Continuous Fluidized Bed Dryer Research Articles

Analysis of the Influence of Process and Formulation Properties on the Drying Behavior of Pharmaceutical Granules in a Semi-Continuous Fluid Bed Drying System

In the last decade, twin-screw wet granulation became an essential technology for continuous pharmaceutical tablet production. Consequently, interest in (semi-)continuous fluidized bed drying systems as a subsequent processing unit has grown. In parallel, it has become pivotal to fully understand and control manufacturing processes in line with in the quality-by-design paradigm. Formulation-generic prediction models would enormously facilitate digitally enhanced process development and require dedicated experimental data collection and process knowledge. To obtain this knowledge, three experimental campaigns were performed in this work. Firstly, an investigation into the effect of dryer process settings on drying behavior is presented. Secondly, the effect of active pharmaceutical ingredient properties on drying was assessed by producing granules of similar particle size and porosity and evaluating their drying and breakage behavior. Finally, additional experiments with varying active pharmaceutical ingredients and drug load were conducted to increase the genericity of the data set. This knowledge can be used in mathematical process modelling.

A Novel Method to Detoxify Steam-Exploded Biomass and Produce a Substrate for Biorefinery

Pre-treatments at relatively high temperatures (range 160 °C–220 °C) are currently used to transform lignocellulosics into biofuels and chemicals. In this step, several molecules with an inhibitory effect in the subsequent fermentation processes are generated. These inhibitors include low-molecular-weight molecules and lignin fragments that can be removed by water washing. However, this procedure also removes valuable soluble carbohydrates which are then difficult to recover from the diluted stream. In this work, a new method to detoxify steam-exploded substrates is reported. The procedure is based on the evaporation of low-weight acids and aldehydes, which leaves all the sugars in the solid matrix, while the cellulose hornification (an irreversible modification of the cellulose fibres that depresses the saccharification yield) is prevented by adding steam to the hot fluidizing flow stream. Two systems were tested: a 0.1 kg/batch oscillating fluidized bed and a continuous fluidized bed dryer operating downstream of a steam explosion plant with a treatment capacity of 150 kg/h. The detoxified substrates were subjected to enzymatic hydrolysis and fermentation to obtain bioethanol, with a yield that was 14% higher than that obtained from substrates detoxified with conventional methods of drying or washing.

Processing of thermosensitive biological API from suspension using an integrated continuous granulation – Drying – Milling line into powder ready for tableting

Drying is broadly used to enhance the stability of thermosensitive biologics (for example proteins, probiotics) despite the risk of inadequate product quality after the drying process. Continuous fluidized bed drying is an attractive technology for these active pharmaceutical ingredients owing to the short mean residence time at elevated temperatures, compared to batch-type drying technologies and the possibility to closely monitor and precisely control the process. In this work, an integrated continuous granulation – drying – milling line was used to manufacture granules ready for tableting from a suspension of probiotic bacteria. A mechanistic drying model suitable to predict the product temperature in the dryer and the moisture content of the granules was built. This allowed finding the optimal operating conditions for maximal bacteria load and low residual moisture content in the product, which has the potential to enable direct integration with the tableting unit. A continuous experiment was carried out with the in silico - optimized process parameters. The produced granules had high probiotic content and were suitable for tableting, which demonstrates the usefulness of the model-based process optimization in complex integrated pharmaceutical manufacturing processes.

Modeling and Flowsheet Simulation of Vibrated Fluidized Bed Dryers

Drying in fluidized beds is an important step in the production of powdered materials. Especially in the food and pharmaceutical industry, fluidized bed dryers are often vibrated to improve the drying process. In the current work, a continuous fluidized bed drying model is implemented in the novel, open-source flowsheet simulation framework Dyssol. The new model accounts for the hydrodynamic characteristics of all Geldart groups as well as the impact of mechanical vibration on the drying process. Distributed particle properties are considered by the model. Comprehensive validation of the model was conducted for a wide range of process parameters, different materials, dryer geometries and dimensions as well as the impact of vibration. Particle properties are predicted accurately and represent the broad experimental data well. A sensitivity analysis of the model confirmed grid independence and the validity of underlying model assumptions.

