WO2016187429A1

WO2016187429A1 - Configuration for optimized waste heat recovery

Info

Publication number: WO2016187429A1
Application number: PCT/US2016/033284
Authority: WO
Inventors: JR. Bradley Karl WRIGHT; William Nicholas Eybergen; Matthew James FORTINI
Original assignee: Eaton Corporation
Priority date: 2015-05-19
Filing date: 2016-05-19
Publication date: 2016-11-24

Abstract

A system for recovering energy from exhaust air and controlling intake air includes a power plant, a compressor, a volumetric energy recovery device, and a heat exchanging device. The compressor is arranged upstream of the power plant and pressurizes air to produce the intake air for the power plant. The volumetric energy recovery device is arranged downstream of the power plant and receives the exhaust air. The volumetric energy recovery device operates to generate useful work as the exhaust air undergoes expansion therethrough. The heat exchanging device is selectively operable to transfer heat from the intake air to the exhaust air and reduce a temperature of the intake air.

Description

CONFIGURATION FOR OPTFMIZED WASTE HEAT RECOVERY

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is being filed on May 19, 2016 as a PCT International Patent Application and claims the benefit of U.S. Patent Application Serial No. 62/163,678, filed on May 19, 2015, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

[0002] The present disclosure relates to a volumetric fluid expander used for recovering energy from exhaust gas.

BACKGROUND

[0003] Some types of power plant systems release hot exhaust air produced by an internal combustion engine or a fuel cell directly into the atmosphere as waste heat. At an air intake, some of these systems employ a supercharger to pressurize the intake air supplied to the power plant. In operation, the supercharger compresses the intake air and in turn increases the temperature of the intake air, thereby reducing the efficiency of the power plant. Improvements to power plant systems that reduce exhaust waste heat and pressurized intake air temperatures are desired.

SUMMARY

[0004] In general terms, this disclosure is directed to an exhaust gas energy recovery system with a heat exchanging device. Various aspects are described in this disclosure, which include, but are not limited to, the following aspects

[0005] One aspect is a system of recovering energy from exhaust air and controlling intake air. The system may include a power plant, a compressor, a volumetric energy recovery device, and a heat exchanging device. The power plant has an air intake and an exhaust outlet. The air intake is configured to receive the intake air, and the exhaust outlet is configured to discharge the exhaust air. The compressor is arranged upstream of the power plant and configured to pressurize air to produce the intake air for the power plant. The volumetric energy recovery device is arranged downstream of the power plant and configured to receive the exhaust air. The volumetric energy recovery device is operable to generate useful work as the exhaust air undergoes expansion therethrough. The heat exchanging device is selectively operable through closed loop feedback to transfer heat from the intake air to the exhaust air and reduce a temperature of the intake air to enable optimized performance of the system.

[0006] In some examples, the heat exchanging device is arranged downstream of the compressor and upstream of the volumetric energy recovery device, and selectively operable to transfer heat from the pressurized air to the exhaust air. In other examples, the heat exchanging device is arranged downstream of the compressor and downstream of the volumetric energy recovery device, and selectively operable to transfer heat from the pressurized air to the exhaust air expanded by the volumetric energy recovery device. In yet other examples, the heat exchanging device is arranged upstream of the compressor and downstream of the volumetric energy recovery device, and selectively operable to transfer heat from ambient air to the exhaust air expanded by the volumetric energy recovery device.

[0007] The energy recovery device may include a housing having an inlet port configured to admit exhaust air and an outlet port configured to discharge a conditioned exhaust airflow stream, the conditioned exhaust air stream having a lower pressure and lower temperature than the exhaust airflow stream. The volumetric energy recovery device further includes first and second twisted meshed rotors rotatably disposed in the housing and configured to expand the relatively high-pressure exhaust air into the relatively low-pressure cool exhaust air, wherein each rotor has a plurality of lobes and an output shaft operatively connected to one of the first and second rotors and rotated by the exhaust air.

[0008] Another aspect is a method for recovering energy from exhaust gas air, the method comprising: compressing, at a compressor, ambient air to form a compressed airflow stream; receiving, at a power plant, the compressed airflow stream, wherein the compressed airflow stream is conditioned at a temperature useable by the power plant; receiving, at a volumetric energy recovery device, an exhaust airflow stream; and transferring heat, using a heat exchanger, from the compressed airflow stream to the exhaust airflow stream. In some examples, the step of transferring heat, using the heat exchanger, from the compressed airflow stream to the exhaust airflow stream is performed before receiving, at the volumetric energy recovery device, the exhaust airflow stream. In other examples, the step of transferring heat, using the heat exchanger, from the compressed airflow stream to the exhaust airflow stream is performed after receiving, at the volumetric energy recovery device, the exhaust airflow stream. [0009] Yet another aspect is a method for recovering energy from exhaust gas air, the method comprising: receiving, at a volumetric energy recovery device, an exhaust airflow stream; transferring heat, using a heat exchanger, from ambient air to the exhaust airflow stream; compressing the heat-transferred ambient air to form a compressed airflow stream; and receiving, at a power plant, the compressed airflow stream, wherein the compressed airflow stream is conditioned at a temperature useable by the power plant.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a schematic diagram of a first example of an exhaust gas energy recovery system using a heat exchanging device.

[0011] Figure 1 A is a schematic diagram of the exhaust gas energy recovery system of Figure 1 with an additional heat exchanger and an inlet bypass included.

