Flue gas low-heat recovery system based on reverse Brayton cycle heat pump energy storage and control method of flue gas low-heat recovery system

Abstract

The invention relates to a flue gas low-heat recovery system based on reverse Brayton cycle heat pump energy storage and a control method of the flue gas low-heat recovery system, and belongs to the technical field of thermoelectric unit pump heat energy storage peak regulation. The system comprises a boiler module, a high-heat circulation module and a low-heat circulation module, and low-heat graded utilization of high-grade and low-grade flue gas is achieved through cooperative operation of the boiler module, the high-heat circulation module and the low-heat circulation module. Flue gas of the boiler module is coupled with the high-heat circulation module through the fused salt heat exchanger, and the low-heat circulation module conducts organic Rankine cycle power generation through low heat of the flue gas. The high heat cycle module stores electric energy and heat energy in the valley electricity period and releases energy in the peak electricity period, and the peak regulation capacity of the system is improved. According to the system and the method, deep integration of low-heat efficient recovery of flue gas and an energy storage technology is realized, the energy utilization efficiency, the system flexibility and the economical efficiency are remarkably improved, and meanwhile, the system and the method have the benefits of environmental protection and sustainable development.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal power unit pump heat storage peak regulation, and in particular to a flue gas low-heat recovery system based on reverse Brayton cycle heat pump energy storage and a control method thereof. Background Art

[0002] With the profound changes in the global energy structure and the comprehensive promotion of the "dual carbon" goals, the efficient use and sustainable development of traditional energy have become core challenges that need to be urgently addressed in the energy field. Coal-fired power generation is an important pillar of the current power system. The medium and low temperature flue gas generated during its operation is often directly discharged into the atmosphere, resulting in a large amount of low-grade thermal energy waste. At the same time, the large-scale grid connection of renewable energy has put forward higher requirements on the stability and flexibility of the power system, and the peak-shaving and frequency-regulating capabilities of coal-fired units need to be improved urgently. Therefore, how to achieve the deep integration of efficient recovery of low-heat flue gas and energy storage technology and build a flexible and efficient energy utilization system has become a key path to solving the above problems.

[0003] Among many energy storage solutions, compressed carbon dioxide energy storage has become an important technical direction for improving the peak-shaving and frequency-regulating performance of coal-fired units and realizing low-heat recovery of flue gas due to its high energy storage density, fast response speed, and environmental friendliness. At the same time, the organic Rankine cycle can effectively absorb low heat from flue gas or reactions as a bottom cycle. However, how to achieve deep coupling of various systems to achieve efficient utilization of low-heat flue gas, while reducing system operating costs and improving the peak-shaving and frequency-regulating capabilities of units is a technical problem that needs to be solved urgently in this field. Summary of the invention

[0004] In order to solve the problems existing in the above-mentioned prior art, the present invention provides a flue gas low heat recovery system based on reverse Brayton cycle heat pump energy storage and a control method thereof, specifically: A flue gas low heat recovery system based on reverse Brayton cycle heat pump energy storage, comprising: a boiler module, a high heat cycle module and a low heat cycle module; In the boiler module, the flue gas side outlet of the superheater in the boiler is connected to the first inlet of the mixer via the first valve and the high heat circulation module; the flue gas side outlet of the air preheater is connected to the second inlet of the mixer via the second valve; the outlet of the mixer is connected to the boiler module via the low heat circulation module.

[0005] Further, the high heat cycle module includes: a thermal energy module and a pressure energy module; Among them, the molten salt side of the first molten salt heat exchanger is connected in series with the high-temperature storage tank, the third valve, the molten salt side of the second molten salt heat exchanger, the low-temperature storage tank and the fourth valve to form a loop, which is a thermal energy module; the working fluid side of the second molten salt heat exchanger is connected in series with the first expander, the low-pressure storage tank, the fifth valve, the compressor, the high-pressure storage tank and the sixth valve to form a loop, which is a pressure energy module.

[0006] Furthermore, the flue gas temperature at the outlet on the flue gas side of the superheater is 500 - 700 °C, and after heat exchange in the first molten salt heat exchanger, the temperature drops to approximately 150 - 250 °C, and it is mixed in the mixer with the flue gas at 50 - 150 °C from the air preheater.

