WASTE HEAT RECOVERY AND CONVERSION SYSTEM AND RELATED METHODS
Various embodiments of a waste heat recovery and conversion system are disclosed. In one exemplary embodiment, the waste heat recovery system may include a heat exchanger for transferring heat from a first fluid to a second fluid and a power conversion unit configured to convert the energy transferred from the first fluid to the second fluid into usable energy. The heat exchanger may include an outer duct defining an inlet and an outlet through which the first fluid flows in and out, respectively, of the outer duct. The heat exchanger may also include an inner duct disposed inside the outer duct and defining an inner channel inside the inner duct and an outer channel between an outer surface of the inner duct and an inner surface of the outer duct. The inner duct may define an internal flow channel through which the second fluid flows to exchange heat energy with the first fluid.
- 1-13. -13. (canceled)
- 14. A system for recovering waste heat from a heat source and converting the recovered waste heat into useable energy, the system comprising:
a heat exchanger configured to transfer heat from the heat source to a working fluid; an expander driven by the working fluid and configured to expand the working fluid; a generator-motor coupled to the expander; a compressor coupled to the generator-motor and configured to compress intake air; a condenser defining a fluid reservoir of the working fluid; and a pump disposed between the generator-motor and the compressor and configured to pump the working fluid from the fluid reservoir to the heat exchanger, wherein the heat exchanger, the expander, the fluid reservoir, and the pump comprise a thermodynamic loop that drives the generator-motor.
- View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
- 25. A system for recovering waste heat from a heat source and converting the recovered waste heat into useable energy, the system comprising:
a heat exchanger configured to transfer heat from the heat source to a working fluid; an expander driven by the working fluid and configured to expand the working fluid; a generator-motor coupled to the expander; a compressor coupled to the generator-motor and configured to compress intake air; a condenser defining a fluid reservoir of the working fluid; and wherein the expander, the generator-motor, the compressor, the pump, and the fluid reservoir are integrally formed inside a housing of the condenser.
- View Dependent Claims (26, 27, 28)
- 29. A system for recovering waste heat from a heat source and converting the recovered waste heat into useable energy, the system comprising:
a heat exchanger configured to transfer heat from the heat source to a working fluid; an expander driven by the working fluid and configured to expand the working fluid; a generator-motor coupled to the expander; a compressor coupled to the generator-motor and configured to compress intake air; a condenser defining a fluid reservoir of the working fluid; and wherein the expander, the generator-motor, the pump, and the compressor are mechanically coupled to a shaft.
- View Dependent Claims (30, 31, 32, 33)
This application claims the benefit of priority under 35 U.S.C § 119(e) of U.S. Provisional Application Nos. 61/457,995, filed Jul. 29, 2011, 61/457,996, filed Jul. 29, 2011, 61/457,997, filed Jul. 29, 2011, and 61/457,998, filed Jul. 29, 2011, all of which are incorporated herein by reference in their entirety.
Various embodiments of the present invention generally relate to a waste heat recovery system and related methods. In particular, certain exemplary embodiments relate to a waste heat recovery and/or power conversion system that can be integrated with a waste heat source.
A variety of industrial processes and/or thermodynamic engines discharge waste heat into the environment. For example, a typical combustion engine used for propulsion of a moving vessel (e.g., a locomotive, automotive, or marine vessel) or power production (e.g., diesel-electric generators) has the thermodynamic efficiency of generally less than 40%, Lower efficiencies may result when these engines are operated outside of their optimal operational conditions, such as, for example, idling, acceleration transients, and low- and high-power engine operations. The efficiency can be further decreased for engines with purely mechanical or unsophisticated fuel metering controls.
For most combustion engine applications, and under most operating conditions, 22% to 46% of the total energy of fuel used by a combustion engine is normally lost through exhaust gases and engine cooling, which represent waste heat discharged into the environment.
Thus, there may be a need for developing a heat recovery system and method for recovering and/or converting waste heat into useable energy. Recovering such waste heat and/or converting it into usable energy may increase efficiency, which results in fuel savings as well as reduction in pollutant emission and thermal discharge into the environment.
Accordingly, various exemplary embodiments of the present disclosure may provide an integral waste heat recovery and conversion system and related methods capable of reliably and cost-effectively recovering and converting waste heat energy. For example, certain exemplary embodiments provide modular high-pressure heat exchanger for extracting waste heat energy from various thermodynamic systems and an integral conversion system for ultimately transforming the extracted waste heat energy into electricity and/or other forms of usable energy.
