JP6741619B2 - Waste heat recovery equipment - Google Patents

Description

The present invention relates to a waste heat recovery device that recovers engine waste heat.

For example, as in Patent Document 1, there is known a waste heat recovery device that recovers the heat of the exhaust gas of the engine, that is, the waste heat of the engine. Such a waste heat recovery device is equipped with a pump, an evaporator, an expander, and a condenser in a circulation circuit through which a working medium circulates. The pump pumps the working medium in the liquid phase to the circulation circuit, and the evaporator causes the working medium in the liquid phase to evaporate by the waste heat of the engine to cause a phase transition to the gas phase. The expander converts the thermal energy of the working medium into mechanical energy by expanding the working medium in the gas phase state, and the condenser condenses the working medium in the gas phase state that has passed through the expander into the liquid phase state. Phase transition to.

JP, 2014-126031, A

Normally, the waste heat recovery device cannot recover the amount of waste heat exceeding the capacity of the device when the engine operating condition is in a high load condition with a large amount of waste heat. The output of the expander decreases when the load is small and low. Therefore, the waste heat recovery device is required to have a measure for efficiently recovering the waste heat of the engine.

An object of the present invention is to provide a waste heat recovery device that can efficiently recover waste heat of an engine.

A waste heat recovery device that solves the above-mentioned problems is a circulation circuit configured such that a working medium can circulate, a pressure-feeding unit that pressure-feeds the working medium to the circulation circuit, and a working medium that is pressure-fed by the pressure-feeding unit to the waste heat of an engine. And an expander that operates by the passage of the working medium that has evaporated in the evaporator, and a condenser that condenses the working medium that has passed through the expander, and the evaporator is the exhaust gas of the engine. A pre-stage heat exchange section in which heat exchange is performed between the gas and the working medium, and a middle-stage heat storage section for storing the heat of the exhaust gas, and the working medium that has passed through the middle-stage heat storage section and the pre-stage heat exchange section. Has a middle-stage heat exchange part that performs heat exchange between the second-stage heat storage part and the second-stage heat storage part that stores the heat of the exhaust gas, and exchanges heat between the second-stage heat storage part and the working medium that has passed through the middle-stage heat exchange part. And a second-stage heat exchange section, in which the middle-stage heat storage section is thermally insulated from the second-stage heat storage section.

According to the above configuration, the middle heat storage unit and the second heat storage unit heat the working medium while storing the waste heat of the engine when the amount of waste heat of the engine is large, and the heat that is stored when the amount of waste heat of the engine is small. To heat the working medium. As a result, the output of the expander is less likely to be affected by changes in the amount of waste heat of the engine. Further, since the front heat exchange section does not have a heat storage section and the middle heat storage section and the rear heat storage section are thermally insulated from each other, each heat exchange even when the amount of waste heat of the engine is small. It becomes easy to secure a temperature difference between the high temperature side (exhaust gas or heat storage section) and the low temperature side (working medium) in the section. As a result, the waste heat of the engine can be efficiently recovered.

In the waste heat recovery device having the above structure, the evaporator may be a counterflow heat exchanger.
According to the above configuration, the temperature difference between the exhaust gas and the rear heat storage section in the rear heat exchange section, and the temperature difference between the rear heat storage section and the working medium are easily secured. The heating can be performed effectively.

In the waste heat recovery device configured as described above, it is preferable that the middle-stage heat storage section has a larger heat storage capacity than the latter-stage heat storage section.
According to the above configuration, the phase transition from the liquid phase state to the gas phase state, which requires the most amount of heat, is easily performed in the middle heat exchange section. As a result, it is possible to raise the temperature of the working medium in the vapor phase state to a higher temperature in the rear heat storage section.

The waste heat recovery device having the above configuration further includes a heat storage state acquisition unit that acquires the heat storage state of the middle heat storage unit, and a control unit that controls the flow rate of the working medium in the circulation circuit, and the control unit is the When the heat storage state becomes the first heat storage state, the circulation of the working medium in the circulation circuit is started, and when the heat storage state becomes the second heat storage state in which the heat storage amount is smaller than that in the first heat storage state, the circulation of the working medium in the circulation circuit. Is preferably prohibited.

According to the above configuration, when the heat storage amount in the middle heat storage unit is small, the heat storage in the middle heat storage unit is preferentially performed. Thereby, the lower limit of the thermal energy of the working medium in the expander can be increased. As a result, the expander can be operated with high efficiency.

In the waste heat recovery device having the above configuration, the heat storage state acquisition unit is a temperature sensor that detects the temperature of the middle heat storage unit, and in the first heat storage state, the detected value of the temperature sensor is higher than the first temperature. The second heat storage state is a state in which the detected value of the temperature sensor is equal to or lower than a second temperature lower than the first temperature, and the first temperature and the second temperature are the operations for the evaporator. It is preferable that the temperature is higher than the saturation temperature at the supply pressure of the medium.

