Liquid Phase Catalytic Exchange Research Articles

Pressure and temperature transients of a cryogenic distillation system during abnormal operation or accidents

Cryogenic distillation system (CDS) is being employed, among other applications, in tritium separation technologies. CDS in combination with a Liquid Phase Catalytic Exchange (LPCE) process or with a Combined Electrolytic Catalytic Exchange (CECE) process is used for tritium removal/recovery from tritiated water. Large amounts of tritiated water can be produced during long time operation of CANDU reactors or in case of ITER mainly by the Detritiation System (DS). The CDS used to remove/recover tritium consists of a cascade of cryogenic distillation columns and a refrigeration unit which provides the cooling capacity for the condensers of CD columns. The columns, together with the condensers and the process heat-exchangers are accommodated in a vacuum insulated cold box. During abnormal events or accidents, significant amount of liquid hydrogen–deuterium–tritium or helium refrigerant can be spilt inside the cold box or even into the building. The paper analyzes some critical scenarios due to single failure mode or various combinations of failures such as: loss of refrigerant in the columns; loss of vacuum insulation; process liquid spilt into the cold box; refrigerant fails into cryogenic distillation columns.

Preparation and characterization of hydrophobic Pt–Fe catalysts with enhanced catalytic activities for interface hydrogen isotope separation

Liquid phase catalytic exchange reactions are mainly used for separation of hydrogen isotopes from liquid water. Based on the carbon-supported Pt and Pt–Fe catalysts, different hydrophobic Pt and Pt–Fe catalysts were fabricated for use in such reactions. The characterization results indicated the Pt–Fe alloy was formed in the Pt3Fe/C catalyst prepared using a citric-acid-assisted NaBH4 reduction method (CA-NaBH4). However, there were more Fe oxide species and the Fe components existed independently in the Pt3Fe/C catalyst prepared by the modified microwave-irradiated ethyl glycol reduction procedure (MI). Performance tests demonstrated that the activities of the hydrophobic Pt–Fe catalysts with appropriate Fe/Pt ratios, using the MI method, were enhanced because of the addition of Fe. In contrast, the hydrophobic Pt3Fe catalyst prepared using the CA-NaBH4 method had lower catalytic activity than pure Pt. Possible reasons were explained by reaction mechanisms of double routes of LPCE catalysis.

Performance Characterization of Hydrogen Isotope Exchange and Recombination Catalysts for Tritium Processing

AECL’s hydrogen isotope exchange catalyst and recombination catalysts have been successfully applied to a wide range of industrial tritium-removal applications. The catalysts are used for Liquid Phase Catalytic Exchange (LPCE) and for gas-phase and trickle-bed recombination of hydrogen isotopes and have led to process simplification, improved safety and operational advantages.Catalyst performance design equations derived from laboratory testing of these catalysts have been validated against performance under industrial conditions. In a Combined Electrolysis and Catalytic Exchange (CECE) demonstration plant analyses of LPCE and recombiner efficiency were carried out as a function of catalyst activity over a wide range of operation. A steady-state process simulation used to model and design the hydrogen-water isotopic exchange processes, such as the CECE detritiation plant, was validated using the results of this demonstration.Catalyst development for isotope-exchange and recombination applications has continued over the last decade. As a result, significant improvements in catalyst performance have been achieved for these applications. This paper outlines the uniqueness of AECL’s specialized catalysts and process designs for these applications with examples from laboratory and industrial case studies.

HTU Dependence on an Isotope Species – Experimental Study on “EVIO” Pilot Plant

Liquid Phase Catalytic Exchange (LPCE) process study is going on in PNPI. Separation performance expressed by Height of Transfer Unit (HTU) in deuterium-protium and deuterium-tritium systems was studied experimentally within one run of exchange column. Testing procedure and experimental results are presented in detail and discussed.

