城市垃圾在回转窑内传输过程的模型和优化

基于物料在回转窑内传输过程是由其在表面层内滚落运动和固定层内回转运动组成的这一特征 ,从散体运动的机理出发继承和发展了回转窑单颗粒轨道模型 ,并首次采用统计平均分析和受力矢量分析研究了窑内颗粒的运动轨迹 ,从而得出了平均停留时间 (MRT)和体积流率 (MVF)的简化模型 ,结合试验采取修正系数ε_t 和ε_f 完善了模型对非均质物料 (如城市垃圾 )、内构件等工况的适用性 ,同时对本文模型和几种已有的计算模型进行了比较研究 ,最后提出了回转窑热解反应器的设计和运行的优化模型 .     

滚筒内柱体内构件对二元颗粒体系混合的影响

针对滚筒内二元颗粒体系在混合过程中产生的混合死区现象,提出在混合死区位置设置柱体内构件的增混方式,以接触数作为混合评价指标,采用离散单元法研究柱体内构件对二元颗粒体系运动混合的影响,并分析其增混机理。研究结果表明:柱体内构件很大程度上破坏了聚集小颗粒的混合死区,强化了二元颗粒间的对流和扩散机制,同时抑制了颗粒的离析作用,提高了颗粒体系整体混合程度,同时,柱体内构件提高了二元颗粒体系的混合效率,改变了颗粒体系混合的稳定性;在一定的范围内,柱体内构件的数量越多,颗粒体系的混合效果越好,但如果数量过多,反而不利于二元颗粒间的混合;在滚筒开始转动的短暂时间内,柱体内构件反而抑制颗粒体系的混合,滚筒继续转动,才起到增混的效果。本研究可为二元颗粒物料增混设备的改进提供参考和依据。     

固体废弃物在回转窑内停留时间的试验研究

在回转窑冷态试验台上，采用着色示踪粒子的试验方法研究了固体废弃物的物料特性（主要是堆积特性）、回转窑的结构特性（壁面粗糙度、长度及内构件）和操作特性（倾角和转速）等因素对固体废弃物在回转窑内停留时间的影响。物料的物理性质对停留时间的影响主要是通过对堆积角的作用而体现出来的。试验物料在回转窑内停留时间的分布与正态分布比较接近。回转窑转速的提高和倾角的增大都将使用得物料停留时间减少，同时，σT^2也减少。沿回转窑长度方向的物料的平均速度是逐渐增加的。出口挡板对MRT的影响是非常显著的。纵肋和环肋的各种组合形式都增加了物料的MRT，但组合式内构件对MRT的影响远小于出口挡板对MRT的影响。壁面粗糙度对停留时间的影响主要是通过其对料床床态的改变而产生的。     

回转干馏炉内油页岩颗粒群断续给料混合运动模式

采用0～12mm油页岩颗粒群,研究回转干馏炉的填充率、转速、抄板形式等对油页岩不同粒度颗粒混合运动特征,探明其在回转干馏炉内运动形态及混合机理。研究结果表明:填充率、转速及抄板形式对颗粒群运动和混合过程有重要影响;混合机理方面,对流、扩散、剪切对混合过程均有一定的作用,但对流起主要作用;随着填充率增大,颗粒群易产生分离效应;转速降低时,采用直角抄板比直抄板颗粒群混合程度好。     

废旧橡胶裂解物料运动和传热的模拟研究

分析裂解回转炉结构并建立废旧橡胶裂解物料颗粒（橡胶物料）运动的数学物理模型,得到回转炉体螺旋角、长度和转速对橡胶物料停留时间的影响公式及橡胶物料在回转炉中充分停留情况下处于滚落运动模式时炉体的理论转速范围;通过颗粒力学仿真软件（EDEM软件）对橡胶物料在回转炉中的运动进行模拟,得到橡胶物料混合程度最佳的炉体转速;对比加入循环介质二氧化锆小球前后的橡胶物料运动状态,分析二氧化锆小球对橡胶物料运动和传热的影响;通过橡胶物料在300 ℃时的传热情况推断出废旧轮胎裂解过程中回转炉内顺丁橡胶的传热效果较好,其次是溴化丁基橡胶,天然橡胶和丁苯橡胶较差。     

