Review of oil separation technologies used in refrigeration systems

Vapor compression refrigeration system is commonly used for air-conditioning and refrigeration. It is also used in domestic & commercial refrigerators and cold storage applications. Industrial sectors like refinery, petrochemical, chemical, pharma & pulp also benefit from it. The refrigeration system cools the process fluids to the desired temperature. The most commonly used process fluids are water, air, and brines. Irrespective of size and application of the system, all of them operate on common thermodynamic cycle called ‘Vapor compression refrigeration cycle’. Oil is used in compressors of refrigeration systems for lubrication, sealing, cooling, reducing pressure pulsations (leading to silencing effect) and for auxiliary functions like capacity control in screw compressors. Oil gets mixed with refrigerant and is discharged out from the compressor along with refrigerant at high pressure & temperature. Oil, if not separated from the discharge gas, can deteriorate heat transfer in heat exchangers in the refrigeration system. In extreme cases, if oil does not return back to compressor then compressor damage can happen. Therefore, separation of oil from refrigerant before the condenser is important. In this paper the conditions when oil separators are necessary in refrigeration systems are discussed. The paper presents a review of variety oil separation technologies used in different types of refrigeration systems. These technologies are based on fluid flow mechanisms involving velocity reduction, change of direction, gravity settling, centrifugal motion, demister pad, impingement separation and coalescing separation. Every technology has unique advantages and limitations. Construction and operation of commonly used oil separators, employing different technologies for oil separation are explained. Though article focuses on refrigeration systems, the concepts discussed are also applicable to any oil-gas separation systems