ENERGY CONVERSION SYSTEM AND METHOD

Abstract

The present invention relates to an energy conversion system for converting thermal energy to mechanical energy, comprising an evaporator, an expander, a condenser, a first tank, and a second tank. The energy conversion system further comprises flow control devices for controlling flow or working fluid between the evaporator, the expander, the condenser and the tanks, and a control unit for controlling operation of the energy conversion system by controlling the flow control devices. Each of the tanks has an outlet connected to an inlet of the evaporator, and an inlet connected to the condenser as well as to an outlet of the evaporator. Hereby, some of the pressurized vapor state working fluid flowing from the outlet of the evaporator can be used for pressurizing liquid state working fluid supplied from one the tanks to the evaporator. This configuration of the energy conversion system provides for improved energy conversion efficiency.

Claims

1. An energy conversion system for converting thermal energy to mechanical energy, comprising: an evaporator for evaporating liquid state working fluid to vapor state working fluid through supply of heat, said evaporator being arranged to receive liquid state working fluid and output vapor state working fluid at a first pressure; an expander for expanding vapor state working fluid and converting expansion into mechanical energy, said expander having an expander inlet connected to said evaporator for receiving vapor state working fluid at said first pressure and an expander outlet for output of vapor state working fluid at a second pressure lower than said first pressure; a condenser for condensing vapor state working fluid to liquid state working fluid by cooling, said condenser having a condenser inlet connected to said expander outlet for receiving vapor state working fluid and a condenser outlet for output of liquid state working fluid; a first tank having a first inlet fluid flow connected to said condenser outlet, a second inlet fluid flow connected to said evaporator for receiving vapor state working fluid from said evaporator, and an outlet fluid flow connected to said evaporator for providing liquid state working fluid to said evaporator; a second tank having a first inlet fluid flow connected to said condenser outlet, a second inlet fluid flow connected to said evaporator for receiving vapor state working fluid from said evaporator, and an outlet fluid flow connected to said evaporator for providing liquid state working fluid to said evaporator; a first flow control device for controlling flow of working fluid from the outlet of the first tank to the evaporator; a second flow control device for controlling flow of working fluid from the condenser outlet to the first inlet of the first tank; a third flow control device for controlling flow of working fluid from the evaporator to the second inlet of the first tank; a fourth flow control device for controlling flow of working fluid from the outlet of the second tank to the evaporator; a fifth flow control device for controlling flow of said working fluid from the condenser outlet to the inlet of the second tank; a sixth flow control device for controlling flow of working fluid from the evaporator to the second inlet of the second tank; and a control unit connected to each of said flow control devices, for controlling operation of said energy conversion system, wherein: said condenser is arranged at a higher vertical level than each of said first tank and said second tank; and said evaporator is at least partly arranged at a lower vertical level than each of said first tank and said second tank.

2. The energy conversion system according to claim 1, further comprising at least one state sensor for sensing a present state of said energy conversion system, wherein said control unit is further connected to said at least one state sensor and configured to control said flow control devices based on a signal from said at least one state sensor.

3. The energy conversion system according to claim 1, wherein said control unit is configured to alternate said energy conversion system between: a first operational state in which each of said first, third and fifth flow control devices is controlled to allow flow of working fluid past the respective flow control devices; and each of said second, fourth and sixth flow control devices is controlled to prevent flow of working fluid past the respective flow control devices; and a second operational state in which each of said second, fourth and sixth flow control devices is controlled to allow flow of working fluid past the respective flow control devices; and each of said first, third and fifth flow control devices is controlled to prevent flow of working fluid past the respective flow control devices.

4. The energy conversion system according to claim 3, wherein said control unit is configured to keep the energy conversion system in said first operational state until said first tank substantially only contains vapor state working fluid, and to keep the energy conversion system in said second operational state until said second tank substantially only contains vapor state working fluid.

5. The energy conversion system according to claim 1, further comprising: a pressure equalization conduit directly connecting said first tank and said second tank; and a seventh flow control device for controlling flow of working fluid directly between said first tank and said second tank.

6. The energy conversion system according to claim 5, wherein said pressure equalization conduit is connected to said first tank in a bottom portion of said first tank, and to said second tank in a bottom portion of said second tank.

7. The energy conversion system according to claim 1, wherein said evaporator comprises: a first evaporator unit fluid flow connected to said expander inlet to provide vapor state working fluid to said expander; and a second evaporator unit fluid flow connected to the second inlet of said first tank and to the second inlet of said second tank.

