A boiler low-load stable combustion system and nitrogen oxide collaborative control method based on coal powder gasification

Abstract

This invention discloses a low-load stable combustion system and control method for a boiler based on pulverized coal gasification, comprising a boiler, a gasifier, and multiple coal mills; the boiler is equipped with multiple burners, including an A-layer burner, a C-layer burner, and a D-layer burner; the coal mills include coal mill A, coal mill C, and coal mill D; the gasifier is provided with a pulverized coal inlet, a secondary air inlet, and a gasification product outlet; the outlet of coal mill A is connected to the A-layer burner; the outlet of coal mill C is connected to both the pulverized coal inlet and the C-layer burner; the outlet of coal mill D is connected to both the pulverized coal inlet and the D-layer burner; the A-layer burner is connected to the A-layer gasification product inlet; the C-layer burner is connected to the C-layer gasification product inlet; the D-layer burner is connected to the D-layer gasification product inlet; the gasification product outlet is connected to the A-layer gasification product inlet, the C-layer gasification product inlet, and the D-layer gasification product inlet.

Description

Technical Field

[0001] This invention belongs to the field of coal-fired boilers and relates to a low-load stable combustion system for boilers based on pulverized coal gasification and a method for coordinated control of nitrogen oxides. Background Technology

[0002] With the large-scale grid connection of new energy sources such as wind power and photovoltaics, the power output is intermittent and fluctuating, and the peak-valley difference of the power grid continues to widen. The function of coal-fired power units is gradually shifting from traditional base load power supply to peak shaving as the main force, requiring frequent participation in deep peak shaving and long-term operation under low load or even ultra-low load conditions. In addition, most existing boilers are designed for high load conditions, resulting in lower furnace temperatures, worse ignition conditions, and imbalance between air and coal at low loads. Furthermore, the actual coal quality used by power plants fluctuates greatly, with a high proportion of low-quality mixed coal, which easily leads to problems such as unstable combustion, flameout and deflagration, insufficient denitrification flue gas temperature, and increased energy consumption and emissions. At the same time, deep peak shaving has been included in the assessment of the power auxiliary service market. In order to meet the requirements of safe and stable operation of the power grid, reduce fuel oil consumption and coal consumption for power generation, meet environmental emission standards, and improve the peak shaving benefits and operational flexibility of the units, it is urgent to carry out the transformation and upgrading of boilers to improve their low-load stable combustion capabilities.

[0003] When a boiler operates at low load and stable combustion, the overall combustion temperature in the furnace is low, the number of burners in operation is reduced, and the flame is concentrated. This easily leads to local combustion imbalance, significantly weakening the effects of air staging and low-NOx combustion organization. Simultaneously, the air-fuel ratio is prone to deviating from the optimal range, resulting in localized oxygen-deficient reducing atmospheres and prolonged afterburning within the furnace. This not only increases fluctuations in fuel-based NOx formation and allows for continued NOx generation in localized high-temperature zones, but also deteriorates combustion stability, disrupts the furnace temperature and oxygen concentration fields, and causes NOx emissions at the denitrification inlet. x Significant fluctuations in nitrogen oxide concentration greatly increase the difficulty of precise control under low-load conditions, easily leading to problems such as exceeding limits, excessive ammonia injection, and ammonia escape. Therefore, nitrogen oxide control needs to be considered simultaneously when the boiler is operating at low load and maintaining stable combustion. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a boiler low-load stable combustion system and control method based on pulverized coal gasification, which achieves stable combustion of the boiler at low load without the aid of any external heat source, while ensuring that nitrogen oxide emissions meet standards when the boiler is operating at low load.

