The Air Separation Unit remains a key piece of equipment across a wide range of applications and industries.
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As the growing demand for industrial gasses continues to increase, the ASU provides a reliable and efficient method for producing these gasses at the required purity levels. At the same time, the air separation process offers a cost-effective means of producing high-purity gasses compared to other methods, generating them in large quantities, leading to economies of scale and reduced per-unit production costs over time.
But what exactly is an Air Separation Unit, how does it work and what are its key applications? Here’s a guide to the ASU, written from our experience in cryogenic engineering and design and manufacture of these structures.
An Air Separation Unit (ASU) is an industrial facility used to separate atmospheric air into its primary components (namely nitrogen, oxygen, and, in some cases, argon and other rare gasses). These units are typically composed of elements such as air compressors, an air purification system, heat exchangers, cryogenic cooling systems and distillation columns, among others.
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While there are various methods that can be performed by an Air Separation Unit, fractional distillation is the primary separation technique employed.
The main working principle behind an ASU is the separation of air via its liquefying and distilling processes. A simplified overview of how an ASU typically operates looks like this:
As the air ascends the column, it is gradually warmed, and different components evaporate at their respective boiling points. For instance, oxygen-rich vapor rises to the top of the column, while nitrogen-rich liquid collects at the bottom. The argon, if present, is usually extracted as a side product at an intermediate point in the column.
Across these operations, it’s key for the Air Separation Unit to operate presenting a very tight integration of heat exchangers and separation columns, ensuring its efficiency.
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With our two-decade knowledge and experience in cryogenic engineering, at Cryospain we are one of the leading suppliers of state-of-the-art air separation plants. Our strength lies in our capacity to adjust to each project’s needs, considering its full lifecycle, potential and limitations.
Through a combination of innovative technologies andend-to-end engineering services, we’ve designed, manufactured and implemented a series of successful ASU projects, all while complying with the relevant standards.
As such, our involvement goes from procuring the materials, to assembling the equipment, electrics and piping, as well as taking care of crucial processes such as factory acceptance testing (FAT) for the containerized ASU’s components. It’s precisely our capacity to dedicate to planning, drawings, calculations and 3D modeling that makes us our strength, so that we can provide a tailored, end-to-end service.
Finally, we present an outstanding production capacity, with two large-scale workshops and two industrial hubs which sum up a combined m2 dedicated to realizing our clients’ projects while guaranteeing the highest quality standards.
Our success stories include:
An air separation plant separates atmospheric air into its primary components, typically nitrogen and oxygen, and sometimes also argon and other rare inert gases.
Link to Chengde Energy Technology
The most common method for air separation is fractional distillation. Cryogenic air separation units (ASUs) are built to provide nitrogen or oxygen and often co-produce argon. Other methods such as membrane, pressure swing adsorption (PSA) and vacuum pressure swing adsorption (VPSA) are commercially used to separate a single component from ordinary air. High purity oxygen, nitrogen, and argon, used for semiconductor device fabrication, require cryogenic distillation. Similarly, the only viable source of the rare gases neon, krypton, xenon is the distillation of air using at least two distillation columns. Helium is also recovered in advanced air separation processes.[1]
Pure gases can be separated from air by first cooling it until it liquefies, then selectively distilling the components at their various boiling temperatures. The process can produce high purity gases but is energy-intensive. This process was pioneered by Carl von Linde in the early 20th century and is still used today to produce high purity gases. He developed it in the year ; the process remained purely academic for seven years before it was used in industrial applications for the first time ().[3]
The cryogenic separation process[4][5][6] requires a very tight integration of heat exchangers and separation columns to obtain a good efficiency and all the energy for refrigeration is provided by the compression of the air at the inlet of the unit.
To achieve the low distillation temperatures, an air separation unit requires a refrigeration cycle that operates by means of the Joule–Thomson effect.
The separated products are sometimes supplied by pipeline to large industrial users near the production plant. Long distance transportation of products is by shipping liquid product for large quantities or as dewar flasks or gas cylinders for small quantities.
Pressure swing adsorption provides separation of oxygen or nitrogen from air without liquefaction. The process operates around ambient temperature; a zeolite (molecular sponge) is exposed to high pressure air, then the air is released and an adsorbed film of the desired gas is released. The size of compressor is much reduced over a liquefaction plant, and portable oxygen concentrators are made in this manner to provide oxygen-enriched air for medical purposes. Vacuum swing adsorption is a similar process; the product gas is evolved from the zeolite at sub-atmospheric pressure.
Membrane technologies can provide alternate, lower-energy approaches to air separation. For example, a number of approaches are being explored for oxygen generation. Polymeric membranes operating at ambient or warm temperatures, for example, may be able to produce oxygen-enriched air (25-50% oxygen). Ceramic membranes can provide high-purity oxygen (90% or more) but require higher temperatures (800-900 deg C) to operate. These ceramic membranes include ion transport membranes (ITM) and oxygen transport membranes (OTM). Air Products and Chemicals Inc and Praxair are developing flat ITM and tubular OTM systems.[citation needed]
Membrane gas separation is used to provide oxygen-poor and nitrogen-rich gases instead of air to fill the fuel tanks of jet liners, thus greatly reducing the chances of accidental fires and explosions. Conversely, membrane gas separation is currently used to provide oxygen-enriched air to pilots flying at great altitudes in aircraft without pressurized cabins.
Oxygen-enriched air can be obtained exploiting the different solubility of oxygen and nitrogen. Oxygen is more soluble than nitrogen in water, so if air is degassed from water, a stream of 35% oxygen can be obtained.[7]
Liquid oxygen for companies such as SpaceX.[8]
Pure oxygen is delivered to large hospitals for use with patients.
In steelmaking, oxygen is required for the basic oxygen steelmaking process. Modern basic oxygen steelmaking uses almost two tons of oxygen per ton of steel.[9]
Nitrogen used in the Haber process to make ammonia.[10]
Large amounts of oxygen are required for coal gasification projects; cryogenic plants producing tons/day are found in some projects.[11]
Inerting with nitrogen storage tanks of ships and tanks for petroleum products, or for protecting edible oil products from oxidation.[citation needed]
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