Power generation system and method to generate power by operation of such power generation system

Abstract

A power generation system comprising a liquid pump section (4) comprising a rotary liquid pump (7) with an impeller in which a working fluid is pressurised and which is driven by a drive shaft (8); an evaporator section comprising an evaporator (9) in which the in the rotary liquid pump (7) pressurised working fluid is at least partly evaporated by addition of heat from a heat source; an expander section (3) comprising a rotary expander (11) with an inlet port (16) and a rotary expander element in which the in the evaporator section at least partly evaporated working fluid is expanded; and a generator section (5) comprising a rotary power generator (13) with a rotor,
whereby the expander section (3), the liquid pump section (4) and the generator section (5) are rotably connected in such a manner that relative rotational speed ratios between the rotary expander element of the rotary expander (11), the impeller of the rotary liquid pump (7) and the rotor of the rotary power generator (13) are mechanically upheld, characterised in that the drive shaft (8) which drives the impeller of the rotary liquid pump (7), is configured to be provided with a throttling device allowing a controlled portion (15) of the working fluid entering the rotary liquid pump (7) to pass from the liquid pump section (4) to the expander section (3) and/or the generator section (5).

Claims

1. A power generation system comprising a liquid pump section (4) comprising a rotary liquid pump (7) with an impeller in which a working fluid is pressurised and which is driven by a drive shaft (8); an evaporator section comprising an evaporator (9) in which the in the rotary liquid pump (7) pressurised working fluid is at least partly evaporated by addition of heat from a heat source; an expander section (3) comprising a rotary expander (11) with an inlet port (16) and a rotary expander element in which the in the evaporator section at least partly evaporated working fluid is expanded; and a generator section (5) comprising a rotary power generator (13) with a rotor, whereby the expander section (3), the liquid pump section (4) and the generator section (5) are rotably connected in such a manner that relative rotational speed ratios between the rotary expander element of the rotary expander (11), the impeller of the rotary liquid pump (7) and the rotor of the rotary power generator (13) are mechanically upheld, wherein the drive shaft (8) which drives the impeller of the rotary liquid pump (7), is configured to be provided with a throttling device allowing a controlled portion (15) of the working fluid entering the rotary liquid pump (7) to pass from the liquid pump section (4) to the expander section (3) and/or the generator section (5).

2. The power generation system according to claim 1, wherein the power generation system (1) is a Rankine cycle, wherein the working fluid circulates.

3. The power generation system according to claim 1, wherein the inlet port (16) of the rotary expander (11) is in a higher position than an outlet port (17) of said rotary expander.

4. The power generation system according to claim 1, wherein the rotary liquid pump (7) is in a lower position than the inlet port (16) of the rotary expander (11).

5. The power generation system according to claim 1, wherein the rotary power generator (13) in the generator section (5) is a synchronous generator.

6. The power generation system according to claim 1, wherein the working fluid is an organic working fluid.

7. The power generation system according to claim 1, wherein the working fluid comprises a lubricant or acts as a lubricant.

8. The power generation system according to claim 1, wherein the rotary expander element is mounted on the drive shaft (8) which drives the impeller of the rotary liquid pump (7).

9. The power generation system according to claim 1, wherein the rotary expander element is mounted on a drive shaft (12) which drives the rotor of the rotary power generator (13).

10. The power generation system according to claim 1, wherein the drive shaft (8) which drives the impeller of the rotary liquid pump (7), is different from the drive shaft (12) which drives the rotor of the rotary power generator (13).

11. The power generation system according to claim 1, wherein the rotor of the rotary power generator (13) is driven by the drive shaft (8) which drives the impeller of the rotary liquid pump (7).

12. The power generation system according to claim 1, wherein the power generation system (1) further comprises a semi-hermetically closed housing (6) which encloses all rotating parts of the rotary expander (11) and the rotary power generator (13).

13. The power generation system according to claim 12, wherein the semi-hermetically closed housing (6) encloses all rotating parts of the rotary liquid pump (7).

14. The power generation system according to claim 13, wherein the position of the expander section (3) in the semi-hermetically closed housing (6) is in between the liquid pump section (4) and the generator section (5).

15. The power generation system according to claim 13, wherein the position of the generator section (5) in the semi-hermetically closed housing (6) is in between the liquid pump section (4) and the expander section (3).

16. The power generation system according to claim 1, wherein the rotary expander (11) is a positive displacement rotary expander.

17. The power generation system according to claim 1, wherein the rotary liquid pump (7) is a positive displacement rotary pump.

