DESCRIPTION

The invention relates to a turbo-machine for a waste heat utilization device as well as a waste heat utilization device.

Waste heat utilization devices are well known from the general prior art and used for using waste heat which usually is lost unused. Modern waste heat utilization technologies utilizing thermal dynamic cycles require very compact, reliable and economically efficient turbo machinery solutions. Conventional approaches very often suggest the implementation of reducing gears, cooling and lubrication systems and two- shaft solutions for two stage turbo expanders leading to reduced efficiency and losses of working fluid used for the thermal dynamic cycle. Hence, conventional approaches do not allow for providing attractive and cost-efficient solutions currently requested by waste heat technologies. Losses of heat energy and working fluid for cooling purposes together with the necessity of two-stage turbo expanders for a huge number of implementation cases represent one of the complex problems limiting the waste heat technology implementation.

It is therefore an object of the present invention to provide a turbo-machine for a waste heat utilization device as well as a waste heat utilization device which can be operated very efficiently and are particularly compact.

This object is solved by a turbo-machine having the features of patent claim 1 and a waste heat utilization device having the features of patent claim 6. Advantageous embodiments with expedient and non-trivial developments of the invention are indicated in the other patent claims.

A first aspect of the present inventions relates to a turbo-machine for a waste heat utilization device. The turbo-machine comprises a shaft which is rotatable about an axis of rotation. The turbo-machine further comprises a first turbine stage having a first turbine wheel coupled to the shaft. Furthermore, the turbo-machine comprises at least one second turbine stage having a second turbine wheel coupled to the shaft, the second turbine stage being arranged downstream of the first turbine stage in the direction of flow of a working fluid flowing through the turbine stages and driving the shaft via the turbine wheels. This means that the working fluid can flow through the turbine stages thereby driving the turbine wheels and the shaft about the axis of rotation. During operation of the turbo-machine, the working fluid flows through the first turbine stage first. Having flowed through the first turbine stage, the working fluid thereafter flows through the second turbine stage.

By means of the turbine wheels and the shaft, energy contained in the working fluid, in particular heat energy, can be transformed into mechanical energy at least partly. Moreover, the turbo-machine comprises a generator unit coupled to the shaft. Thereby, the generator unit can be driven by the shaft. The generator unit is capable of transforming mechanical energy provided by the shaft into electric energy. By means of the turbo-machine, waste heat contained in the working fluid can be transformed into electric energy at least partly. Thus, the waste heat can be used for producing electric energy which then can be used to, for example, drive an electrical consumer. The electric energy can also be stored, for example, in a battery.

The turbo-machine further comprises at least one cooling path for cooling at least a portion of the generator unit by means of the working fluid flowing through the cooling path upstream of the second turbine stage and downstream of the first turbine stage. The working fluid flowing through the cooling path is used to cool the generator unit downstream of the first turbine stage and upstream of the second turbine stage. By cooling the generator unit, the working fluid is heated by the generator unit downstream of the first turbine stage and upstream of the second turbine stage. This means that having flowed through the first turbine stage the working fluid as an exhaust gas of the turbine stage thereafter cools the generator unit and is heated by the generator unit before the working fluid flows through the second turbine stage. For example, the working fluid is heated by the generator unit by a heat transfer from electrical windings and/or from a rotor magnet of the generator unit to the working fluid. Hence, waste heat of the generator unit can be transferred to the working fluid and converted to additional mechanical energy by means of the second turbine stage. From the thermal dynamic point of view this effect is called interstage heating because the working fluid is heated by the generator unit downstream of the first turbine stage and upstream of the second turbine stage. This means that the heat transfer from the generator unit to the working fluid is not only used to cool the generator unit but also to purposely heat the working fluid in order to recuperate the heat energy from the generator unit by means of the second turbine stage. Hence, a very high amount of mechanical energy can be generated in the second turbine stage.

Moreover, the packaging space required by the turbo-machine can be kept to a minimum because the working fluid is used not only for driving the shaft and the generator unit but also for cooling the generator unit. Thereby, a two-shaft design of the turbo-machine can be avoided as well as the implementation of reducing gears and additional cooling and lubrication systems.

