Oxygen-enriched combustion simulation method and system for long-strip-shaped straw particles

Abstract

The invention discloses an oxygen-enriched combustion simulation method and system for long-strip-shaped straw particles, and belongs to the technical field of oxygen-enriched combustion simulation, and the specific scheme comprises the following steps: step 1, modeling the long-strip-shaped straw particles by using EDEM software in combination with geometric characteristics of the long-strip-shaped straw particles; fine mesh modeling is carried out on the hearth of the circulating fluidized bed boiler by using Fluent software, and a boiler mesh model conforming to the characteristics of the long-strip-shaped straw particles is constructed; 2, aiming at the boiler grid model, solving a fluid phase equation and a particle phase equation of an internal three-dimensional space by adopting a multiphase flow discrete particle model in Fluent software to obtain a corresponding mathematical model; and 3, simulating the oxygen-enriched combustion process of the long-strip-shaped straw particles in the circulating fluidized bed boiler by utilizing the mathematical model and combining a chemical reaction formula involved in the oxygen-enriched combustion process to obtain a corresponding oxygen-enriched combustion simulation model. According to the invention, accurate simulation of the combustion process of the long-strip-shaped straw particles in the oxygen-enriched environment is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of oxygen-enriched combustion simulation, and in particular relates to a method and system for simulating oxygen-enriched combustion of long strip straw particles. Background Art

[0002] Biomass oxygen-enriched combustion technology, as an important path to achieving carbon capture and storage (CCUS), has received widespread attention in biomass power plants in recent years. However, existing research has mostly focused on the combustion simulation of homogeneous fuels (such as powdered or short-particle biomass). These models typically assume that the fuel is an idealized sphere or tiny particle (particle size <1 cm), and achieve rapid modeling by simplifying the pyrolysis, oxygen diffusion, and combustion surface renewal processes. Traditional methods have limitations, mainly reflected in the following: existing numerical simulations (such as single-phase flow models) often simplify biomass into homogeneous particles and do not consider the anisotropic oxygen diffusion characteristics of elongated fuels (such as 10 cm straw briquettes). This type of fuel exhibits significant axial and radial pyrolysis differences during combustion, resulting in large errors in temperature field predictions using traditional models. Simulation methods based on the Two-Fluid Model (TFM), while capable of handling gas-solid two-phase flows, cannot accurately characterize the discrete motion of long-strip fuels and their dynamic interactions with the airflow. Existing research often relies on simplified combustion experiments (such as small-scale furnace tests), making it difficult to replicate the staged combustion behavior of long-strip fuels in actual fluidized beds or grate-fired furnaces, resulting in insufficient model calibration data. While existing research has made progress in the macroscopic optimization of biomass oxy-combustion (such as oxygen concentration control), in-depth analysis of the coupling mechanism between fuel morphology and combustion dynamics remains lacking. These issues directly restrict the efficient calculation and precise control of pollutants in circulating fluidized bed boilers during biomass oxy-combustion. There is an urgent need to develop a simulation method for long-strip straw particles to address these technical bottlenecks. Summary of the Invention

[0003] In order to break through the limitations of traditional simulation technology, the present invention provides a method and system for simulating the oxygen-enriched combustion of long straw pellets, which can achieve accurate simulation and efficient calculation of the oxygen-enriched combustion process of long straw pellets.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A method for simulating oxygen-enriched combustion of long straw pellets, comprising:

[0006] First, EDEM software was used to model the long straw pellets based on their geometric characteristics. Fluent software was then used to fine-grid the circulating fluidized bed boiler furnace, constructing a boiler mesh model that conformed to the characteristics of the long pellets.

[0007] For this grid model, the multiphase discrete particle model (DDPM) in Fluent software was used to solve the fluid and particle phase equations within the three-dimensional space. During the solution process, EDEM software efficiently calculated particle motion, optimizing computational efficiency and ensuring that the entire simulation process met the requirements of industrial-grade boiler numerical simulation. This approach also fully accounted for the non-spherical shape of the long straw pellets, their pyrolysis expansion characteristics, and the complex gas-solid interactions, resulting in a mathematical model that closely matched the actual combustion process.

