阅读说明：本技术 发电系统和通过操作这种发电系统来发电的方法 (Power generation system and method of generating power by operating such a power generation system ) 是由 H·奥曼 A·J·戈瑟尔斯 于 2020-02-11 设计创作，主要内容包括：本公开涉及一种发电系统,-液体泵部分(4),所述液体泵部分包括具有叶轮的旋转式液体泵(7),工作流体在所述叶轮中被加压并且所述叶轮由驱动轴(8)驱动；-蒸发器部分,所述蒸发器部分包括蒸发器(9),其中在所述旋转式液体泵(7)中被加压的工作流体通过添加来自热源的热量而在所述蒸发器中至少部分地被蒸发；-膨胀器部分(3),所述膨胀器部分包括具有入口端口(16)和旋转式膨胀器元件的旋转式膨胀器(11),在所述蒸发器部分中至少部分地蒸发的工作流体在所述旋转式膨胀器元件中被膨胀；和-发电机部分(5),所述发电机部分包括具有转子的旋转式发电机(13),其中,所述膨胀器部分(3)、所述液体泵部分(4)和所述发电机部分(5)可旋转地连接成使得所述旋转式膨胀器(11)的旋转式膨胀元件、所述旋转式液体泵(7)的叶轮和所述旋转式发电机(13)的转子之间的相对转速比被机械地保持,其特征在于：驱动所述旋转式液体泵(7)的叶轮的所述驱动轴(8)构造成设置有节流装置,所述节流装置允许进入所述旋转式液体泵(7)的工作流体的受控部分(15)从所述液体泵部分(4)流向所述膨胀器部分(3)和/或所述发电机部分(5)。(The present disclosure relates to an electric power generation system, -a liquid pump section (4) comprising a rotary liquid pump (7) having an impeller in which a working fluid is pressurized and which is driven by a drive shaft (8); -an evaporator section comprising an evaporator (9) in which a working fluid pressurized in the rotary liquid pump (7) is at least partially evaporated by adding heat from a heat source; -an expander section (3) comprising a rotary expander (11) having an inlet port (16) and a rotary expander element in which a working fluid at least partially evaporated in the expander section is expanded; and-a generator part (5) comprising a rotary generator (13) with a rotor, wherein the expander part (3), the liquid pump part (4) and the generator part (5) are rotatably connected such that a relative rotational speed ratio between the rotary expansion element of the rotary expander (11), the impeller of the rotary liquid pump (7) and the rotor of the rotary generator (13) is mechanically maintained, characterized in that: the drive shaft (8) driving the impeller of the rotary liquid pump (7) is configured to be provided with a throttling arrangement allowing a controlled portion (15) of the working fluid entering the rotary liquid pump (7) to flow from the liquid pump portion (4) to the expander portion (3) and/or the generator portion (5).)

1. A power generation system, the power generation system comprising:

-a liquid pump part (4) comprising a rotary liquid pump (7) having an impeller in which a working fluid is pressurized and which is driven by a drive shaft (8);

-an evaporator section comprising an evaporator (9) in which a working fluid pressurized in the rotary liquid pump (7) is at least partially evaporated by adding heat from a heat source;

-an expander section (3) comprising a rotary expander (11) having an inlet port (16) and a rotary expander element in which a working fluid at least partially evaporated in the expander section is expanded; and

-a generator part (5) comprising a rotary generator (13) having a rotor,

wherein the expander section (3), the liquid pump section (4) and the generator section (5) are rotatably connected such that a relative rotational speed ratio between a rotary expansion element of the rotary expander (11), an impeller of the rotary liquid pump (7) and a rotor of the rotary generator (13) is mechanically maintained,

the method is characterized in that:

the drive shaft (8) driving the impeller of the rotary liquid pump (7) is configured to be provided with a throttling arrangement allowing a controlled portion (15) of the working fluid entering the rotary liquid pump (7) to flow from the liquid pump portion (4) to the expander portion (3) and/or the generator portion (5).

2. The power generation system according to claim 1, characterized in that the power generation system (1) is a rankine cycle in which a working fluid is circulated.

3. The power generation system according to claim 1 or 2, wherein the inlet port (16) of the rotary expander (11) is located at a higher position than the outlet port (17) of the rotary expander.