As in the above configuration, the temperature of the middle heat storage unit can be acquired as the heat storage state of the middle heat storage unit. Further, since the second temperature is higher than the saturation temperature at the working medium supply pressure to the evaporator, it is possible to surely evaporate the working medium in the evaporator when the working medium flows.

The figure which shows schematic structure of one Embodiment of a waste-heat recovery apparatus. The figure which shows the schematic structure of an evaporator typically. FIG. 3 is a block diagram showing an example of an electrical configuration of a waste heat recovery device. The flowchart which shows an example of a flow control process. The graph which shows an example of the temperature transition in an evaporator. The figure which shows an example of the result of the simulation performed with the waste heat recovery apparatus. The figure which shows an example of the result of the simulation performed with the waste heat recovery apparatus. The figure which shows the schematic structure of the other form of the waste heat recovery apparatus.

One embodiment of the waste heat recovery device will be described with reference to FIGS.
As shown in FIG. 1, the waste heat recovery device 20 is a waste heat recovery device using a Rankine cycle, and removes the waste heat of the engine 10 from the exhaust gas flowing downstream of the exhaust purification device 12 in the exhaust passage 11 of the engine 10. to recover. The engine 10 includes a turbocharger 16 having a turbine 13 arranged in the exhaust passage 11 and a compressor 15 arranged in the intake passage 14. The waste heat recovery device 20 includes a circulation circuit 21 in which a working medium (for example, water) can be circulated, and the circulation circuit 21 includes a pump 23, an evaporator 24, an expander 25, and a condenser 27. ing.

The pumping unit 23 pumps the working medium in the liquid phase to the circulation circuit 21. The pumping unit 23 is configured to be able to change the flow rate of the working medium in the circulation circuit 21 and the supply pressure p2 that is the pressure of the working medium supplied to the evaporator 24. The supply pressure p2 increases as the flow rate of the working medium increases, and becomes the maximum pressure p1 when the flow rate of the working medium is at the maximum flow rate. An example of the pumping unit 23 is a mechanical pump that pumps a working medium in a liquid phase at a predetermined discharge pressure (for example, maximum pressure p1) in conjunction with rotation of a crankshaft of the engine 10, and a circulation circuit downstream of the pump. 21 and an electronic control valve capable of controlling the flow passage cross-sectional area of the working medium. In one example of the pressure feeding unit 23, the flow rate and the supply pressure p2 are controlled by the opening degree of the electronic control valve. Another example of the pumping unit 23 is an electric pump in which the flow rate and the supply pressure p2 are controlled by the power supplied from the power supply device. The pumping unit 23 has a pumping state in which the working medium is pumped to the circulation circuit 21, and a stop state in which the working medium is prohibited from circulating in the circulation circuit 21 by not pumping the working medium to the circulation circuit 21. The pumping unit 23 is controlled by an ECU (Electronic Control Unit) 50 described later.

The evaporator 24 heats the working medium pumped by the pumping unit 23 with the waste heat of the engine 10 to cause the working medium in the liquid phase to undergo a phase transition to the gas phase. The expander 25 converts the thermal energy of the working medium into mechanical energy for rotating the output shaft 26 by expanding the working medium in the gas phase. The condenser 27 condenses the working medium in the vapor phase state that has passed through the expander 25 to make a phase transition to the liquid phase state. In the waste heat recovery device 20, the working medium circulates in the circulation circuit 21 while repeating the phase transition to recover the waste heat of the engine 10.

As shown in FIG. 2, the evaporator 24 has a flow path through which the working medium flows and a flow path through which exhaust gas flows, and is set in a direction in which the flow direction of the exhaust gas and the flow direction of the working medium are opposite to each other. It is a counter flow type heat exchanger. The evaporator 24 includes a front stage heat exchange section 31, a middle stage heat exchange section 32, and a rear stage heat exchange section 34.

The upstream heat exchange section 31 is a heat exchange section located on the most upstream side in the flow direction of the working medium among the heat exchange sections 31, 32, and 34. The pre-stage heat exchange section 31 directly exchanges heat between the exhaust gas and the working medium through the boundary wall having a small wall thickness on the order of millimeters to heat the working medium in the liquid phase to the medium temperature Tw2 which is the saturation temperature at the supply pressure p2. It is a part intended to be heated up to, and mainly the working medium in a liquid phase flows.

The middle heat exchange section 32 is a heat exchange section that is located downstream of the front heat exchange section 31 in the flow direction of the working medium and into which the working medium that has passed through the front heat exchange section 31 flows. The middle-stage heat exchange section 32 has a middle-stage heat storage section 33 that forms a boundary between a flow path through which a working medium flows and a flow path through which exhaust gas flows. The middle-stage heat exchange section 32 is a part intended to cause the working medium in a liquid phase state to undergo a phase transition to a gas phase state by indirect heat exchange between the working medium and the exhaust gas via the middle-stage heat storage section 33. .. The middle stage heat exchange section 32 mainly circulates a working medium in a mixed phase in which a working medium in a liquid phase state and a working medium in a gas phase state are mixed.

