超细颗粒表面改性后床层塌落行为研究

在直径为56mm的磁流化床中采用小粒径SiO2颗粒对微米级淀粉颗粒进行包裹，在鼓泡流化床中考察包裹后淀粉颗粒的床层塌落行为。实验表明，包裹后淀粉颗粒的床层塌落行为不同于未包裹的淀粉颗粒和Geldart A类颗粒。包裹后淀粉颗粒间粘性力减小，床层滞气能力降低，床层塌落高度增加，揭示磁流化床包裹实验中客体颗粒SiO2存在合适添加比例．证明表面改性是改善超细颗粒流化行为的有效手段。     

冰冻氢氧化铝凝胶法制取氧化铝超细颗粒

根据物理化学原理研究在不同的温度下制取氢氧化铝凝胶,经过冷冻法后脫水,煅烧制取氧化铝超细颗粒的过程。实验证实了采用冰冻凝胶法制取工艺后, 形成了多孔、质地疏松的α-Al_2O_3超细颗粒的可行性。本研究所获得的超细颗粒均小于0.1μm。这种工艺的成功有可能使我国超细颗粒的制备从实验室步入工业化。     

细颗粒振动流态化行为的二维床观察

本文利用一种新型复合振动充化装置，使在一般操作条件下无法实现正常流化的细颗粒床层处于良好的流化状态。通过观察发现，振动的引入可以破坏沟流的存在而使细颗粒流化；其振动流化有三种存在形式，提出了振动流化的物理模型和流化相同，可以解释细颗流化状态与振动条件及其物性的关系。     

基于直接矩积分方法的超细颗粒流态化特性研究

采用欧拉-欧拉气固双流体模型,基于颗粒动理学理论,利用直接矩积分方法求解颗粒数平衡方程,建立颗粒数量与连续性方程、动量方程之间的关系,数值模拟流化床内不同初始粒径的超细颗粒运动、聚并的动态过程,给出了聚团在流动过程中浓度和速度的分布情况,展示了床内各阶矩的变化情况,比较了不同初始粒径对聚团浓度分布影响。研究表明,同一粒径颗粒,随着床层高度的增加,颗粒浓度达到平衡状态需要的时间减短;不同粒径颗粒,随着初始粒径的增加,颗粒浓度减小的速率随着床层高度上升加快,颗粒聚团尺寸达到稳定状态的时间减少,床内颗粒速度逐渐减小,聚团向床层底部聚集的速度增加,床层底部颗粒浓度和颗粒粒径逐渐增加。     

工程相变凝并器内超细颗粒长大与脱除性能分析

传统的除尘系统脱除粗颗粒效率高，而脱除超细颗粒效率非常低，我国燃煤电厂脱除超细颗粒效率无法达到国家标准。湿式相变凝并技术是脱除烟气中超细颗粒的新技术。考虑颗粒性质以及通风因子，改进了超细颗粒凝并长大数学模型。将改进的数学模型写入颗粒群平衡模型中，模拟对比了超细颗粒在管束型相变凝并器和波纹板型相变凝并器内的长大特性及脱除效率。结果表明，两种相变凝并器都能明显提高超细颗粒的脱除效率，但管束型相变凝并器对烟气的冷却效果比波纹板型相变凝并器好。管束型相变凝并器能促进颗粒长大7.71倍，是波纹板型相变凝并器的1.4倍。管束型相变凝并器对颗粒数量浓度脱除效率高达64.7%，而波纹板型相变凝并器对颗粒数量浓度脱除效率为27.2%。     

洗涤塔脱除燃烧源超细颗粒的实验研究

在填料洗涤塔中进行了利用蒸汽相变原理促进燃煤和燃油超细颗粒凝结长大并高效脱除的实验研究;采用电称低压冲击器(ELPI)、SEM及XPS对两种燃烧源细颗粒凝结洗涤前后的数浓度、粒径分布、形貌和元素组分进行了分析测试,考察了洗涤塔进口气液温差、进口烟气含湿量及液气比等对脱除效率的影响。结果表明,燃煤和燃油产生的超细颗粒形貌和组分具有较大的差别,燃煤超细颗粒主要为硅铝矿物质,而燃油超细颗粒主要为含炭物质;在相同条件下,燃煤超细颗粒相变脱除效果优于燃油超细颗粒;脱除效率随洗涤塔进口气液温差的增大而提高,在相同进口气液温差下,增大进口烟气含湿量可显著提高超细颗粒的脱除效率;液气比的影响与填料洗涤塔内是否存在蒸汽相变有关;通过合理调节进口烟气含湿量及进口烟气与洗涤液的温差在填料塔内建立微粒凝结长大所需的过饱和水汽环境可有效脱除燃烧源超细颗粒。     

