Deep cold air separation method

Why is a high-high interlock set for the water level in the air cooling tower of an air separation unit?

The liquid air separation plant includes the lower tower, upper tower, condensing evaporator, argon system, main heat exchanger, subcooler, liquefier and is placed in a separate cold box. After distillation in the lower tower, high purity nitrogen is obtained at the top of the lower tower, which is reheated by the main heat exchanger and then exits the cold box and goes to the nitrogen circulation system to recover the cold from the liquid air separation plant to make liquid nitrogen. The lower ...