WO2023128774A1 - The system and the method for recovery of waste heat energy contained in oil in an oil-cooled air compressor - Google Patents

The system and the method for recovery of waste heat energy contained in oil in an oil-cooled air compressor Download PDF

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Publication number
WO2023128774A1
WO2023128774A1 PCT/PL2022/050075 PL2022050075W WO2023128774A1 WO 2023128774 A1 WO2023128774 A1 WO 2023128774A1 PL 2022050075 W PL2022050075 W PL 2022050075W WO 2023128774 A1 WO2023128774 A1 WO 2023128774A1
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WO
WIPO (PCT)
Prior art keywords
oil
temperature
heat exchanger
temperature sensor
main body
Prior art date
Application number
PCT/PL2022/050075
Other languages
French (fr)
Inventor
Mateusz BARTCZAK
Łukasz BARTCZAK
Grzegorz BARTCZAK
Original Assignee
Asfi Spółka Z O.O.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Asfi Spółka Z O.O. filed Critical Asfi Spółka Z O.O.
Priority to AU2022429418A priority Critical patent/AU2022429418A1/en
Publication of WO2023128774A1 publication Critical patent/WO2023128774A1/en

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
    • F04B39/00—Component parts, details, or accessories, of pumps or pumping systems specially adapted for elastic fluids, not otherwise provided for in, or of interest apart from, groups F04B25/00 - F04B37/00
    • F04B39/06—Cooling; Heating; Prevention of freezing
    • F04B39/062—Cooling by injecting a liquid in the gas to be compressed
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
    • F04B39/00—Component parts, details, or accessories, of pumps or pumping systems specially adapted for elastic fluids, not otherwise provided for in, or of interest apart from, groups F04B25/00 - F04B37/00
    • F04B39/02—Lubrication
    • F04B39/0207—Lubrication with lubrication control systems
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
    • F04B39/00—Component parts, details, or accessories, of pumps or pumping systems specially adapted for elastic fluids, not otherwise provided for in, or of interest apart from, groups F04B25/00 - F04B37/00
    • F04B39/16—Filtration; Moisture separation

