Study on Multivariate Salt Phase Equilibrium Relationship of High Salt Wastewater Under the Influence of Organic Impurities and Fouling Law in Evaporation Process

Abstract

The small amount of organic impurities in the pre-treated saline wastewater will affect the original solubility of the saline wastewater, which is one of the key issues that restrict the evaporation of saline wastewater with near-zero discharge under the working condition. We have investigated the solid-liquid phase equilibrium relationship under typical organic impurities and the prediction study of liquid film dynamic characteristics and fouling sites in falling film evaporation tubes with different parameters. Results show the ternary system under the influence of organic impurities conforms to a simple phase diagram, and the solubility of this system increases with increasing temperature. The solubility of MgCl2 was more affected by temperature and increased by 1.38 % at 373.15 K. Simulations were performed to study the fouling sites at different salt concentrations, inlet temperatures and velocities. It was found higher salt concentration, higher inlet temperature, and lower inlet velocity resulted in a shift of the fouling sites (326mm, 212mm, 396mm). In this paper, a creative study of saline wastewater in the presence of organic impurities under different inlet conditions has been carried out. On top of this, the phase equilibrium data were combined to derive their fouling sites in the evaporator tubes. This study provides a theoretical basis for rational control of salt scaling in the evaporation process of coal chemical industry. It is important to ensure the efficient operation of the evaporator, realize the recycling of inorganic salt products, and ultimately achieve the goal of "near-zero discharge".

Keywords: Organic impurities, Phase equilibrium, Falling-film evaporation, Fouling site