JP2018150873A - Ranking cycle system and control method of ranking cycle system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ranking cycle system which can extract energy from an expander by residual vapor in an evaporator even if the supply of heat to the evaporator of the ranking cycle system is stopped, can promote the decompression and the cooling of the residual vapor, can reduce remaining stress resulting from the remaining vapor after the stop of a ranking cycle, and can be improved in reliability, and a control method of the ranking cycle system.SOLUTION: A ranking cycle system brings a bypass valve 32 into a closed state while receiving heat from an external heat source, continues the drive of a working medium circulation pump 27 and the extraction of energy from an expander 23 while keeping the bypass valve 32 in the closed state when the supply of the heat is stopped, opens the bypass valve 32 when a first condition is satisfied, and stopes the drive of the working medium circulation pump 27 when a second condition is satisfied.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a Rankine cycle system that can extract an output from an expander by residual steam inside an evaporator when a heat source is stopped, and to reduce a residual pressure when the expander is stopped, and a control method for the Rankine cycle system.

  A Rankine cycle system that uses exhaust heat from an internal combustion engine or the like mounted on a vehicle is used. One of these is a refrigerant pump that circulates refrigerant and a heat exchanger that recovers engine waste heat into refrigerant. In the Rankine cycle, the refrigerant is expanded by the expander to extract the power, and the refrigerant expanded by the condenser is condensed. Before the Rankine cycle operation and during the deceleration of the vehicle, the power transmission path from the engine to the refrigerant pump A Rankine cycle has been proposed in which a clutch provided in the middle is engaged and a refrigerant pump is driven by the inertial force of the vehicle (see, for example, Patent Document 1).

  In this Rankine cycle, the driving force of the refrigerant pump for eliminating the uneven distribution of the refrigerant is obtained by the inertial force of the vehicle while the vehicle is decelerating, and the bypass resistance is provided to reduce the passage resistance by bypassing the expander. And the deterioration of fuel consumption is suppressed.

JP2015-59425A

  On the other hand, a general on-board Rankine cycle system uses a heat source that can arbitrarily control the operation state of an internal combustion engine or the like, and when the supply of heat from this heat source is stopped, the working medium circulation pump stops. Therefore, the working medium cannot circulate in the closed circuit of the Rankine cycle, and the output from the expander also stops.

  However, when the working medium circulation pump is stopped simultaneously with the supply of heat from the heat source, there is a high pressure and temperature between the working medium circulation pump and the expander, including upstream and downstream of the evaporator. A working medium (gas phase) with a high and large heat energy remains, while a low pressure, low temperature and low heat energy amount between the expander and the working medium circulation pump, including upstream and downstream of the condenser. A working medium (liquid phase) remains.

  Therefore, after stopping, there is a problem that the working medium is left in a state of high pressure, high temperature, and large heat energy. Due to this high pressure working medium, high pressure remains in the piping before and after the expander and continues to act even after stopping, so it is necessary to take measures against leakage of residual gas.

  It is an object of the present invention to be able to extract energy from the expander by residual steam inside the evaporator, and to reduce the residual steam and promote the cooler even after the supply of heat to the evaporator of the Rankine cycle system is stopped. Accordingly, it is an object of the present invention to provide a Rankine cycle system and a Rankine cycle system control method capable of reducing residual stress caused by residual steam after the Rankine cycle is stopped and improving the reliability of the Rankine cycle system.

  In order to achieve the above object, a Rankine cycle system of the present invention includes an evaporator that receives supply of heat from an external heat source and vaporizes the working medium, an expander that extracts driving force from the vaporized working medium, and an external In the Rankine cycle system having a condenser for releasing heat to liquefy the working medium, a working medium circulation pump for refluxing the working medium, and a control device, a bypass flow path that bypasses the expander is provided, The bypass passage is provided with a bypass valve, and the bypass valve is closed while the control device is receiving heat supply from an external heat source. When the supply of heat is stopped, the operation of the working medium circulation pump and the mechanical energy or heat energy from the expander are kept with the bypass valve closed. When the first condition set in advance is satisfied, the bypass valve is opened and the operation of the working medium circulation pump is continued, and the second condition set in advance is satisfied. In this case, there is provided heat supply stop time control means for performing heat supply stop time control for stopping the operation of the working medium circulation pump.

