A circulation system and method for recovering waste heat from an EGR diesel engine

Abstract

A circulation system and method for recovering waste heat from an EGR diesel engine, comprising a supercritical carbon dioxide Brayton cycle and an organic Rankine cycle. The turbine after the EGR diesel engine and the EGR exhaust gas are used as low-temperature and high-temperature heat sources on the high-temperature sides of the heat exchanger and the EGR cooler to heat the supercritical carbon dioxide working fluid flowing in from the regenerator, respectively. The exhaust gas that has done work in the turbine reaches the low-temperature evaporator through the regenerator, transfers the waste heat to the organic working fluid in the organic Rankine cycle, and then completes a supercritical carbon dioxide Brayton cycle through the precooler and the compressor. The heat of the supercritical carbon dioxide on the high-temperature side of the low-temperature evaporator and the heat of the air on the high-temperature side of the intercooler are used as low-temperature and high-temperature heat sources to heat the organic working fluid, respectively. The exhaust gas that has done work in the turbine is sequentially condensed by the condenser, pressurized by the working fluid pump, and enters the low-temperature evaporator again to complete the organic Rankine cycle. The present invention improves economy and fuel utilization.

Description

Technical Field

[0001] The present invention relates to the technical field of waste heat recovery systems, and in particular to a circulation system and method for recovering waste heat from an EGR diesel engine. Background Art

[0002] EGR diesel engine is a common power device. It uses exhaust gas recirculation (EGR) technology to effectively reduce the generation of NOx at medium and high loads of diesel engines. However, the exhaust gas used for recirculation must be cooled by the EGR cooler before entering the intake pipe. The heat energy of this part of the exhaust gas is usually transferred to the cooling medium in the EGR cooler and wasted. In addition, the exhaust gas after the turbine is directly discharged to the atmosphere, and the air after the supercharger transfers the heat energy to the cooling medium in the intercooler. For diesel engines with high EGR rates, EGR exhaust gas, exhaust gas after the turbine and supercharged air account for more than one-third of the fuel energy, especially the temperature of EGR exhaust gas and exhaust gas after the turbine can reach more than 500°C. Existing diesel engine waste heat recovery systems mostly use organic Rankine cycles to recover the heat energy of exhaust gas after the turbine and cylinder cooling water jackets, and fail to make full use of EGR exhaust gas and supercharged air; for supercritical carbon dioxide Brayton cycle, the low-temperature waste heat before the precooler cannot be recovered. Summary of the invention

[0003] In order to overcome the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a circulation system and method for EGR diesel engine waste heat recovery, which is used to realize waste heat recovery of heat sources of different temperatures of the diesel engine and low-temperature supercritical carbon dioxide before the precooler, realize the cascade utilization of thermal energy, and improve the economy and fuel utilization without much increase in the volume of the entire system.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] A circulation system for recovering waste heat from an EGR diesel engine, comprising a supercritical carbon dioxide Brayton cycle and an organic Rankine cycle, wherein the heat source of the supercritical carbon dioxide Brayton cycle is the exhaust gas after the turbine and the EGR, and the heat source of the organic Rankine cycle is supercritical carbon dioxide and pressurized air;

[0006] The supercritical carbon dioxide Brayton cycle comprises a precooler 7, a compressor 8, a regenerator 5, a heat exchanger 4, an EGR cooler 3, a supercritical carbon dioxide turbine 1, a generator 2, and a low-temperature evaporator 6;

[0007] The outlet of the high temperature side of the precooler 7 is connected to the inlet of the compressor 8, the outlet of the compressor 8 is connected to the inlet of the low temperature side of the regenerator 5, the outlet of the low temperature side of the regenerator 5 is connected to the inlet of the low temperature side of the heat exchanger 4, the outlet of the low temperature side of the heat exchanger 4 is connected to the inlet of the low temperature side of the EGR cooler 3, the outlet of the low temperature side of the EGR cooler 3 is connected to the inlet of the supercritical carbon dioxide turbine 1, the supercritical carbon dioxide turbine 1 is connected to the generator 2, the outlet of the supercritical carbon dioxide turbine 1 is connected to the inlet of the high temperature side of the regenerator 5, the outlet of the high temperature side of the regenerator 5 is connected to the inlet of the high temperature side of the low temperature evaporator 6, and the outlet of the high temperature side of the low temperature evaporator 6 is connected to the inlet of the high temperature side of the precooler 7.

