Secondary flue gas waste heat power generation system

Abstract

The invention relates to a dual-cycle flue gas waste heat power generation system, a water vapor Rankine cycle drives a first turbine to generate power by absorbing flue gas heat, and condensation heat discharged by the water vapor Rankine cycle is transferred to an organic working medium Rankine cycle through a third heat exchanger and a fourth heat exchanger and serves as an evaporation heat source of an organic working medium. According to the method, water vapor Rankine cycle and organic Rankine cycle are organically coupled, flue gas waste heat is utilized in a gradient mode, condensation heat discharged by water vapor cycle serves as an evaporation heat source of organic working medium cycle, and efficient conversion of energy is achieved. The system adopts an optimized process design, stable generation of a steam working medium is ensured through the vaporizer, and continuous supply of a liquid-phase working medium is maintained through the buffer, so that stable operation of the flue gas waste heat power generation system is ensured.

Description

Technical Field

[0001] The invention relates to a secondary flue gas waste heat power generation system, belonging to the technical field of industrial waste heat utilization. Background Art

[0002] In the field of energy utilization, the Rankine cycle is a widely used technology for converting thermal energy into electrical energy. Traditional power generation systems typically utilize a single steam Rankine cycle or an organic Rankine cycle (ORC), each with its own advantages and limitations. The steam Rankine cycle has high thermal efficiency in the high-temperature range, but lower efficiency in the low-temperature range; while the ORC can effectively utilize medium- and low-temperature heat sources (such as industrial waste heat and geothermal energy), its efficiency is limited in the high-temperature range. In existing technologies, these two cycles typically operate independently, failing to fully utilize their respective advantages, resulting in low energy utilization.

[0003] Furthermore, the large amount of waste heat from high-temperature flue gas generated during industrial production is often underutilized. High-temperature flue gas is often directly discharged or a portion of the heat is simply recovered, resulting in low thermal efficiency and energy waste. Efficiently utilizing waste heat from flue gas for power generation and integrating it with steam and organic fluid Rankine cycles has become a pressing technical challenge in the field of energy utilization.

[0004] With growing energy demand and increasing environmental protection requirements, the development of power generation systems that integrate both the steam and organic Rankine cycles and fully utilize waste heat from flue gas has become a technological trend. This system not only improves overall power generation efficiency but also enables cascaded energy utilization and reduces energy waste, offering significant economic and environmental benefits. Summary of the Invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a two-stage flue gas waste heat power generation system, which can realize the step-by-step recovery of flue gas waste heat and efficient energy conversion.

[0006] The technical solutions of the present invention are as follows:

[0007] A two-stage flue gas waste heat power generation system includes a first heat exchanger, a second heat exchanger, a third heat exchanger, a fourth heat exchanger, a fifth heat exchanger, a sixth heat exchanger, a first turbine, a second turbine, a first working fluid pump, a second working fluid pump, a first vaporizer, a second vaporizer, a first buffer, and a second buffer; wherein the first turbine, the second heat exchanger, the third heat exchanger, the first buffer, the first working fluid pump, the first vaporizer, and the second heat exchanger form a water vapor Rankine cycle; the second turbine, the sixth heat exchanger, the second buffer, the second working fluid pump, the fifth heat exchanger, the fourth heat exchanger, and the third heat exchanger form an organic working fluid Rankine cycle; the water vapor Rankine cycle drives the first turbine to generate electricity by absorbing flue gas heat, and the condensation heat discharged by the water vapor Rankine cycle is transferred to the organic working fluid Rankine cycle through the third heat exchanger and the fourth heat exchanger, and serves as an evaporation heat source for the organic working fluid.

[0008] Among them, the exhaust steam outlet of the first turbine is connected to the inlets of the third heat exchanger and the fourth heat exchanger in sequence, the condensate outlet of the fourth heat exchanger is connected to the first evaporator through the first buffer and the first working fluid pump, and the steam outlet of the first evaporator returns to the first turbine through the second heat exchanger to form the water vapor Rankine cycle.

