Mechanism of agglomeration in spray drying with the fine particle recirculation

• Applicant: Privatdozent Dr.-Ing. Abdolreza Kharaghani, Ph.D.
• Subject Area: Chemical and Thermal Process Engineering
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 465347282

A wide range of products that we use in everyday life (such as instant coffee and washing powder) is produced by means of spray drying technology. The attractiveness of these products to customers is attributed to their end-user properties such as wettability, dispersibility and solubility. Key parameters that remarkably impact these properties are the size and size distribution of particles. If particles are too small or the particle size distribution is too narrow, they may create structures difficult to moisten and dissolve. Therefore, it is necessary to combine small particles to form relatively large stable agglomerates in which the basis particles are still distinguishable. In spray drying this process is typically conducted by recycling dry fines (dust) into the drying chamber, which ultimately increases the yield and prevents the particle size distribution from shifting to too low values. This method of agglomeration is however limited because considerable size enlargement by actively initiated and controllable agglomeration cannot be achieved by this method. Central research goal of this project is to investigate the mechanism of agglomeration, which is one of the most crucial mechanisms in spray drying by recycling dry undersized particles into the drying tower. For this purpose, an efficient prediction tool within a computational fluid dynamics (CFD) framework will newly be constructed and assessed by means of spatially and temporally resolved pilot-scale experiments. Specifically, we will combine the advantages of both microscale single droplet/particle analysis and large-scale laboratory spray dryer system, offering a complex multi-scale approach. Determination of drying kinetics with the use of an acoustic levitator and changes in morphology with the help of different imaging techniques (such as X-ray microtomography) at the level of single droplets/particles for which the German team is famous. Measurement of continuous and dispersed phase flow dynamics using advanced measurement techniques (such as particle diffraction analysis) during spray drying is the core expertise of the Polish team. As the keystone of the theoretical parts of this project, an innovative mathematical model of particle agglomeration associated with kinetic models of drying and morphological changes will be developed by both teams in order to describe the mechanism of agglomeration during counter-current spray drying with the return of small product fractions.Summarizing, in the frame of a multiscale approach this project shall make a significant progress towards design and control agglomeration in spray drying and pave the way for estimation of final product properties.

• DFG Programme: Research Grants
• International Connection: Poland
• Co-Investigator: Professor Dr.-Ing. Evangelos Tsotsas
• Cooperation Partner: Professor Dr.-Ing. Maciej Bogusz Jaskulski