Nilpawar, Amol M. (2007) Kinematics and collision kinetics in high shear granulation. PhD thesis, University of Sheffield.
Abstract
High shear granulation (HSG) is an important unit operation in the Pharmaceutieal, Detergent and Food industries. The desired output of HSG is generally a specified granule size distribution (GSD) and bulk density of the granular product. Depending on the final application, homogeneity, strength and internal structure of granules also need to be of desired quality. In industry this operation suffers from problems such as poor reproducibility and high rejection rate. Knowledge in this area is mainly empirical for both operation and scaling up. A generalised universal approach needs to be developed. This is possible if the rate processes in granulation are understood. In this dissertation a new approach to granulation is suggested as follows. The operating conditions and properties of the agglomerating substances dictate the bulk flow and thus the particle relative motion responsible for particle-particle collisions. The particleparticle collisions result in aggregation, breakage or rebound of particles. So only a fraction of colliding particles will result in aggregating successfully. If the relationship between these individual processes is understood, given the initial conditions, it would be possible to predict the output. A novel cost-effective technique to measure surface velocities in HSG has been developed by combining High Speed Imaging and Particle Image Velocimetry. This technique resulted in efficient characterization of the mean and the particulate flow in a vertical axis high shear mixer with high temporally and spatially resolved velocity data. The equipment used for HSG is referred to as high shear mixer (HSM) in the chemical industry. The experimental mixer (Roto Junior, Zanchetta, Italy) was a 10 litre, vertical axis HSM with a provision to change the mixing blade. The test feed material was Calcium carbonate (Durcal 40) and binders used were Polyethylene Glycols (PEG, avg. molar masses 400, 1500 and 4000 g/mol) and Glycerol. Effect of operating conditions and material properties on the flow has been established in the high shear mixer equipped with a 3-blade impeller. The average bed velocities were found to increase with increase in impeller speed, although approaching a stable value at higher impeller speeds. A higher viscosity binder considerably slowed the bed. Also it was noticed during a wet granulation (granulation wherein a liquid binder is used) experiment that the bed velocities were a function of availability of surface binder and the average granule size. The results were found to be highly reproducible for dry granules. A disc impeller was used for further experiments with dry granules mainly to simplify the mean flow in order to extract velocity fluctuations to calculate collision frequencies. The Kinetic Theory of Granular Flow (KTGF) was found to predict particle collision frequencies three orders of magnitude higher than those predicted by the Shear theory. This observation with disc impeller experiments provided a basis to perform further experiments with the 3-blade impeller. In a wet granulation experiment with the 3-blade impeller, simultaneous observation of particle dynamics and GSD was made. By extracting temporal velocities from a single interrogation area, granular temperature and subsequently collision frequencies based on the KTGF were calculated. A discretised population balance equation was fitted to the GSD data by minimising overall sum of square errors to calculate the aggregation rate constant. From the knowledge of the collision rate and the aggregation rate, aggregation efficiency was estimated to be of the order of 4 in 100 million in the initial stages of granulation with gradual decrease in this value as granulation proceeded. This method of extracting particle collision rate, aggregation rate and estimated aggregation efficiency provides a basis for predictive high shear granulation model using population balance modelling and knowledge of particle dynamics.
Metadata
Awarding institution: | University of Sheffield |
---|---|
Academic Units: | The University of Sheffield > Faculty of Engineering (Sheffield) |
Academic unit: | Department of Chemical and Process Engineering |
Identification Number/EthosID: | uk.bl.ethos.506744 |
Depositing User: | EThOS Import Sheffield |
Date Deposited: | 12 Oct 2023 11:56 |
Last Modified: | 12 Oct 2023 11:56 |
You do not need to contact us to get a copy of this thesis. Please use the 'Download' link(s) above to get a copy.
You can contact us about this thesis. If you need to make a general enquiry, please see the Contact us page.