[0005] To achieve the above objectives, the present invention employs the following technical solution: A low-load stable combustion system for a boiler based on pulverized coal gasification includes a boiler, a gasifier, and multiple coal mills; The boiler is equipped with multiple burners, including burners in layers A, C, and D; and multiple coal mills, including mill A, mill C, and mill D. The gasifier is equipped with a pulverized coal inlet, a secondary air inlet, and a gasification product outlet; The outlet of coal mill A is connected to the burner in layer A; the outlet of coal mill C is connected to the pulverized coal inlet and the burner in layer C; the outlet of coal mill D is connected to the pulverized coal inlet and the burner in layer D. The A-layer burner is connected to the A-layer gasification product inlet; the C-layer burner is connected to the C-layer gasification product inlet; the D-layer burner is connected to the D-layer gasification product inlet; the gasification product outlet is connected to the A-layer gasification product inlet, the C-layer gasification product inlet, and the D-layer gasification product inlet, respectively.

[0006] Optionally, valves a, b, c, and d may also be included; Valve b is installed on the pipeline between the outlet of coal mill C and the pulverized coal inlet; valve d is installed on the pipeline between the outlet of coal mill C and the burner in layer C. Valve a is installed on the pipeline between the outlet of the coal mill D and the pulverized coal inlet; valve c is installed on the pipeline between the outlet of the coal mill D and the burner of the D layer.

[0007] Optionally, valves e, f, and g may also be included; A valve g is installed on the pipeline between the gasification product outlet and the gasification product inlet of layer A; A valve f is installed on the pipeline between the gasification product outlet and the C-layer gasification product inlet; A valve e is installed on the pipeline between the gasification product outlet and the gasification product inlet of layer D.

[0008] Optionally, a pre-combustion chamber is arranged inside the A-layer burner; the outer wall of the pre-combustion chamber is connected to the A-layer gasification product inlet.

[0009] Optionally, a pulverized coal thickening device is arranged in front of the A-layer burner.

[0010] Optionally, a C-layer gasification product nozzle is inserted inside the C-layer burner; the front end of the C-layer gasification product nozzle forms a C-layer gasification product inlet; the end of the C-layer gasification product nozzle and the C-layer burner outlet are located on the same end face. The D-layer burner contains a D-layer gasification product nozzle; the front end of the D-layer gasification product nozzle forms the D-layer gasification product inlet; the end of the D-layer gasification product nozzle and the D-layer burner outlet are located on the same end face.

[0011] Optionally, it also includes a B-layer burner and a coal mill B; the outlet of the coal mill B is connected to the B-layer burner.

[0012] Optionally, a gasifier burner is arranged on the top of the gasifier; both the pulverized coal inlet and the secondary air inlet are arranged on the gasifier burner; the secondary air inlet is concentrically arranged outside the pulverized coal inlet.

[0013] A method for synergistic control of nitrogen oxides includes the following process: Step 1: Primary air carrying pulverized coal enters the gasifier through the pulverized coal inlet; secondary air enters the gasifier through the secondary air inlet. Step 2: The pulverized coal entering the gasifier undergoes incomplete combustion in an oxygen-deficient atmosphere, generating gasification products; Step 3: The gasification products are discharged through the gasification product outlet and, depending on the boiler's operating status, are allocated to at least one of the gasification product inlets in layers A, C, and D. Step 4: The gasified products entering the gasification product inlets of layer A, layer C, and layer D enter the boiler for combustion.

[0014] Optionally, the process of allocating resources based on the boiler's operating status in step three includes the following situations: When the boiler is under low load, pulverizers A and C are put into operation; the pulverized coal in pulverizer A enters the A-layer burner with the primary air; the pulverized coal discharged from pulverizer C is controlled to enter the pulverized coal inlet with the primary air. The first portion of the gasification products discharged from the gasification product outlet is introduced into the C-layer gasification product inlet and enters the boiler. The second part of the gasification products discharged from the gasification product outlet is introduced into the gasification product inlet of layer A and enters the pre-combustion chamber; The pulverized coal entering the A-layer burner is carried by the primary air flow through the pulverized coal thickening device to form a pulverized coal airflow that is thick in the center and thin around the edges. The thick pulverized coal airflow in the center enters the pre-combustion chamber and ignites the second part of the gasification products to generate combustible gasification products. The combustible gasification products enter the boiler from the A-layer burner for combustion.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention establishes a multi-path solid-gas material coupling channel between the boiler, gasifier, and coal mills A, C, and D. Part of the pulverized coal is input into the spatially isolated gasifier and converted into a high-temperature, highly chemically active gaseous reducing material. This material is then directed to burner layers at different elevations within the furnace according to operating conditions. This layout overcomes the high ignition energy limitation of direct combustion of all-solid-phase pulverized coal under traditional low-load conditions. Utilizing the extremely low ignition energy and high gas-phase diffusion rate of gaseous fuel, as well as the inherent chemical reducing activity of the gasification products, it provides a self-sustaining heat source and in-situ nitrogen reduction reactants for the furnace, achieving deep peak-shaving flexibility and dynamic control of NO inlet during denitrification. x concentration.

