GB775114A - Improvements in or relating to the production of phosphate-containing fertilizers - Google Patents

Abstract

Phosphate fertilizer in the form of pellets or powder is produced in a single stage operation by forming an aqueous slurry of the ferilizer constituents in the desired proportions and injecting the slurry under <PICT:0775114/III/1> pressure into a rotary drier heated with a concurrent flow of hot gas to form the desired pellets or powder. The resulting pellets or powder are sifted to separate those particles that are larger than the desired size such separated particles being crushed and recycled to the rotary drier separately from the injected slurry, together with any particles that are smaller than the desired size. The slurry may be injected under a pressure of 2 kg/cm2 and the turbulence of the injected spray may be increased by placing helical fins in the spraying tube. The initial slurry may consist either of a paste of simple or triple superphosphate resulting from the action of sulphuric or phosphoric acid on a phosphate or of a slurry obtained by mixing water with a simple or triple superphosphate prepared elsewhere. In either case nitrogenated or potassium fertilizers such as ammonium sulphate or nitrate, or potassium sulphate or chloride may be added. As shown in the drawing a slurry is formed in a vessel 1 provided with an agitator 2 and passed by pump 4 through line 3 to a rotary drier 6 through an injection nozzle 5, under pressure of 2 kg/cm2. The drying cylinder is provided with helical fins to agitate the material as the drier rotates and is heated by combustion gases from a fire box 7 which enter at a temperature below 900 DEG C. The products leave the drier and pass through a sifting mechanism made up of screens 8, 8a and 8b whereby the larger pieces are collected at 11 and after passing through a crusher 9 are recycled through line 10 to the rotary drier. The product size granules of 2-4 mm size are drawn off at 12 whilst fine particles of 1.5-2 mm size are drawn off at 10 for recycling to the drier. A small proportion of particles of 0-1 mm size are withdrawn at 13. According to an example (1) crushed Gafsa phosphate was mixed with 30 per cent phosphoric acid in the ratio of 1 part of P2O5 in the phosphate for every 2.9 parts of P2O5 in the acid. The mixture obtained was injected at a temperature of 55 DEG C. into the drier 6 fed with gases at 550 DEG C. and at the same time twice the quantity of recycled fines were fed hrough line 10. The product had a 6 per cent moisture content.