Preparation and Catalytic Activity of Pt Based Hydrophobic Catalysts Adulterated with Fe Series Elements

Pt based binary catalysts,which were adulterated with Fe series elements,viz Fe,Co,and Ni,were prepared using microwave heating method,with carbon black as carrier and glycol as solvent.Microstructure of the catalysts was characterized by TEM,XRD,EDX and XPS.Results showed that active metal particles were evenly distributed on carrier's surface.After adulterated by Fe,Co,Ni,the distribution of active metal particles' size became narrower and average size decreased from 4.57nm to 2.17nm,2.41nm,2.55nm,respectively.The catalysts were loaded on foam nickel(FN) with polytetrafluoroethylene latex to obtain Pt based hydrophobic catalysts, and then their activity for hydrogen-water liquid phase catalytic exchange(LPCE) was tested.Compared with Pt/C/FN hydrophobic catalyst,the catalytic activity of Pt based binary hydrophobic catalysts adulterated with transition metals increased in evidence.The sequence of these catalysts' activity was as follows, PtFe/C/FNPtCo/C/FNPtNi/C/FNPt/C/FN.The increase of catalytic activity results from the decrease of active metals particles' size,moreover,it could be attributed to the dissociation property of water on Fe series metals' surface to some extent.

The roles of metals and their oxide species in hydrophobic Pt–Ru catalysts for the interphase H/D isotope separation

Liquid phase catalytic exchange is mainly used for separation of hydrogen isotopes from liquid water. Based on the carbon-supported Pt and Pt–Ru catalysts with different metal and oxide species distributions, several hydrophobic catalysts, used in the reaction, were fabricated. The characterization results indicated that alloy and amorphous nanoparticles were formed in the Pt 0.5Ru 0.5/C catalyst using the microwave-irradiated polyol method. After reduction, the content of metallic species increased and that of hydrous Ru oxide species significantly decreased. A Pt 0.5Ru 0.5O 2/C catalyst containing more oxide species was also synthesized by the microwave-irradiated oxidation precipitation method. Performance tests demonstrated that the presence of more metallic Pt species in both the hydrophobic Pt and Pt–Ru catalysts resulted in higher catalytic activity. The addition of Ru, as an alloy or as a hydrous oxide, can improve the catalytic activity of pure Pt. These experimental results were explained by the reaction mechanisms.

Modification of a solid polymer electrolyte (SPE) electrolyser to ensure tritium compatibility

A Water Detritiation System (WDS) is required for the ITER Tritium Plant in order to process tritiated water which is accumulated in various subsystems (e.g. the hall ventilation systems). For the ITER-WDS, the Combined Electrolysis Catalytic Exchange (CECE) process with an electrolyser unit as one of the major components is envisaged. An experimental WDS was built and commissioned at the Tritium Laboratory Karlsruhe (TLK) for the investigation of various subsystems of the CECE process in tritium environment. The TLK-WDS consists of an 8 m Liquid Phase Catalytic Exchange column and two Solid Polymer Electrolyte electrolysers, each with a maximum hydrogen output of 1 m 3/h. The commercially available Hogen40 electrolyser units from Proton Energy Systems are not tritium compatible concerning materials, joints and quality documentation (e.g. necessary certificates). In order to process tritiated water with tritium concentrations up to 370 GBq/kg, tritium compatibility had to be ensured by appropriate modifications. Up to now, the modified system has been operated with tritiated water for 3500 h, the maximum tritium concentration in the electrolysers being 190 GBq/kg. This contribution reports on the necessary modifications of the electrolyser units and the experiences gained thereby. The results are equally important for the ITER-WDS, where the maximum tritium concentration in the feed water of the electrolyser units will be even higher with 11 TBq/kg.

Simulation of CECE Facility for Water Detritiation

This paper presents a program to simulate performance of a liquid phase catalytic exchange (LPCE) column of a water detritiation facility based on combined electrolysis and catalytic exchange (CECE) technology over a wide range of deuterium contents in a feed stream. The program uses rate constants of the chemical isotopic exchange reactions between gaseous hydrogen and water vapor occurring on a hydrophobic catalyst and the mass transfer rate between water vapor and the film of liquid water on packing material in the LPCE column, which have been measured experimentally using a specially developed method and at a low concentration of deuterium in a three-isotope mixture. The effect of the deuterium presence on the kinetics of isotopic exchange reactions and the performance of the LPCE column are taken into account considering several possible mechanisms that can control the overall rate of reaction. Selection of the most suitable mechanism was carried out by comparing the simulations with the results of an experimental test with a large deuterium content.The simulation program allows calculation of isotope profiles in streams of liquid water, water vapor, and gaseous hydrogen along the LPCE column over a very wide range of isotopic compositions and for CECE facilities of several different layouts.