The cooling path can be, for example, bounded by a duct element and/or by at least one wall and/or by at least one component of the generator unit.

By cooling the generator unit by means of the working fluid and by recuperating the heat energy from the generator unit by means of the second turbine stage thereby generating a very high amount of mechanical energy, the turbo-machine according to the present invention can be operated very efficiently.

In an advantageous embodiment of the invention the first turbine wheel having first blades is arranged at a first end of the shaft. The second turbine wheel having second blades is arranged at a second end of the shaft. Since the turbine wheels are mounted on both ends or sides of the shaft, a single-shaft design can be realized. Hence, the complexity of the turbo-machine can be kept to a minimum. Furthermore, axial forces of a rotor comprising the shaft and the turbine wheels can be minimized, thus allowing for a very simple axial support of the shaft. Hence, bearing losses can be kept to a minimum.

In a further particularly advantageous embodiment of the invention at least a portion of the generator unit is arranged between the turbine wheels in the longitudinal direction of the shaft. Thus, the size of the turbo-machine can be kept very low.

It has shown to be particularly advantageous if the turbine wheels are configured as radial turbine wheels. The radial turbine wheels are also referred to as centripetal turbine wheels. In comparison to axial turbine wheels, screw turbine wheels or any other type of turbine wheels, by using radial turbine wheels the packaging space required by the turbo-machine can be kept particularly low. Furthermore, the radial turbine wheels allow for realizing a very high efficiency between, for example, 75 and 85 %.

Advantageously, the turbo-machine comprises at least one housing on which the shaft is rotatably supported about the axis of rotation by means of at least one gas bearing and/or at least one magnetic bearing. The gas bearing can be configured as a foil bearing which is also referred to as foil-gas bearing. The magnetic bearing can be, for example, configured as an electromagnetic bearing. The air bearing and/or magnetic bearing allow for keeping the friction very low. Moreover, said bearings have a long lifetime and are very simple in terms of service. Moreover, that bearings can be operated in relatively wide temperature ranges and in different mediums including organic gases. This means that the functionality of the bearings is not affected negatively by the working fluid which can be an organic working fluid utilized by a thermodynamic cycle, for example, in the form of an organic rankine cycle (ORC) which can be utilized by the waste heat utilization device.

A second aspect of the present invention relates to a waste heat utilization device utilizing a thermodynamic cycle, the waste heat utilization device comprising a working fluid for the thermodynamic cycle. The waste heat utilization device also comprises at least one turbo-machine. Advantageously, the turbo-machine is a turbo-machine according to the first aspect of the invention.

The turbo-machine comprises a shaft which is rotatable about an axis of rotation. The turbo-machine also comprises a first turbine stage having a first turbine wheel coupled to the shaft. Moreover, the turbo-machine comprises at least one second turbine stage having a second turbine wheel coupled to the shaft, the second turbine stage being arranged downstream of the first turbine stage in the direction of flow of the working fluid flowing through the turbine stage is driving the shaft via the turbine wheels.

Additionally, the turbo-machine comprises a generator unit coupled to the shaft, the generator unit being capable of transforming mechanical energy provided by the shaft into electric energy. The turbo-machine further comprises at least one cooling path for cooling at least a portion of the generator unit by means of the working fluid flowing through the cooling path upstream of the second turbine stage and downstream of the first turbine stage. Advantageous embodiments of the first aspect of the invention are to be regarded as advantageous embodiments of the second aspect of the invention and vice versa.

