ARR - Annual Report

• Design of particle-free fall SDD measurement system.
• Adaptation of the existing equipment to the project requirements.
• Measurements of rheological properties of aqueous solutions of selected materials.
• Selection of suitable experimental media and determination of quality criteria.

The research program presented for IFPRI assumes finding the relationship between the rheological properties of the solution and the drying speed on the morphology of the particles obtained by the spray drying method. For this purpose, in the first year of the project, the following tasks were assigned to be implemented:

Spray drying is a complex process. Many process parameters affect not only the operation of drying towers but also the final properties of the product. This complexity makes modelling of spray drying difficult, and the developed mathematical models are usually dedicated to the specific processes and materials (Filkova et al., 2015). Even though the spray drying process has been used for over a century in the industry, mathematical models are still elaborated to predict the physicochemical properties of powders, based on drying process parameters and rheological properties of the sprayed solution.

Spray drying is one of the basic techniques for the formation of particles from liquid solutions, suspensions or slurries. The process involves spraying a solution in the stream of a hot drying medium, usually air. As a result of the rapid spray extension, intensive moisture evaporation takes place without a significant increase in dried material temperature. Short drying time and low product temperature in spray drying are beneficial in many industries, from pharmaceuticals, through food, to chemicals, especially for drying heat-sensitive materials.

of granule structures.

measurement will be combined on an significant set of granules, representing a variation

In the last part of this first period the two aspects of structure description and property

between structural and physical measures is the next step that was performed.

The combination of both kinds of measures to evaluate if there are any significant correlations

between differently structured granules.

The structural as well as the physical parameters provide results that are suitable to distinguish

granules are dispersed in an optical glass cuvette and measured continuously.

measurement of particles size distribution over time in a laser diffraction system. The

beaker test. The second method to measure dissolution behaviour contains the

of granules containing salt within the binder phase can be determined in a standard

Regarding dissolution and disintegration behaviour of the structured granules, the conductivity

positions of granules on a sample container and crushes these granules consecutively.

single granules has to be measured. An experimental set-up was designed that scans

To achieve statistically relevant results for the single particle crushing, a high number of

behaviour by conductivity measurements and online particle sizing respectively.

mechanical strength is measured by single particle crushing and the dissolution or disintegration

For the determination of physical properties three different methods were chosen. The

and covariance function.

were evaluated include volume and surface fraction, star volume, chord length distribution

and used for further calculations of structure descriptors. The structure descriptors that

Three dimensional X-ray micro tomography images of the model granules were recorded

coarse limestone particles was chosen and combined with a polyethylene glycol binder.

to achieve different internal structures. A bimodal particles size distribution of fine and

Model granules were generated containing different size distributions of primary particles

correlation to structure parameters.

this year was about the determination of physical parameters of model granules and their

While the last period of work was focused on the implementation of structure descriptors

Executive Summary

This project year focused on the air classification step of the circuit. Trials in two air classifiers, in laboratory and industrial scales, were conducted. It was compared which aspects of this process are influenced by grinding aid and which are determined by machine design. The main conclusions of the work are as follows:

a.

The classifier corrected cut-size (when no bypass of fines to the course outlet occurs) is not affected by the use of grinding aids, being a result of wheel speed and air volume flow rate;

b.

Grinding aids promoted a reduction in bypass of fines to the course outlet for both classifier scales, although with smaller intensity at very small cut-sizes;

c.

In the industrial scale classifier, it was not observed reduction on powder caking on the chamber walls with grinding aids tested. This fact seems to be due to the chamber design and formation of air stream dead zones, but more studies are required.

d.

The fish-hook effect for ultra-fine particles can be reduced by grinding aids, but is also very affected by the machine design.

e.

Grinding aids promoted an increase in separation sharpness for coarser size classes, reducing coarser residue on the fine product.

In the previous year of the project (first year) batch grinding tests and powder flowability measurements of the product were conducted in order to assess grinding aid contribution to the breakage aspect of milling, without powder transport. It was also conducted initial open-circuit milling trials to study the effect of grinding aids on powder transport, mill holdup and process dynamics and stabilization. It was observed that additives promoted a more stable and efficient process. Although it was also observed that excessively high powder flowability can result in process ineffectiveness by reduction of mill residence time and no reduction of product particle size.

