JP2018168758A - Waste heat recovery device - Google Patents

Abstract

To provide a waste heat recovery device capable of efficiently recovering waste heat of an engine.SOLUTION: A waste heat recovery device includes: a circulation circuit in which working medium circulates; a pressure-feeding section for pressure-feeding the working medium in a liquid-phase state to the circulation circuit; an evaporator for evaporating the working medium in the liquid-phase state pressure-fed by the pressure-feeding section by using waste heat of an engine; an expander operated by passage of the working medium in a gas-phase state evaporated by the evaporator; and a condenser for condensing the working medium in the gas-phase state that has passed through the expander. The evaporator 24 includes: a front stage heat exchange section 31 for exchanging heat between the working medium and exhaust gas of the engine; an intermediate stage heat exchange section 32 for exchanging heat between the working medium that has passed through the front stage heat exchange section 31 and an intermediate stage heat storage section 33 for storing heat of exhaust gas; and a rear stage heat exchange section 34 for exchanging heat between the working medium that has passed through the intermediate stage heat exchange section 32 and a rear stage heat storage section 35 for storing heat of exhaust gas. The intermediate stage heat storage section 33 is thermally insulated from the rear stage heat storage section 35.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a waste heat recovery apparatus that recovers waste heat of an engine.

  For example, as in Patent Document 1, a waste heat recovery device that recovers heat of engine exhaust gas, that is, waste heat of the engine, is known. Such a waste heat recovery apparatus includes 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 phase transition to the gas phase by evaporating the working medium in the liquid phase with the waste heat of the engine. 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 to form a liquid phase state. To phase transition.

JP 2014-126031 A

  Normally, waste heat recovery equipment cannot recover waste heat that exceeds the capacity of the equipment when the engine is in a high load state with a large amount of waste heat. When the load is low, the output of the expander decreases. Therefore, the waste heat recovery device is required to have a method for efficiently recovering engine waste heat.

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

  A waste heat recovery apparatus that solves the above problems includes a circulation circuit configured to circulate a working medium, a pressure feeding unit that pumps the working medium to the circulation circuit, and a working medium pumped by the pressure feeding unit to the waste heat of the engine. An evaporator that evaporates in the evaporator, an expander that operates by passing the working medium evaporated in the evaporator, and a condenser that condenses the working medium that has passed through the expander, and the evaporator exhausts the engine A pre-stage heat exchanging section in which heat is exchanged between the gas and the working medium; and a middle-stage heat accumulating section for accumulating the heat of the exhaust gas, the working medium having passed through the middle-stage heat accumulating section and the preceding-stage heat exchanging section; Heat exchange between the middle stage heat exchange section where the heat exchange is performed and the rear stage heat storage section which stores the heat of the exhaust gas, and the heat exchange between the rear stage heat storage section and the working medium which has passed through the middle stage heat exchange section And a post-stage heat exchange unit for Parts are thermally insulated with respect to the subsequent heat storage unit.

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

In the waste heat recovery apparatus configured as described above, the evaporator may be a counter-flow heat exchanger.
According to the above configuration, the temperature difference between the exhaust gas and the rear stage heat storage unit and the temperature difference between the rear stage heat storage unit and the working medium are easily secured in the rear stage heat exchange unit. Heating can be performed effectively.

In the waste heat recovery apparatus having the above configuration, it is preferable that the middle heat storage unit has a larger heat storage capacity than the rear heat storage unit.
According to the above configuration, the phase transition from the liquid phase state requiring the most heat amount to the gas phase state is easily performed in the middle heat exchange section. Thereby, the working medium in a gas phase can be heated to a higher temperature in the rear stage heat storage unit.

  The waste heat recovery apparatus having the above configuration further includes a heat storage state acquisition unit that acquires a heat storage state of the middle stage heat storage unit, and a control unit that controls a circulation amount of the working medium in the circulation circuit, and the control unit includes: Distribution of the working medium in the circulation circuit starts when the heat storage state becomes the first heat storage state, and distribution of the working medium in the circulation circuit starts when the heat storage state becomes the second heat storage state in which the heat storage amount is smaller than that of the first heat storage state. Is preferably prohibited.

  According to the said structure, when the amount of heat storage in a middle stage heat storage part is small, heat storage with respect to a middle stage heat storage part is performed preferentially. Thereby, the lower limit of the thermal energy which the working medium has in the expander can be increased. As a result, the expander can be operated with high efficiency.

