Final Granule Size Research Articles

Composition-specific granulation characteristics of molten slag at improved throughput and high temperature of 1,723 K

Centrifugal granulation is one key step to enable waste heat recovery from the molten slag in the iron and steel industry. Yet, it remains unknown about the granulation characteristics of molten slag with different chemical compositions, especially at high throughput. In this work, we provided an experimental study on centrifugal granulation with four types of molten slags. The stage-specific centrifugal granulation was recorded and analyzed at first. Both effects of atomizer configuration and chemical compositions on granulation were investigated in detail. The cup-type atomizer favors film-mode disintegration and possesses better anti-adhesion capacity although the final granule size was not strongly affected by the atomizer configuration. Most importantly, centrifugal granulation has been demonstrated with appreciable adaptability to composition-specific blast furnace (BF) slag with binary basicity of 0.9–1.3. The present study not only sheds light on the modest effect of the chemical composition of molten slag on centrifugal granulation characteristics, but also gains credit for the adaptivity of CGATER.

ДОСЛІДЖЕННЯ РОЗМІРУ КОМІРЧИНИ ГРАНУЛЮЮЧОГО ТРАНСПОРТЕРА

У статті наведена теоретичне обґрунтування до встановлення залежності розміру комірчини гранулюючого транспортера. Визначений раціональний склад та вологість органо-мінеральної суміші на основі сапропелю.

Mechanistic modelling of fluid bed granulation, Part I: Agglomeration in pilot scale process.

The present study aims to develop a mechanistic model to predict the performance of a fluid bed granulation process. Therefore, the behavior of the bed was investigated experimentally for various operating conditions. It was observed that the granule Loss on Drying (LoD) and granule size are strongly interrelated. In detail, the maximum final granule size was observed at an intermediate final LoD. Consequently, there is an optimum spray rate and inlet temperature with respect to the granule size. Besides, it was demonstrated that the experiments delivering lower LoD result in a more elongated final granule. Aimed at enabling the prediction of the bed performance numerically, a single-compartment, population-balance-based model was developed and validated against experimental data. The model parameters associated with the growth rate of granule were estimated and mechanistically correlated to the relevant operating conditions. Detailed analysis of the experimental results suggested that these model parameters may be partially connected to the granule LoD. Subsequently, in order to examine the accuracy of the developed model, a simulation was performed for a new set of operating conditions not previously accounted for in the correlations. The comparison of the simulated bed performance, when compared to the experimental results, proved with reasonable accuracy the reliability of the developed model in predicting the temporal evolution of granule size. Therefore, this study can be a step forward in developing a stand-alone granulation model, via modeling heat and mass transfer, to simulate evaporation and drying in a fluid bed granulator.

The effect of process variables on drum granulation behavior and granules of wet distillers grains with solubles

A laboratory scale batch drum granulation process was used to manufacture granules of DDGS by adding condensed distillers solubles (CDS) as a binder to wet distillers grains (WDG), coproducts from corn dry-grind ethanol process, under varying formulation and process conditions. A full factorial experimental design was used to test all combinations of factor levels, which included the amount of CDS binder (30%, 35%, and 40% (w/w)), CDS binder solids content (22% and 38%, wet basis), screen size opening (3.175 and 6.35mm), and residence time (1, 2.5, 5, and 10min). Measured response variables included granule size (geometric mean diameter), granule yield (1.68–3.35mm), bulk density, true density, and porosity. Results show that as the amount of binder added increased from 30% to 40% the granule size significantly increased from 2.08 to 4.45mm, respectively. Increasing the binder solids content resulted in granules with greater bulk density. Granules produced from the low solids CDS had lower porosity as a result of intraparticle voids in them. Screen sizing influenced nucleation and produced significant differences in the final granule size distribution. The greatest growth was observed for granules prepared with 40% amount of binder and low solids content CDS. Compression testing of wet granule compacts corresponded to observed growth behavior; wet pellets made from higher solids CDS had greater resistance to deformation and enhanced plasticity while the opposite was observed for the low solids CDS. The best yields of granules between 1.68 and 3.35mm were achieved at ∼80% using 35% amount of binder with the high solids content CDS, the small screen size opening and residence times between 2.5 and 10min.