One exemplary aspect may provide a scalable, modular waste heat energy recovery and integral conversion system configured to convert waste heat energy produced by any source that rejects thermal energy into the environment, to heat a working fluid circulating within modular high-pressure heat exchangers thermally and hydraulically coupled and integrated with power conversion unit (PCU) for efficient waste heat conversion into usable energy.
The working fluid can be a suitable fluid with thermal-physical properties that favor phase changes from sub-cooled liquid to superheated vapor when exposed to low-grade heat transfer any heat source fluid to the working fluid. The working fluid can also be a gas. In this case, the waste heat recovery and conversion system may simplified as components dedicated to condensation of the working fluid would no longer be required.
The modular heat exchangers, all together with the integrated waste heat conversion system, may be configured to match the ever changing thermodynamic parameters characterizing variable waste heat production sources, especially when these sources are represented by internal combustion engines.
Another aspect may utilize scalable and modular heat exchangers configured to pre-heat and super-heat the working fluid for expansion within the integral waste heat conversion system as non-invasive retrofit for internal combustion engines. In this case, the waste heat recovery and conversion system may be formed by universal, pre-heating interfaces coupling the waste heat source thermal-hydraulic system (i.e., pipes, stuck, ducts transporting waste heat fluid) to at least one turbine expander to a fast alternator and to a high-pressure pump dedicated to pressurize the working fluid, for the conversion of waste heat energy into electricity and other usable energy forms. As an example of usable energy forms, a compressor system may be coupled to the fast rotating components forming the integral power conversion system so as to provide compressed intake air to a combustion engine and increase its performance while reducing Particulate Matter formation at idling and intermediate power settings.
Although bottom cycle technologies dedicated to combustion engines generally show low efficiencies, high manufacturing cost, high maintenance costs, and low reliability, the present invention is intended to provide a solution to the low-reliability, and high-costs represented by similar technologies by relatively simple to manufacture high-pressure heat exchangers with geometries and materials that withstand the harsh conditions in which this equipment operates and that can be assembled as clusters of heat exchangers, or multiple modules, to match the waste heat source availability. The scalable, modular, and integral thermal-hydraulic connectivity feature of the waste heat recovery and conversion system characterizing the present invention allows retrofitting schemes that do not require heavy financing. Individual modules can be installed gradually and in a sequence wherein savings attained by the operation of each module over time can result in “self-financing” for the installation of additional modules up to matching the total waste heat source energy availability.
Waste heat energy transported, for example, by the fluid circulating in the cooling system and exhaust gas tubing of an industrial process or a combustion system heats up a suitable working fluid inside a modular heat exchanger in thermal contact with the fluid transporting waste heat energy without mixing with these fluid. By the modular heat exchanger, the working fluid expands by changing thermodynamic state from liquid to superheated vapor (for working fluid characterized by a system of liquid and vapor, or containing two-phases) within fluid-dynamically optimized channels derived internally the high-pressure heat exchanger.
The channels are formed by surfaces within the modular heat exchanger configured so as to increase the working fluid residence time and to enhance the working fluid thermal coupling with the fluid transporting waste heat energy. The residence time is increased by utilizing channel geometries that force the working fluid through pathways that increase turbulence while the working fluid accelerates as a result of its expansion through the channels and as a result of heat energy transfer from the high-pressure heat exchanger internal surfaces.
Furthermore, residence time is enhanced by configuring the working fluid and the fluid transporting waste heat energy so as to essentially swirl or rotate the working fluid and the fluid transporting waste heat energy while wetting and surrounding the surfaces forming the waste heat source system.
The thermal coupling between the working fluid and the fluid transporting waste heat energy occurs without mixing and is enhanced by utilizing suitable high thermal conductivity materials that form the support structures of the channels so as to make them capable of withstanding high-pressure, thermal stresses and mechanical deformation on all axes. As the working fluid travels through the modular heat exchanger, it becomes superheated and, depending on the selected working fluid, it may change phase from liquid to super heated vapor. At this point, the superheated working fluid exiting the modular heat exchanger may enter a series of modular pre-heating and modular heat exchangers so as to increase the waste heat energy transfer to the working fluid, for direct or indirect expansion of the superheated working fluid vapors within at least one set of turbine-alternator systems for the conversion of the working fluid energy into mechanical and electrical energy respectively.
As mentioned, depending on the application, the modular heat exchanger and waste heat conversion system formed by a turbine and alternator may be mechanically or thermal-hydraulically coupled to an air compressor system for the generation of compressed air. When compressed air is provided to the intake manifold of a combustion engine, the results are pollutant emission reductions and engine performance enhancement.
