THE SYSTEM AND THE METHOD FOR RECOVERY OF WASTE HEAT ENERGY CONTAINED IN OIL IN AN OIL-COOLED AIR COMPRESSOR

Abstract

A system for the recovery of waste heat energy contained in oil in an oil-cooled air compressor, characterised in that the outlet of the oil side of the oil separator (4) is connected to the inlet of the oil side of the heat exchanger (9), and the outlet of the oil side of the heat exchanger is connected to the oil flow divider (10). A method for the recovery of waste heat energy contained in oil in oil-cooled air compressors consists in diverting the receiving medium flow away from the heat exchanger (9) by means of a control device (12), or stopping the receiving medium flow when at least the temperature of the oil returning to the compressor main body (2) is lower than the setpoint or the temperature of the oil entering the heat exchanger (9) is lower than the temperature of the receiving medium.

Claims

1. A system for the recovery of waste heat energy contained in oil in an oil-cooled air compressor, which includes a gas compressor comprising at least a compressor main body, which is connected to an oil separator, which is connected to an oil flow divider, which is connected to an oil cooler and to the compressor main body; an oil temperature sensor; a receiving side temperature sensor; and a heat exchanger, characterised in that the outlet of the oil side of the oil separator (4) is connected to the inlet of the oil side of the heat exchanger (9), and the outlet of the oil side of the heat exchanger is connected to the oil flow divider (10).

2. The system according to claim 1, characterised in that the oil temperature sensor (6) is positioned between the heat exchanger (9) and the oil flow divider (10).

3. The system according to claim 1, characterised in that the oil temperature sensor (18) is positioned at the injection point of the oil into the compressor main body (2).

4. The system according to claim 2, characterised in that an additional oil temperature sensor (5) is positioned between the oil separator (4) and the heat exchanger.

5. The system according to claim 2, characterised in that an additional oil temperature sensor (19) is positioned downstream of the compressor main body (2) and upstream of the oil separator (4).

6. A method for the recovery of waste heat energy contained in oil in an oil-cooled air compressor, which comprises at least a compressor main body, which is connected to an oil separator, which is connected to a heat exchanger, which is connected to an oil flow divider, which is connected to an oil cooler and the compressor main body; a control device; an oil temperature sensor; and a receiving side temperature sensor, characterised in that by means of a control device (12) the flow of the receiving medium is diverted away from the heat exchanger (9), or the flow of the receiving medium is stopped when at least the temperature of the oil returning to the compressor main body (2) is lower than the setpoint or the temperature of the oil entering the heat exchanger (9) is lower than the temperature of the receiving medium.

7. The method according to claim 6, characterised in that the temperature of the oil returning to the compressor main body (2) is measured by means of an oil temperature sensor (6) positioned between the heat exchanger (9) and the oil flow divider (10).

8. The method according to claim 6, characterised in that the temperature of the oil returning to the compressor main body (2) is measured by means of an oil temperature sensor (18) positioned at the injection point of the oil into the compressor main body (2).

9. The method according to claim 6, characterised in that the temperature of the oil entering the heat exchanger (9) is measured by means of an oil temperature sensor (5) positioned between the oil separator (4) and the heat exchanger (9).

10. The method according to claim 6, characterised in that the temperature of the oil entering the heat exchanger (9) is measured by means of an oil temperature sensor (19) positioned between the compressor main body (2) and the oil separator (4).

11. The method according to claim 6, characterised in that the temperature of the water receiving medium is measured by means of a temperature sensor (20) positioned at the entrance to the heat exchanger (9).

12. The method according to claim 6, characterised in that the temperature of the receiving water medium is measured by means of a temperature sensor (13) positioned in the storage tank.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0036] The subject matter of the present invention is further described in three embodiment variants, with their drawings in FIG. 1, FIG. 2, FIG. 3.

First Embodiment of the System

[0037] The first embodiment of the waste heat recovery system in an oil-lubricated and oil-cooled air compressor in accordance with the present invention is shown in the diagram in FIG. 1.

[0038] Designation 2 in FIG. 1 refers to a motor-driven compressor main body, which with reference to the present invention is an oil-lubricated and oil-cooled air compressor. With the motor-driven compressor main body 2 the air gas sucked into the compressor 1 is sucked through filter 17 at the inlet of the compressor main body 2. Compressed air is obtained at the outlet of the compressor main body 2 and flows in the form of an oil/air mixture to the oil separator 4.

