US20240084722A1

US20240084722A1 - A rankine cycle arrangement comprising an ejector

Info

Publication number: US20240084722A1
Application number: US17/767,799
Authority: US
Inventors: Teemu SIHVONEN; Eemeli Tsupari; Kristian Melin
Original assignee: VTT Technical Research Centre of Finland Ltd
Current assignee: VTT Technical Research Centre of Finland Ltd
Priority date: 2019-10-11
Filing date: 2020-10-09
Publication date: 2024-03-14
Also published as: WO2021069802A2; EP4045773A2; WO2021069802A3

Abstract

A rankine cycle arrangement, the arrangement (100) comprising: an expander (1), a heat exchanger (2) connected to an inlet channel (3) of the expander (1) for heating working fluid to be fed in the expander (1), a condenser (5) connected to an outlet channel (6) of the expander (1) for cooling working fluid expanded in the expander (1), and a pump (8) connected to an outlet (9) of the condenser and to an inlet (10) of the heat exchanger for rising pressure of working fluid. The arrangement further comprises an ejector (11) comprising a high-pressure inlet (12), a low-pressure inlet (13), and an outlet channel (14). The ejector (11) is connected in parallel with the expander (1) such that a first portion of working fluid is capable to bypass the expander through said ejector (11).

Description

BACKGROUND

The invention relates to a rankine cycle arrangement.
It is known methods and arrangements that utilize waste heat in producing electricity. A problem with these is that they are working in high pressures and need quite high temperature of waste heat.

BRIEF DESCRIPTION

Viewed from a first aspect, there can be provided a rankine cycle arrangement, the arrangement comprising: an expander for converting heat energy of working fluid into mechanical energy, a heat exchanger connected to an inlet channel of the expander for heating working fluid to be fed in the expander, the heat exchanger comprising a receiving channel being arranged to receive heat energy, a condenser connected to an outlet channel of the expander for cooling working fluid expanded in the expander, the condenser comprising a receiving channel being arranged to receive cooling fluid, a pump connected to an outlet of the condenser and to an inlet of the heat exchanger for rising pressure of working fluid, an ejector comprising a high-pressure inlet, a low-pressure inlet, and an outlet channel, the ejector being connected in parallel with the expander such that a first portion of working fluid is capable to bypass the expander through said ejector, and wherein the outlet channel of the expander is connected to the low-pressure inlet, the outlet channel of the ejector is connected to an inlet of the condenser for conducting working fluid from the ejector to the condenser, and an outlet of the heat exchanger is connected to the high-pressure inlet.
Thereby an arrangement utilizing a low temperature waste heat in converting heat energy to e.g. electrical energy by using Rankine cycle may be achieved. Furthermore, capital expenses of the arrangement may be radically reduced.
The arrangement is characterised by what is stated in the independent claims. Some other embodiments are characterised by what is stated in the other claims. Inventive embodiments are also disclosed in the specification and drawings of this patent application. The inventive content of the patent application may also be defined in other ways than defined in the following claims. The inventive content may also be formed of several separate inventions, especially if the invention is examined in the light of expressed or implicit sub-tasks or in view of obtained benefits or benefit groups. Some of the definitions contained in the following claims may then be unnecessary in view of the separate inventive ideas. Features of the different embodiments of the invention may, within the scope of the basic inventive idea, be applied to other embodiments.
In one embodiment, the expander comprises a turbine. An advantage is that the thermodynamic efficiency of turbines is high.
In one embodiment, said working fluid is carbon dioxide. An advantage is that there is a substantial difference in vapor pressure between evaporation temperature and condensing temperature, and thus a high efficiency of the process may be achieved.
In one embodiment, said working fluid comprises refrigerant, ammonia, hydrocarbon, alcohol or combination thereof. An advantage is that these working fluids enable more efficient conversion of low temperature heat to power compared to a water based standard steam rankine cycle.
In one embodiment, the heat exchanger is a counterflow plate heat exchanger. An advantage is that the efficiency of the heat exchanger is high, and thus a more compact structure may be used.
In one embodiment, the condenser is a counterflow plate heat exchanger. An advantage is that the efficiency of the heat exchanger is high, and thus a more compact structure may be used.
In one embodiment, at least one of the pumps is a centrifugal pump. An advantage is that the pump may have a high flow rate capabilities and relatively simple structure.
In one embodiment, at least one of the pumps is a plunger pump. An advantage is that the pump may be used at high pressures.
In one embodiment, the arrangement comprises at least two ejectors arranged in series, wherein the outlet channel of a preceding ejector is connected to the high-pressure inlet of the following ejector. An advantage using multiple ejectors in series is that a lower amount of motive gas is needed to compress the sucked gas to a certain pressure. Alternatively, using multiple ejectors the sucked gas can be compressed to a higher pressure with the same amount of motive gas.
In one embodiment, the arrangement comprises a controlling means arranged to control the first portion of working fluid in relation to a second portion of working fluid being fed in the expander. An advantage is that input and output pressures of the expander may be controlled, for instance kept constant even if e.g. the temperature of cooling fluid fluctuates.
In one embodiment, the arrangement comprises a generator for generating electricity, and arranged to be rotated by the expander. An advantage is that the heat energy of working fluid may be converted to a more versatile form of energy.
In one embodiment, the arrangement comprises a first conduit system arranged to connect in series: the outlet channel of the ejector, the condenser, the pump, the heat exchanger, and the inlet channel of the expander, the arrangement further comprising a second conduit system arranged to connect with the first conduit system between said heat exchanger and said inlet channel of the expander, the second conduit system further arranged to connect to the high-pressure inlet of the ejector. An advantage is that the structure of the system is simple and only one pump is needed.
In one embodiment, the arrangement comprises a first conduit system arranged to connect in series: the outlet channel of the ejector, the condenser, the pump, the heat exchanger, and the inlet channel of the expander, the arrangement further comprising a third conduit system arranged to connect with the first conduit system between the condenser and the pump, the third conduit system comprising a second pump, a second heat exchanger, the third conduit system further arranged to connect to the high-pressure inlet of the ejector. An advantage is that it is possible to utilize a lower temperature heat energy for compressing working fluid after the expander, but prior to feeding working fluid in the condenser. Thus, a higher net power production may be achieved.

