A NOx Control Method for Chain Grate Machine-Rotary Kiln Based on Multi-Source Fuel Utilization

Abstract

This invention discloses a NOx control method for a chain grate rotary kiln based on multi-source fuel utilization. This method, targeting different levels of environmental warnings and ultra-low emission requirements, first establishes a solid fuel combustion characteristic database including anthracite, bituminous coal, and their blends based on industrial analysis, elemental analysis, and thermogravimetric experiments. Simultaneously, it employs CFD numerical simulation technology, coupling an Eulerian-Lagrange multiphase flow model and a P-1 radiation model, to analyze the flow field and NOx formation patterns under pulverized coal and natural gas co-firing conditions. Upon receiving control commands, it calculates the inlet concentration threshold based on the real-time efficiency of the denitrification system, intelligently recommends the optimal fuel ratio using the multi-source database, and outputs corresponding kiln tail temperature, combustion air volume, and raw material structure control parameters. This invention, through a dual approach of "experimentation + simulation," achieves the suppression of fuel-type and thermal NOx formation at the source, meeting differentiated environmental indicators while ensuring stable production.

Description

Technical Field

[0001] This invention relates to the field of iron ore pellet production and industrial pollutant control technology, and more specifically, to a NOx control method for a chain grate-rotary kiln based on multi-source fuel utilization. Background Technology

[0002] The chain grate-rotary kiln process is currently the mainstream technology for iron ore pellet production, accounting for over 60% of total capacity. In this process, NOx pollutant generation is mainly concentrated in the high-temperature roasting section inside the rotary kiln. This region involves complex multiphase flow, unsteady heat transfer, and multi-component combustion chemical reactions, resulting in intricate mechanisms and theoretically posing numerous challenges to NOx generation and control.

[0003] In recent years, with the continuous tightening of national environmental protection requirements for industry, various regions have frequently implemented tiered emergency control measures during periods of heavy pollution, imposing stringent, step-by-step targets for NOx emission concentrations at pellet production enterprises (such as requiring emission concentrations to be below 40 mg / m³, 35 mg / m³, or even 30 mg / m³, respectively). However, existing emission reduction measures are relatively simplistic and crude, mainly relying on passive "production reduction and restriction" models or end-of-pipe treatment through excessive ammonia injection. This control method not only significantly increases the risk of ammonia escape and operating costs but also makes it difficult to maintain stable denitrification efficiency under low-load conditions.

[0004] Further analysis revealed that the limitation of existing control strategies lies in their neglect of the impact of inherent fuel characteristics on NOx formation mechanisms. In actual production, enterprises often switch between using various fuels such as anthracite, bituminous coal, or natural gas based on cost and supply conditions. Different fuels exhibit significant differences in combustion characteristics, flame temperature, and NOx formation pathways: anthracite has high fixed carbon and nitrogen content, easily generating large amounts of "fuel-type NOx"; bituminous coal has high volatile matter and low nitrogen content, and its combustion behavior is drastically different from that of anthracite; while natural gas, a gaseous fuel, mainly produces "thermal NOx" due to high-temperature, oxygen-enriched conditions.

[0005] Current control methods mostly treat rotary kilns as a "black box model," lacking in-depth coupled analysis of the microscopic physicochemical properties of the aforementioned multi-source fuels and the macroscopic flow field distribution within the kiln. This results in an inability to precisely intervene in the NOx formation pathway from the combustion source. Consequently, when faced with frequent fuel changes and fluctuations in environmental indicators, existing technologies struggle to simultaneously meet ultra-low emission requirements while maintaining the economic efficiency of pellet production and energy consumption.

[0006] Therefore, there is an urgent need to develop a source control method based on fuel characteristics and combustion mechanism to achieve precise NOx control and coordinated energy saving and carbon reduction in the chain grate-rotary kiln process under multiple fuel conditions. Summary of the Invention

[0007] This invention provides a NOx control method for chain grate rotary kilns based on multi-source fuel utilization. By constructing a multi-source database containing experimental data and CFD simulation data, the optimal combination of fuel structure and process parameters can be quickly provided according to real-time control instructions, thereby enabling NOx emissions to meet control requirements. This solves the problems of existing environmental control measures being singular, lacking source emission reduction strategies, and having poor economic efficiency.

