One of the most common methods to produce pure oxygen is by cryogenic distillation of air. With this method, air is cooled to cryogenic temperatures (typically about –300 F) so that it becomes a liquid. The liquid air then is subjected to a distillation process that separates the air into its main components (oxygen, nitrogen, and argon).

    Prior to cooling the air to cryogenic temperatures, it is necessary to remove all of the water and carbon dioxide from the air. Otherwise, the water and carbon dioxide would "freeze-out" when the air is cooled, and eventually "plug up" the cryogenic equipment.

    Air Products uses a technology known as Temperature Swing Adsorption (TSA) to remove water and carbon dioxide from air. This technology uses a vertically oriented pressure vessel that is filled with a granular adsorbent material. Air is fed into the vessel and forced to flow through the granular adsorbent material (also known as the adsorbent bed). As the air flows through the adsorbent bed, water and carbon dioxide are absorbed by the granular material, and the air leaves the vessel free of water and carbon dioxide.

    After several hours of operation, the adsorbent bed becomes saturated and must be regenerated (or cleaned). This is accomplished by flowing heated clean dry regeneration gas (usually nitrogen) through the saturated adsorbent bed in the reverse direction, in order to heat the adsorbent material and "drive-off" the water and carbon dioxide. When the adsorbent bed has been cleaned sufficiently, the regeneration gas is no longer heated, but continues to flow until the adsorbent bed is cooled-down to normal operating temperature. At this point, the adsorbent be is ready once again to resume the removal of water and carbon dioxide from air.

    The granular adsorbent material that is contained within the pressure vessel rests on top of a flat "support screen". The support screen is located near the bottom of the end of the vessel, just above the weld connection between the bottom head and the shell of the vessel. It must be designed to support the weight of the adsorbent bed and any forces due to pressure drop across the bed, to allow gas to flow through it, and to contain the granular adsorbent particles (typically about 2mm dia.).

    One of the primary technical challenges with TSA technology is to design a support screen that can accommodate cyclic temperature swings. During the regeneration step of a TSA cycle, both hot and cold temperature waves propagate through the adsorbent bed and cause severe temperature differences (and consequent differential thermal expansion) between the support screen and the vessel shell.

    A typical design for a support screen is shown in the figure. It consists of a fabricated sandwich type assembly of grating, perforated plate, and wire mesh or an integral wedge wire assembly. To accommodate differential thermal expansion between the support screen and the vessel shell, the periphery of the support screen is sealed against the vessel wall by a packing gland.

Historically, the packing glands have suffered chronic reliability problems that have resulted in the leakage of adsorbent particles around the support screen assembly.