Staged low-nitrogen combustion system and method for anthracite boiler

Abstract

The invention discloses a graded low-nitrogen combustion system and method for an anthracite boiler. The graded low-nitrogen combustion system comprises a hearth body. The burner groups are symmetrically arranged along the periphery of the lower part of the hearth and adopt direct-current burner tangential combustion, each group comprises parallel primary air and secondary air nozzles, and the primary air nozzles are divided into thick pulverized coal nozzles and thin pulverized coal nozzles and are horizontally distributed at intervals; the graded air supply unit is provided with a main secondary air system for supplying air to the main combustion area, a compact type over fire air system above the combustor group and a separated type over fire air system above the compact type over fire air system, and a nozzle of the separated type over fire air system is at least divided into two stages along the height of a hearth to form a three-stage air supply structure; the fuel staged supply unit comprises a coal pulverizing system and a thick-thin separation device, and can be used for separating pulverized coal airflow and conveying the pulverized coal airflow to the corresponding nozzles; the intelligent regulation and control module collects parameters through a sensor set, and a controller adjusts air supply and fuel supply in a linkage mode through an executing mechanism according to the parameters. The atmosphere in the furnace can be organized cooperatively, dynamic adjustment is achieved, and the problem that the combustion efficiency is reduced during deep low-nitrogen emission is solved.

Description

Technical Field

[0001] This invention belongs to the field of thermal power generation equipment and control technology, specifically relating to a staged low-NOx combustion system and method for anthracite boilers. Background Technology

[0002] Nitrogen oxides (NOx) produced during the combustion of pulverized coal in boilers are among the major air pollutants. To control NOx emissions, low-NOx combustion technology, as a solution that controls emissions at the combustion source, is widely used due to its relatively low cost.

[0003] Currently, low-NOx combustion technologies applied to power plant boilers mainly revolve around two approaches: air staging and fuel staging. Air staging technology, by placing burnout air nozzles (such as compact burnout air, CCOFA) above the main combustion zone, creates an initial oxygen-deficient combustion stage, which can suppress NOx formation to some extent. However, for difficult-to-burn coals like anthracite, which have low volatile matter and are difficult to ignite and burn completely, simply using air staging to excessively suppress the oxygen content in the main combustion zone in pursuit of lower NOx emissions can easily lead to incomplete combustion of pulverized coal, increased carbon content in fly ash, and decreased boiler efficiency. Conversely, if the oxygen concentration in the main combustion zone is increased to ensure combustion efficiency, NOx formation will increase significantly. This contradiction is particularly prominent in anthracite combustion. In addition, to further reduce NOx, existing technologies also attempt to introduce fuel staging technology, which involves injecting a portion of fuel into specific areas of the furnace to create a strong reducing zone to reduce the NOx that has already been generated. However, in practical applications, especially in tangential combustion boilers, a key technical challenge is how to accurately deliver and stably maintain the reburning fuel within the intended combustion zone, and effectively coordinate it with air staging, rather than simply mixing it with the main fuel. Simple fuel staging, without a matching combustion space organization, has limited and unstable denitrification effects.

[0004] Therefore, existing technologies lack a combustion system that can systematically and collaboratively organize the combustion atmosphere in the furnace space and has dynamic adjustment capabilities to address the problem of reduced combustion efficiency faced by anthracite boilers when achieving deep low-NOx emissions. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a staged low-NOx combustion system and method for anthracite boilers. Its purpose is to systematically and collaboratively organize the combustion atmosphere in the furnace space, possess dynamic adjustment capabilities, and solve the problem of reduced combustion efficiency faced by anthracite boilers when achieving deep low-NOx emissions.