18. The power generation system according to claim 1, wherein the rotary expander (11) and/or the rotary power generator (13) are mounted in a vertical position.

19. The power generation system according to claim 1, wherein the rotary expander (11) and/or the rotary power generator (13) are mounted in a horizontal position.

20. The power generation system according to claim 1, wherein the throttling device is an opening between the drive shaft (8) on which the impeller of the rotary liquid pump (7) is mounted and a sealing (18) of this drive shaft (8) between the liquid pump section (4) and one of the expander section (3) and generator section (5).

21. A method to generate power by operation of a power generation system (1), the power generation system (1) comprising: a liquid pump section (4) comprising an inlet and a rotary liquid pump (7) with an impeller in which a working fluid is pressurised and which is driven by a drive shaft (8); an evaporator section comprising an evaporator (9) in which the in the rotary liquid pump (7) pressurised working fluid is at least partly evaporated by addition of heat from a heat source; an expander section (3) comprising a rotary expander (11) with a rotary expander element in which the in the evaporator section at least partly evaporated working fluid is expanded; and a generator section (5) comprising a rotary power generator (13) with a rotor, whereby the expander section (3), the liquid pump section (4) and the generator section (5) are rotably connected in such a manner that relative rotational speed ratios between the rotary expander element of the rotary expander (11), the impeller of the rotary liquid pump (7) and the rotor of the rotary power generator (13) are mechanically upheld, wherein a controlled portion (15) of the working fluid entering the rotary liquid pump (7) is allowed to pass from the liquid pump section (4) to the expander section (3) and/or the generator section (5) by means of a throttling device, which the drive shaft (8) by which the impeller of the rotary liquid pump (7) is driven is provided with, whereby the rotary expander (11) and/or rotary power generator (13) is cooled by the controlled portion (15) of the working fluid which passes from the liquid pump section (4) to the expander section (3) respectively the generator section (5).

22. A method to generate power according to claim 21, wherein the at least partly evaporated working fluid which is fed to an inlet port (16) of the rotary expander is in a gaseous or vapour state.

23. A method to generate power according to claim 21, wherein the working fluid which is fed to an inlet port (16) of the rotary expander (11) is a mixture of liquid and gaseous or vaporous working fluid.

24. A method to generate power according to claim 21, wherein the rotor of the rotary power generator (13) is exposed to a pressure exerted by the working fluid which is higher than a working fluid pressure at the inlet of the liquid pump section (4) and lower than a working fluid pressure at an outlet of the liquid pump section (4).

25. A method to generate power according to claim 21, wherein the rotor of the rotary power generator (13) is exposed to a mixture of liquid and gaseous or vaporous working fluid.

26. A method to generate power according to claim 21, wherein a mass flow of the controlled portion (15) of working fluid which is allowed to pass from the liquid pump section (4) to the expander section (3) and/or the generator section (5) by a throttling device, is lower than 25% of a total mass flow of the working fluid which is fed to the inlet of the liquid pump section (4).

Description

(1) With the intention of better showing the characteristics of the invention, a few preferred embodiments of a power generation system according to the invention whereby the drive shaft of the rotary liquid pump is provided with a throttling device, are described hereinafter by way of example, without any limiting nature, with reference to the accompanying drawings, wherein:

(2) FIGS. 1A and 1B schematically show a Rankine circuit including a power generation system according to the invention;

(3) FIGS. 2 to 5 each show a different variant of the power generation system;

(4) FIG. 6 shows in more detail a sealing of a drive shaft of a rotary liquid pump of the power generation system.

(5) In this case, the power generation system 1 in FIG. 1A is a Rankine circuit comprising an integrated combination 2 of an expander section 3, a liquid pump section 4, and a generator section 5

(6) Preferably all rotating parts of the expander section 3 and the generator section 5, and preferably also the liquid pump section 4 are enclosed in a semi-hermetically closed housing 6.

(7) A rotary liquid pump 7 in the liquid pump section 4 drives the working fluid through the circuit by means of a rotating impeller that is driven by a drive shaft 8 of the rotary liquid pump 7. The rotary liquid pump 7 may be a positive displacement rotary pump, preferably a gear pump.

(8) Flow of the working fluid through the circuit is as follows.

(9) The rotary liquid pump 7 drives the working fluid in liquid form through an evaporator section comprising an evaporator 9 which is a first section of a heat exchanger 10. A heating medium providing heat from a heat source flows through a second section of the heat exchanger 10, preferably countercurrently with respect to the working fluid flowing through the evaporator 9.

