基于简单碰撞理论煤粉燃烧动力学模型的研究-PART Ⅲ:氧气可达比表面积

根据不同温度下氧分子平均自由程的大小,比较了小孔、中孔和大孔中三种扩散速率与煤焦表面燃烧速度的大小.研究表明2000 K以内,颗粒表面分子扩散速率比氧化反应速率大1个数量级以上,过度扩散速率不小于氧化速率.温度小于1200K时,燃烧速率比Knudsen扩散速率小1～5个数量级,扩散孔径小于15～28 nm,反应主要在内外表面进行;1200～1600K时,燃烧速率与Knudsen扩散速率相当,扩散临界孔径28～38 nm,反应在外表面及浅层内表面进行;温度1600K以上时,Knudsen扩散速率比燃烧速率小1个数量级,孔径38～50 nm以下内表面上碳的氧化速度受扩散控制.煤焦的氧化主要发生在Knudsen扩散临界孔径10～50 nm以上的氧气可达表面上.     

亚硫酸盐氧化气液反应过程模型研究

亚硫酸盐氧化是湿法烟气脱硫的重要反应过程,本文建立了该反应过程的物理模型,包括氧的相间传质扩散、本征化学反应和亚硫酸根扩散这三个步骤,宏观反应速率由其中最慢的一个步骤来决定,反应分为不同的控制阶段。在双膜理论和质量守恒理论的基础上,建立了稳态单气泡吸收过程的数学模型。在动力学控制阶段,反应速率与气泡的半径呈0阶关系;在...     

石灰石消溶的液固反应模型及消溶速率

基于单颗粒消溶的缩核模型,建立了酸消溶石灰石反应在液膜传质和化学反应共同控制条件下的颗粒群的液固反应模型。实验研究了五种石灰石样品在不同温度、不同pH值和不同粒径分布下的消溶过程,模型理论计算与实验进行了验证,得到了不同种类的石灰石在不同反应条件下的平均整体反应常数k_m,且k_m是一个与反应条件相关的特征数。通过实验数据和理论模型对反应过程中的整体反应常数进行反推,发现同一反应条件下k_m随时间不断缩小并趋于常数,但粒度分布不同和产地不同的样品在相同反应条件下的整体反应常数相差不大。     

合肥光源在反应动力学研究中的进展

正反应动力学研究化学反应随时间变化的动态过程,包括化学反应速率和反应机理等。分子反应动态学(Molecular reaction dynamics)和燃烧反应动力学(Combustion reaction kinetics)是反应动力学中重要的研究领域,主要利用光谱和质谱技术探测化学反应组分随时间的演化过程,来得到化学反应速率和反应机理等信息。从学科发展历程来看,分子反应动态学和燃烧反应动力学研究的进步离不开     

基于有限反应速率的扩散燃烧大涡模拟

本文发展了一种基于有限反应速率的湍流燃烧大涡模拟方法。基于此方法,对常压下,甲烷/空气平板射流扩散燃烧进行了大涡模拟.甲烷/氧气反应采用包含七种组分的四步反应简化反应机理,考虑了基于Arrienius定律的有限化学反应速率,瞬态结果和时均结果与DNS结果都符合很好。为了解决考虑有限反应速率后计算量急剧增加的问题,本文引入等效化学反应速率模型,在压力泊松方程的求解中采用了求解效率较高的快速傅里叶变换方法,并对整个程序进行基于区域分解的MPI并行编程处理。     

在流化床燃烧中用石灰石脱硫

近几年来,在用石灰石脱除流化床燃烧时烟气中所含二氧化硫和三氧化硫方面已有不少报导。在描述石灰石数量对二氧化硫吸收效率的影响这一重要关系时,往往用送进床层的物料中氧化钙含量和可燃硫含量的化学当量比(Ca/S)与吸收效率(η)的关系来表示。这种描述方法局限而且不准确,因为吸收效率不仅与化学当量比(Ca/S)有关,它还和石灰石的粒径分布等因素有关。本文提出了单个石灰石颗粒只有其表面的一层氧化钙能与烟气中的二氧化硫反应的模型;在流化床内对北京丹里地区石灰石的可反应表     