[0009] Among them, the exhaust steam outlet of the second turbine is connected to the sixth heat exchanger, and the liquid organic working fluid outlet is connected to the second vaporizer through the second buffer and the second working fluid pump. The liquid working fluid outlet of the second vaporizer is heated in turn through the fifth heat exchanger and the fourth heat exchanger, and the steam outlet returns to the second turbine through the third heat exchanger to form the organic working fluid Rankine cycle.

[0010] Among them, the first heat exchanger and the first vaporizer constitute a first thermosiphon system, the liquid water outlet of the first vaporizer is connected to the inlet of the first heat exchanger, and the gas-liquid mixture outlet of the first heat exchanger is connected to the evaporation material inlet of the first vaporizer, so as to realize continuous boiling and evaporation of liquid water; the fifth heat exchanger, the fourth heat exchanger and the second vaporizer constitute a second thermosiphon system, the liquid organic working fluid outlet of the second vaporizer is connected to the inlet of the fifth heat exchanger and the fourth heat exchanger in sequence, and the gas-liquid mixture outlet of the fourth heat exchanger is connected to the evaporation material inlet of the second vaporizer, so as to realize continuous boiling and evaporation of liquid organic working fluid.

[0011] The second heat exchanger is provided with a flue gas inlet, the flue gas outlet of the second heat exchanger is connected to the flue gas inlet of the first heat exchanger, the flue gas outlet of the first heat exchanger is connected to the flue gas inlet of the fifth heat exchanger, the liquid water outlet in the first vaporizer is connected to the inlet of the first heat exchanger, and the gas-liquid mixture outlet of the first heat exchanger is connected to the evaporated material inlet of the first vaporizer.

[0012] Among them, the evaporation of the organic working medium is achieved by absorbing the flue gas heat through the fifth heat exchanger and the water vapor condensation heat through the fourth heat exchanger in sequence; among them, the fourth heat exchanger absorbs the heat released by the water vapor in the Rankine cycle during the condensation process to provide evaporation heat for the organic working medium in the Rankine cycle.

[0013] Wherein, the organic working fluid is ethyl chloride or isopentane.

[0014] Among them, the first buffer is arranged between the condensate outlet of the fourth heat exchanger and the first working fluid pump, for maintaining a stable supply of the water working fluid liquid phase; the second buffer is arranged between the liquid organic working fluid outlet of the sixth heat exchanger and the second working fluid pump, for maintaining a stable supply of the organic working fluid liquid phase.

[0015] The present invention has the following beneficial effects:

[0016] The present invention provides a two-stage flue gas waste heat power generation system that couples water vapor and organic working fluid Rankine cycle power generation to achieve energy cascade power generation. The condensation heat released by the water vapor Rankine cycle is used as the evaporation heat of the organic working fluid Rankine cycle, achieving rational energy utilization. Reasonable process design ensures stable system operation, and the vaporizer and buffer serve as buffer equipment for process adjustment. The vaporizer ensures stable steam working fluid generation, and the buffer ensures a stable supply of liquid working fluid. The two-stage flue gas waste heat power generation method provides a process for fully converting flue gas heat within this temperature range into electrical energy.

[0017] The system utilizes both steam and organic Rankine cycles, organically integrated through the third and fourth heat exchangers. The steam Rankine cycle utilizes high-temperature heat energy, while the organic Rankine cycle utilizes low-temperature heat energy. The synergistic design of these two cycles enables cascaded energy utilization, improving energy efficiency.

[0018] The high-temperature flue gas passes through the second heat exchanger, the first heat exchanger and the fifth heat exchanger in sequence, and is used to superheat water vapor, generate water vapor and heat liquid organic working fluid respectively, thereby realizing multi-stage utilization of flue gas waste heat and fully recovering flue gas waste heat.

