Large cryogenic air separation unit

When the amount of processing air is reduced, the rising steam and reflux liquid in the upper column will be reduced, but the reflux ratio will not change. Therefore, the reduction of processing air in a small range will not affect the purity of oxygen and nitrogen, and the reduction of processing air volume will help to reduce the pressure of the upper and lower columns. However, according to the material balance, the production of oxygen and nitrogen will naturally decrease when the amount of processing air is reduced. If the amount of processing air is too small, there will be leakage on the tray. If the heat and mass exchange of the leaked liquid is not sufficient, the purity of oxygen and nitrogen will be greatly affected, and even the normal production can not be realized. Therefore, the minimum allowable load of distillation column is generally specified.

The plant operation cycle between two large heating is related to many factors. From an operational point of view, this mainly depends on when the air passage of the main heat exchanger is blocked. The main reason for the blockage is that the moisture and carbon dioxide content in the air entering the unit exceeds the standard, which accumulates and freezes in the main heat exchanger until it is blocked. The abnormal operation of molecular sieve purification system will shorten the operation cycle of the unit. It is mainly caused by the following reasons: 1. The molecular sieve adsorption bed is short circuited. In the process of operation, due to the unstable gas velocity control or switching, the pressure difference between the two tanks is too large, which will affect the bed layer, make the molecular sieve bed uneven and make the bed layer short circuit. In serious cases, the dust screen of the adsorber will break and the molecular sieve powder will enter the heat exchanger c