Study on Side-entering Agitator Flow Field Simulation in Large Scale Biogas Digester

Abstract

Based on the CFD software Fluent, the multi-reference system method, the RNG κ-ε turbulence model and the pressure-velocity coupled SIMPLEC algorithm are applied to simulate the flow field of a single side-entering agitator in a large biogas digester. And the impact of different installation angle, agitator-to-bottom height, agitating speed and agitator diameter on the agitating power, the effective area percentage and the effective power ratio are analyzed. The results show that: 1) when the agitating speed is more than 450r/min and the agitating diameter is more than 750 mm, the effective area percentage reaches the maximum value; 2) when the horizontal angle is 30 °, the agitating effect is the best; 3) when the vertical angle is inclined to the bottom and the agitator-to-bottom height is less than 8 m, it is helpful to prevent the sediment from appearing. The results of numerical simulation provide a theoretical basis for the design to optimize the agitator.