The effect of binder concentration in fluidized-bed granulation: Transition between wet and melt granulation

BERTÍN, DIEGO; COTABARREN, IVANA M.; VELIZ MORAGA, SUSSY; PIÑA, JULIANA; BUCALA, VERONICA

CHEMICAL ENGINEERING RESEARCH & DESIGN

INST CHEMICAL ENGINEERS

Año: 2018 vol. 132 p. 162 - 169

0263-8762

According to the binder nature, fluidized-bed granulation (FBG) is usually classified aswet or melt granulation. In particular, the industrial urea granulation performed influidized beds, is often called ?melt granulation? because a highly concentrated ureasolution is used as binder (between 95-97 wt%) (Cotabarren et al., 2012). However,plant disturbances can cause changes in binder urea concentration and thus granulationcan shift from melt to wet granulation and vice versa.In a previous investigation, the granulation system urea (seeds) ? urea (binder) wasextensively studied in a pilot-scale batch fluidized-bed granulator (Veliz Moraga et al.,2015). Besides, the effect of seed size, bed temperature, binder flowrate and fluidizationand atomization air flowrates on process variables as well as on product properties werestudied. The aim of this work is to analyze the effect of the binder urea concentration onthe urea granulation performance and product properties. This concentration was variedfrom 87.5 wt% to 98 wt%, while the fluidization air velocity, urea melt flowrate, bedtemperature set-point and atomization air flowrate were kept constant. The productproperties (percentage of agglomerates and coated particles, crushing strength andmoisture content) and granulation efficiency are discussed in terms of the transitionfrom wet to melt granulation. The critical urea content was experimentally found;indeed, urea concentrations lower than the critical one dramatically affect the productquality. Finally, the criterion proposed by Villa et al. (2016) for predicting agglomeratesformation is used to determine the minimum allowable binder urea concentration. Theprediction is consistent with the trends experimentally observed, indicating the goodcapacity of the criterion to identify the boundary for agglomeration occurrence.