(10) The heat source may be waste heat from a process installation such as a compressor installation, such that the power generation system 1 is a so-called WTP (Waste heat To Power) installation transforming recovered waste heat into useful mechanical or electrical energy.

(11) The working fluid evaporates at least partly in the evaporator 9 due to heat transfer from the heating medium to the working fluid, and leaves the evaporator 9 in a gaseous or vapour state or as a mixture of liquid and gas or vapour.

(12) The working fluid is typically characterised by a more favourable evaporation characteristic, which is the boiling temperature at the working fluid pressure in the evaporator 9, with respect to the temperature of a heating medium which provides heat to the working fluid in the evaporator 9.

(13) The lower the boiling temperature of the working fluid in the evaporator 9, the better and more efficient heat is provided to the working fluid by a heating medium at low temperature. Typically, a working fluid is selected whose critical point temperature is close to a maximum temperature of the heating medium in the heat exchanger 10.

(14) Furthermore, the working fluid may comprise a lubricant or act as a lubricant for components of the power generation system 1.

(15) An example of a suitable organic working fluid is 1,1,1,3,3-pentafluoropropane. However, the invention is not limited to this specific working fluid.

(16) The at least partly evaporated working fluid leaving the evaporator 9 is expanded in a rotary expander 11 in the expander section 3. The rotary expander 11 is configured such that it enables thermal energy of the working fluid to be converted into mechanical energy, for example because it is constructed in the form of a rotary expander element which is driven by an outgoing drive shaft 12 that is coupled to a rotor of a rotary power generator 13 in the generator section 5 for supplying electrical energy to a consumer.

(17) The rotary expander 11 in the expander section 3 may be a positive displacement rotary expander, preferably a twin-screw rotary expander.

(18) The rotary power generator 13 in the generator section 5 may be a synchronous generator, preferably a permanent magnet generator.

(19) The expanded working fluid leaving the expander section 3 flows through a condenser section comprising a condenser 14 where it comes into contact with and is cooled by a cooling medium, which ensures that the working fluid completely condenses in order to be able to be pumped around as a liquid by the rotary liquid pump 7 for a subsequent cycle in the Rankine circuit.

(20) A controlled portion 15 of the working fluid entering the rotary liquid pump 7 is allowed to leak from the liquid pump section 4 to the generator section 5 via a throttling device which is provided on the drive shaft 8 which drives the impeller of the rotary liquid pump 7. This controlled portion of the working fluid 15 will pass over and through the rotary power generator 13. In this way, the rotor and other components of the rotary power generator 13 are cooled to a suitable extent.

(21) As indicated in FIG. 1B, the position of the expander section 3 and the generator section 5 may be interchanged in the housing 6, such that the controlled portion 15 of the working fluid is leaking to the expander section 3 via the throttling device provided on the drive shaft 8 of the rotary liquid pump 7. The controlled portion 15 of the working fluid is then used to cool bearings and other components of the rotary expander 11.

(22) It is not excluded that in FIGS. 1A and/or 1B the controlled portion 15 of the working fluid flows through both the expander section 3 and the generator section 5, and is used to cool both components of the rotary expander 11 and components of the generator 13.

(23) The expander section 3, the liquid pump section 4 and the generator section 5 are rotably connected in such a manner that relative rotational speed ratios between the rotary expander element of the rotary expander 11, the impeller of the rotary liquid pump 7 and the rotor of the rotary power generator 13 are mechanically upheld.

(24) This can be achieved by connecting the rotary expander element of the rotary expander 11, the impeller of the rotary liquid pump 7, the rotor of the rotary power generator 13, the drive shaft 8 of the rotary liquid pump 7, and the drive shaft 12 of the rotary power generator 13 by means of gearboxes. However, the rotary expander element of the rotary expander 11 and/or the impeller of the rotary liquid pump 7 may be mounted directly on the drive shaft 8. Similarly, the rotary expander element of the rotary expander 11 and/or the rotor of the rotary power generator 13 may be mounted directly on the drive shaft 12.

(25) In a variant of the invention, the rotary expander element 11 is mounted on the drive shaft 8 which drives the impeller of the rotary liquid pump 7. Furthermore, the rotary expander element of the rotary expander 11 may be mounted on the drive shaft 12 which drives the rotor of the rotary power generator 13.

