How to Select the Right Compressed Air System

Each application requires a different level of air quality and a different combination of air treatment to meet the needed specs

By Neil Mehltretter, Kaeser Compressors

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In the pharmaceutical industry, compressed air is used for a number of production and packaging applications, including blowing off and drying bottles prior to filling, conveying pills, providing air for pneumatically controlled valves and cylinders, as well as breathing air systems.

Each of these applications requires a different level of air quality and a different combination of air treatment to meet the needed quality. Because the uses of compressed air within the industry vary so greatly, there is no set standard in place that every process must adhere to.

While the FDA may not have issued a directive for compressed air quality in the pharmaceutical industry, there is still a resource available to help select appropriate air treatment components for a compressed air system.

ISO 8573.1:2010 was developed by ISO — the International Organization for Standardization — as a reference for specifying compressed air quality. This standard is not industry or application specific and includes three categories: solid particles/dust, humidity and liquid water, and oil. Within these categories are classes, ranging from 0 to X. While there may not be a pharmaceutical industry standard, the equipment used in these processes may have a certain ISO air quality specified, making it relatively easy to select compressed air dryers and filters to
meet the specification. 

Once the facility engineer has selected the appropriate air treatment components to meet the required level of air quality for the process, it's important to understand installation considerations that can impact the air quality and overall reliability of the compressed air supply.

Unfortunately, there is often a fundamental disconnect between selecting equipment and installing it. When there is not a clear understanding of how the individual components work together to create a system or why they were chosen to achieve a certain goal — for example, to attain a specific level or air quality — installation decisions can be made that negate system goals.

A common installation consideration is whether or not to include manual bypasses around the air treatment. There are different schools of thought concerning this practice, but before including them for the sake of convenience, consider how they affect air quality.

Here is an example of what the air treatment part of a system with a manual bypass might look like:

In this example, the two “NC” (normally closed) valves can be manually opened and the two valves closest to the refrigerated dryer and filter can be closed in case of maintenance, service or failure. The air supply would not be interrupted, but it also wouldn't be treated. Therefore moisture, particulates, and other contaminates which are normally removed would be passed along to the distribution system and adversely affect product quality at the point of use. Since many processes in the pharmaceutical industry have a low tolerance for impurities, bypassing air treatment for the sake of flow is generally not acceptable.

The following shows an example of installing air treatment in parallel: 

Piping dryers and filters in parallel allows for built-in redundancy, which does increase capital costs, but it also ensures a reliable level of air quality. With this approach, the components are sized so if one of the trains were to be offline for any reason, the other could still meet the demand. If sized properly, one section can be closed off without disrupting the air supply or the air quality. Furthermore, leaving both trains online will reduce pressure drop and wear and tear on the components, which could offer savings in the long run.

Additionally, when adding multiple dryers in parallel it is highly recommended to select dryers with energy saving controls. If energy is an important consideration, then the dryers (whether they be desiccant or refrigerated dryers) should have some sort of energy management control on them to reduce the overall power consumption associated with each dryer. As a safety precaution, it is recommended to consider a high velocity control valve, also called an air main charging valve, which acts to separate the supply from the demand during start-up.

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