Feed system for phosphoric acid production with decreased foaming

A system for the preparation of phosphoric acid from phosphate rock and sulfuric acid, including in combination:

• (a) a first reaction vessel containing a first slurry comprising calcium sulfate hemihydrate, monocalcium phosphate and phosphoric acid,
• (b) a second reaction vessel containing a second slurry comprising calcium sulfate hemihydrate, monocalcium phosphate, sulfate ions and phosphoric acid,
• (c) means including a draft tube means in each of said vessels for maintaining a continuous circulation of the slurry therein through said draft tube means at a rate of at least 50% of the volume of the slurry in said vessel per minute said draft tube means being disposed centrally in each of said vessels and an agitator means positioned axially in each of said vessels within said draft tube means, whereby on actuation of said agitator means the slurry in each of said vessels will flow from the bottom portion of said draft tube means up through the draft tube means and on exiting the top of the draft tube means, the slurry will flow downwardly in the space between said draft tube means and the inner wall of the vessel,
• (d) a first conduit means interconnecting said first and second reaction vessels for conducting said first slurry from said first reaction vessel to said second reaction vessel,
• (e) a second conduit means interconnecting said vessels for conducting said second slurry from said second reaction vessel to said first reaction vessel,
• (f) means for providing a reduced pressure in said second reaction vessel to effect temperature control in said second reaction vessel by evaporation, means to circulate slurry between said second reaction vessel and said first reaction vessel at a sufficient rate so as to add desired sulfate values and phosphoric acid values to and to effect temperature control in said first reaction vessel, and means to form a vacuum seal between said first and second reaction vessels,
• (g) an inlet pipe means for introducing a mixture of phosphate rock and phosphoric acid to said first reaction vessel,
• (h) means for introducing sulfuric acid to said second reaction vessel,
• (i) means for withdrawing a slurry containing phosphoric acid and calcium sulfate hemihydrate from said second reaction vessel, and
• (j) a vent means connected to said inlet pipe to permit escape of gases and, thus, increase the rate of flow of said mixture of phosphoric rock and phosphoric acid to said first reaction vessel.