Batch Fluidized Bed Dryer Research Articles

Developing and Assessing Performance of a Laboratory-Scale Fluidized Bed Dryer

A laboratory-scale batch fluidized bed dryer with 75 mm bed diameter was designed, fabricated and evaluated to study the hydrodynamics of river sand as well as the drying of cassava mash and bitter kola particulates. The hydrodynamics properties such as minimum fluidization velocity, effect of bed height and pressure drop across the bed, effect of particle size and density on minimum fluidization velocity and stability of the bed column of river sand were studied. Drying of cassava mash to edible garri was carried out at in fluidized bed dryer at controlled temperatures. Drying characteristics of the laboratory fluidized bed dryer was compared with the laboratory WiseVen oven (model number: WOF - 105) using bitter kola particulate material sample. The experimental results from laboratory-scale fluidized bed dryer showed that the minimum fluidization velocity increases as material density increases and the value of the minimum fluidization velocity obtained from the fluidized bed gave good agreement with other empirical correlation such as Kozeny-Carman Equation. The fluidized bed dryer showed high rates of moisture removal over the conventional oven with the ratio of 1:29 under the same operating conditions. Drying of cassava mash to edible garri was achieved at lower drying temperatures of 83 oC \(\pm\) 3 oC at 55 minutes when compared to conventional frying temperatures of cassava mash to edible at 180 – 200 oC thereby saving energy cost. Hence, this fluidized bed dryer is recommended for use in demonstrating hydrodynamics and drying of particulate materials in the laboratory.

An improved batch fluidized drying experimental design based on digital sensors and a minicomputer

AbstractIn most undergraduate programs of chemical engineering in Chinese universities, the batch fluidized bed drying (BFBD) experiment is commonly adopted as a part of the experimental course of chemical engineering unit operation. In those BFBD experiments, the students should dry the material in a dryer, repeatedly sample and measure it outside to get its moisture content. In most cases, each sampling and measuring operation needs more than 5 min. The BFBD drying experiment conducted in that manner cannot obtain adequate, accurate data, making it difficult for the student to perform proper calculation and data analysis. In this article, the authors build a small BFBD prototype equipment and mount a set of digital temperature/humidity sensors. Then they use a Raspberry Pi 3, a kind of mini‐computer, to automatically measure and record the process parameters values online. Aided by those modern information process methods, the data accuracy and amount are all enhanced. Based on the gotten big data set, the student can get much more accurate results and do a more thorough analysis. The data analysis based on the old BFBD equipment is too straightforward and simple because it only needs the mass balance calculations. On the contrary, although the new BFBD equipment adopts an indirect way to measure the drying process, it obtains much more accurate results than before. The students must also apply more theories to get the results, such as mass transmission, the thermal balance, which makes the experiment more comprehensive. That is meaningful and helps to achieve the objectives of the chemical engineering experiments.

Simple Model and Predictive Control of a Pharmaceutical Batch Fluidized Bed Dryer

Abstract The fluidized bed theory can be complex, especially for heterogeneous flow descriptions with bypasses, generally resulting in large differential and algebraic systems of equations. Consequently, their applicability to model-based process control is limited. In this work, a simplified homogeneous model for pharmaceutical batch drying is derived from the two-phase fluidization theory using physical insights and simplifying assumptions, reducing more than a hundred equations to five. A nonlinear model predictive controller with an internal model structure is designed from these simple equations, showing the simplicity of tuning and implementation. Parameters of the model are calibrated through nonlinear grey-box identification using pilot scale experimental data. The validation demonstrates that the proposed simplifications do not impair the ability to replicate the process dynamics adequately with experimental conditions similar to the ones used for calibration. Closed-loop results in simulation attest the robustness of this control strategy.