The second-stage heat exchange section 34 is located downstream of the middle-stage heat exchange section 32 in the flow direction of the working medium, and is a heat exchange section into which the working medium that has passed through the middle-stage heat exchange section 32 flows. The post-stage heat exchange section 34 has a post-stage heat storage section 35 that forms a boundary between the flow path through which the working medium flows and the flow path through which the exhaust gas flows. The post-stage heat exchange section 34 is a part intended to raise the temperature of the working medium in the vapor phase state by indirect heat exchange between the working medium and the exhaust gas via the post-stage heat storage section 35, and is mainly a vapor phase. The working medium in the state is circulated.

The middle-stage heat storage unit 33 and the rear-stage heat storage unit 35 include a heat storage material arbitrarily selected from a sensible heat storage material, a latent heat storage material, and a chemical heat storage material. The sensible heat storage material has a melting temperature higher than the temperature range of the exhaust gas, and stores the sensible heat accompanying the temperature rise. The sensible heat storage material is preferably composed of a material having a low coefficient of thermal expansion and a high specific heat and a high thermal conductivity, and copper is preferable if it is a metal.

The latent heat storage material has a melting temperature in the temperature range of the exhaust gas, and stores the heat of fusion accompanying the phase transition from the solid phase state to the liquid phase state in addition to the sensible heat. The latent heat storage material is formed by enclosing the heat storage material in an enclosure. The enclosure is preferably made of a material having high specific heat and thermal conductivity. The heat storage material is preferably a material having a low coefficient of thermal expansion, a high specific heat and a high thermal conductivity, and a high heat of fusion. Examples of such heat storage material include paraffin, xylitol, and erythritol.

The chemical heat storage material is configured by enclosing a plurality of chemical substances in an enclosure. The chemical heat storage material uses a reversible chemical reaction having a reaction temperature in the temperature range of exhaust gas, which is a chemical reaction of the plurality of chemical substances. In the chemical heat storage material, heat is stored by an endothermic reaction at a temperature higher than the reaction temperature, and heat is released by an exothermic reaction at a temperature lower than the reaction temperature. It is preferable that the reversible reaction by a plurality of chemical substances has a small volume change and a large heat storage density. Examples of such a plurality of chemical substances include a combination of calcium oxide and water, and a combination of strontium chloride and ammonia.

The middle-stage heat storage unit 33 and the rear-stage heat storage unit 35 are thermally insulated from each other by the insulating unit 36 due to, for example, being separated from each other or the interposition of a heat insulating material, so that direct heat transfer is not possible. Has been done. The middle-stage heat storage unit 33 has a larger heat transfer area and a larger heat storage capacity than the latter-stage heat storage unit 35, because the heat of vaporization per unit mass is larger than the constant pressure specific heat in the vapor phase state in the working medium. The heat storage capacity is, for example, the heat storage amount when the assumed maximum value of the exhaust gas temperature is the capacity calculation temperature. The heat storage capacity is the amount of heat calculated by specific heat capacity × mass × capacity calculation temperature for sensible heat storage material, and for latent heat storage material, the heat storage amount by sensible heat in the solid state and the heat of fusion × mass It is an added value of the calculated heat storage amount by the heat of fusion and the heat storage amount by the sensible heat in the liquid phase state.

As shown in FIG. 3, the waste heat recovery device 20 includes an ECU (Electronic Control Unit) 50 that controls the flow rate of the working medium in the circulation circuit 21 by controlling the pressure feeding unit 23. The pumping unit 23 and the ECU 50 configure a control unit that controls the flow rate of the working medium in the circulation circuit 21. The ECU 50 is mainly composed of a microcontroller in which a processor 51, a memory 52, an input interface 53, an output interface 54 and the like are connected to each other via a bus 55.

The ECU 50 receives a detection signal indicating the middle heat storage temperature Tmid, which is the temperature of the middle heat storage unit 33, from the temperature sensor 56 that functions as a heat storage state acquisition unit. The middle-stage heat storage temperature Tmid has a correlation with the heat storage states of the middle-stage heat storage unit 33 and the rear-stage heat storage unit 35, and thus functions as an index indicating the heat storage state. The ECU 50 acquires the middle stage heat storage temperature Tmid output from the temperature sensor 56 through the input interface 53, and executes the flow rate control process based on the obtained middle stage heat storage temperature Tmid and various control programs and various data stored in the memory 52. To do. Through the flow rate control process, the ECU 50 outputs an instruction signal for instructing the flow rate of the working medium to the pressure feeding unit 23 via the output interface 54.

