JP7147642B2 - Rankine cycle system and its control method - Google Patents

Description

The present disclosure relates to Rankine cycle systems and control methods thereof.

A waste heat utilization device for a vehicle (Rankine cycle system for a vehicle) has been proposed (for example, See Patent Document 1).

JP 2014-169673 A

By the way, in the Rankine cycle system of a vehicle, the outlet of the expander (turbine) is connected to the inlet of the condenser (condenser) via a pipe that constitutes the flow path for the working fluid. The condenser inlet may be positioned higher than the expander outlet.

In this case, there is a risk that the working fluid (condensate) in a liquid state in the pipe connecting the inlet of the condenser and the outlet of the expander will flow back to the expander side due to gravity, thereby reducing the output of the expander. Therefore, depending on the amount of condensate stored in this pipe, it is necessary to control the treatment of the condensate, and for this purpose, it is first necessary to estimate the amount of this stored condensate.

An object of the present disclosure is to provide a Rankine cycle system capable of estimating with high accuracy the amount of condensate stored in a flow path between the outlet of an expander and the inlet of a condenser, and a control method thereof.

A Rankine cycle system according to an aspect of the present invention for achieving the above object comprises a flow path for circulating a working fluid, an expander disposed in the flow path for expanding the working fluid, and a downstream side of the expander. a condenser that is arranged in the flow path and whose inlet is arranged at a position higher than the outlet of the expander to condense the working fluid, wherein the outlet of the expander and the a pressure acquisition device disposed in a first flow path, which is the flow path between inlets of the condenser; A plurality of temperature acquisition devices are arranged at intervals from each other, and an arithmetic and control device for calculating and controlling parameters of the Rankine cycle system, wherein the arithmetic and control device calculates the obtained value of the pressure acquisition device and Based on the acquired values of the plurality of temperature acquisition devices, the degree of superheat of the working fluid at the installation position of each of the temperature acquisition devices is calculated, and each of the temperatures is calculated based on the calculated degree of superheat of the working fluid. estimating the phase state of the working fluid at the installation position of the acquisition device, and the installation position of the temperature acquisition device where the estimated phase state of the working fluid is a liquid state and the installation position of the temperature acquisition device where the phase state is a gas state; is configured to perform control for estimating that the liquid level of the working fluid in the liquid state stored in the first flow path is present in the section at both ends.

Further, a method for controlling a Rankine cycle system according to an aspect of the present invention for achieving the above object comprises a flow path for circulating a working fluid, an expander arranged in the flow path for expanding the working fluid, and a condenser arranged in the flow path downstream from the device and having an inlet higher than the outlet of the expander to condense the working fluid; and between the outlet of the expander and the inlet of the condenser. and a pressure acquisition device disposed in a first flow path, which is the flow path of the first flow path, and is spaced from each other in a section formed upwardly from the expander toward the condenser with respect to the first flow path. A method for controlling a Rankine cycle system comprising a plurality of temperature acquisition devices, wherein the pressure of the working fluid passing through the first flow path is acquired by the pressure acquisition device, and the plurality of temperature acquisition devices are arranged. A first step of acquiring the temperature of the working fluid passing through the first flow path at each installation position thereof by a device, and the pressure of the working fluid acquired in the first step and each of the plurality of temperature acquisition devices a second step of calculating the degree of superheat of the working fluid at the installation position of each temperature acquisition device based on the temperature of the working fluid at the installation position; a third step of estimating the phase state of the working fluid at the installation position of each temperature acquisition device based on the temperature acquisition device; a fourth step of estimating that there is a liquid level of the working fluid in a liquid state stored in the first flow path in a section where both ends are the installation position and the installation position of the temperature acquisition device estimated to be in the gas state; is a method characterized by comprising:

According to the present disclosure, the amount of condensate stored in the flow path between the outlet of the expander and the inlet of the condenser can be estimated with high accuracy.

It is a figure which illustrates the Rankine cycle system of this embodiment. Figure 2 is an enlarged view of the flow path for working fluid between the expander and condenser of Figure 1; It is a figure which illustrates the control method of the Rankine cycle system of this embodiment in the form of a control flow.

The Rankine cycle system of the present disclosure will be described below with reference to the drawings. As illustrated in FIG. 1, the Rankine cycle system 1 of the present embodiment includes a working fluid flow path (flow path) 2, a tank 3, a pump (circulation device) 4, an evaporator 5, and an expander. 6 and a condenser 7 .

