In the low-temperature rectification air separation device, the water, carbon dioxide, acetylene, hydrocarbons and other substances in the raw material air must be removed before the air enters the rectification tower. Otherwise, the water and carbon dioxide will freeze and adhere to the heat exchanger and rectification tower in the low-temperature environment, thus reducing the working efficiency and increasing the resistance of the equipment. Methane in liquid oxygen has high solubility and is not easy to precipitate, while other components will precipitate and aggregate in liquid oxygen in the rectification tower, compromise the operation of the device. In order to avoid blockage and explosion of low-temperature equipment, ensure the long-term safe and reliable operation of the device. Therefore, the molecular sieve is the key device in which the air is purified before the air enters the low temperature cold box.
Molecular sieve is a kind of gas-solid phase adsorbent, the molecular sieve loses crystal water by heating, and many holes are formed in the crystal, and its pore size is similar to the diameter of the adsorbed gas molecule, and it is very uniform. It can absorb molecules smaller than the pore diameter into the pore and keep molecules larger than the pore diameter out of the pore. Therefore, it can be based on the size of the molecule, the various components of the separation, "molecular sieve" also hence the name, molecular sieve by two adsorbers, heating equipment, instrument electric control valve pipe composition, two adsorber adsorption, a regeneration, switching each other to use. The adsorption time of the adsorber is usually four hours, and the carbon dioxide of the adsorber is controlled to be less than 1PPM. Because the air pressure in the adsorption stage is high and the pressure required in the regeneration stage is low, the regeneration time of the molecular sieve consists of four stages: depressurization heating, cold blowing, and pressure increase. The regeneration heating is to remove impurities in the adsorbent and achieve the purpose of recycling the adsorbent.
After the air cooling tower cooling air into the adsorber, moisture, acetylene, carbon dioxide are grade molecules, they have a strong affinity, molecular sieve can be quickly absorbed, while the molecular sieve co adsorption properties so that it can absorb the moisture in the air can also be adsorbed on other substances. In the adsorption process of molecular sieve, methane and ethane will soon appear in the air from the adsorbent bed, followed by ethylene, propane and carbon dioxide, and then acetylene, propylene, butane and ethylene will appear in turn.