8. The energy conversion system according to claim 7, wherein said second evaporator unit is arranged at a lower vertical level than each of said first tank and said second tank.

9. The energy conversion system according to claim 1, further comprising: a third tank having a first inlet fluid flow connected to said condenser outlet, a second inlet fluid flow connected to said evaporator for receiving vapor state working fluid from said evaporator, and an outlet fluid flow connected to said evaporator for providing liquid state working fluid to said evaporator; an eighth flow control device for controlling flow of working fluid from the outlet of the third tank to the evaporator; a ninth flow control device for controlling flow of working fluid from the condenser outlet to the first inlet of the third tank; and a tenth flow control device for controlling flow of working fluid from the evaporator to the second inlet of the third tank, wherein said control unit is additionally connected to said eighth, ninth and tenth flow control devices.

10. The energy conversion system according to claim 1, further comprising a generator connected to said expander for converting said mechanical energy into electrical energy.

11. A method of controlling an energy conversion system according to claim 1, said method comprising the steps of: (a) controlling the flow control devices to allow flow of working fluid from the outlet of said first tank, through said evaporator, said expander and said condenser to the first inlet of said second tank, while allowing flow of vapor state working fluid from said evaporator into the second inlet of said first tank; (b) releasing vapor phase working fluid from said first tank; (c) controlling the flow control devices to allow flow of working fluid from the outlet of said second tank, through said evaporator, said expander and said condenser to the first inlet of said first tank, while allowing flow of vapor state working fluid from said evaporator into the second inlet of said second tank; and (d) releasing vapor phase working fluid from said second tank.

12. The method according to claim 11, wherein: step (b) comprises releasing vapor phase working fluid from said first tank to said second tank; and step (d) comprises releasing vapor phase working fluid from said second tank to said first tank.

13. The method according to claim 12, wherein vapor phase working fluid is controlled to flow directly between a bottom portion of said first tank and a bottom portion of said second tank.

14. The method according to claim 11, wherein said steps (a) to (d) are performed repeatedly in sequence.

15. The method according to claim 11, for controlling an energy conversion system further comprising a third tank and a fourth tank, the method further comprising the steps of: (e) controlling the flow control devices to allow flow of working fluid from the outlet of said third tank, through said evaporator, said expander and said condenser to the first inlet of said fourth tank, while allowing flow of vapor state working fluid from said evaporator into the second inlet of said third tank; (f) releasing vapor phase working fluid from said third tank; (g) controlling the flow control devices to allow flow of working fluid from the outlet of said fourth tank, through said evaporator, said expander and said condenser to the first inlet of said third tank, while allowing flow of vapor state working fluid from said evaporator into the second inlet of said fourth tank; and (h) releasing vapor phase working fluid from said fourth tank.

16. The method according to claim 15, wherein said flow control devices are controlled to allow flow of working fluid from each of said tanks from a substantially full state to a substantially empty state of said tank, through said evaporator, said expander and said condenser, to at least two other tanks.

17. The method according to claim 16, wherein the flow to said at least two other tanks is controlled to take place sequentially.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing an example embodiment of the invention, wherein:

[0041] FIG. 1 schematically shows a Rankine cycle based energy conversion system according to the prior art;

[0042] FIG. 2a schematically shows an energy conversion system according to a first embodiment of the present invention;

[0043] FIG. 2b schematically shows an energy conversion system according to a second embodiment of the present invention;

[0044] FIGS. 3a-d schematically illustrate different operational states of the energy conversion system in FIG. 2; and

[0045] FIG. 4 schematically shows an energy conversion system according to a third embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0046] In the present detailed description, various embodiments of the apparatus and method according to the present invention are mainly described with reference to energy conversion systems comprising two or four tanks. Furthermore, pressure sensors and level sensors are shown to sense the pressure and level in each tank.

[0047] It should be noted that this by no means limits the scope of the present invention, which equally well includes, for example, energy conversion systems comprising another number of tanks. Furthermore, the energy conversion process may be controlled using parameters other than sensed pressure and level in the tanks. For instance, the energy conversion may be controlled using preset time durations for each operational state, or other process parameters may be sensed, such as the temperature and/or the energy output by the expander or a generator which may be connected to the expander.

[0048] FIG. 2a schematically illustrates an energy conversion system 1 according to a first example embodiment of the present invention, and FIG. 2b schematically illustrates an energy conversion system 1 according to a second example embodiment of the present invention.

