Patent GB-1142002-A (GB)
Title: Granulation
Inventor: HARRIS GORDON JOHN
IPC: B07B7/01
Filed: 1965-03-24
Abstract: 1,142,002. Granulating molten materials. FISONS FERTILIZERS Ltd. 10 March, 1966 [24 March, 1965; 13 Nov., 1965], Nos. 12377/65 and 48300/65. Heading B5A. [Also in Division Cl] Molten materials are converted into granules by causing droplets thereof to fall down a tower for a minimum of 3ft. through a zone with a countercurrent flow of dust bearing gas of 1À2 to 4ft. per second velocity and of a dust loading of 0À01 to 0À251bs per cu. ft., followed by a fluidized bed of the same or a different dust which breaks the fall of the drops and may extract further heat therefrom. The molten material may be a fertilizer such as ammonium nitrate, ammonium sulphate nitrate, ammonium phosphate, or mixtures of ammonium nitrate with mono- or di-ammonium phosphate or potassium chloride or magnesium oxide, potassium phosphate, potassium nitrate, sodium nitrate, urea or mixtures of these materials together or with other materials. The molten material may also be alkali metal hydroxides. The dust may comprise the material being granulated, limestone, sand, mica, bentonite, gypsum, talc, clays, magnesium oxide, magnesium carbonate, cement, earths or micronized polyethylene. The gas may comprise air or nitrogen. The particle size of the dust is preferably less than 70 microns and preferably less than 10 microns. The temperature of the gas may be 100 C. and the molten material may be provided as a stream or streams of droplets or as a jet or jets. The fluidized bed may contain particles below 150 microns and the droplets may be incompletely solidified and cooled before entering the bed which is preferably surrounded by or contains a water cooler. Hot solidified granules can be removed continuously through the base of the bed through an elutriator. The dust transporting air may be obtained by a high gas flow through the fluidized bed, Fig. 1, not shown, or by the separate injection of a gas bearing dust or of dust and gas separately into the apparatus, Figs. 2 and 3, not shown. The hot granules may be removed from the base of the tower by a belt or screw conveyer and may be subjected to a further cooling operation, Fig. 4, not shown. Hot dust laden air is taken off from the top of the tower and may be separated in cyclones and a filter, with the hot air being vented and the dust recirculated. The fluidized bed air is introduced through the base of the tower and air for the rising dust bed may additionally be introduced at the centre of or at points around the base of the bed, Figs. 2 and 5, not shown, or may be introduced at the top surface of the bed at the centre thereof as in Fig. 7, or around the periphery, Fig. 6, not shown, of the tower. Additionally, with air introduced at the surface of the bed, dust may pneumatically be conveyed to be centrally introduced from the top of the tower, Figs. 8 and 9. not shown, from whence it is deflected downwards by a deflector to provide a higher dust concentration at the top of the tower. The fluidized bed may be operated by air passing through an elutriator at the base thereof or separately through a perforated plate, Fig. 10, not shown. The fluidized bed air may be delivered in pulses and the bed may be provided with a vibrator. Depending on the operating conditions of the process, dust coatings of 0À03% to 20% may be obtained and solidified spherical granules may be obtained in the range of 5 to 22 mesh B.S.S. screen with 76À8% at 10 B.S.S. Granules of uniform 3mm. diameter may be obtained.