脉冲鼓泡流化床压力波动特性的模拟

在分析脉冲气流作用下均匀鼓泡流化床的波动结构和波动机理的基础上,建立了反映其压力波动特性的二维离散单元模型。根据脉冲鼓泡流化床的特点,提出了模型离散单元的划分方法,确定了系统的模型参数。采用直接数值积分的方法,对床层的压力波动进行了模拟研究,计算与实验结果基本上一致。     

大颗粒鼓泡流化床压力脉动信号的小波分析

利用小波分析对试验所测得的大颗粒流化床的压力脉动信号进行小波包的完全分解,并对各个频段的信号的方差进行统计分析。结果表明,分解前后信号的能量是守恒的,脉动能随着流化数的增加逐渐集中在低频段;气泡经过测点的频率在0~12.5H z的范围内,且气泡的运动变化是影响测点压力数据波动的主要因素;通过分析流化床压力信号中的低频成分,可以判断床层物料的流化状态。     

鼓泡流化床中气泡行为的模拟

应用气体拟颗粒模型模拟了单孔、双孔分布板流化床的鼓泡现象,动态地显示了气泡生成、上升、长大以及破裂的全过程,结果与已知的实验观测基本一致.     

大颗粒流化床停留时间分布的研究

通过对流化床尿素造粒的冷模研究，对4种与尿素有类似流化特性的大颗粒物料在两级矩形流化床内的停留时间分布进行了系统的实验研究，分别考察了气速、床高（高径比）、粒径、物料流量等操作变量对停留时间分布的影响。气速是影响停留时间分布的主要因素，随着气速的增加，物料在床内的混合加剧，并同时伴有循环流。大颗粒床层混合程度较差时，更易出现腾涌现象。停留时间分布的测定为流化床造粒器的工业设计提供了基础数据。     

多种固体颗粒流化床（MSFB）的压力波动

在不同实验条件下研究了多种固体颗粒流化床（ＭＳＦＢ）的压力波动。研究的主要目的是找出粗颗粒对压力脉动的影响。压力波动的情况表明：粗颗粒床层的特性差异取决于有地细颗粒处于循环状态。     

鼓泡流化床内粉煤气化的数值模拟

将应用欧拉双流体模型对鼓泡气化炉内的气化过程进行研究。摒弃传统颗粒动理学理论中颗粒光滑无旋转的假设,引入颗粒的旋转运动,构建粗糙颗粒动理学理论来封闭双流体模型。基于燃烧理论建立粉煤热解、气化模型以及鼓泡床内气固之间以及气体和气体之间的传热、传质模型。采用该模型进行数值模拟计算,分析床内的气固反应过程,对比实验结果表明粗糙颗粒动理学理论适用于模拟鼓泡床气化炉内的反应。     

快速流化床中颗粒浓度及颗粒速度的径向分布

本文在φ140mm的气固并流下行快速流化床中,研究了颗粒浓度及颗粒速度的径向分布随操作气速、颗粒循环速率以及床层轴向位置的变化规律。并探讨了颗粒质量通量的径向分布及颗粒流动的均匀性,表明在相同操作条件下,下行快速流化床中气固流动远比上行快速流化床均匀。     

基于动态平衡预测纳米颗粒流化床内聚团尺寸分布

准确预测纳米颗粒流化床内聚团尺寸对研究纳米颗粒流化具有重要意义。鉴于目前文献中主要根据力平衡模型得出聚团尺寸平均值,然而聚团尺寸实际呈宽筛分分布,本工作从动态平衡角度,采用分子动理论中麦克斯韦气体速率分布律类比流化床内聚团速度分布,建立基于微观作用力的聚团解聚—重聚模型,并用以预测纳米颗粒流化床内聚团尺寸分布。通过比较聚团间结合力和分离力的相对大小,判断聚团结合和破碎;在分离力中,碰撞力起着至关重要的作用,且与聚团相对运动速度关系密切。预测结果显示,纳米颗粒流化床内聚团尺寸呈现卡方分布。将模型预测值和文献中的实验数据进行对比,包括TiO_2、Ni、SiO_2等颗粒的团聚尺寸,发现大部分偏差在20%以内。     

