Design and Analysis of Oil Removal System and Helium Cooler for Conversion of Air Compressor to Helium Compressor

Abstract

The Helium Refrigerator/Liquefier (HRL) plant requires the compression of helium gas for the liquefaction of helium. Considering the volumetric flow rate and pressure requirements, the oil injected screw compressors are used for the compression process. In order to avoid high heating and to increase the component life of screw compressor, oil of heavy molecule which has a high specific heat is mixed with helium before compression. Before using this compressed helium (He) gas for refrigeration, it is necessary to cool it to about room temperature and separate the oil from the mixture. For this, there are heat exchangers, bulk oil separator tanks, oil recirculation pumps, coalescers, adsorber beds, filters, valves and other instrumentation needed and this whole system is called as Compressor and Oil Removal System (CORS). An analysis of the modification work has been done related to how an air screw compressor and oil removal system can be used as helium compressor system. In the present work, investigations with analysis and optimization have been done for improvement the performance of this modified system. In the present report, a parametric study of discharge temperature, work, suction pressure, pressure ratio, inlet temperature, oil inlet temperature, oil gas mass ratio, oil intake position, etc. are carried out. Also the effects of these parameters on the volumetric efficiency, adiabatic efficiency and the specific power consumption of twin screw compressor are considered. The performance improvement of CORS is done by theoretical performance calculation so as to minimize the oil concentration in downstream side in order to avoid the damage to the high speed turbine. The coalescer test facility is designed for the removal of the oil after the compression process. Also the theoretical calculation of performance has been made in this report which gives efficiency equal to 99.9999 for a mean oil droplet of diameter 0.12µm. The performance analysis of coalescer has been carried out. The shell and tube type water cooled heat exchanger is used for cooling of the helium gas. The performance analysis of the existing shell and tube heat exchanger is undertaken. Also the theoretical design is compared with the HTRI and ASPEN softwares. The thermo-hydraulic design, optimization and analysis of the helium cooler for the new proposed plant is carried out as per the available parameters.