Pulverized coal combustion method and system suitable for low-load operation of boiler

Abstract

The invention discloses a pulverized coal combustion method and system suitable for low-load operation of a boiler, and the method comprises the steps that high-temperature flames are provided through an independent fire source, so that the high-temperature flames and air distribution of an original combustor form a fire-rich and thin air cascade combustion mode, and the high-temperature flames supplement insufficient fire heat; by controlling the mixing proportion of high-temperature flames and air powder, the hearth temperature and the oxygen concentration are adjusted, so that low-load stable combustion is achieved, and generation of nitric oxide is restrained; by additionally arranging the independent fire source, the insufficient ignition heat is supplemented, and the problems that the boiler is low in hearth temperature, weak in airflow and unstable in combustion during low-load operation are solved. The independent fire source and the original primary air pulverized coal are simultaneously fed into the boiler for continuous combustion. High-temperature flames and air distribution of an original combustor form a fire-rich and thin air cascade combustion mode, and it can be guaranteed that the unit is stably ignited and combusted under any load.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of boiler combustion, and particularly relates to a pulverized coal combustion method and system suitable for low-load operation of a boiler. BACKGROUND

[0002] The statements herein only provide background technology related to the present application, and do not necessarily constitute prior art.

[0003] The "wind-packing-powder" series of thick and thin pulverized coal combustion technology is a series of pulverized coal combustion technology suitable for different furnace types and different coal types, and is one of the mainstream combustion technologies of coal-fired power plant boilers in China. The "wind-packing-powder" technology forms an optimal mixing ratio of air and coal powder through specific design when the coal powder enters the combustion chamber, so as to achieve more efficient and clean combustion. For the straight-flow burner of the four-corner tangential combustion mode, the fire side is a thick pulverized coal gas flow, the outer side is a thin pulverized coal gas flow and secondary air, forming a "wind-packing-powder" combustion mode; for the swirl burner arranged in front and back wall opposition, the center of the burner is fed with a thick pulverized coal gas flow, the outer side is a thin pulverized coal gas flow and inner and outer secondary air, forming a "wind-packing-powder" combustion mode, therefore, the "wind-packing-powder" combustion mode is a thick and thin air combustion mode.

[0004] Under the "double carbon" goal, coal-fired power plants must participate in grid peak shaving through variable load, and low-load operation of the boiler becomes the norm. Under low load, the existing "wind-packing-powder" technology has the following defects: 1. Insufficient combustion stability, at low load, the furnace temperature decreases and the airflow weakens, making it difficult for the coal powder to ignite, and combustion instability or even extinguishing phenomenon is prone to occur, especially when the pulverized coal concentration of the primary air is reduced due to the limitation of the pulverizing system, and the ignition heat supply is insufficient; 2. Increased nitrogen oxide emissions, at low load, the air volume is basically unchanged, but the amount of pulverized coal is reduced, causing excessive air volume in the combustion area, promoting the generation of thermal NOx, and it is difficult to meet environmental protection requirements; 3. Limited adaptability, the existing "wind-packing-powder" technology relies on the self-airflow organization of the furnace and lacks an external heat source supplementing mechanism, and cannot effectively cope with ultra-low load conditions. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the existing "wind-packing-powder" series of thick and thin pulverized coal combustion technology, and to provide a pulverized coal combustion method and system suitable for low-load operation of a boiler, which can realize the combustion of coal powder in a "fire-thick and thin air" combustion mode, solve the problem of unstable combustion or extinguishing of the burner at low load of the boiler, and ensure efficient and stable operation of the boiler.

[0006] In order to achieve the above-mentioned purpose, the present application is realized by the following technical scheme: In a first aspect, an embodiment of the present application provides a pulverized coal combustion method suitable for low-load operation of a boiler, comprising: The high-temperature flame is provided by an independent fire source, the high-temperature flame is mixed with the air of the original burner to form a fire-dense air gradient combustion mode, and the high-temperature flame supplements the shortage of the original fire heat. The furnace temperature and the oxygen concentration are adjusted by controlling the mixing ratio of the high-temperature flame and the air-powder, so that stable combustion at low load is realized and the generation of nitrogen oxides is inhibited.

[0007] As a further technical solution, when the original burner is a straight-flow burner arranged in a four-corner tangential circle mode, the high-temperature flame generated by the independent fire source is sent into the boiler on the fire side in parallel with the primary air powder of the original burner, to form a fire-dense air gradient combustion on the fire side.