(26) The drive shaft 8 which drives the impeller of the rotary liquid pump 7 may be different from the drive shaft 12 which drives the rotor of the rotary power generator 13, for example when the impeller of the rotary liquid pump 7 is driven by a drive shaft 8 connected to a male rotor element of the rotary expander 11 and the rotor of the rotary power generator 13 is driven by a drive shaft 12 connected to a female rotor element of the rotary expander 11 or vice versa. Alternatively, the rotor of the rotary power generator 13 may be driven be the same drive shaft as the impeller of the rotary liquid pump 7, such that drive shafts 8 and 12 become one and the same drive shaft.

(27) Different configurations are possible for the positioning and orientation of the expander section 3, the liquid pump section 4 and the generator section 5 in the semi-hermetically closed housing 6, as indicated in FIGS. 2 to 5.

(28) FIG. 2 schematically shows a combination of an expander section 3, a generator section 5 and a liquid pump section 4, whereby these sections are vertically mounted and rotably connected in such a manner that the relative rotational speed ratios between the rotary expander element of the rotary expander 11, the impeller of the rotary liquid pump 7 and the rotor of the rotary power generator 13 are mechanically upheld. The controlled portion 15 of the working fluid flows from the liquid pump section 4 to the generator section 5 in order to cool the rotor and other internal components of the rotary power generator 15. The rotary expander 11 of the expander section 3 is provided with an inlet port 16 which is in a higher position than the outlet port 17 of this rotary expander 11. The rotary liquid pump 7 of the liquid pump section 4 is in a lower position than the inlet port 16 of the rotary expander 11 to avoid cavitation of the rotary liquid pump 7 and the resulting pumping losses due to internal ascension of mixed phase working fluid and backflow of gaseous or vaporous working fluid from the rotary expander 11 to the rotary liquid pump 7.

(29) FIG. 3 shows a variant of the combination in FIG. 2, whereby the positions of the expander section 3 and the generator section 5 are interchanged, such that the controlled portion 15 of the working fluid allowed by the throttling device which is provided on the drive shaft 8 of the rotary liquid pump 7, flows from the liquid pump section 4 to the expander section 3 in order to cool the bearings and other rotating parts of the rotary expander 11.

(30) FIG. 4 shows a variant of the combination in FIG. 2, whereby the expander section 3, the generator section 5 and the liquid pump section 4 are horizontally mounted.

(31) FIG. 5 shows a variant of the combination of an expander section 3, a generator section 5 and a liquid pump section 4 in FIG. 4, whereby the positions of the expander section 3 and the generator section 5 are interchanged.

(32) In FIG. 6 is demonstrated that the controlled portion 15 of the working fluid is throttled and leaking via the drive shaft 8 of the rotary liquid pump 7 from the liquid pump section 4 at a pressure level p1 to one of the expander section 3 and generator section 5 at a pressure level p2 which is lower than p1. In this case, the throttling device is an opening between the drive shaft 8 on which the impeller of the rotary liquid pump 7 is mounted and a sealing 18 of this drive shaft 8 between the liquid pump section 4 and the one of the expander section 3 and generator section 5.

(33) The controlled portion 15 of the working fluid which is allowed to pass from the liquid pump section 4 to the expander section 3 or the generator section 5 by the throttling device, which the drive shaft 8 which drives the impeller of the rotary liquid pump 7 is provided with, may be used to cool the rotary expander 11 or the rotary power generator 13 in a method to generate power by operation of the power generation system 1 according to the invention.

(34) In this method, the inlet port 16 of the rotary expander 11 in the expander section 3 is fed with at least partly evaporated working fluid coming from the evaporator 9 in the evaporator section.

(35) The rotor of the rotary power generator 13 is cooled by and exposed to working fluid at a pressure level which is higher than a working fluid pressure level at an inlet of the liquid pump section 4 and lower than a working fluid pressure level at an outlet of the liquid pump section 4. As the temperature of the working fluid which is cooling the rotary power generator 13 increases during its cooling action, this working fluid may evaporate such that the rotor of the rotary power generator 13 is exposed to a mixture of liquid and gaseous or vaporous working fluid.

(36) The mass flow of the controlled portion 15 of the working fluid is only a small portion relative to the total mass flow of the working fluid which is fed to the inlet of the liquid pump section 4, preferably lower than 25%, more preferably lower than 10%, even more preferably lower than 5%, yet more preferably lower than 3%.

(37) The present invention is by no means limited to the embodiments described as an example and shown in the drawings, but a power generation system and a method to generate power by operation of such power generation system according to the invention can be realised in all kinds of forms or dimensions without departing from the scope of the invention, and by extension is also applicable to a power generation system with more than one expander section or liquid pump section or a power generation system comprising an expander section with more than one rotary expander or a liquid pump section with more than one rotary liquid pump.