The working fluid flow path 2 is a closed flow path through which the working fluid W is circulated. The tank 3 is arranged in the working fluid flow path 2 and stores the working fluid W. As shown in FIG. The pump 4 is arranged in the working fluid flow path 2 on the downstream side of the tank 3 , and pumps the working fluid W to circulate the working fluid W in the working fluid flow path 2 .

The evaporator 5 is arranged in the working fluid flow path 2 on the downstream side of the pump 4 and heats and evaporates the working fluid W by exchanging heat with the exhaust gas G of the engine (internal combustion engine). The expander 6 is arranged in the working fluid flow path 2 on the downstream side of the evaporator 5 to expand the working fluid W. As shown in FIG. A driving device (engine, motor, etc.) is connected to the output shaft 6a of the expander 6 via a connecting/disconnecting device (clutch, etc.). The resulting power is transmitted to the driving device.

The condenser 7 is arranged in the working fluid flow path 2 on the downstream side of the expander 6 to condense the working fluid W. As shown in FIG. The inlet 7a of the condenser 7 is positioned higher than the outlet 6b of the expander 6. As shown in FIG. In this embodiment, the channel between the outlet 6b of the expander 6 and the inlet 7a of the condenser 7 is called the first channel 2a. The outlet 7b of the condenser 7 is arranged at a position higher than the inlet 3a of the tank 3.

As illustrated in FIGS. 1 and 2 , at least part of the first flow path 2 a is formed with an upward gradient from the expander 6 toward the condenser 7 . In the present embodiment, the channel formed on this upward slope is referred to as section 2b. The working fluid (condensate) WL that has transitioned from the gas state to the liquid state in the first channel 2a is stored in the section 2b. The liquid level LS of the condensate WL increases as the amount of the condensate WL stored increases. The section 2b is configured such that the condensate WL and the gaseous working fluid W can contact each other to the extent that heat exchange is possible. The section 2b is preferably provided at a location where the condensate WL is relatively likely to be generated. The condensed liquid WL is likely to be generated as it approaches the outlet 6b of the expander 6 with respect to the first flow path 2a.

The section 2b of the present embodiment is arranged from the lowermost position (position B1) of the flow path extending vertically downward from the outlet 6b of the expander 6 to the inlet 7a side of the condenser 7 from the lowermost position. , and is higher than the outlet 6b of the expander 6 and lower than the inlet 7a of the condenser 7 (position B5). The condensate WL is accumulated in the channel from the outlet 6b of the expander 6 to the position B1 and the section 2b. As the amount of the stored condensate WL increases, the liquid surface LS of the condensate WL in the section 2b rises upward from the lowest position B1. Similarly, the liquid level of the condensate WL in the flow path from the outlet 6b of the expander 6 to the position B1 rises while maintaining the same height position as the liquid level LS of the condensate WL in the section 2b.

As illustrated in FIG. 2, a pressure sensor (pressure acquisition device) 8 that acquires the pressure of the working fluid W passing through the first flow path 2a is arranged in the first flow path 2a. Since the pressure of the working fluid W hardly changes in the first flow path 2a, the pressure sensor 8 may be arranged at any position within the first flow path 2a where there is no risk of the condensate WL being generated. In this embodiment, the pressure sensor 8 is arranged at the position A1 in the first flow path 2a closer to the inlet 7a of the condenser 7 than the section 2b.

A plurality of (five in this embodiment) temperature sensors (temperature acquisition devices) 9 (9a to 9e) are arranged at intervals in the section 2b of the first flow path 2a. The temperature sensor 9a is located at position B1, the temperature sensor 9b at position B2, the temperature sensor 9c at position B3, the temperature sensor 9d at position B4 and the temperature sensor 9e at position B5. At least one temperature sensor 9 may be placed at a position where the condensate WL may be stored and at least one temperature sensor 9 may be placed at a position where the condensate WL is not likely to be stored, and the number of the sensors to be installed is not particularly limited. .

Positions B1, B2 and B3 are set at positions lower than the outlet 6b of the expander 6. FIG. Even if the liquid surface LS of the condensate WL is present at these positions B1 to B3, the condensate WL does not flow back into the expander 6 . Positions B4 and B5 are set at positions higher than the outlet 6b of the expander 6. FIG. When the liquid surface LS of the condensate WL is present at these positions B4 and B5, the condensate WL flows back into the expander 6. FIG. Positions B1, B2, B3, B4, and B5 are closer to the outlet 6b of the expander 6 (farther from the inlet 7a of the condenser 7) and lower in order.

