Patent Application
20170074121
The present disclosure relates to systems for recovering waste heat. More particularly, the present disclosure relates to waste heat energy recovery from the exhaust and coolant circuit of a power plant with an expansion device, such as a Roots-type expander.
Waste heat energy is necessarily produced in many processes that generate energy or convert energy into useful work, such as a power plant. Typically, such waste heat energy is released into the ambient environment. In one application, waste heat energy is generated from an internal combustion engine. Exhaust gases from the engine have a high temperature and pressure and are typically discharged into the ambient environment without any energy recovery process. Additional waste energy is developed within the power plant which is typically discharged via a radiator without any energy recovery. Although some approaches have been introduced to recover waste energy and re-use the recovered energy in the same process or in separate processes, there is still demand for enhancing the efficiency of energy recovery in power generation systems, such as vehicle engines or electrical generators.
The present teachings include a power generation system for recovering waste heat energy from a power plant. In one aspect, the power plant may be configured as an internal combustion engine having a crankshaft. A coolant circuit may also be provided that extends through the internal combustion engine, wherein the coolant circuit may include a radiator and a coolant pump configured to circulate the coolant between the internal combustion engine and the radiator. The power generation system may also include a waste heat recovery circuit including an expansion device, such as a Roots-type fluid expander, configured to generate power at an output shaft by expanding a portion of the coolant and being configured to deliver the power back to the internal combustion engine crankshaft via the output shaft. The waste heat recovery circuit may also include a circulation pump configured to circulate the portion of the coolant between the expander and the coolant circuit. A condenser may also be provided to condense the portion of the coolant leaving the expander at least down to a saturated liquid.
In one example, the waste heat recovery circuit can be configured such that the circulation pump draws the portion of the coolant after the portion of the coolant has first passed through the internal combustion engine and returns the portion of the coolant at a location upstream of the radiator. In one example, the waste heat recovery circuit can be configured such that the circulation pump draws the portion of the coolant before the portion of the coolant has first passed through the internal combustion engine and returns the portion of the coolant at a location upstream of the radiator. The waste heat recovery circuit may also include additional heat sources, such as an EGR cooler and a post-turbine exhaust recovery system
The present teachings also include a method of recovering waste heat from a power plant. The method can include the steps of providing a liquid cooled power plant having a crankshaft, pumping a coolant with a fluid pump through a coolant circuit including the power plant, drawing a portion of the coolant from coolant circuit, heating the portion of the coolant with heat generated by the power plant, expanding the portion of the coolant with an expansion device, such as a Roots-type fluid expander, such that power is generated at an output shaft of the expander, delivering the power developed at the expander output shaft to the internal combustion engine crankshaft, condensing the coolant to at least a saturated liquid state, and returning the portion of the coolant to the coolant circuit.
A variety of additional aspects will be set forth in the description that follows. These aspects can relate to individual features and to combinations of features. 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 broad concepts upon which the embodiments disclosed herein are based.
Non-limiting and non-exhaustive embodiments are described with reference to the following figures, which are not necessarily drawn to scale, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.
Various embodiments will be described in detail with reference to the drawings, wherein like reference numerals represent like parts and assemblies throughout the several views. Reference to various embodiments does not limit the scope of the claims attached hereto. Additionally, any examples set forth in this specification are not intended to be limiting and merely set forth some of the many possible embodiments for the appended claims.
Referring to
The power plant 4 can be configured to employ a power-generation cycle, wherein the power plant 4 uses a specified amount of oxygen, which may be part of a stream of intake air, to generate power. The power plant 4 also generates waste heat such in the form of a high-temperature exhaust gas which is a byproduct of the power-generation cycle. The power plant also generates additional waste heat which is rejected through a radiator via a coolant. The coolant may be water or another fluid, or a mixture of water and another fluid, such as propylene glycol, ethylene glycol, and ethanol. In one example, the coolant is a mixture of 50 percent water and 50 percent glycol. In one embodiment, the power plant 4 is an internal combustion (IC) engine, such as a spark-ignition or compression-ignition type (i.e. diesel engine) which combusts a mixture of fuel and air to generate power. In one embodiment, the power plant 4 may be or a fuel cell which converts chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent. Where the power plant 4 is located within a vehicle 1, additional waste heat energy is produced when a compression release engine brake (i.e. Jake brake or Jacobs brake) system is utilized. In such a system, significant heat energy in the form of compressed air is produced and discharged through the exhaust.
