Principles for Hydrodynamical and Geometrical Design of Vibrated Bed Driers

ABSTRACT

Processing in vibrated beds is characterized by the versatility and the easy controlability through parameters of vibration (amplitude, frequency and intensity). The main task of the control of processing is the synchronization of the residence time of particles in the processing area with the duration of drying. The drying time depends on the physical properties of the processed material, on the thermal parameters of the bed and on the operational parameters. The residence time depends on the mechanical properties of the particles, on the intensity of transport and on the eometrical parameters of the equipment. Since most of the parameters of the vibrational processing depend on the intensity of vibration, synchronization of the drying time with the residence time of particles, optimization of the process and optimal design of the vibrational equipment in general must be performed by the control of this operational parameter. Therefore a sophisticated algorithm and software for optimal control and design of vibrational processing equipment is needed. Such an algorithm based on the "Classification Scheme of Vibrated Systems" is described in this paper. The design algorithm has been tested using experimental data measured in a laboratory scale aerovibrofluidized bed dryer.     

振动流化床中浅床层时床层与分布板之间的弹性作用

采用A类颗粒作为实验粉体,通过测量床层对分布板的作用力,分析了振动流化床中分布板与床层的作用机理,提出了振动流化床中在浅床层共振时分布板与床层的弹性作用模型. 实验表明,分布板与床层之间是连续的弹性作用,周期性的机械振动通过分布板与床层之间的弹性作用以波动形式在床层中传播. 该模型计算结果与实验测定结果符合的较好.     

振动流化床研究新进展

振动流化床技术具有独特的优越性，近年来得到长足的发展。文内介绍了国内外振动流化床技术的研究应用现状，并指出其研究发展方向。     

振动流化床在季戊四醇干燥中的应用

对比了气流干燥床、振动流化床用于季戊四醇干燥的优缺点，经生产实践证明，振动流化床具有热效率高、干燥成本低、操作简单稳定、操作弹性大、尾粉量少、对风量及热风温度要求不高等优点。     

小型化卧式振动流化床干燥系统的研制

分析了变性淀粉工业生产所用的气流干燥装置不能用在中试或者高校实验的原因,同时叙述了变性淀粉干燥设备应具备的条件及选择卧式振动流化床干燥作为中试用变性淀粉干燥装置的原因。设计了变性淀粉中试用小型化卧式振动流化床干燥系统的工艺设计方案,通过纯胶这种新型的变性淀粉进行干燥,从而验证了小型化卧式振动流化床干燥系统可行性及实用性。     

振动流化床中气泡和颗粒运动特性的数值模拟

基于欧拉模型,应用计算流体力学软件Fluent,数值模拟了二维振动流化床的颗粒运动特性,考察了振动流化床内气泡和颗粒速度的分布规律。模拟结果发现:由于振动的作用,床底部与布分板之间会形成间隙,促进了大气泡的形成;随着振动频率、强度的增加,颗粒运动速度增大,流化床内大气泡的形成减少。     

振动流化床中床层空隙率的分布

在φ１４８ｍｍ的振动圆柱形流化床内,采用树脂、玻璃珠、小米及砂子等Ｇｅｌｄａｒｔ‘Ｂ和Ｄ类物料,测定了振动强度为１－８ｇ,流化床为１．０－３．０条件下气固流化床床层空隙率的变化,考察振动条件下床层轴向径向的空隙率分布,探讨了床层空隙率的一些影响因素,并根据实验结果对振动流化床的平均空隙率进行了无因次数式关联,此关联式对实际振动流化床的操作与工程设计具有一定的指导意义。     

振动流化床在尤里卡沥青干燥中的应用

以工业原料尤里卡沥青为研究对象，分析和讨论了振动流化床干燥器的动力学特征，传热特性及干燥特性，对振动流化床干燥器设计选型的主要参数进行了整理和计算。     

A Test of Lumped-Parameter Methods for the Drying Rate in Fluidized Bed Driers for Bioproducts

For batch fluidized bed drying of bioproducts the distributed parameter model is presented, in which the internal diffusion equation is coupled to the air balance equations. In practice a large part of the process takes place at high relative humidity of the drying air, equivalent to low driving forces. The results of a number of lumped-parameter methods for the estimation of drying times are compared with those of the full model for the case of constant external conditions around a particle. For low relative humidity of the drying air predictions of drying times with the Regular Regime Power Law method correspond well with the full solution, for higher ambient RH large deviations occur. The other methods are shown to give large deviations in all cases.     

A Test of Lumped-Parameter Methods for the Drying Rate in Fluidized Bed Driers for Bioproducts

ABSTRACT

For batch fluidized bed drying of bioproducts the distributed parameter model is presented, in which the internal diffusion equation is coupled to the air balance equations. In practice a large part of the process takes place at high relative humidity of the drying air, equivalent to low driving forces. The results of a number of lumped-parameter methods for the estimation of drying times are compared with those of the full model for the case of constant external conditions around a particle. For low relative humidity of the drying air predictions of drying times with the Regular Regime Power Law method correspond well with the full solution, for higher ambient RH large deviations occur. The other methods are shown to give large deviations in all cases.     

