Roots blower and method for expanding a vaporous medium at high pressure and good tightness

Abstract

The invention relates to a Roots blower (10) for expanding a vaporous medium, having a housing (12) for delimiting a working chamber (22), a first piston shaft (14) that can be connected to a first rotary piston (16), a second piston shaft (18) that can be connected to a second rotary piston (20) that can roll on the first rotary piston (16), and a coupling for torque-transmitting coupling of the second piston shaft (18) to an output shaft (38) provided outside the housing (12), wherein the coupling is designed as a contactless magnetic coupling (30). As a result of the contactless torque transmission with the aid of the magnetic coupling (30), a contacting seal in a rotary union of the second piston shaft (18) through the housing (12) can be saved, as a result of which a Roots blower (10) that can be used in a high pressure range is made possible.

Description

[0001] Rotary lobe blowers and methods for the expansion of a vaporous medium at high pressure and good sealing

[0002] Description

[0003] The invention relates to a rotary lobe blower originally derived from vacuum technology, with which a vaporous medium can be depressurized at high pressure and with good sealing, as well as a depressurization device and a method using such a rotary lobe blower.

[0004] From DE 10 2015 205 452 Al a motor vehicle with a fluid-driven wheel is known, in which the wheel is coupled via a magnetic coupling to a coupling shaft intended for the, in particular, electrical, drive of the motor vehicle.

[0005] From DE 10 2009 022 916 Al a magnetic coupling for coupling an outer rotor with an inner rotor is known, in which a containment pot made exclusively of glass and electrically non-conductive is provided between the outer rotor and the inner rotor.

[0006] From DE 10 2010 045 881 Al, a vacuum pump is known in which lubricant leakage is directed away from a sealing area via a catch groove. From DE 295 18 688 Ul, a drive motor is known which is connected via a magnetic coupling to a centrifugal pump for a system for liquefying media from the gas phase at low temperatures in the range of -190°C, in which a containment shell provided in a magnetic socket of the magnetic coupling seals a ceramic bearing supporting a shaft of the centrifugal pump to the outside.

[0007] From EP 4 047 180 Al it is known, in a rotary piston blower used as a pressure relief device, to apply pressure to the seals for a rotary feedthrough of one of the piston shafts of the rotary piston blower through a housing of the rotary piston blower on both sides, in order to avoid an excessively high pressure difference at the seal which would impair the sealing effect of the seal.

[0008] The rotary lobe blower, originally from vacuum technology, is designed for low pressures only. Therefore, when used as a pressure relief device, it can only be employed in a low pressure range, thus limiting its application. Since pressure differences of only about 1 bar occur when using the rotary lobe blower as a vacuum pump in vacuum technology, using it in higher pressure ranges would lead to insufficient sealing and / or very high wear of the sealing devices.

[0009] There is a need to be able to use a rotary lobe blower even in high pressure ranges.

[0010] The object of the invention is to demonstrate measures that enable a rotary lobe blower to be used in high pressure ranges.

[0011] The task is solved by a rotary lobe blower with the characteristics of the

[0012] Claim 1, a relaxation device having the features of claim 12, and a method having the features of claim 13. Preferred embodiments of the invention are specified in the dependent claims and the following description, each of which, individually or in combination, may represent an aspect of the invention. Where a feature is presented in combination with another feature, this serves only to simplify the presentation of the invention and is not intended to imply that this feature cannot also be a further development of the invention without the other feature, the scope of protection of the invention being defined by the independent claims.

[0013] One aspect of the invention relates to a rotary piston blower for the expansion of a vaporous medium, comprising a housing for delimiting a working space, a first piston shaft connectable to a first rotary piston, a second piston shaft connectable to a second rotary piston that can roll on the first rotary piston, and a coupling for torque-transmitting coupling of the second piston shaft to an output shaft provided outside the housing, wherein the coupling is designed as a contactless magnetic coupling.

