Investigation of flow dynamics of molten glass in different solar glass production units using radiotracer method.

A radiotracer investigation was previously carried out to characterize the flow of the molten glass and to identify the cause of poor quality of the glass sheets produced in an industrial solar glass production unit (SGPU-1) (Pant et al., 2016). Based on the investigations, several flow abnormalities were identified and the design of the unit was modified to improve the quality of the product and meet the product specifications. Subsequently, the radiotracer investigation was repeated in the modified unit (SGPU-1m). The results of the study showed that the dead volume and homogenization time in the modified unit were significantly reduced with improvement in mixing of the molten glass as compared to the SGPU-1. Based on the results of the two investigations, a new glass production unit (SGPU-2) with enhanced capacity was designed, fabricated and commissioned. The radiotracer investigation was repeated in the newly designed unit with an objective to evaluate and validate its design. The results indicated that the performance of SGPU-2 was as per the design criteria and the quality of the glass sheets produced was as per the desired specifications.

Evaluation of mixing performance and validation of CFD simulations in baffled anaerobic digesters using radiotracer technique.

The anaerobic digesters find usage in treating the huge amount of waste such as trash, garbage, human waste and animal waste. The sustained performance of an anaerobic digester depends on the flow pattern and mixing behaviour in the digester. A cylindrical digester tank with vertical baffles can provide flow behaviour approaching that of a plug flow reactor. However, the presence of dead zones and recirculating regions cause non-ideal flow in the digester. In this work, the mixing behaviour in two scaled-down models of baffled digester tanks is characterized by measurement of residence time distribution (RTD) using a radioactive tracer. While the first design has three vertical baffles, the second design include horizontal static flaps on the baffles. The flow behaviour in the digester is also simulated using computational fluid dynamics (CFD) and RTD is obtained computationally. The comparison of RTD curves obtained from CFD simulations with those obtained from radiotracer experiments show good agreement between them. There appear to be only minor difference in the flow behaviour and the RTD curves in the two digester designs. Using the RTD curve data, two commonly used RTD models, tank-in-series and dispersion models, have been fitted and both models are able to predict the RTD in the digester qualitatively.

Investigation of aqueous phase dynamics in a uranium stripping unit using radioactive tracer.

Mixer-setters units are widely used in uranium purification processes. For efficient operations of mixer-settler units, it is essential to measure the hydrodynamics parameters of the different phases involved. The residence time distribution (RTD) measurement is commonly used method to estimate the hydrodynamics parameters of process reactors. In the present study, RTD of the aqueous phase was measured in different stages mixer-settler unit (mixers, settlers and mixer-settler units) used for stripping operation using Iodine-131 as a radiotracer. For the RTD measurements, radiotracer was injected as an impulse in aqueous phase feed line and its movement was monitored at different locations in the stripping unit using NaI(Tl) detectors. The mean residence times (MRTs) of the aqueous phase were estimated from measured RTD curves. For quantification of the degree of mixing, suitable flow models were proposed based on design and nature of the measured RTD curves and subsequently used for simulation. Based on the results of the RTD study, the mixing of aqueous phase was characterized and design of the stripping unit and its sub-units were validated. The optimum conditions were identified for efficient for the operation of the stripping unit.

Residence time distribution study in a pilot-scale liquid phase catalytic exchange (LPCE) column packed with a mixture of hydrophobic and hydrophilic catalysts.

Residence time distribution (RTD) measurements were carried out in a packed bed column designed for exchange of hydrogen isotopes. The main objective of the study was to characterize the liquid phase mixing under various processes and operating conditions. The packed bed was composed of a mixture of two different types of catalytic packing materials, i.e., a hydrophobic material and a hydrophilic material. Technitium-99m (99mTc) as sodium pertechnetate was used as a radiotracer for RTD measurements. From the measured RTD curves, mean residence times (MRTs), liquid holdup and degree of mixing of liquid phase were evaluated. An axial dispersion model exchange with stagnant zones was used to simulate the measured RTD curves. The results of model simulation showed that volume fraction of hydrophobic to hydrophilic packing and gas/liquid superficial velocities affect the liquid holdup, bed pressure drop and liquid phase dispersion/mixing characteristics. The results of the present study will help to screen packing, optimize the volume of the packing fractions, design and construct the catalyst and optimize the operating conditions for scale up of the isotope exchange process.

Hydrodynamic modeling and radiotracer investigations in Kolkata Port Trust, Kolkata, West Bengal, India.