[0006] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution: According to a first aspect of the present invention, a staged low-NOx combustion system for anthracite boilers is provided, comprising: Furnace body; The burner group is symmetrically arranged along the lower perimeter of the furnace body and adopts a direct-flow burner tangential combustion form. Each burner group includes several primary air nozzles and secondary air nozzles arranged in parallel. The primary air nozzles include concentrated pulverized coal nozzles for supplying concentrated pulverized coal and dilute pulverized coal nozzles for supplying dilute pulverized coal. The concentrated pulverized coal nozzles and dilute pulverized coal nozzles are distributed at intervals along the horizontal direction of the furnace. The graded air supply unit includes a main secondary air system that supplies air to the main combustion zone, a compact burnout air system arranged above the burner group, and a separate burnout air system arranged above the compact burnout air system. The nozzles of the separate burnout air system are divided into at least two stages along the furnace height direction, forming a three-stage air supply structure in the vertical direction. The fuel grading supply unit includes a pulverizing system and a concentration-lean separation device connected to the outlet of the pulverizing system, which is used to separate the coal powder gas flow into a concentrated coal powder gas flow and a lean coal powder gas flow, and respectively deliver them to the concentrated coal powder nozzle and the lean coal powder nozzle. The intelligent control module includes a sensor group for collecting combustion state parameters in the furnace, a controller, and an actuator connected to the staged air supply unit and the staged fuel supply unit. The controller is used to adjust the air supply and fuel supply in a coordinated manner through the actuator according to the parameters.

[0007] In one possible implementation of the first aspect, the secondary air nozzles of the staged air supply unit include a main secondary air nozzle whose nozzle axis is parallel to the radial direction of the furnace, and a side secondary air nozzle whose nozzle axis is deflected toward the furnace wall.

[0008] In one possible implementation of the first aspect, the nozzle axis of the secondary air nozzle is adjustable within a deflection angle range of 15° to 25°.

[0009] In one possible implementation of the first aspect, the separate burnout air system includes a primary separate burnout air nozzle and a secondary separate burnout air nozzle, wherein the vertical distance between the primary separate burnout air nozzle and the nozzle of the compact burnout air system is 2.5~3.0m, and the vertical distance between the secondary separate burnout air nozzle and the primary separate burnout air nozzle is 3.0~3.5m.

[0010] In one possible implementation of the first aspect, the air flow ratio of the primary separated burnout air nozzle to the secondary separated burnout air nozzle is 1:1.2 to 1:1.5.

[0011] In one possible implementation of the first aspect, the ratio of the number of concentrated pulverized coal nozzles to the number of dilute pulverized coal nozzles is 4:1; the pulverized coal concentration of the concentrated pulverized coal gas stream output by the concentrated-dilute separation device is 0.8~1.2 kg / kg, and the pulverized coal concentration of the dilute pulverized coal gas stream is 0.2~0.4 kg / kg.

[0012] In one possible implementation of the first aspect, the controller of the intelligent control module integrates a fuzzy PID control algorithm; the sensor group includes at least a NOx concentration sensor and an oxygen content sensor arranged at the furnace outlet.

[0013] In one possible implementation of the first aspect, a furnace soot blowing unit and an anti-coking monitoring unit are also included, wherein the anti-coking monitoring unit includes an infrared temperature sensor disposed on the surface of the furnace water-cooled wall.

[0014] In one possible implementation of the first aspect, the side secondary air nozzles are arranged on the outermost side in the horizontal direction of each burner group.

