Decomposition furnace structure optimization method based on energy quality coupling prediction

Abstract

This invention discloses a method for optimizing the structure of a decomposer based on energy-mass coupling prediction, comprising the following steps: Step 1, establishing a particle fluid dynamics model of the decomposer; Step 2, establishing the fluid phase equation, turbulence model, fluid phase component transport equation, energy conservation equation, particle-related control equation, drag force model, and particle-particle collision force equation for particles, and using the MP-PIC method to simulate and analyze the particle fluid dynamics model of the decomposer; Step 3, post-processing the analysis results from Step 2 to obtain the gas-solid two-phase temperature distribution cloud map, gas phase component distribution cloud map, and streamline diagram within the decomposer; Step 4, based on the diagrams from Step 3, finely adjusting the structure in the particle fluid dynamics model of the decomposer to determine the optimal structure of the decomposer. This invention can achieve precise adjustment and optimization of the decomposer structure, significantly reducing economic costs.

Description

Technical Field

[0001] This invention relates to the field of precalciner structure optimization methods, specifically a precalciner structure optimization method based on energy-mass coupling prediction. Background Technology

[0002] Clinker is one of the key raw materials for cement production, and it is one of the main components of cement. Through the thermal decomposition process in a decomposer, calcium carbonate and other compounds in the raw materials can be decomposed into clinker, providing the necessary raw materials for subsequent cement production.

[0003] The precalciner is a crucial piece of equipment in cement production, primarily used for the thermal decomposition of raw materials such as limestone and clay to produce clinker. Specifically, the combustion of pulverized coal in the precalciner releases a large amount of heat energy, heating the raw materials to high temperatures and causing them to decompose into clinker, producing a large amount of CO2 and a small amount of water vapor. Simultaneously, NOx transported from the kiln tail undergoes a reduction reaction with carbon powder and CO in the precalciner, while the Char-N in the pulverized coal itself undergoes oxidation and reduction reactions to produce NO or N2. The precalciner is the site of significant heat consumption during cement clinker sintering and is the primary site for CaCO3 decomposition. The precalciner can also improve the energy efficiency of cement production by recovering heat energy, reducing environmental pollution and energy waste. Therefore, the precalciner plays a vital role in cement production.

[0004] The structure of the decomposition furnace is as follows Figure 1 , Figure 2 , Figure 3 As shown, it includes a three-stage furnace body 11. The upper end of the component 11 is connected to an outlet 12. The lower end of the component 11 is connected to a secondary furnace body 10. The lower end of the secondary furnace body 10 is connected to a primary furnace body 9. The lower end of the primary furnace body 9 is connected to a coal feeding port 2. The lower end of the coal feeding port 2 is the kiln tail air inlet 1. The side of the primary furnace body 9 is connected to a first air inlet 3 and a second air inlet 4. The side of the outlet 12 is connected to a first discharge port 5, a second discharge port 6, a third discharge port 7, and a fourth discharge port 8.

[0005] In the existing technology patent CN208287788 U, ammonia is directly injected into the flue gas to reduce NOx emissions by reacting with NOx in the flue gas in a low-oxygen flame. Using ammonia in a decomposition furnace to reduce NOx concentration is often necessary, but this invention does not consider the equipment's own role in reducing NOx. Sometimes, an unreasonable equipment structure can lead to excessive ammonia consumption, increasing costs.

[0006] In existing patent CN 104713360 B, NOx concentration is reduced by controlling the amount of fuel injected through the staged fuel injector. Tertiary air is introduced into the side of the vortex pre-combustion chamber to create a strong swirling effect, thereby increasing the residence time of the material. However, the vortex pre-combustion chamber and the tertiary air intake of this invention increase the space occupied by the equipment and the amount of material used, failing to fully utilize the characteristics of the decomposition furnace itself for optimization.

[0007] In the existing technology patent 201610012222.4, a reducing gas is created in the decomposition furnace to target NOx generated in the furnace through staged combustion technology. However, no corresponding measures are taken to reduce NOx in the rotary kiln tail flue gas, so the NOx emission at the decomposition furnace outlet is still relatively large.

