Secondary flue gas waste heat power generation system and method

Abstract

The system is composed of a heat exchange unit (comprising 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 power generation conversion unit (comprising a water vapor turbine and an organic working medium turbine) and a working medium circulation unit (comprising a first working medium pump, a second working medium pump, a first vaporizer, a second vaporizer, a first buffer and a second buffer). 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. Optimized process design is adopted, stable generation of a steam working medium is ensured through the vaporizer, continuous supply of a liquid-phase working medium is maintained through the buffer, and therefore stable operation of the flue gas waste heat power generation system is ensured.

Description

Technical Field

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

[0002] In the energy utilization field, the Rankine cycle is a widely used technology for converting thermal energy into electrical energy. Traditional power generation systems typically utilize either a single water-vapor Rankine cycle or an organic working fluid Rankine cycle, each with its own advantages and limitations. The water-vapor Rankine cycle boasts high thermal efficiency at high temperatures but suffers from low efficiency at low temperatures. The organic working fluid Rankine cycle, on the other hand, can effectively utilize medium- and low-temperature heat sources (such as industrial waste heat and geothermal energy), but its efficiency is limited at high temperatures. In existing technologies, these two cycles typically operate independently, failing to fully leverage their respective strengths and resulting in low energy efficiency.

[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] The purpose of the present invention is to provide a two-stage flue gas waste heat power generation system and method to solve the problem of insufficient utilization of flue gas waste heat power generation, thereby improving the overall power generation efficiency and energy utilization rate.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: 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; The exhaust steam outlet of the first turbine is connected in sequence to the inlets of the third and fourth heat exchangers, where the steam is cooled into condensed water. The condensed water outlet of the fourth heat exchanger is connected in sequence to the inlet of the first buffer and the inlet of the first working fluid pump. The outlet of the first working fluid pump is connected to the condensed water inlet of the first evaporator. The steam outlet of the first evaporator is connected to the steam inlet of the second heat exchanger. The superheated steam outlet of the second heat exchanger is connected to the steam inlet of the first turbine, thereby forming a closed circulation loop. 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 vaporized material inlet of the first vaporizer; The organic working fluid exhaust steam of the second turbine is connected to the organic working fluid inlet of the sixth heat exchanger. The sixth heat exchanger 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 is connected to the liquid organic working fluid inlet of the second vaporizer through the second buffer and the second working fluid pump in sequence; the liquid organic working fluid of the second vaporizer is heated into organic working fluid steam through the fifth heat exchanger and the fourth heat exchanger in sequence; the organic working fluid steam outlet of the second vaporizer is connected to the third heat exchanger, and the superheated organic working fluid steam outlet of the third heat exchanger is connected to the steam inlet of the second turbine to form a closed circulation loop.

[0007] A further improvement of the present invention is that the flue gas used for flue gas waste heat power generation is flue gas with a temperature between 200-350°C.

[0008] A further improvement of the present invention is that the cooling and condensation heat released by the water vapor in the primary power generation cycle provides evaporation and heating heat for the organic working fluid in the secondary power generation cycle; The primary power generation cycle is to absorb heat to evaporate the water working medium to drive the turbine to generate electricity. The exhaust steam from the turbine needs to be condensed into liquid water, and then absorb the waste heat of the high-temperature heat source again to generate steam. The secondary power generation cycle absorbs heat to evaporate the organic working fluid to drive the turbine to generate electricity. The exhaust steam of the organic working fluid discharged by the turbine 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.

[0009] A further improvement of the present invention is that the flue gas provides heat for the primary power generation cycle and the secondary power generation cycle respectively.

[0010] A further improvement of the present invention is that the flue gas provides heat for superheating steam and heat for generating saturated steam in the primary power generation cycle; and the flue gas also provides heat for generating saturated steam in the secondary power generation cycle.

[0011] A further improvement of the present invention is that the first heat exchanger and the first vaporizer form a thermal siphon device, so that the liquid phase of the first vaporizer continuously flows into the heat exchanger to be evaporated; the fifth heat exchanger, the fourth heat exchanger and the second vaporizer form a thermal siphon device, so that the liquid phase organic working fluid of the second vaporizer continuously flows into the heat exchanger to be evaporated.

[0012] A further improvement of the present invention is that the primary power generation cycle and the secondary power generation cycle achieve stable supply of liquid phase through a buffer.

[0013] A further improvement of the present invention is that the evaporation of the organic working medium is achieved by sequentially cooling the flue gas and releasing heat through the condensation of water vapor.

[0014] A further improvement of the present invention is that the organic working fluid used in the power generation system is ethyl chloride or isopentane.