  In the Rankine cycle system, the first condition is that a mechanical energy or thermal energy extraction amount in the expander is lower than a preset set amount, and the second condition is the evaporation The difference between the temperature of the working medium in the vessel and the temperature of the working medium downstream of the condenser is smaller than a preset temperature difference, or the pressure of the working medium in the evaporator; The difference from the pressure of the working medium downstream of the condenser is smaller than a preset pressure difference.

  In addition, the Rankine cycle system control method of the present invention for achieving the above object includes an evaporator for receiving a supply of heat from an external heat source to vaporize the working medium, and taking out a driving force from the vaporized working medium. An expander, a condenser that releases heat to the outside and liquefies the working medium, a working medium circulation pump that circulates the working medium, and a bypass passage that bypasses the expander and includes a bypass valve. In the Rankine cycle system control method of the present invention, while the heat supply from the external heat source is being received, the bypass valve is closed and the supply of heat from the external heat source is stopped Sometimes, while the bypass valve is closed, the operation of the working medium circulation pump and the extraction of mechanical energy or heat energy from the expander are continued and set in advance. When the first condition is satisfied, the bypass valve is opened to continue the operation of the working medium circulation pump. When the second condition set in advance is satisfied, the operation of the working medium circulation pump is performed. Is a control method characterized by stopping.

  According to the Rankine cycle system and the Rankine cycle system control method of the present invention, energy can be extracted from the expander by the residual steam inside the evaporator even after the supply of heat to the evaporator of the Rankine cycle system is stopped. At the same time, the pressure reduction of the residual steam and the promotion of the cooling can be performed, the residual stress caused by the residual steam after the stop of the Rankine cycle can be reduced, and the reliability of the Rankine cycle system can be improved.

It is a figure showing typically composition of a Rankine cycle system of an embodiment concerning the present invention. It is a figure which shows an example of the control flow of the control method of the Rankine cycle system of embodiment which concerns on this invention. It is a figure which shows typically the structure of the Rankine cycle system as a comparative example.

  Hereinafter, a Rankine cycle system and a Rankine cycle system control method according to embodiments of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the Rankine cycle system 20 is a system that uses exhaust heat such as exhaust gas G of a diesel engine (an internal combustion engine, hereinafter referred to as an engine) 10 mounted on a vehicle. In the engine 10, fuel is injected from the fuel injection valve 13 into the intake air A that has flowed into the combustion chamber 12 from the intake pipe 11 and burned in the combustion chamber 12. The exhaust gas G generated by this combustion is sent to the evaporator 21 of the Rankine cycle system 20 via the exhaust pipe 14. That is, the exhaust gas G of the engine 10 is used as a heat source from the outside of the Rankine cycle system 20.

  Further, in the Rankine cycle system 20, an evaporator (evaporator) 21 that receives heat from an external heat source, that is, exhaust gas G, vaporizes the working medium Fw, and an expander that extracts driving force from the vaporized working medium Fw ( (Expander) 23, a condenser (condenser) 25 that releases heat to the outside and liquefies the working medium Fw, and a working medium circulation pump 27 that circulates the working medium Fw, and the working medium is interposed therebetween. The flow paths 22, 24, 26 and 28 are connected. Further, a control device 30 for controlling the Rankine cycle system 20 such as operation of the working medium circulation pump 27 and operation of the expander 23 is provided.

  As the heat source in the evaporator 21, the exhaust gas G of the vehicle-mounted engine 10, in particular, the exhaust gas G after passing through a post-processing device (not shown) is adopted in the configuration of FIG. Instead, the EGR gas of the engine 10, the intake air compressed by the supercharger, the cooling water after heat absorption by the engine body, the cooling water after heat dissipation by the radiator, and the like may be used as the heat source.

  The expander 23 is a device that converts the thermal energy of the working medium Fw such as a steam turbine or a steam boiler into mechanical energy or steam energy of another energy. In the configuration of FIG. 1, a steam turbine is employed. Yes. In this steam turbine, the turbine shaft 23a is connected to the crankshaft of the engine 10 when assisting rotation of the engine 10, and the turbine shaft 23a is connected to a generator (not shown) when used for power generation. Is done. The generated power is charged in a battery (not shown) and used as a power source for electrical components (not shown) of a vehicle (not shown) on which the engine 10 is mounted.

