Parameter identification for discrete element simulation of vertical filling: in-situ bulk calibration for realistic granular foods

Vertical filling of granular media is influenced by resistance of the surrounding medium, especially in the case of a dilute process with relatively large distances between particles and relatively low particle densities. Discrete Element simulations were carried out to calibrate models of such a filling process for two granular food goods. The aim was to perform bulk calibration in-situ, meaning in the process of interest itself, rather than a second setup. To account for the air drag but keep computational cost practical, the computationally cheap free fall was modeled with the Schiller-Naumann correlation for drag force. The predictions where compared to simulations without fluid influence. The results show that the predictive quality of the models was increased with the simple drag model. It is shown that with the expanded model, calibration can be performed in the filling process itself, which might be useful especially for industry application

Study of mass motion on vibrating device: Design and process simulation.

The simulation of mass motion using a vibrating device that was laboratory designed was the main idea of the work. The construction of an experimental vibrating device and the associated measuring station along with the measurement of dynamic properties of the vibrating device depending on preselected input parameters of the device of bulk material on this experimental model is presented. The simulation of the general behavior of particles on an experimental vibrating device at rotational frequencies of 20 Hz, 25 Hz and 35 Hz, and the rotation of contact vibrators at 30°, 45° and 75° by mass flow modeling using software ROCKY DEM is done. It was observed that the particles were moving at the fastest speed at 45° and at 35 Hz and that the top layers fall to the bottom especially at higher rotational frequencies, which may ultimately cause aeration of the particulate matter, thus reducing the angle of internal friction of the bulk material.Web of Science20236380637

Verbesserung der Matrizenfüllung in der pharmazeutischen Tablettierung durch experimentelle und numerische Ansätze

Pharmaceutical tableting consists of three distinct stages: die filling, powder compaction, and tablet ejection. The first step is crucial with respect to the patient's safety as it defines the content and content uniformity of the active pharmaceutical ingredient(s). In this work, different experimental and numerical methods were developed to improve process understanding in die filling as in reality, nontransparent gravity or force feeders impede a detailed examination of the powder transfer into the dies. In the first step, a transparent model die filling system was developed to visualize powder discharge into the die by high speed camera imaging and to discern powder flow patterns. Several mathematical correlations were established to estimate the flowability for new materials in die filling and thus to quantify the effect of particle size enlargement on powder flowability improvement. The Discrete Element Method (DEM), which tracks each individual particle and thus provides a high level of detail in complex powder handling / transporting systems, was utilized to understand die filling in different gravity and force feeders. Thus powder flow patterns through the feeding systems could be discerned and the underlying size segregation mechanisms and dead / high shear zones identified. Those could be related to geometrical properties of the feeder types. First hints to critical material properties (powder cohesivity and particle-wall coefficient of friction) and critical process conditions (turret speed and paddle wheel speed) on critical quality attributes (tablet mass, tablet mass variation, and content uniformity) were provided. The application of different means, such as custom-designed instruments, statistical tools, and DEM, enabled a detailed understanding of powder flow in the tableting machine and its influence on tablet quality. Different levers for process and formulation optimization were presented and could aid pharmaceutical development in the context of the Quality by Design approach.Die Herstellung von Tabletten auf schnell-laufenden Rundläuferpressen kann in drei individuelle Schritte untergliedert werden: die Matrizenfüllung, die Pulverkompaktierung und den Tablettenausstoß. Die Matrizenfüllung sorgt für die Sicherheit des Patienten, da sie die Zusammensetzung und Gleichförmigkeit des Wirkstoffes vorgibt. In der vorliegenden Arbeit wurden experimentelle und numerische Methoden entwickelt, um diesen Prozessschritt besser zu verstehen, da die in der Realität undurchsichtigen Füllschuhgehäusematerialien verhindern, dass der Pulverfluss von außen beobachtet werden kann. Die Visualisierung des Matrizenfüllprozesses in einem transparenten Modell-System mittels einer Hochgeschwindigkeitskamera erlaubte die Identifizierung unterschiedlicher Fließmechanismen. Mathematische Zusammenhänge wurden entwickelt und dienen zur Abschätzung der Fließfähigkeit im Kontext des Matrizenfüllprozesses für neue Materialien und zur Quantifizierung des Einflusses der Partikelgrößenzunahme. In der Diskreten Element Methode (DEM), bei der jeder einzelne Partikel individuell betrachtet und, wurde verwendet, um den Pulvertransports im Kammer- und Rührflügelfüllschuh zu untersuchen. Die hohe Prozessauflösung durch die DEM erlaubte die Identifizierung von Segregationsmechanismen, Tot- und Scherzonen, die auf die geometrischen Eigenschaften der Füllschuhe zurückgeführt wurden. Der Einfluss potentiell kritischer Materialeigenschaften (Reibungskoeffizient Partikel-Geometrie und Kohäsion) und Prozessparametern (Tablettier- und Füllrädergeschwindigkeit) auf kritische Qualitätsmerkmale (Tablettengewicht, und -schwankung und Gleichförmigkeit des Gehalts) wurde aufgedeckt. Der Pulverfluss in der Tablettenpresse und dessen Einfluss auf die Tablettenqualität wurden mittels verschiedener Ansätze untersucht. Es wurden verschiedene Möglichkeiten zur Prozess- und Formulierungsoptimierung entwickelt, die die Entwicklung im Kontext des Quality by Design Ansatzes unterstützen können