[0014] The magnetic coupling allows for the contactless transfer of energy generated during the expansion of the vaporous medium from the interior to the exterior of the rotary lobe blower. This contactless coupling between the input and output sides of the coupling is achieved via magnetic forces that interact with both sides. The torque flow is therefore not purely mechanical. Instead, the mechanical torque flow is interrupted by a segment where torque transmission occurs magnetically.The mechanical interruption of the torque flow, while simultaneously maintaining and uninterrupted torque transmission, makes it possible, in that part of the torque flow that is not mechanical but rather generated by a magnetic field, to provide a particularly hermetically sealed encapsulation of the interior of the rotary lobe blower from its exterior. This eliminates the need for a contact seal, especially a radial shaft seal, between components rotating relative to each other. Consequently, a significantly higher internal pressure can be permitted in the working chamber of the rotary lobe blower, a pressure that would be neither permissible nor expected in the original application of the rotary lobe blower as a vacuum pump in vacuum technology.Therefore, a rotary lobe blower designed as a vacuum pump, in its standard configuration as a catalog product for vacuum technology, can be adapted to function as an energy-generating pressure relief device for higher pressures of, for example, approximately 20 bar ± 10 bar using a magnetic coupling, without requiring significant design modifications to the vacuum pump. The contactless torque transmission via the magnetic coupling eliminates the need for a contact seal in the rotary union of the second piston shaft through the housing, thus enabling the use of a rotary lobe blower in a high pressure range.

[0015] The magnetic coupling allows a rotary feedthrough through the housing of the rotary lobe blower, which requires little or no sealing, as fluidic communication between the working chamber and the environment can be prevented. In particular, it is possible to provide comparably high pressures on both axial sides of the rotary feedthrough, thus avoiding excessive pressure differentials that could impair the sealing effect of the rotary feedthrough. Since fluidic communication between the working chamber and the environment can be excluded, it is also possible to mount the first piston shaft and / or the second piston shaft without additional sealing. Preferably, the first piston shaft and / or the second piston shaft is supported on the housing exclusively by bearings, so that an unsealed mounting of the first piston shaft and / or the second piston shaft is permissible.For example, a sealing pot or containment pot flanged to the housing of the rotary piston blower via a ring seal can be provided, which covers a shaft end of the second piston shaft forming the input side of the magnetic coupling and passes through a magnetic coupling area of ​​the magnetic coupling formed by the magnetic field.

[0016] The first rotary piston can be connected to the first piston shaft in a rotationally fixed manner, for example via a spring-hub connection. Similarly, the second rotary piston can be connected to the second piston shaft in a rotationally fixed manner, for example via a spring-hub connection. The rotary pistons can mesh with each other and roll in opposite directions, so that the vaporous medium is transported, essentially isochorically, from an inlet to an outlet between a vane of each rotary piston and an inner surface of the housing. The rotary piston can be designed, for example, as an oval wheel or with three vanes. The enthalpy of the vaporous medium can be used to drive the rotary pistons, so that mechanical power can be extracted from one of the piston shafts, which can then be converted into electrical energy, particularly with the aid of an electric motor.In an application in vacuum technology, the power flow would run in the opposite direction by introducing a torque generated in an electric machine onto one of the piston shafts in order to pump out gas molecules and create a vacuum, for example down to 10', by electrically driving the rotation of the rotary pistons. 5 mbar, to generate at the inlet side.

[0017] The rotary lobe blower can operate with low gas friction and is simultaneously insensitive to liquid droplets from the vaporous medium. The rotary lobe blower can achieve high rotational speeds at which a sealing edge facing the inside of the housing, located on the outer radius of the respective rotary lobe, can reach relative speeds of more than approximately 1 / 10 of the speed of sound, thus creating a dynamic seal at the sealing edge. Backflow of the vaporous medium past the sealing edge can be avoided or at least negligible at such rotational speeds. Inflow and outflow with an increase or decrease in the displacement volume between the vanes of the rotary lobe and the inside of the housing essentially do not occur. Instead, the vaporous medium is transported by the rotational movement of the respective rotary lobe at a constant volume and therefore with a particularly high efficiency.During the expansion process, the thermal energy of the vaporous working fluid is at least partially converted into mechanical energy.