BRIEF DESCRIPTION OF FIGURES

Some embodiments illustrating the present disclosure are described in more detail in the attached drawings, in which

FIG. 1 is a schematic view of a rankine cycle arrangement,

FIG. 2 is a schematic side view of another rankine cycle arrangement, and

FIG. 3 a schematic side view of a third rankine cycle arrangement.

In the figures, some embodiments are shown simplified for the sake of clarity. Similar parts are marked with the same reference numbers in the figures.

DETAILED DESCRIPTION

FIG. 1 is a schematic view of a Rankine cycle arrangement. The Rankine cycle is an idealized thermodynamic cycle of a heat engine that converts heat into mechanical work while undergoing phase change.
The arrangement 100 comprises an expander 1 for converting heat energy of working fluid into mechanical energy. The expander 1 may comprise e.g. a turbine.
A heat exchanger 2 is connected to an inlet channel 3 of the expander 1 for heating working fluid that is fed in the expander 1 in such an extent that working fluid is evaporating.
In an embodiment, the heat exchanger 2 is a counterflow plate heat exchanger. However, another type of heat exchangers may also be used as the heat exchanger 2.
The heat exchanger 2 comprises a receiving channel 4 being arranged to receive heat energy H from a heat source (not shown). In an embodiment, the heat source is waste heat developed in an industrial plant, in a waste incinerator, or energy producing plant. In another embodiment, the heat is obtained from a solar heating arrangement or a geothermal heat source. The heat energy is carried by a fluid, such as liquid, gas or combination thereof.
A condenser 5 is connected to an outlet channel 6 of the expander 1 for cooling working fluid expanded in the expander 1. Working fluid condenses in the condenser 5 to liquid state. In an embodiment, the condenser 5 is a counterflow plate heat exchanger. However, another type of condensers may also be used as the condenser 5.
The condenser 5 comprises a receiving channel 7 that is arranged to receive cooling fluid C from a cooling fluid source. Said cooling fluid source may be e.g. sea, lake or atmosphere, and the cooling fluid C may comprise e.g. water or some another liquid, gas, such as air, or any of their combinations.
A pump 8 is connected to an outlet 9 of the condenser and to an inlet 10 of the heat exchanger. The pump 8 transports working fluid from the condenser 5 to the heat exchanger 2 while raises pressure thereof. In an embodiment, the pump 8 is a centrifugal pump or a plunger pump. However, another type of pumps may also be used.
The arrangement 100 further comprises an ejector 11 having a high-pressure inlet 12, a low-pressure inlet 13, and an outlet channel 14. The ejector 11 is connected in parallel with the expander 1 such that a first portion of working fluid is capable to bypass the expander 1 through said ejector 11.
The low-pressure inlet 13 of the ejector is connected to the outlet channel 6 of the expander.
The outlet channel 14 of the ejector is connected to an inlet 15 of the condenser and conducts working fluid from the ejector 11 to the condenser 5.
The high-pressure inlet 12 of the ejector is connected to an outlet 16 of the heat exchanger. In an embodiment, about 10 volume-% of the working fluid coming from the outlet 16 is directed to the high-pressure inlet 12 of the ejector.
Fluid received in the high-pressure inlet 12 may be gaseous fluid, liquid fluid or supercritical fluid.
In an embodiment, a by-pass channel 26 (show by dashed line) is arranged to bypass the heat exchanger 2. Portion of fluid passing the heat exchanger 2 may enter at least partly in liquid form in the ejector 11. Said liquid may condense at least part of the gas fed in the low-pressure inlet 13, i.e. the ejector may be a condensing ejector. An advantage of the condensing ejector is that a higher outlet pressure can be achieved when cold motive fluid in liquid form may condense a part of gas sucked from the outlet channel 6 of the expander 1. In addition, less waste heat and a smaller heat exchanger are needed, when all the motive fluid is not vaporized.
The ejector 11 is arranged to use working fluid that is in a higher pressure and coming from the heat exchanger 2 for sucking and compressing working fluid fed from the expander 1 and having a lower pressure and, further, discharge all the working fluid in an intermediate pressure to the condenser 5. Thus, the pressure of working fluid in the condenser 5 is higher and temperature difference (dT) in the condenser 5 may be increased. In an example, dT was raised from 5° C. to 20° C., i.e. dT quadrupled. This, in turn, makes it possible to reduce the size of the condenser (in said example to one fourth) and lower capital expenses of the condenser 5.
