Device and method for carrying out a cyclic process with organic working medium

Abstract

The invention relates to a device for carrying out a cyclic process comprising a thermal fluid energy machine, a condenser, a first pressure changing device, an evaporator, and piping through which the thermal fluid energy machine is fluidically connected to the condenser, the condenser to the first pressure changing device, the first pressure changing device to the evaporator, and the evaporator to the thermal fluid energy machine, wherein the device is filled with an organic working medium, wherein a lubricating oil is added to the working medium, which is miscible with the working medium when the working medium is in the liquid state and which has a higher evaporation temperature than the working medium, and wherein the device has a bypass line extending from a withdrawal point to a region of the thermal fluid energy machine to be supplied with lubricating oil.and has a return line extending from the area of ​​the thermal fluid energy machine to be supplied with lubricating oil to a return point, wherein a further pressure changing device and a bypass evaporator are arranged in the bypass line.

Description

[0001] The present invention relates to a device for carrying out a cyclic process with an organic working medium and to a related method.

[0002] Cyclic processes within the meaning of the present invention are closed cyclic processes in which the working medium undergoes repeated changes of state in the four essential elements of thermal fluid energy machine, condenser, first pressure changing device and evaporator during operation.

[0003] In such a cycle, some of the heat energy supplied at a higher temperature can be converted into work, while the other part of the heat energy is released at a lower temperature. Alternatively, heat energy can be transferred from a colder environment to a warmer environment by expending work. The first case is also called a right-hand cycle. The second case is also called a left-hand cycle.

[0004] A cyclic process that converts heat energy into work using an organic medium is also known as an Organic Rankine Cycle (ORC). The process is essentially the same as that in a steam power plant, except that an organic working medium is used instead of steam. Organic working media with a dry vapor curve are preferred, as this allows for a higher efficiency.

[0005] In a device for carrying out an ORC process, the thermal fluid energy machine is designed as a heat engine. The first pressure-changing device is preferably designed as a feed pump. In an evaporator or steam generator of the device, the working fluid is converted into a vaporous state. The vaporized working fluid is fed from the evaporator to the heat engine, where the gaseous working fluid, present at high pressure, is expanded to a lower pressure. The working fluid releases energy to the heat engine, which is converted into mechanical work. This mechanical work can be used, in particular, to drive an electric generator for electricity production. The working fluid, now at low pressure, is fed to a condenser. In the condenser, thermal energy is extracted from the working fluid, and the working fluid is liquefied.The working fluid, now in a low-pressure, liquid state, flows to the feed pump, which increases the pressure and returns it to the evaporator. The temperature in the evaporator is typically significantly higher than the temperature in the condenser.

[0006] A cyclic process that uses an organic working fluid and the input of work to transport thermal energy from a low-temperature heat reservoir to a high-temperature heat reservoir can be used in refrigeration machines and heat pumps. The thermal fluid energy machine can be designed as a compressor. The first pressure-changing device can, in particular, be designed as a throttle.

[0007] In the evaporator or steam generator of the device, the working fluid is converted into a vaporous state. The vaporized working fluid is fed from the evaporator to the compressor, where the gaseous working fluid, initially at low pressure, is compressed to a high pressure using mechanical work. The working fluid at high pressure is then fed to a condenser. In the condenser, heat energy is extracted from the working fluid, causing it to liquefy. The working fluid, now at high pressure and in liquid form, then flows to the first pressure-changing device, which is typically designed as a throttle. In this device, the high-pressure liquid is reduced to a lower pressure level. The low-pressure liquid is then fed to the evaporator. The evaporation of the low-pressure liquid extracts heat energy from the surrounding medium.Due to pressure changes in the circuit, the temperature level in the evaporator can be lower than the temperature level in the condenser.

[0008] A thermal fluid power machine typically has components that are at least partially moved relative to one another. In particular, the thermal fluid power machine may have bearings or bearing points. Alternatively or additionally, there may be elements where one element moves past the surface of another element. An example of this is a cylinder moving within a piston. The use of an organic working fluid presents particular challenges regarding the lubrication of these areas. In a thermal fluid power machine, the working fluid is essentially gaseous. In this form, it is not suitable for lubrication. Even if it is liquid in certain areas of the thermal fluid power machine due to condensation, the viscosity of the liquid medium is typically too low to provide sufficient lubrication.