Integrated twin-screw wet granulation, continuous vibrational fluid drying and milling: A fully continuous powder to granule line

Highly homogeneous low-dose (50 μg) tablets were produced incorporating perfectly free-flowing granules prepared by a fully integrated Continuous Manufacturing (CM) line. The adopted CM equipment consisted of a Twin-Screw Wet Granulator (TSWG), a Continuous Fluid Bed Dryer (CFBD) and a Continuous Sieving (CS) unit. Throughout the experiments a pre-blend of lactose-monohydrate and corn starch was gravimetrically dosed with 1 kg/h into the TSWG, where they were successfully granulated with the drug containing water-based PVPK30 solution. The wet mass was subsequently dried in the CFBD on a vibratory conveyor belt and finally sieved in the milling unit. Granule production efficiency was maximized by determining the minimal Liquid-to-Solid (L/S) ratio (0.11). Design of Experiments (DoE) were carried out in order to evaluate the influence of the drying process parameters of the CFBD on the Loss-on-Drying (LOD) results. The manufactured granules were compressed into tablets by an industrial tablet rotary press with excellent API homogeneity (RSD < 3%). Significant scale-up was realized with the CM line by increasing the throughput rate to 10 kg/h. The manufactured granules yielded very similar results to the previous small-scale granulation runs. API homogeneity was demonstrated (RSD < 2%) with Blend Uniformity Analysis (BUA). The efficiency of TSWG granulation was compared to High-Shear Granulation (HSG) with the same L/S ratio. The final results have demonstrated that both the liquid distribution and more importantly API homogeneity was better in case of the TSWG granulation (RSD 1.3% vs. 4.5%).

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.

Self-tuning control of continuous fluidized bed drying of baker’s yeast pellets

Uncertainty in the kinetics of the second drying period represents the major challenge in continuous drying of particulate solids which can be overcome by adaptive feedback control. In this contribution, self-tuning control comprising online-state estimation and adaptive PI-control is considered to guarantee desired product moisture. Advantages of the approach over conventional PI-control are discussed. The performance is shown for fluidized bed drying of baker’s yeast. It is shown that the self-tuning approach is superior to nonadaptive approaches in case of parametric uncertainty even at non-nominal steady-states.

Experimental Energy Studies and Artificial Neural Network Modeling For Continuous Wall Heated Fluidized Bed Dryer

Abstract Now a days, scope of research has increased on energy studies due to shortage for fuel inputs. Fluidized bed dryers are prominent among efficient moisture removal equipments in food, pharmaceutical and particle based industries. Various food, pharmaceutical, cement and solid handling industries have adopted continuous fluidized bed drying technique due to its advantages like efficient heat transfer, good moisture removal rate and good solid-gas mixing due to continuous inputs. To optimize the energy consumption it is important to consider energy utilization ratio of any process equipment. From the literature review, it has been observed that only few studies were done on energy analysis of dryers. In the present study, experiments were carried out to determine the drying characteristics and energy utilization ratio of continuous wall heated fluidized bed dryer varying operating conditions like wall temperature from 40 to 60 °C, air velocity from 1.01 to 1.7 m/s and solids flow rate from 5 to 10 kg/h. For predicting the energy utilization ratio, artificial neural network (ANN) model was developed using experimental data.