循环流化床提升管中固体颗粒停留时间的分布

在内径１４０ｍｍ，高１０ｍ的循环流化床提升管中，采用磷光颗粒示踪法对床内固体颗粒的停留时间分布进行了测定。在气速１．５～９．０ｍ／ｓ，固体循环量１０～１４０ｋｇ／ｍ２ｓ的范围内，实验测得的停留时间分布曲线均有明显的双峰分布。这种双峰分布是由于提升管中弥散颗粒和颗粒团共同作用的结果。本文提出的一维两组分扩散叠加模型可较好地描述提升管中固体的混合行为。考察了在实验条件下，操作条件对固体混合行为的影响。发现：气速及固含对颗粒的轴向Ｐｅｃｌｅｔ数影响不大，提升管中颗粒的返混主要是由于颗粒团引起的。将研究结果与近期文献报道的其他研究进行了对比     

利用压力脉动信号特征预测流化床结块故障

气固流化床压力脉动信号隐含了许多有用的信息。然而,压力脉动信号为一非平稳随机信号,非常复杂,必须用新的方法从信号中提取特征参数进行规律性研究。本文通过对流化床压力脉动信号进行Ｗｉｇｎｅｒ谱分析,得到了主频幅值的分布,提出了主频功率Ｐ作为流化床压力脉动信号的特征参数,并对随结块含量变化的规律进行了研究。结果表明,主频功率能充化床层的结块状况。在Φ１１４和Φ３００的流化床中证明该参数在床层结块时有明显     

基于颗粒流运动论的喷动流化床气固流动行为三维模拟

1 INTRODUCTION Spout-fluid beds have been of increasing interest in the petrochemical, chemical and metallurgic indus-tries since spout-fluid beds can reduce some of the limitations of both spouting and fluidization by su-perimposing the two type of systems[1―4]. In recent years, spout-fluid beds have become an alternative for gas/solid contactors in coal gasification. Spout-fluid bed coal gasifiers have been adopted for APFBC-CC (advanced pressurized fluidized bed combus-tion-combined…     

循环流化床提升管压力瞬时波动的功率谱分析

在φ0.4 m×9.1 m循环流化床提升管中,采集了分布板以上不同轴向高度的压力瞬时波动信号,并采用功率谱进行分析。分析发现,压力瞬时波动功率谱谱图中存在一个振幅最大点,即为主频。增大固体颗粒循环速率或减小提升管操作气速,主频对应振幅增大,而功率谱主频减小。相同操作条件下,随轴向位置的增高,压力瞬时波动的主频基本不变,而主频对应振幅减小。     

Size distribution of the particles entrained from fluidized beds: Gas humidity effects

Experimental results obtained with 65 μm sand and 69 μm cracking catalyst showed that the smallest particles were not the most easily elutriated from fluidized beds of mixed size particles. This is in contradiction with the assumption applied to existing models for the prediction of the flux and size distribution of particles elutriated from a fluidized bed. The smallest particles cannot be removed by elutriation from a mixture of particles of various sizes. The smallest particles may be agglomerated with larger particles. Increasing the gas humidity, which would presumably reduce electrostatic effects, did not greatly affect the size distribution of the elutriated particles.     

炭粒床高效工业除尘装置的设计与开发

The new dust removal technical route using the carbon-granular bed filter, packed of carbon particles with appropriate grade derive from an online-process vibration sieve, to replace the traditional baggy filter had been developed successfully for capturing the micro-carbon dusts produced from pulverization of petroleum coke,and the green close loop of carbon materials is thus completed in the combined pulverizing and classifying system and pulverized carbon dust removal process. The high dust removal efficiency greater than 99%, low outlet dust concentration less than 100 mg-m-S, low pressure drop through dust filtration chamber less than 980 Pa, simple and easy design, and flexible and stable operation were achieved also with the carbon-granular bed filter in both bench and industrial scale operations.     