[0016] Furthermore, the shut-off and conduction functions of valves a, b, c, and d achieve the isolation and flexible allocation of the primary air and pulverized coal flow generated by coal mills C and D between the boiler combustion space and the gasifier reaction space. During periods of drastic load fluctuations or transient transitions to peak-shaving conditions, this valve group can precisely control the momentum direction of the two high-concentration gas-solid two-phase flows, effectively preventing crossflow, powder accumulation, or backflow caused by uneven pressure differentials in the primary air and pulverized coal flow between the two-way pipelines. This ensures the fluid dynamic stability of the fuel power supply system and the mass conservation of material input to each reactor during all operating condition transitions.

[0017] Furthermore, valves e, f, and g constitute an asymmetric decoupled regulation matrix for the high-temperature gasification products at the gasifier outlet. By adjusting the flow resistance and opening degree of each valve in this matrix, the limitations of friction resistance between multi-layer burner pipelines and uneven back pressure distribution inside the furnace can be overcome. This allows for proactive control of the mass fraction of gaseous reactants fed into the A-layer pre-combustion chamber, the C-layer gasification product inlet, and the D-layer gasification product inlet. Consequently, spatial decoupling and independent on-demand regulation are achieved between the energy and chemical energy supply for stable combustion in the lower part of the main combustion zone and the reducing agent concentration field ratio for reduction and nitrogen reduction in the upper part of the main combustion zone.

[0018] Furthermore, a pre-combustion chamber is integrated inside the A-layer burner and high-temperature gasification products are directly introduced. The convective and radiative heat release of the combustible gas carried by the gasification products can rapidly heat the local flow field and inner wall surface of the pre-combustion chamber to an extremely high thermodynamic activation energy range. When the solid coal powder gas flows through, instantaneous drying, pyrolysis volatilization and forced ignition can occur within a very short residence time. Thus, under low-load conditions where the overall temperature of the furnace heating surface is low and the heat radiation is insufficient, a fire-facing surface with rigid chemical heat release intensity is established.

[0019] Furthermore, the pulverized coal thickening device reconstructs the axial and radial mass concentration gradients in the front section of the A-layer burner by altering the inertial momentum distribution of the gas-solid two-phase flow, forming a heterogeneous flow field with a concentrated center and a less concentrated periphery. The high-concentration central solid-phase pulverized coal core enters the pre-combustion chamber, lowering the minimum ignition temperature rise threshold for local heterogeneous thermal ignition and enhancing the efficiency of the chain reaction between the gas and solid phases. Meanwhile, the outer layer of less concentrated airflow plays a reasonable role in boundary dynamic envelopment and oxygen distribution, not only preventing high-temperature slagging and coking caused by the dense-phase pulverized coal directly adhering to the walls and edges, but also facilitating the rigid extension of the high-temperature energy released by stable combustion towards the center of the furnace jet.

