In addition to oxygen and nitrogen, there are also small amounts of gases such as water vapor, carbon dioxide, acetylene, and other hydrocarbons in the air, as well as small amounts of solid impurities such as dust. The air entering the air separation equipment first needs to remove some impurities, such as moisture, carbon dioxide, and acetylene. The most commonly used methods for removal are adsorption and freezing.
The adsorption method uses silica gel or molecular sieves as adsorbents to separate impurities such as water, carbon dioxide, and acetylene from the air, as well as acetylene from liquid air and liquid oxygen, and concentrate them on the surface of the adsorbent (without chemical reaction). When heated and regenerated, they are then removed to achieve the purpose of purification. For example, setting up dryers, carbon dioxide adsorbers, liquid air adsorbers, and liquid oxygen adsorbers.
The freezing method is to freeze the moisture and carbon dioxide contained in the air when it passes through a cold storage or switching heat exchanger (acetylene cannot freeze), and then be carried out of the device by dry backflow gas, which is self clearing.
The use of molecular sieve purification process can simultaneously adsorb and remove moisture, carbon dioxide, and acetylene from the air, simplifying the process. It has been widely used in oxygen concentrators.
