Occidental Research Corporation

Occidental Chemical Company

F Michael Gragg

Allen S Adams

James Self

In a multi-stage, multi-vessel phosphoric acid production system where a first reaction vessel contains a first slurry comprising calcium sulfate hemihydrate, monocalcium phosphate and phosphoric acid and a second reaction vessel contains a second slurry comprising calcium sulfate hemihydrate, sulfuric acid and phosphoric acid, in which the reaction slurry undergoes intra- and inter-vessel circulation, preferably through a draft tube, an improved start-up procedure involves filling the system with heated phosphoric acid having a P.sub.2 O.sub.5 analysis in the range of about 28 to about 38% (e.g. 31%), then feeding phosphate rock to the system, preferably in a separate reaction vessel, while phosphoric acid is recycled from a fourth, filter feed vessel, until the solids content in said slurry is in the range of 25-35% (e.g. about 30%) while the sulfate content in the first vessel is maintained at a negative level (e.g. excess calcium ion) and at a positive level in the second, crystallizer vessel. When the solids content, calcium, and sulfate content are at the proper level (e.g. about 30% solids, -5 to -2% sulfate in the first vessel and +2 to +3% sulfate in the second vessel) the slurry is then transported to a filter and the phosphoric acid is separated from the calcium sulfate hemihydrate.

Start-up procedure in producing phosphoric acid by the hemihydrate

A system for the preparation of phosphoric acid from phosphate rock and sulfuric acid, includes in combination a first reaction vessel containing a first slurry comprising calcium sulfate hemihydrate, monocalcium phosphate and phosphoric acid, a second reaction vessel containing a second slurry comprising calcium sulfate hemihydrate, circulation means including a draft tube disposed centrally in each of said vessels and an agitator positioned axially in each of said vessels within said draft tube, a first conduit interconnecting said first and second reaction vessels for conducting said first slurry from said first reaction vessel to said second reaction vessel, a second conduit interconnecting said vessels for conducting said second slurry from said second reaction vessel to said first reaction vessel, an inlet pipe for introducing phosphate rock and phosphoric acid to said first reaction vessel, and wherein a vent is connected to said inlet pipe to permit escape of gases and, thus, increasing the rate of flow of said phosphate rock and phosphoric acid to said first reaction vessel.

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Riverside, CA, United States of America

F Michael Gragg