Spray Drying Tower Experiments

The article presents a full set of spray drying experiments for selected products performed in a co-current spray drying tower developed at Lodz Technical University. The experiments enabled identification of process and atomization parameters (feed properties, feed rate and feed temperature, drying agent temperature, air flow rate, atomization ratio, etc.) on drying and degradation kinetics, spray structure, particle residence time, and final product properties. Drying agent temperature measurements showed, in all cases, the initial increase of gas temperature in the spray envelope caused by the spray expansion and then a decrease induced by liquid evaporation and heat losses to the environment. PDA analysis confirmed that the initial velocity of particles was a function of a diameter and also the function of the distance from the axis. Practically an identical particle size distribution was observed in each cross-sectional area of the dryer. Negative values of particle velocity in the vicinity of the axis and at the edge of the spray envelope were found which proved that recirculation of particles appeared in the column. Analysis of final product properties showed that for agglomerate-like materials a decrease of bulk density with an increase of air temperature was related to morphological changes that occurred during drying and affected the shape of particles, surface structure, etc. The experiments proved that air/liquid ratio for two-fluid atomization and gas temperature were the most decisive factors controlling drying and degradation process rate and final product properties.     

Quality control charts for storage of raisins and dried figs

 Shewhart control charts are constructed by using the Hunter Lab color scale parameters to assure maintenance of the color of raisins and dried figs during storage in modified atmosphere packages, vacuum packages, or nylon bags. These control charts may be used to maintain the quality within acceptable limits and make it possible to readjust storage conditions if the acceptable limits should be violated. Received: 11 March 1996     

Chemical process opportunities for vibrated powders 3. Provisional design for an experimental sidewards flying bed

At a scale suitable for laboratory experimentation, a provisional mechanical design illustrates a concept for a “sidewards flying bed” (SFB), a layer of particulate matter held upon the inner wall of a cylinder that rotates at varying speed. Acting upon the layer are centrifugal and tangential forces whose patterns of variation create time intervals during which the latter is the greater. During such intervals, the layer is postulated to respond by “flying sidewards.” In a laboratory SFB set-up, experiments can elucidate a new area of non-steady-state soil mechanics, with outcomes bearing upon a full-scale SFB's chemical processing potential. An important question is, what will be the delay in the SFB layer's taking flight after the moment tangential force just begins to exceed centrifugal? For the SFB design to be successful, this delay should be significantly shorter than a time interval during which the tangential force dominates.If experiments were to show this not to be so, a “what-then?” might be to install several stationary rakes near the cylinder's inner wall, parallel to its axis. Loosening the particulate layer as the cylinder turns, these should advance the timing of the layer's flight.Achieving adequate flight in an experimental SFB could point to a design at a commercial scale capable of promoting rapid local mixing — more rapid than that afforded by conventional vibrated or fluid beds. Such should become a strong candidate for applications requiring rapid heating of hydrocarbonaceous matter followed by quick separation of vapor product and carbonaceous residue (e.g., flash pyrolysis of coal or oil-shale). The SFB's competencies should include ability to treat moieties of especially large size (e.g., for producing a smokeless solid fuel from coal, for heat-treating a metal part or a polymer, for flash-cooking foodstuffs without oil, for drying large particulates); ability to treat highly heterogeneous matter (e.g., for burning or gasifying comminuted biomass or solid wastes); and ability to promote excellent heat transfer between SFB and stationary surfaces embedded therein (e.g., in an air-cooled SFB steam-condenser).     

一种值得关注的低阶煤高效预干燥工艺

低阶煤的干燥是实现其高效利用所必须的预处理工艺。本文介绍了一种已在德国实现商业运行的"带有内部废热利用的流化床干燥"工艺。其工艺技术概念新颖,具有安全、高效、低耗、低排放的优点,是一种适用于低阶煤预干燥的先进工艺,值得关注。     

埋管流化床干燥机在多聚甲醛干燥中的应用

对喷雾法生产多聚甲醛的普通流化床干燥工艺进行了改进。成功地将埋管流化床干燥机应用于多聚甲醛干燥工艺,其节能和增产效果十分显著。     

聚丙烯粉料干燥效果差的原因与措施

介绍了环管法聚丙烯装置干燥单元的工艺流程和原理。对造成粉料干燥效果差的因素,如洗涤后的氮气温度、汽蒸罐中粉料的湿含量、干燥停留时间、干燥氮气流量和温度、干燥器故障,作了详细的分析。并针对车间产品干燥中出现过的一些问题,提出了干燥系统优良运行的操作措施。     

