STEAM TURBINE

Abstract

The invention relates to a steam turbine (10), in particular for using the waste heat of an internal combustion engine (2), comprising at least one rotor (26) and at least one stator (20), said stator (20) comprising at least two nozzles (22) which are arranged in parallel in relation to each other. The nozzles (22) are designed for different load points of the rotor (26) and can be switched on and off independently from each other.

Description

BACKGROUND OF THE INVENTION

The invention relates to a steam turbine, in particular for using the waste heat of an internal combustion engine.

A steam turbine is known from the German patent application DE 42 14 775 A1, which can be operated at different load conditions. Said steam turbine is characterized by a plurality of nozzle groups of the same design in the stator. In order to control the steam turbine at different load demands, the steam inflow to each nozzle group is adjusted with a control valve. In the case of a low load demand, only one nozzle or one nozzle group is activated. When the power requirements increase, steam is applied to one nozzle group after the other. The control of the steam supply takes place thereby by means of the control slots of a rotary slide valve. It is also common to employ automatic regulators.

SUMMARY OF THE INVENTION

The steam turbine according to the invention has the advantage that a particularly large power spectrum can be covered by the steam turbine through the use of nozzles, which are designed for different load points and can be switched on and off independently from each other.

The different designs of the nozzles can be simply and advantageously predefined by the geometry thereof, the area ratio between the narrowest nozzle cross section and the outlet cross section, the amount of unblocked flow cross section and/or the angle of inclination of the nozzle with respect to the rotor.

The requirement for a large power spectrum occurs especially in steam turbines which are employed for using the waste heat of an internal combustion engine that is operated in a motor vehicle. It is thus particularly advantageous for the different operating points of the internal combustion engine to correspond to the different load points of the rotor. The boundary conditions (steam quantity, temperature, pressure) vary at the inlet into the stator as a function of the respective operating point of the internal combustion engine. An optimal utilization of the energy provided by the internal combustion engine can be achieved by switching differently designed nozzles on and off because said nozzles are adapted to the respective boundary conditions.

A particular advantage results if a nozzle for a high load point of the rotor and another nozzle for a low load point of the rotor are integrated into the stator. A particularly broad power spectrum can be covered with only a few nozzles by means of this measure. This results by virtue of the fact that only the nozzle having the design for the low load points can be switched on for low load points of the internal combustion engine while the other nozzle is switched off. In contrast thereto, only the nozzle having the design for high load points can be switched on for high load points of the internal combustion engine while the other nozzle is switched off. Further load points of the internal combustion engine can be covered by a combination of both nozzles. As a result of the small number of nozzles, costs can be saved in the construction of the steam turbine and a broad power spectrum of the internal combustion engine can be covered at the same time.

Laval nozzles are expediently employed for the acceleration of the steam in the stator. By the use of said Laval nozzles, the steam can thereby be accelerated from ultrasonic velocity to supersonic velocity. On account of the high velocities, a particularly high power output of the steam turbine can be achieved.

The use of partially impinged turbines is advantageous because the diameter of the rotor can be increased by means of the partial impingement, and design sizes of turbines which are small and difficult to implement can thereby be avoided.

A further advantage results if the nozzles of the steam turbine are switched on and off via switching equipment consisting of control valves or aperture plates. Such switching equipment makes a plurality of possible nozzle combinations available.

Switching equipment, which is controlled via a pressure difference present at the stator, is particularly advantageous because the switching of the nozzles on and off can be optimally adapted to the prevailing boundary conditions. It is useful for the switching equipment to be actuated via a servomotor, in particular a multiphase motor, as this allows for a simple and cost effective implementation option.

A nozzle can be advantageously employed as a nozzle bypass, which guides the steam without acceleration onto the rotor in order to allow steam to slowly flow through the rotor during warm-up or in order not to generate any power during deceleration of the internal combustion engine. A bypass implemented in this form is much more cost effective than a bypass which leads the steam past the steam turbine. By allowing steam to slowly flow through the turbine during warm-up, damage to the rotors due to retrograde condensation, which is caused by steam having a lower quality, is furthermore prevented. In addition, problems due to freezing on the rotors resulting from the warm steam prior to startup of the steam turbine can be eliminated.

