碳纤维复合材料回收装置中物料停留时间研究

为保证所回收的碳纤维能及时有效地被排出,用EPE泡沫为示踪物料,在建立热氧裂解法回收碳纤维的装置上,用实验法测定了卧式流化床反应器的流化曲线。经分析流化曲线得出临界流化速度和带出速度并经公式计算确定了临界流化速度和带出速度,考察不同形状物料及混合物料在主反应器内的停留时间。结果表明,流化床内临界流化速度为0.15m/s,颗粒带出速度为0.24m/s;物料形状对其在床内停留时间影响较大;单一形状物料在流化床内停留时间由长到短依次为圆柱体、长方体和球体;球体物料最易排出;混合物料在床内停留时间由长到短依次为球体与圆柱体混合物料、长方体与球体混合物料和长方体与圆柱体混合物料;长方体与圆柱体混合物易排出;为使回收碳纤维尽快排出流化床,可采用长方体和圆柱体混合物料或单一的球形物料进行热试验研究。     

带流动密封阀的循环流化床的研究

在自行设计的循环流化床装置中,测定了床层阻力特性、临界流化速度和带出速度,考察了流动密封阀充气量、流化床流化气速以及装料量对流动密封阀流动特性的影响。结果表明,临界流化速度和带出速度与装料量无关,装料量在700 g左右时,流化系统稳定性高。适度提高流化密封阀底部充气量、流化床流化气速和装料量能够提高物料循环流率。     

大颗粒振动流化床颗粒临界流化速度研究

建立了带内置水平管的振动流化床,并以颗粒状磷酸一铵为实验物料对带内置水平管的大颗粒振动流化床颗粒临界流化速度进行了实验研究。结果表明,振动的引入对颗粒临界流化速度有着明显的降低作用;同样床层条件下振动频率和振幅越大,床层临界流化速度越低;振动对小粒径颗粒的影响稍强于大粒径颗粒;由实验数据拟合出用于预测该类流化床临界流化速度的经验公式,公式与实验数据吻合良好。     

高温流化床中IHI灰样的临界流化速度研究

在D82的不锈钢高温流化床实验台中,以IHI灰样作为实验物料,研究了高温流化床的临界流化速度,结果表明,对于属于B类粒子的IHI灰样,温度由常温升高于1000℃时,雷诺数小于40,流化床运动处于层流运动区范围,随着床层温度升高,物料颗粒的最小流化速度减小,根据实验结果提出了预测不同温度下的该灰样题粒最小流化速度式。     

宽粒度分布颗粒临界流化特性研究

在二维流化床(240mm×80mm)中,以平均粒径为1.675mm的三种宽筛分玻璃珠颗粒为物料,研究了颗粒临界流化特性,得到了三种颗粒临界流化速度,并与其他研究者的结果进行了对比,通过实验数据得到了预测宽筛分颗粒临界流化速度的关联式.结果表明,宽筛分颗粒临界流化速度与窄筛分颗粒的值有较大差别,本研究理论预测的临界流化速度与实验值吻合更好。结果可为宽组分颗粒临界流化特性研究提供参考。     

过热蒸汽流化床流化特性的实验研究

在底部直径为120 mm的锥型流化床中,以玻璃珠为流化颗粒,过热蒸汽为流化介质,研究了固体颗粒在过热蒸汽流化床中的流化特性,考察了操作温度和压力对临界流化速度(umf)的影响.结果表明,过热蒸汽流化床的流化行为与热空气相似,临界流化速度(umf)随床层温度的升高而减小,随床内压力的增大而减小;在相同温度条件下,过热蒸汽流化床的临界流化速度比热空气大.     

振动流化床临界流化速度理论预测与实验研究

根据振动流化床床层动力学特性,提出了第一、第二流化段,第一、第二临界流化速度的概念.从流化床临界流化速度的定义出发,得出了振动流化床第一临界流化速度数学模型.在二维振动流化床内,以不同粒径的玻璃珠为床料进行实验研究,分析了振动和其它操作条件对临界流化速度的影响,通过实验数据关联得到了振动能量传递系数的数学表达式,并将模型预测与实验结果进行了对比.结果表明振动强度增加,第一、第二临界速度均减小,振动对第一临界流化速度影响更显著,当振动强度超过1.57后,不通气体床层也能流化,第一临界流化速度降为零,模型预测与实验结果有较好的一致性.     

