ORC for transporting waste heat from a heat source into mechanical energy and cooling system making use of such an ORC

Abstract

An Organic Rankine Cycle (ORC) device and method for transforming heat from a heat source into mechanical energy. The ORC includes a closed circuit containing a two phase working fluid. The circuit comprises a liquid pump for circulating the working fluid consecutively through an evaporator which is configured to be placed in thermal contact with the heat source; through an expander for transforming the thermal energy of the working fluid into mechanical energy; and through a condenser which is in thermal contact with a cooling element. The expander is situated above the evaporator. The fluid outlet of the evaporator is connected to the fluid inlet of the expander by a raiser column which is filled with a mixture of liquid working fluid and of gaseous bubbles of the working fluid, which mixture is supplied to the expander.

Claims

1. An Organic Rankine Cycle (ORC) installation for transforming heat from a heat source into mechanical energy, the ORC installation comprising: a closed circuit containing a two-phase working fluid, the closed circuit comprising a liquid pump for circulating the two-phase working fluid in the closed circuit consecutively through an evaporator which is configured to be placed in thermal contact with said heat source; through an expander for transforming thermal energy of the two-phase working fluid into mechanical energy; and through a condenser which is in thermal contact with a cooling element, wherein the expander is physically located above the evaporator and a fluid outlet of the evaporator is connected to a fluid inlet of the expander by a raiser column which is filled with a mixture of liquid working fluid and of gaseous bubbles of the working fluid in a way such that the liquid working fluid flows into the evaporator to replace the gaseous bubbles of the working fluid produced in the evaporator, said mixture being supplied to the expander, and in that the raiser column extends with at least a part at a same level or above a level of the fluid inlet of the expander in such a way that a gravitational flow of the liquid working fluid is used to supply at least some of the working fluid from the raiser column to the expander, wherein the condenser is primarily located at a lower level than the expander in such a way that a gravitational flow of the liquid working fluid is used to supply the working fluid from the expander to the condenser, wherein the evaporator is primarily located at a lower level than the condenser in such a way that a gravitational flow of the liquid working fluid is used to supply the working fluid from the condenser to the evaporator, and wherein the ORC installation is designed such that, in case the expander and/or the liquid pump are not operational, the ORC installation operates as a self circulating circuit, driven by thermal gravitational effects on the fluid.

2. The ORC installation according to claim 1, wherein a lowest part of the fluid inlet of the condenser is located lower than a lowest part of the rotative, active parts of the expander.

3. The ORC installation according to claim 1, wherein a lowest part of the fluid inlet of the evaporator is located lower than lowest part of the fluid outlet of the condenser.

4. The ORC installation according to claim 1, wherein the ORC installation is so designed that in at least some operating conditions the evaporator is completely filled with boiling working fluid and in that the raiser column is filled with a mixture of liquid working fluid and of gaseous bubbles of the working fluid, which mixture is supplied to the expander.

5. The ORC installation according to claim 4, wherein a capacity of the liquid pump is chosen such that said liquid pump is pumping more liquid than could be evaporated in the evaporator.

6. The ORC installation according to claim 1, wherein the ORC circuit is provided with a bypass bridging the inlet and the outlet of the liquid pump and comprising a valve with a control for keeping the valve closed during normal operating conditions of the ORC installation and opening the valve in case the liquid pump would not be operational due to failure or other reasons.

7. The ORC installation according to claim 1, wherein the ORC circuit is provided with a bypass bridging the inlet and the outlet of the expander and comprising a valve with a control for keeping the valve closed during normal operating conditions of the ORC installation and opening the valve in case the expander would not be operational due to failure or other reasons.

8. The ORC installation according to claim 4, wherein the control of the valves is such that in case the expander and/or the liquid pump fails, both valves are opened.

9. The ORC installation according to claim 1, wherein the expander is of any kind suitable to accept a mixture of liquid and gaseous working fluid.

10. The ORC installation according to claim 1, wherein the expander is a volumetric expander.

11. The ORC installation according to claim 1, wherein the expander is a screw expander.

12. The ORC installation according to claim 1, wherein a working fluid is used which comprises a lubricant or which acts as a lubricant.

13. The ORC installation according to claim 1, wherein a working fluid is used of which the boiling temperature is lower than 90 C.

14. The ORC installation according to claim 7, wherein a location where the bypass branches to the ORC circuit at the inlet side of the expander is situated at a higher level than the condenser.

15. A cooling system for cooling a source of waste heat, wherein the cooling system comprises an ORC installation according to claim 1 as only means for cooling of the heat source without the need for any additional external cooling, also in conditions of non operation of the expander and/or of non-operation of the liquid pump.

16. The ORC installation according to claim 13, wherein a working fluid is used of which the boiling temperature is lower than 60 C.

