Oxygen measurement on air separation plants

Industry consumes vast quantities of oxygen and nitrogen annually, all of which is obtained from the air around us. There are two main techniques used to separate these two primary gases from air. These processes are cryogenic separation and pressure swing adsorption (PSA).

Regardless of the technique used, the plants producing these pure industrial gases are known as air separation units (ASUs). Such plants may be owned and operated directly by the consumer. In this case, the facility is known as an on-site plant, with the plant infrastructure often supplied and sold by one of the major industrial gas (IG) companies as a modular 'packaged plant' solution. In other situations the ASU is owned and operated directly by the IG company but is often located directly within, or adjacent to, the end-user's site. Occasionally, the plant may be centrally located in an industrial location such as an 'industrial city', and may feed a number of discrete customers. In addition, IG operators run large air separation plants, producing bulk O₂ and N₂ and often argon and other gases, for general distribution, via bulk road and rail tanker or for supply in cylinders for lower volume use.

Air separation units require critical and reliable gas analysis for plant control and product quality. These measurements are fundamental to the safe and efficient operation of the plant and to provide final product quality assurance. In particular, reliable and accurate oxygen measurement is critical to the production of both gases - both to detect the purity of the O₂ being produced and to detect any entrained O₂ in the produced N2 (which may be used for N₂ blanketing or purging, in which entrained oxygen could be potentially hazardous).