Definitions

  • the present invention relates to the system and the method for the efficient recovery of waste heat energy contained in oil in oil-cooled industrial gas compressors (specifically air compressors).
  • waste heat from air compression examples include: JP4329875, JP2006125302, US9897103, EP2949939, US10578339, US10041698.
  • the use of waste heat from compression in a steam-driven air compressor to preheat the condensate or water allowed to generate the steam driving the compression unit is known from invention description JP4329875.
  • Invention description JP2006125302 concerns the use of waste heat from compression in an air compressor to convert it into electricity by means of thermoelectric cells arranged on compressor components emitting a significant amount of heat energy.
  • Invention description US9897103, similarly to JP2006125302, concerns the conversion of heat to electricity in a closed Rankine cycle using heating, thus compressing the working medium followed by expansion in an expander driving the shaft of an electricity generator.
  • oil outlet temperature/oil return temperature is understood as the temperature of the oil running from the heat exchanger towards the compressor main body
  • oil inlet temperature/oil supply temperature is understood as the temperature of the oil running from the compressor main body towards the heat exchanger for waste heat recovery.
  • the waste heat from the compression process contained in the oil and air, as described in the state of the art, is transferred via an exchanger to the working medium on the receiving end to obtain the set temperature of the said medium.
  • the recommended oil injection temperature is not less than 35-45 °C. This is because the temperature of the oil/air mixture (the temperature of the air taken in for compression should also be considered here) entering the oil separator should not preferably drop below 67 °C to avoid condensation. At this temperature, the water contained in the air is transferred along with it to the dryer, where it is separated.
  • thermostatic three-way valve does not provide sufficient protection here, as it is positioned downstream of the separator, at which point the oil is already heated.
  • a temperature sensor has been placed between the compressor main body and the oil separator.
  • this sensor serves to stop the heat recovery process when the temperature of the oil/air mixture downstream of the compressor main body is too low. This raises a technical problem, because by the time the temperature that poses the risk of condensation is reached, it is already too late to stop the recovery. Given the inertia of the system, the potential for water to enter the separator and mix with the oil is significant.
  • the problem described above can be partly solved by a procedure already in use in technology, i.e. the use of an auxiliary three-way valve downstream of the main three-way valve, which is the primary component of the compressor.
  • the main valve ensures the opening of the long oil circuit, while the auxiliary valve protects the oil from overcooling.
  • the valves must then be temperature graded - the opening/closing temperature of the main valve must be greater than the opening temperature of the auxiliary valve.
  • This solution is partly applied in technology, but nevertheless has three significant disadvantages: relatively high inertia, cost of installation and operation of the auxiliary valve as part of the compressor, risk of installation error, e.g. reverse setting of the two thermostats.
  • Another problem is how to control the pump. Given the physics of the process, it is natural to protect the system against reverse energy transfer - heating the compressor back with heat from the system. However, this approach does not produce adequate results in terms of waste energy transfer efficiency and needs to be improved.
  • the objective of the present invention is to provide a system for the recovery of waste heat from a gas compressor, specifically an air compressor, wherein the heat exchanger designed to recover waste heat contained in oil is mounted in a way that makes the installation of an auxiliary three-way valve unnecessary, while the heat recovery is carried out with maximum efficiency (bypassing the main cooler) and in a way that protects the compressor from the occurrence of condensation of steam contained in the compressed air.
  • the essence of the present invention is a system for the recovery of waste heat energy contained in oil in an oil-cooled air compressor.
  • the gas compressor system comprises 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; and a heat exchanger, the water side of which is connected to the receiving circuit.
  • the outlet of the oil side of the oil separator is connected to the inlet of the oil side of the heat exchanger.
  • the outlet of the oil side of the heat exchanger is connected to the oil flow divider.
  • the oil temperature sensor is positioned between the heat exchanger and the oil flow divider.
  • the oil temperature sensor is also conveniently positioned at the injection point of the oil into the compressor main body.
  • An additional oil temperature sensor is placed between the oil separator and the heat exchanger. The additional oil temperature sensor is conveniently placed downstream of the compressor element and upstream of the oil separator.
  • the 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 by means of a control device, or stopping the receiving medium flow when at least the temperature of the oil returning to the compressor main body is lower than the setpoint or the temperature of the oil entering the heat exchanger is lower than the temperature of the receiving medium.
  • the compressor in question 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 medium temperature sensor.
  • the temperature of the oil returning to the compressor main body is measured by an oil temperature sensor positioned between the heat exchanger and the oil flow divider.
  • the temperature of the oil returning to the compressor main body is also conveniently measured with an oil temperature sensor positioned at the injection point of the oil into the compressor main body.
  • the temperature of the oil entering the heat exchanger is measured with an oil temperature sensor placed between the oil separator and the heat exchanger.
  • the temperature of the oil flowing into the heat exchanger is also conveniently measured with an oil temperature sensor placed between the compressor main body and the oil separator.
  • the temperature of the receiving water medium is measured with a temperature sensor positioned at the inlet to the heat exchanger.