[0020] Furthermore, the C-layer and D-layer gasification product nozzles are coaxially integrated within the NOx-reducing burner, with their ends flush with the burner outlet face, forming a parallel mixing jet with parallel gas-solid composition and boundary grading. This structure restricts the contact between highly reducing CO and incompletely reacted coke and external oxygen before they leave the nozzle, preventing premature oxidation and deactivation of the reducing agent. This ensures that the high-NOx concentration is directly delivered to the upper part of the main combustion zone in the form of a high-reducing agent jet. x The core region maximizes the effect of gaseous free radicals and solid carbon particles on fuel-type and thermal NO. x The heterogeneous isomerization reduction reaction kinetics of NO were controlled at the source. x The peak value generated.

[0021] Furthermore, the configuration of the coal mill B and the B-layer burner establishes a physical transition barrier for conventional solid-phase pulverized coal combustion between the lower combustion stabilization layer and the upper-middle nitrogen reduction layer. When the system experiences rapid load increases or decreases, or when the gasifier system undergoes temporary shutdown or valve switching, the B-layer burner, by maintaining a continuous and stable output of conventional power coal, can provide spatial continuity of flow momentum and thermal flow field. This suppresses the disturbance of the tangential shear field at the four corners caused by sudden changes in the three-dimensional geometric flow field inside the furnace, ensuring the uniformity of heat load and thermal stress safety of the water-cooled wall heating surface.

[0022] Furthermore, the axially concentric arrangement of the pulverized coal inlet and the secondary air inlet at the top of the gasifier establishes an axial shear boundary layer with high shear and strong mass diffusion in the upper layer of the reactor inside the gasifier. Under the aerodynamic enclosure and confinement of the outer ring of secondary air, the pulverized coal carried by the primary air is forced to undergo multi-step pyrolysis and incomplete combustion in an extremely oxygen-deficient phase environment with an excess air coefficient of only 0.5. This compact reaction kinetic organization maximizes the chemical conversion rate of solid carbon in coal to gaseous CO, while maintaining the internal self-heating balance of the entire gasifier by utilizing the exothermic reaction itself.

[0023] This invention's control method reconstructs the conventional one-time, high-temperature, strong oxidation process of thermal coal into a two-stage decoupled thermodynamic cycle of external anoxic pyrolysis gasification, staged energy release within the furnace, and in-situ reduction. By artificially creating extremely high concentrations of reducing gaseous phase and micro-regional solid-phase intermediates in the first stage, and by performing directional convection compensation based on the three-dimensional thermal stress and load defects within the furnace in the second stage, it solves the problem that relying solely on adjusting the conventional air-coal ratio within the furnace cannot simultaneously achieve self-sustaining combustion under ultra-low loads and synergistic NO suppression in coal-fired power units. x The resulting natural barriers to the industry.

[0024] Furthermore, under extreme thermodynamic conditions of deep peak shaving at extremely low loads, this control method, by blocking specific coal mills and converting all the output of coal mill C into the chemical reaction flow of the gasifier, concentrates the limited volatile matter energy of the coal powder in the space-constrained gasification reactor into highly efficient reaction potential energy, and implements a two-way heat and mass flow diversion strategy: one path goes to the C-layer nozzle to utilize the locally rich combustion reducing atmosphere to spatially block, intercept, and in-situ reduce the rising NO in the main combustion zone. x Free radicals; another route leads to the A-layer pre-combustion chamber, where, based on a chain ignition kinetic mechanism of highly chemically active gas igniting the dense solid phase and the dense solid phase supporting the light phase, ultra-low load furnace self-sustaining stable combustion and NO are achieved without the assistance of conventional high-cost external fuel oil or plasma heat sources. x The synergistic evolution of ultra-low emissions. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the low-load stable combustion system for boilers based on pulverized coal gasification according to the present invention. Figure 2 This is a schematic diagram of the burner arrangement of the present invention; Figure 3 This is a schematic diagram of the A-layer burner structure of the present invention; Figure 4 This is a schematic diagram of the C-layer burner structure of the present invention; Figure 5 This is a schematic diagram of the D-layer burner structure of the present invention.