Breakage and drying behaviour of granules in a continuous fluid bed dryer: Influence of process parameters and wet granule transfer

Although twin screw granulation has already been widely studied in recent years, only few studies addressed the subsequent continuous drying which is required after wet granulation and still suffers from a lack of detailed understanding. The latter is important for optimisation and control and, hence, a cost-effective practical implementation. Therefore, the aim of the current study is to increase understanding of the drying kinetics and the breakage and attrition phenomena during fluid bed drying after continuous twin screw granulation. Experiments were performed on a continuous manufacturing line consisting of a twin-screw granulator, a six-segmented fluid bed dryer, a mill, a lubricant blender and a tablet press. Granulation parameters were fixed in order to only examine the effect of drying parameters (filling time, drying time, air flow, drying air temperature) on the size distribution and moisture content of granules (both of the entire granulate and of size fractions). The wet granules were transferred either gravimetrically or pneumatically from the granulator exit to the fluid bed dryer. After a certain drying time, the moisture content reached an equilibrium. This drying time was found to depend on the applied airflow, drying air temperature and filling time. The moisture content of the granules decreased with an increasing drying time, airflow and drying temperature. Although smaller granules dried faster, the multimodal particle size distribution of the granules did not compromise uniform drying of the granules when the target moisture content was achieved. Extensive breakage of granules was observed during drying. Especially wet granules were prone to breakage and attrition during pneumatic transport, either in the wet transfer line or in the dry transfer line. Breakage and attrition of granules during transport and drying should be anticipated early on during process and formulation development by performing integrated experiments on the granulator, dryer and mill.

Paddy Drying in Batch Fluidized Bed and Scale-up Simulation in Continuous Operation Mode

The objective of this research is to develop the industrial-scale fluid bed dryer for paddy by scale-up of lab-scale experimental data. The developed dryer was conducted by simulation using a two phase model. Firstly, the experimental works by using lab-scale batch fluid bed dryer, was conducted to determine the drying curve of paddy (Xin 0.32 kg/kg dry base). In the experimental works,the inlet air temperature was varied (°C): 40; 50; 60. The drying rate curves as a function of moisture content showed only decreasing drying rate period. Then, a very good agreement between the measured and simualtion results of the profile of moisture content in solids was produced by simulator. Finally, asimulated continuous fluidized bed dryer for paddy with dimension 5 m of length and 1.5 of width was succesfully performed, in which the influence of mass solid flow rate 0.1; 0.2; 0.4 tons/h, height of bed 0.25; 0.50; 0.75 m, and air temperature 50; 70; 100 °C on drying process were studied. Keywords: Paddy; fluid bed dryer; batch, contonious; modelling; simulation

Threats to Food Safety and Sustainability of Nike (Awaous melanocephalus) in Gorontalo Province

The objective of this research is to develop the industrial-scale fluid bed dryer for paddy by scale-up of lab-scale experimental data. The developed dryer was conducted by simulation using a two phase model. Firstly, the experimental works by using lab-scale batch fluid bed dryer, was conducted to determine the drying curve of paddy (Xin 0.32 kg/kg dry base). In the experimental works, the inlet air temperature was varied (°C): 40; 50; 60. The drying rate curves as a function of moisture content showed only decreasing drying rate period. Then, a very good agreement between the measured and simualtion results of the profile of moisture content in solids was produced by simulator. Finally, a simulated continuous fluidized bed dryer for paddy with dimension 5 m of length and 1.5 of width was succesfully performed, in which the influence of mass solid flow rate 0.1; 0.2; 0.4 tons/h, height of bed 0.25; 0.50; 0.75 m, and air temperature 50; 70; 100 °C on drying process were studied. Keywords: Paddy, fluid bed dryer, batch, contonious, modelling, simulation