  • the temperature of the receiving water medium is also conveniently measured with a temperature sensor positioned in the water storage tank.
  • an oil-cooled gas compressor (specifically an air compressor) a system comprising a compressor main body (compression element) connected to an oil separator for separating oil from the compressed gas supplied from the compressor main body; gas pipes (tubes) connected thereto for transferring the compressed gas separated from oil through the oil separator for use as required; oil pipes (tubes) connected to the separator for returning the separated oil to the compressor main body; a heat exchanger between the oil and the receiving medium (e.g. water) for recovering waste heat energy contained in the oil, which is located immediately after the oil separator and immediately before the three-way oil valve (oil flow divider) for separating the long oil circuit and the short oil circuit.
  • a heat exchanger between the oil and the receiving medium (e.g. water) for recovering waste heat energy contained in the oil, which is located immediately after the oil separator and immediately before the three-way oil valve (oil flow divider) for separating the long oil circuit and the short oil circuit.
  • the heat exchanger serves to recover waste heat energy contained in the oil, which is located in the system directly after the oil separator and directly before the three-way oil valve (oil flow divider) used for the separation of the long and short oil circuit.
  • the oil separator, heat exchanger and three-way valve are connected in the said sequence by oil transfer pipes (tubes).
  • the three-way oil valve connected downstream of the heat exchanger serves to divert the oil flow either directly back to the compressor main body or to the oil cooler. This closes the oil system of the air compressor.
  • the following are interchangeably connected to the receiving (water) side of the heat exchanger by means of a pipeline for the transfer of the receiving medium: a variable-speed pump to ensure the flow of the receiving medium and to regulate the amount of this flow or a fixed- speed pump to ensure the flow of the receiving medium and a three-way valve to regulate the amount of medium flowing through the heat exchanger to maximise recovery.
  • a heat buffer tank water storage tank
  • a heat buffer tank is then connected along the receiving medium pipeline to store the recovered heat energy, e.g. in water or a phase-change substance, and to act as a hydraulic coupling to connect the heat recovery circuit and the circuit which utilises this heat, e.g. a central heating system.
  • Another benefit lies in simplifying the heat recovery system as much as possible.
  • the energy recovered this way can be utilised in a wide range of heating applications in different temperature ranges, whether for heating fresh water (2-12 °C), process water (20 °C) or typical heating circuits (45-55 °C).
  • 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.
  • 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.
  • the motor- driven compressor main body 2 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.
  • 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.
  • 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.
  • 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
  • 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.
  • 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.
  • the system does not constitute an additional water-to- water heat exchanger but increases the total volume of the receiving-side working medium 15.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • the energy recovery process is controlled as follows: if, during the heat recovery process, the control system 12 detects that:
  • control system 12 will stop the heat recovery process immediately or with a preprogrammed delay deemed safe.
  • 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.
  • the pump is a fixed-speed pump and the three-way valve (proportional or diverter) is responsible for triggering recovery and possible adjustments.
  • 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.
  • 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.
  • the motor- driven compressor main body 2 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.
  • 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.
  • 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.
  • 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
  • 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.
  • 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.
  • the system does not constitute an additional water-to- water heat exchanger but increases the total volume of the receiving-side working medium 15.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • a fixed-speed circulating pump 11 previously referred to as the circulating pump
  • 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.
  • 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.
  • 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.
  • the energy recovery process is controlled as follows: if, during the heat recovery process, the control system 12 detects that:
  • 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.
  • 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.
  • 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.
  • the motor- driven compressor main body 2 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.
  • 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.
  • 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.
  • the heat exchanger 9 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.
  • 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.
  • 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.
  • 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).
  • 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.
  • 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.
  • 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 tank - being simultaneously an energy store and a hydraulic coupling - in 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.
  • 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.
  • 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.
  • 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.
  • a fixed-speed circulating pump 11 previously referred to as the circulating pump
  • 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.
  • 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.
  • 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.
  • the energy recovery process is controlled as follows: if, during the heat recovery process, the control system 12 detects that:
  • 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.

