A coupled sequentially pressurized engine cascade waste heat recovery system and method

Abstract

This invention discloses a coupled, sequentially turbocharged engine cascade waste heat recovery system and method, relating to the field of waste heat energy conversion technology. The system includes: a diesel engine, in which, in a sequential turbocharged configuration, an exhaust branch is connected to the exhaust gas inlets of both the first and second turbines, and an intake branch is connected to the air outlets of both the first and second compressors; an EGR system including an EGR on / off valve and a cylinder bypass valve; heat source equipment in the first Rankine cycle system including a turbine exhaust gas heat exchanger; heat source equipment in the second Rankine cycle system including a dual-purpose heat exchanger and a second turbine exhaust gas heat exchanger; and an exhaust steam heat exchanger for heat exchange between the first and second Rankine cycle systems. This invention achieves cascade waste heat recovery and coupled recovery from multiple heat sources through the exhaust steam heat exchanger, and enables coupled operation or independent operation of the first and second Rankine cycle loops through different operating modes.

Description

Technical Field

[0001] This invention relates to the field of waste heat energy conversion technology, and in particular to a cascaded waste heat recovery system and method for coupled sequentially pressurized engines. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Traditional diesel engines have high power-to-weight ratio, economy, and fuel compatibility, and will continue to dominate the shipping industry in the future. However, in actual operation, about 50% of the total fuel energy is lost to the environment through exhaust, scavenging air, and cooling water.

[0004] Currently, diesel engines are developing towards higher power, smaller size, and lower fuel consumption, which places higher demands on waste heat recovery solutions. Exhaust gas turbocharging technology is one of the important measures to achieve these goals, especially sequential turbocharging systems, which consist of two or more turbochargers connected in parallel. The operating modes of the large and small turbochargers are controlled according to changes in the diesel engine's operating conditions to improve fuel economy, power, and emissions performance under different conditions. The operating mode of the sequential turbocharging system significantly affects the type, quality, and distribution of waste heat. Typical waste heat recovery bottom cycles, such as the organic Rankine cycle, are difficult to directly integrate with sequential turbocharging systems. Therefore, designing an engine waste heat recovery system that achieves multi-heat source coupling recovery based on different operating modes of the sequential turbocharging system is a pressing technical challenge. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a coupled, sequentially turbocharged engine cascade waste heat recovery system and method. This system designs an engine waste heat recovery system that adjusts the waste heat recovery circulation path according to different operating modes of the sequentially turbocharged system, thereby rationally controlling the waste heat recovery system and improving the system's energy recovery utilization rate.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] The first aspect of the present invention provides a coupled sequential turbocharging engine cascade waste heat recovery system, comprising: a diesel engine, a sequential turbocharging system, an EGR system, a first Rankine cycle system, and a second Rankine cycle system;

[0008] The diesel engine is connected to the intake manifold and the exhaust manifold;

[0009] The sequential turbocharging system includes a first turbine, a first compressor, a second turbine, and a second compressor; the first turbine can drive the first compressor, and the second turbine can drive the second compressor; the two exhaust branches of the exhaust manifold are respectively connected to the exhaust gas inlets of the first turbine and the second turbine, and the two intake branches of the intake manifold are respectively connected to the air outlets of the first compressor and the second compressor.

[0010] The EGR system includes an EGR switching valve and a cylinder bypass valve; the EGR switching valve connects the exhaust branch on the exhaust gas inlet side of the second turbine and the intake branch on the air outlet side of the second compressor; the cylinder bypass valve connects the exhaust branch on the exhaust gas inlet side of the first turbine and the intake branch on the air outlet side of the first compressor; a dual-purpose heat exchanger is installed on the intake branch after the EGR switching valve.

[0011] The first Rankine cycle system includes a first working fluid pump, a first expander, and a first condenser. The heat source equipment includes a first turbine exhaust heat exchanger located after the exhaust gas outlet of the first turbine.

[0012] The second Rankine cycle system includes a second working fluid pump, a second expander, and a second condenser. The heat source equipment includes a dual-purpose heat exchanger and a second turbine exhaust gas heat exchanger located after the exhaust outlet of the second turbine.

[0013] The exhaust steam heat exchanger includes a first working fluid passage and a second working fluid passage. The first working fluid passage is connected to a first Rankine cycle system, and the second working fluid passage is connected to a second Rankine cycle system.

[0014] Secondly, the present invention provides a method for recovering waste heat from an engine using a coupled-sequential-pressurization cascade waste heat recovery system, comprising the following steps:

[0015] When the diesel engine is operating at low speed, the second turbine and the second compressor are turned on, while the first turbine and the first compressor are turned off. The first working fluid in the first Rankine cycle system circulates between the cylinder liner water heat exchanger and the first condenser. The second Rankine cycle system is turned on, and the second working fluid flows through the second turbine exhaust gas heat exchanger, the second condenser, and the dual-purpose heat exchanger.

