Using Particle Residence Time Distributions as an Experimental Approach for Evaluating the Performance of Different Designs for a Pilot-Scale Spray Dryer

• Published in: Processes Vol. 11; no. 1; p. 40
• Main Authors: Zhou, Zelin, Langrish, Timothy A. G., Cai, Sining
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.01.2023
• Subjects: Automation; Continuously stirred tank reactors; Cylindrical chambers; Design; Drying; Experiments; Flow distribution; Gas flow; Performance evaluation; Physical properties; Residence time distribution; Signal to noise ratio; Simulation; Skim milk; Wall deposition; Washers & dryers; Australia
• ISSN: 2227-9717; 2227-9717
• DOI: 10.3390/pr11010040

The performances of four different designs for a pilot-scale spray dryer have been evaluated and compared based on experimentally measured particle residence time distributions (RTD), recovery rates and physical properties of spray-dried fresh skim milk. The RTDs have been measured using a dye pulse injection method, and the measurements have been fitted to models using continuous stirred-tank reactors in series (CSTR-TIS) for quantitative performance evaluation and comparison. Conical drying chambers and a box connection design have been used in the latest dryer design to reduce the amount of wall deposition and provide a smoother gas flow pattern. The particle-to-gas mean residence time ratio for the latest design is significantly closer to unity (1.6 s/s to 1.0 s/s) compared with earlier designs (2.6 s/s to 1.5 s/s). The latest design has a wider spread of RTD (n = 5–8) compared with earlier designs (n = 13–18), which may be linked to the recirculation zone in the box connection. Although the latest design has a wider spread of RTD, the conical design has shown promising results compared with a cylindrical drying chamber in terms of overall wall deposition behaviours.