Finally, the working fluid exhausting from the turbine system is either cooled by heat exchangers thermally coupled with environmental fluid (i.e., gaseous single phase working fluid), or made to condense within a sudden-condensation chamber (i.e., liquid-vapor phase working fluid), thereby causing a vacuum at the turbine outlet and resulting in increased waste heat recovery and conversion system efficiency.
Certain exemplary embodiments of the present disclosure focus on bottom cycle applications and make its utilization commercially viable in the context of, for example, internal combustion engine applications. Also, various exemplary embodiments may provide the ability of the waste heat recovery and conversion system to be minimally invasive, with the high-pressure heat exchangers sufficiently rugged to withstand full flame immersion for operation in highly corrosive environments for a high-reliability over prolonged periods of time. Overall, the waste heat recovery and conversion system may efficiently transform low- and high-grade waste heat energy into re-usable energy without significantly interfering with the fluid-dynamic conditions characterizing the fluid transporting waste heat energy from the waste heat sources into the environment as the high-pressure pre-heating heat exchangers, and the superheating high-pressure heat exchangers are designed to reduce back pressure normally generated by drag forming between the heat source fluid and the surfaces of the high-pressure heat exchangers.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by the elements and combinations particularly pointed out in the appended claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention.
Reference will now be made in detail to the exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers or letters will be used throughout the drawings to refer to the same or like parts.
Various exemplary embodiments of the present disclosure provide a system and method for recovering waste heat from a heat source and converting it into useable energy. In some exemplary embodiments, the heat recovery system may be formed as a single modular system, where various components of the system are integrated into a single modular unit. For example, as will be described in more detail later, the waste heat recovery and conversion system utilizes a waste heat energy to heat a working fluid circulating within heat exchangers thermally and hydraulically coupled to an integrated power conversion system formed by one or more turbine expanders housed in a power conversion unit and coupled to energy conversion systems (e.g., an electric generator, a high-pressure pump, a clutch or direct mechanical coupler providing torque to drive a compressor or as a torque generator).
The working fluid may be any fluid having thermal-physical properties that favor phase changes from liquid to superheated vapor when exposed to a waste heat source. Alternatively, the waste heat recovery and conversion system may utilize a gaseous working fluid. In this case the integral power conversion unit may be configured to recirculate the gas after expansion in the expander turbine by substituting the high-pressure pump with a compressor/blower and by eliminating the condenser.
The heat exchange of present invention may be utilized to pre-heating and superheating the working fluid and as a mechanical and thermal hydraulic interface to decouple the vibrational and structural environment represented by the heat source from the structures of the heat exchangers. The heat exchangers may be formed by compact high-pressure heat exchanging surfaces containing channels for the circulation of the working fluid and provided with universal flanges for thermal-hydraulic coupling with the waste heat source. The heat exchangers may be modular and configured as stand-alone or clusters of heat exchanger systems all together with the power conversion system forming the integrated waste heat conversion system of the present invention and may be configured to tolerate the stressors generated by ever changing thermodynamic parameters characterizing variable waste heat production sources, especially when these sources are represented by internal combustion engines. To attain the advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, one aspect of the invention provides means to utilize the scalable modular heat exchanger and integral waste heat conversion systems for internal combustion engine applications, wherein the waste heat recovery and conversion system may be formed by coupling at least one turbine expander to an electric generator/motor and to an air compressor for the conversion of waste heat energy into electricity and compressed air respectively through a configuration that can be non-invasively retrofitted on existing combustion engine platforms, as well as to new combustion engines utilized for direct propulsion or for hybrid applications (e.g., diesel-electric vehicles, gas-electric vehicles, and stationary combustion-engine driven electric generator platforms).
As waste heat sources may be represented by different configurations utilizing various fluid for the rejection of waste heat energy into the environment, an objective of the present invention is to provide a universal, scalable, modular, waste heat recovery and integral conversion system for the conversion of various forms of waste heat energy into useful energy easily, with minimally invasively configurations highly adaptable to various waste heat sources requiring minimum maintenance. Depending on the application, the grade, or temperature, of the waste heat source (e.g., high-, intermediate-, low-grade) and mass-flow-rate of the fluid transporting waste heat energy for final rejection into the environment, the scalable modular heat exchanger and integral conversion system of the present invention may be coupled in parallel, in series, or any hybrid configuration (e.g., series and parallel). Similarly, the modules forming the embodiment of the invention may be scaled to directly match the waste heat source availability rating by employing a large single module, or clusters of smaller modules that all together match the total waste heat energy outputted from the waste heat source.