[0008] Because the decomposition furnace involves "three transfers and one reaction," namely heat transfer, mass transfer, momentum transfer, and chemical reaction processes, existing technologies mostly rely on engineering experience to modify the structure of the decomposition furnace to improve the flow field and increase the solid-gas residence time ratio. However, they lack a thorough understanding of the detailed heat transfer, mass transfer, and chemical reactions within the decomposition furnace, making it difficult to explore the detailed reactions inside the furnace and thus hindering the fine-tuning of the decomposition furnace structure. Summary of the Invention

[0009] This invention provides a method for optimizing the structure of a precalciner based on energy-mass coupling prediction, in order to solve the problem that existing technologies cannot achieve fine optimization and adjustment of the precalciner structure.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] The method for optimizing the structure of a precalciner based on energy-mass coupling prediction includes the following steps:

[0012] Step 1: Establish a hydrodynamic model of the decomposer based on the turbulence model, fluid phase component transport equation, and energy conservation equation;

[0013] Step 2: Use the Gidaspow drag model, particle normal stress model, and collision model to perform particle motion simulation analysis on the decomposition furnace fluid dynamics model established in Step 1.

[0014] Step 3: Extract the main chemical reactions of combustion, raw material decomposition, and NOx generation respectively, identify the key reaction chemical equations, establish a global chemical reaction kinetic model based on the conservation of energy and components equations, and combine the particle motion simulation analysis results from Step 2, and finally establish a numerical model of the energy-mass coupling decomposition furnace.

[0015] Step 4: The numerical model of the energy-mass coupled decomposition furnace obtained in Step 3 can yield the following data within the decomposition furnace: the average value of pollutant components along the center height of the decomposition furnace, the gas streamline diagram, and the concentration of pollutants, including CO and NOx.

[0016] Step 5: Based on Step 4, the structure of the decomposer is finely adjusted multiple times. A numerical model of energy-mass coupling is established for each structure, and data such as the average height of the decomposer center, gas streamline diagram, and pollutant concentration are calculated to determine the optimal structure of the decomposer.

[0017] Furthermore, the fluid control equation for step 1 is:

[0018] Continuity equation:

[0019]

[0020] In the formula: θ f For fluid phase volume fraction, ρ f For fluid phase density, u f For fluid phase velocity, δm s Let t be the mass increment and t be time.

[0021] Momentum conservation equation:

[0022]

[0023] In the formula: θ f ρ is the volume fraction of the fluid phase. f The density of the fluid phase; u f For fluid phase velocity; P is pressure; F is body force; τ f It is the momentum transfer rate between the fluid phase and the particle phase; g is the gravitational acceleration. Represents the Hamiltonian operator;

[0024] Turbulence model:

[0025]

[0026] in Δ=(δxδyδz) 1 / 3 C s This is a correction constant, typically 0.01. Δ represents the filtering length in the x, y, and z directions, δx, δy, and δz are the unit lengths in the three directions, ui represents the velocity in the i direction, uj represents the velocity in the j direction, xi represents the displacement in the i direction, and xj represents the displacement in the j direction.

[0027] Furthermore, the drag force model used for particle motion in step 2 is as follows:

[0028] F p =m p D(ua -u p )

[0029]

[0030] Among them, F p θ is the drag force exerted by the fluid on the particle. p θ represents the particle volume fraction. cp D1 represents the volume fraction of the packed state of particles under the close packing limit, D2 represents the Wen-Yu drag coefficient, and D2 represents the Ergun drag coefficient; ua represents the gas velocity, up represents the particle velocity, and mp represents the particle mass.

[0031] Particle normal stress model:

[0032]

[0033] In the formula: P s It is a positive constant with a pressure unit, and the constant ε is a value on the order of 1e-7. This represents the volume fraction of the particles.

[0034] Furthermore, the energy and composition equations in step 3 are conserved as follows:

[0035]

[0036]

[0037] Where, θ f For fluid phase volume fraction, ρ f For fluid phase density, u f Y is the fluid phase velocity. f,i D is the mass fraction of the i-th component; f,i h is the turbulent diffusion rate of the i-th component; f It is the enthalpy of the fluid phase; ΔH rf It is the heat of reaction in the fluid phase; The change in mass caused by a chemical reaction. Here, q is the Hamiltonian operator, and q is the energy per unit volume.