[0008] According to one aspect of the present invention, a method for NOx control in a chain grate rotary kiln based on multi-source fuel utilization is provided, comprising the following steps: Step S1: Analyze the environmental control instructions, determine the current NOx emission target value, and calculate the upper limit of the allowable NOx concentration at the rotary kiln outlet based on the real-time performance of the denitrification system. Step S2: Construct a multi-source fuel combustion characteristic database. The multi-source fuel combustion characteristic database includes a basic physicochemical characteristic database of anthracite, bituminous coal and their blended coal samples obtained based on experimental detection, and a fuel-type NOx generation database. Based on the information in the basic physicochemical characteristic database of anthracite, bituminous coal and their blended coal samples, a CFD numerical simulation model of the combustion process of pulverized coal particles is used. Using the Euler-Lagrange method and the P-1 radiation model, a database of flow field and thermal NOx generation and NOx emission characteristics under the co-firing condition of pulverized coal and natural gas is established. Based on information from fuel-type NOx generation databases, basic physicochemical properties databases, and NOx emission characteristics databases, an optimal allocation decision model is constructed. Step S3: Input the upper limit of NOx concentration allowed at the rotary kiln outlet obtained in step S1 into the optimal fuel blending decision model, and match candidate fuel blending schemes that meet the condition Csim≤Climit in the database. The fuel blending schemes cover pure anthracite mode, anthracite-bituminous coal blending mode and coal-natural gas blending mode. Step S4: Based on the selected fuel ratio scheme, output the corresponding auxiliary process control parameters, including the upper limit of kiln tail temperature, combustion air volume, pulverized coal injection volume, and sulfur content index of the pellets fed into the furnace.

[0009] In a preferred embodiment based on the above scheme, step S1 specifically includes obtaining the current NOx environmental control target value Ctarget and the current maximum denitrification efficiency ηSCR of the SCR denitrification system, and calculating the allowable NOx concentration threshold at the SCR inlet.

[0010] Based on the above scheme, the preferred CFD numerical simulation model of the coal powder combustion process in step S2 includes: Volatile combustion model: The release and combustion of volatiles are described by a single-step reaction kinetic equation in the form of Arrhenius, and the mass formation rate of volatiles is calculated. Coke combustion model: A kinetic / diffusion-controlled reaction rate model is used to calculate the surface combustion rate of coke by weighting the chemical reaction kinetic rate and diffusion rate.

[0011] Based on the above scheme, in step S2, a CFD numerical simulation model of the combustion process of pulverized coal particles is used. The Eulerian-Lagrange method and the P-1 radiation model are employed to establish a database of flow field and thermal NOx generation under the co-firing conditions of pulverized coal and natural gas. Specifically, this includes: S221: The Euler-Lagrange system is used to describe the gas-solid two-phase flow, and the flue gas is regarded as the continuous phase, the pulverized coal particles are regarded as the discrete phase (DPM), and the bidirectional coupling effect between the particles and the gas phase is considered. S222: The Realizable k-ε turbulence model is used to describe the complex gas turbulence and rotating flow field inside the rotary kiln; S223: The P-1 radiation model is used to calculate the radiation heat transfer process in the high-temperature environment inside the kiln, and the transport equation of the incident radiation is solved to obtain the radiation heat flow distribution. S224: The NOx generation process is simulated using a component transport model combined with the Zeldovich extension mechanism. The generation rate constant of thermal NOx is calculated using the Arrhenius equation, and the concentration distribution of O radicals and OH radicals during combustion is calculated using a partial equilibrium method.

