丁烷层流预混火焰多环芳烃生成化学动力学模拟

近年来,随着环保要求的不断提高,碳氢燃料燃烧过程中多环芳烃(polycyclic aromatic hydrocarbons,PAHs)形成、生长和氧化的详细反应动力学研究成为热点。该文通过更新的层流预混火焰中描述丁烷热分解、氧化,苯的形成,多环芳烃生成及氧化等过程的详细机制反应模型,对层流预混C4H10/O2/Ar稳态火焰中芳香烃和多环芳烃的形成和生长进行动力学模拟计算,获得火焰中反应区和燃尽区反应物、主要燃烧产物、中间组分及PAHs的浓度分布,同时采用敏感系数分析法确定了丁烷火焰中影响PAHs生成的主要基元反应。研究结果表明:采用的更新机制模型能够很好地预测丁烷火焰中大多数低分子量的脂肪烃、燃烧副产物、中间组分及PAHs的浓度分布;丙炔基(H2CCCH)的化合反应是苯环生成的主要反应序列;萘(C10H8)生成的主要步骤是环戊二烯基(c-C5H5)的化合反应,活化分子茚基与c-C5H5反应可以形成大量的菲(C14H10);同时模型更近一步论证了PAHs生成的"脱氢加乙炔"机制。     

层流预混乙烷和丙烯火焰中PAHs荧光光谱分析

应用激光诱导荧光(LIF)技术对层流预混乙烷和丙烯火焰中多环芳香烃(PAHs)荧光光谱进行测量,探究PAHs在乙烷和丙烯层流预混火焰中的空间分布及当量比对其生成的影响。实验研究结果表明:乙烷和丙烯不同火焰高度下PAHs荧光光谱峰值位置不发生转移,均在500nm左右;随着火焰高度的增加,PAHs荧光光谱强度随之增强;当量比对火焰中PAHs的生成具有重要影响,随着当量比的增加,PAHs荧光光谱强度逐渐增强且在较高当量比下变化显著;比较乙烷和丙烯层流预混火焰中PAHs荧光光谱归一化强度,发现燃料碳链长度以及碳链饱和度会对火焰中PAHs的生成产生重要影响。     

烟煤燃烧过程中多环芳烃生成研究

煤在燃烧过程中产生强烈的致癌，致癌、致突变作用有机污染物多环芳烃，已受到广泛关注，该文报道小型管式炉燃煤实验，研究不同燃烧条件下17种多环芳烃（包括美国EPA推荐优先监测的16种多环芳烃）排放情况，探讨多环芳烃生成的影响因素和生成机理，该实验对煤的燃烧过程中的多环芳烃生成的各种影响因素做了较全面的分析，为进一步进行煤燃烧过程中多环芳烃高温生成机理研究打下了基础。     

甲烷对冲扩散火焰NOx生成动力学特性研究

根据NOx化学基元反应机理,通过化学动力学方法研究了甲烷燃烧不同工况下NOx的生成特性,分析影响NOx生成的主要因素。研究结果表明:甲烷对冲火焰基元反应机理GRI-Mech2.11对NO浓度预测值比GRI-Mech3.0更接近实际试验值;燃烧速度梯度增加,甲烷燃烧着火提前,NO的排放浓度降低较多;燃烧当量比减少,燃烧高温区域增加,NO的排放浓度基本没有变化;采用高温空气燃烧技术时,降低高温空气中的氧量可以有效降低NOx的排放。     

水蒸汽对焦炉气火焰燃烧速度及NO生成特性影响研究

以山西华鑫肥业有限公司富氧空气转化炉为研究对象,大型化学动力学软件CHEMKIN为计算平台,采用包含53种组分、325个基元反应的甲烷燃烧详细反应机理(GRI-Mech 3.0),研究了水蒸汽对富氧空气转化炉烧嘴火焰燃烧速度及NO生成特性的影响。计算结果表明:H2O对燃烧速度的影响主要是通过解离出的H自由基参与燃烧反应引起的;H2O含量的提高可以有效抑制NO生成速率。     