[0026] Wherein: 1-Boiler, 2-Gasifier, 3-Gasifier burner, 31-Pulverized coal inlet, 32-Secondary air inlet, 4-Gasification product outlet, 5-Pulverizer A, 6-Pulverizer B, 7-Pulverizer C, 8-Pulverizer D, 9-Valve a, 10-Valve b, 11-Valve c, 12-Valve d, 13-Valve e, 14-Valve f, 15-Valve g, 16-A-layer burner, 17-B-layer burner, 18-C-layer burner, 19-D-layer burner, 20-Pre-combustion chamber, 201-A-layer gasification product inlet, 21-Pulverized coal thickening device, 22-C-layer gasification product nozzle, 221-C-layer gasification product inlet, 23-D-layer gasification product nozzle, 231-D-layer gasification product inlet. Detailed Implementation

[0027] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0028] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. 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 indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terms “installation,” “connection,” and “linkage” should be interpreted broadly, for example, as a fixed connection, a detachable connection, or an integral connection; a mechanical connection, an electrical connection, or a connection that allows communication; a direct connection or an indirect connection via an intermediate medium; or a connection within two elements or an interaction between two elements. The term “and / or” as used herein includes any and all combinations of one or more of the associated listed items. Those skilled in the art will understand the specific meaning of the above terms in this invention according to the specific circumstances. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0030] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0031] The following disclosure provides many different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided in this invention, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0032] like Figure 1 As shown, the boiler low-load stable combustion system based on pulverized coal gasification described in this embodiment includes a boiler 1, a gasifier 2, a gasifier burner 3, a pulverized coal inlet 31, a secondary air inlet 32, a gasification product outlet 4, a coal mill A5, a coal mill B6, a coal mill C7, a coal mill D8, valves a9, b10, c11, d12, e13, f14, g15, A-layer burners 16, B-layer burners 17, C-layer burners 18, D-layer burners 19, a pre-combustion chamber 20, an A-layer gasification product inlet 201, a pulverized coal concentration device 21, a C-layer gasification product nozzle 22, a C-layer gasification product inlet 221, a D-layer gasification product nozzle 23, and a D-layer gasification product inlet 231.

[0033] The boiler 1 has burners arranged from bottom to top at its four corners: A-layer burner 16, B-layer burner 17, C-layer burner 18, and D-layer burner 19.

[0034] The inlets of coal mills A5, B6, C7, and D8 are respectively connected to hot primary air. The outlets of coal mills A5 and B6 are respectively connected to burners 16 in layer A and 17 in layer B. The outlet of coal mill C7 is connected to pulverized coal inlet 31 and burner 18 in layer C. A valve b10 is installed on the pipe from the outlet of coal mill C7 to pulverized coal inlet 31, and a valve d12 is installed on the pipe from the outlet of coal mill C7 to burner 18 in layer C. The outlet of coal mill D8 is connected to pulverized coal inlet 31 and burner 19 in layer D. A valve a9 is installed on the pipe from the outlet of coal mill D8 to pulverized coal inlet 31, and a valve c11 is installed on the pipe from the outlet of coal mill D8 to burner 19 in layer D.

[0035] A gasifier burner 3 is arranged at the top of the gasifier 2. A pulverized coal inlet 31 is located at the top of the gasifier 3. A secondary air inlet 32 ​​is arranged concentrically outside the pulverized coal inlet 31. A gasification product outlet 4 is located at the bottom of the gasifier 2. The gasification product outlet 4 is connected to the gasification product inlets 201 (layer A), 221 (layer C), and 231 (layer D). A valve g15 is installed on the pipeline from the gasification product outlet 4 to the gasification product inlet 201 (layer A), a valve f14 is installed on the pipeline from the gasification product outlet 4 to the gasification product inlet 221 (layer C), and a valve e13 is installed on the pipeline from the gasification product outlet 4 to the gasification product inlet 231 (layer D).

[0036] The A-layer burner 16 is a stable combustion burner. A pulverized coal thickening device 21 is arranged in front of the A-layer burner 16. A pre-combustion chamber 20 is arranged inside the A-layer burner 16. The outer wall of the pre-combustion chamber 20 is connected to the A-layer gasification product inlet 201.