  In the waste heat recovery apparatus having the above configuration, the heat storage state acquisition unit is a temperature sensor that detects a temperature of the middle heat storage unit, and the first heat storage state has a detected value of the temperature sensor higher than the first temperature. And the second heat storage state is a state where 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. The temperature is preferably higher than the saturation temperature at the supply pressure of the medium.

  Like the said structure, the temperature of a middle stage thermal storage part is acquirable as a thermal storage state of a middle stage thermal storage part. Further, since the second temperature is higher than the saturation temperature at the supply pressure of the working medium to the evaporator, the working medium can be reliably evaporated 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. The block diagram which shows an example of the electrical structure of a waste heat recovery apparatus. 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 to the waste heat recovery apparatus. The figure which shows an example of the result of the simulation performed to the waste heat recovery apparatus. The figure which shows schematic structure of the other form of a waste heat recovery apparatus.

With reference to FIGS. 1-7, one Embodiment of a waste-heat recovery apparatus is described.
As shown in FIG. 1, the waste heat recovery device 20 is a waste heat recovery device that uses a Rankine cycle, and removes waste heat of the engine 10 from 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 disposed in the exhaust passage 11 and a compressor 15 disposed in the intake passage 14. The waste heat recovery apparatus 20 includes a circulation circuit 21 configured to circulate a working medium (for example, water). The circulation circuit 21 includes a pumping unit 23, an evaporator 24, an expander 25, and a condenser 27. ing.

  The pumping unit 23 pumps the liquid-phase working medium to the circulation circuit 21. The pressure feeding 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 p <b> 2 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 includes a mechanical pump that pumps a liquid-phase working medium at a predetermined discharge pressure (for example, maximum pressure p1) in conjunction with rotation of the crankshaft of the engine 10, and a circulation circuit downstream of the pump. And an electronic control valve capable of controlling the flow path cross-sectional area of the working medium at 21. In this 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 includes 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 stopped state in which the working medium is not circulated 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 liquid-phase working medium to undergo a phase transition to the gas phase. The expander 25 converts the thermal energy of the working medium into mechanical energy that rotates the output shaft 26 by expanding the working medium in a gas phase. The condenser 27 condenses the gas phase working medium that has passed through the expander 25 to cause phase transition to the liquid phase. In the waste heat recovery apparatus 20, the waste heat of the engine 10 is recovered by circulating the circulating fluid through the circulation circuit 21 while the working medium repeats the phase transition.

  As shown in FIG. 2, the evaporator 24 has a flow path through which the working medium flows and a flow path through which the 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. This is a counterflow type heat exchanger. The evaporator 24 includes a front-stage heat exchange unit 31, a middle-stage heat exchange unit 32, and a rear-stage heat exchange unit 34.

  The pre-stage heat exchange unit 31 is a heat exchange unit located on the most upstream side in the flow direction of the working medium among the heat exchange units 31, 32, and 34. The pre-stage heat exchanging section 31 supplies a liquid phase working medium by direct heat exchange between the exhaust gas and the working medium through a boundary wall having a small thickness on the order of millimeters, and a medium temperature Tw2 that is a saturation temperature at the supply pressure p2. The working medium that is intended to be heated up to the main, and the working medium that is mainly in a liquid phase circulates.

  The middle heat exchange unit 32 is located on the downstream side of the front heat exchange unit 31 in the flow direction of the working medium, and is a heat exchange unit into which the working medium that has passed through the front heat exchange unit 31 flows. The middle heat exchange section 32 has a middle heat storage section 33 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 middle heat exchanging section 32 is a part intended to cause a liquid phase working medium to undergo a phase transition to a gas phase by indirect heat exchange between the working medium and the exhaust gas via the middle heat storage section 33. . In the middle heat exchange section 32, a working medium in a mixed phase in which a working medium in a liquid phase and a working medium in a gas phase are mixed flows.

