The effects of three ways of binder delivery into the twin screw granulator (TSG) on the residenc... more The effects of three ways of binder delivery into the twin screw granulator (TSG) on the residence time, torque, properties of granules (size, shape, strength) and binder distribution were studied. The binder distribution was visualised through the transparent barrel using high speed imaging as well as quantified using offline technique. Furthermore, the effect of binder delivery and the change of screw configuration (conveying elements only and conveying elements with kneading elements) on the surface velocity of granules across the screw channel were investigated using particle image velocimetry (PIV). The binder was delivered in three ways; all solid binder incorporated with powder mixture, 50% of solid binder mixed with powder mixture and 50% mixed with water, all the solid binder dissolved in water. Incorporation of all solid binder with powder mixture resulted in the relatively longer residence time and higher torque, narrower granule size distribution, more spherical granules, weaker big-sized granules, stronger small-sized granules and better binder distribution compared to that in other two ways. The surface velocity of granules showed variation from one screw to another as a result of uneven liquid distribution as well as shown a reduction while introducing the kneading elements into the screw configuration.
I n this paper, the applicability of elasto-plastic contact mechanics to predict the coefficient ... more I n this paper, the applicability of elasto-plastic contact mechanics to predict the coefficient of restitution of a dry binderless granule impacting on a flat surface is assessed. The granules were prepared using polystyrene particles to avoid complications arising from energy dissipation by solid and liquid binders since only van der Waals attractive forces operated between these particles. The Young's modulus and yield stress of the granules required to calculate the theoretical coefficient of restitution was extracted from slow diametric compression tests using elasto-plastic force-displacement relationships. Significant deviation of the measured coefficients of restitution from theory was found and thus it was concluded that the energy dissipation of the current granules under impact is not analogous to perfect and finite plastic deformation. The granules were shown to fracture in a semi-brittle manner as a consequence of rapid propagation of unstable meridian cracks preceded by irreversible deformation such as densification of the contact zone. However, impact data obtained at velocities corresponding to such fracture were ignored for the purpose of comparison with theory.
G ranulation is an important process within many well-developed industries such as pharmaceutical... more G ranulation is an important process within many well-developed industries such as pharmaceutical, food and fertilizer production, but also with increasing application outside these 'traditional' fields. This paper examines how granulation could be used to 'improve' the use of a material, by the study of the granulation of zinc oxide powder with a proprietary binder, to produce granules for the ceramics industry. The paper is an example of applied product design, with the aim of producing strong granules with sufficiently low binder content so as to be functional within the ceramic industry.
This paper demonstrates the capability of the 'Smart' sphere to measure a temperature which varie... more This paper demonstrates the capability of the 'Smart' sphere to measure a temperature which varies with axial length and time in a nonstationary system such as a rotary drum mixer. The 'Smart' sphere is a low-cost, low-power, small, wireless (infrared), self-equipped data logger with a built-in temperature sensor, which moves freely when introduced inside the process and measures the surrounding temperature and subsequently stores measured data in its internal memory. This data is subsequently transferred by wireless means to the computer once the sphere is recovered at the end of the process. The 'Smart' sphere, when introduced into the rotary drum mixer, moves with the bulk particles and measures high resolution longitudinal (axial) temperature data. Thus, the capability of free moving measurements by a 'Smart' temperature sphere in rotary drum mixers has been experimentally demonstrated and found satisfactory. Moreover, the 'Smart' sphere measurement has been compared with the fixed point measurements taken at an instant in the drum. Axial temperature variation measured by the sphere in the rotary drum experiment is in good agreement with the reference temperature measured by the temperature probe. Thus, the 'Smart' sphere measurement fills the gaps between the fixed point measurements and provides high resolution temperature data which could be further used for modelling and prediction of such processes.
