Skin Layer on Thermally Dried Sludge Cake

This work utilized an X-ray micro-computerized tomography scanner (micro-CT) to investigate how skin layers—hard and relatively impermeable layers that hinder mass transfer—form and develop on wastewater sludge cake with (cake-O) or without artificial cracks (cake-N). A novel scheme that applies Otsu's algorithm twice was employed to determine the solid phase and skin layers in the scanned cake images. Initial cracks in a cake had significant impact on how the skin layer would form on the cake. A unique correlation between effective surface area to drying (not covered by a skin layer) and moisture content was identified. The advancement velocities of skin layers on drying cake were evaluated.     

Skin Layer on Thermally Dried Sludge Cake

This work utilized an X-ray micro-computerized tomography scanner (micro-CT) to investigate how skin layers—hard and relatively impermeable layers that hinder mass transfer—form and develop on wastewater sludge cake with (cake-O) or without artificial cracks (cake-N). A novel scheme that applies Otsu's algorithm twice was employed to determine the solid phase and skin layers in the scanned cake images. Initial cracks in a cake had significant impact on how the skin layer would form on the cake. A unique correlation between effective surface area to drying (not covered by a skin layer) and moisture content was identified. The advancement velocities of skin layers on drying cake were evaluated.     

Structure of Crack in Thermally Dried Sludge Cake

We examined in this work the drying characteristics of wastewater sludge, considering the weight loss using an electronic balance and the morphology change of drying cake by an X-ray micro-computerized tomography scanner (micro-CT). The drying rates for sludge cake was 50-60% of the pure water test. The corresponding micro-CT images were scanned to explore the change in cake volume and development of internal crack over drying. The Otsu's method was applied to bilevel the scanned images, based on which the three-dimensional model for crack's internal structure was reconstructed. The cake porosity and the geometric factors of cracks, such as the compactness, the boundary fractal dimension, and the Sierpinski carpet fractal dimension, were evaluated. The shrinkage of cake volume and the development of internal crack occurred simultaneously. The skin layer formed by the former mechanism retards further drying. On the other hand, the internal cracks were shown to exhibit zigzagging with a noncircular cross section and fractal-like boundary, which should be able to enhance local drying. A possible role of change in crack structure on the rate of drying was discussed.     

Structure of Crack in Thermally Dried Sludge Cake

Abstract

We examined in this work the drying characteristics of wastewater sludge, considering the weight loss using an electronic balance and the morphology change of drying cake by an X-ray micro-computerized tomography scanner (micro-CT). The drying rates for sludge cake was 50–60% of the pure water test. The corresponding micro-CT images were scanned to explore the change in cake volume and development of internal crack over drying. The Otsu's method was applied to bilevel the scanned images, based on which the three-dimensional model for crack's internal structure was reconstructed. The cake porosity and the geometric factors of cracks, such as the compactness, the boundary fractal dimension, and the Sierpinski carpet fractal dimension, were evaluated. The shrinkage of cake volume and the development of internal crack occurred simultaneously. The skin layer formed by the former mechanism retards further drying. On the other hand, the internal cracks were shown to exhibit zigzagging with a noncircular cross section and fractal-like boundary, which should be able to enhance local drying. A possible role of change in crack structure on the rate of drying was discussed.     

An approximate theory for stresses in dust cake of ceramic candle filters

A simplified theory is developed that yields the approximate stresses within a dust cake on the outer surface of ceramic candle filter and gives the critical factors which ensure complete detachment of cake. The radial and tangential stresses in cake during filtration have been derived by consideration of active state of stress in the dust cake. Back pulses of cleaning gas expand dust cake on the condition, that their power is just adequate to properties of cake, such as angle of internal friction and cohesion. Expansion of the dust cake induces tension cracks and disintegration of the cake. Back pulses of higher values hamper expansion of cake and cause “patchy” cleaning.     

二氧化硅气凝胶的制备和表征

以正硅酸四乙酯为硅源，通过采取老化、表面修饰、溶剂置换和分级干燥等一系列抑制二氧化硅气凝胶干燥中出现缩裂的有效措施，以非超临界干燥技术最终获得了大块无裂纹的二氧化硅气凝胶。该气凝胶的孔径较小且分布均匀，比表面积为684m^2／g，孔体积可达1．38cm^3／g，最可几孔径为3．221nm，平均孔径达2．871m。同时在实验和理论分析的基础上总结二氧化硅气凝胶缩裂的主要原因和抑制缩裂的有效措施。     

ESTIMATION OF THE EFFECT OF PRODUCT SHRINKAGE ON THE DRYING TIMES,HEAT INPUT AND CONDENSER LOAD OF THE PRIMARY AND SECONDARY DRYING STAGES OF THE LYOPHILIZATION PROCESS IN VIALS