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

  The middle heat storage unit 33 and the rear 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 sensible heat as the temperature rises. The sensible heat storage material is preferably composed of a material having a low coefficient of thermal expansion and high specific heat and 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 heat of fusion accompanying the phase transition from the solid phase state to the liquid phase state in addition to sensible heat. The latent heat storage material is configured by enclosing a heat storage material in an enclosure. The enclosure is preferably formed of a material having high specific heat and thermal conductivity. The heat storage material is preferably a material having a small coefficient of thermal expansion, a high specific heat and a high thermal conductivity, and a large heat of fusion. Examples of such a 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 that is a chemical reaction by the plurality of chemical substances and has a reaction temperature in the exhaust gas temperature range. In a chemical heat storage material, heat is stored by an endothermic reaction at a temperature higher than the reaction temperature, and heat is radiated by an exothermic reaction at a temperature lower than the reaction temperature. The reversible reaction by a plurality of chemical substances is preferably one having a small volume change and a large heat storage density. Examples of the 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 section 33 and the rear-stage heat storage section 35 are set in a state in which direct heat transfer is not possible because they are thermally isolated from each other by the insulating section 36 due to, for example, being separated from each other or by interposing a heat insulating material. Has been. The middle heat storage unit 33 has a larger heat transfer area and a larger heat storage capacity than the rear heat storage unit 35 because the evaporation heat per unit mass is larger than the constant pressure specific heat in the gas phase in the working medium. The heat storage capacity is, for example, the amount of heat stored when the assumed maximum value of the exhaust temperature is the capacity calculation temperature. The heat storage capacity is the amount of heat calculated by the specific heat capacity x mass x capacity calculation temperature if it is a sensible heat storage material, and in the case of a latent heat storage material, the heat storage amount due to sensible heat in the solid state and the heat of fusion x mass It is an added value of the heat storage amount by the calculated heat of fusion and the heat storage amount by sensible heat in the liquid phase state.

  As shown in FIG. 3, the waste heat recovery apparatus 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 pumping unit 23. The pumping unit 23 and the ECU 50 constitute a control unit that controls the flow rate of the working medium in the circulation circuit 21. The ECU 50 is mainly configured 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 a middle heat storage temperature Tmid that 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 heat storage temperature Tmid functions as an index indicating the heat storage state because it has a correlation with the heat storage states of the middle heat storage unit 33 and the rear heat storage unit 35. The ECU 50 acquires the intermediate heat storage temperature Tmid output from the temperature sensor 56 through the input interface 53, and executes a flow rate control process based on the acquired intermediate heat storage temperature Tmid and various control programs and various data stored in the memory 52. To do. The ECU 50 outputs an instruction signal instructing the flow rate of the working medium to the pressure feeding unit 23 through the output interface 54 through the flow rate control process.

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 control process, the pumping unit 23 is in a stopped state.
As shown in FIG. 4, the ECU 50 first acquires the middle heat storage temperature Tmid based on the detection signal from the temperature sensor 56, and determines whether or not the acquired middle heat storage temperature Tmid is higher than the first temperature T1. (Step S11). The first temperature T1 is a temperature higher than the saturation temperature Ts1 of the working medium when the supply pressure p2 is at the maximum pressure p1, for example, a temperature about 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 intermediate heat storage section 33, the maximum pressure p1 of the supply pressure p2, the heat transfer area in the intermediate heat exchange section 32, and the like. The The first temperature T1 is a middle heat storage temperature Tmid indicating the first heat storage state. In the first heat storage state, for example, when the supply pressure p2 is the maximum pressure p1, the expansion temperature is equal to or higher than the saturation temperature Ts1 at the maximum pressure p1 for the expander 25 even if no new exhaust gas is supplied to the evaporator 24. The state in which the working medium in a certain gas phase is supplied is a temperature at which the state 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 a stopped state by once ending a 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 a pressure feeding process in which the working medium is pressure-fed by the pressure feeding unit 23 (step S12). In the pressure feeding process, for example, the ECU 50 calculates 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 corresponding to the calculated flow rate to the pressure feeding unit 23. . In this pumping process, the ECU 50 controls the pumping unit 23 so 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 above-described saturation temperature Ts1 and lower than the first temperature T1, and is, for example, about 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 intermediate heat storage section 33, the maximum pressure p1 of the supply pressure p2, the heat transfer area S in the intermediate heat exchange section 32, and the like. Is done. The second temperature T2 is a middle heat storage temperature Tmid indicating the second heat storage state. In the second heat storage state, for example, when the supply pressure p2 is the maximum pressure p1, the expansion temperature 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 at which the working medium in a certain vapor 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 middle heat storage temperature Tmid and the heat storage amount are uniquely defined when the middle heat storage unit 33 is formed of a latent heat storage material (T1, T1). T2 ≠ melting temperature) is preferable. Moreover, it is preferable that 1st temperature T1 and 2nd temperature T2 are temperature higher than reaction temperature, when the intermediate | middle stage heat storage part 33 is comprised with a chemical heat storage material.

