Simulations of aluminum dosage and H2O-H2 flow in a pre-pilot twelve-cell electrocoagulation stack

Abstract

This paper investigates the aluminum dosage generation and H2O-H2 flow simulations in a pre-pilot twelve-cell stack electrocoagulation (EC) reactor in continuous operation mode. Each cell contains two aluminum plate electrodes. The electrochemical reactor is open to the atmosphere at the top to facilitate the H2 release produced at the cathodes, while aluminum oxidation occurs at the anodes. The two-phase (H2O-H2) flow simulations were performed by solving the Navier-Stokes (NS) equations for the continuous (H2O) phase and the bubbly flow model for the dispersed (H2) phase. Since H2 formation is promoted at the cathode due to H2O reduction, the momentum and Laplace's equations were simultaneously solved. The aluminum dosage calculations were attained by solving the diffusion-convection equation. The influence of volumetric inflow rate (8.3 ≤ Q ≤ 33.3 cm3 s−1) and applied current density (4 ≤ j ≤ 8 mA cm−2) on the coagulant dosage, current distribution, and H2O-H2 flow dispersion was systematically examined. The H2 volume fraction showed a typical bubble curtain profile close to the cathode surface. Homogeneous current distribution along the electrodes was obtained due to the well-engineering cell design, guaranteeing even wear of the sacrificial electrodes. There was an excellent agreement between the experimental and theoretical data for residence time distribution (RTD) curves and aluminum dosage generation.