Research On Numerical Simulation Of The Vertical-axis Mechanical Flocculation

Mechanical flocculation is a common equipment of flocculation treatment, it can better adapt to the water changes. Its application is limited because of the mechanical equipment and cost. At present, there are many insufficient on its research and understanding. To optimize the design by studying the hydraulic characteristics of mechanical flocculation, not only can effectively improve the effect of flocculation but also can save investment.In this thesis, the vertical-axis mechanical flocculation based on engineering project was used as the simulate object. The design flows are 6000m3/d and 12500m3/d, respectively. To optimize the mechanical flocculation on the different hydraulic conditions such as inlet size, the size and number of the paddle blades, water way and rotation direction of impeller, turbulent kinetic energy k, turbulent kinetic energy dissipation rate ε and vortex velocity gradient G’are used as the evaluation index based on the numerical simulation. And find out the best flocculation effect, and thus enhanced the water quality of effluent and ensure the safety of drinking water. The results show that:1. The extent of flow disturbance within the first cell reaction of mechanical flocculation is mainly affected by the changes of the inlet size, but the subsequent reactions cell is almost unaffected. Reduce the inlet size appropriately will effectively increase the degree of collision of flocculation particles within the first cell reaction, thereby increasing flocculation of the overall reaction apparatus.2. In the same conditions of paddling area, rotational speed and rotating radius, the frequency of particles collisions and stirring power in the mechanical flocculation tank is impacted no difference with the changes of the three factors including width, length and number of paddle blades. But turbulence intensity and collision probability of particles in the flocculation tank are impacted with different degree, thus leading to significant differences of the final flocculation effect. The width of paddle blade has the greatest effect on the effect of flocculation, followed by the number of paddle blades, and the length of paddle blade has the least influence.3. The flocculation effect of mechanical flocculation equipted with the upper water and impeller of clockwise rotating is better than other ways. In this way, the water turbulence level of the first reaction of flocculation pool is more intense than other ways, while the flow turbulence of the third reaction cell is on the same level. So that flocculation particles collided sufficiently of the first reaction of flocculation pool, and it will effectively flocculate and aggregate, but not easily crush in the subsequent reaction cell, eventually enhance the flocculation effect of the mechanical flocculation.