A mixture transcritical cycle waste heat recovery system and method

Abstract

The present invention discloses a mixture transcritical cycle waste heat recovery system and method, the system includes a high-temperature turbine, a high-temperature regenerator, a medium-temperature regenerator, a gas-liquid separator, a liquid pump, a low-temperature regenerator, a precooler, a main compressor, a low-temperature flue gas heater, a medium-temperature flue gas heater, a low-temperature turbine, and a high-temperature flue gas heater connected in sequence. In the system, a mixture of H2O and C2O is used as a working fluid, the working fluid is in a supercritical mixed state at the high-temperature part, and part of the H2O will be separated from CO2 at the low-temperature part. CO2 is compressed and pressurized by a compressor, and H2O is pressurized by a water pump. The system uses a water pump to replace the recompressor in the traditional CO2 Brayton cycle. The power consumption of compressed liquid is much smaller than that of the recompressor, and the temperature of high-pressure water is also increased, solving the problem of mismatch between the heat absorption of the low-temperature working fluid and the heat release of the heat source. At the same time, it avoids the phenomenon of liquid carrying during gas compression and vaporization during liquid compression. The safety and stability of the equipment are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power generation systems, and in particular to a mixture transcritical cycle waste heat recovery system and method. Background Art

[0002] Among the many thermal cycles, the supercritical Brayton cycle is the most advantageous cycle. New supercritical working fluids such as carbon dioxide, helium and nitrous oxide have inherent advantages such as high energy density, high heat transfer efficiency and simple system. They can greatly improve the heat-to-work conversion efficiency, reduce the size of the equipment and have high economic efficiency.

[0003] However, this traditional supercritical CO2 Brayton cycle has certain difficulties for waste heat recovery. The temperature of the waste heat source is gradually reduced. Waste heat recovery pays more attention to how much electricity can be finally obtained from the fixed waste heat source, rather than just focusing on thermal efficiency. Generally speaking, the lower the flue gas temperature of the waste heat source is, the more heat is recovered from the waste heat source, and the more electricity may be output. However, the temperature of the CO2 working fluid entering the heat source heater after the traditional supercritical CO2 Brayton cycle is very high, which means that the heat of the low-temperature part cannot be recovered. On the contrary, at this time, the Rankine cycle can recover most of the heat from the low-temperature heat source. If the two can be combined, the role of the waste heat source can be better played. Therefore, the more suitable cycle form for waste heat recovery is the transcritical mixed working fluid cycle. After mixing H2O in CO2, the heat of the low-temperature flue gas can be better absorbed, and the role of the waste heat source can be better played.

[0004] However, CO2 mixtures also encounter some problems. For example, adding H2O to CO2 can adjust the physical properties of the mixture very well. However, due to the large difference in the physical properties of the two substances, the mixture is more likely to separate, especially in the parts of the system where throttling or mutation occurs, such as filters, valves, tank inlets and outlets, etc. In addition, to maintain a supercritical mixed state, the ratio of the two substances must be relatively precise, and there are great restrictions on the setting of system parameters, otherwise it will affect the mixing state and physical properties. This greatly limits the practical application of the mixture cycle.

[0005] If there is a system that can realize a mixture state in some parts and two single-phase working fluid states in other parts, and ensure the normal operation of important equipment such as compressors and pumps without cavitation, liquid hammer and other phenomena, the application range of the system can be greatly improved. The present invention is proposed to solve this problem. Summary of the invention