[0018] The working chamber of the rotary lobe blower housing can be divided by the rotary lobes into an inlet working chamber, into which the vaporous medium is supplied, an outlet working chamber, from which the vaporous medium is discharged, and a scooping volume enclosed between the vanes of the respective rotary lobe and the inside of the housing. The inlet working chamber and the outlet working chamber can be fluidly separated from each other by the rotary lobes, so that significantly different pressures and / or temperatures can exist in the inlet working chamber and the outlet working chamber. The housing can be made of cast iron, for example GG20, GG25, or GG30. Preferably, during normal, regular operation of the rotary lobe blower, a total pressure p is present in the inlet working chamber. m of 3 bar < p m < 120 bar, especially 10 bar < p m< 80 bar, preferably 15 bar < p m < 20 bar before.

[0019] The housing of the rotary lobe blower can have an inlet port communicating with the inlet-side working chamber and an outlet port communicating with the outlet-side working chamber, wherein, in particular, a fluid-tight pipe can be flanged to the inlet port and / or the outlet port. The first and / or second piston shaft can be mounted on or in the housing, wherein it is possible that one shaft end of the respective piston shaft can penetrate a housing wall and project into an external space bounded by a separate outer cover, in which, for example, the two piston shafts are rotaryally coupled to each other via interlocking toothed control gears.Preferably, the timing gears are bonded to the respective piston shaft, particularly with the aid of a metal adhesive, wherein the bonding is preferably provided in addition to a positive-locking and / or force-locking connection of the timing gears to the respective associated piston shaft. The meshing gears or timing gears can be made of different steel grades, wherein, in particular, different steel grades and / or materials can be provided for the meshing gears or timing gears. It is also possible to manufacture the gears or timing gears from plastic. The housing, in particular the outer cover of the housing, can have a through-opening through which the second piston shaft can be guided to the outside, wherein, preferably, this through-opening can be fluid-tightly sealed by the magnetic coupling.The through-opening can represent a supported or unsupported rotary feedthrough for the second piston shaft, which preferably has no seal and is instead sealed outside the housing exclusively by the magnetic coupling, in particular by means of a fluid-tight sealing pot or split pot.

[0020] In particular, the magnetic coupling has an inner magnet ring, which is attached, in particular, to the second piston shaft, and an outer magnet ring, which is attached, in particular, to the output shaft. The inner magnet ring and the outer magnet ring, which is magnetically coupled to the inner magnet ring for torque transmission, are radially spaced apart from each other in a common axial area via an annular gap and are arranged essentially coaxially. The inner magnet ring and the outer magnet ring can have several magnets arranged one behind the other in the circumferential direction and / or in the axial direction, which interact with each other to transmit a predefined maximum torque without contact.If a particularly high torque needs to be transmitted, it is possible to increase the axial extent of the inner and outer magnet rings and, accordingly, to provide more magnets arranged axially in series in order to generate a sufficiently strong magnetic field for transmitting the torque. Typically, an electric machine designed to generate electrical energy for a power grid is positioned far enough away from the rotary lobe blower that an axial extension of the magnetic coupling's extent is easily achievable within the available installation space without requiring any change to the radial extent.This allows the same rotary lobe blower to be used for different applications with varying expected maximum torques, simply by adjusting the dimensions of the magnetic coupling, without having to open the rotary lobe blower or make any internal modifications. For example, the magnetic coupling can transmit a maximum torque of 500 Nm, in particular 750 Nm, and preferably 1000 Nm.