[0038] Furthermore, in step 3, the main chemical reactions of combustion, raw material decomposition, and NOx generation are as follows: (1) Pulverized coal pyrolysis

[0039] Coal→Char+CH4+C2H4+CO+H2+HCN+Ash(R0)

[0040] (2) Combustion of volatile components

[0041] CH4 + 1.5O2 → CO + 2H2O (R1)

[0042] C2H4 + 2O2 → 2CO + 2H2O (R2)

[0043] CO + 0.5O₂ → CO₂(R₃)

[0044] H₂ + 0.5O₂ → H₂O(R₄)

[0045] (3) Gasification and Combustion of Coke

[0046] C(s) + 0.5O₂ → CO(R₅)

[0047] C(s) + CO2 → 2CO(R6)

[0048] (4) Formation and reduction of pollutants

[0049] HCN + O2 → NO + CO + 0.5H2 (R7)

[0050] HCN + NO → N2 + CO + 0.5H2 (R8)

[0051] C(s) + NO → 0.5N₂ + CO(R₁₆)

[0052] CO + NO → 0.5N₂ + CO₂ (R₁₀)

[0053] CH4+0.7692NO→0.2308HCN+0.7692CO+1.8846H2+0.2692N2(R11)

[0054] C2H4+2.7586NO→0.8276HCN+1.1724CO+0.9655N2+1.5862H2O(R12)

[0055] (5) Raw material decomposition reaction

[0056] CaCO3(s)→CaO+CO2(R13).

[0057] Furthermore, the grid independence of the energy-mass coupled decomposition furnace numerical model established in step 3 is verified before application. When the NO concentration difference between the two grid schemes is less than 5%, the grid scheme with fewer grids is selected as the final grid scheme.

[0058] Furthermore, the numerical model of the energy-mass coupled decomposer established in step 3 was verified and calibrated using on-site decomposer operation data.

[0059] Compared with the prior art, the advantages of the present invention are:

[0060] This invention utilizes numerical simulation to achieve a detailed simulation of the "three transfers and one reaction" process within a decomposer furnace. Based on extensive numerical simulation experimental data from the decomposer furnace, it quantitatively analyzes NOx concentration and gas flow distribution. With the goal of reducing NOx concentration and improving pulverized coal combustion rate, it can precisely control the temperature and component concentration in various parts of the furnace, thereby enabling precise adjustment and optimization of the decomposer furnace structure. This invention can reduce NOx concentration with only minor adjustments to the decomposer furnace structure, significantly reducing economic costs. This leads to economical, low-carbon, and environmentally friendly cement production. Attached Figure Description

[0061] Figure 1 This is a front view of the decomposition furnace structure.

[0062] Figure 2 This is a side view of the decomposition furnace structure.

[0063] Figure 3 This is a top view of the decomposition furnace structure.

[0064] Figure 4 This is a flowchart of the method according to an embodiment of the present invention.

[0065] Figure 5 The effect of pulverized coal location on NO degree

[0066] Figure 6 The effect of the ratio of two tertiary air volumes on NO concentration

[0067] Figure 7 The effect of the second-stage tertiary air eccentricity of 1.5m on the flow lines inside the furnace (main view)

[0068] Figure 8 Side view of the effect of the second tertiary air eccentricity of 1.5m on the flow lines inside the furnace.

[0069] Figure 9 This is a front view of the adjusted decomposition furnace structure in an embodiment of the present invention.

[0070] Figure 10 This is a top view of the adjusted decomposition furnace structure in an embodiment of the present invention. Detailed Implementation

[0071] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0072] like Figure 4 As shown in the figure, this embodiment discloses a method for optimizing the structure of a precalciner based on energy-mass coupling prediction. The process is as follows:

[0073] Step 1: First, establish a fluid model based on numerical simulation software such as Barracuda and OpenFoam;

[0074] Step 2: After the flow field stabilizes, add particles and use the Gidaspow drag model, particle normal stress model, and collision model to perform particle motion simulation analysis on the hydrodynamic model of the decomposition furnace established in Step 1.

[0075] Step 3: Refine the main chemical reactions of combustion, raw material decomposition, and NOx generation, and establish a global chemical reaction kinetic model based on Step 2;

[0076] Step 4: Post-process the obtained model analysis results data using tools such as Excel and Tecplot to obtain the following data inside the decomposition furnace: average value of pollutant (CO and NOx) components along the center height of the decomposition furnace, and gas streamline diagram;

[0077] Step 5: Perform mesh-free inertia verification and use actual measurement data to verify and calibrate the model.

[0078] Step 6: The furnace structure in the particle fluid dynamics model of the decomposer is finely adjusted multiple times, and the simulation data for each structural scheme is extracted using the method in Step 4. This yields... Figure 5-8 .according to Figure 5-8 The optimal structure of the decomposer was determined by comparing the effects of each structural adjustment on pollutants and gas flow lines.

[0079] The specific adjustments involve fine-tuning the air volume of the tertiary air duct, the position of the pulverized coal injection pipe, and the offset of the tertiary air duct inlet from the center of the furnace body. The adjusted furnace structure is as follows: Figure 9-10 As shown.