[0008] Using this mathematical model and combining it with the chemical reaction equations involved in the oxygen-rich combustion process (such as volatile analysis and coke combustion), a comprehensive simulation of the combustion process of long straw pellets in an oxygen-rich environment was carried out, covering key links such as volatile analysis, coke combustion, and pollutant generation, and ultimately obtaining a simulation model that accurately reflects the combustion process.

[0009] The process of solving the fluid phase equation and the particle phase equation in the three-dimensional space inside the boiler grid model includes solving the fluid phase equation and the particle phase equation using a multiphase flow DDPM method.

[0010] Fluent's DDPM model is used to solve the fluid phase (Eulerian equation) and particle phase (Lagrangian pursuit) control equations. The gas-solid drag force adopts the Nonspherical model, and the interaction between particles is closed by particle dynamics (KTGF).

[0011] The present invention relates to a simulation system constructed based on the above-mentioned method, comprising: a multi-scale modeling construction module, wherein the EDEM module generates a model of elongated straw pellets, and a Fluent module divides the furnace grid. An unstructured grid with an average size of 0.2 m and a number of 450,000 is used, and boundary conditions (primary air / secondary air composition, atmosphere flow) are defined. A mathematical model construction module is used to solve the fluid phase equation and the particle phase equation within the three-dimensional space of the boiler grid model to obtain an accurate mathematical model. A simulation module, using the above-mentioned mathematical model and the chemical reaction formula of straw oxygen-enriched combustion, conducts a detailed numerical simulation of the oxygen-enriched combustion process of the elongated straw pellets to obtain an accurate combustion process simulation model. The above-mentioned mathematical model construction module specifically uses the DDPM model to solve the fluid phase equation and the particle phase equation to obtain an accurate mathematical model. By coupling Fluent with EDEM software, engineering parameters such as primary / secondary air flow and combustion atmosphere can be optimized. Simultaneously, EDEM software can quickly calculate particle motion, optimize computational efficiency, and realize industrial-grade boiler numerical simulation. The present invention uses Fluent coupled EDEM software to consider the long straw particles to build a model. Compared with traditional simulations, it can more accurately simulate the oxygen-enriched combustion process of long fuel and meet the actual needs of the project.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] This invention overcomes the limitations of traditional simulation techniques for elongated straw pellets by constructing a precise oxygen-enriched combustion simulation model, enabling accurate simulation of the combustion process of elongated straw pellets in an oxygen-enriched environment. An efficient computational model suitable for simulating the oxygen-enriched combustion of elongated straw pellets was developed, optimizing the meshing strategy and numerical solution algorithm. This model, based on the characteristics of elongated pellets, generates a high-quality mesh for an industrial-scale circulating fluidized bed boiler furnace, reducing the number of meshes and iterations, improving computational efficiency, and enabling rapid optimization of engineering parameters (such as primary and secondary air flow rates, and excess air coefficient). BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a flow chart of a simulation method for oxygen-enriched combustion of long strip straw pellets;

[0015] Figure 2 This is a schematic diagram of the numerical simulation system structure for oxygen-enriched combustion of long straw pellets. DETAILED DESCRIPTION

[0016] The technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0017] Example 1:

[0018] This embodiment discloses a method for simulating oxygen-enriched combustion based on 10 cm long straw pellets. Figure 1 As shown, the method includes:

[0019] Step S1: Pre-model the circulating fluidized bed boiler and the 10 cm long straw pellets to obtain corresponding simulation models of the circulating fluidized bed boiler and the long straw pellets. It should be noted that there are currently multiple modeling and meshing methods. The most appropriate method can be selected based on the actual simulation requirements and the specific internal structure of the circulating fluidized bed boiler. In this example, Fluent software was used to mesh the circulating fluidized bed boiler furnace.