A performance analysis of batch fluidized bed drying of two pharmaceutical powders by desirability approach

In this work, a multi objective optimization of batch fluidized drying of two pharmaceutical powders (Group A particles and Group B particles) has been performed using desirability function. Optimization was studied based on non-linear models that take into account particle entrainment and combine dense bed and freeboard sections. Optimization criterion was simultaneously minimizing drying time, dense bed specific energy consumption, and freeboard specific energy consumption. The desired solid final moisture content was considered as a constraint. The control variables were air temperature and air velocity. For the Group B particles, simulation results indicated that desirability increase was monotonic with air temperature increase and air velocity decrease. For the Group A particles, it was shown, the existence of a desirability optimum. By comparing static and dynamic control to the real batch operation, the highest percent reduction of drying time, dense bed specific energy consumption, and freeboard specific energy consumption was obtained for static control with a high value of fixed inlet air temperature. Nevertheless, the risk of product overheating and damaging could be reduced by temperature reduction during the drying process as showed by optimal control trajectories obtained in the case of dynamic control.

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

AbstractThe 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.

Development and validation of a batch fluidized bed dryer model for pharmaceutical particles

Batch fluidized bed drying is a common process for water removal in pharmaceutical particles. Multiple phenomenological models for this type of dryer are proposed in the literature, with many of them relying on the two-phase theory. This article elaborates on a two-phase model and extends it for the pharmaceutical case by improving the particle, batch size and heat loss descriptions. An explicit methodology with low computational cost is also developed for solving the fluidized bed equations. Then, based on a grey-box modeling strategy, parameters with known value are fixed, while the unknown parameters are calibrated with experimental data collected on a pilot scale fluidized bed dryer. Lastly, the model is dynamically validated on distinct experimentation datasets. It is shown that the simulations are able to reproduce the pilot data trends, but there is still room for improvements in the heat loss representation.

Modeling batch fluidized bed drying of pharmaceutical powder: Influence of hydrodynamic regime and sorption isotherms

A mathematical modeling, based on the two-phase theory of batch fluidized bed drying of type A particles and type B particles pharmaceutical powders, was performed. A perfectly mixed flow bubbling regime and an axially dispersed plug flow turbulent regime with a freeboard section were assumed. The experiments were carried out in a pilot-scale bed and in an industrial scale bed. The experimental sorption isotherms were used to model the falling rate drying period. The influence of the particles hygroscopic properties on the drying rate and on the temperature profile was discussed. The simulated solid moisture content and temperature profiles are in good agreement with the experimental results.

Energetic and exergetic analyses of Barnyard millet drying using continuous multistage fluidized bed dryer

AbstractMost of the exergy studies reported were in batch fluidized bed drying process. The continuous dryer plays a pivotal role in industrial usage. In this study, exergy and energy analyses of multistage fluidized bed drying of Barnyard millet with stages connected externally were examined. The dryer was operated by changing wall temperature of stages (313–328 K), air inlet velocity (1.01–1.3 m/s), downcomer height (50–70 mm), and flow rate of solids (5–10 kg/h). Drying characteristics of Barnyard millet by changing process operating conditions of the dryer, were reported and the energy utilization ratio, exergy loss and exergy efficiency of dryer were also reported. The EUR of dryer at steady state has been found to be in the range of 0.25–0.46 and the maximum exergy efficiency of dryer was observed as 0.64 and lowest as 0.371 in the continuous drying process.Practical ApplicationsFluidized beds offer many distinct features and advantages for processing of particulate food materials. To decrease the drying time than that for single stage dryers, continuous multistage fluidized bed dryer was introduced. Reducing moisture content from feed materials in continuous dryers while discharging continuously, helps to process large quantity of solid materials with good quality of product. Several dryers with different modifications and designs have been suggested by many earlier investigators but continuous dryers play significant role in particulate industry. The multistage dryer is designed by connecting two or more fluidized beds internally or externally, where each bed is termed as a stage. Advantages of the multistage dryer are improvement in gas–solid axial mixing, which results in good quality of product. Due to stage‐wise contact of solids with gas, dried product with uniform moisture content can be obtained.

