THE PREDICTION OF NOx FORMATION FOR THE COMBUSTION OF NITROGEN-DOPED DROPLETS OF HEXANE INSIDE A REFRACTORY TUBE

The detailed kinetic model developed by Tang and Churchill for the prediction of the combustion of premixed-gaseous or evaporated-liquid hydrocarbon fuels in a refractory plug flow burner has been extended to account for nitrogen compounds in the fuel. In the modified model the nitrogen compounds are postulated to decompose thermally to HCN in the flame front prior to oxidation. The concentrations of NO₂ computed from this model for 0.795% wt. nitrogen in hexane are found to be in excellent agreement with measured values for fuel-lean mixtures doped with diethylamine, isobutylamine, pyridine and piperidine, and in fair agreement for fuel-rich mixtures up to an equivalence ratio of 1.3. The formation of NO₂ from fuel-nitrogen is found to be essentially complete after 1 ms in the postflame zone. All nitrogen-containing species except N₂ and NO are computed to be in negligible concentration for fuel-lean mixtures. Significant concentrations of HCN, NH₃ and HN₂ are predicted for the combustion of very fuel-rich mixtures. The computed concentrations of O, OH and CO are not changed significantly by the addition of fuel-nitrogen.     

A THEORETICAL MODEL FOR COMBUSTION REACTIONS INSIDE A REFRACTORY TUBE

A kinetic and thermal model has been developed for the evaporation and combustion of a single chain of uniformly sized droplets of hexane in a turbulent stream of air inside a refractory tube. A single global rate expression is utilized for the oxidation of hexane to CO and H₂0, but 44 reversible, free-radical mechanisms thereafter. Adiabatic flow is postulated for the post-flame zone and plug flow throughout. An integro-differential energy balance for the wall is avoided by the use of an experimental wall temperature profile for each set of conditions. The model is restricted to external conditions such that evaporation is completed prior to ignition. Calculated concentrations of NO are in good agreement with measured values for fuel-lean mixtures over a wide range of post-flame residence times. Calculated concentrations of CO are up to twice as high as experimental values but demonstrate the same dependence on residence time and equivalence ratio, suggesting that some of the individual rate constants are incorrect. The predictions for both NO and CO are a great improvement over those of prior, simplified models, The predictions of NO deviate increasingly from measured values as the equivalence ratio increases above unity, undoubtedly due to the inapplicability of the global model for the oxidation of rich mixtures of hexane.

The assumption of a pseudo steady state concentration was not found to be valid for any of the free radicals of the detailed model, thereby accounting for the inaccuracy of the various simplified models for the production of NO and the oxidation of CO.     

A THEORETICAL MODEL FOR COMBUSTION REACTIONS INSIDE A REFRACTORY TUBE

A kinetic and thermal model has been developed for the evaporation and combustion of a single chain of uniformly sized droplets of hexane in a turbulent stream of air inside a refractory tube. A single global rate expression is utilized for the oxidation of hexane to CO and H₂0, but 44 reversible, free-radical mechanisms thereafter. Adiabatic flow is postulated for the post-flame zone and plug flow throughout. An integro-differential energy balance for the wall is avoided by the use of an experimental wall temperature profile for each set of conditions. The model is restricted to external conditions such that evaporation is completed prior to ignition. Calculated concentrations of NO are in good agreement with measured values for fuel-lean mixtures over a wide range of post-flame residence times. Calculated concentrations of CO are up to twice as high as experimental values but demonstrate the same dependence on residence time and equivalence ratio, suggesting that some of the individual rate constants are incorrect. The predictions for both NO and CO are a great improvement over those of prior, simplified models, The predictions of NO deviate increasingly from measured values as the equivalence ratio increases above unity, undoubtedly due to the inapplicability of the global model for the oxidation of rich mixtures of hexane.

The assumption of a pseudo steady state concentration was not found to be valid for any of the free radicals of the detailed model, thereby accounting for the inaccuracy of the various simplified models for the production of NO and the oxidation of CO.     

煤燃烧过程中NOx的生成和还原

燃煤过程中ＮＯｘ 的排放是一个复杂的过程, 既包括ＮＯｘ 的生成过程又包括生成的ＮＯｘ 进行均相和多相还原反应． 简述了煤燃烧过程中ＮＯｘ 生成和还原的机理． 认为燃料氮是ＮＯｘ的主要来源,ＮＯｘ 的排放与煤阶、煤中氮含量以及温度等因素有关;ＮＯｘ 与半焦的多相反应是ＮＯｘ还原的主要原因, 其中包括ＮＯｘ 在半焦表面的化学吸附、表面络合物的生成以及产物的生成和脱附等过程     

A NEW EXPERIMENTAL TECHNIQUE FOR THE DETERMINATION OF SINGLE DROPLETS SIZE, VELOCITY AND OPTICAL PROPERTIES INSIDE SPRAYS

A new experimental technique for the determination of the size, velocity and/or the optical properties of single droplets is proposed. It is based on the different behaviour of scattering cross sections upon the size for vertically and horizontally polarized incident light, as it is predicted by the Lorenz-Mie theory. Measurements of the scattering polarization ratio y =C_HH/C_vv in the side scattering region can be employed for sizing transparent droplets while the optical depth kD can be obtained in the forward region for absorbing droplets.

