Optimization of crystalline powders vacuum contact drying with intermittent stirring

Modified literature models were successfully applied to simulate the evolution of the average solvent content (ethanol) of potassium chloride bed during vacuum contact drying with intermittent stirring. Our new modeling approach introduced the following modifications: taking account of jacketed vessel wall heat transfer coefficient; taking account of an accumulation term in the heat balance for the heated wall; application of alternate static bed and stirred bed conditions; modeling of all the three drying phases, namely the constant rate phase, the transition phase and the falling rate phase.Several identification and validation experiments were carried out with a reliable laboratory vacuum contact dryer at different operating conditions. A good agreement between the simulated and experimental drying curves was observed and the experimental drying times were also very well predicted by the improved model with six fitting parameters in the most complicate case. The duration of periods with stirring and without stirring were optimized with the aim to obtain high mean drying rates with a low total stirring time in order to reduce the attrition and agglomeration phenomena.     

Drying kinetics and product quality of green soybean under different microwave drying methods

The objective of this study was to investigate the effect of different microwave drying techniques on the drying kinetics and product quality of dried green soybean. Experiments were conducted using microwave vacuum drying (MVD), pulse-spouted vacuum microwave drying (PSMVD), pulse-spouted microwave drying (PSMD), and microwave freeze drying (MFD). Parameters of apparent density, color, processing temperature, expansion ratio, rehydration ratio, texture, and microstructure of the dried products were determined. The results showed that the MFD green soybean had a small change on bright color, compared with the fresh samples, but the drying time was the longest among the four methods. The bright color value of PSMVD/PSMD/MVD, respectively, was 79.77, 71.43, and 55.45, and drying time of them was slightly different. The PSMVD/PSMD showed advantages over MVD by improving the product quality.     

Assessment of new in-bin drying and storage technology for soybean seed

On-farm, in-bin drying and storage of soybean in environments with unconditioned air often result in repeated drying and rewetting of the grains which may have adverse effects on quality metrics; if done using natural air, as recommended for soybean destined to the seed market, the in-bin drying and storage method require operation at well-defined local weather-dependent strategies to maintain the seed quality. This study simulated in-bin drying and storage of soybeans. Different fan control options and drying strategies were used to assess performance in terms of drying duration to target final moisture content (MC), percent over drying, energy expenditure, and drying cost. Fan operation included running the fan continuously, only at night, only during the day, at a set window of equilibrium MC (EMC) of natural air, and set EMC window with supplemental heating of ambient air as an option (EMC-H). Drying and storage performance were tested for soybean at initial moisture content (IMC) (16–22%, wet basis), air flow rate (1.04–5.0?m³?min^?1 [air] t^?1 [soybean]), and harvesting start dates (August 15 to November 15). Simulation model was validated using a bench-scale pressure drop system filled with soybeans with IMC of 22% wet basis. The result shows that fan control strategies, air flow rates, harvest date, and initial MC of the soybeans significantly (P?χ² was 0.88.     

Experimental and numerical investigation of intermittent drying of timber

Intermittent drying may be of interest in the future to address energy issues. Such drying conditions are also likely to help stress relaxation through mechanosorptive creep. The influence of applying oscillations of temperature and relative humidity during the drying of beech timber on time and drying stresses is discussed in the paper by means of nonsymmetrical and loaded drying. Experimental data were used to validate a numerical model in the case of intermittent drying. The model was then used to perform a numerical investigation of the possibility of using an intermittent energy source to dry wood.     

Batch drying kinetics of corn in a novel rotating jet spouted bed

The batch drying kinetics of corn as a test material were investigated experimentally in a novel rotating jet spouted bed (RJSB) using both continuous and intermittent (on/off) spouting and heating schemes. The parameters investigated include inlet air temperature, bed height, superficial air velocity, nozzle diameter, distributor rotational speed and intermittency of spouting and heat input. The results indicate that the drying kinetics are comparable with conventional spouted and fluidized beds for slow drying materials and that intermittent drying can save up to 40% of the thermal energy as well as air consumption with better quality product.     

