洗衣粉悬浮液在惰性粒子流化床中干燥的研究

针对气体分布板开直孔的惰性粒子流化床,开展了洗衣粉悬浮液在床内的干燥性能研究。测定了流化床的床层压降曲线,考察了进料量、进风温度、进风速度及惰性粒子直径对于流化床传热性能的影响,且与气体分布板开斜孔的传热性能进行了初步比较。结果表明,流化床的床层压降主要是由惰性粒子的流化阻力所致;适当增加进料量和进风速度,或减小惰性粒子直径,以及将气体分布板的孔道由直孔改为斜孔,均可提高流化床的传热性能,但过高的进风温度则可能导致传热性能的下降。     

惰性粒子流化床干燥钻井废泥浆实验研究

实验考察了惰性粒子流化床干燥钻井废泥浆,关联了干燥器的体积传热系数表达式,可定量计算进风速度、进风温度、废泥浆体积流量和含水量等参数的影响。结果表明,惰性粒子流化床干燥热效率达55％,体积传热系数可达6kW·m^-3·K^-1,可用于钻井现场柴油机废气干燥钻井废泥浆。激光粒度分析仪测试干燥产物粒度平均值为12／μm,且分布较为集中,其密度为3．2g·cm^-3,可以回用于钻井泥浆的加重材料。浸毒试验表明,干燥产物CODCr值大幅度下降。     

Drying characteristics of porous material immersed in a bed of hygroscopic porous particles fluidized under reduced pressure

A relatively large wet material was immersed in a fluidized bed of hygroscopic porous particle (silica gel beads) under reduced pressure. And then the drying characteristics were compared with those in the case of inert particle (glass beads). The comparison of drying characteristics is performed experimentally and theoretically. In calculation, the water transfer from the sample to the fluidized bed was considered. The calculation results are in good agreement with the experimental data. The effects of the operational conditions (the pressure in the drying chamber and the temperature of the drying gas) on the drying characteristics were also examined in both fluidizing particles.The drying finishes earlier in the case of hygroscopic porous particle than in the case of inert particle regardless of pressure in the drying chamber, since the water transfer from the sample facilitates the drying in the case of hygroscopic porous particles. The temperature decrement in drying appears in the case of inert particle. This phenomenon is also observed in the case of hygroscopic porous particle, but the decrement degree of the temperature is much smaller than that in the case of inert particle. The difference of the minimum temperature in the sample in drying between the cases of hygroscopic porous particle and inert particle is very slight for different pressures in the drying chamber.     

惰性粒子振动流化床中膏状物料干燥

报道了采用带浸没加热管的惰性粒子振动流化床干燥膏状物料的实验研究结果。考察了加料速率、振动条件、进气温度、进气速度、加热管功率等参数对干燥过程的影响,提出采用体积传热系数来评价干燥器传热性能,并得出了计算体积传热系数的准数关联式。结果表明,在流化床中增设振动和浸没加热管装置,能大大强化传热、传质,干燥器热效率达60%,干燥强度超过300 kg·m^-3·h^-1,体积传热系数可达25 kW·m^-3·K^-1,激光粒度分析仪的测定结果表明产品的粒度分布范围较窄,该流化床干燥可以直接得到平均粒径为0.35 μm、比表面积为5.024 m²·g^-1的粉状产品。     

带浸没管的惰性粒子振动流化床传热特性

采用带浸没加热管的惰性粒子振动流化床对膏状物料干燥进行了实验研究。考察了加料速率、进气温度、进气速度、加热管功率、振动强度等参数对床温和体积传热系数的影响,得出了计算体积传热系数的关联式。结果表明,在流化床中增设振动和浸没加热管装置,能大大强化传热传质,体积传热系数随加料量、振动强度、加热管功率、进风速度的增加而增大,随进气温度的增加而减小。其结果对惰性粒子流化床干燥器的设计和改进具有重要的指导意义。     

内置换热管振动流化床传热特性实验研究

在内置换热管的振动流化床中以玻璃珠为惰性粒子实验物料,测定惰性粒子振动流化床与加热管之间的传热系数,研究了惰性粒子处于流化状态时的传热特性,分析了操作气速、振动频率、惰性粒子直径等因素对传热过程的影响,建立了传热系数与各影响因素之间的关联式。研究结果可为干燥膏状物料时确定适宜的操作参数提供参考。     

Heat transfer between an isolated bubble and the dense phase in a fluidized bed

Heat transfer between the bubble and dense phases of a bubbling fluidized bed plays a very important role in the system performance, especially for applications involving solids drying and gas‐phase combustion. However, very few experimental data are available on this subject in the literature. An experimental and modelling investigation on the heat transfer behaviour of isolated bubbles injected into an incipiently fluidized bed is reported in this paper. A new single‐thermocouple technique was developed to measure the heat transfer coefficient. The effects of bed particle type and size, and bubble size on the heat transfer coefficient were examined. The heat transfer coefficient was found to exhibit a maximum as the bubble size increased in the bubble size range investigated. The bed particle size had a comparatively small effect on the heat transfer coefficient. A simple mathematical model was developed which provides good agreement with experimental data.     