[0012] Based on the above scheme, the basic physicochemical properties and fuel-type NOx generation database of the anthracite, bituminous coal and their blended coal samples mentioned in step S2 can be obtained through the following methods: S211: Conduct industrial and elemental analysis on anthracite and bituminous coal to determine their fixed carbon, volatile matter and nitrogen content; S212: Prepare mixed coal samples according to a preset ratio, and determine the ignition temperature and comprehensive combustion characteristic index of each coal sample using thermogravimetric analysis. S213: The NOx concentration in the flue gas after combustion of each coal sample was determined by combustion experiments, and a quantitative relationship between the proportion of bituminous coal blending and the NOx emission reduction was established.

[0013] Based on the above scheme, the preferred optimal allocation decision model in step S3 is: S231: When When the condition is deemed to be under relaxed control, it is recommended to use high-calorific-value anthracite or a high-anthracite blend; maintain normal production load and control the kiln tail temperature within the conventional roasting temperature range. S232: When When the condition is determined to be under moderate control, a high-volatile anthracite-bituminous coal blend is recommended; implement Level 1 auxiliary control to regulate the kiln tail temperature. Reduce the combustion air volume to 90%-95% of the baseline value; S233: When When the weather is deemed to be under heavy pollution emergency control conditions: a mandatory switch to a coal-natural gas blending scheme or an all-bituminous coal scheme will be implemented; secondary auxiliary control measures will be enforced to limit the amount of coal injected. The process involves switching from high-sulfur ore pellets to low-sulfur ore pellets to reduce the overall sulfur content to below 0.38% and ensuring the denitrification inlet temperature. .

[0014] This invention discloses a NOx control method for a chain grate rotary kiln based on multi-source fuel utilization. Targeting different levels of environmental warnings and ultra-low emission requirements, it establishes a solid fuel combustion characteristic database containing anthracite, bituminous coal, and their blends based on industrial analysis, elemental analysis, and thermogravimetric experiments. Using CFD numerical simulation technology, coupled with an Eulerian-Lagrange multiphase flow model and a P-1 radiation model, it analyzes the flow field and NOx generation patterns under pulverized coal and natural gas co-firing conditions. Upon receiving control commands, it calculates the inlet concentration threshold based on the real-time efficiency of the denitrification system and intelligently recommends the optimal fuel ratio (e.g., all anthracite, bituminous / anthracite blend, mixed coal / natural gas co-firing) using the multi-source database, and outputs corresponding kiln tail temperature, combustion air volume, and raw material structure control parameters.

[0015] This invention uses a combination of experimental and simulation methods to suppress the generation of fuel-based and thermal NOx at the source, thereby meeting differentiated environmental protection standards while ensuring stable production. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 This is a flowchart of the NOx control method for a chain grate machine-rotary kiln based on multi-source fuel utilization according to the present invention. Figure 2 a is a graph showing the temperature and composition characteristics under combustion of six different coal blending schemes according to the present invention; Figure 2 b is a graph showing the temperature and combustion characteristics under six different coal blending schemes of the present invention; Figure 2 c is a database diagram of fuel-type NOx generation under different coal blends according to the present invention; Figure 3 These are temperature field distribution cloud maps of pulverized coal under six different coal blending schemes according to the present invention. Figure 4 This is a temperature field distribution cloud map of the combustion of pulverized coal mixed with natural gas according to the present invention. Detailed Implementation

[0017] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0018] It should be understood that, when used in this specification and the appended claims, the term "comprising" indicates the presence of a descriptive feature, integral, step, operation, element, and / or component, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or sets.

[0019] To keep the drawings concise, only the parts relevant to the invention are shown schematically in each figure, and they do not represent the actual structure of the product. Furthermore, for ease of understanding, in some figures, only one of components with the same structure or function is shown schematically, or only one is labeled. In this document, "one" can mean not only "only one" but also "more than one".

[0020] It should also be further understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0021] In the embodiments shown in the accompanying drawings, the directional indications (such as up, down, left, right, front, and back) used to explain the structure and movement of the various components of the invention are relative rather than absolute. These descriptions are appropriate when these components are in the positions shown in the drawings. If the descriptions of the positions of these components change, these directional indications also change accordingly.

