Application of fractal theory on raceway boundary in COREX melter–gasifier model

Abstract

The raceway has been studied extensively both theoretically and experimentally. In this study, particle velocity contours have been developed to define the raceway boundary. The raceway boundary is coarse and fragmentised, but all of the previous studies are based on Euclidean geometry, which regard the dimension of the raceway as an integer. In this paper, the fractal method of calculating raceway size, which describes the boundary with extremely irregular or fragmented characteristics, is on the data from a cold physical model of the raceway. The results show that the precise raceway boundary can be obtained by the particle velocity contours, that the surface area of the ellipsoidal raceway based on fractal theory is larger than that based on Euclidean geometry and that the data can be used as original boundary conditions of the flow and chemical reaction in the raceway region.     

COREX熔化气化炉风口回旋区的分形研究

以COREX熔化气化炉物理模型为基础,对高速摄影仪记录的回旋区颗粒运动情况进行分析得到模型观察面上回旋区的颗粒速度场,运用分形方法对回旋区内不规则边界的表面积进行研究。结果表明：不同条件下,回旋区内表面边界的分维数变化不大;回旋区内表面积随着风量的增大而增大,当吹气量由106 m3/h变为122 m3/h时,回旋区表面...     

Definition of Raceway Boundary Using Fractal Theory

The particle velocity contours were obtained by tracking the tracer particles in the raceway region of the COREX melter gasifier model and the contours were irregular.According to the fractal theory,the fractal dimensions of different particle velocity contours were determined.Through the analysis of the fractal dimensions,a new method for precise determination of the raceway boundary was proposed.The results show that,when the velocity is less than 0.18m/s,the particles are located in the stagnant zone and the fractal dimensions of particle velocity contours are almost constant as 1.41;when the velocity increases from 0.18 to 0.83m/s,the particles are located in the rapid movement zone and the fractal dimensions decrease gradually from 1.41 to 1.05;when the velocity is greater than 0.83m/s,the particles are located in the cavity zone and the fractal dimensions are again almost constant as approaching to 1.00.Therefore,the velocity contour of 0.18m/s,which is critical to distinguish the rapid movement zone and stagnant zone,can be used to define the raceway boundary.Based on this method,the effect of blowing rate on raceway size was calculated and the results show that the penetration depth and height of the raceway increase with the increase of blowing rate.     

分形理论分析风口回旋区的边界

基于分形理论更能准确的界定风口回旋区边界。建立COREX熔化气化炉的半周三维冷态模型,利用高速摄影的方法跟踪冷态模型内示踪粒子的运动,得到冷模型观察面板处风口回旋区的颗粒运动信息。通过对大量颗粒运动信息的处理得到风口回旋区范围的颗粒速度标量场,最后运用分形理论对利用不同颗粒速度大小等值线界定的回旋区边界的“不规则”程度进行了研究。结果表明：在回旋区内部颗粒快速运动的空腔区,分维数基本不变,且接近于欧几里得维数1;在停滞区,分维数也基本不变,其数值大致为1.4;从空腔区到停滞区分维数逐渐增大;将停滞区分维数基本不变的速度值作为界定回旋区边界的标准,可以确定回旋区的形状和大小,并可通过余维相加定律计算出三维风口回旋区的内表面积;为风口回旋区的宏观动力学计算以及数值模拟提供准确的边界条件。     

片状粉末表面特征的表征方法

对不同片状粉末的显微照片进行了分析，选择四个机械表面粗糙度参数：Ra，Rq，Sk和K对不同粉体颗粒的图像进行表面几何特征的描述，根据片状粉末图像的灰度值计算相应的粗糙度数值。并提出用分形的方法进行进一步表面分析，采用DBC算法计算分形盒子维，作为颗粒表面的分形维数。结果表明，计算得到的粗糙度参数中，Ra，Rq的变化趋势与人为观察结果不符。Sk和K的数值与主观观察结果较为吻合，但是对珠光效应比较敏感。表面分形维数的数值最为稳定，且符合观察结果，与主观视觉效果一致，在一定程度上，可有效地反映粉体表面的粗糙程度。从而为片状粉体的制备和应用研究，提供一个较为合理的表面几何特征的表征方法。     

影响熔化气化炉风口回旋区因素的物理模拟

以COREX实际尺寸和操作参数为基础,假设回旋区内只有气、固两相,根据相似准则建立了COREX熔化气化炉模型用以研究回旋区.实验采用聚乙烯粒子作为模型的填充物料,并用红色粒子作为示踪粒子,研究了回旋区的形成过程;通过颗粒速度场确定的回旋区边界,分析了风速、排料速度(焦炭燃烧速度)、料层高度等因素对回旋区大小的影响.     