[0008] The precooler 7 includes a supercritical carbon dioxide high temperature side and a cooling medium low temperature side, the regenerator 5 includes a supercritical carbon dioxide high temperature side and a low temperature side, the heat exchanger 4 includes a turbine exhaust gas high temperature side and a supercritical carbon dioxide low temperature side, the EGR cooler 3 includes an EGR exhaust gas high temperature side and a supercritical carbon dioxide low temperature side, and the low temperature evaporator 6 includes a supercritical carbon dioxide high temperature side and an organic working fluid low temperature side.

[0009] The EGR exhaust gas high temperature side inlet of the EGR cooler 3 is used to be connected to the EGR exhaust gas end discharged from the diesel engine 16 .

[0010] The diesel engine 16 is provided with a turbine 14 and a compressor 15 . The turbine 14 drives the compressor 15 to form a diesel engine exhaust gas turbocharging system to form post-turbine exhaust gas, which is input into the post-turbine exhaust gas high-temperature side of the heat exchanger 4 .

[0011] The organic Rankine cycle comprises a low-temperature evaporator 6, an intercooler 9, an organic working fluid turbine 10, a generator 2 11, a condenser 12 and a working fluid pump 13;

[0012] The low-temperature side outlet of the low-temperature evaporator 6 is connected to the low-temperature side inlet of the intercooler 9, the low-temperature side outlet of the intercooler 9 is connected to the inlet of the organic working fluid turbine 10, the organic working fluid turbine 10 is connected to the generator 2 11, the outlet of the organic working fluid turbine 10 is connected to the high-temperature side inlet of the condenser 12, the high-temperature side outlet of the condenser 12 is connected to the inlet of the working fluid pump 13, and the outlet of the working fluid pump 13 is connected to the low-temperature side inlet of the low-temperature evaporator 6.

[0013] The low-temperature evaporator 6 includes a supercritical carbon dioxide high-temperature side and an organic working medium low-temperature side, the intercooler 9 includes a boosted air high-temperature side and an organic working medium low-temperature side, and the condenser 12 includes an organic working medium high-temperature side and a condensing medium low-temperature side.

[0014] The high temperature side output end of the intercooler 9 is connected to the diesel engine 16, and the fresh air is connected to the high temperature side input end of the intercooler 9 via the compressor 15. A circulation method for recovering waste heat from an EGR diesel engine comprises the following steps:

[0015] The supercritical carbon dioxide first enters the low temperature side of the regenerator 5 for preheating, and then enters the low temperature side of the heat exchanger 4 and the EGR cooler 3 in turn to absorb the heat of the exhaust gas after the EGR diesel engine turbine and the EGR exhaust gas. The high temperature and high pressure supercritical carbon dioxide expands in the supercritical carbon dioxide turbine 1 to do work, driving the generator 2 to generate electricity. After the work is done, the exhaust gas passes through the regenerator 5 and reaches the high temperature side of the low temperature evaporator 6 to preheat the organic working medium on the low temperature side. Then, it enters the precooler 7 and the compressor 8 in turn, and returns to the low temperature side inlet of the regenerator 5, completing a supercritical carbon dioxide Brayton cycle.

[0016] The organic working fluid first absorbs the heat of the supercritical carbon dioxide on the high-temperature side at the low-temperature side of the low-temperature evaporator 6, and then enters the low-temperature side of the intercooler 9 to absorb the heat of the high-temperature side boosted air, while reducing the temperature of the boosted air to meet the intake conditions of the diesel engine. The organic working fluid then enters the organic working fluid turbine 10 to perform work, driving the generator 2 11 to generate electricity. The exhaust gas that has completed the work is condensed by the condenser 12 and pressurized by the working fluid pump 13, and returns to the low-temperature side inlet of the low-temperature evaporator 6, completing an organic Rankine cycle.