[0022] Furthermore, in the description of this application, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0024] Please see Figure 1 The present invention discloses a NOx control method for a chain grate machine-rotary kiln based on multi-source fuel utilization, comprising the following steps: Step S1: Analyze environmental control instructions and determine the current NOx emission target value. (e.g., 40 mg / m³, 35 mg / m³, or 30 mg / m³), and combined with the maximum denitrification efficiency of the current SCR denitrification system. Calculate the upper limit of allowable NOx concentration at the rotary kiln outlet. ; Step S2, constructing a multi-source fuel combustion characteristic database, specifically including: First, a database of basic physicochemical properties of anthracite, bituminous coal and their different blending ratios, including fuel nitrogen content and volatile matter release characteristics, and a baseline emission level of fuel-type NOx, are constructed based on experimentally obtained data. The specific steps are as follows: S211: Conduct industrial and elemental analysis on anthracite and bituminous coal to determine their fixed carbon, volatile matter and nitrogen content; S212: Prepare mixed coal samples according to a preset ratio, and determine the ignition temperature and comprehensive combustion characteristic index of each coal sample using thermogravimetric analysis. S213: The NOx concentration in the flue gas after combustion of each coal sample was determined by combustion experiments, and a quantitative relationship between the proportion of bituminous coal blending and the NOx emission reduction was established.

[0025] Then, based on the obtained database of basic physicochemical properties of anthracite, bituminous coal and their blended coal samples, a CFD numerical simulation model of the combustion process of pulverized coal particles was used. Using the Euler-Lagrange method and the P-1 radiation model, a database of flow field and thermal NOx generation under the co-firing condition of pulverized coal and natural gas was established.

[0026] The CFD numerical simulation model for the combustion process of pulverized coal particles includes: Volatile component combustion model: The release and combustion of volatile components are described by a single-step reaction kinetic equation in the form of Arrhenius equations, and the mass formation rate of volatile components is calculated. Coke combustion model: A kinetic / diffusion-controlled reaction rate model is used to calculate the surface combustion rate of coke by weighting the chemical reaction kinetic rate and diffusion rate.

[0027] A database of flow field and thermal NOx formation under the co-firing conditions of pulverized coal and natural gas was established using the Eulerian-Lagrange method and the P-1 radiation model. The specific operation steps are as follows: S221: The Euler-Lagrange system is used to describe the gas-solid two-phase flow, and the flue gas is regarded as the continuous phase, the pulverized coal particles are regarded as the discrete phase (DPM), and the bidirectional coupling effect between the particles and the gas phase is considered. S222: The Realizable k-ε turbulence model is used to describe the complex gas turbulence and rotating flow field inside the rotary kiln; S223: The P-1 radiation model is used to calculate the radiation heat transfer process in the high-temperature environment inside the kiln, and the transport equation of the incident radiation is solved to obtain the radiation heat flow distribution. S224: The NOx generation process is simulated using a component transport model combined with the Zeldovich extension mechanism. The generation rate constant of thermal NOx is calculated using the Arrhenius equation, and the concentration distribution of O radicals and OH radicals during combustion is calculated using a partial equilibrium method.

[0028] Step S3: Input the upper limit of the allowable NOx concentration at the rotary kiln outlet obtained in step S1 into the optimal matching decision model, and match the condition in the database that the minimum NOx concentration at the SCR inlet is less than or equal to the allowable NOx concentration threshold at the SCR inlet. Candidate fuel blending schemes under the following conditions, the schemes covering pure anthracite mode, anthracite-bituminous coal blending mode and coal-natural gas blending mode; The optimal allocation decision model is as follows: S231: When When the condition is deemed to be under relaxed control, it is recommended to use high-calorific-value anthracite or a high-anthracite blend; maintain normal production load and control the kiln tail temperature within the conventional roasting temperature range. S232: When When the condition is determined to be under moderate control, a high-volatile anthracite-bituminous coal blend is recommended; implement Level 1 auxiliary control to regulate the kiln tail temperature. Reduce the combustion air volume to 90%-95% of the baseline value; S233: When When the weather is deemed to be under heavy pollution emergency control conditions: a mandatory switch to a coal-natural gas blending scheme or an all-bituminous coal scheme will be implemented; secondary auxiliary control measures will be enforced to limit the amount of coal injected. The process involves switching from high-sulfur ore pellets to low-sulfur ore pellets to reduce the overall sulfur content to below 0.38% and ensuring the denitrification inlet temperature. .