[0021] Preferably, the magnetic coupling has a containment cup attached to the housing, the containment cup covering a shaft end of the second piston shaft that protrudes from the housing. The containment cup can have a tube section that is positioned in an air gap formed between the inner and outer magnetic rings. The tube section can be axially closed at the end facing away from the rotary lobe blower and can be designed in the form of a cup, particularly a deep-drawn one. At the end of the tube section facing the rotary lobe blower, the containment cup can be fluid-tightly connected to the housing provided by the rotary lobe blower, particularly to an outer cover of the housing. For this purpose, the containment cup can be pressed against the housing by means of an annularly closed seal, and in particular flanged to it.The containment cup can provide a fluid-tight seal for a through-hole in the housing of the rotary piston blower, which forms a rotary feedthrough for the second piston shaft, while simultaneously preventing contact with a relatively rotating component. In particular, direct contact between the containment cup and the inner and outer magnetic rings is avoided, so that neither mechanical rubbing occurs nor a contact seal is required. The containment cup is designed for a maximum internal pressure π of 3 bar < π < 120 bar, more specifically 10 bar < π < 80 bar, and preferably 15 bar < π < 20 bar. Particularly preferably, the containment cup has a lower magnetic permeability compared to steel, and is made of aluminum and / or plastic and / or stainless steel.Magnetic shielding of the magnetic field between the inner and outer magnet rings by the containment pot is thus avoided or at least significantly reduced. In particular, the containment pot is preferably made entirely of stainless steel, so that it does not rust, is very robust, and, due to its comparatively low magnetic permeability, allows good magnetic penetration for magnetic interaction between the rotor and the stator of the magnetic coupling.

[0022] Preferably, the containment shell is welded to the housing to seal a shaft end of the second piston shaft protruding from the housing and / or flanged to the housing via a ring seal. This allows for the formation of a substantially hermetic and / or fluid-tight seal between the containment shell and the housing, which provides a media-tight seal between the output shaft and the working chamber. Additional seals, in particular radial shaft seals in the area of ​​the shaft end of the second piston shaft, can be eliminated. The containment shell can extend through a magnetic coupling area formed by the magnetic field of the magnetic coupling. The containment shell can pass through a magnetic gap of the magnetic coupling in a continuous and circumferentially closed manner, i.e., without any through-openings.

[0023] In particular, the containment pot can be pressurized with the internal pressure of the working chamber and / or with pressure supplied by an external pressure source. The internal volume of the containment pot, into which the second piston shaft can project, can be pressure-equalized with the working chamber of the rotary lobe blower by means of a suitable fluidic connection. This allows a vapor barrier to be provided in the rotary feedthrough of the housing for the second piston shaft at the boundary between the housing and the internal volume of the containment pot, preventing the escape of condensable vapor into the internal volume of the containment pot.The internal volume of the cracked pot can be separated from the volume of the working space, for example, by means of a flexible membrane, and it is also possible to provide a continuous equalization channel between the internal volume of the cracked pot and the working space, wherein the equalization channel preferably opens into a region of the working space where little or no steam and condensate are to be expected.

[0024] Preferably, the magnetic coupling comprises at least one electromagnet, wherein the electromagnet can be supplied with electrical energy from a battery, particularly a rechargeable one, and / or a generator driven by the output shaft. The electromagnet only generates a magnetic force when an electric current flows through it. This allows the outer magnet ring to be placed onto the inner magnet ring, or vice versa, without interacting permanent magnets in the outer and inner magnet rings opposing the insertion force. This allows for a particularly small number of permanent magnet pairs in the outer and inner magnet rings, facilitating easy insertion of the magnet rings and enabling the rotary lobe blower to be started while coupled to the output shaft.The electromagnets can then be operated from the electric machine driven by the output shaft in generator mode, thereby strengthening the magnetic coupling and enabling a significantly higher torque to be transmitted during the ongoing (generator) operation of the rotary piston blower and the electric machine.

[0025] In particular, the transmissible torque can be greater than 500 Nm, especially greater than 1000 Nm, preferably greater than 1500 Nm and particularly preferably greater than 2000 Nm.

[0026] Particularly preferably, the second piston shaft is lubricated by grease lubrication in a region of the housing facing the magnetic coupling, allowing it to rotate relatively freely. In particular, the grease lubrication forms a grease barrier to seal an internal volume of the magnetic coupling, especially the internal volume of the magnetic coupling's containment cup, against a receiving volume facing the working chamber. This grease lubrication eliminates the need for lubricating oil for the lubrication and / or bearing of the second piston shaft. Despite the pressure differentials occurring in the area of ​​the rotary feedthrough of the second piston shaft through the housing or the outer cover of the housing, the grease lubrication can remain essentially axially immobile at the designated location, thus eliminating the need to separate lubricating oil from the condensed vapor in the working chamber.Instead, the grease lubrication can even form a grease barrier that acts as a vapor barrier, retaining steam and moist air in the working space and preventing it from entering the internal volume of the split pot.

