Simulation and Validation of Microwave-Assisted Fluidized Bed Drying of Soybeans

A general mathematical model of heat and mass transfer was developed to simulate the microwave-assisted fluidized bed drying of bulk grain. The model was solved using the well-known Runge-Kutta-Gill method. The model is capable of predicting the moisture content of soybean as well as the drying air parameters (i.e., drying air temperature and moisture content) during drying. The values of mean relative deviation (MRD) were less than 8 and 10% for prediction of grain moisture content and outlet air parameters, respectively, which reflects an acceptable accuracy. In comparison with conventional fluidized bed drying of soybean, microwave-assisted fluidized bed drying led to 83.39–98.07% savings in drying time and 82.07–95.22% savings in specific energy consumption when reducing soybean moisture content from 18.32 to 12% (db).     

Drying of Inorganic Particulate Compounds

Inorganic particulates are usually dried in a fixed bed, fluidized bed, or spray dryers. These compounds are easy to dry, once their physical structure, with high porosity, allows moisture content removal with low resistances. For fluidized bed of alumina particle evaluations, a laboratory-scale drying unit was built. The drying experiments were carried out with alumina particles with different diameters to evaluate temperature and air flow rate effects on drying kinetics and bed height. In another case, the dehydration of a mixture of rare-earth chlorides in a fluidized bed was studied, aiming at the production of anhydrous rare-earth chlorides, used to obtain mischmetal by electrolytic and metallothermic processes. The spray drying experiments were carried out in a pilot plant. Spray drying is a technique largely applied in industrial processes to dry solutions or suspensions, converting their solid parts into a dried powder. A set of rare-earth drying experiments was carried out, aiming at the development of techniques to obtain a powder that could satisfy international morphological requirements. The results allowed evaluating the effects of air flow rate, feed concentration, atomizer model, rotation velocity, and atomization pressure on powder density and particle size distribution.     

Drying of Inorganic Particulate Compounds

ABSTRACT

Inorganic particulates are usually dried in a fixed bed, fluidized bed, or spray dryers. These compounds are easy to dry, once their physical structure, with high porosity, allows moisture content removal with low resistances. For fluidized bed of alumina particle evaluations, a laboratory-scale drying unit was built. The drying experiments were carried out with alumina particles with different diameters to evaluate temperature and air flow rate effects on drying kinetics and bed height. In another case, the dehydration of a mixture of rare-earth chlorides in a fluidized bed was studied, aiming at the production of anhydrous rare-earth chlorides, used to obtain mischmetal by electrolytic and metallothermic processes. The spray drying experiments were carried out in a pilot plant. Spray drying is a technique largely applied in industrial processes to dry solutions or suspensions, converting their solid parts into a dried powder. A set of rare-earth drying experiments was carried out, aiming at the development of techniques to obtain a powder that could satisfy international morphological requirements. The results allowed evaluating the effects of air flow rate, feed concentration, atomizer model, rotation velocity, and atomization pressure on powder density and particle size distribution.     

Spray Freeze Drying in a Fluidized Bed at Normal and Low Pressure

The aim of this study is to develop the spray freeze drying process and its hardware and to investigate its capabilities to dry thermosensible substances such as pharma-proteins at normal and low pressures. As the result, the spray freeze fluidized–bed dryer was constructed. During the study, the drying kinetic comparison between classical and spray freeze–drying technologies was done. Spray freeze drying has shown short process times and allows advanced control, product particle shape and size uniformity, and high solubility. This shows that the fluidized-bed freeze-drying process could be an alternative for classical freeze-drying processes. Identified problems are the low yield of the primary drying phase and the strong electrostatic effects during the secondary drying step. However, the innovative process has shown an excellent capability to dry and stabilize the thermosensitive substances, such as pharma-proteins.     

Spray Freeze Drying in a Fluidized Bed at Normal and Low Pressure

The aim of this study is to develop the spray freeze drying process and its hardware and to investigate its capabilities to dry thermosensible substances such as pharma-proteins at normal and low pressures. As the result, the spray freeze fluidized-bed dryer was constructed. During the study, the drying kinetic comparison between classical and spray freeze-drying technologies was done. Spray freeze drying has shown short process times and allows advanced control, product particle shape and size uniformity, and high solubility. This shows that the fluidized-bed freeze-drying process could be an alternative for classical freeze-drying processes. Identified problems are the low yield of the primary drying phase and the strong electrostatic effects during the secondary drying step. However, the innovative process has shown an excellent capability to dry and stabilize the thermosensitive substances, such as pharma-proteins.     

