基于动态自适应反应的煤粉无焰燃烧燃料氮转化机理研究

无焰燃烧是近年来广受关注的新型高效清洁燃烧技术之一,具有容积式低反应速率燃烧区和典型中低温燃烧特性,需耦合详细反应机理并考虑湍流与化学反应交互,以提高无焰燃烧及其NO生成数值模拟精度。基于动态自适应反应机理对煤粉无焰燃烧和NO生成特性进行了高保真数值模拟研究。通过采用动态自适应机理简化算法,模拟过程实时对自主发展的含氮骨架机理进行当地简化。评估发现,相较于单纯采用骨架机理模拟,采用动态自适应反应可在不牺牲计算精度的条件下获得约3倍的计算加速,且对炉内NO生成的预测精度显著优于传统NO后处理模拟方法。基于经试验验证的模拟结果,还获得了HCN和NH_3等典型含氮前驱体的炉内分布,并进一步分析了煤粉无焰燃烧燃料氮转化路径、炉内活跃组分和活跃反应等氮转化关键信息。结果表明,煤粉无焰燃烧NO生成主要取决于NH_3、HCN和N_2O中间体,而NCO和HNO是较为关键的中间组分。HCN中间体主要通过HNCO/CN和NCO路径生成NO。NH_3中间体由HNCO生成,并进一步转化为NH_2和HNO,最终生成NO。N_2O路径主要参与NO还原,对NO生成贡献较低。CH_3CN也是生成NO的重要中间组分,可通过NCO路径生成NO。     

富氧燃烧中气体辐射模型对燃烧与换热数值模拟的影响

富氧燃烧过程中,由于使用再循环烟气代替空气中N₂作为稀释剂,烟气中存在大量CO₂和H₂O。CO₂和H₂O作为非极性三原子分子,具有N₂没有的辐射能力,导致富氧燃烧中气体辐射特性发生变化。在数值模拟过程中,气体辐射模型是一个重要的子模型。前人提出多种修改后适用于富氧燃烧的气体辐射模型,但不同气体辐射模型在不同富氧燃烧工况数值模拟中的影响尚未有统一研究。为了研究不同炉型下,气体燃烧和煤粉燃烧中气体辐射模型对燃烧换热模拟结果的影响,通过编程,将一种考虑CO影响的气体辐射模型以及文献中的6种典型气体辐射模型耦合入数值模拟计算。结果表明,在气体富氧燃烧中,气体辐射模型影响了火焰结构。同时,燃烧温度分布有所变化,不同模型结果之间差别最高可到500 K。气体与壁面之间的辐射换热受到影响。气体辐射模型对炉膛中心火焰区域影响较大,而对非火焰区域影响较小。在煤粉富氧燃烧过程中,当有效辐射层厚度在0.3 m左右时,如在100 kW下行炉中,气体辐射模型对煤粉燃烧数值模拟结果几乎没有影响。这可能是由于颗粒辐射在辐射换热计算中占主导地位。而当有效辐射层厚度在16 m左右时,如1000 MW塔式炉中,气体辐射模型对炉内切圆燃烧火焰温度以及组分浓度影响较大,温度差别可到100 K左右。而气体辐射模型对炉膛中心模拟结果没有影响。     

简化的Solomon热解模型和旋流煤粉燃烧NO生成的数值模拟

提出一种简化的Solomon热解模型, 用于模拟煤粉燃烧NO生成数值模拟中HCN的释放.用纯双流体模型、k-ε-k_p两相湍流模型、EBU-Arrhenius燃烧模型、六热流辐射模型、双方程热解模型、简化的Solomon热解模型以及NO生成湍流反应二阶矩代数模型对旋流煤粉燃烧器内两相流动、煤粉燃烧、HCN释放以及NO生成进行了数值模拟.模拟结果与文献中实验结果的对比表明,基于简化Solomon热解模型的HCN释放模型预报结果比基于双方程热解模型的HCN释放模型预报结果好.     

