Spray-Drying of Pastes with ACLR-Nozzle for Process Intensification

Executive summary  

 

The main objective of this project is to apply a pneumatic nozzle design, the Air-Core-Liquid-Ring (ALCR)-nozzle, for spray-drying of highly viscous liquids and pastes. The project is divided into three main working packages (WP). WP 1 aims to validate the ACLR atomizer technology to enable spraying of highly viscous liquids, using both experimental measurements and CFD simulations. WP 2 aims to evaluate the impact of the composition and morphology of the atomized droplets on the drying kinetics, for highly concentrated feeds. WP 3 aims to join the results of both packages to investigate the applicability of the ACLR nozzle for spray-drying of highly viscous liquids. The followings findings were achieved in the present funding period. 

 

WP 1: Atomization with the ACLR nozzle 

 

• A model system of maltodextrin solutions was chosen and characterized for different dry-matter concentrations, which reaches viscosities up to 3 Pa·s at 20°C at 103 s-1. 

• The experimental analysis of the ACLR nozzle internal flow instabilities was extended for viscosities up to 1.3 Pa·s. 

• An automated algorithm for measuring the spray angle in real time was developed. 

• Experimental droplet size distributions were measured for MD solutions with a dry-matter concentration of up to 57%. The distributions show that atomization is, in principle, possible. The bimodality of the DSD, the high number of large droplets and the apparent time-instability of the distribution still need to be further investigated. 

• A CFD model was implemented to represent the internal flow of the ACLR, and has been validated for viscosities up to 0.14 Pa·s. 

 

WP 2: Evaluation of the impact of the composition and morphology on the drying kinetics and model development by single droplet drying 

 

• Hanging-droplet experimental setups were identified to be an appropriate method due to their advantages in measuring drying kinetics. CFD was employed to investigate the flow characteristics within the drying channel and to ensure an even and stable airflow. Pressurized air is utilized for drying, permitting volume flow rates of up to 850 cm³·min and temperatures of up to 200 °C. Droplets are generated using a syringe and are then transferred to the 0.3 mm thickness glass filament.  

• Exploratory experiments were conducted to evaluate the experimental setups viability in determining drying kinetics, showing good results for solid contents of up to 20 wt.%.  

• Particle morphologies and particle contour area were successfully captured using a high speed camera.  

 

WP 3: Proof-of-concept of industrial applicability of the ACLR nozzle for spray-drying of highly viscous liquids

 

• This WP is planned to start on the funding year 2024-2025.