[0012] Figure IB is a schematic diagram of the exhaust gas energy recovery system of Figure 1 with an additional heat exchanger and an inlet and outlet bypass included.

[0013] Figure 2 is a schematic diagram of a second example of an exhaust gas energy recovery system using a heat exchanging device.

[0014] Figure 3 is a schematic diagram of a third example of an exhaust gas energy recovery system using a heat exchanging device.

[0015] Figure 4 is a schematic cross-section side view of an expander used in the system shown in Figures 1-3.

[0016] Figure 5 is a schematic perspective view of the expander shown in figure 4.

[0017] Figure 6 is a schematic showing geometric parameters of the rotors of the expander shown in figure 4.

[0018] Figure 7 is a schematic cross-sectional view of the expander shown in figure 4.

[0019] Figure 8 is a schematic view of an exemplary air-to-air heat exchanger for the heat exchanging device of Figures 1-3.

[0020] Figure 9 is a schematic view of an exemplary air-to-liquid heat exchanger for the heat exchanging device of Figures 1-3.

[0021] Figure 10 is a schematic view of an exemplary heat pipe for the heat exchanging device of Figures 1-3.

DETAILED DESCRIPTION

[0022] Various examples 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 examples does not limit the scope of the present disclosure. Additionally, any examples set forth in this specification are not intended to be limiting and merely set forth some of the many possible options for practicing the various aspects disclosed herein.

[0023] Referring to the drawings, the figures illustrate a system in which a volumetric energy recovery device 20 having dual interleaved twisted rotors extracts energy from a waste heat stream from a power source that would otherwise be wasted. In some examples, the volumetric energy recovery device (expansion device or expander) 20 returns the extracted energy back to the power plant 52, via an output shaft 38 of the device 20. Accordingly, the volumetric energy recovery device 20 operates to increase the overall efficiency of the power plant 52. Alternatively, extracted energy can be stored in an accumulator or battery or used to power other components in the system such as driving a pump or a motor. As shown below, the volumetric energy recovery device 20 can return the extracted energy to a Roots-style blower or compressor 22 via the output shaft 38 so as to increase the efficiency of the compressor 22.

[0024] Figure 1 is a schematic diagram of a first example of an exhaust gas energy recovery system 100 using a heat exchanging device 18. The system 100 includes a power plant 52, an expansion device 20, a heat exchanging device 18, and a Roots-style blower or compressor 22.

[0025] The power plant 52 operates to generate mechanical or electrical power. The power plant 52 includes an air intake port into which air 106 at temperature T3 is drawn, and an exhaust port from which air 108 at temperature T4 is discharged. In some examples, the power plant 52 is a fuel cell. The fuel cell can include an air conditioning system that controls the temperature T4 of the exhaust air 106. In other examples, the power plant 52 can be of any type, such as an internal combustion engine.

[0026] The expansion device 20 operates to receive the working air to generate mechanical work therefrom. The working air undergoes expansion and increase in temperature as the working air passes through the device 20. In some examples, as shown in Figure 1, the extracted energy from the working air is returned to the compressor 22 via the output shaft 38, thereby increasing the efficiency of the compressor 22. Alternatively, the expansion device 20 and the compressor 22 can be integrally structured for efficiency. Examples of this integral structure are disclosed in U.S. Patent Application No.

61/787,834, the entirety of which is hereby incorporated by reference. [0027] In other examples, energy created from the mechanical work produced by the expansion device 20 can be stored in a storage device 118 such as an accumulator or a battery. Alternatively, it can be used to drive a pump or a motor, or used to power other components of the system 100. The expansion device 20 is described in further detail with reference to FIGS. 4-7.

[0028] The heat exchanging device 18 can be of any type, such as liquid-to-air heat exchangers, air-to-air heat exchangers, or heat pipes. Examples of the heat exchanging device 18 are described in further detail with reference to FIGS. 8-10.

[0029] The Roots-style blower or compressor 22 operates to pressurize the working air, thereby increasing the temperature thereof. Examples of the Roots-style blower are found in U.S. Patent No. 7,488, 164, the entirety of which is hereby incorporated by reference.

[0030] Referring to Figure 1, the power plant 52 discharges exhaust air 108 at temperature T4, and draws intake air 106 at temperature T3. In some examples, the power plant 52 includes an air conditioning system therein for reducing the temperature of the exhaust air 108. The system 100 is configured to manage the intake air 106 in a manner that the pressure and temperature of the intake air 106 falls within predetermined ranges suitable for the power plant 52.

[0031] Ambient air 102 enters the compressor 22 at temperature Tl and atmospheric pressure. The compressor 22 pressurizes the ambient air 102 to a level useable by the power plant 52. The compressor 22 that has drawn the ambient air 102 discharges the pressurized air 104 at temperature T2, which is greater than the temperature Tl .

[0032] The heat exchanging device 18 is arranged downstream of the compressor 22 so as to cool down the air 104 into the intake air 106 at temperature T3, which is acceptable for the power plant 52. In some examples, the heat exchanging device 18 is selectively operated to reduce the temperature of the air 104 from T2 to T3. For example, in some cases where the temperature Tl of the intake air 102 is higher than a typical range of ambient temperature and, therefore, the compressor 22 produces the air 104 at the temperature T2 higher than a level acceptable for the power plant 52, the heat exchanging device 18 is controlled to be in operation to decrease the temperature T2 of the air 104 to the temperature T3 of the air 106, which falls within a range useable by the power plant 52. However, where the temperature T2 of the air 104 is acceptable as an intake air for the power plant 52, the heat exchanging device 18 is not operated so that the air 104 at the temperature T2 directly enters the power plant 52. [0033] The exhaust air 108 discharged from the power plant 52 has the temperature T4, which is lower than the temperature T2. In some examples, the exhaust air 108 is controlled to have the temperature T4 lower than T2. Therefore, in this example, the exhaust air 108 is used at the heat exchanging device 18 to transfer heat or energy from the air 104 to the exhaust air 108. After heat transfer, the heat exchanging device 18 discharges the air 110 at temperature T5 higher than T4.