4. The power generation system according to any one of the preceding claims, wherein the position of the rotary liquid pump (7) is lower than the position of the inlet port (16) of the rotary expander (11).

5. An electric power generation system according to any one of the preceding claims, characterized in that the rotary generator (13) in the generator part (5) is a synchronous generator, preferably a permanent magnet generator.

6. The power generation system of any of the preceding claims, wherein the working fluid is an organic working fluid.

7. The power generation system of any preceding claim, wherein the working fluid comprises or acts as a lubricant.

8. The power generation system according to any one of the preceding claims, wherein the rotary expander element is mounted on the drive shaft (8) driving an impeller of the rotary liquid pump (7).

9. An electric power generation system according to any one of the preceding claims, characterized in that the rotary expander element is mounted on a drive shaft (12) driving the rotor of the rotary electric generator (13).

10. The power generation system according to claims 8 and 9, characterized in that the drive shaft (8) driving the impeller of the rotary liquid pump (7) is different from the drive shaft (12) driving the rotor of the rotary generator (13).

11. The power generation system according to any of the preceding claims 1 to 8, characterized in that the rotor of the rotary generator (13) is driven by a drive shaft (8) driving the impeller of the rotary liquid pump (7).

12. The power generation system according to any of the preceding claims, characterized in that the power generation system (1) further comprises a semi-sealed closed casing (6) enclosing all rotating parts of the rotary expander (11) and the rotary generator (13).

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

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

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

16. Power generation system according to any of the preceding claims, wherein the rotary expander (11) is a volumetric rotary expander, preferably a twin-screw rotary expander.

17. The power generation system according to any one of the preceding claims, wherein the rotary liquid pump (7) is a positive displacement rotary pump, preferably a gear pump.

18. The power generation system according to any one of the preceding claims, wherein the rotary expander (11) and/or the rotary generator (13) are mounted in a vertical position.

19. Power generation system according to any of the preceding claims 1 to 17, characterized in that the rotary expander (11) and/or the rotary generator (13) are mounted in a horizontal position.

20. The power generation system according to any one of the preceding claims, wherein the throttling device is a passage between the drive shaft (8) and a seal (18) of the drive shaft (8), an impeller of the rotary liquid pump (7) being mounted on the drive shaft (8), the seal (18) being located between the liquid pump portion (4) and one of the expander portion (3) and the generator portion (5).

21. A method of generating power by operating a power generation system (1), the power generation system (1) comprising:

-a liquid pump part (4) comprising an inlet and a rotary liquid pump (7) having an impeller in which a working fluid is pressurized and which is driven by a drive shaft (8);

-an evaporator section comprising an evaporator (9) in which a working fluid pressurized in the rotary liquid pump (7) is at least partially evaporated by adding heat from a heat source;

-an expander section (3) comprising a rotary expander (11) having a rotary expander element in which a working fluid at least partially evaporated in the expander section is expanded;

-a generator part (5) comprising a rotary generator (13) having a rotor,

wherein the expander section (3), the liquid pump section (4) and the generator section (5) are rotatably connected such that a relative rotational speed ratio between a rotary expander element of the rotary expander (11), an impeller of the rotary liquid pump (7) and a rotor of the rotary generator (13) is mechanically maintained,

the method is characterized in that:

a controlled portion (15) of the working fluid entering the rotary liquid pump (7) is allowed to flow from the liquid pump portion (4) to the expander portion (3) and/or the generator portion (5) by means of a throttling device, the drive shaft (8) driving the impeller of the rotary liquid pump (7) being provided with the throttling device,

wherein the rotary expander (11) and/or the rotary generator (13) is cooled by a controlled portion (15) of working fluid, the controlled portion (15) of working fluid flowing from the liquid pump portion (4) to the expander portion (3) and the generator portion (5), respectively.

22. The method of power generation as claimed in claim 21, wherein the at least partially vaporized working fluid supplied to the inlet port (16) of the rotary expander is in a gaseous or vaporous state.

23. A method of power generation as claimed in claim 21, wherein the working fluid supplied to the inlet port (16) of the rotary expander (11) is a mixture of liquid and gaseous or vaporous working fluid.

