JP7453940B2 - Exhaust heat recovery system - Google Patents

Description

The present invention relates to an exhaust heat recovery system.

Patent Document 1 discloses an exhaust heat recovery system that converts energy generated when a Rankine cycle working medium heated by compressed gas discharged from a compressor expands in an expander into electric power.

Special table 2014-505826 publication

In the exhaust heat recovery system described in Patent Document 1, lubricating oil is supplied to the bearings of the expander and the like to lubricate them. The supplied lubricating oil is discharged to the outside of the expander together with the working medium, and is separated from the working medium by an oil separator. The separated lubricating oil is supplied to the expander again.

When lubricating oil is supplied to the expander, the lubricating oil is required to have a supply temperature above a certain level. For example, if the lubricating oil supply temperature is low, there is a risk that the working medium will liquefy and mix into the lubricating oil. If lubricating oil mixed with liquefied working medium is injected into a bearing, it may cause damage to the bearing. Furthermore, the lubricating oil supplied to the expander may absorb thermal energy from the working medium, causing a decrease in the amount of power generation.

Furthermore, when lubricating oil is supplied to the expander, oil supply pressure within a certain range is required. For example, if the oil supply pressure is lower than a certain range, there is a possibility that lubricating oil will not be supplied to the expander. On the other hand, if the oil supply pressure is higher than a certain range, the saturation temperature of the working medium may rise and the working medium may liquefy.

Patent Document 1 does not specifically disclose the oil supply pressure and oil supply temperature of lubricating oil.

An object of the present invention is to prevent liquefaction of a working medium in lubricating oil at a pressure within a certain range in an exhaust heat recovery system that recovers thermal energy of compressed gas discharged by a compressor to a Rankine cycle including an expander. shall be.

The present invention provides a first heat exchanger, which is provided in a gas flow path for sending compressed gas discharged from a compressor to a consumer, and in which the compressed gas and a working medium exchange heat, and the temperature of the working medium increases. and a second heat source provided in a bypass flow path connected to the gas flow path so as to bypass the first heat exchanger, the compressed gas and the lubricating oil exchange heat, and the lubricating oil heats up. an exchanger, an expander that expands the working medium that has exchanged heat with the compressed gas in the first heat exchanger, a power recovery section that recovers power from the expander, and fluidly connected to the expander. an oil separator that separates the working medium and the lubricating oil supplied to the expander; and an oil that supplies the lubricant separated by the oil separator to the expander at a pressure within a certain range. a pump; a first channel for supplying the working medium from the oil separator to the expander via the first heat exchanger; and a first channel for supplying the working medium and the lubricating oil from the expander to the oil separator. and a third flow path that supplies the lubricating oil from the oil separator to the expander via the oil pump and the second heat exchanger, The present invention provides an exhaust heat recovery system in which the temperature of the lubricating oil supplied to the machine is higher than the saturation temperature of the working medium with respect to the pressure within the certain range.

According to the exhaust heat recovery system of the present invention, the temperature of the lubricating oil can be made higher than the saturation temperature of the working medium for a pressure within a certain range by exchanging heat between the lubricating oil and the compressed gas in the second heat exchanger. Therefore, liquefaction of the working medium within the lubricating oil can be suppressed. Moreover, the lubricating oil is heated by exchanging heat with the compressed gas in the second heat exchanger. In other words, since the thermal energy of compressed gas is used, energy can be used effectively. Therefore, it is possible to achieve downsizing and energy saving of the exhaust heat recovery system.

The exhaust heat recovery system further includes a flow rate adjustment valve that is provided in the bypass flow path and adjusts the flow rate of the compressed gas flowing into the bypass flow path, and by adjusting the opening degree of the flow rate adjustment valve, the The temperature of the lubricating oil supplied to the expander may be higher than the saturation temperature of the working medium with respect to the pressure within the certain range.