[0039] Centrifugal separation of air and oil takes place in the oil separator 4. The air escapes from the upper part of the oil separator 4 and flows further through the air pipeline 22 to the air cooler 7 for cooling and delivery through the next pipeline to the receiving system. The oil collected in the lower part of oil separator 4 flows further through oil pipeline 24 to the inlet side of heat exchanger 9, positioned for waste heat recovery. The heat exchanger is mounted in a counterflow arrangement, which in practice allows the outlet temperature on the oil side to be close to the inlet temperature on the working medium side, maximising the recovery rate. The oil flowing out of the heat exchanger 9 continues through the oil pipeline 25 to the inlet of the thermostatic (bimetallic or liquid) three-way valve 10, hereinafter referred to as the oil flow divider. The oil flows through the three-way valve 10, and when the oil temperature reaches the opening temperature (no heat extraction in the heat recovery exchanger), it is routed via the oil pipeline 27 to the oil cooler 7, where it is cooled by the air flow, typically forced by means of a variable-speed fan 8, and then returns to the compressor main body via the oil pipeline 28 and oil filter 3. The so-called long oil circuit in the compressor system is thus implemented. When the oil temperature does not reach the opening temperature, the heat is extracted in the heat recovery exchanger, the oil flows through the three-way valve 10, the oil pipeline 26 and oil filter 3, bypassing the cooler 7 back to the compressor main body. The so-called short oil circuit in the compressor system is thus implemented.

[0040] On the water side, the heat exchanger 9 is connected to storage tank 14, the purpose of which is to store the heat recovered by the flow of the working medium through the heat exchanger 9. The working medium, typically water, circulates through the heat exchanger 9 via inlet pipeline 30 and outlet pipeline 31. Thus, the heat generated in the compressor main body 2 is recoverable in the heat exchanger 9 and stored as working medium (water) at an elevated temperature in the storage tank 14.

[0041] In accordance with the present invention, this means that the lower temperature working medium, through the heat exchanger 9, is intended to be heated, while the higher temperature oil is intended to be cooled, with the simultaneous flow of oil and working medium (water) through the heat exchanger 9, in which heat is exchanged from the higher temperature oil to the lower temperature working medium (water).

[0042] The heat exchanger 9 is connected to the storage tank 14 as follows: the working medium pipeline 30 connects the lower part of the storage tank 14 to the inlet of the water side of the heat exchanger 9, while the working medium pipeline 31 connects the upper part of the storage tank 14 to the outlet of the heat exchanger 9. Supply pipeline 33 is connected to the lower part of the storage tank 14, supplying the working medium to be heated, while receiving pipeline 34 is connected to the upper part of the storage tank 14, receiving the heated working medium to be utilised. Configured in this way, the system does not constitute an additional water-to-water heat exchanger but increases the total volume of the receiving-side working medium 15. As such, the receiving-side working medium is heated directly in the heat exchanger 9, with the storage tank itself acting as both energy storage and hydraulic coupling.

[0043] Subsequently, a circulating pump 11 is mounted on the working medium pipeline 30 to ensure circulation of the working medium between the storage tank 14 and the heat exchanger 9. The pump 11 can be mounted either on the inlet pipeline 30 or on the outlet pipeline 31, connected to the exchanger. The essential point is that the inlet of the exchanger 9 is connected to the lower part of the storage tank 14 and the outlet of the exchanger 9 is connected to the upper part of the storage tank 14.

[0044] The system is further equipped with an oil inlet temperature sensor 5, hereinafter referred to as the oil supply temperature sensor, and an oil outlet temperature sensor 6, hereinafter referred to as the oil return temperature sensor. The oil supply temperature sensor 5 monitors the temperature in order to start/stop the heat recovery process and to prevent the oil/air mixture from being too cold, posing a risk of condensation. The oil return temperature sensor 6 monitors the temperature in order to protect the oil from overcooling, due to the maintenance of adequate oil parameters, which further protects against the risk of condensation. The oil supply temperature sensor 5 additionally serves as an operational safeguard for the oil return sensor 6. The oil return temperature sensor 6 additionally serves as an operational safeguard for the oil supply sensor 5.

[0045] The system is furthermore provided with a working medium temperature sensor 13, located in the storage tank, hereinafter referred to as the water temperature sensor. This sensor serves to control the temperature of the medium on the receiving side 15 in order to start/stop the heat recovery process, as well as to regulate the temperature of the medium on the receiving side to the setpoint and to protect the medium on the receiving side from overheating.

