Sergej Knez,a Janez Stražišar,a Janvit Golob,b Andrej Horvatc
aFaculty of Natural Science, Department of Geotechnology and Mining, University of Ljubljana,
 Aškerčeva 12, 1000 Ljubljana, Slovenia;
bFaculty for Chemistry and Chemical Engineering, Aškerčeva 2, 1000 Ljubljana, Slovenia
cSilkem d.o.o., Tovarniška cesta 10, 2325 Kidričevo, Slovenia


Zeolites are crystalline materials most widely used as molecular sieves and ion exchangers. The production process yields the base zeolite material with average particle size of about 5 µm. These particles are later mixed with binder and agglomerated during drying in spray-dryers to produce larger particles with upper size range of about 300 µm, depending predominately on the geometry of the atomizer and it’s speed of rotation. However, some applications require even larger particles that cannot be produced by spray-drying technique.
An important technique for producing large granulates is agglomeration in the fluidized bed. The intensive mixing of solid particles in the fluidized bed facilitates high heat and mass transfer rates and consecutively almost isothermal conditions throughout the bed, resulting in high process yields and effective control. The absence of moving mechanical parts also lowers the maintenance costs. However, there is still a lack of understanding concerning the mechanisms of particle formation and growth in the fluidized bed that leads to difficulties in planning and operating such processes, hence the experiments on semi-industrial scale equipment are needed to obtain the necessary process parameters.
The present work is concerned with the determination of the process parameters for producing granulated zeolite with demanded product characteristics in a semi-industrial scale fluidized bed dryer. The theoretical (and sometimes empirical) knowledge of the operations involved – fluidization, agglomeration, drying – was used to construct the model of the process, which enabled us to identify the relevant process parameters, i.e. those controlling the process and those affecting the product characteristics, and predict their values. Next, the demanded product characteristics were set and  then used as a measure of adequacy of the chosen process parameters and their optimization.
The results of our experimental program confirmed the validity of the model and the possibility of using fluidized bed agglomeration for producing large zeolite particles.