Simulation of the rising of gas bubbles in a pilot-scale external loop airlift photobioreactor

Air-lift reactors offer an interesting option as a microalgae cultivation system, especially for biorefineries. To optimize this application, a precise description of the moving interfaces formed by the liquid and gas phase is critical. In this paper, a coupled Level Set Method (LSM) and finite difference method is used to simulate gas bubbles dynamics in a pilot-scale external loop air-lift photobioreactor in which microalgae are used to capture CO2 from flue gas and to treat wastewater. Numerical simulations are carried out on a rectangular domain representing the section on the vertical axis of the riser. The data employed were either acquired from previous experimental campaigns carried out in the ALR or found in the literature. The rise, shape dynamics and coalescence process of the bubbles of flue gas are studied. The issue of volume loss characteristic of standard LSM is dealt with the conservative level set method. Computation results show good correspondence with the experimental ones.