[0007] Furthermore, the heat storage medium in the high-temperature storage tank and the low-temperature storage tank is solar salt, and the temperature range is set to 220 - 550 °C.

[0008] Furthermore, the pressure of the high-pressure storage tank is set to 8 - 12 MPa, and the pressure of the low-pressure storage tank is set to 5 - 2 MPa.

[0009] Furthermore, the compressor is a positive displacement compressor.

[0010] Furthermore, the first expander is a turbine expander, and the second expander is a screw expander.

[0011] Furthermore, the low-temperature heat cycle module is as follows: the outlet on the working fluid side of the first condenser is connected to the inlet on the working fluid side of the recuperator through a pump, the outlet on the working fluid side of the recuperator is connected in series with the inlet on the working fluid side of the evaporator, the second expander, and the inlet on the medium side of the recuperator in sequence, the outlet on the medium side of the recuperator is connected to the inlet on the working fluid side of the first condenser, condensed water is introduced into the inlet on the medium side of the first condenser, the outlet on the medium side of the first condenser is externally connected to a low-temperature heater, the outlet of the mixer is connected to the inlet on the medium side of the evaporator, and the outlet on the medium side of the evaporator is connected to the dust removal device in the boiler.

[0012] Furthermore, in the waste heat cycle module, the organic working fluid is R245fa, and the end temperature difference of each heat exchanger is specified to be 5 - 10 °C.

[0013] On the other hand, the present invention also provides a control method for controlling any of the above flue gas low-temperature heat recovery systems, including: Energy storage process: During the valley electricity period, open the first valve, the second valve, the fourth valve, and the fifth valve, close the third valve and the sixth valve, use the excess power of the generator set to drive the compressor, compress the carbon dioxide from the low-pressure storage tank to a high-temperature and high-pressure state and store it in the high-pressure storage tank, and the molten salt in the low-temperature storage tank exchanges heat with the high-temperature flue gas in the first molten salt heat exchanger, and the high-temperature molten salt after heat absorption is stored in the high-temperature storage tank, and the energy storage process ends; Energy release process: During the peak electricity period, open the second valve, the third valve, and the sixth valve, close the first valve, the fourth valve, and the fifth valve, the high-pressure carbon dioxide from the high-pressure storage tank enters the first expander to expand and do work after absorbing the heat of the high-temperature molten salt in the high-temperature storage tank through the second molten salt heat exchanger, the molten salt after heat exchange re-enters the low-temperature storage tank, and the low-pressure carbon dioxide after doing work re-enters the low-pressure storage tank to prepare for the next energy storage, and the energy release process ends; The low-temperature cycle module serves as the bottom cycle. The low-temperature and high-pressure working fluid absorbs the low-grade heat of the flue gas in the evaporator and then does work in the second expander.

[0014] The flue gas low-grade heat recovery system based on reverse Brayton cycle heat pump energy storage and its control method of the present invention is a coal-fired flue gas low-grade heat recovery system based on a cascade heat pump. Through the synergistic effect of the low-temperature stage and high-temperature stage heat pump cycles, the hierarchical utilization of high-grade and low-grade flue gas low-grade heat is realized, and both high-grade energy and low-grade energy are fully utilized. By storing energy during off-peak electricity periods and releasing energy during peak electricity periods, the spatio-temporal configuration of energy is optimized, the overall energy utilization efficiency is greatly improved, the low-grade flue gas low-grade heat can be effectively recovered, the peak regulation range of the unit is further expanded, and the load fluctuation is smoothed. Brief Description of the Drawings

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0016] Figure 1 It is a schematic structural diagram of a flue gas low-grade heat recovery system based on reverse Brayton cycle pump heat energy storage of the present invention.

