微波干燥湿法炼锌中和铁渣实验研究

湿法炼锌产出的中和沉铁渣作为重要的二次资源,含有大量的铁、锰、锌等有价金属,具有较高的综合回收利用价值。回收有价金属前需对中和铁渣进行脱水预处理,基于回转窑干燥法存在干燥时间长、干燥效率低、二次污染等问题,本文开展了微波干燥湿法炼锌中和铁渣实验研究,考察了微波功率、物料量对中和铁渣温升行为的影响,表明微波干燥湿法炼锌中和铁渣是可行的;实验考察了微波功率、物料量和干燥时间对中和铁渣脱水率的影响。研究结果表明：在一定程度上,中和铁渣脱水率与干燥时间和微波功率成正比,与物料量成反比。实验控制微波功率为1000W、物料量为50g、微波干燥时间为9min时,中和铁渣脱水率达98.55 %;X射线衍射、红外光谱分析展示微波干燥中和铁渣自由水脱除较为完全,但仍含有部分的结晶水;扫描电镜分析显示微波干燥较常规干燥更为均匀;与常规干燥工艺相比,微波干燥具有干燥时间短、水脱除率高、干燥均匀、清洁无污染等优势。     

褐煤干燥水分回收利用及其研究进展

褐煤干燥提质过程中的水资源化回收利用工艺技术可以提高煤阶并回收宝贵的水资源,降低干燥提质单元能耗。本文从介绍褐煤中水的存在形态出发,围绕烟气直接干燥、蒸汽流化床干燥、微波干燥、机械热压脱水干燥等工艺综述了近年来干燥水回收利用的研究现状和最新进展,讨论分析了褐煤干燥与水回收利用工艺的选择原则。在回收褐煤中丰富的水资源时,除了单纯考虑回收褐煤中的水资源,还应权衡褐煤干燥工艺、干燥温度和干燥介质、干燥水蒸气的余热利用方式以及干燥工艺上下游间的衔接等因素。基于目前褐煤资源的主要用途,将干燥尾气采用换热技术回收低温余热和干燥冷凝水直接净化处理后的二次回用技术将是以后的重要研究和应用方向。     

湿法炼锌泥的微波干燥实验

目前回转窑干燥物料的方法主要存在干燥时间长、环境污染严重、效率低等缺点,为了解决这一问题,开展了微波干燥湿法炼锌泥的实验研究,采用实验室自制的微波干燥设备,考察微波功率、干燥时间以及物料质量对样品脱水率的影响。研究结果表明:在一定条件下,脱水率随干燥时间延长而增加,随着微波功率的增加而提高,随物料质量增加而降低。实验在微波功率600W、物料质量40g、微波加热时间3min时,湿法炼锌泥的脱水率达到99.57%;FT-IR分析可知,干燥后波数1625cm^-1和3300cm^-1附近水分子的伸缩振动峰基本消失,说明微波干燥后物料基本不含水分;与常规干燥进行比较,微波干燥湿法炼锌泥具有干燥时间短、脱水效率高、清洁无污染的优点,是一种高效节能的新型干燥方法。     

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.     

Microwave Convective Drying of Plant Foods at Constant and Variable Microwave Power

Microwave convective drying of plant foods is a promising process due to the shorter drying time and better product quality. High microwave power decreases the drying time but causes charring of the product. In this work, microwave drying under constant and variable microwave power were compared. Temperature-sensitive products, such as plant foods, are especially affected by microwave power during the final drying period. Therefore, drying at variable microwave power was found to be a more suitable drying process. Air (temperature and velocity) has an important role during microwave drying, not only as carrier of evaporated moisture but also as it contributes to a more homogeneous and faster drying.     

Functionalized Cellulose Fibers for Dewatering and Energy Efficiency Improvement

Paper drying accounts for nearly 80% of the energy used in the papermaking process. This is due to the high energy requirements for the process of drying by vaporization. Because the cost-effectiveness of the various physical means of dewatering far exceeds that of thermal drying, significant energy savings can be expected if the physical dewatering effectiveness is improved. To that end, a novel method of enhancing the physical dewatering process that involves the addition of hydrophobic fibers to the pulp furnish is described and evaluated. Freeness and water retention measurements indicate that the addition of hydrophobic fibers at even a few weight percent may have a significant impact on the freeness and water retention properties of the furnish and therefore a significant improvement in the effectiveness of the physical dewatering of webs made using the hydrophobically tailored furnish material.     

