Scaling Trend Simulation in Falling Film Evaporator Dealing with Saline Wastewater Based on Experimental Solid-Liquid Equilibrium in Ternary Systems Nacl-Cacl2-H2o

It is important to master firstly scaling mechanism to slow down scaling, which is one of the important problems faced by saline wastewater treatment with falling film evaporators. In this study, the equilibrium liquid phase and Jänecke dry salt index of NaCl-CaCl2 -H2O at 303.15 ~ 373.15 K were firstly determined, and the scaling trend of the falling film evaporation tube was investigated based on numerical simulations. The results showed that the ternary system was mesostable phase diagram belongs to a simple type, which contained a co-saturation point, two dissolution curves, an unsaturated zone, and three crystallization zones. Moreover, the lower the salt content of the wastewater, the faster the temperature rise of the liquid film in the evaporation tube and the faster the rate of evaporation. At the outlet, the maximum temperature of the four saline wastewaters was 377 K and the minimum value of the liquid volume fraction was 0.39. Comparing the data of wastewater with different salt contents (10% NaCl+9%, 10%, 11%, 12% CaCl2 ) and solid-liquid phase equilibrium experiments, the positions of crystallization during evaporation were obtained as 718 mm, 942 mm, 966 mm, and 1000 mm, respectively. All the data, especially the scaling sites of saline wastewater in the evaporation tube, can provide a basic theoretical basis for dealing with equipment scaling problems