JP7147641B2 - Rankine cycle system and its control method - Google Patents

Description

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

A condensed water tank for storing condensed water (condensed liquid) generated in the refrigerant pipe is provided in the refrigerant pipe near the outlet of the turbine (expander), and the condensed water stored in the condensed water tank is heated to steam by a heating device. A waste heat recovery device (Rankine cycle system for a vehicle) has been proposed (for example, refer to Patent Document 1).

JP 2017-155612 A

In the vehicle Rankine cycle system of Patent Document 1, after the condensate (liquid state working fluid) is transitioned to vapor (gas state working fluid) by the heating device, the vapor is transitioned again to the condensate by the condenser. Therefore, there is a problem that energy is unnecessarily used for these two transitions.

An object of the present disclosure is to provide a Rankine cycle system capable of processing condensate stored in a flow path between an outlet of an expander and an inlet of a condenser in an energy-saving manner, 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; and the condenser downstream from the condenser and upstream from the expander. and a circulation device arranged in the flow path for pumping the working fluid, in the first flow path, which is the flow path between the outlet of the expander and the inlet of the condenser, a storage portion disposed to store a working fluid in a liquid state; and a bypass flow passage connecting the second flow passage, which is the flow passage between the outlet of the condenser and the inlet of the circulation device, and the storage portion. a transfer device disposed in the bypass flow path for transferring the liquid working fluid from the reservoir to the second flow path as needed; and A liquid level estimating device for estimating a liquid level and a control device for controlling the Rankine cycle system, wherein the control device determines the state of the liquid based on the liquid level estimated by the liquid level estimating device. It is determined whether or not the fluid is to be transferred from the reservoir to the second flow path, and if it is determined to be transferred, the transfer device is controlled to transfer the liquid working fluid from the reservoir to the second flow path. It is configured to control the transfer to the flow path.

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 condenser and having an inlet positioned at a position higher than the outlet of the expander to condense the working fluid; and a condenser downstream from the condenser and the expander. a circulating device disposed in the flow path further upstream to pump the working fluid; a reservoir that stores the working fluid of the above; a bypass passage that communicates the second passage that is the passage between the outlet of the condenser and the inlet of the circulation device and the reservoir; a transfer device arranged to transfer the working fluid in a liquid state from the storage portion to the second flow path as needed, wherein the storage portion includes: a first step of estimating the liquid level of the stored liquid state working fluid; and based on the liquid level of the liquid state working fluid estimated in the first step, liquid from the reservoir to the second flow path. a second step of determining whether or not to transfer the working fluid in the liquid state; and if it is determined in the second step that the working fluid in the liquid state is to be transferred, the transfer device is controlled to control the storage portion and a third step of transferring working fluid in a liquid state from to said second flow path.

According to the present disclosure, the condensate stored in the flow path between the outlet of the expander and the inlet of the condenser can be treated with energy saving.

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 on the upstream side of the evaporator 5 and the expander 6 to pump the working fluid W. As shown in FIG. As the working fluid W is pressure-fed by the pump 4 , the working fluid W circulates through the flow path 2 for the working fluid.

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. The outlet 7b of the condenser 7 is arranged at a position higher than the inlet 3a of the tank 3.

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. A U-tube-shaped reservoir 2aa is formed immediately below the outlet 6b of the expander 6 in the first flow path 2a. Although the gaseous working fluid flows through the first flow path 2a, condensate WL, which is the liquid working fluid, may be generated. This condensate WL is stored in the storage portion 2aa. The liquid surface (liquid level) LS of the condensate WL increases as the amount of the condensate WL stored increases. Note that the shape of the storage portion 2aa is not limited to a U-tube shape as long as it can store the condensate WL.

Further, in the present embodiment, the channel between the outlet 7b of the condenser 7 and the inlet of the pump 4 is called a second channel 2b. A working fluid in a liquid state flows through the second flow path 2b.

As illustrated in FIG. 2, a pressure sensor 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 of the first flow path 2a on the downstream side of the reservoir 2aa.

A plurality of (two in this embodiment) temperature sensors 9 (9a, 9b) are arranged at intervals in the reservoir 2aa of the first flow path 2a. The temperature sensor 9a is arranged at a position B1 inside the reservoir 2aa. The temperature sensor 9b is arranged at a position B2 downstream of the position B1 in the reservoir 2aa. Position B2 is a higher position than position B1. The liquid level LS of the condensate WL rises in the direction from the position B1 toward the position B2 as the amount of the condensate WL stored in the storage portion 2aa increases.