[0046] With the present embodiment, the system is equipped with a variable-speed circulating pump 11, previously referred to as the circulating pump, to ensure circulation of the receiving medium (water) through the receiving pipelines 30, 31.

[0047] In addition, the heat recovery system being the subject matter of the described invention is in the present embodiment provided with a control system 12 connected to the pump 11, with a working medium temperature sensor 13, an oil supply temperature sensor 5 and an oil return temperature sensor 6.

[0048] In the present embodiment, the oil supply temperature sensor 5 measures the oil temperature in the separator downstream of the block. If its value is greater than or equal to the setpoint, hereinafter referred to as the recovery start-up temperature, and at the same time its value is greater than the working medium temperature measured by sensor 13, and at the same time the oil return temperature measured by sensor 6 is greater than or equal to the setpoint, the control system 12 activates the working medium circuit pump 13, which results in the actual start of the heat recovery process.

[0049] In the present embodiment, the control system regulates the pump so that it measures the temperature difference between the oil supply temperature, as measured by sensor 5, and the working medium temperature, as measured by sensor 13. The pump speed is inversely proportional to the temperature difference measured as the temperature difference modulus as measured by sensors 13 and 5. Consequently, the control system 12 increases the pump speed as the temperature difference between sensors 13 and 5 decreases. This maximises the heat energy recovered.

[0050] The energy recovery process is controlled as follows: if, during the heat recovery process, the control system 12 detects that: [0051] the temperature of the working medium measured by sensor 13 is higher than the setpoint, or [0052] the oil return temperature measured by sensor 6 is lower than the setpoint, or [0053] the temperature of the working medium measured by sensor 13 is greater than or equal to the oil supply temperature measured by sensor 5, the control system 12 will stop the heat recovery process immediately or with a preprogrammed delay deemed safe. Second Embodiment of the System

[0054] The second embodiment differs from the first in that the pump is a fixed-speed pump and the three-way valve (proportional or diverter) is responsible for triggering recovery and possible adjustments.

[0055] The second embodiment of the waste heat recovery system in an oil-lubricated and oil-cooled air compressor in accordance with the present invention is shown in the diagram in FIG. 2.

[0056] Designation 2 in FIG. 2 refers to a motor-driven compressor main body, which with reference to the present invention is an oil-lubricated and oil-cooled air compressor. With the motor-driven compressor main body 2 the air gas sucked into the compressor 1 is sucked through filter 17 at the inlet of the compressor main body 2. Compressed air is obtained at the outlet of the compressor main body 2 and flows in the form of an oil/air mixture to the oil separator 4.

[0057] Centrifugal separation of air and oil takes place in the oil separator 4. The air escapes from the upper part of the oil separator 4 and flows further through the air pipeline 22 to the air cooler 7 for cooling and delivery through the next pipeline to the receiving system. The oil collected in the lower part of oil separator 4 flows further through oil pipeline 24 to the inlet side of heat exchanger 9, positioned for waste heat recovery. The heat exchanger is mounted in a counterflow arrangement, which in practice allows the outlet temperature on the oil side to be close to the inlet temperature on the working medium side, maximising the recovery rate. The oil flowing out of the heat exchanger 9 continues through the oil pipeline 25 to the inlet of the thermostatic bimetallic or liquid three-way valve 10, hereinafter referred to as the oil flow divider. The oil flows through the three-way valve 10, and when the oil temperature reaches the opening temperature (no heat extraction in the heat recovery exchanger), it is routed via the oil pipeline 27 to the oil cooler 7, where it is cooled by the air flow, typically forced by means of a variable-speed fan 8, and then returns to the compressor main body via the oil pipeline 28 and oil filter 3. The so-called long oil circuit in the compressor system is thus implemented. When the oil temperature does not reach the opening temperature, the heat is extracted in the heat recovery exchanger, the oil flows through the three-way valve 10, the oil pipeline 26 and oil filter 3, bypassing the cooler 7 back to the compressor main body. The so-called short oil circuit in the compressor system is thus implemented.

[0058] On the water side, the heat exchanger 9 is connected to storage tank 14, the purpose of which is to store the heat recovered by the flow of the working medium through the heat exchanger 9. The working medium, typically water, circulates through the heat exchanger 9 via inlet pipeline 30 and outlet pipeline 31. Thus, the heat generated in the compressor main body 2 is recoverable in the heat exchanger 9 and stored as working medium (water) at an elevated temperature in the storage tank 14.