Pt–Ir binary hydrophobic catalysts: Effects of Ir content and particle size on catalytic performance for liquid phase catalytic exchange

Pt/C and Pt–Ir/C catalysts with different atomic ratios were synthesized in a closed PTFE vessel by a microwave-irradiated polyol method. The characterization results indicated that the average Pt–Ir particle size changed only slightly and the face-centered crystalline structure gradually became more amorphous with increasing iridium content. The particle size could be controlled by altering the pH of the synthesis solution and the microwave heating rate. The carbon-supported catalysts and polytetrafluoroethylene were then loaded together on a foamed nickel (FN) carrier to obtain hydrophobic catalysts. The reaction mechanisms were presented for liquid phase catalytic exchange reaction, which could explain that a hydrophobic catalyst with a Pt/Ir molar ratio of 4/1 exhibited the best catalytic activity. Furthermore, the effect of particle size on catalytic performance was investigated. The activity of the Pt 4Ir 1/C/FN catalyst was enhanced by decreasing the average particle size, in the range of 2.5–3.8 nm.

Korea’s Activities for the Development of a Detritiation System

Tritiated gas and water should be properly treated to minimize an environmental tritium emission in nuclear fusion research facilities. Tritiated gas is usually treated in two steps: it is first oxidized to a tritiated water vapor by a catalyst and then the vapor is adsorbed in a molecular sieve drier. We have used a 1wt.% Pt/SDBC polymer catalyst and Zeolite 13X for the tritiated gas removal system. We confirmed that the decontamination factor of the equipment was more than 100 under a gas flow rate of 90 liters/hr and at a temperature of 65-80 °C.Furthermore we have developed a tritiated organic liquid treatment process. We have used a 0.5wt.% Pd/Al2O3 catalyst to oxidize an organic liquid. The simulated organic liquid was converted to water by over 99%. We have also developed a small scale CECE (Combined Electrolysis and Chemical Exchange) process by combining an LPCE (Liquid phase Catalytic Exchange) catalytic column with SPE (Solid Polymer Electrolyte) electrolysis. The experimental results of the CECE process produced a decontamination factor of 13-20. We used the electrolyte Nafion 117 which was coated with Pt as a cathode catalyst and IrO2 as an anode catalyst. We also tested a palladium alloy membrane for a purification of the hydrogen in the detritiation process.

Modification, enhancement and operation of a water detritiation facility at the Tritium Laboratory Karlsruhe

For the design and development proposal of the European procurement package of the Water Detritiation System (WDS) for ITER, an experimental WDS was installed at the Tritium Laboratory Karlsruhe (TLK) to investigate the process and various components of the system. The WDS facility at TLK uses the Combined Electrolysis Catalytic Exchange (CECE) process and consists of two Solid Polymer Electrolyte (SPE) electrolysis cells and a stainless steel Liquid Phase Catalytic Exchange (LPCE) column with an effective length of 8 m. After installation and commissioning, the first experimental runs were performed with a tritium concentration up to 0.6 GBq kg −1 in the feed water to test the operation modes of the facility, all the safety installations and procedures and the performance of the LPCE column during a runtime of up to 130 h. Regarding the final design of the WDS for ITER, the first experiments indicated several aspects which had to be modified in order to enhance the procedural and operating performance of the facility.

Study on the technology of CECE–GC system for water detritiation

Based on the thorough study of electrolysis enrichment, gas–liquid phase catalytic exchange, gas chromatography for hydrogen isotope separation, and hydrogen–oxygen recombination technologies, a CECE–GC prototype system with disposal capability of 10 ton/a of tritiated water was set up in the middle of 2004 at China Academy of Engineering Physics (CAEP). It has successfully fulfilled the demonstration experiment of recovering deuterium from deuterium contained water and simulation operation of recovering tritium from tritiated water. Total concentration factor of CECE about 4, and the separation factor of tritium around 10 for operation time of 240 h with this system. The GC system of 50 m 3/d has successfully recovered 90% hydrogen from 10 m 3 tritiated hydrogen gas in 6 h and the tritium concentration in this part was depleted more than 1000 times. This experimental system served as an important step stone for further engineering works.