[0020] Step S2: Solve the fluid phase equation and the particle phase equation in the three-dimensional space inside the circulating fluidized bed boiler simulation model to obtain a corresponding mathematical model.

[0021] Among them, under different simulation accuracy requirements, the selection of fluid phase equations and particle phase equations will be different. If the simulation accuracy requirement is high, the above-mentioned fluid phase equations and particle phase equations will be relatively complex, and the corresponding amount of calculation will be relatively large; if the simulation accuracy requirement is low, the above-mentioned fluid phase equations and particle phase equations can be simplified to a certain extent, thereby reducing the corresponding amount of calculation. In this embodiment, when using Fluent coupled EDEM software to solve the equations, factors such as the complex interaction between 10 cm long straw particles and the fluid phase in an oxygen-rich atmosphere and the multi-component reaction mechanism are fully considered.

[0022] Step S3: Using a mathematical model and combining the chemical reaction formulas involved in the oxygen-enriched combustion process of a circulating fluidized bed boiler, the oxygen-enriched combustion process of 10 cm long straw particles in the circulating fluidized bed boiler is simulated to obtain a corresponding oxygen-enriched combustion simulation model.

[0023] The above chemical reaction formulas mainly include the pyrolysis of straw volatiles, the oxidation of pyrolysis products and coke in an oxygen-rich environment and other related chemical reaction formulas.

[0024] In Fluent, the primary and secondary air atmospheres were set to 28% O₂ / 72% CO₂, with an initial air temperature of 453 K, a primary air flow rate of 12.03 kg / s, and a secondary air flow rate of 8.02 kg / s. The backflow atmosphere was set to 21% O₂ / 79% N₂, with a flow rate of 0.718 kg / s. The inlet and wall boundary conditions were reflective, while the outlet boundary condition was escape. The standard κ-ε model and the stochastic tracking method were used for the fluid and particle phase turbulence models, respectively. The residual threshold was set to 1.0 × 10 -6 , time step is 0.001s, and the particle tracking time step is synchronized with the flow time step.

[0025] Table 1 Particle properties

[0026]

[0027] A custom UDF is used to achieve bidirectional coupling, and EDEM generates particle trajectory files, which are imported in real time through the Fluent-DPM interface.

[0028] In an embodiment of the present invention, a simulation method for oxygen-enriched combustion based on long strip straw particles includes pre-modeling a circulating fluidized bed boiler and 10 cm long strip straw particles, solving the fluid phase equation and particle phase equation of the internal three-dimensional space after obtaining the corresponding model, obtaining a corresponding mathematical model, and then simulating the oxygen-enriched combustion process of the long strip straw particles in combination with the chemical reaction formula involved in the oxygen-enriched combustion process to obtain a corresponding simulation model. It can be seen that the embodiment of the present invention first models the model, then solves the equation to obtain the mathematical model, and then simulates the chemical reaction formula to obtain the oxygen-enriched combustion simulation model. That is, the embodiment of the present invention constructs a model based on the consideration of the characteristics of the long strip particles. Compared with the traditional simulation method, the influence of the characteristics of the long strip particles and the oxygen-enriched reaction mechanism on the model is increased, so that the mathematical model finally obtained is more consistent with the actual process of oxygen-enriched combustion of the long strip straw, thereby improving the simulation effect of the subsequent oxygen-enriched combustion process. At the same time, by optimizing the grid division and solving the algorithm, the rapid optimization of the engineering parameters is achieved.

[0029] The following further illustrates and optimizes the technical solution of this embodiment.