The Rankine cycle system 1 of the present embodiment is provided with an arithmetic control device 10 that calculates and controls the parameters of the Rankine cycle system 1 (the degree of superheat of the working fluid W, the liquid level, etc.). The arithmetic and control unit 10 includes a CPU (Central Processing Unit) that performs various types of information processing, an internal storage device capable of reading and writing programs and information processing results used for performing the various types of information processing, and various interfaces. Wear. Various devices such as the pressure sensor 8 , the temperature sensor 9 and the pump 4 are electrically connected to the arithmetic control device 10 .

In the Rankine cycle system 1 of the present embodiment, the arithmetic and control unit 10 is based on the acquired value P of the pressure sensor 8 and the acquired values T of the plurality of temperature sensors 9 (Ta, Tb, Tc, Td, Te), respectively , the degree of superheat of the working fluid W at the installation positions B1 to B5 of the temperature sensors 9 is calculated. The degree of superheat is the difference between the temperature of the working fluid W in a superheated state higher than the saturation temperature of the working fluid W and the saturation temperature.

Then, the arithmetic and control unit 10 estimates the phase state (gas state or liquid state) of the working fluid W at each of the installation positions B1 to B5 of the temperature sensors 9 based on the calculated degree of superheat of the working fluid W. In other words, when the obtained value T of the temperature sensor 9 is equal to or higher than the preset temperature T1, the arithmetic and control unit 10 determines that the phase state of the working fluid W at the installation position of the temperature sensor 9 is a gaseous state. If the temperature is lower than the set temperature T1, it is estimated to be in a liquid state. The set temperature T1 is a value that changes according to the pressure P of the working fluid W, and is set in advance by experiments or the like as an index that can be used to estimate that the phase state of the working fluid W is either a gas state or a liquid state. temperature.

In this embodiment, since the temperature Ta of the working fluid W at the position B1, the temperature Tb of the working fluid W at the position B2, and the temperature Tc of the working fluid W at the position B3 are less than the set temperature T1, the arithmetic and control unit 10 controls the position Assume that the working fluid W at B1-B3 is in a liquid state. On the other hand, since the temperature Td of the working fluid W at the position B4 and the temperature Te of the working fluid W at the position B5 are equal to or higher than the set temperature T1, the operation fluid W at the positions B4 and B5 is in a gaseous state. We estimate that

The arithmetic and control unit 10 controls the position of the temperature sensor 9 in which the estimated phase state of the working fluid W is in the liquid state and the position of the temperature sensor 9 in which the phase state is in the gaseous state. It is configured to perform control to estimate that there is a liquid level LS of the stored condensate WL. In the present embodiment, the sections that are both ends are the installation position B3 of the temperature sensor 9c in which the phase state of the working fluid W is the liquid state and the installation position B4 of the temperature sensor 9d in which the phase state of the working fluid W is the gaseous state. This is the interval between

Arithmetic control unit 10 determines that when the section (the section between position B3 and position B4) where liquid level LS of condensate WL exists is part of section 2b and is located above the set section set in advance by experiment or the like. Second, control is performed to reduce the output of the pump 4 so that the flow rate of the working fluid W passing through the working fluid flow path 2 is reduced from the flow rate during normal control. This control for reducing the output of the pump 4 is performed regardless of the operating state of the engine. The set section is a section that is set so that the condensate WL does not flow back into the expander 6 as long as the liquid level LS of the condensate WL remains in this section. In this embodiment, the set section is the section from positions B1 to B3. The flow rate of the working fluid W during normal control of the pump 4 is set based on the temperature and flow rate of the exhaust gas G passing through the evaporator 5 .

By reducing the flow rate of the working fluid W by reducing the output of the pump 4 in this way, the time for heat exchange between the working fluid W and the exhaust gas G in the evaporator 5 is lengthened, and the flow path 2a for the working fluid is increased. The temperature T of the working fluid W passing through is raised to the set temperature T1 or higher. The set temperature T1 is a temperature set in advance by experiments or the like as a temperature at which the condensate WL stored in the first flow path 2a can be evaporated. Since the first flow path 2a is configured such that the condensate WL and the gaseous working fluid W can contact each other to the extent that heat can be exchanged, the working fluid W having a temperature T equal to or higher than the set temperature T1 is the first flow. By passing through the passage 2a, the condensate WL stored in the first passage 2a exchanges heat with the gaseous working fluid W and evaporates.

