Gas‐Phase Residence Time Distribution Characteristics in a Gas–Liquid Stirred Tank With Multiple Impellers

Residence time distribution (RTD) is a standard tool for characterizing the hydrodynamic performance of stirred tanks. In this work, gas‐phase RTD was experimentally investigated in a gas–liquid stirred tank equipped with six multiple‐impeller configurations using four impeller types (WH, HEDT, CBY, and PDT). The effects of impeller speed, gas flow rate, bottom impeller type, impeller flow shape (up‐pumping vs. down‐pumping), and impeller spacing on the mean gas residence time were systematically evaluated. Empirical correlations were developed to predict the average gas residence time for each impeller combination ( R 2 > 0.99), and the gas flow shape was quantitatively analyzed using a tanks‐in‐series model. The results show that the mean gas residence time roughly ranges from 20 to 226 s under the experimental conditions investigated, increasing with impeller speed and decreasing with gas flow rate. Among all configurations tested, the PDT + 2WH D combination exhibits the longest average gas residence time, indicating the strongest gas‐retention capability among the tested configurations. RTD analysis indicates that the overall gas flow shape can be described by a tanks‐in‐series model with equivalent tank number n between 1 and 3, with gas behavior dominated by mixed‐flow characteristics. These findings provide practical guidance for impeller selection, reactor design, and scale‐up of gas–liquid stirred tanks.