Physical and mathematical model of a settling tank with thin-layer modules

The presence of fine impurities in industrial water complicates the operation of fine water purification systems. To solve this problem, thin-layer settling tanks have become widespread in industry due to their high consumption characteristics. Depending on the application and the consumer, the maximum permissible concentrations of dispersed particles can vary in wide ranges. Optimizing the operation of a thin-layer tank requires conducting field experiments in laboratory and industrial installations. Mathematical modeling allows to reduce the number of experiments. The aim of the work is to develop a mathematical proxy model of a settling tank with thin-layer modules, which for the first time considers the influence of the concentration of coagulant and alkali on the particle size distribution, as well as salinity on the particle deposition rate. This model is based on simplified laws of conservation of mass and momentum in the hydraulic approximation. To study the effect of the parameters of the settling tank and reagents on the concentration of dispersed particles at the outlet, experiments were planned and conducted on a laboratory installation in a wide range of changes in these parameters. The values of the concentration of dispersed particles at the outlet at different angles of inclination of the plates, their quantity and concentrations of coagulant, alkali, and salt were obtained. The simulation results are compared with experiments, and their satisfactory agreement with each other is shown with an average error of 3%. Based on the sensitivity analysis, ranges of parameters of the settling tank and chemical reagents were determined, for which the mathematical model gives representative results. It was found that with an increase in the concentration of chemical reagents, the proportion of particles with sizes less than 100 μm in the stream decreases, which leads to an increase in the degree of water purification.