Design of large air separation unit

Shell and tube air separation heat exchanger is the most representative wall heat exchanger. It has a long history of application and is still dominant in all heat exchangers. Shell and tube heat exchanger is mainly composed of shell, tube bundle, tube sheet and head. Most of the shell is round, and there are parallel tube bundles inside. Both ends of the tube bundle are fixed on the tube plate. In shell and tube heat exchanger, there are two kinds of fluids for heat exchange. One kind of fluid flows in the tube, and its stroke is called tube side. The other flows outside the tube and its stroke is called shell side. The wall of tube bundle is the heat transfer surface. In order to improve the heat transfer coefficient of the fluid outside the tube, a certain number of transverse baffles are usually installed in the shell. The baffle can not only prevent the short circuit of the fluid and increase the velocity of the fluid, but also force the fluid to flow through the tube bundle man

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.