Longitudinal staged low-nitrogen combustion system and method for silicon-manganese ore heat furnace exhaust gas

Abstract

The application discloses a longitudinal staged low-nitrogen combustion system and method for silicon-manganese ore heat furnace waste gas, and the system comprises a fuel staged low-nitrogen burner and an overfire air system; the burner adopts a combination of straight-flow / rotational-flow gas injection lances, a two-stage air distribution structure and an external secondary gas injection lance; and the overfire air system realizes longitudinal staged air distribution through preset intervals. A fuel-rich combustion zone is formed by controlling the air volume proportion of the main burner, a 'fuel-rich-oxygen-lack-burnout' three-stage combustion field is established in the furnace by utilizing the high flow rate delayed combustion of straight-flow gas and the secondary gas oxygen-lack reduction mechanism, and the temperature is maintained at 800-1100 DEG C to optimize the reaction activity of CO reducing NO. x The application effectively reduces the NOx emission generated by waste gas combustion, and ensures the combustion stability and thermal efficiency.

Description

Technical Field

[0001] This invention relates to waste gas treatment technology for submerged arc furnaces in the metallurgical industry, and in particular to a longitudinally graded low-NOx combustion system and method for waste gas from ferrosilicon manganese submerged arc furnaces. Background Technology

[0002] NO produced by the combustion of coal gas in a submerged arc furnace x It mainly includes fuel-type and thermal-type, with the fuel-type being the predominant type. The gas composition of electric arc furnaces contains a large amount of nitrogen-containing compounds such as NCN and NH3. During combustion, these nitrogen-containing compounds can be oxidized to NO by O2, or to N2 by O2, or NO can be reduced to N2.

[0003] Traditional burners do not take low NOx requirements into account. x For combustion issues, considering only the need for rapid and complete fuel combustion, a dual-swirl burner structure is typically employed. This type of burner is characterized by concentrated flame, high combustion temperature, and rapid combustion speed. These combustion characteristics are more conducive to the oxidation of NCN and NH3 to NO by O2, therefore, when using traditional burners, the boiler's NO content... x The emissions are all very high.

[0004] In addition, the theoretical combustion temperature of ferroelectric furnace gas is relatively high. This fuel characteristic causes the combustion of ferroelectric furnace gas to produce a certain amount of thermal NO. x Although this portion of thermal NO is burned when using a conventional burner x In total NO x Although it accounts for a small proportion of total emissions, the design of low-NOx combustion systems should also take into account the reduction of thermal NOx. x . Summary of the Invention

[0005] The purpose of this invention is to address the aforementioned problems by providing a longitudinally staged low-NOx combustion system and method for exhaust gas from a ferrosilicon manganese submerged arc furnace. Through staged combustion and burnout air design, it effectively reduces NOx emissions. x emission.

[0006] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows: In a first aspect, a longitudinally staged low-NOx combustion system for exhaust gas from a ferrosilicon manganese submerged arc furnace is provided, comprising: A fuel-stage low-NOx burner, serving as the main burner, includes a primary gas injection gun structure, a two-stage air distribution structure, and a secondary gas injection gun disposed outside the primary gas injection gun structure; wherein, the primary gas injection gun structure includes a direct-flow gas injection gun located in the inner ring and a swirl gas injection gun located in the outer ring. A burnout air system is positioned above the main burner, with a predetermined distance between the burnout air system and the main burner to create staged air distribution within the furnace. For example, the distance to the main burner can be determined through three-dimensional flow field simulation to achieve staged air distribution.

[0007] Optionally, the two-stage air distribution structure includes a central air inlet located at the center of the spray gun, and a main combustion air inlet located on the periphery of the first-stage gas spray gun structure.

[0008] Optionally, the distance between the burnout air nozzle in the burnout air system and the main burner is ≥1.5m.

[0009] Secondly, a low-NOx combustion method based on the above system is provided, comprising the following stages: First-stage combustion (rich fuel combustion): The first-stage gas mixes with the main combustion air to form a low-oxygen environment for combustion in the main combustion zone; in this stage, the high-velocity direct-flow gas delays combustion, and the swirling gas works in conjunction with the combustion air to stabilize the flame; Secondary combustion stage (oxygen-deficient reduction): The gas is directly injected into the oxygen-deficient zone of the flue gas in the furnace through the secondary gas injection gun to promote the reduction reaction of CO and NO. Combustion stage: The combustion air system replenishes the remaining air to the upper part of the furnace to complete the combustion of the unburned fuel and control the overall temperature field within the range of 800-1100℃.

