GB388403A - Process and apparatus for preparing phosphatic fertilizer - Google Patents

Abstract

Phosphatic fertilizers are obtained by charging a mixture of phosphatic material such as finely ground phosphate rock and an acid such as sulphuric or phosphoric acid into a confined container, and supplying heat directly during the reaction period by injection of a heated vapour, preferably steam or super-heated steam. The phosphatic material may be introduced as an ammoniacal slurry, or, if desired, the ground phosphate and acid may be admixed with other fertilizing ingredients such as ammonium sulphate or urea, and/or potassium sulphate or carnallite. The product which is stated to be in a non-caking porous ball form, may also be ammoniated in the autoclave, or before or after screening and grinding. Examples show that the time of charging should be directly proportioned to the "activity" of the mass, as defined by the temperature and concentration of the acid and the degree of fineness of the phosphate dust. In an apparatus for effecting the reaction, Fig. 1, the acid, for example 52-57 DEG B<\>ae sulphuric acid heated to say 90-110 DEG F. by coil 2 in tank 1 is measured in balance 6 and is passed to acid-charging tank 10 which is connected to a source of compressed air through line 13, whereby a suitable velocity of charging is obtainable. Phosphate rock dust from hopper 16 is weighed in balance 23 and is transferred by pump 29 to hopper 32 provided with agitator 34 and connected to a dustcollecting device 40. To render the dust fluid, it is aerated by jets 21, 19<1>, 33. When the predetermined amounts of acid and dust have been admitted to the vessel 10 and hopper 32 respectively, valves 47, 43 are opened and the acid and dust pass to the mixing valve 42. As shown in Fig. 2, the dust is delivered down pipe 58 and is surrounded by a hollow conical spray of acid directed by members 54, 59. The acid delivery pipe 49 is preferably disposed tangentially to the ring-shaped channel 50, whereby a whirling motion of the acid spray and consequent better mixing are obtained. Means for delivering varying quantities of acid are provided by connecting valve member 59 by means of bolt-member 60 to threaded collar 62 which is capable of vertical adjustment by rotation of collar 63. Detachable covers 68, 69 are provided. The mixture passes through trunnion 86 into a heat-insulated lead-lined rotating autoclave 71 and impinges against a baffle 85. The autoclave is adapted for passage of steam thereinto through lines 105, 106, the steam say at 100-300 lbs. sq. in., being taken from main 10 through regulator 102 and safety valve 103. The autoclave is preferably heated prior to the operation, and is also partially <PICT:0388403/III/1> <PICT:0388403/III/2> evacuated before and during charging by means of pump 93. When charging is complete, the components are reacted, say for half an hour at 260-300 DEG F. under a steam pressure of 50-60 lbs. sq. in. The reaction may, however, be effected at atmospheric or subatmospheric pressure. Steam is passed into the container either continuously or intermittently through pipes 105, 106, preferably the latter, whereby the evacuating pipe is kept clear. Excess pressure may be released either continuously or intermittently through valve 90. Thus, steam may be admitted till a pressure of 50-60 lbs. is attained, which is then released, whereby carbon dioxide and fluorine compounds are removed. Fresh steam is then introduced. Operating in this manner, acid of higher concentration may be used, the steam acting as a diluting means. Finally the pressure is released, and the autoclave is evacuated by pump 93. Generally the heat of the mass suffices to dry it, but additional heat may be supplied by the use of a steam jacket. The temperature of drying is about 130-150 DEG F. An absorption system, such as spray tower 94, is provided. After drying for say half an hour, the finished product is discharged through manhole 97 on to conveyer 99. During charging, digesting and drying, the autoclave is rotated continuously. Tables showing the composition and characteristics of products obtained in various runs are given.ALSO:Phosphatic fertilizers are obtained by charging a mixture of phosphatic material such as finely ground phosphate rock and an acid such as sulphuric or phosphoric acid into a confined container, and supplying heat directly during the reaction period by injection of a heated vapour, preferably steam or superheated steam. The phosphatic material may be introduced as an ammoniacal slurry, or if desired, the ground phosphate and acid may be admixed with other fertilizing ingredients such as ammonium sulphate or urea, and/or potassium sulphate or carnallite. The product which is stated to be in a non-caking porous ball form may also be ammoniated in the autoclave, or before or after screening and grinding. Tables showing the composition and characteristics of products obtained in various runs are given.