17. An Organic Rankine Cycle (ORC) installation for transforming heat from a heat source into mechanical energy, the ORC installation comprising: a closed circuit containing a two-phase working fluid, the closed circuit comprising a liquid pump for circulating the two-phase working fluid in the closed circuit consecutively through an evaporator which is configured to be placed in thermal contact with said heat source; through an expander for transforming thermal energy of the two-phase working fluid into mechanical energy; and through a condenser which is in thermal contact with a cooling element, wherein a fluid outlet of the evaporator is connected to a fluid inlet of the expander by a raiser column which is filled with a mixture of liquid working fluid and of gaseous bubbles of the working fluid, and where in the installation is configured so that the liquid working fluid flows into the evaporator to replace the gaseous bubbles of the working fluid produced in the evaporator, said mixture being supplied to the expander, and in that the raiser column extends with at least a part at a same level or above a level of the fluid inlet of the expander in such a way that a gravitational flow of the liquid working fluid is used to supply at least some of the working fluid from the raiser column to the expander, wherein the condenser is primarily located at a lower level than the expander in such a way that a gravitational flow of the liquid working fluid is used to supply the working fluid from the expander to the condenser, wherein the evaporator is primarily located at a lower level than the condenser in such a way that a gravitational flow of the liquid working fluid is used to supply the working fluid from the condenser to the evaporator, and wherein the ORC installation is designed such that, in case the expander and/or the liquid pump are not operational, the ORC installation operates as a self circulating circuit, driven by thermal gravitational effects on the fluid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) With the intention of better showing the characteristics of the invention, hereafter, as an example without any limitative character, some preferred embodiments are described of an ORC according to the invention for transforming waste heat from a heat source into mechanical energy and of a compressor installation making use of such an ORC, with reference to the accompanying drawings, wherein:

(2) FIG. 1 schematically represents a single stage compressor installation making use of an ORC system according to the invention;

(3) FIG. 2 represents the ORC of FIG. 1 in a more realistic way; and

(4) FIG. 3 represents an alternative embodiment of the compressor installation of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

(5) The cooling system 1 represented in FIG. 1 is a cooling system for cooling for example the compressed gas produced by a compressor installation comprising a compressor element 2 with an inlet 3 and an outlet 4, said compressor element 2 being connected to a motor 5 for driving the compressor element 2 for compressing a gas flow Q. Further, the cooling system 1 comprises a cooler 6, which is provided downstream of said compressor element 2, for cooling the compressed gas before it is supplied to a net 7 of consumers of compressed gas.

(6) The cooling installation 1 comprises an ORC 8 according to the invention wherein the above-mentioned cooler 6 is integrated in a heat exchanger 9 which further integrates an evaporator 10 of the ORC 8 for recovering the waste heat of the compressed gas used as a heat source 11 being configured to transform said heat into useful mechanical energy by means of an expander 12 of the ORC 8, for example a turbine driving an electrical generator 13 as shown in the example of FIG. 1.

(7) The ORC comprises a closed circuit 14 containing a two-phase organic working fluid with a boiling temperature below the temperature of the heat source 11, the working fluid being continuously circulated around in the circuit 14 by means of a liquid pump 15 in the direction as indicated with arrows F.

(8) The working fluid is made to flow consecutively through the evaporator 10 which is in thermal contact with the heat source 11; then through the expander 12 and finally through a condenser 16 before being launched again by the liquid pump 15 for a next cycle in the circuit 14.

(9) The condenser 16 is part of a heat exchanger 9 in which the condenser 16 is in thermal contact with a cooling element 17 of a cooling circuit 18 which, in the example of FIG. 1, is represented as a supply of cold water W taken from a tank 19 to circulate through the condenser 16 by means of a pump 20.

(10) According to the invention the condenser 16 is physically located lower than the expander 12, whilst the evaporator 10 is physically located lower than the condenser 16 in such a way that a gravitational flow is possible of the liquid working fluid supplied by the raiser column 24 to the expander 12 and further down from the expander 12 to the condenser 16 and from the condenser 16 to the evaporator 10.

(11) The term lower than does not require that all parts of the condenser/evaporator are located lower. It means that the main parts of the condenser/evaporator at a lower level. The term should be understood in the context of a requirement for creating a gravitational flow of the liquid part of the working fluid.

(12) Preferably at least the lowest part of the fluid inlet of the condenser 16 is physically located lower than the lowest part 12 of the rotative, active parts 12 of the expander 12, as schematically represented in FIG. 2, whilst the lowest part of the fluid inlet of the evaporator 10 is physically located lower than the lowest part of the fluid outlet of the condenser 16, the fluid outlet 22 of the evaporator 10 being connected to the fluid inlet 23 of the expander 12 by means of a so called raiser column 24.

(13) The ORC 8 according to the invention is so designed that in normal operating conditions the evaporator 10 is completely filled with boiling working fluid and in that the raiser column is filled over its entire height with a mixture of working fluid in liquid form and of gaseous bubbles of the working fluid, which mixture is supplied to the fluid inlet 23 of the expander 12 through a bended part 24 of the raiser column 24, which bended part 24 extends with at least with a part above the lowest part of the fluid inlet 23 of the expander 12.

