Why can a deaerator remove oxygen?

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I. First, why is deoxygenation necessary? Excessive dissolved oxygen in the working fluid can cause corrosion and damage to thermal equipment, reducing its service life. In the case of furnace tubes, it may also lead to frequent leaks, resulting in increased economic losses for the plant. Therefore, the dissolved oxygen in the feed water must be removed. Then an deaerator is needed. II. Then, why can a deaerator remove oxygen? To understand why deaerators can remove oxygen, it is first necessary to comprehend two laws: one is Dalton’s law of partial pressures, formulated by John Dalton in 1801; the other is Henry’s law, discovered by a British scientist named Henry in 1803 while studying the solubility of gases in liquids. Dalton’s law of partial pressures states that the partial pressure of a particular gas in a gas mixture is equal to the pressure it would exert if it occupied the entire container alone at the same temperature ； The total pressure of a gas mixture is equal to the sum of the partial pressures of its constituent gases. Henry’s law states that, at constant temperature and pressure, the solubility of a volatile solute (usually a gas) in a solution is proportional to the equilibrium pressure of that solute above the liquid surface. The main method of deoxidation in deaerators is based on these two laws, that is, physical deoxidation. It involves heating the water in the deaerator to its saturation temperature, so that the space above the deaerator on the steam side is entirely filled with steam, while the pressure of other gases approaches zero (according to Dalton’s law of partial pressures). At this point, the other gases present in the condensed water within the deaerator are separated out (according to Henry’s law) and removed from the deaerator, thereby achieving the purpose of deoxygenation. Therefore, many measures have been taken to heat the deaerator to the saturation temperature more effectively. In the first stage, which is the initial phase of deoxygenation, when the condensate water enters the deoxygenator, butterfly nozzles are used to spread the condensate water as widely as possible to form a water film, thereby increasing the contact surface area between the water and steam. Rapidly heating the condensate water to the saturation temperature allows most of the oxygen to be removed. In the second stage, which is also the stage of deep deoxygenation, when water enters the water-side space of the deoxygenator, steam introduced at the bottom of the deoxygenator disturbs the water there, causing the other oxygen and gases dissolved in the water to rise to the surface where they are removed, thereby achieving deoxygenation. Therefore, from the above, we can learn the three necessary conditions for the proper operation of a deaerator: first, heating the water in the deaerator to its saturated temperature at the corresponding pressure; second, ensuring that the condensate and steam entering the deaerator have sufficient contact area; third, providing enough time to ensure that the gas separation process takes place thoroughly.