Application of a mechanistic model of batch fluidized bed drying at laboratory and pilot scale

The aim of this work was to test the feasibility of reducing experimentation during the development of the fluid bed drying process of a pharmaceutical product, by conducting experimentation at laboratory scale and by using a mechanistic model calibrated on the laboratory scale data to simulate the process at pilot scale. The advantage of this approach with respect to a fully empirical approach, is that a limited number of experiments are run at pilot scale with the purpose of scale verification, instead of an extensive experimental campaign. Batch fluidized bed drying experiments were run with two different formulations containing the same active pharmaceutical ingredient (API) at laboratory and pilot scales. A mechanistic model was calibrated at laboratory scale, and then the same parameters describing drying behavior were used in simulations of the drying process at the pilot scale. The setup of the model differed for the two formulations; in particular, for the more hygroscopic formulation, the model needs to account for a higher influence of the material on drying. The simulated product temperature and moisture content in granules were compared with experimental data. Model accuracy is good at steady state for granule moisture content and for product temperature, in particular for the more hygroscopic formulation. During dynamic phases the product temperature prediction is less accurate: this effect is more visible for the less hygroscopic formulation. Finally, the mechanistic model calibrated at laboratory scale was used to simulate experimental results obtained at pilot scale. Good agreement between simulations and experiments could be observed, confirming that the suggested approach could be used in order to considerably decrease experimental effort during process development with respect to a fully empirical approach.

Manufacturing of Pharmaceuticals by Impregnation of an Active Pharmaceutical Ingredient onto a Mesoporous Carrier: Impact of Solvent and Loading

In this study, an active pharmaceutical ingredient (API) was impregnated onto a mesoporous carrier (excipient) in a fluidized bed. Impregnating APIs in porous carriers has the potential to simplify the drug substance development process and leads to the elimination of the blending and granulation unit operations. Impregnation and drying occur simultaneously in fluidized-bed impregnation, and this method precludes several challenges encountered in other impregnation methods. Furthermore, the process ensures a uniform distribution of APIs within the porous carriers. This method also allows for a variety of solvents to be used in the impregnation. Using a batch fluidized-bed dryer, impregnation of acetaminophen (APAP) onto a magnesium/aluminum metasilicate (Neusilin R) was studied. Water and methanol were used as transport solvents to impregnate different loadings (w/w) of APAP, namely, ranging from 24 to 0.1%. Uniformity tests indicated that APAP loadings of all impregnated products are close to their target loadings across carrier size classes. Tests before and after impregnation showed that there were no changes observed in the physical properties of the carrier, such as particle size, compressibility, and flow properties. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analysis performed on the samples indicated that the low loadings APAP was present in the carrier pores in its amorphous state. At high loadings, we observed that APAP was mainly present in its amorphous state, however, some degree of crystallinity was observed. Lastly, dissolution tests on the impregnated product showed enhanced dissolution rates in acidic media, and comparable dissolution rate in de-ionized (DI) water, compared to the pure drug crystals. Our results show that the method of fluidized-bed impregnation yields a product with high uniformity and overcomes several challenges presented by traditional physical blends.

Changes in physicochemical properties of rice in response to high-temperature fluidized bed drying and tempering

ABSTRACTThe effects of high-temperature fluidized bed drying and tempering on pasting, gelatinization, crystalline and microstructural properties of long-grain Vietnamese rice cultivar A10 were examined. The freshly harvest paddy (33% wet basis) was dried at two drying temperatures (80 and 90°C) and two drying durations (2.5 and 3.0 min) using a custom-made lab-scale batch fluidized bed dryer. The dried rice was immediately tempered in sealed containers at 75 and 86°C for various tempering durations (0, 30, 40, and 60 min), followed by thin-layer drying at 35°C to reduce moisture level to 14% wet basis. Characterization of pasting, gelatinization, crystallinity, and microstructure of the dried rice was undertaken using rapid visco analyzer, differential scanning calorimetry, X-ray diffraction (XRD), and environmental scanning electron microscopy (ESEM), respectively. Pasting properties and gelatinization enthalpy decreased with higher drying temperature and longer tempering time while pasting and gelatinization temperatures increased. Degree of crystallinity changed slightly, however, a shift from A-type to A+V-type XRD pattern was observed. ESEM observation demonstrated some degree of collapse of the rice microstructure. The kernel integrity appeared to be enhanced by the gel network formed during partial gelatinization of starch, corroborating with the changes in pasting and gelatinization properties of the fluidized bed dried and tempered rice.