[0080] In the numerical model of the energy-mass co-fiber decomposition furnace in this embodiment, the fluid phase adopts the Navier-Stokes equations, and the continuous phase equation is expressed as:

[0081]

[0082] In the formula: θ f For fluid phase volume fraction, ρ f For fluid phase density, u f For fluid phase velocity, δm s The increment is the mass, and t is time.

[0083] The momentum conservation equation is:

[0084]

[0085] In the formula: θ f ρ is the volume fraction of the fluid phase. f The density of the fluid phase; u f For fluid phase velocity; P is pressure; F is body force; g is gravitational acceleration; τ fIt is the momentum transfer rate between the fluid phase and the particle phase, and t is time.

[0086] The turbulence model is:

[0087]

[0088] in Δ=(δxδyδz) 1 / 3 C s It is a correction constant, typically 0.01. Δ is the filtering length in the x, y, and z directions, and δx, δy, and δz are the unit lengths in the three directions.

[0089] The energy and composition equations are conserved as follows:

[0090]

[0091]

[0092] Where, θ f For fluid phase volume fraction, ρ f For fluid phase density, u f Y is the fluid phase velocity. f,i D is the mass fraction of the i-th component; f,i h is the turbulent diffusion rate of the i-th component; f It is the enthalpy of the fluid phase; ΔH rf It is the heat of reaction in the fluid phase; , This refers to the change in mass caused by a chemical reaction. Here, q is the Hamiltonian operator, and q is the energy per unit volume.

[0093] The particle drag force model in this embodiment is as follows:

[0094] F p =m p D(u a -u p )

[0095]

[0096] Among them, F p θ is the drag force exerted by the fluid on the particle. p θ represents the particle volume fraction. cp D1 represents the volume fraction of the particle packing state, D2 represents the Wen-Yu drag coefficient, and D3 represents the Ergun drag coefficient.

[0097] Particle normal stress model:

[0098]

[0099] In the formula: Ps P is a positive constant with a pressure unit, and the constant ε is a value on the order of 1e-7, where: P s It is a positive constant with a pressure unit, and the constant ε is a value on the order of 1e-7. This represents the volume fraction of the particles.

[0100] This embodiment utilizes numerical software such as Barracdua and OpenFoam to digitize the decomposition furnace, enabling precise control over the average height of pollutant (CO and NOx) components along the furnace center and the gas streamline diagram. This allows for precise adjustments to the furnace structure. This invention can reduce NOx concentration with only minor structural adjustments to the decomposition furnace, significantly lowering economic costs.

[0101] based on Figure 5 , 6 As shown in the data in sections 7 and 8, this embodiment makes fine adjustments to the height of the coal feeding pipe, the position of the tertiary air duct, and the air volume ratio of the tertiary air duct. The optimized decomposition furnace structure is as follows:

[0102] (1) The ratio of the air volume of the first tertiary air duct to the air volume of the second tertiary air duct is 7:3.

[0103] (2) The height of the pulverized coal injection nozzle is lowered by 1.5m;

[0104] (3) The second tertiary air duct is laterally cut into the furnace, with the centerline of the duct offset from the center point of the decomposition furnace by 1.5m, in order to increase the swirl intensity inside the furnace.

[0105] (4) The raw material is fed in stages, and the second and third feeding ports are moved upward to increase the temperature of the first-stage furnace area and increase the rate at which NO is reduced.

[0106] The optimized structure of the decomposition furnace is as follows: Figure 9 , 10 As shown.

[0107] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. These embodiments are merely descriptions of preferred embodiments and are not intended to limit the scope or concept of the invention. The specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. Such combinations, as long as they do not violate the spirit of the present invention, should also be considered as part of this disclosure. To avoid unnecessary repetition, the present invention will not further describe the various possible combinations.

[0108] This invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this invention and without departing from the design idea of ​​this invention, all modifications and improvements made by those skilled in the art to the technical solutions of this invention should fall within the protection scope of this invention. The technical content for which protection is sought in this invention has been fully described in the claims.

