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.

In the process of full low pressure switching air separation unit​, a bypass valve is usually installed on the pipeline from the air to the switching heat exchanger and from the waste nitrogen to the switching heat exchanger, which plays a very important role in the start-up stage: part of the cooled air can return to the switching heat exchanger through the bypass valve to release the cooling capacity.