Nonlinear model predictive control of a batch fluidized bed dryer for pharmaceutical particles

The availability of reliable online moisture content measurements exploiting near-infrared (NIR) spectroscopy and chemometric tools allows the application of online control strategies to a wide range of drying processes in the pharmaceutical industry. In this paper, drying of particles with a pilot-scale batch fluidized bed dryer (FBD) is studied using a in-line NIR probe. A consolidated phenomenological state-space model of an FBD based on mass and energy balances is calibrated applying a nonlinear least-square identification to experimental data (grey-box modeling). Then, relying on the calibrated model, a nonlinear model predictive controller and a moving horizon state estimator are designed. The objective is to reach a specific particle moisture content setpoint at the end of the drying batch while decreasing cycle time and limiting particle temperature. A penalty term on the energy consumption can also be added to the usual tracking control cost function. Compared to a typical FBD operation in industry (mostly open-loop), it is shown that the drying time and the energy consumption can be efficiently managed on the pilot-scale process while limiting various operation problems like under drying, over drying, or particles overheating.

Modeling of moisture diffusivity, activation energy and energy consumption in fluidized bed drying of rough rice

The present work was an attempt to assess the effective moisture diffusivity, activation energy, and energy consumption of rough rice in a batch fluidized bed dryer. Drying experiments were conducted at drying air temperatures of 50, 60, and 70 °C, superficial fluidization velocities of 2.3, 2.5, and 2.8 m/s, and solids holdup of 1.32 kg. Drying kinetics showed that the whole fluidized bed drying of rough rice occurred in the falling rate period. The effective moisture diffusivity was described by an Arrhenius equation. The evaluated effective moisture diffusivity increased with drying air temperature and superficial fluidization velocity and was found to vary from 4.78 × 10−11 to 1.364 × 10−10 m2/s with R2 higher than 0.9643. The activation energy and the pre-exponential factor of Arrhenius equation were found to be in the range of 36.59–44.31 kJ/mol and 4.71 × 10−5–7.15 × 10−4 m2/s, respectively. Both maximum values of the specific energy consumption of 74.73 MJ/kg and the total energy need of 12.43 MJ were obtained at 60 °C drying air temperature and 2.8 m/s superficial fluidization velocity. Both minimum values of the specific energy consumption of 29.98 MJ/kg and the total energy need of 4.85 MJ were obtained under drying air temperature of 70 °C and superficial fluidization velocity of 2.3 m/s.

Improving Three Phase Modeling of Fluidized Bed Dryer

Heat transfer phenomena in batch fluidized bed dryer have been studied and analyzed using three phase model including solid phase, interstitial gas phase and bubble phase based on Rizzi model. New correlations of heat transfer coefficient to surrounding and convection heat transfer coefficient between solid and interstitial gas are being proposed. In addition, some modifications have been done according to the state of flow and particle properties.The model was used to study the effects of particle diameter, particle density and input gas temperature on Geldart group D particles. The numerical results of heat transfer such as solid and gas temperature distributions have been compared with the available experimental data and good agreement between them is observed.

Heat and mass transfer studies in a batch fluidized bed dryer using Geldart group D particles

The drying behavior at low temperatures has been studied with four different uniformly sized particles and three different binary mixtures at different dilutions ranging from 10 to 40 % with an interval of 10 % varying parameters such as air velocity, initial moisture content, initial bed height and temperature. Falling rate period one and two were observed and correlations were developed to predict the drying rate in falling rate periods one and two. Correlations were also developed to predict the average moisture content by considering the effect of various parameters for uniformly sized particles and binary mixture of solids. The heat and mass transfer coefficients have been found for different conditions and compared. Comparison of experimental and predicted average moisture contents for uniformly sized particles and for various binary mixtures has been made and the predicted average moisture content has been found to be in good agreement with experimental average moisture content.