多风道煤粉燃烧器拢焰罩的长度对窑内煤粉燃烧状况影响的研究

本文运用计算流体力学（CFD）技术，以大型流体工程计算软件CFX4．3为工具，模拟研究了喷煤燃烧器的扰焰罩长度对回转窑内煤粉燃烧过程规律的影响，结果表明，一定长度的扰焰罩有利于加强燃烧器出口附近的湍流混合和煤粉燃烧。     

两段式气流床氧/煤比对干煤粉气化特性的影响

基于Eulerian-Lagrangian方法建立了两段式干煤粉气流床的三维CFD计算流体动力学模型,利用均相与非均相多步化学反应动力学确定煤气化反应,用k-ε模型描述气相湍流流动,用随机轨道模型追踪煤粉颗粒的运动轨迹,模拟了气流床内的煤气化过程。在氧/煤质量比为0.9,1.0和1.1时,基于文献实验条件对不同反应机理进行数值模拟,通过结果对比获得最佳反应机理。考察了氧煤比为1.0时上下两阶段煤/氧比对煤气化特性的影响。结果表明,选用焦炭和挥发物完全燃烧反应、忽略CO参与气相燃烧反应的反应机理(Case E)的模拟结果与实验数据非常吻合,误差小于2%。当一级喷嘴(A-A水平)煤和氧化剂喷入量达到并超过给煤量和进气量的50wt%时,合成气组分、碳转化率和有效成分等气化炉总体性能指标较好。在一级喷嘴喷入70wt%煤和60wt%氧气时碳转化率最大,为99.6%,一级喷嘴喷入50wt%煤和50wt%氧气时合成气组分最佳,最大合成气产率为78.24mol%。     

基于热重-质谱联用的煤粉富氧燃烧动力学及污染物生成特性

富氧燃烧是最具工业化前景的燃烧中碳捕集技术之一,为更深入掌握煤粉富氧燃烧的着火模式和污染物生成特性,本文构建了热重-质谱联用实验系统,以烟煤和无烟煤标准煤样为对象,针对3个不同的氧气体积分数：21%、30%和50%,研究了O₂/Ar和O₂/CO₂气氛下煤粉的富氧燃烧特性。结果表明,O₂/CO₂气氛下煤粉着火温度和燃尽温度均降低,燃烧速率提高,燃烧时间缩短;两种煤粉在O₂/Ar气氛下的燃烧都属于非均相着火,而富氧燃烧都属于均相着火模式;氧气体积分数在30%以上时,无烟煤O₂/CO₂燃烧的表观活化能明显低于O₂/Ar气氛,在相同工况下烟煤的表观活化能均低于无烟煤;O₂/CO₂气氛促进了CO和挥发分NO的逸出,生成温度均低于O₂/Ar气氛,CO会对NO起到还原作用。     

富氧燃烧含灰烟气辐射特性的部分光谱k模型

针对煤粉在富氧燃烧方式下烟气为炭黑、飞灰、高浓度CO2和H2O蒸气混合物的辐射换热问题,建立了描述混合物非灰辐射特性的部分光谱k分布模型.为了验证模型的有效性,以文献中煤粉在富氧燃烧方式下烟气生成状况为例,采用该模型与离散坐标法相结合的方法,计算了一维无限大平行平板、单光谱行程和二维矩形封闭系统内混合物的辐射源项和壁面...     

德士古渣油气化炉的数值模拟

渣油在德士古气化炉中发生非常复杂的不完全燃烧反应,它生成了工业生产合成氨所需的原料气。文中建立了这一过程的数值模拟模型,采用κ-εRNG模型来模拟湍流流动,简化的PDF模型来模拟湍流燃烧过程,辐射传热采用离散坐标模型,得到符合生产实验的燃料模型。     

煤粉燃烧过程中硫组分详细反应机理评估及简化

空气分级燃烧等低NO_x燃烧技术广泛应用于电厂锅炉,以降低炉膛出口NO_x浓度,但实际应用过程中会造成锅炉水冷壁腐蚀,严重影响煤粉锅炉的安全运行。为了准确预测锅炉水冷壁附近H_2S浓度,运用Chemkin软件对已建立的H_2S生成详细反应机理模型进行评估并简化。验证C/H/O详细反应机理与H_2S生成详细反应机理的耦合性,表明GRI-3.0能更好地预测煤粉富燃料燃烧过程中重要组分浓度分布;将耦合后的机理作为起始机理,与其他学者建立的硫详细反应机理进行比较,结果表明,本课题组的硫组分详细反应机理模型能够较好地描述煤粉燃烧过程中气态硫组分的演化,将CS_2作为重要硫组分进行研究,能够更好地预测硫组分浓度分布;通过简化结果比较,选择基于误差传递的直接关系图法(DRGEP)的简化结果作为硫组分简化反应机理,包含15个组分和28个基元反应,并在1 373～1 673 K验证,表明该简化机理适用于煤粉富燃料燃烧过程中硫组分浓度分布预测。     