  The condenser 25 is also called a condenser, and in the case of air cooling, a cooling fan (not shown) is disposed and cooled by outside air. In the case of water cooling, the engine 10 is cooled by engine cooling water or intercooler cooling water discharged from the radiator or sub-radiator of the engine 10.

  The working medium circulation pump 27 is a device that boosts the working medium Fw that has become a liquid phase in the condenser 25 and supplies the working medium Fw to the evaporator 21. The pump rotational speed is the working medium Fw that flows into the expander 23. Controlled based on temperature and pressure. Further, the pressure of the working medium Fw at the inlets of the evaporator 21 and the condenser 25 is adjusted by pressure adjusting means (not shown) configured by a pressure reducing valve, a back pressure valve, or the like. Further, a working medium container (not shown) for storing the working medium Fw is provided as necessary.

  The working medium Fw is preferably a two-component mixed medium such as water and ethanol, water and methanol, or water and ethylene glycol. However, pure water, ethanol alone, or a fluorocarbon compound such as a fluorine compound is used. A refrigerant may be used. Here, a mixed medium in which the molar ratio of water and ethanol is 50%: 50% is employed as the mixed medium.

  In the Rankine cycle system 20, the working medium Fw is compressed and circulated in the liquid state by the working medium circulation pump 27, and is sent to the evaporator 21 in the compressed liquid state. In response to the heat from G, the working medium is vaporized into superheated steam. The working medium Fw in the state of high-pressure superheated vapor that has been vaporized and heated at constant pressure is adiabatically expanded by the expander 23 to extract the driving force, and the working medium Fw in the gas state that has become low pressure is condensed. The condenser 25 is discharged with heat to liquefy the working medium Fw and is circulated by the working medium circulation pump 27.

  In the present invention, a bypass flow path 31 that bypasses the expander 23 is further provided. The bypass flow path 31 is provided with a bypass valve 32 that includes a flow path opening / closing valve that opens and closes the flow path. ing. The bypass valve 32 is controlled by the control device 30.

  The control device 30 keeps the bypass valve 32 closed while receiving heat from the exhaust gas G (external heat source), and when the heat supply of the exhaust gas G is stopped. The operation of the working medium circulation pump 27 and the extraction of the driving force from the expander 23 are continued with the bypass valve 32 closed, and when the first preset condition is satisfied, the bypass valve 32 is turned off. When the heat supply is stopped, the operation of the working medium circulation pump 27 is continued and the operation of the working medium circulation pump 27 is continued. It is configured with control means.

  This first condition is a condition related to the amount of energy supplied to the expander 23, and is a condition for determining a limit at which the expander 23 does not function. When a steam turbine is used as the expander 23, the first condition is that the amount of driving force (mechanical energy) extracted from the expander 23 is lower than a preset set driving force (set amount). It is said. On the other hand, when a steam boiler is employed for the expander 23, the first condition is a condition in which the amount of steam (heat energy) taken out from the expander 23 is lower than a preset amount of steam (set amount). .

  The second condition is a condition related to the working medium Fw, and is a condition for checking the degree of decrease in the temperature of the working medium Fw. The second condition is that the difference ΔT (= T1−T2) between the temperature T1 of the working medium Fw in the evaporator 21 and the temperature T2 of the working medium Fw downstream of the condenser 25 (the working medium flow path 26). The temperature is set to be smaller than a preset temperature difference ΔTc. The temperature T1 is detected by a first temperature detection device 33 provided in the evaporator 21, and the temperature T2 is detected by a second temperature detection device 34 provided in the working medium flow path 24.