[0006] In order to overcome the problems encountered when applying supercritical Brayton cycle power generation system to waste heat recovery, a mixed transcritical cycle waste heat recovery system and method are proposed, which adopts a method with relatively low technical difficulty and high feasibility, recovers more heat and outputs more power.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A mixed transcritical cycle waste heat recovery system comprises a high-temperature turbine 1, wherein the medium outlet of the high-temperature turbine 1 is connected to the hot side inlet of a high-temperature regenerator 2, the hot side outlet of the high-temperature regenerator 2 is connected to the hot side inlet of a medium-temperature regenerator 3, the hot side outlet of the medium-temperature regenerator 3 is connected to the inlet of a gas-liquid separator 4, the liquid side outlet of the gas-liquid separator 4 is connected to the inlet of a liquid pump 5, the gas side outlet of the gas-liquid separator 4 is connected to the hot side inlet of a low-temperature regenerator 6, and the hot side outlet of the low-temperature regenerator 6 is connected to the hot side inlet of a gas-liquid separator 4. The hot side inlet of the precooler 7 is connected, and the hot side outlet of the precooler 7 is connected to the inlet of the main compressor 8. The outlet of the main compressor 8 is divided into two paths, one of which is connected to the low temperature side inlet of the low temperature flue gas heater 9, and the other is connected to the low temperature side inlet of the low temperature regenerator 6. The low temperature side outlet of the low temperature regenerator 6 is connected to the cold side inlet of the medium temperature regenerator 3 after merging with the outlet of the liquid pump 5. The cold side outlet of the medium temperature regenerator 3 is divided into two paths, one of which is connected to the cold side inlet of the medium temperature flue gas heater 10, and the other is connected to the cold side inlet of the medium temperature regenerator 3. The low-temperature side outlet of the high-temperature regenerator 2 is connected to the low-temperature side inlet of the high-temperature flue gas heater 12, the low-temperature outlet of the high-temperature flue gas heater 12 is connected to the inlet of the high-temperature turbine 1, the low-temperature side outlet of the low-temperature flue gas heater 9 is connected to the cold side outlet of the medium-temperature regenerator 3 and then connected to the cold side inlet of the medium-temperature flue gas heater 10, the cold side outlet of the medium-temperature flue gas heater 10 is divided into two paths, one of which is connected to the inlet of the low-temperature turbine 11, and the other is connected to the high-temperature flue gas heater 10. The low-temperature outlet of the heat exchanger 12 is connected to the low-temperature side inlet of the high-temperature flue gas heater 12 after merging, the outlet of the low-temperature turbine 11 is connected to the hot side inlet of the medium-temperature reheater 3 after merging, the low-temperature side outlet of the high-temperature flue gas heater 12 is connected to the inlet of the high-temperature turbine 1, the high-temperature side outlet of the high-temperature flue gas heater 12 is connected to the high-temperature side inlet of the medium-temperature flue gas heater 10, and the high-temperature side outlet of the medium-temperature flue gas heater 10 is connected to the high-temperature side inlet of the low-temperature flue gas heater 9.

[0009] The pressure in the gas-liquid separator 4 is between 7.2 MPa and 7.6 MPa, and the temperature is between 130° C. and 170° C. At this temperature and pressure, it is ensured that CO2 is in a supercritical state and its density is closer to that of gas, while water is in a liquid state.

[0010] The ratio of the tank diameter of the gas-liquid separator 4 to the inlet pipe diameter is greater than 10, and the ratio of the effective volume height of the tank to the tank diameter is greater than 1. Under this size ratio, the flow area is significantly expanded, which is more conducive to gas-liquid separation.

[0011] An operating method of a mixture transcritical cycle waste heat recovery system comprises the following steps;

[0012] The supercritical mixed working medium in a mixed state is heated to the highest parameter in the high-temperature flue gas heater 12, and then enters the high-temperature turbine 1 to perform work. After the pressure is reduced, the temperature of the mixed working medium is still relatively high and is still in a supercritical state. It enters the hot side of the high-temperature regenerator 2 and the hot side of the medium-temperature regenerator 3 in turn to release heat. As the working medium temperature decreases, the H2O and CO2 in the mixture are separated in the gas-liquid separator 4, and C2O flows out from the top outlet and enters the hot side of the low-temperature regenerator 6 and the precooler 7 to continue to release heat. The liquid H2O flows out from the bottom of the gas-liquid separator 4 and enters the liquid pump 5 to be pressurized. The cooled CO2 enters the main compressor 8 to be pressurized, and then is divided into two paths, one path enters the low-temperature side of the low-temperature flue gas heater 9 to absorb heat, and the other path enters the low-temperature side of the precooler 7 to absorb heat. The CO2 enters the cold side of the low-temperature regenerator 6 to absorb heat, and then merges with the high-pressure H2O at the outlet of the liquid pump 5 to enter the cold side of the medium-temperature regenerator 3 to absorb heat. At this time, CO2 and H2O are in a supercritical mixed state again. The supercritical mixture at the cold side outlet of the medium-temperature regenerator 3 is divided into two paths, which enter the low-temperature side of the medium-temperature flue gas heater 10 and the cold side of the high-temperature regenerator 2 to absorb heat respectively. Part of the supercritical mixed working fluid at the low-temperature side outlet of the medium-temperature flue gas heater 10 directly enters the low-temperature turbine 11 to do work, and then merges with the working fluid at the hot side of the high-temperature regenerator 2 to enter the hot side inlet of the medium-temperature regenerator 3. The other part of the working fluid merges with the working fluid at the cold side outlet of the high-temperature regenerator 2 and enters the high-temperature flue gas heater 12 to continue to be heated, completing the whole cycle.

