Experimental evaluation of parameters affecting the coating performance of urea seeds in a prototype bottom external mixing spray two-fluid nozzle fluidized bed granulator

• Published in: Chemical engineering research & design Vol. 172; pp. 242 - 253
• Main Authors: Tabeei, A., Keikhosravani, A., Samimi, A., Mohebbi-Kalhori, D., Zakeri, M.
• Format: Journal Article
• Language: English
• Published: Rugby Elsevier B.V 01.08.2021; Elsevier Science Ltd
• Subjects: Atomizing; Coalescing; Coating; Comparative studies; Computational fluid dynamics; Dimensionless numbers; Fluid mechanics; Fluidized bed granulator; Fluidized bed reactors; Fluidized beds; Granulation; Granulators; Growth mechanism; Heat transfer; Mass flow rate; Nozzles; Parameters; Response surface methodology; Seeds; Spraying; Studies; Urea; Ureas; Urea; Fluidized bed granulator; Response surface methodology; Growth mechanism
• ISSN: 0263-8762; 1744-3563
• DOI: 10.1016/j.cherd.2021.06.014

[Display omitted] •Setting up a prototype external mixing bottom spray two-fluid nozzle urea FBG.•Characterizing dominant coating mechanism of urea seeds by molten urea using FBG.•Defining new parameter as performance of coating in urea granulation.•Modelling and optimizing the effect of parameters on coating performance of urea.•Figuring out dimensionless Stock number in mechanisms of urea granulation process. A comparative study was carried out on coating and coalescence mechanisms of urea seeds by molten urea, using external mixing two-fluid nozzle fluidized bed granulator (FBG). In this regard, the variables influencing a new parameter defined as coating performance (CP) of urea granules were modeled. The variables included of spraying and atomizing air pressures, masses of loaded seeds and molten urea, and mass flow rate of fluidization air. Considering all interactions between the variables, the optimum conditions for obtaining the maximum 60% CP was determined. Furthermore, according to cumulative size distributions analyses, the conditions leading to proper size guide number (SGN) and uniformity index (UI) was characterized. The SEM observations showed that, in most cases, the porous initial urea seeds were coated by a compact molten urea layer. Considering the dimensionless Stokes numbers, the extent of fluidized particles’ velocity leading to domination of coating or coalescence was verified.