Design and Analysis for Sizing and Layout of Piping for the CORS of Helium Refrigerator/Liquefier

Abstract

The Helium Refrigerator/Liquefier (HRL) needs compression of helium gas, which is then, cooled and expanded to produce liquid helium at 4.5 K. To avoid high heating and to reduce the work requirement in the compression, oil of heavy molecule, which has high specific heat, is mixed with helium before compression. Before using this 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 tank, oil recirculation pumps, oil vapor coalescers and oil adsorber beds, filters, valves and other instrumentations. This whole system is called as compressor and oil removal system (CORS). Project work involves finding the proper size and layout of pipe lines and valves involved in this CORS, being developed at IPR. These three compressors are oil injected screw compressors which will take Helium gas at 1.05 bar and supply at 14 bar. Tentatively, the nominal helium flow rate through each compressor is 80 g/s. The complete oil removal is performed in two stages: bulk oil removal and molecular oil removal. Bulk oil removal system removes bulk of the oil from the mixtures of helium and oil in an oil tank which is re-circulated by pumps after being cooled by oil cooler. Four coalescers and a charcoal bed performs the final oil removal, so that about 1 PPM (parts per million) or less oil vapor will be there in the helium stream which is then sent to the cold box for producing cooling capacity. Excess helium gas is sent back to the compressor suction via a control valve. The CORS will be connected to helium buffer tank for helium gas supply to the CORS via a control valve and for gas recovery from the application to the buffer tank via another control valve. The sizing and layout of these pipe lines with valves will affect the pressure drop and flow controllability of the operation of CORS which is analyzed in this project, the present study aims in selection of material for the pipe as well as selection of an appropriate nominal diameter for the pipe of the suction route and discharge route of the CORS. Also method to calculate the pressure drop in a bend is presented depending on which appropriate bend radius is selected for a given nominal diameter pipe . Furthermore the selection method is extended for proper valve sizing and selection for both the helium flow and the oil flow. Different loads like, pressure of the fluid, momentum changes in the flow, weight of elements, thermal stress and vibration loads coming from compressors acting on the pipes are analyzed.