Cryogenic Molecular Sieve Bed Research Articles

Development and testing of lab-scale atmospheric molecular sieve bed with zeolite 4A adsorbent

Tritium Extraction System (TES) is one of the most important systems of fusion blanket. The two basic systems of TES are Atmospheric Molecular Sieve Bed (AMSB) and Cryogenic Molecular Sieve Bed (CMSB). AMSB removes ppm levels of water vapour (Q2O), while CMSB removes hydrogen isotopes (Q2), oxygen, and nitrogen from helium purge gas. Though detailed parametric study of AMSB is very important for fuel cycle technology, such studies are very limited. In this work, a lab-scale AMSB is designed and developed at Institute for Plasma Research, Gandhinagar, using Zeolites 4A as an adsorbent material. Experimental break through curves for the adsorption of various concentrations of moisture (H2O) (up to ∼20,000 ppm) at flow rates (1–3 NLPM) from helium gas at room temperature have been generated and compared with theoretical estimation. Adsorption capacity of lab scale AMSB has been estimated at various operating conditions. The effects of the initial moisture concentrations and flow rates on breakthrough curves are studied in detail.

Density Functional Theory Investigation of Cu, Ni, and Ag Inclusion in ZSM-5 to Study Dihydrogen Binding for Cryogenic Molecular Sieve Bed Adsorber in Nuclear Fusion Systems

A computational investigation of Cu-, Ni-, and Ag-introduced ZSM-5 as potential hydrogen storage materials for nuclear fusion energy systems is performed. Among the 24 distinct tetrahedral sites of the monoclinic phase of ZSM-5, systematic periodic density functional theory (DFT) computations have been carried out on 15 experimentally identified T sites that show clear Al site preference and stability in high Si ZSM-5. Adsorption energies estimated from DFT studies have revealed that the T sites in the sinusoidal channels T4 and T10 are the most stable for including all three metal ions. Hence, these should also be considered as potential active sites for dihydrogen binding investigations in addition to the common T12 site in the intersection. The average hydrogen binding energies at these representative T sites were −79 to −45 kJ/mol, which correlates well with both the metal-H2 distance and H-H bond elongation distance. The computed hydrogen bond stretching frequency values were in the 3300 to 3755 cm−1 range upon adsorption of H2 onto the Ni, Cu, and Ag, indicating Kubas-type dihydrogen complex formation. The evidence for dihydrogen binding was also obtained from investigating the σ donation and back donation between the metal ion valence orbitals and the H2σ, H2σ* orbitals through projected density of states and natural bond order analysis. Our analysis indicates that Ni is better stabilized in the framework sites and is considered a potential candidate for dihydrogen binding.

Tritium extraction and recovery system (TER) for the helium cooled pebble beds with steam in the helium purge gas

The Tritium Extraction and Recovery (TER) system is a He-loop with the main purpose to purge the HCPB BBs and consequently remove tritium from the pebble beds, followed by tritium recovery from the purge gas. The tritium recovery from Q2 and Q2O forms from the He purge gas is realized by adsorption of the Q2O form in the Reactive Molecular Sieve Bed (RMSB) followed by Q2 adsorption in the Cryogenic Molecular Sieve Bed (CMSB)/getter beds (Q stands for any H/D/T). During the regeneration of the RMSB and CMSB/getter beds the tritium will be recovered in the Q2 form and finally is processed in the Tritium Plant.The adsorption/desorption process using Reactive Molecular Sieve Beds (RMSB) can be successfully used for removal of the tritiated water from helium purge loop of the TER HCPB. In this case, the tritium recovery from the tritiated water is straight forward by isotopic exchange with a hydrogen/deuterium swamping gas. In addition, the use of the RMSB for the helium purge gas containing steam allows that slightly tritiated water, resulted as tritium recovery by isotopic swamping, to be returned in the helium purge loop. Therefore, there is no need for further processing of tritiated water since the water is used as carrier closed loop of the tritium in the helium purge loop. The water that will be recovered during the full regeneration of the RMSB will contain tritium at levels of at least two order of magnitude lower that in the tritiated water coming out from the BB. By doing so it is not necessary to process the significant amount of water that is contained in the purge gas. Two order of magnitude difference in the tritium concentration in the water, mining the tritium concentration in the water fed in the BB and the tritium concentration in the water coming out from the BB, provides the required gradient in the tritium concentration for the isotopic exchange at the level of pebble beds.The paper aims to present the main advantages of tritium removal from the helium purge loop containing steam based on RMSB technology and a proposal for the configuration of the TER HCPB based on RMSB technology will be presented. The estimation of the tritium inventory based on various purge gas flow rates and steam content in the purge gas will be introduced as well.