[0029] Step S4: Based on the selected fuel ratio scheme, output the corresponding auxiliary process control parameters, including the upper limit of kiln tail temperature, combustion air volume, pulverized coal injection volume, and sulfur content index of the pellets fed into the furnace.

[0030] This invention discloses a NOx control method for a chain grate rotary kiln based on multi-source fuel utilization. Targeting different levels of environmental warnings and ultra-low emission requirements, it establishes a solid fuel combustion characteristic database containing anthracite, bituminous coal, and their blends based on industrial analysis, elemental analysis, and thermogravimetric experiments. Using CFD numerical simulation technology, coupled with an Eulerian-Lagrange multiphase flow model and a P-1 radiation model, it analyzes the flow field and NOx generation patterns under pulverized coal and natural gas co-firing conditions. Upon receiving control commands, it calculates the inlet concentration threshold based on the real-time efficiency of the denitrification system and intelligently recommends the optimal fuel ratio (e.g., all anthracite, bituminous / anthracite blend, mixed coal / natural gas co-firing) using the multi-source database, and outputs corresponding kiln tail temperature, combustion air volume, and raw material structure control parameters.

[0031] This invention uses a combination of experimental and simulation methods to suppress the generation of fuel-based and thermal NOx at the source, thereby meeting differentiated environmental protection standards while ensuring stable production.

[0032] To further verify the effectiveness of the NOx control method of chain grate machine-rotary kiln based on multi-source fuel utilization of the present invention, specific embodiments will be described in detail below.

[0033] The experiment used a rotary kiln (Φ5.9×38m) with a production capacity of 250-300 t / h, a rotation speed of 0.8-1.3 r / min, an inclination of 4.0%, and a kiln tail temperature controlled at 1000℃-1050℃ with a control accuracy of ±10℃. The kiln internal temperature was maintained at 1200℃-1250℃ with a control accuracy of ±20℃. The kiln head temperature was controlled at 1100℃-1150℃ with an accuracy of ±15℃. The operating rotation speed was 0.5-1.2 rpm, and the auxiliary rotation speed was 0.06 rpm. The material layer thickness in the chain grate was 180-220 mm; the temperature in the forced-air drying section was 200℃-250℃ for 3-4 minutes, with a material layer height of 200-300 mm. The temperature in the exhaust drying section was 400℃-450℃ for 6-8 minutes, with a material layer height of 200-300 mm. The first preheating stage involves a temperature of 900℃ to 1000℃ for 5 to 7 minutes, an air velocity of 1.2 to 1.5 meters per second, and a material layer height of 200 to 250 millimeters. The second preheating stage involves a temperature of 1000℃ to 1050℃ for 7 to 10 minutes, an air velocity of 1.5 meters per second, and a material layer height of 200 to 250 millimeters. The rotary kiln firing section involves a temperature of 1250℃ to 1300℃ and a residence time of 15 to 30 minutes. The secondary air temperature is 1100-1400K; the pulverized coal flow rate is 8-13t / h; and the natural gas flow rate is 0-40m / s. Step S1: Obtain the current NOx environmental control target value. (e.g., 40 mg / m³, 35 mg / m³, or 30 mg / m³) and the maximum denitrification efficiency of the current SCR denitrification system. Calculate the allowable NOx concentration threshold at the SCR inlet. .

[0034] Step S2: Construct a multi-source fuel combustion characteristic database First, we constructed a database of basic physicochemical properties and a database of fuel-type NOx generation by selecting typical anthracite and bituminous coal for experimental testing and analysis.

[0035] The detection and analysis include basic physicochemical property data analysis and fuel-type NOx generation data analysis. The basic physicochemical property data includes component characteristics and combustion characteristics.