[0010] Optionally, during the first-stage combustion phase, the flow rate of the DC gas injector is controlled to be 30-50 m / s, and the swirl intensity of the swirl gas injector is controlled to be 0.6-1.2.

[0011] Optionally, the amount of air supplied to the main burner is controlled to be 70%-75% of the total combustion air volume, and the amount of air supplied by the burnout air system is controlled to be 25%-30% of the total air volume.

[0012] Compared with the prior art, the beneficial effects of the embodiments of this application are: This application provides a longitudinally staged low-NOx combustion system and method for exhaust gas from a ferrosilicon manganese submerged arc furnace. Through longitudinally staged combustion and a burnout air system design, it effectively reduces NOx in the exhaust gas from the ferrosilicon manganese submerged arc furnace. x While minimizing emissions, it also ensures combustion stability and efficiency. The gas design consists of an inner ring of direct-flow gas and an outer ring of swirling gas. The direct-flow gas nozzle is a large nozzle design with high flow velocity and long injection distance. The main combustion zone is located in the middle and rear section of the flame, which is beneficial for combustion in low-oxygen environments and effectively suppresses NO. x Generation. Among these, the fuel-air vertical grading process: through a combination of direct / direct gas flow, secondary injection nozzles, and burnout air layout, a three-stage combustion process of "rich fuel - oxygen-deficient - burnout" is formed, suppressing NO. xGeneration path; Dynamic oxygen concentration field control: Optimization of burnout air location to ensure the effectiveness of staged air distribution and avoid premature oxygen mixing. Attached Figure Description

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

[0014] Figure 1 This is a schematic diagram of a low-NOx burner, showing the distribution of central air, combustion air, direct / swirl gas, and the location of the secondary gas injection gun.

[0015] Figure 2 This is a simulation diagram of the wind velocity field of the main burner and burnout system inside the furnace.

[0016] Figure 3 This is a field distribution diagram of O2 concentration.

[0017] Figure 4 This is a map showing the CO concentration field distribution.

[0018] Figure 5 This represents the temperature field distribution.

[0019] Figure 6 This is a schematic diagram of the low-NOx combustion system layout in the furnace, showing the relative spatial relationship between the main burner and the burnout air system.

[0020] Illustration: 10. Main burner; 11. Air inlet; 12. Central air inlet; 13. Combustion air inlet; 14. Central air spray gun; 15. Direct current gas spray gun; 16. Swirl gas spray gun; 17. Combustion air spray gun; 18. Secondary fuel spray gun; 19. Furnace; 20. Combustion exhaust air system. Detailed Implementation

[0021] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0022] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0023] 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 one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0024] Before elaborating on the structure of the specific embodiments of this application, it is necessary to first clarify that NO is produced by the combustion of gas in an electric arc furnace. x The types mainly include fuel-type NO x and thermal NO x Among these, fuel-type gases dominate. Due to the unique nature of the smelting process, the composition of blast furnace gas contains a significant amount of large-molecule nitrogen-containing compounds such as NCN (cyanamide radical) and NH3. These nitrogen-containing compounds are easily oxidized directly by O2 to NO in the high-temperature oxidizing environment of combustion, leading to pollution. However, if properly controlled, they can also be reduced and converted into harmless N2 in a reducing environment. Traditional burners are not designed with low NO levels in mind. x Thermochemical constraints of combustion, considering only the rapid and complete combustion of fuel, typically employ a high-velocity double-swirl structure. These traditional burners are characterized by highly concentrated flames, extremely high peak combustion temperatures, and extremely rapid turbulent combustion speeds. These intense combustion characteristics thermodynamically and kinetically favor the rapid oxidation of NCN and NH3 to NO by O2, leading to increased NO levels in boilers using traditional burners. x Emissions levels significantly exceeded standards. Furthermore, due to the high theoretical combustion temperature of the submerged arc furnace gas, localized ultra-high temperatures (>1200℃) also generate a certain amount of thermal NOx. x The reconstructed staged low-NOx combustion system described in this application aims to reduce the probability of NCN and NH3 being oxidized by O2 by altering the flow and temperature fields through specific spatial physical arrangements, and to enhance the reverse reaction of CO reducing NO to N2 in the furnace, thereby achieving ultra-low NOx emissions. x The purpose of emissions.