The flow rate control process executed by the ECU 50 will be described with reference to FIG. The flow rate control process is repeatedly executed. At the start of the flow rate control process, the pumping unit 23 is in a stopped state.
As shown in FIG. 4, the ECU 50 first acquires the middle stage heat storage temperature Tmid based on the detection signal from the temperature sensor 56, and determines whether or not the acquired middle stage heat storage temperature Tmid is higher than the first temperature T1. Yes (step S11). The first temperature T1 is higher than the saturation temperature Ts1 of the working medium when the supply pressure p2 is at the maximum pressure p1, and is, for example, 20° C. higher than the saturation temperature Ts1. The first temperature T1 is set based on the results of experiments and simulations performed based on the heat storage amount Qmid of the middle heat storage unit 33, the maximum pressure p1 of the supply pressure p2, the heat transfer area of the middle heat exchange unit 32, and the like. It The first temperature T1 is a middle stage heat storage temperature Tmid indicating the first heat storage state. For example, when the supply pressure p2 is the maximum pressure p1, the first heat storage state causes the expander 25 to reach the saturation temperature Ts1 or higher at the maximum pressure p1 even if new exhaust gas is not supplied to the evaporator 24. The temperature at which a working medium in a vapor phase is supplied is maintained for a predetermined first period.

When the middle stage heat storage temperature Tmid is equal to or lower than the first temperature T1 (step S11: NO), the ECU 50 maintains the pumping unit 23 in the stopped state by temporarily ending the series of processes. On the other hand, when the middle-stage heat storage temperature Tmid is higher than the first temperature T1 (step S11: YES), the ECU 50 executes the pressure feeding process for causing the pressure feeding unit 23 to pressure-feed the working medium (step S12). In the pressure feeding process, the ECU 50 calculates, for example, the flow rate of the working medium in the circulation circuit 21 based on the intermediate heat storage temperature Tmid acquired in the immediately preceding step, and outputs an instruction signal according to the calculated flow rate to the pressure feeding unit 23. .. In this pressure feeding process, the ECU 50 controls the pressure feeding unit 23 such that the flow rate of the working medium increases as the intermediate heat storage temperature Tmid increases, that is, the supply pressure p2 approaches the maximum pressure p1 as the intermediate heat storage temperature Tmid increases. ..

In the next step S13, the ECU 50 acquires a new middle stage heat storage temperature Tmid and determines whether or not the acquired middle stage heat storage temperature Tmid is equal to or lower than the second temperature T2. The second temperature T2 is higher than the saturation temperature Ts1 and lower than the first temperature T1 described above, and is, for example, 10° C. higher than the saturation temperature Ts1. The second temperature T2 is set based on the results of experiments and simulations performed based on the heat storage amount Qmid of the middle heat storage unit 33, the maximum pressure p1 of the supply pressure p2, the heat transfer area S of the middle heat exchange unit 32, and the like. To be done. The second temperature T2 is a middle stage heat storage temperature Tmid indicating the second heat storage state. The second heat storage state is, for example, when the supply pressure p2 is the maximum pressure p1 and is equal to or higher than the saturation temperature Ts1 at the maximum pressure p1 with respect to the expander 25 even if new exhaust gas is not supplied to the evaporator 24. The temperature is a temperature at which a state in which a certain working medium in a gas phase is supplied is maintained for a predetermined second period shorter than the first period.

The first temperature T1 and the second temperature T2 are temperatures at which the intermediate heat storage temperature Tmid and the amount of heat storage are uniquely defined when the intermediate heat storage unit 33 is composed of a latent heat storage material (T1, T2≠melting temperature) is preferred. Further, the first temperature T1 and the second temperature T2 are preferably higher than the reaction temperature when the middle heat storage section 33 is made of a chemical heat storage material.

When the middle stage heat storage temperature Tmid is higher than the second temperature T2 (step S13: NO), the ECU 50 executes the pressure feeding process of step S12 using the middle stage heat storage temperature Tmid. On the other hand, when the mid-stage heat storage temperature Tmid is equal to or lower than the second temperature T2 (step S13: YES), the ECU 50 executes a stop process for controlling the pumping unit 23 in the stopped state, and prohibits the working medium from flowing in the circulation circuit 21. Yes (step S14). The ECU 50 that has executed the stop processing in step S14 once ends the series of processing. That is, the ECU 50 controls the pressure-feeding unit 23 to the pressure-feeding state when the middle-stage heat storage temperature Tmid reaches the first temperature T1, and then controls the pressure-feeding unit 23 to the stopped state when the middle-stage heat storage temperature Tmid decreases to the second temperature T2. ..

An example of changes in the temperature of the working medium, the exhaust gas, and the temperature of each heat storage unit in the evaporator 24 when the pressure feeding unit 23 is in the pressure feeding state will be described with reference to FIG. 5. FIG. 5 shows the transition of each temperature when the working medium changes from the liquid phase state of the medium temperature Tw1 to the gas phase state of the medium temperature Tw3, and the exhaust gas temperature decreases from the exhaust temperature Te1 to the exhaust temperature Te4. ing.

In FIG. 5, when the working medium flows into the pre-stage heat exchange section 31 in a liquid state at the medium temperature Tw1, heat exchange with the exhaust gas in the pre-stage heat exchange section 31 causes the medium temperature Tw2 up to the saturation temperature at the supply pressure p2. Be heated. The working medium in the liquid phase at the medium temperature Tw2 flows into the middle heat exchange section 32. In the middle-stage heat exchange section 32, the working medium undergoes heat exchange with the middle-stage heat storage section 33 to gradually undergo a phase transition from the liquid phase state to the vapor phase state while being maintained at the medium temperature Tw2. The working medium in a vapor phase state at the medium temperature Tw2 flows into the rear heat exchange section 34. In the second-stage heat exchange section 34, the working medium is heated to the medium temperature Tw3 higher than the medium temperature Tw2 by heat exchange with the second-stage heat storage section 35.

