Air separation

Air separation

Separation of atmospheric air into its primary constituents. Nitrogen, oxygen, and argon are the primary constituents of air. Small quantities of neon, helium, krypton, and xenon are present at constant concentrations and can be separated as products. Varying quantities of water, carbon dioxide, hydrocarbons, hydrogen, carbon monoxide, and trace environmental impurities (sulfur and nitrogen oxides, chlorine) are present depending upon location and climate. Typical quantities are shown in the table. These impurities are removed during air separation to maximize efficiency and avoid hazardous operation.

Three different technologies are used for the separation of air: cryogenic distillation, ambient temperature adsorption, and membrane separations. The latter two have evolved to full commercial status. Membrane technology is economical for the production of nitrogen and oxygen-enriched air (up to about 40% oxygen) at small scale. Adsorption technology produces nitrogen and medium-purity oxygen (85–95% oxygen) at flow rates up to 100 tons/day. The cryogenic process can generate oxygen or nitrogen at flows of 2500 tons/day from a single plant and make the full range of products.

Composition of dry air
Percent Parts per million
Component by volume Component by volume
Nitrogen 78.084 Carbon dioxide 350–400
tOxygen 20.946 Neon 18.2
Argon 0.934 Helium 5.2
Krypton 1.1
Xenon 0.09
Methane 1–15
Acetylene 0–0.5
Other hydrocarbons 0–5

Air separation is a major industry. Nitrogen and oxygen rank second and third in the scale of production of commodity chemicals; and air is the primary source of argon, neon, krypton, and xenon. Oxygen is used for steel, chemicals manufacture, and waste processing. Important uses are in integrated gasification combined cycle production of electricity, waste water treatment, and oxygen-enriched combustion. Nitrogen provides inert atmospheres for fuel, steel, and chemical processing and for the production of semiconductors.

McGraw-Hill Concise Encyclopedia of Engineering. © 2002 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Industrial gas company Messer North America Inc said on Tuesday that it proposes to invest USD38m for the construction of a new, large-scale air separation unit (ASU) in Indianapolis, Indiana.
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KARACHI -- Pakistan Oxygen Ltd formally approved an investment plan of approximately Rs5.1 billion to set up 'the latest air separation unit (ASU) in its class in Pakistan'.
LAHORE -- Pakistan Oxygen Limited (formerly Linde Pakistan Limited) is set to invest Rs4.4 billion for setting-up the country's largest air separation plant.
Under the terms of the agreement, Linde will conduct a front-end engineering and design (FEED) study for new air separation units, according to UAE state news agency, WAM .
Ltd, a subsidiary of Yankuang Group, aim to establish an Air Products majority-controlled joint venture company, which is to construct, own and operate an air separation, gasification and syngas clean-up system to supply the SFEC site.