洗涤塔内相变脱除燃煤超细颗粒的试验研究

为研究洗涤塔内相变对燃煤超细颗粒的脱除,在洗涤塔液相进口上方注入蒸汽使烟气达到过饱和,由高效除雾器脱除凝并长大的含尘液滴。系统研究了蒸汽添加量、洗涤塔入口气液温差、液气体积比、烟气在相变区域的停留时间等操作参数对燃煤超细颗粒脱除效率的影响规律。结果表明:在塔内添加少量蒸汽,可显著促进燃煤超细颗粒的脱除,蒸汽添加质量浓度为0.03 kg/m3时,数量浓度脱除效率由10%增至60%以上;液气体积比的提高有利于燃煤超细颗粒的脱除,特别是当洗涤塔入口气液温差较大时。研究结果表明利用洗涤塔内相变脱除燃煤细颗粒是一种有应用前景的新方法。     

超细颗粒的制备及应用

超细颗粒的出现对国民经济许多行业的应用研究有着举足轻重的影响，较详细地介绍了超细颗粒的各种制备方法及其在化工，电子，陶瓷，生的医学领域的应用实例，并探讨了颗粒技术的研究方向。     

超细颗粒聚团流化的临界流化速度

在内径50 mm的流化床实验台上,测量SiO_2、Al_2O_3和TiO_2 3种超细颗粒原生粒径从30 nm增加到5μm的临界流化速度(Umf),并以Geldart A类颗粒(粒径45μm)为参照。结果表明:3种超细颗粒的Umf随粒径的变化规律一致,随原生粒径从30 nm增加到5μm,Umf逐渐增大;当颗粒粒径增加到45μm,Umf大幅度减小,其与原生粒径为30和200 nm时接近。对于不同材料,Umf由大至小的顺序依次为TiO_2、Al_2O_3、SiO_2。粉体安息角测量表明:对于同种材料颗粒,原生粒径对超细颗粒的Umf和安息角的影响规律一致,即5μm超细颗粒的安息角最大。聚团尺寸模型计算表明:稳定流化时,聚团尺寸随原生粒径的变化趋势以及随不同材料的变化趋势均与Umf的变化趋势一致。研究结果为超细颗粒流化临界速度预测研究奠定了基础。     

声场流化床流动特性研究进展

声场流化床是将声场引入普通流化床,采用颗粒为床层介质的流固相处理系统。声波可以有效降低颗粒聚团尺寸,显著改善超细颗粒的流化质量。本文介绍了声场流化床的基本原理以及近年来在基础研究和应用方面取得的进展及成果,综述了声场流化床在流体力学特性、颗粒特性、声场参数、流态化模型、颗粒团聚以及流化质量机理等方面的研究,并对声场流化床目前存在的问题及发展趋势提出了一些建议。     

纳米TiO2颗粒在声场流化床中的流化特性

以原生纳米级TiO2颗粒为物料，在内径为130mm的声场流化床中，考察声压、频率对纳米颗粒的流化特性的影响。结果表明，适当的低频强声波的引入能很好的抑制沟流，消除节涌，大大降低了流化床中纳米颗粒聚团的尺寸，使之在低气速下实现稳定流化，从而显著改善纳米颗粒的流化质量。     

Parametric study of fine particle fluidization under mechanical vibration

Investigations into the effects of vibration on fluidization of fine particles (4.8-216 μm average in size) show that the fluidization quality of fine particles can be enhanced under mechanical vibration, leading to larger bed pressure drops at low superficial gas velocities and lower values of u_mf. The effectiveness of vibration on improving fluidization is strongly dependent on the properties (Geldart particle type, size-distribution and shape) of the primary particles used and the vibration parameters (frequency, amplitude and angle) applied. The possible roles of mechanical vibration in fine particle fluidization have been studied with respect to bed voidage, pressure drop, agglomeration, and tensile strength of particle bed. Vibration is found to significantly reduce both the average size and the segregation of agglomerates in the bed, thus improving the fluidization quality of cohesive particles. Also, vibration can dramatically reduce the tensile strength of the particle bed. Obviously, vibration is an effective means to overcome the interparticle forces of fine powders in fluidization and enhance their fluidization quality.     

A study of agglomeration of coal-ash in fluidized beds

Experimental data on agglomeration of coal-ash particles in a fluidized bed have been presented. It has been observed that above the “initial sintering temperature”, the ash particles are defluidized at velocities above their minimum fluidization velocity. The expression for minimum fluidization velocity has been modified by including a force-term due to the phenomenon of sintering in addition to those due to drag, gravity and kinetic energy.     

Factors affecting methanol photocatalytic oxidation and catalyst attrition in a fluidized-bed reactor

A resolution IV fractional factorial experimental design explored the effects of seven factors on both the methanol photocatalytic oxidation (PCO) rate and the catalyst particle size distribution using a fluidized-bed reactor. The seven factors were as follows: calcination temperature, calcination time, grinding order, particle size, vibration amplitude, carrier gas humidity, and fluidization velocity. Decreasing calcination temperature from 726 to 623 K increased the activity of TiO₂/Al₂O₃ catalysts for methanol PCO. Attrition during fluidization liberated small TiO₂ particles from the bulk catalyst and the rate of attrition increased with gas velocity. Attrition was the primary cause of catalyst elutriation and not the presence of fine particles initially present in the bed from catalyst preparation. Increasing humidity caused agglomeration of fine particles, which reduced the amount of catalyst carryover. Removal of fines from the catalyst bed prior to fluidization caused an increase in catalyst attrition until the amount of fines present in the bed was similar to that of a bed in which fines were not removed.     