[0013] The high-temperature flue gas enters from the high-temperature side inlet of the high-temperature flue gas heater 12, releases heat through the high-temperature flue gas heater 12, the medium-temperature flue gas heater 10, and the high-temperature side of the low-temperature flue gas heater 9 in turn, and is then discharged to the outside from the high-temperature side outlet of the low-temperature flue gas heater 9.

[0014] Beneficial effects of the present invention:

[0015] The present invention uses a mixture of H2O and C2O as the working fluid. The working fluid is in a supercritical mixed state at the high temperature part, while part of the H2O will be separated from the CO2 at the low temperature part. The CO2 is compressed and pressurized by a compressor, and the H2O is pressurized by a water pump. The system uses a water pump to replace the recompressor in the traditional CO2 Brayton cycle. The power consumption of the compressed liquid is much smaller than that of the recompressor, and the temperature of the high-pressure water is also increased. In this way, the low-temperature working fluid at the outlet of the compressor can absorb more heat from the low-temperature heat source, solving the problem of mismatch between the heat absorption of the low-temperature working fluid and the heat release of the heat source. At the same time, it avoids the phenomenon of liquid carrying during gas compression and vaporization during liquid compression. The safety and stability of the equipment are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the structure of the system of the present invention.

[0017] Among them, high-temperature turbine 1, high-temperature regenerator 2, medium-temperature regenerator 3, gas-liquid separator 4, liquid pump 5, low-temperature regenerator 6, precooler 7, main compressor 8, low-temperature flue gas heater 9, medium-temperature flue gas heater 10, low-temperature turbine 11, and high-temperature flue gas heater 12. DETAILED DESCRIPTION

[0018] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0019] like Figure 1 As shown, a mixed transcritical cycle waste heat recovery system of the present invention includes a high-temperature turbine 1, a high-temperature regenerator 2, a medium-temperature regenerator 3, a gas-liquid separator 4, a liquid pump 5, a low-temperature regenerator 6, a precooler 7, a main compressor 8, a low-temperature flue gas heater 9, a medium-temperature flue gas heater 10, a low-temperature turbine 11, and a high-temperature flue gas heater 12 which are connected in sequence.

[0020] The outlet of the high-temperature turbine 1 is connected to the hot side inlet of the high-temperature regenerator 2, the hot side outlet of the high-temperature regenerator 2 is connected to the hot side inlet of the medium-temperature regenerator 3, the hot side outlet of the medium-temperature regenerator 3 is connected to the inlet of the gas-liquid separator 4, the liquid side outlet of the gas-liquid separator 4 is connected to the inlet of the liquid pump 5, the gas side outlet of the gas-liquid separator 4 is connected to the hot side inlet of the low-temperature regenerator 6, the hot side outlet of the low-temperature regenerator 6 is connected to the hot side inlet of the precooler 7, and the hot side The outlet is connected to the inlet of the main compressor 8. The outlet of the main compressor 8 is divided into two paths, one of which is connected to the low-temperature side inlet of the low-temperature flue gas heater 9, and the other is connected to the low-temperature side inlet of the low-temperature regenerator 6. The low-temperature side outlet of the low-temperature regenerator 6 is connected to the cold side inlet of the medium-temperature regenerator 3 after merging with the outlet of the liquid pump 5. The cold side outlet of the medium-temperature regenerator 3 is divided into two paths, one of which is connected to the cold side inlet of the medium-temperature flue gas heater 10, and the other is connected to the low-temperature side inlet of the high-temperature regenerator 2. The low-temperature side outlet of the high-temperature reheater 2 is connected to the low-temperature side inlet of the high-temperature flue gas heater 12, the low-temperature outlet of the high-temperature flue gas heater 12 is connected to the inlet of the high-temperature turbine 1, the low-temperature side outlet of the low-temperature flue gas heater 9 is connected to the cold side inlet of the medium-temperature flue gas heater 10 after merging with the cold side outlet of the medium-temperature reheater 3, the cold side outlet of the medium-temperature flue gas heater 10 is divided into two paths, one path is connected to the inlet of the low-temperature turbine 11, and the other path is connected to the low-temperature side inlet of the high-temperature flue gas heater 12 after merging with the low-temperature outlet of the high-temperature flue gas heater 12, the outlet of the low-temperature turbine 11 is connected to the hot side inlet of the medium-temperature reheater 3 after merging with the hot side outlet of the high-temperature reheater 2, the low-temperature side outlet of the high-temperature flue gas heater 12 is connected to the inlet of the high-temperature turbine 1, the high-temperature side outlet of the high-temperature flue gas heater 12 is connected to the high-temperature side inlet of the medium-temperature flue gas heater 10, and the high-temperature side outlet of the medium-temperature flue gas heater 10 is connected to the high-temperature side inlet of the low-temperature flue gas heater 9.

