supplies a cooling fluid to the
isothermal compressor to keep cool the gas in the isothermal
compressor; an isothermal expander for expanding the heated
compressed gas to produce mechanical power by extracting mechanical
energy from the gas as the gas expands; the counter-flow heat
exchanger heats, with heat energy from gas flowing from the
isothermal expander, the compressed gas flowing from the isothermal
compressor; the heater keeps hot the fluid flowing in the
isothermal expander; the means for conducting the expanded gas back
through the counter-flow heat exchanger comprises means for
conducting gas from the expander to heat compressed gas flowing
from the compressor; and the isothermal compressor compresses
cooled and expanded gas drawn from the isothermal expander via the
counter-flow heat exchanger, and forces the gas into the
counter-flow heat exchanger.
3. An isothermal power generating system according to claim 2,
wherein the isothermal compressor and isothermal expander each
comprise: a piston in a cylinder; a connecting rod operatively
connected to the piston for moving the piston; spaced-apart piston
components on a face of the piston for promoting heat transfer
between the piston components and the gas to keep the gas
substantially close to isothermal; spaced-apart cylinder components
on an end of the cylinder for promoting heat transfer between the
cylinder components and the gas to keep the gas substantially close
to isothermal; at least one channel within each of the piston
components and each of the cylinder components for conducting fluid
for transferring heat energy to or from the piston components and
cylinder components; at least one channel within the connecting rod
and the piston for conducting fluid to the channels in the piston
components on the face of the piston; at least one channel within
the end of the cylinder for conducting fluid to the channels in the
cylinder components on the end of the cylinder; wherein when the
piston approaches the end of the cylinder, the piston components on
the face of the piston are fittable between the cylinder components
on the end of the cylinder.
4. An isothermal power generating system according to claim 3
wherein the piston components and the cylinder components comprise
tapered plates.
5. An isothermal power generating system according to claim 3
wherein the piston components and the cylinder components comprise
tapered concentric circular forms.
6. An isothermal power generating system according to claim 2,
wherein the isothermal compressor and isothermal expander each
comprises: two rotatable pistons attached to shafts within a
housing, which rotatable pistons roll together to form a seal
there-between; spaced-apart piston components on the inside of the
rotatable pistons for transferring heat energy between the piston
components and the gas to keep the gas substantially close to
isothermal; spaced-apart housing components on the housing for
transferring heat between the housing components and the gas to
keep the gas substantially close to isothermal; at least one
channel within each of the piston components and each of the
housing components for conducting fluid for transferring heat
energy to or from the piston components and housing components; at
least one channel within each shaft for conducting fluids to and
from the channel in the piston components on the inside of the
rotatable pistons; and at least one channel within the housing for
conducting fluids to and from the channels in the housing
components on the housing.
7. An isothermal power generating system according to claim 6,
wherein: spaced-apart piston components on first sides of the
rotatable pistons are fittable between spaced-apart housing
components on first sides of the housing when the rotatable pistons
rotate toward the first sides of the housing, and wherein
spaced-apart piston components on a second side of the rotatable
pistons are fittable between spaced-apart housing components on a
second side of the housing when the rotatable pistons rotate toward
the second side of the housing.
8. An isothermal power generating system according to claim 6
wherein the piston components and the cylinder components comprise
tapered plates.
9. An isothermal power generating system according to claim 6
wherein the piston components and the cylinder components comprise
tapered concentric circular forms.
10. An isothermal power generating system according to claim 2,
wherein the isothermal compressor and isothermal expander each
comprises: a casing for a turbine, which casing contains upper
channels and lower channels therein for conducting heating or
cooling fluid; a central core for the turbine, which central core
contains channels for conducting heating or cooling fluid; a first
external pipe in fluid connection with the top of the casing for
delivering heating or cooling fluid from a fluid source to the top
of the casing; a second external pipe in fluid connection with the
bottom of the casing for retrieving heating or cooling fluid from
the bottom of the casing to the fluid source; upper turbine stator
blades, attached to the casing and to the central core of the
turbine, containing interior channels for the conducting of heating
or cooling fluids for transferring heat to or from gas flowing
through the turbine; lower turbine stator blades, attached to the
casing and to the central core of the turbine, containing interior
channels for the conducting of heating or cooling fluids for
transferring heat to or from gas flowing through the turbine; a
central shaft, inside the central core, containing: a first shaft
channel for providing heating or cooling fluids; and a second shaft
channel for retrieving heating or cooling fluids; and rotatable
blades on the central shaft and having interior channels for
conducting heating or cooling fluids into and out of the rotatable
blades for transferring heat energy to or from gas that flows
through the turbine; wherein fluid flows through the upper channels
to the interior channels in the upper turbine stator blades, then
through the interior channels in the upper turbine stator blades to
channels in the central core, through the channels in the central
core to channels in the lower turbine stator blades, through the
interior channels in the lower turbine stator blades to the lower
channels, and then flows through the lower channels to the second
external pipe at the bottom of the casing, and wherein heating or
cooling fluid flows in one end of the central shaft through the
first shaft channel to channels in the rotatable blades, through
the channels in the rotatable blades to the second shaft channel in
the central shaft, through the second shaft channel in the central
shaft to the other end of the central shaft, and then flows out to
the fluid source.