An interpherometric apparatus has been realized for the simultaneous determination of the polarization ratio and velocity of individual droplets. Experimental results obtained on arrays of monodisperse and bidisperse droplets with different refractive index illustrate the potentiality of the method.     

条件矩模型对CH4-空气扩散燃烧及其NOx生成的数值模拟

采用Bilger提出的条件矩模型 ,在考虑辐射热损失的情况下对CH₄-空气湍流射流扩散燃烧及其NO_x生成进行了数值模拟 .对于湍流流动和混合分数场采用k -ε - f - g模型 ,对于组分浓度场采用条件矩模型的抛物线型方程 .将模型的模拟数据与美国Sandia国家实验室的实验数据对照结果表明 :条件矩模型能够很好地预报出湍流扩散燃烧的速度场、温度场和主要组分 (CH₄、CO₂ )浓度场 ,对NO的浓度场的预报结果与实验值的发展趋势相一致 ,偏差尽管大些但可以接受     

管内对流换热系数的瞬态测量方法

<正>1前言 直接测定对流换热系数的方法分稳态法和瞬态法,前者对实验条件要求苛刻.近年来,瞬态法倍受人们关注”-”.Hausen和Kast’‘·”相继阐述了利用周期变化的流体温度在固体壁内的传播特性确定对流换热系数的原理,即根据流体与固体温度变化之间的相位角滞后（或振幅衰减）确定对流换热系数.Roetzel‘”提出了一套适用于任意形式周期振荡流体温度的瞬态测量方法. 对实测的流体温度波Tf（t）,利用傅里叶级数分析方法把Tf＊）展开为傅里叶级数,其一次谐波正弦和余弦函数项的系数表述为 u。——一Ill（t）Slnwtdt.u。——一11’（）cosnddt（l）则一次谐波可表达为 01。“fslflO此十贝）（2）式（2）中,振幅u;一 Vu: + ug,相位角9一 arc ig（uc/us）,一次谐波的周期 P—Zt。,角速度。一。八。2 测量基础2.1 模型A——霉壁面导热热阻 忽略管壁导热热阻,管壁的能量方程为 厂dL川t一。S叮f一几）一兄凡（几一瓦）（3）若求得的管壁周期振荡温度的一次谐波为Tw（t）一u。sinnd,则流体温度超前相位角9和振幅U;分别为 .y.,o\ It【._o\“工_P_\“ 9”sfCtg WN .Ut=U。。l---- W l e -- （4）一旦实际测得相位角差贝或振幅比ff八。,即可确定对流换热系数。;.显然,当ac《a时,管外对流换热的影响甚小.当液体在管     

氨燃烧器内部蒸汽过热器爆管原因分析及对策

通过金相组织对比、实验模拟流量分配、CFD软件计算管壁温度,得知过热器爆管的原因是管中蒸汽流量分配不均匀,采用管内加节流环的办法使得蒸汽重新分配,解决了过热器爆管问题。     

煤燃烧过程中硫化物的生成特性研究

采用化学热力平衡分析方法 ,分别选取了高硫、中硫、低硫三种煤样 ,在 1 0 1 k Pa,40 0 K～ 2 0 0 0 K温度范围内 ,不同的过量空气系数 α的情况下 ,初步研究了典型的煤燃烧条件下硫化物的生成情况 ,力图揭示煤样中的硫分和不同的燃烧条件对硫化物生成规律的影响     

二氧化碳压缩机入口管道结干冰的原因分析及预防措施

对四川天华股份有限公司尿素装置所发生的二氧化碳压缩机入口管道结干冰事故进行简要总结分析,提出相应的预防处理见解.     

COAL PROPERTY EFFECTS ON N2O AND NOx FORMATION FROM CIRCULATING FLUIDIZED BED COMBUSTION OF COAL

The effects of coal properties on N₂O and NO_x formation from circulating fluidized bed combustion of coal was examined through burning nine typical coals and a coal shale, widely used in China over a wide range of coal ranks, in a bench-scale circulating fluidized bed. It was found that N₂O and NO_x formation had similar dependence on coal rank. Fixed carbon content and nitrogen content were the most important coal properties to influence N₂O and NO_x emissions from circulating fluidized bed combustion of coal. A coal with high fixed carbon content had high conversion ratio of fuel-N into N₂O and NO_x. The conversion ratio of fuel-N into N₂O or NO_x increased with nitrogen content of coal, whereas it decreased with O/N ratio. No significant correlation between conversion ratio of fuel-N into N₂O or NO_x and C/N ratio was identified. To clarify the coal property effect, investigation of a wide range of coal rank, is important.     