[0021] The specific working process of the system of the present invention is:

[0022] The supercritical mixed working medium in a mixed state is heated to the highest parameter in the high-temperature flue gas heater 12, and then enters the high-temperature turbine 1 to perform work. After the pressure is reduced, the temperature of the mixed working medium is still relatively high and is still in a supercritical state. It enters the hot side of the high-temperature regenerator 2 and the hot side of the medium-temperature regenerator 3 in turn to release heat. As the working medium temperature decreases, the H2O and CO2 in the mixture are separated in the gas-liquid separator 4, and C2O flows out from the top outlet and enters the hot side of the low-temperature regenerator 6 and the precooler 7 to continue to release heat. The liquid H2O flows out from the bottom of the gas-liquid separator 4 and enters the liquid pump 5 to be pressurized. The cooled CO2 enters the main compressor 8 to be pressurized, and then is divided into two paths, one path enters the low-temperature side of the low-temperature flue gas heater 9 to absorb heat, and the other path enters the low-temperature side of the precooler 7 to absorb heat. The CO2 enters the cold side of the low-temperature regenerator 6 to absorb heat, and then merges with the high-pressure H2O at the outlet of the liquid pump 5 to enter the cold side of the medium-temperature regenerator 3 to absorb heat. At this time, CO2 and H2O are in a supercritical mixed state again. The supercritical mixture at the cold side outlet of the medium-temperature regenerator 3 is divided into two paths, which enter the low-temperature side of the medium-temperature flue gas heater 10 and the cold side of the high-temperature regenerator 2 to absorb heat respectively. Part of the supercritical mixed working fluid at the low-temperature side outlet of the medium-temperature flue gas heater 10 directly enters the low-temperature turbine 11 to do work, and then merges with the working fluid at the hot side of the high-temperature regenerator 2 to enter the hot side inlet of the medium-temperature regenerator 3. The other part of the working fluid merges with the working fluid at the cold side outlet of the high-temperature regenerator 2 and enters the high-temperature flue gas heater 12 to continue to be heated, completing the whole cycle. In this system, high-temperature flue gas enters from the high-temperature side inlet of the high-temperature flue gas heater 12, releases heat through the high-temperature flue gas heater 12, the medium-temperature flue gas heater 10, and the high-temperature side of the low-temperature flue gas heater 9 in turn, and is then discharged to the outside from the high-temperature side outlet of the low-temperature flue gas heater 9.