Low-pressure adsorption of hydrogen isotopologues on LTA4A zeolites - A grand canonical Monte Carlo simulation study

Effective removal of the trace quantities of hydrogen and its isotopologues is crucial for the proper functioning of the tritium extraction system (TES) in the fuel cycle system of the fusion reactor. Zeolite molecular sieves of Linde Type A (LTA) framework are considered potential adsorbent materials for the cryogenic molecular sieve bed (CMSB) of the TES. However, the adsorption isotherm data of H2, HD, D2, HT, DT, and T2 on LTA 4A zeolites at low pressures (1–1000 Pa) and 77.4 K temperature is scarce in the literature. Grand canonical Monte Carlo (GCMC) simulations were performed to study the hydrogen isotopologues adsorption in the pressure and temperature ranges of operation of the CMSB of TES. The adsorption isotherms show that the equilibrium loading capacity is larger for T2, followed by D2 and H2 at 77.4 K. In the case of heteronuclear isotopologues, the loading capacity is larger for DT, followed by HT and HD under the same conditions of interest. The increase in the equilibrium adsorption capacity with isotopic mass could be attributed to the difference in the zero-point energies of the isotopologues. The effect of Si/Al ratio in the LTA zeolites on the cryosorption of hydrogen isotopes is investigated. The results show that, as the Si/Al ratio decreased, the equilibrium loading of the hydrogen molecules increased. The results obtained from this work are in good agreement with our experimental results and published data in the literature.

Study and characterization of potential adsorbent materials for the design of the hydrogen isotopes extraction and analysis system

One of the most challenging tasks in the design of the inner fuel cycle system lies in the effective design of Tritium Extraction System (TES), which involves proper extraction and purification of tritium in a fusion reactor. A prototype Hydrogen Isotopes Recovery System (HIRS) is being developed to validate the concepts for tritium extraction by adsorption mass transfer mechanism. The two main systems of HIRS are Atmospheric Molecular Sieve Bed (AMSB) adsorber and Cryogenic Molecular Sieve Bed (CMSB) adsorber. AMSB removes ppm levels of water vapour while CMSB removes ppm levels of hydrogen isotopes, oxygen and nitrogen gas from Helium purge gas. Selection of appropriate adsorbents for the HIRS is important for its efficient functioning. Adsorbents, namely, Zeolites 3A, 4A, 5A, 13X and Activated Carbon have been studied in detail at cryogenic temperatures to understand their surface characteristics and adsorption potential. In this work, we have generated the adsorption isotherms for hydrogen isotopes on potential adsorbents using a volumetric adsorption apparatus for a wide range of pressure from 1 Pa to 105 Pa. The BET and DFT models are applied for the determination of the textural properties of the adsorbents and the Langmuir-Freundlich composite model is used to fit the isotherm data. The parameters of the model were determined using nonlinear regression analysis. The enthalpy of adsorption is determined and is in the range of 8–11.5 kJ/mol for the adsorbate loadings corresponding to the partial pressure of hydrogen isotopes of ∼ 50–500 Pa in the TES. At low pressures of hydrogen isotopes, the free energy plot followed Henry’s law. The isotherms and enthalpy of adsorption clearly indicate reversible physisorption and monolayer formation of hydrogen isotopes on the potential adsorbents. Amongst hydrogen and deuterium, hydrogen is more strongly adsorbed on Zeolites 4A, whereas deuterium is more strongly adsorbed on Zeolites 13X. In case of activated carbon, no isotopic selectivity was observed. This study facilitates the selection of potential adsorbents for the CMSB and quantification of the parameters associated with the adsorbents.