高纯度大豆粉末磷脂干燥技术的进展

磷脂是一种天然的表面活性剂，在食品、医药、化妆品等方面有广泛的应用。详细介绍了高纯度粉末磷脂制备工艺中干燥过程的研究进展。总结了真空干燥、超临界二氧化碳干燥、真空冷冻干燥、振动流化床干燥等六种干燥高钝粉末磷脂的方法进展，并提出了超临界二氧化碳干燥和真空冷冻干燥两种有效的高纯粉末磷脂干燥方法。     

Drying of soybean seeds in a crossflow moving bed

The aim of this work was to investigate simultaneous heat and mass transfer between air and soybean seeds in a crossflow moving bed dryer. A model was developed from mass and energy conservation applied to the fluid and particulate phases. The equilibrium, heat transfer and mass transfer equations were taken from studies published earlier. Equations for drying kinetics were obtained from a thin layer study, and the equilibrium equation was chosen from rival model discrimination based on nonlinearity measures. The experimental part of this work involved the determination of air temperature distribution, grain moisture through the bed and air humidity at the bed outlet. The model equations were discretized by orthogonal collocation in the air flow direction. The resulting differential-algebraic equations were solved using a method based on backward differential formulas. Simulation results showed good agreement with experimental data.     

Air impingement and intermittent drying: Application to apple and to mango

An original drying process combining air impingement and intermittent drying was studied on apple slices and mango cubes. The influence of four operating parameters (air velocity, drying/tempering periods, upper height, and air temperature) on the drying time and on the drying rate was evaluated. Continuous and intermittent drying were compared. The intermittency α = 1/7 (τ_on = 10 seconds and τ_off = 60 seconds) gave the best results. A time savings of 54% for apple and 67% for mango was reached. In continuous drying, a time savings of 4620 seconds was observed by increasing the air velocity from 6 to 40 m s^?1 for apple. Air temperatures of 328 K for apple and of 328 K or 338 K for mango were determined as optimum to prevent case‐hardening. Experimental results were fitted with the analytical solution of Fick's second law and the modified Page equation (average values R² = 0.985 and 0.961, for apple and mango, respectively). For both products, the apparent moisture diffusivity D_app, the drying constant k, the drying coefficient n, and the activation energy E_a, were identified. Activation energies calculated from the analytical solution were 30.3 and 36.8 kJ mol^?1 and were 25.4 and 30.0 kJ mol^?1 using the modified Page equation for apple and mango, respectively. Mango has an increased temperature sensitivity and thus will need less energy for drying than apple.     

A Mathematical Model for Constant and Intermittent Batch Drying of Grains in a Novel Rotating Jet Spouted bed

ABSTRACT

A diffusion-bared mathdcal model is prswmed for batch drying of corn in a novel rotating jn spouted bcd device under constant as well as intermitted drying conditions. Such a device is suited for drying of large partides (e.g. grains, beam, seed, etc) for which internal heat and mass tranfer rates control the drying kinetics. Based on literature data for moisture diffusivities the model predictions are compared with experimental data for both continous and time-dependend air supply and/or heat input. Effects of dcvant parameter are evaluated and discussed in the light of potential pnrctieal applications.     

Energy analysis of intermittent drying in the spouted bed

Abstract

The aim of this study was to evaluate different intermittency ratios applied to a spouted bed used to dry alumina, from the energy perspective. Two types of intermittency (reduction and total interruption of the air flow) and five different intermittency profiles were evaluated, including the use of time-variant intermittency ratios. The use of intermittency provided higher energy efficiency and better use of the energy supplied, compared to the continuous process. Reductions of energy consumption in the range from 13.2% to 67.2% were obtained, relative to the continuous process. The findings showed that the use of intermittency is a promising way to optimize energy consumption in spouted beds.     

A Mathematical Model for Constant and Intermittent Batch Drying of Grains in a Novel Rotating Jet Spouted bed

A diffusion-bared mathdcal model is prswmed for batch drying of corn in a novel rotating jn spouted bcd device under constant as well as intermitted drying conditions. Such a device is suited for drying of large partides (e.g. grains, beam, seed, etc) for which internal heat and mass tranfer rates control the drying kinetics. Based on literature data for moisture diffusivities the model predictions are compared with experimental data for both continous and time-dependend air supply and/or heat input. Effects of dcvant parameter are evaluated and discussed in the light of potential pnrctieal applications.     