多孔颗粒内气体传递反应双阶段描述

本文采用双阶段模型描述多孔颗粒与气体的传递反应。反应分为两个阶段:气体反应物在扩散进入颗粒内部同时与颗粒发生反应的第一阶段;形成产物层后,扩散和反应用双区域模型来描述的第二阶段。分析发现,蒂勒数是描述过程特性的重要参数,同时反映反应和扩散速度的影响,且与总阻力存在一定关系。利用TGA进行了脱硫反应实验,分析了反应温度、颗粒大小等对反应的影响,实验结果很好地证实了理论分析结论。     

微流燃料电池空气阴极物质传输孔隙尺度模拟

采用格子Boltzmann方法研究了微流燃料电池空气阴极多孔扩散层内多组分物质传输特性。随机重构了扩散层,获得渗透率及有效扩散系数。建立了耦合边界电化学反应的二维模型,研究了过电位、孔隙率对氧气、水蒸气浓度分布及局部反应速率的影响。结果表明,常用的Bruggeman经验关联式会高估氧气有效扩散系数;扩散层孔隙结构对物质传输有重要影响,孔隙率减小使得传质阻力增大,导致局部氧气浓度降低,局部反应速率降低,而水蒸气浓度增大,当孔隙率从0.83降至0.7,催化界面平均氧气浓度从8.472降至8.466 mol·m^-3。     

自定义标量法模拟丙烷燃烧过程

采用自定义标量法模拟丙烷扩散燃烧,该方法通过把反应组分定义为Fluent程序的自定义标量、化学反应速率作为源项求解质量、动量、能量和组分守恒方程,并用化学反应引起的能量变化修正能量方程.考虑了详细的化学反应机理,整个燃烧反应机理包括27种化学物质(不含N2)和83个基元反应.合理地模拟出了丙烷的燃烧过程,并将火焰的长度、温度、丙烷、氧气以及中间产物的分布与实验数据进行比较.     

4H-SiC同质外延生长Grove模型研究

本文通过对4H-SiC同质外延化学反应和生长条件的分析,建立了4H-SiC同质外延生长的Grove模型,并结合实验结果进行了分析和验证.通过理论分析和实验验证,得到了外延中氢气载气流量和生长温度对4H-SiC同质外延生长速率的影响.研究表明:外延生长速率在衬底直径上为碗型分布,中心的生长速率略低于边缘的生长速率;随着载气流量的增大,生长速率由输运控制转变为反应速率控制,生长速率先增大而后逐渐降低;载气流量的增加,会使高温区会发生漂移,生长速率的理论值和实验出现一定的偏移;随着外延生长温度的升高,化学反应速率和气相转移系数都会增大,提高了外延速率;温度对外延反应速率的影响远大于对生长质量输运的影响,当温度过分升高后,外延生长会进入质量控制区;但过高的生长温度导致源气体在生长区边缘发生反应,生成固体粒子,使实际参与外延生长的粒子数减少,降低了生长速率,且固体粒子会有一定的概率落在外延层上,严重影响外延层的质量.通过调节氢气流量,衬底旋转速度和生长温度,可以有效的控制外延的生长速度和厚度的均匀性.     

CaO高温分离CO2过程的数值模拟

钙基吸收剂煅烧-碳酸化循环法(CCRs)是一种新兴的分离燃煤锅炉尾部烟气中CO2的方法.CaO与CO2碳酸化反应对于CCRs法的应用起着非常重要的作用.本文采用随机孔隙模型(RPM)对CaO与CO2碳酸化反应过程进行了研究,结果表明,适当提高CaO与CO2碳酸化反应的温度和系统压力,增加CaO吸收剂的初始孔隙率、优化CaO的初始比表面积等措施能够有效提高CaO碳酸化转化率和对CO2的吸收容量.     

炭/碳粒在CO_2/O_2气氛中燃烧速率的研究

１引言大量的研究表明,近一个世纪以来,大气中温室气体（主要是ＣＯ２）含量的迅速增加是引起全球气候变化的一个重要因素。而且,在今后若干年内,随着人类从矿物燃料中获取能源的进一步增加,ＣＯ２的排放量亦将持续增长。其中煤的利用量及在燃烧过程中ＣＯ２的排放量...     

