Abstract
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.
Highlights
The attention to renewable energy sources, from topic of interest solicited by the necessary awareness towards sustainable development, is starting to be seen as an economic opportunity, embracing the triple paradigm of the properly-defined sustainability
An example is offered by the integrated system presented in [1] that makes use of waste frying oils, solid organic and algal biomass to produce biodiesel and energy while treating wastewater and flue gases as well as possibly
To simulate the hydrodynamic environment inside the riser, a physically-based mathematical model was built upon the Conservative Level Set Method (CLSM)
Summary
The attention to renewable energy sources, from topic of interest solicited by the necessary awareness towards sustainable development, is starting to be seen as an economic opportunity, embracing the triple paradigm of the properly-defined sustainability (economic, environmental, social). A sort of evolution of bubble columns, ALRs represent a class of pneumatic reactors capable of achieving good mixing conditions without high energy demand thanks to the prompting of a swirling motion of natural circulation due to density gradients. Due to these qualities, as well as the possibility of obtaining very fast photoperiods, ALRs display superior performances in terms of microalgae cultivation with respect to most other microalgae culture systems [2]. A precise understanding of the bubble flow regime is vital to improving the efficiency of the processes happening inside ALRs and the ability to opportunely manipulate the bubble flow would represent a major achievement for microalgae cultivation
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