Modeling fixed-bed drying of bark

A model for fixed-bed drying of bark has been developed. The model takes heat and mass transfer between the air and bark into account and the volumetric heat transfer coefficient was used as fitting parameter in the model. The assumption of adiabatic saturation of the air leads to too high drying rates but a model with three size fractions shows good agreement both between experimental laboratory data and data from an industrial dryer. A sensitivity analysis for different air temperatures, air velocities, and bed heights show how the dryer capacity depends on these parameters.     

Effects of intermittent microwave drying on quality characteristics of pistachio nuts

In this research, the effect of intermittent microwave drying (IMD) on drying time and quality characteristics for three varieties of Iranian pistachio nuts was investigated and compared with the sun drying method. The quality parameters, such as chemical characteristics, physical parameters, and sensory evaluation were considered. Three varieties, Kal-Khandan, Kaleh-Bozi, and Ghermez, were dried in an 800-W, 2,450-MHz domestic microwave oven. Experiments were conducted in three material loads of 50, 100, and 150?g under intermittent method at 6?s of power-on and 70?s of power-off with three replications. The total drying time was in the range of 114.03–266.07?min, depending on material loads and varieties. The higher the material load, the longer the drying time. The results showed that the effect of drying method on the shell splitting size was very significant (p?p?相似文献   

Experimental study of paddy drying in a vortex chamber

The intensification of interfacial mass, heat, and momentum transfer makes vortex chambers potentially interesting for the efficient drying of paddy, allowing shorter drying times and/or more compact equipment. The presence of a shell introduces particular challenges. Intraparticle diffusion limitations are strong and may reduce the advantage from intensified interfacial mass and heat transfer and the efficiency of air usage. Furthermore, high shear and normal stresses in the fast rotating particle bed may cause damage to the paddy shell, posing problems for transport and storage. With these specific aspects in mind, the use of vortex chambers for paddy drying is experimentally evaluated.     

不同加热功率下含油污泥的干燥

辽河油田的含油污泥含有大量的水分,为了更有效地进行油泥热解和减少热解过程中的能耗,需运用干燥技术处理油泥。实验考察了不同干燥功率对油泥干燥速率、湿分比的影响。实验结果表明:油泥干燥可以分成3个阶段,即恒速干燥阶段、第1降速干燥阶段和第2降速干燥阶段;加热功率越大,达到平衡含水质量分数所用的时间越短,恒速干燥速率越大。然后运用干燥方程求得干燥时间。最后运用热分析动力学对实验数据进行处理,得到干燥动力学的数学模型。模拟结果表明修正Page模型符合油泥干燥过程。     

Experimental research on intermittent heat pump drying with constant and time-variant intermittency ratio

The aim of this article was to estimate the effectiveness of intermittent drying with constant and time-variant intermittency ratio, compared with continuous drying. Intermittent drying was accomplished by periodically changing the heat input and air velocity. To achieve accurate control of drying temperature, a new parallel conversion controller was used. Based on the well-controlled heat pump drying system, the drying kinetics of green soybean were analyzed using seven intermittent drying profiles. The increase of intermittency ratio caused decrease of effective drying time and increase of specific moisture extraction rate (SMER). SMERs of intermittent drying were 1.21–4.94 and 0.93–5.40 times more than the continuous drying for different initial moisture content (23 and 28%), respectively. Changes of drying rate (DR) and SMER became relatively moderate when intermittent drying with time-variant intermittency ratio was used. A comprehensive evaluation parameter, based on DR and SMER, was proposed and calculated. Experimental results indicated that intermittent drying (α?=?5/6) and intermittency drying with time-variant ratio gave the best two comprehensive performances.     

聚氯乙烯干燥工艺介绍与对比

介绍了PVC干燥的3种常用工艺并进行了比较,认为流化床干燥工艺在装置规模、蒸汽消耗及产品质量等方面具有优势,是当前新建项目的首选工艺.     

卧式沸腾干燥床在PVC生产中的应用

简单介绍了卧式沸腾干燥床干燥工艺的工艺流程及特点,比较了目前PVC生产中的几种干燥工艺,分析了卧式沸腾干燥床在实际生产中存在的问题及改进措施。