Chaotic mixing process of fly ash in acid leaching tank intensified by rigid-flexible impeller

In the traditional fly ash aluminizing process, the acid immersion stirring tank adopts a rigid stirring paddle. Due to the limited pumping capacity of rigid impellers, some problems such as settlement of solid particles, deficiently of chaotic, and low efficiency of mixing in this process often occur in solid-liquid mixing processes. Thus, the rigid-flexible impeller was adopted to enhance solid-liquid chaotic mixing behavior in acid leaching process. In a fly ash-water system with a solids concentration of 30%, the chaotic mixing characteristics and energy dissipation were investigated in STRs equipped with rigid-flexible impeller. Torque sensor was employed to collect the torque time series signal. The largest Lyapunov exponents and the multi-scale entropy were compiled and calculated by Matlab to indicate the degree of chaotic mixing based on the torque time series signal. Meanwhile, the power consumption per unit volume was used to characterize the stirred reactor power characteristics. The effects of impeller types, rotation speed, flexible piece width/length, and impeller off-bottom clearance on chaotic mixing behavior were taken into consideration in the solid-liquid mixing processes. The results showed that the rigid-flexible impeller could effectively promote the chaotic mixing and reduce the accumulation of solid particles at the bottom of STRs in the fly ash-water system. Largest Lyapunov exponents of the system reached the maximum value of 0.0645 and multi-scale entropy was bigger than that of other conditions at the rotation speed of 120 r/min, the off-bottom clearance of T/4, the flexible piece length of 1.2H1 and width of D/8. The power consumption increases exponentially with the increase of rotation speed. © All Right Reserved.