Bubbles in a fluidized bed: A fast X‐ray scanner

We present experiments on a bubble train in a 23‐cm‐diameter fluidized bed of a Geldart B powder. The bubbles are injected via a single capillary inserted in the bed. We use our double X‐ray tomographic scanner to measure the solids distribution in two parallel cross sections of the bed. We report data for four different heights of the measuring planes above the capillary outlet. The velocity of individual bubbles is found from the time of flight from the lower to the upper plane. We have done separate calibration experiments for the velocity. In this article, we present data for the size and velocity of individual bubbles. From the bubble velocity, we could obtain the vertical dimension of the bubbles. This makes it possible to measure the volume of each bubble. The results show that our scanner is capable of measuring properties of bubbles with a size of 2.5 cm and above. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Axial segregation in bubbling gas‐fluidized beds with Gaussian and lognormal distributions of Geldart Group B particles

Bubbling, gas‐fluidized bed experiments involving Geldart Group B particles with continuous‐size distributions have been carried out. Sand of various widths of Gaussian or lognormal distributions were completely fluidized, then axial concentration profiles were obtained from frozen‐bed sectioning. Similar to previous works on binary systems, results show that mean particle diameter decreases with increasing bed height, and that wider Gaussian distributions show increased segregation extents. Surprisingly, however, lognormal distributions exhibit a nonmonotonic segregation trend with respect to distribution widths. In addition, the shape of the local‐size distribution is largely preserved with respect to that of the overall distribution. These findings on the nature of local‐size distribution provide experimental confirmation of previous results for granular and gas‐solid simulations. Lastly, an interesting observation is that although monodisperse Geldart Group D particles cannot be completely fluidized, their presence in lognormal distributions investigated still results in complete fluidization of all particles. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Time-series analysis of the characteristic pressure fluctuations in a conical fluidized bed with negative pressure

The negative pressure conical fluidized bed is widely used in the pharmaceutical industry. In this study, experiments based on the negative pressure conical fluidized bed are carried out by changing the material mass and particle size. The pressure fluctuation signals are analyzed by the time and the frequency domain methods. A method for absolutely characterizing the degree of the energy concentration at the main fre-quency is proposed, where the calculation is to divide the original power spectrum by the average signal power. A phenomenon where the gas velocity curve temporarily stops growing is observed when the mate-rial mass is light, and the particle size is small. The standard deviation and kurtosis both rapidly change at the minimum fluidization velocity and thus can be used to determine the flow regime, and the variation rule of the kurtosis is independent of both the material mass and particle size. In the initial fluidization stage, the dominant pressure signal comes from the material movement;with the increase in the gas veloc-ity, the power of a 2.5 Hz signal continues to increase. A method of dividing the main frequency by the aver-age cycle frequency can conveniently determine the fluidized state, and a novel concept called stable fluidized zone proposed in this paper can be obtained. Controlling the gas velocity within the stable flu-idized zone ensures that the fluidized bed consistently remains in a stable fluidized state.     

Link between bubbling and segregation patterns in gas‐fluidized beds with continuous size distributions

Experiments involving a bubbling, gas‐fluidized bed with Gaussian and lognormal particle‐size distributions (PSDs) of Geldart Group B particles have been carried out, with a focus on bubble measurements. Previous work in the same systems indicated the degree of axial species segregation varies non‐monotonically with respect to the width of lognormal distributions. Given the widely accepted view of bubbles as “mixing agents,” the initial expectation was that bubble characteristics would be similarly non‐monotonic. Surprisingly, results show that measured bubble parameters (frequency, velocity, and chord length) increase monotonically with increasing width for all PSDs investigated. Closer inspection reveals a bubble‐less bottom region for the segregated systems, despite the bed being fully fluidized. More specifically, results indicate that, the larger the bubble‐less layer is, the more segregated the system becomes. The direct comparison between bubbling and segregation patterns performed provides a more complete physical picture of the link between the two phenomena. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

水平管内气液段塞流液塞长度发展规律的实验和模拟研究

In petroleum industry, the slug flow is a fre-quently encountered flow regime in multiphase flowpipeline. For pipeline designers, the liquid slug lengthdistribution is important for the proper design ofdownstream facilities, such as slug catcher and sepa-ration system. However, for its transient and unsteadynature, it is a great challenge for engineers to correctlypredict the flow parameters of slug flow, especiallythe maximum liquid slug length. The unit cell model for slug flow in horizontal…