Drying behavior of uniform and binary mixture of solids in a batch fluidized bed dryer

The drying behavior of solids has been studied in a batch fluidized bed dryer using different uniformly sized solids and various binary mixtures of solids at different dilutions in falling rate periods one and two. To predict the drying behavior in falling rate periods one and two, correlations were developed for uniformly sized particles and for binary mixture of solids. The mixing index has been incorporated to develop the correlations for two types of falling rate periods. The average moisture content has been taken to predict the effect of various parameters on drying behavior. The correlations for average moisture content have been developed by considering the effect of various parameters such as air velocity, initial moisture content of solids, temperature, initial bed height and particle diameter for uniformly sized particles. The effect of various parameters on drying behavior has been investigated for different binary mixture of solids. To predict the drying behavior of binary solid mixtures, mixing index has been incorporated with other parameters in correlation development. The mixing index has been found to decrease with increase in the dilution of fine particles with coarse particles. The drying behavior of binary mixture of solids has been found to be similar to the uniformly sized particles. Effect of dilution on drying has been investigated, where in it is noticed that 10% diluted binary mixture gave highest drying rate and no improvement in drying behavior is found for dilution beyond 30%. The work finds importance in practice, as it involves the use of solid mixtures. The experimental results were compared with the predicted values and are found to be in good agreement.

Energy and exergy analysis of fluidized bed dryer based on two-fluid modeling

Energy and exergy analysis for batch fluidized bed dryer based on the Eulerian two-fluid model (TFM) is performed to optimize the input and output and keep the quality of products in good condition. The two-fluid model is used based on a continuum assumption of each phase. Two sets of conservation equations are applied for gas–solid phases and are considered as interpenetrating continuum. Further this study considers the two-dimensional, axis-symmetrical cylindrical energy and exergy equations for both phases and numerical simulation is preformed. The governing equations are discretized using a finite volume method with local grid refinement near the wall and inlet. The effects of parameters such as: the inlet gas velocity, inlet gas temperature and the particle size diameter on the energy, exergy efficiencies and the availability of gas are sought. Two-fluid model prediction indicates good agreement between the available experimental results and reported non-dimensional correlations and other model predictions. It is illustrated that at the beginning of the drying process, the energy efficiency is higher than the exergy efficiency for a very short time. However two efficiencies come closer to each other at the final stage of the drying. Increasing particle size will decrease both efficiencies and the gas availability at the starting process.

Optimal quality control of baker's yeast drying in large scale batch fluidized bed

Optimal quality control of drying process of baker's yeast in large scale batch fluidized bed dryer is presented using neural network based models and modified genetic algorithm (GA). The objective of this study is to determine optimal conditions to maximize product quality while minimizing energy consumption. For this purpose, the drying process and quality models based on neural network with delay units are combined for predicting the dry matter, product temperature, change in dry matter and the quality loss while minimizing energy consumption and this model is then used for optimal quality control. A stochastic method based optimization structure is designed in order to solve the optimization problem whose the objective function is discontinuous, non-differentiable, complex and highly non-linear. The results obtained by optimal quality control based on modified GA showed that the performance of the existing industrial scale drying process was improved. The constructed optimal quality control structure is very convenient for the production process applications and may be applied without too much modification.

Model‐Based Nonlinear Control of Batch Fluidized Bed Dryers

AbstractControl of a batch fluidized bed dryer is required in many industries. In this paper, the optimization and feedback control of material moisture content in a batch fluidized bed dryer are studied. The optimal operating conditions of the dryer have been found and a generic model control (GMC) strategy has been implemented to achieve a desired drying rate for wet materials. As it is usually impractical to measure moisture content directly, an extended Kalman filter (EKF) observer is used to estimate the moisture content on‐line in order to detect the drying end‐point and to provide a state estimate for feedback control. Studies show that the EKF observer and the GMC controller can provide satisfactory estimation and control of the particle moisture content even if the process model error is significant.

Dynamic Model Analysis of Batch Fluidized Bed Dryers

AbstractIn this work, a lumped mechanistic model has been developed to describe the heat and mass transfer between solid, gas and bubble phases in a batch fluidized bed dryer. To minimize the computational load, an approximation of the bubble temperature has been made in the model and it is shown that this does not significantly reduce the accuracy of the model. Model parameter sensitivity analysis has indicated that the performance characteristics of a bath fluidized bed dryer are affected not only by the inlet gas superficial velocity and temperature, but also by the features of particle and bubble phases, in particular, the particle and bubble sizes. Experimental validation shows that the proposed lumped dynamic model can be used to predict the particle moisture content and temperature profiles during the drying process in a fluidized bed dryer.