干燥方法对几种植物染色能力的影响

本文研究了蓝桉树皮和洋葱皮干燥方法对化学浆染色能力的影响。这些植物材料含有丰富的多酚类化合物,如单宁酸、花青素和其他黄酮类化合物,是天然的着色剂。本文研究了不同条件下的自然干燥、空气干燥和冷冻干燥三种方法。此外,还研究了提取条件对两种植物样本染色能力的影响。自然干燥的植物样本与空气干燥和冷冻干燥的植物样本相比,呈现出很弱的染色能力。空气干燥和冷冻干燥具有相似的染色结果。在空气干燥实验中,在低温（T=30℃）和高湿度（95％RH）条件下干燥可以获得很强的染色能力。而对于提取条件,染色能力主要取决于提取温度,而停留时间对染色能力影响甚微。     

Fluidized bed drying of a pharmaceutical powder: A parametric investigation of drying of dibasic calcium phosphate

A parametric analysis of four fluidized bed dryer operating parameters—initial moisture content, material loading, heating air temperature, and air flux—was carried out using two factorial experimental designs. Two different dryer scales, the Glatt GPCG-1 and MiniGlatt, with chamber volumes of 23 and 3?L, respectively, were used to dry dibasic calcium phosphate powders. According to a Pareto analysis, initial moisture content and air flux were the most significant variables. For the larger GPCG-1, the four variables used in the factorial tests were found to be independent. For the smaller MiniGlatt, the interaction of the initial moisture content and the air flow rate was also significant. From the parametric analysis, it was observed that drying is dominated by the constant drying stage, and zero-order kinetics, for the mild drying conditions (appropriate for many pharmaceutical products) we considered in this work. A comparison of the two dryers and an evaluation of energy efficiency were also carried out. It was found that drying should be carried out with relatively low temperatures and high air fluxes for both the large- and small-scale dryers in order to maximize the energy efficiency.     

Study and comparison of different drying processes for dehydration of raspberries

The aim of the present study was to evaluate and compare different drying methods (microwave, hot air?+?microwave, and osmotic dehydration?+?microwave) in raspberries (cv. Heritage). A portion of raspberries was pretreated with osmotic dehydration (60°Brix sucrose solution at 20°C for 360?min) and another with hot air drying (HAD) (1.5?m/s air speed at 60°C for 300?min). Pretreated raspberries were then dried by microwave and at three different intensities (3.5, 7.5, and 11?W/g). Physicochemical properties (moisture content, water activity, and drying rate) and quality parameters (optical properties, mechanical properties, antioxidant capacity, and rehydration capacity) of dried raspberries were evaluated. Results showed that the microwave drying (MWD) at 7.5?W/g (50?min and final temperature of 79?±?5.1°C) allowed a high yield of dried raspberries. The combined processes were not efficient to accelerate the decrease of moisture content, due to the low drying rate of the pretreatments. In terms of quality, none of the drying processes allowed a high retention of the antioxidant capacity. However, they allowed an appropriate rehydration performance. The combination of HAD with MWD allowed obtaining a good appearance and desirable texture on the dried product. Thus, this last option seems to be the best among the drying methods tested, but additional studies are required to improve the efficiency of the process and the effect on the antioxidant capacity during drying.     

A Moisture Transfer Model for Isothermal Drying of Plant Cellular Materials Based on the Pore Network Approach

Plant materials with cellular structure, like fruits and vegetables, are often viewed as porous media in terms of model building of the drying process, on the basis of a hypothesis that all of the moisture of a plant tissue is trapped in a continuous and connected pore network system. However, most of the moisture in the plant tissue is contained naturally in enclosed cells. In the course of drying, the trapped moisture has to cross the cell membranes and then migrates in the extracellular space. Based on this concept, a pore network model for isothermal drying of plant materials was developed in which two stages of moisture movement—transmembrane transfer and extracellular transfer in the pore network—were considered. Finally, the isothermal convective air-drying processes of a potato slice were simulated. The calculated results were validated by the experiments conducted under the simulation conditions.     