[0009] Lubricating greases are therefore typically used. Since the organic working fluids typically used act as solvents for organic substances such as lubricating greases, this presents particular challenges regarding sealing. Depending on the organic working fluid used, polymer-based seals can be attacked by it. If the seal is inadequate, there is also the risk that the working fluid penetrating the seal will dissolve and wash away the existing lubricant. The thermal fluid power machine then requires more frequent maintenance and / or is subject to increased wear. Furthermore, there is a risk that the working fluid will be contaminated by the washed-out lubricant.

[0010] The object of the present invention is to address this problem.

[0011] According to the invention, the problem is solved by adding a lubricating oil to the working medium, which is particularly miscible with the working medium when the working medium is in a liquid state. The working medium and the lubricating oil preferably form a common phase. The lubricating oil has an evaporation temperature that is sufficiently above the evaporation temperature of the working medium so that the lubricating oil is always in liquid form during operation of the device.

[0012] The device features a bypass line extending from a draw-off point to a section of the thermal fluid power machine requiring lubricating oil. This section can also be referred to as the lubrication point. Preferably, the draw-off point is located in a region of the device where the working medium is in liquid form during operation. In this liquid state, the working medium is mixed with the lubricating oil. The liquid mixture of working medium and lubricating oil is conveyed via the bypass line to the lubricating point. A pressure-changing device and a bypass evaporator are arranged within the bypass line. The pressure-changing device adjusts the pressure of the working medium containing the lubricating oil. In the liquid state, pressure changes, particularly pressure increases, are easily achieved.In a bypass evaporator, the working fluid is evaporated, while the lubricating oil remains in a liquid state. The increase in volume of the evaporating working fluid transports the liquid lubricating oil towards the point requiring lubrication. This ensures a continuous supply of fresh lubricating oil to the point, thus lubricating it.

[0013] A return line extends from the point requiring lubricating oil to a return point. The gaseous working fluid is returned to the main cycle via this return line from the lubricating point. The working fluid cycle is completely closed.

[0014] This device is particularly advantageous if the area to be supplied with lubricating oil can already be adequately lubricated with comparatively small amounts of lubricating oil.

[0015] Preferably, the return point is located in a region of the device where the working medium is present at low pressure. These regions of the device are also referred to as the low-pressure section. The transport of the working medium and lubricating oil through the bypass line and the return line can be implemented particularly easily if the working medium is returned to a part of the device where a low pressure prevails during operation.

[0016] Preferably, the amount of lubricating oil added to the working medium is chosen to be as large as possible, so that deposits of the lubricating oil in the evaporator are reduced to an acceptable level or even completely avoided. The amount is measured to be at least large enough to ensure that even if the lubricating oil should collect at unavoidable dead points in the working medium circuit of the device, the lubrication of the areas to be lubricated is still guaranteed. Dead points in the system are points where the flow velocity of the medium is so low that any accumulated lubricating oil is not carried away. Furthermore, there is at least a local gradient, so that no gravity-driven transport of deposits, such as liquid lubricating oil, accumulated at the dead point occurs.

[0017] The proportion of lubricating oil in the working medium is particularly preferred to be at least 0.01 vol% and at most 1 vol%.

[0018] The thermal fluid energy machine can have at least one shaft via which mechanical work can be applied to the gaseous working medium or via which mechanical work performed by the gaseous working medium can be transmitted. Such a shaft is typically rotatably mounted in at least one bearing. The bearing then constitutes a region to be supplied with lubricating oil. The solution according to the invention is particularly advantageous in a thermal fluid energy machine equipped with a shaft mounted in a bearing.

[0019] Preferably, the shaft comprises two bearings spaced apart longitudinally along the shaft. The bypass line then extends from the extraction point to both bearings. In other words, the bypass line preferably splits after the bypass evaporator, with each split leading to the two bearings. Two return lines are also provided, each originating in one of the bearings. These return lines can be joined into a common return line before the return point. In this way, both bearings of the thermal fluid power machine can be lubricated by the lubricating oil contained in the working medium.

[0020] Preferably, the return line is arranged in the direction of gravity at the bottom of the area to be lubricated, and the return point is located in the direction of gravity below this area. The return line not only returns gaseous working fluid but also lubricating oil that is not needed in the area being lubricated. By appropriately arranging the return line, the transport of liquid lubricating oil from the bearing to the return point can be achieved with gravity assistance. The device is particularly reliable.