According to the above configuration, the temperature of the lubricating oil can be adjusted by adjusting the opening degree of the flow rate regulating valve. That is, by increasing the opening degree of the flow rate regulating valve, the amount of heat exchanged in the second heat exchanger is increased, and the temperature of the lubricating oil can be increased. Similarly, by reducing the opening degree of the flow rate regulating valve, the temperature of the lubricating oil can be lowered. Therefore, when the pressure fluctuates within a certain range, the temperature of the lubricating oil can be adjusted to be higher than the saturation temperature of the working medium with respect to the pressure. Therefore, thermal energy can be used efficiently and energy savings can be achieved.

The exhaust heat recovery system is provided between the second heat exchanger and the expander in the third flow path, and detects the temperature of the lubricating oil heat exchanged in the second heat exchanger. The apparatus may further include a sensor and a first control device that controls the opening degree of the flow rate adjustment valve according to the temperature detected by the temperature sensor.

According to the above configuration, the temperature of the lubricating oil can be automatically adjusted by monitoring the temperature of the lubricating oil and controlling the opening degree of the flow rate regulating valve with the first control device according to the temperature of the lubricating oil. Therefore, when the pressure fluctuates within a certain range, the temperature of the lubricating oil can be automatically adjusted to be higher than the saturation temperature of the working medium for that pressure. Therefore, the temperature of the lubricating oil can be reliably controlled.

a first pressure sensor that is provided between the oil pump and the expander in the third flow path and detects oil supply pressure that is the pressure of the lubricating oil supplied from the oil pump to the expander; The second control device further includes a second control device that controls the output of the oil pump according to the pressure detected by the first pressure sensor, and the second control device controls the oil pump so that the oil supply pressure is within the predetermined range. The output of the oil pump may also be controlled.

According to the above configuration, while monitoring the lubricating oil supply pressure, the second control device controls the output of the oil pump according to the lubricating oil supply pressure, thereby automatically adjusting the lubricating oil supply pressure within a certain range. It can be contained within the internal pressure. Therefore, the oil supply pressure can be reliably kept within a certain range.

According to the present invention, in an exhaust heat recovery system that recovers thermal energy of compressed gas discharged by a compressor to a Rankine cycle including an expander, the working medium is prevented from liquefying in lubricating oil at a pressure within a certain range. be able to.

1 is a schematic diagram of the configuration of an exhaust heat recovery system according to the present invention. FIG. 2 is a schematic diagram of the expander of FIG. 1. FIG. 3 is a graph showing the relationship between oil pump power consumption and oil supply pressure. 1 is a flowchart of an exhaust heat recovery system according to the present invention.

With reference to FIG. 1, an exhaust heat recovery system 1 according to the present embodiment will be described.

In the exhaust heat recovery system 1 , thermal energy of compressed gas (compressed air in this embodiment) discharged from the compressor 3 is recovered into a Rankine cycle including an expander 31 .

A drive motor 2 is mechanically connected to the compressor 3, and the compressor 3 is driven by the drive motor 2. A gas passage 10 for sending the compressed gas discharged from the compressor 3 to a consumer is connected to the discharge port 3b of the compressor 3, and the gas passage 10 is connected to a consumer 9. Further, a first heat exchanger 11 is provided in the gas flow path 10 .

Gas (in this embodiment, air) sucked in from the suction port 3a by the compressor 3 is compressed to become a high-temperature compressed gas, and is discharged from the discharge port 3b into the gas flow path 10. The compressed gas is cooled by the first heat exchanger 11 interposed in the gas flow path 10 and supplied to the consumer 9 .

In this embodiment, the bypass flow path 20 is connected to the gas flow path 10 so as to bypass the first heat exchanger 11. One end (upstream end) of the bypass flow path 20 is connected to a portion of the gas flow path 10 between the compressor 3 and the first heat exchanger 11, and the other end (downstream end) of the bypass flow path 20 is connected to a portion of the gas flow path 10 between the compressor 3 and the first heat exchanger ) is connected to a portion of the gas flow path 10 between the first heat exchanger 11 and the customer 9 . Further, a second heat exchanger 21 is provided in the bypass passage 20 .

