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

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

• The ACLR can achieve stable atomization with feed viscosities as high as 3 Pa·s, at relatively low pressures (7 bar) and low air-to-liquid ratios (0.8).
• The internal flow and the external spray instabilities can be directly correlated with each other. 
• A CFD model was successfully adapted in STAR-CCM+ v.2206 to predict the internal flow of non-Newtonian maltodextrin solutions being atomized with an ACLR nozzle. In general, the predicted ALRs from the simulations agree with what was observed in experiments. Additionally, the liquid lamella thickness inside the nozzle follows the same trend in the simulations as what is observed in experiment: A smaller internal lamella variation is observed as the ALR increases.
• The possibility of using simulations to evaluate operating conditions outside of experimental capabilities was evidenced. The lamella variation can be severely reduced by increasing the operating pressure to 15 bar, which is still far below the 50-250 bar that is common in pressure swirl nozzles.

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

• A method for the analysis of the mass data and calculation of the drying kinetics was developed.
• Experiments were conducted to evaluate the impact of initial solids concentrations of up to 45 wt%. The results for the particle size, mass and drying kinetics showed good agreement with theoretical considerations.
• The impact of the drying temperature was evaluated. While the impact of the drying temperature on the drying time agrees well with expectation, its influence on the drying kinetics showed no apparent trend. 

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

 The simulation plan to optimize the geometrical design of the nozzle has been formulated, and it is currently being carried out.