[0049] Referring first to FIG. 2a, the energy conversion system 1 comprises an evaporator 2, a primary expander 3, a condenser 4, a first tank 5, a second tank 6, an auxiliary expander 7, and a control unit 8 for controlling operation of the energy conversion system 1. As is indicated in FIG. 2, the energy conversion system further comprises a first pressure sensor 9 for sensing the pressure in the first tank 5, a first level sensor 10 for sensing the liquid level in the first tank 5, a second pressure sensor 11 for sensing the pressure in the second tank 6, and a second level sensor 12 for sensing the liquid level in the second tank 6.

[0050] As is also shown in FIG. 2, the evaporator 2 has an evaporator inlet 14 and an evaporator outlet 15, the primary expander 3 has an expander inlet 16 and an expander outlet 17, the condenser 4 has a condenser inlet 18 and a condenser outlet 19, the first tank 5 has an inlet 20 and an outlet 21, the second tank 6 has and inlet 22 and an outlet 23, and the auxiliary expander 7 has an auxiliary expander inlet 24 and an auxiliary expander outlet 25.

[0051] The various parts of the energy conversion system 1 in FIG. 2 are fluid flow connected by conduits schematically indicated as solid lines in FIG. 2, and control lines (which may be wired or wireless) are indicated by dashed lines. Flow of working fluid through the conduits can be controlled using flow controlled devices, here in the form of controllable valves 30a-i.

[0052] An example of a suitable working fluid is the Genetron R-245fa from Honeywell. The skilled person will realize that this is merely an example, and that there is a large number of commercially available working fluids that may be suitable for different embodiments depending on various factors, such as the thermal power provided by the evaporator etc.

[0053] The second embodiment of the energy conversion system 1 in FIG. 2b differs from the first embodiment described above with reference to FIG. 2a in that the evaporator 2 is shown to include a first evaporator unit 2a and a second evaporator unit 2b. As is schematically shown in FIG. 2b, the first evaporator unit 2a is arranged to receive liquid phase working fluid from the first tank 5 and the second tank 6, and to provide vapor phase working fluid to the expander 3, and the second evaporator unit 2b is arranged to receive liquid phase working fluid from the first tank 5 and the second tank 6, and to provide vapor phase working fluid to second inlets 20, 22 of the first tank 5 and the second tank 6, respectively. The second evaporator unit 2b is arranged at a lower vertical level than the outlet 21 of the first tank 5 and the outlet 23 of the second tank 6. As is schematically indicated in FIG. 2b, the second evaporator unit 2b may comprise an evaporator container and a heater to evaporate working fluid in the evaporator container. As is also schematically shown, liquid phase working fluid enters the evaporator container at a relatively low vertical level, and vapor phase working fluid exits the evaporator container at a relatively high vertical level. The heat supplied to the second evaporator unit may emanate from any suitable heat source, such as steam, thermal oil, or electricity. The first 2a and second 2b evaporator units may advantageously be supplied with heat from the same heat source.

[0054] By controlling the states (open or closed) of the valves 30a-i, the control unit 8 can control the energy conversion system to different operational states for achieving a sustained conversion of thermal energy, supplied to the working fluid circulating through the conduits of the energy conversion system 1 by the evaporator 2, to mechanical energy provided by the expander 3.

[0055] This will now be illustrated for the relatively simple first embodiment of the energy conversion system 1 of FIG. 2a with reference to FIGS. 3a-d. Corresponding control is equally applicable to the second embodiment of the energy conversion system 1 illustrated by FIG. 2b.

[0056] To more clearly illustrate the different operational states of the energy conversion system 1 in FIG. 2a, the schematic illustrations in FIGS. 3a-d only include parts of the energy conversion system 1 that are active in the particular operational state.

[0057] Referring first to FIG. 3a, this schematic illustration only includes the flow path from the outlet 21 of the first tank 5 sequentially via the evaporator 2, the primary expander 3, and the condenser 4 to the inlet 22 of the second tank 6. To define this flow path, the control unit 8 (not shown in FIG. 3a) controls valves 30a, 30c and 30g to open. In the operational state schematically shown in FIG. 3a, the remaining valves in FIG. 2a are closed.

[0058] With reference to FIG. 3a, liquid state working fluid flows from the outlet 21 of the first tank 5 to the inlet 14 of the evaporator 2. In the evaporator 2, thermal energy is supplied to the liquid state working fluid, which evaporates to vapor state working fluid. The vapor state working fluid is provided from the evaporator outlet 15 to the expander inlet 16 and to the inlet 20 of the first tank 5. The vapor state working fluid provided to the inlet 20 of the first tank 5 increases the pressure of the liquid state working fluid supplied from the outlet 21 of the first tank 5 to the evaporator inlet 14. The vapor state working fluid supplied to the expander inlet 16 is expanded and the expansion converted by the expander 3 to mechanical energy. In the exemplary case when the expander 3 is provided in the form of a turbine, the expansion is converted to rotation, which can be used to drive a generator. After leaving the expander 3 through the expander outlet 17, the expanded vapor state working fluid is condensed to liquid state working fluid in the condenser 4, before being supplied to the second tank 6 through the inlet 22 of the second tank 6.

