The process developed in the TVA pilot plant involves partial ammoniation of phosphoric acid in a preneutralizer and completion of ammoniation in a rotary ammoniatorgranulator. Granulation is controlled by recycling product fines to the drum. Addition of excess ammonia to the drum allows reaction to an 3: 3 4 mole ratio of about 2.0, thereby decreasing the solubility of the ammonium phosphates and improving control of granulation. The excess ammonia is recovered by scrubbing the gases from the drum with the feed acid before preneutralization. The granular material is dried and then screened to obtain a closely sized diammonium phosphate of 18-46-0 to 21-53-0 grade. N-P-K grades, such as 18-18-18, 15-15-15, and 14-35-14, can be produced by adding other feed materials.

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Small-scale tests of the reaction of phosphate rock with sulfuric acid resulted in the identification of conditions that yielded superphosphate of high phosphorous pentoxide availability and of such physical condition that it could be ammoniated about 1 hour after mixing. These results were verified in a pilot plant that consisted of a TV A funnel-type mixer and a continuous den. A conversion of 95% was achieved in 1 hour by slightly overacidulating finely ground rock with acid of about 60% concentration. Fresh superphosphate from the den was used immediately in the production of several grades of granular fertilizers by the TV A continuous ammoniation process. ORDINARY superphosphate, made

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