[0008] As a further technical solution, when the original burner is a swirl burner arranged in a front-back wall opposite mode, the high-temperature flame generated by the independent fire source is sent into the original burner through a central pipe of the original burner, and is mixed with the primary air and the secondary air to form a central fire-dense air gradient combustion.

[0009] As a further technical solution, the independent fire source is ignited by an out-of-furnace oil burner, a gas burner or a coal powder burner and is then sent in.

[0010] In a second aspect, an embodiment of the present application provides a coal powder combustion system suitable for low-load operation, comprising: a primary air pipeline, a straight-flow burner, an independent fire source and a boiler. The primary air pipeline is connected with the straight-flow burner, and the air-powder mixture is delivered to the straight-flow burner; the straight-flow burner is arranged in a four-corner tangential circle mode in the boiler; and the independent fire source is arranged in parallel with the straight-flow burner.

[0011] As a further technical solution, the high-temperature flame ignited by the independent fire source is sent into the four-corner tangential circle straight-flow burner on the fire side.

[0012] As a further technical solution, the independent fire source is an out-of-furnace oil burner, a gas burner or a coal powder burner.

[0013] In a third aspect, an embodiment of the present application provides a coal powder combustion system suitable for low-load operation, comprising: a primary air pipeline, a swirl burner, an independent fire source and a boiler. The primary air pipeline is connected with the straight-flow burner, and the air-powder mixture is delivered to the straight-flow burner; the swirl burner is arranged in a front-back wall opposite mode in the boiler; and the independent fire source is arranged at a central position of the swirl burner.

[0014] As a further technical solution, the independent fire source enters the swirl burner through a central pipe of the swirl burner.

[0015] As a further technical solution, the central pipe is made of a high-temperature-resistant and wear-resistant material.

[0016] The beneficial effects of the above-mentioned embodiments of the present application are as follows: (1) When the boiler is in low load operation, the furnace temperature is low, and due to the restriction of the coal pulverizing system and the conveying system, the concentration of the primary air pulverized coal is low, which affects the ignition and stable combustion. By adding an independent fire source, the shortage of ignition heat is supplemented, and the problems of low furnace temperature, weak gas flow and unstable combustion of the boiler in low load operation are solved. The independent fire source and the original primary air pulverized coal are simultaneously sent into the boiler for continuous combustion. The high-temperature flame and the air distribution of the original burner form a "fire-thin and thick air" cascade combustion mode, which can ensure stable ignition and combustion of the unit at any load. The "fire-thin and thick air" cascade ignition and combustion mode can control the combustion temperature and oxygen content in the furnace to reduce the formation of thermal NOx in the furnace, thereby achieving the purpose of reducing NOx.

[0017] (2) The combustion method provided by the present application can construct a "fire-thin and thick air" cascade combustion mode of different burner forms according to various arrangement modes of the unit, and the number and layers of the original burner transformation are not limited. The original burner is actually an air and pulverized coal mixing injector, which relies on the flame in the furnace to supply ignition heat, and only by mutual cooperation and coordination can the ignition and combustion be realized (except for the pre-chamber). When the boiler is in low load operation, the furnace temperature is low, the gas flow is weak, and the ignition and stable combustion are affected. By adding an independent fire source, the shortage of ignition heat is supplemented in time to ensure stable combustion at low load.

[0018] (3) For the four-corner tangential arrangement of the straight-flow burner, the independent fire source is arranged in parallel with the straight-flow burner on the fire side of the four-corner tangential burner, and the high-temperature flame on the fire side and the primary air injected by the original burner form a "fire-thin and thick air" cascade combustion mode. For the front and back wall opposing arrangement of the swirl burner, the independent fire source is arranged at the center pipe position of the original burner, and the center high-temperature flame and the primary and secondary air of the original burner form a "fire-thin and thick air" cascade combustion mode to ensure stable combustion of the unit at low load. The present application is reasonable in design and simple in operation. The independent fire source is arranged outside the furnace, and the original system is slightly changed. The independent fire source can be repaired online during normal operation of the boiler without affecting the normal operation of the boiler. At the same time, it can ensure stable combustion of the boiler at low load and low NOx emission, and has strong functionality and is easy to popularize. BRIEF DESCRIPTION OF DRAWINGS

[0019] The drawings accompanying the specification of the present application form a part thereof, serve to provide further understanding of the present application, and together with the description of the exemplary embodiments of the present application and the explanation thereof, explain the present application, and do not constitute an improper limitation of the present application.

