Further Theoretical Studies on Rotary Drying Processes Represented By Distributed Systems

Mathematical tools for studying panicle transpon in rotary drying and cooling processes are developed in this paper. In contrast to conventional approaches aimed at deriving empirical or xmi-empirical correlations, a rigorous mathematical analysis which employs dilferential calculus and analytical geometry is emphasis4 in the current research. These developments allow accurale computations of solid flowrate, retention time and particle holdup in rotary dryers with arbilrary flight configurations. Consequently, optimal dryer configuration design in terms of drum dimension, flight number and geometry can be achieved through a better understanding of the mathematical insight of rotary drum performance.

Techniques developed using this method are applied to the distributed parameter model eslablished earlier by the authors (Wang el al., 1993) to replace out-dated correlations for the determination of retention Lime and solid holdup. As a result of the new developments, the distributed parameter approach to the dynamics of rotary drying processes becomes more general and more reliable.     

Evaluation of Textile Bobbins Drying Processes: Experimental and Modelling Studies

ABSTRACT

Drying of textile bobbins was carried out on two kinds of laboratory-scale dryers: in a cross circulation drying rig, atmospheric pressure heating air is used, while in the through circulation drying apparatus, the heating air is pressurized before the drying process takes place. In both cases, a bobbin was fitted with seven thermocouples, placed in a plane normal to the bobbin axis but at different radial distances, in order to provide temperature data during the drying process. In cross circulation drying, plots of temperature against time indicated the presence of two moving fronts, one starting from inside the bobbin, another from the outside, while in through circulation drying, similar plots showed the presence of an evaporation front, moving from inside the bobbin to the outside. In both canes, numerical models were developed to simulate the drying processes.     

Evaluation of Textile Bobbins Drying Processes: Experimental and Modelling Studies

Drying of textile bobbins was carried out on two kinds of laboratory-scale dryers: in a cross circulation drying rig, atmospheric pressure heating air is used, while in the through circulation drying apparatus, the heating air is pressurized before the drying process takes place. In both cases, a bobbin was fitted with seven thermocouples, placed in a plane normal to the bobbin axis but at different radial distances, in order to provide temperature data during the drying process. In cross circulation drying, plots of temperature against time indicated the presence of two moving fronts, one starting from inside the bobbin, another from the outside, while in through circulation drying, similar plots showed the presence of an evaporation front, moving from inside the bobbin to the outside. In both canes, numerical models were developed to simulate the drying processes.     

微波真空组合干燥技术的研究

微波真空干燥是综合微波干燥和真空干燥各自优点的一项新技术,将微波干燥的快速高效性和真空干燥的低温高质相结合,在真空条件下利用微波对物料进行干燥处理,从而实现物料的快速低温干燥。着重阐述了微波真空组合干燥技术的机理、特点、干燥动力学以及影响微波真空干燥的重要因素,并对微波真空组合干燥的应用研究进行了介绍。     

Analysis and Identification of Distributed Parameter Model for Wood Drying Systems

Abstract

A new approach based on the decomposition, in position-time space, of operating functions (OFs) is proposed and various criteria of parameter identification like the output least squares (OLS) and the regularized least squares (RLS) are formulated and incorporated in the framework. Several optimization algorithms such as the Gauss-Newton, conjugate gradient and Levenberg-Marquardt are diligently modified and computed in order to search the performed algorithm to identify, in space and time, the numerical fields of the model parameters. Because the sensitivity of the criteria to the design variables plays a very important role in the optimization problem, various techniques such as finite difference method and direct differentiation method are tested. The enhanced performance of the model with the newly identified OFs is proved by a higher conformity of its predictions with the real data of drying wood systems (DWSs).     

Analysis and Identification of Distributed Parameter Model for Wood Drying Systems

A new approach based on the decomposition, in position-time space, of operating functions (OFs) is proposed and various criteria of parameter identification like the output least squares (OLS) and the regularized least squares (RLS) are formulated and incorporated in the framework. Several optimization algorithms such as the Gauss-Newton, conjugate gradient and Levenberg-Marquardt are diligently modified and computed in order to search the performed algorithm to identify, in space and time, the numerical fields of the model parameters. Because the sensitivity of the criteria to the design variables plays a very important role in the optimization problem, various techniques such as finite difference method and direct differentiation method are tested. The enhanced performance of the model with the newly identified OFs is proved by a higher conformity of its predictions with the real data of drying wood systems (DWSs).     