The Rankine cycle system 1 of this embodiment includes a liquid level estimation device 10 . The liquid level estimating device 10 estimates the liquid level LS of the condensate WL stored in the storage section 2aa based on the acquired value of the pressure sensor 8 and the acquired value of the temperature sensor 9 . The liquid level estimation device 10 includes a CPU (Central Processing Unit) that performs various types of information processing, an internal storage that can read and write programs and information processing results used for performing the various types of information processing, and various interfaces. Hardware. The liquid level acquisition device 10 may be configured separately from the control device 13 to be described later, or may be incorporated as a part of the control device 13 .

The liquid level estimation device 10 determines the phase state ( gas state or liquid state). When the phase state of the working fluid W at the position B1 is a gaseous state, the liquid level estimation device 10 estimates that the liquid level LS of the condensate WL is at a position in the first flow path 2a lower than the position B1. When the phase state of the working fluid W at the position B1 is liquid and the phase state of the working fluid W at the position B2 is gas, the liquid level estimation device 10 determines that the liquid level LS of the condensate WL is Assume that it is located at the position of the first flow path 2a between the position B1 and the position B2. When the phase states of the working fluid W at the positions B1 and B2 are both liquid states, the liquid level estimation device 10 estimates that the liquid level LS of the condensate WL is at the position of the first flow path 2a higher than the position B2. do.

The Rankine cycle system 1 of this embodiment is provided with a bypass flow path 11 . The bypass flow path 11 is a flow path that connects the second flow path 2b and the storage portion 2aa. The bypass channel 11 is provided with a second pump 12 (transfer device) 12 . The second pump 12 transfers the condensate WL from the reservoir 2aa to the second flow path 2b when it is driven (as necessary) based on a control signal from the control device 13, which will be described later. The second pump 12 is a device with a smaller output than the pump 4 .

The Rankine cycle system 1 of this embodiment includes a control device 13 that controls the Rankine cycle system 1 . The control device 13 is hardware composed of 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. is. Various devices such as the liquid level estimation device 10 , the pump 4 and the second pump 12 are electrically connected to the control device 13 .

In the Rankine cycle system 1 of the present embodiment, the control device 13 determines whether to transfer the condensate WL from the reservoir 2aa to the second flow path 2b based on the liquid level LS estimated by the liquid level estimation device 10. judge. When it is determined to transfer the condensate WL, the second pump 12 is controlled to transfer the condensate WL from the reservoir 2aa to the second flow path 2b. For example, when the liquid level LS estimated by the liquid level estimating device 10 is higher than the set position B2, it is determined that the condensate WL is to be transferred. This set position is set in advance by experiment or the like as a position where the condensate WL may affect the output of the expander 6 if the liquid level LS of the condensate WL is higher than this set position. . The set position may be position B1 instead of position B2.

Thus, by transferring the condensate WL from the reservoir 2aa to the second channel 2b through which the liquid working fluid flows according to the liquid level LS of the condensate WL stored in the reservoir 2aa, condensation The liquid WL can be processed in an energy-saving manner without transitioning to a gaseous state. The energy consumed for driving the second pump 12 is the sum of the energy required for the condensate WL to transition to the gas state and the energy required for the condensate WL that has transitioned to the gas state to re-transition to the liquid state. very small compared to

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, the liquid level LS of the condensate WL stored in the storage portion 2aa is estimated in step S10 (first step). After performing step S10, the process proceeds to step S20.

In step S20 (second step), it is determined whether or not to transfer the condensate WL from the reservoir 2aa to the second flow path 2b based on the liquid level LS of the condensate WL estimated in step S10. (First liquid level determination). In other words, it is determined whether or not the liquid level LS of the condensate WL is higher than the position B2. If the liquid level LS of the condensate WL is to be transferred higher than the position B2 (YES), the process proceeds to step S30. When the liquid level LS of the condensate WL is lower than the position B2 and the transfer is not performed (NO), the process proceeds to step S40.

In step S30 (third step), the second pump 12 is controlled (driven) to start transferring the condensate WL from the reservoir 2aa to the second flow path 2b. After executing step S30, the process returns to step S10.

In step S40, it is determined whether or not the condensed liquid WL is being transferred by the second pump 12 or not. In other words, it is determined whether step S30 has been passed. If the condensed liquid WL is being transferred by the second pump 12 (YES), the process proceeds to step S50. If the condensed liquid WL is not being transferred by the second pump 12 (NO), the flow proceeds to RETURN and ends this control flow.