Accelerating pharmaceutical tablet development by transfer of compaction equipment across types and scales

openRoller compaction is a key unit operation in a dry granulation line for pharmaceutical tablet manufacturing. However, determining the optimal settings for a roller compactor (RC) typically requires extensive material-consuming experimental campaigns. This amount of material, in particular if active pharmaceutical ingredients are involved, may not be available during development phases, or may be very expensive. For this reason, a compactor simulator (CS) is usually employed to emulate the behaviour of compacted powders at a much smaller scale, with significant savings of materials, time, and money. However, the experimental conditions at which a CS shall be run to obtain a product with assigned specifications are different from those required to obtain the same product from a full-scale RC. How to find these conditions is an open issue. In this study, historical data from both CS and RC experiments are used to develop a transfer methodology that allows the experimenter to obtain optimal RC setup from the CS experimental results solely. The developed correlation, which has been applied to six different pharmaceutical powder blends, successfully captures the differences between the two equipment scales. Implementing this transfer methodology can result in reliable prediction of RC machine settings, thus enabling significant resource, time and money savings.Roller compaction is a key unit operation in a dry granulation line for pharmaceutical tablet manufacturing. However, determining the optimal settings for a roller compactor (RC) typically requires extensive material-consuming experimental campaigns. This amount of material, in particular if active pharmaceutical ingredients are involved, may not be available during development phases, or may be very expensive. For this reason, a compactor simulator (CS) is usually employed to emulate the behaviour of compacted powders at a much smaller scale, with significant savings of materials, time, and money. However, the experimental conditions at which a CS shall be run to obtain a product with assigned specifications are different from those required to obtain the same product from a full-scale RC. How to find these conditions is an open issue. In this study, historical data from both CS and RC experiments are used to develop a transfer methodology that allows the experimenter to obtain optimal RC setup from the CS experimental results solely. The developed correlation, which has been applied to six different pharmaceutical powder blends, successfully captures the differences between the two equipment scales. Implementing this transfer methodology can result in reliable prediction of RC machine settings, thus enabling significant resource, time and money savings

Mathematical Methods for Design of Zone Structured Catalysts and Optimization of Inlet Trajectories in Selective Catalytic Reduction (SCR) and Three Way Catalyst (TWC)