黏性颗粒流态化的气固流动模型研究进展

黏性颗粒间存在较强的范德华力、液体桥力、静电力等黏附力作用,在流态化时易发生聚团现象,影响流化床的正常操作. 连续介质模型、离散颗粒模型和拟颗粒模型用于研究颗粒聚团流态化行为时各有优缺点. 基于欧拉方法的连续介质模型无法具体描述颗粒间的相互作用;采用拉格朗日法则能从颗粒微观受力、颗粒碰撞、聚团流动等多尺度研究黏性颗粒的流态化特性. 但受限于巨大的运算量,离散颗粒模型模拟的颗粒数有限,拟颗粒模型目前仅适合处理纳微尺度问题. 随着高性能计算机的发展和普及,基于拉格朗日法的黏性颗粒流动模型应用前景广阔.     

微细粉体在振动流化床中团聚行为的研究

本文研究了微细粉体在振动流化床中的团聚行为和振动参数对团聚物尺寸的影响。观察了床层流化现象,并发展了团聚物的测量方法。提出了Ｃ类粉体振动流化的团聚机理。     

Review on the nanoparticle fluidization science and technology

Gas fluidization has an ability to turn static particles to fluid-like dense flow, which allows greatly improved heat transfer among porous powders and highly efficient solid processing to become reality. As the rising star of current scientific research, some nanoparticles can also be fluidized in the form of agglomerates, with sizes ranging from tens to hundreds of microns. Herein, we have reviewed the recent progress on nanomaterial agglomeration and their fluidization behavior, the assisted techniques to enhance the fluidization of nanomaterials, including some mechanical measures, external fields and improved gas injections, as well as their effects on solid fluidization and mixing behaviors. Most of these techniques are effective in breaking large agglomerates and promoting particulate fluidization, meanwhile, the solid mixing is intensified under assisted fluidization. The applications of nanofluidization in nanostructured material production and sustainable chemical industry are further presented. In summary, the fluidization science of multidimensional, multicomponent and multifunctional particles, theirmulti-phase characterization, and the guideline of fluidized bed coupled process are prerequisites for the sustainable development of fluidized bed based materials, energy and chemical industry.     

Effect of agitation on fluidization characteristics of fine particles in a fluidized bed

The effect of agitation on the fluidization characteristics of fine particles was investigated in a fluidized bed with an I.D. of 6 cm and a height of 70 cm. The agitator used was of the pitched-blade turbine type and phosphor particles were employed as the bed material. The particle size was 22 μm and the particle density was 3938 kg/m³. The effect of the agitation speed on the fluidization characteristics was examined by statistical (average absolute deviation (AAD), probability density function (PDF)), spectral (auto-correlation function, power spectrum) and chaos analysis (strange attractor, Hurst exponent, correlation dimension). The results showed that smoother fluidization was observed with increasing agitation speed, because the agglomeration and channeling were reduced by the mechanical agitation. The signals of the pressure drop fluctuation had the shape of a short-term correlation with different agitation speed. The void fraction increased with increasing agitation speed at the constant fluidizing gas velocity.     

The effects of agglomeration/defluidization on emission of heavy metals for various fluidized parameters in fluidized-bed incineration

The agglomeration/defluidization may be produced to generate the secondary pollutant during incineration. However, the effects of agglomeration/defluidization on heavy metal distribution have rarely been examined. Therefore, the effects of the agglomeration/defluidization process on heavy metal emission in flue gas are studied. The artificial waste is employed to simulate municipal waste and to form agglomerates, which contain alkali metals, earth alkali metals, a mixture of metals (Pb, Cr and Cd) and sawdust. The fluidized parameters (including gas velocity, sand particle size and static bed height) are varied to determine their influences on heavy metal emission. The results indicate that addition of Na increases the risk of agglomeration/defluidization, but the emission concentration of heavy metals decreases during agglomeration/defluidization. The heavy metals may react with Na to form the eutectics or are covered and adhered by the liquid-phase eutectics of Na to stay in sand particle and lead to a decrease in the emission of heavy metals.The system was operated at a low gas velocity that not only easily resulted in agglomeration/defluidization but also increased the emission concentration of heavy metals. Large particles (920 μm), which have a poor fluidized quality, had the highest emission concentration. Small particles (645 μm) were uniformly fluidized to enhance the fluidization quality and to decrease the emission concentration. Additionally, adding Ca did not decrease the heavy metal emission concentration, but maintained the fluidization during eutectic accumulation. The Ca prevented the sand bed from quickly achieving defluidization and prolonged the increased emission of heavy metals after defluidization.