Evaluation of Mass Transfer Performance for Caustic-Side Solvent Extraction of Cesium in a Conventional 5-cm Centrifugal Contactor PDF Download

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Languages : en
Pages : 31

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Tests have been conducted to determine if satisfactory mass transfer performance is achieved using a fully pumping 5-cm centrifugal contactor under conditions present in the Caustic-Side Solvent Extraction (CSSX) process. Tests utilized a commercially available contactor that had been modified by installation of a rotor housing bottom that had straight radial vanes on the process side. As received from the vendor, the housing bottom was equipped with curved (impeller-type) vanes that were intended to promote phase separation by minimizing mixing of influent solutions. Stage efficiencies exceeding 85% were obtained under conditions, present in the extraction section of the CSSX flowsheet. Under CSSX stripping conditions the stage efficiency exceeded 90%. In both cases, the efficiencies obtained exceed the minimum requirement for acceptable transfer of cesium in the CSSX process.

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Languages : en
Pages : 44

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A test program has been conducted in which the use of pilot-scale centrifugal solvent extraction contactors for cesium removal from an alkaline waste stream has been successfully demonstrated. The program was designed specifically to evaluate the use of centrifugal contactors having 5-cm-diam rotors for the removal of cesium from alkaline high-level waste (HLW) that was generated and is being stored at the U.S. Department of Energy's Savannah River Site (SRS). The removal of cesium from this waste is highly desirable because it will reduce the volume of waste that must be treated and disposed of as HLW. The parameters applied in the test effort are those that have been established for the Caustic-Side Solvent Extraction (CSSX) process, a multistage extraction operation that has been designed by researchers at Oak Ridge National Laboratory (ORNL) and Argonne National Laboratory (ANL). In the CSSX process, cesium is extracted by calix(4)arene-bis-(fert-octylbenzo-crown-6), commonly referred to as BOBCalixC6. The extract is scrubbed with dilute (0.05 M) nitric acid, both to remove coextracted elements (primarily potassium and sodium) and to adjust the pH of the extract to facilitate recovery of the cesium. The scrubbed solvent is contacted with 0.001 M HNO3, which results in the stripping of the cesium from the solvent into the aqueous acid. The CSSX process flow rates have been established so to produce a cesium concentration in the strip effluent that is 12 to 15 times the concentration in the waste stream that enters the extraction section of the cascade. Results from initial hydraulic testing of a commercially available 5-cm contactor under CSSX conditions indicated that the mixing of feed solutions within the unit (which is critical to efficient solute transfer) was limited by a feature of the contactor that was designed to increase throughput and improve separation performance. In the design, phase separation is improved by reducing turbulence within the contactor. Subsequent to the initial hydraulic test: cesium transfer tests were performed using contactors arranged in both single-stage and multistage arrangements. Results of these tests confirmed that phase mixing within the contactor was inadequate. In an effort to improve mixing within the contactor and thereby increase mass transfer efficiency, two minor modifications were made to a single contactor unit. One modification was the replacement of the bottom plate from the vendor-supplied contactor housing, which was equipped with curved (impeller-type) vanes, with a bottom assembly that had straight radial vanes. The latter configuration is the standard used in all existing ANL, ORNL, and SRS contactor designs. The second modification involved enlargement of the opening in the bottom of the rotor through which dispersion from the contactor mixing zone enters the rotor for separation. By increasing the rotor opening sufficiently, the rotor loses pumping efficiency to such an extent that accumulation of a hydrostatic head in the annular mixing zone is required for solution to be pumped through the contactor to the organic and aqueous discharge ports. By causing a volume of liquid to accumulate in the mixing zone, it is expected that phase mixing will be improved. Following modification of a contactor, hydraulic testing was repeated to determine flow parameters to be applied in mass transfer testing using the modified device. As expected, test results indicated that the maximum throughputs that could be achieved using the modified contactor under extraction and stripping conditions were lower than those obtained using the ''as-received'' unit. However, phase separation performance within the reduced operating envelope was excellent. Most importantly, cesium transfer stage efficiencies were significantly improved over those obtained using the unmodified device and resulted in attainment of the target CSSX process decontamination factor of 40,000 when extrapolated to the baseline CSSX contactor cascade.