Abgaskatalysatoren zählen zu den wichtigsten Maßnahmen, um Schadstoffemissionen von Verbrennungsmotoren zu vermindern. Mit der stetigen Verschärfung der Emissionsstandards nahm über die Jahre der Forschungsbedarf zu Abgasnachbehandlungssystemen signifikant zu. Der Fokus dieser Arbeit liegt auf der Lösung von Optimierungsproblemen im Bereich der Autoabgaskatalyse, um die Effizienz zu steigern. Dabei werden drei Problemklassen behandelt: 1) Die Light-Off-Verzögerung beim Kaltstart in Oxidationskatalysatoren, 2) Die effiziente Ammoniakdosierung bei der selektiven katalytischen Reduktion (SCR), um Ammoniakdurchbrüche zu vermeiden, 3) Die Spannungsstabilisierung der Lambda-Sonde im Drei-Wege-Katalysator (TWC) während einer Schubabschaltung. Das erste Problem wird durch eine modellbasierte mathematische Optimierung beschrieben, bei der das Beladungsprofil von gezont-strukturierten Katalysatoren auf Basis von Platingruppen-Metallen (PGM) optimiert wird. Dazu wird ein Optimierungsproblem aufgestellt, bei dem ein katalytisch aktiver Kanal in Zonen aufgeteilt wird, die mit unterschiedlichen Mengen von PGM beladen werden. Eine solche Beladung kann auch experimentell getestet werden. Die Effekte der Beladung auf Diffusionslimitierungen im Washcoat werden ebenso berücksichtigt. Ziel ist es, die axiale Verteilung der Beladung zu optimieren, wobei die Gesamtmenge an PGM konstant gehalten wird, um den Gesamtumsatz unter transienten Bedingungen zu maximieren. Dabei wird ein transientes 1D+1D-Modell mit dem impliziten Differentialgleichungslöser DASPKADJOINT numerisch gelöst und in ein nichtlineares Optimierungsproblem übersetzt, das mit einem beliebigen ableitungsbasierten nichtlinearen Optimierungslöser (NLP) behandelt werden kann. Dieses Modell wird auf zwei Beispielfälle angewandt: die CO-Oxidation auf einem Pt/Al2O3 Dieseloxidationskatalysator (DOC), um die Kaltstart-Emissionen zu minimieren, sowie die CH4-Oxidation auf Pd/Al2O3 unter Minimierung der Deaktivierungseffekte. In beiden Fällen wird beobachtet, dass bei der optimalen Lösung ein Beladungsmaximum am Kanaleingang zu einer Umsatzsteigerung führt. Die präsentierte Methode ist darüber hinaus allgemeingültig und kann auf andere Systeme mit unterschiedlicher Chemie angewandt werden, so dass auch signifikant andere Lösungen generiert werden können. Die Fähigkeit, NOx effizient durch Ammoniak zu reduzieren, ist Grundlage der SCR-Technologie für die Dieselabgasnachbehandlung. Ammoniak wird diskontinuierlich durch Zersetzung von Harnstoff-Wasser-Lösung dem SCR-Katalysator zugeführt. Bei der Anwendung im Fahrbetrieb ist es wegen hochgradig transienter Wechsel der Emissionen nicht sinnvoll, konstante Menge Ammoniak zu dosieren. Eine effiziente optimale Dosierungsstrategie ist wichtig, um einerseits hohen Umsatz zu gewährleisten und andererseits NH3-Schlupf zu vermeiden. Die Entwicklung einer optimalen Dosierungsstrategie erfordert die Anwendung einfacher, aber hinreichend akkurater mathematischer Modelle und robuster Optimierungsalgorithmen, um eine Lösung für eine große Anzahl zu optimierender Parameter zu erhalten. Mehrere Modellreduktionstechniken aus der Literatur wurden verwendet, um ein Grey-Box-Modell zu konstruieren. Die Methode der orthogonalen Kollokation über finiten Elementen (OCFE) wird genutzt, um die differential-algebraischen Gleichungen aus dem Optimierungsproblem in ein nichtlineares Programm zu überführen. Das Modell wird auf eine Simulation des WHTC-Testzyklus angewandt, um die NH3-Dosierung für jede Sekunde des Zyklus zu optimieren. Die optimale Lösung verbessert die Effizienz des Reduktion unter Einhaltung eines Schlupf-Maximums von 10 ppm zu jedem Zeitpunkt. Die präsentierte Methode lässt sich auch auf ähnliche Probleme zur Optimierung transienter Eingangsbedingungen anwenden. Im dritten Beispiel wird dieselbe Optimierungsmethode erweitert, um eine optimale Lambda-Trajektorie zu berechnen, die das Lambdasensorsignal am Katalysatorausgang stabilisiert, um Durchbrüche fetter Abgasgemische zu vermeiden. Zunächst wurde ein Beobachtermodell mit vereinfachter Kinetik entwickelt und gegen Versuchsstand-Experimente kalibriert. Direkte Kollokation auf Basis der OCFE wird genutzt, um das Optimierungsproblem in ein nichtlineares Programm zu überführen. Die optimale Lösung zeigt eine schnelle Stabilisierung der Ausgangssensor-Spannung ohne Überschwingungen. Diese Strategie verringert die Relaxationszeit der Sensorspannung signifikant, was wichtig für den Einsatz als Feedback-Controller in einem Dreiwegekatalysator wäre