[0017] In the figure: 1. Boiler, 2. Superheater, 3. Air preheater, 4. First valve, 5. First molten salt heat exchanger, 6. High-temperature storage tank, 7. Third valve, 8. Second molten salt heat exchanger, 9. Low-temperature storage tank, 10. Fourth valve, 11. First expander, 12. Low-pressure storage tank, 13. Fifth valve, 14. Compressor, 15. High-pressure storage tank, 16. Sixth valve, 17. Second valve, 18. Mixer, 19. Condenser, 20. Pump, 21. Regenerator, 22. Evaporator, 23. Second expander. Detailed Embodiments

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

[0019] As an important pillar of the current power system, coal-fired power generation often directly discharges medium- and low-temperature flue gas generated during its operation into the atmosphere, resulting in a large amount of waste of low-grade heat energy. At the same time, the large-scale grid connection of renewable energy has put forward higher requirements for the stability and flexibility of the power system, and the peak regulation and frequency modulation capabilities of coal-fired units need to be improved urgently. For this reason, the present invention provides a flue gas low-grade heat recovery system and control method based on reverse Brayton cycle pump heat energy storage, as Figure 1As shown in the figure, the system includes: a boiler module, a high-temperature circulation module, and a low-temperature circulation module; the output end of the boiler module is connected to the heat exchange components of the high-temperature circulation module and the low-temperature circulation module; In the boiler module, the flue gas side outlet of the superheater 2 in the boiler 1 is connected to the first inlet of the mixer 18 through the first valve 4 and the high-temperature circulation module; the flue gas side outlet of the air preheater 3 is connected to the second inlet of the mixer 18 through the second valve 17; the outlet of the mixer 18 is connected to the boiler module through the low-temperature circulation module.

[0020] Preferably, the high-temperature circulation module is a carbon dioxide energy storage module, preferably including: a thermal energy module and a pressure energy module; among them, the molten salt side of the first molten salt heat exchanger 5 is sequentially connected in series with the high-temperature storage tank 6, the third valve 7, the molten salt side of the second molten salt heat exchanger 8, the low-temperature storage tank 9, and the fourth valve 10 to form a loop, which is the thermal energy module; the working fluid side of the second molten salt heat exchanger 8 is sequentially connected in series with the first expander 11, the low-pressure storage tank 12, the fifth valve 13, the compressor 14, the high-pressure storage tank 15, and the sixth valve 16 to form a loop, which is the pressure energy module.

[0021] Preferably, the low-temperature circulation module includes: the working fluid side outlet of the first condenser 9 is connected to the working fluid side inlet of the regenerator 21 through the pump 20, the working fluid side outlet of the regenerator 21 is sequentially connected in series with the working fluid side of the evaporator 22, the second expander 23, and the medium side inlet of the regenerator 21, the medium side outlet of the regenerator 21 is connected to the working fluid side inlet of the first condenser 9, the medium side inlet of the first condenser 9 is introduced with condensed water, the medium side outlet of the first condenser 9 is externally connected to a low-temperature heater (for example: leading to a certain stage of low-temperature heater to replace part of the extraction steam), the outlet of the mixer 18 is connected to the medium side inlet of the evaporator 22, and the medium side outlet of the evaporator 22 is connected to the dust removal device in the boiler 1.

[0022] Preferably, the flue gas temperature at the flue gas side outlet of the superheater 2 is about 600 °C, and after heat exchange through the first molten salt heat exchanger 5, the temperature drops to about 200 °C, and it is mixed with the flue gas at about 100 °C from the air preheater 3 in the mixer 18 to improve the low-temperature recovery rate and optimize the overall operation performance of the system.

[0023] Preferably, the heat storage medium in the high-temperature storage tank 6 and the low-temperature storage tank 9 is solar salt, and the temperature range is set to 220 - 550 °C to achieve efficient heat storage and release, and at the same time ensure the stability and economy of the system within a wide temperature range.

[0024] Preferably, the pressure of the high-pressure storage tank 15 is set to 8 - 12 MPa, and the pressure of the low-pressure storage tank is set to 5 - 2 MPa to balance the energy density and safety of the carbon dioxide energy storage module and ensure the efficient and stable operation of the system.

[0025] Preferably, the compressor 14 is a positive displacement compressor, the first expander 11 is a turbine expander, and the second expander 23 is a screw expander.

[0026] Preferably, in the waste heat recycling module, the organic working fluid is R245fa, and the end temperature difference of each heat exchanger is specified to be 5-10 °C to ensure the heat exchange efficiency and ensure safe and stable operation at the same time.