[0015] A further improvement of the present invention is that the high-temperature flue gas enters the second heat exchanger to further heat the water vapor from the first vaporizer to make it fully superheated, and the cooled flue gas passes through the first heat exchanger to vaporize the liquid working medium water to generate water vapor; the flue gas outlet of the first heat exchanger is connected to the flue gas inlet of the fifth heat exchanger to vaporize the liquid organic working medium.

[0016] A secondary flue gas waste heat power generation method, based on the aforementioned secondary flue gas waste heat power generation system, comprises: High-temperature, high-pressure water vapor enters the first turbine, driving it to generate power and discharging low-temperature, low-pressure water vapor exhaust. The water vapor exhaust from the first turbine enters the third heat exchanger, exchanging heat with the gaseous organic working medium, releasing heat and lowering its temperature. The water working medium discharged from the third heat exchanger enters the fourth heat exchanger, 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 and the first working medium pump at the outlet of the fourth heat exchanger, and is pressurized and transported to the first vaporizer. In the first vaporizer, 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, 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 from the outlet of the second heat exchanger, completing the water vapor Rankine cycle. The high-temperature, high-pressure organic working fluid steam enters the second turbine, driving the turbine to generate power and discharging low-temperature, low-pressure organic working fluid exhaust steam. The organic working fluid exhaust steam discharged from the second turbine enters the sixth heat exchanger, where it is cooled by circulating water and condensed into liquid organic working fluid. From the outlet of the sixth heat exchanger, the liquid organic working fluid passes through the second buffer and the second working fluid pump in sequence, and is pressurized and transported to the second vaporizer. The liquid organic working fluid in the second vaporizer absorbs heat from the high-temperature flue gas through the fifth heat exchanger, and then absorbs condensation heat from the water vapor through the fourth heat exchanger, heating it to organic working fluid steam. The organic working fluid steam enters the third heat exchanger from the outlet of the second vaporizer, undergoes heat exchange with the water vapor exhaust steam, and is further heated to produce superheated organic working fluid steam. The superheated organic working fluid steam returns to the second turbine from the outlet of the third heat exchanger, completing the organic working fluid Rankine cycle. The heat utilization of high-temperature flue gas is as follows: the high-temperature flue gas first enters the second heat exchanger to heat the water vapor into superheated water vapor, and then enters the first heat exchanger to heat the liquid water working medium into water vapor working medium; the cooled flue gas discharged from the first heat exchanger enters the fifth heat exchanger to further heat the liquid organic working medium, thereby making full use of the waste heat of the flue gas.

[0017] Compared with the prior art, the present invention has at least the following beneficial technical effects: The present invention provides a two-stage flue gas waste heat power generation system and method 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 the heat of flue gas within this temperature range into electrical energy.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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

[0022] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 This is a structural block diagram of a two-stage flue gas waste heat power generation system of the present invention.

[0024] In the attached figure: 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

[0025] Hereinafter, only certain exemplary embodiments are briefly described. As will be appreciated by those skilled in the art, the described embodiments may be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and description are to be considered as illustrative in nature and not restrictive.

[0026] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0027] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0028] In the present invention, unless otherwise expressly specified or limited, terms such as "mounted," "connected," "connect," and "fixed" should be understood broadly. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection, or communication; direct connection or indirect connection through an intermediate medium; and internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0029] In the present invention, unless otherwise expressly specified or limited, a first feature being "above" or "below" a second feature may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Furthermore, a first feature being "above," "above," and "above" a second feature may include the first feature being directly above or obliquely above the second feature, or may simply mean that the first feature is higher in level than the second feature. A first feature being "below," "below," and "below" a second feature may include the first feature being directly above or obliquely above the second feature, or may simply mean that the first feature is lower in level than the second feature.

[0030] It should also be understood that the terms used in the present specification are only for the purpose of describing particular embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms unless the context clearly indicates otherwise.

[0031] It should be further understood that the term "and / or" used in the present description and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0032] The accompanying drawings illustrate various schematic diagrams of structures according to embodiments disclosed herein. These figures are not drawn to scale; for clarity, some details are exaggerated and some details may be omitted. The shapes of the various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are merely exemplary and may deviate in practice due to manufacturing tolerances or technical limitations. Those skilled in the art may design regions / layers with different shapes, sizes, and relative positions as needed.

[0033] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0034] Example 1 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.

[0035] The water vapor exhaust 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, and 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; 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, and the first vaporizer 1 1 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; 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 through the second buffer 14 and the second working fluid pump 10 in sequence; the liquid organic working fluid of the second vaporizer 12 is heated to organic working fluid steam through the fifth heat exchanger 5 and the fourth heat exchanger 4 in sequence; 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.

[0036] The liquid water in the first vaporizer 11 flows 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 vaporizer automatically flows into the heat exchanger 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 of the second vaporizer 12 continuously flows into the heat exchanger to be boiled and evaporated.

