Separation Of Heavy Water Research Articles

Data-driven molecular dynamics simulation of water isotope separation using a catalytically active ultrathin membrane.

Water isotope separation, specifically separating heavy from light water, is a technologically important problem due to the usage of heavy water in applications such as nuclear magnetic resonance, nuclear power, and spectroscopy. Separation of heavy water from light water is difficult due to very similar physical and chemical properties between the isotopes. We show that a catalytically active ultrathin membrane (e.g., a nanopore in MoS2) can enable chemical exchange processes and physicochemical mechanisms that lead to efficient separation of deuterium from hydrogen. The separation process is inherently multiscale in nature with the shorter times representing chemical exchange processes and the longer timescales representing the transport phenomena. To bridge the timescales, we employ a deep learning methodology which uses short time scale ab initio molecular dynamics data for training and extends the timescales to the classical molecular dynamics regime to demonstrate isotope separation and reveal the underlying complex physicochemical processes.

Conjugated mass transfer in an inclined thermal-diffusion column for heavy water enrichment with plate aspect ratio variations

A two-dimensional mathematical model was developed theoretically to predict the degree of separation of heavy water in an inclined flat-plate thermal-diffusion column. An orthogonal expansion technique for solving separation problems of heavy water enrichment under plate aspect ratio and inclination angle variations was carried out analytically. The effects of plate aspect ratio and inclination angle on the degree of separation have been investigated with a consideration of a fixed operating expense. Considerable improvements in device performance are obtained if the thermal-diffusion columns are inclined at the optimal angles as compared to the vertical orientation. Further improvement can be achieved if the flow-rate fractions of top and bottom products are suitably adjusted.

The analytical study on heavy water enrichment in concentric circular thermal-diffusion columns with optimal plate spacing for improved performance

A two-dimensional mathematical model was developed theoretically to predict the degree of separation of heavy water in concentric circular thermal-diffusion columns with total fixed expense and with plate spacing variations. An orthogonal expansion technique for solving separation problems of heavy water enrichment to estimate optimal plate spacing for maximum separation has been developed analytically. Considerable improvements in device performance were obtained when the thermal-diffusion column with optimal plate spacing were used. The effects of plate spacing and mass flow rate and on the degree of separation have been investigated with a consideration of the fixed total expense. Further improvement can be achieved if the feed position and flow-rate fractions of top and bottom products are suitably adjusted.

Enrichment of heavy water in flat-plate thermal-diffusion columns with optimal plate aspect ratio

The optimum plate aspect ratios for maximum separation of heavy water, maximum production rate and minimum plate surface area in flat-plate thermal-diffusion column with plate surface area fixed, have been determined. Essential improvement in performance is obtainable if the column is constructed with the best plate aspect ratio, so that the desirable cascading effect can be enhanced, while the undesirable remixing effect can be properly reduced. The maximum separation and maximum production rate are achieved without changing any total expense, while the design with minimum plate surface area results in minimizing the total expense.

Optimal plate aspect ratio for the enrichment of heavy water from water–isotope mixture in a flat-plate thermal diffusion column with transverse sampling streams

Suitably adjusting the plate aspect ratio in a flat-plate thermal diffusion column is one of the flexible ways of properly controlling the convective strength, resulting in reducing the remixing effect while still preserving the effectively cascading effect, and thereby leading to improved separation. The optimal plate aspect ratios for the performances of the separation of heavy water from water–isotope mixture in flat-plate thermal diffusion columns with transverse sampling streams have been determined. The maximum separation and maximum production rate are achieved without changing the total expenditure, while the design with minimum plate surface area results in minimizing the total expenditure.

Effects of inclination angle and plate spacing on the enrichment of heavy water in continuous-type flat-plate thermal diffusion columns

Abstract The effects of inclination angle and plate spacing on the separation of heavy water from water isotope mixture in continuous-type flat-plate thermal diffusion columns, has been investigated with the consideration of a fixed operating expense. Although there do not exist simultaneously the optimal angle of inclination and optimal plate spacing for maximum separation, increasing either the inclination angle or plate spacing will increase, respectively, the optimal plate spacing or optimal inclination angle, as well as the corresponding maximum separations. The equations for the optimal inclination angle and optimal plate spacing, as well as the corresponding maximum separations, have been derived. Considerable improvement in separation is achievable if the operations are conducted with the optimal operating conditions.

Design of flat-plate thermal diffusion columns for enrichment of heavy water with transverse sampling streams

Although there does not exist simultaneously the optimal angle of inclination and optimal plate spacing for maximum separation of heavy water from water–isotope mixture in flat-plate thermal-diffusion columns, increasing either inclination angle or plate spacing will increase, respectively, the optimal plate spacing or optimal inclined angle, as well as the corresponding maximum separations. The equations for the optimal angle of inclination and optimal plate spacing, as well as the corresponding maximum separations, have been derived. Considerable improvement in separation is achievable if the operations are conducted with the optimal conditions.