[0027] On the other hand, the present invention provides a control method for controlling any of the above-mentioned flue gas low heat recovery systems, including: 1. Energy storage process: During the valley electricity period, open the first valve 4, the second valve 17, the fourth valve 10, and the fifth valve 13, close the third valve 7 and the sixth valve 16, and use the surplus power of the generator set to drive the compressor 14 to compress the carbon dioxide from the low-pressure storage tank 12 to a high-temperature and high-pressure state and store it in the high-pressure storage tank 15. The molten salt in the low-temperature storage tank 9 exchanges heat with the high-temperature flue gas in the first molten salt heat exchanger, and the high-temperature molten salt after absorbing heat is stored in the high-temperature storage tank 6, and the energy storage process ends.

[0028] 2. Energy release process: During the peak electricity period, open the second valve 17, the third valve 7, and the sixth valve 16, close the first valve 4, the fourth valve 10, and the fifth valve 13. The high-pressure carbon dioxide from the high-pressure storage tank 15 absorbs the heat of the high-temperature molten salt in the high-temperature storage tank 6 through the second molten salt heat exchanger and then enters the first expander 11 to expand and do work. The molten salt after heat exchange re-enters the low-temperature storage tank 9, and the low-pressure carbon dioxide after doing work re-enters the low-pressure storage tank 12 to prepare for the next cycle, and the energy release process ends.

[0029] 3. The low heat recycling module serves as the bottom cycle, and the low-temperature and high-pressure working fluid absorbs the low heat of the flue gas in the evaporator 22 and then does work in the second expander 23.

[0030] Advantages of the present invention: 1) The present invention provides a flue gas low heat recovery system based on reverse Brayton cycle heat pump energy storage and its control method, which is a coal-fired flue gas low heat recovery system based on a cascaded heat pump, capable of effectively recovering the low-grade flue gas low heat, further expanding the unit peak shaving range, and smoothing the load fluctuation.

[0031] Specifically: In this energy storage process, electrical energy and low-grade heat energy are converted into high-grade heat energy and pressure energy for storage; in this energy release process, high-grade heat energy and pressure energy are converted into low-grade heat energy and electrical energy for release; and the low heat recycling module operates during both the energy storage and energy release processes to absorb waste heat. Through the synergistic effect of the low-temperature and high-temperature heat pump cycles, the hierarchical utilization of high-grade and low-grade flue gas low heat is realized, both high-grade and low-grade energy sources are fully utilized, and through the energy storage during the valley electricity period and the energy release during the peak electricity period, the spatio-temporal configuration of energy is optimized, and the overall energy utilization efficiency is greatly improved.

[0032] 2) The present invention enhances the flexibility and economy of the system. The high-temperature heat cycle module can store electrical energy and thermal energy during low-demand periods of electricity, release energy during high-demand periods of electricity, and can quickly respond to the frequency fluctuations of the power system, improving the flexibility of the system. In addition, by recovering the low heat of flue gas and using low-cost electricity during off-peak hours, the operating cost of the system is reduced and the economy is improved.

[0033] 3) The present invention also has significant environmental protection and sustainable development benefits. By efficiently recovering the low heat of coal-fired flue gas and reducing the extraction steam of the unit, the energy waste of coal-fired power plants is reduced, and carbon emissions are indirectly reduced. The low-temperature heat cycle module uses the environmentally friendly working medium R245fa, reducing the negative impact on the environment. In addition, the system realizes the recycling of the low heat of flue gas, electrical energy and thermal energy, which conforms to the concept of sustainable development.

[0034] The above control method is created based on the above-mentioned low-heat recovery system of flue gas and will not be elaborated here. The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A flue gas low-temperature heat recovery system based on a reverse Brayton cycle heat pump energy storage, characterized in that: Including: A boiler module, a high-temperature circulation module, and a low-temperature circulation module; In the boiler module, the flue gas side outlet of the superheater in the boiler is connected to the first inlet of the mixer through the first valve and the high-temperature circulation module; the flue gas side outlet of the air preheater is connected to the second inlet of the mixer through the second valve; the outlet of the mixer is connected to the boiler module through the low-temperature circulation module.