  When the middle 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 heat storage temperature Tmid. On the other hand, when the middle 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 to a stop state, and prohibits circulation of the working medium in the circulation circuit 21. (Step S14). The ECU 50 that has executed the stop process in step S14 once ends the series of processes. That is, the ECU 50 controls the pumping unit 23 to the pumping state when the middle stage heat storage temperature Tmid reaches the first temperature T1, and then controls the pumping unit 23 to the stop state when the middle stage heat storage temperature Tmid decreases to the second temperature T2. .

  With reference to FIG. 5, an example of the transition of the temperature regarding the working medium in the evaporator 24, exhaust gas, and each heat storage part when the pumping part 23 is in a pumping state is demonstrated. FIG. 5 shows the transition of each temperature when the working medium changes from the liquid phase state at the medium temperature Tw1 to the gas phase state at 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 the liquid phase state of the medium temperature Tw1, the heat medium exchanges with the exhaust gas in the pre-stage heat exchange section 31 until the medium temperature Tw2 that is the saturation temperature at the supply pressure p2. Heated. A liquid-phase working medium at the medium temperature Tw2 flows into the middle heat exchanger 32. In the intermediate heat exchange section 32, the working medium gradually undergoes a phase transition from the liquid phase state to the gas phase state while maintaining the medium temperature Tw2 by heat exchange with the intermediate heat storage section 33. The working medium in a gas phase at the medium temperature Tw2 flows into the rear heat exchange section 34. In the rear stage heat exchanging unit 34, the working medium is heated to the medium temperature Tw3 higher than the medium temperature Tw2 by heat exchange with the rear stage heat storage unit 35.

  On the other hand, the exhaust gas flows into the rear heat exchange section 34 at the exhaust temperature Te1. In the rear stage heat exchanging section 34, the temperature of the exhaust gas decreases to the exhaust temperature Te2 due to heat exchange with the rear stage heat storage section 35. The post-stage heat storage unit 35 is at the post-stage heat storage temperature Tlat that is lower than the exhaust temperature Te2 and higher than the medium temperature Tw3, and stores the amount of heat based on the post-stage 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 by heat exchange with the middle heat storage section 33. The middle heat storage section 33 is at a middle heat storage temperature Tmid that is lower than the exhaust temperature Te3 and higher than the second temperature T2, and stores the amount of heat based on the middle heat storage temperature Tmid. The middle heat storage unit 33 stores a larger amount of heat than the rear heat storage unit 35, although the temperature is lower than that of the rear heat storage unit 35. 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.

  Note that when the pumping unit 23 is in a stopped state, the circulation of the working medium in the circulation circuit 21 is prohibited, while the inflow of exhaust gas to the evaporator 24 is continued. Therefore, in the middle stage heat storage unit 33, the heat absorption amount due to heat exchange with the exhaust gas is larger than the heat radiation amount for the working medium staying in the middle stage heat exchange unit 32, and the difference between the heat radiation amount and the heat absorption amount is increased. The amount of heat is stored. Similarly, in the rear stage heat storage unit 35, the amount of heat absorbed by the heat exchange with the exhaust gas is larger than the amount of heat released to the working medium staying in the rear stage heat exchange unit 34, and The amount of heat for the difference is stored.

The operation of the above-described waste heat recovery apparatus 20 will be described.
The evaporator 24 of the waste heat recovery apparatus 20 includes a front heat exchange unit 31, a middle heat exchange unit 32 having a middle heat storage unit 33, and a rear heat exchange unit 34 having a rear heat storage unit 35. According to such a configuration, each of the heat storage units 33 and 35 heats the working medium while storing waste heat when the amount of waste heat of the engine 10 is large, and heat stored when the amount of waste heat of the engine 10 is small. The working medium is heated. Thereby, even if the amount of waste heat of the engine 10 changes, the output P of the expander 25 is not easily affected.

