Dual cycle thermal power generation system

Abstract

The present application belongs to the technical field of thermal power generation, and relates to a double-cycle thermal power generation system, comprising a boiler, an sCO2 Brayton cycle power generation system and a steam Rankine cycle power generation system. The sCO2 Brayton cycle power generation system is used for absorbing high-temperature flue gas energy and can reach a temperature exceeding the rated initial parameter of an sCO2 turbine. The steam Rankine cycle power generation system absorbs low-temperature flue gas energy, can generate superheated steam to do work and generate power, and further absorbs part of the energy of sCO2 higher than the rated initial parameter through a heat exchanger to reach the rated temperature parameter of a steam turbine. Both the sCO2 Brayton cycle and the steam Rankine cycle adopt a high-position turbine arrangement mode. Compared with the existing thermal power generation system with a single steam cycle system structure, the system can fully and reasonably utilize the flue gas heat of the boiler, improve the energy utilization efficiency and system power generation efficiency, reduce the use of high-temperature pipe materials, weaken the high-temperature corrosion of the medium to the materials, and reduce the system cost.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of thermal power generation, and relates to a double-circulation thermal power generation system. BACKGROUND

[0002] In order to further improve the steam Rankine cycle efficiency of thermal power generation, countries around the world are successively carrying out technical research on ultra-supercritical thermal power generation units with higher parameters, expecting to increase the turbine inlet temperature to 700 DEG C and the power generation cycle efficiency to 50% level. However, the steam corrosion problem is serious, and the high-cost nickel-based alloy high-temperature steam pipeline becomes one of the main bottlenecks restricting this technology. China proposes a method of high-position arrangement of the steam turbine, which effectively shortens the arrangement distance of the high-temperature steam pipeline, reduces the material consumption and the cost, and lays a foundation for the development of the next generation of thermal power generation industry.

[0003] On the other hand, the supercritical carbon dioxide (sCO2) Brayton cycle has better characteristics in the medium-high temperature heat source system and has received widespread attention in recent years. Compared with the existing steam Rankine cycle system, the sCO2 Brayton cycle applied to the thermal power generation system has the following advantages: first, the sCO2 Brayton cycle has higher cycle efficiency under medium-high temperature conditions; the volume and weight of the turbine equipment and the heat exchanger are small, the occupied area is reduced, and the high-position arrangement method is more convenient; in addition, carbon dioxide has weak corrosion to metal, and the material cost is also significantly reduced. However, the sCO2-based coal-fired boiler is quite different from the traditional steam boiler, and it also faces problems such as large medium flow (8 times the steam flow of the same order of magnitude), more tail flue gas waste heat (500 DEG C below flue gas cannot be absorbed by carbon dioxide), and needs further in-depth research. SUMMARY

[0004] In view of the above problems, the present application provides a double-circulation thermal power generation system, which couples the sCO2 Brayton cycle and the steam Rankine cycle, and uses water and sCO2 as the two medium working fluids of the double-circulation thermal power generation system. Compared with the existing single steam cycle system of the thermal power generation system, the system of the present application can fully and reasonably utilize the boiler flue gas heat, improve the energy utilization efficiency and the system power generation efficiency, reduce the use of high-temperature pipe materials, weaken the high-temperature corrosion of the medium to the material, and reduce the system cost.

[0005] The double-cycle thermal power generation system comprises a boiler, an sCO2 Brayton cycle power generation system taking high-temperature flue gas in the boiler as a heat source and taking sCO2 as a circulating working medium, and a steam Rankine cycle power generation system taking low-temperature flue gas in the boiler as a heat source and taking steam as a circulating working medium, an external heat exchanger of the boiler is provided, the heat exchanger is used for exchanging excess energy absorbed by sCO2 to steam, sCO2 exchanges heat with the high-temperature flue gas, after passing through the heat exchanger, sCO2 sequentially passes through a first power device, a first cooling device and a first pressure increasing device to complete the sCO2 Brayton cycle, steam exchanges heat with the low-temperature flue gas, after passing through a second power device and exchanging heat with sCO2 in the heat exchanger, steam sequentially passes through a third power device, a fourth power device, a second cooling device and a second pressure increasing device to complete the steam Rankine cycle.

