Application of Computational Fluid Dynamics for Optimization of Grid Flocculation Tank

Abstract

Flocculation is a very important component of the overall suite of treatment processes. The need for a profound understanding and successful design/optimization of flocculation processes is important since the requirements for the removal of particulates have become increasingly stringent. The computational fluid dynamics (CFD) was used to design the flocculating tanks. The values of turbulent kinetic energy (k), turbulent dissipation rate (ε) and velocity gradient (G) were employed to evaluate the parameters of the flocculation tank using the realizable k − ε model. The best size of the grid in the front part of the tank was 80 mm × 80 mm. In this condition, the average value of k and ε were 0.00152 m2/s2 and 0.000570 m2/s3, respectively, and the percentage of G in the range of 70–100/s was 35.5%. For the middle part of the tank, the best size of the grid was 110 mm × 110 mm, with the average value of k and ε, as well as the percentage of G in the range of 40–60/s, were 0.00167 m2/s2, 0.000568 m2/s3 and 34.3%, respectively. In order to protect the flocs from being broken by stir, there was no grid in the terminal part of the tank. The optimized slice gap for both of the front part and the middle part of the tank were 600 mm.