Mechanism Of Granule Formation Research Articles

Powder wetting behavior and granule formation mechanism expansion in single-drop granulation

Single-drop granulation is performed under a variety of conditions to characterize the behavior that results from a liquid droplet impacting a powder bed. Drop impact velocity, liquid binder properties, powder bed consolidation status, and primary particle size are all demonstrated to have significant effects on the resulting granule formation mechanism. The process is broken down into a drop impact/drop deformation stage, a drop rebound stage, and a drop imbibition stage. These stages are often in competition with each other to determine the overall drop penetration behavior. Twelve granule formation mechanisms are identified and characterized in this study, in addition to two established granule formation mechanisms that were not observed in this work.

Advanced 3D and 4D microstructure study of single granule formation for pharmaceutical powders using synchrotron x‐ray imaging

AbstractMonitoring the microstructure of the granule in the wet granulation process could play a decisive role in obtaining high‐quality granules. Due to the complex, fast and opaque nature of wet granulation, it cannot be captured by conventional methods. In this study, synchrotron x‐ray imaging was employed for the first time to investigate the internal real‐time pore evolution during the granule formation process, based on the single droplet impact method. It was found that granules from coarser and more homogenous powders experienced a higher rate of pore evolution during nucleation with a more uniform pore distribution. Dynamic wetting studies showed the granule formation mechanisms, the crater mechanism was found for most binary mixtures with 50 wt. % excipients. According to the physical tests, the granules with lower porosity and finer pores exhibited higher hardness and a slower dissolution rate.

Binder Jet 3D Printing of Magnesium Oxychloride Cement-Based Concrete: A Framework to Design the Rate of Voxel

The present work addresses the powder bed binder jet 3D printing as an additive manufacturing process for cement-based materials in the constructions industry. Features are created through the interaction among the droplets of the liquid binding agent and the layered powder bed. The printhead movement over the powder bed at a given feed rate forms voxels and single-lines from the coalesce of successive droplets and adjacent lines are consolidated to create the designed cross-section. Here, statistical models have been developed to study the effect of printing parameters (aggregate particle size, feed rate, velocity of powder spread, pressure of the fluid and nozzle diameter) on the resultant dimension of a single printed line, using a factorial design of experiment. The hardware of the 3D printer, the physical properties of the powder blend and binder are initial constraints for designing voxels. Linear regression models of significant parameters are presented. Pressure is one of the most significant factors, it has a profound effect on the granule formation mechanism. Cubic samples printed with higher pressure level are characterized by higher residual porosities from crater channels during the printing process. The results demonstrate a fundamental understanding of the binder–powder interaction for cementitious materials which can be leveraged to determine the minimum printable feature with required dimensional accuracy, based on the chosen process parameters.

Distinctive differences in the granulation of saline and non-saline enriched anaerobic ammonia oxidizing (AMX) bacteria

The growing interest in the anaerobic ammonium oxidizing (AMX) process in treating high nitrogen containing wastewaters and a comprehensive study into the granulation mechanism of these bacteria under diverse environmental conditions over the years have been unequal. To this effect, the distinctive differences in saline adapted AMX (S_AMX) and non-saline adapted AMX (NS_AMX) granules are presented in this study. It was observed that substrate utilisation profiles, granule formation mechanism, and pace towards granulation differed marginally for the two adaptation conditions. The different microbial dominant aggregation types aided in splitting the 471 days operated lab-scale SBRs into three distinct phases. In both reactors, phase III (granules dominant phase) showed the highest average nitrogen removal efficiency of 87.9% ± 4.8% and 85.6% ± 3.6% for the S_AMX and NS_AMX processes, respectively. The extracellular polymeric substances (EPS) quantity and major composition determined its role either as a binding agent in granulation or a survival mechanism in saline adaptation. It was also observed that granules of the S_AMX reactor were mostly loosely and less condensed aggregates of smaller sub-units and flocs while those of the NS_AMX reactor were compact agglomerates. The ionic gradient in saline enrichment led to an increased activity of the Na+/K+ – ATPase, hence enriched granules produced higher cellular adenosine triphosphate molecules which finally improved the granules active biomass ratio by 32.96%. Microbial community showed that about three to four major known AMX species made up the granules consortia in both reactors. Proteins and expression of functional genes differed for these different species.