11. An isothermal power generating system according to claim 2,
wherein the isothermal compressor and isothermal expander each
consist of: a container comprising: a circular top; a circular
bottom; and a circular bellows forming the circular side walls; a
push rod for moving the circular top of the container; spaced-apart
top components on the inside of the circular top for receiving heat
from compressing gas or supplying heat to expanding gas, thereby to
keep the gas substantially close to isothermal; spaced-apart bottom
components on the inside of the circular bottom for receiving heat
from compressing gas or supplying heat to expanding gas, thereby to
keep the gas close to isothermal; channels within the top and
bottom components for conducting heating or cooling fluids to
transfer heat energy to or from the top and bottom components;
channels within the push rod and within the circular top for
conducting heating or cooling fluids to the channels in the top
components; and channels within the circular bottom for conducting
heating or cooling fluids to the channels in the bottom components;
wherein when the circular top approaches the circular bottom of the
container, the spaced-apart top components on the circular top are
fittable between the spaced-apart bottom components on the circular
bottom.
12. An isothermal power generating system according to claim 11
wherein the spaced-apart top components and the spaced-apart bottom
components comprise tapered plates.
13. An isothermal power generating system according to claim 11
wherein the spaced-apart top components and the spaced-apart bottom
components comprise tapered concentric circular forms.
14. An isothermal power generating system according to claim 1,
adapted for two-phase fluids and wherein: the means for adding
energy comprises a boiler for boiling a working fluid to produce a
working fluid vapor; the counter-flow heat exchanger comprises a
first counter-flow heat exchanger for superheating the working
fluid vapor; the isothermal expander expands the heated working
fluid vapor to extract mechanical energy from the working fluid
vapor; and the heater supplies hot fluid to the isothermal expander
to keep hot the working fluid vapor that is flowing through the
isothermal expander; the isothermal power generating system further
comprises: a pump to pump the liquid toward the boiler; and a
second counter-flow heat exchanger for preheating the liquid feed
to the boiler; the means for conducting comprises means for
conducting the expanded working fluid vapor from the isothermal
expander back through the first counter-flow heat exchanger to heat
working fluid vapor flowing from the boiler and through the second
counter-flow heat exchanger for preheating the liquid feed to the
boiler; the cooler comprises a condenser for condensing the working
fluid vapor to a liquid; and wherein the working fluid vapor flows
into the condenser to be condensed to a liquid, and is then pumped
to the boiler by the pump via the second counter-flow heat
exchanger.
15. An isothermal power generating system according to claim 14
wherein the isothermal expander comprises: a piston in a cylinder;
a connecting rod operably connected to the piston for moving the
piston; and spaced-apart piston components on the face of the
piston for supplying heat to the expanding working fluid vapor to
keep the working fluid vapor substantially close to isothermal;
spaced-apart cylinder components on an end of the cylinder for
supplying heat to expanding working fluid vapor to keep the working
fluid vapor substantially close to isothermal; at least one channel
within each of the piston and cylinder components for conducting
heating fluids to add heat to the piston and cylinder components;
channels within the connecting rod and the piston for conducting
heating fluids to the channel in the piston components; and
channels within the end of the cylinder for conducting heating
fluids to the channel in the cylinder component on end of the
cylinder; wherein when the piston approaches the bottom of the
cylinder, the piston components on the face of the piston are
fittable between the cylinder components on the end of the
cylinder.
16. An isothermal power generating system according to claim 15
wherein the piston components and the cylinder components comprise
tapered plates.
17. An isothermal power generating system according to claim 15
wherein the piston components and the cylinder components comprise
tapered concentric circular forms.
18. An isothermal power generating system according to claim 14,
wherein the isothermal expander comprises: two rotating pistons
attached to shafts within a housing, which rotating pistons roll
together to form a seal there-between; spaced-apart piston
components on the inside of the rotating pistons for supplying heat
to the expanding working fluid vapor to keep the working fluid
vapor substantially close to isothermal; spaced-apart housing
components on the housing for supplying heat to the expanding
working fluid vapor to keep the working fluid vapor substantially
close to isothermal; channels within the piston components and the
housing components for conducting heating fluids to add heat to the
piston components and to the housing components; channels within
the shafts for conducting heating fluids to and from the channels
in the piston components; and channels within the housing for
conducting heating fluids to and from the channels in the housing
components.
19. An isothermal power generating system according to claim 18,
wherein: spaced-apart piston components on first sides of the
rotatable pistons are fittable between spaced-apart housing
components on first sides of the housing when the rotatable pistons
rotate toward the first sides of the housing, and wherein
spaced-apart piston components on a second side of the rotatable
pistons are fittable between spaced-apart housing components on a
second side of the housing when the rotatable pistons rotate toward
the second side of the housing.