不同初始含水率湿天然橡胶微波干燥特性研究

对不同初始含水率的湿天然橡胶(NR)微波干燥特性进行了研究。结果表明,湿天然橡胶微波干燥的全过程可分为加速、减速、相对恒速干燥三个阶段;湿天然橡胶快速干燥和较快速干燥阶段为物料干燥的主要阶段;不同的初始含水率对湿天然橡胶的干燥过程和产品表观质量影响较大,胶料初始含水率越高,干燥速率越快,但干燥时间较长,且产品表观质量较差,初始含水率越低,干燥时间短,产品表观质量较好;湿天然橡胶微波干燥较佳初始含水率范围为10%～20%。     

Diffusive Model with Shrinkage in the Thin-Layer Drying of Fish Muscles

Fish fillets present large variation in volume during drying, due to their high initial moisture content. A kinetical study on the drying of fish muscles in slabs shaped with constant air conditions at three temperature levels is presented. For the modeling of the drying process of these materials, a diffusive model can be used, assuming a one-dimensional volume change. A linear correlation was considered between the thickness of the material and its moisture content, where the linear shrinkage coefficient has been determined. The resulting dimensionless nonlinear partial differential equation was solved numerically by the finite differences technique.     

重庆市珞璜污泥热干化工程案例

重庆市珞璜污泥热干化工程一期规模为600 t/d(含水率为80%),干化厂厂址位于重庆华能珞璜电厂厂区内。污泥处置工艺采用半干化+热电厂掺烧,干燥机设备选用圆盘式干化设备,污泥干化程度由含水率80%降至含水率30%左右。干污泥送至热电厂按照一定比例与煤掺烧,干化需要的热源采用电厂提供的蒸汽。污泥干化过程中产生的高温高浓度臭气由引风机送至热电厂锅炉焚烧除臭,低温低浓度臭气采用生物滤池除臭;污泥干化过程中产生的冷凝废水经预处理后送至珞璜工业园区污水处理厂,处理后达标排放。本工程实现了污泥处理处置的稳定化、无害化和资源化。     

Energy Analysis of Low-Rank Coal Pre-Drying Power Generation Systems

Low-rank coal (LRC) is widely used for power generation in many regions of the world. However, due to the high moisture content of LRC, the overall efficiency of LRC-fired power plants without a pre-drying system is relatively low. Studies show that the overall efficiency can be improved by pre-drying the coal, and the fluidized bed drying technique is found to be a desirable choice because of its high drying rate, high processing capacity, and low maintenance cost. In this paper, two novel, fluidized-bed, LRC pre-drying systems were integrated into a 1000 MW LRC-fired power plant. Superheated steam and hot air were used as the fluidizing medium. Models for each component of these power generation systems were developed based on material and energy balances. The performances of these power plants were calculated under the typical operating conditions, and parametric analyses were also performed to evaluate the effect of operating parameters. The power generation efficiency is found to increase remarkably with a properly operated LRC pre-drying system.     

Conditions for Accurate CFD Modeling of Spray-Drying Process

The paper presents concluding results of extensive experimental and theoretical research on confident CFD modeling of spray drying. An earlier developed experimental method to determine spray-drying kinetics in a lab scale allowed us to find a critical material moisture content and to determine generalized spray-drying curves. The generalized drying curves, identical in shape in the laboratory and pilot plant units, were used in the CFD model of spray drying process. Extensive simulations for spray drying of 10, 30, and 50% of initial solid content of maltodextrin proved high accuracy of the predictions of discrete (particle size distribution, particle moisture content, particle velocity, spray temperature) and continuous-phase parameters (gas temperature and humidity). Maximum error of the predictions of discrete-phase parameters was on the level of 20%, which is probably close to the current capacity of the CFD technique for modeling of spray-drying process. Comparison of experimental measurements and theoretical results shows that incorporation of realistic spray-drying kinetics into the CFD model and correct definition of initial drying and atomization parameters enable reliable simulations of spray-drying process.     

Continuous fluidized bed drying: Residence time distribution characterization and effluent moisture content prediction

The mixing and drying behavior in a continuous fluidized bed dryer were investigated experimentally by characterizing the residence time distribution (RTD) and incorporating a micromixing model together with the drying kinetics obtained from batch drying. The RTD of the dryer was modeled using a tank-in-series model. It was found that a high initial material loading and a low material flow rate resulted in a reduced peak height and broaded peak width of the RTD curve. To predict the continuous dryer effluent moisture content, we combined: (a) the drying kinetics as determined in a batch fluidized bed dryer, (b) the RTD model, and (c) micromixing models—segregation and maximum mixedness models. It was found that the segregation model overpredicted the effluent moisture content by up to 5% for the cases we have studied while the maximum mixedness model gave a good prediction of the effluent moisture content.     