钾基CO2吸收剂再生反应特性

通过热重分析试验研究了钾基 CO2 吸收剂的再生反应特性.深入分析了气氛、分解终温和升温速率对再生转化率和分解反应速率的影响.通过热分析方法求取了反应动力学参数.研究发现,其分解终温最佳值为 200℃;CO2 和H2O 在分解终温较低时对反应过程的影响较大;升温速率对反应的影响程度在其高于 10℃/min 后明显减弱;KHCO3分解反应的表观活化能为 90～120 kJ/mol.本文为干法 K2CO3/KHCO3 循环脱除 CO2 的研究提供了一定的基础数据.     

利用甲醇氧化烟气中NO的实验研究

对利用甲醇氧化烟气中NO的反应开展了系统的实验研究。研究了反应时间、反应温度、甲醇用量比例、烟气中O2、SO2及夹带的固体颗粒对NO氧化率的影响。结果表明,在一定的条件下,甲醇能够氧化烟气中的NO;NO氧化率受反应时间和反应温度的综合影响,随着反应时间的增加,有效反应温度区域向低温方向移动,最大NO氧化率降低;随着甲醇用量比例的增加, NO氧化率增加;O2浓度增加可促进NO氧化;烟气中的SO2对反应有催化作用,可显著提高NO氧化率;烟气中固体颗粒的存在阻碍了自由基反应的进行,显著降低了NO的氧化率。     

Theoretical and experimental study on the effects of particle size and temperature on the reaction kinetics of cubic nano-Cu<Subscript>2</Subscript>O

The activities, selectivities, and stabilities of nanoparticles in heterogeneous reactions are size-dependent. In order to investigate the influencing laws of particle size and temperature on kinetic parameters in heterogeneous reactions, cubic nano-Cu₂O particles of four different sizes in the range of 40–120 nm have been controllably synthesized. In situ microcalorimetry has been used to attain thermodynamic data on the reaction of Cu₂O with aqueous HNO₃ and, combined with thermodynamic principles and kinetic transition-state theory, the relevant reaction kinetic parameters have been evaluated. The size dependences of the kinetic parameters are discussed in terms of the established kinetic model and the experimental results. It was found that the reaction rate constants increased with decreasing particle size. Accordingly, the apparent activation energy, pre-exponential factor, activation enthalpy, activation entropy, and activation Gibbs energy decreased with decreasing particle size. The reaction rate constants and activation Gibbs energies increased with increasing temperature. Moreover, the logarithms of the apparent activation energies, pre-exponential factors, and rate constants were found to be linearly related to the reciprocal of particle size, consistent with the kinetic models. The influence of particle size on these reaction kinetic parameters may be explained as follows: the apparent activation energy is affected by the partial molar enthalpy, the pre-exponential factor is affected by the partial molar entropy, and the reaction rate constant is affected by the partial molar Gibbs energy.

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Graphical abstract In situ microcalorimetry, combined with theoretical models, was used to investigate the reaction kinetic parameters of cubic nano-Cu₂O, and those effects of particle size and temperature were discussed systematically.

     

Comparison of Activated Carbon,Multiwalled Carbon Nanotubes,and Cadmium Hydroxide Nanowire Loaded on Activated Carbon as Adsorbents for Kinetic and Equilibrium Study of Removal of Safranine O

Activated carbon (AC), multiwalled carbon nanotube (MWCNT), and cadmium hydroxide nanowire loaded on activated carbon (Cd(OH)₂-NW-AC) have been used for the removal of safranine O (SO) from wastewater. The effects of various parameters including pH, temperature, concentration of the dye, amount of adsorbents, and contact time on the SO adsorption efficiency for all adsorbents has been investigated. Graphical correlation of fitting experimental data to various adsorption isotherm models like those of Langmuir, Freundlich, Tempkin, and Dubinin–Radushkevich for all adsorbents have been calculated. It was found that safranine O adsorption on all adsorbents was endothermic and feasible in nature. Fitting the experimental data to different kinetic models suggests that the adsorption process follows pseudo-second-order kinetics with involvement of the particle diffusion mechanism.     

