Operation Analysis Of PandaX-4T Ultra-high Purity Xenon Cryogenic Distillation System For Krypton Removal And Gas-liquid Two-phase Flow Simulation

As the scale of PandaX dark matter detection experiments continues to upgrade,the demand for the detection medium xenon is greater,and the purity requirements of xenon is higher.The previous generation of distillation system can not meet the requirements of the experiment.The PandaX-4T collaboration group designs and develops a new ultra-high purity xenon cryogenic distillation system,which is used to reduce the mole fraction of krypton in commercial xenon from 5×10-7 mol/mol to 1×10-14 mol/mol,through the McCabe-Thiele(M-T)method and the quality and energy conservation method.Experimental operation analysis and simulation research are carried out based on the newly designed cryogenic distillation system.Uncoupled with dark matter detector,PandaX-4T cryogenic distillation system independently runs for 1.5 months.The comprehensive performance of the cryogenic distillation system has been studied by analyzing the parameters such as temperature,pressure,flow rate and xenon purity in each operation stage.And the numerical simulation software Fluent is used to simulate and analyze the gas-liquid two-phase countercurrent flow of xenon in the packing channel on the basis of experimental data.The specific research content and main conclusions are as follows:(1)The operation process of PandaX-4T cryogenic distillation system is introduced,and the system status in each operation stage has been analyzed.The system is in a stable thermal state in the five operating stages of pre-cooling,gas charging,total reflux,purification and collection.And there is no flooding during the 1.5-month period.The distillation system is reliable.(2)The distillation system operates at a large flow rate of 10 kg/h,which is the maximum purification flow rate that can be achieved by a cryogenic distillation system of the same use available in domestic and foreign country.The mole fraction of krypton in the product xenon is less than 7.99 × 10-12 mol/mol,and a total amount of 5.75 tons ultra-high purity xenon has been produced.(3)Generally speaking,the distillation system performs well under the large flow of 10 kg/h.The average liquid phase fractionation of the feed is 0.964,which basically meets the requirement of all-liquid feed.In the precooling process of original xenon,the average heat recovery efficiency of the plate heat exchanger is 94.3%.The resistance of the structured packing PACK-13C to fluid is relatively low,and the pressure drop of gas is 16.758.3 Pa/m.The variation range of the gas load factor is from 0.0215(?)to 0.0235(?),which is much smaller than the flooding point parameter of 1.42(?)Flooding will not occur under compliance operations.(4)It is noticed that the feed-related parameters such as the pressure of the original xenon,the thermal compensation power of the condenser and the liquid level in the reboiler change periodically during the experiment.It is speculated that this change is caused by the vertical height difference of the feed pipes and the U-shaped pipe structure.(5)Fluent is used to simulate the gas-liquid two-phase flow process in the packing channel under the working conditions of R=45,90,135,180,respectively.The simulation results show that the gas occupies most space of the packing channel,and the space occupied by the liquid is very small.The liquid flows along one side of the packing in the form of stream.There is some entrainment of mist and backflow in the gas-liquid two-phase countercurrent process.Since almost all the feed flows to the stripping section,the gas phase has a greater impact on the liquid phase in the rectifying section,and there are more reflux and mist entrainment in the rectifying section than in the stripping section.However,the reflux phenomenon under the 4 working conditions is not significant enough to cause flooding.So it is suggested to appropriately increase the reflux ratio during the distillation process to improve the purification performance of the system.The operation analysis and numerical simulation research of PandaX4T ultra-high purity xenon cryogenic distillation system for krypton removal has very vital theoretical research value and practical engineering significance,and it is also a very important reference for optimizing the next stage of distillation operation.