Optimization study of soybean intermittent drying in fixed-bed drying technology

Intermittent drying of materials is an alternative operation that aims at reducing energy consumption, improve the preservation of dried products or decrease effective drying time. Intermittent drying supplies the system with time-varying input air properties that are opposite to traditional operations, where air properties are constant at the dryer inlet. The major objective of this study is to establish the most satisfactory patterns of air temperature and velocity modulation at the dryer entrance to reduce energy consumption. This optimization study was based on a heterogeneous model for the drying of grains in fixed bed validated with experimental data. Intermittent and conventional operation experiments were conducted using equal energy consumption, and the influence of air temperature and velocity modulation on the drying rates related to the percentage of evaporated water were assessed. Results indicated that higher drying rates can be achieved under intermittent operation, and the validated model based on these results could reasonably predict temperature and moisture content profiles. Simulations pointed out that the best modulation patterns of air properties is a function of a variety of system conditions such as initial temperature and moisture content of both soybean and drying air. However, a tendency to reduce energy consumption was observed when the system operation is initially at high temperature and constantly at low velocity.     

Experimental Investigation of a Solar Bamboo Dryer

ABSTRACT

An experimental investigation was conducted on the performance of a solar box dryer for drying bamboo operating under tropical weather conditions. The dryer is a greenhouse-type designed for multi-crop solar drying. Air circulation was by electrically-operated fan. The results showed that the moisture content of the bamboo could be brought dovn to about 19% from an initial value of nearly 90% in 17 days by operating the dryer over 8 hours each day. under natural drying conditions, the final moisture content reached was only 22%. Although solar drying of bamboo was only marginally faster than natural drying. nonetheless. final moisture content was lower.     

DRYING CHARACTERISTICS OF SLOT JET REATTACHMENT NOZZLE AND COMPARISON WITH A SLOT JET NOZZLE

ABSTRACT

Slot Jet Reattachment (SJR) nozzle is an extension of the Radial Jet Reattachment (RJR) concept used to provide high heat and mass transfer while minimizing flow exerted forces on the reattachment surface. The SJR is a slot jet nozzle with a bottom plate attached to it, which is machined to direct impinging flow at different angles to the surface. The drying characteristics of the SJR nozzle with four exit angles on a paper sample were studied for three Reynolds numbers, three temperatures and two initial moisture contents. Dry air was used as the jet fluid. Correlations to predict drying rates and moisture content for the SJR nozzle as a function of exit angle, temperature, Reynolds number and drying time, for a given initial moisture content, were developed. A comparison of the drying characteristics and net forces of the slot jet and SJR nozzles was also performed under the same flow power and surface peak pressure.     

Experimental Investigation of a Solar Bamboo Dryer

ABSTRACT

An experimental investigation use conducted on the performance of a solar box dryer for drying bamboo operating under tropical rearher conditions. The dryer is a greenhouse-type designed for multi-crap solar drying. Air circulation was by electrically-operated fan. The results shoved that the moisture content of the bamboo could be brought down to about 19% from an initial value of nearly 90% in 17 days by operating the dryer over 8 hours each day. Under natural drying conditiona. the final moisture content reached was only 12%. Although eolar drying of bamboo vaa only marginally faster than nacural drying. noncrhelesa. final moisture content was lower.     

Scanning Electron Microscopic Study of Microstructure of Gala Apples During Hot Air Drying

Microscopic changes that occur in plant food materials during drying significantly influence the macroscopic properties and quality factors of the dried food materials. It is critical to study the microstructure to understand the underlying cellular mechanisms to improve the performance of food drying techniques. However, there is limited research on such microstructural changes of plant food material during drying. In this work, Gala apple parenchyma tissue samples were studied using a scanning electron microscope for gradual microstructural changes as affected by temperature, time, and moisture content during hot air drying at two drying temperatures: 57 and 70°C. For fresh samples, the average cellular parameter values were as follows: cell area, 20,000 µm²; ferret diameter, 160 µm; perimeter, 600 µm; roundness, 0.76; elongation, 1.45; and compactness, 0.84. During drying, a higher degree of cell shrinkage was observed with cell wall warping and an increase in intercellular space. However, no significant cell wall breakage was observed. The overall reductions in cell area, ferret diameter, and perimeter were about 60, 40, and 30%. The cell roundness and elongation showed overall increments of about 5% and the compactness remained unchanged. Throughout the drying cycle, cellular deformations were mainly influenced by the moisture content. During the initial and intermediate stages of drying, cellular deformations were also positively influenced by the drying temperature and the effect was reversed at the final stages of drying, which provides clues regarding case hardening of the material.     

