Corporate Buyers Guide

To choose a dryer for compressed air, some important parameters have to be considered. 1. The pressure and temperature of the compressor output. 2. The air capacity. 3. Air or water cooled. 4. The desired dew point (humidity) of the air, 5. The cost to purchase dryer, 6. The operating costs.

For refrigerated air dryers:

1.      The performance of a refrigerated air dryer are based on an inlet temperature of 100 F and pressure of 100 psig.

2.      The air capacity is rated in scfm as usually the same rating as the compressor.

3.      Both, air and water cooling are available. Water cooled units have a slightly higher rating but, are more expensive.

4.      The normal dew point rating is 35 F. This can be lowered by operating below the rated capacity. The humidity of the surrounding air has to be considered. Humid regions will have a higher dew point air output.

5.      The initial cost to purchase a refrigerated air dryer is lower than for desiccant dryers. The installation cost is simpler and less expensive

6.      The refrigerated air dryer uses large amounts of electricity. This makes the operating costs high

One advantage of refrigerated air dryers is that they can operate at higher inlet temperatures and pressure than desiccant air dryers.. Therefore, for plastic molding machines plus in many food and pharmaceutical applications the refrigerated air dryer is used at the output of piston compressors.

Mist collectors are often called “Oil Mist Collectors”. Three methods of mist removal are available. Coalescing filters are the standard fiber woven filters. Electrostatic filters have static charged plates which draw the vapor particles to the plates. Centrifugal force mist collectors use fans to move the air in a centrifuge type structure and the vapor particles fly to an outside surface where they are trapped and drained off.

Both, the electrostatic and the centrifugal mist collectors are for small volumes of air ( less than 1000cfm)  With both methods, the vapor particles can drain from the surfaces and as such are well suited for continuous operation. The oil or coolant draining from the collector surfaces can be fed back into the coolant container for re use.

The coalescing filters trap the vapor particles but the drain off is slow. Also, since the air passes through the filter, any dirt particles in the air will get trapped and drained off with the oil. These filters have to be cleaned periodically. These filters are relatively inexpensive and it pays to have multiple filters which can be switched back and forth for easy cleaning. To reuse this oil, it will have to be filtered to remove any particulates.

High speed metal cutting machines use a large amount of cooling fluid to keep the cutting tools from overheating. Most of these cooling fluids are water based, but whether water or oil based the vapors they create have to be drawn from the machine and filtered. The liquid portion can be returned to the cooling fluid container and the air released to the atmosphere.