[0025] To illustrate the technical solution described in this application, specific embodiments are provided below.

[0026] Example 1: Longitudinal Staged Low-NOx Combustion System for Exhaust Gas from Ferromanganese Submerged Arc Furnace Please see Figure 1 and Figure 6This embodiment provides a longitudinally staged low-NOx combustion system for exhaust gas from a ferrosilicon manganese submerged arc furnace, mainly composed of a low-NOx burner (main burner 10) and a burnout air system 20. The system is installed on a furnace 19 with furnace insulation, aiming to effectively reduce NOx emissions by altering the combustion dynamic field inside the furnace through longitudinally staged air distribution and longitudinally segmented fuel jet technology. x emission.

[0027] The main burner 10 has an air inlet 11, a central air inlet 12, and a combustion air inlet 13 at its air intake end. To overcome the drawbacks of excessively concentrated flames and localized high temperatures in traditional burners, and to achieve flexible, segmented mixing and combustion of fuel and air, the main burner 10 employs a fuel-staged flow field design. Specifically, the primary combustion gas is divided into two parts with different hydrodynamic characteristics: the inner ring is equipped with a direct-flow gas nozzle 15, which features a large cross-section and long straight pipe section, resulting in a high-velocity (30-50 m / s) jet gas that provides a strong penetration distance. This design forces the main combustion zone of the gas to shift to the middle and rear sections of the flame. The middle and rear sections of the flame represent the later stages of the combustion reaction, where a large amount of oxygen has been consumed. When the direct-flow gas is ignited in this region, it is essentially in a low-oxygen, mild combustion environment, effectively suppressing NO₂. x The initial generation is achieved through a swirling gas injector 16 in the outer ring. This injector imparts tangential angular momentum to the fluid through its swirling blades and works in conjunction with the adjacent combustion air injector 17. The lower axial velocity of the swirling gas and the resulting central recirculation zone stabilize the flame root. This combination of outer-ring swirling combustion stabilization and inner-ring direct-flow penetration not only significantly extends the combustion zone but also effectively overcomes the safety hazards of pure direct-flow gas injectors being prone to flameout and unstable combustion, ensuring the burner's safe and stable operation. In the entire longitudinal fuel staging technology path, the inner-ring direct-flow gas injector has the fastest velocity, reaching the middle and rear sections of the furnace for combustion; the outer-ring swirling gas has a lower velocity, burning in the front and middle sections of the furnace; while the subsequently injected secondary fuel has the slowest velocity, undergoing oxygen-deficient reforming at the outer periphery of the furnace front.

[0028] In terms of combustion air distribution structure, this system creatively adopts a two-stage air distribution design, unlike the traditional single-stage powerful air distribution mode. The central air nozzle 14 is arranged at the geometric center of the burner nozzle, serving as the first-stage air distribution; while the main combustion air nozzle 17 is arranged around the periphery of the first-stage gas passage, serving as the second-stage air distribution. In actual operation, the gas injected through the first-stage gas passage accounts for only a portion of the total gas supply, but all the combustion air from the burner mixes and burns with this portion of gas in the first-stage combustion zone. This non-equilibrium mass flow design results in a severe excess of combustion air in the center of the main combustion zone, and the mixing of a large amount of cold air causes a significant drop in the overall combustion temperature. Compared to the traditional single-stage air distribution mode, this two-stage air distribution technology makes the air mixing more uniform across the entire cross-section, and the nozzle flame distribution range is wider. It successfully constructs a low-temperature combustion zone with a very wide coverage area in the front of the furnace, eliminating the generation of thermal NO. x Localized high temperature stimulation.

[0029] In addition, a secondary fuel injector 18 is independently installed outside the primary gas injector structure of the main burner 10. The arrangement logic of the secondary fuel injector 18 is that the gas injected does not directly mix with the main combustion air in physical space, but uses its own low-speed kinetic energy to directly inject into the high-temperature flue gas in the furnace 19, where oxygen has been consumed by the primary combustion. Due to the use of the extremely low oxygen thermochemical environment in the furnace flue gas environment, this part of the gas undergoes incomplete pure oxygen-deficient combustion in this area, thus providing a continuous source of CO precursors for the efficient reduction reaction in subsequent steps.