[0037] The C-layer burner 18 and D-layer burner 19 are nitrogen-reducing burners. The C-layer burner 18 is equipped with a gasification product nozzle 22. The front end of the gasification product nozzle 22 is the C-layer gasification product inlet 221, and the end of the gasification product nozzle 22 is on the same end face as the outlet of the C-layer burner 18. The D-layer burner 19 is equipped with a gasification product nozzle 23. The front end of the gasification product nozzle 23 is the D-layer gasification product inlet 231, and the end of the gasification product nozzle 23 is on the same end face as the outlet of the D-layer burner 19.

[0038] The method for coordinated control of nitrogen oxides in a low-load stable combustion system of a boiler based on pulverized coal gasification is as follows: The gasifier 2 is used for pulverized coal gasification. Primary air flows through pulverizer C7 (pulverizer D8) to form a primary air-pulverized coal gas flow, which enters the gasifier 2 through pulverized coal inlet 31. Secondary air enters the gasifier 2 through secondary air inlet 32. The oxygen required for pulverized coal combustion is provided by both primary and secondary air. The excess air coefficient for pulverized coal combustion is 0.5. Under an oxygen-deficient atmosphere, pulverized coal undergoes incomplete combustion, generating gasification products mainly composed of CO and reducing gasification products such as coke.

[0039] When the boiler is operating at high load, pulverizers A5, B6, C7, and D8 are put into operation. Valves a9 and d12 are opened, and valves c11 and b10 are closed. The pulverized coal from pulverizers A5, B6, and C7 is directly carried by primary air through the corresponding burners and fed into the boiler for combustion. The pulverized coal from pulverizer D8 is carried by primary air into the gasifier, where oxygen-deficient combustion of the pulverized coal occurs, generating gasification products mainly composed of CO and reducing gasification products such as coke. Valve e13 is opened, and valves f14 and g15 are closed. The gasification products flow out from gasification product outlet 4 and enter the D-layer gasification product inlet 231, and are finally sent into the furnace through the D-layer gasification product nozzle 23. In the furnace, the reducing gasification products reduce the NOx generated by the combustion of pulverized coal in the furnace, thus reducing NOx emissions.

[0040] When the boiler is operating at medium load, pulverizers A5, B6, and C7 are put into operation. Valve b10 is opened, and valves a9, c11, and d12 are closed. The pulverized coal in pulverizers A5 and B6 is directly carried by primary air and fed into the boiler for combustion through the corresponding burners. The pulverized coal in pulverizer C7 is carried by primary air into the gasifier, where oxygen-deficient combustion of pulverized coal occurs, generating gasification products mainly composed of CO and reducing gasification products such as coke. Valve f14 is opened, and valves e13 and g15 are closed. The gasification products flow out from gasification product outlet 4 and enter the C-layer gasification product inlet 221, and are finally sent into the furnace through the C-layer gasification product nozzle 22. In the furnace, the reducing gasification products reduce the NOx generated by the combustion of pulverized coal in the furnace, thus reducing NOx emissions.

[0041] When the boiler is operating at low load, coal mills A5, B6, and C7 are put into operation. The coal mills reduce their output according to the unit load, opening valve b10 and closing valves a9, c11, and d12. The pulverized coal from coal mills A5 and B6 is directly carried by primary air through the corresponding burners into the boiler for combustion. The pulverized coal from coal mill C7 is carried by primary air into the gasifier, where oxygen-deficient combustion occurs, generating gasification products mainly composed of CO and reducing gasification products such as coke. Open valves f14 and a15, close valve e13. Part of the gasification products flow out from gasification product outlet 4 and into C-layer gasification product inlet 221, and finally into the furnace through C-layer gasification product nozzle 22. In the furnace, the reducing gasification products reduce the NOx generated by the combustion of pulverized coal in the furnace, reducing NOx emissions. Another part of the gasification products flow out from gasification product outlet 4 and into A-layer gasification product inlet 201, and then into pre-combustion chamber 20. After the primary air pulverized coal flow passes through the pulverized coal thickening device 21, it forms a state of concentrated in the middle and diluted around the edges. The concentrated pulverized coal flow in the center enters the pre-combustion chamber and is ignited by the high-temperature gasification products in the pre-combustion chamber to generate more combustible gasification products. All combustible gasification products enter the furnace from A-layer burner 16. Because the gasification products are very easy to burn, stable combustion at low load is achieved in the boiler.