In this project, dry grinding of the materials alpha alumina and calcium carbonate is studied. Three substance classes were adopted as grinding aids: An Alcohol, a Carboxylic acid and a Glycol. For the experiments, a 47-liter batch-wise or continuously operated ball mill as well as a reflector-wheel air classifier are selected.

• Amount of material coated on equipment surfaces.
• Total mass of product inside the mill and residence time
• Powder flowability;
• Tendency of fine particle agglomeration;
• Product fineness after grinding;

This project aims in developing a system engineering approach for understanding, optimizing and scaling industrial dry grinding processes, with a special focus on the manipulation of the material properties and, thus, the grinding and classification efficiency by grinding aids. Grinding aids are defined here as liquid or dry substances that are added to the process in order to increase the product throughput, decrease the specific energy consumption and/or to reach a certain product fineness. During milling operations, grinding aids impact powder material mainly in:

Abstract

In this report, we quantitatively assess the effectiveness of discrete element method (DEM) calibration methods utilised by 8 industrial DEM practitioners for a number of differing experimental geometries, particulate media, and combinations thereof. The accuracy of the methods is assessed by comparing the outputs of simulations performed following the procedures of the 8 participants with detailed experimental data produced using Positron Emission Particle Tracking (PEPT), a technique which allows the dynamics of particulate systems to be imaged, in three dimensions, with sub-millimetre spatial resolution and sub-millisecond temporal resolution. Strikingly, of all the participants surveyed, no two institutions adopted the same practices, highlighting the need for a more standardised approach and best practice. Our results show that while most contemporary calibration methods are able to successfully capture the dynamics of simple, free-flowing, spherical particles under low-shear conditions, the vast majority of procedures tested were unable to correctly reproduce the behaviours of smaller, more cohesive particles, or higher-shear environments. For the latter case, though qualitative agreement and visual similarity between simulated and experimental systems could be observed, deeper and more quantitative analysis using PEPT revealed significant disparities. A number of methodologies were able to successfully capture the dynamics of aspherical, highly-angular particles, but no advantage was observed in the implementation of complex and computationally-intensive geometric models over the simpler and more efficient rolling-friction method for the materials and systems explored. Of the calibration methods examined, the most effective – indeed the only one to consistently reproduce the experimentally-measured dynamics of the cohesive systems tested – involved the combination of both static and dynamic powder characterisation tests, suggesting this to be the best practice for multi-parameter DEM calibration.

Executive Summary

Project ARR-98 focused on mixing rules for powder mixing in rotating drum flows. The first phase of the project explored the viability of PEPT measurements to yield the desired measurements for validating and complimenting a granular flow model of rotating drum flows. In this regard, coarse graining strategies proved integral to the success of the project. A useful outcome was the observation of the reverse Brazil nut effect observed for a binary mixture (by size).

Phase two built upon the serendipitous finding of a Peclet-based rheology that underpinned most of the granular flow phase space. ~200 DEM simulations across a wide range of flow configurations was used to successfully validate the new rheology.

Paper II related to year 3 deliverables is under correction and will be submitted soon.

Year 3 Deliverables

• (2) Empirical models able to predict reconstitution times from powder physicochemical characteristics.
• (1) Fitting of reconstitution kinetics followed by granulometry;

The third year of the PhD work was dedicated to modelling. On one hand, a new approach of descriptive modelling of food powders reconstitution kinetics followed by granulometry was investigated. The developed model allows to describe the different reconstitution steps by successive first-order indicial responses, thus allowing to calculate characteristic times and rates of each step. On the other hand, it was tried to develop a predictive model for reconstitution times in reconstitution conditions employed in year 1 based on physicochemical properties of powder characterized in year 1. The deliverables were achieved in November 2021:

This part, focused on AFM, will be continued during the 4th year of IFPRI project (Feb. 22 – Feb. 23) by a post doc or a technician working on the project.

