Air Separation Unit (ASU): Working Principle and Applications

The Air Separation Unit (ASU) plays a crucial role in a wide range of industries and applications.

As the demand for industrial gases continues to rise, the ASU offers a reliable and efficient solution for producing gases at the required purity levels. Additionally, the air separation process provides a cost-effective way to produce high-purity gases compared to alternative methods. By generating large quantities, it enables economies of scale and reduces per-unit production costs over time.

But what exactly is an Air Separation Unit, how does it function, and what are its key applications? Here's an in-depth guide to the ASU, drawing from our extensive experience in cryogenic engineering and the design and manufacturing of these systems.

What is an Air Separation Unit?

An Air Separation Unit (ASU) is an industrial facility designed to separate atmospheric air into its key components—primarily nitrogen, oxygen, and, in some cases, argon and other rare gases. These units typically consist of various components, including air compressors, air purification systems, heat exchangers, cryogenic cooling systems, and distillation columns, among others.

How Does an Air Separation Unit Work?

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:

Compression: In this initial stage, atmospheric air is drawn into the ASU and passed through a series of compressors to increase its pressure. This step enhances the efficiency of subsequent cooling and separation processes, with typical pressure ranges between 5 and 10 bar gauge.

Purification: Before further processing, the compressed air undergoes purification to remove impurities such as moisture, carbon dioxide, and trace contaminants. This ensures the high purity of the separated gases and prevents issues like the freezing or clogging of cryogenic equipment.

Cooling: The purified, compressed air is then cooled to cryogenic temperatures using heat exchangers and refrigeration cycles. This process liquefies the air, as cryogenic distillation relies on the varying boiling points of its components.

Separation: The cooled, liquefied air is fed into distillation columns, where the air is separated into its primary components based on their boiling points:

- Nitrogen has a lower boiling point (-196°C or -321°F) than oxygen (-183°C or -297°F).

- Argon, if present, has an even lower boiling point (-186°C or -303°F).

As the air ascends the column, it is gradually warmed, causing the components to evaporate at their respective boiling points. Oxygen-rich vapor rises to the top, while nitrogen-rich liquid collects at the bottom. If argon is present, it is typically extracted from an intermediate point in the column.

Collection, Storage, and Delivery: The separated gases are collected and sent to storage tanks, either pressurized or cryogenic. From there, they are distributed to various industries and applications, depending on their purity requirements.

Throughout this process, it is essential for the ASU to maintain a tightly integrated system of heat exchangers and separation columns to ensure optimal efficiency.

Applications of an ASU

Healthcare: An ASU plays a vital role in providing oxygen and other technical gases used in medical treatments, enhancing patient care and supporting healthcare facilities with reliable gas supplies.

Industrial Processes: The ASU is integral to various cryogenic technologies used in industries such as metal fabrication, chemical production, and wastewater treatment. It also helps generate high-purity gases essential for semiconductor manufacturing, including wafer production and device fabrication.

Food and Beverage: Nitrogen, a key component of "food gases," is used in the food and beverage industry for packaging and preserving products, helping to extend shelf life and maintain quality.

Energy Production: ASUs supply high-purity oxygen for combustion processes in power plants and steel mills, improving efficiency and enabling cleaner, more effective energy production.