[0034] The air 110 is then drawn into the expansion device 20. As shown in Figure 1, the expansion device 20 is connected to the compressor 22 via the output shaft 38, and thus the extracted mechanical energy is returned to the compressor 22, thereby improving the efficiency of the compressor 22. Alternatively, energy created from the mechanical work produced by the expansion device 20 can be stored in a storage device 118 such as an accumulator or a battery.

[0035] As described with reference to Figures 4-7, the expansion device 20 relies upon the pressure of the air 108 to rotate an output shaft, thereby creating mechanical energy while reducing the pressure and temperature of the air. Thus, the expansion device 20 produces cooled air 112 at a temperature T6 that is lower than T5, and discharges the air 112 into the surroundings.

[0036] In this example, because the air 110 at the temperature T5, which is higher than the temperature T4 of the exhaust gas 108, is supplied to the expansion device 20, the expansion device 20 can generate greater mechanical work than one that would be created with the exhaust gas 108 at the temperature T4.

[0037] Figures 1 A and IB are schematic diagrams of a modified version of the exhaust gas energy recovery system 100 shown in Figure 1. As many of the concepts and features are similar to the first example shown in Figure 1, the description for the first example is hereby incorporated by reference for the second example. Where like or similar features or elements are shown, the same reference numbers will be used where possible. The following description for the second example will be limited primarily to the differences between the first and second examples.

[0038] In the examples shown, an optional intercooler 600 is provided between the compressor 22 and the heat exchanger 418. The intercooler 600 is a heat exchanger that can, for example, use coolant from the vehicle internal combustion engine cooling system to cool the air leaving the compressor 22 to a temperature lower than temperature T2 which will in turn maximize the temperature differential of the fluids entering heat exchanger 418. The intercooler 600 can also be an air-to-air heat exchanger that utilizes ambient air or air from another source and can also be configured to selectively utilize either air or liquid from within or without of the system as the cooling medium depending upon operating condition to achieve optimal performance of the system. The example shown in Figure 1 A also includes a second heat exchanging system including heat exchangers 518A, 518B and a pump 120 interconnected by lines 1 14, 1 16. A description of the configuration and operation of a system of this type is provided later in this specification and need not be further explained here, except to the extent that a bypass valve 130 is provided in the system to selectively divert some or all of the air leaving the compressor 22 and/or intercooler 600 (if provided) through the heat exchanger 518A. In the example shown at Figure 1 A, all of the exhaust leaving the power plant 52 passes through both heat exchanger 518B and heat exchanger 418. In the example shown at Figure IB, a second bypass valve 132 is provided that enables the some or all of the exhaust air from the power plant 52 to be bypassed into the heat exchanger 518B and around the heat exchanger 418. Accordingly, valves 130 and 132 can be operated together to control the percentage of flow that is directed through heat exchanger to optimal performance of the system based on closed loop feedback. Closed loop feedback can be provided, at least in part, by the various pressure and temperature sensors located throughout the system, as illustrated at Figures 1-3. In those drawings, a circle with a "P" inside represents a pressure sensor while a circle with a "T" inside represents a

temperature sensor. Although valves 130 and 132 are shown as being three-way control valves, two two-way control valves could also be utilized instead of each three-way valve.

[0039] Figure 2 is a schematic diagram of a second example of an exhaust gas energy recovery system 200 using a heat exchanging device 18. As in the first example, the system 200 includes the power plant 52, the expansion device 20, the heat exchanging device 18, and the Roots-style blower or compressor 22. As many of the concepts and features are similar to the first example shown in Figure 1, the description for the first example is hereby incorporated by reference for the second example. Where like or similar features or elements are shown, the same reference numbers will be used where possible. The following description for the second example will be limited primarily to the differences between the first and second examples.

[0040] In this example, the expansion device 20 is arranged upstream of the heat exchanging device 18 and directly connected to the power plant 52 to receive exhaust air 208 from the power plant 52. The power plant 52 emits exhaust air 208 at temperature T4, which flows into the expansion device 20. Subsequently, the expansion device 20 generates mechanical work, which, in some examples, can be supplied to the compressor 22, while discharging the air 210 at temperature T5 lower than T4.

[0041] In this example, the heat exchanging device 18 utilizes the air 210 at the temperature T5, which is lower than T4. Therefore, the heat exchanging device 18 transfers more heat or energy from the air 204 to the air 210, compared with the first example, in which the heat exchanging device 18 uses the exhaust air 108 at the temperature T4. Accordingly, the heat exchanging device 18 in this example accomplishes greater temperature drop between the temperatures T2 and T3 than in the first example.