[0030] When constructing the circulating fluidized bed boiler and straw pellet models, EDEM software was used to generate a biomass pellet model that conformed to the size and shape characteristics of a 10-cm long straw strip. Then, based on the actual dimensions of the circulating fluidized bed boiler, Fluent software was used for meshing, resulting in a circulating fluidized bed boiler mesh model that accommodated the movement and reactions of the long strips of straw. This example employed Fluent's multiphase flow (DDPM) software to solve the fluid and particle phase equations within the three-dimensional space within the circulating fluidized bed boiler mesh model. In the DDPM model, the fluid phase, acting as a continuous medium, was solved using the Euler equations, while the particle phase was tracked using the Lagrangian method. A nonspherical model was used for the gas-solid drag force model, and particle interactions were closed using particle dynamics (KTGF). This approach effectively describes the movement, heat transfer, and reaction processes of 10-cm long straw pellets within the furnace.

[0031] In the DDPM model, the fluid phase continuity equation describes mass conservation, while the particle phase is tracked using the Lagrangian method, taking into account the average particle size distribution (size 100 mm × 10 mm × 10 mm) and a pyrolysis expansion coefficient of 1.0. Specifically, the Ranz and Marshall correlation is used to calculate the gas-solid heat transfer coefficient. For the chemical reaction processes, the pyrolysis of straw volatiles, the combustion of pyrolysis products in an oxygen-rich environment, and the gasification of char are considered. A single-rate model is used for pyrolysis, a finite-rate / eddy-dissipation model for volatile combustion, and a "single shrinking core model" for char combustion.

[0032] The DDPM model treats the particles as discrete particle groups and the fluid phase as the continuous phase. Its continuity equation is established based on the Euler method for the fluid phase. This equation describes the conservation of mass in the fluid phase and is mathematically expressed as:

[0033]

[0034] In the formula is the fluid phase density, is the fluid phase velocity, is the fluid phase physical time, It is a mass source term, such as the mass change of the fluid phase caused by processes such as particle evaporation and combustion. For the particle phase, it uses the Lagrangian method to track the motion of individual particles or particle clusters, and does not directly establish the continuity equation for the particle phase.

[0035] The momentum equation of the fluid phase is established based on the Euler method to describe the conservation of momentum of the fluid phase. Its form is:

[0036]

[0037] Where, is the fluid phase pressure, is the stress tensor of the fluid phase, is the acceleration due to gravity, is the drag force of the particle on the fluid phase.

[0038] The momentum equation of the particle phase uses the Lagrangian method to describe the force and motion of a single particle or particle cluster, and the expression is:

[0039]

[0040] Where, is the particle mass, is the particle velocity, is the drag force of the particle on the fluid phase, is the gravitational force on the particle, It is other forces, such as Brownian force, Saffman force, etc.

[0041] Example 2

[0042] This embodiment discloses an oxygen-enriched combustion simulation system for long straw pellets based on embodiment 1, the system comprising:

[0043] The mesh model building module 21 uses Fluent and EDEM software to perform mesh modeling based on the structure of the circulating fluidized bed boiler and the size and shape of the long straw particles, generating a high-quality boiler mesh model;

[0044] Mathematical model construction module 22 uses the DDPM model in Fluent software to solve the fluid phase equation and particle phase equation within the boiler grid model, fully considering the characteristics of 10 cm long straw particles and the oxygen-enriched combustion reaction mechanism to obtain an accurate mathematical model. EDEM software can efficiently calculate particle motion and optimize computational efficiency, ensuring that the entire simulation process meets the requirements of industrial-grade boiler numerical simulation.

[0045] The simulation module 23 uses the constructed mathematical model and the chemical reaction formula of straw oxygen-enriched combustion to perform a detailed numerical simulation of the oxygen-enriched combustion process of 10 cm long straw pellets, thereby obtaining a simulation model that accurately reflects the combustion process.

[0046] For more specific working processes of the above modules, please refer to the relevant content in the aforementioned embodiments, which will not be described in detail here.

[0047] This example first constructed the model using EDEM and Fluent software, then solved the equations using the DDPM model in Fluent software to obtain a mathematical model. Finally, a combustion process simulation model was generated by combining chemical reaction equations. Compared to traditional simulation techniques, this example fully considers the particle characteristics of 10cm long straw pellets and the reaction mechanism of oxygen-enriched combustion, improving simulation accuracy and computational efficiency, and better meeting actual engineering needs.

