Understanding Air Separation Units and Their Applications

When discussing air separation units (ASUs), it is essential to distinguish between the diverse applications in the field. This article explores the principles behind ASUs, particularly those in the context of hydronic systems and industrial processes. We will delve into the methods of separating various gases from liquid air and explore the fundamental concepts behind ASUs in different settings.

Introduction to Air Separation Units

Generally, an air separation unit refers to a device used to separate the various components of air, such as nitrogen and oxygen. However, in the context of hydronic systems, an ASU can be referred to as a method for removing entrained air from water-based heat transfer systems. This process is crucial for maintaining the efficiency and longevity of the system. In this article, we will clarify the distinction and explore how these units function in practical applications.

The Basics of Air Separation in Hydronic Systems

Hydronic systems, or water-based heat transfer systems, are utilized in various industrial and residential applications. These systems require the removal of air to ensure optimal performance. There are three principal types of ASUs used in hydronic systems, each designed to address specific needs and challenges.

The Air Scoop ASU

The air scoop ASU is the oldest type. It operates by creating a drop in velocity as the water enters a chamber that is larger than the pipe. This design, combined with the fact that the water entering the system is the hottest and at the lowest pressure, facilitates the release of entrained air from the solution. The released air is then vented away, ensuring that the system remains free of air bubbles.

The Centrifugal ASU

The centrifugal ASU works by having water enter near the top of a vertical cylinder tangentially and exiting the same side near the bottom in a swirling motion. This swirling flow generates a low-pressure vortex in the center of the cylinder. The low pressure effectively pulls air out of solution and allows it to rise to the surface, where it can be vented away. This method is effective in removing entrained air and improving the system's efficiency.

The Microbubble Resorber ASU

The most effective ASU in hydronic systems is the microbubble resorber. This unit features a high-surface area matrix, such as a wire-bristle brush or small rings known as Pall Rings. The high surface area provides a surface for entrained air to coalesce and come out of solution, facilitating efficient air removal. This method ensures minimal air entrainment, leading to better system performance and longer operational life.

The Process of Separating Cryogenic Gases

Another application of air separation units is the separation of cryogenic gases, where the differential evaporation rates of gases play a crucial role. In this process, liquid air is cooled to extremely low temperatures, and as the air is heated, the gases with different boiling points evaporate at different rates. Nitrogen, for instance, evaporates at a lower temperature than oxygen, allowing for its separation from the liquid air.

This method involves the following steps:

First, air is compressed and cooled to form liquid air. Then, the liquid air is heated gradually, causing the gases to evaporate at different rates. Finally, the separated gases are collected and stored or used for various applications.

This process is widely used in industrial applications such as the production of oxygen, nitrogen, and other industrial gases.

Conclusion

Understanding the function and applications of air separation units is crucial for maintaining and optimizing the performance of hydronic systems and industrial processes. The three types of ASUs discussed here—air scoop, centrifugal, and microbubble resorber—each have their unique methods of removing entrained air, ensuring the system operates efficiently.

Whether you are involved in the design, operation, or maintenance of a hydronic system, or working with cryogenic gas separation, knowledge of ASUs can be invaluable. By selecting and employing the appropriate ASU, you can ensure that your system remains free of air entrainment, leading to improved performance and longevity.