[0042] Figure 3 is a schematic diagram of a third example of an exhaust gas energy recovery system 300 using a heat exchanging device 18. As in the second example, the system 300 includes the power plant 52, the expansion device 20, the heat exchanging device 18, and the Roots-style blower or compressor 22. As many of the concepts and features are similar to the second example shown in Figure 2, the description for the second example is hereby incorporated by reference for the third example. Where like or similar features or elements are shown, the same reference numbers will be used where possible. The following description for the third example will be limited primarily to the differences between the second and third examples.

[0043] In contrast to the second example, the compressor 22 in this example is arranged downstream of the heat exchanging device 18 and directly connected to the power plant 52 to provide intake air 306 to the power plant 52. The heat exchanging device 18 transfers heat or energy from ambient air 302 to air 310, thereby discharging air 312 to the surroundings and air 304 flowing into the compressor 22. The temperature T6 of the air 312 is greater than the temperature T5 of the air 310, and the temperature T2 of the air 304 is lower than the temperature Tl of the ambient air 302.

[0044] In this example, the heat exchanging device 18 cools down the ambient air 302 from the temperature Tl to T2 before the air 304 is drawn into the compressor 22.

Accordingly, the lower temperature T2 of the air 304 leads to a decrease in power consumption by the compressor 22.

[0045] As in the first and second examples, the heat exchanging device 18 is selectively operated to reduce the temperature of the air 302 from Tl to T2, depending on the temperature Tl and/or the operational condition of the compressor 22. In some cases, for example, the temperature Tl of the intake air 102 is higher than a typical range of ambient temperature, and, therefore, the compressor 22 can produce the air 306 at the temperature T3 higher than a level acceptable for the power plant 52. In these cases, the heat exchanging device 18 operates to decrease the temperature Tl of the ambient air 302 to the temperature T2 of the air 304, and supply the cooled-down air 304 to the

compressor 22, so that the compressor 22 produces the intake air 306 at the temperature T3, which falls within a range useable by the power plant 52. However, where the temperature Tl of the ambient air 302 is sufficiently low, and/or where the compressor 22 is not in full operation, the heat exchanging device 18 can cease to operate, and allows the ambient air 302 to bypass so that the ambient air 302 is directly drawn into the compressor 22.

[0046] Figures 8-10 illustrate various examples of a heat exchanging device 18 employed in Figures 1-3. Figure 8 is a schematic view of an exemplary air-to-air heat exchanger 418. Figure 9 is a schematic view of an exemplary air-to-liquid heat exchanger 518. Figure 10 is a schematic view of an exemplary heat pipe 618.

[0047] As shown in Figure 8, the heat exchanging device 18 is configured as the air- to-air heat exchanger 418. The heat exchanger 418 operates to transfer heat or energy between two incoming airs with different temperatures. In some embodiments, the air-to- air heat exchanger 418 is more efficient than other exchangers having an independent circulation system, such as a pump. Because the heat exchanger 418 does not have such a circulation system, the heat exchanger 418 does not require additional power consumption. In some examples, the air-to-air heat exchanger 418 can be controlled to permit incoming airs to bypass so that heat transfer does not occur between the incoming airs.

[0048] As shown in Figure 9, the heat exchanging device 18 includes the air-to-liquid heat exchangers 518. In this example, the heat exchanging device 18 transfers heat or energy between incoming airs with different temperatures by circulating a working liquid through lines 114 and 116. By way of example, a first heat exchanger 518A operates to cool down an air passing therethrough by transferring heat from the incoming air to a liquid in the line 116, which has a lower temperature than the air. On the other hand, the liquid is heated by heat transfer at the heat exchanger 518A and sent back to a second heat exchanger 518B via the line 114. The second heat exchanger 518B operates to cool down the liquid passing therethrough by transferring heat from the liquid to an incoming air, which has a lower temperature than the liquid. The second heat exchanger 518B returns the cooled liquid to the first heat exchanger 518A via the line 116 and discharges the heated air.

[0049] In this example, the heat exchanging device 18 can employ an independent liquid circulation system or pump 120 for circulating the liquid in a loop. The pump 120 requires additional power consumption, as described above. In some examples, the pump 120 can be selectively controlled to operate so as to permit incoming airs to bypass the heat exchangers 518 without heat transfer.

[0050] As shown in Figure 10, the heat exchanging device 18 is configured as the heat pipe 618. The heat pipe 618 is made from thermal superconductors with a high heat transfer coefficient for boiling and condensation, and operates under the principles of thermal conductivity and phase transition to manage heat transfer between two solid interfaces. Various types of heat pipes can be employed, which is suitable for the systems described in Figures 1-3. In some examples, the heat pipe 618 can be controlled to permit incoming airs to bypass so that heat transfer does not occur between the incoming airs.

[0051] Figures 4-7 illustrate an expander used in the system shown in Figures 1-3. Figure 4 is a cross-sectional side view of an example of a volumetric fluid expander having features that are examples of aspects in accordance with the principles of the present disclosure. In general, the volumetric energy recovery device 20 relies upon the kinetic energy and static pressure of the working fluid 12-1 to rotate an output shaft 38. Where the device 20 is used in an expansion application, additional energy is extracted from the working fluid via fluid expansion. In such instances, the device 20 may be referred to as an expander or expansion device, as so presented in the following paragraphs. However, it is to be understood that the device 20 is not limited to applications where a working fluid is expanded across the device.