The application of twin screw granulation in the pharmaceutical industry has generated increasing... more The application of twin screw granulation in the pharmaceutical industry has generated increasing interest due to its suitability for continuous processing. However, an understanding of the impact of formulation properties such as hydrophobicity on intermediate and finished product quality has not yet been established. Hence, the current work investigated the granulation behaviour of three formulations containing increasing amounts of hydrophobic components using a Consigma™-1 twin screw granulator. Process conditions including powder feed rate, liquid to solid ratio, granulation liquid composition and screw configuration were also evaluated. The size of the wet granules was measured in order to enable exploration of granulation behaviour in isolation without confounding effects from downstream processes such as drying. The experimental observations indicated that the granulation process was not sensitive to the powder feed rate. The hydrophobicity led to heterogeneous liquid distribution and hence a relatively large proportion of un-wetted particles. Increasing numbers of kneading elements led to high shear and prolonged residence time, which acted to enhance the distribution of liquid and feeding materials. The bimodal size distributions considered to be characteristic of twin screw granulation were primarily ascribed to the breakage of relatively large granules by the kneading elements.
A numerical simulation of a particle in a horizontal pipe has been carried out, and the variation... more A numerical simulation of a particle in a horizontal pipe has been carried out, and the variation of aerodynamic forces is described. The major forces that control particle motion are drag in the axial direction, and lift due to air velocity gradient and due to spin in the transverse direction. An elastic contact model based on rigid body sliding has been incorporated, which avoids particle settlement without having to use any form of irregular bounce. The results from the simulation agree closely with experimental time-of-flight measurements. D Y D , the retarding torque T R acting on the surface of the particle, the lift force due to the particle rotation F Y M , and the lift force 0032-5910/$ -see front matter D
The impact behaviour of wet granules was studied by measuring their restitution coefficient and m... more The impact behaviour of wet granules was studied by measuring their restitution coefficient and maximum contact area. A flat semiinfinite rigid target was used for this purpose and the impact and rebound speeds were recorded by using two high-speed cameras. Different granules were produced by varying the liquid to solid ratio, primary particle size, binder viscosity and granulation time. The data were compared with existing analytical models, which were found to provide an approximate description. However, it is clear that real granular collisions may involve a significantly greater complexity and this will require the refinement of such models. D
In industrial scale mixer granulation, liquid binder is usually sprayed onto the agitated powder ... more In industrial scale mixer granulation, liquid binder is usually sprayed onto the agitated powder bed by means of a nozzle in order to enhance the agglomeration process. The early stage of this process, where granule nuclei are formed and grow, is not well understood. As it is desirable to model the agglomeration state right from the beginning of the process for the purposes of control and modeling, this nucleation step is therefore an important field of interest.
The wet granulation process starts when a liquid drop makes contact with the powder bed. In a pow... more The wet granulation process starts when a liquid drop makes contact with the powder bed. In a powder bed, drops are subjected to centripetal and gravitational forces. These forces may affect the size and shape of the drop as it is incorporated into the bed. The majority of experiments studying droplet behaviour have been performed on static bed surfaces. This paper seeks to demonstrate droplet behaviour during the initial contact stage with a dynamic powder bed representative of that occurring during high shear granulation. Particle image velocimetry (PIV) is used to determine droplet and powder bed surface velocities. Due to inclination of powder bed part of drop de-accelerate slowly moved downward while other parts remain attached to powder bed this result in their deformation and breakage. Amount of deformation of drop and span of area where it occurred was increased as drop was added farther from the outer edge of the mixer. This paper shows that the binder drop may deform or break in high shear granulator depending on its initial impact position. This will affect size distribution and other properties of nuclei.
High speed images of the bulk motion in a flat disc high shear granulator have been analysed usin... more High speed images of the bulk motion in a flat disc high shear granulator have been analysed using particle image velocimetry (PIV) to obtain surface velocity fields. The fluctuations in the temporal surface velocity field are found to exhibit a Gaussian distribution, allowing direct measurement of the granular temperature from the velocity field. The spatial correlation of fluctuations is examined, indicating a high level of correlation at the length scale of granule diameter, which then decreases rapidly with increasing distance. This spatial correlation profile is shown to be consistent with the expected profile for uncorrelated motion, confirming that individual granules exhibit random fluctuations during bulk motion.