[0016] Optionally, the first turbine switch valve and the first compressor switch valve are closed; the second turbine switch valve and the second compressor switch valve are open; the EGR switch valve and the cylinder bypass valve are closed, the auxiliary fan bypass valve is open, and the auxiliary fan switch valve is closed; the second turbine exhaust gas heat exchanger switch valve is open, the second turbine exhaust gas heat exchanger bypass valve is closed, the A inlet of the second three-way valve is not connected to the B outlet and the C outlet, and the A inlet of the first three-way valve is only connected to the B outlet.

[0017] When the diesel engine is operating at medium speed, the first turbine and the first compressor are turned on, the second turbine and the second compressor are turned off, the first Rankine cycle system is turned on, and the second Rankine cycle system is turned off.

[0018] Optionally, the first turbine switch valve and the first compressor switch valve are open, and the second turbine switch valve and the second compressor switch valve are closed; the EGR switch valve and the cylinder bypass valve are closed; the A inlet of the first three-way valve is not connected to the B outlet and the C outlet; the A inlet of the second three-way valve is not connected to the B outlet and the C outlet.

[0019] When the diesel engine is operating at high speed, the first turbine and the first compressor are turned on, the second turbine and the second compressor are turned on, the first Rankine cycle system is turned on, the second Rankine cycle system is turned on, and the second working fluid flows through the exhaust gas heat exchanger, the dual-purpose heat exchanger, the second turbine exhaust gas heat exchanger, and the second condenser.

[0020] Optionally, the first turbine switch valve and the first compressor switch valve are open, the second turbine switch valve and the second compressor switch valve are open; the EGR switch valve and the cylinder bypass valve are closed; the auxiliary fan switch valve is closed, and the auxiliary fan bypass valve is open; the second turbine exhaust gas heat exchanger switch valve is open, and the second turbine exhaust gas heat exchanger bypass valve is closed; the A inlet of the first three-way valve is simultaneously connected to both the B outlet and the C outlet; the A inlet of the second three-way valve is only connected to the B outlet.

[0021] When it is necessary to introduce some exhaust gas to participate in the in-cylinder combustion process, the first turbine and the first compressor are turned on, the second turbine and the second compressor are turned off, the EGR switch valve and the cylinder bypass valve are turned on, the first Rankine cycle system is turned on, the second Rankine cycle system is turned on, and the second working fluid flows through the exhaust steam heat exchanger and the dual-purpose heat exchanger.

[0022] Optionally, the first turbine switch valve and the first compressor switch valve are open, while the second turbine switch valve and the second compressor switch valve are closed; the EGR switch valve and the cylinder bypass valve are open; the auxiliary fan switch valve is open, while the auxiliary fan bypass valve is closed; the second turbine exhaust gas heat exchanger switch valve is closed; the second turbine exhaust gas heat exchanger bypass valve is open; the A inlet of the first three-way valve is connected only to the C outlet; and the A inlet of the second three-way valve is connected only to the C outlet.

[0023] The beneficial effects of this invention are as follows:

[0024] 1. This invention can realize engine waste heat recovery through multi-heat source coupling recovery according to different operating modes of the successive supercharging system. Through different operating modes, the first Rankine cycle loop and the second Rankine cycle loop can be coupled or operated separately. Heat exchange is achieved between the first Rankine cycle loop and the second Rankine cycle loop through the exhaust steam heat exchanger, thus realizing cascade waste heat recovery.

[0025] 2. This invention includes multiple operating modes and is equipped with a first three-way valve and a second three-way valve. By switching the states of the two three-way valves, the heat source devices in the first Rankine loop and the second Rankine loop can be flexibly adjusted, thereby realizing the coupled recovery of multiple heat sources. Attached Figure Description

[0026] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0027] The diagram exaggerates the spacing or dimensions between parts to show their positions; the diagram is for illustrative purposes only.

[0028] Figure 1 This is a schematic diagram of a coupled, sequentially pressurized, cascaded waste heat recovery system for engines in a specific implementation.

[0029] Figure 2 This is a schematic diagram of a coupled, sequentially pressurized engine cascade waste heat recovery system in a specific implementation at low speeds.

[0030] Figure 3 This is a schematic diagram of a coupled, sequentially pressurized engine cascade waste heat recovery system in a specific implementation at medium speed.

[0031] Figure 4 This is a schematic diagram of a coupled, sequentially pressurized engine cascade waste heat recovery system under high-speed operating conditions in a specific implementation.

[0032] Figure 5 This is a schematic diagram of the working condition of the coupled and successively pressurized engine cascade waste heat recovery system in a specific implementation, in which some exhaust gas is introduced to participate in the in-cylinder combustion process.

