Flue gas recirculation system for low load of circulating fluidized bed boiler

Abstract

The invention discloses a low-load flue gas recirculation system for a circulating fluidized bed boiler. The low-load flue gas recirculation system comprises a hearth, and one end of a fifth pipeline is fixedly connected to the hearth; according to the invention, a part of flue gas is led out from the opening of the outlet flue of the induced draft fan and is introduced into the fourth pipeline, primary air heated by the first fan heater and the second fan heater is mixed, then pressurized by the first primary air fan and the second primary air fan and heated by the first preheater and the second preheater, and then enters a boiler air chamber; a dynamic parameter adjusting mechanism in the self-adaptive adjusting system adopts a feedforward-feedback composite control structure, the reheating steam temperature can be increased by about 2 DEG C every time the recirculation air volume is increased by 1%, the NOx concentration fluctuation is predicted in real time by applying an LSTM neural network, PID parameters are dynamically corrected through fuzzy reasoning, fuel characteristic changes are adapted, and the reheating steam temperature is increased by about 2 DEG C; and the amount of recycled flue gas is properly adjusted according to the load change to ensure that the unit is in the deep peak regulation load interval, and the unit operates to realize stable ultralow emission of NOx.

Description

Technical Field

[0001] This invention relates to the field of flue gas recirculation system technology, and in particular to a flue gas recirculation system for low-load circulating fluidized bed boilers. Background Technology

[0002] When a circulating fluidized bed boiler is running at low load, in order to ensure the minimum fluidizing air volume and the dual operation of the secondary air fan, the oxygen content of the boiler is very high, and the NO inside the furnace is very high. x High nitrogen production rates are observed in circulating fluidized bed boilers operating at ultra-low loads. To ensure fluidization on the furnace bed, the primary air volume must exceed the critical fluidization air volume. This results in a primary air volume significantly exceeding the combustion requirements during ultra-low load operation, hindering the formation of a reducing atmosphere for combustion. Consequently, the furnace outlet flue gas temperature is low during ultra-low load operation, and the existing SNCR denitrification efficiency is low, leading to high NO₂ levels in the boiler. x The original emissions have increased sharply and cannot meet the environmental protection requirements for ultra-low emissions; secondly, the adaptive adjustment system cannot achieve coordinated optimization of air volume, coal feed rate and oxygen content; therefore, it is necessary to design a flue gas recirculation system for low-load circulating fluidized bed boilers. Summary of the Invention

[0003] The purpose of this invention is to provide a flue gas recirculation system for low-load circulating fluidized bed boilers, in order to solve the NO problem in existing boilers. x The original emissions are high, which fails to meet the environmental protection requirements for ultra-low emissions and the system cannot achieve coordinated optimization of air volume, coal feed, and oxygen content through adaptive adjustment.

[0004] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a flue gas recirculation system for low-load circulating fluidized bed boilers, comprising a furnace, an induced draft fan, and an adaptive adjustment system. One end of a fifth pipe is fixedly connected to the furnace, and an induced draft fan is installed on the fifth pipe. A chimney is installed on the other end of the fifth pipe. One end of a fourth pipe is fixedly connected to the fifth pipe, and a recirculation fan is installed on the fourth pipe. The other end of the fourth pipe is fixedly connected to one end of a first pipe and one end of a second pipe. A first primary air fan and a first preheater are installed on the first pipe, and a second preheater and a second primary air fan are installed on the second pipe. The adaptive adjustment system is installed on the fifth pipe, and the adaptive adjustment system includes a dynamic parameter adjustment mechanism and an intelligent decision-making mechanism.

[0005] As a further technical solution of the present invention, one end of the flue gas bypass is fixedly connected to the fourth pipe, and the other end of the flue gas bypass is fixedly connected to the fifth pipe.

[0006] As a further technical solution of the present invention, a third shut-off valve is provided on the flue gas bypass, and a first shut-off valve is provided on the fourth pipeline.

[0007] As a further technical solution of the present invention, a first flue gas recirculation system and a first warm air blower are provided on the first pipe, and the other end of the first pipe is fixedly connected to the furnace.

[0008] As a further technical solution of the present invention, a second flue gas recirculation system and a second warm air blower are provided on the second pipe, and the other end of the second pipe is fixedly connected to the furnace.

[0009] As a further technical solution of the present invention, a third pipe is fixedly connected to the second pipe, the third pipe is fixedly connected to the fourth pipe, the third pipe is fixedly connected to the first pipe, and a second shut-off valve is provided on the third pipe.

[0010] As a further technical solution of the present invention, a sixth pipe is fixedly connected to the fourth pipe, and a fourth shut-off valve is provided on the sixth pipe.

[0011] As a further technical solution of the present invention, the recirculation fan is connected to an inert gas storage tank.