Microwave Convective Drying of Plant Foods at Constant and Variable Microwave Power

Microwave convective drying of plant foods is a promising process due to the shorter drying time and better product quality. High microwave power decreases the drying time but causes charring of the product. In this work, microwave drying under constant and variable microwave power were compared. Temperature-sensitive products, such as plant foods, are especially affected by microwave power during the final drying period. Therefore, drying at variable microwave power was found to be a more suitable drying process. Air (temperature and velocity) has an important role during microwave drying, not only as carrier of evaporated moisture but also as it contributes to a more homogeneous and faster drying.     

不同干燥因素对天然橡胶微波干燥过程的影响

使用动态称量微波干燥设备研究了不同微波功率密度、不同胶样厚度和不同初始含水率3种因素对湿天然橡胶微波干燥过程及表观质量的影响。结果表明,3种因素对湿天然橡胶微波干燥过程和胶样表观质量的影响较大;微波功率密度越大,失水速率就越大,干燥时间就越短,胶样易出现干燥发粘现象;胶样厚度越厚,失水速率越小,干燥时间就越长,易出现部分夹生和发粘现象;初始含水率越高,失水速率就越大,干燥时间就越长,胶样易出现部分发粘现象。微波干燥湿天然橡胶较为合适的微波功率密度、胶样厚度和初始含水率分别为30.14-34.2W/dm3,5~15mm和10%-20%。     

胡萝卜微波真空干燥试验研究

以胡萝卜为原料，采用均匀设计对微波真空干燥的微波功率、干燥温度及料层厚度进行试验研究，分析各试验条件下的水分含量及胡萝卜素含量，得到了干燥曲线和胡萝卜素保有量曲线，得出了胡萝卜失水量、胡萝卜素含量与各因素之间的回归方程，可用于描述胡萝卜的微波真空干燥特性。     

Heat and mass transfer model of dielectric-material-assisted microwave freeze-drying of skim milk with hygroscopic effect

A new porous media mathematical model for freeze-drying was developed based on the adsorption-desorption relationship proposed in this paper. A finite difference solution was obtained from a moving boundary problem for the dielectric-material-assisted microwave freeze-drying process. Silicon carbide (SiC) was selected as the dielectric material; and frozen skim milk was used as the aqueous solution to be dried. Simulation results showed that the dielectric material can significantly enhance the microwave freeze-drying process. The drying time was 33.1% shorter than that of ordinary microwave freeze-drying under typical operating conditions. When the solid content of the solution to be freeze-dried was very low, or the solid product had a very small loss factor, microwave heating was less effective without the assistance of dielectric material. The mechanisms of heat and mass transfer during drying were analyzed based on profiles of ice saturation, temperature and vapor concentration. Drying rate-controlling factors were discussed. A comparison was made between the model predictions and the reported experimental data.     

Analysis of Effectiveness and Stress Development during Convective and Microwave Drying

The aim of the article is to study the effectiveness of convective and microwave drying with respect to drying time and stress generation in clay-like dried bodies. The theoretical analysis of stresses was confined to the constant drying rate period because clay shrinks and the stresses are generated mainly in this period. The theoretical prediction of stress development was validated using an acoustic emission method by monitoring the micro- and macrocracks formation caused by the stresses. Apart from the stress analysis, the combined convective-microwave drying was examined experimentally during whole process in order to show that the volumetric heat supply due to microwave heating enhances convective drying and, apart from this, such a combined drying process develops less stress in dried material. The theoretical and experimental studies were performed on a kaolin sample in the form of a thin plate.     

Analysis of Effectiveness and Stress Development during Convective and Microwave Drying

The aim of the article is to study the effectiveness of convective and microwave drying with respect to drying time and stress generation in clay-like dried bodies. The theoretical analysis of stresses was confined to the constant drying rate period because clay shrinks and the stresses are generated mainly in this period. The theoretical prediction of stress development was validated using an acoustic emission method by monitoring the micro- and macrocracks formation caused by the stresses. Apart from the stress analysis, the combined convective-microwave drying was examined experimentally during whole process in order to show that the volumetric heat supply due to microwave heating enhances convective drying and, apart from this, such a combined drying process develops less stress in dried material. The theoretical and experimental studies were performed on a kaolin sample in the form of a thin plate.     

微波辐射干燥硫酸钠的工艺研究

研究了利用微波干燥硫酸钠的工艺 ,并分析了微波功率、辐射时间、物料质量和物料厚度对硫酸钠脱水率的影响     

Optimizing Drying Conditions for the Microwave Vacuum Drying of Enzymes

The aim of this study was the methodological use of experimental planning for the optimization of microwave vacuum drying of enzymes using α-amylase as a model. A factorial in star designwas used to optimize the microwave vacuum–drying process, and the variables were power output and vacuum pressure. The material dehydrated by this technique was analyzed with regard to its enzymatic activity, water activity, and moisture content. Response surface methodology was used to estimate the main effects of vacuum pressure and power on the enzymatic and water activities. The experimental in star design revealed that microwave vacuum drying is influenced mainly by power. The dehydrated product showed high enzymatic activity and low water activity.     

