Abstract SYMPHOS 2011

BACKGROUND
Granulation of phosphatic and complex NPK fertilizers, attempts to mechanically bind, blend and compact fine
crystalline components into individual spherical granules.
This process inherently, is inefficient due to the acicular nature of the crystalline materials and the mechanism
of simultaneous crystallization and solidification of such materials, which occurs during the granulation process.
These phenomena lead to poor product quality ( high porosity, low crush strength, non uniform shape ) and also
lead to inefficiencies in process ( high quantity of fines & recycle, heavy dust generation.
Filtra’s work on granulating aids NPTUFF, was aimed at developing a suitable chemical additive, which at low
dosages could address the above physical and chemical phenomena that lead to difficulties in granulation, thereby
improving product quality and increasing granulation efficiency. These improvements are applicable to various
grades of NPK made from phosphatic fertilizers.
METHODOLOGY
Filtra’s R&D team evaluated various materials to alter the mechanism of crystallization of the N,P,K components, to
aid uniform blending and binding of the components.
Re-crystallization behavior of fertilizer components was studied under an optical microscope and a distinct change
in crystal structure was observed on addition of the granulating aid. NPTUFF series of granulating aids is an
outcome of such studies.
NPTUFF was then tested in field trials at an 800 TPD, NPK production facility, producing granules by steam
granulation. The granulating aid was dosed into the granulator through the fresh water feed line, at a rate of 0.6 –
0.7 Kg per ton of final product. Observations were made on the following criteria :
(1) Finished product quality : Crush Strength, Granule Size Distribution, Sphericity
(2) Production parameters : Production rate, Recycle rate, Dust Generation
OBSERVATIONS
Re-Crystallization Study :
The microscopic images of crystal growth taken with and without addition of the granulating aid show a distinct
change in the nature of crystal growth.
Raw materials used in NPK fertilizers are known to have a tendency to form acicular crystals. These are long needle
shaped crystals which tend to grow linearly when unhindered. As a result a mass formed of such crystals tends to
have crystal planes that have crystals which are directionally aligned. Such a structure is easily fractured under load.
The crystal behavior with addition of granulating aid is markedly different. The crystals lose their linear growth
tendency and the material appears more polycrystalline with smaller, more polygonal crystals. Such structures
have considerably higher crush strength and tend to form more uniform surfaces.
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USE OF GRANULATING AIDS FOR ENHANCED PRODUCTIVITY OF
PHOSPHATE FERTILIZERS
WS3 -1
FILTRA CATALYSTS & CHEMICALS LTD.