Waste heat recovery with rotative compressor-expander assembly

Abstract

The present disclosure concerns a waste heat recovery system designed to circulate a heat transfer fluid in a heat exchange relationship with a waste heat stream. The system includes a closed circuit with a waste heat recovery unit, a high pressure duct, a rotative compressor-expander assembly, an power generator, a low pressure duct, and a heat exchanger. The rotative compressor-expander assembly comprises a case containing a first and second shaft, a compression section, and an expansion section. The compression and expansion sections are designed to compress and expand a finite volume of the heat transfer fluid respectively, facilitating the conversion of heat 10 into useful work.

Description

Waste Heat Recovery with Rotative Compressor-Expander AssemblyDescriptionTECHNICAL FIELD

[0001] The present disclosure concerns waste heat recovery technologies, specifically through heat exchange between a waste heat source and a working fluid, or heat transfer fluid, operated in a thermodynamic cycle to convert heat into useful work or energy.

[0002] Embodiments disclosed herein specifically concern closed-loop thermodynamic cycle system wherein the heat transfer fluid is heated by a waste heat stream and undergoes thermodynamic transformations to convert heat into useful work in a closed circuit comprising a rotative compressor-expander assembly.BACKGROUND ART

[0003] Waste heat recovery is a significant aspect of energy conservation and efficiency in various industrial applications such as such glass, steel, cement, and others. These industries generate a substantial amount of waste heat, which if not recovered, leads to energy wastage and increased operational costs. Existing waste heat recovery technologies, such as organic Rankine cycle or supercritical carbon dioxide Brayton cycle, are often not economically viable due to their high costs and long payback periods. Moreover, high-temperature waste heat recovery systems that rely on supercritical carbon dioxide Brayton cycles and turbomachines face challenges in terms of efficiency and operability, especially for the plant sizes needed for industrial applications. Reciprocating compressors and expanders, which are commonly used in these systems, are known to lack efficiency and to involve high costs. Therefore, there is a need for an efficient and cost-effective solution for waste heat recovery in industrial applications.SUMMARY