Simulation-Assisted Design of Polycrystalline Zeolite Catalysts

Zeolite membranes have shown promising applications in catalytic and separation processes in chemical industry. A simulation-assisted design method based on experiments and simulations is shown to guide the development of hierarchically structured catalyst systems based on zeolite membranes by predicting the optimal catalyst structure. A cornerstone of this method is a 3-D pore network model – crystallite-pore network model for simulation of diffusion and reaction in polycrystalline zeolites

Experimental and model-based analysis of twin-screw wet granulation in pharmaceutical processes

A shift from batch to continuous processing is challenging but equally rewarding for the pharmaceutical sector. This opportunity for moving beyond traditional batch processing is possible due to a change of attitude in the regulatory environment by the publication of the process analytical technology (PAT) guidance. However, in order to utilise this opportunity, detailed process understanding about the key processes in pharmaceutical manufacturing is required to turn this transformation to the continuous mode into a success. Continuous wet granulation is a crucial part of future continuous manufacturing of solid dosage forms. Continuous high shear wet granulation is performed using a twin-screw granulator (TSG) which is characterised by a modular screw profile including a sequence of different screw elements with various shapes, orientations and functions. A TSG achieves mixing and granulation by a complex interplay between the screw configuration and process settings (e.g. feed rate, screw speed, etc.) to produce granules with certain specifications in a short time. Therefore, a fundamental understanding of these complex phenomena is required to optimise and control this new technology. Analysing the twin-screw wet granulation to a satisfactory degree is only possible when sufficient information on the rheo-kinetic characteristics of the granulation mixture is available. Thus an investigation of residence time distribution (RTD), the solid-liquid mixing, and the resulting granule size distribution (GSD) evolution governed by the field conditions in the TSG contain interesting information about mixing and different granulation rate processes such as aggregation and breakage. For this purpose, a combination of experimental and mathematical techniques/approaches was applied in this work. Additionally, a single placebo formulation based on α-lactose monohydrate was granulated in the experimental studies performed to verify the hypothesis proposed in this work. The characterisation of wetted material transport and mixing inside the confined spaces of the rotating screws was performed by the experimental determination of the residence time distribution at different process conditions and screw configurations using near infrared chemical imaging. The experimental data was later compared with a conceptual model based on classical chemical engineering methods to estimate the parameters of the model and to analyse the effects of changes in number of kneading discs and their stagger angle, screw speed, material throughput and liquid-to-solid ratio (L/S) on RTD. According to this study, increased screw speed resulted in a low mean residence time mean residence time and wider RTD, i.e. more axial mixing. Increasing powder feed rate increased mean residence time by higher throughput force while increasing L/S increased mean residence time by raising the sluggishness or inertia of the material in the barrel. The material transport in the mixing zone(s) of the TSG became more plug-flow like. Thus, an increase in the number of kneading discs reduced the axial mixing in the barrel. In addition, to understand the GSD dynamics as a function of individual screw modules along the TSG