On the other hand, the exhaust gas flows into the post-stage heat exchange section 34 at the exhaust temperature Te1. In the post-stage heat exchange section 34, the temperature of the exhaust gas is reduced to the exhaust temperature Te2 by heat exchange with the post-stage heat storage section 35. The rear heat storage unit 35 is at a rear heat storage temperature Tlat that is lower than the exhaust gas temperature Te2 and higher than the medium temperature Tw3, and stores heat based on the rear heat storage temperature Tlat. In the middle heat exchange section 32, the temperature of the exhaust gas decreases from the exhaust temperature Te2 to the exhaust temperature Te3 due to heat exchange with the middle heat storage section 33. The middle-stage heat storage unit 33 is at a middle-stage heat storage temperature Tmid that is lower than the exhaust gas temperature Te3 and higher than the second temperature T2, and stores heat based on the middle-stage heat storage temperature Tmid. Although the middle-stage heat storage unit 33 has a lower temperature than the latter-stage heat storage unit 35, it stores a larger amount of heat than the latter-stage heat storage unit 35. Then, in the upstream heat exchange section 31, the temperature of the exhaust gas decreases from the exhaust temperature Te3 to the exhaust temperature Te4 higher than the medium temperature Tw1 due to heat exchange with the working medium.

When the pumping unit 23 is in the stopped state, the circulation of the working medium in the circulation circuit 21 is prohibited, while the exhaust gas continues to flow into the evaporator 24. Therefore, in the intermediate heat storage unit 33, the amount of heat absorbed by heat exchange with the exhaust gas is larger than the amount of heat released to the working medium staying in the intermediate heat exchange unit 32, and the difference between the amount of heat released and the amount of heat absorbed is calculated. Is stored. Similarly, in the rear heat storage unit 35, the amount of heat absorbed by heat exchange with the exhaust gas is larger than the amount of heat released to the working medium staying in the second heat exchange unit 34, and the amount of heat released and the amount of heat absorbed The amount of heat corresponding to the difference is stored.

The operation of the waste heat recovery device 20 described above will be described.
The evaporator 24 of the waste heat recovery device 20 includes a front heat exchange section 31, a middle heat exchange section 32 having a middle heat storage section 33, and a rear heat exchange section 34 having a second heat storage section 35. According to such a configuration, each heat storage unit 33, 35 heats the working medium while storing waste heat when the amount of waste heat of the engine 10 is large, and uses the heat that has been stored when the amount of waste heat of the engine 10 is small. Heat the working medium. As a result, even if the amount of waste heat of the engine 10 changes, the output P of the expander 25 is unlikely to be affected.

Further, in the waste heat recovery device 20, since the middle heat storage part 33 and the second heat storage part 35 are thermally insulated, direct heat transfer between the middle heat storage part 33 and the second heat storage part 35 is achieved. It is impossible. With such a configuration, the temperatures are not averaged between the middle-stage heat storage unit 33 and the second-stage heat storage unit 35. Therefore, even when the amount of waste heat of the engine 10 is small, the middle-stage heat exchange unit 32 and the second-stage heat exchange unit A temperature difference between the heat storage section and the working medium is easily secured at each position in each of the sections 34.

Further, as shown in FIG. 5, for example, in the middle-stage heat exchange section 32, the middle-stage heat storage temperature Tmid is maintained at the exhaust temperature Te3 or lower, which is the temperature of the exhaust gas flowing out from the middle-stage heat exchange section 32. Further, the working medium flows out of the middle heat exchange section 32 at a temperature equal to or lower than the middle heat storage temperature Tmid. For this reason, in the case shown in FIG. 5, if the pre-stage heat storage section 31 is arranged in the pre-stage heat exchange section 31, the pre-stage heat storage section at each position of the pre-stage heat exchange section 31 has the exhaust temperature Te4 or less in FIG. The heat storage temperature of the previous stage is maintained. Therefore, the working medium heated in the pre-stage heat storage section flows out from the pre-stage heat exchange section 31 at a temperature equal to or lower than the pre-stage heat storage temperature, in other words, an exhaust temperature Te4 or lower. That is, when the pre-stage heat storage section 31 is provided with the pre-stage heat storage section, the high-temperature side (pre-stage heat storage section) and the low-temperature side (working medium) are located at each position of the pre-stage heat exchange section 31 compared to the case shown in FIG. Not only the temperature difference becomes small, but it is difficult to raise the temperature of the working medium to the medium temperature Tw2 unless the exhaust temperature Te4 is higher than the medium temperature Tw2. On the other hand, in the waste heat recovery device 20, since the evaporator 24 is configured without providing the pre-stage heat storage section in the pre-stage heat exchange section 31, at each position of the pre-stage heat exchange section 31, the high temperature side (exhaust gas ) And the low temperature side (working medium) are easily secured, and the working medium is easily heated to the medium temperature Tw2.