When trying to meet final product specifications for porosity of granules made using high-shear g... more When trying to meet final product specifications for porosity of granules made using high-shear granulation there are many choices for the formulation recipe and processing conditions. This paper presents the concept of a Critical Packing State of the primary particles forming a granule and the associated Limiting Binder Ratio, which allows granule consolidation to be modelled.
The study of breakage in granulation is important from a process and from a product quality persp... more The study of breakage in granulation is important from a process and from a product quality perspective. Breakage is considered an important rate process in granulation, and plays roles in granule homogeneity and strength. Understanding this rate process has important implications in the design and control of the granulation process. From a product perspective, the study of breakage has important implications for the subsequent processing, transport, handling and final use of granular products. Breakage behaviour of granules can be a strong signature of the consistency of properties between nominally identical granular products. This paper reviews the study of breakage from the process scale down to the single granule and sub-granule scale, discussing largely experimental results complemented with some modelling results.
The breakage behaviour of wet granules produced in a high-shear mixer was investigated experiment... more The breakage behaviour of wet granules produced in a high-shear mixer was investigated experimentally using single granule impact tests and the results are described in terms of the critical impact velocity, breakage pattern, and extent of breakage. The failure patterns of these wet granules have a number of common features that have been observed for dry granules including the formation of debris with a conical geometry. A more quantitative description is presented of the factors that control the volume of these conical regions. The granules were produced with negligible air voidage and there were unusual strength characteristics with varying binder content. Most previous studies have involved a reduction in the air voidage of granules as the binder content is increased, which leads to a maximum in the strength at some critical binder content. For the granules studied in the current work, the strength either showed a minimum value or decreased monotonically with increasing binder content depending on the size of the primary particles.
The effects of three ways of binder delivery into the twin screw granulator (TSG) on the residenc... more The effects of three ways of binder delivery into the twin screw granulator (TSG) on the residence time, torque, properties of granules (size, shape, strength) and binder distribution were studied. The binder distribution was visualised through the transparent barrel using high speed imaging as well as quantified using offline technique. Furthermore, the effect of binder delivery and the change of screw configuration (conveying elements only and conveying elements with kneading elements) on the surface velocity of granules across the screw channel were investigated using particle image velocimetry (PIV). The binder was delivered in three ways; all solid binder incorporated with powder mixture, 50% of solid binder mixed with powder mixture and 50% mixed with water, all the solid binder dissolved in water. Incorporation of all solid binder with powder mixture resulted in the relatively longer residence time and higher torque, narrower granule size distribution, more spherical granules, weaker big-sized granules, stronger small-sized granules and better binder distribution compared to that in other two ways. The surface velocity of granules showed variation from one screw to another as a result of uneven liquid distribution as well as shown a reduction while introducing the kneading elements into the screw configuration.
I n this paper, the applicability of elasto-plastic contact mechanics to predict the coefficient ... more I n this paper, the applicability of elasto-plastic contact mechanics to predict the coefficient of restitution of a dry binderless granule impacting on a flat surface is assessed. The granules were prepared using polystyrene particles to avoid complications arising from energy dissipation by solid and liquid binders since only van der Waals attractive forces operated between these particles. The Young's modulus and yield stress of the granules required to calculate the theoretical coefficient of restitution was extracted from slow diametric compression tests using elasto-plastic force-displacement relationships. Significant deviation of the measured coefficients of restitution from theory was found and thus it was concluded that the energy dissipation of the current granules under impact is not analogous to perfect and finite plastic deformation. The granules were shown to fracture in a semi-brittle manner as a consequence of rapid propagation of unstable meridian cracks preceded by irreversible deformation such as densification of the contact zone. However, impact data obtained at velocities corresponding to such fracture were ignored for the purpose of comparison with theory.