A BOLTZMANN-LIKE MODEL FOR THE SIZE DISTRIBUTION OF BUBBLES OR DROPLETS IN A WELL MIXED DISPERSION

Results of the named model are derived and shown to compare favorably with other single parameter equations. Also, the distribution is shown to possess the unusual property of stereological in variance.     

原位燃烧合成Al-Zr-N系复相陶瓷--燃烧产物的相组成和热力学分析

原位燃烧合成法能够制备分散性良好的复相陶瓷,对于提高复相陶瓷的性能有着重要的意义.本课题研究了Al-Zr-N系复相陶瓷的燃烧合成反应. 由于金属铝的熔点较低(660℃),而金属锆的熔点较高(1855℃),在燃烧反应的高温下,金属铝要熔融团聚, 阻碍氮气向试样内部的渗透.在燃烧温度低于金属锆的熔点时,金属锆不发生熔化现象.实验结果表明,氮气向试样内部的渗透性对于反应产物的物相组成有着重要的影响.通过X射线衍射和热力学分析得到了燃烧参数和反应产物物相组成之间的关系及其内在规律.     

炉管蠕变损伤的随机计算模型

炉管服役寿命的预测问题一直受到人们关注。由于蠕变问题的随机性研究较困难,过去的研究主要集中在确定性蠕变损伤问题上。本文提出了新的蠕变损伤随机计算模型。通过 Ｍｏｎｔｅ Ｃａｒｌｏ 方法与蠕变损伤随机计算模型结果的比较,验证了蠕变损伤随机计算模型的正确。蠕变损伤随机性的描述为今后炉管蠕变损伤可靠性的评估奠定了基础。     

采空区温度场模拟及煤自燃状态预测

建立了采空区温度场的数学模型 ,并用有限差分数值方法进行模拟计算。通过计算得出了煤因氧化放热导致煤温随时间变化呈指数上升的规律以及点热源附近温度场随时间的变化规律。提出采用测量煤层中两点间温差的变化来预报高温点温度的方法 ,此法由于消除了矿井空气温度波动因素的影响 ,具有较高的稳定性。     

己内酰胺聚合管V型挡板的研制

在己内酰胺直型聚合管设计中采用了 V型挡板 ,经模拟试验和实际应用 ,效果均十分明显。采用 V型挡板改善聚己内酰胺熔体的径向混合效果 ,有效地减少己内酰胺熔体的径向温差 ,确保聚合物相对分子质量的稳定     

A BOLTZMANN-LIKE MODEL FOR THE SIZE DISTRIBUTION OF BUBBLES OR DROPLETS IN A WELL MIXED DISPERSION

Results of the named model are derived and shown to compare favorably with other single parameter equations. Also, the distribution is shown to possess the unusual property of stereological in variance.     

煤粉燃烧过程中SO2和NOx生成规律的研究

讨论了煤粉在实验室滴管护中燃烧时,SO2,NOx的生成量与炉内温度、停留时间以及煤粉粒度间的关系。实验温度范围为600℃～1000℃,煤粉停留时间为0．32s～0．55s,煤粉粒度为＜0．063mm和0．112mm～0．2mm,实验结果对了解锅炉炉膛内SO2的分布规律具有一定的意义。     

VK管内锥形挡板结构最优化的计算机辅助设计

采用有限差分法求解二维流动的控制方程，计算出二维流场的径向混合、速度分布及停留时间分布，从理论上阐明了消除死角的方法。对挡板倾斜角、相邻两挡板的间距及开孔率的最优化进行了具体讨论。     

煤粉颗粒粒度对低温NOx和SO2生成特性的影响

在实验室水平管式电炉上, 在较低温升速率和低温燃烧 （３００℃～５５０℃） 的条件下分别对合山高硫烟煤和晋城烟煤的四种不同粒度煤样的燃料ＮＯｘ 和有机硫分ＳＯ２ 的生成特性进行了研究,并且得到了在当前试验条件下颗粒粒度与燃料ＮＯｘ 和有机硫分ＳＯ２ 生成特性的定性关系及结论． 还研究了以ＣＯ为主的还原气氛在煤燃烧过程中对固氮和固硫所产生的影响以及煤粉超细化燃烧方式下ＮＯｘ 和ＳＯ２ 的生成特性．