How does a boiler deaerator use steam to remove oxygen from water?

The principle of removing oxygen from water by boiler steam deaerator is based on two key physical and chemical effects: as the temperature increases, the solubility of gas in water decreases, and oxygen is diffused by steam.

The function of a deaerator is divided into several continuous stages:

1. Heating steam feed water (usually with alkaline reagents such as ammonia added to stabilize pH) reaches the top of the deaerator, where it is sprayed into thin droplets or films. This increases the contact area between water and steam. Hot steam is transported to the bottom or middle of the equipment, heating water to a temperature close to the boiling point at the working pressure of the deaerator (usually 100-110 ° C or higher at atmospheric pressure).

   As the temperature increases, the solubility of oxygen and other gases (such as nitrogen) in water sharply decreases. For example, at 20 ° C, dissolve about 9 mg of O ₂ in 1 liter of water, and dissolve less than 0.1 mg of O ₂ at 100 ° C.

2. browsesteam oxygenDuring the heating process, dissolved gases are expelled from the water in the form of bubbles. At the same time, steam passes through the water droplet layer and generates high concentration Presi ó n steam and low concentration Presi ó n oxygen in the gas phase inside the deaerator. According to Henry's Law, the concentration of dissolved gases in a liquid is proportional to the partial pressure on its surface. Therefore, the oxygen discharged from the water actively diffuses into the steam environment and is discharged from the deaerator together with steam and other non condensable gases through special exhaust ports (vents).

3. Deoxidized water and condensate separated deoxygenated water are collected from the bottom of the deoxidizer and transported to the boiler. Part of the steam used for heating and exhaust condenses in water, increasing the volume and temperature of the water.

It is worth noting that the degassing efficiency depends on the pressure, water temperature, contact area and contact time between water and steam inside the device. In order to meet the required standard (oxygen concentration in boiler feedwater should not exceed 0.03 mg/l, according to the standard), steam deaerators are usually supplemented with chemical deaeration (adding reducing agents such as hydrazine or sodium sulfite) to eliminate residual oxygen.