石英砂流化床床料的磨损实验与灰色关联分析

针对工业装置运行中的实际问题,在综合热态流化床实验台上研究了不同运行参数下石英砂的磨损规律.实验的设计采用正交实验方法,研究不同运行参数（初始颗粒平均直径、床温、流化数、床料高度）对石英砂床料磨损的影响并作灰色关联分析,得到各运行参数的影响程度排序为：初始颗粒平均直径>床温>流化数>床料高度.     

流化床数学模型进展

本文回顾了近代流化床反应器数学模型的发展状况，比较了三类主要模型的优缺点，提出了不同模型的应用范围及以后的发展方向。     

增压流化床燃煤锅炉数学模型

以某 6 0t·h^-1增压流化床锅炉为对象 ,建立了动态数学模型 .模型采用了分小室和分段结合的离散化方法 ,以反映沿炉膛高度方向上温度的分布特性 ;通过描述密相床内不同相区间的气体交换现象 ,使得模型能够模拟氧气通过气泡短路通过密相床的现象 ;以动态固体质量平衡、氧质量平衡、碳质量平衡和总体能量平衡为主体建立动态数学模型 .模型稳态计算结果与实际电厂的运行数据对比 ,表明模型具有一定的定量准确性 .文中最后对快排床料的动态过程进行了仿真和分析 ,结果表明所建模型可以模拟“快加快排”这种增压流化床特有的变负荷方式 ,也较为本质地反映了增压流化床的燃烧机制     

流化床内石英砂的热破碎及其灰色预测模型

在热态流化床实验台上进行了流化床床料-石英砂的热破碎实验,实验中考虑了初始颗粒尺寸（2.5～6 mm）和床温(650～950℃)对破碎的影响。研究发现,随着床温的升高和颗粒初始尺寸的增大破碎指数Sf明显增大。当床温低于650℃时,Sf＜2,表明在此床温下颗粒基本不发生破碎现象。破碎后的粒度分析表明石英砂的破碎是在表面进行的,破碎的主要动力是温度梯度引起的在颗粒表面产生的压应力。基于灰色系统理论建立了关于预测床料破碎的灰色模型GM(1,3),预测结果与实验数据对比表明该预测模型精度较高,预测平均误差为8.79%。应用灰色模型GM(1,3) 预测了一定床温下颗粒破碎的临界破碎直径。     

流化床干燥玉米数学模型的讨论

对流化床干燥玉米的试验数据进行了理论分析，利用Page方程和扩散方程拟合试验数据，得到了流化床干燥玉米的数学模型，并将两种模型进行了分析比较。     

循环流化床燃烧数学模型

介绍了有关文献中循环流化床燃烧的数学模型。按照各模型所使用的流体动力学模型的差异，将它们分成了不同的类别。同时也简要介绍了几种目前应用于循环流化就数学模型的气固两相流数值模拟方法。在评述各模型的优缺点和分析目前所存在问题的基础上，初步提出了进一步发展的方向。     

循环流化床流动数学模型综述

综述了有关循环流化床内气固两相流动的数学模型,包括欧拉坐标系下的两相流体模型以及近年来兴起的颗粒动力学双流体模型、基于拉格朗日坐标下的颗粒轨道模型、被很多学者应用的“小室模型”等,对由这些基本模型发展出的更新的一些模型进行了分类,并比较了其各自优缺点,提出了可能的发展方向。     

A model on attrition of quartzite particles as a bed material in fluidized beds

In this paper, a model on attrition of quartzite particles as an inert bed material in fluidized beds has been established on the particle-particle collision. For the convenience of describing the attrition of quartzite particles in fluidized beds, we chose the attrition rate constant (k_ARC) as one main characteristic parameter to develop the model.In order to verify the validity of the developed model, an attrition experiment of quartzite particles has been carried out in a lab-scale circulating fluidized bed. The predicted results from the population model were close to the experimental data as far as the engineering use is concerned. Finally, a sensitivity analysis was performed by using the developed model to examine effects of initial particle diameter, attrition time, and fluidization number on k_ARC.     