  Further, in the waste heat recovery apparatus 20, since the middle heat storage unit 33 and the rear heat storage unit 35 are thermally insulated, direct heat transfer between the middle heat storage unit 33 and the rear heat storage unit 35 is achieved. The configuration is impossible. According to such a configuration, since the temperature is not averaged between the middle heat storage unit 33 and the rear heat storage unit 35, even when the amount of waste heat of the engine 10 is small, the middle heat exchange unit 32 and the rear heat exchange. A temperature difference between the heat storage unit and the working medium is easily secured at each position in each of the units 34.

  Further, as shown in FIG. 5, for example, in the middle stage heat exchange unit 32, the middle stage heat storage temperature Tmid is maintained below the exhaust temperature Te <b> 3 that is the temperature of the exhaust gas flowing out from the middle stage heat exchange unit 32. Further, the working medium flows out from 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 unit 31 is disposed in the pre-stage heat exchange unit 31, the pre-stage heat storage unit is below the exhaust temperature Te4 in FIG. The pre-stage heat storage temperature is maintained. Therefore, the working medium heated by such a front-stage heat storage unit flows out from the front-stage heat exchange unit 31 at a temperature equal to or lower than the previous-stage heat storage temperature, in other words, the exhaust temperature Te4 or lower. That is, when the front stage heat storage unit 31 is disposed in the front stage heat exchange unit 31, the high temperature side (previous stage heat storage unit) and the low temperature side (working medium) at each position of the front stage heat exchange unit 31 than the case shown in FIG. Not only does the temperature difference become small, but it is difficult to raise the working medium to the medium temperature Tw2 unless the exhaust temperature Te4 is higher than the medium temperature Tw2. In contrast, in the waste heat recovery apparatus 20, the evaporator 24 is configured without providing the pre-stage heat storage section in the pre-stage heat exchange section 31, so the high temperature side (exhaust gas) at each position of the pre-stage heat exchange section 31. ) And the low temperature side (working medium) is easily secured, and the working medium is easily heated to the medium temperature Tw2.

  Next, an example of the result of simulation performed on the waste heat recovery apparatus 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 Q common to the above-described waste heat recovery apparatus 20 and the waste heat recovery apparatus of the comparative example is given as an input value. It is a graph which shows transition. The amount of heat input Q is the amount of heat based on the state quantity of the exhaust gas flowing into the evaporator, and the saturation temperature Ts is the temperature of the working medium at a position immediately before flowing into the expander 25. In FIG. 6 and FIG. 7, the solid line has shown the result of the simulation performed for the waste heat recovery apparatus 20 mentioned above. On the other hand, the dotted line does not include the heat storage units 33 and 35, and the result of the simulation performed on the waste heat recovery apparatus of the comparative example in which the flow rate of the working medium in the circulation circuit 21 increases as the heat input Q increases. Is shown. In the waste heat recovery apparatus 20, a correlation was recognized between the saturation temperature Ts and the middle heat storage temperature Tmid.

FIG. 6 shows an example of simulation results when the ratio of the operating state of the engine 10 to the high load state is high.
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 in the heat input Q at that time, that is, the differential element related to the heat input Q. Admitted to do. In addition, it was recognized that both the saturation temperature Ts and the output P tend to continue to decrease in a state where 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 is 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. . And it was recognized that when the amount of heat input Q is extremely large, a surplus heat amount ΔQ is generated in a state where the saturation temperature Ts and the output P are maintained at constant values. The surplus heat amount ΔQ is calculated based on, for example, a difference between a boundary value indicating the presence / absence of the surplus heat amount ΔQ and a value obtained by subtracting the heat amount based on the state quantity 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 apparatus 20, it was recognized that the pumping unit 23 is maintained in the pumping state. Further, both the saturation temperature Ts and the output P gradually decrease even in a state where the heat input amount Q is extremely small, and both the saturation temperature Ts and the output P both decrease even in a state where the heat input amount Q is extremely large. Was observed to rise moderately. That is, it is recognized that both the saturation temperature Ts and the output P change in accordance with an integral factor related to the total amount of heat input Q in a predetermined period immediately before the change in the amount of heat input Q at that time, that is, the amount of heat input Q. It was. Then, it was recognized that the surplus heat amount ΔQ in a state where the heat input amount Q is extremely large as compared with the waste heat recovery apparatus of the comparative example is remarkably small, and the total output amount of the expander 25 is also large.