Referring to
In one aspect, the WHRC 100 can include an expansion device 20 to transform the heat energy in the coolant to power that can be transferred back to the power plant 4. Types of expansion devices 20 usable with WAHRC 100 are non-volumetric expanders, such as screw and scroll-type expanders 20, and volumetric expanders, such as Roots-type expanders 20. Roots-type expanders 20 useful for use with the concepts disclosed herein are fully described in Patent Cooperation Treaty (PCT) international Application Publication Number WO 2013/30774; Patent Cooperation Treaty (PCT) International Application Publication Number WO 2014/117159; and Indian Provisional Application No. 4024/DEL/2014, filed Dec. 30, 2014 and entitled OPTIMAL EXPANDER OUTLET PORTING, the entireties of which are incorporated herein by reference. As used herein, the term “Roots-type expander” is intended to mean a volumetric or positive displacement fluid expansion device provided with a pair of intermeshed, non-contacting helical rotors that rotate synchronously in opposite directions such that a working fluid passing there through undergoes a pressure drop which imparts rotational movement onto the rotors, thus creating mechanical work at an output shaft 21. As described in WO 2014/117159, the Roots-type expander may have one or more pairs of rotors 30, 32 for single stage or multiple stage operation in which the working fluid is sequentially routed from one stage to the next.
Roots-type expanders 20 are advantageous for use with some of the architectures disclosed below because they remain fully operable with either single phase or two-phase working fluid flow. As such, the entering heated coolant can have a vapor quality (i.e. mass fraction of coolant that is a vapor) of anywhere between 0% to 100% (i.e. between being in a fully liquid state to being superheated) without adversely affecting the expander 20. In fact, the efficiency of the expander 20 can be expected to increase where two-phase flow is present, as the liquid portion of the flow acts to seal the necessary clearance gaps between the rotors and the housing within which the rotors are disposed.
Still referring to
After leaving the expansion device 20, the expanded coolant 110 is then condensed in a cooling zone 112 to at least a saturated liquid state to form a condensed coolant 114. The cooling zone 112 for condensing the expanded coolant 110 can take a variety of forms, as explained herein. For example, the expanded coolant 110 can be condensed by reintroducing the expanded coolant 110 into the main coolant flow stream. This approach is most valuable when the expanded coolant 110 flow is a relatively small fraction of the total coolant flow through the power plant 4. The expanded coolant 110 can also be condensed by passing the expanded coolant 110 through an air cooled condenser or by passing the expanded coolant 110 through a liquid cooled recuperator. Where an air cooled condenser is used, the air through the condenser can be provided by a cooling fan of the power plant 4. Where a recuperator is used, the coolant stream 102 can be used to provide a cooling flow stream to the recuperator. Other means for condensing the expanded coolant 110 may also be utilized.
This general process is shown in the flow chart at
With reference to
As presented, the power plant 4 is liquid cooled by a coolant circuit. As such, a coolant passes through the power plant 4 via an inlet 8 and an outlet 9, and then flows to a radiator 13. Where the power plant 4 is an internal combustion engine, the coolant flows through and maintains the temperature of the engine block of the engine. A fan 14, driven by the power plant 4, may be provided to draw air through the radiator 13 such that the temperature of the coolant is reduced as it flows through the radiator 13. The fan 14 may be mechanically driven through crankshaft 5 or a hydraulic circuit, or may be driven with an electric motor. The coolant flow through the radiator 13 is controlled by a coolant pump 15 and a thermostat 16. In one example, the thermostat 16 is configured to open at a coolant temperature of 90° C. An expansion tank 17 may also be provided in the coolant circuit.
As described previously, the power generation system 3 may also include the WHRC 100 which may include an expansion device 20 in fluid communication with the coolant circuit 102. In one architecture option, a circuit 102a may be utilized in which a portion of the coolant is directed towards the expansion device 20 at a location downstream of the power plant 4. In this configuration, the coolant that is ultimately delivered to the expansion device 20 is first heated by the power plant 4 itself. In an alternative architecture option, a circuit 102b may be utilized in which a portion of the coolant is directed towards the expansion device 20 at a location upstream of the power plant 4. In this configuration, the coolant that is ultimately delivered to the expansion device 20 bypasses the power plant 4 and is therefore not first heated by the power plant 4. Although it is conceivable that circuits 102a and 102b could be used together in some configurations,
As shown, two distinct heat exchanging zones 104a and 104b are presented in the schematic shown at
With continued reference to
As will be appreciated from the disclosures herein, the portion of coolant that passes through the expansion device 20 is essentially subjected to a Rankine cycle in which the power plant 4 and/or the heat exchanging zone(s) 104 (104a, 104b) heat the coolant; the circulation pumps 15, 23 act as the pressure source; the expansion device 20 acts as the expansion source; and the condenser 19, the radiator 13, and/or the main coolant flow, act as the sources of temperature reduction to ensure the coolant is returned to a saturated liquid. Thus, as the coolant passes through the expander 20, the coolant undergoes expansion and a corresponding temperature and pressure drop to generate power or useful work at shaft 21.