[0052] The expansion device 20 has a housing 22 with a fluid inlet 24 and a fluid outlet 26 through which the working fluid 12-1 undergoes a pressure drop to transfer energy to the output shaft 38. The inlet port 24 is configured to admit the working fluid 12-1 at a first pressure from the heat exchanger 18 (shown in Figures 1-3), whereas the outlet port 26 is configured to discharge the working fluid 12-2 at a second pressure lower than the first pressure. The output shaft 38 is driven by synchronously connected first and second interleaved counter-rotating rotors 30, 32 which are disposed in a cavity 28 of the housing 22. Each of the rotors 30, 32 has lobes that are twisted or helically disposed along the length of the rotors 30, 32. Upon rotation of the rotors 30, 32, the lobes at least partially seal the working fluid 12-1 against an interior side of the housing at which point expansion of the working fluid 12-1 only occurs to the extent allowed by leakage which represents and inefficiency in the system. In contrast to some expansion devices that change the volume of the working fluid when the fluid is sealed, the volume defined between the lobes and the interior side of the housing 22 of device 20 is constant as the working fluid 12-1 traverses the length of the rotors 30, 32. Accordingly, the expansion device 20 may be referred to as a "volumetric device" as the sealed or partially sealed working fluid volume does not change.

[0053] As additionally shown in Figure 5, each rotor 30, 32 has four lobes, 30-1, 30-2, 30-3, and 30-4 in the case of the rotor 30, and 32-1, 32-2, 32-3, and 32-4 in the case of the rotor 32. Although four lobes are shown for each rotor 30 and 32, each of the two rotors may have any number of lobes that is equal to or greater than two. Additionally, the number of lobes is the same for both rotors 30 and 32. This is in contrast to the

construction of typical rotary screw devices and other similarly configured rotating equipment which have a dissimilar number of lobes (e.g. a male rotor with "n" lobes and a female rotor with "n+1" lobes). Furthermore, one of the distinguishing features of the expansion device 20 is that the rotors 30 and 32 are identical, wherein the rotors 30, 32 are oppositely arranged so that, as viewed from one axial end, the lobes of one rotor are twisted clockwise while the lobes of the meshing rotor are twisted counter-clockwise. Accordingly, when one lobe of the rotor 30, such as the lobe 30-1 is leading with respect to the inlet port 24, a lobe of the rotor 32, such as the lobe 30-2, is trailing with respect to the inlet port 24, and, therefore with respect to a stream of the high-pressure working fluid 12-1.

[0054] As shown, the first and second rotors 30 and 32 are fixed to respective rotor shafts, the first rotor being fixed to an output shaft 38 and the second rotor being fixed to a shaft 40. Each of the rotor shafts 38, 40 is mounted for rotation on a set of bearings (not shown) about an axis XI, X2, respectively. It is noted that axes XI and X2 are generally parallel to each other. The first and second rotors 30 and 32 are interleaved and continuously meshed for unitary rotation with each other.

[0055] The first and second rotors 30 and 32 are interleaved and continuously meshed for unitary rotation with each other. With renewed reference to Figure 4, the expander 20 also includes meshed timing gears 42 and 44, wherein the timing gear 42 is fixed for rotation with the rotor 30, while the timing gear 44 is fixed for rotation with the rotor 32. The timing gears 42, 44 are also configured to maintain the relative position of the rotors 30, 32 such that contact between the rotors is entirely prevented between the rotors 30, 32 which could cause extensive damage to the rotors 30, 32. Rather, a close tolerance between the rotors 30, 32 is maintained during rotation by the timing gears 42, 44. As the rotors 30, 32 are non-contacting, a lubricant in the fluid 12 is not required for operation of the expansion device 20, in contrast to typical rotary screw devices and other similarly configured rotating equipment having rotor lobes that contact each other.

[0056] The output shaft 38 is rotated by the working fluid 12 as the working fluid undergoes expansion from the higher first pressure working fluid 12-1 to the lower second pressure working fluid 12-2. As may additionally be seen in both Figures 9 and 10, the output shaft 38 extends beyond the boundary of the housing 22. Accordingly, the output shaft 38 is configured to capture the work or power generated by the expander 20 during the expansion of the working fluid 12 that takes place in the rotor cavity 28 between the inlet port 24 and the outlet port 26 and transfer such work as output torque from the expander 20. Although the output shaft 38 is shown as being operatively connected to the first rotor 30, in the alternative the output shaft 38 may be operatively connected to the second rotor 32. The output shaft 38 can be coupled to the power plant 52 such that the energy from the exhaust can be recaptured.

[0057] In one aspect of the geometry of the expander 20, each of the rotor lobes 30-1 to 30-4 and 32-1 to 32-4 has a lobe geometry in which the twist of each of the first and second rotors 30 and 32 is constant along their substantially matching length 34. As shown schematically at Figure 6, one parameter of the lobe geometry is the helix angle HA. By way of definition, it should be understood that references hereinafter to "helix angle" of the rotor lobes is meant to refer to the helix angle at the pitch diameter PD (or pitch circle) of the rotors 30 and 32. The term pitch diameter and its identification are well understood to those skilled in the gear and rotor art and will not be further discussed herein. As used herein, the helix angle HA can be calculated as follows: Helix Angle (HA) = (180/.pi.* arctan (PD/Lead)), wherein: PD = pitch diameter of the rotor lobes; and Lead = the lobe length required for the lobe to complete 360 degrees of twist. It is noted that the Lead is a function of the twist angle and the length LI, L2 of the lobes 30, 32, respectively. The twist angle is known to those skilled in the art to be the angular displacement of the lobe, in degrees, which occurs in "traveling" the length of the lobe from the rearward end of the rotor to the forward end of the rotor. As shown, the twist angle is about 120 degrees, although the twist angle may be fewer or more degrees, such as 160 degrees.