[0030] Please refer to it again. Figure 6 The burnout air system 20 is located above the main burner 10. The core function of this system is to trap a portion of the air, thereby creating an overall low-oxygen environment in the main combustion zone. The vertical distance between the burnout air system 20 and the main burner 10 is not arbitrary; it must have a preset distance of ≥1.5m. The reason for setting this critical distance height is that during actual combustion in a high-temperature furnace, the violently rising hot airflow at the flame center generates a significant negative pressure suction effect. This hot negative pressure forces the high-pressure cold air jet from the burnout air nozzle to undergo a non-linear deflection, tending to move downwards towards the main flame area. If the burnout air nozzle is too close to the main burner (less than 1.5m), the burnout air jet will be prematurely drawn in and participate in the main flame combustion. This not only negates the initial purpose of staged air distribution but also disrupts the carefully created oxygen-deficient reduction zone in the lower part of the furnace, leading to denitrification failure. Therefore, a layout height of ≥1.5m, optimized through rigorous three-dimensional flow field CFD simulation, is the physical boundary guarantee to resist negative pressure shift, avoid premature mixing, and ensure that the longitudinal graded air distribution effect can be implemented.

[0031] Example 2: Low-NOx Combustion Method Based on the system constructed above, this application further provides a low-NOx combustion method. Combined with... Figures 2 to 5 The three-dimensional flow field velocity distribution and simulation diagrams of O2, CO, temperature, and concentration fields show that the implementation of this low-NOx combustion method is divided into the following three distinct but interconnected stages: 1. First-stage combustion (fuel-rich, low-speed combustion stage): During operation, the burnout air system 20 forcibly intercepts a portion of the air that should have been supplied to the furnace 19 from the main burner 10 all at once, significantly reducing the actual air supply to the main burner 10 to 70%-75% of the total air required for combustion. This operation directly creates a fuel-rich, oxygen-deficient combustion zone with an excess air coefficient α < 1 in the large space in the lower part of the furnace 19. At this time, the primary combustion gas mixes and burns with all the combustion-supporting air supplied by the system in this zone. Due to the overall low-oxygen and low-temperature inhibitory environment, the combustion reaction rate and overall temperature level in this primary combustion zone are significantly reduced. This not only effectively delays the transient heat release of the combustion process on the time axis, but more importantly, under the dominance of the reducing atmosphere, it greatly reduces the reaction conversion rate of the NCN and NH3 compounds unique to the aforementioned coal gas being directly oxidized by O2 to produce NO. Meanwhile, to match the thermodynamic environment at this stage, the system controls the flow rate of the DC gas injector 15 to be maintained at 30-50 m / s, using high momentum to delay the release of the main combustion zone; and controls the swirl intensity of the peripheral swirl gas injector 16 to be maintained in the range of 0.6-1.2, so as to match and support the combustion air, maintain the safety and stability of the root flame, and prevent flameout.

[0032] 2. Secondary combustion stage (extreme oxygen-deficient reduction stage): As the rising airflow propels the gas, the secondary fuel injector 18 directly injects the gas into the extremely oxygen-deficient zone of the flue gas in the furnace 19. Because this invention employs a multi-stage air distribution structure unique to low-NOx burners, its flame propagation and combustion speed are slower compared to traditional burners. Figure 3 and Figure 4 As shown in the simulated O2 and CO concentration field distribution, this "slow combustion" significantly expands the area of ​​the reducing environment in physical space and substantially prolongs the residence time of NO-containing flue gas in the reducing zone in time. Under this extremely oxygen-deficient reducing environment, the large amount of CO gas contained in the ferrosilicon manganese submerged arc furnace gas itself, as well as the large amount of CO gas produced by incomplete combustion in the previous stage, becomes an excellent reducing agent. The extended reaction time allows CO to undergo a catalytic reduction reaction with the trace amounts of NO molecules generated in the earlier combustion stage, with the reaction equation: 2NO + 2CO = N2 + 2CO2. This reaction stage efficiently reduces NO and converts it into naturally occurring, environmentally harmless nitrogen gas N2 in the air.