[0027] In particular, the grease lubrication consists of a bearing grease based on perfluoropolyether (PFPE) and / or with a temperature resistance of at least 180°C. Such bearing greases are known, for example, from the aerospace industry. This type of bearing grease can provide good lubrication even in applications with extremely high speeds and high temperatures, where conventional mineral, synthetic, or silicone oil-based greases would fail. Since PFPE can have polymer chains consisting essentially only of carbon, oxygen, and fluorine, it is a very stable chemical compound that does not age prematurely in such application conditions.The bearing grease for grease lubrication can behave inertly and compatiblely in the vast majority of environments, so that not only water vapor but also various media containing water vapor can be depressurized in the rotary lobe blower, thus significantly expanding the range of applications of the rotary lobe blower.

[0028] Preferably, the first piston shaft and / or the second piston shaft is supported by at least one bearing, wherein the bearing is sealed by means of a first bearing grease facing the working chamber and a second bearing grease facing away from the working chamber, wherein the first bearing grease is exposed to vapor from the working chamber on an axial side facing the working chamber and the second bearing grease is exposed to vapor from the working chamber on an axial side facing away from the working chamber, wherein, in particular, the first bearing grease and the second bearing grease are based on perfluoropolyether (PFPE) and / or have a temperature resistance of at least 180°C. The bearing grease eliminates the need for a contact seal in the bearing area and / or oil lubrication. In particular, the bearing grease can form a vapor barrier at the bearings.

[0029] The bearing for the respective support of the first piston shaft and / or the second piston shaft can in particular be sealed and subjected to a comparable pressure on both sides, as is described in more detail in EP 4 047 180 Al with reference to the low-pressure sealing device and to which reference is hereby made as part of the invention.

[0030] A further aspect of the invention relates to a pressure relief device for generating mechanical and / or electrical energy from a vaporous medium, comprising a rotary lobe blower, which can be designed and further developed as described above, for pressure relief of the vaporous medium, wherein the second piston shaft is coupled to the output shaft and the output shaft is coupled to a rotor of an electric machine for generating electrical energy. The pressure relief device can be designed and further developed as explained above with reference to the rotary lobe blower. The contactless torque transmission using the magnetic coupling eliminates the need for a contact seal in a rotary feedthrough of the second piston shaft through the housing of the rotary lobe blower, thus enabling a pressure relief device that can be used in a high pressure range.

[0031] Another aspect of the invention relates to methods for operating a rotary lobe blower, which can be designed and further developed as described above, in particular for use in a pressure relief device, which can be designed and further developed as described above, in which a total pressure p is maintained in the inlet-side working chamber for an incoming vaporous medium. m of 3 bar < p m < 120 bar, especially 10 bar < p m < 80 bar, preferably 15 bar < p m < 20 bar. The contactless torque transmission using the magnetic coupling eliminates the need for a contact seal in the rotary union of the second piston shaft through the housing, thus enabling a rotary lobe blower that can be used in a high pressure range.

[0032] It is particularly preferred that a sealing edge facing the inner surface of the housing, located on the outer radius of the respective rotary piston, forms a relative velocity of more than 1 / 10 of the speed of sound relative to the housing. This creates a dynamic seal at the sealing edge. Backflow of the vaporous medium past the sealing edge can be avoided or at least neglected at such rotational speeds. Inflow and outflow with an increase or decrease in the pumped volume between the vanes of the rotary piston and the inner surface of the housing essentially do not occur. Instead, the transport of the vaporous medium via the rotational movement of the respective rotary piston takes place at a constant volume and thus with a particularly high efficiency.

