Apparatus useful for wet process phosphoric acid production

Apparatus useful for the preparation of phosphoric acid from phosphate rock and sulfuric acid, comprising in combination:

• (a) a first reaction vessel or series of first reaction vessels having a slurry inlet means and suitable for containing a reaction mixture comprising a first slurry comprising calcium sulfate, monocalcium phosphate and phosphoric acid;
• (b) means including a draft tube means in said first reaction vessel or in each vessel in said series of first reaction 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 said vessel or series of vessels and an agitator means within said draft tube means, whereby on actuation of said agitator means, the slurry in said vessel will flow through the interior of the draft tube means and, on exiting the draft tube means, the slurry will flow in the space between said draft tube means and the inner wall of the vessel;
• (c) a second reaction vessel or series of second reaction vessels suitable for containing a second slurry comprising calcium sulfate, monocalcium phosphate, sulfuric acid and phosphoric acid;
• (d) means including a draft tube means in said second reaction vessel or in each vessel in said series of second reaction 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 said vessel or series of vessels and an agitator means within said draft tube means, whereby on actuation of said agitator means the slurry in said vessel will flow through the interior of said draft tube means and on exiting the draft tube means, the slurry will flow in the space between said draft tube means and the inner wall of the vessel;
• (e) a first conduit means inter-connecting said first and second reaction vessels or said series of first and second reaction vessels for conducting said first slurry from said first reaction vessel or series of first reaction vessels to said second reaction vessel or series of second reaction vessels;
• (f) a second conduit means interconnecting said first and second reaction vessels or series of first and second reaction vessels for conducting said second slurry from said second reaction vessel or series of second reaction vessels to said first reaction vessel or series of first reaction vessels;
• and
• (g) means for providing reduced pressure in said second reaction vessel or at least one vessel in a series of said second reaction vessels whereby temperature control can be effected in said second reaction vessel or series of second reaction vessels by evaporation, means to circulate slurry between said second reaction vessel, or series of second reaction vessels 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 or series of vessels;
• (h) inlet means suitable for introducing phosphate rock and phosphoric acid to said first reaction vessel or at least one vessel in a series of said first reaction vessels, said inlet means having a discharge means to the interior of the draft tube means in said first reaction vessel or at least one said vessel in a series of said first reaction vessels;
• (i) means adapted for introducing sulfuric acid to said second reaction vessel or at least one vessel in a series of said second reaction vessels;
• and;
• (j) means suitable for withdrawing slurry containing phosphoric acid and calcium sulfate from said second reaction vessel or at least one vessel in a series of said second reaction vessels.