[0019] The condensed working fluid water is pressurized by the first buffer and the first working fluid pump at the outlet of the fourth heat exchanger and then transported to the first vaporizer, where it absorbs heat from the high-temperature flue gas and is converted into water vapor. The liquid organic working fluid absorbs heat from the high-temperature flue gas through the fifth heat exchanger and condenses the water vapor through the fourth heat exchanger, heating it to organic working fluid steam. Recovering the waste heat from the condensed working fluid water significantly improves overall system energy utilization and power generation efficiency.

[0020] The water vapor is further heated by the high-temperature flue gas in the second heat exchanger to form superheated steam. The organic working fluid steam then exchanges heat with the water vapor exhaust in the third heat exchanger, further heating it to form superheated organic working fluid steam. This superheated steam technology further enhances the power generation stability and efficiency of the water vapor and organic working fluid Rankine cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 For the present invention.

[0022] The reference numerals in the figures are as follows:

[0023] 1. First heat exchanger; 2. Second heat exchanger; 3. Third heat exchanger; 4. Fourth heat exchanger; 5. Fifth heat exchanger; 6. Sixth heat exchanger; 7. First turbine; 8. Second turbine; 9. First working fluid pump; 10. Second working fluid pump; 11. First vaporizer; 12. Second vaporizer; 13. First buffer; 14. Second buffer. DETAILED DESCRIPTION

[0024] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] See also Figure 1 , the invention provides a technical solution:

[0026] Example 1:

[0027] like Figure 1 As shown, the present invention provides a two-stage flue gas waste heat power generation system, including a first heat exchanger 1, a second heat exchanger 2, a third heat exchanger 3, a fourth heat exchanger 4, a fifth heat exchanger 5, a sixth heat exchanger 6, a first turbine 7, a second turbine 8, a first working fluid pump 9, a second working fluid pump 10, a first vaporizer 11, a second vaporizer 12, a first buffer 13 and a second buffer 14.

[0028] The exhaust steam outlet of the first turbine 7 is connected with the inlet of the third heat exchanger 3 and the fourth heat exchanger 4 in sequence, that is, it first absorbs heat through the third heat exchanger 3 and then enters the fourth heat exchanger 4 to absorb heat. The third heat exchanger 3 performs sensible heat exchange (the water vapor is cooled but not condensed), and the fourth heat exchanger 4 performs latent heat release (the water vapor phase changes and liquefies). Since the fourth heat exchanger plays the core role of condensation heat recovery, the water vapor is cooled into condensed water through the third heat exchanger 3 and the fourth heat exchanger 4; the condensed water outlet of the fourth heat exchanger 4 is connected with the inlet of the first buffer 13 and the inlet of the first working fluid pump 9 in sequence; the outlet of the first working fluid pump 9 is connected with the condensed water inlet of the first vaporizer 11; the water vapor outlet of the first vaporizer 11 is connected with the water vapor inlet of the second heat exchanger 2; the superheated water vapor outlet of the second heat exchanger 2 is connected with the steam inlet of the first turbine 7 to form a closed circulation loop, that is, the water vapor Rankine cycle; the second heat exchanger 2 is provided with a flue gas inlet, and the flue gas outlet of the second heat exchanger 2 is connected to The flue gas inlet of the first heat exchanger 1 and the flue gas outlet of the first heat exchanger 1 are connected to the flue gas inlet of the fifth heat exchanger 5, the liquid water outlet in the first vaporizer 11 is connected to the inlet of the first heat exchanger 1, and the gas-liquid mixture outlet of the first heat exchanger 1 is connected to the evaporative material inlet of the first vaporizer 11; the organic working fluid exhaust steam of the second turbine 8 is connected to the organic working fluid inlet of the sixth heat exchanger 6, and the sixth heat exchanger 6 is provided with a circulating water inlet and outlet to condense the organic working fluid. The liquid organic working fluid from the sixth heat exchanger 6 is connected to the liquid organic working fluid inlet of the second vaporizer 12 in turn through the second buffer 14 and the second working fluid pump 10; the liquid organic working fluid of the second vaporizer 12 is heated into organic working fluid steam through the fifth heat exchanger 5 and the fourth heat exchanger 4 in turn; the organic working fluid steam outlet of the second vaporizer 12 is connected to the third heat exchanger 3, and the superheated organic working fluid steam outlet of the third heat exchanger 3 is connected to the steam inlet of the second turbine 8 to form a closed circulation loop, that is, the organic working fluid Rankine cycle.