[0058] In another aspect of the expander geometry, the inlet port 24 includes an inlet angle 24-1, as can be seen schematically at Figure 4. In one example, the inlet angle 24-1 is defined as the general or average angle of an inner surface 24a of the inlet port 24, for example an anterior inner surface. In one example, the inlet angle 24-1 is defined as the angle of the general centerline of the inlet port 24, for example as shown at Figure 4. In one example, the inlet angle 24-1 is defined as the general resulting direction of the working fluid 12-1 entering the rotors 30, 32 due to contact with the anterior inner surface 24a, as can be seen at Figure 4. As shown, the inlet angle 24-1 is neither perpendicular nor parallel to the rotational axes XI, X2 of the rotors 30, 32. Accordingly, the anterior inner surface 24a of the inlet port 24 causes a substantial portion of the working fluid 12-1 to be shaped in a direction that is at an oblique angle with respect to the rotational axes XI, X2 of the rotors 30, 32, and thus generally parallel to the inlet angle 24-1.

[0059] Furthermore, and as shown in Figure 4, the inlet port 24 may be shaped such that the working fluid 12-1 is directed to the first axial ends 30a, 32a of the rotors 30, 32 and directed to the rotor lobe leading and trailing surfaces (discussed below) from a lateral direction. However, it is to be understood that the inlet angle 24-1 may be generally parallel or generally perpendicular to axes XI, X2, although an efficiency loss may be anticipated for certain rotor configurations. Furthermore, it is noted that the inlet port 24 may be shaped to narrow towards the inlet opening 24b, as shown in Figure 4.

[0060] Referring to Figure 7, it can be seen that the inlet port 24 has a width W that is slightly less than the combined diameter distance of the rotors 30, 32. The combined rotor diameter is equal to the distance between the axes XI and X2 plus the twice the distance from the centerline axis XI or X2 to the tip of the respective lobe. In some examples, width W is the same as or more than the combined rotor diameter.

[0061] In another aspect of the expander geometry, the outlet port 26 includes an outlet angle 26-1, as can be seen schematically at Figure 4. In one example, the outlet angle 26-1 is defined as the general or average angle of an inner surface 26a of the outlet port 26. In one example, the outlet angle 26-1 is defined as the angle of the general centerline of the outlet port 26, for example as shown at Figure 4. In one example, the outlet angle 26-1 is defined as the general resulting direction of the working fluid 12-2 leaving the rotors 30, 32 due to contact with the inner surface 26a, as can be seen at Figure 4. As shown, the outlet angle 26-1 is neither perpendicular nor parallel to the rotational axes XI, X2 of the rotors 30, 32. Accordingly, the inner surface 26a of the outlet port 26 receives the leaving working fluid 12-2 from the rotors 30, 32 at an oblique angle which can reduce backpressure at the outlet port 26. In one example, the inlet angle 24-1 and the outlet angle 26-1 are generally equal or parallel, as shown in Figure 4. In one example, the inlet angle 24-1 and the outlet angle 26-1 are oblique with respect to each other. It is to be understood that the outlet angle 26-1 may be generally perpendicular to axes XI, X2, although an efficiency loss may be anticipated for certain rotor configurations. It is further noted that the outlet angle 26-1 may be perpendicular to the axes XI, X2. As configured, the orientation and size of the outlet port 26-1 are established such that the leaving working fluid 12-2 can evacuate each rotor cavity 28 as easily and rapidly as possible so that backpressure is reduced as much as possible. The output power of the shaft 38 is maximized to the extent that backpressure caused by the outlet can be minimized such that the working fluid can be rapidly discharged into the lower pressure working fluid at the condenser.

[0062] The efficiency of the expander 20 can be optimized by coordinating the geometry of the inlet angle 24-1 and the geometry of the rotors 30, 32. For example, the helix angle HA of the rotors 30, 32 and the inlet angle 24-1 can be configured together in a complementary fashion. Because the inlet port 24 introduces the working fluid 12-1 to both the leading and trailing faces of each rotor 30, 32, the working fluid 12-1 performs both positive and negative work on the expander 20.

[0063] To illustrate, Figure 5 shows that lobes 30-1, 30-4, 32-1, and 32-2 are each exposed to the working fluid 12-1 through the inlet port opening 24b. Each of the lobes has a leading surface and a trailing surface, both of which are exposed to the working fluid at various points of rotation of the associated rotor. The leading surface is the side of the lobe that is forward most as the rotor is rotating in a direction Rl, R2 while the trailing surface is the side of the lobe opposite the leading surface. For example, rotor 30 rotates in direction Rl thereby resulting in side 30-la as being the leading surface of lobe 30-1 and side 30-lb being the trailing surface. As rotor 32 rotates in a direction R2 which is opposite direction Rl, the leading and trailing surfaces are mirrored such that side 32-2a is the leading surface of lobe 32-2 while side 32-2b is the trailing surface.