20. An isothermal power generating system according to claim 18
wherein the piston components and the cylinder components comprise
tapered plates.
21. An isothermal power generating system according to claim 18
wherein the piston components and the cylinder components comprise
tapered concentric circular forms.
22. An isothermal power generating system according to claim 14,
wherein the isothermal expander comprises: a casing for a turbine,
which casing contains upper channels and lower channels therein for
conducting heating or cooling fluid; a central core for the
turbine, which central core contains channels for conducting
heating fluid; a first external pipe in fluid connection with the
top of the casing for delivering heating fluid from a fluid source
to the top of the casing; a second external pipe in fluid
connection with the bottom of the casing for retrieving heating
fluid from the bottom of the casing to the fluid source; upper
turbine stator blades, attached to the casing and to the central
core of the turbine, containing interior channels for the
conducting of heating fluids for transferring heat to gas flowing
through the turbine; lower turbine stator blades, attached to the
casing and to the central core of the turbine, containing interior
channels for the conducting of heating fluids for transferring heat
to gas flowing through the turbine; a central shaft, inside the
central core, containing: a first shaft channel for providing
heating; and a second shaft channel for retrieving heating fluids;
and rotatable blades on the central shaft and having interior
channels for conducting heating fluids into and out of the
rotatable blades for transferring heat energy to gas that flows
through the turbine; wherein fluid flows through the upper channels
to the interior channels in the upper turbine stator blades, then
through the interior channels in the upper turbine stator blades to
channels in the central core, through the channels in the central
core to channels in the lower turbine stator blades, through the
interior channels in the lower turbine stator blades to the lower
channels, and the flows through the lower channels to the second
external pipe at the bottom of the casing, and wherein heating
fluid flows in one end of the central shaft through the first shaft
channel to channels in the rotatable blades, through the channels
in the rotatable blades to the second shaft channel in the central
shaft, through the second shaft channel in the central shaft to the
other end of the central shaft, and then flows out to the fluid
source.
23. An isothermal power generating system according to claim 14,
wherein the isothermal expander comprises: a container comprising:
a circular top; a circular bottom; and a circular bellows forming
the circular side walls; a push rod for moving the circular top of
the container; spaced-apart top components on the inside of the
circular top for receiving heat from compressing gas or supplying
heat to expanding gas, thereby to keep the gas substantially close
to isothermal; spaced-apart bottom components on the inside of the
circular bottom for supplying heat to expanding gas, thereby to
keep the gas close to isothermal; channels within the top and
bottom components for conducting heating fluids to transfer heat
energy to the top and bottom components; channels within the push
rod and within the circular top for conducting heating fluids to
the channels in the top components; and channels within the
circular bottom for conducting heating fluids to the channels in
the bottom components; wherein when the circular top approaches the
circular bottom of the container, the spaced-apart top components
on the circular top are fittable between the spaced-apart bottom
components on the circular bottom.
24. An isothermal power generating system according to claim 23
wherein the spaced-apart top components and the spaced-apart bottom
components comprise tapered plates.
25. An isothermal power generating system according to claim 23
wherein the spaced-apart top components and the spaced-apart bottom
components comprise tapered concentric circular forms.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This claims priority to and the benefit of Provisional U.S.
Patent Application Ser. No. 60/914,036, filed Apr. 26, 2007, the
entirety of which is hereby incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] Most of the heat engines in use today use adiabatic
expansion of gases to produce power. The Rankine, Brayton, Otto
cycles, and others use adiabatic expansions, and some of them also
use adiabatic compressions. This disclosure shows that isothermal
expansion and compression have some important efficiency
advantages.
[0003] The isothermal cycle can use a working fluid such as water,
ammonia, or propylene that are boiled and then expanded
isothermally in an engine to produce power. The vapors are then
condensed back to a liquid to repeat the cycle. It can also use a
gas such as air or helium that can be compressed isothermally,
heated, and then expanded isothermally in an engine that drives an
electric generator or drives some other machine. Since the exhaust
gas from the expander is still hot, its heat can be used to heat
the compressed gas flowing from the compressor to the expander.
[0004] Some US patents that are somewhat related to embodiments of
the present invention are U.S. Pat. Nos. 4,023,366, 4,207,027,
4,455,825, 4,676,067, 5,641,273, 6,186,755, 6,205,788, 6,225,706,
7,062,913, and 7,124,585.
SUMMARY OF THE INVENTION
[0005] In order to have isothermal compression and expansion of
gases, heat must be removed from the gas while it is being
compressed, and heat must be supplied to the gas during expansion.
One purpose of this invention is to provide means of transferring
heat to and from gases quickly.
[0006] By providing appropriate heat exchangers at appropriate
points in the design, the disclosed isothermal systems provide a
method that allows the exhaust from the expander engine to flow
through the heat exchangers to supply all the superheat for the
vapor flowing from the boiler or compressor to the expander engine.