[0004] In one aspect, the subject matter disclosed herein is directed to a rotative com- pressor-expander assembly comprising an expansion section and a compression section, wherein the rotative compressor-expander assembly comprises a case containinga first shaft mounted to the case and free to rotate in a first direction of rotation around a first central axis, and a second shaft mounted to the case and free to rotate in a second direction of rotation around a second central axis, parallel to the first central axis, the second direction of rotation being inverse to the first direction of rotation; the second shaft being parallel and coupled to the first shaft via synchronizing means, the first shaft or the second shaft having an end coupled to the shaft of the power generate, wherein the compression section comprises a compression housing with a first cylindrical section and a second cylindrical section, with respective geometrical axes and radiuses, the axis of the first cylindrical section and the axis of the second cylindrical section being parallel to each other and the distance between the axis of the first cylindrical section and the axis of the second cylindrical section being smaller than the sum of the radius of the first cylindrical section and the radius of the second cylindrical section, so that a shared zone is defined between the first cylindrical section and the second cylindrical section, a pair of compression rotors, respectively coupled on the outer surface of the first and second shafts, a first compression rotor with a cylindrical body having a lateral outer surface with an outer diameter configured to seal the space between the lateral outer surface of the cylindrical body of the first compression rotor and the lateral internal surface of the first cylindrical section of the compression housing and having a surface axial notch allowing a first compression space enclosed between the surface axial notch and the lateral internal surface of the first cylindrical section of the compression housing, and a second compression rotor having a main body with a lateral outer surface and an axial paddle protruding radially from the lateral outer surface of the main body of the second compression rotor, the outer diameter of the main body of the second compression rotor being configured to allow a second compression space between the outer surface of the main body of the second compression rotor and the internal surface of the second cylindrical section of the compression housing and the height of the axial paddle of the second compression rotor being configured to seal the space between its outer surface and the internal surface of the second cylindrical section of the compression housing, the axial paddle of the secondcompression rotor being configured to be inserted in the first compression space for every rotation of the first and second shafts, in correspondence of the shared zone between the first cylindrical section and the second cylindrical section, a compression section inlet, coupled with the second cylindrical section of the compression housing, to allow fluidic connection with the second compression space, a connection passage between an outlet of the second cylindrical section of the compression housing and an inlet of the first cylindrical section of the compression housing, to allow fluidic connection between the second compression space and the first compression space, and a compression section outlet, coupled with the first cylindrical section of the compression housing, to allow fluidic connection with the first compression space, and wherein the expansion section comprises an expansion housing with a first cylindrical section and a second cylindrical section, with respective geometrical axes and radiuses, the axis of the first cylindrical section and the axis of the second cylindrical section being parallel to each other and the distance between the axis of the first cylindrical section and the axis of the second cylindrical section being smaller than the sum of the radius of the first cylindrical section and the radius of the second cylindrical section, so that a shared zone is defined between the first cylindrical section and the second cylindrical section, a pair of expansion rotors, respectively coupled on the outer surface of the first and second shafts, a first expansion rotor with a cylindrical body having a lateral outer surface with an outer diameter configured to seal the space between the lateral outer surface of the cylindrical body of the first expansion rotor and the lateral internal surface of the first cylindrical section of the expansion housing and having a surface axial notch allowing a first expansion space enclosed between the surface axial notch and the lateral internal surface of the first cylindrical section of the expansion housing, and a second expansion rotor having a main body with a lateral outer surface and an axial paddle protruding radially from the lateral outer surface of the main body of the second expansion rotor, the outer diameter of the main body of the second expansion rotor being configured to allow a second expansion spacebetween the outer surface of the main body of the second expansion rotor and the internal surface of the second cylindrical section of the expansion housing and the height of the axial paddle of the second expansion rotor being configured to seal the space between its outer surface and the internal surface of the second cylindrical section of the expansion housing, the axial paddle of the second expansion rotor being configured to be inserted in the first expansion space for every rotation of the first and second shafts, in correspondence of the shared zone between the first cylindrical section and the second cylindrical section, an expansion section inlet, coupled with the first cylindrical section of the expansion housing, to allow fluidic connection with the first expansion space, a connection passage between an outlet of the first cylindrical section of the expansion housing and an inlet of the second cylindrical section of the expansion housing, to allow fluidic connection between the first expansion space and the second expansion space, and an expansion section outlet, coupled with the second cylindrical section of the expansion housing, to allow fluidic connection with the second expansion space.

[0005] In one aspect, the volume of the compression housing is smaller than the volume of the expansion housing. This configuration allows the use of the rotative com- pressor-expander assembly of the present disclosure with a Brayton cycle.

[0006] In an alternative aspect, the compression housing is larger than the volume of the expansion housing. This configuration allows the use of the rotative compressorexpander assembly of the present disclosure with a reverse Brayton cycle.

[0007] In one aspect, the rotative compressor-expander assembly is part of a waste heat recovery system, configured to circulate a heat transfer fluid in heat exchange relationship with a waste heat stream to heat the heat transfer fluid, the heat transfer fluid being processed in a closed circuit and undergoing thermodynamic transformations to convert heat into useful work, the closed circuit comprising a low pressure sub-circuit, in which the fluid stream of the heat transfer fluid flows at a low pressure, the low pressure sub-circuit being coupled with the expansion section outlet of the rotative compressor-expander assembly andwith the compression section inlet of the rotative compressor-expander assembly; a high pressure sub-circuit, in which the fluid stream of the heat transfer fluid flows at a high pressure, the high pressure sub-circuit being coupled with the compression section outlet of the rotative compressor-expander assembly and with the expansion section inlet of the rotative compressor-expander assembly; a heat exchanger, configured to exchange heat between the high pressure heat transfer fluid stream and the low pressure heat transfer fluid stream, the heat exchanger comprising a cold section and a hot section, separated by a heat exchange interface, the cold section being arranged along the low pressure subcircuit and the hot section being arranged along the high pressure sub-circuit; a waste heat recovery unit, configured to exchange heat between the waste heat stream and the high pressure heat transfer fluid stream, the waste heat recovery unit being arranged along the high pressure sub-circuit, downstream of the heat exchanger, and a power generator coupled with the rotative compressor-expander assembly.