Analytical solutions of the particle breakage equation by the Adomian decomposition and the variational iteration methods

The breakage in batch and continuous systems has attained high interest in chemical engineering and granulation from a process and from a product quality perspective. The wet granule breakage process in a high shear mixer will influence and may control the final granule size distribution. In this work, we developed analytical solutions of the particle breakage using the population balance equation (PBEs) in batch and continuous flow systems. To allow explicit solutions, we approximate particle breakage mechanisms with assumed functional forms for breakage frequencies. This new framework for solving (PBEs) for batch and continuous flow systems proposed in this work uses the Adomian decomposition method (ADM) and the variational iteration method (VIM). These semi-analytical methods overcome the crucial difficulties of numerical discretization and stability that often characterize previous solutions in of the PBEs. The results obtained in all cases show that the predicted particle size distributions converge exactly in a continuous form to that of the analytical solutions using the two methods.

Foam granulation: Liquid penetration or mechanical dispersion?

There have been significant advances in the understanding of wet granulation processes. Foam granulation is the latest development and an emerging area of interest for pharmaceutical manufacturing. Single foam penetration experiments were carried out on static powder beds, followed by short-nucleation experiments (where nuclei are formed by a nucleation-only mechanism) and full foam granulation experiments (where nucleation, growth and breakage are occurring simultaneously). All experiments were performed with lactose monohydrate powder using a 5 L high shear mixer–granulator. The foam penetration/dispersion behaviour was examined and the granule size distributions were investigated as a function of foam quality (83–97% FQ), impeller speed (105–515 rpm) and wet massing period (0–4 min). Nucleation in foam granulation is postulated to undergo either “foam drainage” or “mechanical dispersion” controlled mechanisms. For “foam drainage” mechanism, the foam penetrates the powder bed to form coarse and broad granule size distributions. For “mechanical dispersion” mechanism, the wetting and nucleation conditions are governed by the powder mixing conditions and similar granule size distributions are produced. Regardless of the mechanism, the initial wetting and nucleation behaviour controls the initial nuclei size distribution, and this initial distribution is retained in the final granule size distribution. This work demonstrated the critical importance of the nucleation and binder distribution in determining the granule size distributions for foam granulation process.

A priori performance prediction in pharmaceutical wet granulation: Testing the applicability of the nucleation regime map to a formulation with a broad size distribution and dry binder addition

In this study, Hapgood's nucleation regime map ( Hapgood et al., 2003) was tested for a formulation that consists of an active pharmaceutical ingredient (API) of broad size distribution and a fine dry binder. Gabapentin was used as the API and hydroxypropyl cellulose (HPC) as the dry binder with deionized water as the liquid binder. The formulation was granulated in a 6 l Diosna high shear granulator. The effect of liquid addition method (spray, dripping), liquid addition rate (29–245 g/min), total liquid content (2, 4 and 10%), and impeller speed (250 and 500 rpm) on the granule size distribution and lump formation were investigated. Standard methods were successfully used to characterize the process parameters (spray drop size, spray geometry and powder surface velocity) for calculating the dimensionless spray flux. However, the addition of dry binder had a very strong effect on drop penetration time that could not be predicted from simple capillary flow considerations. This is most likely due to preferential liquid penetration into the fine pores related to the dry binder particles and subsequent partial softening and dissolution of the binder. For systems containing a dry binder or other amorphous powders, it is recommended that drop penetration time be measured directly for the blended formulation and then scaled to the drop size during spraying. Using these approaches to characterize the key dimensionless groups (dimensionless spray flux and drop penetration time), Hapgood's nucleation regime map was successfully used to predict a priori the effect of process conditions on the quality of the granule size distribution as measured by lump formation and the span of the size distribution, both before and after wet massing for range of conditions studied. Wider granule size distributions and higher amount of lumps were obtained moving from intermediate to mechanical dispersion regime. Addition of the liquid in the dripping mode gave the broadest size distribution with ungranulated fines and highest percentage of lumps compared to spraying mode. Addition of the liquid by spraying in the intermediate regime gave the narrowest size distribution with the lowest amount of lumps. The effects of impeller speed and wet massing time on granule size distribution were complex. At 2% liquid content, increasing the impeller speed and adding wet massing time caused some breakage of lumps and the production of fines. At higher liquid contents, the effects were less clear, likely due to a balance between increased breakage and increased granule consolidation and growth. Nevertheless, this work has demonstrated that for complex formulations with dry binder addition, the final granule size distribution still depends strongly on the homogeneity of the initial liquid distribution which is well predicted by the nucleation regime map analysis.

