煤粉复合旋流火焰燃烧特性研究（2）：数值模拟

本文数值模拟了煤粉旋流火焰燃烧过程，燃烧数值计算包括理论物理模型建立，数值方法两个大部分，计算模型处理了气相湍流与燃烧、气固两相流动、煤颗粒燃烧过程和辐射传热等物理化学过程，以ｋ－ε模型模拟湍流流动；ＰＤＦ法模拟气相扩散火焰燃烧；颗粒运动计算颗粒运动少颗粒湍流浓度方程模拟颗粒湍流扩散；通量法计算火焰辐射传热，煤粉颗粒复杂燃烧模型计算了颗粒尺寸、形状变化和颗粒孔隙内部燃烧、表面平度对整个颗粒的燃烧过程影响。计算获得了气相速度分布场、气相ｋ和ε分布场、气相温度场、气相组份场和颗粒浓度场及运动过程，揭示了煤粉复合旋流燃烧特性。     

600MW超临界W火焰锅炉燃烧特性及水冷壁分布参数混合模拟

以东方锅炉600MW超临界W火焰锅炉为研究对象,从非预混燃烧、气相湍流、颗粒相轨道模型、辐射传热、煤粉挥发分燃烧等模型入手,运用计算流体力学软件FLUENT进行了计算流体力学(CFD)模拟,同时建立了炉膛水冷壁一维分布参数模型,将其得到的水冷壁温度分布作为CFD模拟的边界条件,通过两种模型的混合模拟,得到了更为准确的基础工况和变负荷工况下炉膛内温度场、流场、组分浓度场的分布特性,并分析了炉内煤粉燃烧规律的变化。     

旋风炉内气相燃烧及两相流动的数值模拟

在有反应两相流动及煤粉燃烧的全双流体模型（ＰＴＦ模型,ｐｕｒｅ ｔｗｏ－ｆｌｕｉｄ ｍｏｄｅｌ）基础上,采用修正的ｋ－ε－ｋｐ两相湍流模型,对旋风炉内的湍流气相燃烧（甲烷和一氧化碳的燃烧）及在气相燃烧条件下的两相流动进行了数值模拟研究,模拟结果表明,在有燃烧的情况下,在旋风炉的底部存在近壁回流区,该回流区有利于火焰稳定,气粒两相切向速度分布具有类似的Ｒａｎｋｉｎｅ涡结构,该研究为煤粉燃烧的数值模拟     

煤粉MILD燃烧NOx生成和还原机理的数值分析

采用计算流体动力学(CFD)软件分析了国际火焰研究基金会(IFRF)试验系统上煤粉低氧稀释(MILD)燃烧特性和NO_x排放特性。比较了不同的湍流与化学反应相互作用模型、挥发分气相反应机理和焦炭燃烧模型对煤粉MILD燃烧特性预测的影响,通过对比烟气速度场、温度场、组分浓度场的模型预报结果与试验结果,得到了能够准确预测煤粉MILD燃烧特性的模型组合,即EDC-WD-MSR模型。采用此模型对煤粉MILD燃烧NO_x生成和还原路径进行分析,结果表明：煤粉MILD燃烧中燃料型NO占主导地位,热力型NO、N₂O中间体路径和快速型NO之和对NO总排放的贡献小于10%。煤粉MILD燃烧存在强烈的NO均相和异相还原反应,其中NO异相还原反应使燃料型NO的排放量占单独计算的焦炭NO和挥发分NO排放量之和的71.1%。     

电弧等离子体点火器湍流燃烧流场传热与流动数值模拟

对燃气轮机燃烧室电弧等离子体点火器内湍流燃烧流场,进行了传热与流动数值模拟。采用了RNGk-ε湍流模型、扩散燃烧模型和离散传播辐射DTRM模型。计算域包括点火器内的等离子体发生器和点火器主体。将计算结果与未考虑辐射的温度场和流场进行了比较。结果表明辐射模型对其温度场有影响,对速度场影响不大;在点火器出口处的径向温度分布是均匀的。     

10t/h垃圾焚烧锅炉炉内过程数值分析

对一台SZL10-1.25-MJ造纸垃圾焚烧锅炉的炉内过程进行数值模拟,采用Species Transport模型,用标准k-ε湍流模型模拟气相湍流运输,用P-1辐射模型计算辐射传热.分析了炉膛内温度场、速度场和气相各组分浓度场的分布规律,并对模拟结果进行分析与对比,模拟计算结果呈现出与实际炉内过程较好的一致性.     