[0008] In one aspect, the waste heat recovery system further comprises a cooler arranged along the low pressure sub-circuit, downstream of the heat exchanger.

[0009] In one aspect, the subject matter disclosed herein is directed to the use of the rotative compressor-expander assembly in a Brayton cycle.

[0010] In one aspect, the subject matter disclosed herein is directed to the use of the of the rotative compressor-expander assembly a reversed Brayton cycle.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] A more complete appreciation of the disclosed embodiments of the invention and many of the attended advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:Fig. l shows a schematic view of a waste heat recovery system according to an embodiment of the present disclosure;Fig.2 shows a schematic sectional side view of a rotative compressor-expander assembly according to another embodiment of the present disclosure;Fig.3 shows a schematic sectional front view of the compression section of the rotative compressor-expander assembly of Fig.2;Fig.4 shows a schematic sectional front view of the expansion section of the rotative compressor-expander assembly of Fig.2;Fig.5 shows a sequence of positions of the compression section of Fig.3; and Fig. 6 shows a sequence of positions of the expansion section of Fig.4.DETAILED DESCRIPTION OF EMBODIMENTS

[0012] Reference now will be made in detail to various embodiments of the disclosure, which is illustrated in figures 1-6 by way of explanation of the disclosure, not limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. Reference throughout the specification to “one embodiment” or “an embodiment” or “some embodiments” means that the particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrase “in one embodiment” or “in an embodiment” or “in some embodiments” in various places throughout the specification is not necessarily referring to the same embodiment(s). Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

[0013] When introducing elements of various embodiments, the articles “a”, “an”, “the”, and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including”, and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[0014] Referring now to the drawings, Fig.1 shows a schematic of an exemplary waste heat recovery system 10 to capture waste heat and convert it into useful work. It utilizes a supercritical carbon dioxide closed-loop Brayton cycle, which is a part of the broader category of waste heat recovery technologies and is described by way of explanation of the disclosure, not limitation of the disclosure. This mechanism is particularly relevant for industries that produce high-temperature waste heat (glass, steel, cement).

[0015] The waste heat recovery system 10 includes the supercritical carbon dioxideclosed-loop Brayton cycle, which serves as the core of the system where the carbon dioxide is used as the working fluid, i.e. as the heat transfer fluid. The working fluid undergoes a series of thermodynamic transformations within the closed-loop to extract energy from the waste heat. The waste heat recovery system 10 comprises a waste heat recovery unit 11 configured to exchange heat between a waste heat stream 12 and a heat transfer fluid circulating inside a heat transfer fluid circulation system 13, a rotative expander-compressor assembly 14 with a power generator module 15 and a heat exchanger 16 or regenerator 16. In the exemplary embodiment shown in Fig.1 the heat transfer fluid is carbon dioxide. Carbon dioxide is used as the working fluid because of its high density at supercritical conditions, allowing for smaller components and more compact systems compared to other working fluids. Supercritical carbon dioxide also exhibits excellent heat transfer characteristics, leading to higher cycle efficiency, additionally, the supercritical state allows for operation across a broader range of temperatures, making it suitable for various applications.

[0016] The heat transfer fluid circulation system 13 ensures the movement of the heat transfer fluid through the system, allowing it to absorb heat from the waste heat stream 12. The rotative expander-compressor unit 14 compresses and expands the heat transfer fluid, transforming thermal energy into mechanical work. The heat transfer fluid circulation system 13 comprises a low-pressure circuit 131, connecting an expansion section outlet 272 of the expander section 141 of the rotative compressor-expander assembly 14 to the cold side of the heat exchanger 16 and then to a compression section inlet 241 of the compression section 142 of the rotative compressor-expander assembly 14. As used herein, the term “low-pressure” is expressly defined to include any pressure that is lower than the pressure at the outlet of the compression section 142 of the rotative compressor-expander assembly 14, but is not limited to a particular range of pressure. In the exemplary embodiment shown in Fig.1 the low pressure can be 80 bar. The heat transfer fluid circulation system 13 additionally comprises a high pressure circuit 132, connecting a compression section outlet 242 of the compression section 142 of the rotative compressor-expander assembly 14 to the hot side of the heat exchanger 16, then to the waste heat recovery unit 11 and finally to an expansion section inlet 271 of the expansion section 141 of the rotative compressor-expander assembly 14. As used herein, the term “high-pressure” is expressly defined to include any pressure that is higher than the pressure at the outlet of the expansion section 141 of therotative compressor-expander assembly 14, but is not limited to a particular range of pressure. In the exemplary embodiment shown in Fig.1 the high pressure can be 260 bar. The power generator module 15 is connected to the rotative expander-compressor unit 14 and converts the mechanical work into electric power. The heat exchanger 16 facilitates the exchange of heat between the high and low pressure streams of the heat transfer fluid, optimizing the energy recovery process.