It is thereby particularly advantageous if the nozzle, which serves as the nozzle bypass, changes the direction of the steam jet in such a manner that a resulting torque is not produced at the rotor. In so doing, a power output of the steam turbine during deceleration is prevented.

In steam turbines, which have a plurality of stages consisting of stators and rotors disposed one behind the other, it is advantageous if the nozzles of the downstream stages consisting of stator and rotor are disposed in such a manner that said nozzles correspond in the disposal and design thereof with the nozzles of the first stage consisting of stator and rotor. By means of this disposal, additional switching equipment in the downstream stages can be avoided and costs are therefore saved.

The employment of a steam turbine having the previously mentioned features is particularly advantageous if said turbine is disposed in a circuit comprising a feed pump, heat exchanger and condenser and the heat exchanger serves the purpose of using the waste heat of an internal combustion engine and produces the steam which is supplied to the nozzles of the stator. This is the case because a particularly broad power spectrum results from this disposal.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are depicted in the drawings and explained in detail in the description below. In the drawings:

FIG. 1 shows a steam turbine in a schematic depiction according to a first exemplary embodiment.

FIG. 2 shows a Laval nozzle in perspective depiction.

FIG. 3 shows a steam turbine in schematic depiction according to a second exemplary embodiment and

FIG. 4 shows a steam turbine comprising a circuit in a schematic depiction.

DETAILED DESCRIPTION

FIGS. 1 and 3 show a steam turbine 10 in a schematic depiction comprising a rotor 26, a stator 20 and switching equipment 28. At least two nozzles 22 are disposed in the stator 20, which convert the potential energy of the steam into kinetic energy in said stator 20.

The nozzles 22 are disposed in parallel in relation to each another in the stator 20; and therefore the steam enters in a plane which is the same for all nozzles 22 and is perpendicular to the main flow direction and leaves said nozzles 22 in another plane which is perpendicular to the main flow direction. The nozzles 22 are circularly disposed in the stator 20 This can relate to a fully impinged steam turbine 10, in which said nozzles are disposed around the entire stator 20 or to a partially impinged steam turbine 10, in which said nozzles 22 occupy only parts or a sector of the circle of the said stator 20.

The nozzles 22 are designed for different load points of the rotor 26, wherein at least one of the nozzles 22 is designed for a high load point of the rotor 26 and at least one of the nozzles 22 is designed for a low load point of said rotor 26.

The different design of the nozzles 22 is primarily determined by the geometry thereof, the amount of unblocked flow cross section, the area ratio between the narrowest nozzle cross section and the outlet cross section and/or the angle of inclination of the nozzle 22 with respect to the rotor 26. The design of the individual nozzles 22 is determined on the basis of the operating conditions encountered, such as mass flow, temperature and pressure conditions. Said operating conditions fluctuate particularly sharply in a steam turbine which is used for the recovery of waste heat of an internal combustion engine.

The nozzles 22 are preferably Laval nozzles 24, as they are depicted in FIG. 2, and guide the steam in an accelerated manner onto the rotor 26 of the steam turbine 10. The Laval nozzles 24 are configured as rectangular channels having a convergent and divergent cross-sectional profile. Due to their special design, Laval nozzles 24 are capable of accelerating gas flows from subsonic to supersonic velocities.

Provision can be made for further nozzles 22 for other load points of the rotor 26 or for a plurality of nozzles 22 for the same load point of the rotor 26. The nozzles 22 can be disposed in nozzle groups or individually in the stator 20.

Switching equipment 28 is disposed upstream of the stator 20, said switching equipment switching the nozzles 22 in said stator 20 independently from each other. By means of the switching equipment 28, each nozzle 22 can be opened alone while the other nozzles 22 are closed, or a plurality of nozzles 22 can be opened simultaneously. If the nozzles 22 are disposed in nozzle groups, entire nozzle groups can also be opened or closed via the switching equipment 28.

The switching equipment 28 can consist of control valves or of an aperture plate and can be disposed in front of or behind the stator 20. The switching equipment 28 can be controlled via a pressure difference prevailing at the stator 28. As a function of the prevailing pressure difference, one or a plurality of nozzles 22 adapted to this boundary condition are activated while other nozzles 22 are closed. The switching equipment 28 can be actuated via a servomotor, in particular a multiphase motor.