[0012] This invention provides a flue gas recirculation system for low-load circulating fluidized bed boilers. Its advantages include: flue gas is sent to the induced draft fan via a fifth pipe through the furnace; a portion of the flue gas is drawn out at the induced draft fan outlet flue and connected to a fourth pipe; it is mixed with primary air heated by a first and second warm air fan, then pressurized by the first and second primary air fans, heated by the first and second preheaters, and enters the boiler air chamber; then, as fluidizing air, it enters the furnace through the air distributor and air cap. The dynamic parameter adjustment mechanism in the adaptive control system adopts a feedforward-feedback composite control structure; each 1% increase in recirculated air volume can increase the reheat steam temperature by approximately 2°C; and an LSTM neural network is applied to predict NO in real time. x The concentration fluctuation is controlled with an accuracy of ±5 mg / m³. Fuzzy inference dynamically corrects PID parameters to adapt to changes in fuel characteristics. A digital twin model of the combustion process is established in the intelligent decision-making mechanism to predict operating conditions. Model predictive control (MPC) is used to balance denitrification efficiency, energy consumption, and reagent consumption. The recirculated flue gas volume is adjusted appropriately according to load changes to ensure the unit operates within the deep peak load range, achieving NO reduction. xStable ultra-low emissions; the flue gas recirculation duct is treated with anti-corrosion measures, and the duct expansion joint is made of corrosion-resistant non-metallic expansion joint. When the system is shut down, to prevent flue gas from leaking into the pipeline and corroding the pipeline, a flue gas bypass is used to ensure that if the shut-off valve is not tight and a slight leak occurs, the flue gas can be discharged in time. The first and second flue gas recirculation systems can deliver hot primary air to the inlet of the primary air fan in extreme cases. The secondary hot air in the sixth duct can flow back and be delivered to the outlet of the induced draft fan through the flue gas bypass, which can heat the pipeline and prevent the hot flue gas from condensing and corroding when it flows through the cold pipeline in the early stage of operation. Inert gas is added to the fourth duct through the recirculation fan 6 to reduce the local oxygen concentration, enhance the turbulence of the flue gas in the furnace, and extend the residence time in the high-temperature zone. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0015] Figure 2 for Figure 1 A magnified view of a portion of region A in the middle.

[0016] In the diagram: 1. Furnace; 2. Induced draft fan; 3. Chimney; 4. First shut-off valve; 5. Flue gas bypass; 6. Recirculation fan; 7. First flue gas recirculation system; 8. First warm air fan; 9. First primary air fan; 10. First preheater; 11. First pipeline; 12. Second pipeline; 13. Third pipeline; 14. Second flue gas recirculation system; 15. Second warm air fan; 16. Fourth pipeline; 17. Second preheater; 18. Second primary air fan; 19. Second shut-off valve; 20. Dynamic parameter adjustment mechanism; 21. Intelligent decision-making mechanism; 22. Adaptive adjustment system; 23. Fifth pipeline; 24. Third shut-off valve; 25. Fourth shut-off valve; 26. Sixth pipeline; 27. Inert gas storage tank. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Please see the appendix Figure 1 -Appendix Figure 2 An embodiment of the present invention provides a flue gas recirculation system for a circulating fluidized bed boiler at low load, comprising a furnace 1, an induced draft fan 2, and an adaptive adjustment system 22. One end of a fifth pipe 23 is fixedly connected to the furnace 1, and the induced draft fan 2 is installed on the fifth pipe 23. A chimney 3 is installed at the other end of the fifth pipe 23. One end of a fourth pipe 16 is fixedly connected to the fifth pipe 23, and a recirculation fan 6 is installed on the fourth pipe 16. The other end of the fourth pipe 16 is fixedly connected to one end of a first pipe 11 and a second pipe 12. A first primary air fan 9 and a first preheater 10 are installed on the first pipe 11, and a second preheater 17 and a second primary air fan 18 are installed on the second pipe 12. The adaptive adjustment system 22 is installed on the fifth pipe 23, and the adaptive adjustment system 22 includes a dynamic parameter adjustment mechanism 20 and an intelligent decision-making mechanism 21. One end of the fourth pipe 16 is fixedly connected to a flue gas bypass 5. The other end is fixedly connected to the fifth pipe 23. A third shut-off valve 24 is installed on the flue gas bypass 5. A first shut-off valve 4 is installed on the fourth pipe 16. A first flue gas recirculation system 7 and a first warm air blower 8 are installed on the first pipe 11. The other end of the first pipe 11 is fixedly connected to the furnace 1. A second flue gas recirculation system 14 and a second warm air blower 15 are installed on the second pipe 12. The other end of the second pipe 12 is fixedly connected to the furnace 1. A third pipe 13 is fixedly connected to the second pipe 12. The third pipe 13 is fixedly connected to the fourth pipe 16. The third pipe 13 is fixedly connected to the first pipe 11. A second shut-off valve 19 is installed on the third pipe 13. A sixth pipe 26 is fixedly connected to the fourth pipe 16. A fourth shut-off valve 25 is installed on the sixth pipe 26. The secondary hot air from the sixth pipe 26 can flow in reverse and is sent to the outlet of the induced draft fan 2 via the flue gas bypass 5, which serves to heat the pipe. The recirculation fan 6 is connected to the inert gas storage tank 27.