An Analytical Study of Separation Efficiency on the Enrichment of Heavy Water in Double-Flow Thermal-Diffusion Columns with Flow-Rate Fraction Variations

Considerable improvement in heavy water separation efficiency in a thermal diffusion column is obtainable by inserting an impermeable sheet or permeable barrier in parallel to divide an open duct into two subchannels for double-flow operations. The analytical results developed and investigated using an orthogonal expansion technique are represented graphically and compared with that in a Clusius-Dickel column of the same size. The impermeable-sheet or permeable-barrier location effect on heavy water separation efficiency enhancement is also discussed.

Effects of Inclined Angle and Aspect Ratio on Heavy Water Separation Efficiencies in Double‐Flow Thermal‐Diffusion Columns with External Refluxes

The heavy water separation efficiency enhancement in double‐flow, by inserting an impermeable sheet or a permeable barrier into double‐flow thermal‐diffusion columns with external refluxes at the ends has been investigated analytically. The analysis is conducted when using an orthogonal expansion technique. The separation efficiencies are compared with conventional Clusius–Dickel columns of the same size. Considerable improvements in heavy water enrichment in double‐flow thermal‐diffusion columns can be obtained by increasing the inclined angle and/or by decreasing the aspect ratio. Analytical results also show that both the recycle ratio and the position of insertion are important design parameters.

Separation of Heavy Water by Vapor-Phase Thermal Diffusion Coupled with Distillation and Condensation

A study on the enrichment of heavy water in a vapor-phase thermal-diffusion column has been conducted. With the combination of the effects of distillation, vapor-phase thermal diffusion, and partial condensation, considerable improvement in the degree of enrichment has been achieved in a vapor-phase column rather than in a liquid-phase column. It was also found that even the part of enrichment contributed only by vapor-phase thermal-diffusion effect is much higher than that obtained by liquid-phase thermal diffusion.

Deuterium pilots new hydrogen technology

The heavy water used in CANDU reactors has required extensive research into isotope separation methods. Many of these involve hydrogen and so expertise has developed in a number of areas of application to hydrogen technology. From work done at CRNL in the 1970s, a wetproofed catalyst has been developed to allow the exchange of hydrogen isotopes between liquid water and hydrogen. One consequence is a process for by-product separation of heavy water that may be economically very attractive if hydrogen is produced in sufficient quantity. Alternative applications of the catalyst give hydrogen-water exchange the premier position as the basis of a process for the 1990s to extract heavy water. Megawatts of electrolytic cells have been used for many years at CRNL to upgrade heavy water. However, new applications of the catalyst have required innovations in electrolytic cell design. This work, some of it performed in collaboration with industry, includes (a) reduced cell inventory of water, and (b) greater leak-tightness of cells required to contain heavy water with a tritium content. In some applications, hydrogen had to be reconverted to water and early difficulties with recombination led to development of a variant of the wetproofed catalyst able to recombine hydrogen and oxygen in the presence of liquid water. This appears to be a broadly applicable technology since the hydrogen needs no dilution before recombination and liquid water flowing over the catalyst provides simple, direct cooling.

Numerical Analysis on Heavy Water Separation Characteristics for Pair of Bithermal Trickle-Bed Type H2/H2O-Exchange Columns

In order to study how the operating pressure and temperature have influence on the heavy water separation characteristics for a pair of bithermal trickle-bed type H2/H2O-exchange columns packed with the hydrophobic Pt catalyst, the authors utilized the analytical expressions derived from the differential equations expressing the material balance of the three components, hydrogen, water vapor and water in the exchange column. The cases where the operating temperature in a hot column is 200°C, the deuterium enrichment factor is 3, the hydrogen superficial velocity is (0.2)×(Operating pressure (atm)) (Nm/s) and the column efficiency is high and low were studied. As the results, the optimum operating pressure is about 50 atm in both cold and hot column, the optimum operating temperature in a cold column is 100°C and other important parameters such as the optimum length of a cold and a hot column, the optimum hydrogen to feed water molar flow ratio and the optimum degradation ratio were also obtained.

Numerical analysis on heavy water separation characteristics for pair of bithermal trickle-bed type H2/H2O-exchange columns.

