GB990487A - Improvements in and relating to granular ammonium nitrate compositions - Google Patents

Abstract

Granules of ammonium nitrate are formed by spraying a melt of ammonium nitrate containing not more than 6% of water into a zone containing an agitated bed of ammonium nitrate granules while a gas, e.g. air or fuel combustion gases, passes therethrough, and the granules are showered through the gas so that they become coated with the dispersed ammonium nitrate and substantially dry enlarged granules are removed. The process may be operated in a drum provided with lifters. The melt may be sprayed through one or more vortex spray nozzles or air-operated atomizers either at the inlet to the zone or on to the bed of granules. The process is operated continuously and the fines, crushed oversize, and, if desired, product size granules are recycled. The ratio weight of ammonium nitrate sprayed: weight of recycled granules fed per unit time is from 1 : 2 to 3 : 1. The grading of the product is 1 to 4 mms. and that of the feed 0.5 to 2 mms. The melt to be sprayed may be kept 10-20 DEG C. above its melting point. The melt may be produced in situ by reacting nitric acid and ammonia, concentrating the solution in a falling film evaporator, or in a Stengel reactor/evaporator, and feeding the hot solution to the nozzle. The gas stream may be countercurrent at ambient temperature, or co-current, when the gas is heated preferably so that the outlet temperature of the gas is 60-120 DEG C. When the water content of the melt is 3-6% the granules are porous, e.g. 15-26%, and with water content not more than 0.5%, dense, e.g. 7-15% porosity granules are formed. Minor proportions of aluminium, magnesium or calcium oxides or salts, e.g. nitrates, may be included in the melt to modify hardness, crystal habit, and storage properties. Thus, 0.5% MgO or 2% Al2(SO4)3. 18H2O may be added. Specification 894,773 is referred to.