Premium
Re‐entrainment of wall deposits from a laboratory‐scale spray dryer
Author(s) -
Hanus M. J.,
Langrish T. A. G.
Publication year - 2007
Publication title -
asia‐pacific journal of chemical engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.348
H-Index - 35
eISSN - 1932-2143
pISSN - 1932-2135
DOI - 10.1002/apj.47
Subject(s) - entrainment (biomusicology) , nozzle , relative humidity , air entrainment , humidity , materials science , chemistry , environmental science , mechanics , meteorology , composite material , thermodynamics , physics , rhythm , acoustics
This work has determined the magnitude of re‐entrainment and established the operational parameters that may be manipulated to influence re‐entrainment of salt particles for a small‐scale spray dryer (Buchi B‐290). The wetness of the spray dryer wall deposits was found to significantly influence the magnitude of re‐entrainment. It was shown both experimentally and numerically that wet deposits form at low nozzle air‐to‐liquid ratios (<2000), which form large droplets that dry slowly, while the initial droplet velocity did not have a large influence on wet deposition. Wet deposits form strong liquid and solid bridges, and thus deposits formed from wet particles were difficult to re‐entrain. Less than 2% of deposits formed at nozzle air‐to‐liquid ratios less than 2000 were re‐entrained, while 15.4 to 21.2% of dry deposited particles (formed at nozzle air‐to‐liquid ratios ranging from 2308 to 3409) were re‐entrained. The threshold re‐entrainment velocity of sodium chloride particles in the Buchi B‐290 spray dryer was found to be between 4 and 7.7 ms −1 , which is consistent with the lower‐end threshold velocities presented in the literature. No significant trend relating relative humidity to the magnitude of re‐entrainment was found in the 0.2–7.4% average relative humidity range, suggesting that the adhesive forces in spray dryer wall deposits are fairly constant across this relative humidity range. Decreasing wall deposit wetness through use of high (>2000) nozzle air‐to‐liquid ratios and use of high main gas velocities increased the re‐entrainment of wall deposits in this spray dryer. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd.