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Computational and Experimental Study of Granulation in Fluidized Beds

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A special issue of Processes (ISSN 2227-9717). This special issue belongs to the section "Particle Processes".

Deadline for manuscript submissions: closed (20 August 2023) | Viewed by 26767

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Prof. Dr. Stefan Heinrich

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Guest Editor

Institute of Solids Process Engineering and Particle Technology, Hamburg University of Technology, 21073 Hamburg, Germany
Interests: fluidized bed technology; particle formulation; granulation; agglomeration; coating; particle simulation methods; particle characterization
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Evangelos Tsotsas

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Guest Editor

Thermal Process Engineering, Otto-von-Guericke University Magdeburg, Universitaetsplatz 2, 39106 Magdeburg, Germany
Interests: particle technology; drying; agglomeration; coating; heat and mass transfer; modeling
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Fertilizers, detergents, pharmaceuticals, animal feed or food ingredients—many products of our daily life—are solids produced in fluidized beds via spray granulation or agglomeration. Particle growth is induced through the injection of solids in liquid form into a granulator, either as a melt or suspended or dissolved in a liquid, whereby the particle bed is fluidized using the inflowing air and thereby mixed. The injected droplets are deposited on the particles and interact with the gas phase. In the case of agglomeration, the liquid acts as a binder between the primary particles, whereby a liquid bridge forms and solidifies after the liquid evaporates due to the hot fluidization gas. In layering granulation or coating, the droplets come into contact with the particle surface, where they spread and form a liquid film around the particle. Due to evaporation of the liquid, this film becomes a thin solid shell defined as a coating, whereas granulation refers to an onion-like structure of layering. The variation of process conditions is used to generate particle product properties such as certain sizes, shapes or structures, which then determine the desired high-quality application properties such as flowability, stability, controlled release or taste and odor masking.

This Special Issue on “Computational and Experimental Study of Granulation in Fluidized Beds” aims to gain a deeper insight into the effect of different process parameters on the micro and transport processes in fluidized beds and the resulting granule properties structures, which is invaluable for the production of tailor-made particles. For this, knowledge on novel experimental and simulation methods is required.

Suitable topics include but are not limited to:

Characterization methods for granule properties;
Characterization methods for fluid and particle dynamics in wet gas-solid fluidized beds;
Population balance modeling;
Flowsheet simulation;
CFD/DEM simulations;
Heat and mass transfer in spray fluidized beds;
Influence of drying on granulation;
Adhesive forces and binding mechanism during granulation;
Modeling and scale-up of fluidized bed spray granulation.

Prof. Dr. Stefan Heinrich
Prof. Dr. Evangelos Tsotsas
Guest Editors

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Keywords

granulation
coating
agglomeration
fluidized bed
CFD/DEM simulation
particle properties
particle formulation

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Published Papers (11 papers)

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Research

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20 pages, 2014 KiB

Open AccessArticle

Discrete-Element-Method-Based Determination of Particle-Level Inputs for the Continuum Theory of Flows with Moderately Cohesive Particles

by Kevin M. Kellogg, Peiyuan Liu and Christine M. Hrenya

Processes 2023, 11(9), 2553; https://doi.org/10.3390/pr11092553 - 25 Aug 2023

Cited by 2 | Viewed by 996

Abstract

In this work, the cohesion-specific inputs for a recent continuum theory for cohesive particles are estimated for moderately cohesive particles that form larger agglomerates via discrete element method (DEM) simulations of an oscillating shear flow. In prior work, these inputs (critical velocities of agglomeration and breakage and collision cylinder diameters) were determined for lightly cohesive particles via the DEM of simple shear flow—i.e., a system dominated by singlets and doublets. Here, the DEM is again used to extract the continuum theory inputs, as experimental measurements are infeasible (i.e., collisions between particles of a diameter of <100 μm). However, simulations of simple shear flow are no longer feasible since the rate of agglomeration grows uncontrollably at higher cohesion levels. Instead, oscillating shear flow DEM simulations are used here to circumvent this issue, allowing for the continuum theory inputs of larger agglomerate sizes to be determined efficiently. The resulting inputs determined from oscillating shear flow are then used as inputs for continuum predictions of an unbounded, gas–solid riser flow. Although the theory has been previously applied to gas–solid flows of lightly cohesive particles, an extension to the theory is needed since moderately cohesive particles give rise to larger agglomerates (that still readily break). Specifically, the wider distribution of agglomerate sizes necessitates the use of polydisperse kinetic-theory-based closures for the terms in the solids momentum and granular energy balances. The corresponding continuum predictions of entrainment rate and agglomerate size distribution were compared against DEM simulations of the same system with good results. The DEM simulations were again used for validation, as it is currently extremely challenging to detect agglomerate sizes and the number of fractions in an experimental riser flow. Full article

(This article belongs to the Special Issue Computational and Experimental Study of Granulation in Fluidized Beds)

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18 pages, 2178 KiB

Open AccessEditor’s ChoiceArticle

The Evolution of Variance and Entropy of the Granule Size Distribution in Fluidized Bed Agglomeration

by Kevin Cronin and Francisco Javier Gutiérrez Ortiz

Processes 2023, 11(8), 2247; https://doi.org/10.3390/pr11082247 - 26 Jul 2023

Viewed by 904

Abstract

The evolution of the variance and entropy of granule size in the fluidized bed agglomeration process using two different aggregation kernels is examined. The first is a constant kernel (aggregation is independent of both time and granule size) and permits the most unconstrained agglomeration process that can occur where granules in any size class (up to a maximum size) can be formed at any point in time. This gives the fastest and largest increase in the variance and entropy of the resulting granule size distribution. The second kernel is a mechanistic kernel including a granule growth-limiting mechanism, in this case implemented by the consideration that not all collisions result in coalescence. This markedly changes the evolution of the variance and entropy of the distribution and reduces both significantly. Quantifying the entropy of the distribution provides another perspective on the change in the size distribution in an agglomeration process. It is shown that entropy can provide a better measure of size evolution than variance in that it represents the changing shape of the distribution more closely. Full article

(This article belongs to the Special Issue Computational and Experimental Study of Granulation in Fluidized Beds)

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17 pages, 5849 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Development of In-Line Measurement Techniques for Monitoring Powder Characteristics in a Multi-Stage Spray Drying Process

by Jennifer Frank, Tobias V. Raiber, Laura Grotenhoff and Reinhard Kohlus

Processes 2023, 11(7), 1931; https://doi.org/10.3390/pr11071931 - 27 Jun 2023

Viewed by 2045

Abstract

The integration of spray drying and agglomeration offers significant advantages, such us continuous production with lower energy consumption. However, it is a knife-edge process with a narrow operating window and limited degrees of freedom that decide between successful agglomeration and fluidized bed blockage due to excessive moisture. In this contribution, factors influencing the spray-through agglomeration process of skim milk powder as a model system were investigated via a design of experiments. Three in-line monitoring methods were applied and tested to observe the most important parameters in the agglomeration process—the product moisture and particle size distribution. Regarding the moisture content, a capacitive moisture sensor was calibrated with linear regression and a near-infrared sensor with partial least squares regression. Near-infrared spectroscopy was found to be the suitable method for determining the moisture content, while the capacitive moisture sensor mainly provides information on the bulk density, filling level, or fluidization state in the fluidized bed. Additionally, particle size distribution data were extracted from the spectral data using in-line data from a spatial filter velocimetry probe in the fluidized bed. This opens the potential to monitor both parameters in real time with a single non-invasive sensor. Full article

(This article belongs to the Special Issue Computational and Experimental Study of Granulation in Fluidized Beds)

