Patent GB-795820-A (GB)
Title: Granular fertilizer
IPC: B01J2/10
Filed: 1955-04-19
Abstract: 795,820. Complete fertilizer granules. DORR-OLIVER, Inc. April 19, 1955 [April 30, 1954], No. 11235/55. Class 111. Granular complete fertilizers are prepared by forming a slurry having a moisture content of 15 to 25 per cent by weight, containing nitrogen and phosphorus and adding to such slurry dry potassium chloride solids in a size of 10 to 28 mesh (Tyler) in a weight ratio of such dry solids to slurry of 5 to 1 to 12 to 1, mixing the slurry and solids to produce the complete fertilizer in the form of a potassium chloride nucleus with a moist slurry coating, withdrawing the coated particles and drying them, classifying the dried granules into the desired product size, over-size and under-size, and recirculating the under-sized and crushed over-sized granules through the mixing and drying steps in an amount such that the weight ratio of the total of fines, crushed over-size and the dry potassium chloride solids to the slurry is in the range of 5 to 1 to 20 to 1. The product size granules withdrawn have a size of 6 to 20 mesh. The initial slurry containing nitrogen and phosphorus may consist of monoammonium phosphate with or without diammonium phosphate and ammonium sulfate, a mixture of ammonium phosphate, sulfate and nitrate with urea or a mixture of ammonium phosphate and dicalcium phosphate. In addition to the potassium chloride dry solids, ammonium nitrate or sulfate or urea may also be introduced in dry form. As shown in the Figure, 40 per cent strength aqueous phosphoric acid is introduced into a reactor 16 together with gaseous ammonia in a mole ratio of 1 to produce monoammonium phosphate. The slurry passes to a second reactor 24 where further ammonia is passed in, the reaction temperature reaching the slurry boiling point of about 100‹ to 110‹C. The slurry then passes to a reactor 32 where cooling air is passed in thereby producing a cool slurry of 15 to 25 per cent moisture content. If ammonium sulfate is required sulphuric acid is introduced into the initial reactor together with the necessary additional ammonia to form the sulfate. In place of anhydrous ammonia a solution of ammonium nitrate or urea in anydrous ammonia may be employed in the first and second stage reactors. Alternatively the slurry may be prepared by reacting phosphoric acid and phosphate rock to form monocalcium phosphate and introducing a mixture of anhydrous ammonia with ammonium nitrate or urea into the slurry as it leaves the third reactor 32 or in the subsequent granulator. The slurry from the reactor 32 passes to a paddle mixer 40 to which fines are added through line 44 in a weight ratio of 5 to 1 to 20 to 1. The granules produced are dried in a drier 48 and pass via a lift 64 to a sieve 66. Product size granules are withdrawn through line 72 and fines and oversize granules are passed through receptacles 76 and 70 with associated crusher 82 to line 44 for recirculation. Dust from the drier passes to a cyclone 60 and the dust so recovered is also recycled to line 44. Storage bins 86, 90, 94 and 91 are provided respectively for potassium chloride, urea, ammonium nitrate, and ammonium sulfate respectively. Specification 789,747 is referred to.