[0033] The components include: 1. First compressor; 2. First compressor on / off valve; 3. Intake manifold; 4. Diesel engine; 5. Exhaust manifold; 6. First turbine on / off valve; 7. First turbine; 8. Cylinder bypass valve; 9. Second compressor; 10. Second compressor on / off valve; 11. Dual-purpose heat exchanger; 12. Auxiliary fan on / off valve; 13. Auxiliary fan; 14. Auxiliary fan bypass valve; 15. Second turbine on / off valve; 16. Second turbine; 17. EGR on / off valve; 18. First turbine. 19. First expander; 20. First generator; 21. Exhaust gas heat exchanger; 22. First condenser; 23. First working fluid pump; 24. Cylinder liner water heat exchanger; 25. Second turbine exhaust gas heat exchanger; 26. Second expander; 27. Second generator; 28. Second condenser; 29. ​​Second working fluid pump; 30. First three-way valve; 31. Second three-way valve; 32. Second turbine exhaust gas heat exchanger on / off valve; 33. Second turbine exhaust gas heat exchanger bypass valve. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0035] Example 1

[0036] A coupled sequential turbocharged engine cascade waste heat recovery system includes: a diesel engine, a sequential turbocharger system, an EGR system, a first Rankine cycle system, and a second Rankine cycle system;

[0037] like Figure 1 As shown, the diesel engine 4 connects the intake manifold 3 and the exhaust manifold 5;

[0038] The sequential supercharging system includes a first turbine 7, a first compressor 1, a second turbine 16, and a second compressor 9; the first turbine 7 can drive the first compressor 1, and the second turbine 16 can drive the second compressor 9; the exhaust manifold 5 connects to multiple exhaust branches, and two exhaust branches are respectively connected to the exhaust gas inlets of the first turbine 7 and the second turbine 16; the intake manifold 3 connects to multiple intake branches, and two intake branches are respectively connected to the air outlets of the first compressor 1 and the second compressor 9.

[0039] The EGR system includes an EGR switch valve 17 and a cylinder bypass valve 8; the EGR switch valve 17 connects the exhaust branch on the exhaust gas inlet side of the second turbine 16 and the intake branch on the air outlet side of the second compressor 9, and the cylinder bypass valve 8 connects the exhaust branch on the exhaust gas inlet side of the first turbine 7 and the intake branch on the air outlet side of the first compressor 1; a dual-purpose heat exchanger 11 is installed on the intake branch after the EGR switch valve 17.

[0040] The first Rankine cycle system contains a first working fluid, which includes a first working fluid pump 23, a first expander 19, and a first condenser 22. The heat source equipment includes a first turbine exhaust heat exchanger 18 located after the exhaust gas outlet of the first turbine 7.

[0041] The second Rankine cycle system contains a second working fluid. The second Rankine cycle system includes a second working fluid pump 29, a second expander 26, and a second condenser 28. The heat source equipment includes a dual-purpose heat exchanger 11 and a second turbine exhaust gas heat exchanger 25 located after the exhaust outlet of the second turbine 16.

[0042] The exhaust steam heat exchanger 21 includes a first working fluid passage and a second working fluid passage. The first working fluid passage is connected to the first Rankine cycle system, and the second working fluid passage is connected to the second Rankine cycle system. The exhaust steam heat exchanger 21 is used for heat exchange between the first Rankine cycle system and the second Rankine cycle system.

[0043] Through the above settings, the first Rankine cycle loop and the second Rankine cycle loop can be coupled or operated separately through different operating modes. Heat exchange is achieved between the first Rankine cycle loop and the second Rankine cycle loop through the waste steam heat exchanger 21, realizing cascade waste heat recovery.

[0044] Optionally, the diesel engine 4 is connected to the cylinder liner water circulation system, which is equipped with a cylinder liner water heat exchanger 24. The medium-temperature cylinder liner water of the diesel engine 4 is cooled by the cylinder liner water heat exchanger 24 and then flows back to the diesel engine cylinder liner. The heat source equipment in the first Rankine cycle system includes the cylinder liner water heat exchanger 24.

[0045] Optionally, the exhaust outlet of the first turbine 7 is connected to the exhaust inlet of the first turbine exhaust heat exchanger 18, and the exhaust outlet of the second turbine 16 is connected to the exhaust inlet of the second turbine exhaust heat exchanger 25. The exhaust outlets of the second turbine exhaust heat exchanger 25 and the first turbine exhaust heat exchanger 18 discharge the exhaust gas generated by the diesel engine 4 into the atmospheric environment.

[0046] Optionally, a second turbine switch valve 15 is installed on the exhaust branch between the second turbine 16 and the EGR switch valve 17, and a second compressor switch valve 10 is installed on the intake branch between the second compressor 9 and the EGR switch valve 17.

[0047] Optionally, a first turbine switching valve 6 is installed on the exhaust branch between the first turbine 7 and the cylinder bypass valve 8, and a first compressor switching valve 2 is installed on the intake branch between the first compressor 1 and the cylinder bypass valve 8.