24. Method for generating electricity according to any of the previous claims 21 to 23, characterized in that the rotor of the rotary generator (13) is exposed to a pressure exerted by the working fluid which is higher than the working fluid pressure at the inlet of the liquid pump section (4) and lower than the working fluid pressure at the outlet of the liquid pump section (4).

25. Method for generating electricity according to any of the previous claims 21 to 24, characterized in that the rotor of the rotary generator (13) is exposed to a mixture of liquid and gaseous or vaporous working fluid.

26. Method for generating electricity according to any of the previous claims 21 to 25, characterised in that the mass flow of the controlled part (15) of the working fluid, which is allowed to flow from the liquid pump part (4) to the expander part (3) and/or the generator part (5) by means of a throttling device, is lower than 25%, preferably lower than 10%, more preferably lower than 5%, even more preferably lower than 3% of the total mass flow of the working fluid supplied to the inlet of the liquid pump part (4).

Technical Field

The present invention relates to a power generation system including an expander section that expands a working fluid, a liquid pump section that pressurizes the working fluid, and a generator section, wherein the expander section, the liquid pump section, and the generator section are rotatably connected such that a relative rotation speed ratio between the expander section, the liquid medium section, and the generator section is mechanically maintained.

Specifically, the power generation system also includes a semi-sealed closed housing that encloses all of the rotating components of the expander portion, the liquid pump portion, and the generator portion, but the power generation system is not so limited.

Background

It is known in expansion machines to generate power by converting energy associated with the pressure of a working fluid into mechanical kinetic energy of an expander, which is a turbine or the like having a rotor, a piston or the like. This kinetic energy can be further converted into electrical energy in a rotary generator with a rotor which is rotatably connected to the expansion machine by means of a shaft, coupling, gear, belt or the like. The expansion machine can be driven by a working fluid circulating in a closed circuit called rankine cycle or rankine circuit. The closed circuit is provided with a liquid pump to circulate the working fluid through the closed circuit in sequence

-an evaporator section comprising one or more evaporators in which working fluid from a liquid pump is at least partially converted into a high pressure gas or vapour;

-an expander section;

a condenser section comprising one or more condensers connected to a cooling circuit of a coolant (for example water or air) to enable complete condensation of the working fluid into a liquid which is pumped back again (pump around) by a liquid pump for subsequent circulation.

To close the rankine cycle, an outlet of the liquid pump portion is fluidly connected to an inlet of the evaporator portion, an outlet of the evaporator portion is fluidly connected to an inlet of the expander portion, an outlet of the expander portion is fluidly connected to an inlet of the condenser portion, and an outlet of the condenser is fluidly connected to an inlet of the liquid pump portion.

The working fluid may alternatively be an Organic working fluid, where the Rankine Cycle is referred to as an Organic Rankine Cycle (ORC). Organic working fluids have the disadvantage that they are generally explosive, toxic or expensive. Accordingly, mechanical shaft seals are required at the locations where the rotating components of the rotary expander and/or rotary generator pass through a housing containing the working fluid surrounding the expander rotor or generator and are in contact with the ambient air. Such mechanical shaft seals are expensive and often require extensive maintenance.

A common approach to avoiding the use of mechanical shaft seals between the working fluid and the ambient air is to design a compact "semi-sealed" or "integrated" combination of expander and generator. The "semi-sealed" or "integrated" combination of expander and generator means that the expander and generator combination is contained in a housing in which all rotating parts of the expander and generator are completely enclosed by the housing and are thus isolated from contact with ambient air. Examples of semi-sealed or integrated combinations of expanders and generators are described, inter alia, in US 4185465 and DE 102012016488. EP 0004609 shows a combination of semi-seals of a screw expander, a screw compressor and an electric motor in a refrigerant working fluid. JPH 05195808 and CN 206290297 show an integrated combination of expander, generator and liquid pump.

