System and method for recovering waste heat energy contained in oil in an oil-cooled air compressor

Abstract

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

Description

[Technical field]

[0001] The present invention relates to a system and method for efficiently recovering the waste heat energy contained in the oil in oil-cooled industrial gas compressors, particularly air compressors. [Background technology]

[0002] It is estimated that industrial compressors installed in Europe consume approximately 57 TWh of electricity per year. (Table 3-7 Baseline (BAU) energy consumption (TWh / year) Ecodesign Preparatory Study on Electric Motor Systems / Compressors Final Report of DG ENER Lot 31 Tasks 6, 7, 8)

[0003] Considering the relatively 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 is released to the atmosphere as heat. Faced with greenhouse gas (mainly CO2) emissions and limited fossil fuel resources, this method of consuming electricity is inefficient.

[0004] This issue has also been taken up by the European Commission, which in the first iteration of its Ecodesign work programme (2009-2011) identified the product group classified as "compressors" as a priority axis.

[0005] The low efficiency of compressors is due to the physics of the process and the thermodynamic transformations that take place during compression. While the compressor is working under load (compression / discharge), about 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. If we consider the above 92-94% usable thermal energy as 100%, the breakdown is as follows: about 9% is heat from the motor, 72% due to oil cooling, 13% is lost in compressed air cooling and about 4% remains in the cooled air.

[0006] As can be seen above, most of the available thermal energy is contained in the oil, which both cools and lubricates the compressor body.

[0007] Inventions that explore the use of waste heat from air compression include: JP4329875, JP2006125302, US9897103, EP2949939, US10578339, US10041698.

[0008] The use of waste heat from compression in a steam-driven air compressor to preheat condensate or water that is allowed to generate steam to drive the compression unit is known from patent specification JP4329875. The summary of the invention in JP2006125302 relates to the use of waste heat from compression in an air compressor to convert it into electricity by means of thermoelectric cells arranged in the compressor components that release a significant amount of thermal energy. The summary of the invention in patent specification US9897103, like JP2006125302, relates to the conversion of heat into electricity in a closed Rankine cycle using heating, where a working medium is compressed and then expanded in an expander that drives the shaft of a generator.

[0009] The remaining description of the invention described concerns the utilization of waste heat resulting from the compression of air in a compressor, and the thermal energy contained in lubricating and cooling oils (about 72%) and in the compressed air (about 13%). These solutions include transferring said thermal energy to a receiving medium (water) for use in any purpose, such as heating buildings or hot water supply. Summary of the Invention [Problem to be solved by the invention]

[0010] In the present invention description: Oil outlet temperature / oil return temperature is understood as the temperature of the oil flowing from the heat exchanger towards the compressor body; Oil inlet temperature / oil supply temperature is understood as the temperature of the oil flowing from the compressor body towards the heat exchanger for waste heat recovery.

[0011] Waste heat from the compression process contained in the oil and air is transferred to the receiving working medium via an exchanger, as described in the art, to obtain a set temperature for said medium.

[0012] The problem is the location of the heat exchanger in the compressor oil system, the so-called long oil loop (downstream of a bimetallic valve or a liquid 3-way thermostatic valve that is integral to the compressor design), in which case the oil cooled in the heat exchanger practically always passes through a cooler. Another problem is the lack of temperature measurement of the oil returning to the compressor body.

[0013] The above challenges result in two negative outcomes: 1. Some heat is always lost to the atmosphere (leading to inefficient use of energy), 2. The oil return temperature to the compressor body is poorly controlled, which creates a risk of overcooling of the oil and subsequent steam condensation. The recommended oil injection temperature is not lower than 35-45 degrees Celsius. This is because it is desirable that the temperature of the oil-air mixture entering the oil separator (the temperature of the air taken in for compression should also be taken into account here) should not be lower than 67 degrees Celsius to avoid condensation. At this temperature, the moisture contained in the air moves together with it to the dryer, where it is separated.

[0014] The risk of condensation occurs in particular when the waste heat contained in the oil is transferred to a medium with a significantly lower temperature, such as fresh water (2-12 degrees Celsius).