[0006] The first power device, the second power device and the third power device are arranged in a high position and coupled with the boiler, or the first power device, the second power device and the third power device are arranged in a high position and separately arranged outside the boiler.

[0007] The boiler can be a π-shaped boiler or a tower boiler, comprising a hearth, a main flue and a tail flue, the main flue is located in a high-temperature region of the boiler, and the tail flue is located in a low-temperature region of the boiler.

[0008] The hearth is used for burning fossil fuels such as coal, and the top end of the hearth is communicated with an inlet of the main flue.

[0009] The flue can be a horizontal flue (π-shaped boiler) or a vertical flue (tower boiler), which is used for high-temperature flue gas flow and heating surface arrangement, and an outlet of the main flue is communicated with an inlet of the tail flue.

[0010] The tail flue can be arranged with low-temperature heating surfaces and waste heat utilization equipment, and an outlet of the tail flue is communicated with an external chimney.

[0011] The sCO2 Brayton cycle power generation system is a closed cycle system taking sCO2 as a heat exchange and power generation medium. Main components include: sCO2 low-temperature superheater, sCO2 high-temperature superheater, heat exchanger, sCO2 turbine, CO2 high-temperature regenerator, CO2 low-temperature regenerator, cooler, main compressor, re-compressor, first three-way valve and second three-way valve, the sCO2 high-temperature superheater and the sCO2 low-temperature superheater are respectively located in the high-temperature region of the boiler.

[0012] The sCO2 low-temperature superheater and the sCO2 high-temperature superheater are connected and arranged in the main flue of the boiler, sCO2 flows into the sCO2 low-temperature superheater from the inlet and flows out from the outlet of the sCO2 high-temperature superheater; sCO2 flows into the inlet of the sCO2 low-temperature superheater, and the outlet of the sCO2 low-temperature superheater is communicated with the inlet of the sCO2 high-temperature superheater; the hot side inlet of the CO2 high-temperature recuperator is communicated with the outlet of the sCO2 turbine, the hot side outlet of the CO2 low-temperature recuperator is communicated with the hot side inlet of the CO2 low-temperature recuperator, the cold side inlet of the CO2 high-temperature recuperator is communicated with the cold side outlet of the CO2 low-temperature recuperator, the cold side outlet of the CO2 high-temperature recuperator is communicated with the cold side inlet of the sCO2 low-temperature superheater, and the cold side inlet of the CO2 low-temperature recuperator is communicated with the outlet of the compressor; the first three-way valve is respectively communicated with the inlet of the main compressor, the hot side outlet of the low-temperature recuperator and the hot side inlet of the cooler, and the second three-way valve is respectively communicated with the outlet of the re-compressor, the cold side outlet of the low-temperature recuperator and the cold side inlet of the high-temperature recuperator.

[0013] The heat exchanger is arranged at the top end outside the boiler and used for sCO2 and steam heat exchange, the hot side fluid of the heat exchanger is sCO2, the hot side inlet is communicated with the outlet of the sCO2 high-temperature superheater, and the hot side outlet is communicated with the inlet of the sCO2 turbine, the cold side inlet of the heat exchanger is communicated with the outlet of the steam turbine high-pressure cylinder, and the cold side outlet of the heat exchanger is communicated with the inlet of the steam turbine medium-pressure cylinder.

[0014] The sCO2 turbine is arranged in a high position, the height of the sCO2 turbine is equivalent to the heating surface of the sCO2 high-temperature superheater, and the sCO2 turbine is arranged close to the sCO2 high-temperature superheater; the sCO2 turbine is arranged in the outer periphery of the boiler in a coupled manner or separately.