Effects of the gas–liquid ratio on the optimum catalyst quantity for the CECE process with a homogeneously packed LPCE column

In order to improve the separative performance of a combined electrolysis catalytic exchange (CECE) process, we have carried out experimental studies on hydrogen isotope separation by a CECE process using a liquid phase catalytic exchange (LPCE) column of trickle-type packed beds. Two types of trickle beds were tested in our previous study. One was the layered bed, where layers of Kogel catalysts and Dixon gauze rings were alternately filled in the column. The other was the homogeneous bed, where Kogel catalysts and Dixon gauze rings were homogeneously mixed and filled in the column. We found that (1) the homogeneously packed bed was more efficient than the layered packed bed, and (2) the catalyst quantity was optimal, which resulted in the highest separative performance. In this study, the effect of the gas–liquid ratio ( G/ L) on the optimum catalyst quantity was studied experimentally in a homogeneously packed bed. When the value of G/ L was 1.7, total separation factors were relatively small and the optimum catalyst quantity could not be determined. On the other hand, when the values of G/ L were 0.9 and 0.7, the values of the total separation factors had maximums and the optimal quantities of the catalyst were clearly obtained.

Experiments on Water Detritiation and Cryogenic Distillation at TLK; Impact on ITER Fuel Cycle Subsystems Interfaces

The ITER Isotope Separation System (ISS) and Water Detritiation System (WDS) should be integrated in order to reduce potential chronic tritium emissions from the ISS. This is achieved by routing the top (protium) product from the ISS to a feed point near the bottom end of the WDS Liquid Phase Catalytic Exchange (LPCE) column. This provides an additional barrier against ISS emissions and should mitigate the memory effects due to process parameter fluctuations in the ISS. To support the research activities needed to characterize the performances of various components for WDS and ISS processes under various working conditions and configurations as needed for ITER design, an experimental facility called TRENTA representative of the ITER WDS and ISS protium separation column, has been commissioned and is in operation at TLK.The experimental program on TRENTA facility is conducted to provide the necessary design data related to the relevant ITER operating modes. The operation availability and performances of ISS-WDS have impact on ITER fuel cycle subsystems with consequences on the design integration. The preliminary experimental data on TRENTA facility are presented.

Development of Water Detritiation Facility for JET

This paper presents results from the concept evaluation, experimental trials, and design of a water detritiation facility (WDF) for the JET fusion machine. The design is based on the combined electrolysis and catalytic exchange process and will allow construction of the plant and for its integration into the JET tritium plant in three stages.The first stage includes a liquid phase catalytic exchange column and electrolyzer to concentrate the water into a smaller amount of tritium-enriched water. There would then be three options for dealing with this water: processing off-site, conversion to solid intermediate-level waste for disposal, and further processing on-site for complete tritium recovery. The latter option will require the second stage of implementation to integrate the WDF with the isotope separation system of the tritium plant. The third stage might be desirable to reduce the amount of time that the existing isotope separation system would need to be involved in the recovery of tritium from the WDF.

Integrated Tests of Water Detritiation and Cryogenic Distillation in View of ITER Design

One of the main concerns related to licensing of ITER is the amount of potentially tritium release into the environment and the qualification of the barriers against tritium release. The final barrier of tritium release from fuel cycle is the Water Detritiation System (WDS) which will be operated in combination with the Isotope Separation System (ISS). To investigate the performances of various components of these systems, an experimental facility based on Combined Electrolysis Catalytic Exchange (CECE) process with a Cryogenic Distillation (CD) process was built at Tritium Laboratory Karlsruhe. The investigations are focused on two main issues: to quantify the separation performances of deuterium and tritium within the Liquid Phase Catalytic Exchange (LPCE) and CD processes in steady state and in dynamic mode of operation and to develop an integrated control system to be used in ITER ISS, in order to minimize the tritium inventory and to reduce at maximum extent the tritium releases. At TLK the two systems, CECE and CD have been commissioned and the experimental program and preliminary functionality tests of the main components are presented.