Understanding the effect of CaO on HCN conversion and NOx formation during the circulating fluidized combustion process using DFT calculations

Hydrogen cyanide (HCN) is an important intermediate during the conversion of fuel nitrogen to NO_x. The mechanism of HCN oxidation to NO, N₂, and N₂O on the CaO (100) surface model was investigated using density functional theory calculations to elucidate the effect of in-furnace SO_x removal on HCN oxidation in circulating fluidized bed boilers. HCN adsorption on the CaO (100) surface releases as high as 1.396 eV and the HC bond is strongly activated. The CaO (100) surface could catalyze the oxidation of CN radical to NCO with the energy barrier decreasing from 1.560 eV for the homogeneous case to 0.766 eV on the CaO (100) surface. The succeeding oxidation of NCO by O₂ forming NO is catalyzed by the CaO (100) surface with the energy barrier decreasing from 0.349 eV (homogeneous process) to 0.026 eV on the CaO (100) surface, while the reaction between NCO and NO forming either NO or N₂ is prohibited in comparison with corresponding homogeneous routes. The rate constants of these reactions under fluidized bed combustion temperature range are provided, and the calculation results lead to the conclusion that CaO (100) surface catalyzes the HCN conversion and improves the NO selectivity during HCN oxidation in the HCN/O₂/NO atmosphere, which could well explain previous experimental observations. Kinetic parameters of HCN oxidation on the CaO (100) surface are provided in the Arrhenius form for future kinetic model development.     

Sintering mechanism of CaO during carbonation reaction in the presence of water vapor

In this paper, CaO sintering in the presence of water vapor for CO₂ capture were carried out by ReaxFF(Reactive Force Field) molecular dynamics. The CaO sintering model was simulated at different temperatures (873 K-1273 K) and atmospheres (CO₂, H₂O), respectively. The results showed that water vapor could significantly promote the sintering process of CO₂ capture by CaO. The Mean-square displacement (MSD) and Boltzmann–Arrhenius dependency were used to study the diffusion properties of CaO particles. The decreased diffusion activation Ea and increased pre-exponential factor D₀ indicate that CaO particles have a stronger initial diffusivity and a lower diffusion barrier in the presence of CO₂ and H₂O. The inner and outer regions of CaO atoms were analyzed and it was found that the activation energy is the main factor to enhance the diffusion in the presence of CO₂ for CaO sintering process, whereas the pre-exponential factor dominates with both CO₂ and H₂O. Water vapor enhanced the sintering pf CaO carbonation reaction is mainly achieved by promoting atoms in the inner layers of CaO particles. The types and numbers of sintering atoms during the sintering process were counted, and the distances between Ca and O atoms were calculated, which found that water vapor first dissociates into hydroxyl and H protons on the CaO surface, and the hydroxyl group will stay on the surface of CaO and combine with CO₂, while the H proton will combine with O inside CaO to promote the sintering of CaO further.     

气体NO／SO2／N2／O2等离子体反应机理及动力学分析

本文研究了在低温等离子体条件下,电子碰撞NO/SO2/N2/O2气体引发离解反应的反应机理.应用碰撞理论和波尔兹曼方程分析,对能量分布函数及反应速率常数进行数值模拟,得到离解反应速率常数与温度的曲线,分析预报各反应过程及表现.最后将速率常数拟合为Arrhenius公式的形式.     

Reaction-diffusion processes in the “adsorbate-substrate” system

We obtain a chain of quantum kinetic reaction-diffusion-type equations for “adsorbate-substrate” system taking into account the coupling of a light particle with a metallic surface, the adsorbate surface diffusion by the tunnelling mechanism and the occurrence of bimolecular chemical reactions. We calculate the temperature dependence of the kinetic kernels related to the diffusion coefficients and the reaction rates. It is shown that one can alter the temperature dependence of the reaction rates by changing the “adsorbate-substrate” coupling. It is also shown that the mean field terms contribute to the activation energies of the reaction rates, while their contribution to the activation energies of the diffusion coefficients vanishes.