Study On The Enrichment And Separation Of Hydrogen Isotopes By 5A Molecular Sieve Displacement Chromatography

The development of hydrogen isotope separation techniques on large scale in china has been promoted for several years by the urgent requirements of the projects including the International Thermonuclear Experimental Reactor(ITER),China Fusion Engineering Test Reactor(CFETR)and inland nuclear power plant.Among varieties of hydrogen isotope separation techniques,displacement chromatography is a promising candidate because of its advantages of smaller column capacity,lower construction and running cost.Aiming to improve the performance of the displacement adsorption process,the separation properties of zeolite 5A as the separation material were systematically studied,and the separation performance of several techiques based on displacement chromatography was tested.Using the experimental results of the adsorption isotherms of pure protium and pure deuterium on zeolite 5A,the adsorption isotherms of the pure isotopologues including HD,HT,DT,and T2 were calculated on the basis of the micro-pore filling model,respectively.Based on the ideal solution model,the separation factors for several hydrogen isotopes mixture were also calculated.According to the calculated separation factors,the thermodynamic isotope effect under various conditions was analyzed.The results show that at temperature range from 77.4 K to 157 K and pressure range from 10 Pa to 0.2 MPa,the separation factor varies from 5.80 to 1.04.The isotope effect increase with the rise of the mass difference between isotopic components,and decreases exponentially with the increase of temperature.Under the pressure condition of less than 10 kPa,both the total pressure and the gas composition have no obvious effect on the separation factor,while the separation factor significantly drops when the total gas pressure changes from 10 kPa to 100 kPa,and obviously declines with the increase of the heavier hydrogen isotope content.In order to optimize the process parameters,based on the material conservation equation,momentum conservation equation,adsorption isotherms and mass transfer dynamics equations,the mathematical models for the process simulation of hydrogen displacement adsorption and vacuum adsorption were established,respectively,and successfully solved by using a self-developed procedure.Simulation results of hydrogen displacement adsorption show that a maximum of the sum of the enrichment factor and recovery ratio appears with the increase of adsorption amount,and the maximum rises with the decreasing of the operation pressure of the separation column.Under the condition that the outlet column pressure is slightly higher than normal pressure,the enrichment factor and the recovery ratio corresponding to the maximum value are 2.06 and 0.88,respectively.Within the length range from 10 m to 40 m,increasing both the length of the separation column and the flow rate can make the process simultaneously have higher enrichment factor,recovery ratio and separation capacity.When the length/diameter ratio is large enough,enlarging the separation column diameter and simultaneously increasing the flow rate can improve production capacity while the original level of the enrichment factor and recovery ratio maintain.For D2 enrichment from the H2-0.1 vol%D2 mixture,the simulation results of the vacuum adsorption process show that,under the conditions that the flow rate ranges from 0.5 SL/min to 2.0 SL/min,and column length ranges from 0.5 m to 1.5 m,raising the flow rate and/or column length are conducive to deuterium enrichment at the inlet of the separation column and depletion at the outlet.During the adsorption,the deuterium abundance level in the gas phase of the outlet declines drastically at the beginning and then steadily increases with the rising of the pressure in the column,and it is lower than one ppm when the final outlet pressure is near atmospheric pressureIn order to verify the rationality of the simulation results,a separation device was set up and the deuterium enrichment performance was experimentally studied based on hydrogen displacement adsorption process and vacumm adsoption process,respectively.The experimental results are in good agreement with the simulational ones,which indicates that the conclusion of the process simulation is reasonable.Based on the above research results,a new hydrogen isotope enrichment process named dual column temperature-pressure swing adsorption process was proposed and experimentally verified to run efficiently and stably.In this process,deuterium enrichment from the protium-deuterium mixture is realized by the combined work of two identical separation columns,which mainly includes the following steps low-temperature vacuum adsorption,raffinate extraction,vacuum thermal desorption,product extraction,raw material supply,and cooling.The experiment test results show that for the raw gas with D2 abundance of 3.63%,under the condition of column capacity of 71 SL,the raffinate extraction amount for a single column can reach 15 SL,the recovery ratio of D2 can be better than 99%,the enrichment factor is about 20,and the daily treatment capacity can reach 560 SL/day.Through the comprehensive comparison with other process,it was found that the process has better level of the processing capacity,the enrichment factor,and the recovery ratio.