[0048] Optionally, an auxiliary fan 13 is installed on the intake branch between the dual-purpose heat exchanger 11 and the diesel engine 4. An auxiliary fan switch valve 12 is installed between the auxiliary fan 13 and the dual-purpose heat exchanger 11. The air outlet of the auxiliary fan 13 and the air inlet of the auxiliary fan switch valve 12 are connected through an intake pipe equipped with an auxiliary fan bypass valve 14.

[0049] Optionally, the first Rankine cycle system includes a first turbine exhaust heat exchanger 18, a first expander 19, an exhaust steam heat exchanger 21, a first condenser 22, a first working fluid pump 23, and a cylinder liner water heat exchanger 24 connected sequentially along the flow direction of the first working fluid. The working fluid outlet of the cylinder liner water heat exchanger 24 is connected to the working fluid inlet of the first turbine exhaust heat exchanger 18. The first expander 19 is used to drive the first generator 20.

[0050] The heat source in the first Rankine cycle system includes the medium-temperature cylinder liner water in the cylinder liner water heat exchanger 24 and the high-temperature exhaust gas after the first turbine 7. The first working fluid pump 23 sends the first working fluid to the cylinder liner water heat exchanger 24 to exchange heat until it reaches a saturated liquid state. The saturated liquid first working fluid flows through the first turbine exhaust gas heat exchanger 18 and becomes superheated steam. The superheated steam enters the first expander 19 to expand and do work. The medium-temperature exhaust steam after doing work releases heat through the exhaust steam heat exchanger 21 and flows into the first condenser 22 to be cooled to a saturated liquid state and then sent back to the first working fluid pump 23.

[0051] Optionally, the second Rankine cycle system includes a second turbine exhaust heat exchanger 25, a second expander 26, a second condenser 28, a second working fluid pump 29, an exhaust steam heat exchanger 21, and a dual-purpose heat exchanger 11 connected sequentially along the flow direction of the second working fluid. The working fluid outlet of the dual-purpose heat exchanger 11 is connected to the working fluid inlet of the second turbine exhaust heat exchanger 25. The second expander 26 is used to drive the second generator 27. The outlet of the second working fluid pump 29 is also connected to the working fluid inlet of the dual-purpose heat exchanger 11, and the working fluid outlet of the exhaust steam heat exchanger 21 is also connected to the working fluid inlet of the second turbine exhaust heat exchanger 25.

[0052] Optionally, a first three-way valve 30 is installed at the working fluid outlet of the second working fluid pump 29. The A inlet of the first three-way valve 30 is connected to the working fluid outlet of the second working fluid pump 29, the B outlet of the first three-way valve 30 is connected to the working fluid inlet of the dual-purpose heat exchanger 11, and the C outlet of the first three-way valve 30 is connected to the second working fluid inlet of the exhaust steam heat exchanger 21. The on / off states of the first three-way valve 30 include: the A inlet is only connected to the B outlet, or the A inlet is only connected to the C outlet, or the A inlet is connected to both the B outlet and the C outlet, or the A inlet is not connected to either the B outlet or the C outlet.

[0053] Optionally, a second three-way valve 31 is installed at the second working fluid outlet of the exhaust steam heat exchanger 21. The A inlet of the second three-way valve 31 is connected to the second working fluid outlet of the exhaust steam heat exchanger 21, the B outlet of the second three-way valve 31 is connected to the working fluid inlet of the second turbine exhaust gas heat exchanger 25, and the C outlet of the second three-way valve 31 is connected to the working fluid inlet of the dual-purpose heat exchanger 11. The on / off states of the second three-way valve 31 include: the A inlet is only connected to the B outlet, or the A inlet is only connected to the C outlet, or the A inlet is connected to both the B outlet and the C outlet, or the A inlet is not connected to either the B outlet or the C outlet.

[0054] The heat sources in the second Rankine cycle system include the intermediate-temperature air after the second compressor 9, the high-temperature exhaust gas from the EGR, the high-temperature exhaust gas after the second turbine 16, and the intermediate-temperature exhaust steam formed by the first working fluid output from the first expander 19.

[0055] After being pressurized by the second working fluid pump 29, the second working fluid is divided into two parallel paths through the first three-way valve 30: one path flows from the B outlet of the first three-way valve 30 to the dual-purpose heat exchanger 11 to reach a saturated liquid state; the other path flows from the C outlet of the first three-way valve 30 into the exhaust steam heat exchanger 21 to reach a saturated liquid state.

[0056] The saturated liquid second working fluid output from the exhaust heat exchanger 21 flows into the A inlet of the second three-way valve 31 and is further divided into two parallel paths: one path flows out from the B outlet of the second three-way valve 31 and merges with the saturated liquid first working fluid output from the dual-purpose heat exchanger 11; after passing through the second turbine exhaust gas heat exchanger 25, it becomes saturated steam and enters the second expander 26 to do work. The exhaust steam after doing work flows into the second condenser 28 to be cooled to saturated liquid and then sent back to the second working fluid pump 29; the other path flows out from the C outlet of the second three-way valve 31, enters the dual-purpose heat exchanger 11 to become saturated steam, and enters the second expander 26 to do work.