电除尘器对多环芳烃排放的影响

在某300MW机组燃煤锅炉电除尘器上对PAHs排放进行了试验研究，分析比较了不同煤种燃烧后电除尘器前后PAHs的浓度变化。为了定量评价不同PAHs排放对环境的危害，引入了毒性当量的概念。试验结果表明，电除尘器对PAHs脱除效果并不理想，且受工况影响较大。     

基于敏感性分析的H2/O2反应机理最优简化

已有的反应流计算方法通常采用简单的化学反应机理。由于火焰中不同区域的化学特性变化较大，有时简单反应机理不能精确描述燃烧过程的化学特性；而计算包含详细反应机理的复杂反应流问题仍然是十分费时的。最优简化法可根据设定的化学精度要求实现详细反应机理的最优简化。通过对包含20个可逆基元反应的H2/O2燃烧机理的简化结果与原机理计算结果的比较，取得了良好的效果。同时，结合敏感性分析法深入揭示了氢、氧燃烧的化学过程。     

三种煤的部分气化生成多环芳烃的试验研究

多环芳烃(PAHs)是煤气化过程中产生的一类有害有机物质，具有强烈的致癌性和致突变性，越来越受到人们的关注。文中在一台小型常压流化床气化炉上进行了以空气和水蒸气为气化剂的3种煤部分气化试验，采用高效液相色谱法(HPLC)对煤气化产物中被美国环保署(USEPA)指定的16种PAHs进行了测定，研究了煤部分气化过程中煤自身性质对多环芳烃生成和赋存规律的影响。试验结果表明：煤部分气化PAHs生成量高于原煤PAHs含量(徐州烟煤除外)；原煤固定碳和硫含量增加，煤部分气化PAHs生成量先增后降，挥发分含量增加，PAHs生成量却呈现出相反的变化规律：提高灰分含量或采用低发热量原煤，可以降低煤部分气化PAHs生成。     

声场作用下甲烷部分预混火焰不同当量比和流速对NOx生成的影响

采用Rijke型脉动燃烧试验台,利用火焰直拍图像、NOx采集系统,对声场作用下甲烷部分预混火焰在不同当量比和流速下的NOx生成特性进行了比较和分析.结果表明,随着当量比的增大,在3.3～4处NO排放因子(NOemissionindex,EINO)出现拐点φEI,当量比小于φEI时,EINO随当量比的增大而先增后减;当量比大于φEI时,EINO随当量比的增大而增大.当量比在2～4时,混合气流速对EINO的影响较小;当量比大于4时,EINO随着流速的增加而增加,但相对于稳态燃烧,EINO随流速增加的速率明显减小,原因在于,流速的增大致使火焰长度增加,燃料在高温区域停留时间变大,而相对于稳态火焰,脉动声场的作用使火焰长度变短.     

湍流热伴流条件下二甲醚射流推举火焰的冷焰特性与稳定机理

发动机内的湍流射流推举火焰具有部分预混燃烧的特征,并且伴随着与冷焰的强耦合作用,因此对其开展基础研究具有重要的理论与应用价值。基于高压热伴流条件下二甲醚(dimethyl ether,DME)湍流狭缝射流燃烧过程的直接数值模拟结果,采用化学爆炸模式分析(chemical explosive mode analysis,CEMA)方法,研究了推举高度内的冷焰结构与反应动力学特性、冷焰与湍流的相互作用,以及它对推举稳定性的影响。结果表明:冷焰反应主要发生在富燃当量比的范围内,冷焰的自着火过程由参与燃料裂解反应的大分子碳氢组分所控制,而热焰的自着火过程由小分子氧化放热反应所控制。CEMA分析表明,火焰不同区域内具有不同的火焰结构、燃烧模式、以及主导组分与基元反应。DME推举火焰的稳定性由稳定点上游贫燃侧窄带区内由链分支反应所引起的自着火过程所控制。尽管湍流拉伸作用会抑制冷焰反应,但是由冷焰反应所产生的低温组分,对于诱导高温着火、形成推举稳定点具有重要作用。     