[0037] In this embodiment, the cooling and condensation heat released by the water vapor in the primary power generation cycle provides evaporation and heating heat for the organic working fluid in the secondary power generation cycle; wherein, the primary power generation cycle is to drive the turbine to generate electricity by absorbing heat from the heat source to evaporate the water working fluid, and the water vapor exhaust steam discharged by the turbine needs to be condensed into liquid water, and then absorb the waste heat of the high-temperature heat source again to generate steam; the secondary power generation cycle is to drive the turbine to generate electricity by absorbing heat from the heat source to evaporate the organic working fluid, and the organic working fluid exhaust steam discharged by the turbine 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.

[0038] In this embodiment, the flue gas provides heat for the primary power generation cycle and the secondary power generation cycle respectively.

[0039] In this embodiment, the flue gas provides heat for superheating steam and heat for generating saturated steam in the primary power generation cycle; the flue gas provides heat for generating saturated steam in the secondary power generation cycle.

[0040] In this embodiment, the primary power generation cycle and the secondary power generation cycle achieve stable supply of liquid phase through the buffer.

[0041] Example 2 like Figure 1 As shown, the present invention provides a two-stage flue gas waste heat power generation method, comprising: High-temperature, high-pressure water vapor enters the first turbine 7, driving the turbine 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. 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.

[0042] 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.

[0043] Example 3 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.

[0044] Liquid condensate is pressurized by the first working fluid pump 9 and enters the vaporizer, 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 in the superheater heat exchanger and then enters the first turbine 7 to generate electricity. The turbine outlet is low-temperature superheated steam. The low-temperature superheated steam is cooled in the third heat exchanger 3 and the fourth heat exchanger 4 before being converted 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.

[0045] 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.

[0046] 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, passing through the fifth heat exchanger 5 and the fourth heat exchanger 4 during the boiling and vaporization process. The saturated organic working fluid vapor is heated by the third heat exchanger 3 to high-temperature superheated organic working fluid vapor, which 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 into organic working fluid condensate. The organic working fluid condensate enters the second buffer 14, where it 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. In the sixth heat exchanger 6, the low-temperature superheated organic working fluid passes through the circulating cooling water and condenses into liquid organic working fluid.

[0047] The system's power generation accounts for approximately 15.1% of the total heat released by the flue gas, of which the primary cycle power generation accounts for approximately 7.1% of the total heat released by the flue gas, and the secondary cycle power generation accounts for approximately 8.0% of the total heat released by the flue gas.

[0048] Example 4 The steps for 200°C flue gas are the same as those in Example 3, but the working fluid flow rates of the primary and secondary power generation cycles need to be adjusted. In this example, the system's power generation accounts for approximately 10.3% of the total heat released by the flue gas, of which the primary cycle accounts for approximately 1.8% and the secondary cycle accounts for approximately 8.5%.

[0049] Example 5 The steps for 350°C flue gas are the same as those in Example 3, but the working fluid flow rates of the primary and secondary power generation cycles need to be adjusted. In this example, the system's power generation accounts for approximately 16.7% of the total heat released by the flue gas, of which the primary cycle accounts for approximately 8.9% and the secondary cycle accounts for approximately 7.8%.

[0050] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, from all points of view, the embodiments should be regarded as illustrative and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes that fall within the meaning and range of equivalents of the claims are included in the present invention. Any reference signs in the claims should not be construed as limiting the claim to which they relate.

[0051] In addition, it should be understood that although this specification describes the embodiments, not every embodiment contains only one independent technical solution. This description is for clarity only. Those skilled in the art should consider the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only for the purpose of illustrating the technical concept of the present invention and cannot be used to limit the scope of protection of the present invention. Any changes made based on the technical solution in accordance with the technical concept proposed by the present invention fall within the scope of protection of the claims of the present invention.

Claims

1. A two-stage flue gas waste heat power generation system, characterized in that: The heat exchanger comprises 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; The exhaust steam outlet of the first turbine is connected in sequence to the inlets of the third and fourth heat exchangers, where the steam is cooled into condensed water. The condensed water outlet of the fourth heat exchanger is connected in sequence to the inlet of the first buffer and the inlet of the first working fluid pump. The outlet of the first working fluid pump is connected to the condensed water inlet of the first evaporator. The steam outlet of the first evaporator is connected to the steam inlet of the second heat exchanger. The superheated steam outlet of the second heat exchanger is connected to the steam inlet of the first turbine, thereby forming a closed circulation loop. 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 vaporized material inlet of the first vaporizer; The organic working fluid exhaust steam of the second turbine is connected to the organic working fluid inlet of the sixth heat exchanger. The sixth heat exchanger 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 is connected to the liquid organic working fluid inlet of the second vaporizer through the second buffer and the second working fluid pump in sequence; the liquid organic working fluid of the second vaporizer is heated into organic working fluid steam through the fifth heat exchanger and the fourth heat exchanger in sequence; the organic working fluid steam outlet of the second vaporizer is connected to the third heat exchanger, and the superheated organic working fluid steam outlet of the third heat exchanger is connected to the steam inlet of the second turbine to form a closed circulation loop.