A Moisture Transmembrane Transfer Model for Pore Network Simulation of Plant Materials Drying

The drying of plant materials with cellular tissue is often viewed as drying of porous media that is assumed to consist of cell cytoskeleton and intercellular space. Various approaches have been reported in the literature to describe heat and mass transfer during drying of such porous materials. However, the fact remains that the water in a cellular tissue is mostly intracellular and it should be driven out of the cells across cell membranes before transporting in cell gaps, as in a general porous media. In the present study, the transport process of moisture in a cellular tissue was analyzed. A mathematical model for moisture transport across the cell membrane was established, which was correlated to a self-developed, dual-scale pore network model (cell and pore network) for drying of plant materials. The relationship between mass volumetric flux and average intracellular moisture content was developed based on the microscopic images and the drying experiments.     

Immersion Drying of Wheat Using Al-PILC, Zeolite, Clay, and Sand as Particulate Media

Wheat (Triticum durum) was dried by immersion in a particulate medium grain dryer using natural clay, pillared aluminum clay (Al-PILC), zeolite 13X, and sand as particulate medium at different initial bed temperatures and residence times in the dryer. Results showed that zeolite caused the highest grain moisture loss for a given drying time, followed by Al-PILC, natural clay, and, finally, the sand. The drying capacity of the Al-PILC was similar to that of the zeolite. The Al-PILC transferred an amount of heat equivalent to 85-94% of the heat transferred by zeolite and evaporated 83-93% of the moisture removed by zeolite. Results also showed that the zeolite and the Al-PILC had the best heat and mass transfer properties of the four particulate materials used and that the Al-PILC can be used as an alternative of the zeolite in particulate medium immersion grain drying.     

高水分玉米真空低温干燥工艺生产性试验研究

东北是我国玉米的主产区，产量占全国的30％～40％。受自然条件的影响，玉米收获水分常达22％～30％；成熟度及含水率都不均匀。根据玉米热敏性物料干燥的热特性及市场要求，考虑到它的热稳定性及破碎敏感性的特点，采用真空低温干燥技术进行了生产性试验，设计了300t／d高水分玉米真空低温连续干燥工业自动化生产线，对生产性试验关键技术进行了分析和研究。依据试验结果，分析玉米含水率、干燥介质温度、真空度、玉米温度、干燥时间、汽化蒸发温度等参数之间的联系与相互作用。生产试验表明：玉米含水率在24％时，维持干燥塔内真空度，采用高温水加热，汽化蒸发温度40～43℃，一次降水幅度达到10％～15％，保证了玉米品质的色、香、味、形及营养成分，具有干燥品质好、降水速度快、产量高、能耗低、操作方便、经济性价比高等优点。     

Immersion Drying of Wheat Using Al-PILC,Zeolite, Clay,and Sand as Particulate Media

Wheat (Triticum durum) was dried by immersion in a particulate medium grain dryer using natural clay, pillared aluminum clay (Al-PILC), zeolite 13X, and sand as particulate medium at different initial bed temperatures and residence times in the dryer. Results showed that zeolite caused the highest grain moisture loss for a given drying time, followed by Al-PILC, natural clay, and, finally, the sand. The drying capacity of the Al-PILC was similar to that of the zeolite. The Al-PILC transferred an amount of heat equivalent to 85–94% of the heat transferred by zeolite and evaporated 83–93% of the moisture removed by zeolite. Results also showed that the zeolite and the Al-PILC had the best heat and mass transfer properties of the four particulate materials used and that the Al-PILC can be used as an alternative of the zeolite in particulate medium immersion grain drying.     

Development and Thermal Modeling of a New Construction Biomass Dryer

A new dryer construction has been developed for drying biomass basic materials for energy purposes (straw, sawdust, and other light granular materials). As a result of its simple design, the machine is perfectly suitable for reducing moisture by heat transfer. Compared to the machine types applied thus far, this new construction provides a better ratio of dryer floor space and drying distance and, as a result, a longer drying time. A differential equation system for convection drying was applied for the thermal modeling of the equipment; the mathematical model produced on the basis there of is suitable for examining the heat and mass transfer processes within the dryer. In the course of experimental measurements performed in an industrial size apparatus, the temperature and moisture content of the drying gas were recorded with the initial and final moisture content and surface temperature of the product. The measured values were compared to the results of calculations using the mathematical model.