Heat source fluid 2 may be in the form of gas or liquid. Heat source fluid 2, transporting waste heat energy from heat source 1, is made to exchange its thermal energy with 1st Heat Exchanger 3 configured to pre-heat working fluid 4 prior to entering into the 2nd Heat exchanger 5 configured to superheat working fluid 4 while transiting within its channels. Working fluid 4 circulates in a closed-loop and does not mix with heat source fluid 2. 1st heat exchanger 3 and 2nd heat exchanger 5 may be configured with a flexible thermal-hydraulic and mechanical coupling to attenuate vibrational stressors induced by coupling of the heat exchangers with heat source 1, thereby providing an interface between the heat exchangers and the heat source to mitigate vibrational and thermal stressors. As heat source fluid 2 transfers its thermal energy to working fluid 4, heat source fluid 2 lowers its energy content for final discharge into the environment at lower temperatures.
The heat exchangers in pre-heating interface 3 may have sufficiently large heat transfer surfaces to directly obtain superheating of working fluid 4. If working fluid 4 is a liquid-vapor phase fluid, working fluid 4 may be in a sub-cooled state at the inlet of pre-heating interface 3. Depending on the thermodynamic state of heat source fluid 2, working fluid 4 may exit pre-heating interface 3 in a sub-cooled liquid, a mixed vapor-liquid, or superheated thermodynamic state.
Working fluid 4 exiting 1st heat exchanger 3 enters the 2nd heat exchanger 5 configured as a stand alone high pressure heat exchanger or as a cluster of modular heat exchangers, to provide additional thermal energy exchange between heat source fluid 2 and working fluid 4 through its extended heat transfer surfaces. Superheated working fluid 4 exiting 2nd heat exchanger 5 then enters a power conversion unit (PCU) 6 for expansion within a set of turbines or expander for conversion of heat source 1 into electricity, compressed air, and/or any other usable energy forms while providing pumping power for working fluid 4 to circulate through the closed-loop formed by coupling 1st heat exchanger, 2nd heat exchanger and the PCU 6. PCU 6 may be integral as its expander, pump, alternator/motor, torque coupler and condenser may be configured as a single piece within the same housing. This configuration is particularly suitable for applications dedicated to internal combustion engines coupled to electric generators as the waste heat recovery and conversion system of the present disclosure converts a portion of the recovered waste heat energy into electricity for ready electrical voltage and phase coupling with the electrical generators and equipment driven by the internal combustion engine.
The conversion of a portion of the waste heat energy into compressed air may be required to satisfy pollutant reduction features of the waste heat recovery and conversion system. Converting a portion of the recovered heat source 1, when applied to combustion engines, into compressed air provides the combustion engine with excess oxygen (air) when the engine operates at low Revolution per Minute (RpM) and/or at high transient loads. Most internal combustion engines operating in these conditions manifest high pollutant emissions. Therefore, providing compressed air as a result of waste heat recovery and conversion results in pollutant emission reductions, while enhancing the combustion engine performance at low RpM and during transients in which the combustion engine duty cycle is changed from low-to high-loads.
As a result of thermal energy transfer with working fluid 4, heat source fluid 2, exiting the 2nd heat exchanger 5, may be characterized by lower temperatures, thereby allowing for Emission Gas Recirculation methodologies and further decrease pollutant emissions.
For waste heat sources characterized by non air-breathing processes (e.g., requiring compressed air to improve their pollutant emissions), the modular heat exchangers forming 1st and 2nd heat exchangers 3 and 5 respectively may be configured to increase working fluid 4 energy content for expansion within an expander, for example, formed by a turbine-generator system for electricity production only. For applications requiring conversion of waste heat energy into mechanical torque, working fluid 4 may be expanded through an expander (i.e. turbines) coupled, for example, via gear-box or through a magnetic or hydraulic clutch, to provide shaft work. As working fluid 4 exits the expander system it enters a condenser 7 integrated with the volumes and surfaces formed by the power conversion unit housing so as to provide compact thermal-coupling and a vacuum or a low-pressure state at the exit of the expander. This low-pressure thermodynamic state may be induced by condensation caused by thermal exchange with the compressor fluid (e.g., air). Additionally, auxiliary cooling may be provided by external cooling sources as it will be shown in
To summarize the exemplary embodiments shown in
The working fluid may be represented by water which may be used to describe the exemplary embodiments of the invention. It should be understood, however, that any other fluid having suitable thermodynamic properties may be used alternatively or additionally. For example, for configurations wherein working fluid is in a gaseous form, condenser 7 may be configured to function as an intercooler while the high-pressure pump integrated with the power conversion unit may be configured to operate as a re-circulator or blower.