[0029] The liquid water in the first vaporizer 11 flows through a pipeline into the first heat exchanger 1 for heating. A gas-liquid mixture flows out of the outlet of the first heat exchanger 1, wherein the liquid phase falls back into the first vaporizer 11 and the vapor phase enters the water vapor outlet of the first vaporizer 11. The first heat exchanger 1 and the first vaporizer 11 form a thermal siphon device, so that the liquid phase of the first vaporizer 11 automatically flows into the first heat exchanger 1 to achieve continuous boiling and evaporation. The outlet of the liquid organic working medium in the second vaporizer 12 is connected to the inlet of the fifth heat exchanger 5 and the fourth heat exchanger 4 in sequence, and the gas-liquid mixture outlet of the fourth heat exchanger 4 is connected to the evaporating material inlet of the second vaporizer 12. The fifth heat exchanger 5, the fourth heat exchanger 4 and the second vaporizer 12 form a thermal siphon device, so that the liquid organic working medium in the second vaporizer 12 continuously flows into the fifth heat exchanger 5 and the fourth heat exchanger 4 to achieve boiling and evaporation.

[0030] In this embodiment, the cooling and condensation heat released by the water vapor in the water vapor Rankine cycle provides evaporation and heating heat for the organic working fluid in the organic working fluid Rankine cycle; wherein, the water vapor Rankine cycle is to evaporate the water working fluid by absorbing heat from the heat source to drive the first turbine 7 to generate electricity, and the water vapor exhaust steam discharged by the first turbine 7 needs to be condensed into liquid water and then absorb the waste heat of the high-temperature heat source again to generate steam; the organic working fluid Rankine cycle is to evaporate the organic working fluid by absorbing heat from the heat source to drive the second turbine 8 to generate electricity, and the organic working fluid exhaust steam discharged by the second turbine 8 needs to be condensed into liquid organic working fluid and then absorb the waste heat of the high-temperature heat source again to generate steam.

[0031] In this embodiment, the flue gas provides heat for the water vapor Rankine cycle and the organic working fluid Rankine cycle respectively.

[0032] In this embodiment, the flue gas provides steam superheating heat and heat for generating saturated steam in the water vapor Rankine cycle; the flue gas provides heat for generating saturated steam in the organic working fluid Rankine cycle.

[0033] Example 2

[0034] like Figure 1 As shown, the present invention provides a two-stage flue gas waste heat power generation method, comprising:

[0035] High-temperature, high-pressure water vapor enters the first turbine 7, driving it to generate power and discharging low-temperature, low-pressure water vapor exhaust. The water vapor exhaust from the first turbine 7 enters the third heat exchanger 3, exchanges heat with the gaseous organic working medium, and its temperature decreases after releasing heat. The water working medium discharged from the third heat exchanger 3 enters the fourth heat exchanger 4, where it is further cooled by releasing heat from the vaporized liquid organic working medium and condensed into liquid water. The condensed water passes through the first buffer 13 and the first working medium pump 9 at the outlet of the fourth heat exchanger 4, and is pressurized and transported to the first vaporizer 11. In the first vaporizer 11, the condensed water absorbs heat from the high-temperature flue gas and is converted into water vapor. The water vapor enters the second heat exchanger 2, where it is further heated by the high-temperature flue gas to produce superheated water vapor. The superheated water vapor returns to the first turbine 7 from the outlet of the second heat exchanger 2, completing the water vapor Rankine cycle.