For a two-phase fluid, the gas from the expander that flows through
the heat exchanger still has enough heat left over to partially
preheat the feed liquid flowing to the boiler. This cannot be done
with an adiabatic expander, because the vapor exhaust from the
adiabatic expander is normally cooler than the superheat
temperature.
[0007] Another important feature of the isothermal engine is that
the same amount of gas can be expanded to much larger volumes than
the adiabatic machine, and this provides more output energy.
[0008] We can consider an example to compare the isothermal steam
engine with a Rankine cycle steam engine. Suppose we begin with
liquid water and boil it at 400 K (127.degree. C.). If one kilogram
(0.731 m.sup.3) per second of steam flows from the boiler at a
pressure of 2.455 bar and is superheated to 800 K (527.degree. C.),
the power produced by an isothermal expander is defined (for an
ideal gas) by
W=P.sub.sV.sub.sln(V.sub.e/V.sub.s)
where P.sub.s is the pressure of the superheated gas (same as the
boiler pressure), V.sub.s is the volume of the superheated gas, and
V.sub.e is the volume of the expanded gas flowing out of the
expander. The "ln" is the natural log function. The volume V.sub.s
is 1.462 m.sup.3 (since the temperature is twice as high as the
boiling temperature at constant pressure). If we let the gas expand
in the isothermal expander to the condenser pressure, 0.03531 bar,
the vapor volume will be 101.65 m.sup.3, and the power will be
1.522 MW. The efficiency will be 38.77%.
[0009] For an adiabatic expander, the power is defined by
W=(P.sub.sV.sub.s-P.sub.sV.sub.s)/(1-.gamma.)
where .gamma. is the ratio of specific heats of the gas. For this
example, we let .gamma.=1.32. If we let the superheated gas expand
adiabatically to P.sub.e=0.03531 bar (same as in the isothermal
case), the volume will be only 36.35 m.sup.3. The power will be
0.72 MW. This is only 47% of the power that the isothermal system
put out. The isothermal case requires 15% more heat input, but it
uses that heat more efficiently. The efficiency of the adiabatic
(Rankine) cycle is 21.16%.
[0010] For an ideal gas, the internal energy depends on only on the
temperature. Thus, all the heat that is input to the isothermal
engine is used to generate power as it maintains the gas
temperature at a constant value (no change in internal energy of
the gas). Then, when the gas is exhausted from the expander, it is
still at the same temperature as the input temperature, and its
energy can be used to superheat the boiler vapor in the
counter-flow heat exchanger as its temperature theoretically drops
down to the boiler temperature. In an actual machine, we would want
the input heat to the isothermal engine to be at a little higher
temperature than the superheat temperature in order to provide the
temperature differential to cause adequate heat flow.
[0011] For the adiabatic case, after the gas expands to 36.35
m.sup.3, its temperature is only 286 K, which is too cold to supply
any heat to superheat the gas flowing out of the boiler.
[0012] The following table gives some calculated values for the
performance of the isothermal heat engine that uses steam as the
working fluid. These calculations were made by a computer program
called "Isoengine.exe." For comparison, the next-to-the-last column
gives the efficiency of an ordinary Rankine cycle steam engine. The
last column gives the performance of a Rankine cycle steam engine
with single reheat. The values in the table are theoretical values,
but the comparison between the isothermal engine and the Rankine
steam engines is valid. The power values are for a flow of one
kilogram per second of steam. The values in the Rankine columns
were calculated with a single gamma value and constant heat
capacity of the steam, which provide slightly inconsistent values,
since the gamma varies with temperature and pressure.
TABLE-US-00001 TABLE I Isothermal Rankine Boiler Condenser
Superheat Engine Cycle Rankine Temperature Temperature Temperature
Power Efficiency Eff. Cycle with (Degrees C.) (Degrees C.) (Degrees
C.) (MW) (%) (%) Reheat, Eff. 80 27 90 0.446 15.53 9.81 10.52 127
27 227 0.951 28.35 16.05 17.82 127 27 727 1.903 44.18 23.70 25.10
200 27 700 2.577 52.47 27.68 30.21 300 27 800 2.760 56.80 25.66
27.98 300 27 1000 3.276 60.94 27.46 29.61 200 27 1000 3.371 59.10
31.15 33.39 300 27 1200 3.900 64.36 28.95 30.93 22 12 27 0.095 3.68
2.66 22 12 127 0.126 4.86 3.28 22 12 227 0.158 6.00 3.82 22 12 480
0.237 8.77 4.90 22 12 800 0.339 12.05 5.88
[0013] The first row in the table represents values that would be
appropriate for a system that uses heat from a solar pond where the
temperature of the pond might be 90.degree. C.
[0014] The last five rows are for OTEC applications. No
multi-staging is involved. Efficiencies could be higher if
multi-stages were used. The Rankine cycle with reheat is not listed
for these five rows, because the temperature differences are too
small to use reheat.
[0015] Using a system that has isothermal compression and expansion
of single-phase gases provides performances that are even better
than isothermal system of the two-phase fluids, such as water-steam
(Rankine cycle). Air can be used as the working fluid. Helium has
high heat transfer properties and might be used. It is used in
Stirling engines.