多粒径颗粒在圆形偏心滚筒内的运动混合

采用离散单元法(DEM),对5种粒径颗粒在滚筒内的运动混合进行数值模拟,研究了偏心距对滚筒内颗粒体系分区及区域变化、大颗粒速度变化和多粒径颗粒混合程度的影响。结果表明;非偏心滚筒内处于滚落运动模式的颗粒体系分为3个区域:平流层、活动层和涡心;偏心滚筒内不存在实际的涡心,随着滚筒转动,"移动涡心"的形状大小和位置都在周期性变化。在不同颗粒运动周期中,非偏心滚筒内的大颗粒在平流层中的匀速度基本相等;而在偏心滚筒内,大颗粒在相邻两次平流层中的两次匀速度基本都不相等,且偏心距越大的滚筒内,颗粒匀速度的变化越明显。偏心距基本不影响滚筒内多粒径颗粒的接触效果,多粒径颗粒在滚筒内的混合过程中,接触数的变化类似阻尼振动曲线变化。     

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。     

内构件对于提升管中颗粒混合行为的影响

对加设了钝体式内构件的提升管内颗粒的轴径向混合为进行了研究。研究结果表明，内构件的存在并不能明显减少提升管内颗粒的轴向返混，这与提升管内稳定的微观两相结构密切相关，但颗粒的径向混合能力却可大大加强，而且在越高的气速和固含条件下，这种加强作用越明显，其原因是内构件的存在加强了边壁区颗粒的脉动，有利于破坏提升管边壁区的颗粒浓环，促进颗粒的径向交换与混合。     

布风方式对流化床混合特性的影响

通过将离散单元法同计算流体力学相结合,对流化床内物料混合过程进行了研究。给出了水平布风板均匀布风、倾斜布风板非均匀布风2种情况下的示踪颗粒场历变过程。模拟结果表明:瞬时颗粒场组图能够较为直观表征床内混合现象;其中,在均匀布风情况下,床内气泡横向运动受到限制,颗粒整体横向运动能力较弱,混合方式以扩散混合为主;而对于非均匀布风流化床,床内存在较大的横向颗粒浓度梯度,对流混和起主要作用,且混合速度较为迅速。     

回转圆筒内固体颗粒径向偏析的研究

混合固体颗粒在回转圆筒内运动时要发生径向偏析,笔者认为颗粒的渗流以及粗细颗粒的流动性不同是引起颗粒偏折的主要原因。本文通过实验得到了筒体转速及填充系数对偏析的影响。     

回转干馏炉内扰流件的扰动及增混特性

采用离散单元法（DEM）模拟了二组元颗粒体系在有扰流件回转干馏炉内的流动和混合。根据涡心区（混合死区）的位置和尺寸在回转干馏炉中分别安装了外接圆半径相等的圆柱、前半圆、后半圆和直板扰流件，研究了扰流件类型对扰流件尾流、颗粒平均速度和大小颗粒混合程度的影响。研究表明：当各扰流件穿过颗粒物料时，其尾流分别经历了左偏尾流、近似对称尾流和右偏尾流。扰流件类型不同，在相同的时刻其尾流的大小存在差异。当回转干馏炉内无扰流件或者有直板扰流件时，颗粒平均速度的波动范围较小，且波动较为不规则。当安装圆柱、前半圆和后半圆扰流件时，平均速度的波动范围较大，且波动规律性较强，每一个波动过程均由一个大波动和一个小波动构成。对于圆柱和前半圆扰流件，小波动位于波动范围的低值区，对于后半圆扰流件，小波动位于波动范围的中值区。对于二组元颗粒系统，当外接圆半径相等时，后半圆扰流件的增混效果最好，但干馏炉耗能最快。圆柱和前半圆扰流件的增混效果次之。直板增混效果最差，但相比于其他绕流件耗能最慢。较大的绕流件终末卸料角更有利于颗粒的增混。     

含聚结构件油水分离器性能研究

由沉降和聚结机理可知选取适当的聚结构件可增加油水乳状液的粒径,加快沉降速度,从而提高分离器性能.今设计了一种含聚结构件的分离器,在长为1800 mm,内径为384 mm的重力式分离器内安装入口构件和聚结板,通过测量不同流速和工况条件下四种聚结板对油水乳状液的粒径质量分离效率,研究分离器性能.结果表明,倒T型入口构件可有效减少分离器流场中的回流和二次涡流,还引入了重力消能和水洗作用.聚结板可显著提高油水分离效率,在流量较大的时候,聚结板分离效果下降,出现对粒径选择性的单一分离作用.聚结板的结构和材质对液滴的聚结沉降影响很大,应根据工况和处理条件进行合理选择.     