[0057] Therefore, the second working fluid, after being pressurized by the second working fluid pump 29, can flow into the dual-purpose heat exchanger 11 through the first three-way valve 30 and the second three-way valve 31.

[0058] Optionally, the first and second working fluids may have the same or different compositions.

[0059] Optionally, the first working medium can be one of water, organic working medium, or CO2;

[0060] Optionally, the second working medium can be selected from water, organic working medium, or CO2;

[0061] Optionally, the first working medium may be water and the second working medium may be an organic working medium, or the first working medium may be an organic working medium and the second working medium may be water, or the first working medium may be CO2 and the second working medium may be an organic working medium.

[0062] Optionally, a second turbine exhaust gas heat exchanger switch valve 32 is installed at the working fluid inlet of the second turbine exhaust gas heat exchanger 25, and the working fluid inlet of the second turbine exhaust gas heat exchanger switch valve 32 and the working fluid outlet of the second turbine exhaust gas heat exchanger 25 are connected by a pipeline equipped with a second turbine exhaust gas heat exchanger bypass valve 33.

[0063] The method for recovering waste heat from a coupled, sequentially pressurized engine using the aforementioned coupled, sequentially pressurized engine cascade waste heat recovery system includes the following steps:

[0064] like Figure 2As shown, when the diesel engine is in low-speed operation, the second turbine 16 and the second compressor 9 are turned on, the first turbine 7 and the first compressor 1 are turned off, and the first working fluid in the first Rankine cycle system flows through the cylinder liner water heat exchanger 24 and the first condenser 22; the second Rankine cycle system is turned on, and the second working fluid flows through the second turbine exhaust gas heat exchanger 25, the second condenser 28 and the dual-purpose heat exchanger 11.

[0065] Optionally, the first turbine switch valve 6 and the first compressor switch valve 2 are closed; the second turbine switch valve 15 and the second compressor switch valve 10 are open; the EGR switch valve 17, the cylinder bypass valve 8 and the auxiliary fan switch valve 12 are closed; the auxiliary fan bypass valve 14 is open; the second turbine exhaust gas heat exchanger switch valve 32 is open; the second turbine exhaust gas heat exchanger bypass valve 33 is closed; the A inlet of the second three-way valve 31 is not connected to the B outlet and the C outlet; and the A inlet of the first three-way valve 30 is only connected to the B outlet.

[0066] At this time, the second working fluid in the second Rankine cycle absorbs the heat from the medium-temperature air after the second compressor 9 through the dual-purpose heat exchanger 11, and absorbs the heat from the high-temperature exhaust gas after the second turbine 16 through the second turbine exhaust gas heat exchanger 25. After being pressurized by the second working fluid pump 29, the second working fluid flows into the dual-purpose heat exchanger 11 to reach a saturated liquid state, and continues to flow into the second turbine exhaust gas heat exchanger 25 through the second turbine exhaust gas heat exchanger switch valve 32 to form superheated steam. The superheated steam does work through the second expander 26 to form exhaust steam, which is cooled by the second condenser 28 and then sent back to the second working fluid pump 29, realizing the efficient recovery of energy from the air after the second compressor 9 and the exhaust gas after the second turbine 16 under low speed conditions.

[0067] like Figure 3 As shown, when the diesel engine 4 is in medium speed operation, the first turbine 7 and the first compressor 1 are turned on, the second turbine 16 and the second compressor 9 are turned off, the first Rankine cycle system is turned on, and the second Rankine cycle system is turned off.

[0068] Optionally, the first turbine switch valve 6 and the first compressor switch valve 2 are open, and the second turbine switch valve 15 and the second compressor switch valve 10 are closed; the EGR switch valve 17 and the cylinder bypass valve 8 are closed; the A inlet of the first three-way valve 30 is not connected to the B outlet and the C outlet; the A inlet of the second three-way valve 31 is not connected to the B outlet and the C outlet.

[0069] At this time, the first working fluid in the first Rankine cycle loop absorbs the heat of the medium-temperature cylinder liner water of the diesel engine 4 through the cylinder liner water heat exchanger 24, and absorbs the heat of the high-temperature exhaust gas after the first turbine 7 through the first turbine exhaust gas heat exchanger 18, thereby achieving efficient recovery of the cylinder liner water of the diesel engine 4 and the exhaust energy after the first turbine 7 under medium speed conditions.