Drying Behavior of Meat Samples at Various Fiber Directions and Air Conditions

The aim of this study was to investigate the effects of meat fiber directions and air conditions on moisture and temperature developments, shrinkage, and effective diffusivity constants compared to homogenous minced meat samples. The lean meat with three fiber directions and minced meat samples were dried at temperatures of 48 and 70°C and air flow rates of 0.5, 1.0, and 1.7 m/s. The minced meat samples showed 1.0 ± 0.19 to 4.4 ± 0.03°C higher temperature values and 2.3 ± 0.004 to 6.2 ± 0.003% lower moisture losses than the lean meat samples in all fiber directions. The lowest temperatures were observed in lean meat with h ₁ (normal flow, normal drying) fiber direction. The highest moisture loss and diffusion coefficient were observed in lean meat with h ₂ (parallel flow, normal drying) and v (normal flow, parallel drying) fiber directions, which also possessed the shortest drying times (10.4 and 13.4 h, respectively). The estimated diffusion coefficient values ranged between 1.11 × 10^?9 and 5.54 × 10^?9. The results indicated that lean and minced meat samples differed in their drying behaviors in a tray dryer under the tested conditions with >90% reproducibility (or ≤10% coefficient of variation).     

Effect of Different Drying Methods on the Microwave Extraction of Phenolic Components and Antioxidant Activity of Highbush Blueberry Leaves

In the last few decades, researchers have found blueberry leaves to be an interesting source of different phenolic compounds, and drying is an important part of their postharvest and sample preparation processes. In the current study, blueberry leaves were dried using microwave-assisted hot air drying or hot air drying alone at 45, 60, and 75°C to 10–15% wet basis. Corresponding drying characteristics were determined by fitting the moisture ratio obtained in each case with eight theoretical and semitheoretical models for hot air and microwave drying stages. It was observed that best fitting drying models for blueberry leaves depended not only on the nature of the biomaterial but also on the method of drying and the temperature of drying. Phenolic content, monomeric anthocyanin content, and the corresponding antioxidant activity in terms of 2,2-diphenyl-1-picrylhydrazyl (DPPH) inhibition activity and ferric reducing ability of plasma (FRAP) activity were evaluated for the leaf extract obtained following microwave extraction of the dried samples obtained using the above-mentioned drying methods and were compared to the corresponding bioactive compositional characteristics of freeze-dried blueberry leaves. It was observed that the freeze-dried sample had the highest content of total phenolics and total monomeric anthocyanins along with high antioxidant activity. Furthermore, extracts obtained from the microwave-dried leaf samples obtained with a drying temperature of 60°C had highest total phenolic content and highest total monomeric anthocyanin content among all other drying methods and the extract had an antioxidant activity similar to the freeze-dried blueberry leaf samples, implying that microwave drying at 60°C is a potential alternative to freeze drying for preservation of the phenolic components and antioxidant activity of dried blueberry leaves.     

Comparison of Three New Drying Methods for Drying Characteristics and Quality of Shiitake Mushroom (Lentinus edodes)

This articles provides results of an experimental investigation of three hybrid drying technologies on the drying characteristics and key quality parameters of shiitake mushroom (Lentinus edodes). The drying techniques tested at the laboratory scale are mid-infrared-assisted convection drying (MIRCD), hot air coupled with radio frequency drying (HCRFD), and hot air coupled with microwave drying (HCMD). For comparison, the standard drying technique using hot air was also tested. The quality parameters include texture, color, rehydration rate, shrinkage, nutrient retention, microstructure, etc. These four drying tests were conducted at fixed air temperature (60°C), and the power level for HCRFD, MIRCD, and HCMD was fixed at 4 W/g. The results showed that hot air coupled with microwave drying gave the shortest drying time, and mid-infrared-assisted convection and hot air coupled with radio frequency drying showed better color attributes and nutrient retention. Under the conditions tested, mid-infrared-assisted convection drying yielded minimal shrinkage (maximal rehydration) and lower hardness upon rehydration. The uniform honeycomb network and less collapsed structure of MIRCD samples can be used to explain these better quality characteristics.     

Thermal analysis of drying process of durum wheat dough under the programmed temperature-rising conditions

The effects of temperature and moisture content on the drying rate of durum wheat pasta were examined using thermogravimetry and differential scanning calorimetry (DSC) at temperature-rising rates of 0.2–1.0 °C/min. The activation energy for the mass transfer coefficient of drying was estimated to be ca. 32 kJ/mol at a moisture contents of 0.14 kg-H₂O/kg-d.m. or higher, but increased rapidly as the moisture content dropped below this level. The conclusion temperature of the endothermic peak in the DSC and the temperature of the inflection point of the drying characteristics curve were located near the glass transition curve of the durum semolina flour.