The rectification system of air separation equipment is the core link to separate air components and obtain high-purity oxygen, nitrogen and argon. The core of its working principle is to realize accurate separation of components based on the difference of boiling points of air components and in combination with cryogenic refrigeration and steam-liquid heat and mass transfer.
Preconditions for rectification are air pretreatment and liquefaction: first compress and purify the air to remove impurities such as water and carbon dioxide, so as to avoid blocking the equipment due to icing at low temperature; Then, the turbine expander provides cooling capacity to cool the purified air below - 170 ℃, so that part of the purified air is liquefied to form liquid air, which lays a foundation for rectification.
The actual separation is completed through the double-column rectification structure: the liquid air first enters the high-pressure column for rough separation. Since the boiling point of nitrogen (--19.8 ℃) is lower than that of oxygen (- 183 ℃), the nitrogen with low boiling point is preferentially vaporized to the top of the column, and the oxygen with high boiling point is left at the bottom of the column to form oxygen-enriched liquid. The oxygen-enriched liquid enters the low-pressure column after depressurization. The rising gas in the column fully contacts with the falling liquid, and repeated vaporization and condensation occur for further purification.
High-purity nitrogen is produced at the top of LP column, high-purity liquid oxygen is collected at the bottom of column, and argon by-product can be extracted from the side line. The tray or packing in the rectifying column increases the steam-liquid contact area, the main heat exchanger recovers cold energy, and the two cooperate to ensure the separation efficiency and purity. The whole system operates continuously to achieve stable separation of air components.