Attrition of Victorian brown coal during drying in a fluidized bed

Analyzing the attrition of Victorian brown coal during air and steam fluidized bed drying, the change in particle size distribution over a range of initial moisture contents (60% to 0%) and residence times (0 to 60 minutes) was determined. Dried at a temperature of 130°C with a fluidization velocity 0.55 m/s and an initial particle size of 0.5–1.2 mm, both fluidization mediums show a shift in the particle size distribution between three and four minutes of fluidization, with a decrease in mean particle size from 665 µm to around 560 µm. Using differential scanning calorimetry (DSC), the change in particle size has been attributed to the transition between bulk and non-freezable water (approximately 55% moisture loss) and can be linked to the removal of adhesion water, but not to fluidization effects. This is proved through the comparison of air fluidized bed drying, steam fluidized bed drying, and fixed bed drying—the fixed bed drying is being used to determine the particle size distribution as a function of drying. The results show the three drying methods produce similar particle size distributions, indicating that both fluidization and fluidization medium have no impact upon the particle size distribution at short residence times around ten minutes. The cumulative particle size distribution for air and steam fluidized bed dried coal has been modeled using the equation P_d = A₂ + (A₁ ? A₂)/(1 + (d/x₀)^p), with the resultant equations predicting the effects of moisture content on the particle size distribution. Analyzing the effect of longer residence times of 30 and 60 minutes, the particle size distribution for steam fluidized bed dried coal remains the same, while air fluidized bed dried coal has a greater proportion of smaller particles.     

Effects of freezing pretreatment and hygroscopicity of fluidizing particles on drying characteristics of carrots in fluidized bed under reduced pressure

Abstract

A method for low-temperature drying with high drying rate was developed for heat-sensitive foods and agricultural products. A freezing pretreatment was combined with fluidized bed drying under reduced pressure. Cylindrical carrot samples were frozen and then placed without thawing in a fluidized bed of hygroscopic porous silica gel particles that adsorbed water from the sample during the drying process. The effects of the freezing pretreatment and hygroscopicity of fluidizing particles on the drying characteristics of carrots were examined. A higher drying rate was achieved when carrots samples were subjected to freezing pretreatment than without it. At 12?kPa, the volume change was smaller in carrots subjected to freezing pretreatment than in untreated samples. A larger amount of water was absorbed during rehydration by carrots dried at 12?kPa than at 101?kPa within 120?min. The properties of dried carrots were affected not only by freezing pretreatment but also by the pressure applied during the drying process.     

卧式沸腾干燥床在PVC生产中的应用

简单介绍了卧式沸腾干燥床干燥工艺的工艺流程及特点,比较了目前PVC生产中的几种干燥工艺,分析了卧式沸腾干燥床在实际生产中存在的问题及改进措施。     

流化床氛围下多孔物料干燥传热传质的数值模拟

用有限差分法数值求解一个热、质传递耦合模型,理论研究多孔物料流化床干燥过程。方程离散采用全隐格式的控制容积方法,三对角矩阵法（TDMA）用来求解线性方程组。选用球形的苹果丁作为多孔物料。在典型操作条件下,通过分析温度、饱和度和压力的分布侧形,讨论了物料内部的热、质传递机理。在对比条件下,考察了气体入口温度、气速和床面积因子对干燥过程的影响。结果表明：干燥过程受气、固相间的耦合传热传质的影响十分明显,干燥时间随气体入口温度和气速的提高而减少;随床面积因子的增大而增加。     

带内置水平管的大颗粒振动流化床流体力学研究

以大颗粒MAP（磷酸-铵）为试验物料对带内置水平管的大颗粒振动流化床流体力学进行了试验研究,结果表明,振动的引入对床层临界压降有明显的降低作用;同样床层条件下振动频率越大床层临界压降越低,振幅的改变对床层压降影响不大;低气速下振动使床层孔隙率降低而导致压降高于普通流化床;在带内置水平管的大颗粒振动流化床中,振动对大粒径颗粒的影响小于小粒径颗粒;由试验拟合出经验公式,与试验数据吻合良好。     

振动流化床中大颗粒与水平管局部传热特性

在二维振动流化床中,以平均粒径1.83 mm的玻璃珠为物料,研究了大颗粒与水平管间局部传热规律;考察了气速、振动频率等因素对局部传热系数的影响,同时与小米和小玻璃珠实验结果进行对比。结果表明:大颗粒与小颗粒局部传热系数有很大差异;对于大颗粒,低速下局部传热系数随振动频率的增大先增加后减小,高速下局部传热系数随着振动频率的增加而降低;一定振动频率下,气速小时局部传热系数在60°左右达到最大,气速逐渐增加后,其最大值向90°转移。通过实验数据得到了计算大颗粒与水平管局部传热系数的关联式,计算值与实验值吻合较好,误差在±20%范围内。结果可为带浸没水平管的振动流化床设计和研究提供参考。     