Measurement of Absorbed Power of Glass Particle Layer on Moisture Content and Drying Rate by Combined Convective and Microwave Drying

Dependency of absorbed power by microwave on the local moisture content in a glass particle layer was measured with a new method; that is, heating the wet layer. The heating experiment was performed using a laboratory-scale combined convective and microwave heater/dryer that was manufactured by modifying a domestic microwave oven at 2.45 GHz. The measured result was strongly dependent on the local moisture content and showed a maximum and a minimum within the measured range of the moisture content. This dependency can be explained by the assumption that moisture in the wet layer behaves as a mass of the free water. The combined drying rate of the wet layer measured with the heater/dryer was simulated with both the power dependency and the experimental convective-only drying rate. Power dependency on temperature is as important as the moisture content in the simulation. Simulated results agree very well with experimental ones.     

壳牌煤气化磨煤干燥系统设备故障分析及处理

神华煤直接液化项目采用壳牌煤气化装置。介绍了壳牌煤气化装置磨煤干燥系统的工艺原理和工艺流程;分析了磨煤机、称重给料机、循环风机、助燃空气风机、煤粉收集器、碎煤仓的故障原因,提出了相应的处理措施和技改方案。     

氟硅酸氨化制高补强性白炭黑干燥方式研究

以磷肥副产氟硅酸为原料,氨水为氨解剂制备了高补强性白炭黑。为获得团聚少．质量好的白炭黑产品,研究了烘箱干燥、真空干燥、喷雾干燥、溶剂置换干燥对白炭黑比表面积和粒度的影响。实验结果表明,通过溶剂置换干燥能有效防止白炭黑形成硬团聚,所得白炭黑粒度小,比表面积大。同时分析了4种干燥方式中白炭黑粉体硬团聚形成的机理。     

A Funtadamental Study on Particle Transport Through Rotary Dryers for Flight Design and System Optimisation

A model for particle transport in a flighted horizontal rotary dryer is developed in this paper. Mathematical principles applied to the current study are in the areas of differential calculus and analytical geomentry. In contrast to the conventional approaches which are either based on mpirical/semi-empirical correlations or obtained from the investieation of single particle trajectories, this paper develops rigorous mathematical analysis of the transport of bulk solids. A variety of important issues in rotary drying, such as axial flowrate of solids, retention time distribution and solid holdup are addressed and treated by using non-traditional methods. Since the model takes dimension, number and geometry of flights into account, it possesses the following two haracteristics : (1) it is not only useful in the study of rotary drying dynamics, but lso applicable to other processes employing flighted rotating cylinders (such as granulation drumsand crushers) and (2) based on the model, an optimal drum configuration can be designed by using optimisation techniques. The model can be incorporated within a distributed arameter dryer model developed previously to form a more rigorous integrated dynamic model. A heoretical foundation for optimal flight design by using the current model is explained.

A pilot scale perspex rotary dryer equipped with a video camera has been constructed and used for model validation. Raw sugar was handled in the experiments. Particle transport was observed and measured by using a flow visualisation technique supplemented with traditional sampling methods. A significant model quality improvement has been observed through a comparative study between the newly developed model and conventional ones.     

A Funtadamental Study on Particle Transport Through Rotary Dryers for Flight Design and System Optimisation

ABSTRACT

A model for particle transport in a flighted horizontal rotary dryer is developed in this paper. Mathematical principles applied to the current study are in the areas of differential calculus and analytical geomentry. In contrast to the conventional approaches which are either based on mpirical/semi-empirical correlations or obtained from the investieation of single particle trajectories, this paper develops rigorous mathematical analysis of the transport of bulk solids. A variety of important issues in rotary drying, such as axial flowrate of solids, retention time distribution and solid holdup are addressed and treated by using non-traditional methods. Since the model takes dimension, number and geometry of flights into account, it possesses the following two haracteristics : (1) it is not only useful in the study of rotary drying dynamics, but lso applicable to other processes employing flighted rotating cylinders (such as granulation drumsand crushers) and (2) based on the model, an optimal drum configuration can be designed by using optimisation techniques. The model can be incorporated within a distributed arameter dryer model developed previously to form a more rigorous integrated dynamic model. A heoretical foundation for optimal flight design by using the current model is explained.