[0015] In view of the optimization of cycle efficiency, the sCO2 can be reheated in the main flue after turbine expansion, and one or two reheating turbines and other devices and arrangements can be added;

[0016] The hot side of the CO2 high-temperature recuperator is connected with the hot side of the CO2 low-temperature recuperator, and the cold side of the CO2 high-temperature recuperator is connected with the cold side of the CO2 low-temperature recuperator, and the CO2 high-temperature recuperator can be in the form of a tube-shell heat exchanger, a plate-fin heat exchanger or a printed circuit board heat exchanger (PCHE); in view of the heat exchange efficiency, equipment volume and cost, the PCHE is preferably selected;

[0017] The cooler inlet, the re-compressor inlet and the CO2 low-temperature regenerator hot side outlet form a three-way, and CO2 is divided into two streams at the low-temperature regenerator hot side outlet, one of which flows to the cooler inlet, and the other flows to the re-compressor inlet.

[0018] The main compressor is connected with the cooler, and CO2 is cooled to the parameters near the critical point, then enters the main compressor to complete pressure increase, and then flows to the CO2 low-temperature regenerator cold side inlet after pressure increase.

[0019] The re-compressor outlet, the CO2 low-temperature regenerator cold side outlet and the CO2 high-temperature regenerator cold side inlet form a three-way, and the divided streams are combined before the CO2 high-temperature regenerator cold side inlet, and then enter the CO2 high-temperature regenerator to be heated.

[0020] The steam Rankine cycle power generation system provided by the application is a cycle system taking water vapor as heat exchange and working medium.

[0021] The water cooled wall is connected with the water pump outlet and the steam superheater outlet, is coated on the periphery of the furnace chamber, and the water working medium flows in the interior.

[0022] The steam superheater is arranged at the tail of the boiler flue, and the outlet thereof is connected with the cold side inlet of the heat exchanger.

[0023] The heat exchanger is the same device as the sCO2 Brayton cycle system, the cold side fluid is low-pressure superheated steam, and the cold side outlet is connected with the steam turbine inlet.

[0024] The steam turbine high-pressure cylinder and the steam turbine medium-pressure cylinder, i.e., the high-pressure cylinder and the medium-pressure cylinder of the steam turbine unit, are also arranged in a high position, the height thereof is equivalent to the heating surface of the steam superheater, and the steam turbine is arranged close to the steam superheater.

[0025] The condenser and the water pump are the same as those of the conventional thermal power generation system, and are used for condensation and water supply pressure increase, respectively.

[0026] Compared with the existing thermal power generation cycle system, the application has at least the following advantages:

[0027] 1. The application adopts sCO2 turbine, steam turbine high-pressure cylinder and steam turbine low-pressure cylinder high arrangement mode, so that the distance between the heat exchanger and the sCO2 turbine, the steam turbine high-pressure cylinder and the steam turbine low-pressure cylinder is shortened, the pipeline distance of the high-temperature superheated working medium to the turbine unit is effectively shortened, the use of high-temperature high-pressure pipe materials is greatly reduced, and the system cost is effectively controlled.

[0028] 2. The application selects sCO2 to absorb the energy of the flue gas in the medium-high temperature area, because CO2 has weak high-temperature corrosion to metal materials, can reach a higher temperature (more than 700 DEG C), so that the medium-high temperature area power generation cycle efficiency is improved.

[0029] 3. The application selects water working medium to absorb the energy of the medium-low temperature flue gas, can make the water reach the superheated steam state, and further transfers the energy higher than the rated initial parameter absorbed by sCO2 to the low-pressure superheated steam through the heat exchanger, can be matched with the steam Rankine cycle power generation, realizes the effective utilization of the medium-low temperature flue gas.