In an embodiment, the arrangement 100 comprises a first conduit system 18 that is arranged to connect in series the outlet channel 14 of the ejector, the condenser 5, the pump 8, the heat exchanger 2, and the inlet channel 3 of the expander, and further a second conduit system 19 arranged to connect with the first conduit system 18 between said heat exchanger 2 and said inlet channel 3 of the expander and further arranged to connect to the high-pressure inlet 12 of the ejector. Thus, the second conduit system 19 provides a by-pass channel to the expander 1, through which by-pass channel a first portion of heat-transfer fluid is capable to bypass the expander 1.
In an embodiment, the arrangement 100 is provided with a controlling means 17 that is arranged to control the first portion of working fluid in relation to a second portion of working fluid, i.e. the portion being fed in the expander 1. The controlling means 17 may comprise e.g. a three-way valve.
The arrangement 100 further comprises a power transmission 23 arranged to be used by the energy of working fluid expanding in the expander 1. In an embodiment, the power transmission 23 comprises a rotating power transmission axle that is connected to e.g. a generator 24 that generates electricity, to a gas compressor, a pump or any apparatus using rotating mechanical energy.
FIG. 2 is a schematic side view of another rankine cycle arrangement. The arrangement 100 comprises the first conduit system 18 described above, thus being arranged to connect in series the outlet channel 14 of the ejector, the condenser 5, the pump 8, the heat exchanger 2, and the inlet channel 3 of the expander. In some embodiments, the arrangement 100 further comprises a third conduit system that connects with the first conduit system 18 between the condenser 5 and the pump 8 and comprises a second pump 21 and a second heat exchanger 22. The third conduit system is further connected to the high-pressure inlet 12 of the ejector. According to an idea, the third conduit system 20, or the second heat exchanger 22 therein, is using heat energy H2 being in a lower temperature as the heat energy H1 used in the (first) heat exchanger 2 arranged in the first conduit system 18. For example, the temperature of the heat energy H1 fed in the (first) heat exchanger 2 may be about 80° C. or less, whereas the temperature of the heat energy H2 fed in the second heat exchanger 22 may be about 40° C. or less. Thus, it is possible to utilize a lower temperature heat energy H2 for compressing working fluid after the expander 1, but prior to feeding working fluid in the condenser 5. This way higher net power production may be achieved.
In an embodiment, the heat energy H2 fed in the second heat exchanger 22 is coming from an outlet of the heat energy 1 of the (first) heat exchanger 2. This embodiment is represented by a connecting conduit 25 in FIG. 2 .
In an embodiment, the working fluid used in the arrangement 100 is carbon dioxide (CO 2). The working fluid may also be practically any fluid used in organic rankine cycles, such as refrigerants ammonia, hydrocarbons, alcohols etc., or any of their combinations. Preferably, the working fluid has a big difference in vapor pressure between evaporation temperature and condensing temperature.
FIG. 3 is a schematic side view of a third rankine cycle arrangement. The arrangement 100 may comprise plurality of ejectors arranged in series such that the outlet channel 14 of a preceding ejector is connected to the high-pressure inlet 12 of the following ejector.
The embodiment shown in FIG. 3 comprises two ejectors 11 a, 11 b arranged in series.
It is to be noted, that said embodiment of plurality of ejectors arranged in series may be use also in connection with the embodiments described in description of FIG. 2 .
A controlling means 17, such as a three-way valve, may be arranged to the arrangement 100 for controlling the portions of the expanded fluid in the outlet channel 6 fed in the ejectors.
The invention is not limited solely to the embodiments described above, but instead many variations are possible within the scope of the inventive concept defined by the claims below. Within the scope of the inventive concept the attributes of different embodiments and applications can be used in conjunction with or replace the attributes of another embodiment or application.
The drawings and the related description are only intended to illustrate the idea of the invention. The invention may vary in detail within the scope of the inventive idea defined in the following claims.