[0033] The invention is now explained by way of example with reference to the accompanying drawings and preferred embodiments, wherein the features shown below can represent an aspect of the invention both individually and in combination. If a feature is shown in combination with another feature in a specific embodiment, this serves only to simplify the presentation of the invention with reference to that embodiment and is in no way intended to imply that this feature cannot also be a further development of the invention without the other feature, the scope of protection of the invention being defined by the independent claims. The drawings show:

[0034] Fig. 1: a schematic cross-sectional view of a rotary lobe blower, Fig. 2: a schematic principle representation of a release device with the rotary lobe blower from Fig. 1 and Fig. 3: a schematic sectional view of a magnetic coupling used for the rotary lobe blower from Fig. 1 in the release device from Fig. 2.

[0035] The rotary lobe blower 10 shown in Fig. 1 can be dimensioned and designed specifically for use in vacuum technology, particularly as a vacuum pump. The rotary lobe blower 10 has a housing 12 in which a first rotary lobe 16, connected to a first piston shaft 14, and a first rotary lobe 20, connected to a second piston shaft 18, are arranged to roll against each other. The rotary lobes 16, 20, which are designed, for example, as oval gears, can be moved along an inner surface 24 of the housing, which defines a working chamber 22, and against each other, with the smallest possible sealing gap. In its application as a vacuum pump, one of the piston shafts 14, 18 would be driven by an electric motor to pump out gas molecules to generate a vacuum.In the application of the rotary lobe blower 10 relevant here, for the expansion of a vaporous medium, the vaporous medium entering the working chamber 22 on the inlet side is expanded at the rotary lobe 20, which is driven by the energy content of the vaporous medium, so that the vaporous medium can leave the working chamber 22 at a lower energy level. Mechanical power can be extracted at one of the piston shafts 14, 18 and, in particular, supplied to an electric machine 34 operated in generator mode to generate electrical energy.

[0036] As shown in Fig. 2, the working chamber 22 of the rotary piston blower 10 can be sealed by a sealing device 26, which also includes a bearing 28 for supporting the respective piston shaft 14, 18. The sealing of the sealing device 26 is formed in particular by a bearing grease based on PFPE, which can serve as a vapor barrier for the vapor from the working chamber 22. A shaft end 32 of the second piston shaft 18, extending from the housing 12, can be coupled contactlessly via a magnetic coupling 30 to connect the electric machine 34 and form a pressure relief device 33. The magnetic coupling 30, shown in detail in Fig. 3, can have an inner magnetic ring 36, which is connected in particular to the shaft end 32 of the second piston shaft 18 and interacts magnetically and contactlessly with an outer magnetic ring 40 connected to an output shaft 38 leading to the electric machine 34, or vice versa.The inner magnet ring 36 and the outer magnet ring 40 can have a defined number of magnets 42 arranged side by side in the circumferential and / or axial direction to transmit a defined torque without contact. The respective magnets 42 can be designed wholly or partially as permanent magnets or as electromagnets. The inner magnet ring 36 and the outer magnet ring 40 are arranged coaxially to each other and form an annular air gap 44 between them, through which a containment shell 46, closed on one axial side, extends. The containment shell 46 can be attached to an outer surface of the housing 12, in particular in a fluid-tight manner, especially by flange mounting. The containment shell 46 can enclose the shaft end 32 of the second piston shaft 18 and the inner magnet ring 36 within its internal volume 48 and separate it fluid-tight from the surroundings.In particular, the internal volume 48 is subjected to an internal pressure which can essentially correspond to a pressure in the working chamber 22 of the rotary piston blower 10.

Claims

Claims 1. Rotary piston blower (10) for expanding a vaporous medium, comprising a housing (12) for delimiting a working space (22), a first piston shaft (14) connectable to a first rotary piston (16), a second piston shaft (18) connectable to a second rotary piston (20) which can roll on the first rotary piston (16) and a coupling for torque-transmitting coupling of the second piston shaft (18) to an output shaft (38) provided outside the housing (12), characterized in that the coupling is designed as a contactless magnetic coupling (30).