Particle population modeling in fluidized bed-spray granulation—analysis of the steady state and unsteady behavior

Owing to its intensive mass and heat transfer ratios and its coupling of the process stages of drying, shaping and homogenization as well as classification, continuous fluidized bed-spray granulation drying has gained acceptance as a thermal treatment process for granular solids. In this study, a balance of the particle populations is completed for a continuous fluidized bed-spray granulation with external classification. Thus, it ought to be possible to describe the particle size distributions changing over time in the fluidized bed and in the product flow [Powder Technol. 82 (1995) 37; H. Uhlemann, L. Mörl, Wirbelschicht-Sprühgranulation, Springer Verlag, 2000, ISBN 3-540-66985-X.].     

己二酸生产中沸腾床干燥和气流干燥工艺性能比较

在目前己二酸生产中,用于固体物料干燥的代表性工艺是气流式及沸腾床式2种,对2种T艺在己二酸干燥中应用进行了综合性比较。     

Analysis of the start-up process in continuous fluidized bed spray granulation by population balance modelling

A physics-based population balance model is constructed for continuous fluidized bed spray granulation with internal and external separations. A balance area around the granulator and around the separator is described, including all input and output particle and mass flows. A simplified growth and attrition model is developed for the diameter change of the particles in the granulator. The population balances facilitate the calculation of the particle size distributions changing over time in the fluidized bed and in the product flow. It is demonstrated that an unsteady start-up phase occurred in every case, which possibly leads to instability (oscillating behaviour). This may be regulated by controlling the overall nuclei balance.     

Drying Characteristics of Coriander Seed Particles in a Reduced Pressure Superheated Steam Fluidized Bed

Drying characteristics of coriander seed particles were experimentally analyzed in a reduced pressure superheated steam fluidized bed. The typical moisture gain, reported in some other studies during the warm-up period of the process, was reduced in most of the cases by supplying additional heat into the column. The experimental results demonstrated that the drying rate increases and the equilibrium moisture content decreases by increasing the operating temperature. However, variation of the operating pressure (40–67 kPa) and the superficial steam velocity (2.3–4.0 m/s) did not present significant effects on the moisture contents. The degree of superheating was found to be the most important parameter for the process. The experiments also showed that the equilibrium moisture content decreases upon increasing the degree of superheating. Finally, employing a reduced pressure superheated steam fluidized bed appears as an option to carry out drying processes at relatively lower temperatures.     

Drying of Pepper Seed Particles in a Superheated Steam Fluidized Bed Operating at Reduced Pressure

A series of drying experiments was performed in a reduced-pressure superheated steam fluidized bed, employing pepper seed particles and some novel data were obtained. Experiments were carried out using different chamber pressures (40–67 kPa), temperatures (90–122°C), steam velocities (2.35–4.10 m/s), and mass flow rates (0.0049–0.0134 kg/s). In the majority of the experiments, the moisture gain observed in some other studies in the warm-up period of the process was prevented through some supplementary heat provided to the column. The drying rate was found to be increasing by operating temperature; however, it was not affected much by the superficial gas velocity and the operating pressure. Nevertheless, the reduced pressure operation increases the degree of superheating that appears as the most important parameter of the process. The experimental results showed that the equilibrium moisture content decreases by the increasing degree of superheating. On the other hand, the critical moisture content assumes higher values for the greater degrees of superheating. It was concluded that a relatively lower temperature process can be achieved through a reduced-pressure superheated steam fluidized bed.     

Simultaneous Optimization of Process Design and Solvent in a Flowsheet Simulator

For processes using auxiliaries, the selection of the process fluid should not be separated from the process design. To solve the simultaneous process and fluid optimization problem for industrial applications, a flowsheet simulator is required. The implementation of the two-stage CoMT-CAMD approach in CHEMASIM, the in-house flowsheet simulator of BASF SE, allows for large process topologies with a large variety of unit operation models to be modeled, while sustainability criteria like cost and life cycle assessment (LCA) objectives, are directly accessible and can be solved with single or multicriteria optimization methods. The modifications required for the implementation and the user interface designed for this purpose are presented here.     