[0036] The high-temperature, high-pressure organic working fluid steam enters the second turbine 8, driving the turbine to work and generate electricity, and discharging low-temperature, low-pressure organic working fluid exhaust steam; the organic working fluid exhaust steam discharged from the second turbine 8 enters the sixth heat exchanger 6, is cooled by circulating water, and condensed into liquid organic working fluid; the liquid organic working fluid passes through the second buffer 14 and the second working fluid pump 10 from the outlet of the sixth heat exchanger 6 in sequence, and is pressurized and transported to the second vaporizer 12; the liquid organic working fluid in the second vaporizer 12 absorbs heat from the high-temperature flue gas through the fifth heat exchanger 5, and then absorbs the condensation heat of water vapor through the fourth heat exchanger 4, heating it to organic working fluid steam; the organic working fluid steam enters the third heat exchanger 3 from the outlet of the second vaporizer 12, exchanges heat with the water vapor exhaust steam, and is further heated to obtain superheated organic working fluid steam; the superheated organic working fluid steam returns to the second turbine 8 from the outlet of the third heat exchanger 3, completing the organic working fluid Rankine cycle.

[0037] The heat of the high-temperature flue gas is utilized as follows: the high-temperature flue gas first enters the second heat exchanger 2 to heat the water vapor into superheated water vapor, and then enters the first heat exchanger 1 to heat the liquid water working medium into water vapor working medium; the cooled flue gas discharged from the first heat exchanger 1 enters the fifth heat exchanger 5 to further heat the liquid organic working medium, thereby fully utilizing the waste heat of the flue gas.

[0038] Example 3

[0039] The flue gas temperature of the flue gas waste heat power generation system is 200-350°C, and the following steps are performed in sequence: superheating water vapor in the second heat exchanger 2; vaporizing liquid water in the first heat exchanger 1; and heating the liquid organic working medium in the fifth heat exchanger 5.

[0040] The 300°C flue gas releases heat through the second heat exchanger 2 to heat the saturated water vapor to obtain superheated water vapor, and then releases heat in the first heat exchanger 1 to heat the condensed water to obtain saturated water vapor.

[0041] Liquid condensate is pressurized by the first working fluid pump 9 and enters the first vaporizer 11, where it is vaporized into saturated steam. The vaporizer uses siphon boiling to convert the condensate into saturated steam. The saturated steam is heated to high-temperature superheated steam by the second superheating heat exchanger 2 and then enters the first turbine 7 to generate electricity. The outlet of the first turbine 7 is low-temperature superheated steam. The low-temperature superheated steam is cooled by the third and fourth heat exchangers 3 and 4, converting it into liquid condensate. The liquid condensate enters the buffer 13, where it is then pressurized by the first working fluid pump 9 and enters the vaporizer 11 for vaporization, completing the working fluid cycle of the power generation system.

[0042] The flue gas from the first heat exchanger 1 is cooled by the fifth heat exchanger 5 to a low temperature of about 80°C. Since the flue gas from the first heat exchanger 1 has acid condensation at its dew point, the pipes and equipment that the flue gas passes through are subsequently protected against corrosion.

[0043] The liquid organic working fluid is pressurized by the second working fluid pump 10 and enters the vaporizer 12, where it is vaporized into saturated organic vapor. The vaporizer uses siphon boiling to vaporize the liquid organic working fluid into saturated organic working fluid vapor. During the vaporization and boiling process, it passes through the fifth heat exchanger 5 and the fourth heat exchanger 4. The saturated organic working fluid vapor is heated to high-temperature superheated organic working fluid vapor by the third heat exchanger 3 and then enters the second turbine 8 to generate electricity. The turbine outlet is low-temperature superheated organic working fluid vapor. The low-temperature superheated organic working fluid vapor is condensed by the sixth heat exchanger 6 and becomes organic working fluid condensate. The organic working fluid condensate enters the buffer 14, is then pressurized by the second working fluid pump 10, and enters the vaporizer for vaporization, completing the working fluid cycle of the power generation system.