[0017] Beneficial effects of the present invention:

[0018] The advantage of the present invention is that it combines the advantages of the supercritical carbon dioxide Brayton cycle with the organic Rankine cycle, recovers the waste heat of the EGR diesel engine EGR exhaust gas, the exhaust gas after the turbine, and the air after the supercharger step by step according to the temperature, and utilizes the low-temperature waste heat before the precooler in the supercritical carbon dioxide Brayton cycle, realizing the cascade utilization of the system's thermal energy. Since the supercritical carbon dioxide Brayton cycle system has a compact structure, and the electricity generated by supercritical carbon dioxide and organic working fluids can be used for both storage and power output, the economy and fuel utilization rate are improved under the premise that the volume of the entire system does not increase much. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The diagram is a schematic diagram of a circulation system and method for recovering waste heat from an EGR diesel engine in an embodiment of the present invention.

[0020] Description of reference numerals:

[0021] 1-supercritical carbon dioxide turbine; 2-generator 1; 3-EGR cooler; 4-heat exchanger; 5-supercritical carbon dioxide regenerator; 6-low-temperature evaporator; 7-supercritical carbon dioxide precooler; 8-supercritical carbon dioxide compressor; 9-intercooler; 10-organic working fluid turbine; 11-generator 2; 12-condenser; 13-working fluid pump; 14-turbine; 15-compressor; 16-diesel engine DETAILED DESCRIPTION

[0022] The present invention is further described in detail below in conjunction with embodiments.

[0023] Figure 1 It is a circulation system and method for EGR diesel engine waste heat recovery in the embodiment of the present invention, including a supercritical carbon dioxide Brayton cycle and an organic Rankine cycle for waste heat recovery. It is characterized in that: a precooler 7, a compressor 8, a regenerator 5, a heat exchanger 4, an EGR cooler 3, a supercritical carbon dioxide turbine 1, a generator 2, and a low-temperature evaporator 6 constitute a supercritical carbon dioxide Brayton cycle; a low-temperature evaporator 6, an intercooler 9, an organic working fluid turbine 10, a condenser 12 and a working fluid pump 13 constitute an organic Rankine cycle.

[0024] Specifically, for the supercritical carbon dioxide Brayton cycle, the regenerator 5 includes a supercritical carbon dioxide high temperature side and a low temperature side, the heat exchanger 4 includes a supercritical carbon dioxide low temperature side and a turbine exhaust gas high temperature side, the EGR cooler 3 includes a supercritical carbon dioxide low temperature side and an EGR exhaust gas high temperature side, the low temperature evaporator 6 includes a supercritical carbon dioxide high temperature side and an organic working fluid low temperature side, and the precooler 7 includes a supercritical carbon dioxide high temperature side and a precooling working fluid low temperature side.

[0025] The exhaust gas discharged from the exhaust pipe of the diesel engine is divided into two streams, one of which passes through the turbine 14 to drive the compressor 15 to form the diesel engine exhaust gas turbocharger system, and the other exhaust gas does not pass through the turbine and is used for exhaust gas recirculation, namely EGR exhaust gas. The exhaust gas after the turbine expands and does work, and its pressure and temperature are lower than the EGR exhaust gas. The high-temperature sides of these two exhaust gases in the heat exchanger 4 and the EGR cooler 3 are used as low-temperature and high-temperature heat sources of the supercritical carbon dioxide Brayton cycle to heat the supercritical carbon dioxide flowing out of the low-temperature side of the regenerator 5. The supercritical carbon dioxide then expands and does work in the supercritical carbon dioxide turbine 1, driving the generator 2 to generate electricity. After the exhaust gas has done work, it passes through the high-temperature side of the regenerator 5 and reaches the high-temperature side of the low-temperature evaporator 6 to preheat the organic working medium on the low-temperature side, and then enters the high-temperature side of the precooler 7, the compressor 8 and the low-temperature side of the regenerator 5 in sequence, completing a supercritical carbon dioxide Brayton cycle.

[0026] It should be noted that the regenerator 5 given in this example can be either a single regenerator or divided into multiple regenerators. In this example, the compressor 8 can be driven by a motor or directly driven by the supercritical carbon dioxide turbine 1. Obviously, the illustrated embodiments are only part of the embodiments of the present invention. Based on the embodiments of the present invention, any changes or equivalent substitutions to the illustrated embodiments by those skilled in the art without creative work shall fall within the scope of protection of the present invention.