The waste heat utilization device can be operated very efficiently since the working fluid is used not only for driving the shaft via the turbine wheels but also for cooling the generator unit and recuperating the heat energy from the generator unit back by means of the second turbine stage. In other words, the heat energy that is transferred from the generator unit to the working fluid when cooling the generator unit is transported to the second turbine stage by the working fluid at least partly. By means of the second turbine stage the heat energy can be transformed into additional mechanical energy at least partly. Thereby, a very high amount of mechanical energy can be provided. Hence, waste heat which conventionally is lost unused can be used to generate additional mechanical energy thereby allowing for a very efficient operation of the waste heat utilization device. In a further particularly advantageous embodiment of the invention the thermodynamic cycle is configured as an organic rankine cycle. The organic rankine cycle allows for realizing a particularly efficient and safe operation of the waste heat utilization device. Generally, any fluid can be used as the working fluid. Advantageously, the working fluid comprises at least one fluoroketone. For example, NOVEC™ 649 can be used as the working fluid. Thereby, the working fluid can be used for temperatures above 150°C. The working fluid can comprise at least one methoxyheptafluoropropane. For example, as the working fluid NOVEC™ 7000 can be used. The working fluid can comprise at least one tetrafluoropropene. For example, as the working fluid -1234yf can be used. By using NOVEC™ 7000 or R-1234yf the working fluid can be used for temperatures below 150°C which in terms of thermo physical properties provides a very good efficiency of the turbo-machine and the thermodynamic cycle.

With regard to said fluoroketone, said methoxyheptafluoropropane, and said tetrafluoropropane all positional isomers are to be regarded as disclosed within the scope of the invention.

Further advantages, features, and details of the invention derive from the following description of preferred embodiments as well as from the drawing. The features and feature combinations previously mentioned in the description as well as the features and feature combinations mentioned in the following description of the figures and/or shown in the figures alone can be employed not only in the respective indicated combination but also in any other combinations or taken alone without leaving the scope of the invention.

The drawing shows in:

FIG 1 a schematic longitudinal sectional view of a turbo-machine for a waste heat utilization device, the turbo-machine comprising at least one cooling path for cooling at least a portion of a generator unit of the turbo-machine by means of a working fluid flowing through the cooling path upstream of a second turbine stage and downstream of a first turbine stage of a turbo-machine; and

FIG 2 schemes of thermodynamic cycles utilized in a single-stage turbo- machine, a two-stage turbo-machine, and a two-stage turbo-machine with interstage heating. In the figures the same elements or element having the same functions are equipped with the same numerical reference.

FIG 1 shows a turbo-machine 10 in the form of a two-stage turbo generator for a waste heat utilization device. The turbo-machine 10 comprises a shaft 12 which is rotatable about an axis of rotation 14. For this purpose, the shaft 12 is, for example, rotatably supported on at least one housing of the turbo-machine 10, the housing not being shown in FIG 1. The shaft 12 is supported on the housing by means of a bearing device not shown in FIG 1. The bearing device comprises, for example, at least one foil bearing and/or at least one electromagnetic bearing for supporting the shaft 12 with only very low friction.

The turbo-machine 10 also comprises a first turbine stage 16 and a second turbine stage 18. A working fluid of the waste heat utilization device can flow through the turbine stages 16, 18, wherein the direction of flow of the working fluid is illustrated by directional arrows 20 in FIG 1. For example, the working fluid which is also referred to as actuating fluid is an organic medium so that the waste heat utilization device utilizes a thermodynamic cycle in the form of an organic rankine cycle (ORC). In said organic rankine cycle, the turbo-machine 10 is an expansion device for expanding the working fluid.

The first turbine stage 16 comprises a first turbine wheel 22 having first blades not shown in FIG 1. The first turbine wheel 22 is coupled to the shaft 12. Thereby, the working fluid flowing through the first turbine stage 16 drives the first turbine wheel 22 and the shaft 12 about the axis of rotation 14. As can be seen from FIG 1, the first turbine wheel 22 is arranged at a first distal end 24 of the shaft 12. The second turbine stage 18 comprises a second turbine wheel 26 coupled to the shaft 12. Thereby, the working fluid flowing through the second turbine stage 18 can drive the second turbine wheel 26 and the shaft 12. The second turbine wheel 26 has second blades not shown in FIG 1. As can be seen from FIG 1 , the second turbine wheel 26 is arranged at a second distal end 28 of the shaft 12. By arranging the turbo wheels 22, 26 at the distal ends 24, 28 respectively, axial forces can be avoided or kept very low so that an axial bearing can be avoided or kept very simple. Moreover, bearing frictions of the turbo-machine 10 can be kept to a minimum, thus facilitating a very efficient operation. With regard to the direction of flow of the working fluid through the turbo-machine 10, the second turbine stage 18 is arranged downstream of the first turbine stage 16.