This control for reducing the output of the pump 4 is performed at least until the liquid level LS of the condensate WL falls within the set interval. In this embodiment, the control for reducing the output of the pump 4 is performed until the liquid surface LS of the condensate WL falls within the interval between positions B1 to B3. It should be noted that the arithmetic and control unit 10 performs the control to reduce the output of the pump 4 when the phase state of the working fluid W at all the temperature measurement positions (B1 to B5 in this embodiment) is a gaseous state. It may be configured to perform until it is determined that. In this case, almost no condensed liquid WL is stored in the first flow path 2a, so that a decrease in the output of the expander 6 due to the reverse flow of the condensed liquid WL can be greatly suppressed.

When the arithmetic and control unit 10 estimates that the liquid level LS of the condensate WL is in the section between positions B4 and B5, the condensate WL flows backward into the expander 6, and the output of the expander 6 is decreasing. In this case, the arithmetic and control unit 10 controls the output of the pump 4 to be further lowered than when the liquid level LS of the condensate WL is in the interval between the positions B3 and B4, thereby further reducing the temperature of the working fluid W. It is preferable to raise the temperature. By doing so, the evaporation of the condensate WL is further promoted, so that the output reduction of the expander 6 can be suppressed.

A control flow based on the Rankine cycle system 1 of the present embodiment, in other words, a control method of the Rankine cycle system, will be described with reference to FIG. 3 in the form of a control flow. The control flow shown in FIG. 3 is a control flow that is periodically performed when the engine is in operation.

When the control flow shown in FIG. 3 starts, in step S10 (first step), the pressure sensor 8 acquires the pressure P of the working fluid W passing through the first flow path 2a, and the plurality of temperature sensors 9 Obtain the temperature T of the working fluid W passing through the first flow path 2a at each of the installation positions B1 to B5. After performing step S10, the process proceeds to step S20.

In step S20 (second step), each The degrees of superheat of the working fluid W at the installation positions B1 to B5 of the temperature sensors 9 are calculated. After performing step S20, step S30 is performed.

In step S30 (third step), the phase states of the working fluid W at the installation positions B1 to B5 of the temperature sensors 9 are estimated based on the degrees of superheat calculated in step S20. After performing step S30, the process proceeds to step S40.

In step S40 (fourth step), the installation position B3 of the temperature sensor 9 where the phase state of the working fluid W was estimated to be in the liquid state in step S30 and the installation position B4 of the temperature sensor 9 in which the phase state was estimated to be in the gaseous state. It is estimated that there is a liquid surface LS of the condensate WL stored in the first flow path 2a in the section where are both ends. After performing step S40, the process proceeds to step S50.

In step S50, it is determined whether or not the section in which the liquid level LS of the condensate WL estimated in step S40 is located above the set section (first section determination). If the section with the liquid level LS of the condensate WL is located above the set section (YES), the process proceeds to step S60. If the section with the liquid level LS of the condensate WL is not located above the set section (NO), the process proceeds to step S70.

In step S60, control is performed to reduce the output of the pump 4 so that the flow rate of the working fluid W passing through the first flow path 2a is reduced from the flow rate during normal control. By controlling in this manner, the temperature T of the working fluid W passing through the first flow path 2a is raised to the set temperature T1 or higher, and the condensate WL stored in the first flow path 2a is evaporated. After executing step S60, the process returns to step S10.

In step S70, it is determined whether or not the output of the pump 4 is lower than the output during normal control. In other words, it is determined whether step S60 has been passed. If the output of the pump 4 is lower than the output during normal control (YES), the process proceeds to step S80. If the output of the pump 4 is not lower than the output during normal control (NO), the process proceeds to RETURN and terminates this control flow.

In step S80, it is determined whether or not the section in which the liquid level LS of the condensate WL is estimated in step S40 is in a second set section that is a part of the set section and is set in advance as a relatively lower section ( second section judgment). The second set section is a period from the end of the control to reduce the output of the pump 4 to the start of the next control to reduce the output of the pump 4, which is a period of time that does not affect the durability of the pump 4. This is the interval where it is possible to In this embodiment, the second set section is the section between position B1 and position B2. If the section with the liquid level LS of the condensate WL is in the second set section (YES), the process proceeds to step S90. If the section with the liquid level LS of the condensate WL is not in the second set section (NO), the process returns to step S10.

