Patent GB-588054-A (GB)
Title: Process for the production of ammonium nitrate
IPC: C05C1/02
Filed: 1944-12-15
Abstract: Granular ammonium nitrate is produced by spraying, at a temperature above its saturation temperature, an aqueous ammonium nitrate solution having a saturation temperature between 115 DEG  and 135 DEG C. (corresponding to a strength of 94 to 97 per cent. into a gaseous cooling medium maintained at a lower temperature, whereby granules are formed, cooling the granules to below 84 DEG C. in suspension in the medium, removing the granules to a heated gaseous drying medium to remove the major part of the moisture content, and thereafter cooling and drying the granules in a cooler gaseous medium to reduce the moisture content to less than 0.5 per cent.  In an example, the ammonium nitrate solution is sprayed upwards at an angle of 45 DEG to the horizontal at the top of a tall tower through nozzles designed to impart a whirling motion to the stream of fluid, so that each spray is ejected in the form of a narrow, rotating cone.  A stream of air at normal temperature is injected at the bottom of the tower to act as the cooling medium.  The granules from the bottom of the tower at temperatures of 50 to 80 DEG  C. are removed as quickly as possible to a rotary drier, and, if necessary, may be cooled to a temperature not exceeding 50 DEG  C. at the entrance thereto by a stream of cool air.  Dried granules from a later stage with a moisture content of 0.5 to 1.0 per cent. may be added to bring the moisture content of the total feed to the drier down to 2 per cent. The temperature of the granules may be allowed to rise to 70 DEG C. at this stage by a counter current stream of warm air as the drying medium.  The granules are passed to a second rotary drier, when, by the use of a countercurrent stream of air at ordinary temperatures, the granules are cooled to approximately ordinary temperatures and dried to a moisture content of about 0.2 per cent.  Fines are screened out, if necessary, and together with fines separated from air from the driers, are returned to the supply tank of strong liquor for the spray tower.  The granules may be coated with the usual coating and dusting agents; finely divided limestone, gypsum, siliceous materials, phosphate and waxes are referred to as coating agents in prior processes.ALSO:The Specification as open to inspection under Sect. 91 comprises the production of crystalline urea from highly concentrated solutions thereof by a method similar to that described below.  This subject-matter does not appear in the Specification as accepted, wherein an aqueous ammonium nitrate solution having a saturation temperature between 115 DEG  and 135 DEG C. is sprayed at a higher temperature than this into a gaseous cooling medium maintained at a lower temperature, whereby granules are formed, the granules are cooled to below 84 DEG  C. in suspension in the medium, and removed to a heated gaseous drying medium to remove the major part of the moisture content, and thereafter cooled and dried in a water gaseous medium to reduce the moisture content to less than 0.5 per cent.  In an example, the solution is sprayed upwards at an angle of 45 degrees to the horizontal at the top of a tall tower through nozzles designed to impart a whirling motion, so that each spring is ejected in the form of a narrow, rotating cone. A stream of air at normal temperature is injected at the bottom of the tower to act as the cooling medium, and the granules therefrom at temperatures of 50 to 80 DEG  C. are removed quickly to a rotary drier, being cooled, if necessary to a temperature not above 50 DEG C. at the entrance thereto by a stream of cool air.  Dried granules from a later stage with a moisture content of 0.5 to 1.0 per cent may be added to bring the mean moisture content of the feed to the drier to 2 per cent.  The granule temperature may be allowed to rise to 70 DEG  C. at this stage by a countercurrent stream of warm air as the drying medium.  The granules are then passed to a second rotary drier, where a countercurrent stream of air at ordinary temperature cools them and dries them to a moisture content of about 0.2 per cent.  Fines are screened out, if necessary, and together with fines separated from air from the driers are returned to the supply tank of strong liquor for the spray tower.  The granules may be coated with the usual coating and dusting agents; finely divided limestone, gypsum, siliceous materials, phosphates and waxes are referred to as coating agents in prior processes.ALSO:The Specification as open to inspection under Sect. 91 comprises the production of crystalline mixtures of ammonium nitrate and ammonium phosphate from highly concentrated solutions thereof by a method similar to that described below.  This subject-matter does not appear in the Specification as accepted, wherein an aqueous ammonium nitrate solution having a saturation temperature between 115 degs. and 135 degs. C. is sprayed at a higher temperature than this into a gaseous cooling medium maintained at a lower temperature, whereby granules are formed, the granules are cooled to below 84 degs. C. in suspension in the medium, and removed to a heated gaseous drying medium to remove the major part of the moisture content, and thereafter cooled and dried in a cooler gaseous medium to reduce the moisture content to less than 0.5 per cent.  In an example, the solution is sprayed upwards at an angle of 45 degs. to the horizontal at the top of a tall tower through nozzles designed to impart a whirling motion, so that each spray is ejected in the form of a narrow, rotating cone.  A stream of air at normal temperature is injected at the bottom of the tower to act as the cooling medium, and the granules therefore at temperatures of 50 to 80 degs. C. are removed quickly to a rotary drier, being cooled if necessary to a temperature not above 50 degs. C. at the entrance thereto by a stream of cool air.  Dried granules from a later stage with a moisture content of 0.5 to 1.0 per cent. may be added to bring the mean moisture content of the feed to the drier to 2 per cent. The granule temperature may be allowed to rise to 70 degs. C. at this stage by a countercurrent stream of warm air as the drying medium. The granules are then passed to a second rotary drier where a counter-current stream of air at ordinary temperature cools them and dries them to a moisture content of about 0.2 per cent.  Fines are screened out, if necessary, and together with fines separated from air from the driers, are returned to the supply tank of strong liquor for the spray tower.  The granules may be coated with the usual coating and dusting agents; finely divided limestone, gypsum, siliceous materials, phosphates and waxes are referred to as coating agents in prior processes.