[0030] 4. Compared with direct flue gas heat exchange, the form of the heat exchanger can greatly reduce the corrosion and wear of the particles and acidic components in the flue gas to the outer wall of the high-temperature steam superheater pipeline; in addition, the pressure difference of the heat exchange medium on both sides of the traditional steam superheater is large, and using the heat exchanger, the pressure difference of the medium on both sides is small, which is beneficial to reduce the pipeline thermal stress.

[0031] 5. The CO2 temperature required by the Brayton cycle is generally 600-650 DEG C, and the steam temperature required by the steam Rankine cycle is generally 580-620 DEG C. Because of the weak corrosion, the use of CO2 to absorb high-temperature flue gas heat can reach more than 700 DEG C. By setting the heat exchanger, the excess heat of CO2 is transmitted to water, so that the temperatures of the two are matched to the high-efficiency power generation cycle system, and the work amount and work efficiency of the medium-low pressure cylinder of the steam unit are improved.

[0032] 6.The sCO2 Brayton cycle power generation system of the present application is used to absorb high-temperature flue gas energy, and sCO2 can reach a temperature higher than the rated initial parameter of the sCO2 turbine turbine, while reducing the use of high-temperature pipe materials. The steam Rankine cycle power generation system absorbs low-temperature flue gas energy, can generate superheated steam to do work and generate electricity, and further absorbs part of the energy of sCO2 higher than the rated initial parameter through a heat exchanger to reach the rated temperature parameter of the steam turbine. The sCO2 turbine in the sCO2 Brayton cycle and the high-pressure cylinder and the medium-pressure cylinder of the steam turbine in the steam Rankine cycle all adopt a turbine high-position arrangement, compared with the structure of the existing single steam cycle system of the thermal power generation system, the system can not only fully and reasonably utilize the heat of the boiler flue gas, improve the capacity utilization efficiency and system power generation efficiency, but also reduce the material and cost problems caused by high-temperature corrosion of the medium. Moreover, the low-pressure steam coming out of the steam after doing work in the second work device enters the heat exchanger, and the heat exchanger is used as the heat source of the steam of the third work device, which can absorb the excess energy of CO2 and improve the efficiency of the third work device. Compared with the steam directly entering the heat exchanger from the boiler without passing through the second work device, the pressure of the steam entering the heat exchanger is reduced by passing through the second work device, so that the pressure bearing of the heat exchanger is reduced, and the production and manufacturing difficulty of the heat exchanger is also reduced, and the engineering feasibility is better. On the other hand, the heat exchange area requirement of the heat exchanger is reduced, so that the small-size heat exchanger and the second work device, the third work device and the first work device are suitable for high-position arrangement at the top of the boiler. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 It is a principle diagram of the double-cycle thermal power generation system in the first embodiment of the present application.

[0034] Figure 2 It is a principle diagram of the double-cycle thermal power generation system in the second embodiment of the present application.

[0035] Among them, 1 is a boiler, 2 is a water wall, 3 is a steam superheater, 4 is a heat exchanger, 5a is a steam turbine high-pressure cylinder, 5b is a steam turbine medium-pressure cylinder, 5c is a steam turbine low-pressure cylinder, 6 is a condenser, 7 is a water pump, 8 is a sCO2 high-temperature superheater, 9 is a sCO2 low-temperature superheater, 10 is a sCO2 turbine, 11 is a CO2 high-temperature regenerator, 12 is a CO2 low-temperature regenerator, 13 is a cooler, 14 is a main compressor, 15 is a re-compressor, 16 is a steel frame support structure, a first three-way valve 17, a second three-way valve 18, and 19 is a low-pressure cylinder reheater. DETAILED DESCRIPTION

[0036] The present application will be further described in conjunction with the following specific embodiments and drawings. The present application is not limited to the following embodiments, and various modifications, transformations, combinations and improvements under the technical concept of the present application within the knowledge of those skilled in the art are all within the protection scope of the present application.