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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.

Description

The system and the method for recovery of waste heat energy contained in oil in an oil- cooled air compressor
The present invention relates to the system and the method for the efficient recovery of waste heat energy contained in oil in oil-cooled industrial gas compressors (specifically air compressors).
Industrial compressors installed in Europe are estimated to consume approx. 57 TWh of electricity per year. [Table 3-7 Baseline (BAU) Energy consumption (TWh/yr) Ecodesign preparatory Study on Electric motor systems / Compressors DG ENER Lot 31 FINAL Report of Task 6, 7 & 8],
Given the relative low efficiency of air compressors (6-8%), 3.42-4.56 TWh are converted into usable mechanical energy contained in the compressed air. The remaining 53.58-52.44 TWh are emitted as heat into the atmosphere. Faced with tackling greenhouse gas emissions (mainly CO2) and limited fossil fuel resources in general, such a way of consuming electricity is inefficient.
The issue has been addressed by the European Commission, with the designation of the product group classified under 'Compressors' as a priority axis in the first iteration of the Ecodesign Working Plan (2009-2011).
The low efficiency of compressors is due to the physics of the process and the thermodynamic transformations occurring during compression. While the compressor is operating under load (compression/discharging), approx. 6-8% of the supplied usable energy resulting from the so- called shaft power (electrical power minus the efficiency of the induction motor) is converted into usable mechanical energy contained in the compressed air. The remaining 92-94% is lost as heat. Considering the above 92-94% as 100% of the available heat energy, its breakdown is as follows: approx. 9% constitutes heat from the motor, 72% comes from oil cooling, 13% is lost in the compressed air cooler, and approx. 4% is residual in the cooled air.
As can be seen from the above, most of the usable heat energy is contained in the oil, which acts as both cooling and lubrication for the compressor main body.
Inventions considering the use of waste heat from air compression include: JP4329875, JP2006125302, US9897103, EP2949939, US10578339, US10041698. The use of waste heat from compression in a steam-driven air compressor to preheat the condensate or water allowed to generate the steam driving the compression unit is known from invention description JP4329875. Invention description JP2006125302 concerns the use of waste heat from compression in an air compressor to convert it into electricity by means of thermoelectric cells arranged on compressor components emitting a significant amount of heat energy. Invention description US9897103, similarly to JP2006125302, concerns the conversion of heat to electricity in a closed Rankine cycle using heating, thus compressing the working medium followed by expansion in an expander driving the shaft of an electricity generator.
The remainder of the invention descriptions listed relate to the use of waste heat from the compression of air in the compressor, contained in the lubricating and cooling oil (approx. 72%), as well as the heat energy contained in the compressed air (approx. 13%). These solutions involve the transfer of said heat energy to a receiving medium (water) for further use for any purpose, e.g. heating a building, hot water supply, etc.
In the description of the present invention:
- oil outlet temperature/oil return temperature is understood as the temperature of the oil running from the heat exchanger towards the compressor main body,
- oil inlet temperature/oil supply temperature is understood as the temperature of the oil running from the compressor main body towards the heat exchanger for waste heat recovery.
The waste heat from the compression process contained in the oil and air, as described in the state of the art, is transferred via an exchanger to the working medium on the receiving end to obtain the set temperature of the said medium.
Problems include the location of the heat exchanger in the compressor's oil system - in the so- called long oil circuit (downstream of a bimetallic or liquid three-way thermostatic valve, which is an integral part of the compressor's design), so that in this case the oil cooled in the heat exchanger practically always flows through a cooler. Another issue is the lack of temperature measurement of the oil returning to the compressor main body.
The challenges outlined above result in two negative outcomes:
1. A portion of the heat is always emitted into the atmosphere (causing inefficient use of energy), 2. There is a lack of control of the oil return temperature to the compressor main body, resulting in a risk of oil overcooling and subsequent steam condensation. The recommended oil injection temperature is not less than 35-45 °C. This is because the temperature of the oil/air mixture (the temperature of the air taken in for compression should also be considered here) entering the oil separator should not preferably drop below 67 °C to avoid condensation. At this temperature, the water contained in the air is transferred along with it to the dryer, where it is separated.
The risk of condensation described above occurs especially if the waste heat contained in the oil is transferred to a medium of significantly lower temperature, e.g. fresh water (2-12 °C).
It should be noted that the thermostatic three-way valve does not provide sufficient protection here, as it is positioned downstream of the separator, at which point the oil is already heated.
Thus, if oil enters the separator and continues through the thermostatic three-way valve to the cooler at too low a temperature (below the condensation limit), it still makes several runs through the circuit within the inertia of the thermostatic valve. This allows condensed water from the air to enter the oil separator.
With reference to patent descriptions EP2949939, US10578339 and US10041698, a temperature sensor has been placed between the compressor main body and the oil separator. Among other things, this sensor serves to stop the heat recovery process when the temperature of the oil/air mixture downstream of the compressor main body is too low. This raises a technical problem, because by the time the temperature that poses the risk of condensation is reached, it is already too late to stop the recovery. Given the inertia of the system, the potential for water to enter the separator and mix with the oil is significant.
The problem described above can be partly solved by a procedure already in use in technology, i.e. the use of an auxiliary three-way valve downstream of the main three-way valve, which is the primary component of the compressor. The main valve ensures the opening of the long oil circuit, while the auxiliary valve protects the oil from overcooling. The valves must then be temperature graded - the opening/closing temperature of the main valve must be greater than the opening temperature of the auxiliary valve. This solution is partly applied in technology, but nevertheless has three significant disadvantages: relatively high inertia, cost of installation and operation of the auxiliary valve as part of the compressor, risk of installation error, e.g. reverse setting of the two thermostats. Another problem is how to control the pump. Given the physics of the process, it is natural to protect the system against reverse energy transfer - heating the compressor back with heat from the system. However, this approach does not produce adequate results in terms of waste energy transfer efficiency and needs to be improved.
The objective of the present invention is to provide a system for the recovery of waste heat from a gas compressor, specifically an air compressor, wherein the heat exchanger designed to recover waste heat contained in oil is mounted in a way that makes the installation of an auxiliary three-way valve unnecessary, while the heat recovery is carried out with maximum efficiency (bypassing the main cooler) and in a way that protects the compressor from the occurrence of condensation of steam contained in the compressed air.
The essence of the present invention is a system for the recovery of waste heat energy contained in oil in an oil-cooled air compressor. The gas compressor system comprises 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; and a heat exchanger, the water side of which is connected to the receiving circuit. Wherein the outlet of the oil side of the oil separator is connected to the inlet of the oil side of the heat exchanger. The outlet of the oil side of the heat exchanger is connected to the oil flow divider. The oil temperature sensor is positioned between the heat exchanger and the oil flow divider. The oil temperature sensor is also conveniently positioned at the injection point of the oil into the compressor main body. An additional oil temperature sensor is placed between the oil separator and the heat exchanger. The additional oil temperature sensor is conveniently placed downstream of the compressor element and upstream of the oil separator.