Mixing large and small particles in a pilot scale rotary kiln

The mixing of solid alternative fuel particles in cement raw materials was studied experimentally by visual observation in a pilot scale rotary kiln. Fuel particles were placed on top of the raw material bed prior to the experiment. The percentage of particles visible above the bed as a function of time was evaluated with the bed predominantly in the rolling bed mode. Experiments were conducted to investigate the effects of fuel particle size and shape, fuel particle density, rotary kiln fill degree and rotational speed. Large fuel particles and low-density fuel particles appeared more on top of the bed than smaller particles and high-density fuel particles. Fuel particle dimensions and sphericity were important parameters for the percentage of visible particles. Increasing bed fill degree and/or increasing rotational speed decreased the percentage of particles visible on top of the bed.Results can be up-scaled to industrial conditions in cement rotary kilns and show that even relatively large fuel particles will predominantly be covered by raw material after less than 30 s in the rotary kiln. This affects the heating and combustion mechanisms for the fuel particles.     

An approach to qualify the intensity of mixing on a forward acting grate

The objective of this study is to derive methods on a statistical basis to describe quantitatively the mixing process of a packed bed on a forward acting grate. The packed bed was represented by spherical particles, whereby a varying size accounts for the variety of particle geometries in a combustion chamber. In order to describe accurately the motion of a packed bed e.g. its particles, the discrete element method (DEM) was applied. Thus, detailed data on all the particle's paths and velocities are available. These data were used for the two proposed methods based on particles’ velocities and trajectories to assess mixing and segregation of a packed bed. Both methods describe the mixing process very satisfactorily, whereby the trajectory based method is more favourable to describe segregation.     

Predicting the fraction of the mixing zone of a rolling bed in rotary kilns

The thermal efficiency of a rotary kiln is predominantly influenced by the amount of lateral mixing of the material bed. In this paper, the fraction of the mixing zone in the material bed is predicted for the rolling motion. For a given material, the fraction is found to depend only on three dimensionless variables—the ratio of the particle diameter to the kiln diameter, the Froude number and the filling degree. Experiments were carried out on a rotating cylinder with beans as testing material. The predicted results are in good agreement with the measurements with a maximal error of 12%. The fraction of the mixing zone is then analyzed for industrial rotary kilns. Its value is found to increase approximately linearly with increasing Froude number and the dynamic angle of repose of the material. For all investigated cases, the fraction of the mixing zone lies in the range of 20–45%. Results of this study can provide orientating values of the mixing zone fraction, which are needed to calculate the thermal efficiency of the rotary kiln.     

再论新型干法回转窑的优化设计与增产节能——NSP窑的节能技术方案和节能窑型推广之我见

随着我国新型干法水泥生产工艺、技术装备和系统控制的日趋成熟,NSP窑斜度、转速、窑内物料停留时间、平均负荷率和装机功率等设计参数得到了逐步优化,窑系统产量和综合效益得到大幅提高。通过采集大量2000～2500t/d熟料和4000～5000t/d熟料NSP窑技术方案的最新生产数据,和通过生产实践及研究成果捏合建立一个表征性数学模型,对二大类各11个设计方案的详实计算和分析比较,以探索设计参数间变化规律和对能耗的影响。结果表明:NSP窑的斜度和长径比对节能的影响巨大。其中斜度从3.5%加大为4.0%时,节能13%左右;从4.0%加大为4.5%时,节能11%左右;长径比每减少1.0,则能实现节能约6%～7%。在此计算分析的基础上,提出了全新的节能新窑型设计方案——二支承新型超短窑。     