[0021] Preferably, the device is configured to carry out an Organic Rankine Cycle (ORC) process. The thermal fluid energy machine is then configured as a heat engine, and the first pressure-changing device is a feed pump. The liquid medium is fed to the evaporator at high pressure via the feed pump. The intake point is preferably located in the area extending from the feed pump to the evaporator, where the working medium is present in liquid form at high pressure. This area can include parts of the feed pump and / or parts of the evaporator. The working medium, which is present at high pressure and evaporated by the evaporator, is expanded to a lower pressure in the heat engine. In doing so, it performs mechanical work. The working medium, which is gaseous and at low pressure after leaving the heat engine, is liquefied in the condenser and fed back to the feed pump.Such a process can efficiently extract mechanical energy from a temperature gradient between the evaporator and the condenser.

[0022] The device is particularly advantageous when the heat engine is designed as a turbine coupled to a generator. The turbine has a rotatably mounted shaft. Sealing the turbine shaft, especially between a bearing and the part of the turbine that comes into contact with the working fluid, is a challenge because pressure differences typically exist between the areas of the turbine in contact with the working fluid and the bearing, and the turbine shaft has a high relative velocity to the housing containing the turbine. Gap seals are typically used here, which, by their very nature, do not provide a complete seal for a gaseous working fluid.

[0023] If such a bearing, sealed with a gap seal, is supplied with lubricating oil via the bypass line, which is transported by means of the working fluid vaporized in the bypass line, some of the vaporized working fluid can enter the turbine area through the gap seal from the bearing area. This increases the sealing effect of the gap seal.

[0024] However, even if this is not the case, the existing risk of lubricant being washed out by the working fluid is reduced in known ORC devices with turbines, since the bearing is lubricated by the lubricating oil, which is constantly supplied to the bearing via the bypass line. A conventional lubricant such as grease, which could be washed out by the working fluid, is therefore not required.

[0025] A particularly preferred configuration is a generator-turbine coupled to a generator, in which a turbine wheel of the turbine is arranged directly on a generator shaft of the generator. The generator shaft forms the shaft of the turbine. The turbine shaft, which in this case is formed by the generator shaft, is then supported by bearings of the generator shaft. One bearing is typically arranged adjacent to the turbine. This bearing point can be sealed against the turbine by a gap seal. The device is particularly advantageous when using a heat engine designed as a generator-turbine.

[0026] Preferably, the further pressure-changing device is designed as a pressure-reducing element, in particular as an orifice, a throttle, a nozzle, or a valve. The pressure-reducing element can thus be designed particularly simply as a passive component.

[0027] The valve can also be designed as a pressure regulating valve. The pressure in the bypass line can be easily controlled via such a pressure regulating valve. The high pressure is typically in the range of 10 bar to 30 bar. The low pressure is in the range of 0.5 bar to 1 bar. The high temperature is in the range of 180 °C to 220 °C, and the low temperature is in the range of 30 °C to 80 °C, particularly around 50 °C. The specific values ​​used depend on the organic working fluid used in the cycle.

[0028] In an alternative preferred embodiment, the device is configured as a heat pump. The thermal fluid energy machine is then designed as a combined heat and power (CHP) engine, and the first pressure-changing device is a pressure-reducing element, in particular a throttle. In the CHP engine, the gaseous working fluid, which is present at low pressure, is compressed to a higher pressure by the application of mechanical work. The compressed gaseous working fluid is fed to the condenser and liquefied. The liquid working fluid, which is present at high pressure, is brought to the lower pressure level in the first pressure-changing device and fed to the evaporator. There, the working fluid evaporates, extracting thermal energy from the surroundings of the evaporator. Such a process can efficiently transport thermal energy against a temperature gradient between the evaporator and the condenser by applying mechanical energy.

[0029] The extraction point is located in the area where the working fluid is in liquid form. The pressure-changing device is primarily designed as a pump. This allows the working fluid in the bypass line to be easily brought to the desired pressure. This pressure can be higher than that of the liquid working fluid in a high-pressure section of the device. This ensures that the working fluid in the bypass line operates at a higher pressure than the working fluid exiting the heat engine. Pressure losses in the condenser, the bypass evaporator, and the respective line sections can thus be easily compensated.