[0059] In accordance with the present invention, this means that the lower temperature working medium, through the heat exchanger 9, is intended to be heated, while the higher temperature oil is intended to be cooled, with the simultaneous flow of oil and working medium (water) through the heat exchanger 9, in which heat is exchanged from the higher temperature oil to the lower temperature working medium (water).

[0060] The heat exchanger 9 is connected to the storage tank 14 as follows: the working medium pipeline 30 connects the lower part of the storage tank 14 to the inlet of the water side of the heat exchanger 9, while the working medium pipeline 31 connects the upper part of the storage tank 14 to the outlet of the heat exchanger 9. Supply pipeline 33 is connected to the lower part of the storage tank 14, supplying the working medium to be heated, while receiving pipeline 34 is connected to the upper part of the storage tank 14, receiving the heated working medium to be utilised. Configured in this way, the system does not constitute an additional water-to-water heat exchanger but increases the total volume of the receiving-side working medium 15. As such, the receiving-side working medium is heated directly in the heat exchanger 9, with the storage tank itself acting as both energy storage and hydraulic coupling.

[0061] A three-way valve is mounted on the working medium pipeline 30 to enable the flow through the exchanger to be activated or to divert the flow outside the exchanger via the working medium pipeline 32 used for this purpose. If equipped with a suitable drive, the valve can also provide quantitative control of the flow of the receiving medium (water) through the exchanger.

[0062] A circulating pump 11 is mounted on the working medium pipeline to ensure circulation of the working medium between the storage tank 14 and the heat exchanger 9. With this embodiment, the pump 11 is mounted on the inlet pipeline 30, which is connected to the exchanger upstream of the three-way valve 10. Such a connection between the pump 11 and the three-way valve 16 allows for the separation of two hydraulic circuits in order to regulate the amount of medium flowing through the heat exchanger 9, that is the proportion of the streams flowing through the heat exchanger 9 and pipelines 32 and 35 via the so-called bypass.

[0063] The essential point is that the inlet of the exchanger 9 is connected to the lower part of the storage tank 14 and the outlet of the exchanger 9 is connected to the upper part of the storage tank.

[0064] The system in question is equipped with an oil inlet temperature sensor 5, hereinafter referred to as the oil supply temperature sensor, and an oil outlet temperature sensor 6, hereinafter referred to as the oil return temperature sensor. The oil supply temperature sensor 5 monitors the temperature in order to start/stop the heat recovery process and to prevent the oil/air mixture from being too cold, posing a risk of condensation. The oil return temperature sensor 6 monitors the temperature in order to protect the oil from overcooling, due to the maintenance of adequate oil parameters, which further protects against the risk of condensation. The oil supply temperature sensor 5 additionally serves as an operational safeguard for the oil return sensor 6. The oil return temperature sensor 6 additionally serves as an operational safeguard for the oil supply sensor 5.

[0065] The system is furthermore provided with a working medium temperature sensor 13, located in the storage tank 14, hereinafter referred to as the water temperature sensor. This sensor serves to control the temperature of the medium on the receiving side in order to start/stop the heat recovery process, as well as to regulate the temperature of the medium on the receiving side to the setpoint and to protect the medium on the receiving side from overheating.

[0066] With the present embodiment, the system is equipped with a fixed-speed circulating pump 11, previously referred to as the circulating pump, to ensure circulation of the receiving medium (water) through the receiving pipelines 30, 31, 32.

[0067] In addition, the heat recovery system being the subject matter of the described invention is in the present embodiment provided with a control system 12 connected to the three-way valve 16, with a working medium temperature sensor 13, an oil supply temperature sensor 5 and an oil supply temperature sensor 6.

[0068] In the present embodiment, the oil supply temperature sensor 5 measures the oil temperature in the separator downstream of the block. If its value is greater than or equal to the setpoint, hereinafter referred to as the recovery start-up temperature, and at the same time its value is greater than the working medium temperature measured by sensor 13, and at the same time the oil return temperature measured by sensor 6 is greater than or equal to the setpoint, the control system 12 diverts the flow of the working medium through the exchanger, which results in the actual start of the heat recovery process.