[0020] Figure 1 is a top view of the pulverized coal combustion system suitable for low load operation of embodiment 2 of the present application; Figure 2 is a schematic view of the independent fire source and the straight-flow burner outlet of embodiment 2 of the present application; Figure 3 This is a schematic diagram of the internal structure of the swirl burner in Embodiment 3 of the present invention; Figure 4 This is a schematic diagram of the independent fire source and swirl burner outlet in Embodiment 3 of the present invention.

[0021] The diagram is for illustrative purposes only. Among them, 1. Primary air duct; 2. DC burner; 3. Independent fire source; 4. Boiler; 5. Flame outlet of independent fire source on the fire side; 6. DC burner outlet; 7. Secondary air outlet; 8. Furnace wall; 9. Swirl burner; 10. Flame outlet of independent fire source in the center of swirl burner; 11. Primary air inlet of swirl burner; 12. Secondary air inlet of swirl burner. Detailed Implementation

[0022] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0023] Example 1 The existing "air-coated pulverized coal" combustion method in power plant boilers is a rich-lean air combustion method. If an external flame can enhance the rich-lean air or supplement the ignition heat, it can play a role in stabilizing combustion. Therefore, this invention proposes a "fire-rich-lean air" combustion method to supplement the insufficient ignition heat. This flame can be introduced after the external fuel burner, such as oil, gas, or pulverized coal, is ignited. This flame eliminates the phenomenon of low furnace temperature and weak airflow, which leads to unstable combustion when the boiler is operating at low load.

[0024] Specifically, in a typical embodiment of the present invention, a pulverized coal combustion method suitable for boiler operation at low load is provided, comprising: A high-temperature flame is provided by an independent fire source 3, which forms a fire-rich-lean air stepped combustion mode with the original burner air supply, so that the high-temperature flame can supplement the lack of fire heat. By controlling the mixing ratio of high-temperature flame and pulverized coal, the furnace temperature and oxygen concentration can be adjusted to achieve stable combustion under low load and suppress the generation of nitrogen oxides.

[0025] When boiler 4 operates at low load, the furnace temperature is low and the airflow is weak, making it difficult for pulverized coal to ignite and easily leading to flameout. The high-temperature flame of the independent ignition source 3 directly supplements the ignition heat, overcoming the limitations of traditional "air-coated pulverized coal" technology that relies on its own internal heat source. This allows pulverized coal to ignite stably even in low-temperature environments, extending the lower load limit to an ultra-low range. By controlling the mixing ratio of the high-temperature flame and air-coal mixture, the local temperature field and oxygen concentration in the furnace can be precisely adjusted, suppressing the formation conditions of thermal NOx. The cascade combustion method creates a high-temperature, low-oxygen zone, reducing the excess air coefficient and thus reducing NOx emissions by 20%-30%, meeting environmental protection requirements. This method does not rely on the inherent structure of boiler 4 and can dynamically adjust the flame intensity of the independent ignition source 3 according to the actual load, avoiding uneven pulverized coal concentration caused by a constant airflow in the pulverizing system, ensuring the sustainability of combustion efficiency. Overall, this method achieves efficient adaptation of boiler 4 to low-load conditions with minimal intervention.

[0026] In this embodiment, when the original burner is a DC burner 2 with a tangential arrangement at the four corners, the high-temperature flame generated by the independent fire source 3 is fed into the fire side of the boiler 4 in parallel with the primary air and pulverized coal of the original burner, forming a fire-rich-lean air stepped combustion on the fire side.

[0027] Understandably, the tangential combustion method relies on the tangential airflow organization within the furnace. At low loads, the tangential intensity weakens, affecting flame propagation. With the independent fire source 3 placed on the fire-facing side, the high-temperature flame and primary air jet flow in parallel, enhancing the tangential rotational momentum and forming a stable high-temperature flame core zone, preventing airflow deflection or flameout. For example... Figure 2 As shown, the independent ignition source's flame outlet 5 on the fire-side is parallel to the direct-flow burner outlet 6, with the flame enveloping the pulverized coal airflow, enhancing the continuity of the ignition front. This method only requires adding an independent ignition source 3 next to the existing burner, without altering the primary air duct 1 or the furnace wall 8 structure, retaining the advantages of the "air-enveloping-pulverized-coal" technology, while overcoming its low-load deficiency through external heat source compensation. Furthermore, the high-temperature region on the fire-side accelerates the release of volatile matter from the pulverized coal and the complete combustion of coke, enabling the boiler 4 to maintain high combustion efficiency even under low load, reducing unburned carbon loss and improving combustion efficiency.

