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What is Air separation unit?

20.10.2014
What is Air separation unit?
  Air separation units (ASUs) are commonly used to produce gaseous and liquid nitrogen, oxygen, and argon in different branches of industry.
  Depending on the objectives and needs of the Customer our company offers three types of air separation units, according to separation method: cryogenic, membrane and adsorptive.
  Adsorptive air separation method is based on the principle of selective absorption of gas mixture components. Absorption is performed by special molecular sieves (MS) under swing adsorption. The underlying part of the process is dependence of gas absorption by means of adsorbent from pressure: the ability of the adsorbent to absorb gas is directly proportional to pressure. Thus adsorption is performed at an increased pressure and desorption process is carried out by means of depressurization.
  Membrane air separation method is based on the principle of selective permeability of membranes. The principle of operation of membrane gas separation units underlies in different permeation rate of gases through polymeric membranes under the influence of partial pressure differential on the membrane. In both cases, the membrane unit is supplied with pre-filtered compressed air and driving force of separation is the difference between partial pressures of each component of the air on both sides of the membrane, which results in different permeation rate. In this regard, air components can be divided into two classes: easily penetrating (EP) or ‘fast gases’, hard penetrating (HP) or ‘slow gases’. After compressed air comes into contact with overmembrane surface ‘fast gases’ penetrate with low-pressure zone, thus gas at membrane outlet is enriched by easily penetrating component. Not penetrated portion of air is enriched with hard penetrating component and is withdrawn from overmembrane surface.
  Cryogenic separation method is based on heat-mass transfer processes, particularly on low-temperature distillation process, based on the difference of boiling points of air components and the difference of compositions which are in the equilibrium with liquid and vapor mixtures.
  During air separation at cryogenic temperatures there is heat exchange between air components which are in contact with liquid and vapor phases. As a result, vapor phase is saturated with low-boiling component (a component having a lower boiling point) meanwhile liquid phase is saturated with high-boiling component. Thus, going up the distillation column, vapor is saturated with low-boiling component that is nitrogen; liquid which goes down is saturated with high boiling component that is oxygen
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