barrel, the change in GSD was investigated both experimentally and mathematically. Using a TSG which allows the opening of the barrel, samples from several locations inside the TSG barrel were collected after granulation at different process conditions and screw configurations. A detailed experimental investigation was hence performed to understand the granule size and shape dynamics in the granulator. The experimental data from this study together with the residence time measurements was then used for calibrating a population balance model for each kneading disc module in the twin-screw granulator in order to obtain an improved insight into the role of the kneading discs at certain locations inside the TSG. The study established that the kneading block in the screw configuration acts as a plug-flow zone inside the granulator. It was found that a balance between the throughput force and conveying rate is required to obtain a good axial mixing inside the twin-screw granulator. Also, a high throughput can be achieved by increasing the liquid-solid ratio and screw speed. Furthermore, the study indicated that the first kneading block after wetting caused an increased aggregation rate, which was reduced after the material processing by the second kneading block. In contrast, the breakage rate in the increased successively along the length of the granulator. Such a reversion in physical phenomena indicated potential separation between the granulation regimes, which can be promising for future design and advanced control of the continuous twin-screw granulation process. In another experimental study the transport and mixing (both axial and bulk mixing of solid-liquid) was linked to the GSD of the produced granules. This study demonstrated that insufficient solid-liquid mixing due to inability of the currently used kneading discs is the reason behind the inferior performance of the TSG in terms of yield. It was shown that other factors which support mixing such as higher axial mixing at a high screw speed and a low fill ratio support an increase in the yield. However, more effort is required to explore non-conventional screw elements with modified geometries to find screws which can effectively mix the solid-liquid material. Furthermore, in order to generalise the TSG knowledge, a regime map based approach was applied. Herewith, the scale independent parameters, L/S and specific mechanical energy (SME) were correlated. It was shown that an increasing L/S strongly drives the GSD towards a larger mean granule size. However, an increasing energy input to the system can effectively be used to lower the mean granule size and also narrow the width of the size distribution. Along with this, particle-scale simulations for the characterisation of liquid distribution in the mixing zone of the granulator were performed. It was found that the agglomeration is rather a delayed process which takes place by redistribution of liquid once the excess liquid on the particle surface is transferred to the liquid bridges. Moreover, the transfer of liquid from particle surface to liquid bridges, i.e. initialisation of agglomeration, is most dominant in the intermeshing region of the kneading discs. Besides the major outcomes of this work, i.e. building fundamental knowledge on pharmaceutical twin-screw wet granulation by combining experimental and theoretical approaches to diagnose the transport, mixing and constitutive mechanisms, several gaps and potential research needs were identified as well. As the regulators have opened up to increasingly rely on the science- and risk-based holistic development of pharmaceutical processes and products for commercialisation, the opportunity as well as responsibility lies with academic and industrial partners to develop a systematic framework and scientific approach to utilise this opportunity efficiently