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Languages : en
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The Caustic-Side Solvent Extraction (CSSX) process has been selected for the separation of cesium from Savannah River Site high-level waste. The solvent composition used in the CSSX process was recently optimized so that the solvent is no longer supersaturated with respect to the calixarene crown ether extractant. Hydraulic performance and mass transfer efficiency testing of a single stage of 5.5-cm ORNL-designed centrifugal contactor has been performed for the CSSX process with the optimized solvent. Maximum throughputs of the 5.5-cm centrifugal contactor, as a function of contactor rotor speed, have been measured for the extraction, scrub, strip, and wash sections of the CSSX flowsheet at the baseline organic/aqueous flow ratios (O/A) of the process, as well as at O/A's 20% higher and 20% lower than the baseline. Maximum throughputs are comparable to the design throughput of the contactor, as well as with throughputs obtained previously in a 5-cm centrifugal contactor with the non-optimized CSSX solvent formulation. The 20% variation in O/A had minimal effect on contactor throughput. Additionally, mass transfer efficiencies have been determined for the extraction and strip sections of the flowsheet. Efficiencies were lower than the process goal of greater than or equal to 80%, ranging from 72 to 75% for the extraction section and from 36 to 60% in the strip section. Increasing the mixing intensity and/or the solution level in the mixing zone of the centrifugal contactor (residence time) could potentially increase efficiencies. Several methods are available to accomplish this including (1) increasing the size of the opening in the bottom of the rotor, resulting in a contactor which is partially pumping instead of fully pumping, (2) decreasing the number of vanes in the contactor, (3) increasing the vane height, or (4) adding vanes on the rotor and baffles on the housing of the contactor. The low efficiency results obtained stress the importance of proper design of a centrifugal contactor for use in the CSSX process. A prototype of any centrifugal contactors designed for future pilot-scale or full-scale processing should be thoroughly tested prior to implementation.

Author: K. Gloe
Publisher: Springer Science & Business Media
ISBN: 1402036876
Category : Science
Languages : en
Pages : 450

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Macrocyclic Chemistry: Current Trends and Future Perspectives illustrates essential concepts in this expanding research field covering both basic and applied studies. Written by well-known experts from around the world, the topics of the chapters range from new macrocyclic architectures with different functions and self-assembly processes through to the modeling and dynamics of such systems. The content also reflects on application possibilities in analytical chemistry, separation processes, material preparation and medicine. Thus this book serves as a creative source of research strategies and methodic tools. Providing an excellent overview of the field, this book will be a valuable resource for researchers in industry and academic institutions as well as for teachers of science and graduate students. This book is devoted to the long-standing tradition of the International Symposia on Macrocyclic Chemistry (ISMC) and published to coincide with the 30th meeting, Dresden, Germany.

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Languages : en
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This report summarizes the FY 2010 and 2011 accomplishments at Oak Ridge National Laboratory (ORNL) in developing the Next Generation Caustic-Side Solvent Extraction (NG-CSSX) process, referred to commonly as the Next Generation Solvent (NGS), under funding from the U.S. Department of Energy, Office of Environmental Management (DOE-EM), Office of Technology Innovation and Development. The primary product of this effort is a process solvent and preliminary flowsheet capable of meeting a target decontamination factor (DF) of 40,000 for worst-case Savannah River Site (SRS) waste with a concentration factor of 15 or higher in the 18-stage equipment configuration of the SRS Modular Caustic-Side Solvent Extraction Unit (MCU). In addition, the NG-CSSX process may be readily adapted for use in the SRS Salt Waste Processing Facility (SWPF) or in supplemental tank-waste treatment at Hanford upon appropriate solvent or flowsheet modifications. Efforts in FY 2010 focused on developing a solvent composition and process flowsheet for MCU implementation. In FY 2011 accomplishments at ORNL involved a wide array of chemical-development activities and testing up through single-stage hydraulic and mass-transfer tests in 5-cm centrifugal contactors. Under subcontract from ORNL, Argonne National Laboratory (ANL) designed a preliminary flowsheet using ORNL cesium distribution data, and Tennessee Technological University developed a chemical model for cesium distribution ratios (DCs) as a function of feed composition. Inter Laboratory efforts were coordinated in complementary fashion with engineering tests carried out (and reported separately) by personnel at Savannah River National Laboratory (SRNL) and Savannah River Remediation (SRR) with helpful advice by Parsons Engineering and General Atomics on aspects of possible SWPF implementation.