Installation of liquid phase catalytic exchange columns for the Wolsong tritium removal facility

The catalyst loading and installation of liquid phase catalytic exchange (LPCE) columns for the Wolsong tritium removal facility (WTRF) was completed on the 22nd of April 2006. Two LPCE columns are connected in series. The first column has 28 sections, a sump and a separate overhead condenser. The second column has 27 sections, a sump and a humidifier. Each section of the LPCE columns consists of three parts: mass transfer packing bed, separate catalyst bed and liquid distributor. The Sulzer CY packing for the vapor–liquid mass transfer is packed into the inner shell of each section and the wet proofed catalyst for the vapor–gas reaction is loaded into between the inner and outer shell. The liquid distributors are equipped on the Sulzer CY packing of each section. The performance test will be accomplished according to the WTRF construction and commissioning schedule. The WTRF is the first commercial facility applying LPCE process for the tritium removal. The WTRF is expected to remove 7 MCi-tritium per year at least from the Wolsong CANDU6 reactors and will be a main tritium source for the ITER.

The performance of a trickle-bed reactor packed with a Pt/SDBC catalyst mixture for the CECE process

The combined electrolysis and catalytic exchange (CECE) process with a hydrophobic catalyst is a very effective method to remove small quantities of tritium from light or heavy wastewater streams because of its high separation factor and mild operating conditions. A hydrophobic platinum/styrene-divinyl benzene copolymer (Pt/SDBC) catalyst which was developed for the liquid-phase catalytic exchange (LPCE) column of the Wolsong tritium removal facility (WTRF) has been tested in a trickle bed reactor for the design of the CECE process. An experimental apparatus has been built for the testing of the catalyst at various temperatures and gas velocities. The catalyst column was packed with a mixture of a hydrophobic catalyst and a hydrophilic packing (Dixon gauze ring) to improve the liquid distribution and vapor/liquid transfer area. Many tests have been carried out at Korea Atomic Energy Research Institute (KAERI) to measure the activity of the catalyst, K y a (1 s −1), under various operating conditions. K y a increases with the hydrogen flow rates in the range of 0.4–1.6 m s −1 at STP. The height of the catalyst column was determined from these K y a values according to the reaction temperatures and hydrogen flow rates.

Commissioning of water detritiation and cryogenic distillation systems at TLK in view of ITER design

The ITER Isotope Separation System (ISS) and Water Detritiation System (WDS) will be integrated in order to reduce potential chronic tritium releases from the ISS by routing the top (protium) product from the ISS into the Liquid Phase Catalytic Exchange (LPCE) column of WDS. This provides an additional barrier against ISS tritium releases and should mitigate the memory effects due to process parameter fluctuations in the ISS. To support the research activities needed to characterize the performances of various components for WDS and ISS processes in various working conditions and configurations as needed for ITER design, an experimental facility called TRENTA and representative of the ITER WDS and ISS protium separation column has been commissioned at Tritium Laboratory Karlsruhe (TLK). The TRENTA facility consists of Combined Electrolysis Catalytic Exchange (CECE) process, with an LPCE column of 8 m, in combination with a cryogenic distillation (CD) process. The processes description and the status of commissioning of TRENTA facility is presented.

Operational analysis of a liquid phase catalytic exchange column for a detritiation of heavy water

An operational analysis for a liquid phase catalytic exchange column was carried out by the model equations, composed of a material balance and equilibrium relationships for a scrubbing and catalyst bed. The solutions were determined by using the Newton–Raphson method and the parametric investigations were simulated for the effect of the operating variables on the detritiation factor. It was observed that the maximum detritiation performance could be obtained at certain temperature conditions by considering the flow ratio of the water vapor to the given hydrogen stream in the catalyst bed and the water vapor–liquid equilibrium in the scrubbing bed. The optimum operating temperature should be chosen at the larger detritiation conditions providing a reasonable processing flow rate.