The turbo-machine 10 further comprises a generator unit designated as a whole by reference 30. The generator unit 30 comprises at least one component 32. The component 32 is, for example, a stator of the generator unit 30. The stator can be mounted on the housing, the stator not being movable in relation to the housing.

The generator unit 30 can also comprise a rotor not shown in FIG 1 , the rotor corresponding to the stator. The rotor is coupled to the shaft 12 so that the shaft 12 and the rotor can rotate about the axis of rotation 14 together in relation to the stator (component 32). The generator unit 30 serves for transforming mechanical energy provided by the shaft 12 into electric energy. The turbine stages 16, 18 serve for transforming energy contained in the working fluid into mechanical energy provided by the shaft 12. Hence, energy, for example, in the form of waste heat contained in the working fluid can be transformed into electric energy by means of the turbo-machine 10. In order to realize a very compact design of the turbo-machine 10, the component 32 is arranged at least partly between the turbine wheels 22, 26 in the longitudinal direction of the shaft 12. The working fluid flowing through the turbo-machine 10 is expanded by the turbine stages 16, 18. This expansion is illustrated by a first pressure PI and a first temperature Tl of the working fluid upstream of the first turbine wheel 22, a second pressure P2 and a second temperature T2 of the working fluid downstream of the first turbine wheel 22 and upstream of the second turbine wheel 26 and the component 32, a third pressure P3 and a third temperature T3 of the fluid downstream of the component 32 and upstream of the second turbine wheel 26, and a fourth pressure P4 and a fourth temperature T4 of the working fluid downstream of the second turbine wheel 26.

In FIG 1 a first flow path 34 of the working fluid can be seen. Having flowed through the first turbine stage 16, the working fluid as an exhaust gas of the first turbine stage 16 can flow via or through the first flow path 34 from the first turbine stage 16 to the second turbine stage 18 so that the working fluid thereafter can flow through the second turbine stage 18. The turbo-machine 10 also comprises a second flow path configured as a cooling path 36. The cooling path 36 serves for cooling the component 32 of the generator unit 30 by means of the working fluid flowing via or through the cooling path 36 upstream of the second turbine stage 18 and downstream of the first turbine stage 16. This means that the working fluid is heated by a heat transfer from the component 32 to the working fluid downstream of the first turbine stage 16 and upstream of the second turbine stage 18 thereby cooling the component 32. In other words, having flowed through the first turbine stage 16 the working fluid is heated by a heat transfer from the component 32 to the working fluid before the working fluid flows through the second turbine stage 18. Thereby, a so-called interstage heating of the working fluid is realized. By means of the interstage heating, the working fluid is heated before flowing through the second turbine stage 18 and driving the second turbine wheel 26 and the shaft. Hence, the heat transferred from the component 32 to the working fluid can be transformed into mechanical energy at least partly by means of the second turbine stage 18. Thus, a very high amount of mechanical energy can be provided by the second turbine stage 18 for generating a very high amount of electric energy by means of the generator unit 30.

Said amount of additional mechanical energy or additional work which can be obtained by the interstage heating can be clearly seen in a thermodynamic diagram 38 shown in FIG 2, the thermodynamic diagram 38 being a scheme for illustrating the organic rankine cycle utilized by the turbo-machine 10. The diagram 38 has an ordinate 40 showing the temperature T of the working fluid. The diagram 38 also has an abscissa 42 showing the entropy S of the working fluid.

The letter h in the diagram 38 refers to the enthalpy of the working fluid, wherein the indices 1 , 2, 3 and 4 refer to the respective position in the turbo-machine 10. This means that the index 1 refers to the position upstream of the first turbine wheel 22. The index 2 refers to the position downstream of the first turbine wheel 22 and upstream of the component 32. The index 3 refers to the position upstream of the second turbine wheel 26 and downstream of the component 32. The index 4 refers to the position downstream of the second turbine wheel 26. This means that, for example, \ refers to the working fluid's enthalpy upstream of the first turbine wheel 22. The index s refers to the ideal expansion process illustrated by a dotted line 44. The real expansion process is illustrated by solid lines in the diagram 38.