玻璃窑炉局部富氧燃烧的研究

本文建立了燃煤玻璃马蹄焰窑炉局部富氧燃烧与不采用富氧燃烧数学模型,对不同富氧空气下燃烧温度的影响进行了计算机模拟,对模拟结果进行了回归分析,对比了采用富氧燃烧与不采用富氧燃烧对节能效果的影响,分析了在小炉底板上面通富氧空气产生的效果.对燃煤玻璃马蹄焰窑炉富氧燃烧提出了建设性的意见.     

Chemistry and radiation in oxy-fuel combustion: A computational fluid dynamics modeling study

In order to investigate the role of combustion chemistry and radiation heat transfer in oxy-fuel combustion modeling, a computational fluid dynamics (CFD) modeling study has been performed for two different oxy-fuel furnaces. One is a lab-scale 0.8 MW oxy-natural gas flame furnace whose detailed in-flame measurement data are available; the other is a conventional 609 MW utility boiler which is assumed to be operating under oxy-fuel combustion condition with dry flue gas recycle. A new model for gaseous radiative properties is developed, validated, and then implemented in the CFD simulations. The CFD results are compared to those based on the widely used model in literature, as well as the in-flame measurement data. The importance and advantage of the new model for gaseous radiative properties have been well demonstrated. Different combustion mechanisms are also implemented and compared in the CFD simulations, from which significant difference in the predicted flame temperature and species is observed. This difference is consistent with those expected from the equilibrium calculation results. As a conclusion, the appropriate combustion mechanisms applicable to oxy-fuel combustion modeling are identified. Among the key issues in combustion modeling, e.g., mixing, radiation and chemistry, this paper derives useful guidelines on radiation and chemistry implementation for reliable CFD analyses of oxy-fuel combustion, particularly for industrial applications.     

煤粉富氧燃烧着火温度预测的优化随机森林(GA-RF)模型

二氧化碳排放是造成温室效应的主要原因之一,富氧燃烧作为一种有效的碳减排与封存技术具有广泛的研究前景。在燃煤电厂中煤粉富氧燃烧的着火温度是燃烧器设计和运行安全的重要指标,并且与煤粉组成成分、煤粉粒径以及燃烧氛围都有复杂的相关性。因此,对煤粉富氧燃烧着火温度的预测模型研究意义重大。采用滴管炉分别测量了5种煤粉在O2体积分数为30%、35%、40%、50%、60%、70%、80%、90%、100%富氧条件下的着火温度,分析了氧气体积分数和煤粉的组成成分与着火温度之间的关系。研究发现,随着氧气体积分数分数的增加,5种煤样的着火温度均显著下降,且挥发分越高的煤,下降幅度越大。将45组试验着火温度数据与其他研究者采用同样方法测得的69组着火温度数据组成机器学习样品库,以煤粉的元素分析、工业分析、煤粉粒径及氧气体积分数为输入条件,以着火温度T为目标输出,构建了遗传算法优化的随机森林模型(GA-RF模型),准确预报了煤粉富氧燃烧的着火温度,其预报精度为:R2>0.99,RMSE<16,MAE<8。通过模型参数重要性分析发现,氢组分超过5%后,着火温度出现阶跃式上升,现有煤粉着火数据也证实了该现象。     

Numerical modelling and simulation of pulverized solid‐fuel combustion in swirl burners

A finite‐volume numerical model for computer simulation of pulverized solid‐fuel combustion in furnaces with axisymmetric‐geometry swirl burner is presented. The simulation model is based on the k ? ε single phase turbulence model, considering the presence of the dispersed solid phase via additional source terms in the gas phase equations. The dispersed phase is treated by the particle source in cell (PSIC) method. Solid fuel particle devolatilization, homogenous and heterogeneous chemical reaction processes are modelled via a global combustion model. The radiative heat transfer equation is also resolved using the finite volume method. The numerical simulation code is validated by comparing computational and experimental results of pulverized coal in an experimental furnace equipped with a swirl burner. It is shown that the developed numerical code can successfully predict the flow field and flame structure including swirl effects and can therefore be used for the design and optimization of pulverized solid‐fuel swirl burners.     