A fundamental study of raceway size in two dimensions

Blast furnace raceway zones are formed by the force of the air blast injected through the tuyeres evacuating a region of the packed bed directly in front of these tuyeres. Raceway depths in blast furnaces have been historically predicted through the use of empirical correlations based on measurements on cold and hot models. These correlations are not found to be universal in application, however, with many researchers finding only fair agreement between their experi-mental data and the correlations proposed by other researchers. We present here an alternative physical mechanism approach for raceway formation based on examination of the fundamental properties of the system. The study includes two-dimensional experiments where raceway depths and shapes are measured and an accompanying theoretical and numerical analysis of the under-lying mechanisms. Gas flow distributions around the raceway zone are also examined. It is found that the raceway size for given blast conditions and particle properties is such that the total gas drag on the solids vertically above the raceway balances the solid bed weight, with some allowance for solid holdup by walls. The formulation of this theory leads to the further conclusion that the total surface area of the raceway walls as a fraction of the horizontal cross-sectional area of the container or furnace is a unique function of three factors: (a) the gas flow rate as a fraction of the gas flow rate required to fluidize the bed, (b) a particle Reynolds number calculated at the particle's incipient fluidization velocity, and (c) the shape of the horizontal cross section of the bed.     

钢中夹杂物的分形维数及其与形貌特征的关系

 利用Matlab图像处理功能计算了钢中夹杂物SEM图像的边缘、二维和三维分形维数,并讨论了边缘分形维数与夹杂物颗粒微观凝聚机制和三维分形维数与其融入顶渣中动力学之间的关系。结果表明：边缘分形维数可定量地表征夹杂物边界轮廓线的曲折复杂程度;对非润湿夹杂物颗粒来说,其边缘分形维数越大,表明气泡易于在其表面生成,从而更加有力于夹杂物的碰撞凝聚长大;夹杂物颗粒的三维分形维数越小,更有利于夹杂物融入渣中而被去除;分形维数是一个影响不规则夹杂物颗粒碰撞、凝聚和去除的重要参数。     

模具钢电渣重熔铸坯凝固组织形貌的分形特征

为了更为精细化地表达及控制铸坯质量,以H13模具钢电渣重熔铸坯凝固组织为研究对象,引入分形维数对其主体形貌特征进行定量描述。结果表明,基于数盒子法计算得到的分形维数可定量表征凝固组织形貌的自相似复杂程度,其值从柱状晶向中心等轴晶先减小后增大;凝固组织分形维数可作为衡量铸坯偏析程度（偏析率大小）的指标,且分形维数越大,对应区域偏析率越小,偏析越轻;通过凝固组织分形维数、偏析率和偏析点平均面积与二次枝晶间距关系的研究发现,使用二次枝晶间距表征铸坯凝固组织形貌差异并由此反映偏析程度的方法存在局限性。     

Applicability of fractal concepts to surface roughness

The stochastic part of metal surface profiles can be described by means of fractal geometry. The scaling behaviour of the roughness-depth as function of the basis length is related to the non-integral fractal dimension. Regular fractals, which are constructed similarly to the Koch-curve, are not capable of reproducing typical roughness-depth distributions. More adequate is the Weierstraß-Mandelbrot function. If the bearing area ratio approximately follows a power law, the parameters can be easily determined from the exponent and the form of the roughness-depth distribution, as is shown for a technical surface after cold-rolling. If the Weierstraß-Mandelbrot function is used in two classical friction models, the influence of the parameters including the fractal dimension on the friction coefficient in the case of dry surfaces can qualitatively be estimated.     

含硫充填体膨胀裂隙发育特性与单轴抗压强度的关联分析

含硫胶结充填体随着养护龄期的延长会出现膨胀开裂现象,存在明显裂隙的充填体试件再进行单轴抗压强度测试其结果十分离散,已不能有效地获得充填体力学参数.在室内进行配比试验,采用数字图像处理技术对得到的充填体表面裂隙图像进行二值化、去噪等预处理,而后计算其分形维数并分析其演化规律,且将分形维数与单轴抗压强度关联分析.研究结果表明：充填体试件面表的裂隙存在自相似性,表面裂隙越发育,其分形维数越大;分形维数与单轴抗压强度存在负相关关系,分形维数越小,其单轴抗压强度越高;分形维数可判别含硫充填体试件的完整性,当充填体表面裂隙的分形维数小于某阈值时,强度试验的结果更为可靠.     