With reference to
As heat source fluid 2 transfers energy to channels 10 by thermal transfer via channel fins 11 and/or via outer and inner jacket walls 17 and 18 respectively, without mixing with working fluid 4, the thermodynamic state of working fluid changes from inlet 8 to outlet 9 as it expands and accelerates within channel 10. Depending on the thermodynamic state and mass-flow-rate of heat source fluid 2, and on the dimensions and materials forming the high-pressure heat exchanger of 1st heat exchanger 3, working fluid 4 may exit outlet 9 as sub-cooled liquid single phase, as liquid-vapor two-phase, or as superheated vapor single phase. Superheated fluid 21 denotes a single-phase superheated fluid. If working fluid 4 is gaseous, the gas or mixed gases increase their energy content from inlet 8 to outlet 9. As the heat source may be formed by a system inducing vibrational stressors, flexible member flange 14 allows for mechanical coupling with flexible member 12 whose vibrational decoupling of flange 15 allows for mechanical and thermal-hydraulic coupling with modular 2nd heat exchanger(s) 5 without transferring structural loads and vibrational stresses associated with the system representing heat source 1.
With reference to
To minimize drag and reduce backpressure 2nd heat exchanger 5 may be configured to feature aerodynamically optimized drag reducing entrance 24 and end 25. Additionally, to further reduce aerodynamic drag, 2nd heat exchanger 5 may be configured to be “floating” within a heat source duct 20 by providing hydraulic and mechanical connections through flexible hydraulic couplers 19. The heat source duct 20 may be provided with the heat source equipment (i.e., exhaust gas manifolds for applications involving waste heat recovery and conversion from combustion engines). Alternatively, a heat source 1 hydraulic conduit may be formed by configuring hydraulic conduit 20 with flanges 29 for modular coupling with clusters of 2nd heat exchangers 5 thermal-hydraulically connected in series, parallel or mixed series-parallel configurations. As working fluid 4 enters 2nd heat exchanger 5 at inlet 8, its energy content increases due to thermal exchange with heat source fluid 2 and becomes superheated while transiting through channels 22. Outlet 9 and inlet 8 are interchangeable, thus allowing for various counter-flow, parallel-flow, or hybrid parallel-counter-flow configurations.
With reference to
By hydraulically coupling the power conversion unit 6 to the 1st and 2nd heat exchangers the thermodynamic loop shown in
Thermal transfer between the condensing working fluid 33 and the thermodynamic environment represented by condenser 7 may be induced by circulating the working fluid via condenser auxiliary cooling 49 (e.g., radiator system), and/or by thermal transfer with a second fluid 41 (e.g., air) circulating, for example, via compressor 40 in combination or independently of the cooling impact induced by enhancing condenser cooling fins 48. In this configuration, prior to entering compressor 40, secondary fluid 41 provides cooling to condenser 7 through fins 48.
The electric generator/motor 36 may be configured to mechanically couple expander 34 through shaft 35. When the integral power conversion unit 6 is configured to recover and convert waste heat source 1 energy from combustion engines, the compressor 40 may provide features to reduce pollutant emissions while increasing engine efficiency. In this configurations there are combustion engine operating conditions (e.g., low thermal loads) that may reduce waste heat source 1 ability to provide sufficient waste heat energy to drive expander 34. To ensure compressor 40 maintains the function of compressing secondary fluid 41, the electric generator/motor may be actively configured to switch from “generator mode” to “motor mode”, thereby electrically driving compressor 40. Compressor 40 represents a usable form of converted waste heat source. Shaft 35 may be coupled to compressor 40 or any other torque requiring auxiliary system by shaft coupler 39 which may involve various types of clutch systems (e.g., electrical, hydraulic, magnetic, friction and/or centrifugally driven).
Cooling of the electric generator/motor 36 may be accomplished by means comprising the generator/motor cooling system 38. These cooling means may be particularly required for high compact “fast RpM” generator/motors and may independently or jointly include a third cooling fluid 47 to transfer thermal energy with the electric generator/motor 36 and its electric interface 43 by electric interface cooling fins 45, and/or thermal transfer to cooling fluid circulating in the condenser 7 (i.e., via condenser cooling auxiliary 49), and/or thermal transfer with secondary fluid 41 by electric interface cooling fins 46.
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.