In this study, hydrodynamic modeling and radiotracer investigations were conducted in Kolkata Port Trust, Kolkata, West Bengal, India to investigate the dispersion of sediments and to evaluate the suitability of three different dumping sites (Upper Auckland, Lower Auckland and Eden) for dredged sediments along a navigation channel. Scandium-46 (148-240 GBq) comprising scandium glass powder with a particle size distribution ranging from 75-100 µm was used as a radiotracer. The radiotracer was injected onto the seabed at the selected site using a remotely operated injection system and its movement on the seabed was tracked over a period of three months using waterproof NaI(Tl) scintillation detector. The tracer concentration curves were plotted on a site map of the area for different trackings and isocount contours were plotted. Qualitative information was obtained from the isocount contours such as the general direction of movement and spread of the radiotracer. The isocount contours showed that the sediment predominantly moved away from the navigation channel. From the isocount, a transport diagram was plotted based on isocount counter and sediment transport parameters such as the general direction of movement by sediments on the seabed, transport velocity, transport thickness and bed load movement rate were determined for all the sites. The dispersion patterns obtained for the sediments by modeling were compared with the experimental results and they were found to be similar. Thus, the model results were validated and the proposed sites were found to be suitable for dumping the dredged material because the sediments did not return to the navigation channel.

Methods of preparation of microparticles for radioactive particle tracking experiments.

Radioactive particle tracking (RPT) technique is a relatively newer technique for the characterization of flow of process materials (liquids, solids) in laboratory- and pilot-scale industrial systems. The technique uses a single particle labelled with a suitable radioisotope having similar physical properties to that of the bulk of the process material. The preparation of a representative radioactive microparticle is a challenging task in the implementation of the technique. There are no standard methods available for the preparation of radioactive microparticles. This paper discusses some of the methods of preparation of radioactive microparticles for RPT studies. A few examples of RPT applications using the prepared microparticles are also discussed.

Investigation of flow dynamics of primary coolant in a delay tank of a swimming pool-type nuclear reactor using radiotracer technique.

Radiotracer investigations were carried out for tracing primary coolant in a delay tank of a swimming pool type nuclear reactor. The delay tank was designed to provide a certain delay or residence time to the primary coolant so that the short-lived radioisotopes such as (nitrogen-16 and oxygen-19) decay to a safer level before exiting from the delay tank. However, soon after commissioning of the reactor, the radiation levels at the exit of the reactor core and delay tank, in the working area were found to be higher than the permissible levels. Therefore, the main objectives of the investigations were to measure breakthrough and residence times and, to investigate flow dynamics of the coolant within the tank. Residence time distributions (RTDs) of the coolant were measured in the delay tank using technetium-99m as sodium pertechnatate as a radiotracer. The breakthrough time (BTT) and mean residence time (MRT) were determined from the measured RTD and the same were found to be inadequate to allow the decay of short-lived radioisotopes to the permissible levels. Axial dispersion model with two parallel flow streams was used to simulate the measured RTD curves. Results of the model simulation indicated bypassing of the coolant. Based on the results of the radiotracer investigations, necessary modifications were carried out in the design of the tank. After implementing the modifications, the radiotracer experiments were repeated and, the BTT and the MRT were found to increase sufficient enough to allow decay of the produced radioisotopes and thus to reduce the radiation levels at the exit of the delay tank and in the working area to the safer and permissible levels.

Radiotracer investigation in a pilot-scale fluidized bed coal gasifier (FBCG).

Radiotracer investigations were carried out for measurement and analysis of residence time distribution (RTD) of coal particles in a pilot-scale gasifier fitted with a flat air/steam distributor. Measurements were made at different operating conditions using gold-198 (198Au) labeled coal particles as a radiotracer. The measured RTDs were treated and mean residence times (MRTs) were determined. Furthermore, the treated RTDs were simulated using a suitably conceptualized mathematical model and detailed information about hydrodynamics of coal particles within the gasifier was obtained. Results of model simulation indicated that the gasifier behaved as an ideal mixer of fine coal particles exiting from the top of the gasifier. A small fraction of the coarser particles was found to be bypassing at ambient temperature.

Radiotracer investigation on the measurement of residence time distribution in an ethyl acetate reactor system with a large recycle ratio.

A radiotracer investigation was carried out on the measurement of residence time distribution (RTD) of process fluid in an industrial-scale ethyl acetate reactor system, which consists of two independent reactors with recirculation and connected in series with each other. Bromine-82 as ammonium bromide was used as the radiotracer for the RTD experiments at different operating conditions. The individual reactors and the overall reactor system were modelled using physically representative phenomenological models comprising of continuously stirred tank reactors (CSTRs). The results showed that the recirculation rate considerably affected the flow mixing behaviour and mean residence time of the process fluid in the reactor system. The results also showed that there was bypassing of the fluid in the first reactor that ranged from 12% to 22% and 40% dead volume at different operating conditions, whereas the second reactor behaved closely as an ideal CSTR. The results of the investigation can be used to optimise the process parameters and design new improved reactor systems for the production of ethyl acetate.

Flow investigation in an industrial-scale soaker using radiotracer technique.

Flow dynamics of heavy petroleum residue in an industrial-scale soaker operating in a petroleum refinery was investigated. Residence time distributions (RTDs) of the residue were measured using radiotracer technique. Bromine-82 as dibromobiphenyl was used as radiotracer for tracing the petroleum residue. The measured RTDs were treated and mean residence times (MRTs) were determined. The measured RTD data was simulated using a combined model i.e. axial dispersion model in parallel with tanks-in-series with stagnant volume and exchange. The results of the model simulation fitted very well to the experimentally measured data and identified bypassing or existence two parallel flow paths within the soaker.