[0036] The component characteristic analysis revealed that anthracite has a high fixed carbon content (65.25%) and a nitrogen content of 0.995%; bituminous coal has a high volatile matter content (33.94%) and a nitrogen content of 0.395%. Anthracite combustion produces more fuel-type NOx. For details, please refer to [link to relevant documentation]. Figure 2 As shown in a.

[0037] Combustion characteristic analysis revealed that thermogravimetric analysis showed the ignition temperature of anthracite (Ti=467.4℃) was higher than that of bituminous coal (Ti=375.4℃). Combustion curves of the mixed coal samples (Plan 1-Plan 6) showed that combustion performance remained stable with increasing bituminous coal proportions, indicating that blending bituminous coal does not drastically alter the thermal regime. For details, please refer to [link to relevant documentation]. Figure 2 As shown in b.

[0038] For the curve showing the relationship between fuel-type NOx formation data and temperature, please refer to [link / reference needed]. Figure 2 As shown in Figure C, the NOx emission characteristics analysis shows that the NOx emission of pure anthracite is 7.99 mg / kg, and that of pure bituminous coal is 4.14 mg / kg. With the increase of bituminous coal ratio, the NOx generation shows a linear decreasing trend.

[0039] Based on the above analysis data, a basic physicochemical property database and a fuel-type NOx generation database for anthracite, bituminous coal and their blended coal samples were constructed to form the present invention.

[0040] The second step involves using a CFD numerical simulation model of the combustion process of pulverized coal particles based on a database of the basic physicochemical properties of anthracite, bituminous coal, and their blended coal samples.

[0041] First, a three-dimensional geometric model of the rotary kiln and its supporting burner is established, with the mesh size controlled at approximately 918,000. Considering the complex processes such as turbulent flow, pulverized coal pyrolysis and combustion, and gas-solid two-phase heat and mass transfer within the rotary kiln, the following mathematical model is established for description: 1. Fluid flow governing equations: The combustion process is described by the conservation equations of mass, momentum, and energy. Among them, the mass conservation equation is: (1) in, For time; For density.

[0042] Momentum conservation equation (taking the x-direction as an example): (2) in, For time; For speed; Density; For pressure; The volume force term is in the x-direction; Energy conservation equation: (3) in, For time; For temperature; Density; Thermal conductivity; It is a specific heat at constant pressure.

[0043] 2. Turbulence model: Standard model adopted. Equations describing turbulent flow: Turbulent kinetic energy equation: (4) Dissipation rate equation: (5) in, For time; For fluid density; is the average velocity component; k is the turbulent kinetic energy; It is the molecular viscosity coefficient; This is the eddy viscosity coefficient; Prandtl number of k; This is the turbulent kinetic energy generation term produced by the average velocity gradient; This refers to the turbulent kinetic energy term generated by buoyancy. The turbulent kinetic energy dissipation rate; , and This is an empirical constant.

[0044] 3. Pulverized coal combustion model Volatile combustion: The release of volatiles is described using the Arrhenius equation. (6) in, The mass formation rate of volatile matter. For activation energy, This represents the particle temperature.

[0045] Coke combustion: A kinetic / diffusion-controlled reaction rate model was adopted, with the combustion rate determined by the chemical reaction kinetic rate. and diffusion rate We get the weighted average: (7) (8) in, For coke quality; For time; The diameter of the coke; The reaction rate; It is the activation energy; This represents the particle temperature.

[0046] 4. Radiation Model: Considering the large optical thickness inside the kiln, the P-1 radiation model is selected. Its incident radiation... The transmission equation is: (9) Where a is the absorption coefficient; The absorption coefficient; For incident radiation; These are the coefficients of the linear anisotropic phase function.

[0047] Heat Flow Vector Represented as: (10) NOx formation model: mainly simulates thermal NOx, adopts the Zeldovich mechanism, and calculates the concentrations of O and OH free radicals through a partial equilibrium method.