[0069] In the present embodiment, the control system regulates the three-way valve 16 so that it measures the temperature difference between the oil supply temperature, as measured by sensor 5, and the working medium temperature, as measured by sensor 13. The medium flow is inversely proportional to the temperature difference measured as the temperature difference modulus as measured by sensors 13 and 5. Consequently, the control system 12 increases the flow as the temperature difference between sensors 13 and 5 decreases. This maximises the heat energy recovered.

[0070] The energy recovery process is controlled as follows: if, during the heat recovery process, the control system 12 detects that: [0071] the temperature of the working medium measured by sensor 13 is higher than the setpoint, or [0072] the oil return temperature measured by sensor 6 is lower than the setpoint, or [0073] the temperature of the working medium measured by sensor 13 is greater than or equal to the oil supply temperature measured by sensor 5, the control system 12 will stop the heat recovery process, i.e. immediately divert the working medium (water) flow through pipeline 32 away from the heat exchanger used for waste energy recovery, or with a preprogrammed delay deemed safe.

Third Embodiment of the System

[0074] The third embodiment of the waste heat recovery system in an oil-lubricated and oil-cooled air compressor in accordance with the present invention is shown in the diagram in FIG. 3.

[0075] Designation 2 in FIG. 3 refers to a motor-driven compressor main body, which with reference to the present invention is an oil-lubricated and oil-cooled air compressor. With the motor-driven compressor main body 2 the air gas sucked into the compressor 1 is sucked through filter 17 at the inlet of the compressor main body 2. Compressed air is obtained at the outlet of the compressor main body 2 and flows in the form of an oil/air mixture to the oil separator 4.

[0076] Centrifugal separation of air and oil takes place in the oil separator 4. The air escapes from the upper part of the oil separator 4 and flows further through the air pipeline 22 to the air cooler 7 for cooling and delivery through the next pipeline to the receiving system. The oil collected in the lower part of oil separator 4 flows further through oil pipeline 30 to the inlet side of heat exchanger 9, positioned for waste heat recovery. The heat exchanger is mounted in a counterflow arrangement, which in practice allows the outlet temperature on the oil side to be close to the inlet temperature on the working medium side, maximising the recovery rate. The oil flowing out of the heat exchanger 9 continues through the oil pipeline 31 to the inlet of the thermostatic bimetallic or liquid three-way valve 10, hereinafter referred to as the oil flow divider. The oil flows through the three-way valve 10, and when the oil temperature reaches the opening temperature (no heat extraction in the heat recovery exchanger), it is routed via the oil pipeline 27 to the oil cooler 7, where it is cooled by the air flow, typically forced by means of a variable-speed fan 8, and then returns to the compressor main body via the oil pipeline 28 and oil filter 3. The so-called long oil circuit in the compressor system is thus implemented. When the oil temperature does not reach the opening temperature, the heat is extracted in the heat recovery exchanger, the oil flows through the three-way valve 10, the oil pipeline 26 and oil filter 3, bypassing the cooler back to the compressor main body. The so-called short oil circuit in the compressor system is thus implemented.

[0077] On the water side, the heat exchanger 9 is connected to storage tank 14, the purpose of which is to store the heat recovered by the flow of the working medium through the heat exchanger 9. The working medium-water-circulates through the heat exchanger 9 via inlet pipeline 30 and outlet pipeline 31. Thus, the heat generated in the compressor main body 2 is recoverable in the heat exchanger 9 and stored as working medium (water) at an elevated temperature in the storage tank 14.

[0078] This means that the lower temperature working medium, through the heat exchanger 9, is intended to be heated, while the higher temperature oil is intended to be cooled, with the simultaneous flow of oil and working medium (water) through the heat exchanger 9, in which heat is exchanged from the higher temperature oil to the lower temperature working medium (water).

[0079] The heat exchanger 9 is connected to the storage tank 14 as follows: the working medium pipeline 30 connects the lower part of the storage tank 14 to the inlet of the water side of the heat exchanger 9, while the working medium pipeline 31 connects the upper part of the storage tank 14 to the outlet of the heat exchanger 9. Supply pipeline 33 is connected to the lower part of the storage tank 14, supplying the working medium to be heated, while receiving pipeline 34 is connected to the upper part of the storage tank 14, receiving the heated working medium.

[0080] A three-way valve is further mounted on the working medium pipeline 30 to enable the flow through the exchanger to be activated or to divert the flow outside the exchanger via the working medium pipeline 32. If equipped with a suitable drive, the valve can also provide quantitative control of the flow of the receiving medium (water) through the exchanger (9).