Year 2 Deliverables

• (2) Effect of surface modifiers (quantities to cover the surface, distribution at the particle surface, minimal quantity necessary to improve wetting, etc.).
• (1) Surface chemical mapping and nanoindentation to establish correlations with powder wettability;

The second year of the PhD work was focused on a powder presenting a low wettability (i.e. whey protein powder), which was coated with sugars to improve its wetting behavior. In agreement with IFPRI partners, five sugars (i.e. sucrose, lactose, glucose, fructose, and galactose) were chosen for their wide range of physicochemical properties: solubility, chain length, structure, glass transition temperature, hydrophilicity, etc. Links between powder wetting and sugar nature, surface modification, quantity, and coating depth were thoroughly investigated. The deliverables were achieved at the end of July 2021:

Paper I has been published in Powder Technology and is related to year 1 deliverables. https://doi.org/10.1016/j.powtec.2021.01.056.

Year 1 Deliverables

• (2) First statistical correlations between the various powder characteristics and their wettability and reconstitutability.
• (1) Powder classification according to their reconstitution behavior;

The first year of the PhD work dealt with the systematic physicochemical analysis of powders and their classification according to their reconstitutability. It was achieved at the end of January 2020 with the following deliverables:

(PhD duration: 1st February 2019 – 31th January 2022)

Executive summary until October 2021 – year 3

Executive Summary

In the immediate future, work within this project will focus on disintegration model sensitivity analysis, model calibration and validation. The disintegration model will then be linked to an existing model for high shear granulation, and the process of inverse problem solving for the linked process-product model initiated.

Initial experimental method development is also presented. In this work, the relationship between granulation process parameters, internal granule structure and granule dissolution kinetics was studied. The results demonstrate the important role of granule porosity in granule dissolution, and provide important steer for the development of validation experiments for granule disintegration.

A preliminary parametric sensitivity analysis was conducted for the unified granule disintegration model, which investigated the effects of initial granule size, disintegrant particle size, initial granule porosity and disintegrant absorption ratios on granule size distributions and size evolution. The model was found to be sensitive to all four parameters, with faster disintegration promoted by increased granule size, decreased disintegrant particle size, lower initial porosity and increased absorption ratios.

This annual report summarises key progress toward the project aims made over the past 12 months. In particular, a mechanistic single granule model has been developed, which includes rates processes such as liquid penetration, liquid absorbance, swelling and stress build-up. This single granule model has been coupled with a population balance model, to enable the modelling of swelling driven breakage for populations of granules.

The aim of this project is to demonstrate the ability to link process and product models for wet granulation processes, and to initiate solution of the inverse problem, i.e. to determine the required process parameters and material properties to provide desired granule performance. A case study of granule disintegration/dispersion has been chosen as the product performance model for this work.

1. the lack of mechanistic models which relate granule structure and material properties to granule properties, and
2. the cooperative development of linked process and product models, to ensure essential parameters are modelled throughout the process and product.

While these performance criteria are typically the driving reason to granulate in the first place, we are still unable to confidently design granulation processes which optimise for desired product performance. There are several reasons for this, but two of the largest hurdles to overcome are:

The vast majority of granular products are granulated to produce some desired function and performance. This function may be improved flow, reduced dustiness, specific granule strengths and attrition resistance, or could be specific criteria for dispersion or dissolution.

Goals

1 compare with the formulation guidelines obtained from (1).

3. Apply these methods to simplified industrial dispersion by industrial partners and

• Local scale tribological measurements using AFM.

during flow (4D imaging)

• High resolution confocal microscopy to probe structural development in situ

which aspect of the particles or formulation controls the rheology

the nature of the stress during flow (elastic or viscous), which helps to identify

high frequency rheometry and superposition rheometry, which help identify

• Advanced rheological methods which allow for stress deconvolution such as

the rheological response of the such dispersions, focusing on

2. To further develop a limited number of rheological and structural tools to interrogate

control of shear thinning/thickening and the control of the thixotropic response.

