GB1039177A - Improvements in and relating to the production of granular compositions such as fertilizers - Google Patents

Abstract

A method of producing granular compositions, e.g. of ammonium nitrate comprises providing and maintaining a spouted bed of granules by means of an upwardly directed stream of gas, e.g. air, which is preferably heated, spraying a liquid melt, solution or suspension of the desired composition through a tube of relatively small diameter into the said stream at, or near, the point of entry of the gas stream, whereby granules maintained in the stream are coated and, if a volatile liquid such as water is present, are substantially dried, cleaning the said tube by mechanical means while maintaining the spouted bed. The process may be carried out in vertical cylindrical vessel fitted with a frusto-conical base in which the slope of the conical surface may be greater than angle of repose of the crystals of the bed. The said tube may be surrounded by a further tube through which air is passed to atomize the said liquid. The angle of the cone is arranged so that in conjunction with the flow of gas the liquid inlet is kept clear. The liquid tube may be heated, e.g. by an electric element or by fluid circulating through a jacket surrounding the tube 2-10% of water in the liquid is suitable. The process may be operated continuously - oversize particles being separated and recycled to the bed after grinding if necessary. Some, or all of the feed material may be introduced with the gas stream forming the spouted bed. Dust particles in the exit are recovered by a cyclone and the product is dried in a countercurrent of air, which is used as feed air for the spouted bed. Slurries used may be prepared by mixing continuously in a stirred jacketed vessel a 10% moisture content slurry of ammonium phosphate (N/P ratio 1.4) at 115 DEG C. with a 3% moisture content solution of ammonium nitrate at 160 DEG C. at the same time adding at ambient temperature, ammonia gas or liquid and solid potassium chloride to produce a N/P ratio of 1.8. The final temperature may be adjusted by heating or cooling. The temperature of the liquid composition is chosen to produce a viscosity of up to 30 poises. Fertilizer compositions based on ammonium nitrate, mono- and di-ammonium phosphate, potassium salts, e.g. the chloride and ammonium sulphate may be prepared by the method which may also be used for applying anti-caking agents, e.g. formaldehyde to urea or to apply a plastic material, e.g. bitumen or resin to decrease the rate of solution of granules of a chemical substance or fertilizer. Reference has been directed by the Comptroller to Specification 962,265.