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

  As shown in FIG. 7, in the waste heat recovery apparatus of the comparative example, it was recognized that both the saturation temperature Ts and the output P change according to a differential element related to the heat input amount Q. Further, since the ratio of the operating state of the engine 10 to the low load state is high, it was confirmed that the saturation temperature Ts is low overall, and the output P of the expander 25 is low overall.

  On the other hand, in the waste heat recovery apparatus 20, the state where the saturation temperature Ts is higher than that of the waste heat recovery apparatus of the comparative example by repeating the stop state and the pumping state of the pumping unit 23 according to the middle heat storage temperature Tmid. Was found to be easy to maintain. Further, for 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, an output P higher than that of the waste heat recovery apparatus of the comparative example is obtained. It was recognized that it was easy to be done. And it was recognized that the total output amount of the expander 25 becomes remarkably large compared with the waste heat recovery apparatus of the comparative example.

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

  (2) The evaporator 24 is a counterflow type heat exchanger in which the flow direction of the working medium and the flow direction of the exhaust gas are set to be opposite to each other in each of the heat exchange units 31, 32, and 34. Accordingly, a temperature difference between the rear heat storage unit 35 and the working medium is more easily ensured in the rear heat exchange unit 34 than in the parallel flow type heat exchanger. The temperature T1 can be set to a lower temperature. As a result, the working medium can be effectively heated using the waste heat of the engine 10.

  (3) The middle stage heat storage unit 33 has a larger heat storage capacity than the rear stage heat storage unit 35. According to such a configuration, it is possible to increase the probability that the phase transition from the liquid phase state that requires the most heat to the gas phase state is performed in the middle heat exchange section 32. Thereby, the probability that the working medium flowing into the rear heat exchange section 34 is in a gas phase state is increased, and a 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, it is possible to raise the temperature of the working medium in the gas phase to a higher temperature in the rear heat exchanging section 34, so that even when the amount of waste heat of the engine 10 is small, higher energy is given to the expander 25. The working medium can be supplied.

  (4) The waste heat recovery apparatus 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 turns the pumping unit 23 when the middle stage heat storage temperature Tmid falls to the second temperature T2. Control to stop. According to such a configuration, when the amount of heat stored in each of the heat storage units 33 and 35 is small, the pumping unit 23 is controlled to be stopped, and heat storage on each of the heat storage units 33 and 35 can be performed intensively. Thereby, since the thermal energy of the working medium supplied to the expander 25 is increased when the pumping unit 23 is in the pumping state, the expander 25 can be operated with higher efficiency.

  (5) In the waste heat recovery apparatus 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 rear heat storage unit 35. According to such a configuration, the amount of heat stored in the middle heat exchange section 32 is grasped with high accuracy, and therefore the phase transition of the working medium from the liquid phase state to the gas phase state is more reliably performed in the middle heat exchange section 32. Can be done. Further, it is possible to acquire the heat storage state with a simple configuration as compared with the case where the heat storage state is acquired based on the middle heat storage temperature Tmid and the rear heat storage temperature Tlat.

  (6) The first temperature T1 and the second temperature T2 are defined based on the saturation temperature Ts1 at the maximum pressure p1. Thereby, a working medium can be circulated in the state whose intermediate | middle stage heat storage temperature Tmid is higher than the saturation temperature of the working medium pumped by the pumping part 23. FIG.

(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 said embodiment can also be suitably changed and implemented as follows.

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

  For example, as shown in FIG. 8, the waste heat recovery device 60 includes the above-described circulation circuit 21, a pressure feeding unit 23 (first pressure feeding unit), an evaporator 24 (first evaporator), an expander 25, and a condenser. 27, a branch circuit 61, a second pumping unit 63, and a second evaporator 64 are provided. The branch circuit 61 is a part of the circulation circuit 21, 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 exchanger. The second evaporator 64 heats the working medium that has passed through the second pumping unit 63 using the exhaust gas flowing upstream of the EGR cooler 18 in the EGR passage 17 as a heat source, thereby converting the working medium in a liquid phase into a gas phase state. Phase transition. In such a configuration, the ECU 50 can control the driving state of the second pumping unit 63 based on the temperature of the middle heat storage unit, similarly to the pumping unit 23.