The 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 by means of a control device, or stopping the receiving medium flow when at least the temperature of the oil returning to the compressor main body is lower than the setpoint or the temperature of the oil entering the heat exchanger is lower than the temperature of the receiving medium. Wherein the compressor in question 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 medium temperature sensor. The temperature of the oil returning to the compressor main body is measured by an oil temperature sensor positioned between the heat exchanger and the oil flow divider. The temperature of the oil returning to the compressor main body is also conveniently measured with an oil temperature sensor positioned at the injection point of the oil into the compressor main body. The temperature of the oil entering the heat exchanger is measured with an oil temperature sensor placed between the oil separator and the heat exchanger. The temperature of the oil flowing into the heat exchanger is also conveniently measured with an oil temperature sensor placed between the compressor main body and the oil separator. The temperature of the receiving water medium is measured with a temperature sensor positioned at the inlet to the heat exchanger. The temperature of the receiving water medium is also conveniently measured with a temperature sensor positioned in the water storage tank.
To address the problems described in the state of the art, the invention employs in an oil-cooled gas compressor (specifically an air compressor) a system comprising a compressor main body (compression element) connected to an oil separator for separating oil from the compressed gas supplied from the compressor main body; gas pipes (tubes) connected thereto for transferring the compressed gas separated from oil through the oil separator for use as required; oil pipes (tubes) connected to the separator for returning the separated oil to the compressor main body; a heat exchanger between the oil and the receiving medium (e.g. water) for recovering waste heat energy contained in the oil, which is located immediately after the oil separator and immediately before the three-way oil valve (oil flow divider) for separating the long oil circuit and the short oil circuit. The heat exchanger serves to recover waste heat energy contained in the oil, which is located in the system directly after the oil separator and directly before the three-way oil valve (oil flow divider) used for the separation of the long and short oil circuit. The oil separator, heat exchanger and three-way valve are connected in the said sequence by oil transfer pipes (tubes).
The three-way oil valve connected downstream of the heat exchanger serves to divert the oil flow either directly back to the compressor main body or to the oil cooler. This closes the oil system of the air compressor.
The following are interchangeably connected to the receiving (water) side of the heat exchanger by means of a pipeline for the transfer of the receiving medium: a variable-speed pump to ensure the flow of the receiving medium and to regulate the amount of this flow or a fixed- speed pump to ensure the flow of the receiving medium and a three-way valve to regulate the amount of medium flowing through the heat exchanger to maximise recovery. A heat buffer tank (water storage tank) is then connected along the receiving medium pipeline to store the recovered heat energy, e.g. in water or a phase-change substance, and to act as a hydraulic coupling to connect the heat recovery circuit and the circuit which utilises this heat, e.g. a central heating system.
With the present invention, it is possible to obtain a heat recovery system from an oil-cooled gas compressor, providing maximum waste heat recovery by locating the heat exchanger in the oil system, which means bypassing the compressor cooling system and reducing heat emission to the atmosphere, while controlling the heat recovery in a way that ensures maximum energy recovery factor.
Another benefit lies in simplifying the heat recovery system as much as possible.
The placement of the heat exchanger between the oil separator and the compressor's three-way valve (oil flow divider) makes it neutral to the compressor's operation. Consequently, in the absence of heat recovery by the heat recovery system, it flows via a long circuit through the compressor's integral cooling system and its protective devices. In turn, two temperature sensors - oil return (downstream of the heat exchanger) and working medium temperature (upstream of the heat exchanger) - connected to a single controller are responsible for controlling the recovery system itself. This ensures that the compressor is well-protected against the occurrence of condensation.
The energy recovered this way can be utilised in a wide range of heating applications in different temperature ranges, whether for heating fresh water (2-12 °C), process water (20 °C) or typical heating circuits (45-55 °C).
Additional thermostats do not have to be used and graded accordingly.
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
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.
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.
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.
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.
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). 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.
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.
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.
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. 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.
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.
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.
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.
The energy recovery process is controlled as follows: if, during the heat recovery process, the control system 12 detects that:
- the temperature of the working medium measured by sensor 13 is higher than the setpoint, or
- the oil return temperature measured by sensor 6 is lower than the setpoint, or
- 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 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.
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.
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.
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.
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.
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).
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.
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.
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.
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. 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.
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.
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.
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.
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.
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.
The energy recovery process is controlled as follows: if, during the heat recovery process, the control system 12 detects that:
- the temperature of the working medium measured by sensor 13 is higher than the setpoint, or
- the oil return temperature measured by sensor 6 is lower than the setpoint, or
- 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
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.
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.
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.
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.
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).
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.
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). 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.
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.
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.
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 tank - being simultaneously an energy store and a hydraulic coupling - in 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.
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.
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.
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.
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.
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.
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.
The energy recovery process is controlled as follows: if, during the heat recovery process, the control system 12 detects that:
- the temperature of the working medium measured by sensor 13 is higher than the setpoint, or
- the oil return temperature measured by sensor 6 is lower than the setpoint, or
- 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.