FIG 2 also shows a thermodynamic diagram 46 illustrating an organic rankine cycle utilized by a single-stage turbo-machine. Such a single-stage turbo-machine comprises one turbine wheel or one turbine stage only. Hence, the index 1 refers to the position upstream of the single turbine wheel, wherein the index 4 refers to the position downstream of the single turbine- wheel. Moreover, FIG 2 shows a thermodynamic diagram 48 illustrating an organic rankine cycle utilized by a two-stage turbo-machine having, for example, the two turbine wheels 22, 26 but not having the interstage heating. The turbine work L _{t s} of the single-stage turbo-machine can be computed with regard to the ideal expansion process to:

L _{t s} = hi - h4s- The turbine work L _t , of the single-stage turbo-machine can be computed as follows: L _{t I} = hi - L(. The turbine work L _t „ of the two-stage turbo- machine not having the interstage heating can be computed as follows: L _{t n} = (hi - h ₂ ) + (h ₃ - I14). The turbine work L,„ ' of the two-stage turbo-machine 10 utilizing the interstage heating can be computed as follows: L,„ ' = (hi - h ₂ ) + (h ₃ ' - hn'). The turbine work L _{t s} is higher than the turbine work L _{t Il0} , wherein the turbine work L _{t Il0} is higher than the turbine work L _{t n} . And the turbine work L _t „ is higher than the turbine work L _t , .

Generally, any fluid can be used as the working fluid. Advantageously, the working fluid to be used in the organic rankine cycle turbo-machine 10 can be NOVEC™ 649, NOVEC™ 7000 or R-1234yf, depending on the temperature range and application. Said working fluids allow for realizing an environmentally friendly and particularly efficient operation of the turbo-machine 10 at advantageous temperature levels. Moreover, said working fluids allows for achieving required operational parameters such as pressure and temperature level with relatively low and acceptable rotational frequencies or rotational speeds of the shaft 12. Furthermore, the dimensions of the turbine wheels 22, 26 can be adjusted to advantageous values which allow for realizing a high thermal efficiency of the thermodynamic cycle and the turbo-machine 10 with, for example, an efficiency η ₅ = 75 - 85%. The turbo-machine 10 can be configured as a high speed turbo-machine that can be operated depending on the scale at rotational speeds up to 100000 rpm. As can be seen from FIG 1 , the turbine wheels 22, 26 can be configured as radial turbine wheels which are also referred to as centripetal turbine wheels. Radial turbine wheels provide a very high efficiency even for low mass flow rates and essential pressure ratios. A gas channel part of such radial turbines is usually mounted as a console part on the shaft 12 and can easily be incorporated into a joint casing of the turbo-machine 10.

The generator unit 30 can be configured as a high frequency electrical generator. Experience accumulated by specialists in this field shows that for high frequencies and power below 200 kW it is more reasonable to implement electrical generators with excitation from permanent magnets. For higher power, alternative solutions are possible. Even such high frequency electrical generators can be cooled sufficiently by utilizing said interstage heating.

Said bearing device provides a stable rotation at high speeds of the shaft 12. Axial forces can be compensated by the bearing device. Foil gas dynamic bearings or electromagnetic bearings can be used depending on the power range and the weight of a rotor comprising at least the shaft 12 and the turbine wheels 22, 26. Foil bearings and electromagnetic bearings can be operated in wide temperature ranges and in different working fluids including organic gases.

By using a two-stage turbo-machine very high efficiencies for organic rankine cycle applications can be realized. Single-stage turbo-machines can either not be used or provide a low efficiency only. Axial turbines are more complex and expensive and are also limited with regard to implementing gas and electromagnetic bearings.

The dimensions of the turbo-machine 10 can be kept to a minimum because additional cooling systems can be avoided since at least one electric part (component 32) of the turbo-machine 10 can be cooled by the working fluid as an exhaust gas of the first turbine stage 16 sufficiently. The usage of interstage heating allows for recuperating heat energy and generating a very high amount of mechanical power obtained in the second turbine stage 18.