[0015] According to a second aspect of the present invention, a method for staged low-NOx combustion in an anthracite boiler based on the said system is provided, comprising the following steps: The prepared pulverized coal is separated into concentrated pulverized coal gas flow and dilute pulverized coal gas flow through a concentration separation device. The concentrated pulverized coal gas flow and dilute pulverized coal gas flow are then sent into different areas of the furnace through concentrated pulverized coal nozzles and dilute pulverized coal nozzles, respectively, to achieve horizontal staged supply of fuel. Combustion air is supplied in three stages along the height of the furnace through the main and secondary air systems, the compact burnout air system, and the separate burnout air system. The oxygen-deficient combustion conditions are maintained in the main combustion zone, and the subsequent burnout of pulverized coal is achieved through the upper burnout air system. By adjusting the air delivery direction of the side secondary air nozzles, a central fuel-rich zone and a near-wall oxygen-rich zone are formed radially in the furnace. The NOx concentration at the furnace outlet and parameters reflecting boiler efficiency are monitored in real time, and the air distribution ratio of the graded air supply unit and the distribution ratio of the fuel graded supply unit are adjusted in conjunction to coordinate the control of NOx emissions and combustion efficiency.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects: This invention provides a staged low-NOx combustion system for anthracite boilers. First, a fuel staged supply unit pre-separates pulverized coal into rich and lean streams. Then, the burner assembly delivers the rich and lean pulverized coal into the furnace through nozzles at different locations, achieving initial horizontal staged fuel classification. Simultaneously, a staged air supply unit constructs a gradient oxygen concentration field vertically from the primary combustion zone (oxygen-deficient) to the burnout zone (oxygen-rich) through primary and secondary air, compact burnout air, and two-stage separated burnout air. This allows the furnace to simultaneously contain a reducing primary combustion zone conducive to suppressing NOx formation and an oxygen-rich burnout zone conducive to ensuring combustion efficiency. From a physical structure perspective, this overcomes the problem of incomplete combustion caused by sacrificing oxygen in pursuit of low NOx in traditional technologies. In existing technologies, air staged and fuel staged systems are often used independently or in simple combinations, easily leading to poor airflow-fuel matching and unstable reburning zones. This invention organically integrates vertical air staged, horizontal air staged, and fuel staged systems through its system structure. The placement of the pulverized coal nozzles is coordinated with the staged air supply design to ensure that reburning fuel is delivered and stably present in the expected reducing atmosphere region, thereby effectively reducing NOx rising from the main combustion zone. This synergistic design allows the low-NOx and burnout processes to be seamlessly integrated and mutually reinforcing within the furnace space, rather than mutually restricting each other. To address the changes in operating conditions caused by fluctuations in coal quality and load during boiler operation, the intelligent control module uses a sensor array to monitor the combustion status in the furnace in real time, such as NOx concentration and oxygen content, and uses the controller to adjust the air distribution ratio of the air supply unit and the allocation ratio of the fuel staged supply unit. When an upward trend in NOx concentration is detected, the air-coal ratio can be adjusted in a timely manner to enhance the reducing atmosphere; when the burnout condition is deemed poor, the burnout air supply strategy can be optimized. This ensures that the system can automatically optimize and maintain the best balance between low NOx and high efficiency under various operating conditions. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings used in the description of the specific embodiments 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 from these drawings without creative effort.

[0018] Figure 1 This is a schematic block diagram of a staged low-NOx combustion system for anthracite boilers. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions 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.

[0020] like Figure 1 As shown, the present invention provides a staged low-NOx combustion system for anthracite boilers, which mainly includes a furnace body, a burner group, a staged air supply unit, a staged fuel supply unit, and an intelligent control module. Through structural design, it realizes the systematic staged and coordinated operation of air and fuel in the furnace space.

[0021] The burner groups are symmetrically arranged along the lower perimeter of the furnace body, and adopt a direct-flow burner tangential combustion form. Each burner group includes several primary air nozzles and secondary air nozzles arranged in parallel. The primary air nozzles include concentrated pulverized coal nozzles for supplying concentrated pulverized coal and dilute pulverized coal nozzles for supplying dilute pulverized coal. The concentrated pulverized coal nozzles and dilute pulverized coal nozzles are distributed at intervals along the horizontal direction of the furnace.

[0022] The staged air supply unit includes a main secondary air system that supplies air to the main combustion zone, a compact burnout air system arranged above the burner group, and a separate burnout air system arranged above the compact burnout air system. The nozzles of the separate burnout air system are divided into at least two stages along the furnace height direction, forming a three-stage air supply structure in the vertical direction.

[0023] The fuel grading supply unit includes a pulverizing system and a concentration-lean separation device connected to the outlet of the pulverizing system, which is used to separate the coal powder gas flow into a concentrated coal powder gas flow and a lean coal powder gas flow, and respectively deliver them to the concentrated coal powder nozzle and the lean coal powder nozzle.

[0024] The intelligent control module includes a sensor group for collecting combustion state parameters in the furnace, a controller, and an actuator connected to the staged air supply unit and the staged fuel supply unit. The controller is used to adjust the air supply and fuel supply in a coordinated manner through the actuator according to the parameters.

[0025] Specifically, the furnace body, serving as the combustion space, adopts a π-shaped arrangement. For example, the furnace body has a width of 33.6m, a depth of 15.8m, a height of 68.2m, and a furnace volume of approximately 35,000 m³. 3 This design is suitable for the evaporation requirements of large generator sets. The furnace water-cooled walls adopt a membrane wall structure, for example, using tubes made of SA-213T23 material with a specification of φ51×6.5 mm and a pitch of 63.5 mm. A cold ash hopper with an inclination angle of 55° is installed at the bottom of the furnace.