A disadvantage of the integrated combination of expander, generator and liquid pump is that undesirable internal leakage of working fluid occurs within the housing between the expander section containing the expander, the generator section containing the generator and the liquid pump section containing the liquid pump, because there is a significant difference in the pressure level of the working fluid in these sections of the housing. Such internal leakage not only reduces the power generation efficiency, but also reduces the reliability of the power generation system due to severe flashing when the working fluid is in a mixed liquid-gas or mixed liquid-vapor state. In addition, when high-pressure vapor of the working fluid leaks from the expander part or the generator part to the liquid pump, a cavitation phenomenon occurs in the liquid pump. Further, a large amount of liquid may leak from the liquid pump to the condenser via the drive shaft of the liquid pump without passing through the evaporator, resulting in a decrease in power generation efficiency, where "power generation efficiency" is defined as the ratio of the mechanical energy generated in the expander section to the sum of the heat transferred to the working fluid in the evaporator section and the work delivered to the liquid pump. Instead, tight seals on the drive shaft of the liquid pump to avoid leakage from the liquid pump via the drive shaft of the liquid pump are prone to wear and require undesirable maintenance.

Furthermore, if the generator is a permanent magnet generator, the magnets of the permanent magnet generator may be subject to insufficient cooling due to the compact size of the integrated combination of the expander, generator and liquid pump, resulting in permanent impairment of performance.

EP 2386727 discloses a power generation system designed as a rankine cycle comprising a turboexpander comprising an integrated combination of an expander section, a liquid pump section and a motor-generator section, wherein the motor-generator section is cooled by a portion of the working fluid pressurized by the liquid pump section. A disadvantage of this system design is that the generator is internally exposed to high working fluid pressure at the outlet of the liquid pump section, which may cause permanent damage to the rotor and other internal parts of the generator.

WO 82/02741 discloses a rankine cycle turbogenerator system having an integrated combination of an expander section, a liquid pump section and a generator section on a single vertical shaft in a sealed housing, wherein a portion of the working fluid from the condenser is pumped by a booster pump upstream of the liquid pump section to the bearings of the shaft for lubrication and cooling purposes. Cooling of the generator is achieved by leakage of working fluid from the top bearing assembly and the liquid pump in the liquid pump section. A disadvantage of this system is that, in addition to the liquid pump, a booster pump is required to pressurize that part of the working fluid used to lubricate and cool the bearings in order to avoid evaporation of that part of the working fluid and the generation of steam in the bearing cavity due to the addition of a small amount of heat, which can impair the proper function of the fluid as a dynamic lubricant in the bearings. Furthermore, the rotor and other internal components of the generator are again exposed to high working fluid pressures in the bearing cavity and at the outlet of the liquid pump section.

Disclosure of Invention

It is an object of the present invention to provide a solution to one or more of the above and/or other disadvantages.

To this end, the invention relates to a power generation system comprising:

-a liquid pump section comprising a rotary liquid pump having an impeller in which a working fluid is pressurized and driven by a drive shaft;

-an evaporator section comprising an evaporator in which a working fluid pressurized in a rotary liquid pump is at least partially evaporated by adding heat from a heat source;

-an expander section comprising a rotary expander having an inlet port and a rotary expander element in which a working fluid at least partially evaporated in the evaporator section is expanded; and

a generator part comprising a rotary generator having a rotor,

wherein the expander section, the liquid pump section and the generator section are rotatably connected such that a relative rotational speed ratio between a rotary expander element of the rotary expander, an impeller of the rotary liquid pump and a rotor of the rotary generator is mechanically maintained, characterized in that a drive shaft driving the impeller of the rotary liquid pump is configured to be provided with a throttling device allowing a controlled portion of working fluid entering the rotary liquid pump to be diverted from the liquid pump section to the expander section and/or the generator section.

The power generation system according to the present invention has an advantage of being able to directly connect the rotary liquid pump of the liquid pump section to the rotor of the rotary power generator if the controlled portion of the working fluid is diverted from the liquid pump section to the power generator section, while avoiding a cavitation phenomenon of the rotary liquid pump due to leakage of the working fluid vapor into the rotary liquid pump, and avoiding a loss of power generation efficiency due to a large amount of the working fluid directly flowing from the rotary liquid pump to the rotary power generator without passing through the evaporator. The small controlled portion of working fluid that the throttling device allows to bypass from the liquid pump section to the generator section is just enough to keep the rotary generator cool to a suitable level, mainly by local evaporation. The rotary generator is exposed to a working fluid at a lower pressure than the working fluid pressure at the outlet of the liquid pump portion, preventing damage to the rotor or other internal components of the rotary generator due to too high a working fluid pressure.