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Languages : en
Pages : 5

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A modified solvent has been developed at Oak Ridge National laboratory (ORNL) for a caustic-side solvent extraction (CSSX) process that removes cesium (Cs) from Savannah River Site (SRS) tank waste. The modified solvent was evaluated using the same CSSX flowsheet, SRS simulant, and 33-stage minicontactor (2-cm centrifugal contactor) that had been used to test the previous CSSX solvent. As with the previous solvent, the key process goals were achieved: (1) the Cs was removed from the waste with decontamination factors greater than 40,000 and (2) the recovered Cs was concentrated by a factor of 15 in dilute nitric acid. Thus, the modified CSSX solvent can be used in place of the previous solvent while maintaining satisfactory hydraulic performance and still achieving process requirements at the bench scale.

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Languages : en
Pages : 12

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A 32-stage centrifugal contactor underwent proof-of-concept testing for its potential use in caustic-side solvent extraction for removal of cesium from radioactive waste now stored in underground tanks at the Savannah River Site. This contactor met the performance goals. Maintaining this performance, however, depends on adequate temperature management. Subsequent calculations and measurements determined the effect of several sources of heat on the temperature of the liquid inside the contactor stages: heats of solvation and dilution, heat generated by the rotor in the mixing zone, and heat from the motor used to spin the rotor. The results indicated that over 90% of the heat comes from the motors, generating 12 W of thermal energy per stage. It was concluded that satisfactory temperature management of the contactor should be achievable by cooling the extraction section to remove 12 W of heat per stage.

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Category :
Languages : en
Pages : 239

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Book Description
This report summarizes the FY 2010 and 2011 accomplishments at Oak Ridge National Laboratory (ORNL) in developing the Next Generation Caustic-Side Solvent Extraction (NG-CSSX) process, referred to commonly as the Next Generation Solvent (NGS), under funding from the U.S. Department of Energy, Office of Environmental Management (DOE-EM), Office of Technology Innovation and Development. The primary product of this effort is a process solvent and preliminary flowsheet capable of meeting a target decontamination factor (DF) of 40,000 for worst-case Savannah River Site (SRS) waste with a concentration factor of 15 or higher in the 18-stage equipment configuration of the SRS Modular Caustic-Side Solvent Extraction Unit (MCU). In addition, the NG-CSSX process may be readily adapted for use in the SRS Salt Waste Processing Facility (SWPF) or in supplemental tank-waste treatment at Hanford upon appropriate solvent or flowsheet modifications. Efforts in FY 2010 focused on developing a solvent composition and process flowsheet for MCU implementation. In FY 2011 accomplishments at ORNL involved a wide array of chemical-development activities and testing up through single-stage hydraulic and mass-transfer tests in 5-cm centrifugal contactors. Under subcontract from ORNL, Argonne National Laboratory (ANL) designed a preliminary flowsheet using ORNL cesium distribution data, and Tennessee Technological University confirmed a chemical model for cesium distribution ratios (DCs) as a function of feed composition. Inter laboratory efforts were coordinated with complementary engineering tests carried out (and reported separately) by personnel at Savannah River National Laboratory (SRNL) and Savannah River Remediation (SRR) with helpful advice by Parsons Engineering and General Atomics on aspects of possible SWPF implementation.