Design and thermal fluid structure interaction analysis of liquid nitrogen cryostat of cryogenic molecular sieve bed adsorber for hydrogen isotopes removal system

Efficient design of Tritium Extraction System (TES) for the fuel cycle of any fusion reactor is very important to maintain the tritium breeding ratio and hence sustain the fusion reaction. Hydrogen Isotopes Removal System (HIRS) for Indian Tritium Breeder Blanket removes Q2 (Q = H, D or T) and impurities using Cryogenic Molecular Sieve Bed (CMSB) adsorber at 77 K. The CMSB is maintained at liquid nitrogen temperature using a double walled cryostat made up of SS304. The paper describes the design and thermal Fluid Structure Interaction (FSI) analysis of cryostat assembly for CMSB of HIRS. The coupled analysis performed in this work involves solving for the fluid domain and transferring the results to ANSYS Thermal-Static structural set up to determine the stresses and displacement due to combined effects in the system. The mechanical design of the cryostat components is analytically performed using ASME codes. The velocity, pressure drop and time taken to cool the CMSB are determined by solving the fluid and energy equations in ANSYS Fluent analysis system. The solutions are imported into ANSYS Thermal-Static structural analysis system and the thermal-structural stresses and deformations are determined considering the temperature, pressure and acceleration loads. The space between inner and outer vessel is maintained at vacuum, which might lead to buckling. So, the critical buckling load multiplier factor is determined. These results are used in fabricating the complete cryostat system for CMSB of HIRS.

Hydrogen adsorption performance for large-scale cryogenic molecular sieve bed

Cryogenic hydrogen adsorption using molecular sieve beds is considered to be one of the main candidate processes for recovery of produced tritium from purge gas in breeding blankets and it has been chosen for separating hydrogen isotopes in Tritium Extraction System (TES) of Korean Helium Cooled Ceramic Reflector (HCCR) Test Blanket System (TBS). Various adsorbents and their performance have been studied for the cryogenic adsorption using small-scale experiments. However, large-scale experiments comparable to TBS-relevant scale are required to have sufficient confidence for component design and performance prediction of Cryogenic Molecular Sieve Bed (CMSB) for the TBS and beyond. To properly evaluate hydrogen adsorption performance of a large size CMSB, a series of experiments have been performed using PGLoop facility which is constructed and operated in the National Fusion Research Institute. The experimental conditions were set to include breeding-blankets-relevant parameters. As such, the effects of swamping ratio, total pressure, and flow rates on the performances of CMSB were studied in the range of hydrogen partial pressures from 100 to 700 Pa. While a slight reduction in hydrogen adsorption performance is observed in comparison to the small isotherm experiments, which can be attributed to scale-up effects, it shows that the experimental results agree reasonably well with existing literature data.

Experimental Investigation of ZrCo Getter Beds as Candidate Process for the Tritium Extraction Systems of the European Test Blanket Modules

ZrCo is a well-known tritium storage material and has been studied intensively in the literature. The most interesting properties with regards to the thermodynamics of the ZrCo-H system are the very low H2 partial pressure in equilibrium with ZrCoH3 at room temperature and the ease to reach sufficiently high temperature to completely release the stored H2. These properties motivate also to use ZrCo not as a simple storage, but rather as a concentrator of hydrogen isotopologues from inert gases like He. With such function, ZrCo getter beds are the reference solution adopted in the conceptual design of the tritium extraction system of the European Test Blanket Modules (TBM) to replace the cryogenic molecular sieve bed previously proposed. An experimental campaign was carried out on ZrCo in order to consolidate this choice. The results confirmed that ZrCo performs well as getter material but only substantially below the maximum loading capacity. They revealed that the dynamic thermo-mechanical response of the material, controlled by temperature and H2 concentration, is the main limiting factor for the component performance.