工业废盐的流态化行为

目前工业废盐的处理方式较为单一,效果不理想。为了解决这一问题,提出了一种可用于处理工业废盐的流化床装置,采用自制的流化床对工业废盐进行流化,并对气固流化床的压力脉动信号进行实时监测,研究了流化数和床层压力波动的关系。介绍了温度对流化床临界流化速度的影响,并提出了临界流化速度与温度的关联式。对流化过程中产生的气泡进行了研究,讨论了气泡运动过程中的形貌和大小。介绍了一种可以考察床层物料流化效果的方法,并运用Improfile函数将三维空间内物料颗粒的混合情况转化为函数,通过强度和时间关系说明了返混程度的强弱。描述了工业废盐的床层塌落过程,最后通过扫描电镜对工业废盐表面上的有机物进行比较得出流化床处理工业废盐的可能性。     

气固搅拌流化床流化和干燥特性实验研究

通过测定不同搅拌速度、床层高度下床层压降与表观气速间的关系,研究了水平桨气固搅拌流化床的流化特性。实验表明,搅拌增强了气固接触,明显改善了流化床的流化质量。对不同气速、不同搅拌速度下气固流化床的干燥特性进行了实验研究,结果表明,搅拌能加快流化床的传热速率,提高干燥速度。     

湿污泥颗粒的流化床干燥实验及模型

在鼓泡流化床内以河砂为干燥介质,对单颗粒湿污泥的流态化干燥特性进行实验研究,得到了流化床温度、污泥初始水分、污泥粒径及流化速度对干燥速率的影响规律：流化床温度及污泥粒径对干燥速率的影响都呈指数规律;污泥的水分越大,干燥速率越大;在鼓泡流化床流化速度达到2倍临界流化速度以上时,充分流化,流化速度再增大(2~5倍临界流化速度)对干燥速率没有明显影响. 在基本的扩散传质理论的基础上,利用实验数据回归得到湿污泥在鼓泡流化床内干燥的半经验模型,为流化床污泥干燥器的设计提供了基础数据和依据.     

Simulation of bubbling fluidized bed of fine particles using CFD

Computational fluid dynamics (CFD) simulation for bubbling fluidized bed of fine particles was carried out. The reliability and accuracy of CFD simulation was investigated by comparison with experimental data. The experimental facility of the fluidized bed was 6 cm in diameter and 70 cm in height and an agitator of pitched-blade turbine type was installed to prevent severe agglomeration of fine particles. Phosphor particles were employed as the bed material. Particle size was 22 μm and particle density was 3,938 kg/m³. CFD simulation was carried by two-fluid module which was composed of viscosity input model and fan model. CFD simulation and experiment were carried out by changing the fluidizing gas velocity and agitation velocity. The results showed that CFD simulation results in this study showed good agreement with experimental data. From results of CFD simulation, it was observed that the agitation prevents agglomeration of fine particles in a fluidized bed.     

气固移动流化床干燥器流化与传热特性研究

以不同粒径的分子筛颗粒与炼焦煤颗粒为原料分别在气固移动流化床干燥器内进行了双组分颗粒分级流化行为特性与气固间传热特性的实验研究。考察操作气速、颗粒直径与不同粒径配比的变化以及搅拌转速对床层阻力的影响,并对流化状态加以描述分析,研究了干燥器气固间传热特性,得出了相应的表面传热系数关联式,计算值与实验值的误差小于15％。     

气固搅拌流化床中压力脉动特性

气固搅拌流化床反应器可用于黏结性聚合物颗粒的流态化过程,流化床中通气湍动与搅拌的相互作用关系仍不明确。通过压力脉动的统计分析、功率谱分析和小波分析,考察了搅拌桨型式和搅拌转速对流态化特性的影响规律。实验发现,搅拌转速和搅拌桨型式对床层压力影响较小,但对压力脉动影响显著。搅拌流化床中搅拌与通气湍动对流态化共同作用,双层锚式桨、框式桨等小桨叶面积的搅拌桨在较高转速条件下能强化流态化过程,与普通流化床相比具有更小的气泡尺寸和压力脉动,搅拌可抑制气泡聚并、破碎气泡,维持床层均匀流态化;而新型具有大桨叶面积的自清洁桨的搅拌作用强烈,在较高的转速下易形成桨叶前方的颗粒堆积和桨叶后方的气体短路等非正常流化现象,适宜于中等转速的操作条件。     

EXPERIMENTAL RESEARCH ON MASS TRANSFER IN A CENTRIFUGAL FLUIDIZED BED DRYER

The influences of bed thickness, particle diameter, rotating speed of the basket and operating gas velocity on the mass transfer between gas and particles in the centrifugal fluidized bed dryer (CFBD) were examined. The experimental correlation used to calculate the mass transfer coefficient in the centrifugal fluidized bed dryer was obtained.     