[0017] In operation, the waste heat recovery system 10 circulates the heat transfer fluid through the system. In the waste heat recovery unit 11 the heat transfer fluid at high pressure absorbs thermal energy from a waste heat stream 12. In the exemplary embodiment shown in Fig.1 the temperature of the waste heat stream 12 can be higher than 350°C, typically ranging up to 800°C. The heated high-pressure heat transfer fluid can reach a temperature of approximately 50°C lower that the waste heat stream 12 and then flows to the rotative compressor-expander assembly 14, in particular to the expansion section 141, where the heat transfer fluid expands, performing work on a shaft connected to the shaft of the power generator 15. Thus, the mechanical work is transferred to the power generator 15, which produces electrical power. The low-pressure fluid exits the expansion section 141 through the low pressure circuit 131 and passes through the heat exchanger 16, where it transfer heat to the high-pressure heat transfer fluid stream in the high-pressure circuit 132, downstream the compression section 142 of the rotative compressor-expander assembly 14. The low-pressure heat transfer fluid is subsequently additionally cooled by a cooler 17, which in the exemplary embodiment shown in Fig.l is an air cooler 17 and is subsequently routed to the inlet of the compression section 142 of the rotative compressor-expander assembly 14, wherein the heat transfer fluid is compressed, which increases its pressure and temperature, enhancing its energy content. After compression, the high-pressure heat transfer fluid is directed to the cold side of the heat exchanger 16 to be heated by exchanging heat with the low-pressure heat transfer fluid stream. Finally, the high-pressure heat transfer fluid is directed to the waste heat recovery unit 11, completing the cycle. The synchronization of the compressor and expander rotors must be maintained to ensure continuous flow and pressure balance, which is essential for the system’s efficiency. The design minimizes mechanical losses and maintenance needs, contributing to the system’s performance and longevity.

[0018] The heat transfer fluid circulation system 13 plays a role in the movement ofthe heat transfer fluid throughout the waste heat recovery system 10. This component ensures the flow of the fluid at both high and low pressures, facilitating the absorption and release of heat at different stages of the Brayton cycle. The efficiency of the heat transfer fluid circulation system 13 impacts the overall performance of the waste heat recovery system 10.

[0019] The rotative compressor-expander assembly 14 integrates both compression and expansion functions into a single assembly with two wheels mounted on shafts. The design allows for synchronized rotation and eliminates the need for poppet valves. The power generator 15 that is coupled to the rotative compressor-expander assembly 14 converts the mechanical energy produced by the assembly into electric power. Accordingly, this closed-loop operation maintains the system’s energy efficiency and ensures the continuous conversion of waste heat into electric power.

[0020] With continuing reference to Fig.1, Fig.2 illustrates an embodiment of a rotative compressor-expander assembly 14 according to the present disclosure. The rotative compressor-expander assembly 14 comprises a case 20 containing rotors mounted on two shafts, respectively a first shaft 21 mounted to the case 20 and free to rotate in around a first central axis x, and a second shaft 22 mounted to the case 20 and free to rotate around a second central axis, parallel to the first central axis x. In particular, the direction of rotation of the first shaft 21 is inverse to the direction of rotation of the second shaft 22, the shafts 21, 22 being coupled via synchronizing means 23. According to the exemplary embodiment of Fig.2, the second shaft 22 has an end coupled to the shaft of the power generator 5 previously described with reference to Fig.1.