Application of Computational Fluid Dynamics for the Simulation of Cryogenic Molecular Sieve Bed Adsorber of Hydrogen Isotopes Recovery System for Indian LLCB-TBM

One of the most challenging tasks in the design of the fuel cycle system lies in the effective design of Tritium Extraction System (TES) which involves proper extraction and purification of tritium in the fuel cycle of the fusion reactor. Indian Lead Lithium cooled Ceramic Breeder Test Blanket Module (LLCB-TBM) would extract hydrogen isotopes through Cryogenic Molecular Sieve Bed (CMSB) adsorber system. A prototype Hydrogen Isotopes Recovery System (HIRS) is being developed to validate the concepts for tritium extraction by adsorption mass transfer mechanism. In this study, a design model has been developed and analyzed to simulate the adsorption mass transfer kinetics in a fixed bed adsorption column. The simulation leads primarily to effective design of HIRS, which is a state-of-the-art technology. The paper describes the process simulation approach and the results of Computational Fluid Dynamics (CFD) analysis. The effects of different operating conditions are studied to investigate their influence on the hydrogen isotopes adsorption capacity. The results of the present simulation study would be used to understand the best optimized transport phenomenon before realizing the TES as a system for LLCB-TBM.

Recent Activities on Tritium Technologies for ITER and Fusion Reactors at JAEA

The design studies of Atmosphere Detirtiation System (ADS) have been carried out in Japan Atomic Energy Agency (JAEA) as a contribution of Japan to ITER. The performance of ADS has also been investigated under accidental conditions such as fire and co-existing of a poison gas for catalyst like SF6. There is no degradation of Detritiation Factor (DF) under co-existing of CO or CO2 up to 20% as a simulated fire condition. However, only 0.1% of SF6 degrades the DF from more than 1000 to 50, following reduction of water by SF4 etc. (decomposition products of SF6) at 773K of catalyst bed.For the tritium processing technologies, our efforts have been focused on the R & D of the tritium recovery system of breeding blanket. In case of ITER Test Blanket Module, a cryogenic molecular sieve bed system was designed and demonstrated. Furthermore, electro-chemical pumping system using a proton conductor is also investigated to design more effective system. The durability of electrolysis cell for Water Detritiation System (WDS) has been investigated and it is expected that the cell can endure more than 3 years’ operation under the ITER WDS design condition.A series of fundamental studies on tritium safety technologies has been carried out as another major activity of JAEA for ITER and future fusion demo reactors. Tritium behavior in various confinement materials, tritium monitoring & accountancy, and detritiation were studied under collaboration programs with universities, using Caisson Assembly for Tritium Safety study.

Experimental and simulation study on adsorption of hydrogen isotopes on MS5A at 77 K

Extraction of tritium from the sweep gas of the ITER Helium Cooled Pebble Bed (HCPB) Test Blanket Module is proposed to be carried out in a two-step process: trapping of water in a cryogenic cold trap, and adsorption of hydrogen isotopes (H 2, HT, T 2) in a Cryogenic Molecular Sieve Bed (CMSB) at 77 K. A CMSB mock-up in a semi-technical scale (1/6 of the flow rate of the ITER-HCPB) was designed and constructed at the Forschungszentrum Karlsruhe. In this work, the adsorption isotherms of hydrogen and deuterium on the MS5A adsorbent were investigated by the volumetric method. The correlation of the experimental adsorption isotherms of hydrogen and deuterium on the MS5A adsorbent were performed. To validate the cryogenic adsorption process, breakthrough experiments were performed using the CMSB mock-up. The experimental breakthrough curves obtained were analyzed with model mass balance equations, and scale-up numerical simulations were carried out.