Powder bed packing and API content homogeneity of granules in single drop granule formation

Single drop granule formation on a static powder bed of pharmaceutical mixtures was studied to investigate the effects of hydrophobicity and primary particle size distribution on the powder bed packing structure and the content homogeneity of active pharmaceutical ingredient (API) in granules formed. The granule formation mechanisms, drop penetration time, granule morphology and internal structure have been previously investigated in a mixture of coarse microcrystalline cellulose (MCC) and fine acetaminophen (APAP). When the APAP amount increased (decreasing particle size and increasing hydrophobicity), drop penetration time increased, formation mechanisms transitioned from Spreading to Tunneling, the granules became smaller in size, and the internal porosity of the granules decreased (Gao et al., 2018). In the current study, single drop granulation on mixtures of MCC and APAP with different particle sizes were investigated for formation mechanisms and granule morphology. Additionally, the powder bed packing structure was characterized by X-ray micro-CT and the API content uniformity was measured by UV–vis spectrometry. It was found that in the mixture made from coarse MCC and fine APAP, the internal structure became heterogeneous and there were dense aggregate regions in both the powder bed and granules from 25% APAP proportion, where the transition from Spreading to Tunneling occurs. The content uniformities of granules from fine powder beds are much more compromised (indicating a discrepancy between the actual value and theoretical value) than those from coarse powder beds. This content discrepancy becomes much larger when the APAP proportion in the powder bed is higher (above 50%). This was previously observed by other researchers (Nguyen et al., 2010) and was attributed to the preferential wetting of the ingredients. It is believed that the primary particle size of the powder bed is more significant than the hydrophobicity in affecting the formation mechanism, granule internal structure, and content uniformity.

Slow growers possess a high pollutant removal potential through granule formation for wastewater treatment

For the upgradation and building of wastewater treatment plants in limited areas, biological wastewater treatment processes with a high pollutant removal loading rate are required. Biofilm or membrane-based systems can achieve a high pollutant removal loading rate through high microbial biomass concentrations and/or activities. The sludge separation is the primary bottleneck for achieving high biomass concentrations inside the biological reactors. In addition, low growers including anaerobic ammonia oxidation bacteria and methanogens are usually easier to form granules and induce high nutrient removal loading rates. The possible granule formation mechanisms should be clarified through physical, chemical and biological aspects, including hydraulic control, microbial extracellular polymeric substances formation, biological energy utilization control, microbial interactions and also other microbial processes. In future, the possible mechanisms should be further clarified, and then high-efficient bioreactors, new microbial ecology control strategy and novel biofilm carriers should be developed for advancing biological wastewater treatment processes with high pollutant removal loading rates.

Assessing Particle Segregation Using Near-Infrared Chemical Imaging in Twin Screw Granulation.

In the present study the application of near-infrared chemical imaging (NIR-CI) for assessing particle segregation in granules from continuous twin screw granulation (TSG) granules, were the complex attributes of the machinery configuration in relation to particle segregation is not well understood was investigated. Experiments were performed along the compartmental length of the TSG barrel channel by varying the screw element type and liquid binder viscosity. Examination of the data showed a direct correlation between dispersion due to shear force and de-mixing of particles, which allowed for identification of fundamental granule segregation mechanisms affecting content uniformity in TSG. Particle segregation behavior was linked to dispersion due to shear force through a proposed regime mapping approach which links de-mixing potential to controlling granule formation mechanisms with a new dimensionless mixing number. This was carried out in order to provide a general guideline of how particles segregate along the length of the TSG barrel channel.

