Patent GB-407988-A (GB)
Title: Improvement in process of producing concentrated fertilizer
IPC: C05B7/00
Filed: 1932-08-22
Abstract: In the production of fertilizers a part of al<1> the chemical constituents of the fertilizer are reacted in a chamber and the composition ground as the reaction proceeds, the composition is then mixed and kneaded in a moist state to form a plastic mass, subjected to extrusion and dried.  The salts are preferably ground to a fineness of less than 80 mesh.  Fertilizers containing potash salts and mono- and/or di-ammonium phosphates are obtained by allowing ammonia and phosphoric acid to <PICT:0407988/III/1> <PICT:0407988/III/2> react in the reaction chamber in the presence of the potash salts. A combined grinding, reaction, mixing and kneading apparatus and apparatus for extruding, drying, screening, and breaking the product are described.  Various methods of performing the reaction between the ammonia and the phosphoric acid are described.  The ammonia may be derived from aqua ammonia or from liquid ammonia which may be added as such or converted into gaseous ammonia outside the reaction chamber and the gaseous ammonia then led into the chamber.  The phosphoric acid and the ammonia may be sprayed into the reaction chamber, the ammonia inlet being preferably just below the acid inlet.  Alternatively liquid ammonia containing salts such as ammonium nitrate, urea or other fertilizers soluble in liquid ammonia may be added; by this method the salts are obtained in a particularly fine state of subdivision.  The velocity of the reaction may be increased by the introduction of water in mist or vapour state, the salts being maintained in a comparatively dry loose state; accordingly it is preferred to add only sufficient water during the neutralization stage to accelerate the reaction, the remainder of the water for forming the plastic mass being added after the reaction is completed.  The reaction may be carried out under atmospheric pressure, but preferably under a higher pressure; this higher pressure will increase the rate of reaction so that care must be taken to accelerate the cooling means to ensure formation of ammonium phosphates.  The degree of ammoniation may be controlled by (a) weighing and measuring the ammonia before and during its introduction into the reaction chamber; (b) sampling the solids in the reaction chamber; (c) controlling the temperature in the reaction chamber, e.g. by thermostatic means, to that of the predetermined equilibrium of the desired ammonium phosphate compounds under the vapour pressure conditions prevailing in the chamber; it is preferable to keep the temperature down at the beginning of the reaction and allow it to rise to the critical point when all the phosphoric acid has been added.  Specification 315,700, [Class 1 (ii)], is referred to.  The combined grinding, reaction, mixing and kneading apparatus comprises a closed chamber 17 containing a rotatable mixing pan 9 in which are mounted a number of rollers 15.  The rollers 15 are each suspended by stirrups 38 connected to cables 42 so that the height of the rollers may be adjusted vertically, the full weight of the rollers being on the salts for grinding, but the rollers being partly raised for kneading.  Levellers 66 and scrapers 61, 63 to scrape the material from the bottom of the pan and from the rollers respectively ensure that a kneading action takes place.  Inlets 21--24 are provided for the solid, liquid and gaseous materials and the resulting plastic mass is removed into a storage chamber 71 by lowering one end of a scoop 73 into the pan 9.  The pan 9 is surrounded by water or other heat transfer medium for regulating the temperature, when water is used it may be covered with a layer of oil to prevent absorption of ammonia &c.  Water evaporated by the heat of reaction in the p an 9 may be condensed at the cover 18 of the chamber 17, which cover is cooled by a spray 35; the water falls into a reservoir 25 mounted beneath the cover.  A conduit 29 from the reservoir 25 serves for returning water to the pan 9 as needed and a conduit 28 serves for removal of excess water.