[0028] In this embodiment, when the original burner adopts a swirl burner 9 with opposing front and rear walls, the high-temperature flame generated by the independent fire source 3 is sent in through the central tube of the swirl burner and mixed with the primary and secondary air to form a central fire-rich-lean air stepped combustion.

[0029] Understandably, the swirl burner 9 relies on the intensity of the swirl to create a stable combustion zone in the recirculation area, but this recirculation weakens at low loads. With the independent ignition source 3 integrated into the central tube, the high-temperature flame forms a stable ignition source at the center of the burner, enhancing the internal recirculation effect and strengthening the stability of central ignition. This allows the primary and secondary air pulverized coal to ignite rapidly in the core flame area, avoiding flame flickering or flameout problems at low loads.Figure 4 As shown, the central high-temperature flame and the surrounding air-coal form a "fire-rich-lean air" gradient. The central fuel-rich zone reduces the oxygen concentration, while the outer air-rich zone ensures complete combustion, achieving staged combustion control. This staged combustion effectively suppresses local high-temperature peaks and reduces the formation of thermal NOx. In addition, the independent ignition source 3 can be maintained online without affecting the main operation, making it particularly suitable for heating units or peak-shaving boilers 4 that operate at low loads for extended periods.

[0030] In this embodiment, the independent fire source 3 is supplied after ignition by an external oil burner, gas burner, or pulverized coal burner. Multiple fuel options allow the power plant to flexibly choose according to local resources. For example, gas burners have fast start-up and shutdown and low pollution, pulverized coal burners are low-cost, and oil burners have high calorific value. This flexibility ensures the universality of the method under different geographical locations and fuel supply conditions. The external fuel burner can be independently controlled, avoiding interference with the main pulverized coal system. It can be operated on demand during low loads and shut down during normal loads, reducing auxiliary fuel consumption. Simultaneously, the multi-fuel backup design improves system reliability; when one fuel is interrupted, other types can be switched to prevent boiler 4 from extinguishing. Finally, the modular design of the independent fire source 3 facilitates installation and maintenance, reduces dependence on the main boiler 4 system, and conforms to the principle of economical power plant operation and maintenance.

[0031] Example 2 The present invention provides a pulverized coal combustion system suitable for low-load operation, such as... Figure 1 and Figure 2 As shown, it includes: primary air duct 1, DC burner 2, independent heat source 3, and boiler 4; The primary air duct 1 is connected to the DC burner 2, which transports the air-coal mixture to the DC burner 2. The DC burner 2 is arranged in a tangential arrangement at the four corners inside the boiler 4. The independent fire source 3 is arranged parallel to the DC burner 2.

[0032] Furthermore, the high-temperature flame ignited by the independent fire source 3 is sent to the fire-facing side of the four-corner tangential DC burner 2.

[0033] Furthermore, the independent fire source 3 is an external fuel oil burner, gas burner, or pulverized coal burner.

[0034] The working principle of the pulverized coal combustion system provided in this embodiment is as follows: An independent fire source 3 is added next to the DC burner 2. The flame of the independent fire source 3 is injected into the furnace from the four corners of the tangential boiler 4 towards the fire side. The flame outlet 5 of the independent fire source towards the fire side is parallel to the original DC burner outlet 6 in the furnace. The flame of the independent fire source 3 and the primary air-coal mixture at the original burner outlet form a "fire-rich-lean air" stepped combustion mode.

[0035] The independent fire source 3 can be supplied after the burner of various fuels such as oil, gas, and pulverized coal is ignited outside the furnace. This flame supplements the insufficient ignition heat and eliminates the phenomenon of low furnace temperature and weak airflow, which leads to unstable combustion when the boiler 4 is operating at low load.

[0036] Specifically, the ignited high-temperature flame is sent to the fire-facing side of the four-corner tangential burners, forming a high-temperature, low-oxygen flame zone in the center of the boiler's fourth furnace, while the four corners of the furnace wall have a relative excess of air. This achieves a "fire-rich-lean air" combustion mode in the furnace, which not only helps reduce thermal NOx but also improves stable combustion.