[0026] Specifically, the burner group adopts direct-flow burners, symmetrically arranged along the front, rear, left, and right walls of the lower part of the furnace body, forming a tangential combustion pattern. For example, 6 to 8 burner groups can be arranged on each side wall; exemplarily, 7 burner groups are arranged on each side wall, for a total of 28 groups on all four sides. The primary air nozzles of adjacent burner groups form a tangential combustion trajectory with a diameter of 1.8 to 2.2 m. A double tangential arrangement with opposite rotation directions can be used to suppress coking and flue gas temperature deviation. Each burner group includes several primary air nozzles and secondary air nozzles arranged in parallel. The primary air nozzles and secondary air nozzles are arranged alternately, forming an alternating primary and secondary air structure. The primary air nozzles are further divided into concentrated pulverized coal nozzles and dilute pulverized coal nozzles, which are distributed alternately in the horizontal direction of the burner group. The concentrated pulverized coal nozzles can adopt a contraction-expansion type nozzle with an outlet velocity designed to be 28 to 32 m / s; the dilute pulverized coal nozzles can adopt a straight-cylinder type nozzle with an outlet velocity designed to be 22 to 26 m / s. An adjustment baffle is installed at the inlet of the primary air nozzle to adjust the coal powder flow rate according to the characteristics of the coal type, with an adjustment range of 50% to 100%.

[0027] Specifically, the staged air supply unit is responsible for achieving vertical deep air grading. This unit includes a primary and secondary air system, a compact burnout air (CCOFA) system, and a separate burnout air (SOFA) system. The nozzles of the primary and secondary air system are connected to the burner assembly. The air supply duct can adopt a dual-inlet structure with a diameter of 1.2m, and the air temperature is 320~350℃, responsible for supplying the basic air required for combustion to the main combustion zone of the furnace. The nozzles of the compact burnout air (CCOFA) system are arranged adjacent to the uppermost secondary air nozzles of the burner assembly, at a vertical distance of, for example, 1.2m. The nozzle diameter can be 0.6m, and the outlet velocity is 40~45 m / s. The air flow rate of the CCOFA nozzle is 30%~40% of the flow rate of the corresponding secondary air nozzle below it. The nozzles of the Separate Burnout Air (SOFA) system are positioned above the CCOFA system and are divided into two stages along the furnace height: a primary SOFA nozzle and a secondary SOFA nozzle. Together with the main and secondary air and the CCOFA, this forms a three-stage air supply structure in the vertical direction. The SOFA nozzles can be designed to be oscillating, with an oscillation angle of ±30°.

[0028] Specifically, the fuel grading and supply unit is responsible for achieving fuel concentration separation and targeted supply, including a pulverizing system, a concentration separation device, a pulverized coal distributor, and conveying pipelines. The pulverizing system can employ a medium-speed coal mill, such as the ZGM-113G model, with a total of 6 units, each with an output of 60 t / h, and its outlet pulverized coal fineness R90 controlled at 8%~12%. A weighing belt feeder is used at the coal mill inlet, with a feeding accuracy of ±1%. The concentration separation device is connected to the outlet of the pulverizing system, employing, for example, a cyclone separator structure, with 2 units corresponding to each coal mill, internally equipped with guide vanes and cyclones, achieving a separation efficiency ≥90%. Under centrifugal force, the pulverized coal airflow is separated into a concentrated pulverized coal airflow with a higher pulverized coal concentration and a dilute pulverized coal airflow with a lower pulverized coal concentration. The concentrated pulverized coal airflow is conveyed to the concentrated pulverized coal nozzles of the burner group through the concentrated pulverized coal distributor, and the dilute pulverized coal airflow is conveyed to the dilute pulverized coal nozzles through the dilute pulverized coal distributor. A pulverized coal flow equalizer is installed between the pulverizing system and the pulverized coal distributor to ensure that the pulverized coal flow deviation of each nozzle does not exceed ±5%. The pulverized coal conveying pipeline can be made of wear-resistant seamless steel pipe with an inner diameter of 300mm, and the flow velocity is controlled at 20~24 m / s.

[0029] Specifically, the intelligent control module is used to achieve dynamic coordinated control, including a sensor group and controller arranged in the furnace and flue, as well as actuators connected to the air supply and fuel supply pipelines. For example, the sensor group collects parameters such as temperature, oxygen content, NOx concentration, and flow rate, while the actuators may include adjusting baffles, swing mechanisms, and feeder speed control devices. Based on the real-time parameters collected by the sensors, the controller calculates and outputs commands to the actuators, thereby coordinating and adjusting the air supply volume, air volume distribution, fuel supply, and nozzle status. The intelligent control module also features a human-machine interface such as an industrial touchscreen, supporting manual / automatic mode switching and fault diagnosis and alarm functions.