2. The flue gas low-temperature heat recovery system according to claim 1, wherein: The high-temperature circulation module includes: a thermal energy module and a pressure energy module; Among them, the molten salt side of the first molten salt heat exchanger, the high-temperature storage tank, the third valve, the molten salt side of the second molten salt heat exchanger, the low-temperature storage tank, and the fourth valve are sequentially connected in series to form a loop, which is the thermal energy module; the working fluid side of the second molten salt heat exchanger, the first expander, the low-pressure storage tank, the fifth valve, the compressor, the high-pressure storage tank, and the sixth valve are sequentially connected in series to form a loop, which is the pressure energy module.

3. The flue gas low-temperature heat recovery system according to claim 2, wherein: The flue gas temperature at the flue gas side outlet of the superheater is 500 - 700 °C, and after heat exchange in the first molten salt heat exchanger, the temperature drops to about 150 - 250 °C, and it is mixed with the flue gas at 50 - 150 °C from the air preheater in the mixer.

4. The flue gas low-temperature heat recovery system according to claim 3, wherein: The heat storage medium in the high-temperature storage tank and the low-temperature storage tank is solar salt, and the temperature range is set to 220 - 550 °C.

5. The flue gas low-temperature heat recovery system according to claim 4, wherein: The pressure of the high-pressure storage tank is set to 8 - 12 MPa, and the pressure of the low-pressure storage tank is set to 5 - 2 MPa.

6. The flue gas low-temperature heat recovery system according to claim 5, wherein: The compressor is a positive displacement compressor.

7. The flue gas low-temperature heat recovery system according to claim 6, characterized in that: The first expander is a turbine expander, and the second expander is a screw expander.

8. The flue gas low-temperature heat recovery system according to any one of claims 2-7, characterized in that: The low-temperature circulation module is: the outlet of the working fluid side of the first condenser is connected to the inlet of the working fluid side of the regenerator through a pump, the outlet of the working fluid side of the regenerator is connected in series with the working fluid side of the evaporator, the second expander, and the inlet of the medium side of the regenerator in sequence, the outlet of the medium side of the regenerator is connected to the inlet of the working fluid side of the first condenser, the inlet of the medium side of the first condenser is fed with condensed water, the outlet of the medium side of the first condenser is externally connected to a low-temperature heater, the outlet of the mixer is connected to the inlet of the medium side of the evaporator, and the outlet of the medium side of the evaporator is connected to the dust removal device in the boiler.

9. The flue gas low-temperature heat recovery system according to claim 8, wherein: In the waste heat circulation module, the organic working fluid is R245fa, and the end difference of each heat exchanger is specified to be 5 - 10 °C.

10. A control method for controlling the flue gas low-temperature heat recovery system according to any one of claims 8-9, characterized in that, Including: Energy storage process: During the valley electricity period, open the first valve, the second valve, the fourth valve, and the fifth valve, close the third valve and the sixth valve, use the excess power of the generator set to drive the compressor, compress the carbon dioxide from the low-pressure storage tank to a high-temperature and high-pressure state and store it in the high-pressure storage tank, and the molten salt in the low-temperature storage tank exchanges heat with the high-temperature flue gas in the first molten salt heat exchanger, and the high-temperature molten salt after heat absorption is stored in the high-temperature storage tank, and the energy storage process ends; Energy release process: During the peak electricity period, open the second valve, the third valve, and the sixth valve, close the first valve, the fourth valve, and the fifth valve, the high-pressure carbon dioxide from the high-pressure storage tank absorbs the heat of the high-temperature molten salt in the high-temperature storage tank in the second molten salt heat exchanger and then enters the first expander to expand and do work, the molten salt after heat exchange re-enters the low-temperature storage tank, and the low-pressure carbon dioxide after doing work re-enters the low-pressure storage tank to prepare for the next energy storage, and the energy release process ends; The low-temperature circulation module serves as the bottom cycle, and the low-temperature and high-pressure working fluid absorbs the low heat of the flue gas in the evaporator and then does work in the second expander.

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