The compressed gas discharged from the compressor 3 is branched between the compressor 3 and the first heat exchanger 11, cooled by the second heat exchanger 21 interposed in the bypass passage 20, and then transferred to the first heat exchanger 21. It joins between the exchanger 11 and the customer 9. That is, the compressed gas discharged from the compressor 3 bypasses the flow path where it is cooled by the first heat exchanger 11 and is supplied to the consumer 9 as described above, and the first heat exchanger 11, and is transferred to the second heat exchanger 11. It flows through a flow path that is cooled by an exchanger 21.

Thermal energy recovered from the compressed gas by the first heat exchanger 11 and the second heat exchanger 21 is used in the Rankine cycle. Hereinafter, the Rankine cycle of the exhaust heat recovery system 1 according to the present embodiment will be explained.

The exhaust heat recovery system 1 includes an expander 31 and an oil separator 41 fluidly connected downstream of the expander 31. In addition, the exhaust heat recovery system 1 includes a first flow path 30 (double-dashed line in FIG. 1) through which the working medium of the Rankine cycle (after lubricating oil separation) flows, and a second flow path through which the working medium (before lubricating oil separation) flows. It includes a passage 40 (dotted line in FIG. 1) and a third flow path 50 (bold line in FIG. 1) through which lubricating oil for the expander 31 flows. In this embodiment, the lubricating oil is a synthetic ester and the working medium is an organic fluid with a lower boiling point than water.

One end (upstream end) of the first flow path 30 is connected to the upper part of the oil separator 41, and the other end (downstream end) is connected to the intake port 31b of the expander 31 (see FIG. 2). has been done. In the first flow path 30, the working medium after the lubricating oil has been separated flows in a liquid or gas state.

Further, the second flow path 40 has one end (upstream end) connected to the discharge port 31c (see FIG. 2) of the expander 31, and the other end (downstream end) connected to the oil separator 41. has been done. In the second flow path 40, the working medium before the lubricating oil is separated flows.

A condenser 33, a pump 34, and a first heat exchanger 11 are provided in the first flow path 30 in this order from the oil separator 41 side. The gaseous working medium separated by the oil separator 41 is cooled by the condenser 33 and condensed (liquefied), and is supplied to the pump 34 . In the pump 34, the working medium is pressurized and discharged toward the first heat exchanger 11.

The discharged working medium is heated in the first heat exchanger 11 to be vaporized again, and then supplied to the expander 31 . In the expander 31, the thermal energy and pressure of the working medium are extracted as energy, and converted into electric power via a generator (power recovery section) 32 that recovers the power from the expander 31.

As will be described later, in the expander 31, lubricating oil is supplied to bearings 37A, 37B (see FIG. 2) of the expander 31. Therefore, the working medium flows into the oil separator 41 via the second flow path 40 along with the lubricating oil in the expander 31 . In the oil separator 41, the working medium and lubricating oil are separated, the working medium flowing through the first flow path 30, and the lubricating oil flowing through the third flow path 50.

One end (upstream end) of the third flow path 50 is connected to the oil reservoir 41a at the bottom of the oil separator 41, and the other end (downstream end) is the oil supply port 31a of the expander 31 (FIG. (see).

The third flow path 50 is provided with an oil pump 51 and a second heat exchanger 21 in this order from the oil separator 41 side. The oil pump 51 is driven by a motor 52 as power. The motor 52 is provided with an inverter 53, and the rotation speed of the motor 52 is changed by the inverter 53. When the rotational speed of the motor 52 increases, the lubricating oil supply pressure increases, and when the rotational speed of the motor 52 decreases, the lubricating oil supplying pressure decreases.

The lubricating oil separated by the oil separator 41 is pressurized to a pressure within a certain range by the oil pump 51 and discharged toward the second heat exchanger 21 . The discharged lubricating oil is heated by the second heat exchanger 21 and supplied to the expander 31.

Referring to FIG. 2, the expander 31 is connected to a first flow path 30, a second flow path 40, and a third flow path 50. In the expander 31, the working medium that has been heated by exchanging heat with the compressed gas in the first heat exchanger 11 is expanded. In this embodiment, a screw expander having a screw rotor 36 that is rotationally driven by the energy of a working medium is used as the expander 31. As the expander 31, a centrifugal type, a scroll type, or the like may be used.

