More sieve plate towers are used for the lower tower from 15000 to 50000 grades. The diameter tower with circulating tray below 15000 grades has advantages (the liquid flow is longer than convection, but the manufacturing is complex). The convection tower below 30000 grades is used more, the large tower with four overflow streams above 30000 grades has advantages, and the packed tower has low energy consumption.

Air separation equipment is an equipment that takes air as raw material, turns air into liquid through compression circulation and deep freezing, and then gradually separates from liquid air through distillation to produce inert gases such as oxygen, nitrogen and argon. There are many forms and types of air separation equipment produced in China.