(14) The expression filled with boiling liquid working fluid means that the gaseous bubbles created by boiling do not accumulate at the top of the evaporator 10, such that the working fluid in the evaporator 10 is not separated in a liquid part and a gaseous part accumulated in a space on top of the liquid part as in known ORC's.

(15) Normal operation of the ORC 8 according to the invention is that the working fluid is made to boil in the evaporator 10 by the heat of the compressed gasses which at the same time are cooled.

(16) The liquid pump 15 is designed to assure that it is pumping more working fluid to the evaporator 10 than can be evaporated by the heat of the compressed gas to be sure that the evaporator is completely filled with boiling liquid for maximum recovery of the heat from the compressed gas.

(17) In the raiser column 24 is a mixture of gas bubbles from the working fluid and of working fluid in liquid form which, as schematically represented in FIG. 2, is transported and supplied to the inlet 23 of the expander 12 which therefore has to be chosen amongst types of expanders which are able to deal with such a two phase mixture.

(18) The bent 24 should be located at the same level or at a higher level than the fluid inlet 23 of the expander in order that the liquid coming with the gas bubbles through the raiser column 24 will flow over the bent 24 and fall downwards by gravity through the expander 12 and to the condenser 16, from where it is supplied again to the evaporator 10 via the conduit 25 of the circuit 14 connecting the condenser 16 with the evaporator 10.

(19) The gas bubbles produced in the evaporator 10 will tend to rise in the raiser column 24 as well as in the conduit 25 but will take the passage of least resistance via the raiser column 24.

(20) As such, a kind of self circulating effect is created by the raiser column 24 which helps to circulate the working fluid in the circuit 14.

(21) Even when the liquid pump 15 or the expander 12 gets blocked, the ORC continues to circulate the working fluid in the circuit 14 assisted by the force of gravity, thereby providing sufficient cooling of the compressed gas in the evaporator 10 to avoid dangerous conditions to arise until the liquid pump 15 or the expander 12 can be fixed.

(22) It is clear that an ORC 8 according to the invention can also be used in other applications than for cooling compressed gas, such as cooling flue gasses, steam, etc.

(23) Cooling of the condenser 16 can be realized in other ways than in the example of FIG. 1, for example by blowing ambient air over the condenser 16 by means of a fan or the like.

(24) The expander 12 can be any kind of expander capable of generating mechanical energy by expansion of a two phase fluid supply, preferably a volumetric expander like a screw expander or a mechanical cylinder or the like which can accept a mixture of liquid and gaseous working fluid.

(25) Preferably a working fluid is used of which the boiling temperature is lower than 90 C. or even lower than 60 C., depending on the temperature of the available heat source 11.

(26) An example of a suitable organic working fluid is 1,1,1,3,3-pentafluoroprophane. The organic fluid could be mixed with a suitable lubricant for the lubrication of at least part of the moving parts of the ORC.

(27) Summarized, the raiser column 24 should be designed with appropriate dimensions to accommodate the following effects: ensure that the evaporator surfaces are always in contact with liquid; create a desirable pressure difference between evaporator and expander inlet; create a suitable difference of elevation between expander and condenser; allow a suitable difference of elevation between condenser and liquid pump; ensure that the WTP-system operates as a heat pipe/thermo siphon when expander and/or liquid pump is non-operable.

(28) It has to be understood that, when evaluating prior art documents in the field of ORC, the relative locations of the constituting components in the schematics of the ORC's do not necessarily correspond to the relative physical locations of said components.

(29) In FIG. 3 an alternative embodiment is shown of a cooling installation according to the invention which differs from the embodiment of FIG. 1 in that the ORC circuit is provided with a bypass 26 bridging the inlet 27 and the outlet 28 of the liquid pump 15.

(30) Said bypass 26 comprising a valve 29 connected to a control 30 for keeping the valve 29 closed during normal operating conditions of the ORC 8 and opening the valve 29 in case the liquid pump 15 would not be operational due to failure or other reasons. The control 30 is therefore coupled to a sensor 31 by means of an electric harness 32 for sensing when the liquid pump 15 is not operational.

(31) Similarly the ORC of FIG. 3 is provided with a bypass 33 bridging the inlet 23 and the outlet 21 of the expander 12 and comprising a valve 34 connected via the harness 32 to the control 30 for keeping the valve 34 closed during normal operating conditions of the ORC 8 and opening the valve 34 in case the input signal coming from a sensor 35 on the expander 12 would indicate that the expander 12 is not operational.

(32) The control 30 can either open only one of the bypass valves 29 or 34 depending on which of the liquid pump 15 and expander 12 would not be operational or can open both valves 29 and 34 simultaneously.

(33) The location 36 where the bypass 34 branches to the ORC circuit 14 at the inlet side of the expander 12 would preferably need to be situated at a higher level than the condenser 16.

(34) The present invention is in no way limited to the form of embodiments described by way of an example and represented in the figures, however, such an ORC according to the invention for transforming waste heat from a heat source into mechanical energy and of a compressor installation making use of such an ORC can be realized in various forms without leaving the scope of the invention.