The third flow path 50 is connected to the expander 31 so as to supply lubricating oil to the bearings 37A, 37B and the rotor chamber 39. The lubricating oil supplied to the expander 31 is discharged from the discharge port 31c together with the working medium.

Referring to FIG. 1, the first heat exchanger 11 is provided in the gas flow path 10. Further, the first heat exchanger 11 is interposed in the first flow path 30. In the first heat exchanger 11, the high temperature compressed gas flowing through the gas flow path 10 and the working medium flowing through the first flow path 30 exchange heat, and the temperature of the working medium increases. That is, the working medium is heated by receiving thermal energy from the high-temperature compressed gas, and the compressed gas is cooled.

The second heat exchanger 21 is provided in the bypass flow path 20. Further, the second heat exchanger 21 is interposed in the third flow path 50. In the second heat exchanger 21, the high temperature compressed gas that branches from the gas flow path 10 and flows through the bypass flow path 20 and the lubricating oil flowing through the third flow path 50 exchange heat, and the temperature of the lubricating oil increases. That is, the lubricating oil is heated by receiving thermal energy from the high-temperature compressed gas, and the compressed gas is cooled.

A flow rate regulating valve 22 is provided in the bypass passage 20 . By adjusting the opening degree of the flow rate adjustment valve 22, the flow rate of the compressed gas flowing through the bypass channel 20 is adjusted. That is, the flow rate of the compressed gas flowing through the second heat exchanger 21 is adjusted, and the amount of thermal energy heat exchanged with the lubricating oil is also adjusted. That is, increasing the opening degree of the flow rate regulating valve 22 increases the temperature of the lubricating oil, and decreasing the opening degree of the flow rate regulating valve 22 lowers the temperature of the lubricating oil.

A temperature sensor 55 and a pressure sensor (first pressure sensor) 56 are provided in the third flow path 50 immediately before the expander 31, specifically between the second heat exchanger 21 and the expander 31. ing. The temperature sensor 55 detects the temperature to of the lubricating oil supplied to the expander 31. The pressure sensor 56 detects the pressure (oil supply pressure) Po of lubricating oil supplied to the expander 31.

The temperature value detected by the temperature sensor 55 is transmitted to the first control device 100. The first control device 100 controls the opening degree of the flow rate regulating valve 22 according to the received temperature value of the lubricating oil.

The pressure value detected by the pressure sensor 56 is transmitted to the second control device 200. The second control device 200 changes the rotation speed of the motor 52 via the inverter 53 and controls the output of the pump 34 according to the received pressure value of the lubricating oil.

A pressure sensor 35 is provided in the first flow path 30 immediately before the expander 31, specifically between the first heat exchanger 11 and the expander 31. The pressure sensor 35 detects the pressure (suction pressure) Ps of the working medium flowing into the expander 31. Further, a pressure sensor 45 is provided in the second flow path 40 immediately after the expander 31 . The pressure sensor 45 detects the pressure (discharge pressure) Pd of the working medium containing lubricating oil flowing out from the expander 31. The detected pressures Ps and Pd are sent to the second control device as pressure values.

The exhaust heat recovery system 1 operates according to the flowchart shown in FIG.

In step S1, when the exhaust heat recovery system 1 starts, the pressure sensors 35 and 45 detect the pressures Ps and Pd, the temperature sensor 55 detects the temperature to, and the pressure sensor 56 detects the pressure Po. . In step S2, the temperature to is received by the first control device 100 as a detection signal, and the pressures Ps, Pd, and Po are received by the second control device 200 as detection signals.

In step S3, the second control device 200 calculates the pressure Px as the average pressure of the pressure Ps and the pressure Pd (Px=(Ps+Pd)/2), and the pressure Py is calculated as a pressure slightly smaller than the pressure Ps. (For example, Py=Ps-0.1 MPa).

In this embodiment, the pressure Px is the lowest pressure for lubricating oil to be supplied to the expander 31. Moreover, the pressure Py is the maximum pressure for lubricating oil to be supplied to the expander 31 without excessive power consumption of the oil pump 51. That is, referring to FIG. 3, the greater the oil supply pressure of the oil pump 51, the greater the power consumption, so in this embodiment, a maximum pressure Py is provided.

