Design of efficient oil coales for helium compressor and oil removal system.

In the screw compressor of helium refrigerator/liquefier, large quantity of lubricating oil is mixed with helium gas during compression process, which is removed by the oil removal system (ORS), placed at the downstream of the compressor. All most all oil should be removed from helium stream before it goes to the cold box for its liquefaction. The ORS has coalescer system to remove oil particles by coalescing technique. Present analysis is related to the design of coalescer for removal of oil particles from the helium stream at pressure 14 bar and temperature about 300 K. The estimated oil content at the outlet of the second coalescer
housing is 50 PPB (parts per billion) by volume. This paper will discuss the concept and details of finding coalescing efficiency and coalescing mechanisms. Different coalescing mechanisms contribute in capturing of oil droplets depending on size of oil droplets. Fibre diameter and face velocity play major roles for deciding the efficiency of coalescing. Analysis shows that as fibre diameter decreases, pressure drop increases and coalescing efficiency increases. All these details are discussed in this paper.