Semi-Technical Cryogenic Molecular Sieve Bed for the Tritium Extraction System of the Test Blanket Module for ITER

The tritium extraction from the ITER Helium Cooled Pebble Bed (HCPB) Test Blanket Module purge gas is proposed to be performed in a two steps process: trapping water in a cryogenic Cold Trap, and adsorption of hydrogen isotopes (H2, HT, T2) as well as impurities (N2, O2) in a Cryogenic Molecular Sieve Bed (CMSB) at 77K. A CMSB in a semi-technical scale (one-sixth of the flow rate of the ITER-HCPB) was design and constructed at the Forschungszentrum Karlsruhe. The full capacity of CMSB filled with 20 kg of MS-5A was calculated based on adsorption isotherm data to be 9.4 mol of H2 at partial pressure 120 Pa. The breakthrough tests at flow rates up to 2 Nm3h-1 of He with 110 Pa of H2 conformed with good agreement the adsorption capacity of the CMSB. The mass-transfer zone was found to be relatively narrow (12.5 % of the MS Bed height) allowing to scale up the CMSB to ITER flow rates.

Interlinked Test Results for Fusion Fuel Processing and Blanket Tritium Recovery Systems Using Cryogenic Molecular Sieve Bed

A simulated fuel processing (cryogenic distillation columns and a palladium diffuser) and CMSB (cryogenic molecular sieve bed) systems were linked together, and were operated. The validity of the CMSB was discussed through this experiment as an integrated system for the recovery of blanket tritium. A gas stream of hydrogen isotopes and He was supplied to the CMSB as the He sweep gas in blanket of a fusion reactor. After the breakthrough of tritium was observed, regeneration of the CMSB was carried out by evacuating and heating. The hydrogen isotopes were finally recovered by the diffuser. At first, only He gas was sent by the evacuating. The hydrogen isotopes gas was then rapidly released by the heating. The system worked well against the above drastic change of conditions. The amount of hydrogen isotopes gas finally recovered by the diffuser was in good agreement with that adsorbed by the CMSB. The dynamic behaviors (breakthrough and regeneration) of the system were explained well by a set of basic codes.

Adsorption Isotherms of Hydrogen Isotopes on Molecular Sieves 5A at Low Temperature

Cryogenic Molecular Sieve Bed (CMSB) is considered to be applied to the bred tritium recovery system or the helium glow discharge exhaust gas cleanup system of nuclear fusion reactor. Molecular Sieves 5A (MS5A) is one of the most possible candidate adsorbents for CMSB. To design the CMSB, adsorption isotherm of hydrogen isotopes for MS5A must be investigated in liquid nitrogen temperature region (around 77 K) and above, and isotherm equation which can express the experimental data obtained in wide pressure range with good accuracy needs to obtaining. The present authors carried out the experiments using the volumetric method to obtain the adsorption isotherm of H2 and D2 for MS5A. Adsorption isotherms were obtained in the pressure range between about lPa and 0.2MPa at 77K (liquid nitrogen), 87K (liquid argon), 113K (isopentane), 143 K (n-pentane), 155 K (ethanol) and 195 K (dry ice/ethanol). Two Sites Langmuir Model was applied to understand adsorption isotherms, and was able to express the experimental observation with fairly good accuracy. The apparent heats of adsorption for two kinds of activated adsorption sites were obtained from temperature dependence of adsorption isotherms. Furthermore, parameters of adsorption isotherms for residual 4 hydrogen isotopes (HD, HT, DT and T2) were estimated using reduced mass.

Development of a tritium fuel processing system using an electrolytic reactor for ITER

A system composed of a palladium diffuser and an electrolytic reactor has been proposed and then developed for the fuel cleanup system of ITER. The performance of the system has been studied in detail in a stand-alone test. A fuel simulation loop of ITER was constructed by connecting the fuel cleanup and hydrogen isotope separation systems developed; and the function of each system in the loop has been demonstrated. For tritium recovery from the exhaust gas during helium glow discharge cleaning of the vacuum chamber of ITER, a cryogenic molecular sieve bed system has been proposed and demonstrated.