In step S4, if the pressure Po at the lubricating oil pressure sensor 56 is greater than Px, it is determined that the lubricating oil has a pressure that can be supplied into the expander 31, and the process moves to step S6. In step S4, if the pressure Po is less than or equal to Px, it is determined that lubricating oil has not been supplied into the expander 31, and the rotation speed of the oil pump is increased in step S5.

In step S6, if the pressure Po is less than Py, it is determined that the power consumption of the oil pump 51 is appropriate, and the rotation speed of the oil pump 51 is maintained in step S8. In step S6, if the pressure Po is equal to or higher than Py, it is determined that the power consumption of the oil pump 51 is excessive, and the rotation speed of the oil pump 51 is decreased in step S7.

That is, the second control device 200 controls the output of the oil pump 51 so that the oil supply pressure Po falls within a certain range (Px<Po<Py).

When the rotation speed of the oil pump 51, that is, the pressure Po is maintained by the second control device 200, the saturation temperature tos of the working medium with respect to the pressure Po is calculated in step S9. When the temperature of the working medium is higher than the saturation temperature tos, the working medium becomes a gas, and when the temperature of the working medium is lower than the saturation temperature tos, the working medium becomes a liquid.

When the lubricating oil is supplied to the expander 31, in step S10, if the lubricating oil temperature to is higher than the saturation temperature tos, the temperature of the working medium in contact with the lubricating oil does not fall below the saturation temperature tos, and the lubricating oil liquefies. No mixed working medium. In this case, in step S12, the temperature of the lubricating oil is maintained, that is, the opening degree of the flow rate regulating valve 22 is maintained. In step S10, if the temperature to is lower than the saturation temperature tos, there is a possibility that the temperature of the working medium in contact with the lubricating oil will become equal to or lower than the saturation temperature tos, and there is a possibility that the liquefied working medium will be mixed into the lubricating oil. In this case, in step S11, the temperature of the lubricating oil is increased, that is, the opening degree of the flow rate regulating valve 22 is increased.

In this embodiment, the exhaust heat recovery system 1 operates continuously according to the flowchart in FIG. 4 . That is, the flow rate is adjusted so that the temperature to of the lubricating oil supplied from the second heat exchanger 21 to the expander 31 is higher than the saturation temperature tos of the working medium for a pressure within a certain range (Px<Po<Py). The opening degree of the valve 22 is constantly adjusted.

According to the exhaust heat recovery system 1 of the present embodiment, the lubricating oil and the compressed gas are heat exchanged in the second heat exchanger 21, so that the lubricating oil is supplied from the second heat exchanger 21 to the expander 31. Since the temperature to can be made higher than the saturation temperature tos of the working medium for a pressure within a certain range (Px<Po<Py) (to>tos), liquefaction of the working medium in the lubricating oil can be suppressed. Furthermore, the lubricating oil is heated by exchanging heat with the compressed gas in the second heat exchanger 21 . In other words, since the thermal energy of compressed gas is used, energy can be used effectively. Therefore, it is possible to achieve downsizing and energy saving of the exhaust heat recovery system 1.

Further, by adjusting the opening degree of the flow rate adjustment valve 22, the temperature of the lubricating oil can be adjusted. That is, by increasing the opening degree of the flow rate regulating valve 22, the amount of heat exchanged in the second heat exchanger 21 is increased, and the temperature of the lubricating oil can be increased. Similarly, by reducing the opening degree of the flow rate regulating valve 22, the temperature of the lubricating oil can be lowered. Therefore, when the pressure Po fluctuates within a certain range (Px<Po<Py), the temperature to of the lubricating oil can be adjusted to be higher than the saturation temperature tos of the working medium with respect to the pressure Po. Therefore, thermal energy can be used efficiently and energy savings can be achieved.