[0070] like Figure 4As shown, when the diesel engine 4 is in high-speed operation, the first turbine 7 and the first compressor 1 are turned on, the second turbine 16 and the second compressor 9 are turned on, the first Rankine cycle system is turned on, the second Rankine cycle system is turned on, and the second working fluid flows through the exhaust steam heat exchanger 21, the dual-purpose heat exchanger 11, the second turbine exhaust gas heat exchanger 25 and the second condenser 28.

[0071] Optionally, the first turbine switch valve 6 and the first compressor switch valve 2 are open, the second turbine switch valve 15 and the second compressor switch valve 10 are open; the EGR switch valve 17 and the cylinder bypass valve 8 are closed; the auxiliary fan switch valve 12 is closed, and the auxiliary fan bypass valve 14 is open; the second turbine exhaust gas heat exchanger switch valve 32 is open, and the second turbine exhaust gas heat exchanger bypass valve 33 is closed; the A inlet of the first three-way valve 30 is simultaneously connected to both the B outlet and the C outlet; the A inlet of the second three-way valve 31 is only connected to the B outlet.

[0072] At this time, the state of the first Rankine cycle loop is the same as when the diesel engine 4 is in the medium-high speed condition; in the second Rankine cycle loop, the second working fluid absorbs the heat of the medium-temperature exhaust gas at the outlet of the first expander 19 through the exhaust gas heat exchanger 21, absorbs the heat of the medium-temperature air after the second compressor 9 through the dual-purpose heat exchanger 11, and absorbs the heat of the exhaust gas after the second turbine 16 through the second turbine exhaust gas heat exchanger 25.

[0073] like Figure 5 As shown, when some exhaust gas needs to be introduced to participate in the in-cylinder combustion process, the first turbine 7 and the first compressor 1 are turned on, the second turbine 16 and the second compressor 9 are turned off, the EGR switch valve 17 and the cylinder bypass valve 8 are turned on, the first Rankine cycle system is turned on, the second Rankine cycle system is turned on, and the second working fluid flows through the exhaust steam heat exchanger 21 and the dual-purpose heat exchanger 11.

[0074] Optionally, the first turbine switch valve 6 and the first compressor switch valve 2 are open, while the second turbine switch valve 15 and the second compressor switch valve 10 are closed; the auxiliary fan switch valve 12 is open, and the auxiliary fan bypass valve 14 is closed; the second turbine exhaust gas heat exchanger switch valve 32 is closed; the second turbine exhaust gas heat exchanger bypass valve 33 is open; the A inlet of the first three-way valve 30 is connected only to the C outlet; and the A inlet of the second three-way valve 31 is connected only to the C outlet.

[0075] At this time, part of the air flowing through the first compressor switch valve 2 flows into the exhaust manifold 5 through the cylinder bypass valve 8. The high-temperature exhaust from one exhaust branch enters the dual-purpose heat exchanger 11 through the EGR switch valve 17, and then enters the intake manifold 3 through the auxiliary fan 13 to participate in the in-cylinder combustion process of the diesel engine 4. The state of the first Rankine cycle loop is the same as when the diesel engine 4 is in the medium-high speed condition; in the second Rankine cycle loop, the second working fluid absorbs the heat of the EGR exhaust gas through the dual-purpose heat exchanger 11, and the second working fluid absorbs the heat of the medium-temperature exhaust gas in the first Rankine cycle system through the exhaust steam heat exchanger 21.

[0076] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A coupled, sequentially pressurized, cascaded waste heat recovery system for an engine, characterized in that, include: Diesel engine, sequential turbocharging system, EGR system, first Rankine cycle system and second Rankine cycle system; The diesel engine is connected to the intake manifold and the exhaust manifold; The sequential supercharging system includes a first turbine, a first compressor, a second turbine, and a second compressor; the first turbine can drive the first compressor, and the second turbine can drive the second compressor; the two exhaust branches of the exhaust manifold are respectively connected to the exhaust gas inlets of the first turbine and the second turbine, and the two intake branches of the intake manifold are respectively connected to the air outlets of the first compressor and the second compressor. The EGR system includes an EGR switching valve and a cylinder bypass valve; the EGR switching valve connects the exhaust branch on the exhaust gas inlet side of the second turbine and the intake branch on the air outlet side of the second compressor; the cylinder bypass valve connects the exhaust branch on the exhaust gas inlet side of the first turbine and the intake branch on the air outlet side of the first compressor; a dual-purpose heat exchanger is installed on the intake branch after the EGR switching valve. The first Rankine cycle system includes a first working fluid pump, a first expander and a first condenser, and the heat source equipment includes a first turbine exhaust heat exchanger disposed after the exhaust gas outlet of the first turbine. The second Rankine cycle system includes a second working fluid pump, a second expander and a second condenser, and the heat source equipment includes: the dual-purpose heat exchanger and a second turbine exhaust heat exchanger disposed after the exhaust gas outlet of the second turbine; The exhaust steam heat exchanger includes a first working fluid passage and a second working fluid passage. The first working fluid passage is connected to the first Rankine cycle system, and the second working fluid passage is connected to the second Rankine cycle system.

