NETmix technology as ozone gas injection system: Assessment of the gas-liquid mass transfer

This work proposes an innovative high-intensity mixer based on the NETmix technology to promote the contact between ozone (O3) gas and water. The NETmix consists of a network of unit cells comprising mixing cylindrical chambers interconnected by prismatic channels. Its exclusive geometry generates successive contacting and splitting of flows, boosting mass transfer rates and rapidly developing an O3-enriched liquid stream. The gas -liquid mass transfer performance of NETmix was evaluated by measuring the volumetric mass transfer coefficient (kLa), standard oxygen transfer rate, standard oxygen transfer efficiency, and energy expenditure parameters. A co-current continuous flow condition was used to introduce a gas stream (consisting of either O3/oxygen (O2) or synthetic air) and a liquid stream (water), whereby it was varied the direction of co-current fluid flow (downwards or upwards) and the injected gas (QG) and liquid (QL) flowrates. The downward flow of gas and liquid streams enhanced the mass transfer phenomenon by at least 43 %. Moreover, the kLa values increased with QL and QG, reaching 2.46 s-1 at a low specific power consumption (25 kW m-3). The NETmix showed kLa values at least one order of magnitude larger than conventional contactors, maintaining a high-energy utilization efficiency (up to 19.4 kgO3 kWh-1).