A deaerator preheats boiler feedwater and removes dissolved gases, especially oxygen and carbon dioxide. These gases are undesirable because they cause corrosion and increase treatment chemical requirements.
Deaerators operate based on the reduced solubility of dissolved gases as temperature increases. For example, the solubility of oxygen decreases from about five ppm at 150ºF to about two ppm at 190ºF. Virtually all the free carbon dioxide gas is removed by increasing the temperature to greater than 170ºF.