Next, an example of the result of the simulation performed on the waste heat recovery device will be described with reference to FIGS. 6 and 7. 6 and 7 show the saturation temperature Ts and the output P of the expander 25 when the heat input amount Q common to the waste heat recovery device 20 described above and the waste heat recovery device of the comparative example are given as input values. It is a graph which shows change. The heat input amount Q is the heat amount based on the state amount of the exhaust gas flowing into the evaporator, and the saturation temperature Ts is the temperature of the working medium at the position immediately before flowing into the expander 25. 6 and 7, the solid line shows the result of the simulation performed on the waste heat recovery device 20 described above. On the other hand, the dotted line shows the result of the simulation performed on the waste heat recovery device of the comparative example in which the heat storage parts 33 and 35 are not provided and the flow rate of the working medium in the circulation circuit 21 increases as the heat input Q increases. Is shown. In addition, in the waste heat recovery apparatus 20, the correlation was recognized between the saturation temperature Ts and the middle stage heat storage temperature Tmid.

FIG. 6 shows an example of the result of simulation in the case where the operating state of the engine 10 is in a high load state at a high rate.
As shown in FIG. 6, in the waste heat recovery apparatus of the comparative example, as a whole, both the saturation temperature Ts and the output P change according to the change of the heat input amount Q at that time, that is, according to the differential element related to the heat input amount Q. Was approved. Further, it was confirmed that both the saturation temperature Ts and the output P tend to continue to decrease when the heat input Q is extremely small. In addition, in a state where the heat input amount Q is extremely large (for example, t1 to t2), it was recognized that both the saturation temperature Ts and the output P are maintained at approximately constant values even if the heat input amount Q changes. .. Then, it was confirmed that the surplus heat amount ΔQ is generated in a state where the saturation temperature Ts and the output P are maintained at constant values when the heat input amount Q is extremely large. The surplus heat amount ΔQ is calculated, for example, based on the difference between the boundary value indicating the presence or absence of the surplus heat amount ΔQ and the value obtained by subtracting the heat amount based on the state amount difference of the working medium before and after the evaporator 24 from the heat input amount Q.

On the other hand, in the waste heat recovery device 20, it was confirmed that the pressure feeding section 23 was continuously maintained in the pressure feeding state. Further, both the saturation temperature Ts and the output P gradually decrease even when the heat input Q is extremely small, and both the saturation temperature Ts and the output P even when the heat input Q is extremely large. Was confirmed to rise moderately. That is, it is recognized that both the saturation temperature Ts and the output P change according to the sum of the heat input amount Q in a predetermined period immediately before the change of the heat input amount Q at each time, that is, an integral element related to the heat input amount Q. It was It was confirmed that the amount of surplus heat ΔQ in the state where the amount of heat input Q was extremely large was significantly smaller than that of the waste heat recovery device of the comparative example, and the total output amount of the expander 25 was also large.

FIG. 7 shows an example of the result of the simulation when the operating state of the engine 10 is in the low load state at a high rate. Note that, in FIG. 7, since the surplus heat amount ΔQ is not generated in this simulation, the driving state of the pumping unit 23 is described instead of the surplus heat amount ΔQ in FIG. 6. In FIG. 7, “ON” indicates that the pressure feeding unit 23 is in the pressure feeding state, and “OFF” indicates that the pressure feeding unit 23 is in the stopped state.

As shown in FIG. 7, in the waste heat recovery apparatus of the comparative example, it was confirmed that both the saturation temperature Ts and the output P change according to the differential element regarding the heat input amount Q. It was also found that the saturation temperature Ts was low overall and the output P of the expander 25 was also low overall because the operating state of the engine 10 was high in the low load state.

On the other hand, in the waste heat recovery device 20, the state in which the saturation temperature Ts is higher than that of the waste heat recovery device of the comparative example by repeating the stopped state and the pumped state of the pumping unit 23 according to the intermediate heat storage temperature Tmid. Was found to be easily maintained. Further, with respect to the expander 25, the output P cannot be obtained when the pumping unit 23 is in the stopped state, but when the pumping unit 23 is in the pumping state, a higher output P than that of the waste heat recovery device of the comparative example is obtained. It was recognized that they were easily affected. It was confirmed that the total output amount of the expander 25 was significantly larger than that of the waste heat recovery device of the comparative example.

According to the waste heat recovery device 20 of the above embodiment, the following operational effects can be obtained.
(1) According to the waste heat recovery device 20, the output P of the expander 25 is less likely to be affected even if the amount of waste heat of the engine 10 changes, and each heat exchange is performed even when the amount of waste heat of the engine 10 is small. A temperature difference with the working medium is easily secured in the parts 31, 32, 34. From these, the output P of the expander 25 can be stably obtained, and as a result, the waste heat of the engine 10 can be efficiently recovered.