Treatment of 17α‑ethinylestradiol, 4‑nonylphenol, and carbamazepine in wastewater using an aerobic granular sludge sequencing batch reactor

This study quantifies the removal of a mixture of commonly detected emerging contaminants, 17α‑ethinylestradiol (EE2), 4‑nonylphenol (NP), and carbamazepine (CBZ) from synthetic wastewater using aerobic granular sludge in a sequential batch reactor. The emerging contaminant concentration in the influent wastewater was maintained near 500 μg/L for the duration of the experiment. Removal of EE2, NP, and CBZ is comprised of both adsorption and degradation. In general, the main removal mechanism for the emerging contaminants was initially adsorption, however it transitions to degradation as the adsorption capacity is saturated. The stabilized degradation for EE2 and NP in the SBR, was 16.09 μg/g and 20.05 μg/g, respectively. There was limited degradation of CBZ during the anaerobic phase. Both the Langmuir and Freundlich adsorption isotherms fit the data well and constants for the equations are calculated. The constants for the Langmuir Isotherm are found to be (X/m)max = 36.23, b = 0.0019 for EE2 and (X/m)max = 44.25, b = 0.0004 for CBZ. None of the tested compounds were found to be detrimental to the performance of the aerobic granules, and high macronutrient removal efficiency was maintained. The granule sludge bed and particle size were not negatively affected by EE2 and NP, however, carbamazepine appeared to interfere with the mechanism of granule formation resulting in a decrease in particle size during the experiment.

Granule formation and structure from single drop impact on heterogeneous powder beds

Single drop impact of liquid on a static powder bed was studied to investigate the granule formation mechanism, droplet penetration time, as well as the characterization of granules (morphology, surface structure and internal structure). Water was used as the liquid and two pharmaceutical powders, microcrystalline cellulose (MCC) and acetaminophen (APAP), were mixed to make heterogeneous powder beds. The complete drop impact and penetration was recorded by a high speed camera. Two granule formation mechanisms that have been identified previously occurred: Spreading and Tunneling. Spreading occurred for mixtures with an APAP amount of less than 20%, while Tunneling started to occur when the APAP amount increased above 20%. With an increase of APAP concentration, the mean particle size decreased, drop penetration time increased, and the granules formed became smaller in size, which was in good agreement with previous literature. The granule morphology, surface structure, and internal structure were characterized by a prism method with image analysis, scanning electron microscopy (SEM), and X-ray microtomography, respectively. The Spreading mechanism produced flat disks with a porous internal structure, while the Tunneling mechanism produced round granules with a dense internal structure. There is a clear trend of decreasing porosity and increasing roundness of granules made from heterogeneous mixtures within the transition from Spreading to Tunneling. It is believed that the mean particle size of the powder bed and the powder-liquid contact angle are the predominant factors in influencing the formation mechanism, drop penetration time, and granule properties.

Treatment of tapioca processing wastewater in a sequencing batch reactor: Mechanism of granule formation and performance

The formation of aerobic granular sludge was carried out in a sequencing batch reactor (SBR) for tapioca processing wastewater treatment. The effect of organic loading rates (OLRs) in the range of 2.5–10.0 kg COD m−3 day−1 on the granulation was investigated. The size and settleability of the aerobic granular sludge increased with increasing OLR from 2.5 to 7.5 kg COD m−3 day−1. The mature granules had an average size of 2.5 mm and good settleability with the sludge volume index (SVI) lower than 50 mL g−1. The granules had a layered structure consisting of anoxic sludge core with nematodes and an outer aerobic layer surrounded by stalked ciliates. Removal efficiencies of chemical oxygen demand (COD) and NH4+-N reached 90.0%–93.0% and 86.6%–92.5%, respectively. Simultaneous nitrification and denitrification at the OLR of 7.5 kg COD m−3 day−1 resulted in the improvement of total nitrogen (TN) removal efficiency to 66.1%.

