(21c) Effects of Initial Liquid Height on Gas Distribution in Major Column Diameter Center-Rising Airlift Reactor

The effects of the initial liquid height, H₀, on the total gas holdup, local gas holdup, liquid circulation velocity, and bubble size were investigated in the Ф1.2m×5.2m pilot-scale center-rising airlift reactor (CR_ALR) with the air-water system. The flow field in the CR_ALR was divided according to the local gas holdup. The results indicate that the increase of H₀ can prolong the time of shear force of Rayleigh-Taylor instability effect on the gas core in the plume regime and increase the number of small bubbles generated by the gas core breakup could increase the local gas holdup. Meanwhile, the bubbles in the plume regime feature rotation-diffusion to the inner wall of the draft tube by transverse lift force and concentration gradient, which makes the radial distribution of bubbles more homogeneous in the riser. The increase of H₀ reduces the turbulence intensity of the liquid phase and increases the probability of bubbles coalescence above the draft tube, which increases the resistance of bubbles entering the downcomer and decreases the local gas holdup. Therefore, H₀ has dual effects on total gas holdup and fluid circulation velocity. The experimental results also imply that appropriately increasing the damping of bubble motion can improve the problem of uneven bubble distribution caused by equipment scale-up.