Refrigeration Cycle: Oil Separators

Most compressors are configured with an oil separator downstream of the compressor. An oil separator is a vessel that is specially designed to “separate” any oil in the discharge vapor and return it back to the compressor where it is wanted. Oil that escapes the separator is unwanted and results in fouling on heat exchange surfaces and increased maintenance. 

The first generation of oil separators were small vessels that were internally fabricated to cause directional change of the oil-laden refrigerant. Changing directions provides an opportunity for oil droplets to “separate” from the ammonia and be returned to the compressor. 

Coalescing oil separators are widely used on screw compressors and provide superior separating capabilities. Coalescing oil separators are also vessels, but have two distinct sections. The first section receives oil-laden refrigerant from the compressor where large droplets are allowed to drop out and collect at the bottom of the vessel. The refrigerant then passes through a filter, called a “coalescer”, which is designed to remove smaller droplets of oil.