Automatic control system for phosphoric acid plant

An apparatus for automatically controlling a phosphoric acid plant to a predetermined operating point, comprising:

• means for measuring actual excess sulfate in a reactor;
• means for integrating a sulfuric acid feed rate during a time period by frequently sampling the sulfuric acid feed rate and calculating a total amount of sulfuric acid added to the reactor during the time period;
• means for integrating a phosphate rock feed rate and calculating a total amount of phosphate rock added to the reactor during the time period;
• means for calculating a new set ratio from the total amounts of phosphate rock and sulfuric acid added to the reactor over the time period, and the actual excess sulfate, wherein the set ratio is the ratio of sulfuric acid demand per unit of phosphate rock which has been calculated to partially control said plant to the predetermined operating point;
• means for calculating a sulfuric acid set point, and a phosphate rock set point;
• and
• means for adjusting one of said feed rates to be approximately equal to its respective set point to approximately achieve said set ratio.

An apparatus for automatically controlling a phosphoric acid plant to have a predetermined value of excess sulfate, said apparatus comprising:

• means for measuring an excess sulfate in a reactor;
• means for controlling a sulfuric acid feed rate to the reactor;
• means for controlling a phosphate rock mass flow rate to the reactor;
• and
• programmable means for:
• (a) calculating a total amount of sulfuric acid added to the reactor over a time period;
• (b) calculating a total amount of rock added to the reactor over the time period;
• (c) calculating a new sulfuric acid feed rate to cause excess sulfate resulting from reaction of incoming acid and phosphate rock to have the predetermined value of excess sulfate;
• (d) calculating a number of gallons of sulfuric acid to be added to the reactor or subtract from the reactor to correct the excess sulfate of material already in the reactor;
• and
• (e) generating control signals to cause said sulfuric acid feed rate to change and causing said number of gallons to be added to or subtract from the reactor using a pulse of said acid which decays to said new sulfuric acid feed rate.

A method for automatically controlling a phosphoric acid plant to maximize recovery of phosphoric acid, said method comprising the steps of:

• determining an amount of sulfuric acid added to a reactor over a time period;
• determining an amount of phosphate rock added to the reactor over said time period;
• and
• determining a new sulfuric acid feed rate wherein a reaction of incoming rock and sulfuric acid fed in at the new sulfuric acid feed rate results in an excess sulfate approximately equal to a predetermined value of excess sulfate;
• and
• adjusting said sulfuric acid feed rate whereby the phosphoric acid recovery is maximized at the predetermined value of excess sulfate.

A method for automatically controlling a phosphoric acid plant to have a predetermined value of excess sulfate in a reactor, said method comprising the steps of:

• determining an actual rock mass flow rate into the reactor;
• determining an actual sulfuric acid feed rate into the reactor;
• and
• adjusting either said actual rock mass flow rate or said actual sulfuric acid feed rate to cause the reactor to have the predetermined value of excess sulfate.

A method for automatically controlling a phosphoric acid plant to maximum efficiency of a reactor for converting phosphate rock to phosphoric acid, said method comprising the steps of:

• measuring an excess sulfate in a reactor;
• controlling a sulfuric acid feed rate to the reactor;
• controlling a phosphate rock mass flow rate to the reactor;
• and
• calculating a total amount of sulfuric acid added to the reactor over a time period;
• calculating a total amount of rock added to the reactor over the time period;
• calculating a new sulfuric acid feed rate to cause excess sulfate resulting from reaction of incoming acid and phosphate rock to have a predetermined value of excess sulfate, wherein said predetermined value of excess sulfate causes the phosphoric acid plant to operate at the maximum efficiency;
• calculating a number of gallons of sulfuric acid to be added to the reactor to correct the excess sulfate of material already in the reactor;
• and
• generating control signals to cause said sulfuric acid feed rate to change and causing said number of gallons to be added using a pulse of said acid which decays to said new sulfuric acid feed rate.