Fluidized bed spray granulation: Analysis of the system behaviour by means of dynamic flowsheet simulation

Nowadays, software tools for the flowsheet simulation of industrial processes are commonly used for design, simulation, balancing, troubleshooting and optimization purposes. Most of the tools are applicable to fluid processes only and cannot be effectively used for processes which involve solids.In this contribution we want to present the conceptual design of a new system applicable for the dynamic flowsheet simulation of complex solids processes. This system is developed as an enhancement to the existing simulation program.The novel software is able to simulate the unsteady behaviour of complex circuits of granulation processes. The transient behaviour during the start-up and changing of the process or material parameters can also be examined.As flowsheet examples, a typical spray granulation process with different schemes consisting of fluidized bed granulators, screens, mill and splitters was used. The mathematical model of the fluidized bed granulator is described by a one-dimensional population balance equation and coupled with heat and mass transfer and simple fluid dynamics.Received simulation results have shown that the proposed concept of the dynamic flowsheet simulation of granulation processes can be used effectively and has the potential to be generalized for other types of solids processes.     

CFD Modeling of Microwave-Assisted Fluidized Bed Drying of Moist Particles Using Two-Fluid Model

The drying behavior of moist spherical particles in a microwave-assisted fluidized bed dryer was simulated. The two-fluid Eulerian model incorporating the kinetic theory of granular flow was applied to simulate the gas–solid flow. The simulations were carried out using the commercial computational fluid dynamics (CFD) package Fluent 6.3.26. The effects of different levels of microwave power densities as well as initial gas temperature on the prediction of solids moisture content, gas temperature, and gas absolute humidity were investigated. The effect of microwaves was incorporated into calculations using a concatenated user-defined function (UDF). The simulation results were compared with experimental data obtained from drying of soybeans in a pilot-scale microwave-assisted fluidized bed dryer and reasonable agreement was found. The mean relative deviation for prediction of solids moisture content, gas temperature, and gas absolute humidity were less than 3, 10, and 5%, respectively. Further work is needed to validate the proposed model for large-scale plants.     

Combined Microwave/Fluidized Bed Drying of Fresh Peppercorns

Abstract

A fluidized bed dryer (FBD) and a combined microwave/fluidized bed dryer (CMFD) are used to dry the fresh ripe peppercorns. The average moisture content vs. elapsed drying time, and drying rate vs. average moisture content are experimentally investigated. It is found that the microwave field from the CMFD can increase the potential of the conventional fluidized bed drying. The drying rates of both dryers are dependent on the inlet air temperature and velocity. For the CMFD, the effects of the air velocity on the drying rate are found to be opposite to our previous results tested with white pepper seeds i.e., the drying rates of the fresh ripe peppercorns decreased with increasing air velocity. By using a CMFD, the drying time required to reach the desired moisture content can be reduced to 80–90% of the drying time required for a FBD at the same drying air temperature and velocity. The color of the product dried by a CMFD is also attractive: it becomes flaming yellow, instead of black as obtained from a FBD. The physical structure of the peppercorn, before and after the drying process is also investigated by a metallurgical macroscope and an image analyzer. Different from drying by a FBD, the external form and matter of the white pepper seed are still maintained, even after passing through the drying process.     

Combined Microwave/Fluidized Bed Drying of Fresh Peppercorns

A fluidized bed dryer (FBD) and a combined microwave/fluidized bed dryer (CMFD) are used to dry the fresh ripe peppercorns. The average moisture content vs. elapsed drying time, and drying rate vs. average moisture content are experimentally investigated. It is found that the microwave field from the CMFD can increase the potential of the conventional fluidized bed drying. The drying rates of both dryers are dependent on the inlet air temperature and velocity. For the CMFD, the effects of the air velocity on the drying rate are found to be opposite to our previous results tested with white pepper seeds i.e., the drying rates of the fresh ripe peppercorns decreased with increasing air velocity. By using a CMFD, the drying time required to reach the desired moisture content can be reduced to 80-90% of the drying time required for a FBD at the same drying air temperature and velocity. The color of the product dried by a CMFD is also attractive: it becomes flaming yellow, instead of black as obtained from a FBD. The physical structure of the peppercorn, before and after the drying process is also investigated by a metallurgical macroscope and an image analyzer. Different from drying by a FBD, the external form and matter of the white pepper seed are still maintained, even after passing through the drying process.     