振动流化床浸没水平管传热特性研究

为了深入研究振动流化床浸没水平管的传热特性,分别以沙子和玉米细颗粒作为实验物料,用水平探头测定了振动流化床中这2种床层颗粒与浸没水平管间的传热系数,分析了操作气速、振动频率、空气进口温度等因素对传热过程的影响。结果表明:在低气速下,振动是影响振动流化床中传热的主要因素,振动的引入可以明显改善流化作用,可以在低气速下得到较好的传热效果,同时达到节能的效果。通过分析实验结果,建立了振动流化床的传热关联式,模型计算值与实测值能较好吻合。研究结果可为干燥膏状物料时确定适宜的操作参数提供参考。     

Measurement of solid circulation rate in a circulating fluidized bed

A method using an optical mouse sensor was developed to monitor the moving velocity of a solid mass. Calibration was carried out using a rotating plate. Results clarified that the developed method is useful to monitor the velocity up to some limit (v < 0.3 m/s), which depends on the optical mouse sensor used. A solid circulation rate in a circulating fluidized bed (CFB) was measured using this method. Results obtained using this method show agreement with those of visual observations.     

Heat transfer and bubble dynamics in a three-phase inverse fluidized bed

In this study, surface-to-bed heat transfer experiments were performed to gain insight on heat transfer and hydrodynamics in a three-phase inverse fluidized bed. Air, tap water or 0.5 wt.% aqueous ethanol, and polypropylene were, respectively, the gas, liquid and solid phases. The solid loading was varied from 0 to 30 vol.%, and the gas and liquid superficial velocities from 2 to 50 mm/s and 0 to 21 mm/s, respectively. Visual observations were associated with measured phase holdups and instantaneous heat transfer coefficients. Larger gas velocities lead to an increase in bubble size due to the transition to the coalesced bubble flow regime. The greater turbulence induced by the larger bubbles increases the average heat transfer coefficient. On the other hand, adding ethanol reduces the heat transfer coefficient. Solid concentrations up to ∼13 vol.% increase the average heat transfer coefficient whereas higher solid concentrations tend to lower it. The distribution of instantaneous heat transfer coefficient peak height is wider at higher gas and liquid velocities while the addition of a surfactant narrows it. Gas holdups and average heat transfer coefficients are both compared with existing correlations, which are then adjusted for a better fit.     

内热式惰性粒子流化床中膏状物料干燥模型

通过对惰性粒子流化床中膏状物料干燥机理的分析,得到了干燥时间及单位面积床层水分汽化量的数学计算式,可对干燥器的性能进行预测。采用带浸没加热管的惰性粒子流化床对膏状钛白物料进行干燥中试研究,采用气流式喷嘴将膏状物料分散成200～400μm的小液滴喷洒在惰性粒子表面进行干燥,探索了适宜的干燥条件,测定和确定了最佳的干燥工艺参数、操作参数和设备参数。结果表明:该干燥工艺能强化床内传热传质,促进高黏性膏糊状物料很好地分散,床层温度分布均匀,干燥器的操作弹性大,热量消耗低,干燥强度高,传热系数可达300W·m-2·K-1以上。     

An optimization model of the operating costs of a fluidized bed steam‐drying plant

A model is developed to determine an optimum apparatus geometry and, for given apparatus dimensions, a financially optimal fluidized bed height. The parameters that effect the operating costs are the bed mass, the apparatus diameter and the gas mass flow rate. To implement such cost optimization, a physics‐based mathematical model for describing the thermodynamic processes in fluidized bed steam‐drying is briefly explained and presented. The most important conclusion is not to operate the fluidized bed for a drying process below a certain minimum cost, calculated with the help of the modelling. The problem, when describing the drying process and consequently the mass transfer, is that in the superheated steam drying case studied here, water is evaporated as moisture and withdrawn into an atmosphere of vapor water.     

旋流振动流化床干燥性能的研究

文章以聚四氟乙烯粒子和蔗糖为物料研究了旋流振动流化床的流体力学及干燥特性,并与振动流化床的各种特性进行了对比。实验在一个干燥室直径为240 mm的小型圆筒振动流化床中进行,采用斜孔分布板使床内产生旋流。实验结果表明:在空气分布板开孔率相差不多的情况下,物料流化以前,旋流振动流化床的床层压降要大于普通振动流化床,一旦物料达到正常流化状态以后,2种振动流化床的床层压降相差不多;旋流振动流化床可以降低物料的临界含湿质量分数。     

High-velocity fluidization of solid particles in a liquid-solid circulating fluidized bed system

Particulate and aggregative fluidizations in a liquid-solid circulating fluidized bed system are characterized by chaotic time series analysis of local voidage and heat transfer fluctuations in terms of the correlation dimension and Kolmogorov entropy. Both correlation dimension and Komogorov entropy of the voidate fluctuation are found to decrease with decreasing bed voidage in both fluidization regimes, suggesting the suppression of chaotic motion of individual particles due to high solid concentration. The correlation dimension of the heat transfer fluctation in the aggregative fluidization regime is higher than that in the particulate fluidization regime. This reflects the complex convective motion of liquid and solid phases induced by the formation of the liquid streaks and aggregates of particles.