Claims

1. A method for optimizing the structure of a precalciner based on energy-mass coupling prediction, characterized in that, Includes the following steps: Step 1: Establish a hydrodynamic model of the decomposer based on the turbulence model, fluid phase component transport equation, and energy conservation equation; Step 2: Use the Gidaspow drag model, particle normal stress model, and collision model to perform particle motion simulation analysis on the decomposition furnace fluid dynamics model established in Step 1. Step 3: Extract the main chemical reactions of combustion, raw material decomposition, and NOx generation respectively, identify the key reaction chemical equations, establish a global chemical reaction kinetic model based on the conservation of energy and components equations, and combine the particle motion simulation analysis results from Step 2, and finally establish a numerical model of the energy-mass coupling decomposition furnace. Step 4: The numerical model of the energy-mass coupling decomposer obtained in Step 3 can yield the following data within the decomposer: the average height of pollutant components along the center of the decomposer, the gas streamline diagram, and the concentration of pollutants, including CO and NOx. Step 5: Based on Step 4, the structure of the decomposer is finely adjusted multiple times. A numerical model of energy-mass coupling for each structure is established and the average height of the decomposer center, gas streamline diagram, and pollutant concentration data are calculated. The optimal structure of the decomposer is then determined. The fluid control equation for step 1 is: Continuity equation: ， In the formula: For fluid phase volume fraction, For fluid phase density, For fluid phase velocity, Let t be the mass increment and t be time. Momentum conservation equation: ， In the formula: It represents the volume fraction of the fluid phase. The density of the fluid phase; For fluid phase velocity; It represents pressure; F represents physical strength. It is the momentum transfer rate between the fluid phase and the particle phase; g is the gravitational acceleration. Represents the Hamiltonian operator; Turbulence model: ， in , , , It is a correction constant, which is 0.01; Filter lengths in the x, y, and z directions. Let be the unit length in three directions, ui represent the velocity in the i direction, uj represent the velocity in the j direction, xi represent the displacement in the i direction, and xj represent the displacement in the j direction.

2. The method for optimizing the structure of a precalciner based on energy-mass coupling prediction according to claim 1, characterized in that, The drag force model used for particle motion in step 2 is as follows: ， ， in, The drag force exerted by the fluid on the particles. This represents the particle volume fraction. D1 represents the volume fraction of the packed state of particles under the close packing limit, D2 represents the Wen-Yu drag coefficient, and D2 represents the Ergun drag coefficient; ua represents the gas velocity, up represents the particle velocity, and mp represents the particle mass. Particle normal stress model: ， In the formula: It is a positive constant with a unit of pressure. It is a value on the order of 1e-7. This represents the volume fraction of the particles.

3. The method for optimizing the structure of a precalciner based on energy-mass coupling prediction according to claim 1, characterized in that, In step 3, the energy and composition equations are conserved as follows: ， ， in, For fluid phase volume fraction, For fluid phase density, For fluid phase velocity, It is the mass fraction of the i-th component; It is the turbulent diffusion rate of the i-th component; It is the enthalpy of the fluid phase; It is the heat of reaction in the fluid phase; , The change in mass caused by a chemical reaction. q represents the energy per unit volume.

4. The method for optimizing the structure of a precalciner based on energy-mass coupling prediction according to claim 1, characterized in that, In step 3, the main chemical reactions involved in combustion, raw material decomposition, and NOx generation are as follows: (1) Pulverized coal pyrolysis Coal Char+CH4+C2H4+CO+H2+HCN+Ash(R0), (2) Combustion of volatiles CH4 + 1.5O2→ CO + 2H2O (R1), C2H4 + 2O2 →2CO + 2H2O (R2), CO + 0.5O2 → CO2(R3) H2 + 0.5O2 → H2O (R4) (3) Gasification and combustion of coke C(s) + 0.5O2 → CO(R5), C(s) + CO2 → 2 CO(R6), (4) Formation and reduction of pollutants HCN + O2 →NO + CO + 0.5H2 (R7), HCN + NO →N2+ CO + 0.5H2 (R8), C(s) + NO → 0.5N2+ CO (R9), CO + NO → 0.5N2+ CO2 (R10), CH4+0.7692NO→0.2308HCN+0.7692CO+1.8846H2+0.2692N2 (R11), C2H4+2.7586NO→0.8276HCN+1.1724CO+0.9655N2+1.5862H2O (R12), (5) Raw material decomposition reaction CaCO3(s) → CaO + CO2 (R13).

5. The method for optimizing the structure of a precalciner based on energy-mass coupling prediction according to claim 1, characterized in that, Before applying the numerical model of the energy-mass coupled decomposition furnace established in step 3, the grid independence was verified. When the NO concentration difference between the two grid schemes was less than 5%, the grid scheme with fewer grids was selected as the final grid scheme.

6. The method for optimizing the structure of a precalciner based on energy-mass coupling prediction according to claim 1, characterized in that, The numerical model of the energy-mass coupled decomposer established in step 3 was verified and calibrated using on-site decomposer operation data.

Images