煤调湿蒸汽管回转干燥机密封结构的设计

介绍了煤调湿技术的发展现状和蒸汽管回转干燥机常用密封结构存在的问题,并对实际生产中出现的问题进行分析.设计了一种新的密封结构,以解决泄漏及使用寿命短等问题.     

带浸没加热管的惰性粒子振动流化床干燥强度研究

采用带浸没加热管的惰性粒子振动流化床对（石灰）膏状物料干燥进行了实验研究。利用正交实验，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强度的影响，得出了计算干燥器干燥强度的关联式。结果表明，由于浸没加热管热量的引入，能显著增加干燥器的干燥能力，实验条件下干燥器干燥强度超过250kg·（m^3·h）^-1，干品湿含量可降至1．5％以下，质量能达到要求，相关数据可为膏状物料干燥器的设计和开发提供借鉴。     

Design Optimization of Convective Driers by Using Spreadsheets

The optimal design of a convective drier is hereby considered by means of using a well-known spreadsheet: Microsoft Excel 5. OTm.The degree of freedom analysis enabled a non linear equations system to be set up, in such a way that it was possible for different design variables to be considered. The equations system was keyed in to provide a possible solution via the iterative procedure built in the spreadsheet. Other complementary variables were computed to provide a unit cost for the operation, thus occasioning the opportunity of considering an economic objective function.Constraint and design variables were identified in the program. By giving initial values to the design variables, and by using the optimization capabilities included in Microsoft Excel 5.0Tm, an optimal set of values for the design variables was determined.Finally, the influence of constraint and design variables was analyzed, where both the input air temperature and the relative humidity of exhaust air were binding factors.     

Design Optimization of Convective Driers by Using Spreadsheets

ABSTRACT

The optimal design of a convective drier is hereby considered by means of using a well–known spreadsheet: Microsoft Excel 5. OTm.The degree of freedom analysis enabled a non linear equations system to be set up, in such a way that it was possible for different design variables to be considered. The equations system was keyed in to provide a possible solution via the iterative procedure built in the spreadsheet. Other complementary variables were computed to provide a unit cost for the operation, thus occasioning the opportunity of considering an economic objective function.Constraint and design variables were identified in the program. By giving initial values to the design variables, and by using the optimization capabilities included in Microsoft Excel 5.0Tm, an optimal set of values for the design variables was determined.Finally, the influence of constraint and design variables was analyzed, where both the input air temperature and the relative humidity of exhaust air were binding factors.     

振动流化床中双组分颗粒流化特性的研究

本文研究了内径为１４８ｍｍ振动圆柱床中等密度和不等密度的双组分颗粒流化特性,考察了不同振动强度对双组分颗粒的床层空隙率、最小流化速度及相图的影响,给出了床层空隙率和最小流化速度的计算式,此计算值与实验值基本相符,且对振动流化床的实际操作和工程设计起到一定的指导作用。     

振动流化床干燥装置干燥特性计算方法研究

通过对振动流化床（ＶＦＢ） 干燥装置中传热与传质过程的分析,建立了物料在其中的干燥特性模型, 得到了振动流化床干燥装置物料出口含湿量与温度的计算公式。     

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.     

硼砂在内热式振动流化床中的干燥特性研究

采用内热式振动流化床对硼砂进行了干燥实验,考察了流化气速、进气温度和振动频率对硼砂干燥特性的影响,分析了硼砂湿含量、含水分子个数和干燥速率的变化规律。结果表明,干燥速率随着流化气速和进气温度的增加而增加,随着振动频率增加变化不大。通过实验数据得到了计算干燥速率的关联式,计算值与实验值吻合较好,误差在±20%范围内。结果可为内热式振动流化床的设计和研究提供参考。     

酒精污泥在内热式振动流化床中的干燥特性研究

以干污泥颗粒为惰性粒子,采用内热式振动流化床对酒精污泥进行了干燥实验,考察了流化气速、进气温度、振动频率和内加热功率对污泥干燥特性的影响,分析了污泥湿含量和干燥速率的变化规律。结果表明,干燥速率随着流化气速、进气温度和内加热功率的增加而增加,随着振动频率增加呈先增长后降低的趋势。适度提高流化气速、进气温度、振动频率和内加热功率可以降低最终湿含量。将干燥过程分为降速I段和降速Ⅱ段,根据扩散传质理论,建立了内热式振动流化床中污泥干燥的数学模型,模型计算值和实测值的误差在20%以内,符合较好。实验结果为酒精污泥干燥过程的工业设计和操作提供了实验依据。     

振动流化床与浸没水平管间局部传热系数的测试方法

本文提出了振动流化床中测试水平加热管局部传热系数的新方法。该法考虑了管体温度场的非均匀性对测量结果的影响。根据管体的材质和结构。扣除了由于分布引起热损失。从而采用较简单的测试手段就能够获得较准确的局部传热系数数据。将本所所得测试结果与其他研究者的测试结果作了比较。并上局部热系数求得的平均传热系数和实测的平均传热作了比较。结果表明,本文提出的测试方法可靠。