Key Takeaways & Executive Findings
- •• • For both HEDT and WH impellers, the critical Froude number (Fr) decreased significantly with increasing gas flow number (FlG), indicating that higher gas flow rates facilitate complete dispersion at lower impeller speeds, which can reduce energy consumption in industrial operations. • • At L/D = 0.75, the optimal impeller installation height, overall gas holdup was maximized while power consumption was minimized, achieving a balance between mass transfer efficiency and energy savings. • • The HEDT impeller exhibited a higher relative power demand (RPD) than the WH impeller under identical conditions, meaning its agitation power was less affected by gas introduction, making it more suitable for high-speed gas-liquid dispersion operations. • • The porous tube sparger improved bubble distribution uniformity and gas-liquid mixing efficiency, leading to enhanced mass transfer rates compared to conventional spargers, as evidenced by higher gas holdup at equivalent power inputs.
Abstract
Gas-liquid stirred tanks are widely used in oxidation, hydrogenation, and other chemical processes, where the gas dispersion state directly affects production efficiency. This study systematically investigated the effects of impeller type, impeller installation height, and rotational speed on gas-liquid dispersion in a stirred tank equipped with a porous tube sparger. Two typical impellers, a wide hydrofoil (WH) and a half-elliptical disk turbine (HEDT), were tested at various installation heights (L/D ratios) and gassing rates. The critical rotational speed for complete gas dispersion, agitation power consumption, and overall gas holdup were measured. Results showed that for both impellers, the critical Froude number (Fr) decreased significantly with increasing gas flow number (FlG). Under the same gassing rate, the HEDT impeller generally required a higher critical Fr and greater agitation power for complete dispersion compared to the WH impeller. Relative power demand (RPD) decreased as FlG increased, with a more pronounced decline at higher L/D ratios. At different impeller positions, the RPD of the HEDT impeller was higher than that of the WH impeller, indicating that the HEDT impeller's power was less affected by gas. Notably, the impeller installation height significantly influenced gas holdup and power consumption. When L/D = 0.75, higher gas holdup and lower power consumption were observed. This work provides crucial theoretical and data support for optimizing the design of gas-liquid stirred tanks with gas sparging, offering clear engineering value for enhancing mass transfer efficiency and energy-saving operation in chemical processes.
1. Introduction
Gas-liquid stirred tanks are pivotal in chemical processes such as oxidation and hydrogenation, where the efficiency of gas dispersion directly dictates mass transfer rates and overall productivity. Conventional spargers often suffer from poor bubble distribution and high energy penalties, limiting process intensification. The porous tube sparger offers a distributed gas inlet that promises more uniform bubble dispersion, yet its interaction with impeller design and placement remains inadequately characterized.
This study addresses the bottleneck by systematically evaluating two impeller types—wide hydrofoil (WH) and half-elliptical disk turbine (HEDT)—across varying installation heights and operating speeds within a porous-tube-equipped stirred tank. By quantifying critical dispersion speeds, power consumption, and gas holdup, the research identifies optimal configurations that maximize mass transfer while minimizing energy input, providing actionable data for reactor design and scale-up.
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SUN Ruiyu, XIE Ping, CAI Ziqi, LIU Xinwei, GAO Zhengming, BAO Yuyun (2026). Gas-liquid dispersion characteristics in a stirred tank equipped with porous aeration tube. The Chinese Journal of Process Engineering. https://doi.org/10.12034/j.issn.1009-606X.225213
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Frequently Asked Questions
What is the optimal impeller installation height (L/D) for achieving high gas holdup with low power consumption?
The study found that L/D = 0.75 yields the highest overall gas holdup and lowest power consumption for both HEDT and WH impellers, making it the recommended installation height for energy-efficient gas-liquid dispersion.
How does the critical Froude number vary with gas flow number for the tested impellers?
For both HEDT and WH impellers, the critical Froude number (Fr) decreases significantly as the gas flow number (FlG) increases, indicating that higher gas flow rates reduce the impeller speed required for complete dispersion, which can lower energy demands.
Which impeller type is more suitable for high-speed gas-liquid dispersion operations?
The HEDT impeller is more suitable for high-speed operations because it exhibits a higher relative power demand (RPD) compared to the WH impeller, meaning its power draw is less affected by gas introduction, ensuring stable performance at elevated speeds.
What are the advantages of using a porous tube sparger over conventional spargers?
The porous tube sparger provides distributed gas inlet, leading to more uniform bubble dispersion and improved gas-liquid mixing efficiency. This results in higher gas holdup at equivalent power inputs, enhancing mass transfer rates without additional energy costs.
How does the relative power demand (RPD) change with gas flow number and impeller position?
RPD decreases as FlG increases for both impellers, with a more pronounced decline at higher L/D ratios. At different impeller positions, the HEDT impeller consistently shows higher RPD than the WH impeller, indicating its power is less sensitive to gas loading.
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