If the controlled portion of the working fluid is diverted from the liquid pump section to the expander section, the power generation system according to the present invention has an advantage of being able to directly connect the rotary liquid pump of the liquid pump section to the rotor of the rotary expander, while avoiding cavitation of the rotary liquid pump due to leakage of the working fluid vapor into the rotary liquid pump, and avoiding loss of power generation efficiency due to a large amount of working fluid flowing directly from the rotary liquid pump to the rotary expander without passing through the evaporator. The small controlled portion of working fluid diverted from the liquid pump section to the expander section allowed by the throttling device is just enough to keep the bearings and other rotating parts of the rotary expander cool to a suitable level, primarily by local evaporation.

Another advantage is that if the rotary generator is a permanent magnet generator and if the controlled portion of the working fluid allowed by the throttling means is diverted from the liquid pump section to the generator section, this controlled portion of the working fluid can be used to cool the magnets of the rotary generator.

In a preferred embodiment of the invention, the power generation system is arranged as a rankine circuit, preferably an ORC circuit with an organic working fluid.

In another preferred embodiment of the invention, the inlet port of the rotary expander of the expander section is located at a higher level than the outlet port of said rotary expander. Further, the rotary liquid pump is located at a lower position than the inlet port of the rotary expander.

This brings the advantage of allowing expanded working fluid in a mixed liquid-vapor phase to exit the rotary expander without pumping losses due to internal lift-off of the mixed phase working fluid.

The invention can be used in an integrated combination of a single expander section, a single liquid pump section and a generator section.

However, the invention may also be used for integrated combinations of two or more expander sections, two or more liquid pump sections and a generator section. Each of the expander or liquid pump sections can include a plurality of rotary expanders or rotary liquid pumps, respectively.

The invention also relates to a method of generating power by operating a power generation system comprising:

-a liquid pump section comprising an inlet and a rotary liquid pump having an impeller in which a working fluid is pressurised and which is driven by a drive shaft;

-an evaporator section comprising an evaporator in which a working fluid pressurized in the rotary liquid pump is at least partially evaporated by adding heat from a heat source;

-an expander section comprising a rotary expander having a rotary expander element, wherein a working fluid at least partially evaporated in the evaporator section is expanded in the rotary expander element; and

a generator part comprising a rotary generator having a rotor,

wherein the expander section, the liquid pump section and the generator section are rotatably connected such that a relative rotational speed ratio between a rotary expander element of the rotary expander, an impeller of the rotary liquid pump and a rotor of the rotary generator is mechanically maintained, characterized in that a controlled portion of a working fluid entering the rotary liquid pump is allowed to flow by means of a throttling means from the liquid pump section to the expander section and/or the generator section, a drive shaft driving the impeller of the rotary liquid pump being provided with the throttling means, wherein the rotary expander and/or the rotary generator is cooled by the controlled portion of the working fluid flowing from the liquid pump section to the expander section and the generator section, respectively.

In a preferred embodiment of the invention, the mass flow rate of the controlled part of the working fluid allowed to flow from the liquid pump section to the expander section and/or the generator section by the throttling means is less than 25%, preferably less than 10%, more preferably less than 5%, even more preferably less than 3% of the total mass flow rate of the working fluid supplied to the inlet of the liquid pump section. Thus, the controlled portion of the working fluid is just sufficient to cool the rotor and other components of the rotary generator, the bearings of the rotary expander and other rotating components, respectively, to a suitable level, primarily by local evaporation.

Drawings

In order to better illustrate the characteristics of the invention, several preferred embodiments of the power generation system according to the invention are described below, by way of example and without any limitation, with reference to the accompanying drawings, wherein the drive shaft of the rotary liquid pump is provided with a throttling device, wherein:

FIGS. 1A and 1B schematically illustrate a Rankine circuit including a power generation system according to the present disclosure;

fig. 2 to 5 show different variants of the power generation system, respectively;

figure 6 shows the sealing of the drive shaft of the rotary liquid pump of the power generation system in more detail.

DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION

In this case, the power generation system 1 in fig. 1A is a rankine circuit, which includes an integrated combination 2 of an expander portion 3, a liquid pump portion 4 and a generator portion 5.

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

The rotary liquid pump 7 in the liquid pump section 4 drives the working fluid through the circuit by means of a rotating impeller which 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.

The flow of working fluid through the circuit is as follows.

The rotary liquid pump 7 drives the working fluid in liquid form through an evaporator section comprising an evaporator 9, which evaporator 9 is a first part of a heat exchanger 10. The heating medium, which provides heat from the heat source, flows through the second portion of the heat exchanger 10, preferably in the opposite direction with respect to the working fluid flowing through the evaporator 9.

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

Due to the heat transfer from the heating medium to the working fluid, the working fluid is at least partially evaporated in the evaporator 9 and leaves the evaporator 9 in a gaseous or vapour state or as a mixture of liquid and gas or vapour.

The working fluid is typically characterized by more favorable evaporation characteristics, i.e., boiling temperature at the pressure of the working fluid in the evaporator 9 relative to the temperature of the heating medium providing heat to the working fluid in the evaporator 9.

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 the heating medium at low temperature. Typically, the working fluid is selected to have a critical point temperature near the maximum temperature of the heating medium in heat exchanger 10.

Further, the working fluid may include a lubricant or serve as a lubricant for components of the power generation system 1.

An example of a suitable organic working fluid is 1,1,1,3, 3-pentafluoropropane. However, the present invention is not limited to this particular working fluid.

The at least partially vaporized 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 is capable of converting the thermal energy of the working fluid into mechanical energy, for example because it is configured in the form of a rotary expander element driven by an output drive shaft 12 coupled to the rotor of a rotary generator 13 in the generator section 5 to supply electrical energy to consumers.

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

The rotary generator 13 in the generator portion 5 may be a synchronous generator, preferably a permanent magnet generator.

The expanded working fluid leaving the expander section 3 flows through a condenser section comprising a condenser 14 where it is contacted and cooled by a cooling medium, which ensures that the working fluid is fully condensed to be able to be pumped back as liquid by the rotary liquid pump 7 for subsequent circulation in the rankine circuit.

A controlled portion 15 of the working fluid entering the rotary liquid pump 7 is allowed to leak from the liquid pump portion 4 to the generator portion 5 via a throttling arrangement 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 through and past the rotary generator 13. In this way, the rotor and other components of the rotary generator 13 are cooled to a suitable extent.

As shown in fig. 1B, the positions of the expander section 3 and the generator section 5 in the housing 6 may be interchanged, such that a controlled portion 15 of the working fluid leaks to the expander section 3 via a 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 the bearings and other components of the rotary expander 11.

It is not excluded in fig. 1A and/or 1B that 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 the components of the rotary expander 11 and the components of the generator 13.

The expander section 3, the liquid pump section 4 and the generator section 5 are rotatably connected such that the relative rotational speed ratio between the rotary expander element of the rotary expander 11, the impeller of the rotary liquid pump 7 and the rotor of the rotary generator 13 is mechanically maintained.

This can be achieved by means of a gearbox connecting the rotary expander elements of the rotary expander 11, the impeller of the rotary liquid pump 7, the rotor of the rotary generator 13, the drive shaft 8 of the rotary liquid pump 7 and the drive shaft 12 of the rotary generator 13. 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 elements of the rotary expander 11 and/or the rotor of the rotary generator 13 may be mounted directly on the drive shaft 12.

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 elements of the rotary expander 11 may be mounted on a drive shaft 12 which drives the rotor of a rotary generator 13.

The drive shaft 8 driving the impeller of the rotary liquid pump 7 may be different from the drive shaft 12 driving the rotor of the rotary generator 13, for example when the impeller of the rotary liquid pump 7 is driven by the drive shaft 8 connected to the male rotor element of the rotary expander 11 and the rotor of the rotary generator 13 is driven by the drive shaft 12 connected to the female rotor element of the rotary expander 11, or when the impeller of the rotary liquid pump 7 is driven by the drive shaft 8 connected to the female rotor element of the rotary expander 11 and the rotor of the rotary generator 13 is driven by the drive shaft 12 connected to the male rotor element of the rotary expander 11. Alternatively, the rotor of the rotary generator 13 may be driven by the same drive shaft as the impeller of the rotary liquid pump 7, so that the drive shafts 8 and 12 are the same drive shaft.