  Next, a control method for the Rankine cycle system according to the embodiment of the present invention will be described. The Rankine cycle system control method includes an evaporator 21 that receives heat supplied from an exhaust gas G (external heat source) and vaporizes the working medium, an expander 23 that extracts driving force from the vaporized working medium, an external device A condenser 25 that liquefies the working medium Fw by releasing heat, a working medium circulation pump 27 that recirculates the working medium Fw, a bypass flow path 31 that bypasses the expander 25 and includes a bypass valve 32; A Rankine cycle system control method comprising:

  In this control method, while the heat supply from the exhaust gas G is received, the bypass valve 32 is closed, and when the heat supply from the exhaust gas G is stopped, the bypass valve 32 is closed. The operation of the working medium circulation pump 27 and the extraction of mechanical energy or heat energy from the expander 23 are continued. When the preset first condition is satisfied, the bypass valve 32 is opened and the operation of the working medium circulation pump 27 is continued. In this control method, the operation of the working medium circulation pump 27 is stopped when a preset second condition is satisfied during the operation.

  This control can be implemented by a control flow as shown in FIG. When the engine 10 starts, the control flow of FIG. 2 is called from the advanced control flow and starts. When the engine 10 stops operating, the control flow of FIG. 2 performs necessary control and then returns to the advanced control flow. Then, the process ends when the advanced control flow ends.

  When the control flow of FIG. 2 starts, it is determined in step S11 whether or not the engine 10 has been stopped. If the operation of the engine 10 is not stopped in step S11, the normal operation of the Rankine cycle is performed with the bypass valve 32 closed in step S12, and the process returns to step S11. On the other hand, if it is determined in step S11 that the engine 10 has stopped operating, the control at the time of heat supply stop at step S20 is performed. End with the end of the advanced control flow.

  In the heat supply stop control in step S20, the operation of the working medium circulation pump 27 and the extraction of mechanical energy or heat energy from the expander 23 are continued with the bypass valve 32 closed in step S21. In the next step 22, it is determined whether or not the first condition is satisfied. If it is determined that the first condition is not satisfied, the process returns to step S21. On the other hand, when it is determined that the first condition is satisfied, the process goes to step S23 to open the bypass valve 32. The operation of the working medium circulation pump 27 is continued.

  In the case where a steam turbine is used as the expander 23, the determination as to whether or not the first condition is satisfied is made by setting the drive force (mechanical energy) extraction amount in the expander 23 to a preset set drive force (set amount). It is determined by whether or not it is lower than. The amount of driving force taken out can be determined by the driving torque or the rotational speed of the steam turbine or the magnitude of the generated power when the driving force is used in the generator.

  On the other hand, when a steam boiler is employed as the expander 23, the determination is made based on whether or not the amount of steam (heat energy) taken out from the expander 23 is lower than a preset steam amount (set amount). The amount of steam can be determined by the flow rate or temperature of the generated steam, or the magnitude of generated power when steam is used in the generator.

  In the next step 24, it is determined whether or not the second condition is satisfied. If it is determined that the second condition is not satisfied, the process returns to step S23. On the other hand, when it is determined that the second condition is satisfied, the process goes to step S25, and the operation of the working medium circulation pump 27 is stopped. Thereby, the control at the time of stopping the heat supply in step S20 is finished, the process returns to the advanced control flow, and is finished together with the end of the advanced control flow.

  Whether the second condition is satisfied is determined by the temperature T1 (or pressure P1) of the working medium Fw in the evaporator 21 detected by the first temperature detector 33 provided in the evaporator 21; A difference ΔT (= T1−T2) from the temperature T2 of the working medium Fw downstream of the condenser 25, detected by the second temperature detecting device 34 provided in the working medium flow path 24, is a preset set temperature. The determination is made based on whether or not the difference ΔTc is smaller. Alternatively, the difference ΔP (= P1−P2) between the pressure P1 of the working medium Fw in the evaporator 21 and the pressure P2 of the working medium Fw downstream of the condenser 25 is smaller than a preset set pressure difference ΔPc. Judged by whether or not.

  On the other hand, in the Rankine cycle system 20X of the comparative example as shown in FIG. 3, when the operation of the engine 10 is stopped and the supply of heat from the exhaust gas G is stopped, the working medium circulation pump 27 is stopped, As the working medium Fw circulates in the closed circuit of the Rankine cycle system 20X, the output from the expander 23 also stops.