[0048] The third step is to apply tiered allocation and control strategies. Based on the basic physicochemical properties database of anthracite, bituminous coal and their blended coal samples and the fuel NOx generation database; Based on CFD numerical simulation of NOx emission characteristics databases for pulverized coal particles and natural gas, an optimal allocation decision-making model is formulated, namely the following graded control implementation plan: 1. Scenario 1: Relaxed control period (control target NOx) 40 mg / m³ Fuel strategy: Prioritize 100% anthracite (Plan 1) or 80% anthracite + 20% bituminous coal (Plan 2), taking advantage of the high calorific value (31.67 MJ / kg) of anthracite to reduce costs.

[0049] Process parameters: Maintain normal production load, and execute the kiln tail temperature and combustion air volume according to normal production standards.

[0050] 2. Scenario 2: Moderate control period (35 mg / m³) Control objectives 40 mg / m³ Fuel strategy: Switch to anthracite-bituminous coal blending mode, with a recommended ratio of 40% anthracite + 60% bituminous coal (Plan 4). This ratio reduces the NOx formation potential to 6.02 mg / kg19 and utilizes the high volatile matter content of bituminous coal to maintain combustion stability.

[0051] Auxiliary control: Implement Level 1 control.

[0052] Cooling: Control the kiln tail temperature to below 1050 ℃ to suppress thermal NOx.

[0053] Airflow control: Reduce the combustion airflow to around 9000 m³ / h to lower the oxygen concentration.

[0054] Scenario 3: Emergency control period for heavy pollution (control target <35mg / m³) Fuel strategy: Implement a coal-gas co-firing mode (e.g., 40% coal + 60% natural gas) or a 100% bituminous coal mode (Plan 6). Simulations show that adding 60% natural gas can reduce the peak flame temperature to 2100K, significantly reducing thermal NOx; while pure bituminous coal has the lowest NOx emissions (4.14 mg / kg). Please refer to [link to relevant documentation]. Figure 3 and Figure 4 As shown.

[0055] Assisted regulation: Implement Level II strong control measures.

[0056] Reduced capacity: Production load is reduced to 55%, and the amount of coal injected is limited to below 10.5 tons / hour.

[0057] Raw material optimization: High-sulfur green pellets were converted to low-sulfur green pellets, reducing the overall sulfur content from 0.49% to 0.38%.

[0058] Denitrification protection: Ensure that the denitrification inlet temperature is not lower than 330℃ to maintain catalyst activity.

[0059] Finally, the method described in this application is merely a preferred embodiment and is not intended to limit the scope of protection of this invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A grate-kiln NOx control method based on multi-source fuel utilization, characterized in that, Includes the following steps: Step S1, analyze the environmental protection control instruction to determine the current NOx emission target value And combine the real-time performance of the denitration system to calculate the upper limit of the NOx concentration allowed at the rotary kiln outlet. Step S2: Construct a multi-source fuel combustion characteristic database. The multi-source fuel combustion characteristic database includes a basic physicochemical characteristic database of anthracite, bituminous coal and their blended coal samples obtained based on experimental detection, and a fuel-type NOx generation database. Based on the information in the basic physicochemical characteristic database of anthracite, bituminous coal and their blended coal samples, a CFD numerical simulation model of the combustion process of pulverized coal particles is used. Using the Euler-Lagrange method and the P-1 radiation model, a database of flow field and thermal NOx generation and NOx emission characteristics under the co-firing condition of pulverized coal and natural gas is established. Based on information from fuel-type NOx generation databases, basic physicochemical properties databases, and NOx emission characteristics databases, an optimal allocation decision model is constructed. Step S3: Input the upper limit of the allowable NOx concentration at the rotary kiln outlet obtained in step S1 into the optimal fuel blending decision model, and match candidate fuel blending schemes in the database that meet the condition that the minimum NOx concentration at the SCR inlet is less than or equal to the allowable NOx concentration threshold at the SCR inlet. The fuel blending schemes cover pure anthracite mode, anthracite-bituminous coal blending mode and coal-natural gas blending mode. Step S4: Based on the selected fuel ratio scheme, output the corresponding auxiliary process control parameters, including the upper limit of kiln tail temperature, combustion air volume, pulverized coal injection volume, and sulfur content index of the pellets fed into the furnace.

