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Publication numberUS20080264062 A1
Publication typeApplication
Application numberUS 12/104,797
Publication dateOct 30, 2008
Filing dateApr 17, 2008
Priority dateApr 26, 2007
Also published asUS20090260361, WO2008134283A2, WO2008134283A3
Publication number104797, 12104797, US 2008/0264062 A1, US 2008/264062 A1, US 20080264062 A1, US 20080264062A1, US 2008264062 A1, US 2008264062A1, US-A1-20080264062, US-A1-2008264062, US2008/0264062A1, US2008/264062A1, US20080264062 A1, US20080264062A1, US2008264062 A1, US2008264062A1
InventorsMelvin L. Prueitt
Original AssigneePrueitt Melvin L
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Isothermal power
US 20080264062 A1
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.
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Claims(25)
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

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

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.

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.

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

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.

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.

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.

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° C.). If one kilogram (0.731 m3) per second of steam flows from the boiler at a pressure of 2.455 bar and is superheated to 800 K (527° C.), the power produced by an isothermal expander is defined (for an ideal gas) by


W=P s V sln(V e /V s)

where Ps is the pressure of the superheated gas (same as the boiler pressure), Vs is the volume of the superheated gas, and Ve is the volume of the expanded gas flowing out of the expander. The “ln” is the natural log function. The volume Vs is 1.462 m3 (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 m3, and the power will be 1.522 MW. The efficiency will be 38.77%.

For an adiabatic expander, the power is defined by


W=(P s V s −P s V s)/(1−γ)

where γ is the ratio of specific heats of the gas. For this example, we let γ=1.32. If we let the superheated gas expand adiabatically to Pe=0.03531 bar (same as in the isothermal case), the volume will be only 36.35 m3. 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%.

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.

For the adiabatic case, after the gas expands to 36.35 m3, its temperature is only 286 K, which is too cold to supply any heat to superheat the gas flowing out of the boiler.

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 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

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° C.

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.

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.

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° C., and the volume is 1 cubic meter per second. The air is compressed in the compressor to 0.2 m3.

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

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.

It is therefore an object of the present invention to provide an economical means of producing power using isothermal compressors and isothermal expanders.

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.

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.

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.

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.

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.

It is another object of the present invention to provide means for reducing mechanical losses in the compression and expansion devices.

It is another object of the present invention to provide methods to effectively produce approximate isothermal compression and expansion of gases.

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

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:

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.

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.

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.

FIG. 4 is a schematic isometric view of tapered concentric circular forms for increasing surface contact with gases for isothermal compressors and expanders.

FIG. 5 is an artists conception of an inside top view of a rotating piston engine.

FIG. 6 is a schematic top view of a modified rotating piston engine featuring tapered plates for isothermal operation.

FIG. 7 is a schematic end view of an embodiment of the present invention showing the stator blades of an isothermal turbine.

FIG. 8 is a schematic end view of a rotor blade of an isothermal turbine.

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

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.

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.

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.

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.

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

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.

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.

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

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.

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).

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.

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.

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.

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

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.

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.

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.

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US8037677Feb 5, 2010Oct 18, 2011Lightsail Energy, Inc.Compressed air energy storage system utilizing two-phase flow to facilitate heat exchange
US8061132Aug 25, 2010Nov 22, 2011Lightsail Energy, Inc.Compressed air energy storage system utilizing two-phase flow to facilitate heat exchange
US8065874Aug 25, 2010Nov 29, 2011Lightsale Energy, Inc.Compressed air energy storage system utilizing two-phase flow to facilitate heat exchange
US8146354Jan 28, 2010Apr 3, 2012Lightsail Energy, Inc.Compressed air energy storage system utilizing two-phase flow to facilitate heat exchange
US8196395Jun 25, 2010Jun 12, 2012Lightsail Energy, Inc.Compressed air energy storage system utilizing two-phase flow to facilitate heat exchange
US8240142Aug 2, 2011Aug 14, 2012Lightsail Energy Inc.Compressed air energy storage system utilizing two-phase flow to facilitate heat exchange
US8656712Oct 3, 2008Feb 25, 2014Isentropic LimitedEnergy storage
WO2010035891A1 *Sep 24, 2009Apr 1, 2010Sanden CorporationFluid machine
WO2010135123A2 *May 13, 2010Nov 25, 2010Renewable Thermodynamics, LlcExternally heated engine
Classifications
U.S. Classification60/670, 60/671
International ClassificationF01K27/00, F01K25/00
Cooperative ClassificationF01K27/00
European ClassificationF01K27/00