2. The coupled sequential pressurization engine cascade waste heat recovery system according to claim 1, characterized in that, The diesel engine is connected to the cylinder liner water circulation system, which is equipped with a cylinder liner water heat exchanger. The medium-temperature cylinder liner water of the diesel engine is cooled by the cylinder liner water heat exchanger and then flows back to the diesel engine cylinder liner. The heat source equipment in the first Rankine cycle system includes the cylinder liner water heat exchanger.

3. The coupled sequential pressurization engine cascade waste heat recovery system according to claim 1, characterized in that, The exhaust outlet of the first turbine is connected to the exhaust inlet of the first turbine exhaust heat exchanger, and the exhaust outlet of the second turbine is connected to the exhaust inlet of the second turbine exhaust heat exchanger. The exhaust outlets of the second turbine exhaust heat exchanger and the first turbine exhaust heat exchanger discharge the exhaust gas generated by the diesel engine into the atmosphere. A second turbine switch valve is installed on the exhaust branch between the second turbine and the EGR switch valve, and a second compressor switch valve is installed on the intake branch between the second compressor and the EGR switch valve. A first turbine switching valve is installed on the exhaust branch between the first turbine and the cylinder bypass valve, and a first compressor switching valve is installed on the intake branch between the first compressor and the cylinder bypass valve. An auxiliary fan is installed on the intake branch between the dual-purpose heat exchanger and the diesel engine. An auxiliary fan switch valve is installed between the auxiliary fan and the dual-purpose heat exchanger. The air outlet of the auxiliary fan and the air inlet of the auxiliary fan switch valve are connected through an intake pipe equipped with an auxiliary fan bypass valve.

4. The coupled sequential pressurization engine cascade waste heat recovery system according to claim 1, characterized in that, The first Rankine cycle system includes a first turbine exhaust gas heat exchanger, a first expander, an exhaust steam heat exchanger, a first condenser, a first working fluid pump, and a cylinder liner water heat exchanger connected in sequence along the flow direction of the first working fluid. The working fluid outlet of the cylinder liner water heat exchanger is connected to the working fluid inlet of the first turbine exhaust gas heat exchanger. The first expander is used to drive the first generator. The heat source in the first Rankine cycle system includes the medium-temperature cylinder liner water in the cylinder liner water heat exchanger and the high-temperature exhaust gas after the first turbine. The first working fluid pump sends the first working fluid to the cylinder liner water heat exchanger to exchange heat until it reaches a saturated liquid state. The saturated liquid first working fluid flows through the first turbine exhaust gas heat exchanger and becomes superheated steam. The superheated steam enters the first expander to expand and do work. The medium-temperature exhaust steam after doing work releases heat through the exhaust steam heat exchanger and flows into the first condenser to cool to a saturated liquid state before being sent back to the first working fluid pump.

5. The coupled sequential pressurization engine cascade waste heat recovery system according to claim 1, characterized in that, The second Rankine cycle system includes a second turbine exhaust gas heat exchanger, a second expander, a second condenser, a second working fluid pump, a waste steam heat exchanger, and a dual-purpose heat exchanger, which are connected sequentially along the flow direction of the second working fluid. The working fluid outlet of the dual-purpose heat exchanger is connected to the working fluid inlet of the second turbine exhaust gas heat exchanger. The second expander is used to drive the second generator. The outlet of the second working fluid pump is also connected to the working fluid inlet of the dual-purpose heat exchanger, and the working fluid outlet of the waste steam heat exchanger is also connected to the working fluid inlet of the second turbine exhaust gas heat exchanger. The working fluid outlet of the second working fluid pump is equipped with a first three-way valve. The A inlet of the first three-way valve is connected to the working fluid outlet of the second working fluid pump, the B outlet of the first three-way valve is connected to the working fluid inlet of the dual-purpose heat exchanger, and the C outlet of the first three-way valve is connected to the second working fluid inlet of the exhaust steam heat exchanger. The exhaust steam heat exchanger is equipped with a second three-way valve at its second working fluid outlet. The A inlet of the second three-way valve is connected to the second working fluid outlet of the exhaust steam heat exchanger, the B outlet of the second three-way valve is connected to the working fluid inlet of the second turbine exhaust gas heat exchanger, and the C outlet of the second three-way valve is connected to the working fluid inlet of the dual-purpose heat exchanger.

