The main objective of this project was to apply an innovative 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 aimed to validate the ACLR atomizer technology to enable spraying of highly viscous liquids, using both experimental measurements and CFD simulations. WP 2 aimed to evaluate the impact of the composition and morphology of the atomized droplets on the drying kinetics, for highly concentrated feeds. WP 3 aimed to join the results of both packages to investigate the applicability of the ACLR nozzle for spray-drying of highly viscous liquids. The project schedule is shown in Fehler! Verweisquelle konnte nicht gefunden werden.. This is a short overview of the main findings of the project:
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 are directly correlated.
- 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 experimental results. Additionally, the liquid lamella thickness inside the nozzle follows the same trend in simulations and experiments: 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 in a single droplet drying (SDD) setup.
- 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.
- Experiments were conducted to evaluate the impact of initial solids concentrations up to 53 wt%. The results for the particle size, mass and drying kinetics showed good agreement with theoretical considerations. Looking at the drying time, it was revealed that the impact of lower water contents and lower water flux seem to level out at constant droplet size for higher solids concentrations.
- The results showed a significantly shorter time to the locking point for higher dry matter concentrations, reducing the risk of powder stickiness.
WP 3: Proof-of-concept of industrial applicability of the ACLR nozzle for spraydrying of highly viscous liquids
- The numerical investigation for an optimized nozzle design identified that a shorter outlet length, a larger mixing chamber inclination, and rounded internal edges lead to thinner and more stable liquid lamellas.
- Two improved nozzle designs were proposed, and the one with the shortest outlet length (0.8 mm) was shown to consistently produce the thinnest and most stable lamellas.
- The optimized nozzle demonstrated consistent performance improvements, leading to thinner lamellas and smaller droplets compared to the original design in both simulations and experimental tests.
- The improved design highlights significant potential for energy consumption and operating cost reductions, as it outperformed the original nozzle even when operating at lower pressures and air-to-liquid ratios.
- Optimized ACLR nozzle design leads to 33 % smaller spray droplets (x90,3) compared to the initial (basic) design.
- has been elucidated in WP 2.