Characterization and hydrodynamics of a novel helix airlift reactor

A novel pilot scale helix airlift reactor (helix-ALR) consisting of a regular draft tube airlift reactor (A_d/A_r = 1.17) and helical tubes attached to riser or downcomer, or both, was studied in different configurations with varying air inputs. The helical tubes acted as helical flow promoters (HFP) and additional gas spargers. The aim was to investigate the performance of these HFP-gas spargers and study their effect on oxygen transfer in ALR. HFP-gas spargers improved the volumetric oxygen transfer coefficients of the ALR radically even without additional energy, reaching up to 3 times higher k_La-values (over 0.1 l/s) when compared to regular ALR. Small bubbles from the HFP-gas spargers played an important role in the oxygen transfer, and downcomer helix had greater effect in general on k_La and hydrodynamics than riser helix. Empirical correlations regarding mass transfer and gas holdups were formed. When compared to stirred tank reactors (STR) the required specific power input of the helix-ALR for a level of k_La 0.1 l/s was around 0.34 kW/m³ while for STR 2.0 kW/m³, suggesting that the helix-ALR is very energy efficient. HFP-gas spargers can significantly improve the performance of ALRs regarding oxygen transfer, lower their operating costs and improve the total energy economy.