石英砂热形态和表面微观结构

使用由德国生产的LEIAZ-ⅡA型高温热显微镜对异密度循环流化床床料——石英砂在加热过程中所表现出的熔融特性和热膨胀特性进行了研究。高纯度石英砂在升温过程（室温～1600℃）中存在3个相对独立的特征温度区间：缓慢膨胀区（室温～870℃），在此区间试样尺寸变化比较均匀，线膨胀速率k比较小；膨胀停滞区(1000～1350℃)内，试样的体积和形状几乎不随温度的升高而改变，k在此区间近于零；快速膨胀区(1400～1550℃)内，k在此区间突然增大，形成一个陡峭的波峰。升温过程中高纯度石英砂试样的膨胀特性与其多晶型转变温度有对应关系。通过不同纯度两个试样的对比实验发现，纯度直接影响石英砂的熔融特性，纯度高，则相应的特征温度值高。利用HITACHI S2150型扫描电子显微镜（SEM）对加热到不同终端温度并冷却到室温的高纯度石英砂颗粒亚稳相的微米级表面结构进行观察，当终端温度进入快速膨胀区后，试样由于剧烈的膨胀在表面和内部产生大量微观裂纹，大量微观裂纹的存在导致试样的力学性能急剧下降，表现为弹性能力的消失。     

汽-液-固循环流化床蒸发器颗粒磨损特性

在不同循环流量和固含率条件下,通过1～2个月的操作运行实验,得到了汽-液-固三相循环流化床蒸发器内聚乙烯颗粒的磨损产物,分析了三相流化床的固含率和循环流量等条件对颗粒磨损速率、磨损粉体的直径和多分散度的影响,并探讨了颗粒磨损的机理。结果表明：磨损产物的粒径呈现三峰对数-正态分布,具有混合磨损机理特征;颗粒的磨损速率随固含率的减小和循环流量的增加而增大;较低固含率条件下,循环流量对颗粒的磨损速率影响较大;磨损速率随着运行时间的延长而减小;磨损粉体的粒径随固含率、循环流量、磨损时间的增加而减小;磨损颗粒的多分散度随固含率和循环流量的增加而减小。     

Effect of the grid-velocity on attrition in gas fluidized beds

Changes in particle size distribution play an important role in fluidized bed processes, and these changes are dominated by elutriation and carryover of fines and by attrition or agglomeration. In this study on attrition in gas-fluidized beds, we found that the attrition is a function of the particle size distribution, the jet velocities and the overall superficial gas velocity. Empirical equations have been developed to predict the attrition rate.     

Sulphation of limestones in a fluidized bed combustor: The relationship between particle attrition and microstructure

Sulphation of two limestones in a fluidized bed combustor has been investigated. One limestone (coarse‐grained) was characterized by a significant population of relatively large pores after calcination; the other (fine‐grained) presented a finer and fairly unimodal pore size distribution. Differences in the microstructure were reflected by different thickness of the sulphate shell formed upon sulphation and ultimate calcium conversion degree. Particle attrition/fragmentation were fairly small under moderately bubbling fluidization conditions. Fragmentation upon impact was significant. The fine‐grained limestone, characterized by a thinner sulphate shell, was more susceptible to fragmentation than the other. Particle fragmentation discloses unreacted CaO enabling secondary sulphation of exhausted particles.     

Particle attrition mechanism with a sonic gas jet injected into a fluidized bed

High velocity gas jets in fluidized beds provide substantial particle attrition: they are used industrially to control the particle size in fluid bed cokers and to grind products such as toner, pharmaceutical or pigment powders. One method to control the size of the particles in the bed is to use an attrition nozzle, which injects high velocity gas and grinds the particles together. An important aspect of particle attrition is the understanding and modeling of the particle breakage mechanisms. The objective of this study is to develop a model to describe particle attrition when a sonic velocity gas jet is injected into a fluidized bed, and to verify the results using experimental data. The model predicts the particle size distribution of ground particles, the particle breakage frequency, and the proportion of original particles in the bed which were not ground. It was found that the particle breakage frequency can be used to predict the attrition results in different bed sizes. A correlation was also developed, which uses the attrition nozzle operating conditions such as gas density and equivalent speed of sound to predict the mass of particles broken per unit time.     

Modelling fast pyrolysis of biomass in a fluidized bed reactor

A compartmental one-dimensional model of a fluidized bed pyrolytic converter of biomass is presented. Reference conditions are those of non-catalytic fast pyrolysis of biomass in a shallow fluidized bed with external regeneration of the bed material. The fate of biomass and of the resulting char has been modelled by considering elutriation of biomass and char particles, char attrition as well as bed drain/regeneration. The course of primary and secondary pyrolitic reactions is modelled according to a semi-lumped reaction network using well-established kinetic parameters taken from the literature. A specific focus of the present study is the role of the heterogeneous volatile–char secondary reactions, whose rate has been modelled by borrowing a kinetic expression from the neighbouring area of tar adsorption/decomposition over char. The results of computations highlight the relevance of heterogeneous volatile–char secondary reactions and of the closely associated control of char loading in the bed. The sensitivity of the reactor performance to char elutriation and attrition, to proper management of bed drain/regeneration, and to control of gas phase backmixing is demonstrated. Model results provide useful guidelines for optimal design and control of fluidized bed pyrolyzers and pinpoint future research priorities.