一次风速度和煤粉质量浓度对等离子燃烧器一级燃烧筒点火特性的影响

为了研究一次风速度和煤粉质量浓度对等离子燃烧器一级燃烧筒点火特性的影响,建立了等离子燃烧器一级燃烧筒点火特性试验台。通过测量一级燃烧筒内煤粉火焰的温度,以及观察燃烧筒喷口煤粉火焰的稳定性,得到了煤粉质量浓度和一次风速度对点火特性的影响规律。试验表明:在燃用蒙南烟煤的情况下,等离子直接引燃煤粉过程中,挥发分的析出和着火比常规点火方式提前,煤粉燃烧的整体温度较高;当一次风速度为18m/s,要形成稳定的火焰,一级燃烧筒内的煤粉质量浓度不能低于0.15kg/kg。     

W型火焰锅炉性能研究

在介绍W型火焰锅炉主要特点的基础上，对鄂州电厂W型火焰锅炉炉内冷态空气动力场、低负荷稳燃、结渣特性进行了分析，通过实际运行情况和试验，认为炉内气流情况良好；稳燃性能良好，结渣情况轻微。     

新型煤粉燃烧器的燃烧机理分析

分析了国内超临界和超超临界锅炉采用的几种新型煤粉燃烧器的燃烧机理。主要特点是采用多级配风技术灵活控制燃烧器出口的煤粉火焰燃烧过程;实现着火初期低氧燃烧和火焰内NOx还原技术;在旋流式燃烧器内采用煤粉浓缩技术和环形齿状稳燃器或直流过渡风,在喷口附近煤粉气流着火初期,加强热烟气回流和维持高温及低氧燃烧,促进挥发分析出过程中的NOx还原,并实现快速着火和低负荷稳定燃烧;在A-PM型直流式燃烧器上采用带扩压管的缩放型小喷口结构,增强稳燃能力和维持高温和低氧燃烧,促进NOx还原,并均衡火焰温度,降低水冷壁的热负荷;设置可调节燃尽风进一步提高炉内脱氮效果和提高燃烧效率等。     

Influence of the technique for injection of flue gas and the configuration of the swirl burner throat on combustion of gaseous fuel and formation of nitrogen oxides in the flame

How the points at which the flue gas was injected into the swirl burner and the design of the burner outlet influence the formation and development of the flame in the submerged space, as well as the formation of nitrogen oxides in the combustion products, have been studied. The object under numerical investigation is the flame of the GMVI combined (oil/gas) burner swirl burner fitted with a convergent, biconical, cylindrical, or divergent throat at the burner outlet with individual supply of the air and injection of the gaseous fuel through tubing. The burners of two designs were investigated; they differ by the absence or presence of an inlet for individual injection of the flue gas. A technique for numerical simulation of the flame based on the CFD methods widely used in research of this kind underlies the study. Based on the summarized results of the numerical simulation of the processes that occur in jet flows, the specific features of the aerodynamic pattern of the flame have been established. It is shown that the flame can be conventionally divided into several sections over its length in all investigations. The lengths of each of the sections, as well as the form of the fields of axial velocity, temperatures, concentrations of the fuel, oxygen, and carbon and nitrogen oxides, are different and determined by the design features of the burner, the flow rates of the agent, and the compositions of the latter in the burner ducts as well as the configuration of the burner throat and the temperature of the environment. To what degree the burner throat configuration and the techniques for injection of the flue gas at different ambient temperatures influence the formation of nitrogen oxides has been established. It is shown that the supply of the recirculation of flue gas into the fuel injection zone enables a considerable reduction in the formation of nitrogen oxides in the flame combustion products. It has been established that the locations of the zones of intensive fuel burnout and generation of nitrogen oxides do not coincide over the flame length, and the ambient temperature has a significant impact on the combustion stability at low values and on the concentration of nitrogen oxides in the combustion products at high values.     

