Moisture in compressed air can cause a range of problems in industrial applications, from corrosion to freezing and reduced efficiency. In this post, we’ll look at how moisture gets into compressed air, the devices used in compressors to prevent liquid water at the outlet, and the options available for drying air.
Ambient Humidity. The Air has Water In It
Air naturally contains water vapour, and the amount of moisture in the air varies depending on the temperature, pressure and how wet the environment is. Warmer air can hold more water vapour than colder air and lower pressure air can hold more vapour than higher pressure air. The amount of water in the air, it’s humidity, is measured as the amount of water vapour that air contains relative to the amount it can old. 100% humidity means the air contains all of the water it can hold.
When air is compressed it’s relative humidity rises as the pressure increases, it’s water carrying capacity is reduced but at the same time, its temperature rises, which reduces the relative humidity and increases the water vapour carrying capacity of the air. As the compressed air leaves the compressor it cools and, depending on the ambient conditions the compressor is being used in the vapour condenses and a mixture of air and water will be coming from the outlet of the compressor.
No Liquid Water at the Outlet
Clearly liquid water coming out of a compressor when it’s used on a warm, humid summer’s day would severely limit the applications for that compressor and as standard all of our of our compressors are specced to prevent that.
To prevent liquid water at the outlet all of our compressors are equipped with water separators and all but our smallest 120cfm machines are equipped with inter coolers to cool the air between compression stages and after coolers that cool the compressed air before it goes through the water separator and leaves the compressor.
These devices are effective at producing air dry enough for most applications such as blasting where a medium has to be relatively dry. However, they may not be sufficient for applications where extremely dry air is required, such as in the pharmaceutical and food industries.
Processes That Require Air to be Measurably Dry
For some applications the absence of liquid water isn’t a good enough measure of dryness. Air is required to be dry to a minimum pressure dew point. Pressure dew point is the temperature at which water vapour begins to condense into liquid water at a given pressure.
There are several options available for drying air and they all happen after the compression stage. They dry the air that the compressor produces. These options include refrigerated dryers, desiccant dryers, and membrane dryers. Refrigerated dryers cool the compressed air to remove moisture, membrane dryers use a semi-permeable membrane to remove moisture,.while desiccant dryers use a material that absorbs moisture from the air.
Of these options, desiccant dryers are the best choice for applications where extremely dry air is required and the most flexible for rental applications. Desiccant dryers pass the compressed air through a material to absorb the moisture, as standard our dryers use a desiccant that produces air with a -40°c pressure dew point as standard with available -70°c by request.
Desiccant dryers, as well as producing the driest air, are inherently more reliable than other options with a long service life and ease of installation.
At GenAir we understand compressed air and whether you need air that’s just “dry enough” that it doesn’t clag up your blasting medium or if you need air that’s dry and clean enough to be used in a pharmaceutical laboratory we have the a solution and the experience to implement it.