Investigation of the kinetic laws affecting the organic suspension granulation in the fluidized bed

The authors prove that it is possible to reduce economic and environmental parameters in the processes of granulation and produce fertilizers by recycling , and further reprocessing of chicken manure. This prevents unprocessed manure from getting into the environment, and due to the organic origin of the material, the soil is not contaminated. In order to reduce the cost of processing wet substances and increase homogeneity of the final product granulometric composition, it is proposed to fulfill granulation of organic suspensions in the fluidized bed devices. The mechanism of granule formation in a fluidized bed was studied and granulation temperature modes of organic suspensions were experimentally established. The process operating parameters have been determined, namely, maintaining temperature in the fluidized bed at 70 °C, one can continuously produce organic granules of high density and strength. Heat transfer kinetics of organic suspension dehydration was studied, as well as convective heat transfer in the suspended layer was determined. Based on the obtained experimental data, the coefficient of heat transfer from the heat agent (air) to the surface of solid particles during evaporation of the suspension was calculated. The obtained criteria dependence makes it possible to predict a value of the heat transfer coefficient for the granulation process of chicken manure suspension. The technological scheme of the production line for granular organic fertilizers for the cultivation of ecologically pure food products, which also takes into account the specific properties of unprocessed chicken manure, is proposed.

In-depth experimental analysis of pharmaceutical twin-screw wet granulation in view of detailed process understanding

Twin-screw wet granulation is gaining increasing interest within the pharmaceutical industry for the continuous manufacturing of solid oral dosage forms. However, limited prior fundamental physical understanding has been generated relating to the granule formation mechanisms and kinetics along the internal compartmental length of a twin-screw granulator barrel, and about how process settings, barrel screw configuration and formulation properties such as particle size, density and surface properties influence these mechanisms. One of the main reasons for this limited understanding is that experimental data is generally only collected at the exit of the twin-screw granulator barrel although the granule formation occurs spatially along the internal length of the barrel. The purpose of this study is to analyze the twin-screw wet granulation process using both hydrophilic and hydrophobic formulations, manufactured under different process settings such as liquid-to-solid ratio, mass throughput and screw speed, in such a way that the mechanisms occurring in the individual granulator barrel compartments (i.e., the wetting and different conveying and kneading compartments) and their impact upon granule formation are understood. To achieve this, a unique experimental setup was developed allowing granule characteristic data-collection such as size, shape, liquid and porosity distribution at the different compartments along the length of the granulator barrel. Moreover, granule characteristic information per granule size class was determined. The experimental results indicated that liquid-to-solid ratio is the most important factor dictating the formation of the granules and their corresponding properties, by regulating the degree of aggregation and breakage in the different compartments along the internal length of the twin-screw granulator barrel. Collecting appropriate and detailed experimental data about granule formation along the internal length of the granulator barrel is thus crucial for gaining fundamental physical understanding of the twin-screw wet granulation process.

Technological aspects of the use of mechanical activation effects in energy-saving granulation processes

Some results of studying the compaction processes of multicomponent polydisperse materials (MPMs) with their preliminary surface treatment were presented. The efficiency of the use of mechanically activated MPMs in granulation processes compared with powder materials has been shown, and granule formation mechanisms have been established. Some process flowsheets have been developed for the production of granular materials by compaction.

Twin screw granulation: Understanding the mechanism of granule formation along the barrel length