Combining microwave resonance technology to multivariate data analysis as a novel PAT tool to improve process understanding in fluid bed granulation

A set of 192 fluid bed granulation batches at industrial scale were in-line monitored using microwave resonance technology (MRT) to determine moisture, temperature and density of the granules. Multivariate data analysis techniques such as multiway partial least squares (PLS), multiway principal component analysis (PCA) and multivariate batch control charts were applied onto collected batch data sets. The combination of all these techniques, along with off-line particle size measurements, led to significantly increased process understanding. A seasonality effect could be put into evidence that impacted further processing through its influence on the final granule size. Moreover, it was demonstrated by means of a PLS that a relation between the particle size and the MRT measurements can be quantitatively defined, highlighting a potential ability of the MRT sensor to predict information about the final granule size. This study has contributed to improve a fluid bed granulation process, and the process knowledge obtained shows that the product quality can be built in process design, following Quality by Design (QbD) and Process Analytical Technology (PAT) principles.

Producing hollow granules from hydrophobic powders in high-shear mixer granulators

The formation of hollow granules from hydrophobic powders in a high-shear mixer granulator has been investigated by changing the binder/powder mass ratio and studying its effects on granule size and structure. In this study, a mixer granulator was filled with 100 g of hydrophobic fumed silica and then varying quantities of 5% Hydroxy Propyl Cellulose solution was slowly sprayed into granulator. A range of liquid to solid mass ratios between from 0.5:1 to 15:1 was used. Granules were then dried at 60 °C in a fan forced oven. This paper compares the particle size distributions, scanning electron microscopy (SEM) images and X-ray tomography (XRT) images of hollow granules as a function of the liquid to solid mass ratio. The granule mean size increased and the fraction of un-granulated (fine) particles decreased as the liquid to solid mass ratio increased. Simultaneously, the morphology and structure of the hollow granules changed from a spherical to a deformed structure which indicates the importance of choosing the optimal liquid to solid mass ratio. The optimal liquid to solid mass ratio for Aerosil R202 powder in this study was found to be between 3:1 and 6:1. The final granule shape and size distribution are dependent on the liquid to solid ratio if the liquid marble nucleation process starts with a preformed droplet template.

Variation of granule mass fraction with coordination number in wet granulation process

In granulation, fine particles combine to form a coarse granule in the form of a particle matrix partially or fully saturated with a binder liquid. The final product of granulation possesses a wide variety of granule size distributions with surface mean diameters which differ with operating conditions. The final granule size depends on the operating conditions, e.g. operating gas velocity, inlet air temperature, initial feed particle size, and viscosity of the binder. The objective of this paper is to find out the uniformity in the relation between the granule mass fraction in the final granule size distribution and the number of feed particles present in the granules. The total number of granules obtained depends on the experimental conditions but the granule mass fraction and the number of feed particles forming a single granule are independent of operating variables, feed material and method of granulation. The paper purports further to compare the uniform nature of mass fraction of the granules in final granule size distribution and the primary particles required to form that particular granule size irrespective of experimental conditions of granulation.

Manufacturing pharmaceutical granules: Is the granulation end-point a myth?