Effect of distributor on performance of a continuous fluidized bed dryer

Proper gas distribution is very important in fluidized bed drying in industrial practice. Improper distribution of gas may lead to non-idealities like channeling, short circuiting and accumulation which gives rise to non-uniform quality of dried product. Gas distribution depends on the distributor plate used. Gas distribution mainly depends on orifice diameter, number of orifices and opening area of the distributor plate. Small orifice diameter leads to clogging, and a large orifice diameter gives uneven distribution of gas. The present work involves experimental studies using different distributor plates and simulation studies using ASPEN PLUS steady state simulator. The effect of various parameters such as orifice diameter, number of orifices and the opening area of the distributor plate on the performance of fluidized bed dryer have been studied through simulation and experimentation. Simulations were carried out (i) with increasing air inlet temperature to study the characteristics of solid temperature and moisture in outlet (ii) with increasing orifice diameter and (iii) with increase in number orifices to study the solid outlet temperature profiles. It can be observed from the simulation that, an increase in orifice diameter and number orifices increases solid outlet temperature upto certain condition and then after there is no effect with further increase. Experiments were carried out with increasing opening area (3.4 to 42%) in the form of increasing orifice diameter keeping the number of orifices constant and increasing number of orifices of the distributor plate keeping the orifice diameter constant. It can be seen that the drying rate and solid outlet temperature increase upto certain condition and then after with further increase in the orifice diameter and number of orifices, the change in the drying rate and solid outlet temperature observed is little. The optimum values of orifice diameter and number of orifices from experimentation are found to be 5 mm and 60 (22% opening area).

Drying of Soybean Seeds in Fluidized Bed: Experimental and Scale-up Simulation in Continuous Operation Mode

The drying curve of the soybean seed (X_in 0.4 kg/kg dry base) was obtained experimentally by fluid bed dryer. The experimental works was performed by varying inlet air temperature (°C): 35; 40; 45, bed mass of particles (kg): 0.2; 0.3; 0.4 and superficial air velocity (m/sec): 7.6; 8.4; 9.1. The drying rate curves as a function of moisture content showed only the decreasing rate period. Among the variables examined, only temperature had a significant influence on the soybean seed drying in fluidized bed. The normalized drying curve of the single particles as well as the critical moisture content (X_cr 0.5) was derived. A simulated continuous fluidized bed dryer for soybean with capacuty 500 kg/h seed had been successfully designed by scale-up method.

On Dryer Energy Performance and Controllability: Generalized Modeling and Experimental Validation

This work presents an approach to compute dryer energy efficiency using air flowrate step responses and establish a link between drying energy efficiency and process controllability. The approach is based on the temperature drop between the dryer inlet and outlet air under adiabatic conditions and so decouples water evaporation from heat loss and product heating effects on dryer temperature drop. As such, the computation is accurate even for dryers with significant heat losses where the traditional use of actual temperature drop measurements is grossly inaccurate. The approach is tested and verified on two experimental case studies involving significant heat losses: the first, a continuous fluidized-bed dryer (from literature); the second, a conventional and zeolite wheel-assisted batch dryer designed in the current study.

An analytical solution of population balance equations for continuous fluidized bed drying

Continuous fluidized bed drying is widely used to remove moisture or solvents from granular materials. It is known that different residence times of the wet particles may lead to a distribution of product properties, e.g. different moistures. The prediction of such moisture distributions in fluidized bed dryers is of particular interest in industrial practice. In the present study, a simple analytical approach is introduced to calculate moisture distributions at the outlet of a continuous fluidized bed dryer. The model provides an analytical solution of the simple one-dimensional population balances. It will be contrasted with a traditional model approach based on averages and with experimental investigations conducted in a lab scale fluidized bed dryer under variation of the particle and the gas flow rate. Furthermore, the moisture distributions of the dried product were estimated by single particle measurements using nuclear magnetic resonance spectroscopy. It will be demonstrated that the developed analytical approach is capable to predict such moisture distributions for continuous drying processes.

Optimization of baker's yeast drying in industrial continuous fluidized bed dryer

