Absorption by Reactive Sprays with Appreciable Liquid Phase Mass Transfer Resistance: The Washout of Methyl Iodide by Reactive Sprays

A study was made of the washout of organic iodides by reactive liquid sprays. Although the reactive additive used in this study was hydrazine, the results would be applicable to other additives. Falling drop absorption was calculated, assuming surface saturation and first order reaction rates, for stagnant and well mixed drops. For drops having diameters smaller than about 500 μm, and for reaction velocities less than 100 sec-1, the two models gave predicted removal rates which were similar. Computer evaluation of the infinite series solution to the absorption equation was carried out for a range of drop sizes, temperature, fall heights, and reaction velocities. Absorption by liquid wall films is an important part of the overall absorption for the spray systems described in this work. The penetration theory model of absorption into flowing films was used in this study to predict wall film absorption. The overall absorption model thus accounts for absorption by drops and wall film. The washout of methyl iodide by aqueous hydrazine sprays was measured in spray chambers approximately 4 ft in diameter by 10 ft tall. Measured washout half-times ranged from 8 minutes to several hours, depending on the spray rates, hydrazine concentrations, and temperatures. Collection of the drops and wall liquid permitted measurement of the relative importance of wall and drop absorption in these experiments. Based on the absorption model developed and the experimental results, the removal rate of methyl iodide in larger containment systems was predicted for a range of drop sizes, reaction velocities, temperatures, and vessel heights. (author)