Moreover, the temperature to of the lubricating oil can be automatically adjusted by controlling the opening degree of the flow rate adjustment valve 22 with the first control device 100 according to the temperature to of the lubricating oil while monitoring the temperature to of the lubricating oil. Therefore, when the pressure Po fluctuates within a certain range (Px<Po<Py), the temperature to of the lubricating oil can be automatically adjusted to be higher than the saturation temperature tos of the working medium with respect to the pressure Po. Therefore, the temperature to of the lubricating oil can be controlled reliably.

In addition, while monitoring the lubricating oil supply pressure Po, the second control device 200 controls the output of the oil pump 51 according to the lubricating oil supply pressure Po, thereby automatically adjusting the lubricating oil supply pressure Po, and controlling the lubricating oil supply pressure Po within a certain range. (Px<Po<Py). Therefore, the oil supply pressure Po can be reliably kept within a certain range (Px<Po<Py).

As described above, according to the present embodiment, in the exhaust heat recovery system 1 that recovers thermal energy of compressed gas discharged by the compressor 3 to the Rankine cycle including the expander 31, the pressure within a certain range (Px<Po<Py ) can prevent the working medium from liquefying in the lubricating oil.

1 Exhaust heat recovery system 2 Drive motor 3 Compressor 3a Suction port 3b Discharge port 9 Demand destination 10 Gas flow path 11 First heat exchanger 20 Bypass flow path 21 Second heat exchanger 22 Flow rate adjustment valve 30 First flow path 31 Expander 31a Oil supply port 31b Intake port 31c Discharge port 32 Generator (power recovery section)
33 Condenser 34 Pump 35 Pressure sensor 36 Screw rotor 37A, 37B Bearing 38 Rotating shaft 39 Rotor chamber 40 Second channel 41 Oil separator 45 Pressure sensor 50 Third channel 51 Oil pump 52 Motor 53 Inverter 55 Temperature sensor 56 Pressure Sensor (first pressure sensor)
100 first control device 200 second control device

Claims (4)

a first heat exchanger that is installed in a gas flow path for sending compressed gas discharged from a compressor to a demand destination, the compressed gas and a working medium exchange heat, and the temperature of the working medium increases;
a second heat exchanger provided in a bypass flow path connected to the gas flow path so as to bypass the first heat exchanger, the compressed gas and lubricating oil exchange heat, and the temperature of the lubricating oil increases; and,
an expander that expands the working medium that has exchanged heat with the compressed gas in the first heat exchanger;
a power recovery unit that recovers power from the expander;
an oil separator that is fluidly connected to the expander and separates the working medium and the lubricating oil supplied to the expander;
an oil pump that supplies the lubricating oil separated by the oil separator to the expander at a pressure within a certain range;
a first flow path for supplying the working medium from the oil separator to the expander via the first heat exchanger;
a second flow path for supplying the working medium and the lubricating oil from the expander to the oil separator;
a third flow path for supplying the lubricating oil from the oil separator to the expander via the oil pump and the second heat exchanger,
An exhaust heat recovery system, wherein the temperature of the lubricating oil supplied to the expander is higher than the saturation temperature of the working medium with respect to the pressure within the certain range. Further comprising a flow rate adjustment valve provided in the bypass flow path and adjusting the flow rate of the compressed gas flowing into the bypass flow path,
The temperature of the lubricating oil supplied to the expander is made higher than the saturation temperature of the working medium with respect to the pressure within the certain range by adjusting the opening degree of the flow rate regulating valve. Exhaust heat recovery system. a temperature sensor that is provided between the second heat exchanger and the expander in the third flow path and detects the temperature of the lubricating oil that has been heat exchanged with the second heat exchanger;
The exhaust heat recovery system according to claim 2, further comprising: a first control device that controls the opening degree of the flow rate regulating valve according to the temperature detected by the temperature sensor. a first pressure sensor that is provided between the oil pump and the expander in the third flow path and detects oil supply pressure that is the pressure of the lubricating oil supplied from the oil pump to the expander;
further comprising: a second control device that controls the output of the oil pump according to the pressure detected by the first pressure sensor;
The exhaust heat recovery system according to any one of claims 1 to 3, wherein the output of the oil pump is controlled by the second control device so that the oil supply pressure is within the predetermined range.

Images