Packed bed absorption of dilute iodine vapor from air to aqueous caustic soda: mass transport modelling and validation

This study investigates the removal of low-concentration iodine vapor from air using aqueous sodium hydroxide (NaOH) in a laboratory-scale packed column, employing both experimental and modelling approaches. Experiments were conducted to determine the overall volumetric mass transfer coefficient (KGaeff) and assess the influence of gas flow rate, liquid flow rate, NaOH concentration, and packing type. Results showed that KGaeff and the effective interfacial area were strongly dependent on the gas-phase Reynolds number (ReG), while liquid-phase parameters had minimal impact under most conditions. However, at high gas Reynolds numbers and low NaOH concentrations, the liquid flow rate progressively affected KGaeff, indicating a transition in the controlling mass transfer regime. A correlation for KGaeff was developed and integrated into a one-dimensional finite difference solver to simulate the absorption process. The predicted outlet iodine concentrations agreed with experimental results, with deviations within 10%. Phase resistance analysis revealed a shift from gas-phase-controlled to mixed gas-liquid controlled mass transfer at ReG ≥ 25 and [OH]≤ 0.25 M. Additionally, porosity was found to inversely affect KGaeff, underscoring the importance of selecting packing materials that minimize gas-phase resistance. These findings highlight the critical role of gas-phase hydrodynamics and hydroxide concentration in optimizing iodine removal. The insights gained are valuable for the design and operation of caustic scrubbers intended to control radioactive iodine emissions in nuclear and radiochemical facilities.本研究采用实验与建模相结合的方法，探究了实验室规模填料塔内以氢氧化钠水溶液（NaOH）脱除空气中低浓度碘蒸气的过程。本实验通过调控气体流速、液体流速、NaOH浓度及填料类型等参数，测定了总容积传质系数（KGaeff），并评估了各参数对传质过程的影响。实验结果表明，KGaeff与有效界面积主要受气相雷诺数（ReG）影响，多数工况下液相参数对其影响微弱。但在高气相雷诺数与低NaOH浓度工况下，液体流速对KGaeff的影响逐渐凸显，表明传质控制机制发生了转变。本研究构建了KGaeff的关联式，并将其嵌入一维有限差分解算器以模拟该吸收过程。模拟得到的出口碘蒸气浓度与实验结果吻合良好，相对偏差不超过10%。相阻力分析显示，当ReG≥25且氢氧根浓度≤0.25 M时，传质过程从气相控制转变为气液混合控制。此外，研究发现填料孔隙率与KGaeff呈负相关，这凸显了选用可降低气相阻力的填料的重要性。上述研究结果阐明了气相流体力学与氢氧根浓度在优化碘蒸气脱除效果中的关键作用。本研究所得结论可为核设施与放射化学设施中用于控制放射性碘排放的碱性洗涤塔的设计与运行提供重要参考。