Abstract: Thermodynamic analysis of ammonium phosphate polluted droplets formation in the tail gas discharged from a 600 (kt/a) diammonium phosphate (DAP) production line was made. A unique technique was developed to make a full use of the limited driving force for heat transfer by integrating the processes of partial condensation of tail gas with falling film evaporation of raw phosphoric acid. The feasibility was demonstrated by the pilot experiments. Phosphate acid concentration (P₂O₅%) was in the range of 21.1%—41.7% and water content in the tail gas was reduced to below 0.065 kg H₂O/(kg air)。The influence of phosphate acid falling film Re and subcooling fall film on evaporation of phosphate acid falling film was studied by spot experiment. It displayed the possibility of phosphoric acid concentration at a temperature below 55℃. The experimental results were valuable for phosphoric acid concentration.