[0030] In one possible implementation, the secondary air nozzles of the staged air supply unit include a main secondary air nozzle whose nozzle axis is parallel to the radial direction of the furnace, and a side secondary air nozzle whose nozzle axis is deflected toward the furnace wall.

[0031] This embodiment further refines the structural design of the secondary air nozzles in the staged air supply unit to enhance the horizontal air grading effect. Specifically, the nozzle axis of the main secondary air nozzle is designed to be basically parallel to the radial direction of the furnace, with an outlet velocity of 45~50 m / s, allowing the jet to directly participate in organizing tangential combustion in the center of the furnace. The nozzle axis of the side secondary air nozzle is designed to deflect towards the adjacent furnace wall. This deflection design changes the direction of a portion of the secondary air jet, resulting in a slightly higher outlet velocity, for example, 50~55 m / s. This creates a difference in air distribution between the central region and the near-water-cooled wall region in the horizontal cross-section of the furnace. The flow rate ratio of the main secondary air nozzle to the side secondary air nozzle is 3:1~4:1.

[0032] Preferably, the adjustable deflection angle range of the nozzle axis of the secondary air nozzle is 15° to 25°.

[0033] Specifically, the adjustable deflection angle of the side secondary air nozzle's nozzle axis is set between 15° and 25° via a mechanical adjustment mechanism. This angle range achieves a balance between forming an effective near-wall oxygen-enriched zone to protect the water-cooled wall and avoiding excessive interference with the central tangential combustion airflow.

[0034] In one possible implementation, the split burnout air system includes a primary split burnout air nozzle and a secondary split burnout air nozzle, wherein the vertical distance between the primary split burnout air nozzle and the nozzle of the compact burnout air system is 2.5~3.0m, and the vertical distance between the secondary split burnout air nozzle and the primary split burnout air nozzle is 3.0~3.5m.

[0035] Specifically, the SOFA system includes a primary SOFA nozzle and a secondary SOFA nozzle. For example, the nozzle diameter is 0.8 m, and the exit velocity is 55–60 m / s. To achieve deep grading and effective burnout, the vertical distance between the primary SOFA nozzle and the nozzle of the compact burnout air system below is 2.5–3.0 m, and the vertical distance between the secondary SOFA nozzle and the primary SOFA nozzle is 3.0–3.5 m. This arrangement creates a sufficiently high burnout space in the upper part of the furnace.

[0036] As a more preferred embodiment, the air flow ratio of the primary separated burnout air nozzle to the secondary separated burnout air nozzle is 1:1.2 to 1:1.5.

[0037] In other words, the airflow ratio between the primary SOFA nozzle and the secondary SOFA nozzle is set to 1:1.2 to 1:1.5. That is, the airflow of the secondary SOFA is slightly higher than that of the primary SOFA. This ratio design achieves progressive combustion, which is beneficial to balancing the relationship between combustion effect and suppression of thermal NOx formation.

[0038] In one possible implementation, the ratio of the number of concentrated pulverized coal nozzles to the number of dilute pulverized coal nozzles is 4:1; the pulverized coal concentration of the concentrated pulverized coal gas stream output by the concentrated-dilute separation device is 0.8~1.2 kg / kg, and the pulverized coal concentration of the dilute pulverized coal gas stream is 0.2~0.4 kg / kg.

[0039] In other words, the ratio of concentrated pulverized coal nozzles to dilute pulverized coal nozzles in each burner group is set to 4:1. For example, if there are 5 primary air nozzles in a group, then 4 of them are concentrated pulverized coal nozzles and 1 is a dilute pulverized coal nozzle. After passing through the concentrated-dilute separation device, the pulverized coal concentration of the output concentrated pulverized coal airflow is controlled at 0.8~1.2 kg / kg, that is, 0.8~1.2 kg of pulverized coal per kilogram of air, while the pulverized coal concentration of the dilute pulverized coal airflow is controlled at 0.2~0.4 kg / kg.

[0040] In one possible implementation, the controller of the intelligent control module integrates a fuzzy PID control algorithm; the sensor group includes at least a NOx concentration sensor and an oxygen content sensor arranged at the furnace outlet.