[0033] 3. Combustion stage (temperature field control and final oxidation stage): like Figure 2 and Figure 5 As shown in the flow field and temperature field distribution, as the unburned flue gas continues to rise, the pre-intercepted burnout air, accounting for 25%-30% of the total air volume, is horizontally injected into the upper space of the furnace 19 through the burnout air system 20, which is ≥1.5m away from the main combustion zone, to replenish the final remaining air. This oxygen curtain mixes thoroughly with the flue gas rising from below, which contains a large amount of unburned hydrocarbons and CO. Under oxygen-rich conditions with an overall excess air coefficient α>1, the final oxidation and combustion process of all fuel is completely completed. This not only recovers all the calorific value of the coal gas, but also solves the technical pain points of incomplete combustion, reduced boiler thermal efficiency, and excessive CO in the exhaust gas that are easily caused by simply using "low excess air combustion technology" in industry.

[0034] In all three dynamic stages described above, precise control of the macroscopic three-dimensional temperature field of the furnace is the mechanism for achieving ultra-low emissions. It must be pointed out that the reduction reaction of NO and CO, 2NO + 2CO = N2 + 2CO2, is subject to strict temperature window constraints. Thermodynamic studies show that when the local temperature exceeds 1200℃, the reduction capacity of CO and NO decreases sharply or even stops; more seriously, once the critical point of 1200℃ is exceeded, a large amount of free nitrogen atoms will be generated in the furnace, leading to the thermal reduction of NO. x An exponential second surge occurs. The catalytic reaction of CO reducing NO to N2 only reaches its peak activity when the temperature is in the range of 800-1100℃.

[0035] The essence of this invention lies precisely in the longitudinal spatial grading design of the fuel and air distribution, and the alternating combination of direct current and swirling currents, which ensures that the flame not only avoids concentrating into spikes but is instead evenly dispersed across the entire furnace bottom cross-section. This is similar to the combustion temperature field in a three-dimensional simulation (…). Figure 5 It has been clearly verified that, after adopting the system of this invention, the peak temperature of the furnace flame is significantly reduced by approximately 200°C compared to using a traditional dual-swirl burner. This crucial 200°C reduction not only extinguishes thermal NOxes caused by localized overheating... x The surge in source risks has further ensured that the overall temperature field in the extremely broad lower and rear sections of the furnace is stably and firmly controlled within the ideal range of 800-1100℃. By precisely matching the highest active temperature window of the aforementioned reduction-denitrification reaction, this invention achieves NO reduction while ensuring high combustion thermal efficiency in metallurgical waste heat boilers. x The goal of achieving ultra-low emissions by reducing displacement.

[0036] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A longitudinally staged low-NOx combustion system for exhaust gas from a ferrosilicon manganese submerged arc furnace, characterized in that, include: A fuel-stage low-NOx burner, serving as the main burner, includes a primary gas injection gun structure, a two-stage air distribution structure, and a secondary gas injection gun disposed outside the primary gas injection gun structure; wherein, the primary gas injection gun structure includes a direct-flow gas injection gun located in the inner ring and a swirl gas injection gun located in the outer ring. A burnout air system is installed above the main burner, and there is a preset distance between the burnout air system and the main burner to form a staged air distribution in the furnace.

2. The system according to claim 1, characterized in that: The two-stage air distribution structure includes a central air inlet located at the center of the spray gun, and a main combustion air inlet located on the periphery of the first-stage gas spray gun structure.

3. The system according to claim 1, characterized in that: The distance between the burnout air nozzle in the burnout air system and the main burner is ≥1.5m.

4. A low-NOx combustion method based on the system according to any one of claims 1-3, characterized in that, Includes the following stages: First-stage combustion (rich fuel combustion): The first-stage gas mixes with the main combustion air to form a low-oxygen environment for combustion in the main combustion zone; in this stage, the high-velocity direct-flow gas delays combustion, and the swirling gas works in conjunction with the combustion air to stabilize the flame; Secondary combustion stage (oxygen-deficient reduction): The gas is directly injected into the oxygen-deficient zone of the flue gas in the furnace through the secondary gas injection gun to promote the reduction reaction of CO and NO. Combustion stage: The combustion air system replenishes the remaining air to the upper part of the furnace to complete the combustion of the unburned fuel and control the overall temperature field within the range of 800-1100℃.

5. The method according to claim 4, characterized in that: During the first-stage combustion phase, the flow rate of the DC gas injector is controlled to be 30-50 m / s, and the swirl intensity of the swirl gas injector is controlled to be 0.6-1.

2.

6. The method according to claim 4, characterized in that: The air supply to the main burner is controlled to be 70%-75% of the total combustion air volume, and the air supply of the burnout air system is controlled to be 25%-30% of the total air volume.

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