REFERENCE SYMBOLS

- 1 expander
- 2 heat exchanger
- 3 inlet channel of expander
- 4 heat energy receiving channel of heat exchanger
- 5 condenser
- 6 outlet channel of expander
- 7 cooling fluid receiving channel of condenser
- 8 pump
- 9 outlet of condenser
- 10 inlet of heat exchanger
- 11 ejector
- 12 high-pressure inlet of ejector
- 13 low-pressure inlet of ejector
- 14 outlet channel of ejector
- 15 inlet of condenser
- 16 outlet of heat exchanger
- 17 controlling means
- 18 first conduit system
- 19 second conduit system
- 20 third conduit system
- 21 second pump
- 22 second heat exchanger
- 23 power transmission
- 24 generator
- 25 connecting conduit
- 26 by-pass channel
- 100 arrangement
- H heat energy
- C cooling fluid

Claims

1-12. (canceled)

13. A rankine cycle arrangement, the arrangement comprising:

an expander for converting heat energy of working fluid into mechanical energy,

a heat exchanger connected to an inlet channel of the expander for heating working fluid to be fed in the expander, the heat exchanger comprising a receiving channel being arranged to receive heat energy,

a condenser connected to an outlet channel of the expander for cooling working fluid expanded in the expander, the condenser comprising a receiving channel being arranged to receive cooling fluid,

a pump connected to an outlet of the condenser and to an inlet of the heat exchanger for rising pressure of working fluid,

an ejector comprising a high-pressure inlet, a low-pressure inlet, and an outlet channel, the ejector being connected in parallel with the expander such that a first portion of working fluid is capable to bypass the expander through said ejector, and wherein

the outlet channel of the expander is connected to the low-pressure inlet,

the outlet channel of the ejector is connected to an inlet of the condenser for conducting working fluid from the ejector to the condenser, and

an outlet of the heat exchanger is connected to the high-pressure inlet.

14. The arrangement as claimed in claim 13, wherein the expander comprises a turbine.

15. The arrangement as claimed in claim 13, wherein said working fluid is carbon dioxide (CO₂).

16. The arrangement as claimed in claim 13, wherein said working fluid comprises refrigerant, ammonia, hydrocarbon, alcohol or combination thereof.

17. The arrangement as claimed in claim 13, wherein the heat exchanger is a counterflow plate heat exchanger.

18. The arrangement as claimed in claim 13, wherein the condenser is a counterflow plate heat exchanger.

19. The arrangement as claimed in claim 13, wherein at least one of the pumps is a centrifugal pump or a plunger pump.

20. The arrangement as claimed in claim 13, comprising at least two ejectors arranged in series, wherein

the outlet channel of a preceding ejector is connected to the high-pressure inlet of the following ejector.

21. The arrangement as claimed in claim 13, comprising a controlling means arranged to control the first portion of working fluid in relation to a second portion of working fluid being fed in the expander.

22. The arrangement as claimed in claim 13, comprising a generator for generating electricity, and arranged to be rotated by the expander.

23. The arrangement as claimed in claim 13, comprising

a first conduit system arranged to connect in series:

the outlet channel of the ejector,

the condenser,

the pump,

the heat exchanger, and

the inlet channel of the expander,

and further comprising

a second conduit system arranged to connect with the first conduit system between said heat exchanger and said inlet channel of the expander, the second conduit system further arranged to connect to the high-pressure inlet of the ejector.

24. The arrangement as claimed in claim 13, comprising

a first conduit system arranged to connect in series:

the outlet channel of the ejector,

the condenser,

the pump,

the heat exchanger, and

the inlet channel of the expander,

and further comprising

a third conduit system arranged to connect with the first conduit system between the condenser and the pump, the third conduit system comprising

a second pump,

a second heat exchanger,

the third conduit system further arranged to connect to the high-pressure inlet of the ejector.