[0041] Specifically, the controller uses a Siemens S7-400 series PLC, which integrates a fuzzy PID control algorithm with a response time of ≤0.5 s. The sensor array includes at least a NOx concentration sensor (e.g., a laser in-situ measurement sensor) located at the furnace outlet, and an oxygen content sensor (e.g., a zirconium oxide sensor). Temperature sensors, such as K-type thermocouples, are also located in the main combustion zone, recombustion zone, and burnout zone, with an insertion depth of 300 mm into the furnace. Flow sensors, such as vortex flow meters, are installed on the air supply and pulverized coal pipelines. The sampling probes of the NOx and oxygen content sensors face the airflow direction.

[0042] In one possible implementation, the combustion system further includes a furnace soot blowing unit and an anti-coking monitoring unit, the anti-coking monitoring unit including an infrared temperature sensor disposed on the surface of the furnace water-cooled wall.

[0043] For example, the furnace soot blowing unit uses steam soot blowers, arranged in layers every 3 to 4 meters along the height of the furnace, for a total of 12 layers, with 4 blowers in each layer. The soot blowing steam pressure is 3.5 MPa and the temperature is 400℃.

[0044] The anti-coking monitoring unit includes infrared temperature sensors installed on the surface of the furnace water-cooled walls, with eight sensors arranged on each wall, for real-time monitoring of wall temperature distribution. It also includes high-temperature resistant industrial cameras positioned at the four corners of the furnace, cooled by water jackets, for real-time image capture of combustion within the furnace. When an abnormal increase in local temperature is detected, such as exceeding 400°C, an alarm or soot blowing mechanism can be triggered.

[0045] In one implementation, the side secondary air nozzles are arranged on the outermost horizontal direction of each burner group. That is, in each burner group, the secondary air nozzles located closest to the two furnace walls are designed as deflectable side secondary air nozzles. This arrangement allows the deflected secondary air to most effectively cover and cool the near-water-cooled wall area.

[0046] This invention provides a staged low-NOx combustion method for anthracite boilers based on any of the above-mentioned systems, specifically including the following steps: Fuel grading supply process: The pulverizing system grinds anthracite into pulverized coal with a fineness R90 of 8%~12%. This pulverized coal gas stream then passes through a concentration separator, separating it into a concentrated pulverized coal gas stream and a dilute pulverized coal gas stream. Approximately 80% of the pulverized coal is fed into the main combustion zone of the furnace through a concentrated pulverized coal nozzle, while approximately 20% is fed into the upper region of the furnace through a dilute pulverized coal nozzle. By feeding two different concentrations of pulverized coal from nozzles at different locations, grading of fuel supply is achieved in the horizontal direction of the furnace, and the area where the dilute pulverized coal jet is located constitutes the reburning reduction zone.

[0047] Vertical staged air supply procedure: Combustion air is divided into three streams and introduced in stages along the furnace height. First, the main and secondary air systems supply 60%–70% of the theoretical air volume to the main combustion zone through their nozzles, maintaining the excess air coefficient in the main combustion zone at 0.8–0.9, creating oxygen-deficient combustion conditions. Subsequently, the compact burnout air (CCOFA) system supplies 10%–15% of the theoretical air volume to the upper part of the main combustion zone. Finally, the separate burnout air (SOFA) system introduces the remaining air in stages through the primary and secondary nozzles, controlling the total burnout air rate to approximately 30%, ensuring complete combustion of unburned carbon particles. The temperature in the main combustion zone is controlled at 1200–1350℃, the temperature in the reburning zone (i.e., the area where pulverized coal is introduced) is controlled at 1100–1250℃, and the temperature in the burnout zone is controlled at 900–1100℃. The excess air coefficient at the furnace outlet is maintained at 1.15–1.20.

[0048] Horizontal grading organization steps: By adjusting the side secondary air nozzles, the air is deflected 15°~25° towards the furnace wall. Differentiated air distribution is organized on the radial cross section of the furnace. The central area is relatively oxygen-deficient due to the deflection of the side secondary air, forming a central fuel-rich reduction zone with an oxygen content ≤3%; while the area near the water-cooled wall forms a near-wall oxygen-rich zone with an oxygen content ≥8% due to the wall adhesion effect of the side secondary air, thereby protecting the furnace wall.