(2) The evaporator 24 is a counterflow heat exchanger in which the flow directions of the working medium and the exhaust gas in the heat exchange sections 31, 32, and 34 are set to be opposite to each other. As a result, the temperature difference between the rear-stage heat storage unit 35 and the working medium is more easily secured in the rear-stage heat exchange unit 34 than in the parallel-flow heat exchanger. Therefore, for example, the first control that controls the pressure-feeding unit 23 to the pressure-feeding state. The temperature T1 can be set to a lower temperature. As a result, it is possible to effectively heat the working medium using the waste heat of the engine 10.

(3) The middle heat storage unit 33 has a larger heat storage capacity than the rear heat storage unit 35. With such a configuration, it is possible to increase the probability that the phase transition from the liquid phase state to the gas phase state, which requires the most amount of heat, is performed in the middle heat exchange unit 32. As a result, the probability that the working medium flowing into the rear heat exchange section 34 is in the gas phase is increased, and the temperature difference between the rear heat storage section 35 and the working medium in the rear heat exchange section 34 is easily secured. As a result, since the working medium in the vapor phase state can be heated to a higher temperature in the latter stage heat exchange section 34, higher energy is supplied to the expander 25 even when the amount of waste heat of the engine 10 is small. A working medium having can be supplied.

(4) The waste heat recovery device 20 controls the pumping unit 23 to the pumping state when the middle-stage heat storage temperature Tmid rises to the first temperature T1, and then controls the pumping unit 23 when the middle-stage heat storage temperature Tmid drops to the second temperature T2. Control to stop state. According to such a configuration, when the heat storage amount in each heat storage unit 33, 35 is small, the pumping unit 23 is controlled to be in a stopped state, and heat can be intensively stored in each heat storage unit 33, 35. This increases the thermal energy of the working medium supplied to the expander 25 when the pumping unit 23 is in the pumping state, so that the expander 25 can be operated with higher efficiency.

(5) In the waste heat recovery device 20, the middle heat storage temperature Tmid is set as an index indicating the heat storage state of the middle heat storage unit 33 and the second heat storage unit 35. With such a configuration, the amount of heat stored in the middle heat exchange section 32 is grasped with high accuracy, so that the middle heat exchange section 32 can more reliably perform the phase transition of the working medium from the liquid phase state to the gas phase state. Can be done. Further, the heat storage state can be acquired with a simpler configuration than the case where the heat storage state is acquired based on the middle-stage heat storage temperature Tmid and the second-stage heat storage temperature Tlat.

(6) The first temperature T1 and the second temperature T2 are defined with reference to the saturation temperature Ts1 at the maximum pressure p1. As a result, the working medium can be circulated in a state where the intermediate heat storage temperature Tmid is higher than the saturation temperature of the working medium pumped by the pumping unit 23.

(7) Since the exhaust gas that has passed through the exhaust purification device 12 flows into the evaporator 24, it is possible to suppress a decrease in the thermal efficiency of the evaporator 24 due to the particulate matter contained in the exhaust gas.
In addition, the above-described embodiment can be implemented with appropriate modifications as follows.

The waste heat recovery device may be configured to operate the expander with the working medium that has been evaporated using the waste heat of the engine. Therefore, the waste heat recovery device may be configured to use the heat of the exhaust gas recirculated to the intake side as the exhaust heat of the engine in a vehicle equipped with EGR (Exhaust Gas Recirculation).

For example, as shown in FIG. 8, the waste heat recovery device 60 includes the circulation circuit 21, the pressure feeding unit 23 (first pressure feeding unit), the evaporator 24 (first evaporator), the expander 25, and the condenser described above. In addition to 27, a branch circuit 61, a second pumping section 63, and a second evaporator 64 are provided. The branch circuit 61 is a part of the circulation circuit 21, and branches from between the condenser 27 and the pumping unit 23 in the circulation circuit 21 and is connected between the evaporator 24 and the expander 25. The second pumping unit 63 is configured to be able to change the flow rate of the working medium in the branch circuit 61, and can have the same basic configuration as the pumping unit 23. The second evaporator 64 has the same basic configuration as the evaporator 24, and includes a front-stage heat exchange section, a middle-stage heat exchange section having a middle-stage heat storage section, and a rear-stage heat exchange section having a rear-stage heat storage section. It is an exchange. The second evaporator 64 heats the working medium that has passed through the second pressure feeding portion 63 using the exhaust gas flowing upstream of the EGR cooler 18 in the EGR passage 17 as a heat source to bring the working medium in the liquid phase state to the gas phase state. Phase transition. In such a configuration, the ECU 50 can control the drive state of the second pressure feeding unit 63 based on the temperature of the middle heat storage unit, similarly to the pressure feeding unit 23.

The waste heat recovery device 60 can recover the waste heat of the engine 10 not only from the exhaust gas flowing through the exhaust passage 11 but also from the EGR gas flowing through the EGR passage 17. Moreover, since the EGR gas before flowing into the EGR cooler 18 is used as a heat source, the capacity of the EGR cooler can be reduced.