[0015] It should be noted that the thermostatic three-way valve is located downstream of the separator and does not provide sufficient protection here since the oil is already heated at that point.

[0016] Therefore, if the oil enters the separator and passes through the thermostatic three-way valve to the cooler, and the temperature is too low (below the condensation limit), it will pass through the circuit several times within the inertia of the thermostatic valve, which will cause the condensed water in the air to enter the oil separator.

[0017] With reference to patent specifications EP2949939, US10578339 and US10041698, a temperature sensor is placed between the compressor body and the oil separator. In particular, this sensor is responsible for stopping the heat recovery process if the temperature of the oil / air mixture downstream of the compressor body is too low. This causes technical problems, because by the time a temperature is reached at which there is a risk of condensation, it is already too late to stop the recovery. Given the inertia of the system, there is a high probability that water will enter the separator and mix with the oil.

[0018] The above problem can be partially solved by a procedure already used in the technology, namely the use of an auxiliary three-way valve downstream of the main three-way valve, which is the main component of the compressor. The main valve ensures the opening of a long oil passage, and the auxiliary valve protects the oil from overcooling. The opening and closing temperature of the main valve must be higher than that of the auxiliary valve. This solution, although partially applied in the technology, still has three significant drawbacks: a relatively high inertia, the cost of installing and operating the auxiliary valve as part of the compressor, and the risk of installation errors, such as reverse setting of two thermostats.

[0019] Another problem is how to control the pump. Given the physics of the process, it makes sense to protect the system from reverse energy transfer, i.e. to heat the compressor back up with heat from the system. However, this approach does not provide sufficient results in terms of the efficiency of wasted energy transfer and needs improvement. [Means for solving the problem]

[0020] The object of the present invention is to provide a system for recovering waste heat from gas compressors, in particular air compressors, in which a heat exchanger designed to recover the waste heat contained in the oil is mounted in such a way that it does not require the installation of an auxiliary three-way valve, while said heat recovery is carried out with maximum efficiency (bypassing the main cooler) and in such a way that said compressor is protected from the occurrence of condensation of the vapour contained in the compressed air.

[0021] The gist of the present invention is a system for recovering waste heat energy contained in oil of an oil-cooled air compressor. This gas compressor system is composed of at least a compressor body, an oil separator connected to the compressor body, an oil cooler connected to the oil separator, an oil flow divider connected to the compressor body, an oil temperature sensor, and a heat exchanger whose water side is connected to a heat receiving circuit. The oil side outlet of the oil separator is connected to the oil side inlet of the heat exchanger. The oil side outlet of the heat exchanger is connected to the oil separator. The oil temperature sensor is arranged between the heat exchanger and the oil separator. The oil temperature sensor is also conveniently arranged at the point where the oil is injected into the compressor body. An additional oil temperature sensor is arranged between the oil separator and the heat exchanger. The additional oil temperature sensor is arranged downstream of the compressor element and upstream of the oil separator.

[0022] The method for recovering the waste heat energy contained in the oil in an oil-cooled air compressor comprises diverting the flow of the heat receiving medium from the heat exchanger by a control device, or stopping the flow of the heat receiving medium at least when the temperature of the oil returning to the compressor body is lower than a set point or the temperature of the oil entering the heat exchanger is lower than the temperature of the heat receiving medium. Here, the compressor at least comprises a compressor body connected to an oil separator, a heat exchanger, an oil flow divider connected to an oil cooler and a compressor body, a control device, an oil temperature sensor, and a heat receiving medium temperature sensor. The temperature of the oil returning to the compressor body is measured by an oil temperature sensor arranged between the heat exchanger and the oil separator. The temperature of the oil returning to the compressor body is conveniently also measured by an oil temperature sensor arranged at the point of oil injection into the compressor body. The temperature of the oil entering the heat exchanger is measured by an oil temperature sensor installed between the oil separator and the heat exchanger. The temperature of the oil entering the heat exchanger is also conveniently measured by an oil temperature sensor located between the compressor body and the oil separator. The temperature of the receiving aqueous medium is measured by a temperature sensor located at the inlet of the heat exchanger. The temperature of the receiving aqueous medium is also conveniently measured by a temperature sensor located in a water storage tank.