[0049] Intelligent closed-loop control steps: During system operation, the NOx concentration at the furnace outlet and parameters reflecting boiler efficiency, such as flue gas oxygen content and temperature, are continuously monitored in real time. The controller of the intelligent control module performs comprehensive calculations using a fuzzy PID algorithm based on the deviations between the real-time values ​​of these parameters and the target values, and outputs a linkage control command. For example, the target value is a NOx concentration ≤ 150 mg / Nm³. 3 The boiler efficiency target is ≥94%. For example, when the NOx concentration exceeds 150 mg / Nm³. 3When the boiler efficiency is below 94%, the controller increases the SOFA air supply volume and decreases the main and secondary air supply volumes. When the boiler efficiency is below 94%, the distance between the primary SOFA nozzle and the main combustion zone is adjusted. The intelligent control module adjusts the following parameters with the following accuracy: the ratio deviation of rich and lean pulverized coal distribution ≤ ±2%, the flow deviation of each air supply duct ≤ ±3%, and the deflection angle adjustment accuracy of the side secondary air nozzles ±1°. This allows for finding and maintaining a dynamic optimal balance between suppressing NOx formation and ensuring combustion efficiency. When coal type fluctuates, if increased volatile matter leads to increased NOx, the proportion of lean pulverized coal supply is automatically increased to 25%, and the SOFA air volume is increased; if decreased volatile matter leads to decreased efficiency, the side secondary air deflection angle is reduced to 15°, and the distance between the primary SOFA and the main combustion zone is shortened to promote complete pulverized coal combustion.

[0050] Compared to existing low-NOx combustion technologies, which often optimize only a single combustion stage, resulting in limited NOx reduction rates (typically 30%–50%) and susceptibility to emission rebound due to incomplete combustion, this invention, through a synergistic design of vertical three-stage air supply and fuel rich-lean separation, combined with intelligent closed-loop control, can construct and maintain zoned combustion environments within the furnace. It not only controls the oxygen content in the main combustion zone at a low level (2%–4%) to suppress fuel-type NOx formation, but also achieves control over flame temperature and combustion process through pulverized coal reburning and tiered burnout air arrangement. Practical application shows that this system can stably control the initial NOx emission concentration of anthracite boilers at 150 mg / Nm³. 3 The lower NOx levels effectively reduce the load and operating costs of the flue gas denitrification system, alleviating pollution control pressure at the source. Traditional technologies often reduce boiler thermal efficiency by 2% to 3% in pursuit of low NOx, while this invention, while achieving deep NOx reduction, ensures complete combustion of pulverized coal, maintaining boiler thermal efficiency above 94%, achieving simultaneous improvement in environmental protection and energy conservation. For difficult-to-burn coal types such as anthracite and actual operating conditions with frequent load fluctuations, the system, through multi-point monitoring and adaptive control modules, ensures stable and reliable combustion across a wide load range and with varying coal quality, reducing risks such as slagging and flameout, and improving unit availability. For the large number of existing units urgently needing retrofitting, the system structure of this invention has excellent modular adaptability; its main modifications can be carried out on the basis of existing burners and bellows without large-scale alterations to the furnace structure, shortening the retrofit cycle and reducing investment. Simultaneously, by optimizing the overall combustion atmosphere, this technology reduces NOx and also reduces carbon black particles generated by incomplete combustion, lowering particulate matter emission concentration by 15% to 20%, and has a positive effect on inhibiting SO2 conversion.

[0051] In the description of this invention, it should be understood that the terms "upper", "lower", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this 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. Therefore, they should not be construed as limitations on this invention.

[0052] 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 technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0053] In this invention, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0054] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0055] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0056] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit them. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the scope of the technology disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, 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, and should all be covered within the scope of protection of the present invention.

