Later with the boiler water boiler causing oxygen corrosion phenomenon was discovered, boiler water was deoxygenated already included in the key. In response to this phenomenon, the various methods of oxygen gradually been adopted. However, these new method is still unable to meet the oxygen large steam boiler operating conditions. Thermal deaerator principle is based on dissolved gas law (Dalton and Henry's Law): Any gas solubility in water and the gas pressure in the sub-surface of the soda is proportional to the boundary. When the water temperature in an open apparatus, a boundary surface soda water vapor partial pressure is increased, reducing the partial pressure of various gases, the solubility in water decreases. When the water temperature reaches the boiling point, vapor pressure and the external pressure are equal soda interface, the partial pressure of other gases is reduced to zero, the gases are insoluble in water, had a variety of dissolved gases in water will be parsed. Therefore, not only thermal deaerator oxygen, but also to remove CO2 and other gases in the water. Thermal deaerator use oxygen in the water solubility characteristics, through the steam boiler feed water heating, according to Henry's law and Dalton's law, dissolved in water, oxygen and carbon dioxide and other non-condensable gases from the water precipitated by the top of the exhaust port vented deaerator head, so as to achieve the purpose of oxygen.