[0023] In the problem to be solved by the invention, the present invention employs a system having a compressor body (compression element) connected to an oil separator for separating oil from compressed gas supplied from the compressor body, a gas pipe (pipe) connected thereto for transferring the compressed gas separated from the oil through the oil separator as necessary, an oil pipe (pipe) connected to the compressor body for returning the separated oil to the compressor body, and a heat exchanger provided between the oil and a heat receiving medium (e.g., water), and placed immediately after the oil separator and immediately before a three-way oil valve (oil flow divider) for separating a long oil circuit from a short oil circuit, for recovering waste heat energy contained in the oil. The heat exchanger plays a role in recovering waste heat energy contained in the oil, and is located immediately after the oil separator and immediately before the three-way valve (oil flow divider) used for separating the long and short oil circuits. The oil separator, heat exchanger, and three-way valve are connected in the above order by an oil transfer pipe (tube).

[0024] The three-way oil valve connected downstream of the heat exchanger serves to either return the oil flow directly to the compressor body or to bypass the oil cooler, thereby closing off the oil circuit of the air compressor.

[0025] The receiving side (water) of the heat exchanger is interchangeably connected to a pipeline for transporting the heat receiving medium: a variable speed pump to ensure the flow of the heat receiving medium and to adjust the amount of the flow, or a fixed speed pump to ensure the flow of the heat receiving medium and a three-way valve to adjust the amount of medium flowing through the heat exchanger to maximize recovery.

[0026] A thermal buffer tank (water storage tank) is connected along the heat receiving medium pipeline to store the recovered thermal energy, for example in water or a phase change material, and to act as a hydraulic connector connecting the heat recovery circuit to a circuit that utilizes this heat (for example a central heating system). Effect of the Invention

[0027] The present invention provides a heat recovery system from an oil cooled gas compressor, where the heat exchanger is located in the oil system, providing maximum waste heat recovery, which means bypassing the compressor cooling system and reducing heat dump to the atmosphere, while controlling the heat recovery in a way that ensures maximum energy recovery.

[0028] Another advantage is to keep the heat recovery system as simple as possible.

[0029] The heat exchanger is located between the oil separator and the compressor's three-way valve (oil divider) and is therefore in a neutral position with respect to the operation of the compressor. As a result, in the absence of heat recovery by the heat recovery system, it flows through a long circuit through the compressor's integrated cooling system and its protection device. Two temperature sensors connected to one control device are then responsible for controlling the recovery system itself: oil return (downstream of the heat exchanger) and working medium temperature (upstream of the heat exchanger). This ensures that the compressor is protected from condensation.

[0030] The energy recovered in this way can be used for a wide range of heating applications at different temperatures, such as heating fresh water (2-12°C), process water (20°C) and general heating circuits (45-55°C).

[0031] There is no need to use an additional thermostat and the rating will be determined accordingly. [Brief description of the drawings]

[0032] The subject matter of the invention is further illustrated in three embodiment variants in FIGS. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] First embodiment of the system A first embodiment of a waste heat recovery system for an oil-lubricated and oil-cooled air compressor according to the present invention is shown in the diagram of FIG.

[0034] Reference numeral 2 in Fig. 1 denotes a motor-driven compressor body, which is an oil-lubricated and oil-cooled air compressor in reference to the present invention. The air gas sucked into the compressor 1 by the motor-driven compressor body 2 is sucked through a filter 17 at the inlet of the compressor body 2. Compressed air is obtained at the outlet of the compressor body 2 and flows to an oil separator 4 in the form of an oil / air mixture.