Claims

1. A staged low-NOx combustion system for anthracite boilers, characterized in that, include: Furnace body; The burner group is symmetrically arranged along the lower perimeter of the furnace body and adopts a direct-flow burner tangential combustion form. Each burner group includes several primary air nozzles and secondary air nozzles arranged in parallel. The primary air nozzles include concentrated pulverized coal nozzles for supplying concentrated pulverized coal and dilute pulverized coal nozzles for supplying dilute pulverized coal. The concentrated pulverized coal nozzles and dilute pulverized coal nozzles are distributed at intervals along the horizontal direction of the furnace. The graded air supply unit includes a main secondary air system that supplies air to the main combustion zone, a compact burnout air system arranged above the burner group, and a separate burnout air system arranged above the compact burnout air system. The nozzles of the separate burnout air system are divided into at least two stages along the furnace height direction, forming a three-stage air supply structure in the vertical direction. The fuel grading supply unit includes a pulverizing system and a concentration-lean separation device connected to the outlet of the pulverizing system, which is used to separate the coal powder gas flow into a concentrated coal powder gas flow and a lean coal powder gas flow, and respectively deliver them to the concentrated coal powder nozzle and the lean coal powder nozzle. The intelligent control module includes a sensor group for collecting combustion state parameters in the furnace, a controller, and an actuator connected to the staged air supply unit and the staged fuel supply unit. The controller is used to adjust the air supply and fuel supply in a coordinated manner through the actuator according to the parameters.

2. The staged low-NOx combustion system for anthracite boiler according to claim 1, characterized in that, The secondary air nozzles of the staged air supply unit include a main secondary air nozzle whose nozzle axis is parallel to the radial direction of the furnace, and a side secondary air nozzle whose nozzle axis is deflected toward the furnace wall.

3. The staged low-NOx combustion system for anthracite boiler according to claim 2, characterized in that, The adjustable deflection angle of the nozzle axis of the secondary air nozzle is from 15° to 25°.

4. The staged low-NOx combustion system for anthracite boiler according to claim 1, characterized in that, The separate burnout air system includes a primary separate burnout air nozzle and a secondary separate burnout air nozzle. The vertical distance between the primary separate burnout air nozzle and the nozzle of the compact burnout air system is 2.5~3.0m, and the vertical distance between the secondary separate burnout air nozzle and the primary separate burnout air nozzle is 3.0~3.5m.

5. The staged low-NOx combustion system for anthracite boiler according to claim 4, characterized in that, The air flow ratio between the primary separate burnout air nozzle and the secondary separate burnout air nozzle is 1:1.2 to 1:1.

5.

6. A staged low-NOx combustion system for anthracite boilers according to claim 1, characterized in that, The ratio of concentrated pulverized coal nozzles to dilute pulverized coal nozzles is 4:1; the pulverized coal concentration of the concentrated pulverized coal gas stream output by the concentrated pulverized coal separation device is 0.8~1.2 kg / kg, and the pulverized coal concentration of the dilute pulverized coal gas stream is 0.2~0.4 kg / kg.

7. The staged low-NOx combustion system for anthracite boiler according to claim 1, characterized in that, The controller of the intelligent control module integrates a fuzzy PID control algorithm; the sensor group includes at least a NOx concentration sensor and an oxygen content sensor arranged at the furnace outlet.

8. The staged low-NOx combustion system for anthracite boiler according to claim 1, characterized in that, It also includes a furnace soot blowing unit and an anti-coking monitoring unit, wherein the anti-coking monitoring unit includes an infrared temperature sensor installed on the surface of the furnace water-cooled wall.

9. A staged low-NOx combustion system for anthracite boiler according to claim 2 or 3, characterized in that, The secondary air nozzles are arranged on the outermost side in the horizontal direction of each burner group.

10. A method for staged low-NOx combustion in an anthracite boiler based on the system described in any one of claims 1 to 9, characterized in that, Includes the following steps: The prepared pulverized coal is separated into concentrated pulverized coal gas flow and dilute pulverized coal gas flow through a concentration separation device. The concentrated pulverized coal gas flow and dilute pulverized coal gas flow are then sent into different areas of the furnace through concentrated pulverized coal nozzles and dilute pulverized coal nozzles, respectively, to achieve horizontal staged supply of fuel. Combustion air is supplied in three stages along the height of the furnace through the main and secondary air systems, the compact burnout air system, and the separate burnout air system. The oxygen-deficient combustion conditions are maintained in the main combustion zone, and the subsequent burnout of pulverized coal is achieved through the upper burnout air system. By adjusting the air delivery direction of the side secondary air nozzles, a central fuel-rich zone and a near-wall oxygen-rich zone are formed radially in the furnace. The NOx concentration at the furnace outlet and parameters reflecting boiler efficiency are monitored in real time, and the air distribution ratio of the graded air supply unit and the distribution ratio of the fuel graded supply unit are adjusted in conjunction to coordinate the control of NOx emissions and combustion efficiency.

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