Air separation plants use cryogenic distillation to separate atmospheric air into its component gases, including oxygen, nitrogen, and argon. The process involves cleaning, compressing, purifying, and cooling the air, before distilling it in a column to produce liquefied gases. These gases are used in various industrial processes and can be transported in liquid or gaseous forms.
An air separation plant is an industrial plant that separates natural air, or atmospheric air, into its component gases. Gases collected in the process include oxygen, nitrogen and argon as well as some inert gases such as neon, xenon and krypton. Since nitrogen and oxygen are the two most common gases in the earth’s atmosphere, these two elements make up the majority of gases collected in this process.
The process employed in an air separation plant is called cryogenic distillation. By cooling atmospheric air to extremely low temperatures, the component gases can be separated and collected. Liquid forms of nitrogen or oxygen can also be harvested in some plants.
The cryogenic distillation process is a four step procedure. In the first stage, atmospheric air is cleaned and compressed to a pressure range of 5 to 10 bars (4 to 9 atmospheres). The cleaning process removes dust and contaminants that could interfere with the cooling process. The compression process heats the air to remove traces of moisture before passing the compressed air to a heat exchanger for cooling.
When the compressed air has been cooled down, the next step is purification. This process involves passing air through a molecular sieve, which filters the air through a process called adsorption. In this process, gases or molecules are attracted to an adsorbent surface and form a layer on top of the adsorbent material. Molecular sieves are designed to remove carbon dioxide, water and hydrocarbon gases.
After the air has been purified, it can be safely passed to the cooling and distillation chamber. The cooling chamber consists of a heat exchanger and cryogenic flows. When air is passed through this chamber, it reaches temperatures low enough to allow distillation of the component gases.
The distillation of air takes place in the distillation column. Depending on the gases to be collected, air may pass through more than one distillation column. This component uses refrigerant and an expander or valve to generate a Joule-Thomson effect, which causes the component gases of air to cool and reach a liquid state. The liquefied gases are then collected and heated to room temperature for storage or use.
The gases produced by an air separation plant are used in many industrial processes. In some cases, these gaseous forms of these elements are transported to industrial users via direct pipelines. In other cases, the collected elements can be stored in liquid or gaseous forms for subsequent transport and use. Larger quantities of the distillate gases are usually transported in their liquid forms by road tankers. Smaller quantities may be transported in pressurized cylinders as gas.
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