[0042] Traditional pulverized coal boiler low-load stable combustion technology usually requires fuel oil or plasma, necessitating an external heat source. Furthermore, NOx emissions from low-load boilers are difficult to control. In this embodiment, a portion of pulverized coal undergoes a gasification reaction. The gasification products are then fed into the boiler for stable combustion and to reduce nitrogen oxide generation. Low-load stable combustion of the boiler is achieved through pulverized coal gasification, while the strong reducing properties of the gasification products are used to reduce NOx generated during pulverized coal combustion, thus achieving synergistic control of low-load stable combustion and nitrogen oxides.

[0043] The sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0044] In the above embodiments of this application, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0045] In the several embodiments provided in this application, it should be understood that the disclosed technical content can be implemented in other ways. The device embodiments described above are merely illustrative; for example, the division of units can be a logical functional division, and in actual implementation, there may be other division methods. For instance, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the displayed or discussed mutual coupling, direct coupling, or communication connection may be through some interfaces; the indirect coupling or communication connection between units or modules may be electrical or other forms.

[0046] 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 units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0047] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

[0048] It should be understood that the above description is for illustrative purposes and not for limitation. Many embodiments and applications beyond the provided examples will be apparent to those skilled in the art upon reading the above description. Therefore, the scope of this application should not be determined by reference to the above description, but rather by reference to the foregoing claims and the full scope of their equivalents. For purposes of completeness, all articles and references, including patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein in the foregoing claims is not intended as a waiver of that subject matter, nor should it be construed as an indication that the applicant has not considered that subject matter as part of the disclosed inventive subject matter.

Claims

1. A low-load stable combustion system for boilers based on pulverized coal gasification, characterized in that, It includes a boiler (1), a gasifier (2), and multiple coal mills; The boiler (1) is equipped with multiple burners; the multiple burners include A-layer burners (16), C-layer burners (18) and D-layer burners (19); the multiple coal mills include coal mill A (5), coal mill C (7) and coal mill D (8); The gasifier (2) is equipped with a pulverized coal inlet (31), a secondary air inlet (32) and a gasification product outlet (4); The outlet of coal mill A (5) is connected to the A-layer burner (16); the outlet of coal mill C (7) is connected to the pulverized coal inlet (31) and the C-layer burner (18) respectively; the outlet of coal mill D (8) is connected to the pulverized coal inlet (31) and the D-layer burner (19) respectively. The A-layer burner (16) is connected to the A-layer gasification product inlet (201); the C-layer burner (18) is connected to the C-layer gasification product inlet (221); the D-layer burner (19) is connected to the D-layer gasification product inlet (231); the gasification product outlet (4) is connected to the A-layer gasification product inlet (201), the C-layer gasification product inlet (221) and the D-layer gasification product inlet (231) respectively.

2. The low-load stable combustion system for boilers based on pulverized coal gasification according to claim 1, characterized in that, It also includes valve a (9), valve b (10), valve c (11) and valve d (12); Valve b (10) is arranged on the pipeline between the outlet of coal mill C (7) and the pulverized coal inlet (31); valve d (12) is arranged on the pipeline between the outlet of coal mill C (7) and the burner (18) of layer C. Valve a (9) is arranged on the pipeline between the outlet of the coal mill D (8) and the coal powder inlet (31); valve c (11) is arranged on the pipeline between the outlet of the coal mill D (8) and the burner (19) of the D layer.