In one aspect, the fluid expansion device 20 may also include a power transmission link 22 configured to transfer useful work from the fluid expansion device 20. Such mechanical work generated by the rotation of the output shaft 21 of the fluid expansion device 20 may be delivered to any elements or devices as necessary. For example, the output shaft 21 can be directly or indirectly coupled to the power plant 4, another fluid expansion device, a turbocharger, a supercharger, a generator, a motor, a hydraulic pump, and/or a pneumatic pump via gears, belts, chains or other structures. In some examples, the recuperated energy may be accumulated in an energy storage device, such as a battery or an accumulator, and the energy storage device may release the stored energy on demand. In other examples, the recovered energy may return to the power plant 4 by mechanically coupling the output shaft of the device 21 to the crankshaft 5 or any other power input location of the power plant 4. The power transmission link 22 may also be employed between the volumetric fluid expander 20 and the power plant 4 to provide a better match between rotational speeds of the power plant 4 and the output shaft 21 of the expander 20. In some embodiments, the power transmission link 22 can be configured as a planetary gear set to provide two outputs for the power plant 4 and a generator.
As mentioned previously, the heat exchanging zone 104 may include one or more zones (e.g 104a, 104b) and each of the zones may include one or more heat sources or heat exchangers to heat the coolant prior to entering the expansion device 20. One example of a suitable heat exchanger is a charge air cooler 12 which utilizes the coolant to cool the intake air after being compressed, for example by a supercharger or a turbocharger. Another example of a suitable heat exchanger is an exhaust gas recovery (EGR) cooler 10 which utilizes the coolant to cool a portion of the exhaust gases before reintroduction into the intake air. Yet another example is an exhaust heat exchanger 26 in which the coolant can be utilized to absorb heat energy directly from the power plant exhaust. A post-turbine boiler 11 may also be utilized in which heat energy is captured by the coolant from an exhaust stream leaving a turbocharger.
Also, a heat exchanger in the form of a recuperator 24 may also be used. In such an application, the recuperator 24 can be located downstream of the expansion device 20 and can act to transfer heat from the expanded to coolant to either of the first and second heat exchanging zones 104a, 104b. Where used, the recuperator 24 will act to cool the expanded coolant and can be sized such that a condenser 19 does not also need to be placed in the system or can be sized to work in conjunction with a condenser 19. The recuperator 24 allows for some of the remaining heat energy in the coolant leaving the expander 20 to be recaptured rather than being lost in the condenser 19 and/or being dissipated through the radiator 13.
Another example of a heat exchanger is an exhaust manifold cooler 25 which utilizes the coolant to cool the exhaust gases leaving the exhaust manifold. An exhaust manifold cooler is useful in applications where the leaving exhaust gas temperature from the power plant 4 exceeds temperature limits of downstream components, for example turbochargers and emissions components. Recent demands for performance improvements of internal combustion engines have resulted in smaller displacement engines producing exhaust at relatively high temperatures, for example temperatures of 1000° C. or more. As emissions components (e.g. catalysts) and turbochargers require significantly lower temperatures, for example temperatures below 700° C., an exhaust manifold cooler can be provided to address this circumstance. As mentioned previously, although several types of heat exchangers are discussed in the previous paragraphs, other heat exchangers may be used without departing from the concepts herein, including those heat exchangers transfer heat to the coolant from sources outside of the power plant 4.
Myriad possible arrangements exist when applying the above identified heat exchangers to the various optional architectures shown in
It is noted that Architectures 7-9 may be particularly suited to applications where a vehicle 1 is a passenger car and the power plant utilized gasoline as the fuel. Architectures 19 and 21 may be best suited for heavy duty applications while Architectures 20 and 22 may be best suited for medium duty applications involving diesel power plants.