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Languages : en
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A solvent extraction system for removal of cesium (Cs) from alkaline solutions was developed utilizing a novel solvent invented at the Oak Ridge National Laboratory (ORNL). This solvent consists of a calix[4]arene-crown-6 extractant dissolved in an inert hydrocarbon matrix. A Modifier is added to the solvent to enhance the extraction power of the calixarene and to prevent the formation of a third phase. An additional additive, called a suppressor, is used to improve stripping performance. The process that deploys this solvent system is known as Caustic Side Solvent Extraction (CSSX). The solvent system has been deployed at the Savannah River Site (SRS) in the Modular CSSX Unit (MCU) since 2008. Subsequent development efforts by ORNL identified an improved solvent system that can raise the expected decontamination factor (DF) in MCU from H"00 to more than 40,000. The improved DF is attributed to an improved distribution ratio for cesium [D(Cs)] in extraction from H"5 to H"0, an increased solubility of the calixarene in the solvent from 0.007 M to>0.050 M, and use of boric acid (H3BO3) stripping that also yields improved D(Cs) values. Additionally, the changes incorporated into the Next Generation CSSX Solvent (NGS) are intended to reduce solvent entrainment by virtue of more favorable physical properties. The MCU and Salt Waste Processing Facility (SWPF) facilities are actively pursuing the changeover from the current CSSX solvent to the NGS solvent. To support this integration of the NGS into the MCU and SWPF facilities, the Savannah River Remediation (SRR)/ARP/MCU Life Extension Project requested that the Savannah River National Laboratory (SRNL) perform testing of the new solvent for the removal of Cs from the liquid salt waste stream. Additionally, SRNL was tasked with characterizing both strip (20-in long, 10 micron pore size) and extraction (40-in long, 20 micron pore size) coalescers. SRNL designed a pilot-scale experimental program to test the full size strip (V5) and extraction (V10) centrifugal contactors and the associated strip and extraction effluent coalescers to determine the hydraulic and mass transfer characteristics with the NGS. The test program evaluated the amount of organic carryover and the droplet size of the carryover phases using several analytical methods. Provisions were also made to enable an evaluation of coalescer performance. Stage efficiency and mass distribution ratios were determined using Cs mass transfer measurements. Using 20 millimolar (mM) extractant (instead of 50 mM), the nominal D(Cs) measured was 16.0-17.5. The data indicate that equilibrium is achieved rapidly and maintained throughout sampling. The data showed good stage efficiency for extraction (Tests 1A-1D), ranging from 98.2% for Test 1A to 90.5% for Test 1D. No statistically-significant differences were noted for operations at 12 gpm aqueous flow when compared with either 4 gpm or 8 gpm of aqueous flow. The stage efficiencies equal or exceed those previously measured using the baseline CSSX solvent system. The nominal target for scrub Cs distribution values are H".0-2.5. The first scrub test yielded an average scrub value of 1.21 and the second scrub test produced an average value of 0.78. Both values are considered acceptable. Stage efficiency was not calculated for the scrub tests. For stripping behavior, six tests were completed in a manner to represent the first strip stage. For three tests at the baseline flow ratios (O:A of 3.75:1) but at different total flow rates, the D(Cs) values were all similar at H".052. Similar behavior was observed for two tests performed at an O:A ratio of 7:1 instead of 3.75:1. The data for the baseline strip tests exhibited acceptable stage efficiency, ranging from 82.0% for low flow to 89-90% for medium and high flow. The difference in efficiency may be attributable to the low volume in the contactor housing at lower flow rates. The concentrations of Isopar L{reg_sign} and Modifier were measured using semi-volatile organic analysis (SVOA) and Fourier Transform Infrared (FTIR) Spectroscopy. However, due to issues associated with sample point configuration, the two methods cannot be correlated by this data. SVOA measurements provided a measure of Isopar L{reg_sign} and Modifier carryover for both stripping and extraction. For low-flow conditions in stripping, Isopar L{reg_sign} concentration measured H"00-500 mg/L. For moderate-flow conditions, Isopar L{reg_sign} was H"800-1900 mg/L. For high-flow conditions, Isopar L{reg_sign} was H"350-1750 mg/L for one test and H"00-800 mg/L for a second test. In extraction, the quantity of Isopar L{reg_sign} was H"60 mg/L at low flow, H"50-350 mg/L at moderate flow, and H"20-390 mg/L at high flow. For the above Isopar L{reg_sign} concentrations, Modifier was also present at the nominal Isopar-to-Modifier ratio of 3.65.

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Category :
Languages : en
Pages : 21

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A caustic-side solvent extraction (CSSX) process to remove cesium from Savannah River Site (SRS) high-level waste was tested in a minicontactor (2-cm centrifugal contactor). In the first phase of this effort, the minicontactor stage efficiency was improved from 60% to greater than 80% to meet the SRS process requirements using a 32-stage CSSX flowsheet. Then, the CSSX flowsheet was demonstrated in a 32-stage unit, first without solvent recycle, then with it. In both cases, the key process goals were achieved: (1) the cesium was removed from the waste with decontamination factors greater than 40,000 and (2) the recovered cesium was concentrated by a factor of 15 in dilute nitric acid. Oak Ridge National Laboratory (ORNL) analysis of the recycled solvent showed no evidence of impurity buildup.