[0044] In the sixth heat exchanger 6, the low-temperature superheated organic steam passes through the circulating cooling water and is condensed into liquid working fluid.

[0045] The specific workflow is:

[0046] High-temperature flue gas (200-350°C) first enters the second heat exchanger 2, heating the saturated steam from the first vaporizer 11 into superheated steam. The cooled flue gas then enters the first heat exchanger 1, where it interacts with the thermosiphon mechanism formed by the first vaporizer 11 to continuously boil liquid water and generate saturated steam. After further cooling, the flue gas enters the fifth heat exchanger 5, preheating the liquid organic fluid in the Rankine cycle. At this point, the superheated steam drives the first turbine 7 to generate electricity. The exhausted water vapor flows through the third and fourth heat exchangers 3 and 4, releasing some heat in the third heat exchanger 3. The heat of condensation is then released in the fourth heat exchanger 4, where it is liquefied into condensed water. The condensed water is stabilized by the first buffer 13 and pressurized by the first fluid pump 9 before returning to the first vaporizer 11, completing the water cycle.

[0047] Meanwhile, the liquid organic working fluid absorbs heat in two stages in the second vaporizer 12: first, it absorbs waste heat from the flue gas in the fifth heat exchanger 5, and then absorbs heat of condensation from water vapor in the fourth heat exchanger 4, transforming into organic working fluid steam. This steam then absorbs waste heat from the water vapor in the third heat exchanger 3, becoming superheated and driving the second turbine 8 to generate electricity. The exhaust steam is condensed into liquid form by the sixth heat exchanger 6, stabilized by the second buffer 14, and pressurized by the second working fluid pump 10 before returning to the circulation.

[0048] It is worth mentioning that the organic working fluid continuously circulates between the pipeline and key equipment. The specific path is: after being discharged from the exhaust steam outlet of the second turbine 8, it enters the sixth heat exchanger 6 and is condensed into liquid organic working fluid by circulating water. The liquid working fluid flows through the second buffer 14 to absorb flow fluctuations and maintain a stable supply of liquid phase, and is then pressurized and transported to the liquid inlet of the second vaporizer 12 by the second working fluid pump 10; in the second vaporizer 12, the liquid organic working fluid is driven by thermal siphon action to flow through the fifth heat exchanger 5 to absorb the waste heat of the flue gas and the fourth heat exchanger 4 to absorb the condensation heat of water vapor, and is gradually heated and evaporated into saturated steam. After being superheated by the third heat exchanger 3, it returns to the inlet of the second turbine 8, forming a closed dynamic cycle.

[0049] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention's description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A two-stage flue gas waste heat power generation system, characterized by: The invention comprises a first heat exchanger (1), a second heat exchanger (2), a third heat exchanger (3), a fourth heat exchanger (4), a fifth heat exchanger (5), a sixth heat exchanger (6), a first turbine (7), a second turbine (8), a first working fluid pump (9), a second working fluid pump (10), a first vaporizer (11), a second vaporizer (12), a first buffer (13) and a second buffer (14); wherein the first turbine (7), the third heat exchanger (3), the fourth heat exchanger (4), the first buffer (13), the first working fluid pump (9), the first vaporizer (11), the second vaporizer (12), the first buffer (13) and the second buffer (14) are The catalytic converter (11) and the second heat exchanger (2) form a water vapor Rankine cycle; the second turbine (8), the sixth heat exchanger (6), the second buffer (14), the second working fluid pump (10), the fifth heat exchanger (5), the fourth heat exchanger (4) and the third heat exchanger (3) form an organic working fluid Rankine cycle; the water vapor Rankine cycle drives the first turbine (7) to generate electricity by absorbing the heat of the flue gas, and the condensation heat discharged by the water vapor Rankine cycle is transferred to the organic working fluid Rankine cycle through the third heat exchanger (3) and the fourth heat exchanger (4) and serves as an evaporation heat source for the organic working fluid.