G ranulation is an important process within many well-developed industries such as pharmaceutical... more G ranulation is an important process within many well-developed industries such as pharmaceutical, food and fertilizer production, but also with increasing application outside these 'traditional' fields. This paper examines how granulation could be used to 'improve' the use of a material, by the study of the granulation of zinc oxide powder with a proprietary binder, to produce granules for the ceramics industry. The paper is an example of applied product design, with the aim of producing strong granules with sufficiently low binder content so as to be functional within the ceramic industry.
This paper demonstrates the capability of the 'Smart' sphere to measure a temperature which varie... more This paper demonstrates the capability of the 'Smart' sphere to measure a temperature which varies with axial length and time in a nonstationary system such as a rotary drum mixer. The 'Smart' sphere is a low-cost, low-power, small, wireless (infrared), self-equipped data logger with a built-in temperature sensor, which moves freely when introduced inside the process and measures the surrounding temperature and subsequently stores measured data in its internal memory. This data is subsequently transferred by wireless means to the computer once the sphere is recovered at the end of the process. The 'Smart' sphere, when introduced into the rotary drum mixer, moves with the bulk particles and measures high resolution longitudinal (axial) temperature data. Thus, the capability of free moving measurements by a 'Smart' temperature sphere in rotary drum mixers has been experimentally demonstrated and found satisfactory. Moreover, the 'Smart' sphere measurement has been compared with the fixed point measurements taken at an instant in the drum. Axial temperature variation measured by the sphere in the rotary drum experiment is in good agreement with the reference temperature measured by the temperature probe. Thus, the 'Smart' sphere measurement fills the gaps between the fixed point measurements and provides high resolution temperature data which could be further used for modelling and prediction of such processes.
The application of twin screw granulation in the pharmaceutical industry has generated increasing... more The application of twin screw granulation in the pharmaceutical industry has generated increasing interest due to its suitability for continuous processing. However, an understanding of the impact of formulation properties such as hydrophobicity on intermediate and finished product quality has not yet been established. Hence, the current work investigated the granulation behaviour of three formulations containing increasing amounts of hydrophobic components using a Consigma™-1 twin screw granulator. Process conditions including powder feed rate, liquid to solid ratio, granulation liquid composition and screw configuration were also evaluated. The size of the wet granules was measured in order to enable exploration of granulation behaviour in isolation without confounding effects from downstream processes such as drying. The experimental observations indicated that the granulation process was not sensitive to the powder feed rate. The hydrophobicity led to heterogeneous liquid distribution and hence a relatively large proportion of un-wetted particles. Increasing numbers of kneading elements led to high shear and prolonged residence time, which acted to enhance the distribution of liquid and feeding materials. The bimodal size distributions considered to be characteristic of twin screw granulation were primarily ascribed to the breakage of relatively large granules by the kneading elements.
A numerical simulation of a particle in a horizontal pipe has been carried out, and the variation... more A numerical simulation of a particle in a horizontal pipe has been carried out, and the variation of aerodynamic forces is described. The major forces that control particle motion are drag in the axial direction, and lift due to air velocity gradient and due to spin in the transverse direction. An elastic contact model based on rigid body sliding has been incorporated, which avoids particle settlement without having to use any form of irregular bounce. The results from the simulation agree closely with experimental time-of-flight measurements. D Y D , the retarding torque T R acting on the surface of the particle, the lift force due to the particle rotation F Y M , and the lift force 0032-5910/$ -see front matter D
The impact behaviour of wet granules was studied by measuring their restitution coefficient and m... more The impact behaviour of wet granules was studied by measuring their restitution coefficient and maximum contact area. A flat semiinfinite rigid target was used for this purpose and the impact and rebound speeds were recorded by using two high-speed cameras. Different granules were produced by varying the liquid to solid ratio, primary particle size, binder viscosity and granulation time. The data were compared with existing analytical models, which were found to provide an approximate description. However, it is clear that real granular collisions may involve a significantly greater complexity and this will require the refinement of such models. D
In industrial scale mixer granulation, liquid binder is usually sprayed onto the agitated powder ... more In industrial scale mixer granulation, liquid binder is usually sprayed onto the agitated powder bed by means of a nozzle in order to enhance the agglomeration process. The early stage of this process, where granule nuclei are formed and grow, is not well understood. As it is desirable to model the agglomeration state right from the beginning of the process for the purposes of control and modeling, this nucleation step is therefore an important field of interest.
