What is the principle of acidic water stripping?

It works on a principle similar to that of a deaerator, except that one is used for deoxygenation while the other is used to remove acidic gases.

Acidic water is an aqueous solution containing weakly volatile electrolytes such as H2S, NH3, and CO2. In water, the aforementioned components exist in the form of ammonium salts such as NH3HS, (NH3)2CO3, and NH3HCO3. These salts of weak acids and weak bases ionize in water and simultaneously undergo hydrolysis to produce H2S, NH3, and CO2 molecules. In addition to being in an ionization equilibrium with ions, these molecules are also in equilibrium with those in the gas phase. This system is a complex one in which chemical equilibrium, ionization equilibrium, and phase equilibrium coexist. Therefore, controlling the appropriate conditions for chemistry, ionization, and phase equilibrium is key to treating acidic water and selecting suitable operating conditions. Since both ionization and hydrolysis are reversible processes, various substances exist in the liquid phase in both ionic and molecular forms. Ions cannot pass from the liquid phase into the gas phase; hence it is referred to as a \"fixed state\"” ； Molecules can move from the liquid phase to the gas phase, hence it is called the \"free state\". The amounts of various substances in ionic and molecular form in water are related to the operating temperature, operating pressure, and their concentrations in water. Based on the properties of the H2S, NH3, CO2, and H2O system, the hydrolysis reaction constant KH for compounds such as NH3HS in water increases as temperature rises; therefore, the temperature in the stripping tower should be above 110°C. Phase equilibrium is related to the concentration of each phase in the liquid phase, its solubility and volatility, as well as whether it can react with other molecules or ions in the solution. For example, CO2 has very low solubility in water, a low relative volatility, and small equilibrium constants for reactions with other molecules or ions in the solution; as a result, it is most easily transferred from the liquid phase to the gas phase. NH3, on the other hand, is different: it not only has a high solubility in water, but also has large reaction equilibrium constants with CO2 and H2S. Only when it reaches saturation under certain conditions can free NH3 molecules transfer from the liquid phase to the gas phase. Clearly, the introduction of water vapor serves a dual purpose: it heats the mixture and reduces the partial pressures of H2S, NH3, and CO2 in the phase, thereby facilitating their transfer from the liquid phase to the gas phase and achieving the purification of acidic water.

Does introducing steam have the effect of reducing the partial pressure of acidic gas components?

The introduction of steam serves a dual purpose: it heats the mixture and reduces the partial pressures of hydrogen sulfide, ammonia, and carbon dioxide in the gas phase, thereby facilitating their transfer from the liquid phase to the gas phase and achieving the purification of sulfur-containing wastewater.

This post was last edited by ylb913 on 2017-2-10 06:44: The equilibrium between ionization and hydrolysis； Higher temperature leads to lower solubility and lower degree of ionization ； Steam reduces their partial pressure in the gas phase, thereby decreasing their solubility in water.

It is easy to understand that the temperature rises and solubility decreases when steam is introduced, but how can the decrease in their partial pressures be explained?

Search for Dalton’s law of partial pressures on Baidu and you’ll understand