2. The NOx control method for a chain grate machine-rotary kiln based on multi-source fuel utilization as described in claim 1, characterized in that, The step S1 specifically comprises obtaining a current NOx environmental protection control target value and a maximum denitration efficiency of a current SCR denitration system , calculating an SCR inlet allowable NOx concentration threshold .

3. A grate-kiln NOx control method based on multi-source fuel utilization according to claim 1, characterized in that, The CFD numerical simulation model of the coal powder combustion process in step S2 includes: Volatile combustion model: The release and combustion of volatiles are described by a single-step reaction kinetic equation in the form of Arrhenius, and the mass formation rate of volatiles is calculated. Coke combustion model: A kinetic / diffusion-controlled reaction rate model is used to calculate the surface combustion rate of coke by weighting the chemical reaction kinetic rate and diffusion rate.

4. A method for NOx control in a grate-kiln system based on multi- fuel utilization as claimed in claim 3, wherein, The basic physicochemical properties and fuel-type NOx generation database of anthracite, bituminous coal and their blended coal samples mentioned in step S2 are obtained through the following methods: S211: Conduct industrial and elemental analysis on anthracite and bituminous coal to determine their fixed carbon, volatile matter and nitrogen content; S212: Prepare mixed coal samples in a preset ratio, and determine the ignition temperature of each coal sample by using a thermogravimetric analysis method and a comprehensive combustion characteristic index ; S213: The NOx concentration in the flue gas after combustion of each coal sample was determined by combustion experiments, and a quantitative relationship between the proportion of bituminous coal blending and the NOx emission reduction was established.

5. A method for NOx control in a grate-kiln system based on multi- fuel utilization as claimed in claim 1, wherein, In step S2, a CFD numerical simulation model of the combustion process of pulverized coal particles is used. The Euler-Lagrange method and the P-1 radiation model are employed to establish a database of flow field and thermal NOx generation and emission characteristics under the co-firing conditions of pulverized coal and natural gas. Specifically, this includes: S221: The Euler-Lagrange system is used to describe the gas-solid two-phase flow, and the flue gas is regarded as the continuous phase, the pulverized coal particles are regarded as the discrete phase (DPM), and the bidirectional coupling effect between the particles and the gas phase is considered. S222: The Realizable k-ε turbulence model is used to describe the complex gas turbulence and rotating flow field inside the rotary kiln; S223: The P-1 radiation model is used to calculate the radiation heat transfer process in the high-temperature environment inside the kiln, and the transport equation of the incident radiation is solved to obtain the radiation heat flow distribution. S224: The NOx generation process is simulated using a component transport model combined with the Zeldovich extension mechanism. The generation rate constant of thermal NOx is calculated using the Arrhenius equation, and the concentration distribution of O radicals and OH radicals during combustion is calculated using a partial equilibrium method.

6. The NOx control method for a chain grate machine-rotary kiln based on multi-source fuel utilization as described in claim 5, characterized in that, The optimal matching decision model in step S2 is as follows: S231: When When the condition is deemed to be under relaxed control, it is recommended to use a high-calorific-value anthracite coal or a high-anthracite coal blend. Maintain normal production load and control the kiln tail temperature within the conventional roasting temperature range; S232: When When the condition is determined to be under moderate control, a high-volatile anthracite-bituminous coal blend is recommended; implement Level 1 auxiliary control to regulate the kiln tail temperature. Reduce the combustion air volume to 90%-95% of the baseline value; S233: When When the weather is deemed to be under heavy pollution emergency control conditions: a mandatory switch to a coal-natural gas blending scheme or an all-bituminous coal scheme will be implemented; secondary auxiliary control measures will be enforced to limit the amount of coal injected. The process involves switching from high-sulfur ore pellets to low-sulfur ore pellets to reduce the overall sulfur content to below 0.38% and ensuring the denitrification inlet temperature. .

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