[0064] In generalized terms, the working fluid 12-1 impinges on the trailing surfaces of the lobes as they pass through the inlet port opening 24b and positive work is performed on each rotor 30, 32. By use of the term positive work, it is meant that the working fluid 12-1 causes the rotors to rotate in the desired direction: direction Rl for rotor 30 and direction R2 for rotor 32. As shown, working fluid 12-1 will operate to impart positive work on the trailing surface 32-2b of rotor 32-2, for example on surface portion 47. The working fluid 12-1 is also imparting positive work on the trailing surface 30-4b of rotor 30-1, for example of surface portion 46. However, the working fluid 12-1 also impinges on the leading surfaces of the lobes, for example surfaces 30-1 and 32-1, as they pass through the inlet port opening 24b thereby causing negative work to be performed on each rotor 30, 32. By use of the term negative work, it is meant that the working fluid 12-1 causes the rotors to rotate opposite to the desired direction, Rl, R2.

[0065] Accordingly, it is desirable to shape and orient the rotors 30, 32 and to shape and orient the inlet port 24 such that as much of the working fluid 12-1 as possible impinges on the trailing surfaces of the lobes with as little of the working fluid 12-1 impinging on the on the leading lobes such that the highest net positive work can be performed by the expander 20.

[0066] One advantageous configuration for optimizing the efficiency and net positive work of the expander 20 is a rotor lobe helix angle HA of about 35 degrees and an inlet angle 24-1 of about 30 degrees. Such a configuration operates to maximize the impingement area of the trailing surfaces on the lobes while minimizing the impingement area of the leading surfaces of the lobes. In one example, the helix angle is between about 25 degrees and about 40 degrees. In one example, the inlet angle 24-1 is set to be within (plus or minus) 15 degrees of the helix angle. In one example, the helix angle is between about 25 degrees and about 40 degrees. In one example, the inlet angle 24-1 is set to be within (plus or minus) 15 degrees of the helix angle HA. In one example, the inlet angle is within (plus or minus) 10 degrees of the helix angle. In one example, the inlet angle 24-1 is set to be within (plus or minus) 5 degrees of the helix angle HA. In one example, the inlet angle 24-1 is set to be within (plus or minus) fifteen percent of the helix angle HA while in one example, the inlet angle 24-1 is within ten percent of the helix angle. Other inlet angle and helix angle values are possible without departing from the concepts presented herein. However, it has been found that where the values for the inlet angle and the helix angle are not sufficiently close, a significant drop in efficiency (e.g. 10-15% drop) can occur.

The Electronic Control System

[0067] The disclosed exhaust gas energy recovery systems 100, 200, 300 can be controlled by an electronic control system that monitors and allows for various control sequences to operate at various times to achieve optimal performance of the system. Closed loop feedback is incorporated into the configuration to ensure the overall plant performance is optimal. Active monitoring of the inlet temperatures and pressures to the supercharger/compressor and exhaust volumetric device is implemented to ensure the optimal energy balance is achieved for the system. Adaptive controls are implemented to actively adjust the inlet/outlet pressures and temperatures through the heat exchanger to achieve the optimal system level performance across all operating points. [0068] In one aspect, an electronic controller 50 monitors various sensors and operating parameters of the exhaust gas energy recovery system to configure the exhaust gas energy recovery system into the most efficient mode of operation. The electronic controller 50 is schematically shown as including a processor 50A and a non-transient storage medium or memory 50B, such as RAM, flash drive or a hard drive. Memory 50B is for storing executable code, the operating parameters, the input from the operator interface while processor 50A is for executing the code.

[0069] Electronic controller 50 may have a number of inputs and outputs that may be used in a closed loop feedback system for optimized operation. For example, inputs and outputs may be in the form of pressure and temperature sensors (see Figures 1-lB), the expander output, the bypass valves, the intercooler capacity, mass flow rates of the intake and exhaust air, and/or pump activation and speed 120. Another example of an input are power plant operating parameters (e.g. exhaust pressure and temperature), which may be provided as a direct input into the electronic controller 50 or may be received from another portion of the control system via a control area network (CAN).

[0070] The electronic controller 50 may also store a number of predefined and/or configurable parameters and offsets for determining when each of the modes is to be initiated and/or terminated. As used herein, the term "configurable" refers to a parameter or offset value that can either be selected in the controller (i.e. via a dipswitch) or that can be adjusted within the controller.

[0071] In one example, the controller 50 senses operating conditions (e.g. the temperature and pressure of the fluid streams upstream of each heat exchanger 418, 518A, 518B) and calculates whether better heat exchange performance would be obtained by using heat exchanger 418 exclusively, by using heat exchangers 518A and 518B exclusively, or by using all of the heat exchanger with a calculated amount of flow being directed to each heat exchanger. Based on the results of this analysis, the controller 50 can then command the bypass valves 130, 132 to a specified position, along with the activation of the pump 120) and can continue to monitor system heat exchange performance such that the system readily responds to changing conditions to ensure optimal operation occurs. For the particular system shown at Figures 1 A and IB (and wherever an air-to- liquid heat exchange / runaround loop is utilized), the system can monitor heat exchanger performance via temperature (and pressure) sensors located in the liquid supply and return piping between the heat exchangers. The controller 50 can also control operation of the intercooler 600 to switch between two or more heat exchange medium types to optimize operation of the intercooler via the operation of one or more bypass valves.

[0072] The various examples described above are provided by way of illustration only and should not be construed to limit the scope of the present disclosure. Those skilled in the art will readily recognize various modifications and changes that may be made without following the example examples and applications illustrated and described herein, and without departing from the true spirit and scope of the present disclosure.