In step S50, it is determined whether or not the liquid level LS of the condensate WL estimated in step S10 is lower than the position B1 (second liquid level determination). If it is lower than the position B1 (YES), proceed to step S60. If it is higher than the position B1 (NO), the process returns to step S10.

In step S60, the second pump 12 is controlled (stopped) to end transfer of the condensate WL from the reservoir 2aa to the second flow path 2b. After step S60 is executed, the process proceeds to RETURN and terminates this control flow.

As described above, according to the Rankine cycle system 1 and its control method of the present embodiment,
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 can be treated with energy saving.

Although the second pump is used as the transfer device 12 in this embodiment, an on-off valve may be used. In the case where the transfer device 12 is configured as an on-off valve, when the on-off valve is in an open state, the condensate WL is stored to the extent that the condensate WL can flow through the bypass flow path 11 from the storage portion 2aa toward the second flow path 2b. A large differential pressure is required between the portion 2aa and the second flow path 2b. If the diameter of the pipe forming the bypass flow path 11 is made smaller than the diameter of the pipe forming the first flow path 2a (storage section 2aa), the differential pressure between the storage section 2aa and the second flow path 2b is relatively small. However, when the on-off valve is open, the condensate WL can easily flow from the bottom of the reservoir 2aa toward the bypass channel 11 communicating with the bottom, which is preferable. Further, the diameter of the pipe forming the bypass flow path 11 is configured to be smaller than the diameter of the pipe forming the second flow path 2b so that the working fluid W passes through the second flow path 2b from the tank 3 toward the pump 4. be done.

Reference Signs List 1 Rankine cycle system 2 Flow path 2a for working fluid First flow path 2aa Reservoir 2b Second flow path 3 Tank 3a Tank inlet 4 Pump (circulation device)
5 Evaporator 6 Expander 6a Output shaft 6b Expander outlet 7 Condenser 7a Condenser inlet 7b Condenser outlet 8 Pressure sensors 9, 9a, 9b Temperature sensor 10 Liquid level estimation device 11 Bypass flow path 12 Second pump (transfer device)
13 Control device WL Condensate LS Liquid level of condensate

Claims (3)

a channel for circulating a working fluid; an expander arranged in the channel to expand the working fluid; a condenser that is arranged at a position to condense the working fluid; and a circulation device that is arranged in the flow path on the downstream side of the condenser and on the upstream side of the expander and pumps the working fluid. In a Rankine cycle system composed of:
a reservoir disposed in the first flow path, which is the flow path between the outlet of the expander and the inlet of the condenser, for storing a working fluid in a liquid state;
a bypass channel that communicates the second channel, which is the channel between the outlet of the condenser and the inlet of the circulation device, and the reservoir;
a transfer device disposed in the bypass flow path for transferring the liquid working fluid from the reservoir to the second flow path as needed;
a liquid level estimating device for estimating the liquid level of the liquid state working fluid stored in the reservoir;
A control device that controls the Rankine cycle system,
The control device
Based on the liquid level estimated by the liquid level estimating device, it is determined whether or not to transfer the working fluid in the liquid state from the reservoir to the second flow path. A Rankine cycle system configured to control a device to control the transfer of said working fluid in liquid form from said reservoir to said second flow path. 2. The Rankine cycle system according to claim 1, wherein the transfer device is configured as an on-off valve, and the diameter of the piping that constitutes the bypass flow path is made smaller than the diameter of the piping that constitutes the first flow path. . a channel for circulating a working fluid; an expander arranged in the channel to expand the working fluid; a condenser arranged at a position to condense the working fluid; a circulation device arranged in the flow path downstream from the condenser and upstream from the expander for pumping the working fluid; and the expander. and a reservoir for storing a working fluid in a liquid state, and between the outlet of the condenser and the inlet of the circulating device. and a bypass channel that communicates the second channel, which is the channel of the above, with the storage part, and a bypass channel that is disposed in the bypass channel and, if necessary, operates the liquid state from the storage part to the second channel A transfer device for transferring a fluid, and a control method for a Rankine cycle system comprising:
a first step of estimating a liquid level of the liquid state working fluid stored in the reservoir;
a second step of determining whether or not to transfer the liquid working fluid from the reservoir to the second channel based on the liquid level of the working fluid in the liquid state estimated in the first step;
A third step of controlling the transfer device to transfer the liquid working fluid from the reservoir to the second channel when it is determined in the second step that the liquid working fluid is to be transferred. a step;
A control method for a Rankine cycle system, comprising:

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