Claims

Patent 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. 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). 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). 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). 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). 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). 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.
PCT/PL2022/050075 2021-12-31 2022-11-04 The system and the method for recovery of waste heat energy contained in oil in an oil-cooled air compressor WO2023128774A1 (en)

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PL440055A PL440055A1 (en) 2021-12-31 2021-12-31 System and method of recovery of waste thermal energy contained in oil in an oil-cooled air compressor
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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2610495A1 (en) * 2010-08-27 2013-07-03 Hitachi Industrial Equipment Systems Co., Ltd. Oil-cooled gas compressor
EP2949939A1 (en) * 2013-01-28 2015-12-02 Hitachi Industrial Equipment Systems Co., Ltd. Waste-heat recovery system in oil-cooled gas compressor
CN214065050U (en) * 2020-12-18 2021-08-27 思安新能源股份有限公司 Air compressor waste heat recovery and ground source heat pump combined heat supply system

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2610495A1 (en) * 2010-08-27 2013-07-03 Hitachi Industrial Equipment Systems Co., Ltd. Oil-cooled gas compressor
EP2949939A1 (en) * 2013-01-28 2015-12-02 Hitachi Industrial Equipment Systems Co., Ltd. Waste-heat recovery system in oil-cooled gas compressor
CN214065050U (en) * 2020-12-18 2021-08-27 思安新能源股份有限公司 Air compressor waste heat recovery and ground source heat pump combined heat supply system

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