回转窑内利用液化残渣共热褐煤以抑制其粉化的影响因素分析

在公斤级回转窑中研究了共热解过程不同液化残渣与褐煤质量配比及粒度配比因素对抑制褐煤粉化效果的影响。结果表明：550℃共热解条件下,随液化残渣的添加比例由10%升至40%,共热解半焦的粉化率β由7.55%降至1.98%,造粒率λ由2.73%升至4.90%,液化残渣添加量的提升有效促进了对粉化的抑制及混合造粒;3～1 mm液化残渣与3～1 mm褐煤的共热解半焦β为2.82%,较与6～3/13～6/25～13 mm褐煤颗粒热解后的产物粉化率均低,而λ则达到24.99%,远高于其他粒度配比下的产物造粒率。灰色关联分析显示,粒度配比因素对β和λ的影响权重均大于质量配比因素。结合分析上述配比因素影响粉化抑制作用的内在诱因（强化粘连捕集颗粒行为,促进孔隙充填补强作用,颗粒穿层行为影响）,形成了回转窑热解过程配比因素对抑制褐煤粉化的影响过程模型。     

Longitudinal mixing in horizontal rotary drum reactors

The longitudinal mixing of sodium carbonate (soda) (mean particle size 137 μm) has been investigated in a laboratory horizontal rotary drum reactor 250 mm in diameter and 600 mm long. The distributions of residence times have been estimated by means of a pulse of a small amount of sodium bicarbonate. The concentration of the tracer at the reactor discharge has been evaluated by thermal decomposition of the samples and by measuring their weight loss.The hold-ups, the mean residence times and the variances of the distribution of residence times were evaluated as a function of the rotational speed of the reactor and the feed rate of the particles. By applying a dispersion model, the Peclet numbers were evaluated from the standardized variances and plotted as a function of the feed rate and rotational speed. The mean residence time of the particles was calculated by means of an extended model of Vahl and Kingma. They correspond with the experiments.     

STOCHASTIC ANALYSIS OF AXIAL SOLIDS MIXING IN A FLUIDIZED BED

Particulate mixing systems lend themselves to a stochastic analysis due to the finite number of discrete particles involved. The physics of mixing at a single particle level can best be seen as a random process since the trajectory of the particle is influenced by many competing factors. In this work, a stochastic model for axial mixing of particles in a fluidized bed is formulated by resorting to the multivariate master equation. Configuration of the bed is cylindrical; it is divided into small axially distributed compartments. The behavior of the bed following the addition of tracer particles to the top of the bed is studied. Experimental data from Qu and Kwauk (1985) are used to estimate the single parameter in the model. Expressions are derived for the mean tracer concentration as well as its variance. The density function of the first passage time for a tracer particle to reach the bottom of the bed is derived, and other extreme value statistics are discussed. A maximum likelihood estimator of the axial dispersion coefficient based on the first passage time for a single tracer particle between two points in the bed is also derived.     

Fate of solids fed pneumatically through a jet into a fluidized bed

Solid tracer particles were fed pneumatically through a jet into a fluidized bed to simulate the feeding of solids via a pneumatic transport line into a fluidized-bed reactor operating in the slugging-bed mode. The fluidized bed was defluidized instantaneously at different times after the initiation of the tracer particle injection. The bed was then sampled layer by layer to provide the radial and axial concentration profiles of the tracer. Regular and high-speed movies (1,000 frames per second) were taken to study the operation of the fluidized bed and the phenomena of the gas-solid two-phase jet. Experimental results on solid mixing, jet constriction and slugging frequencies, slugging bed height, slug length, jet penetration, and jet half-angle at three nominal jet velocities of 52, 37, and 25 m/s and corresponding solids loadings are presented. Additional experimental results on jet constriction and slugging frequencies, and slug volume (axial slug size) obtained for a wider range of jet velocities confirm the hydrodynamic trends observed during the tracer particle injection experiments. The results indicate that solids mixing increases, and well-mixed conditions are reached earlier, with an increase in jet injection velocity. The obtained mixing times were correlated successfully in terms of the excess gas velocity. The experimental data on jet penetration and slug motion were satisfactorily correlated by modified versions of existing theoretical relations. The modifications included the effect of the injected solids on jet penetration and jet half-angle and also the effect of our semicircular column geometry and single wall-slug configuration on the observed slug motion.