  Therefore, in the comparative example, in the working medium flow paths 22 and 28 between the working medium circulation pump 27 and the expander 23, including upstream and downstream of the evaporator 21, the heat energy is high and the temperature is high. Amount of working medium (gas phase) Fw remains, while the working medium flow path 24.26 between the expander 23 and working medium circulation pump 27, including upstream and downstream of the condenser 25, is low. A working medium (liquid phase) Fw having a small amount of heat energy at a low pressure and temperature remains.

  As a result, in the comparative example, even after the operation of the Rankine cycle system 20X is stopped, the working medium Fw is left with a high pressure, a high temperature, and a large amount of heat energy. Therefore, even after the stop, a high pressure remains in the working medium flow paths 22 and 24 before and after the expander 23 and continues to act, so it is necessary to take measures against leakage of residual gas.

  On the other hand, according to the Rankine cycle system 20 and the Rankine cycle system control method according to the embodiment of the present invention having the above-described configuration, the operation of the engine 10 is stopped, and the Rankine cycle system 20 is supplied to the evaporator 21. Even after the supply of heat from the exhaust gas G is stopped, energy can be extracted from the expander 23 by the residual vapor of the high-pressure and high-temperature working medium Fw inside the evaporator 21, and by taking out this energy, the working medium Fw It is possible to reduce the residual steam pressure and promote the cooling, reduce the residual stress in the equipment due to the residual pressure of the residual steam after the working medium circulation pump 27 of the Rankine cycle system 20 is stopped, and the Rankine cycle system. 20 reliability can be improved.

DESCRIPTION OF SYMBOLS 10 Diesel engine 20, 20X Rankine cycle system 21 Evaporator 22, 24, 26, 28 Working medium flow path 23 Expander 25 Condenser 27 Working medium circulation pump 30 Control device 31 Bypass flow path 32 Bypass valve (flow path on-off valve) )
33 First temperature detection device 34 Second temperature detection device A Intake air Fw Working medium G Exhaust gas (heat source)

Claims (5)

An evaporator that vaporizes the working medium in response to heat supplied from an external heat source, an expander that extracts driving force from the vaporized working medium, a condenser that releases heat to the outside and liquefies the working medium, and operates In a Rankine cycle system having a working medium circulation pump for refluxing a medium and a control device,
A bypass flow path that bypasses the expander is provided, and a bypass valve is provided in the bypass flow path.
The control device is
While receiving heat supply from an external heat source, the bypass valve is closed,
When the supply of heat from the external heat source is stopped, the operation of the working medium circulation pump and the extraction of mechanical energy or heat energy from the expander are continued with the bypass valve closed. ,
When the preset first condition is satisfied, the bypass valve is opened and the operation of the working medium circulation pump is continued.
A Rankine cycle system comprising heat supply stop time control means for performing heat supply stop time control for stopping the operation of the working medium circulation pump when a preset second condition is satisfied.   The first condition is that a mechanical energy or thermal energy extraction amount in the expander is lower than a preset set amount, and the second condition is the temperature of the working medium in the evaporator, The difference between the temperature of the working medium downstream of the condenser is smaller than a preset temperature difference, or the pressure of the working medium in the evaporator and the operation downstream of the condenser The Rankine cycle system according to claim 1, wherein the difference from the pressure of the medium is smaller than a preset set pressure difference.   The Rankine cycle system according to claim 1 or 2, wherein the heat source is a heat source caused by heat generated from an internal combustion engine.   The Rankine cycle system according to claim 3, wherein the heat source is exhaust gas of an internal combustion engine. An evaporator that vaporizes the working medium in response to heat supplied from an external heat source, an expander that extracts driving force from the vaporized working medium, a condenser that releases heat to the outside and liquefies the working medium, and operates In a Rankine cycle system control method comprising a working medium circulation pump for refluxing a medium, and a bypass flow path that bypasses the expander and includes a bypass valve,
While receiving heat supply from an external heat source, the bypass valve is closed,
When the supply of heat from the external heat source is stopped, the operation of the working medium circulation pump and the extraction of mechanical energy or heat energy from the expander are continued with the bypass valve closed. ,
When the preset first condition is satisfied, the bypass valve is opened and the operation of the working medium circulation pump is continued.
The Rankine cycle system control method, wherein when the second condition set in advance is satisfied, the operation of the working medium circulation pump is stopped.

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