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-sealed closed housing 6, as shown in fig. 2 to 5.

Fig. 2 schematically shows a combination of an expander section 3, a generator section 5 and a liquid pump section 4, wherein these sections are vertically mounted and rotatably connected such that the relative rotational speed ratio between the rotary expander element of the rotary expander 11, the impeller of the rotary liquid pump 7 and the rotor of the rotary generator 13 is mechanically maintained. A controlled portion 15 of the working fluid flows from the liquid pump portion 4 to the generator portion 5 to cool the rotor and other internal components of the rotary generator 15. The rotary expander 11 of the expander section 3 is provided with an inlet port 16 at a higher position than an outlet port 17 of the rotary expander 11. The rotary liquid pump 7 of the liquid pump section 4 is located at a lower position than the inlet port 16 of the rotary expander 11 to avoid a cavitation phenomenon of the rotary liquid pump 7 and a pumping loss due to internal rising (internal shock) of the mixed-phase working fluid and backflow of the gaseous or vaporous working fluid from the rotary expander 11 to the rotary liquid pump 7.

Fig. 3 shows a variation of the combination of fig. 2, wherein the expander section 3 and the generator section 5 are interchanged in position, such that a throttling device provided on the drive shaft 8 of the rotary liquid pump 7 allows a controlled portion 15 of the working fluid to flow from the liquid pump section 4 to the expander section 3 for cooling the bearings and other rotating parts of the rotary expander 11.

Fig. 4 shows a variant of the combination in fig. 2, in which the expander section 3, the generator section 5 and the liquid pump section 4 are mounted horizontally.

Fig. 5 shows a variation of the combination of the expander section 3, the generator section 5 and the liquid pump section 4 of fig. 4, wherein the positions of the expander section 3 and the generator section 5 are interchanged.

The controlled portion 15 of the working fluid is throttled as shown in fig. 6 and leaks from the liquid pump portion 4 at a pressure level p1 to one of the expander portion 3 and the generator portion 5 at a pressure level p2 below p1 via the drive shaft 8 of the rotary liquid pump 7. In this case the restriction means is a passage between the drive shaft 8 and a seal 18 of the drive shaft 8, the impeller of the rotary liquid pump 7 being mounted on the drive shaft 8, the seal 18 being located between the liquid pump part 4 and one of the expander part 3 and the generator part 5.

The controlled portion 15 of the working fluid, which is allowed to flow from the liquid pump section 4 to the expander section 3 or the generator section 5 by the throttling means provided on the drive shaft 8 driving the impeller of the rotary liquid pump 7, can be used to cool the rotary expander 11 or the rotary generator 13 in a method of generating electricity by operation of the power generation system 1 according to the present invention.

In the method, the inlet port 16 of the rotary expander 11 in the expander section 3 is supplied with at least partially evaporated working fluid from the evaporator 9 in the evaporator section.

The rotor of the rotary generator 13 is cooled by and exposed to the working fluid at a pressure level that is higher than the working fluid pressure level at the inlet of the liquid pump portion 4 and lower than the working fluid pressure level at the outlet of the liquid pump portion 4. As the temperature of the working fluid cooling the rotary generator 13 increases during its cooling action, the working fluid may evaporate, exposing the rotor of the rotary generator 13 to a mixture of liquid and gaseous or vaporous working fluid.

The mass flow of the controlled portion 15 of the working fluid is only a small fraction, preferably below 25%, more preferably below 10%, even more preferably below 5%, yet more preferably below 3%, of the total mass flow of the working fluid supplied to the inlet of the liquid pump portion 4.

The invention is in no way limited to the embodiments described as an example and shown in the drawings, but a power generation system according to the invention and a method of generating power by operating such a power generation system can be realized in various forms or sizes without departing from the scope of the invention, and is, by extension, also applicable to power generation systems having more than one expander section or liquid pump section, or power generation systems comprising expander sections having more than one rotary expander or rotary liquid pump sections having more than one rotary liquid pump.