[0035] Centrifugal separation of air and oil takes place in the oil separator 4. Air leaves the top of the oil separator 4 and flows through air line 22 to the air cooler 7 for cooling and then through the next line to the receiving system. The oil collected at the bottom of the oil separator 4 further flows through oil line 24 to the inlet side of the heat exchanger 9 arranged for waste heat recovery. The heat exchangers are mounted in a counter-current arrangement, which in practice allows the outlet temperature of the oil side to approach the inlet temperature of the working medium side, thus maximizing the recovery rate. The oil leaving the heat exchanger 9 continues through oil line 25 to the inlet of a thermostatic (bimetallic or liquid) three-way valve 10 (hereinafter referred to as 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 sent via oil line 27 to the oil cooler 7, where it is cooled by an air flow, usually forced by a variable speed fan 8, and returns to the compressor body via oil line 28 and oil filter 3. In this way, a so-called long oil circuit is realized in the compressor system. If the oil temperature does not reach the opening temperature, heat is extracted in the heat recovery exchanger, and the oil flows through the three-way valve 10, oil line 26, oil filter 3, bypasses the cooler 7, and returns to the compressor body. In this way, a so-called short oil circuit is realized in the compressor system.

[0036] On the water side, a heat exchanger 9 is connected to a storage tank 14, the purpose of which is to store the heat recovered by the flow of the working medium through said heat exchanger 9. The working medium, typically water, circulates through said heat exchanger 9 via an inlet line 30 and an outlet line 31. Thus, the heat generated in the compressor body 2 can be recovered in said heat exchanger 9 and stored as working medium (water) at high temperature in the storage tank 14.

[0037] According to the invention, this means that a simultaneous flow of oil and working medium (water) through said heat exchanger 9 is intended to exchange heat from hot oil to cold working medium (water), heating the cold working medium passing through said heat exchanger 9 whilst cooling the hot oil.

[0038] The heat exchanger 9 is connected to the storage tank 14 as follows: a working medium line 30 connects the lower part of the storage tank 14 to the water-side inlet of the heat exchanger 9, and a working medium line 31 connects the upper part of the storage tank 14 to the outlet of the heat exchanger 9. A supply line 33 is connected to the lower part of the storage tank 14 and supplies the working medium to be heated, and a receiving line 34 is connected to the upper part of the storage tank 14 and receives the heated working medium to be utilized. The system thus constructed does not constitute an additional water-to-water heat exchanger, but rather increases the total volume of the receiving working medium 15. In this way, the receiving working medium is heated directly in the heat exchanger 9, and the storage tank itself serves both as an energy store and a fluid coupling.

[0039] A circulation pump 11 is then attached to the working medium line 30 to ensure the circulation of the working medium between the storage tank 14 and the heat exchanger 9. The pump 11 can be attached either to the inlet line 30 or to the outlet line 31 connected to the heat exchanger. The important point is that the inlet of the heat exchanger 9 is connected to the bottom of the storage tank 14 and the outlet of the heat exchanger 9 is connected to the top of the storage tank 14.

[0040] The system further comprises 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 to start / stop the heat recovery process and to prevent the oil / air mixture from becoming too cold and creating the risk of condensation. The oil return temperature sensor 6 monitors the temperature to protect the oil from overcooling by maintaining proper oil parameters, further protecting against the risk of condensation. The oil supply temperature sensor 5 also serves as an operational safeguard for the oil return temperature sensor 6. The oil return temperature sensor 6 also serves as an operational safeguard for the oil supply sensor 5.

[0041] The system further comprises a working medium temperature sensor 13 (hereinafter referred to as water temperature sensor) installed in the storage tank, which 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 a set value and to protect the medium on the receiving side from overheating.

[0042] In this embodiment, the system comprises a variable speed circulation pump 11 (previously referred to as circulation pump) to ensure the circulation of the receiving medium (water) through the receiving lines 30,31.

[0043] Furthermore, in this embodiment, the heat recovery system that is the subject of the present invention comprises a control system 12 connected to the pump 11 and equipped with a working medium temperature sensor 13, an oil supply temperature sensor 5 and an oil return temperature sensor 6.

[0044] In this embodiment, the oil supply temperature sensor 5 measures the oil temperature in the separator downstream of the block. If its value is equal to or greater than a set value (hereinafter referred to as recovery start temperature) and at the same time 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 equal to or greater than a set value, the control system 12 activates the working medium circuit pump 13, so that the heat recovery process is actually started.

