There are also salts and acidic gases in the exhaust gas; why is falling film absorption generally used to remove them?
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The exhaust gas also contains salts and acidic gases, which are generally removed through falling film absorption. Why can’t a condenser be used to condense these salts and acidic gases into a liquid form for removal?
Firstly, saline acidity is hydrogen chloride gas, and the liquefaction of this gas requires very low temperatures. Secondly, the so-called hydrochloric acid is actually an aqueous solution of hydrogen chloride; therefore, even when cooled, water must be absorbed in order to obtain hydrochloric acid. Finally, higher concentrations of hydrochloric acid will also volatilize hydrogen chloride gas at room temperature; therefore, a large amount of water is needed to dilute the liquid and maintain a low concentration of hydrochloric acid. Therefore, from a practical standpoint, it is not possible to liquefy hydrogen chloride gas in exhaust gases by cooling, as the cost would be very high. A feasible method is to dissolve hydrogen chloride gas in water vapor that has been condensed into water. However, due to the limited amount of water vapor, a salt acid solution with a high concentration is formed, and some hydrogen chloride gas still evaporates into the gas phase, resulting in poor removal efficiency; therefore, simple cooling alone is not very effective. The absorption method is simple and highly operational. I hope this helps you.
If the goal is to recycle hydrogen chloride gas of high quality, it is best to use low-temperature chilled water for cooling in order to remove the water and obtain hydrogen chloride gas. However, if the purpose is merely exhaust gas treatment, an absorption method is a good approach; whether to use falling film absorption or a tower-type circulation system, I believe both methods will work, with the difference lying only in the format used. I hope this helps!
Thank you, Deputy Super Editor of the Salt Seller Section! There’s also satellite 411:victory:
If the exhaust gas contains HCl at a concentration of 600 mg/m3, with an exhaust gas flow rate of 50,000 cubic meters per hour, should alkaline absorption be used via water spraying or the falling film absorption method?