气流干燥过程的数学模拟

针对颗粒和空气在干燥管内的相互作用和传质传热机理,首先建立了直管式气流干燥数学模型,然后通过分析脉冲式气流干燥器的结构特点,求出了管径变化的微分方程,将其和直管式气流干燥的五个常微分方程耦合在一起,构成了脉冲式气流干燥的传质传热数学模型。根据模型方程的特点,运用四阶龙格-库塔法对其进行了数值求解。通过实验结果验证,该模型正确可靠。     

Sugarcane Bagasse Drying in a Cyclone: Influence of Device Geometry and Operational Parameters

Sugarcane bagasse is becoming more and more commonly used in generating electrical energy, steam, and bioethanol. Drying is important in sugarcane and other types of biomass because it can be used to improve the calorific value and overall energetic use. In this work, sugarcane bagasse was treated by drying in a cyclonic dryer. The influence of the geometry of the device (the conical part of the cyclone) and process parameters (bagasse mass flow rate and temperature) were tested. The modification on the conical part was related to two different angles and with two different inferior outlets (B). Experimental design was carried out for each geometry. The independent variables were the drying agent temperature (35 to 275°C) and the bagasse mass flow rate (0.1 × 10^?2 to 2.9 × 10^?2 kg s^?1). The air flow rate was kept constant at 7.5 × 10^?2 kg s^?1. The dependent variables were moisture reduction (MR) and average particle residence time (t_res) in the cyclonic dryer. For both cyclonic geometries, it was observed that MR was directly proportional to the temperature and inversely proportional to the bagasse mass flow rate. t_res was also inversely proportional to the bagasse mass flow rate. Decreasing B tended to increase tres and MR.     

Coupled CFD-PBE Simulation of Nucleation in Fluidized Bed Spray Granulation

Fluidized bed spray granulation is used to produce porous granular particles from suspensions, solutions, and melts. It is the general aim of our work to provide a physics-based simulation tool for this process. For this the process-relevant mechanisms such as droplet deposition, dust integration, and drying are implemented using computational fluid dynamics (CFD) to generate growth kinetics of the granules and of the dust particles. The latter gives rise to the nucleation rate. This kinetics is applied to simulate the development of the particle size distribution of granules for a continuously operated fluidized bed spray granulation process using population balance equations of the granules.     

Drying of Suspensions in a Fluidized Bed of Inert Particles Under Reduced Pressure

A drying method in which a heat-sensitive material is immersed in a fluidized bed under reduced pressure was used to continuously obtain dispersed, dry, fine powders of that material from a dilute suspension or solution at a low temperature with a high drying rate. The mass velocities of the drying gas, sample flow rate, and chamber pressure were varied, and the effects of these variations on the corresponding drying characteristics were examined.

The fluidization state of a fluidized bed of inert particles strongly affects the drying rate in the bed and has a greater effect than the chamber pressure on the corresponding drying characteristics. In other words, it is important to maintain a vigorous fluidization state to achieve a high drying rate. Although the maximum drying rate is independent of the chamber pressure, it can be achieved at a low mass velocity of the drying gas under reduced pressure. That is, at a low chamber pressure a high drying rate can be achieved, even at a relatively low mass velocity of the drying gas. The bed temperature at the time of drying is strongly influenced by the drying rate and decreases linearly with an increase in the maximum drying rate when the sample flow rate is equal to the drying rate.     

Modeling Particle Formation at Spray Drying Using Population Balances

There have been several efforts to simulate the physical processes in a single droplet during spray drying in the last several years, but most of the models do not describe the solid formation in detail. In this work, the development of the microscopic solid structure in a droplet during spray drying is simulated. A radial-symmetric model of the droplet is used to simulate the mass and heat transport. The solid formation at every radial discretization point is obtained by the solution of population balances. This way, the distribution of the particle number density in the droplet depending on the macroscopic process parameters can be predicted. The model equations are solved in a normalized coordinate system to be able to describe the shrinkage of the droplet. The suitability of these population balances will also be discussed. For the validation, monodisperse single droplets consisting of a solution or suspension are dried with constant boundary conditions.