[0027] Specifically, for the organic Rankine cycle, the low-temperature evaporator 6 includes a supercritical carbon dioxide high-temperature side and an organic working fluid low-temperature side, the intercooler 9 includes an organic working fluid low-temperature side and a boosted air high-temperature side, and the condenser 12 includes an organic working fluid high-temperature side and a condensing medium low-temperature side.

[0028] The supercritical carbon dioxide on the high temperature side of the low temperature evaporator 6 serves as the low temperature heat source of the organic Rankine cycle. The temperature and pressure of the fresh air increase after being pressurized by the diesel compressor 15. The heat energy needs to be transferred to the organic working fluid on the low temperature side at the high temperature side of the intercooler 9 to reduce the temperature to meet the diesel engine intake conditions. This is the high temperature heat source of the organic Rankine cycle. The organic working fluid then enters the organic working fluid turbine 10 to perform work, driving the generator 2 11 to generate electricity. The exhaust gas that has completed the work is condensed on the high temperature side of the condenser 12 in turn, pressurized by the working fluid pump 13, and returned to the low temperature side of the low temperature evaporator 6, completing an organic Rankine cycle.

[0029] It can be seen from the above embodiments that the present invention provides a circulation system and method for EGR diesel engine waste heat recovery, including a supercritical carbon dioxide Brayton cycle and an organic Rankine cycle for waste heat recovery. Combining the advantages of the supercritical carbon dioxide Brayton cycle in medium-temperature heat source and the organic Rankine cycle in low-temperature heat source, the waste heat of the EGR diesel engine EGR exhaust gas, the exhaust gas after the turbine, and the air after the supercharger is recovered step by step according to the temperature, and the low-temperature waste heat before the precooler in the supercritical carbon dioxide Brayton cycle is utilized to achieve the cascade utilization of the system's thermal energy. Since the supercritical carbon dioxide Brayton cycle system has a compact structure, and the electricity generated by supercritical carbon dioxide and organic working fluids can be used for both storage and power output, the economy and fuel utilization are improved without increasing the volume of the entire system.

[0030] As a new type of power cycle, the supercritical carbon dioxide Brayton cycle has a compact and flexible system structure and high thermal conversion efficiency, and is suitable for waste heat recovery from medium-temperature heat sources. The organic Rankine cycle is suitable for waste heat recovery from low-temperature heat sources. Combining the two can fully realize the waste heat recovery of heat sources of different temperatures before the diesel engine and the precooler and the cascade utilization of thermal energy. Finally, it should be noted that the above embodiments are only part of the embodiments of the present invention, and those skilled in the art can still modify or replace the aforementioned embodiments with equivalents, and these modifications or replacements should be included in the protection scope of the present invention.