3. The low-load stable combustion system for boilers based on pulverized coal gasification according to claim 1, characterized in that, It also includes valve e (13), valve f (14) and valve g (15); A valve g (15) is installed on the pipeline between the gasification product outlet (4) and the gasification product inlet (201) of layer A. A valve f (14) is arranged on the pipeline between the gasification product outlet (4) and the gasification product inlet (221) of layer C. A valve e (13) is installed on the pipeline between the gasification product outlet (4) and the gasification product inlet (231) of layer D.

4. The low-load stable combustion system for boilers based on pulverized coal gasification according to claim 1, characterized in that, The A-layer burner (16) has a pre-combustion chamber (20) inside; the outer wall of the pre-combustion chamber (20) is connected to the A-layer gasification product inlet (201).

5. The low-load stable combustion system for boilers based on pulverized coal gasification according to claim 4, characterized in that, A coal pulverizer (21) is arranged in front of the A-layer burner (16).

6. The low-load stable combustion system for boilers based on pulverized coal gasification according to claim 1, characterized in that, A C-layer gasification product nozzle (22) is inserted inside the C-layer burner (18); the front end of the C-layer gasification product nozzle (22) forms a C-layer gasification product inlet (221); the end of the C-layer gasification product nozzle (22) and the outlet of the C-layer burner (18) are located on the same end face; The D-layer burner (19) is equipped with a D-layer gasification product nozzle (23); the front end of the D-layer gasification product nozzle (23) forms a D-layer gasification product inlet (231); the end of the D-layer gasification product nozzle (23) and the outlet of the D-layer burner (19) are located on the same end face.

7. The low-load stable combustion system for boilers based on pulverized coal gasification according to claim 1, characterized in that, It also includes a B-layer burner (17) and a coal mill B (6); the outlet of the coal mill B (6) is connected to the B-layer burner (17).

8. The low-load stable combustion system for boilers based on pulverized coal gasification according to claim 1, characterized in that, A gasifier burner (3) is arranged on the top of the gasifier (2); the pulverized coal inlet (31) and the secondary air inlet (32) are both arranged on the gasifier burner (3); the secondary air inlet (32) is arranged concentrically outside the pulverized coal inlet (31).

9. A method for coordinated control of nitrogen oxides based on the system according to any one of claims 1-8, characterized in that, Includes the following processes: Step 1: Primary air carrying pulverized coal enters the gasifier (2) through the pulverized coal inlet (31); secondary air enters the gasifier (2) through the secondary air inlet (32); Step 2: The pulverized coal entering the gasifier (2) undergoes incomplete combustion in an oxygen-deficient atmosphere, generating gasification products; Step 3: The gasification products are discharged through the gasification product outlet (4) and, according to the operating status of the boiler (1), are allocated to at least one of the gasification product inlets of layer A (201), layer C (221), and layer D (231); Step 4: The gasification products entering the gasification product inlet (201) of layer A, the gasification product inlet (221) of layer C and the gasification product inlet (231) of layer D enter the boiler (1) for combustion.

10. The nitrogen oxide synergistic control method according to claim 9, characterized in that, Step three, which involves allocating resources based on the operating status of boiler (1), includes the following situations: When the boiler (1) is under low load, the coal mill A (5) and coal mill C (7) are put into the boiler (1); the coal powder in the coal mill A (5) enters the A layer burner (16) with the primary air; the coal powder discharged from the coal mill C (7) is controlled to enter the coal powder inlet (31) with the primary air. The first part of the gasification products discharged from the gasification product outlet (4) is introduced into the gasification product inlet (221) of layer C and enters the boiler (1); The second part of the gasification products discharged from the gasification product outlet (4) is introduced into the gasification product inlet (201) of layer A and enters the pre-combustion chamber (20); The pulverized coal entering the A-layer burner (16) is carried by the primary air flow through the pulverized coal thickening device (21) to form a pulverized coal airflow that is thick in the center and thin around the edges; the thick pulverized coal airflow in the center enters the pre-combustion chamber (20) and ignites the second part of the gasification products to generate combustible gasification products; the combustible gasification products enter the boiler (1) from the A-layer burner (16) for combustion.

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