The cold box in an air separation unit is a highly engineered large rectangular box enclosing the major cryogenic equipment. Some suppliers use a round silo design in which the equipment is primarily supported by the cold box foundation. The cold box wall is made up of steel panels that are welded onto the cold box frame. The space between the cold box wall and the equipment is filled with insulating material.

The cold box frame and foundation are designed to support the weight of all process equipment, as well as piping and valves containing the maximum operating level of liquid. It must also withstand high wind loadings as required by national codes and be suitable for the earthquake zone in which it is installed.

In air separation plants you can see square columns installed. Those are actually cryogenic cold boxes used to minimize heat leakage to the environment. The temperature inside the cold box is usually in the range of -196 Deg C. To prevent heat transfer vacuum is used.