Phosphoric Acid in the process of filtration
B- PROCESS Phosphate Rock handling
Phosphate Rock is imported by ship from countries such as Jordan, Tunisia, Algeria and Morocco, to RPC Jetty and transferred to the storage nearby the plant, by belt conveyors.
Phosphate Rock is transferred from storage to the ungrounded silo through elevators and belt conveyor, which after grinding by the mill is transferred to ground silo. The grinded rock is fed to the reaction (attack) tank by means of belt weigh feeder.
In the reaction stage, ground phosphate rock is fed to the attack tank, plus concentrated sulfuric acid supplied by RPC. The reaction between sulfuric acid and phosphate rock results in production of Phosphoric Acid and gypsum mixture in the form of slurry. The slurry then enters into the digestion tanks and remains there for a time. Due to this retention time the crystallization of gypsum and fluosili- cates are completed and crystals begin to grow, so that in the filtration process
it could be separated from Phosphoric Acid more easily.
Mixture of Phosphoric Acid and gypsum enters from digestion tanks by pump to the rotary filter, where dilute phosphoric acid is separated from gypsum. Dilute Phosphoric Acid is transferred to storage tank, and, gypsum is collected in a tank after washing and transferred to sea by means of pumps.
Dilute Phosphoric Acid (26~28%) is transferred to concentration section from storage tank by pump. Acid enters acid heater in which it will be warmed up by steam, and therefrom enters the evaporator.
Acid is circulated by pump through acid heater and evaporator. Vacuum is maintained inside evaporator vessel by vacuum pumps, from the top of evaporator. By the effect of heating and vacuuming, part of the water in dilute Phosphoric Acid is evaporated and concentrated acid (about 54%) is extracted from the top level of acid solution in the evaporator, and delivered to the acid product storage tank.
The extracted vapors from evaporator are washed in droplet separators, precondensers and condensers before leaving the plant.
All fumes emitted from attack and digestion tanks, as well as out of filtration area are collected by means of fan and ducts and washed in the scrubber by water sprayers.
Wash waters re-enters into the attack tank and clean air is drawn from the scrubber by a fan and discharged to atmosphere.