Compressed Air Drying in Hot Ambient with Air Cooled Equipment
Over the years of reviewing compressed air systems through North America we have observed a growing application problem in applying air compressors and compressed air dryers in “High Temperature Ambient”, particularly in general industry with medium sized air compressors, 50 HP to 300 HP.
The plant installs a new rotary compressor package. It is usually air cooled, because cooling water is “expensive” and or requires significant treatment. Air cooled compressors with a “built in” air cooled aftercooler carries a significantly lower initial price than a water cooled unit with a separate cooling tower / pumping station.
Rotary compressor packages have been the predominant number of units sold over the years. Air cooled oil coolers / after coolers is also the predominant choice of cooling media.
Next comes the filter, dryer for “General Industrial Air” – little or no liquid water with a pressure dewpoint 20 degree F or more below the expected plant temperature. By normal standards a two stage refrigerated dryer is selected to deliver a rated +40 degree F pressure dewpoint when the inlet air is 100 psig, 100 degree F inlet temperature and the ambient temperature is 100 degree F. The ambient temperature rating reflects the effect of ambient temperature on the AIR COOLED EVAPORATOR.
Often the refrigerated dryer is selected with the full flow rating in SCFM to meet the full load delivered air from the compressor. For example: you might have a rotary screw compressor with a full load delivered air of 1000 scfm at 100 psig and air cooled oil and after coolers. To this the plant applies a refrigerated dryer rated to handle a full load flow of 1000 scfm at 100 degree F inlet temperature and 100 degree F ambient temperature, and 100 psig inlet pressure. If the ambient temperature is expected to be over 100 degree F, a water cooled evaporator will enhance the refrigerated system performance compared to air cooled. For this exercise, we will disregard this effect either way.