[0021] With reference to Fig.2, the compression section 142 of the rotative compressor-expander assembly 14 comprises a compression housing 24, being a portion of the case 20 comprising a first end portion of both the first shaft 21 and the second shaft 22. On the outer surface of the first and second shafts 21, 22 are respectively coupled a first compression rotor 25 and a second compression rotor 26, which are housed in a respective first cylindrical section 24’ and second cylindrical section 24” of the compression housing 24. The expansion section 141 of the rotative compressor-expander assembly 14 comprises an expansion housing 27, being a portion of the case 20 comprising a second end portion of both the first shaft 21 and the second shaft 22, the second end portion being opposed to the first end portion and being greater than thefirst end portion. On the outer surface of the second end portion of first and second shafts 21, 22 are respectively coupled a first expansion rotor 28 and a second expansion rotor 29, which are housed in a respective first cylindrical section 27’ and second cylindrical section 27” of the expansion housing 27.

[0022] With continuing reference to Figs.1 and 2, a sectional front view of the compression section of the rotative compressor-expander assembly 2 is shown in Fig.3. The same reference numbers designate the same or corresponding parts, elements or components already illustrated in Fig.2 and described above, and which will not be described again.

[0023] The first compression rotor 25 has a cylindrical body having a lateral outer surface with an outer diameter configured to seal the space between the lateral outer surface of the cylindrical body of the first compression rotor 25 and the lateral internal surface of the first cylindrical section 24’ of the compression housing 24, the first compression rotor 25 additionally having a surface axial notch 251 allowing a first compression space 252 enclosed between the surface axial notch 251 and the lateral internal surface of the first cylindrical section 24’ of the compression housing 24. The second compression rotor 26 has a main surface with a lateral outer surface and an axial paddle 261 protruding radially with respect to the lateral outer surface of the main body of the second compression rotor 26, the outer diameter of the main body of the second compression rotor 26 being configured to allow a second compression space 262 between the outer surface of the main body of the second compression rotor 26 and the internal surface of the second cylindrical section 24” of the compression housing 24 and the height of the axial paddle 261 of the second compression rotor 26 being configured to seal the space between its outer surface and the internal surface of the second cylindrical section 24” of the compression housing 24. Additionally, the axial paddle 261 is configured to be inserted in the first compression space 252 for every rotation of the first and second shafts 21, 22.

[0024] The compression housing 24 also comprises a compression section inlet 241, through which the low pressure sub-circuit 131 is fluidly connected to the second compression space 262 and a compression section outlet 242, through which the first compression space 252 is fluidly connected to the high pressure sub-circuit 132. Moreover, a connection passage 253 connects an outlet 262’ of the second compression space 262and an inlet 252’ of the first compression space 252. As a consequence, the fluid in the second compression space 262 is compressed by the axial paddle 261 of the second compression rotor 26 until the first compression space 252 enclosed between the surface axial notch 251 and the lateral internal surface of the first cylindrical section 24’ of the compression housing 24 of the first compression rotor 25 intersects the inlet 252’, allowing the fluid to flow through the outlet 262’ and the connection passage 253 from the second compression space 262 to the first compression space 252.

[0025] With continuing reference to Figs 1, 2 and 3, a sectional front view of the expansion section of the rotative compressor-expander assembly 2 is shown in Fig.4. The same reference numbers designate the same or corresponding parts, elements or components already illustrated in Figs 2 and 3 and described above, and which will not be described again. The first expansion rotor 28 has a cylindrical body with a lateral outer surface with an outer diameter configured to seal the space between the lateral outer surface of the cylindrical body of the first expansion rotor 28 and the lateral internal surface of the first cylindrical section 27’ of the expansion housing 27, the first expansion rotor 28 additionally having a surface axial notch 281 allowing a first expansion space 282 enclosed between the surface axial notch 281 and the internal surface of the first cylindrical section 27’ of the expansion housing 27. The second expansion rotor 29 has main body with a lateral outer surface and an axial paddle 291, protruding radially with respect to the lateral outer surface of the main body of the second expansion rotor 29, the outer diameter of the main body of the second expansion rotor 29 being configured to allow a second expansion space 292 between the outer surface of the main body of the second expansion rotor 29 and the internal surface of the second cylindrical section 27” of the expansion housing 27 and the height of the axial paddle 291 of the second expansion rotor 29 being configured to seal the space between its outer surface and the internal surface of the second cylindrical section 27” of the expansion housing 27. Additionally, the surface radial paddle 291 of the second expansion rotor 29 is configured to be inserted in the first expansion space 282 for every rotation of the first and second shafts 21, 22.