[0045] In this embodiment, the control system adjusts the pump to measure the temperature difference between the oil supply temperature measured by sensor 5 and the working medium temperature measured by sensor 13. The pump speed is inversely proportional to the temperature difference measured by sensors 13 and 5, measured as a temperature difference coefficient. As a result, the control system 12 increases the pump speed as the temperature difference between sensors 13 and 5 decreases. This maximizes the thermal energy recovered.

[0046] The energy recovery process is controlled as follows: during the heat recovery process, if the control system 12 detects: the temperature of the working medium measured by the sensor 13 is higher than the set value, or - the oil return temperature measured by sensor 6 is lower than the set value, or If the temperature of the working medium measured by sensor 13 is equal to or greater than the supply temperature measured by sensor 5, the control system 12 stops the heat recovery process immediately or with a pre-programmed delay that is deemed safe.

[0047] Second embodiment of the system The second embodiment differs from the first embodiment in that the pump is a fixed speed pump and the three-way valve (proportional or diverter valve) is responsible for triggering and possible regulation of withdrawal.

[0048] A second embodiment of the waste heat recovery system in an oil-lubricated and oil-cooled air compressor according to the present invention is shown in the diagram of FIG.

[0049] Designation 2 in Fig. 2 indicates a motor-driven compressor body, and referring to the present invention, this compressor body is an oil-lubricated and oil-cooled air compressor. Air gas sucked into compressor 1 by said motor-driven compressor body 2 is sucked through filter 17 at the inlet of said compressor body 2. Compressed air is obtained at the outlet of said compressor body 2 and flows to oil separator 4 in the form of oil / air mixture.

[0050] Centrifugation of air and oil takes place in the oil separator 4. Air leaves the top of the oil separator 4 and flows through air line 22 to the air cooler 7 for cooling and then through the next line to the receiving system. The oil collected at the bottom of the oil separator 4 further flows through oil line 24 to the inlet side of the heat exchanger 9 arranged for waste heat recovery. The heat exchangers are mounted in a counter-current arrangement, which in fact allows the outlet temperature of the oil side to approach the inlet temperature of the working medium side, maximizing the recovery rate. The oil leaving the heat exchanger 9 continues through oil line 25 to the inlet of a thermostatic bimetallic or liquid three-way valve 10 (hereinafter referred to as 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), is sent through the oil line 27 to the oil cooler 7, where it is cooled, usually by forced airflow by a variable speed fan 8, and returns to the compressor body via the oil line 28 and the oil filter 3. In this way, a so-called long oil circuit in the compressor system is realized. If the oil temperature does not reach the opening temperature, heat is extracted in the heat recovery exchanger and the oil flows through the three-way valve 10, the oil line 26, the oil filter 3, bypasses the cooler 7, and returns to the compressor body. In this way, a so-called short oil circuit in the compressor system is realized.

[0051] On the water side, the heat exchanger 9 is connected to a 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 an inlet line 30 and an outlet line 31. Thus, the heat generated in the compressor body 2 can be recovered in the heat exchanger 9 and stored as working medium (water) at high temperature in the storage tank 14.

[0052] According to the invention, this means that the simultaneous flow of oil and working medium (water) through said heat exchanger 9 is intended to exchange heat from hot oil to cold working medium (water), while the cold working medium through said heat exchanger 9 is heated, so that the hot oil is cooled.

[0053] The heat exchanger 9 is connected to the storage tank 14 as follows: the working medium line 30 connects the lower part of the storage tank 14 to the water-side inlet of the heat exchanger 9, and the working medium line 31 connects the upper part of the storage tank 14 to the outlet of the heat exchanger 9. A supply line 33 is connected to the lower part of the storage tank 14 to supply the heated working medium, and a receiving line 34 is connected to the upper part of the storage tank 14 to receive the heated working medium to be utilized. The system thus constructed does not constitute an additional water-to-water heat exchanger, but rather increases the total volume of the receiving working medium 15. The receiving working medium is thus heated directly in the heat exchanger 9, and the storage tank itself serves both as an energy store and as a hydraulic coupler.