[0037] The first embodiment of the present application provides a double-cycle thermal power generation system, which comprises a boiler, an sCO2 Brayton cycle power generation system taking high-temperature flue gas in the boiler 1 as a heat source and taking sCO2 as a circulating working medium, and a steam Rankine cycle power generation system taking low-temperature flue gas in the boiler 1 as a heat source and taking steam as a circulating working medium. The boiler 1 is externally provided with a heat exchanger 4, which is used to exchange the excess energy absorbed by the sCO2 to the steam. The sCO2 exchanges heat with the high-temperature flue gas, and after the heat exchanger 4, the sCO2 completes the sCO2 Brayton cycle through work, cooling and pressure boosting. The steam exchanges heat with the low-temperature flue gas, and after the heat exchanger 4, the steam completes the steam Rankine cycle through work, cooling and pressure boosting.

[0038] Please refer to Figure 1 The first embodiment of the present application provides a double-cycle thermal power generation system, which comprises a boiler, an sCO2 Brayton cycle power generation system taking high-temperature flue gas in the boiler 1 as a heat source and taking sCO2 as a circulating working medium, and a steam Rankine cycle power generation system taking low-temperature flue gas in the boiler 1 as a heat source and taking steam as a circulating working medium. The boiler 1 is externally provided with a heat exchanger 4, which is used to exchange the excess energy absorbed by the sCO2 to the steam. The sCO2 exchanges heat with the high-temperature flue gas, and after the heat exchanger 4, the sCO2 completes the sCO2 Brayton cycle through work, cooling and pressure boosting. The steam exchanges heat with the low-temperature flue gas, and after the heat exchanger 4, the steam completes the steam Rankine cycle through work, cooling and pressure boosting.

[0039] Specifically, the sCO2 Brayton cycle power generation system is a recompression Brayton cycle system, which comprises an sCO2 low-temperature superheater 9, an sCO2 high-temperature superheater 8, a heat exchanger 4, an sCO2 turbine 10, a CO2 high-temperature regenerator 11, a CO2 low-temperature regenerator 12, a cooler 13, a main compressor 14, a recompression compressor 15, a first three-way valve 17 and a second three-way valve 18. The sCO2 high-temperature superheater 8 and the sCO2 low-temperature superheater 9 are respectively located in the high-temperature region of the boiler 1 and are arranged along the horizontal direction of the main flue. The connection relationship between the components in the recompression Brayton cycle system is a conventional practice in the art, and will not be described here. The steam Rankine cycle power generation system comprises, in sequence and in a loop: a water wall 2, a steam superheater 3, a steam turbine high-pressure cylinder 5a, the heat exchanger 4, a steam turbine medium-pressure cylinder 5b, a steam turbine low-pressure cylinder 5c, a condenser 6 and a water pump 7. The steam superheater 3 is arranged in the low-temperature region of the boiler 1. The hot side inlet of the heat exchanger 4 is communicated with the high-temperature flue gas outlet of the boiler 1, and the hot side outlet of the heat exchanger 4 is communicated with the inlet of the sCO2 turbine 10. The cold side inlet of the heat exchanger 4 is communicated with the outlet of the steam turbine high-pressure cylinder 5a, and the cold side outlet of the heat exchanger 4 is communicated with the inlet of the steam turbine medium-pressure cylinder 5b.

[0040] In the embodiment of the present application, the sCO2 turbine 10 adopts a high-position arrangement mode, the height of which is equivalent to the heating surface of the sCO2 high-temperature heat exchanger 8 and is arranged close to the sCO2 high-temperature heat exchanger 8. The steam turbine high-pressure cylinder 5a and the steam turbine medium-pressure cylinder 5b also adopt a high-position arrangement mode, the height of which is equivalent to the heating surface of the steam superheater 3 and is arranged close to the steam superheater 3. Specifically, as shown inFigure 1 As shown, the boiler 1 is suspended below the steel frame support frame 16, the sCO2 turbine 10, the steam turbine high-pressure cylinder 5a, the steam turbine medium-pressure cylinder 5b and the heat exchanger 4 are arranged at the top of the boiler 1; in some embodiments, the sCO2 turbine 10, the steam turbine high-pressure cylinder 5a and the steam turbine medium-pressure cylinder 5b can also be arranged alone at the outer periphery of the boiler 1; the sCO2 turbine 10, the steam turbine high-pressure cylinder 5a and the steam turbine medium-pressure cylinder 5b are supported by the steel frame support structure 16 respectively to achieve high-position arrangement.