A pilot scale perspex rotary dryer equipped with a video camera has been constructed and used for model validation. Raw sugar was handled in the experiments. Particle transport was observed and measured by using a flow visualisation technique supplemented with traditional sampling methods. A significant model quality improvement has been observed through a comparative study between the newly developed model and conventional ones.     

Studies on the Microwave Freeze Drying Technique and Sterilization Characteristics of Cabbage

The vacuum freeze-drying (FD) technique used in the food industry can yield a high-quality product, but it is very expensive and requires a long processing time. Besides, the quantity of microorganisms in FD products can often exceed the required standard. As a result, it will be important to develop a new freeze-drying technique. In this article, cabbage was used as a model material, and the microwave field was used as a heat source to supply sublimation heat so that the drying time was shortened greatly. The effect of the microwave sterilization during the drying process was evaluated. Effects of the pressure, thickness of material being dried, and the input microwave power on such indices as drying time and the microorganism number were studied. Compared with the method of ordinary freeze drying, microwave freeze drying (MFD) can greatly reduce the drying time and has a notable sterilization effect.     

Studies on the Microwave Freeze Drying Technique and Sterilization Characteristics of Cabbage

The vacuum freeze-drying (FD) technique used in the food industry can yield a high-quality product, but it is very expensive and requires a long processing time. Besides, the quantity of microorganisms in FD products can often exceed the required standard. As a result, it will be important to develop a new freeze-drying technique. In this article, cabbage was used as a model material, and the microwave field was used as a heat source to supply sublimation heat so that the drying time was shortened greatly. The effect of the microwave sterilization during the drying process was evaluated. Effects of the pressure, thickness of material being dried, and the input microwave power on such indices as drying time and the microorganism number were studied. Compared with the method of ordinary freeze drying, microwave freeze drying (MFD) can greatly reduce the drying time and has a notable sterilization effect.     

Studies on Hot Air and Microwave Vacuum Drying of Wild Cabbage

Wild cabbage was dehydrated by a combination of hot-air drying and microwave vacuum drying. It showed that the total drying time was reduced by about half while the retention values of the nutrient components and chlorophyll were improved significantly. Microwave/vacuum-dried products had a more porous texture. Finally, microwave drying showed effective bactericidal action in the product with acceptable quality of dried product.     

超高分子量聚丙烯酰胺水解干燥条件的研究

分析了聚丙烯酰胺水解、干燥过程中影响分子量及溶解性的主要因素。通过实验,对影响聚丙烯酰胺分子量的水解剂、水解温度、水解时间、水解浓度、胶体粒度、水解加热方法以及干燥时间、干燥温度等因素进行了优化选择,确定了聚丙烯酰胺后水解的工艺参数。并以此工艺参数为基础,确定了适合工业化生产的超高分子量聚丙烯酰胺水解及干燥条件。     

Studies on Hot Air and Microwave Vacuum Drying of Wild Cabbage

Abstract

Wild cabbage was dehydrated by a combination of hot-air drying and microwave vacuum drying. It showed that the total drying time was reduced by about half while the retention values of the nutrient components and chlorophyll were improved significantly. Microwave/vacuum-dried products had a more porous texture. Finally, microwave drying showed effective bactericidal action in the product with acceptable quality of dried product.     

Simulation of Drying on the Basis of Nonequilibrium Thermodynamics of Beterogeneous Multiphase Polydispersed Systems.Formation of the Morphological Structure of Emulsive Elastomers Using Method of Spray - Drying for Latexes

ABSTRACT

The process and the technology of fine - dispersed rubber powder production on the basts of spray - drying for latexes were considered. The practical recommendations on usage of physical modification method for elastomers on the basis of interaction mechanism between solid -phase dispersed filler and polymeric panicles were given.

The mathematical model for latex drops during drying in the presence of structured adsorptive layer of surface active substances on the surface of drops was worked out, that allowed us to give the recommendations for production of monolithic particles.     

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。     

木材除湿干燥过程中循环风旁通率调控理论分析

从木材除湿干燥的临界分析入手,分析了通过除湿蒸发器前后湿空气的焓差、含湿量差以及除湿量与旁通率的关系,理论上印证了最佳旁通率的存在,并提出了最佳旁通率的调控思路,为调控循环风旁通率实现木材除湿干燥节能提供了理论基础。