[0037] Example 3 In a typical embodiment of the present invention, a pulverized coal combustion system suitable for low-load operation is provided, such as... Figure 3 and Figure 4 As shown, it includes: primary air duct 1, swirl burner 9, independent heat source 3 and boiler 4; The primary air duct 1 is connected to the direct current burner 2, which transports the air-coal mixture to the direct current burner 2. The swirl burner 9 is arranged in a front-to-back wall arrangement inside the boiler 4. The independent fire source 3 is located at the center of the swirl burner 9.

[0038] Furthermore, the independent fire source 3 enters the swirl burner 9 through the central tube of the swirl burner 9.

[0039] Furthermore, the central tube is made of a high-temperature resistant and wear-resistant material.

[0040] The working principle of the pulverized coal combustion system provided in this embodiment is as follows: an independent fire source 3 is added at the bend of the primary air duct 1. The flame of the independent fire source 3 enters the original burner through the central tube of the swirl burner 9. The flame outlet 10 of the independent fire source in the center of the swirl burner, together with the primary air inlet 11 and the secondary air inlet 12 of the swirl burner, form a stepped combustion mode of central "fire-rich and lean air".

[0041] The independent fire source 3 can be supplied after the burner of various fuels such as oil, gas, and pulverized coal is ignited outside the furnace. This flame supplements the insufficient ignition heat and eliminates the phenomenon of low furnace temperature and weak airflow, which leads to unstable combustion when the boiler 4 is operating at low load.

[0042] Specifically, the center tube of the swirl burner 9 needs to be replaced with a high-temperature resistant and wear-resistant material, while the size of the center tube remains unchanged.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A pulverized coal combustion method suitable for low load operation of a boiler, characterized by, include: By providing a high-temperature flame through an independent fire source, the high-temperature flame and the original burner air supply form a fire-rich-lean staged combustion mode, so that the high-temperature flame supplements the lack of fire heat. By controlling the mixing ratio of high-temperature flame and pulverized coal, the furnace temperature and oxygen concentration can be adjusted to achieve stable combustion under low load and suppress the generation of nitrogen oxides.

2. The pulverized coal combustion method suitable for a low load operation of a boiler according to claim 1, characterized by, When the original burner adopts a direct-flow burner with a tangential arrangement at the four corners, the high-temperature flame generated by the independent fire source is fed into the boiler fire side in parallel with the primary air and pulverized coal of the original burner, forming a fire-rich-lean air stepped combustion on the fire side.

3. The pulverized coal combustion method suitable for low load operation of a boiler according to claim 1, wherein When the original burner adopts a swirl burner with opposing front and rear walls, the high-temperature flame generated by the independent fire source is sent into the central tube of the original burner and mixed with the primary and secondary air to form a central fire-rich-lean air stepped combustion.

4. The pulverized coal combustion method suitable for low load operation of a boiler according to claim 1, wherein The independent fire source is supplied after the external fuel oil burner, gas burner, or pulverized coal burner is ignited.

5. A pulverized coal combustion system suitable for low load operation for realizing the pulverized coal combustion method according to claim 1 or 2, characterized by, include: Primary air duct, DC burner, independent heat source and boiler; The primary air duct is connected to the DC burner, which delivers the air-coal mixture to the DC burner. The DC burner is arranged in a tangential configuration within the boiler, and the independent fire source is set parallel to the DC burner.

6. The pulverized coal combustion system suitable for low load operation as recited in claim 5, wherein The high-temperature flame ignited by the independent fire source is sent to the fire-facing side of the four-corner tangential DC burner.

7. The pulverized coal combustion system suitable for low load operation according to claim 5, wherein The independent ignition source is an external fuel oil burner, gas burner, or pulverized coal burner.

8. A pulverized coal combustion system suitable for low load operation for realizing the pulverized coal combustion method according to claim 1 or 3, characterized by, include: Primary air duct, swirl burner, independent heat source and boiler; The primary air duct is connected to the DC burner, which delivers the air-coal mixture to the DC burner. The swirl burner is arranged with the front and rear walls facing each other inside the boiler, and the independent fire source is located at the center of the swirl burner.

9. The pulverized coal combustion system suitable for low load operation according to claim 8, wherein The independent ignition source enters the swirl burner through the central tube of the swirl burner.

10. The pulverized coal combustion system suitable for low load operation according to claim 9, wherein The central tube is made of a high-temperature resistant and wear-resistant material.

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