Adsorption Isotherms of Hydrogen Isotopes on Molecular Sieves 5A at Low Temperature.

Cryogenic Molecular Sieve Bed (CMSB) is considered to be applied to the bred tritium recovery system or the helium glow discharge exhaust gas cleanup system of nuclear fusion reactor. Molecular Sieves 5A (MS5A) is one of the most possible candidate adsorbents for CMSB. To design the CMSB, adsorption isotherm of hydrogen isotopes for MS5A must be investigated in liquid nitrogen temperature region (around 77 K) and above, and isotherm equation which can express the experimental data obtained in wide pressure range with good accuracy needs to obtaining. The present authors carried out the experiments using the volumetric method to obtain the adsorption isotherm of H2 and D2 for MS5A. Adsorption isotherms were obtained in the pressure range between about lPa and 0.2MPa at 77K (liquid nitrogen), 87K (liquid argon), 113K (isopentane), 143 K (n-pentane), 155 K (ethanol) and 195 K (dry ice/ethanol). Two Sites Langmuir Model was applied to understand adsorption isotherms, and was able to express the experimental observation with fairly good accuracy. The apparent heats of adsorption for two kinds of activated adsorption sites were obtained from temperature dependence of adsorption isotherms. Furthermore, parameters of adsorption isotherms for residual 4 hydrogen isotopes (HD, HT, DT and T2) were estimated using reduced mass.

Tritium Test of Cryogenic Molecular Sieve Bed for He GDC Gas Cleanup by 60 SLM Test Loop

This work presents demonstrative test results of CMSB by simulated helium glow discharge exhaust gas condition in 60 l/min of flow rate. This work focused on H{sub 2} and HT adsorption and regeneration performance of CMSB and optimum regeneration procedure, so that the operation cycle time becomes smaller. Test results showed consistency with bench-scale experiments. Obtained engineering data are applicable for the design of the CMSB process for ITER He GDC gas cleanup. As the results of this work, it was demonstrated that CMSB process could clean up 54.3 SLM of He stream with H{sub 2}(400) ppm+HT(0.5 ppm). Regeneration performance in various total pressure were obtained and evaluated by the calculation and clarified necessary information for determining the optimum regeneration procedure of CMSB which allow continuous operation in the shorter period of operation cycle (adsorption and regeneration). 6 refs., 5 figs., 1 tab.

Recovery of Hydrogen Isotopes and Impurity Mixture by Cryogenic Molecular Sieve Bed for GDC Gas Cleanup

Experimental results showed that Q2 gas was adsorbed effectively by CMSB on an early stage of breakthrough even though CH4 exists in the inlet gas. Particularly, in the case of Q2 with low concentration of CH4, the break through curve of Q2 showed almost the same curve as in the case of pure Q 2 adsorption. However, CH 4 gas spilled over adsorbed Q 2 in the course of CH 4 break-through. This means that the CMSB will eventually lose the ability to adsorb Q 2 in the final stage of adsorption. The critical time when the CMSB loses the adsorption ability depends on the inlet CH 4 concentration. Analysis of the results showed that the adsorption of Q 2 and CH 4 mixture can be roughly described by assuming the multi-component adsorption equations for Q 2 and CH 4 using Langmuir's equations. It was certified that the analysis model described and predicted the experimental observations very well.

Recovery of Tritium by Cryogenic Molecular Sieve Bed in Breeding Blanket Interface Condition

Experiments were performed to obtain detailed adsorption and desorption characteristics of tritium (HT) by Cryogenic Molecular Sieve Bed (CMSB) in liquid nitrogen temperature under the simulated Breeding Blanket Interface (BBI) condition. Computer simulation analyses gave the values of separation factor and mass transfer coefficient of HT in H{sub 2}, which are very important basic parameters for the optimum design of CMSB process in BBI.