[0054] A three-way valve is fitted in the working medium line 30 and can actuate the flow through the heat exchanger or divert it out of the heat exchanger via the working medium line 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.

[0055] A circulation pump 11 is attached to the working medium line to ensure the circulation of the working medium between the storage tank 14 and the heat exchanger 9. In this embodiment, the pump 11 is attached to the inlet line 30 which is connected to the heat exchanger upstream of the three-way valve 10. Such a connection between the pump 11 and the three-way valve 16 makes it possible to separate the two hydraulic circuits in order to adjust the amount of medium flowing through the heat exchanger 9 and the proportion of the flow through the heat exchanger 9 and through lines 32 and 35 via a so-called bypass.

[0056] The important point is that the inlet of the heat exchanger 9 is connected to the bottom of the storage tank 14 and the outlet of the heat exchanger 9 is connected to the top of the storage tank.

[0057] The system includes an oil inlet temperature sensor 5 (hereafter referred to as oil supply temperature sensor) and an oil outlet temperature sensor 6 (hereafter referred to as oil return temperature sensor). The oil supply temperature sensor 5 monitors the temperature to start / stop the heat recovery process and to prevent the oil / air mixture from becoming too cold and creating the risk of condensation. The oil return temperature sensor 6 monitors the temperature to protect the oil from overcooling by maintaining proper oil parameters, further protecting against the risk of condensation. The oil supply temperature sensor 5 also serves as an operational safeguard for the oil return temperature sensor 6. The oil return temperature sensor 6 also serves as an operational safeguard for the oil supply sensor 5.

[0058] The system further includes a working medium temperature sensor 13 (hereinafter referred to as water temperature sensor) installed in the storage tank 14. This sensor serves to control the temperature of the medium on the receiving side to start / stop the heat recovery process, and also to regulate the temperature of the medium on the receiving side to a set value and protect the medium on the receiving side from overheating.

[0059] In this embodiment, the system comprises a constant speed circulation pump 11, conventionally called a circulation pump, to ensure the circulation of the receiving medium (water) through the receiving lines 30, 31, 32.

[0060] Furthermore, in this embodiment, the heat recovery system that is the subject of the present invention comprises a control system 12 connected to the three-way valve 16 and having the working medium temperature sensor 13 , an oil supply sensor 5 and an oil supply temperature sensor 6 .

[0061] In this embodiment, the oil supply sensor 5 measures the oil temperature in the separator downstream of a block. If this value is equal to or greater than a set value (hereafter called recovery start temperature) and at the same time 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 equal to or greater than a set value, the control system 12 diverts the flow of the working medium through the heat exchanger, so that the heat recovery process is actually started.

[0062] In this embodiment, the control system adjusts the three-way valve 16 to measure the temperature difference between the oil supply temperature measured by sensor 5 and the working medium temperature measured by sensor 13. The flow rate of the medium is inversely proportional to the temperature difference measured by sensors 13 and 5, measured as a temperature difference coefficient. As a result, the control system 12 increases the flow rate as the temperature difference between sensors 13 and 5 decreases. This maximizes the thermal energy recovered.

[0063] The energy recovery process is controlled as follows: during the heat recovery process, if the control system 12 detects: the temperature of the working medium measured by the sensor 13 is higher than a set value, or - if the return temperature measured by sensor 6 is lower than a set value, or If the temperature of the working medium measured by sensor 13 is equal to or greater than the oil supply temperature measured by sensor 5, the control system 12 stops the heat recovery process, i.e. diverts the flow of the working medium (water) through line 32 from the heat exchanger used for waste energy recovery immediately or with a pre-programmed delay that is deemed safe.

[0064] Third embodiment of the system A third embodiment of the waste heat recovery system in an oil-lubricated and oil-cooled air compressor according to the present invention is shown in the diagram of FIG.