[0016] Table II gives some calculations of performance for this
design that were made by a program called "Isotherm5.exe." Again,
these are theoretical calculations that do not include friction and
thermal conduction losses. For each item in the table, the air
pressure at the entrance to the isothermal compressor is 10 bar,
the temperature is 27.degree. C., and the volume is 1 cubic meter
per second. The air is compressed in the compressor to 0.2
m.sup.3.
TABLE-US-00002 TABLE II Superheat Temperature Power Output
Efficiency (Degrees C.) (MW) (%) 100 0.3916 19.57 200 0.9281 36.58
300 1.4650 47.64 400 2.0010 55.40 500 2.5375 61.19 600 3.0740 65.65
700 3.6105 69.17 800 4.1470 72.04 900 4.6835 74.43 1000 5.2199
76.43 1200 6.2929 79.63
[0017] Note that at the same temperatures of superheat, the
efficiencies for this device with isothermal compressor and
isothermal expander are significantly higher than those for the
device that has a boiler and an isothermal expander, as shown in
Table I. In fact, when the single-phase simulations were run with
the computer program, the efficiencies turned out to be Carnot
efficiencies. When friction and heat conduction losses are
included, the efficiencies will be less, but they should still be
higher than the devices in Table I, when losses are included in
those calculations.
[0018] It is therefore an object of the present invention to
provide an economical means of producing power using isothermal
compressors and isothermal expanders.
[0019] It is another object of the present invention to utilize
solar energy or other heat sources to provide energy to generate
electrical power using isothermal compression and expansion
engines.
[0020] It is another object of the present invention to utilize
solar energy or other heat sources to provide energy to generate
electrical power using a boiler and an isothermal expansion
engine.
[0021] It is another object of the present invention to utilize
solar energy or other heat sources to provide the heat required to
maintain near-isothermal conditions in isothermal expanders.
[0022] It is another object of the present invention to utilize the
hot exhausts gas from an isothermal expander to superheat the
compressed gas from an isothermal compressor in a counter-flow heat
exchanger.
[0023] It is another object of the present invention to utilize the
hot steam, or other two-phase working fluid, that exhausts from an
isothermal expander to superheat the vapor from a boiler in a
counter-flow heat exchanger.
[0024] It is another object of the present invention to provide
means for reducing mechanical losses in the compression and
expansion devices.
[0025] It is another object of the present invention to provide
methods to effectively produce approximate isothermal compression
and expansion of gases.
[0026] Other objects, advantages and novel features, and further
scope of applicability of the present invention will be set forth
in part in the detailed description to follow, taken in conjunction
with the accompanying drawings, and in part will become apparent to
those skilled in the art upon examination of the following, or may
be learned by practice of the invention. The objects and advantages
of the invention may be realized and attained by means of the
instrumentalities and combinations particularly pointed out in the
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The accompanying drawings, which are incorporated into and
form a part of the specification, illustrate embodiments of the
present invention and, together with the description, serve to
explain the principles of the invention. The drawings are only for
the purpose of illustrating preferred embodiments of the invention
and are not to be construed as limiting the invention. In the
drawings:
[0028] FIG. 1 is a schematic side view of an embodiment of the
present invention showing an isothermal compressor, an isothermal
expander, a counter-flow heat exchanger, a heater, and a
cooler.
[0029] FIG. 2 is a schematic side view of an embodiment of the
present invention that illustrates the use of a boiler,
counter-flow heat exchangers, an isothermal expander, a heater, and
a condenser.
[0030] FIG. 3 is a schematic side sectional view of an isothermal
compressor or isothermal expander, which has a piston in a cylinder
and has tapered plates that transfer heat to and from the gas.
[0031] FIG. 4 is a schematic isometric view of tapered concentric
circular forms for increasing surface contact with gases for
isothermal compressors and expanders.
[0032] FIG. 5 is an artists conception of an inside top view of a
rotating piston engine.
[0033] FIG. 6 is a schematic top view of a modified rotating piston
engine featuring tapered plates for isothermal operation.
[0034] FIG. 7 is a schematic end view of an embodiment of the
present invention showing the stator blades of an isothermal
turbine.
[0035] FIG. 8 is a schematic end view of a rotor blade of an
isothermal turbine.
[0036] FIG. 9 is a side view schematic of a bellows compressor
and/or expander.
DETAILED DESCRIPTION OF THE INVENTION
Single-Phase Gas Isothermal Heat Engine
[0037] FIG. 1 shows a layout for the single-phase gas isothermal
engine system. The gas is compressed in the isothermal compressor.
In order to keep the gas at constant temperature, a cooler is
necessary, since compression of a gas tends to heat it.
[0038] For efficient heat transfer, the cooler can supply a liquid
to channels beneath the surfaces in the compressor. The liquid
evaporates as it removes heat from the surfaces. The vapor flows to
the cooler, where it is condensed and returned to the
compressor.