  According to the waste heat recovery device 60, the waste heat of the engine 10 can be recovered not only from the exhaust gas flowing through the exhaust passage 11, but also from the EGR gas flowing through the EGR passage 17. In addition, 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.

  -1st temperature T1 and 2nd temperature T2 should just be temperature higher than the saturation temperature in the supply pressure p2 of a working medium. Therefore, for example, the ECU 50 acquires the supply pressure p2 of the working medium at a predetermined control cycle based on the driving state of the pressure sensor and the pressure feeding unit 23, and the first temperature T1 and the second temperature based on the acquired supply pressure p2. T2 may be changed.

  -ECU50 is not restricted to the structure which acquires middle stage heat storage temperature Tmid as a parameter | index which shows the heat storage state of the middle stage heat storage part 33, or the heat storage state of the middle stage heat storage part 33 and the back | latter stage heat storage part 35. For example, the ECU 50 may acquire the heat storage state based on the middle-stage heat storage temperature Tmid and the rear-stage heat storage temperature Tlat that is the temperature of the rear-stage heat storage section 35, or acquires the rear-stage 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 a calculation using a model that uses a state quantity indicating the operating state of the engine 10 or a flow rate of the working medium in the circulation circuit 21 as an input value.

The heat storage capacity of the middle heat storage unit 33 may be equal to or less than the heat storage capacity of the rear heat storage unit 35.
The evaporator 24 may be a parallel flow heat exchanger in which the flow direction of the exhaust gas and the flow direction of the working medium are set in the same direction. The evaporator 24 only needs to heat the working medium 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 using a heat transfer tube. Good. In the plate heat exchanger, the plate itself can be set as the heat storage section. In the shell-and-tube heat exchanger, a heat storage unit can be disposed around the heat transfer tube.

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

  DESCRIPTION OF SYMBOLS 10 ... Engine, 11 ... Exhaust passage, 12 ... Exhaust gas purification device, 13 ... Turbine, 14 ... Intake passage, 15 ... Compressor, 16 ... Turbocharger, 17 ... EGR passage, 18 ... EGR cooler, 20 ... Waste heat recovery device, DESCRIPTION OF SYMBOLS 21 ... Circulation circuit, 23 ... Pumping part, 24 ... Evaporator, 25 ... Expander, 26 ... Output shaft, 27 ... Condenser, 31 ... Pre-stage heat exchange part, 32 ... Middle stage heat exchange part, 33 ... Middle stage heat storage part, 34: Rear heat exchange unit, 35: Rear heat storage unit, 36: Insulating unit, 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 unit, 64 ... second evaporator.

Claims (5)

A circulation circuit configured to allow the working medium to circulate;
A pumping unit for pumping the working medium to the circulation circuit;
An evaporator for evaporating the working medium pumped by the pumping section with waste heat of the engine;
An expander that operates by passing the working medium evaporated in the evaporator;
A condenser that condenses the working medium that has passed through the expander,
The evaporator is
A pre-stage heat exchange section in which heat exchange is performed between the exhaust gas of the engine and the working medium;
A middle heat storage section that stores the heat of the exhaust gas, and a heat exchange section that performs heat exchange between the middle heat storage section and the working medium that has passed through the previous heat exchange section;
A rear heat storage section that stores the heat of the exhaust gas, and a rear heat exchange section that performs heat exchange between the rear heat storage section and the working medium that has passed through the middle heat exchange section,
The middle heat storage unit is thermally insulated from the rear heat storage unit. The waste heat recovery apparatus according to claim 1, wherein the evaporator is a counter-flow heat exchanger. The waste heat recovery apparatus according to claim 1, wherein the middle stage heat storage unit has a larger heat storage capacity than the rear stage heat storage unit. A heat storage state acquisition unit for acquiring a heat storage state of the middle heat storage unit;
A control unit for controlling the flow rate of the working medium in the circulation circuit,
The controller 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 where the heat storage amount is smaller than that of the first heat storage state, the working medium in the circulation circuit The waste heat recovery apparatus according to any one of claims 1 to 3, 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 where the detection value of the temperature sensor is higher than the first temperature,
The second heat storage state is a state where the detection value of the temperature sensor is equal to or lower than a second temperature lower than the first temperature,
The waste heat recovery apparatus according to claim 4, wherein the first temperature and the second temperature are higher than a saturation temperature at a supply pressure of a working medium to the evaporator.

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