[0065] Designation 2 in Fig. 3 indicates a motor-driven compressor body, and referring to the present invention, this compressor body is an oil-lubricated and oil-cooled air compressor. The air gas sucked into the compressor 1 by the motor-driven compressor body 2 is sucked through a filter 17 at the inlet of the compressor body 2. Compressed air is obtained at the outlet of the compressor body 2 and flows to an oil separator 4 in the form of an oil / air mixture.

[0066] Centrifugation of air and oil takes place in the oil separator 4. Air leaves the top of the oil separator 4 and flows through air line 22 to the air cooler 7 for cooling and then through the next line to the receiving system. The oil collected at the bottom of the oil separator 4 further flows through oil line 30 to the inlet side of the heat exchanger 9 arranged for waste heat recovery. The heat exchangers are mounted in a counter-current arrangement, which in fact allows the outlet temperature of the oil side to approach the inlet temperature of the working medium side, maximizing the recovery rate. The oil leaving the heat exchanger 9 continues through oil line 31 to the inlet of a thermostatic bimetallic or liquid three-way valve 10 (hereinafter referred to as 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), is sent through the oil line 27 to the oil cooler 7, where it is cooled, usually by forced airflow by a variable speed fan 8, and returns to the compressor body via the oil line 28 and the oil filter 3. In this way, a so-called long oil circuit in the compressor system is realized. If the oil temperature does not reach the opening temperature, heat is extracted in the heat recovery exchanger and the oil flows through the three-way valve 10, the oil line 26, the oil filter 3, bypasses the cooler 7, and returns to the compressor body. In this way, a so-called short oil circuit in the compressor system is realized.

[0067] On the water side, the heat exchanger 9 is connected to a 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 an inlet line 30 and an outlet line 31. Thus, the heat generated in the compressor body 2 can be recovered in the heat exchanger 9 and stored as working medium (water) at high temperature in the storage tank 14.

[0068] That is, the cold working medium passing through said heat exchanger 9 is intended to be heated, while the hot oil is intended to be cooled. The simultaneous flow of oil and working medium (water) through said heat exchanger 9 results in heat exchange from the hot oil to the cold working medium (water).

[0069] The heat exchanger 9 is connected to the storage tank 14 as follows: the working medium line 30 connects the lower part of the storage tank 14 to the water side inlet of the heat exchanger 9, and the working medium line 31 connects the upper part of the storage tank 14 to the outlet of the heat exchanger 9. A supply line 33 is connected to the lower part of the storage tank 14 to supply the heated working medium, and a receiving line 34 is connected to the upper part of the storage tank 14 to receive the heated working medium.

[0070] A three-way valve is furthermore fitted in the working medium line 30 and is capable of actuating the flow through the heat exchanger or of diverting the flow out of the heat exchanger via the working medium line 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).

[0071] A circulation pump 11 is attached to the working medium line 30 to ensure the circulation of the working medium between the storage tank 14 and the heat exchanger 9. In this embodiment, the pump 11 is attached to the inlet line 30, which is connected to the heat exchanger via the three-way valve 16 and to the return line 31 via line 32. The important point is that the inlet of the heat exchanger 9 is connected to the bottom of the storage tank 14 and the outlet of the heat exchanger 9 is connected to the top of the storage tank.

[0072] The storage tank has a coil inside it which constitutes a water-to-water heat exchanger 21. The coil inside the storage tank can be used to hydraulically separate the heat recovery circuit from the heat receiving circuit, which may be necessary, for example, for hygiene reasons.

[0073] The indirect heat transfer described above also makes it possible to use two different heating media, for example water in the recovery circuit and glycol in the heat receiving circuit.

[0074] By installing a coil 21 in the storage tank 14, a hybrid system of direct and indirect transfer of recovered heat can be created, where heat is transferred directly through the storage tank (which is both energy store and hydraulic coupler), i.e. with the same heat medium, to the central heating circuit, while domestic hot water is prepared via the coil. At this point, the domestic hot water is prepared inflow or the coil can heat an additional tank, for example a double-walled tank.