The wet granulation process starts when a liquid drop makes contact with the powder bed. In a pow... more The wet granulation process starts when a liquid drop makes contact with the powder bed. In a powder bed, drops are subjected to centripetal and gravitational forces. These forces may affect the size and shape of the drop as it is incorporated into the bed. The majority of experiments studying droplet behaviour have been performed on static bed surfaces. This paper seeks to demonstrate droplet behaviour during the initial contact stage with a dynamic powder bed representative of that occurring during high shear granulation. Particle image velocimetry (PIV) is used to determine droplet and powder bed surface velocities. Due to inclination of powder bed part of drop de-accelerate slowly moved downward while other parts remain attached to powder bed this result in their deformation and breakage. Amount of deformation of drop and span of area where it occurred was increased as drop was added farther from the outer edge of the mixer. This paper shows that the binder drop may deform or break in high shear granulator depending on its initial impact position. This will affect size distribution and other properties of nuclei.
High speed images of the bulk motion in a flat disc high shear granulator have been analysed usin... more High speed images of the bulk motion in a flat disc high shear granulator have been analysed using particle image velocimetry (PIV) to obtain surface velocity fields. The fluctuations in the temporal surface velocity field are found to exhibit a Gaussian distribution, allowing direct measurement of the granular temperature from the velocity field. The spatial correlation of fluctuations is examined, indicating a high level of correlation at the length scale of granule diameter, which then decreases rapidly with increasing distance. This spatial correlation profile is shown to be consistent with the expected profile for uncorrelated motion, confirming that individual granules exhibit random fluctuations during bulk motion.
When trying to meet final product specifications for porosity of granules made using high-shear g... more When trying to meet final product specifications for porosity of granules made using high-shear granulation there are many choices for the formulation recipe and processing conditions. This paper presents the concept of a Critical Packing State of the primary particles forming a granule and the associated Limiting Binder Ratio, which allows granule consolidation to be modelled.
The study of breakage in granulation is important from a process and from a product quality persp... more The study of breakage in granulation is important from a process and from a product quality perspective. Breakage is considered an important rate process in granulation, and plays roles in granule homogeneity and strength. Understanding this rate process has important implications in the design and control of the granulation process. From a product perspective, the study of breakage has important implications for the subsequent processing, transport, handling and final use of granular products. Breakage behaviour of granules can be a strong signature of the consistency of properties between nominally identical granular products. This paper reviews the study of breakage from the process scale down to the single granule and sub-granule scale, discussing largely experimental results complemented with some modelling results.
The breakage behaviour of wet granules produced in a high-shear mixer was investigated experiment... more The breakage behaviour of wet granules produced in a high-shear mixer was investigated experimentally using single granule impact tests and the results are described in terms of the critical impact velocity, breakage pattern, and extent of breakage. The failure patterns of these wet granules have a number of common features that have been observed for dry granules including the formation of debris with a conical geometry. A more quantitative description is presented of the factors that control the volume of these conical regions. The granules were produced with negligible air voidage and there were unusual strength characteristics with varying binder content. Most previous studies have involved a reduction in the air voidage of granules as the binder content is increased, which leads to a maximum in the strength at some critical binder content. For the granules studied in the current work, the strength either showed a minimum value or decreased monotonically with increasing binder content depending on the size of the primary particles.
Uploads
Papers by Agba Salman