Patent Application
20110265837
The present invention generally relates to a rotating heat exchanger. More particularly, the present invention pertains to a rotating heat exchanger for use with a device to extract energy from a temperature differential.
In 2007, U.S. coal, nuclear and natural gas fueled power plants generated 3,700 billion kilowatt hours (kWh) of electricity. All of these power plants utilize a heat source to generate high pressure, super heated steam to rotate a steam turbine. In general, to function properly, steam turbines require steam on the order of 300° C. to 500° C. and 3 to 8 mega Pascals (Mpa) of pressure. However, after all usable heat energy has been extracted by the turbines, a significant amount of ‘low-grade waste heat’ remains—most of which is expelled into the environment via cooling towers, rivers or the ocean. In 2007, these power plants produced nearly 6,837 billion kWh of low-grade waste heat. Unfortunately, while a variety of energy generating systems have been proposed to make use of this low-grade heat, none of these systems have proven to be economically feasible.
In addition, even in situations in which higher temperature differentials are available, conventional heat engines suffer from a number of disadvantages. Specifically, conventional heat engines typically include complex mechanical and control systems that are expensive to build and maintain.
Accordingly, it is desirable to provide a system and device capable of overcoming the disadvantages described herein at least to some extent.
The foregoing needs are met, to a great extent, by the present invention, wherein in one respect a device and system to simplify the extraction of energy from a temperature differential is provided.
An embodiment of the present invention pertains to a system for generating power from a low grade heat source. The system includes a heat source inlet, heat sink inlet, heat exchanger unit, and a heat engine. The heat source inlet conveys a flow of a heated fluid into the system. The heat sink inlet conveys a flow of a cooled fluid into the system. The heat exchanger unit is configured to rotate. A portion of the heat exchanger unit alternates between thermal contact with the heated fluid and thermal contact with the cooled fluid in response to being rotated. The heat engine is configured to generate power in response to the heat exchanger unit being rotated between the heat source and the heat sink.
Another embodiment of the present invention relates to a power plant having a system for generating power from a low grade heat source. This includes a heat source inlet, heat sink inlet, heat exchanger unit, and a heat engine. The heat source inlet conveys a flow of a heated fluid into the system. The heat sink inlet conveys a flow of a cooled fluid into the system. The heat exchanger unit is configured to rotate. A portion of the heat exchanger unit alternates between thermal contact with the heated fluid and thermal contact with the cooled fluid in response to being rotated. The heat engine is configured to generate power in response to the heat exchanger unit being rotated between the heat source and the heat sink.
Another embodiment of the present invention pertains to a heat exchanger. The heat exchanger unit includes a heat source, heat sink, and a plurality of conduits. The heat source inlet is to convey a flow of a heated fluid to the heat exchanger. The heat sink inlet is to convey a flow of a cooled fluid to the heat exchanger. The plurality of conduits are disposed about a central axis of the heat exchanger. The plurality of conduits are configured to rotate in unison about the central axis. Each of the plurality of conduits alternate between thermal contact with the heated fluid and thermal contact with the cooled fluid in response to being rotated and the plurality of conduits are configured for thermal contact with a heat engine configured to generate energy in response to rotation of the plurality of conduits.
There has thus been outlined, rather broadly, certain embodiments of the invention in order that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention that will be described below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.
The present invention provides, in various embodiments, a rotary heat exchanger device and a system which utilizes the rotary heat exchanger device for generating energy across a relatively low temperature differential. For the purposes of this disclosure, the term, ‘low temperature differential’ refers to a temperature differential of about 1° C. to about 30° C. and the term, ‘low-grade waste heat’ refers to a heat source at about 35° C. to about 100° C. It is an advantage of one or more embodiments of the invention that the low-grade waste heat may be utilized to generate usable energy rather than being exhausted or rejected into the environment. In some embodiments, the rotary heat exchanger device is utilized to rotate a heat engine or a portion thereof between a heat source and a heat sink. In response to being subjected to the temperature differential between the heat source and the heat sink, the heat engine is configured to generate an amount of work. For the purposes of this disclosure, a heat engine includes any substance, device, or system capable of converting thermal energy into work. The work may be in the form of mechanical, electrical, or chemical energy. In general, suitable heat engines may operate by exploiting a chemical change, phase change, adsorption/desorption of a working fluid, thermoelectric material properties, and the like. Specific examples of suitable heat engines include a hydride compressor, sterling engine, thermoelectric generator, and the like. A particular example of a suitable hydride compressor includes a multi-stage hydride/hydrogen compressor or the like. The work output of the motor may be used directly and/or may be used to drive a generator.
Preferred embodiments of the invention will now be described with reference to the drawing figures, in which like reference numerals refer to like parts throughout.