水平管加压密相煤粉气力输送沙丘流的数值模拟

对Johnson等提出的摩擦正应力模型和Syamlal等提出的摩擦剪切黏度模型进行了修正,并将其与颗粒动理学理论相结合,建立了可以描述加压密相气力输送的气固湍流流动状况的三维多相流模型.该模型充分考虑了颗粒间碰撞和摩擦力作用,以及气相和颗粒团湍流脉动之间的相互作用.采用该模型对加压密相气力输送水平管沙丘流流动特性进行了三维数值模拟,并预测了单个沙丘和连续沙丘的形成及运动状况.结果表明:随着表观气速的增加,煤粉颗粒浓度减小,压降梯度呈现先减小后增大的趋势;在横截面上,煤粉颗粒分布呈现上窄下宽的趋势,且煤粉颗粒在管道底部沉积,并呈现月牙形状.模拟结果与试验结果吻合较好.     

分级进风旋流燃烧室内湍流燃烧的数值模拟

应用考虑湍流-化学反应相互作用的代数二阶矩-概率密度函数(PDF)湍流燃烧模型,对分级进风旋流燃烧室内两组工况下的甲烷湍流燃烧进行了数值模拟,得到的二氧化碳浓度和气体轴向脉动速度均方根值分布与实验数据相符合,得到的气体轴向和切向速度、轴向一切向脉动速度关联量、温度和氧气浓度分布与实验数据基本相符合.研究结果表明,选取适当的二次风率可以起到优化燃烧过程的作用.     

旋流煤粉多相流动与燃烧一维数学模型及应用

为了发展和有效地进行旋流煤粉多相流动与燃烧数值模拟,作者在多连续介质模型的框架中建立了综合考虑气-固两相旋流流动,燃烧与传热的旋流煤粉燃烧一维数学模型。应用这一模型对涡旋燃烧炉环形通道内煤粉燃烧和气体燃烧的数值计算表明,该模型可快速有效地用于模拟旋流煤粉多相流动与燃烧过程,给出炉内温度、速度与浓度分布以及燃烧效率等主要参数。     

旋流燃烧室内甲烷湍流燃烧的数值模拟

为合理考虑湍流-复杂化学反应的相互作用,建立了甲烷湍流四步反应的温度脉动简化概率密度函数(PDF)模型.应用该模型对TECFLAM燃烧室内的甲烷湍流旋流燃烧进行了数值模拟,得到了与实验相符合的气体轴向、径向与切向速度、温度、温度脉动均方根值及甲烷、氧气、二氧化碳与水蒸气质量分数分布.得到的一氧化碳和氢气质量分数分布与实验基本符合.     

Numerical studies on the combustion properties of char particle clusters

Particle clustering is an important phenomenon in dense particle–gas two-phase flow. One of the key problems worth studying is the reacting properties of particle clusters in coal particle combustion process in the dense particle region. In this paper, a two-dimensional mathematical model for the char cluster combustion in airflow field is established. This char cluster consists of several individual particles. The comprehensive model includes mass, momentum, and energy conservation equations for both gas and particle phases. Detailed results regarding velocity vector, mass component, and temperature distributions inside and around the cluster are obtained. The micro-scale mass and heat transfer occurred inside and around the char cluster are revealed. By contrastively studying the stable combustion of char particle clusters consisting of different particles, the combustion properties of char clusters in various particle concentrations are presented and discussed.     

Experimental analysis of the effects of hydrogen addition on methane combustion

This paper presents gas emissions from turbulent chemical flow inside a model combustor, for different blending ratios of hydrogen–methane composite fuels. Gas emissions such as CO and O₂ from the combustion reaction were obtained using a gas analyzer. NOx emissions were measured with a NOx analyzer. The previously obtained flame temperature distributions were also presented. As the amount of hydrogen in the mixture increases, more hydrogen is involved in the combustion reaction, and more heat is released, and the higher temperature levels are resulted. The results have shown that the combustion efficiency increases and CO emission decreases when the hydrogen content is increased in blending fuel. It is also shown that the hydrogen–methane blending fuels are efficiently used without any important modification in the natural gas burner. Copyright © 2011 John Wiley & Sons, Ltd.     

Simulation of swirl-stabilized turbulent partially premixed combustion

Properly describing turbulence-complex reaction interactions is crucial for predicting turbulent combustion and pollutant emission. A presumed probability density function model for temperature fluctuation is adopted in the present paper. It incorporates a 25-step skeletal mechanism for methane combustion. The gas turbulent transport is simulated with the algebraic Reynolds stress model for turbulence-swirl interactions. These models are applied to the simulation of swirl-stabilized turbulent partially premixed jet flame. The calculated gas velocities, fluctuating velocities, Reynolds shear stresses, temperature, and species mass fractions are in agreement with the measured test data.     