The moist agglomeration process by high-shear mixing/granulation, i.e. the wet massing, screening and subsequent drying is a wide spread but critical unit operation. Since for decades formulators are looking for the correct “end-point” of this important process, i.e. when do you need to stop massing or stop with the addition of granulating liquid? What is the correct amount of granulating liquid? A similar situation exists in case of the moist agglomeration in fluidized bed equipment. In the latter case the simultaneous drying of the still moist granules have to be taken into account. Recently a science-based virtual equipment simulator could be developed mimicking the granule size evolution in a fluidized bed granulator during the addition of granulating liquid. For the simultaneous drying the Mollier chart is used. With this virtual equipment simulator it is possible to simulate “crash situations”, i.e. by overwetting or by an incorrect use of the parameter setting. However the determination of the “end-point” depends only on the operator, who desires a certain granule size distribution and a well-defined final moisture content of the batch. Thus the existence of a process intrinsic “end-point” has to be questioned. The same situation can be reported in case of high-shear mixing/granulation based on many years of research. In fact nobody could clearly show the existence of an intrinsic “end-point”. However during the continuous addition of a granulating low viscous liquid a sudden increase in power consumption can be measured, which levels off. Such a measurement depends on the formulation and leads to an “early signal” not to the “end-point”. This signal can be used for a tight control of the granulation process and leads to a low batch to batch variability in the final granule size distribution. The latter is the goal of the PAT (Process Analytical Technology) Initiative emphasizing “Quality by Design”.

Kinetics of fluidised bed melt granulation I: The effect of process variables

This paper is the first of a series to study the influence of operating conditions on the kinetics of fluidised bed melt granulation. First, we identify the rate processes responsible for the net growth in granule size in a top-sprayed fluidised bed granulator and propose a sequence of events based on these rate processes. The overall kinetics during the process is identified to be a combination of particle aggregation, binder solidification and granule breakage. By conducting experiments in a small-scale modified commercial fluidised bed granulator, the influence of various operating conditions (binder spray rate, bed temperature, atomising pressure, fluidising air velocity) on the granule growth behaviour was examined. The results indicate the granule growth rate to be directly dependent on the relative amount of binder sprayed into the bed, which essentially determines the speed of the aggregation process. The overall granule growth rate is observed to increase relatively with increased bed temperature for a more viscous PEG4000, while a maximum growth is seen for a lower viscosity PEG1500. A larger droplet size was also seen to have increased the overall growth rate, even though a smaller droplet seems to be able to induce a faster initial growth. The results also reveal the increase in fluidising air velocity to reduce the overall granule growth rate. The final granule size distribution was also observed to become narrower with increased bed temperature and fluidising air velocity. These observations are effectively explained using the proposed sequence of rate events.

Determination of fluidized bed granulation end point using near‐infrared spectroscopy and phenomenological analysis

Simultaneous real‐time monitoring of particle size and moisture content by near‐infrared spectroscopy through a window into the bed of a fluidized bed granulator is used to determine the granulation end point. The moisture content and particle size determined by the near‐infrared monitor correlates well with off‐line moisture content and particle size measurements. The measured particle size is modeled using a population balance approach, and the moisture content is shown to follow accepted models during drying. Given a known formulation, with predefined parameters for peak moisture content, final moisture content, and final granule size, the near‐infrared monitoring system can be used to control a fluidized bed granulation by determining when binder addition should be stopped and when drying of the granules is complete. © 2005 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:604–612, 2005