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17 pages, 60408 KiB

Open AccessArticle

Secondary Motion of Non-Spherical Particles in Gas Solid Flows

by Cihan Ates, Joel Arweiler, Habeb Hadad, Rainer Koch and Hans-Jörg Bauer

Processes 2023, 11(5), 1369; https://doi.org/10.3390/pr11051369 - 30 Apr 2023

Cited by 2 | Viewed by 1326

Abstract

Objective of this study is to investigate the effect of secondary motion of particles in multiphase gas-solid flows parametrically and test the relative impacts of particle shape and orientation information on particle distribution. For that purpose, predictive accuracies of simplified drag coefficient models are assessed for the conditions relevant to a wood recovery plant operating at dilute flow regime. After demonstrating the strong impact of the shape and orientation information on the force balance for single particles, we compared the steady state Eulerian-Lagrangian simulation results for particle volume fractions, residence times and particle diameter distributions within the chamber for different (i) superficial gas velocities (5 m/s, 7.5 m/s), (ii) orientation tendencies and (iii) particle shapes. Transient simulations are performed until the system reaches steady state conditions by monitoring the mass flow rates of the particulate phases leaving the chamber. The secondary motion of non-spherical particles is represented by stochastic sampling from the available experimental data. Analysis of the force balance on single particles revealed log-scale variations if the orientation of the particles with respect to flow fluctuates. Variations in the single particle force balances are found to be still visible in the CFD analysis, where the secondary motion of particles drastically changed the particle distribution in the chamber. The native non-spherical model which only accounts for the shape correction was found to over-predict the entrainment, leading to a significantly different particle volume fraction and diameter distributions. Spherical particle assumption also caused significant errors in the particle distribution, which increases as aspect ratio of the cylindrical particle diverges from one. Results show that particle orientation statistics are extremely important to capture the particle mixing and segregation patterns at dilute regime, which cannot be captured with such simplifying assumptions. Full article

(This article belongs to the Special Issue Computational and Experimental Study of Granulation in Fluidized Beds)

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12 pages, 2081 KiB

Open AccessArticle

Statistical Investigation of Rotary Fluidized Bed Agglomeration Process with Tangential Spray and In-Line Particle Size Measurement for PAT Process Control

by Marcel Langner, Biwen Zhou, Florian Priese and Bertram Wolf

Processes 2023, 11(4), 1066; https://doi.org/10.3390/pr11041066 - 2 Apr 2023

Cited by 2 | Viewed by 1870

Abstract

A statistical design of experiments for a rotary fluidized bed agglomeration process is performed to improve both the knowledge of the process and the influence of the process parameters. Agglomerates of a pharmaceutical formulation are manufactured in a laboratory fluidized bed rotor apparatus with a tangential spray nozzle. Particle size is measured in-line over the entire agglomeration process with a spatial filter velocimetry probe installed directly in the process chamber and off-line with dynamic image analysis for comparison. The influence of the process parameters spray rate, spray pressure, rotor speed, and process air temperature on the fluidized bed is investigated using a central composite design. In-line measurement of particle size is possible over the entire rotor process. Spray pressure, spray rate, square of process air temperature, and some interactions proved to be statistically significant. Particle size measured with spatial filter velocimetry and dynamic image analysis indicates good agreement and a similar trend. The successful application of particle size measurement in a fluidized bed rotor agglomeration at a laboratory scale using spatial filter velocimetry to improve process control and reduce the risk of failed batches serves as the basis for transferring to a production scale. Full article

(This article belongs to the Special Issue Computational and Experimental Study of Granulation in Fluidized Beds)