[0026] The expansion housing 27 also comprises an expansion section inlet 271, through which the high pressure sub-circuit 132 is fluidly connected to the first expansion space 282, and an expansion section outlet 272, through which the second expansion space 292 is fluidly connected to the low pressure sub-circuit 131. Moreover, aconnection passage 283 connects an outlet 282’ of the first expansion space 282 with an inlet 292’ of the second expansion space 292. As a consequence, when the first expansion space 282 of the first expansion rotor 28 intersects the outlet 282’, the fluid is allowed to flow through the outlet 282’, the connection passage 283 and the inlet 292’ from the first expansion space 282 to the second expansion space 292.

[0027] With continuing reference to Figs.l, 2, 3 and 4, a sequence of sectional front view of the compression section of the rotative compressor-expander assembly 2 is shown in Fig.5. The same reference numbers designate the same or corresponding parts, elements or components already illustrated in Figs 2 and 3 and described above, and which will not be described again. Proceeding from the top-left to the top-right and subsequently from the bottom left to the bottom right, the heat transfer fluid from the low pressure sub-circuit 131 enters the compression section through the compression section inlet 241 and occupies the second compression space 262. The shaft 21 rotating in a clockwise direction, the axial paddle 261 of the second compression rotor 26 reduces the volume of the second compression space 262. As a consequence, the fluid is compressed in the second compression space 262 and the connection passage 253 but cannot reach the first compression space 252. In fact, the inlet 252’ of the first compression space 252 is closed by the rotor 25, the first compression space 252 being positioned far from the inlet 252’. When the first compression space 252 reaches the inlet 252’, as represented in the figure on the bottom left, some of the compressed fluid passes from the second compression space 262 to the first compression space 252. The rotation continues and the first compression space 252 reaches the compression section outlet 242, allowing the compressed fluid to flow through the high pressure sub-circuit 132. The rotation continues and the cycle is repeated.

[0028] With continuing reference to Figs.l, 2, 3, 4 and 5, a sequence of sectional front view of the expansion section of the rotative compressor-expander assembly 2 is shown in Fig.6. The same reference numbers designate the same or corresponding parts, elements or components already illustrated in Figs 2 and 4 and described above, and which will not be described again. Proceeding from the top-left to the top-right and subsequently from the bottom left to the bottom right, the heat transfer fluid from the high pressure sub-circuit 132 enters the expansion section through the expansion section inlet 271 when the expansion section inlet 271 is positioned in correspondenceof the first expansion space 282 (top central figures). The shaft 21 rotating in a counterclockwise direction, the first expansion space 282 reaches the outlet 282’, as represented in the second figure on the bottom from the left, some of the heat transfer fluid passes to the second expansion space 292. While the rotation continues, the shaft 22 rotating in a clockwise direction, the axial paddle 291 of the second expansion rotor 29 allows the second expansion space 292 to connect to the expansion section outlet 272, through which the heat transfer fluid flows to the low pressure sub-circuit 131. The rotation continues and the cycle is repeated.

[0029] The heat exchange process within the heat exchanger 16 occurs at the intersection of the high and low pressure sub-circuits. Here, the low pressure, heated fluid transfers its thermal energy to pre-heat the high pressure fluid. This direct heat exchange between the two streams enhances the system’s efficiency by pre-heating the high pressure fluid before it returns to the waste heat recovery unit 11 and cooling the low pressure fluid before it returns to the compression section. The process is continuous and adjusts dynamically to the operational conditions of the system, ensuring optimal heat transfer. This contributes to the efficiency and effectiveness of the waste heat recovery system by reducing the need for additional external cooling or heating sources.