[0039] For adequate heat flow, the heater should supply heat at
slightly higher temperature than the isothermal temperature of the
expander, and the cooler should supply a fluid that is at slightly
lower temperature than the compressor isothermal temperature.
[0040] In FIG. 1, the isothermal compressor 120 draws air (or other
gas) in through pipe 126 and compresses it. The compressed gas from
the isothermal compressor then flows through the counter-flow heat
exchanger 122, where it is heated by the exhaust from the
isothermal expander 123. After the gas leaves the heat exchanger,
it flows through the isothermal expander 123 to produce power,
which drives electrical generator 130. The exhaust gas from the
isothermal expander flows back through the counter-flow heat
exchanger 122 and returns to the isothermal compressor 120 to
repeat the cycle.
[0041] For this design, the cooler 128, keeps the compressor cool.
The cooler could use water-cooling, evaporative cooling, or even
ambient air to provide a means to dispose of the heat. The
isothermal expander is kept hot by heater 127. The heat could be
supplied by solar energy or other heat source.
Steam Isothermal Power Generator
[0042] An isothermal expander can be used to produce power with
steam (or other working fluid). In FIG. 2, steam is produced in
boiler 140. The steam flows through a counter-flow heat exchanger
141, which superheats the steam. From there, the steam flows
through an isothermal expander 142, which produces power by the
steam expansion and drives the generator 148. Since the expander is
isothermal, there would be no problem with steam condensation.
After the steam leaves the expander, it flows back through the
counter-flow heat exchanger 141 where its temperature decreases as
it provides heat to superheat the steam coming from the boiler.
[0043] The steam still has sufficient heat to preheat the boiler
feed water in the counter-flow heat exchanger 143. The steam is
then condensed in the condenser 144. The condensate is then pumped
by pump 146 back into the boiler 140 through counter-flow heat
exchanger 143.
[0044] Even though the engine is called "isothermal," in order to
have heat transfer into the expanding steam, the fluid flowing from
the heater 147 is at a higher temperature than the "isothermal"
temperature. The steam flowing out of the isothermal engine 142 is
hotter than the steam coming from the counter-flow heat exchanger
141.
Designs for Isothermal Compressors and Expanders
[0045] In my patent application Ser. No. 11/739,580 for the
invention entitled "Water Extraction from Air and Desalination,"
some designs for isothermal compressors and expanders are
described. Some of the drawings and descriptions are repeated here
in order to show the kinds of isothermal engines can be used to
keep the gases close to isothermal.
[0046] FIG. 3 is a schematic that illustrates an isothermal
compressor or expander. In order to increase heat transfer from the
gas to the metal, the metal surface area is greatly increased by
placing components such as tapered plates 22 on the front of the
piston 21 and on the bottom of the isothermal engine cylinder 20,
leaving channels for gas flow. (We refer to the piston and cylinder
as an "isothermal engine," since it performs as a compressor or an
expander). These components could have flat surfaces as shown in
the diagram, or they could have circular concentric configurations
(FIG. 4).
[0047] In operation as a compressor, as the piston 21 in the
isothermal engine 20 moves upward, it draws in air (or other gas)
through check valve 26. When the piston reaches its maximum height,
valve 26 closes, and the piston is forced downward, compressing the
gas. As the gas is compressed, it tends to increase in temperature,
but the tapered plates absorb the heat of the gas. Since the heat
capacity of the metal plates is about 2000 times as great as the
gas (per unit volume), the plates' temperature does not rise very
much during one half cycle.
[0048] When the piston has traveled down far enough to provide the
appropriate pressure the gas, check valve 36 opens to allow the gas
to flow out. The piston continues to move downward to force the
compressed gas out.
[0049] In operation as an expander, check valve 26 is replaced by a
controlled valve. As the piston 21 in the isothermal engine 20
moves upward, it draws in air (or other gas) through controlled
valve 26. When the piston reaches the designed height, valve 26
closes, and the piston continues to rise, expanding the gas and
extracting energy from the gas. As the gas is expanded, it tends to
decrease in temperature, but the tapered plates provide heat for
the gas. When the piston 21 moves downward, it forces the gas out
through check valve 36.
[0050] For the compressor, the tapered plates can have interior
channels in which a cooling fluid can flow. The cooling fluid could
be a liquid that evaporates to absorb the heat. For the tapered
plates 22, the fluid would have to be delivered and retrieved
through channels in the piston rod 27. The fluid can be delivered
to tapered plates 23 through channels in the cylinder. Calculations
show that the gas will remain near isothermal during both
compression and expansion, since the gas has close proximity to the
plates for heat transfer, and the motion of the plates create
turbulence that further enhance heat transfer.
[0051] For the expander, heating fluids are required. The heating
fluids could be gas or liquid, or they could be vapor that
condenses to a liquid in the channels of the tapered plates to
release the heat of condensation.