[0023] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A mixture transcritical cycle waste heat recovery system, characterized in that: The invention comprises a high-temperature turbine (1), wherein the medium outlet of the high-temperature turbine (1) is connected to the hot side inlet of a high-temperature regenerator (2), the hot side outlet of the high-temperature regenerator (2) is connected to the hot side inlet of a medium-temperature regenerator (3), the hot side outlet of the medium-temperature regenerator (3) is connected to the inlet of a gas-liquid separator (4), the liquid side outlet of the gas-liquid separator (4) is connected to the inlet of a liquid pump (5), the gas side outlet of the gas-liquid separator (4) is connected to the hot side inlet of a low-temperature regenerator (6), the hot side outlet of the low-temperature regenerator (6) is connected to the hot side inlet of a precooler (7), and the hot side outlet of the precooler (7) is connected to the hot side inlet of a precooler (7). The hot side outlet of the precooler (7) is connected to the inlet of the main compressor (8). The outlet of the main compressor (8) is divided into two paths, one of which is connected to the low temperature side inlet of the low temperature flue gas heater (9), and the other is connected to the low temperature side inlet of the low temperature regenerator (6). The low temperature side outlet of the low temperature regenerator (6) is connected to the outlet of the liquid pump (5) and then connected to the cold side inlet of the medium temperature regenerator (3). The cold side outlet of the medium temperature regenerator (3) is divided into two paths, one of which is connected to the cold side inlet of the medium temperature flue gas heater (10), and the other is connected to the high temperature regenerator (11). The low temperature side inlet of the high temperature regenerator (2) is connected to the low temperature side inlet of the high temperature flue gas heater (12), the low temperature side outlet of the high temperature regenerator (2) is connected to the low temperature side inlet of the high temperature flue gas heater (12), the low temperature side outlet of the high temperature flue gas heater (12) is connected to the inlet of the high temperature turbine (1), the low temperature side outlet of the low temperature flue gas heater (9) merges with the cold side outlet of the medium temperature regenerator (3) and is connected to the cold side inlet of the medium temperature flue gas heater (10), the cold side outlet of the medium temperature flue gas heater (10) is divided into two paths, one of which is connected to the inlet of the low temperature turbine (11) and the other is connected to the inlet of the high temperature flue gas heater (11). The low-temperature outlet of the high-temperature flue gas heater (2) is connected to the low-temperature side inlet of the high-temperature flue gas heater (12); the outlet of the low-temperature turbine (11) is connected to the hot side outlet of the high-temperature regenerator (2) and is connected to the hot side inlet of the medium-temperature regenerator (3); the low-temperature side outlet of the high-temperature flue gas heater (12) is connected to the inlet of the high-temperature turbine (1); the high-temperature side outlet of the high-temperature flue gas heater (12) is connected to the high-temperature side inlet of the medium-temperature flue gas heater (10); and the high-temperature side outlet of the medium-temperature flue gas heater (10) is connected to the high-temperature side inlet of the low-temperature flue gas heater (9); The pressure in the gas-liquid separator (4) is between 7.2 MPa and 7.6 MPa, and the temperature is between 130° C. and 170° C.; The ratio of the tank diameter of the gas-liquid separator (4) to the diameter of the inlet pipe is greater than 10, and the ratio of the effective volume height of the tank to the tank diameter is greater than 1.

2. The operating method of a mixture transcritical cycle waste heat recovery system according to claim 1, characterized in that: The steps include: The supercritical mixed working medium in a mixed state is heated to the highest parameter in the high-temperature flue gas heater (12), and then enters the high-temperature turbine (1) to perform work. After the pressure is reduced, the temperature of the mixed working medium is still relatively high and is still in a supercritical state. It enters the hot side of the high-temperature regenerator (2) and the hot side of the medium-temperature regenerator (3) in turn to release heat. As the working medium temperature decreases, the H2O and CO2 in the mixture are separated in the gas-liquid separator (4). C2O flows out from the top outlet and enters the hot side of the low-temperature regenerator (6) and the precooler (7) to continue to release heat. Liquid H2O flows out from the bottom of the gas-liquid separator (4) and enters the liquid pump (5) to be pressurized. The cooled CO2 enters the main compressor (8) to be pressurized, and then is divided into two paths. One path enters the low-temperature side of the low-temperature flue gas heater (9) to absorb heat, and the other path enters the low-temperature side of the low-temperature flue gas heater (9) to absorb heat. It enters the cold side of the low-temperature regenerator (6) to absorb heat, then merges with the high-pressure H2O at the outlet of the liquid pump (5) and enters the cold side of the medium-temperature regenerator (3) to absorb heat. At this time, CO2 and H2O are in a supercritical mixed state. The supercritical mixture at the cold side outlet of the medium-temperature regenerator (3) is divided into two paths, which respectively enter the low-temperature side of the medium-temperature flue gas heater (10) and the cold side of the high-temperature regenerator (2) to absorb heat. Part of the supercritical mixed working fluid at the low-temperature side outlet of the medium-temperature flue gas heater (10) directly enters the low-temperature turbine (11) to perform work, then merges with the working fluid at the hot side of the high-temperature regenerator (2) and enters the hot side inlet of the medium-temperature regenerator (3). The other part of the working fluid merges with the working fluid at the cold side outlet of the high-temperature regenerator (2) and enters the high-temperature flue gas heater (12) to continue to be heated, completing the entire cycle.

3. The operating method of a mixture transcritical cycle waste heat recovery system according to claim 2, characterized in that: The high-temperature flue gas enters from the high-temperature side inlet of the high-temperature flue gas heater (12), releases heat through the high-temperature flue gas heater (12), the medium-temperature flue gas heater (10), and the high-temperature side of the low-temperature flue gas heater (9) in sequence, and is then discharged to the outside from the high-temperature side outlet of the low-temperature flue gas heater (9).

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