In order to study how the operating pressure and temperature have influence on the heavy water separation characteristics for a pair of bithermal trickle-bed type H2/H2O-exchange columns packed with the hydrophobic Pt catalyst, the authors utilized the analytical expressions derived from the differential equations expressing the material balance of the three components, hydrogen, water vapor and water in the exchange column. The cases where the operating temperature in a hot column is 200°C, the deuterium enrichment factor is 3, the hydrogen superficial velocity is (0.2)×(Operating pressure (atm)) (Nm/s) and the column efficiency is high and low were studied. As the results, the optimum operating pressure is about 50 atm in both cold and hot column, the optimum operating temperature in a cold column is 100°C and other important parameters such as the optimum length of a cold and a hot column, the optimum hydrogen to feed water molar flow ratio and the optimum degradation ratio were also obtained.

Numerical analysis of pressure effects on heavy water separation characteristics for a pair of dual temperature multistage-type H2/H2O-exchange columns.

In order to study how the operating pressure has influence on the heavy water separation characteristics for a pair of dual temperature multistage-type H2/H2O-exchange columns, the authors utilized the analytical expressions derived from the finite difference equation describing the material balance in the exchange column. The separation characteristics of the system were studied theoretically under the conditions where the temperature in a hot column th=200°C, the pressure in a hot column π≦50atm and the pressure in a cold column π = 5–50atm.As the results, the optimum modified specific column volume v*opt decreases with the increase of π and then keeps the nearly constant value, and is smaller at ≦=50atm than at ≦=30atm in the case where the temperature in a cold column tc is constant. Other important parameters such as the optimum operating temperature in a cold column tcopt the optimum numbers of stages in a hot column Mopt and in a cold column topt, the optimum hydrogen to feed water molar flow ratio γ opt and the optimum degradation ratio δopt were also calculated.

Numerical analysis on heavy water separation characteristics for a pair of dual temperature multistage-type H2/H2O-exchange columns.

In order to study the separation characteristics for a pair of dual temperature multistage-type H2/H2O-exchange columns, each stage of which is composed of the scrubbing packed bed for the water/vapor isotopic exchange and the hydrophobic Pt catalyst bed for the vapor/hydrogen isotopic exchange, the authors tried to compose the finite difference equations considering the water/vapor isotopic exchange and the vapor/hydrogen isotopic exchange and then made it possible to calculate the D-content in the water, vapor and hydrogen at any point in a pair of dual temperature multistage-type H2/H2O-exchange columns by way of six variable—one order matrix equation derived from the six boundary conditions. Utilizing the results mentioned above, the authors tried a further study to get an optimum value of hydrogen/water molar flow ratio, number of stages in a cold column and a hot column, degradation ratio ((z w B -z- w F /z w B ) and specific volume (m3/kmol D2O-h) of a pair of dual temperature multistage-type H2/H2...

Heavy water production with geothermal steam

As the separation of heavy water from ordinary water is a process which is highly energy consuming it is in some respects the ideal chemical process for utilizing geothermal steam as process heat and, conversely, cheap geothermal steam is an ideal energy source for the process. A calculation has been made of the manufacturing cost of heavy water by the H2S/H2O ion exchange method with geothermal steam supplying the process heat. The results of this calculation show that heavy water produced in such a manner would at present be 10–15% less costly than heavy water produced with heat derived from natural gas or from steam economically available as exhaust steam from turbines, which is the cheapest way of producing heavy water. The characteristics of geothermal steam cause modifications in the optimization of the heat recovery system of a heavy water plant, namely that low cost leads to a lesser optimal degree of heat recovery and the price vs temperature characteristics of the steam make it economical to split the heaters into low and high temperature sections. The relatively low pressures of geothermal steam make it necessary to strip the H2S from the waste water at a lower pressure than the main process pressure. This in turn leads to a modification of the process and the introduction of an absorber in the feed water stream where the H2S stripped from the waste water is returned to the system so as to minimize compression work. The cost of heat delivered to the process will be further reduced by a factor of two if the water accompanying the steam from the borehole can also be used, but this is as yet uncertain because silica and other solids in the hot water may lead to scaling in the heat exchangers.

Separation of Heavy Water in Phase Equilibria Involving Pure Water or Salt-Water Systems.

Separation of Heavy Water in Phase Equilibria Involving Pure Water or Salt-Water Systems.

An Effect of Rectified Current from a Tunger Valve upon the Electrolytic Separation of Heavy Water

An Effect of Rectified Current from a Tunger Valve upon the Electrolytic Separation of Heavy Water

The relative efficiencies of the multistage and one stage process in the electrolytic preparation of heavy water

A quantitative estimate has been given on the basis of Urey’s equation, of the decrease in efficiency in the electrolytic separation of heavy water (assumed to be present in small proportions) due to the continual addition of fresh-water in terms of the variables involved. It is shown that compared with a single stage process, there will beno less in efficiency, if fresh-water be addedcontinuously. A relation connecting the decrease in efficiency with the relative magnitude of the step has been derived.