Phosphoric Acid Concentration

Vacuum-evaporation units’ capacity (VEU) for WPA concentration, developed by JSC NIUIF:

  • 100 thousand tons of Р2О5 per year with obtaining 52÷54% Р2О5 WPA when concentrating dihydrate WPA (27÷28% Р2О5);
  • 200÷240 thousand tons of Р2О5 per year when concentrating hemihydrate WPA (35÷37% Р2О5).

VEU capacity per evaporated water is 25÷30 t/h.

Operating time is more than 300 days per year subject to the scheduled service washes.

Main design features:

  • open type heating tank with submersible elements made of stainless steel;
  • two vacuum-evaporators of the “submerged” type (operating acid level is ensured by maintaining a vacuum in the system);
  • the circulation of acid in the heating tank is ensured by high-performance circulation feed pumps to the vacuum evaporator;
  • two-stage scrubber system, including sprayed gas duct at the first stage and high-speed foam scrubber at the second stage, with the possibility of producing fluorosilicic acid (18÷22% H2SiF6).

Two VEUs are successfully operating in the hemihydrate production of WPA at JSC Apatit, Cherepovets.


The flowsheet with two vacuum-evaporators of the “submerged” type was used during the revamp of three VEU dihydrate WPA production (PhosAgro-Cherepovets). Modern carbon fiber-reinforced plastic materials were used in the manufacture of new vacuum-evaporators, a circulation scheme for washing heating elements and vacuum-evaporators with nitric acid was introduced. This revamp made it possible to increase production capacity by 15% of the design capacity.

In alternative to VEU with heating tank, it is possible to make VEU with shell-and-tube graphite heat exchangers. The concentration process flowsheet with shell-and-tube heat exchangers with a capacity of 200÷240 thousand tons of P2O5 per year with hemihydrate WPA concentration (35÷37% P2O5) is shown in Figure 1.

Figure 1. Сoncentration unit flowsheet