The determination in step S80 may be substituted by determination of whether or not the phase state of the working fluid W at all the temperature measurement positions (B1 to B5 in this embodiment) has become a gaseous state. . If the phase state of the working fluid W at all the temperature measurement positions of the working fluid W is gaseous (YES), the process proceeds to step S90. If there is a temperature measurement position where the phase state of the working fluid W is not a gaseous state (NO), the process returns to step S10.

In step S90, the output of the pump 4 is returned to the output during normal control. After executing step S90, the process proceeds to RETURN and terminates this control flow.

As described above, according to the Rankine cycle system 1 of the present embodiment and the control method thereof, the amount of the condensate WL stored in the first flow path 2a between the outlet 6b of the expander 6 and the inlet 7a of the condenser 7 is It can be estimated with high accuracy.

1 Rankine cycle system 2 flow path for working fluid 2a first flow path 2b upslope section of first flow path 3 tank 3a tank inlet 4 pump 5 evaporator 6 expander 6a output shaft 6b expander outlet 7 condensation vessel 7a condenser inlet 7b condenser outlet 8 pressure sensor (pressure acquisition device)
9, 9a, 9b, 9c, 9d, 9e temperature sensor (temperature acquisition device)
10 Arithmetic control device WL Condensed liquid LS Condensed liquid level

Claims (3)

a channel for circulating a working fluid; an expander arranged in the channel to expand the working fluid; a condenser positioned at a position to condense the working fluid, in a Rankine cycle system comprising:
a pressure acquisition device positioned in the first flow path between the expander outlet and the condenser inlet;
a plurality of temperature acquisition devices arranged at intervals in a section formed with an upward gradient from the expander toward the condenser with respect to the first flow path;
An arithmetic control device that calculates and controls the parameters of the Rankine cycle system,
The arithmetic and control device is
Based on the acquired value of the pressure acquisition device and the acquired values of the plurality of temperature acquisition devices, the degree of superheat of the working fluid at the installation position of each of the temperature acquisition devices is calculated, and the calculated superheat of the working fluid is calculated. estimating the phase state of the working fluid at the installation position of each temperature acquisition device based on the temperature, and the estimated phase state of the working fluid is the installation position of the temperature acquisition device in which the liquid state and the gas state are A Rankine cycle system configured to perform control for estimating that there is a liquid level of the liquid state working fluid stored in the first flow path in a section having both ends at an installation position of the temperature acquisition device. A circulation device for circulating the working fluid is provided in the flow path,
The arithmetic and control device is
a flow rate of the working fluid passing through the flow path when the section where the liquid level of the working fluid in the liquid state is present is located above a predetermined set section in a part of the section formed with an upward slope; By reducing the output of the circulation device so that the flow rate is lower than the flow rate during normal control, the temperature of the working fluid passing through the flow path is reduced to that of the liquid state working fluid stored in the first flow path. 2. The Rankine cycle system according to claim 1, which is configured to perform control to raise the temperature above a set temperature preset as a temperature at which evaporation is possible. a channel for circulating a working fluid; an expander arranged in the channel to expand the working fluid; a condenser positioned at a position to condense a working fluid; a pressure acquisition device positioned in the first flow path, which is the flow path between the expander outlet and the condenser inlet; A method of controlling a Rankine cycle system comprising:
The pressure acquisition device acquires the pressure of the working fluid passing through the first flow path, and the plurality of temperature acquisition devices acquire the temperature of the working fluid passing through the first flow path at each installation position. a first step to
degree of superheat of the working fluid at the installation position of each of the temperature acquisition devices, based on the pressure of the working fluid acquired in the first step and the temperature of the working fluid at each installation position of the plurality of temperature acquisition devices; a second step of calculating
a third step of estimating the phase state of the working fluid at the installation position of each of the temperature acquisition devices based on the degree of superheat of the working fluid calculated in the second step;
In the section where the installation position of the temperature acquisition device where the phase state of the working fluid is estimated to be in the liquid state and the installation position of the temperature acquisition device where the phase state of the working fluid is estimated to be in the gaseous state in the third step, the first a fourth step of estimating that there is a liquid level of the liquid state working fluid stored in the channel;
A control method for a Rankine cycle system, comprising:

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