[0081] A circulating pump 11 is mounted on the working medium pipeline 30 to ensure circulation of the working medium between the storage tank 14 and the heat exchanger 9. With this embodiment, the pump 11 is mounted on the inlet pipeline 30, which is connected via the three-way valve 16 to the exchanger and to the return pipeline 31 via the pipeline 32. The essential point is that the inlet of the exchanger 9 is connected to the lower part of the storage tank 14 and the outlet of the exchanger 9 is connected to the upper part of the storage tank.

[0082] The storage tank has a coil inside, which constitutes a water-to-water heat exchanger 21. The use of a coil inside the storage tank allows for the hydraulic separation of the heat recovery circuit from the receiving circuit. Such separation may be necessary, e.g. due to sanitary regimes.

[0083] Owing to the indirect heat transfer described above, it is also possible to use two different heating media, e.g. water in the recovery circuit and glycol in the receiving circuit.

[0084] Thanks to the use of a coil 21 located in the storage tank 14, it is possible to construct a hybrid system for the transfer of recovered heat, i.e. both directly and indirectly at the same time. This is the case when the heat is transferred through the storage tankbeing simultaneously an energy store and a hydraulic couplingin a direct manner, i.e. with the same heating medium to the central heating circuit, while the domestic hot water is prepared via the coil. At this point, the domestic hot water can be prepared in a flow-through manner or the coil can heat an additional tank, e.g. a double-walled tank.

[0085] The system is further equipped with an oil inlet temperature sensor 5, hereinafter referred to as the oil supply temperature sensor, and an oil outlet temperature sensor 6, hereinafter referred to as the oil return temperature sensor. The oil supply temperature sensor 5 monitors the temperature in order to start/stop the heat recovery process and to prevent the oil/air mixture from being too cold, posing a risk of condensation. The oil return temperature sensor 6 monitors the temperature in order to protect the oil from overcooling, due to the maintenance of adequate oil parameters, which further protects against the risk of condensation. The oil supply temperature sensor 5 additionally serves as an operational safeguard for the oil return sensor 6. The oil return temperature sensor 6 additionally serves as an operational safeguard for the oil supply sensor 5.

[0086] The system is furthermore provided with a working medium temperature sensor 13, located in the storage tank, hereinafter referred to as the water temperature sensor. This sensor serves to control the temperature of the medium on the receiving side 15 in order to start/stop the heat recovery process, as well as to regulate the temperature of the medium on the receiving side to the setpoint and to protect the medium on the receiving side from overheating.

[0087] With the present embodiment, the system is equipped with a fixed-speed circulating pump 11, previously referred to as the circulating pump, to ensure circulation of the receiving medium (water) through the receiving pipelines 30, 31, 32.

[0088] In addition, the heat recovery system is provided with a control system 12 connected to the three-way valve 16, with a working medium temperature sensor 13, an oil supply temperature sensor 5 and an oil supply temperature sensor 6.

[0089] In the present embodiment, the oil supply temperature sensor 5 measures the oil temperature in the separator downstream of the block. If its value is greater than or equal to the setpoint, hereinafter referred to as the recovery start-up temperature, and at the same time its value is greater than the working medium temperature measured by sensor 13, and at the same time the oil return temperature measured by sensor 6 is greater than or equal to the setpoint, the control system 12 diverts the flow of the working medium through the exchanger, which results in the actual start of the heat recovery process.

[0090] In the present embodiment, the control system regulates the three-way valve 16 so that it measures the temperature difference between the oil supply temperature, as measured by sensor 5, and the working medium temperature, as measured by sensor 13. The medium flow is inversely proportional to the temperature difference measured as the temperature difference modulus as measured by sensors 13 and 5. Consequently, the control system 12 increases the flow as the temperature difference between sensors 13 and 5 decreases. This maximises the heat energy recovered.

[0091] The energy recovery process is controlled as follows: if, during the heat recovery process, the control system 12 detects that: [0092] the temperature of the working medium measured by sensor 13 is higher than the setpoint, or [0093] the oil return temperature measured by sensor 6 is lower than the setpoint, or [0094] the temperature of the working medium measured by sensor 13 is greater than or equal to the oil supply temperature measured by sensor 5, the control system 12 will stop the heat recovery process, immediately divert the working medium (water) flow away from the heat exchanger used for waste energy recovery, or with a preprogrammed delay deemed safe.