[0059] FIG. 3a schematically shows the beginning of the illustrated operational state, with the first tank 5 being almost filled with liquid state working fluid and the second tank 6 being almost empty (or rather the level of liquid state working fluid being low). As the illustrated operational state is maintained, the liquid level in the first tank 5 will decrease, while the liquid level in the second tank 6 increases. When the first tank 5 is empty or almost empty (only contains vapor state working fluid), the control unit 8 controls the energy conversion system 1 to a new operational state for pressure equalization. It may be determined by the control unit 8 that the first tank 5 is empty or almost empty based on signals provided by one or both of the first pressure sensor 9 and the first level sensor 10.

[0060] Referring now to FIG. 3b, this schematic illustration only includes the flow path from the outlet 21 of the first tank 5 to the outlet 23 of the second tank 6. To define this flow path, the control unit 8 (not shown in FIG. 3b) controls valve 30d to open. In the operational state schematically shown in FIG. 3b, the remaining valves in FIG. 2a are closed. As is shown in FIG. 3b, the first tank 5 now has a low liquid level (is empty), while the second tank 6 has a high liquid level (is full).

[0061] With reference to FIG. 3b, hot vapor state working fluid at high pressure, such as about 20 bar, is released to the second tank 6 through the outlet 23 of the second tank 6. The hot vapor state working fluid bubbles through the relatively cool liquid state working fluid in the second tank 6, heats the liquid state working fluid in the second tank 6, partly condenses and increases the pressure in the second tank 6. The transfer of vapor state working fluid from the first tank 5 to the second tank 6 stops when the pressure is equalized in the system formed by the first 5 and second 6 tanks. The pressure in the second tank 6 (and in the first tank 5) may then be about 5 bar, and the liquid state working fluid stored in the second tank has been preheated.

[0062] Turning to FIG. 3c, this schematic illustration only includes the flow path from the outlet 23 of the second tank 6 sequentially via the evaporator 2, the primary expander 3, and the condenser 4 to the inlet 20 of the first tank 5. To define this flow path, the control unit 8 (not shown in FIG. 3c) controls valves 30f, 30b and 30h to open. In the operational state schematically shown in FIG. 3c, the remaining valves in FIG. 2a are closed.

[0063] With reference to FIG. 3c, liquid state working fluid flows from the outlet 23 of the second tank 6 to the inlet 14 of the evaporator 2. In the evaporator 2, thermal energy is supplied to the liquid state working fluid, which evaporates to vapor state working fluid. The vapor state working fluid is provided from the evaporator outlet 15 to the expander inlet 16 and to the inlet 22 of the second tank 6. The vapor state working fluid provided to the inlet 22 of the second tank 6 increases the pressure of the liquid state working fluid supplied from the outlet 23 of the second tank 6 to the evaporator inlet 14. The vapor state working fluid supplied to the expander inlet 16 is expanded and the expansion converted by the expander 3 to mechanical energy. In the exemplary case when the expander 3 is provided in the form of a turbine, the expansion is converted to rotation, which can be used to drive a generator. After leaving the expander 3 through the expander outlet 17, the expanded vapor state working fluid is condensed to liquid state working fluid in the condenser 4, before being supplied to the first tank 5 through the inlet 20 of the first tank 5.

[0064] FIG. 3c schematically shows the beginning of the illustrated operational state, with the second tank 6 being almost filled with liquid state working fluid and the first tank 5 being almost empty (or rather the level of liquid state working fluid being low). As the illustrated operational state is maintained, the liquid level in the second tank 6 will decrease, while the liquid level in the first tank 5 increases. When the second tank 6 is empty or almost empty (only contains vapor state working fluid), the control unit 8 controls the energy conversion system 1 to a new operational state for pressure equalization. It may be determined by the control unit 8 that the second tank 6 is empty or almost empty based on signals provided by one or both of the second pressure sensor 11 and the second level sensor 12.

[0065] The final pressure equalization operational state before the energy conversion system 1 is again back to the initial configuration shown in FIG. 3a, is shown in FIG. 3d. As can be seen by comparing FIG. 3b and FIG. 3d, the configuration is the same. The only difference is that the direction of fluid flow between the first 5 and second 6 tanks is now from the second tank 6 to the first tank 5.