Numerical simulation on fluidization characteristics of tobacco particles in fluidized bed dryers

Three-dimensional simulations have been carried out to examine the gas–particle flow behavior of tobacco material in a fluidized bed dryer. The Euler–Euler model has been used to study the distribution of particles in the fluidized bed dryer. The simulation results indicate that tobacco particles usually concentrate in the near-wall region, and there exists a maximum particle concentration in the feed pipe. The predictions on the regions with high concentration of particles in the fluidized bed dryer agree well with the experimental findings. Moreover, this kind of dynamic particle aggregation might lead to particle clusters, and investigations of the particle motion and mixing behavior in the simulated systems indicate that there are particle clusters during fluidization. The diverse nature of clusters enriches the flow behaviors of particles and consequently leads to the macro-scale heterogeneity featuring fast fluidization: dilute at the top and dense at the bottom in the axial direction as well as the core–annulus structure in the radial direction. Therefore, the particle clusters is one of the key problems in drying processes, which must be known for understanding the material distribution inside the dryer, as well as for the system design of fluidized bed dryers. According to the results, some improvements on the fluidized bed dryer have been brought out and the relative numerical experiments have been performed. The numerical experiments show that the improvements can realize better uniformity and lead to a decrease in the particle concentration, which provides useful ways to solve the clustering problem.     

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.     

Determination of PVC powder drying kinetics at particle scale: Experimental study and modeling

An original experimental method is used to determine drying kinetic at particle scale. The particle scale kinetics was obtained by immersion of a small mass of wet polyvinyl chloride (PVC) particles (cake) in a batch dense fluidized bed containing inert hot particles (glass bead). The results are summarized here and prove clearly that the PVC drying is controlled by a competition between internal and external transfers. The drying kinetic was described by a particle scale model taking into account the convective–diffusive (mass transfer) and the convective–evaporative (heat transfer) phenomena. To validate this model with the experimental data, the experimental fluidized bed dryer is modeled following two different approaches: a perfect stirred reactor model and a 3D numerical simulation using the multiphase flow code NEPTUNE_CFD. The aim of this 3D simulation is to simulate the phenomena occurring, at local scale, in a dense fluidized bed dryer and to show the limitations of the perfect stirred reactor model.     

EXPERIMENTAL RESEARCH ON MASS TRANSFER IN A CENTRIFUGAL FLUIDIZED BED DRYER

Abstract

The influences of bed thickness, particle diameter, rotating speed of the basket and operating gas velocity on the mass transfer between gas and particles in the centrifugal fluidized bed dryer (CFBD) were examined. The experimental correlation used to calculate the mass transfer coefficient in the centrifugal fluidized bed dryer was obtained.     

气固搅拌流化床内压力脉动特性的数值模拟

在传统气固流化床中引入搅拌桨,可减轻聚合物颗粒的黏附并强化流态化过程。采用计算流体力学(CFD)方法对搅拌流化床内的压力脉动特性进行数值模拟,考察流态化过程中的气泡行为。模拟过程采用多重参考坐标系方法解决搅拌桨区域的运动问题,由欧拉双流体模型和颗粒动力学方法模拟气固两相流。床层压力脉动的统计分析和功率谱分析表明,随着搅拌桨转速的增加,流化床内的压力脉动标准偏差和功率谱幅值变小,床层内的平均气泡尺寸减小,床层可由鼓泡流态化向散式流态化转变。     

垂直内挡板对流态化流体动力学及谷物干燥特性之影响

The effect of vertical internal baffles on the particle mixing and grain drying characteristics in a batch fluidized bed column is investigated. Experimental work was carried out in a 3 m high rectangular fluidized bed dryer of cross sectional area of 0.15 mx0.61 m at different operating conditions using paddy, a group D particle, as the fluidizing material. The results of the study showed that the fluidized bed dryer system with vertical internal baffles gave better particle mixing effect in the bed of particles than that without vertical internal baffles. This is due to the fact that the vertical internal baffle act as gas bubble breakers by breaking up the large gas bubbles into smaller ones. The smaller bubbles cause a more vigorous mixing in the bed of particles before finally erupting at the bed surface. This improves the contacting efficiency and enhanced the heat and mass transfer of the fluidized bed system. Thus a higher drying rate was obtained in the falling rate period because the higher contactin efficiency increases the evaporation rate at the particle surface. However, the drying rate in the diffusion regiol shows little improvement because the moisture diffusivity does not depend on the contacting efficiency. The fluidized bed dryer with vertical internal baffles could therefore be used in the initial rapid drying stage in a two stage drying strategy for paddy. The insertion of vertical internal baffles into a fluidized bed system improves the processing of Group D particles in a fluidized bed system especially if the system is large in scale.