[0052] In this document, components that are used to increase the
surface area in contact with the gas are mostly referred to as
"tapered plates," because it is easy to illustrate the tapered
plates in the drawings. In many applications, it may be better to
use tapered concentric circular forms that are approximately
cylindrical. FIG. 4 is a schematic drawing showing the tapered
concentric circular forms 38 mounted on a base 39. The circular
forms would fit better in a cylinder such as 20 in FIG. 3 than flat
plates. The tapered plates 23 of FIG. 3 could actually be the
tapered concentric circular forms 38. Similar circular forms could
be attached to piston 21 in FIG. 3. The radii of the upper circular
forms and the lower circular forms must be defined so that the
circular forms fit together as the piston descends.
More Efficient Compressors and Expanders
[0053] One of the main sources of inefficiency for a compressor or
expander that is needed for the isothermal engine is sliding
friction of the piston. I have a U.S. Pat. No. 6,401,686 on a
device that is often referred to as "MECH," which stands for motor,
expander, compressor, and hydraulics. Since it uses rolling
friction between two rotating pistons rather than sliding friction
of a standard piston engine, the friction losses are much less. The
rotating pistons do not touch the cylinder walls. There is sliding
friction on the ends of the pistons, but this can be relatively
small by making the pistons long compared to the diameter.
[0054] It is well known that rolling friction is only about 1/100
as large as sliding friction. A MECH prototype demonstrated only 8%
as much energy loss as a comparable size piston engine. It provides
an engine with unprecedented economy for producing water from the
air or for desalinating seawater.
[0055] FIG. 5 is an artist's conception of a MECH engine 65 with
the end plate removed. One can see how the two rotating pistons 66
roll together at the contact line 67. It could be used as a
compressor or expander. Cavities 68 and 69 within the engine 65 are
locations in which gases are compressed or expanded. Similar
cavities are present on the other side of the engine next to the
other rotating piston.
[0056] FIG. 6 shows a top view of a compressor/expander that is
similar to a MECH engine in that it has two rotating surfaces that
roll together. It is designed to be an isothermal compressor or
expander. The MECH compressor already has one advantage over
standard compressors for isothermal compression: it has larger
surface areas of the cylinder walls and piston surfaces for
absorbing heat during compression and for returning heat to the gas
during expansion. The rotating pistons rotate almost 180 degrees in
one direction and then reverse directions for almost 180 degrees.
The pistons do not touch the cylinder walls. Sliding friction
occurs only at the ends of the pistons where they meet the ends of
the cylinders. The seal to prevent gas leakage is formed at the
rolling contact point between the two pistons.
[0057] FIG. 6 is a schematic top view of a modified MECH
compressor. Cylinders 75 are machined out of a block 70. Each
rotating piston 71 consists of a hollow half-cylinder that is open
on one side. The half-cylinder is connected to the shaft 77 by
partition 74. Tapered plates 72, similar to those in FIG. 3 are
placed inside the half-cylinder 71. (The drawing shows a top view
of the plates, whereas FIG. 3 shows the plates edge-on). The top
and bottom of the rotating cylinder are closed with half-circle
plates; they are not shown, because they are on the near end and
far end of the half-cylinder (above and below the page). When the
right piston rotates to the right and the left piston rotates to
the left, the upper tapered plates will move into the volume where
stationary tapered plates 73 are located and will fit between the
stationary plates. The gas in the spaces will be compressed and
squeezed out (for a compressor) the exhaust/intake pipes 76. At the
same time, gas will be drawn into the bottom half of the engine
through the pipes 78. When it rotates the other direction, gas in
the bottom half will be compressed. For an expander, the gas is
drawn in, expanded, and pushed out.
[0058] The tapered plates provide large surface areas for the
transfer of heat to and from the gas. The motion of the tapered
plates relative to the stationary plates causes gas turbulence in
the small gaps between them, and this enhances heat flow.
[0059] In order for the expander or compressor of FIG. 6 to perform
isothermally, heating or cooling fluid needs to be supplied to the
surfaces inside the device. To supply heating or cooling fluid to
the rotating tapered plates 72, the fluid can flow through an axial
hole in the center of the shaft 77 and flow through channels in the
rotating plates to cool or heat the rotating plates. After the
fluid flows through the channels, it would flow back to near the
other end of the shaft 77 and enter a hole in the shaft that would
take the fluid out the other end of the shaft. The stationary
plates 73 can receive fluid through the separator 79. The walls can
have fluid channels on the outside.
[0060] Instead of flat tapered plates, this embodiment of the
invention could use tapered concentric circular forms as described
above and illustrated in FIG. 4. In this case, the circular forms
would not be complete circles, but would be partial circular
configurations.
Isothermal Turbines
[0061] In an isothermal turbine expander, the heating fluid can
flow through the turbine walls, stator blades, and rotating blades.
FIG. 7 is an expander. Although there are cases in which the
heating fluid can be a liquid or a gas, in the following
discussion, the heating fluid will enter as a vapor and will
condense to release the latent heat of condensation. FIG. 7 is a
schematic drawing showing the stator blades and the flow paths of
the heating fluid. The hot vapor flows in the inlet pipe 161 into
the top of the turbine 160 and flows through a vapor channel 162 on
the upper half of the turbine. It flows through channels (not
shown) within the upper stator blades 163 toward the center of the
turbine. The turbine shaft 169 is at the center of the turbine.