2. The two-stage flue gas waste heat power generation system according to claim 1, characterized in that: The exhaust steam outlet of the first turbine (7) is connected to the inlets of the third heat exchanger (3) and the fourth heat exchanger (4) in sequence. The condensed water outlet of the fourth heat exchanger (4) is connected to the first vaporizer (11) via the first buffer (13) and the first working fluid pump (9). The steam outlet of the first vaporizer (11) returns to the first turbine (7) via the second heat exchanger (2) to form the water vapor Rankine cycle.

3. The two-stage flue gas waste heat power generation system according to claim 1, characterized in that: The exhaust steam outlet of the second turbine (8) is connected to the sixth heat exchanger (6), and the liquid organic working medium outlet is connected to the second vaporizer (12) via the second buffer (14) and the second working medium pump (10). The liquid working medium outlet of the second vaporizer (12) is heated in turn by the fifth heat exchanger (5) and the fourth heat exchanger (4), and the steam outlet returns to the second turbine (8) via the third heat exchanger (3) to form the organic working medium Rankine cycle.

4. The two-stage flue gas waste heat power generation system according to claim 1, characterized in that: The first heat exchanger (1) and the first vaporizer (11) form a first thermosiphon system, the liquid water outlet of the first vaporizer (11) is connected to the inlet of the first heat exchanger (1), and the gas-liquid mixture outlet of the first heat exchanger (1) is connected to the evaporation material inlet of the first vaporizer (11), thereby realizing continuous boiling and evaporation of liquid water; the fifth heat exchanger (5), the fourth heat exchanger (4) and the second vaporizer (12) form a second thermosiphon system, the liquid organic working medium outlet of the second vaporizer (12) is connected to the inlet of the fifth heat exchanger (5) and the fourth heat exchanger (4) in sequence, and the gas-liquid mixture outlet of the fourth heat exchanger (4) is connected to the evaporation material inlet of the second vaporizer (12), thereby realizing continuous boiling and evaporation of the liquid organic working medium.

5. The two-stage flue gas waste heat power generation system according to claim 1, characterized in that: The second heat exchanger (2) is provided with a flue gas inlet, the flue gas outlet of the second heat exchanger (2) is connected to the flue gas inlet of the first heat exchanger (1), the flue gas outlet of the first heat exchanger (1) is connected to the flue gas inlet of the fifth heat exchanger (5), the liquid water outlet in the first vaporizer (11) is connected to the inlet of the first heat exchanger (1), and the gas-liquid mixture outlet of the first heat exchanger (1) is connected to the vaporized material inlet of the first vaporizer (11).

6. The two-stage flue gas waste heat power generation system according to claim 1, characterized in that: The evaporation of the organic working medium is achieved in sequence by the fifth heat exchanger (5) absorbing the flue gas heat and the fourth heat exchanger (4) absorbing the water vapor condensation heat; wherein the fourth heat exchanger (4) absorbs the heat released by the water vapor in the Rankine cycle during the condensation process, providing evaporation heat for the organic working medium in the Rankine cycle.

7. The two-stage flue gas waste heat power generation system according to claim 1, characterized in that: The organic working fluid is ethyl chloride or isopentane.

8. The two-stage flue gas waste heat power generation system according to claim 1, characterized in that: The first buffer (13) is arranged between the condensed water outlet of the fourth heat exchanger (4) and the first working fluid pump (9) to maintain a stable supply of the water working fluid liquid phase; the second buffer (14) is arranged between the liquid organic working fluid outlet of the sixth heat exchanger (6) and the second working fluid pump (10) to maintain a stable supply of the organic working fluid liquid phase.

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