The objective of this study was to develop a detailed understanding of the roles and effects of the screw elements in the granule formation along the length of barrel in the twin screw granulator (TSG) by incremental addition of the elements in the screw configuration. The number of kneading and conveying elements in the screw configuration, liquid to solid ratios (L/S) and screw speeds were varied while studying their effects on the mechanism of granule formation and the granule attributes (size, shape and structure). In order to study the granule formation mechanism, the length of TSG barrel was divided into 10 Parts. This was done to mimic and understand the actual granulation process that occurs in the individual Parts (sections) when total barrel length (cumulative length of all 10 Parts) comprising both conveying and kneading zones in the screw configuration is used. Part-1 consisted two long pitch conveying elements (LPCE) followed by four short pitch conveying elements (SPCE). Part-2 consisted of two kneading elements (KE) placed at the end of the granulator after 4SPCE. Similarly, Part-3 to Part-7 subsequently consisted 4, 6, 8, 10 and 12KE. In Part-8, 2SPCE were placed next to 12KE which is named as 12KE+2SPCE. Same thing was repeated for Part-9 with 4SPCE and Part-10 with 6SPCE. In a separate experiment, last 4SPCE in Part-10 were replaced by 2LPCE to study the effect of increase in the screw channel width on the granule size and structure.It was found that the granules became bigger in size, elongated and denser with increasing number of KE (Part-2 to Part-7) due to increase in shear and compaction forces acting on them. The influence is more evident at higher L/S. However, the presence of SPCE in addition to the KE (Part-8 to Part-10) reduced the size and elongation of granules due to the shearing and cutting action of SPCE. The granule formation and growth in the TSG was found to be the function of the type and number of elements in the screw configuration and the L/S. Presence of 2LPCE at the end of the screw configuration resulted in an increase in the granule size and structural voids due to the coalescence or re-agglomeration of granules.

Asymmetric distribution in twin screw granulation

Positron Emission Particle Tracking (PEPT) was successfully employed to validate measured transverse asymmetry in material distribution in the conveying zones of a Twin Screw Granulator (TSG). Flow asymmetry was established to be a property of the granulator geometry and dependent on fill level. The liquid distribution of granules as a function of fill level was determined. High flow asymmetry at low fill level negatively affects granule nucleation leading to high variance in final uniformity. Wetting of material during nucleation was identified as a critical parameter in determining final granule uniformity and fill level is highlighted as a crucial control factor in achieving this. Flow asymmetry of dry material in conveying zones upstream of binder fluid injection leads to poor non-uniform wetting at nucleation and results in heterogeneous final product. The granule formation mechanism of 60°F kneading blocks is suggested to be primarily breakage of agglomerates formed during nucleation. Optimisation of screw configuration would be required to provide secondary growth. This work shows how fill dependent flow regimes affect granulation mechanisms.

Granulation of snow: From tumbler experiments to discrete element simulations

It is well known that snow avalanches exhibit granulation phenomena, i.e., the formation of large and apparently stable snow granules during the flow. The size distribution of the granules has an influence on flow behavior which, in turn, affects runout distances and avalanche velocities. The underlying mechanisms of granule formation are notoriously difficult to investigate within large-scale field experiments, due to limitations in the scope for measuring temperatures, velocities, and size distributions. To address this issue we present experiments with a concrete tumbler, which provide an appropriate means to investigate granule formation of snow. In a set of experiments at constant rotation velocity with varying temperatures and water content, we demonstrate that temperature has a major impact on the formation of granules. The experiments showed that granules only formed when the snow temperature exceeded −1∘C. No evolution in the granule size was observed at colder temperatures. Depending on the conditions, different granulation regimes are obtained, which are qualitatively classified according to their persistence and size distribution. The potential of granulation of snow in a tumbler is further demonstrated by showing that generic features of the experiments can be reproduced by cohesive discrete element simulations. The proposed discrete element model mimics the competition between cohesive forces, which promote aggregation, and impact forces, which induce fragmentation, and supports the interpretation of the granule regime classification obtained from the tumbler experiments. Generalizations, implications for flow dynamics, and experimental and model limitations as well as suggestions for future work are discussed.

Simulation of the Spray Drying of Single Granules: The Correlation Between Microscopic Forces and Granule Morphology

In the ceramic industry, spray drying is an important process transforming fine primary powder into processable granular material. Granule formation at spray drying has been investigated in the past and plausible explanatory models have been established for the governing mechanisms of granule formation. In this study, we use numerical modeling via coupled discrete element method and computational fluid dynamics simulations to investigate this formation process. The focus lies on the evolution of the granule morphology during drying of single droplets. In addition to a demonstration, that the simulation results support the propositions made by the experimentally‐based models, a new correlation was found which leads to an extension of those models for granule formation in terms of the granule stability.