[0030] The expansion section 141 is integral to the waste heat recovery system described. This module is tasked with expanding the heat transfer fluid, which is a necessary step in the conversion of thermal energy into mechanical work. The efficiency and effectiveness of the Brayton cycle within the system are heavily dependent on the design and operation of this section. The connection of the shaft 22 with the shaft of the power generator 15 allows to convert mechanical work into electricity.

[0031] While aspects of the invention have been described in terms of various specific embodiments, it will be apparent to those of ordinary skill in the art that many modifications, changes, and omissions are possible without departing form the spirit and scope of the claims.

Claims

CLAIMS1. A rotative compressor-expander assembly (14) comprising an expansion section (141) and a compression section (142), wherein the rotative compressor-expander assembly (14) comprises a case (20) containing- a first shaft (21) mounted to the case (20) and free to rotate in a first direction of rotation around a first central axis (x), and- a second shaft (22) mounted to the case (20) and free to rotate in a second direction of rotation around a second central axis, parallel to the first central axis (x), the second direction of rotation being inverse to the first direction of rotation; the second shaft (22) being parallel and coupled to the first shaft (21) via synchronizing means (23), the first shaft (21) or the second shaft (22) having an end coupled to the shaft of the power generator (5), wherein the compression section (142) comprises a compression housing (24) with a first cylindrical section (24’) and a second cylindrical section (24”), with respective geometrical axes and radiuses, the axis of the first cylindrical section (24’) and the axis of the second cylindrical section (24”) being parallel to each other and the distance between the axis of the first cylindrical section (24’) and the axis of the second cylindrical section (24”) being smaller than the sum of the radius of the first cylindrical section (24’) and the radius of the second cylindrical section (24”), so that a shared zone is defined between the first cylindrical section (24’) and the second cylindrical section (24”), a pair of compression rotors (25, 26), respectively coupled on the outer surface of the first and second shafts (21, 22), a first compression rotor (25) with a cylindrical body having a lateral outer surface with an outer diameter configured to seal the space between the lateral outer surface of the cylindrical body of the first compression rotor (25) and the lateral internal surface of the first cylindrical section (24’) of the compression housing (24) and having a surface axial notch (251) allowing a first compression space (252) enclosed between the surface axial notch (251) and the lateral internal surface of the first cylindrical section (24’) of the compression housing (24), and a second compression rotor (26) having a main body with a lateral outer surface and an axial paddle (261) protruding radially from the lateral outer surface of the main body of the second compression rotor (26), the outer diameter ofthe main body of the second compression rotor (26) being configured to allow a second compression space (262) between the outer surface of the main body of the second compression rotor (26) and the internal surface of the second cylindrical section (24”) of the compression housing (24) and the height of the axial paddle (261) of the second compression rotor (26) being configured to seal the space between its outer surface and the internal surface of the second cylindrical section (24”) of the compression housing (24), the axial paddle (261) of the second compression rotor (26) being configured to be inserted in the first compression space (252) for every rotation of the first and second shafts (21, 22), in correspondence of the shared zone between the first cylindrical section (24’) and the second cylindrical section (24”), a compression section inlet (241), coupled with the second cylindrical section (24”) of the compression housing (24), to allow fluidic connection with the second compression space (262), a connection passage (253) between an outlet (262’) of the second cylindrical section (24”) of the compression housing (24) and an inlet (252’) of the first cylindrical section (24’) of the compression housing (24), to allow fluidic connection between the second compression space (262) and the first compression space (252), and a compression section outlet (242), coupled with the first cylindrical section (24’) of the compression housing, to allow fluidic connection with the first compression space (252), and wherein the expansion section (141) comprises- an expansion housing (27) with a first cylindrical section (27’) and a second cylindrical section (27”), with respective geometrical axes and radiuses, the axis of the first cylindrical section (27’) and the axis of the second cylindrical section (27”) being parallel to each other and the distance between the axis of the first cylindrical section (27’) and the axis of the second cylindrical section (27”) being smaller than the sum of the radius of the first cylindrical section (27’) and the radius of the second cylindrical section (27”), so that a shared zone is defined between the first cylindrical section (27’) and the second cylindrical section (27”),- a pair of expansion rotors (28, 29), respectively coupled on the outer surface of the first and second shafts (21, 22), a first expansion rotor (28) with a cylindrical body having a lateral outer surfacewith an outer diameter configured to seal the space between the lateral outer surface of the cylindrical body of the first expansion rotor (28) and the lateral internal surface of the first cylindrical section (27’) of the expansion housing (27) and having a surface axial notch (281) allowing a first expansion space (282) enclosed between the surface axial notch (281) and the lateral internal surface of the first cylindrical section (27’) of the expansion housing (27), and a second expansion rotor (29) having a main body with a lateral outer surface and an axial paddle (291) protruding radially from the lateral outer surface of the main body of the second expansion rotor (29), the outer diameter of the main body of the second expansion rotor (29) being configured to allow a second expansion space (292) between the outer surface of the main body of the second expansion rotor (29) and the internal surface of the second cylindrical section (27”) of the expansion housing (27) and the height of the axial paddle (291) of the second expansion rotor (29) being configured to seal the space between its outer surface and the internal surface of the second cylindrical section (27”) of the expansion housing (27), the axial paddle (291) of the second expansion rotor (29) being configured to be inserted in the first expansion space (282) for every rotation of the first and second shafts (21, 22), in correspondence of the shared zone between the first cylindrical section (27’) and the second cylindrical section (27”), an expansion section inlet (271), coupled with the first cylindrical section (27’) of the expansion housing (27), to allow fluidic connection with the first expansion space (282), a connection passage (283) between an outlet (282’) of the first cylindrical section (27’) of the expansion housing (27) and an inlet (292’) of the second cylindrical section (27”) of the expansion housing (27), to allow fluidic connection between the first expansion space (282) and the second expansion space (292), and an expansion section outlet (272), coupled with the second cylindrical section (27”) of the expansion housing (27), to allow fluidic connection with the second expansion space (292).

