Air Treatment Overview

As the name suggests, air dryers are primarily used for the removal of water vapor from the compressed air. Removing water vapor is essential to avoid common issues such as corrosion, product spoilage or equipment malfunctions and failures. Dryers are typically integrated into the compressor to ensure the correct level of air purity for the application.  The unique differences in the type of dryer is based on the integrated agents in the machine to dry the incoming air.

• Refrigerated Dryers. This is the most common type of compressed air dryers and can be water- or air-cooled. They use a refrigerant circuit and heat exchanger(s) to pre-cool the compressed air, cool it to a level that condenses the water vapor for removal, and then reheat the air to prevent pipe sweating downstream. Refrigerant dryers can lead to a pressure dew point (PDP) as low as +37.4°F/+3°C
• Desiccant Dryers. Two towers filled with desiccant are the distinguishing difference with desiccant dryers. While one tower is drying the compressed air, the other is being regenerated. Desiccant dryers can achieve dew points as low as -40°F/-40°C and -100°F/-70°C. The use of a porous desiccant adsorbs the moisture by collecting it in its myriad pores, allowing large quantities of water to be retained by a relatively small quantity of desiccant. Desiccant types include silica gel, activated alumina, and molecular sieves.
• Membrane Dryers. These dryers consist of cylinders that house thousands of hollow, polymer fibers with an inner coating. As filtered, wet compressed air enters the cylinder, the membrane coating allows water vapor to permeate the membrane wall and collect between the fibers, while the dry air continues through the fibers in the cylinder at almost the same pressure as the incoming wet air.

Compressed air is filled with particles, aerosols, and water/oil vapor that can contaminate the compressed air, causing potential harm to its end users or application. Inline filters are integral to a compressed air system, helping trap dirt, particles and other impurities that could contaminate the compressed air. Essentially, they work to remove contaminants from the compressed air after compression has occurred. The type of filter required depends on the air quality of your application needs, but can include: 

• Particulate Filters. These remove dry, solid particles of all sizes from the compressed air. The finer the particulate size, measured in microns, the higher the cost associated with removing them due to filter element life and system pressure drop. ISO 8573-1:2010 can be used to specify the level of solid particles removal needed.
• Coalescing Filters. These filters bring small droplets of liquid together in order to form large droplets, which then fall from the filter into a moisture trap as they increase in size. This results in a cleaner and dryer compressed air stream. While used for collecting water, coalescing filters are not the best for trapping water vapor.
• Vapor Removal Filters. These filters employ an absorption process in order to capture the gaseous contaminants that pass through a coalescing filter. By utilizing activated carbon granules, carbon cloth or paper filters, vapor filters can capture and remove the gaseous contaminants.  Activated charcoal is the most common filter media because it has a large open pore structure.

Compressed air produces gallons of condensate that contains oil and other contaminants. Collecting and disposing of this polluted condensate is can be difficult and costly, yet very essential. Oil-water separators capture the oil in a compressor's condensate to allow for proper disposal in a safe and environmentally-friendly way. Separating oil and water through a multistage cascade filtration system results in rinsed water, which can be discharged into the sewage system and limits the volume of oil that requires specialized disposal.

Often the most ignored of the compressed air ancillary products, drains must properly operate in order for the filters and separators to be successful in completing their task. These provide automatic condensate drainage that collects at multiple points in the compressed air system, including the compressor aftercooler, filter drains, refrigerant dryer drains, the bottom of the air receiver, and other low points in the system after compression. In many cases, drains are electronically controlled, monitoring condensate build-up with liquid level sensors that detect and know when absolutely necessary to evacuate the condensate, minimizing spoilage of already compressed air.

Colloquially known as a compressed air tank, air receivers are used to store compressed air before it enters into piping or compressed air equipment. This acts as a buffer between the fluctuating pressure caused by demand changes on the usage side and the air compressor itself. Air receivers additionally allow for more efficient use of compressed air by reducing unstable pressure peaks, frequent starts and stops of the compressor, and lower the risk of condensate entering into the airnet.

An aftercooler is a heat exchanger that cools the hot compressed air to remove the water that would otherwise condense in the pipe system or equipment. In many cases an aftercooler is built into the compressor itself. Aftercoolers remove both moisture and water vapor in compressed air systems by cooling the air below its dew point. When this occurs, water vapor condenses into liquid form. Aftercoolers can be water-cooled or air-cooled and are generally equipped with an automatically draining water separator, which should be placed close to the air compressor.