[0041] The boiler 1 in the embodiment of the present application takes a π-shaped boiler commonly used in coal-fired power plants as an example, the boiler is provided with a water-cooled wall 2 at the periphery, the top main flue is a horizontal flue, the sCO2 high-temperature superheater 8, the sCO2 low-temperature superheater 9 and the steam superheater 3 are arranged in the main flue, and the heat exchanger 4 is arranged at the top of the boiler 1.

[0042] The sCO2 Brayton cycle power generation system in the embodiment of the present application has the following basic cycle process: the sCO2 passes through the low-temperature superheater 9 and the high-temperature superheater 8 in turn, absorbs the heat of the high-temperature flue gas, the temperature reaches above 700℃, which exceeds the rated inlet temperature parameter of the sCO2 turbine of the Brayton cycle system; the high-temperature and high-pressure sCO2 enters the hot side of the heat exchanger 4, exchanges part of the heat to the low-pressure superheated steam on the cold side, and at the same time, itself is reduced to the rated initial parameter range of the sCO2 turbine, about 630-650℃; the sCO2 with the rated initial parameter enters the sCO2 turbine 10 to expand and do work to generate electricity, the expanded sCO2 enters the hot side of the CO2 high-temperature recuperator 11 and the hot side of the CO2 low-temperature recuperator 12 in turn, exchanges the remaining energy to the high-pressure sCO2 on the cold side; the sCO2 at the outlet of the hot side of the CO2 low-temperature recuperator 12 is divided by the first three-way valve 17 according to a certain split ratio, and flows to the cooler 13 and the re-compressor 15 respectively; the flow into the cooler 13 is cooled to the vicinity of the critical point temperature (about 32℃), enters the main compressor 14, is compressed and raised in pressure by the main compressor 14, and then enters the cold side of the CO2 low-temperature recuperator 12; the flow into the re-compressor 15 is directly compressed, and then is combined with the flow at the outlet of the cold side of the CO2 low-temperature recuperator 12 at the second three-way valve 18; after the combination, the flow enters the cold side of the CO2 high-temperature recuperator 11, is further heated to about 500℃, and returns to the sCO2 low-temperature superheater 9 to absorb heat, to complete one cycle. In view of the optimization and improvement of the cycle efficiency, after the expansion of the sCO2 turbine 10, the sCO2 can also return to the main flue for reheating, and the arrangement mode of one or two reheating turbines and the like can be increased, specifically, after the expansion of the sCO2 turbine 10, the sCO2 can also return to the main flue, pass through a reheater (not shown in the figure) in turn for reheating, pass through a reheating turbine (not shown in the figure) to do work, and then enter the sCO2 low-temperature superheater 9 to repeat the cycle.

[0043] The basic cycle of the steam Rankine cycle power generation system in this embodiment of the invention is as follows: feedwater absorbs heat from the furnace through the water-cooled wall 2, then enters the steam superheater 3 at the tail of the main flue to absorb heat and become superheated steam; the superheated steam enters the high-pressure cylinder 5a of the steam turbine to do work, then enters the cold side of the heat exchanger 4 to absorb part of the heat from sCO2, further increasing its temperature to the initial temperature level of the ultra-supercritical unit, specifically, 600-620℃, and enters the intermediate-pressure cylinder 5b of the steam turbine to do work and generate electricity again; after expansion, it is heated by the low-pressure cylinder reheater 19 and enters the low-pressure cylinder 5c of the steam turbine to continue doing work and generating electricity; the low-temperature, low-pressure wet steam after further expansion enters the condenser 6 and condenses into saturated liquid water; after being pressurized by the water pump 7, it returns to the water-cooled wall 2 to absorb heat, completing one cycle. Considering the optimization and improvement of cycle efficiency, after being pressurized by the water pump, it can also first enter the economizer (not shown in the figure) in the tail waste heat flue for preheating, and then return to the water-cooled wall 2.

