Agglomeration in counter-current spray drying towers. Part A: Particle growth and the effect of nozzle height

Victor Francia, Luis Martín, Andrew E. Bayly, Mark J. H. Simmons

Research output: Contribution to journalArticlepeer-review

15 Citations (Scopus)
43 Downloads (Pure)

Abstract

Agglomeration of particles and droplets is critical to the operation of spray dryers, however it remains relatively unexplored. This paper studies the effect of the nozzle height on product properties, wall deposits and dryer conditions in a counter-current spray drying tower of detergent with a swirling air flow. The process efficiency is driven by changes in particle agglomeration. To interpret the results and facilitate the study of swirl towers, it is useful to subdivide these units according to the sources of growth in (a) spray region(s), (b) concentrated near-wall region(s) and (c) wall deposits. The particles formed are very heterogeneous and show a size-dependent composition. In this case, particle properties are driven by the separation of solid and liquid phases during atomization and the formation of a heterogeneous set of droplets. Agglomeration serves to homogenise the product and create a distinct source of porosity. The capacity and energy consumption of the dryer are also determined by the evolution of the particle size, as fine powder is elutriated from the tower top and coarse particles are removed from the product. When the nozzle is moved to lower positions in the tower the increased temperature near the spray suppresses agglomeration, however the residence time is shortened and ultimately it leads to creation of wet, coarse granules. An optimum location is found high enough to maintain the drying efficiency but sufficiently far from the top exit to minimise the loss of fine particles. In this way, a capacity ratio (i.e. product vs spray dried powder) C > 90% can be obtained and energy efficiency maximised.

Original languageEnglish
Pages (from-to)1330-1343
Number of pages14
JournalPowder Technology
Volume301
Early online date10 May 2016
DOIs
Publication statusPublished - Nov 2016

Keywords

  • Agglomeration
  • Atomization
  • Detergent
  • Particle growth
  • Phase separation
  • Spray dryer

ASJC Scopus subject areas

  • Chemical Engineering(all)

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