Not only can the system shown in
In a first operational configuration of Architecture 13, and further detailed at
In a second operational configuration of Architecture 13, and further detailed at
In an operational configuration of Architecture 14, and further detailed at
In a first operational configuration of Architecture 15, and further detailed at
In a first operational configuration Architecture 16, and further detailed at
In a second operational configuration of Architecture 16, and further detailed at
In a third operational configuration of Architecture 16, and further detailed at
In the operational configurations shown in
The performance characteristics of the above described operational configurations are summarized in Table 2 below:
With respect to the “Baseline” architecture noted in Table 2, it is noted that this configuration is simply a standard power plant 4 with an EGR cooler 10 that does not include the use of a WHRC 100. All of the other configurations are modeled using the same power plant and EGR cooler as the baseline configuration, which has an associated heat load of 292 kW. It is also noted that the highest net power results are generally associated for WHRC 100 configurations implementing higher coolant pressures. For example, the highest net power calculated was the result of utilizing a superheated coolant entering the expander 20 at a pressure of 25 bar, as illustrated at
It is also noted that creating a superheated coolant in the WHRC 100 also functions to increase the engine heat load (see configurations of
As the disclosed WHRC 100 utilizes the existing engine coolant as the working fluid, the need to provide a separate working fluid circuit in the system is entirely eliminated. This feature allows the WHRC 100 to be easily added to existing power plan designs. As the WHRC 100 works in cooperation with a standard power plant 4, the resulting system is able to operate at a low speed which minimizes costs and maximizes reliability with respect to coupling the WHRC 100 to the power plant drivetrain. Additionally, a Roots-type expander 20 is robust to liquid and can be expected to operate reliably. Furthermore, by using the existing engine coolant, the WHRC 100 will have no unexpected freeze issues since the WHRC 100 is entirely compatible with coolant antifreeze strategies used in internal combustion engines.
In comparison to steam based and other types of systems which pressurize working fluids up to and well beyond pressures of 100 bar, the disclosed WHRC 100 operates as a relatively low pressure system which minimizes costs and maximizes reliability. As importantly, low operating pressures enable a number of operational options for the WHRC 100. For example, the low operating pressures allow for the safer use of ethanol as a coolant, alone or in a mixture of water. Low operating pressures also allow for the controlled boiling of glycol based coolants such that degradation of the glycol is avoided, which would be unavoidable in high pressure/temperature applications. Additionally, low operating pressures allow a coolant mixture of glycol and water to be boiled such that a portion of the glycol remains as a liquid. The liquid glycol can act as a highly effective sealant between the expander housing and the rotors disposed therein which increases operational efficiency of the expander 20. Yet another benefit of low pressure operation is that the parasitic losses associated with the circulation pumps can be minimized.
Although multiple architectures and operational configurations are presented herein, it is noted that the concepts disclosed herein are not limited to only the disclosed architectures and configurations. Rather, the concept of utilizing the coolant as a working fluid with a Roots-type expander, or another type of energy extraction device, may be implemented in a wide variety of additional approaches. Additionally, the implementation of the disclosed WHRC 100 system does not require the power plant 4 to be specifically designed or redesigned to accommodate the WHRC 100. However, the disclosure is not limited only to such an application and it is fully contemplated in the disclosure that a power plant 4 could be designed to operate optimally with the disclosed WHRC 100. For example, the operating conditions of the power plant 4 (e.g. EGR cooler leaving exhaust temperature and the power plant coolant inlet temperature) could be treated as open variables in the design of the power plant 4, rather than as the fixed values used in the models above. Additionally, other types of equipment could be used for heat transfer to the working fluid or coolant, such as specialized cooling jackets.
The various embodiments described above are provided by way of illustration only and should not be construed to limit the claims attached hereto. Those skilled in the art will readily recognize various modifications and changes that may be made without following the example embodiments and applications illustrated and described herein, and without departing from the true spirit and scope of the disclosure.
This application is being filed on Mar. 3, 2015, as a PCT International Patent application and claims priority to U.S. Patent Application Ser. No. 61/947,389 filed on Mar. 3, 2014; U.S. Patent Application Ser. No. 62/065,433 filed on Oct. 7, 2014; U.S. Patent Application Ser. No. 62/081,514 filed on Nov. 18, 2014; and U.S. Patent Application No. 62/116,844 filed on Feb. 16, 2015, the disclosures of which are incorporated herein by reference in their entireties.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US15/18372 | 3/3/2015 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61947389 | Mar 2014 | US | |
| 62065433 | Oct 2014 | US | |
| 62081514 | Nov 2014 | US | |
| 62116844 | Feb 2015 | US |