Sedimentology and geochemistry of Archean silica granules

The production of biogenic silica has dominated the marine silica cycle since early Paleozoic time, drawing down the concentration of dissolved silica in modern seawater to a few parts per million (ppm). Prior to the biological innovation of the first silica biomineralizing organisms in late Proterozoic time, inputs of silica into Precambrian seawater were balanced by strictly chemical silica and silicate precipitation processes, although the mechanics of this abiotic marine silica cycle remain poorly understood. Cherty sedimentary rocks are abundant in Archean sequences, and many previous authors have suggested that primary precipitation of amorphous silica could have occurred in Archean seawater. The recent discovery that many pure chert layers in early Archean rocks formed as sedimentary beds of sand-sized, subspherical silica granules has provided direct evidence for primary silica deposition. Here, we provide further sedimentological and geochemical analyses of early Archean silica granules in order to gain a better understanding of the mechanisms of granule formation. Silica granules are common components of sedimentary cherts from a variety of depositional settings and water depths. The abundance and widespread distribution of silica granules in Archean rocks suggest that they represented a significant primary silica depositional mode and that most formed by precipitation in the upper part of the water column. The regular occurrence of silica granules as centimeter-scale layers within banded chert alternating with layers of black or ferruginous chert containing few granules indicates episodic granule sedimentation. Contrasting silicon isotopic compositions of granules from different depositional environments indicate that isotopic signatures were modified during early diagenesis. Looking to modern siliceous sinters for insight into silica precipitation, we suggest that silica granules may have formed via multiple stages of aggregation of silica nanospheres and microspheres. Consistent with this hypothesis, Archean ocean chemistry would have favored particle aggregation over gelling. Granule formation would have been most favorable under conditions promoting rapid silica polymerization, including high salinity and/or high concentrations of dissolved silica. Our observations suggest that granule sedimentation was often episodic, suggesting that granule formation may have also been episodic, perhaps linked to variations in these key parameters.

A regime map for granule formation by drop impact on powder beds

“Tunneling,” “Spreading,” and “Crater Formation” are the three granule formation mechanisms known to occur when single drops impact static powder beds. To quantify the conditions under which each mechanism will occur, dimensional analysis was performed, and a new regime map was created that plots the powder bed porosity against the modified granular Bond number (Bog*), which is a ratio of the capillary force to the gravitational force acting on a particle. Tunneling occurred for Bog* > 65,000 for all values of bed porosity, whereas Spreading and Crater Formation occurred when Bog* < 65,000 for all values of bed porosity below the minimum fluidization porosity. The granule formation mechanism regime map provides a useful tool to design and predict wet granulation processes by predicting the granule formation mechanism, and thereby general granule shape, from a few key dimensionless groups involving formulation properties and process parameters that can be calculated a priori. © 2012 American Institute of Chemical Engineers AIChE J, 59: 96–107, 2013

Modeling the granule formation mechanism from single drop impact on a powder bed

Granule formation from drop impact on a powder bed can occur by either Tunneling or Spreading/Crater Formation. The governing regime can be specified by the experimentally determined modified Bond number (Bog∗), which is a ratio of the capillary force to the gravitational force acting on a particle. It was hypothesized that Tunneling would occur when the capillary and surface tension forces exceeded the weight of a powder aggregate in contact with the drop. To confirm this hypothesis, force balances were derived for a drop in contact with a single particle and separately for a drop in contact with an aggregate to predict when a particle or aggregate will be sucked into the drop. The force ratios derived for each case were compared to the Bog∗ force ratio used in a previously published regime map that separates Tunneling from Spreading/Crater Formation. The force balance model correctly predicts the trends of the impact of powder and liquid properties on the governing regime. However, the single particle model does not quantitatively predict the critical Bond number for regime change in Tunneling. The aggregate model gave a better prediction of the Tunneling boundary than the single particle model, but it still under predicts the experimentally determined Tunneling criterion given by the Bond number. Potential reasons for this discrepancy are discussed.