ABSTRACT

The effects of cake shrinkage on the drying times and energy requirements of the primary and secondary drying stages of the freeze drying process involving the drying of a material in a vial, are estimated through the construction and solution of an extended unsteady state and spatially multidimensional model that accounts for the changes introduced by cake shrinkage on the internal and external mass and heat transfer mechanisms of the freeze drying     

Modeling of Thin-Layer Drying on an Inert Sphere

A semi-empirical model was developed for the drying of press cake on an inert sphere in the spout region of a dryer. The coefficients for the Lewis and Page (for the prediction of moisture ratio) and the Chung-Pfost (for the prediction of equilibrium moisture content) models were determined experimentally. The predicted temperature of the press cake was validated using three trials conducted at drying conditions (temperature, relative humidity): 55°C, 55%; 65°C, 45%; and 75°C, 43%. Predicted temperatures were within ～10% of the experimental temperatures. Improved prediction accuracy was achieved as press cake temperature approached air temperature.     

Filtration and Drying Study of Phosphatidylinositol Fraction from De-Oiled Soy Lecithin

Separation and purification of phosphatidylcholine (PC) and phosphatidylinositol (PI) fractions to their utmost purity is still a challenging task industrially due to the molecular and structural complexity of lecithin molecules. The present study deals with the filtration of the PI-rich fraction followed by drying of the cake for its further purification and value addition. Filtration of the PI-rich fraction was carried out under constant pressure conditions followed by the drying of the cake in a vacuum tray dryer. The average specific cake resistance (α_av) as a function of operating pressure was studied and it showed little variation with respect to the applied pressure differential. The initial solvent content in the cake after filtration was found to be in the vicinity of 1 kg solvent/kg dry solid, which was then subsequently reduced in the drying stage to 0.04 kg solvent/kg dry solid. The drying kinetics of the cake was studied at different drying temperatures in a vacuum tray dryer operated under varying degree of vacuum. The drying rate curve showed a prominent falling rate period with the effective solvent diffusivity in the range of 5.4 × 10^?10 m²s^?1 to 1.42 × 10^?9 m²s^?1within the temperature range of 40–60°C. Critical analysis of the dried PI fraction was carried out in terms of phosphatidylinositol content and color. The drying data were analyzed using various models and Das et al.'s model, the modified Henderson and Pabis model, and the Page model were found to provide the best fit sin terms of root mean square error (RMSE), chi square, and correlation coefficient (R ²).     

A study on air jet drying for water content reduction of sludge

An air jet drying system composed of a turbo blower, an air ejector and three stage cyclones is constructed to produce a dried powder through water content reduction of dewatered cake obtained from sludge treatment process. The air flow to be ventilated by the turbo blower forms a high speed flow field by passing through the air ejector and a circulative flow field by passing through the cyclones. Dewatered cake, 100 mm in size, is disintegrated by jet and collision through passing the air ejector and becomes fragmented with size no more than 2mm. These fragmented particles follow air flow and are dried as moisture is evaporated from particle surface. A powder composed of 1.6 mm spherical particles is produced from pilot scale equipment of 1 ton/hr under the conditions of air velocity, maximum flow rate and air temperature profile of 84 m/sec, 180 m³/min and 73-28 °C, respectively. The air dried powder with average water content of 49.8 wt% is recovered after drying the dewatered cake with water content of 83.3 wt% in a real operation, indicating 33.5 wt% decrease in water content. It is estimated that the power consumption of the air jet drying system requires 92 kWh/Ton to reduce the water content by 33.5 wt%, which is no more than a half against heat drying system to consume 164 kWh/ton.     

从软泥状到粉末

描述了旋转瞬时干燥设备利用机械能与热能，对糊状物与滤饼进行高效干燥的过程、设备的设计与干燥的成本，以及与之相关的其它方面。     

Humidity Drying of Plastic Clay

The humidity drying cycle gives rise to surface and body cracks in plastic clay. The cracks appear in the initial stages when the clay is being heated in a saturated atmosphere. Various factors affecting cracking in this initial heating stage were studied using a purified kaolin in the plastic state, and appropriate experimental models were used to isolate certain aspects for study. It is shown that the condensation of moisture on the clay surface is the major factor influencing the cracking of the plastic clay. The effect of thermal diffusion is insignificant and the loss of mechanical strength is of secondary importance. The balance af evidence from the literature and from this study indicates that capillarity plays a major part in the movement of moisture and the production of stresses during drying. When air spaces are present in the body, thermal capillarity may become important. Stresses caused by thermal expansion oppose those caused by drying shrinkage, while the thermal expansion of capillaries will have a negligible effect.     

