Seeking guidance from experts on theoretical knowledge
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Generally, when the temperature difference between the temperature of the gas entering the absorption tower and the temperature of the acid exceeds 100°C (or 120°C), acid mist is likely to be generated, causing the exhaust gases to emit white smoke. We generally call it the cold shock effect. However, when the sulfuric acid concentration is 98.3% or higher and the temperature is above 25°C, there is no water vapor present above the surface of the sulfuric acid. How can we explain the phenomenon of excessive acid mist resulting from a large difference between the acidity level and the temperature?
The last edit to this post was made by Yuanlai Shi on 2015-10-29 at 17:58. My own explanation is as follows: From a physical-chemical perspective, taking an acid concentration of around 98.3% as an example, when the temperature of the gas entering the tower is too high, the partial pressures of sulfuric acid and sulfur trioxide on the surface of the sulfuric acid increase; in some cases, the partial pressure of water vapor may also rise. Therefore, generally speaking, when the temperature difference between the acid and the ambient temperature is too large, raising the acid temperature not only fails to reduce acid mist but also hinders absorption. But this explanation overlooks one issue: the rate of evaporation of a liquid is directly proportional to the temperature difference between the liquid and its surrounding environment, in accordance with Newton’s law of cooling. Can it be said that when the temperature difference between the acid temperature in the tower and the ambient temperature is large, a large amount of acid mist is generated at the bottom of the acid tower due to the rapid evaporation of sulfuric acid; increasing the acid temperature simply means sacrificing a slight amount of absorption efficiency in order to reduce the temperature difference between the gas and the liquid, thereby reducing the formation of acid mist inside the tower. I said that to others, and I have always doubted my own misconception, because Newton’s law of cooling isn’t that reliable. Seeking advice from experts! One more thing: this is only discussed in the context of a single absorption tower.
This process is called high-temperature absorption; aside from not easily producing acid mist, it is beneficial for conversion, thermal balance, and improving thermal efficiency. Please feel free to correct me if I’m wrong
This post was last edited by Yuanlai Shiyou on 2015-10-30 at 19:58. Thank you, I’ve found the answer. Thank you, the person above
Thank you all for your advice; I’ve found the answer. I recently read some books and think it’s necessary to explain it from the perspective of the mechanism behind acid fog formation. I haven’t studied * for a long time; I’m asking such a simple question, hoping it won’t embarrass anyone.
There is an article online. “The Issue of White Smoke from Sulfuric Acid Exhaust” explains this problem clearly.
I just read the article on the white smoke issue with sulfuric acid exhaust; thank you. I think maybe I didn’t express myself clearly. I’m not sure if this phrasing makes it clearer: Why does a large temperature difference between the acid and the temperature of the gas entering the tower lead to the formation of acid mist, or why is acid mist more likely to form inside the tower? At least, that’s what I think now: just like in purification processes, the main reason is that a sudden drop in temperature or lower temperatures create conditions favorable for the formation and growth of acid mist, which then forms inside the tower. Regarding the phenomena that may occur due to the formation of acid mist inside the tower: in severe cases, this can lead to an increase in condensed acid during the conversion process, as well as higher levels of exhaust gases ； Severe secondary combustion can result in very poor exhaust conditions, with white smoke being emitted.