Claims

WHAT IS CLAIMED IS:

1. A system of recovering energy from exhaust air and controlling intake air, the system comprising:

a power plant having an air intake and an exhaust outlet, the air intake configured to receive the intake air, and the exhaust outlet configured to discharge the exhaust air; a compressor arranged upstream of the power plant and configured to pressurize air to produce the intake air for the power plant;

a volumetric energy recovery device arranged downstream of the power plant and configured to receive the exhaust air, the volumetric energy recovery device operable to generate useful work as the exhaust air undergoes expansion therethrough; and

a heat exchanging device selectively operable to transfer heat from the intake air to the exhaust air and reduce a temperature of the intake air.

2. The system of claim 1, wherein the heat exchanging device is arranged

downstream of the compressor and upstream of the volumetric energy recovery device, and selectively operable to transfer heat from the pressurized air to the exhaust air.

3. The system of claim 1, wherein the heat exchanging device is arranged

downstream of the compressor and downstream of the volumetric energy recovery device, and selectively operable to transfer heat from the pressurized air to the exhaust air expanded by the volumetric energy recovery device.

4. The system of claim 1, wherein the heat exchanging device is arranged upstream of the compressor and downstream of the volumetric energy recovery device, and selectively operable to transfer heat from ambient air to the exhaust air expanded by the volumetric energy recovery device.

5. The system of claim 1, wherein the volumetric energy recovery device includes: a housing having an inlet port configured to admit the exhaust air and an outlet port configured to discharge a conditioned exhaust air stream, the conditioned exhaust air stream having a lower pressure and lower temperature than the exhaust air stream;

first and second twisted meshed rotors rotatably disposed in the housing and configured to expand the exhaust air, wherein each rotor has a plurality of lobes; and an output shaft operatively connected to one of the first and second rotors and rotated by the exhaust air.

6. The system of claim 1, wherein the volumetric energy recovery device is connected to the compressor and configured to deliver the generated useful work to the compressor.

7. The system of claim 1, wherein the volumetric energy recovery device is integrally formed with the compressor.

8. The system of claim 1, wherein the heat exchanging device is an air-to-air heat exchanger.

9. The system of claim 1, wherein the heat exchanging device is a heat pipe.

10. The system of claim 1, wherein the heat exchanging device is an air-to-liquid heat exchanger.

11. A method for recovering energy from exhaust gas air, the method comprising: compressing, at a compressor, ambient air to form a compressed airflow stream; receiving, at a power plant, the compressed airflow stream, wherein the

compressed airflow stream is conditioned at a temperature useable by the power plant;

receiving, at a volumetric energy recovery device, an exhaust airflow stream; and transferring heat, using a heat exchanger, from the compressed airflow stream to the exhaust airflow stream.

12. The method of claim 11, wherein transferring heat, using the heat exchanger, from the compressed airflow stream to the exhaust airflow stream is performed before receiving, at the volumetric energy recovery device, the exhaust airflow stream.

13. The method of claim 11, wherein transferring heat, using the heat exchanger, from the compressed airflow stream to the exhaust airflow stream is performed after receiving, at the volumetric energy recovery device, the exhaust airflow stream.

14. The method of claim 11, wherein receiving, at the volumetric energy recovery device, the exhaust airflow stream includes generating useful work as the exhaust airflow stream undergoes expansion therethrough.

15. The method of claim 14, wherein receiving, at the volumetric energy recovery device, the exhaust airflow stream further includes delivering the generated useful work to the compressor.

16. The method of claim 11, wherein the volumetric energy recovery device is integrally formed with the compressor.

17. A method for recovering energy from exhaust gas air, the method comprising: receiving, at a volumetric energy recovery device, an exhaust airflow stream; transferring heat, using a heat exchanger, from ambient air to the exhaust airflow stream;

compressing the heat-transferred ambient air to form a compressed airflow stream; and

receiving, at a power plant, the compressed airflow stream, wherein the

compressed airflow stream is conditioned at a temperature useable by the power plant.

18. The method of claim 17, wherein receiving, at the volumetric energy recovery device, the exhaust airflow stream includes generating useful work as the exhaust airflow stream undergoes expansion therethrough.

19. The method of claim 18, wherein receiving, at the volumetric energy recovery device, the exhaust airflow stream further includes delivering the generated useful work to the compressor.

20. The method of claim 17, wherein the volumetric energy recovery device is integrally formed with the compressor.

21. A system of recovering energy from exhaust air and controlling intake air, the system comprising:

a volumetric energy recovery device arranged downstream of the power plant and configured to receive the exhaust air, the volumetric energy recovery device operable to generate useful work as the exhaust air undergoes expansion therethrough;

a first heat exchanging device selectively operable to transfer heat from the intake air to the exhaust air and reduce a temperature of the intake air; and

a second heat exchanging device selectively operable to transfer heat from the intake air to the exhaust air and reduce a temperature of the intake air.

22. The system of claim 21, wherein the first heat exchanging device is an air-to-air heat exchanger.

23. The system of claim 22, wherein the second heat exchanging device includes a first air-to-liquid heat exchanger in fluid communication with the intake air and a second air-to liquid heat exchanger in fluid communication with the exhaust air, wherein the first and second air-to-liquid heat exchangers are interconnected by a circulation pump.

24. The system of claim 21, further including a first bypass valve configured to selectively direct intake air from the compressor to one of the first heat exchanging device, the second heat exchanging device, and a combination of the first and second heat exchanging devices.

25. The system of claim 24, further including a second bypass valve configured to selectively direct exhaust air from the power plant to one of the first heat exchanging device, the second heat exchanging device, and a combination of the first and second heat exchanging devices.