If an aperture plate is provided, the actuation of the switching equipment 28 can then actively take place by means of a servomotor or passively by using the prevailing pressure difference.

A further exemplary embodiment is depicted in FIG. 3, in which a further nozzle is provided, which serves as a nozzle bypass 32, beside the nozzles 22 which serve to accelerate the steam onto the rotor 26. Said nozzle bypass 32 is not embodied as a Laval nozzle 24 because the nozzle bypass 32 is to guide the steam without acceleration onto the rotor 26. Said nozzle bypass 32 has a large flow cross section in comparison to other nozzles 22; and therefore the pressure in the high pressure part upstream of the steam turbine 10 reduces very quickly and the steam achieves only very low flow velocities when entering the rotor 26. Due to the low flow velocities, no significant power output is achieved in the rotor 26.

The power output of the rotor 26 can be still further reduced if the nozzle bypass 32 changes the direction of the steam jet escaping from the nozzle bypass 32 in such a manner that no resulting torque is produced. This can be brought about by said steam jet flowing against the rotor 26 in the axial direction or in the reverse direction of rotation.

The steam turbine 10 can also be embodied as a multistage steam turbine 10, in which a plurality of stages consisting of stators 20 and rotors 26 is disposed one behind the other.

In each of the turbine stages, the nozzles 22 of the rotor 20 can be switched on and off via switching equipment 28 and corresponding to the two exemplary embodiments pursuant to FIG. 1 and FIG. 3.

Alternatively switching equipment 28 for controlling the nozzles 22 can be situated only in the first stage of the steam turbine 10, which consists of stator 20 and rotor 26 and is situated directly behind the steam source. The nozzles 22 of the downstream stages consisting of stator 20 and rotor 26 can be arranged in such a manner that said nozzles correspond from the positioning thereof to the nozzles 22 of the first stage. In so doing, the steam jet of the nozzle 22, which is released in the first stage, should only enter into the corresponding nozzle 22 of the second stage. The corresponding nozzles 22 are designed such that they achieve an optimal degree of efficiency at the prevailing boundary conditions.

The steam turbine 10 is particularly suited for the recovery of waste heat in applications in motor vehicles. The steam turbine 10 of the invention is however also suited for other applications.

FIG. 4 shows a steam turbine 10 according to one of the preceding exemplary embodiments in a circuit 4 for the recovery of waste heat of an internal combustion engine 2. A heat exchanger 8, a condenser 12, a feed pump 6 and the steam turbine 10 are disposed in the circuit 4 containing a circulating working medium.

The internal combustion engine 2 burns fuel in order to produce mechanical energy. The exhaust gases ensuing from this process are discharged via an exhaust gas system, in which an exhaust gas catalyst can be disposed. A duct section of the exhaust gas system is led through a heat exchanger 8. Heat energy from the exhaust gases or the exhaust gas recirculation is given off to the working medium in the heat exchanger 8 so that said working medium can be evaporated and superheated in said heat exchanger 8.

The heat exchanger 8 of the circuit 4 is connected via a line to the steam turbine 10. The evaporated working medium flows via the line to said steam turbine 10 and drives the same. Said steam turbine 10 has an output shaft 11, via which said steam turbine 10 is connected to a load. In this way, mechanical energy can, for example, be transferred to a drive train or used to drive an electrical generator, a pump or something similar. After flowing through said steam turbine 10, the working medium is led via a line to a condenser 12. The working medium which was expanded via said steam turbine 10 is cooled in the condenser 12 and condenses. Said condenser 12 can be connected to a cooling circuit. The working medium liquefied in said condenser 12 is transported via a line from a feed pump 6 into the line to the heat exchanger 8.

A flow direction of the working medium through the circuit 4 is provided by the feed pump 6. Heat energy, which can be released in the form of mechanical energy to the shaft 11, can therefore be continuously extracted via the heat exchanger 2 from the exhaust gases and the constituent parts of the exhaust gas recirculation of the internal combustion engine 2.