As shown in
By way of example, in 2007, approximately 312,738 Megawatts (MW) of power was generated by coal-fired power plants in the United States. These coal-fired plants utilized the equivalent of 8486 cooling tower units. An embodiment of the present invention may be capable of producing 150 kilowatts (kW) of power per cooling tower unit or 1273 MW of additional power. Coal-fired plants emit approximately 2.11 pounds (lb) or 0.957 kilograms (kg) of CO2 per kWh of electricity. Accordingly, implementing an embodiment of this invention in coal-fired plants alone would offset 6.9 million metric tons of CO2 emissions. In terms of oil, this additional power is roughly equivalent to 10.9 million barrels of oil. These figures are based on coal-fired power generation in 2007 which may increase in the future. Furthermore, embodiments of the invention are suitable for use with other forms of power plants such as, for example, gas and oil-fired, nuclear, some forms of solar, and the like.
The rotary heat exchanger/heat engine system 12 according to a particular embodiment of the invention includes a heat engine 26 disposed within a rotary heat exchanger 28. The heat engine 26 includes any suitable heat engine. A particular example of a suitable heat engine includes a compressor 30 such as a metal hydride hydrogen compressor. A particular example of a suitable metal hydride hydrogen compressor is described in U.S. Pat. No. 5,623,987, titled MODULAR MANIFOLD GAS DELIVERY SYSTEM, the disclosure of which is incorporated herein in its entirety. The compressor 30 is configured to rotate relative to a heat source 32 and a heat sink 34. As described herein, by rotating the compressor 30 relative to the heat source 32 and the heat sink 34, one or more faces of the compressor 30 are subjected to a temperature that cycles between the temperature of the heat source 32 and the temperature of the heat sink 34. When cooled below a predetermined adsorption temperature, the metal hydride is configured to adsorb hydrogen gas. When warmed above a predetermined desorption temperature, the metal hydride is configured to release or desorb hydrogen. By configuring the metal hydride such that the predetermined adsorption temperature is above the temperature of the heat sink 34 and the predetermined desorption temperature is below the temperature of the heat source 32, hydrogen may be drawn in and expelled by rotating the compressor 30 relative to the heat source 32 and the heat sink 34. This creates a flow of relatively high pressure hydrogen between the metal hydride exposed to the heat source and the metal hydride exposed to the heat sink.
The metal hydride is disposed in a series of chambers, each chamber connected to the next via a one-way valve. In this manner, the pressure of the hydrogen may be increased stepwise at each chamber. For example, using a metal hydride configured to adsorb/release 2-3 volumes of hydrogen, the pressure may be increased from about 10 pounds per square inch (psi) (0.70 kilogram-force per square centimeter (kgf/cm2)) to about 8000 psi (562 kgf/cm2) in 6 to 10 stages. In a specific example using water at 122° F. (50° C.) as the heat source and returning water at 104° F. (40° C.) and having a total flow rate of about 2000 pounds/second (908 Liters/second), the pressure may be increased from about 550 psi (38.67 kgf/cm2) to about 800 psi (56.25 kgf/cm2) in about 3 to 5 stages.
This relatively high pressure hydrogen is supplied to a motor 36 to urge the motor 36 to rotate. Rotation of the motor 36 may be utilized directly, such as, for example to power a pump. In addition or alternatively, the rotation of the motor 36 may be utilized to turn a generator 38 configured to generate electricity.
To increase the surface area exposed to the flow of relatively hotter and cooler fluid, the plurality of conduits 60 are arranged at a perimeter of the generally cylindrically shaped rotating assembly 56. The distribution bells 48 and 50 direct the flow from/to the respective supply/outlet conduits. In a particular example, the distribution bells 48 and 50 increase the cross-sectional area of the supply/outlet conduits sufficiently to cover the diffuser rings 52 and 54. To isolate the flow of relatively hot fluid from the flow of relatively cool fluid, a partition 64 and 66 may be disposed respectively within the distribution bells 48 and 50. In another example, a plurality of manifold assemblies or the like may replace the distribution bells 48 and 50. For example, an inlet pipe may branch into several or a multitude of pipes that connect with ports disposed in the diffuser rings 52 or 54.
The diffuser rings 52 and 54 facilitate a smooth transition of flow from the distribution bells 48 and 50 to the plurality of conduits 60. In addition, as further described herein, the diffuser rings 52 and 54 may be configured to impart an angular momentum on the flow of fluid to urge the heat exchanger unit to rotate.
Various embodiments of the invention enjoy many advantages over conventional power generating systems. Some of these advantages include: 1) ability to generate power from heat sources conventionally viewed as ‘waste heat’; 2) reduction of mechanical complexity; 3) reduction or elimination of electro/mechanical control systems; 4) improved reliability; 5) provides direct rotational force and thus eliminates reciprocal movement; and 6) ability to operate at extremely high flow rates. In addition, it is to be noted that although particular examples of the inventive rotary heat exchanger/heat engine system 12 are capable of generating power from waste heat (e.g., low ΔT), in other examples, the rotary heat exchanger/heat engine system 12 is capable of generating power from relatively higher ΔT sources. When utilizing these relatively higher ΔT sources, the various embodiments of the invention continue to enjoy the benefits described herein.
In various examples, the motor 36 and/or the generator 38 may be secured to the shaft 80 to receive the output of the compressor 30 and/or the motor 36. In a particular example, the motor 36 is disposed in the rotary heat exchanger 28 and the shaft 80 transmits torque generated by the motor 36 to the generator 38 and/or a pump disposed outside the rotary heat exchanger 28.
The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.