[0044] [Second Implementation Method]

[0045] Please see Figure 2 As shown, the second embodiment of the present invention provides a dual-cycle thermal power generation system. The difference between this system and the first embodiment is that the boiler 1 is a tower boiler with a vertical flue. The sCO2 high-temperature superheater 8, the sCO2 low-temperature superheater 9, and the steam superheater 3 are arranged sequentially from bottom to top within the vertical flue. The flue gas diffuses upwards within the boiler 1, and its temperature decreases as the diffusion height increases. The sCO2 turbine 10, the steam turbine high-pressure cylinder 5a, and the steam turbine intermediate-pressure cylinder 5b are coupled to the boiler 1 and arranged at the top of the boiler 1. Specifically, the boiler 1 is suspended by a steel support structure 16 (boiler tower). The sCO2 turbine 10, the steam turbine high-pressure cylinder 5a, and the steam turbine intermediate-pressure cylinder 5b are supported at a high position by the boiler tower, and the suspension height of the sCO2 turbine 10, the steam turbine high-pressure cylinder 5a, and the steam turbine intermediate-pressure cylinder 5b is approximately equal to the height of the top surface of the boiler 1.

[0046] Those skilled in the art will understand that many technical details have been provided in the above embodiments to facilitate a better understanding of this application. However, even without these technical details and various variations and modifications based on the above embodiments, the technical solutions claimed in the claims of this application can be substantially achieved. Therefore, in practical applications, various changes in form and detail can be made to the above embodiments without departing from the spirit and scope of the invention.

Claims

1. A dual-cycle thermal power generation system, characterized in that: The system includes a boiler, an sCO2 Brayton cycle power generation system using high-temperature flue gas from the boiler as a heat source and sCO2 as the circulating working fluid, and a steam Rankine cycle power generation system using low-temperature flue gas from the boiler as a heat source and steam as the circulating working fluid. The boiler is equipped with an external heat exchanger, which is used to transfer excess energy absorbed by sCO2 to steam. sCO2 exchanges heat with the high-temperature flue gas, and after passing through the heat exchanger, it sequentially passes through a first working device, a first cooling device, and a first pressurizing device to complete the sCO2 Brayton cycle. Steam exchanges heat with the low-temperature flue gas, and after passing through a second working device and exchanging heat with sCO2 in the heat exchanger, it sequentially passes through a third working device, a fourth working device, a second cooling device, and a second pressurizing device to complete the steam Rankine cycle. The second working device reduces the pressure of the steam entering the heat exchanger; The heat exchanger, the first working device, the second working device, and the third working device are all arranged in a high-level configuration and coupled to the boiler, or the heat exchanger, the first working device, the second working device, and the third working device are all arranged in a high-level configuration and separately arranged on the outer periphery of the boiler. The suspension height of the first working device, the second working device, and the third working device is approximately equal to the height of the top surface of the boiler.

