Abstract
Granulation is an important step during the production of urea granules. Most of the commercial binders used for granulation are toxic and non-biodegradable. In this study, a fully biodegradable and cost-effective starch-based binder is used for urea granulation in a fluidized bed granulator. The effect of binder properties such as viscosity, surface tension, contact angle, penetration time, and liquid bridge bonding force on granulation performance is studied. In addition, the effect of fluidized bed process parameters such as fluidizing air inlet velocity, air temperature, weight of primary urea particles, binder spray rate, and binder concentration is also evaluated using response surface methodology. Based on the results, binder with higher concentration demonstrates higher viscosity and higher penetration time that potentially enhance the granulation performance. The viscous Stokes number for binder with higher concentration is lower than critical Stokes number that increases coalescence rate. Higher viscosity and lower restitution coefficient of urea particles result in elastic losses and subsequent successful coalescence. Statistical analysis indicate that air velocity, air temperature, and weight of primary urea particles have major effects on granulation performance. Higher air velocity increases probability of collision, whereby lower temperature prevents binder to be dried up prior to collision. Findings of this study can be useful for process scale-up and industrial application.
Highlights
Fluidized bed granulation is used in a range of industries such as pharmaceuticals, foods, detergents, and fertilizer products
Starch penetrates into the intermolecular gaps of water molecules and fills this gap by molecules’ chains of starch and urea such that volume of the solution increases per unit mass
The results indicate that granulated urea and fluidizing air temperature on granulated urea weight
Summary
Fluidized bed granulation is used in a range of industries such as pharmaceuticals, foods, detergents, and fertilizer products. Granular material is subjected as a solid state to behave like a fluid. The synthesized fertilizer is usually converted into particulate material either through granulation or prilling. Since granules possess better characteristics than prills, granulation becomes the preferred route for urea fertilizer production [1]. Granulation is an enlargement process that combines fine particles into a larger mass of aggregates by spraying a binder solution onto the dry powder bed [2]. A powder bed is agitated by air and granules are formed with the addition of a liquid binder.
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