PROCESS DESIGN OF ROTARY DRYERS FOR OLIVE CAKE

Olive-mill cake is one of the most widespread biomaterials for bioenergy exploitation in Greece. It is a sludge-type material, produced as byproduct from olive-mill extraction process. Its energy content is higher than 15 MJ/kg db and it can be used for direct burning, after drying. The drying process of olive cake is examined in the present paper. Drying kinetics data as well as the related thermophysical properties are obtained experimentally. The appropriate dryer model is proposed, validated and used to design an industrial rotary dryer. Economic analysis of the process is also discussed. A characteristic case study of an industrial rotary dryer for olive cake is included to illustrate the effectiveness of the proposed approach.     

利用恒沸蒸馏干燥超细二氧化硅凝胶的研究

研究了利用恒沸蒸馏脱除超细二氧化硅滤饼中水分的可行性和具体实现方法。研究结果表明：利用恒沸蒸馏可以明显地减弱颗粒之间的团聚和结块现象。这主要是因为作为蒸馏液的正丁醇较为彻底地将颗粒间隙的水分通过形成共沸物的方法脱出。正丁醇本身具有的较低表面张力和较低极性使粉体内部空间结构得到了较好的保护。证据显示，蒸馏过程不会对二氧化硅颗粒表面的活性基团造成明显改变。     

Wiederbefeuchtung bei der Pressfiltration

During press filtration, the filter cake experiences a plastic deformation. However, a filter cake expansion may occur once the pressing forces are released, which is confirmed by experiments with an aqueous coal suspension. Rewetting of the cake occurs when a liquid film is present during cake swelling, which deteriorates the cake dryness significantly. However, this can be prevented when the liquid film is successfully removed, and lower pressures suffice for mechanical cake drying.     

Cracking during freeze-drying in dense freeze cast ceramics: Role of drying rate

Cracks can form during the freeze-drying of freeze cast ceramic suspensions while attempting to produce dense ceramics. The suspensions contain alumina particles dispersed in cyclohexane. The rate of drying is controlled by the pressure and temperature during drying (slow drying at atmospheric pressure and −15°C and fast drying under vacuum while the temperature slowly increases from −80°C to room temperature). X-Ray micro-computed tomography was used to characterize internal crack formation. Cracks were found to occur during freeze-drying rather than during freezing. Both slow and fast drying produced cracks, although two different morphologies were observed. Mechanistic models are proposed for the formation of both types of cracks. The rate of freezing was found to influence the formation of cracks. Slow freezing tended to reduce the formation of drying cracks because the slower freezing produced a more heterogeneous distribution of particles and porous regions, which tends to allow stress to be relieved by opening up existing pores rather than forming cracks in the more homogeneous fast frozen bodies.     

Test Model for Studying Sun Drying of Rough Rice Using Far-Infrared Radiation

The effect of heat input, mixing at regular intervals, airflov over the surface and the relative humidity were investigated within a radiation chamber. Likening to sun drying as practiced in the tropics, the chamber was constructed to study the direct radiant heat drying of rough rice under various bed thicknesses. Graphic results showing the variations of rough rice surface temperature during the experiments are presented. Comparisons are also made between the relative contributions of bed depth and mixing on the drying rate. A non-mixed bed of 3 cm dried just as fast as a 6 cm mixed bed although moisture content was nonuniform in the former case. After drying, the grains were dehusked by hand and examined for physical defects like cracks. Possible constraints involved in drying thick beds of rough rice under direct radiation were investigated with the aim of defining suitable strategies for improving actual sun drying.     

Stress Cracking During High-Intensity Drying and its Effect on Grain Quality

Convective and microwave-assisted thin-layer drying of wheat has been studied to identify the relationship between drying parameters and stress cracks affecting the grain quality. Internal cracks developed during drying were visualized by the soft X-ray photography and quantified by a binary index. Definite effects from drying conditions on stress cracks and further on the grain quality categorized in terms of the germination capacity, sprout length and mechanical strength have been found. This confirms suitability of the X-ray method of cracks detection for selection of optimum drying parameters.     

PROCESS DESIGN OF ROTARY DRYERS FOR OLIVE CAKE

ABSTRACT

Olive-mill cake is one of the most widespread biomaterials for bioenergy exploitation in Greece. It is a sludge-type material, produced as byproduct from olive-mill extraction process. Its energy content is higher than 15 MJ/kg db and it can be used for direct burning, after drying. The drying process of olive cake is examined in the present paper. Drying kinetics data as well as the related thermophysical properties are obtained experimentally. The appropriate dryer model is proposed, validated and used to design an industrial rotary dryer. Economic analysis of the process is also discussed. A characteristic case study of an industrial rotary dryer for olive cake is included to illustrate the effectiveness of the proposed approach.