2. The dual-cycle thermal power generation system as described in claim 1, characterized in that: The sCO2 Brayton cycle power generation system is a recompression Brayton cycle system, including a sCO2 low-temperature superheater, a sCO2 high-temperature superheater, a heat exchanger, a sCO2 turbine, a CO2 high-temperature regenerator, a CO2 low-temperature regenerator, a cooler, a main compressor, a recompressor, a first three-way valve, and a second three-way valve. The sCO2 high-temperature superheater and the sCO2 low-temperature superheater are located in the high-temperature region of the boiler. sCO2 flows into the inlet of the sCO2 low-temperature superheater, and its outlet is connected to the inlet of the sCO2 high-temperature superheater. The hot-side inlet of the CO2 high-temperature regenerator is connected to the sCO2 turbine. The outlet of the CO2 high-temperature regenerator is connected to the hot-side inlet of the CO2 low-temperature regenerator, the cold-side inlet of the CO2 high-temperature regenerator is connected to the cold-side outlet of the CO2 low-temperature regenerator, the cold-side outlet of the CO2 high-temperature regenerator is connected to the cold-side inlet of the sCO2 low-temperature superheater, and the cold-side inlet of the CO2 low-temperature regenerator is connected to the outlet of the compressor; the first three-way valve is connected to the inlet of the main compressor, the hot-side outlet of the low-temperature regenerator, and the hot-side inlet of the cooler, respectively; the second three-way valve is connected to the outlet of the re-compressor, the cold-side outlet of the low-temperature regenerator, and the cold-side inlet of the high-temperature regenerator, respectively. The steam Rankine cycle power generation system includes, in sequence, a water-cooled wall, a steam superheater, a high-pressure cylinder of a steam turbine, a heat exchanger, a medium-pressure cylinder of a steam turbine, a low-pressure cylinder of a steam turbine, a condenser, and a water pump, wherein the steam superheater is located in the low-temperature region of the boiler. The hot-side inlet of the heat exchanger is connected to the outlet of the sCO2 high-temperature superheater, and the hot-side outlet of the heat exchanger is connected to the inlet of the sCO2 turbine; the cold-side inlet of the heat exchanger is connected to the outlet of the high-pressure cylinder of the steam turbine, and the cold-side outlet of the heat exchanger is connected to the inlet of the intermediate-pressure cylinder of the steam turbine.

3. The dual-cycle thermal power generation system as described in claim 2, characterized in that: Boiler is The boiler is a shaped boiler or a tower boiler, the boiler including a furnace, a main flue and a tail waste heat flue, the main flue being a horizontal or vertical flue, the main flue being located in the high-temperature region, and the tail waste heat flue being located in the low-temperature region.

4. The dual-cycle thermal power generation system as described in claim 3, characterized in that: The height of the sCO2 turbine is approximately equal to the heating surface of the sCO2 high-temperature superheater, and it is positioned close to the high-temperature superheater.

5. The dual-cycle thermal power generation system as described in claim 3, characterized in that: The height of the high-pressure cylinder and the intermediate-pressure cylinder of the steam turbine are approximately equal to the heating surface of the steam superheater, and they are located close to the steam superheater.

6. The dual-cycle thermal power generation system as described in claim 2, characterized in that: In a Brayton cycle power generation system, sCO2 absorbs heat to above 700°C in the sCO2 high-temperature superheater, which is higher than the rated initial parameters of the sCO2 turbine.

7. The dual-cycle thermal power generation system as described in claim 2, characterized in that: The heat exchanger is arranged on the top of the boiler and is located close to the CO2 turbine, the high-pressure cylinder of the steam turbine, and the medium-pressure cylinder of the steam turbine.

8. The dual-cycle thermal power generation system as described in claim 7, characterized in that: The hot side of the heat exchanger is CO2, and the cold side is superheated steam.

9. The dual-cycle thermal power generation system as described in claim 7 or 8, characterized in that: The heat exchanger transfers the excess energy absorbed by sCO2 to steam, thereby reducing the temperature of sCO2 to the rated initial temperature of the Brayton cycle sCO2 turbine and further increasing the temperature of the steam to the initial temperature level of the ultra-supercritical unit.

10. The dual-cycle thermal power generation system as described in claim 4, characterized in that: The sCO2 working fluid from the outlet of the sCO2 turbine returns to the main flue and is reheated by the reheater. After the reheated turbine performs work, it enters the cryogenic superheater.

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