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13 pages, 447 KiB

Open AccessFeature PaperArticle

Stability of Combined Continuous Granulation and Agglomeration Processes in a Fluidized Bed with Sieve-Mill-Recycle

by Eric Otto, Robert Dürr and Achim Kienle

Processes 2023, 11(2), 473; https://doi.org/10.3390/pr11020473 - 4 Feb 2023

Cited by 1 | Viewed by 1530

Abstract

Particle formation in fluidized beds is widely applied in an industrial context for the solidification of liquids and size enlargement of granular materials. The two main size-enlargement mechanisms are layering growth and agglomeration. For continuous process configurations with sieve-mill-recycle and layering growth only, the occurrence of undesired self-sustained oscillations in the particle size distribution under certain process conditions is well-known. This contribution investigates the stability of the practically relevant process with additional particle agglomeration by means of a model-based numerical bifurcation analysis. It is shown that the occurrence of stable limit cycles is inhibited by an increased rate of particle agglomeration for a variety of different process conditions and different agglomeration kinetics. These results enhance the understanding of the agglomeration and layering growth dynamics and are relevant for the process design and operation. Full article

(This article belongs to the Special Issue Computational and Experimental Study of Granulation in Fluidized Beds)

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19 pages, 11694 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Fluidized Bed Spray Coating for Improved Mechanical Properties of Particles

by Maike Orth, Sonja Rotter, Wasif Safdar, Süreyya Tasdemir, Swantje Pietsch-Braune, Stefan Heinrich and Alexander Düster

Processes 2023, 11(2), 314; https://doi.org/10.3390/pr11020314 - 18 Jan 2023

Cited by 2 | Viewed by 2499

Abstract

When designing crash absorber particles for application as a filling material in the double-hull of ships, the main goal is to achieve an optimal mechanical performance, in combination with a low-density particle structure, while fulfilling several additional requirements regarding, for example, non-toxic and hydrophobic behavior. In this study, a fluidized bed was used to coat Poraver^® glass particles with Candelilla wax and silicone to attain these specifications. A uniform coating was achieved with wax, but the process turned out to be far more challenging when using silicone. To evaluate the suitability of coated particles as a granular filling material, and to compare their performances with that of untreated Poraver^® particles, several mechanical tests, as well as structural investigations, were conducted. While no notable improvement in mechanical behavior was observed on the single-particle level, bulk tests showed promising results regarding compressibility and abrasion resistance of coated particles compared to untreated ones. Full article

(This article belongs to the Special Issue Computational and Experimental Study of Granulation in Fluidized Beds)

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18 pages, 1199 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Investigation of Island Growth on Fluidized Particles Coated by Means of Aerosol

by Serap Akbas, Kaicheng Chen, Torsten Hoffmann, Franziska Scheffler and Evangelos Tsotsas

Processes 2023, 11(1), 165; https://doi.org/10.3390/pr11010165 - 5 Jan 2023

Cited by 1 | Viewed by 1752

Abstract

In this study, an aerosol fluidized bed is used to coat particles. A new aerosol generator is used to obtain coating solution droplets with a diameter of around 1

μ

m or smaller. Glass particles, which have a mean diameter of 653

μ

[...] Read more.

In this study, an aerosol fluidized bed is used to coat particles. A new aerosol generator is used to obtain coating solution droplets with a diameter of around 1

μ

m or smaller. Glass particles, which have a mean diameter of 653

μ

m, were the non-porous core material and the coating solution was sodium benzoate. Scanning electron microscope pictures were analyzed by MATLAB image processing for evaluating the coverage with the curvature effect. Monte Carlo simulation was used to describe the coating of fluidized particles by aerosol droplets. The purpose of this work was the determination of possible island growth on particles, and investigation of the reasons of it by comparing the experimental and simulation results. The preferential deposition of droplets on already occupied positions is seen as the main possible reason for island growth. Full article

(This article belongs to the Special Issue Computational and Experimental Study of Granulation in Fluidized Beds)