6. The coupled sequential pressurization engine cascade waste heat recovery system according to claim 5, characterized in that, The heat sources in the second Rankine cycle system include the intermediate-temperature air after the second compressor, the high-temperature exhaust gas from the EGR, the high-temperature exhaust gas after the second turbine, and the intermediate-temperature exhaust steam formed by the first working fluid output from the first expander. After being pressurized by the second working fluid pump, the second working fluid is divided into two parallel paths through the first three-way valve: one path flows from the B outlet of the first three-way valve to the dual-purpose heat exchanger to reach saturated liquid state; the other path flows from the C outlet of the first three-way valve into the exhaust steam heat exchanger to reach saturated liquid state. The saturated liquid second working fluid output from the exhaust heat exchanger flows into inlet A of the second three-way valve and is further divided into two parallel paths: one path flows out from outlet B of the second three-way valve and merges with the saturated liquid first working fluid output from the dual-purpose heat exchanger; it then passes through the second turbine exhaust heat exchanger and enters the second expander to do work. The exhaust steam after doing work flows into the second condenser to be cooled to saturated liquid and is then sent back to the second working fluid pump; the other path flows out from outlet C of the second three-way valve, enters the dual-purpose heat exchanger to become saturated steam, and then enters the second expander to do work.

7. The coupled sequentially pressurized engine cascade waste heat recovery system according to claim 6, characterized in that, The working fluid inlet of the second turbine exhaust gas heat exchanger is equipped with a second turbine exhaust gas heat exchanger switch valve. The working fluid inlet of the second turbine exhaust gas heat exchanger switch valve and the working fluid outlet of the second turbine exhaust gas heat exchanger are connected by a pipeline equipped with a second turbine exhaust gas heat exchanger bypass valve.

8. The coupled sequentially pressurized engine cascade waste heat recovery system according to claim 1, characterized in that, The composition of the first working fluid flowing in the first Rankine cycle system and the second working fluid flowing in the second Rankine cycle system may be the same or different.

9. A method for recovering waste heat from an engine using a coupled-sequential-boosting cascaded waste heat recovery system as described in any one of claims 1-8, characterized in that, When the diesel engine is operating at low speed, the second turbine and the second compressor are turned on, while the first turbine and the first compressor are turned off. The first working fluid in the first Rankine cycle system flows through the cylinder liner water heat exchanger and the first condenser. The second Rankine cycle system is turned on, and the second working fluid flows through the second turbine exhaust gas heat exchanger, the second condenser, and the dual-purpose heat exchanger. The first turbine switch valve and the first compressor switch valve are closed; the second turbine switch valve and the second compressor switch valve are open; the EGR switch valve, the cylinder bypass valve, and the auxiliary fan switch valve are closed; the auxiliary fan bypass valve is open; the second turbine exhaust gas heat exchanger bypass valve is closed; the A inlet of the second three-way valve is not connected to the B outlet and the C outlet; and the A inlet of the first three-way valve is only connected to the B outlet.

10. The cascade waste heat recovery method for coupled sequentially pressurized engines according to claim 9, characterized in that, When the diesel engine is operating at medium speed, the first turbine and first compressor are on, the second turbine and second compressor are off, the first Rankine cycle system is on, and the second Rankine cycle system is off; the first turbine switching valve and the first compressor switching valve are on, and the second turbine switching valve and the second compressor switching valve are off; the EGR switching valve and the cylinder bypass valve are off; the A inlet of the first three-way valve is not connected to the B outlet and the C outlet; the A inlet of the second three-way valve is not connected to the B outlet and the C outlet. Alternatively, when the diesel engine is operating at high speed, the first turbine and first compressor are activated, the second turbine and second compressor are activated, the first Rankine cycle system is activated, the second Rankine cycle system is activated, and the second working fluid flows through the exhaust gas heat exchanger, the dual-purpose heat exchanger, the second turbine exhaust gas heat exchanger, and the second condenser; the first turbine on / off valve and the first compressor on / off valve are activated, as are the second turbine on / off valve and the second compressor on / off valve; the EGR on / off valve and the cylinder bypass valve are closed; the auxiliary fan on / off valve is closed, and the auxiliary fan bypass valve is open; the second turbine exhaust gas heat exchanger on / off valve is open, and the second turbine exhaust gas heat exchanger bypass valve is closed; the A inlet of the first three-way valve is simultaneously connected to both the B outlet and the C outlet; the A inlet of the second three-way valve is only connected to the B outlet. Alternatively, when it is necessary to introduce some exhaust gas to participate in the in-cylinder combustion process, the first turbine and the first compressor are turned on, the second turbine and the second compressor are turned off, the EGR switch valve and the cylinder bypass valve are turned on, the first Rankine cycle system is turned on, the second Rankine cycle system is turned on, and the second working fluid flows through the exhaust steam heat exchanger and the dual-purpose heat exchanger. The first turbine switch valve and the first compressor switch valve are open, while the second turbine switch valve and the second compressor switch valve are closed; the auxiliary fan switch valve is open, while the auxiliary fan bypass valve is closed; the second turbine exhaust gas heat exchanger switch valve is closed; the second turbine exhaust gas heat exchanger bypass valve is open; the A inlet of the first three-way valve is connected only to the C outlet; the A inlet of the second three-way valve is connected only to the C outlet.

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