Part of the vapor condenses and releases the latent heat of
condensation. The condensed liquid and the remaining vapor flow
into the vapor and liquid channel 164.
[0062] From there, the vapor and liquid flow to the lower stator
blades 165 and flow through channels in those blades. In the stator
blade channels, more of the vapor condenses. The liquid and the
remaining vapor flow into the liquid channel 166 on the lower half
of the turbine. They return to the heating fluid boiler (not shown)
through the condensed liquid outlet 167. After boiling, the vapor
returns again to the isothermal expander turbine.
[0063] For an isothermal turbine compressor, the geometry looks
much like the expander of FIG. 7. The cooling liquid enters from
the top 161. It must be designed so that the liquid will be
directed into each of the upper stator blades. As the liquid flows
down through channels in the blades, some of it evaporates and
provides cooling by the latent heat of evaporation. The vapor and
the remaining liquid flow to the vapor and liquid channel near the
center of the turbine. Appropriate guides must be designed to
direct liquid into each of the lower stator blades. The vapor flows
along with the liquid. More liquid vaporizes in the lower stator
blade channels.
[0064] Finally, the vapor and any remaining liquid flow out the
bottom and flow back to a cooler, which condenses the vapor to a
liquid. The liquid is pumped back to the turbine compressor to
repeat the cycle.
[0065] Alternatively, the liquid can be pumped into the bottom of
the compressor. As it flows up through the lower stator blades, it
boils. The vapor it creates blows liquid as a mist up through the
rest of the system. The mist droplets strike surfaces and
evaporate, removing heat and continuing the process of blowing
liquid droplets up through the upper blades.
[0066] If the stator blades do not provide sufficient heat removal
for the compressor, the rotating blades can also be designed to
receive liquid that evaporates and removes heat. The liquid enters
one end of the shaft that holds the turbine blades. The liquid then
flows through a channel in the shaft until it reaches the channels
in the blades. As it flows through the blade channels, it
evaporates and removes heat. The vapor flows back to the shaft and
flows through another channel in the shaft to the other end of the
shaft and then flows back to the cooler.
[0067] It is not that simple for the isothermal expander turbine.
If vapor is put into the rotating blades, it condenses to a liquid,
which has high density. Centrifugal force causes the liquid to move
to the tips of the blades. It would require high pressure to force
the liquid back to the shaft against the centrifugal force. The
density of the liquid can effectively be reduced by mixing it with
the vapor. By supplying more vapor than is necessary to deliver the
required heat, the extra vapor will flow back to the shaft through
a small-diameter channel and will carry a mist of liquid with
it.
[0068] A schematic drawing of a single rotating turbine blade 180
for an expanding turbine is shown in FIG. 8. Hot vapor flows from
one end of shaft 181 through channel 182 inside the shaft 181 to
the vapor channel 183 and flows through vapor channel 183 in the
blade. Part of the vapor condenses in the vapor channel and
releases heat to keep the blade hot. The condensed liquid flows by
centrifugal force to the space 184 near the end of the blade. The
vapor at high pressure is forced to flow through the small-diameter
liquid and vapor return pipe 185 at high speed back to the shaft
and into the liquid and vapor output channel 186. Since it is
flowing at high velocity, it will carry a mist of liquid with it.
The vapor and the liquid will flow through the channel 186 to the
other end of the shaft, where they will flow into a coupling that
takes the vapor and liquid back to the boiler.
[0069] Another alternative would be to use a liquid to transfer
heat to the rotating blades. The liquid flowing from the shaft to
the tip of the blade would provide the pressure to push the liquid
back to the shaft. The liquid flowing back to the shaft would be
slightly denser than the liquid flowing toward the tip, because it
is cooler. Extra pressure in the input channel would be
required.
[0070] In order to enhance the heat transfer between the turbine
blades and the gas, the blades should probably be closer together
and be wider than blades in standard turbines.
Other Isothermal Designs
[0071] FIG. 9 shows a compressor/expander design that incorporates
bellows 83 to compress and expand gas. The bellows is connected to
the top 80 and to a base 85. Push rod 81 moves the top up and down.
The purpose of the displacer 84 is to push out as much gas as
possible when the bellows is compressed as far as possible. gas
flows in and out of pipe 86.
[0072] For an isothermal compressor, the tapered plates like those
of FIG. 3 can be connected to the displacer 84 and to the base 85.
Rather than use flat tapered plates, it would probably be better to
use tapered concentric circular forms as illustrated in FIG. 4.
[0073] If we can increase the efficiency of standard power
generating plants by replacing the adiabatic engines with
isothermal engines, it would reduce the release of greenhouse gases
into the atmosphere. For solar thermal power plants, the isothermal
engines would produce more power for the same size solar
collectors.
* * * * *