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29 pages, 7925 KiB

Open AccessEditor’s ChoiceArticle

Product-Property Guided Scale-Up of a Fluidized Bed Spray Granulation Process Using the CFD-DEM Method

by Paul Kieckhefen, Swantje Pietsch-Braune and Stefan Heinrich

Processes 2022, 10(7), 1291; https://doi.org/10.3390/pr10071291 - 30 Jun 2022

Cited by 6 | Viewed by 2625

Abstract

In this work, a method to predict the surface structures of particles produced by fluidized bed spray layering granulation using the CFD-DEM method was developed. A simple state-variable/event tracking approach was implemented to capture indirect quantifiers of the progression of structure-forming microprocesses. The state of the droplet at the time of impact on the particle surface, as well as the time required for drying, is correlated to product properties that quantify surface structure morphology such as roughness. A workflow for scale-up of fluidized bed granulation guided by product-property predictors is presented. The approach was tested on a demonstration case from the literature, where a particle core is coated with sodium benzoate solution. The experiment was scaled-up by a factor of eight to pilot-scale using the developed method. Varying the number of nozzles in use in the pilot-scale granulation affected the particle surface roughness due to the differing drying conditions encountered. On this basis, the ability of the tracked-quantity approach to capture the relationship between product properties and geometric feature or process conditions is demonstrated. Full article

(This article belongs to the Special Issue Computational and Experimental Study of Granulation in Fluidized Beds)

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Review

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45 pages, 6607 KiB

Open AccessReview

Challenges in the Simulation of Drying in Fluid Bed Granulation

by Maryam Askarishahi, Mohammad-Sadegh Salehi and Stefan Radl

Processes 2023, 11(2), 569; https://doi.org/10.3390/pr11020569 - 13 Feb 2023

Cited by 4 | Viewed by 3752

Abstract

Fluid bed granulation is faced with a high level of complexity due to the simultaneous occurrence of agglomeration, breakage, and drying. These complexities should be thoroughly investigated through particle–particle, particle–droplet, and particle–fluid interactions to understand the process better. The present contribution focuses on the importance of drying and the associated challenges when modeling a granulation process. To do so, initially, we will present a summary of the numerical approaches, from micro-scale to macro-scale, used for the simulation of drying and agglomeration in fluid bed granulators. Depending on the modeled scale, each approach features several advantages and challenges. We classified the imposed challenges based on their contributions to the drying rate. Then, we critically scrutinized how these challenges have been addressed in the literature. Our review identifies some of the main challenges related to (i) the interaction of droplets with particles; (ii) the drying kinetics of granules and its dependence on agglomeration/breakage processes; as well as (iii) the determination of drying rates. Concerning the latter, specifically the surface area available for drying needs to be differentiated based on the state of the liquid in the granule: we propose to do this in the form of surface liquid, pore liquid, and the liquid bridging the primary particles. Full article

(This article belongs to the Special Issue Computational and Experimental Study of Granulation in Fluidized Beds)

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25 pages, 3363 KiB

Open AccessReview

Review of CFD-DEM Modeling of Wet Fluidized Bed Granulation and Coating Processes

by Yinqiang Song, Tuo Zhou, Ruiqi Bai, Man Zhang and Hairui Yang

Processes 2023, 11(2), 382; https://doi.org/10.3390/pr11020382 - 26 Jan 2023

Cited by 8 | Viewed by 5154

Abstract

Wet fluidized bed granulation and coating processes have been widely used in the pharmaceutical and food industries. The complex gas–solid flow coupled with heat and mass transfer in such processes made it hard to form complete control over the apparatuses. To serve better design, scaling-up, and optimization of granulators and coaters, the underlying micro-scale mechanisms must be clarified. Computational fluid dynamics coupled with the discrete element method (CFD-DEM) provides a useful tool to study in-depth the gas-solid hydrodynamics of the granulation and coating processes. This review firstly introduced the fundamental theory of CFD-DEM from governing equations, force calculation, and coupling schemes. Then the application of CFD-DEM in simulating wet fluidized bed granulation and coating was presented. Specifically, the research focus and the role of CFD-DEM in resolving issues were discussed. Finally, the outlook on the development of CFD-DEM in the context of granulation and coating was given. Full article

(This article belongs to the Special Issue Computational and Experimental Study of Granulation in Fluidized Beds)

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