Claims

1. A circulation system for recovering waste heat from an EGR diesel engine, characterized in that: It includes supercritical carbon dioxide Brayton cycle and organic Rankine cycle. The heat source of supercritical carbon dioxide Brayton cycle is the exhaust gas after turbine and EGR, and the heat source of organic Rankine cycle is supercritical carbon dioxide and pressurized air. The supercritical carbon dioxide Brayton cycle comprises a precooler (7), a compressor (8), a regenerator (5), a heat exchanger (4), an EGR cooler (3), a supercritical carbon dioxide turbine (1), a generator (2), and a low-temperature evaporator (6); The outlet of the high temperature side of the precooler (7) is connected to the inlet of the compressor (8), the outlet of the compressor (8) is connected to the inlet of the low temperature side of the regenerator (5), the outlet of the low temperature side of the regenerator (5) is connected to the inlet of the low temperature side of the heat exchanger (4), the outlet of the low temperature side of the heat exchanger (4) is connected to the inlet of the low temperature side of the EGR cooler (3), the outlet of the low temperature side of the EGR cooler (3) is connected to the inlet of the supercritical carbon dioxide turbine (1), the supercritical carbon dioxide turbine (1) is connected to the generator 1 (2), the outlet of the supercritical carbon dioxide turbine (1) is connected to the inlet of the high temperature side of the regenerator (5), the outlet of the high temperature side of the regenerator (5) is connected to the inlet of the high temperature side of the low temperature evaporator (6), and the outlet of the high temperature side of the low temperature evaporator (6) is connected to the inlet of the high temperature side of the precooler (7); The precooler (7) includes a supercritical carbon dioxide high temperature side and a cooling medium low temperature side, the regenerator (5) includes a supercritical carbon dioxide high temperature side and a low temperature side, the heat exchanger (4) includes a turbine exhaust gas high temperature side and a supercritical carbon dioxide low temperature side, the EGR cooler (3) includes an EGR exhaust gas high temperature side and a supercritical carbon dioxide low temperature side, and the low temperature evaporator (6) includes a supercritical carbon dioxide high temperature side and an organic working medium low temperature side; The EGR exhaust gas high temperature side inlet of the EGR cooler (3) is used to be connected to the EGR exhaust gas end discharged from the diesel engine (16); The diesel engine (16) is provided with a turbine (14) and a compressor (15), the turbine (14) drives the compressor (15) to form a diesel engine exhaust gas turbocharging system, forming post-turbine exhaust gas, and the post-turbine exhaust gas is input into the post-turbine exhaust gas high-temperature side of the heat exchanger (4); The organic Rankine cycle comprises a low-temperature evaporator (6), an intercooler (9), an organic working fluid turbine (10), a second generator (11), a condenser (12) and a working fluid pump (13); The low-temperature side outlet of the low-temperature evaporator (6) is connected to the low-temperature side inlet of the intercooler (9), the low-temperature side outlet of the intercooler (9) is connected to the inlet of the organic working fluid turbine (10), the organic working fluid turbine (10) is connected to the second generator (11), the outlet of the organic working fluid turbine (10) is connected to the high-temperature side inlet of the condenser (12), the high-temperature side outlet of the condenser (12) is connected to the inlet of the working fluid pump (13), and the outlet of the working fluid pump (13) is connected to the low-temperature side inlet of the low-temperature evaporator (6).

2. A circulation system for EGR diesel engine waste heat recovery according to claim 1, characterized in that: The low-temperature evaporator (6) includes a supercritical carbon dioxide high-temperature side and an organic working medium low-temperature side, the intercooler (9) includes a boosted air high-temperature side and an organic working medium low-temperature side, and the condenser (12) includes an organic working medium high-temperature side and a condensing medium low-temperature side.

3. A circulation system for EGR diesel engine waste heat recovery according to claim 1, characterized in that: The high-temperature side output end of the intercooler (9) is connected to the diesel engine (16), and the fresh air is connected to the high-temperature side input end of the intercooler (9) via the compressor (15).

4. A method for using a circulation system for EGR diesel engine waste heat recovery according to any one of claims 1 to 3, characterized in that: The following steps are involved: The supercritical carbon dioxide first enters the low temperature side of the regenerator (5) for preheating, and then enters the low temperature side of the heat exchanger (4) and the EGR cooler (3) in sequence to absorb the heat of the exhaust gas after the EGR diesel engine turbine and the EGR exhaust gas. The high temperature and high pressure supercritical carbon dioxide expands in the supercritical carbon dioxide turbine (1) to do work, driving the generator (2) to generate electricity. The exhaust gas that has done work passes through the regenerator (5) and reaches the high temperature side of the low temperature evaporator (6), preheating the low temperature side organic working fluid, and then enters the precooler (7) and the compressor (8) in sequence, and returns to the low temperature side inlet of the regenerator (5), completing a supercritical carbon dioxide Brayton cycle; The organic working fluid first absorbs the heat of the supercritical carbon dioxide on the high temperature side at the low temperature side of the low temperature evaporator (6), and then enters the low temperature side of the intercooler (9) to absorb the heat of the supercharged air on the high temperature side, while reducing the temperature of the supercharged air to meet the intake conditions of the diesel engine. The organic working fluid then enters the organic working fluid turbine (10) to perform work, driving the generator 2 (11) to generate electricity. The exhaust gas that has completed the work is condensed by the condenser (12), pressurized by the working fluid pump (13), and returned to the low temperature side inlet of the low temperature evaporator (6), completing an organic Rankine cycle.

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