2. A two-stage flue gas waste heat power generation system according to claim 1, characterized in that: The flue gas used for flue gas waste heat power generation is flue gas with a temperature between 200-350℃.

3. The two-stage flue gas waste heat power generation system according to claim 1, characterized in that: The cooling and condensation heat released by the water vapor in the primary power generation cycle provides evaporation and heating heat for the organic working fluid in the secondary power generation cycle; The primary power generation cycle is to absorb heat to evaporate the water working medium to drive the turbine to generate electricity. The exhaust steam from the turbine needs to be condensed into liquid water, and then absorb the waste heat of the high-temperature heat source again to generate steam. The secondary power generation cycle absorbs heat to evaporate the organic working fluid to drive the turbine to generate electricity. The exhaust steam of the organic working fluid discharged by the turbine 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.

4. The two-stage flue gas waste heat power generation system according to claim 3, characterized in that: The flue gas provides heat for the primary power generation cycle and the secondary power generation cycle respectively.

5. The two-stage flue gas waste heat power generation system according to claim 3, characterized in that: The flue gas provides steam superheating heat and heat for generating saturated steam in the primary power generation cycle; and the flue gas provides heat for generating saturated steam in the secondary power generation cycle.

6. The two-stage flue gas waste heat power generation system according to claim 1, characterized in that: The first heat exchanger and the first vaporizer form a thermal siphon device, so that the liquid phase of the first vaporizer continuously flows into the heat exchanger to be evaporated; the fifth heat exchanger, the fourth heat exchanger and the second vaporizer form a thermal siphon device, so that the liquid phase organic working fluid of the second vaporizer continuously flows into the heat exchanger to be evaporated.

7. The two-stage flue gas waste heat power generation system according to claim 1, characterized in that: The evaporation of the organic working fluid is achieved by cooling the flue gas and releasing heat through the condensation of water vapor.

8. 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.

9. The two-stage flue gas waste heat power generation system according to claim 1, characterized in that: The high-temperature flue gas enters the second heat exchanger to further heat the water vapor from the first vaporizer to make it fully superheated. The cooled flue gas passes through the first heat exchanger to vaporize the liquid working medium water to generate water vapor; the flue gas outlet of the first heat exchanger is connected to the flue gas inlet of the fifth heat exchanger to vaporize the liquid organic working medium.

10. A secondary flue gas waste heat power generation method, characterized in that: The method is based on a two-stage flue gas waste heat power generation system according to claim 1, comprising: High-temperature, high-pressure water vapor enters the first turbine, driving it to generate power and discharging low-temperature, low-pressure water vapor exhaust. The water vapor exhaust from the first turbine enters the third heat exchanger, exchanging heat with the gaseous organic working medium, releasing heat and lowering its temperature. The water working medium discharged from the third heat exchanger enters the fourth heat exchanger, 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 and the first working medium pump at the outlet of the fourth heat exchanger, and is pressurized and transported to the first vaporizer. In the first vaporizer, 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, 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 from the outlet of the second heat exchanger, completing the water vapor Rankine cycle. The high-temperature, high-pressure organic working fluid steam enters the second turbine, driving the turbine to generate electricity and discharging low-temperature, low-pressure organic working fluid exhaust steam. The organic working fluid exhaust steam discharged from the second turbine enters the sixth heat exchanger, where it is cooled by circulating water and condensed into liquid organic working fluid. From the outlet of the sixth heat exchanger, the liquid organic working fluid passes through the second buffer and the second working fluid pump in sequence, and is pressurized and transported to the second vaporizer. The liquid organic working fluid in the second vaporizer absorbs heat from the high-temperature flue gas through the fourth heat exchanger, and then absorbs condensation heat from the water vapor through the fifth heat exchanger, heating it to organic working fluid steam. The organic working fluid steam enters the third heat exchanger from the outlet of the second vaporizer, undergoes heat exchange with the water vapor exhaust steam, and is further heated to produce superheated organic working fluid steam. The superheated organic working fluid steam returns to the second turbine from the outlet of the third heat exchanger, completing the organic working fluid Rankine cycle. The heat utilization of high-temperature flue gas is as follows: the high-temperature flue gas first enters the second heat exchanger to heat the water vapor into superheated water vapor, and then enters the first heat exchanger to heat the liquid water working medium into water vapor working medium; the cooled flue gas discharged from the first heat exchanger enters the fifth heat exchanger to further heat the liquid organic working medium, thereby making full use of the waste heat of the flue gas.

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