Instant active dry baker's yeast is a well-known product widely used for leavening of bread, produced by fermentation, and usually dried by hot air to 94–96% dry matter content. Multi-stage fluidized bed drying process is a commercial effective method for yeast drying. In this work, optimum operating parameters of an industrial continuous fluidized bed dryer for the production of instant active dry yeast were investigated. The dryer contained four zones separated with moving weirs. The operating conditions such as temperature, loading rate of compressed yeast granules, and hot air humidity had direct effects on both yeast activity and viability. The most important factors that affected the quality of the product were loading rate and the operational temperature in each zone on the bed. Optimization was performed for three loading rates of the feed to the dryer, using response surface methodology for the experimental design. The most significant factor was shown to be the loading rate with mean fermentation activity values of 620, 652, and 646 cm 3 CO 2/h for 300, 350, and 400 kg/h loading rates, respectively. The data analysis resulted in an optimal operating point at a loading rate of 350 kg/h and temperatures of zones 1, 2, 3, and 4 controlled at 33, 31, 31, and 29 °C, respectively. The best activity value was predicted as 668 ± 18 cm 3 CO 2/h, and confirmation experiments resulted in 660 ± 10 cm 3 CO 2/h. At the same operating point, the average viability of the cells was predicted as 74.8 ± 3.7% and confirmed as 76.4 ± 0.6%. Compared with the normal operating conditions at the plant, the optimization resulted in more than 12% and 27% improvement in the yeast activity and viability, respectively.

Drying Characteristics of Chili Using Continuous Fluidized-Bed Dryer

Problem statement: The objective of this study was to obtain the dying characteristics of the Jinda chili, a commonly grown variety in the Northeatern of Thailand, using the continuous fluidizedbed dryer in reducing moisture content of dried chili up to 13% wet basis as comparable to the dried chili in the market and to investigate the effect of drying temperature and drying air velocity. Approach: Drying characteristics was to study under varying conditions of drying temperature (50, 60, 70, 80, 90 and 100°C) and drying air velocity (4, 5 and 6 m sec-1). Results: The drying time decreased within the increasing of drying temperature and drying air velocity. Drying air velocity affected the drift and continuously moves of chili particle outward from dryer chamber under continuous fluidized-bed technique. The decreasing of moisture content effected with increasing of a compound capsaicin of dried chili compare to fresh chili. The diffusion coefficient of moisture content increased with increasing all drying temperature and drying air velocity. Conclusion: Drying temperature was the significant factor of the chili moisture content reduction. Drying air velocity affected the move of chili outward from chamber under the continuous fluidized bed drying process.

Mathematical modeling of a continuous fluidized bed dryer

In this work, a numerical simulation of a fluidized bed dryer based on the two-phase theory of fluidization has been proposed. Solid particles in the emulsion phase are considered lumped and in the bubble phase is assumed plug while in the emulsion phase is considered totally mixed. Moreover, the bubble size variations along the bed height are taken into consideration. Influence of the superficial gas velocity, input temperature of drying gas, particle size and mean residence time of solid particles on the drying process have been reported. The simulation results show an improvement to the prediction of other models that consider uniform size bubble and other simplification assumptions.

Modeling of a continuous fluidized bed dryer using artificial neural networks

The work involves experimentation on drying of solids in a continuous fluidized bed dryer covering different variables like bed temperature, gas flow rate, solids flow rate and initial moisture content of solids. The data are modeled using artificial neural networks. The results obtained from artificial neural networks are compared with those obtained using Tanks-in-series model. It was found that results obtained from ANN fit the experimental data more accurately compared to the RTD model with less percentage error. This indicates a better fit of artificial neural networks to experimental data compared to various mathematical models.

Simulation of a cross-flow continuous fluidized bed dryer for paddy rice

Fluidized bed drying is an alternative drying method of paddy, which offers many advantages over other forms of drying. In this study a mathematical model is developed to simulate the drying of moist paddy in a cross-flow continuous fluidized bed dryer (CFCFBD). The model is based on the differential equations, which are obtained by applying the momentum, mass and energy balances to each element of the dryer and also on the drying properties of paddy. The proposed model is solved by writing a computer program, which takes the operating conditions as input and gives the hydrodynamic properties as well as the variation of moisture content of paddy through the dryer as output. Different fluidizing characteristics of paddy, needed in the program, are determined from the drying experiments in the literature. Some experimental data of CFCFBD are used to validate the predictions of the model. The predictions of the model show good agreement with experimental results.