Water or another liquid, which corresponds to the thermodynamic requirements, can be used as the working medium. The working medium experiences thermodynamic changes in state when flowing through the circuit 4. In the liquid phase, said working medium is brought by the feed pump 6 to the pressure level required for evaporation. The heat energy of the exhaust gas is subsequently given off to said working medium via the heat exchanger 8. In so doing, said working medium is isobarically evaporated and subsequently superheated. The steam is then adiabatically expanded in the steam turbine 10. In so doing, mechanical energy is obtained and transferred to the shaft 11. Said working medium is then cooled in the condenser 12, liquefied and supplied again to the feed pump 6.

As a function of the operating point of the internal combustion engine 2, a variable amount of waste heat is provided to the heat exchanger 8. The heat exchanger 8 produces the steam, which is available to the steam turbine 10. The steam turbine 10 has to work as a function of the operating point of the internal combustion engine 2 with other boundary conditions (amount of steam, temperature, pressure) and adapt accordingly to the load points thereof. This takes place by switching the nozzles 22 in the stator 20 of the steam turbine 10 on and off, which nozzles correspond to the different load points of the internal combustion engine 2.

Claims

1. A steam turbine (10), comprising at least one rotor (26) and at least one stator (20), said stator (20) comprising at least two nozzles (22) which are arranged in parallel in relation to each other, characterized in that the nozzles (22) are designed for different load points of the rotor (26) and can be switched on and off independently from each other.

2. The steam turbine (10) according to claim 1, wherein the steam turbine uses the waste heat of an internal combustion engine, and characterized in that the different load points of the rotor (26) correspond to different operating points of the internal combustion engine (2).

3. The steam turbine (10) according to claim 1, characterized in that the different design of the nozzles (22) is defined by at least one of a geometry thereof, an amount of unblocked flow cross section and an angle of inclination of the nozzle (22) with respect to the rotor (26).

4. The steam turbine (10) according to claim 1, characterized in that one of the nozzles (22) is designed for a low load point of the rotor (26) and another of the nozzles (22) is designed for a high load point of the rotor (26).

5. The steam turbine (10) according to claim 1, characterized in that at least one of the nozzles (22) is a Laval nozzle (24).

6. The steam turbine (10) according to claim 1, characterized in that the rotor (26) is partially impinged with steam.

7. The steam turbine (10) according to claim 1, characterized in that the nozzles (22) are switched on and off via switching equipment (28) consisting of control valves (30) or aperture plates.

8. The steam turbine (10) according to claim 7, characterized in that the switching equipment (28) is controlled via a pressure difference prevailing at the stator (20).

9. The steam turbine (10) according to claim 1, characterized in that one of the nozzles (22) serves as a nozzle bypass (32), which guides the steam without acceleration onto the rotor (26).

10. The steam turbine (10) according to claim 9, characterized in that the nozzle (22) which serves as the nozzle bypass (32) changes a steam jet in such a manner that no resulting torque is produced.

11. The steam turbine (10) according to claim 1, characterized in that a plurality of stages consisting of stators (20) and rotors (26) is disposed one behind the other.

12. The steam turbine (10) according to claim 10, characterized in that the nozzles (22) of the downstream stages consisting of stator (20) and rotor (26) are disposed in such a manner that said nozzles correspond in a configuration thereof to the nozzles (22) of a first stage consisting of stator (20) and rotor (26).

13. The steam turbine (10) according to claim 1 wherein the steam turbine uses the waste heat of an internal combustion engine, and comprising a circuit (4), characterized in that a feed pump (6), a heat exchanger (8) and a condenser (12) are disposed in the circuit (4) and in that the heat exchanger (8) serves in using the waste heat of an internal combustion engine (2) and produces the steam which is supplied to the nozzles (22) of the stator (20).

14. The steam turbine (10) according to claim 1, characterized in that the different design of the nozzles (22) is defined by the geometry thereof.

15. The steam turbine (10) according to claim 1, characterized in that the different design of the nozzles (22) is defined by an amount of unblocked flow cross section.

16. The steam turbine (10) according to claim 1, characterized in that the different design of the nozzles (22) is defined by an angle of inclination of the nozzle (22) with respect to the rotor (26).