The first temperature T1 and the second temperature T2 may be higher than the saturation temperature at the working medium supply pressure p2. Therefore, the ECU 50 acquires the supply pressure p2 of the working medium in a predetermined control cycle based on, for example, the driving state of the pressure sensor or the pressure feeding unit 23, and based on the acquired supply pressure p2, the first temperature T1 and the second temperature T1. You may change T2.

The ECU 50 is not limited to the configuration that acquires the intermediate heat storage temperature Tmid as an index indicating the heat storage state of the middle heat storage unit 33 or the heat storage state of the middle heat storage unit 33 and the rear heat storage unit 35. For example, the ECU 50 may acquire the heat storage state based on the middle heat storage temperature Tmid and the second heat storage temperature Tlat that is the temperature of the second heat storage unit 35, or may acquire the second heat storage temperature Tlat as an index indicating the heat storage state. Good. Further, for example, the ECU 50 may acquire the heat storage state by calculation using a model in which the state quantity indicating the operating state of the engine 10 and the flow rate of the working medium in the circulation circuit 21 are input values.

The heat storage capacity of the middle heat storage unit 33 may be equal to or less than the heat storage capacity of the second heat storage unit 35.
The evaporator 24 may be a parallel-flow heat exchanger in which the exhaust gas flow direction and the working medium flow direction are set in the same direction. Further, the evaporator 24 may be one that heats the working medium by using the waste heat of the engine 10 as a heat source, and may be a plate-type heat exchanger or a shell-and-tube heat exchanger that uses heat transfer tubes. Good. In the plate heat exchanger, the plate itself can be set as the heat storage unit. In the shell-and-tube heat exchanger, it is possible to dispose the heat storage section around the heat transfer tube.

The waste heat recovery device 20 may be any device as long as it can convert the heat energy of the exhaust gas, which is the waste heat of the engine, into mechanical energy. The engine may be a diesel engine or a gasoline engine. It may be a gas engine.

10... Engine, 11... Exhaust passage, 12... Exhaust purification device, 13... Turbine, 14... Intake passage, 15... Compressor, 16... Turbocharger, 17... EGR passage, 18... EGR cooler, 20... Waste heat recovery device, 21... Circulation circuit, 23... Pumping section, 24... Evaporator, 25... Expander, 26... Output shaft, 27... Condenser, 31... Pre-stage heat exchange section, 32... Middle stage heat exchange section, 33... Middle stage heat storage section, 34... Post-stage heat exchange section, 35... Post-stage heat storage section, 36... Insulation section, 50... ECU, 51... Processor, 52... Memory, 53... Input interface, 54... Output interface, 55... Bus, 56... Temperature sensor, 60 ... Waste heat recovery device, 61... Branch circuit, 63... Second pumping section, 64... Second evaporator.

Claims (5)

A circulation circuit configured so that the working medium can circulate,
A pumping section for pumping the working medium to the circulation circuit,
An evaporator that evaporates the working medium pumped by the pumping unit with engine waste heat,
An expander that operates by passage of the working medium evaporated in the evaporator,
A condenser for condensing the working medium that has passed through the expander,
The evaporator is
A pre-stage heat exchange section in which heat is exchanged between the exhaust gas of the engine and the working medium,
Having a middle-stage heat storage unit that stores heat of the exhaust gas, a middle-stage heat exchange unit in which heat exchange is performed between the middle-stage heat storage unit and the working medium that has passed through the front-stage heat exchange unit,
It has a post-stage heat storage unit that stores the heat of the exhaust gas, and a post-stage heat exchange unit that performs heat exchange between the post-stage heat storage unit and the working medium that has passed through the middle-stage heat exchange unit,
The said intermediate|middle heat storage part is a waste heat recovery apparatus thermally insulated with respect to the said second heat storage part. The waste heat recovery device according to claim 1, wherein the evaporator is a counterflow heat exchanger. The waste heat recovery device according to claim 1 or 2, wherein the middle-stage heat storage unit has a larger heat storage capacity than the latter-stage heat storage unit. A heat storage state acquisition unit that acquires the heat storage state of the middle heat storage unit,
Further comprising a control unit for controlling the flow rate of the working medium in the circulation circuit,
The control unit is
When the heat storage state becomes the first heat storage state, the circulation of the working medium in the circulation circuit is started, and when the heat storage state becomes the second heat storage state in which the heat storage amount is smaller than that in the first heat storage state, the working medium in the circulation circuit is The waste heat recovery device according to claim 1, wherein distribution is prohibited. The heat storage state acquisition unit is a temperature sensor that detects the temperature of the middle heat storage unit,
The first heat storage state is a state in which the detected value of the temperature sensor is higher than the first temperature,
The second heat storage state is a state in which a detection value of the temperature sensor is equal to or lower than a second temperature lower than the first temperature,
The waste heat recovery device according to claim 4, wherein the first temperature and the second temperature are temperatures higher than a saturation temperature at a supply pressure of a working medium to the evaporator.

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