煤粉锅炉炉膛燃烧一维数学模型的研究

为了有效地进行直流煤粉多相流动与燃烧数值模拟,实现煤粉低NOx燃烧,本文在连续介质模型的框架中建立了综合考虑气—固两相流流动、燃烧与传热的直流煤粉燃烧一维数学模型。应用这一模型对一维煤粉炉炉膛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直流煤粉多相流动与燃烧过程,给出炉内温度、NOx分布等主要参数。     

Large-eddy simulation of coal combustion in 15 MW pilot-scale boiler-simulation facility

High-fidelity modeling provides a useful approach to investigate the multiscale multiphysics mechanism in the pulverized coal combustion. This research focuses on understanding the pulverized coal combustion in a pilot-up facility: General electric (GE) 15 MW pilot-scale boiler simulation facility (BSF). The heat flux to the boiler water wall, O₂ concentration, and gas temperature are the quality of interest (QoI's) for this research, as they are the most important parameters for designing a full-scale pulverized coal boiler. Even the heat flux in boiler is largely determined by the heat transfer mechanism, and other detailed multiphysics mechanisms, including multiphase turbulent flow, radiation heat transfer, ash deposition, coal devolatilization, and oxidation, also need to be accounted. This work applies large-eddy simulation (LES) code on high-performance computing facility to simulate pulverized coal combustion in BSF. The physics-based submodel that contains the significant sensitivity for QoI's has been identified using the detailed impact factor analysis on this high-fidelity modeling. Results indicate that the most sensitive submodel on QoI's is the wall-heat-transfer coupling with the ash-deposition model, which allows us to prioritize to improve this submodel in the LES simulation. Thus, ash deposition and wall-heat-transfer processes have been modeled and integrated into coal combustion numerical simulation. The simulation results show quantitative agreement between the simulation with experimental data regarding gas temperature, O₂ concentration, and heat-flux profile across the exposed boiler walls. Another implication of this research is to demonstrate a positive societal impact of extreme computing and accelerate the development of new combustion technology using a capable exascale computing technique.     

Transient group combustion of the pulverized coal particles in spherical cloud

A transient group combustion model for the pulverized coal particles in a spherical cloud is developed to predict the transient group combustion characteristics. The submodels, which account for the detailed combustion process of both homogeneous and heterogeneous reactions, are also applied for the pulverized coal particles. The numerical simulation of the collective behaviors of ignition and its subsequent burning were carried out. The ignition mechanism is characterized by the heterogeneous process of the dilute cloud and the homogeneous process of the dense cloud. Two dominant flame structures are observed: one flame penetrating inside the cloud and the other moving outside the cloud. The effects of various parameters (i.e., radiation heat transfer, group combustion number, air temperature, air oxygen concentration, particle size distribution, and particle number density) on the particle mass burning rate and on the overall performance of the group combustion are examined. The results are in good agreement with existing experimental data.     

Simulation of gas-particle turbulent combustion in a pulverized coal-fired swirl combustor

A particle stochastic trajectory model for turbulence-particle reaction interactions is proposed and formulated in the present paper. This model provides the basis for a comprehensive model of pulverized coal combustion. It is applied to the simulation of gas-particle turbulent flow and combustion in a pulverized coal-fired swirl combustor. The results are compared with the measured test data and those obtained by the particle stochastic trajectory model without considering turbulence-particle reaction interactions. The predicted gas temperature and species concentrations in the upstream region of the combustor are improved by utilizing the model with turbulence-particle reaction interactions.     

强旋湍流气-固两相流动和煤粉燃烧数学模型及其在涡旋燃烧炉的应用(Ⅱ)——应用

应用本文(Ⅰ)报建立和发展的二维强旋湍流气-固两相流动和煤粉燃烧的数学模型、对新型燃煤涡旋燃烧炉内的冷态流动、气体燃烧和煤粉燃烧进行了系统的数值模拟,得到了与冷、热态实验数据基本相符合的结果,揭示了炉内流动、传热和燃烧的基本性质和特点。