Dewatering of Phosphatic Clay Waste by Flocculation

This work focuses on the dewatering of phosphatic clay waste of Egyptian Abu‐Tartur phosphate ore by flocculation using polyacrylamides to enhance the dewatering rate and recycling of the process water. The experimental program includes sieving, hydrocyclone separation and flocculation of the overflow of hydrocyclone. Results revealed that the coarser fraction larger than 32 micron is enriched with P₂O₅ whereas the undersize fraction is only clay. Hydrocyclone successfully separates two cuts; the underflow fraction is enriched with phosphate while the other is just clay. By this technique, the P₂O₅ content is increased from 15.57 % in the feed to 26 % in the underflow cut which constitutes about 39.8 % by weight. Flocculation helps to increase both the settling rate of phosphatic clay waste and recycling the process water. The former criteria increased 37 times by using anionic polyacrylamide (A130) as compared to the natural settling rate of the same waste. Results were explained in the light of a model which suggests that the flocculation mechanism involves two stages: the first stage involves the adsorption of the reagent on the particles whereas the second forms aggregate flocs. Formation of aggregate flocs takes place by tangling the polymer molecules, so that one polymer molecule will be adsorbed at several points on the surface of the particle, leaving loops which may be of varying lengths, projecting out from the surface. Partially covered particles would collide to form bridges.     

Quality optimisation of combined osmotic dehydration and microwave assisted air drying of pineapple using constant power emission

Combination of osmotic dehydration with microwave assisted air drying offers increased flexibility for process control and product quality. Osmotic dehydration (55°Brix solution at 40 °C for 90 min) combined with microwave assisted air drying (MWAD) was tested on smooth cayenne pineapples. The influence of the four most relevant processing parameters (osmotic treatment time, microwave power, air temperature and air velocity) was studied using a 2⁴ circumscribed central composite experimental design. The product quality was evaluated in terms of charred appearance at the surface, moisture content, soluble solids content, water activity, firmness, colour and volume. Microwave power and air temperature were the two most important processing parameters that influenced the quality of the dehydrated pineapple, with the parameters most affected by the operating conditions being water content and percentage of charred pieces. Only in the latter was a significant quadratic effect found, all others were approximately linear. There was also a significant interactive effect between microwave power and air temperature affecting the percentage of charred pieces. Model predictions using a quadratic surface for water content and % charred pieces were validated with an additional experiment. Quadratic models were used to indicate optimum drying conditions for various targets.     

吸湿多孔介质冷冻干燥传质传热模型

本研究在作者提出的吸附—解吸平衡关系的基础上,建立了一个全新的考虑吸湿效应的多孔介质冷冻干燥数学模型。模型用有限差分法进行求解,并带有一个移动边界,以模拟介电材料辅助的微波冷冻干燥过程。介电材料选用碳化硅（SiC）,原料液为脱脂奶。模拟结果表明：介电材料能够有效强化微波冷冻干燥过程。在典型操作条件下,介电材料辅助的微波冷冻干燥所用的时间比普通微波冷冻干燥减少33.1%。当料液中固体含量较低或者固体产品的损耗因子较小时,介电材料对微波加热的效果不明显。基于冰饱和度、温度和水蒸气浓度的分布,本文分析了干燥过程中的传质传热机理,并对干燥速率控制因素进行了讨论。     

Quality Enhancement for Thermosensitive Materials Dried with Solid Carriers

Thermal drying is a widely applied method for dewatering of bioproducts. However, due to high thermolability of biomaterials, such a drying process may cause serious damage of the product quality. To minimize product degradation, the drying of biomass with porous solid carriers was applied. A set of experiments designed by the orthogonal method was carried out in a laboratory vibrofluidized bed dryer. A substantial improvement is documented in the final quality of the products when dried in the presence of a porous solid carrier. The effect of process parameters on quality retention is also presented.     

藤茶中二氢杨梅素的微波萃取

以干藤茶叶为原料,在微波辐射条件下,以水为溶剂提取二氢杨梅素,考察了微波功率、微波辐射时间、料液比、浸提时间等因素对提取率的影响,通过单因素分析和正交试验设计确定了最佳提取工艺条件。确定的最佳提取工艺条件为:微波功率为高档,微波辐射时间为3min,料液比为1:20,水浴浸提时间为2h。在此条件下二氢杨梅素的提取率为29%。