Computer simulation of wet granulation

Agglomeration of fine particles in wet granulation is achieved by introducing a binder fluid onto a shearing mass of powder. Owing to the viscosity and the surface tension of the fluid, powder particles are bound together to form larger aggregates. Despite its widespread use in the chemical, pharmaceutical and food industries, little effort has gone into comprehensive modeling of the overall process from first principles. Modeling is important however, if one needs to estimate a-priori agglomerated granule characteristics such as size, shape and density, from knowledge of operating conditions and powder and binder physical and chemical properties. In this work, we present a model of wet granulation that is essentially a computer simulation of shear flows of solid particles, some of which are wet (covered by binder and therefore sticky) while the rest are dry. While simulations of shear flows of dry solid particles have earlier been reported in the literature, present work takes this simulation a step further and introduces a liquid surface layer to some particles in the domain. The additional force experienced by two relatively moving particles interacting via their binder-covered layers is modeled by using results from lubrication theory and Stokesian dynamics. The numerical simulations reflect two distinct regimes of agglomeration: that of granule growth and that of granule breakup. The granule growth regime takes place in all granulators including low and high shear machines while granule break-up is mainly characteristic of medium and high-shear devices in which agitation as generated by some mechanical means. During granule growth-simulations, the movement of sticky (binder covered) particles is studied in a constant shear, rapid granular flow regime. From these simulations, final granule size, shape and size distributions were obtained using a pattern-recognition technique. A second kind of simulation, also using rapid granular flow modeling, follows the deformation and break-up of an agglomerate made from particles held together by a liquid, viscous binder. Results from these simulations yield critical values of a dimensionless parameter that contains inertial and viscous dissipation effects (the so-called Stokes number). Below a critical value of the Stokes number, agglomerates are stable and only rotate in response to shear while above the critical value they break into several pieces. Around the critical value, they attain a steady elongation. These simulations allow one to obtain correlations between critical sizes, i.e., granules that deform somewhat but do not break, and different parameters of the problem.

Particle agglomeration in high shear mixers

Agglomeration mechanisms and liquid requirements in the batch granulation of fine powders in high shear mixers are discussed. Many experiments have revealed a close correlation between the degree of liquid saturation of the agglomerates and the growth rate. The saturation degree is determined by the amount of binder liquid and the particle packing density. Its effects on the agglomerate growth can be applied in the analysis of, for example, effects of mixer scale and processing conditions on liquid requirements and the final granule size. Studies of the growth kinetics show that agglomeration of fine powders may result into uniformly sized granules of spherical shape. This can be applied in the development of modified release products.

粉砕を伴う回転円錐型容器による微細造粒粒子の連続生成 造粒粒子径に及ぼす操作条件の影響

A continuous granulation process for the smaller and more spherical granules is developed by using a single rotating conical vessel in which a simultaneous operation of granulation, grinding and separation might be performed with grinding media.It is experimentally confirmed by granulating CaCO3-powder with water that the final granule size (_??_1mm) is affected by the feed ratio of the binder to powder and grinding conditions. The experimental results can be explained by a granulation process model of the simultaneous operation in a continuous rotating conical vessel. The present model is based on the following granulation characteristics: (1) The amount of the larger granules increases with the feed ratio, (2) the larger granules segregate toward the grinding zone near the wider end of the vessel and are selectively ground into smaller granules, the size of which is given by the grinding intensity, and (3) the final product size is given by the amount and size of granules ground in the wider end and rounded in the narrower one of the vessel.As a result, the final granule size decreases with a larger grinding effect and increases with a smaller grinding effect on the larger granules, as the feed ratio increases.

A mathematical model for the prediction of granule size distribution for multicomponent sinter feed.

Based on a mechanistic understanding of the factors affecting the growth of granules, a mathematical model of the granulation process has been developed. The model predicts the final granule size distribution based on the feed size distribution, the quantity of water added and physical properties of the feed. There was good agreement between the model and laboratory results for a wide range of ore types and feed size distributions. The model can be used to compare quantitatively the granulating ability of different ore blends, and to study the sensitivity of granulation to changes in the sinter feed mix.

Granulation in a Fluidized Bed II Effect of Binder Amount on the Final Granules

AbstractThere are many parameters affecting the properties of the final granules prepared in a fluidized bed. In this study one of the product parameters, quantity of the binder, has been studied for its effect on the final granule size, size distribution and friabilityDetermination of granule size change as a function of binder quantity leaded us to study the growth mechanisms during fluidized bed granulation. Two mechanisms are suggested;1) Snowballing of primary granules (nuclei)2) Agglomeration of primary granulesIt has been shown that there is a critical amount of binder at which the formation of the primary granules comes to an end if more binder is added to the system. Then granule growth occurs by agglomeration of the primary granules. The physical properties of the granules formed before and after this critical binder concentration varies significantly