催化肋片对微燃烧室内燃烧特性的影响

针对带有催化肋片的微燃烧室内部的氢氧预混合燃烧过程,利用CFD计算软件建立数值模型,在实验验证的基础上进行了模拟计算。结果表明:不同流速下,燃烧室内布置催化肋片能提高燃烧室外壁面平均温度以及燃烧效率。在低流速时催化肋片布置越靠近入口,表面催化反应对气相反应的抑制程度越大;肋片位置越靠近出口,燃烧室外壁面平均温度越高。在高流速下,催化肋片位置越靠近出口,表面催化反应对气相反应的促进作用越明显,使得燃烧室外壁面温度分布越均匀、燃烧室出口截面温度越高。     

Multimode heat transfer in cyclic flow reversal combustion in a porous medium

Experimental and numerical studies of combustion and multimode heat transfer in a porous medium, with and without a cyclic flow reversal of a mixture through a porous medium, were performed. Parametric studies were done in order to understand combustion characteristics such as maximum flame temperature and radiative heat flux using a one‐ dimensional conduction, convection, radiation and premixed flame model. The porous medium was assumed to emit and absorb radiant energy, while scattering is ignored. Non‐local thermodynamic equilibrium between the solid an d gas is taken into account by introducing separate energy equations for the gas and the solid phase. As a prelimina ry study, the combustion regime was described by a one‐step global mechanism with an internal heat source uniformly dist ributed along the reaction zone. The effects of the flame position, cyclic flow reversal, period of the cyclic flow rever sal, the optical thickness and the flow velocity on the burner performance were clarified by a rigorous radiation analysis. Th e model was validated by comparing the theoretical results with the experiments. It was shown that, for maximizing the fl ame temperature and the net radiative heat flux feedback, the flame should be stabilized near the centre of the po rous medium with a cyclic flow reversal, the period of which should be as small as possible. A high optical thickness prod uced a high flame temperature and a high net radiative feedback. Also, a high flow velocity at low period of the cyclic f low reversal of mixture yielded a high value of both the flame temperature and the net radiative feedback. Thermal structure predictions in terms of the gas‐phase and the solid‐phase temperature distributions along the axis of the combustor show good agreement with the experimental ones. Copyright © 1999 John Wiley & Sons, Ltd.     

Numerical modelling of a three-zone combustion for heavy fuel oil in inert porous media reactor

Numerical model for heavy fuel oil and air mixtures combustion is presented to simulate the behavior of the fuel in an inert porous medium reactor for hydrogen production. Three-zone combustion of oil and petroleum cokes separated by temperature ranges starting from ambient temperature to 560 K, from 560 K to 673 K, and above 673 K, is presented. Hydrogen production is achieved using water gas shift equilibrium reaction on the combustion products at different temperatures. Results show a high enthalpy contribution due to coke combustion formed in the low temperature oxidation reaction, being the most important reaction in relation to its zone size. Simulations increasing filtration velocity (from 0.05 to 0.9 m/s) has a favorable effect on the maximum temperature and the combustion front velocity. The effect of the simplified combustion model lowers computational time, with acceptable results for temperature as well as hydrogen production in contrast to laboratory tests and other software simulation such as COMSOL Multiphysics.     

Gas–solid turbulent flow and heat transfer with collision effect in a vertical pipe

A turbulent gas–solid suspension upward flow in a vertical pipe is simulated numerically using Eulerian–Lagrangian approach. Particle–particle and particle–wall collisions are simulated based on deterministic approach. The influence of particle collisions on the particle concentration, mean temperature and fluctuating velocities are investigated. Numerical results are presented for different values of loading ratios. The profiles of particle concentration, mean velocity and temperature are shown to be flatter by considering inter-particle collisions, while this effect on the gas mean velocity and temperature is not significant. It is demonstrated that the effect of inter-particle collisions have a dramatic influence on the particle fluctuation velocity. It is shown that the profiles of particle concentration and particle velocity are flattened due to inter-particle collisions and this effect becomes more pronounced with increasing loading ratio. Also, the attenuation of turbulence by inter-particle collisions in the core region of the pipe is increased by increasing loading ratio.     

多孔介质中预混式燃烧的数值研究

本文考虑向燃烧室中插入高孔隙率的多孔介质的燃烧过程,根据气固两相局部非热平衡假设,建立了混合气体在惰性多孔介质中预混燃烧的一维数学模型,模拟了不同条件下甲烷-空气的预混合气在多孔介质中燃烧时的温度分布及气体流速、当量比和吸收系数对燃烧室气体温度峰值的影响.结果表明,多孔介质的存在明显改善了燃烧室的换热性能,强化了对新鲜混合气的预热,加速了燃烧反应的进行,燃烧室利用率提高.     

Simulation of Swirling Turbulent Flow and Combustion in a Combustor

An algebraic concentration moment (ACM)-PDF turbulent combustion model is proposed. It is formulated by jointly utilizing the explicit algebraic expressions for the second-order-moment of concentration fluctuation and the presumed probability density function (PDF) of gas instantaneous temperature. A set of analytical expressions for the time-averaged temperature relevant quantity is obtained for the closure of the time-averaged reaction rate. The model is applied to the simulation of turbulent flow and combustion in a swirl combustor. The calculated gas velocity, temperature, species concentrations, and turbulent fluctuating velocity are in agreement with the measured data. They are much improved over those obtained by the EBU-Arrhenius model.