Fractal analysis on the fatigue fracture surface along the crack propagation direction

The fractal dimension along the crack propagation direction on the fatigue fracture surface of a dual-phase steel was investigated by both vertical section profile method and secondary electron line scanning method. Results from the vertical section profile method showed that during the crack propagation, the fractal dimension of the fracture surface increases with increasing stress intensity factor, however, the secondary electron line scanning method presented somewhat different results of fractal dimension and was proved not feasible in all kinds of fracture surfaces, so this method is not suggested in calculating the fractal dimension of the fracture surface.     

风口回旋区的数字图像处理方法

风口回旋区对高炉及COREX熔化气化炉冶炼过程起着十分重要的作用,人们对风口回旋区进行了大量的试验与模拟研究.目前通过试验方法得到的风口回旋区仅仅是由若干个测量点确定.物理参数场可以用来准确确定回旋区边界,但是目前为止所有的研究风口回旋区的物理参数场都是由数值模拟确定,并且没有明确的回旋区的定义标准.在本研究中利用CO...     

高炉焦炭微观气孔结构演变及分形特征研究

为了研究孔结构对高炉焦炭降解过程的影响,通过溶损-转鼓实验分析了不同溶损焦炭的孔结构分形特征和微观组织结构变化.在此基础上,通过引入考虑分形特征的物料破碎方程,分析了焦炭降解能耗与表面分形维数之间的联系.结果表明:考虑分形特征的功耗方程可以较好地应用于冶金焦炭的降解过程中,焦炭降解能耗与分形维数之间存在明显的相关性,反...     

硫酸盐侵蚀作用下纤维锂渣混凝土裂缝的分形特征

为探究新型混凝土受硫酸盐侵蚀后的力学性能,采用质量分数为5%的硫酸盐溶液全浸泡加速侵蚀法,对11组聚丙烯纤维混凝土（PC）试块、11组聚丙烯纤维锂渣混凝土（PLiC）试块、8根PC大偏心受压柱和8根PLiC大偏心受压柱进行侵蚀试验,得到了不同侵蚀时间下混凝土的力学性能。基于分形理论分析了试块及构件破坏时表面裂缝分布的分形特征,详细讨论了试块及构件表面裂缝分形维数与其侵蚀时间、抗压强度、极限承载力之间的关系。研究表明,PC和PLiC立方体抗压强度随侵蚀天数先增加后降低,在120 d达到最大;试块及构件破坏时表面裂缝分布具有分形特征,试块表面裂缝分形维数随侵蚀天数的增加呈现先增加后减少再增加的规律,随试块抗压强度的提高而减少;PC及PLiC混凝土大偏心柱极限承载力随侵蚀天数的增加先增加后减少,锂渣的掺入可以提高聚丙烯纤维混凝土柱的抗硫酸盐侵蚀能力,构件破坏时表面裂缝分形维数随硫酸盐侵蚀天数呈现震荡上升的趋势;因此混凝土表面裂缝的分形特征可作为判定构件损伤程度的指标之一,可为今后对在役混凝土结构承载力和寿命预测提供参考。      

钒氮合金粉体的分形特征研究

粉体的物性特征对粉体性能和工程应用具有重大的影响,分形理论和显微图像分析技术的发展使得对于粉体物性特征的分析更全面、完善.针对在包芯线中应用的钒氮合金粉体,应用分形分析得到粉体粒度分布分形特征和颗粒形貌分形特征,表明钒氮合金粉体具有良好的分形特性,粉体流动性各表征参数与粒度分布分维有良好的相关关系;颗粒表面分维包含颗粒...     

Effects of Microwave Heating on Pore Fractal Properties of Blast Furnace Sludge

Effects of microwave heating on the pore fractal properties of blast furnace sludge (BFS) and relative mechanism were studied. The results show that the morphology features of iron bearing sinter and coke particles, which arc the main constituents of the BFS, were remarkably changed by microwave heating. The porosity, surface roughness and specific surface area of modified particle surface all increased obviously. Combining with fractal method called Sicrpinski model, the fractal dimensions of sinter, coke and others increased from 2.35, 2. 21 and 2. 58 to 2.65, 2.44 and 2.61 respectively, after modification by microwave heating. The results predicted that the reaction mechanism of microwave heating for BFS is related to two aspects. Different mineral phases existed in BFS particles incline to dissociate each other due to their different microwave absorbability; some recombination or reconstruction of matters or structure leads to structure defects, which have great influences on the surface morphology characteristics and chemical properties. The research indicated that fractal dimension can be used as an effective factor for quantitative analysis of the pore changes in morphology of the sludge. Furthermore, it is helpful for separation and extraction of valuable constituent from BFS.