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Why dry compressed air is essential

Compressed Air Wiki Air Treatment Drying

All atmospheric air contains some amount of water vapor. Imagine your work environment as a sponge, retaining moisture. If we were to squeeze it out, there'd be excess water. The same happens when air is rapidly pressurized, and why equipment is needed to achieve dry compressed air.

Since rapid temperature changes occur during the high heat compression process, water vapor is created. This level of moisture is called a pressure dew point (PDP), which is further explained in this article.

To avoid potential problems, including increased maintenance costs and shutdowns, it's important to dry compressed air with an aftercooler and drying equipment.

Risks from not removing water vapor include corrosion, microorganisms, and increased moisture in humid environments. Not only do these factors affect an air compressor's life cycle, but also overall production quality.

As you'll find out in this article, condensate contains more than water. When compressed air is dried, contaminants are removed in the process. If your application requires clean air, using a proper dryer set up is essential.

Read on below to learn more about the various solutions available, including on board aftercoolers.

 

What is an aftercooler?

Some air compressors come with an integrated aftercooler to eliminate up to 70% of moisture. This is ideal for most applications, and makes the drying process easy.

However, if you work in an environment that's humid or an application requiring the driest possible air, you'll want to add a dryer. Deciding on the right equipment depends on your needs and space.

How to achieve dry compressed air

Atmospheric air contains more water vapor at high temperatures and less at lower temperatures. This fluctuation affects water concentration when the air is compressed.

For example, a compressor with 7 bar pressure, 200 l/s capacity, and 20˚C temperature with 80% humidity releases 10 l/hour of water. As a result of this precipitation in the pipes and connected equipment, problems can occur. To avoid this, the compressed air must be dried.

In addition to an integrated aftercooler, you can opt for integrated or standalone drying equipment. When researching the best solution, you'll want to pay attention to the PDP in your environment.

Read more on choosing the right dryer for your application and about specific dryers - Aftercoolers - Refrigerant dryers - Over compression - Absorption and Adsorption Drying (Desiccant dryers) - Membrane dryers.

All atmospheric air contains some amount of water vapor. Now, consider the atmosphere as a giant, slightly wet, sponge. If we squeese that sponge very hard, the water absorbed will drip out. The same happens when air is compressed, which means the water concentration will increase. To avoid future problems in the compressed air system, the wet air needs to be treated. This takes place using an aftercooler and drying equipment. 

Two main dryer types

When choosing a dryer, you'll usually see two types prominently discussed, refrigerant and desiccant. The right one for you is determined by your setup, budget, and application(s).

Refrigerant dryers

The more cost-effective option, refrigerant dryers are suitable for most applications requiring high pressure air. As inferred from its name, this equipment works by cooling air down. This drying process occurs through piping connected to an air compressor.

They tend to achieve dew point levels of 2(C) to 10(C), and are fairly energy efficient. In addition, refrigerant gases used in newer equipment limit global warming as much as possible.

Desiccant dryers

If seeking a more robust dry compressed air solution, desiccant dryers are what you're after. While the initial cost of investment is higher than refrigerant dryers, they're more energy efficient, and deliver cleaner air.

Desiccant dryers work through a chemical process that binds to moist air, eliminating vapor during production. As a result, desiccant dryers can reach a PDP of -40(C).

Since this equipment requires less electricity than a refrigerant dryer, the operation cost is much lower.

Drying compressed air is important

What is the pressure dew point?

Referenced above, PDP is used to describe the water content in compressed air. It is the temperature at which water vapor condenses into water. Low PDP values indicate small amounts of water vapor in compressed air.

When evaluating different dryers, it's worth noting that atmospheric dew point isn't comparable to PDP. For example, a PDP of +2˚C at 7 bar is equivalent to –23˚C at atmospheric pressure. It's also important to understand that using a filter to remove moisture isn't effective.

This is because further cooling leads to continued precipitation of water condensation. To select the right type of drying equipment, you'll need to understand the PDP. Taking cost into account that the lower the dew point required, the higher the investment.

Five techniques exist for achieving dry compressed air. These include, cooling plus separation, over-compression, membranes, absorption, and absorption drying.

With air drying comes the need to handle waste when dry air is separated from vapors and lubricants. The following section provides further information on this topic.

How to dispose of condensate?

Anyone who runs a compressed air system (using oil-injected technology) needs to know how to dispose of condensate. When vapor is released from an air compressor, it contains particles of oil not visible to the naked eye. This is why it's important to follow environmental guidelines.

Not only is incorrect disposal bad for the planet, but you could incur a fine and damage your reputation as a responsible company. There are many rules concerning waste disposal, which are clearly pointed out at recycling centers.

Following these guidelines is easy. Walk around your compressed air equipment to see where the condensate drains empty out. Ideally, these pipes should go to an oil/water separator and then off to a foul drain.

If they are going straight from a drain onto the floor or into a standard plastic container, then this should raise a red flag. Oil/water separators are very easy to install. Note that rules change from region to region, and it's important to check your local requirements.

In this guide you will learn everything you need to know on air treatment. From different types of contaminants to knowing your air quality requirements; this guide covers all important air treatment topics.

Do you have any specific questions for us or do you need more support? Our air treatment experts are happy to help you. Get in contact by clicking the button below.

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