within. The properties aimed for, after discussing with IFPRI members, are the

formulation guidelines to do “more with less” or simplifying formulations from

simple formulations a wide range of behaviors can be ”built in”, i.e. obtaining

changing the properties of the building blocks of the suspensions, so that even in

with near hard interactions, we can widen the range of rheological responses by

1. To explore how, moving away from model systems containing spherical colloids

Our goals within the IFPRI project are threefold

5. Preliminary experiment results for continuous crystallization with wet mill and recycle

4. Investigation of model-based crystallization design with milling for shape optimization

3. Investigation of the effect of recycle on crystal size

2. Investigation of the effect of recycle on purity

1. Development of the overall model of the integrated system consisting of the continuous crystallization cascade, wet mill, ideal classifiers and recycle

Achieved Deliverables

This year, the focus was on system integration both in simulation and experimentally. A one-dimensional (1D) model was used for process intensification and integration. A model for a cascade of multi-stage continuous crystallizers connected to a downstream wet mill and two ideal classifiers were developed and the effect of recycle on crystal size and purity was studied. An attainable region was found for crystal size by optimizing the process for feed, recycle and mill ratio and temperatures of the three crystallizers. A model was developed for tracking impurity in crystals and effect of recycle on impurity was investigated. Prior experience was used to correlate one dimensional (1D) crystallization model outcomes to bulk properties to use the 1D model for fast optimization of the process to obtain large crystals with short aspect ratio. This work poses an example to what must be considered and learned from experimental data to formulate process optimization routines or 2D model for more accurate shape control. Preliminary experiments were done on a small-scale integrated process including two crystallizers, a wet mill and use of recycle. A model for real classification process including separation efficiency was also proposed to later implement in the system and investigate its effect both through simulation and experiments.

This report summarizes the main achievements during the year 2021 of the project with the aim of developing process systems engineering approaches for improved crystal size, shape, and purity control during crystallization processes. The successful crystallization process and system design requires an interdisciplinary effort, which ranges from population balance model (PBM) development of the system concept, through efficient implementation of model equations to soft-sensor development, which is required for the model predictive control (MPC) design as well. This report gives a deeper insight into these interdisciplinary development efforts, which also highlights the achievable improvements enabled by the combination of process modeling, high performance process simulation and optimization.

Executive Summary

EXECUTIVE SUMMARY

2

geometry, where faster flows will be possible.

Behringer hopper for use in future experiments to test these observations in a very different

fluctuations emanating from the outer wall. Finally we have repaired and modified the IFPRIfunded

not only the roughness/smoothness of the wall (as expected), but also to the magnitude of force

this to be true. We have further observed that we can associate different amounts of wall slip to

conditions. After resolving some issues with sensitivity to changes in humidity, we have found

given set of particles, and test whether they were constant across use under different boundary

boundaries. This allowed us to measure the 3 nonlocal constitutive parameters (A; b; s) for a

both particle-dynamics and stress fields under controlled conditions for six different-roughness

As Year 6 comes to a close, we have used fully-developed experimental protocols to measure

properties.

on separating which flow properties are set by the particle properties, versus those set by the wall

and (2) use these parameters to predict flows in other geometries. Thus, our current work focuses

can we (1) make flow measurements in one geometry which determine the constitutive parameters

and apply NLR to real granular systems. We aim to establish that, for a given set of particles,

In Years 4-6 of this project, we aim to address current shortcomings in how to calibrate

(A; b; s), but that we must know the amount of slip at the wall from geometry-dependent measurements.

packing densities, particle sizes and shapes, and shear rates, using just 3 constitutive properties

In Years 1-3, we established that NLR successfully models granular flows across different

particle properties, and the boundary conditions at the walls.

particles). Doing this requires a quantitative understanding of which properties are set by both the

determine the constitutive parameters for use in predicting flows in other geometries (for the same

the aim is to make a set of flow measurements for a set of particles in one geometry, and then

intermittent, creeping, quasi-static, and intermediate flows. In order for these models to be useful,

set of particles, which then can be used to predict flow fields and stresses over a large range of

promise of permitting the determination of a small number of empirical parameters for a particular

been the development of various nonlocal rheologies [1–7]. These constitutive models hold the

In the field of granular rheology, one of the most promising advances of the past decade has