新型煤粉燃烧器--PCSB燃烧器的研制及开发

用火焰传播理论对现有燃烧器在稳燃方面存在的问题进行了分析,根据NOx生成机理对挖掘燃烧器的低NOx潜力进行论证。提出PCSB燃烧器的新构思和设计,PCSB燃烧器是根据煤粉气流分步燃烧原理、火焰传播理论以及强制点火原理研制开发的理念新颖,结构简便的新型煤粉燃烧器,阐述其低NOx原理和稳燃原理,归纳了其性能和特点。结合煤种特性总结PCSB燃烧器的设计原则。PCSB系列燃烧器对各种煤具有很好的适应性,非常适宜我国火电厂切圆燃烧锅炉和墙式燃烧锅炉推广应用。     

Numerical investigation of a pulverized-coal startup vortex burner

The design of a two-channel vortex pulverized-coal startup burner is proposed, in which fuel-air mixture is admitted through the burner’s primary channel. Necessary and sufficient conditions for obtaining stable ignition of pulverized coal during operation of this burner are formulated. A procedure of using the Fluent software system for numerically studying the influence of fuel characteristics and operating parameters on the stability of flame ignition and formation is developed. The results of numerical investigations aimed at determining the effect the flowrate of a mixture of mechanically activated micropowdered coal with air has on the combustion process for a particular design of the startup burner installed in the central part of the main direct-flow round burner used in the PK-40-1 boiler at the Belovo district power station are presented. A conclusion is drawn from these results regarding the extent to which the flowrate of mixture affects the performance of this startup burner.     

Development of combined low-emissions burner devices for low-power boilers

Low-power water boilers are widely used for autonomous heat supply in various industries. Firetube and water-tube boilers of domestic and foreign manufacturers are widely represented on the Russian market. However, even Russian boilers are supplied with licensed foreign burner devices, which reduce their competitiveness and complicate operating conditions. A task of developing efficient domestic low-emissions burner devices for low-power boilers is quite acute. A characteristic property of ignition and fuel combustion in such boilers is their flowing in constrained conditions due to small dimensions of combustion chambers and flame tubes. These processes differ significantly from those in open combustion chambers of high-duty power boilers, and they have not been sufficiently studied yet. The goals of this paper are studying the processes of ignition and combustion of gaseous and liquid fuels, heat and mass transfer and NO _x emissions in constrained conditions, and the development of a modern combined low-emissions 2.2 MW burner device that provides efficient fuel combustion. A burner device computer model is developed and numerical studies of its operation on different types of fuel in a working load range from 40 to 100% of the nominal are carried out. The main features of ignition and combustion of gaseous and liquid fuels in constrained conditions of the flame tube at nominal and decreased loads are determined, which differ fundamentally from the similar processes in steam boiler furnaces. The influence of the burner devices design and operating conditions on the fuel underburning and NO _x formation is determined. Based on the results of the design studies, a design of the new combined low-emissions burner device is proposed, which has several advantages over the prototype.     

新型缝隙式直流燃烧器的研究与应用

针对缝隙式燃烧器“W”型火焰锅炉存在的燃烧稳定性差、燃烧效率低、结渣严重等问题,通过燃烧机理分析和数值模拟试验,设计了一种新型缝隙式直流燃烧器。其主要特点是将乏气风火嘴布置于炉膛中心侧相邻的2条二次风处,一次风喷口背火侧布置1个二次风喷口。实践证明,新型缝隙式直流燃烧器使锅炉燃烧稳定性和锅炉燃烧效率得到提高,炉膛结渣现象得到有效控制。     

锅炉水冷壁高温腐蚀原因及对策

通过对水冷壁高温腐蚀形成机理和过程的分析，结合运行工况，确认了华能南通电厂水冷壁高温腐蚀产生的主要原因是煤的含硫质量分数过高和炉内长期欠风燃烧，机组长期高负荷运行和燃烧器安装质量不良、燃烧调整不够等因素加快了水冷壁高温腐蚀的速度。提出将水冷壁管屏倒排使用并喷涂防腐材料，可有效延长水冷壁的使用寿命。经采取降低空气预热器漏风率、提高煤粉细度、注重燃烧调整等措施后，遏制了高温腐蚀的形成和发展，取得了良好的综合效益。