[0019] Specifically, in operation, the flue gas in the furnace 1 is first sent to the induced draft fan 2 through the fifth pipe 23. A portion of the flue gas is drawn out from the outlet flue of the induced draft fan 2 and connected to the fourth pipe 16. After being heated by the first warm air fan 8 and the second warm air fan 15, the flue gas is mixed with the primary air, pressurized by the first primary air fan 9 and the second primary air fan 18, heated by the first preheater 10 and the second preheater 17, and then enters the boiler air chamber. It then enters the furnace as fluidized air through the air distribution plate and the air cap. The dynamic parameter adjustment mechanism 20 in the adaptive adjustment system 22 adopts a feedforward-feedback composite control structure. Each 1% increase in recirculated air volume can increase the reheat steam temperature by about 2°C. The NO is predicted in real time using an LSTM neural network. xConcentration fluctuations are controlled with an accuracy of ±5 mg / m³. PID parameters are dynamically corrected through fuzzy inference to adapt to changes in fuel characteristics. A digital twin model of the combustion process is established in the intelligent decision-making mechanism 21 to predict operating conditions. A model predictive control (MPC) algorithm is used to balance denitrification efficiency, energy consumption, and reagent consumption. The recirculated flue gas volume is adjusted appropriately according to load changes to ensure the unit operates within the deep peak load range, achieving NO reduction. x Stable ultra-low emissions; the flue gas recirculation duct is treated with anti-corrosion, and the duct expansion joint is made of corrosion-resistant non-metallic expansion joint. When the system is shut down, in order to prevent flue gas from leaking into the pipeline and corroding the pipeline, the flue gas bypass 5 ensures that if the shut-off valve is not tight when the recirculation system is not in use, the slight leakage of flue gas can be discharged in time; the first flue gas recirculation system 7 and the second flue gas recirculation system 14 realize the function of sending hot primary air to the inlet of the primary air fan in extreme cases. The secondary hot air in the sixth pipeline 26 can flow back and be sent to the outlet of the induced draft fan 2 through the flue gas bypass 5, which plays the role of heating the pipeline and preventing the hot flue gas from flowing through the cold pipeline and causing condensation and corrosion problems in the early stage of flue gas recirculation. Inert gas is added to the fourth pipeline 16 through the recirculation fan 6 to reduce the local oxygen concentration, enhance the flue gas turbulence in the furnace 1, and extend the residence time in the high temperature zone.

[0020] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0021] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0022] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A flue gas recirculation system for a circulating fluidized bed boiler under low load, comprising a furnace (1), an induced draft fan (2), and an adaptive control system (22), characterized in that: The furnace (1) is fixedly connected to one end of the fifth pipe (23), and the fifth pipe (23) is equipped with an induced draft fan (2). The other end of the fifth pipe (23) is equipped with a chimney (3). The fifth pipe (23) is fixedly connected to one end of the fourth pipe (16), and the fourth pipe (16) is equipped with a recirculation fan (6). The other end of the fourth pipe (16) is fixedly connected to one end of the first pipe (11) and the second pipe (12). The first pipe (11) is equipped with a first primary air fan (9) and a first preheater (10). The second pipe (12) is equipped with a second preheater (17) and a second primary air fan (18). The fifth pipe (23) is equipped with an adaptive adjustment system (22), which includes a dynamic parameter adjustment mechanism (20) and an intelligent decision-making mechanism (21).

2. The flue gas recirculation system for a circulating fluidized bed boiler at low load according to claim 1, characterized in that: One end of the flue gas bypass (5) is fixedly connected to the fourth pipe (16), and the other end of the flue gas bypass (5) is fixedly connected to the fifth pipe (23).

3. The flue gas recirculation system for a circulating fluidized bed boiler at low load according to claim 2, characterized in that: The flue gas bypass (5) is equipped with a third shut-off valve (24), and the fourth pipeline (16) is equipped with a first shut-off valve (4).

4. The flue gas recirculation system for low-load circulating fluidized bed boilers according to claim 1, characterized in that: The first pipe (11) is equipped with a first flue gas recirculation system (7) and a first warm air blower (8), and the other end of the first pipe (11) is fixedly connected to the furnace (1).

5. A flue gas recirculation system for low-load circulating fluidized bed boilers according to claim 1, characterized in that: The second pipe (12) is equipped with a second flue gas recirculation system (14) and a second warm air blower (15), and the other end of the second pipe (12) is fixedly connected to the furnace (1).

6. A flue gas recirculation system for low-load circulating fluidized bed boilers according to claim 5, characterized in that: A third pipe (13) is fixedly connected to the second pipe (12), the third pipe (13) is fixedly connected to the fourth pipe (16), the third pipe (13) is fixedly connected to the first pipe (11), and a second shut-off valve (19) is provided on the third pipe (13).

7. A flue gas recirculation system for a circulating fluidized bed boiler at low load according to claim 6, characterized in that: A sixth pipe (26) is fixedly connected to the fourth pipe (16), and a fourth shut-off valve (25) is installed on the sixth pipe (26).

8. A flue gas recirculation system for low-load circulating fluidized bed boilers according to claim 1, characterized in that: The recirculation fan (6) is connected to the inert gas storage tank (27).

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