Greenhouse gas and ammonia emissions from dairy barns

Livestock farming is blamed to bear the bulk of certain gaseous emissions from agriculture such as ammonia (NH3) and methane (CH4). Emission measurement in naturally ventilated buildings in general, but the determination of the air exchange rate in particular, is very complex. Consequently, there is a lack of knowledge regarding gaseous emissions from modern, naturally ventilated dairy cattle buildings. The objectives of the thesis comprise the development and the utilization of measuring and modelling methods in order to determine NH3 and CH4 emissions from dairy barns. The first study focused on the development of a robust method for the long-term measurement of CH4 and NH3 emissions from a naturally ventilated dairy barn. A rough but solid model for the calculation of the ventilation rate by means of wind parameters was developed. At zero wind speed, the ventilation level in the building was over 870 m3 h-1 LU-1 and each m s-1 increase in wind speed increased the ventilation rate by 1,500 m3 h-1 LU-1. The second study presents results of a one-year measurement campaign in a tripartite, naturally cross ventilated dairy barn allowing for an accurate comparison of the two housing systems slatted floor and solid floor including emissions from barn and storage. Emissions from slatted floor including storage with low intensity of slurry homogenization led to lowest NH3 and CH4 emissions (324.9 ± 123.6 g CH4 LU-1 and 29.8 ± 13.1 g NH3 LU-1 d-1 as annual average, respectively). The effect of slurry homogenization beneath the slatted floor was affecting the level of both CH4 and NH3 emissions in a similar way (+17 and +29% higher emissions due to higher intensity of manure homogenization). Furthermore, in the third chapter emission modelling and measuring science was brought together and discussed in an interdisciplinary study. Therefore, the greenhouse gas calculation module of the dairy farm-level model DAIRYDYN was validated by long-term measurement data. The comparison of indicator-modelled CH4 emissions with online measurements offered relatively moderate deviations in case of very detailed indicator schemes (between -6.4 and 10.5%) compared with findings from literature. As a whole, the thesis contributes to the development and improvement of measuring methods for gaseous emissions from naturally ventilated dairy barns offering links for further research activities in this field. The thesis provides emission factors for different housing systems and manure management practices for dairy cows.Klimagas- und Ammoniakemissionen aus Milchviehställen Die landwirtschaftliche Nutztierhaltung ist für einen Großteil der gasförmigen Emissionen des Agrarsektors, wie Methan (CH4) und Ammoniak (NH3), verantwortlich. Die Messung dieser umwelt- oder klimaschädlichen Gase und insbesondere die Bestimmung des Luftwechsels von frei belüfteten, modernen Tierställen ist jedoch sehr komplex und die Datengrundlage daher gering. Ziel dieser Arbeit war die Entwicklung und Anwendung von Messmethoden und Modellen zur Bestimmung von gasförmigen Emissionen aus Milchviehställen. Die erste Studie beschreibt die Entwicklung einer robusten Messmethodik für die Bestimmung der CH4 und NH3 Emissionen aus einem frei belüfteten Milchviehstall. Dazu wurde anhand von Windparametern ein Luftwechselmodell für das Stallgebäude entwickelt. Bei Windstille wurde ein Luftvolumenstrom von mehr als 870 m3 h-1 LU-1 ermittelt, wobei ein Anstieg der Windgeschwindigkeit um 1 m s-1 eine Erhöhung des Luftvolumenstroms von etwa 1.500 m3 h-1 LU-1 zur Folge hatte. Die zweite Studie umfasst Ergebnisse einer einjährigen Messreihe in einem frei belüfteten, dreigeteilten Milchviehstall und ermöglichte einen Vergleich der zwei Haltungsvarianten „Spaltenboden“ und „planbefestigte Laufflächen“ unter Einbeziehung der Emissionen aus dem Flüssigmistlager. Das Stallabteil mit Spaltenboden wies bei geringer Intensität des Flüssigmist-Homogenisierens im Jahresmittel die geringsten NH3 und CH4 Emissionen auf (324,9 ± 123,6 g CH4 GV-1 d-1 und 29,8 ± 13,1 g NH3 GV-1 d-1). Das intensive Homogenisieren des Flüssigmistes unter dem Spaltenboden führte im Jahresmittel sowohl bei CH4 als auch bei NH3 zu signifikant höheren Emissionsraten im Vergleich zum weniger intensiven Homogenisieren (+17% bei CH4 und +29% bei NH3). Darüber hinaus wurden in der dritten Studie Erkenntnisse aus Emissionsmessung und -modellierung in einer interdisziplinären Arbeit zusammengeführt. Das Klimagas-Berechnungsmodul des einzelbetrieblichen Simulationsmodells DAIRYDYN wurde anhand von Ergebnissen aus Langzeit Messungen validiert. Bei Einbeziehung sehr detaillierter Produktionsparameter in das Modell wurden im Vergleich zur Literatur relativ geringe Abweichungen (-6,4 bis 10,5%) zu den Messergebnissen festgestellt. Die vorliegende Arbeit leistet somit einen Beitrag zur Entwicklung und Verbesserung der Messmethoden für gasförmige Emissionen aus frei belüfteten Milchviehställen und zeigt weiteren Forschungsbedarf in diesem Themengebiet auf. Darüber hinaus liefert die Arbeit Emissionsfaktoren für verschiedene Haltungsverfahren bzw. Entmistungsvarianten für Milchkühe bei unterschiedlichem Flüssigmistmanagement