[0066] A full main energy conversion cycle of the energy conversion system 1 in FIG. 2a has now been described with reference to FIGS. 3a-d. To simplify the description and make the explanation clearer, there has so far been no reference to the auxiliary expander 7 in FIG. 2a. The purpose of the auxiliary expander 7 is to use the thermal energy remaining in an empty tank following the pressure equalization process described above with reference to FIG. 3b and FIG. 3d. Considering, for example, the state of the energy conversion system 1 following the pressure equalization process described with reference to FIG. 3b. The control unit 8 may then control valves 30a, 30b, and 30c to their closed states, and control valve 30e to its open state. Vapor state working fluid remaining in the first tank 5 can then be expanded by the auxiliary expander 7. Hereby, the pressure in the first tank 5 can be reduced further, and more energy can be converted to mechanical energy.

[0067] As can readily be understood from the above process description, the energy conversion device 1 in FIG. 2a (or FIG. 2b) will not supply mechanical energy (or electrical energy converted from the mechanical energy) continuously due to the pressure equalization processes described with reference to FIG. 3b and FIG. 3d. By adding further tanks, such as one more set of two tanks, a pressure equalization between two tanks in a first set of two tanks can be timed to take place while liquid state working fluid stored in a first tank in a second set of two tanks is used for energy conversion as described above with reference to FIG. 3a and FIG. 3c.

[0068] A third embodiment of the energy conversion system according to the present invention is schematically shown in FIG. 4. The energy conversion system 50 in FIG. 4 differs from the embodiments of the energy conversion system 1 described above with reference to FIGS. 2a-b and FIGS. 3a-d in that a second set of two tanks 51 and 52 has been added. These added tanks 51 and 52 are connected to each other as well as to the other parts of the energy conversion system 50 (the evaporator 2, the primary expander 3, the condenser, and the auxiliary expander 7 using controllable valves in exactly the same way as was described above with reference to FIG. 2. To avoid cluttering the drawing and to dispense with an unnecessarily lengthy description, pressure and level sensors, inlets and outlets and controllable valves associated with the added tanks 51 and 52 have been omitted from the drawing.

[0069] Furthermore, the control unit 8 is configured to control these controllable valves associated with the added tanks 51 and 52 in the same way as the controllable valves 30a-i associated with the first 5 and second 6 tanks were controlled to transition the energy conversion system 1 in FIGS. 2a-b between operational states.

Example

[0070] According to an example embodiment of the inventive method, the energy conversion system according to the above-described third embodiment may be controlled asynchronously to provide for a uniform output of mechanical (or electrical) energy from the energy conversion system.

TABLE-US-00001 Time Tank 1 Tank 2 Tank 3 Tank 4 5 Full, outlet open Empty, 2:nd expander Half full, filling Empty, outlet open 10 , outlet Empty, condensing , filling Empty, outlet closed 15 Half full, outlet Empty, filling , preheated Empty, preheating 20 , outlet , filling Full, preheated Empty, preheating 25 Empty, outlet open Half full, filling Full, outlet open Empty, 2:nd expander 30 Empty, outlet closed , filling , outlet Empty, condensing 35 Empty, preheating , preheated Half full, outlet Empty, filling 40 Empty, preheating Full, preheated , outlet , filling 45 Empty, 2:nd Full, outlet open Empty, outlet open Half full, filling expander 50 Empty, condensing , outlet Empty, outlet closed , filling 55 Empty, filling Half full, outlet Empty, preheating , preheated 60 , filling , outlet Empty, preheating Full, preheated 65 Half full, filling Empty, outlet open Empty, 2:nd expander Full, outlet open 70 , filling Empty, outlet closed Empty, condensing , outlet 75 , preheated Empty, preheating Empty, filling Half full, outlet 80 Full, preheated Empty, preheating , filling , outlet

[0071] In the table above, the tanks are denoted by numbers from left to right in FIG. 4. Furthermore, the transition between operational states of the energy conversion system is determined by a predetermined duration of the different steps. When a tank is referred to as being empty, this means that the tank only contains vapor phase working fluid. A tank that is preheating is connected to a tank that is preheated, and pressure equalization as described above with reference to FIG. 3b and FIG. 3d takes place.

[0072] The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, many other operational sequences of emptying, filling, and pressure equalizing the tanks are possible and may be beneficial depending on application and configuration of the energy conversion system.

[0073] In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.