[0048] As used herein, the terms "comprises", "includes" or any other variants thereof are intended to cover non-exclusive inclusion, such that a process, method, article or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus. In the absence of further restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or apparatus comprising the element. The above describes in detail a method and system for simulating oxygen-enriched combustion of elongated straw particles provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and scope of application. In summary, the contents of this specification should not be understood as limiting the present invention.

Claims

1. A method for simulating oxygen-enriched combustion of long straw particles, characterized in that: The following steps are involved: Step 1: Based on the geometric characteristics of the long straw pellets, EDEM software was used to model them. Fluent software was used to fine-mesh the circulating fluidized bed boiler furnace and construct a boiler mesh model that conforms to the characteristics of the long straw pellets. Step 2: For the boiler grid model, the multiphase flow discrete particle model in Fluent software is used to solve the fluid phase equation and particle phase equation in the internal three-dimensional space to obtain the corresponding mathematical model; Step 3: Using the mathematical model and combining it with the chemical reaction formulas involved in the oxygen-enriched combustion process, the oxygen-enriched combustion process of the long straw particles in the circulating fluidized bed boiler is simulated to obtain the corresponding oxygen-enriched combustion simulation model.

2. The method for simulating oxygen-enriched combustion of long straw particles according to claim 1, characterized in that: In step 2, during the equation solving process, EDEM software is used to calculate particle motion and optimize computational efficiency, so that the entire simulation process can meet the requirements of industrial-grade boiler numerical simulation.

3. The method for simulating oxygen-enriched combustion of long straw particles according to claim 1, characterized in that: In step 2, in the multiphase flow discrete particle model, the fluid phase is solved as a continuous medium using the Euler equation, while the particle phase uses the Lagrangian method to track particle clusters, the gas-solid drag model uses the Nonspherical model, and the interaction between particles is closed using particle dynamics.

4. The method for simulating oxygen-enriched combustion of long straw particles according to claim 3, characterized in that: The momentum equation of the fluid phase is established based on the Euler method to describe the conservation of momentum of the fluid phase, and its form is: In the formula is the fluid phase density, is the fluid phase velocity, is the fluid phase physical time, is the fluid phase pressure, is the stress tensor of the fluid phase, is the acceleration due to gravity, is the drag force of the particle on the fluid phase; The momentum equation of the particle phase uses the Lagrangian method to describe the force and motion of a single particle or particle cluster, and the expression is: Where, is the particle mass, is the particle velocity, is the gravitational force on the particle, It is other forces.

5. The method for simulating oxygen-enriched combustion of long straw particles according to claim 1, characterized in that: In step three, the chemical reaction formula includes pyrolysis of straw volatiles, and oxidation of pyrolysis products and coke in an oxygen-rich environment.

6. A simulation system constructed based on the oxygen-enriched combustion simulation method of long straw particles according to any one of claims 1 to 5, characterized in that: The simulation system includes a network model construction module, a mathematical model construction module and a simulation module. The network model construction module includes an EDEM module and a Fluent module. The EDEM module generates a long straw particle model, and the Fluent module performs fine grid modeling on the circulating fluidized bed boiler furnace. The mathematical model construction module is used to solve the fluid phase equation and particle phase equation in the three-dimensional space inside the boiler grid model to obtain a mathematical model; the simulation module uses the mathematical model and combines it with the chemical reaction formula of straw oxygen-enriched combustion to carry out detailed numerical simulation of the oxygen-enriched combustion process of long straw particles to obtain its accurate combustion process simulation model.

7. The simulation system according to claim 6, characterized in that: The mathematical model building module specifically adopts a multiphase flow discrete particle model to solve the fluid phase equation and the particle phase equation to obtain an accurate mathematical model.

Images