[0030] The invention is further solved by a method in which an organic working medium is fed from a first pressure-changing device to an evaporator. In the evaporator, the working medium is evaporated. The evaporated working medium is fed to a thermal fluid energy machine, in which the pressure of the evaporated working medium is changed. The evaporated working medium is fed to a condenser, where it condenses into a liquid. The liquid is then fed back to the first pressure-changing device, in which the pressure of the liquid is changed in the opposite direction to the pressure change in the thermal fluid energy machine. The cycle is thus closed. Additional elements, in particular intermediate heat exchangers, can be arranged between these stages. A lubricating oil is added to the working medium; this oil is mixed with the working medium and has a higher evaporation temperature than the working medium.A bypass stream is drawn from the fluid at a sampling point and fed to a section of the thermal fluid power machine that requires lubricating oil. The pressure of the working fluid in the bypass stream is adjusted by a pressure regulator, and the working fluid in the bypass stream is evaporated in a bypass evaporator. The evaporated working fluid carries the lubricating oil, which does not evaporate in the bypass evaporator, to the section of the thermal fluid power machine that requires lubricating oil. The working fluid and any excess lubricating oil are returned to a return point, thus closing the bypass circuit.

[0031] Pentane can be used as an organic working fluid. The lubricating oil used is primarily an ester oil.

[0032] Further advantages and details of the invention can be found in the following description of the figures. It shows schematically: Fig. 1 shows a first embodiment of the device according to the invention; Fig. 2 shows an alternative embodiment of the device according to the invention. Individual technical features of the embodiments described below can be combined with the features of the main claims as well as with the features of individual embodiments described above to form articles according to the invention.

[0033] Fig. 1 Figure 1 schematically shows an embodiment of the device 1 according to the invention, which is configured to carry out a cycle or Organic Rankine Cycle process. In this device 1, the thermal fluid energy machine 2 is designed as a turbine 12, in this case as a generator turbine. The first pressure changing device 6 is designed as a feed pump. The device essentially comprises the four elements turbine 12, condenser 4, feed pump, and evaporator 8. These elements are connected to each other via a piping 10. The piping 10 connects the four elements in a closed circuit. The connection between turbine 12 and condenser 4, condenser 4 and feed pump, feed pump and evaporator 8, and evaporator 8 and turbine 12 can each be direct. Alternatively, further elements can be provided, in particular intermediate heat exchangers.

[0034] The turbine 12 is connected to a generator 16 via a shaft 14. The shaft 14 is supported by two bearing points 15 of the generator 16. The shaft 14 is formed by the generator shaft of the generator 16, on which the turbine 12 is directly mounted.

[0035] Between the feed pump and the evaporator 8 is a draw-off point 18, from which a bypass line 20 extends. A pressure reducing element 22 and a bypass evaporator 24 are arranged in the bypass line 20. The bypass line 20 extends to the bearings 15 of the shaft 14 of the generator 16. The organic working fluid is mixed with a lubricating oil. The working fluid is, in particular, pentane. The lubricating oil is preferably an ester oil.

[0036] The working fluid is gaseous at low pressure in the area between turbine 12 and condenser 4. Between condenser 4 and feed pump, the working fluid is liquid at low pressure. The feed pump increases the pressure of the liquid working fluid. Between feed pump and evaporator 8, the working fluid is liquid at high pressure. After evaporation in evaporator 8, the working fluid is gaseous at high pressure between evaporator 8 and turbine 12. It is expanded to a lower pressure in turbine 12, which drives generator 16 via shaft 14.

[0037] At the extraction point 18, the working fluid is present in liquid form at high pressure. The pressure is reduced by the pressure reducing element 22. In the bypass evaporator 24, the working fluid is evaporated. The lubricating oil remains liquid. The liquid lubricating oil is driven by the expanding working fluid in the bypass evaporator 22 towards the bearing 15 of the heat engine 2. From the bearing, there is a return line 26, which in this case opens into a low-pressure section of the turbine 12 and returns the working fluid and lubricating oil in a closed loop.

[0038] Fig. 2 Figure 1 schematically shows an embodiment of the invention as a heat pump. A condenser 4 and an evaporator 8 are also present. The thermal fluid energy machine 2 is designed as a compressor 30, which is driven by a motor 32 via a shaft 14 supported by bearings 15. The first pressure changing device 6 is designed by a throttle.

[0039] In the illustrated embodiment, the extraction point 18 and the return point 28 are located between the first pressure-changing device 6 and the evaporator 8. Here, the working fluid is present in liquid form, mixed with the lubricating oil, at low pressure. In the bypass line 20, the liquid is pressurized by the further pressure-changing device 22, which is designed as a pump, and the working fluid is evaporated in the bypass evaporator 24. The pump overcomes the pressure losses in the bypass line 20, the bearings 15, and the return line 26.

[0040] The transport through the secondary line 20 and the return line 26 is carried out analogously to the embodiment shown in the illustration. Fig. 1 .