[0075] The system further comprises an oil inlet temperature sensor 5 (hereinafter referred to as oil supply temperature sensor) and an oil outlet temperature sensor 6 (hereinafter referred to as oil return temperature sensor). The oil supply temperature sensor 5 monitors the temperature to start / stop the heat recovery process and to prevent the oil / air mixture from becoming too cold and creating the risk of condensation. The oil return temperature sensor 6 monitors the temperature to protect the oil from overcooling by maintaining proper oil parameters, further protecting against the risk of condensation. The oil supply temperature sensor 5 also serves as an operational safeguard for the oil return temperature sensor 6. The oil return temperature sensor 6 also serves as an operational safeguard for the oil supply sensor 5.

[0076] The system further comprises a working medium temperature sensor 13 (hereinafter referred to as water temperature sensor) installed in the storage tank, which serves to control the temperature 15 of the receiving medium in order to start / stop the heat recovery process, and also to regulate the temperature of the receiving medium to a set value and protect the receiving medium from overheating.

[0077] In this embodiment, in order to ensure the circulation of the receiving medium (water) through the receiving pipelines 30, 31, 32, a constant speed circulating pump 11, conventionally called a circulating pump, is provided.

[0078] Furthermore, the heat recovery system comprises a control system 12 connected to a three-way valve 16 with a working medium temperature sensor 13 , an oil supply temperature sensor 5 and an oil supply temperature sensor 6 .

[0079] In this embodiment, the feed oil temperature sensor 5 measures the oil temperature in the separator downstream of the block. If its value is equal to or greater than a set value (hereafter called recovery start temperature) and at the same time 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 equal to or greater than the set value, the control system 12 diverts the flow of the working medium through the exchanger, so that the heat recovery process is actually started.

[0080] In this embodiment, the control system adjusts the three-way valve 16 to measure the temperature difference between the oil supply temperature measured by sensor 5 and the working medium temperature measured by sensor 13. The flow rate of the medium is inversely proportional to the temperature difference measured by sensors 13 and 5, measured as the temperature difference coefficient. As a result, the control system 12 increases the flow rate as the temperature difference between sensors 13 and 5 decreases. This maximizes the thermal energy recovered.

[0081] The energy recovery process is controlled as follows: during the heat recovery process, if the control system 12 detects: the temperature of the working medium measured by the sensor 13 is higher than the set value, or - the oil return temperature measured by sensor 6 is lower than the set value, or If the temperature of the working medium measured by sensor 13 is equal to or greater than the oil supply temperature measured by sensor 5, the control system 12 stops the heat recovery process and immediately directs the flow of the working medium (water) away from the heat exchanger used for waste energy recovery, or with a pre-programmed delay that is deemed safe.

Claims

1. A system for recovering waste heat energy contained in oil in an oil-cooled air compressor, including a gas compressor, comprising: At least one compressor body, the compressor body being connected to an oil separator, an oil flow divider, a cooler, and the compressor body; An oil temperature sensor, A temperature sensor on the receiving side; A heat exchanger, characterized in that the oil-side outlet of the oil separator (4) is connected to the oil-side inlet of the heat exchanger (9) and the oil-side outlet of the heat exchanger is connected to the oil divider (10). The system has:

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

3. 2. The system according to claim 1, characterized in that the oil temperature sensor (18) is arranged at the point where the oil is injected into the compressor body (2).

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

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

6. A method for recovering waste heat energy contained in oil of an oil-cooled air compressor, comprising the steps of: At least one compressor body connected to an oil separator, an oil divider, a cooler, and the compressor body; A control device; An oil temperature sensor, a receiving-side temperature sensor, characterized in that, when at least the temperature of the oil returning to the compressor body (2) is lower than a set value or the temperature of the oil entering the heat exchanger (9) is lower than the temperature of the receiving medium, the flow of the receiving medium is diverted from the heat exchanger (9) by a control device (12) or the flow of the receiving medium is stopped; The method comprising:

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

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

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

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

11. 7. The method according to claim 6, characterized in that the temperature of the receiving medium is measured by a temperature sensor (20) arranged at the inlet of the heat exchanger (9).

12. 7. The method according to claim 6, characterized in that the temperature of the receiving aqueous medium is measured by a temperature sensor (13) arranged in the storage tank.

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