2. The rotative compressor-expander assembly (14) of claim 1, wherein the volume of the compression housing (24) is smaller than the volume of the expansion housing (27).

3. The rotative compressor-expander assembly (14) of claim 1, wherein the volume of the compression housing (24) is larger than the volume of the expansion housing (27).

4. The rotative compressor-expander assembly (14) of claim 2, wherein the rotative compressor-expander assembly (14) is part of a waste heat recovery system (10), configured to circulate a heat transfer fluid in heat exchange relationship with a waste heat stream (12) to heat the heat transfer fluid, the heat transfer fluid being processed in a closed circuit (13) and undergoing thermodynamic transformations to convert heat into useful work, the closed circuit (13) comprising a low pressure sub-circuit (131), in which the fluid stream of the heat transfer fluid flows at a low pressure, the low pressure sub-circuit (131) being coupled with the expansion section outlet (272) of the rotative compressor-expander assembly (14) and with the compression section inlet (241) of the rotative com- pressor-expander assembly (14); a high pressure sub-circuit (132), in which the fluid stream of the heat transfer fluid flows at a high pressure, the high pressure sub-circuit (132) being coupled with the compression section outlet (242) of the rotative compressor-expander assembly (14) and with the expansion section inlet (271) of the rotative com- pressor-expander assembly (14); a heat exchanger (16), configured to exchange heat between the high pressure heat transfer fluid stream and the low pressure heat transfer fluid stream, the heat exchanger (16) comprising a cold section and a hot section, separated by a heat exchange interface, the cold section being arranged along the low pressure subcircuit (131) and the hot section being arranged along the high pressure subcircuit (132); a waste heat recovery unit (11), configured to exchange heat between the waste heat stream (12) and the high pressure heat transfer fluid stream, the waste heat recovery unit (11) being arranged along the high pressure sub-circuit (132), downstream of the heat exchanger (16), and a power generator (15) coupled with the rotative compressor-expander assembly (14).

5. The waste heat recovery system (10) of claim 4, further comprising a cooler (17) arranged along the low pressure sub-circuit (131), downstream of the heatexchanger (16).

6. Use of the rotative compressor-expander assembly (14) of claim 2 in a Brayton cycle.

7. Use of the of the rotative compressor-expander assembly (14) of claim 3 in a reversed Brayton cycle.

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