Claims

1. Device (1) for carrying out a cyclic process comprising a thermal fluid energy machine (2), a condenser (4), a first pressure changing device (6), an evaporator (8) and a piping system (10) through which the thermal fluid energy machine (2) is fluidically connected to the condenser (4), the condenser (4) to the first pressure changing device (6), the first pressure changing device (6) to the evaporator (8) and the evaporator (8) to the thermal fluid energy machine (2), wherein the device is filled with an organic working medium, characterized by the fact thata lubricating oil is added to the working medium, which is miscible with the working medium when the working medium is in the liquid state and which has a higher evaporation temperature than the working medium, wherein the device has a bypass line (20) extending from a withdrawal point (18) to a region of the thermal fluid energy machine (2) to be supplied with lubricating oil, and a return line (26) extending from the region of the thermal fluid energy machine (2) to be supplied with lubricating oil to a return point (28), wherein a further pressure changing device (22) and a bypass evaporator (24) are arranged in the bypass line (20).

2. Device according to claim 1, characterized by the fact that the extraction point (18) is located in an area of ​​the device in which the working medium is liquid during operation of the device.

3. Device according to claim 1 or 2, characterized by the fact thatthe return point (28) is located in a low-pressure part of the device.

4. Device according to one of the preceding claims, characterized by the fact that The working medium contains at least 0.01 vol% and at most 1 vol% lubricating oil.

5. Device according to one of the preceding claims, characterized by the fact that the thermal fluid energy machine (2) has at least one shaft (14) which is rotatably mounted via at least one bearing (15), wherein the bearing (15) forms a region of the thermal fluid energy machine (2) which is to be supplied with lubricating oil.

6. Device according to claim 5, characterized by the fact that the shaft (14) has two bearings (15) spaced apart from each other in the longitudinal direction along the shaft (14).

7. Device according to one of the preceding claims, characterized by the fact thatthe return line (26) is arranged in the direction of gravity at the bottom of the area to be supplied with lubricating oil and the return point (28) is arranged in the direction of gravity below the area to be supplied with lubricating oil.

8. Device according to one of the preceding claims, characterized by the fact that the device is set up to carry out an Organic Rankine Cycle (ORC) process and the thermal fluid energy machine (2) is designed as a heat engine and the first pressure changing device (6) is designed as a feed pump (6).

9. Device according to claim 8, characterized by the fact that the further pressure changing device (22) is designed as a throttle, a nozzle, an orifice or a valve, in particular a pressure regulating valve.

10. Device according to claim 8 or 9, characterized by the fact that the heat engine is formed by a turbine (12) coupled to a generator (16).

11. Device according to claim 10 including claim 5, characterized by the fact that the turbine (12) coupled to the generator (16) is designed as a generator turbine, in which a turbine wheel of the turbine (12) is arranged directly on a generator shaft of the generator (16), the generator shaft forming the shaft (14).

12. Device according to any one of claims 1 to 7, characterized by the fact that the device is set up as a heat pump and the thermal fluid energy machine (2) is designed as a power heat engine and the first pressure changing device (6) as a pressure reducing element.

13. Device according to claim 12, characterized by the fact that the further pressure changing device (22) is designed as a pump.

14. Device according to claim 12 or 13, characterized by the fact that The combined heat and power engine is designed by a compressor equipped with a motor.

15. A method in which an organic working medium is fed from a first pressure changing device (6) to an evaporator (8) and evaporated there, wherein the evaporated working medium is fed to a thermal fluid energy machine (2) in which the pressure of the evaporated working medium is changed, wherein the evaporated working medium is fed to a condenser (4) where it condenses to a liquid, wherein the liquid is fed to the first pressure changing device (6) in which the pressure of the liquid is changed opposite to the pressure change in the thermal fluid energy machine (2). characterized by the fact thata lubricating oil is added to the working medium, which is mixed with the working medium in the liquid and has a higher evaporation temperature than the working medium, wherein a bypass stream is taken from the liquid at a withdrawal point (18) and supplied to a region of the thermal fluid energy machine (2) to be supplied with lubricating oil, wherein the pressure of the bypass stream is adjusted by a further pressure changing device (22) and the working medium contained in the bypass stream is evaporated in a bypass evaporator (24), wherein the evaporated working medium transports non-evaporated lubricating oil to the region of the thermal fluid energy machine (2) to be lubricated, wherein the working medium and excess lubricating oil are returned to a return point (28).

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