2. Rotary piston blower (10) according to claim 1, wherein the magnetic coupling (30) has an inner magnetic ring (36) which is attached, in particular to the second piston shaft (18), and an outer magnetic ring (40) which is attached, in particular to the output shaft (38), wherein the inner magnetic ring (36) and the outer magnetic ring (38) which is magnetically coupled to the inner magnetic ring (36) for torque transmission are radially spaced apart from each other in a common axial area via an annular gap (44) and are arranged substantially coaxially to each other.

3. Rotary piston blower (10) according to claim 1 or 2, wherein the magnetic coupling (30) has a containment pot (46) attached to the housing (12), wherein the containment pot (46) covers a shaft end (32) of the second piston shaft (18) protruding from the housing (12).

4. Rotary piston blower (10) according to claim 3, wherein the containment pot (46) has a lower magnetic permeability compared to steel.

5. Rotary piston blower (10) according to claim 4, wherein the split pot (46) is made of aluminium and / or plastic.

6. Rotary piston blower (10) according to claim 4 or 5, wherein the containment pot (46) is welded to the housing (12) and / or flanged to the housing (12) via a ring seal to seal a shaft end (32) of the second piston shaft (18) protruding from the housing (12).

7. Rotary piston blower according to one of claims 3 to 6, wherein the cavity (46) can be pressurized with an internal pressure of the working chamber (22) and / or a pressure provided by an external pressure source.

8. Rotary piston blower (10) according to one of claims 1 to 7, wherein the magnetic coupling (30) has at least one electromagnet, wherein the electromagnet can be supplied with electrical energy from a, in particular rechargeable, battery and / or a generator driven by the output shaft (38).

9. Rotary piston blower (10) according to one of claims 1 to 8, wherein the second piston shaft (18) is lubricated relatively rotatably on the housing (12) via grease lubrication in a region of the housing (12) facing the magnetic coupling (30), wherein the grease lubrication forms a grease barrier for sealing an internal volume (48) of the magnetic coupling (30), in particular an internal volume (48) of a / the containment pot (46) of the magnetic coupling (30), against a receiving volume facing the working chamber (22).

10. Rotary piston blower (10) according to claim 9, wherein the grease lubrication is formed from a bearing grease based on perfluoropolyether (PFPE) and / or a temperature resistance of at least 180°C.

11. Rotary piston blower (10) according to any one of claims 1 to 10, wherein the first piston shaft (14) and / or the second piston shaft (18) is supported by at least one bearing (28), wherein the bearing (28) is sealed by means of a first bearing grease pointing towards the working chamber (22) and by means of a second bearing grease pointing away from the working chamber (22), wherein the first bearing grease is exposed to steam from the working chamber (22) on an axial side pointing towards the working chamber (22) and the second bearing grease is exposed to steam from the working chamber (22) on an axial side pointing away from the working chamber (22), wherein in particular the first bearing grease and the second bearing grease are made on the basis of perfluoropolyether (PFPE) and / or have a temperature resistance of at least 180°C.

12. Expansion device (33) for generating mechanical and / or electrical energy from a vaporous medium, comprising a rotary piston blower (10) according to one of claims 1 to 11 for expanding the vaporous medium, wherein the second piston shaft (18) is coupled to the output shaft (38) and the output shaft (38) is coupled to a rotor of an electric machine (34) for generating electrical energy.

13. Method for operating a rotary lobe blower (10) according to one of claims 1 to 11, wherein a total pressure p is maintained in the inlet-side working chamber (22) for an incoming vaporous medium. m of 3 bar < p m < 120 bar, especially 10 bar < p m < 80 bar, preferably 15 bar < p m < 20 bar is present.

14. Method according to claim 13, wherein a sealing edge pointing towards an inner side of the housing (12) forms a relative velocity of more than 1 / 10 of the speed of sound on the outer radius of the respective rolling piston (16, 20) relative to the housing (12).

15. Method according to claim 13 or 14, wherein a maximum torque of 500 Nm, in particular 750 Nm, preferably 1000 Nm, more preferably 1500 Nm and particularly preferably 2000 Nm is transmitted via the magnetic coupling (30).

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