Study of adsorption characteristics of Au(III) onto coal particles and their application as radiotracer in a coal gasifier.

This paper describes a systematic study carried out to investigate adsorption characteristics of 198Au onto the surface of coal particles using a radiotracer technique. The main objective of the study was to optimize labeling conditions and utilize the labeled coal particles as a radiotracer for tracing coal particles in fluidized bed coal gasifiers. The effect of various experimental factors such as pH, amount of adsorbent, initial gold concentration, temperature and contact time between adsorbate and adsorbent were studied to obtain optimum conditions for maximum adsorption of 198Au on coal particles from an aqueous solution. Analysis of the data showed that the Langmuir model was found most suitable to describe the adsorption phenomena. The thermodynamic analysis showed that the adsorption process is feasible, spontaneous and endothermic in nature. The results of the kinetics suggested that the adsorption presumably follows second order kinetics and chemisorption in nature. Based on the optimized conditions, the amount of coal particles and activity to be used for tracing the coal phase in pilot-scale gasifiers was estimated. Accordingly, the radiotracer was prepared and successfully used for measurement of residence time distribution (RTD) in a pilot-scale coal gasifier.

Investigation of holdup and axial dispersion of liquid phase in a catalytic exchange column using radiotracer technique.

Holdup and axial dispersion of liquid phase in a catalytic exchange column were investigated by measuring residence time distributions (RTD) using a radiotracer technique. RTD experiments were independently carried out with two different types of packings i.e. hydrophobic water-repellent supported platinum catalyst and a mixture (50% (v/v)) of hydrophobic catalyst and a hydrophillic wettable packing were used in the column. Mean residence times and hold-ups of the liquid phase were estimated at different operating conditions. Axial dispersion model (ADM) and axial dispersion with exchange model (ADEM) were used to simulate the measured RTD data. Both the models were found equally suitable to describe the measured data. The degree of axial mixing was estimated in terms of Peclet number (Pe) and Bodenstein number (Bo). Based on the obtained parameters of the ADM, correlations for total liquid hold-up (HT) and axial mixing in terms of Bo were proposed for design and scale up of the full-scale catalytic exchange column.

Production of gaseous radiotracers for industrial applications.

This paper describes prerequisite tests, analysis and the procedure for irradiation of gaseous targets and production of gaseous radioisotopes i.e. argon-41 ((41)Ar) and krypton-79 ((79)Kr) in a 100MWTh DHRUVA reactor located at Bhabha Atomic Research Center (BARC), Trombay, Mumbai, India. The produced radioisotopes will be used as radiotracers for tracing gas phase in industrial process systems. Various details and prequalification tests required for irradiation of gaseous targets are discussed. The procedure for regular production of (41)Ar and (79)Kr, and assay of their activity were standardized. Theoretically estimated and experimentally produced amounts of activities of the two radioisotopes, irradiated at identical conditions, were compared and found to be in good agreement. Based on the various tests, radiological safety analysis and standardization of the irradiation procedure, necessary approval was obtained from the competent reactor operating and safety authorities for regular production of gaseous radiotracers in DHRUVA reactor.

Radiotracer investigation in a glass production unit.

A radiotracer investigation was carried out in a glass production unit in a glass industry. Lanthanum-140 as lanthanium oxide mixed with silica was used as a radiotracer to trace the molten glass in various sections of the unit. Residence time distributions of molten glass were measured and analyzed to identify the flow abnormities. The flow parameters such as breakthrough time, mean residence time, homogenization time, dead volume and flow patterns in different sections of the unit were obtained from the measured RTD data. The results of the investigation were used to improve and optimize the operation of the glass production unit.

Discharge rate measurements in a canal using radiotracer methods.

Discharge rates of water were measured in a canal using radiotracer methods with an objective to validate the efficacy of Concrete Volute Pumps (CVPs) installed at various pumping stations along the canal. Pulse velocity and dilution methods were applied to measure the discharge rates using Iodine-131 as a radiotracer. The discharge rate measured in one of the sections of the canal using the pulse velocity method was found to be 22.5m(3)/s, whereas the discharge rates measured using the dilution method in four different sections of the canal varied from 20.27 to 20.62m(3)/s with single CVP in operation. The standard error in discharge rate measurements using dilution method ranged from ±1.1 to ±1.8%. The experimentally measured values of the discharge rate were in good agreement with the design value of the discharge rate (20m(3)/s) thus validating the performance of the CVPs used in the canal.

Synthesis, characterization and application of Au-198 nanoparticles as radiotracer for industrial applications.

This paper describes synthesis and characterization of radioactive gold nanoparticles ((198)Au-NPs), and explores their utility as a radiotracer for tracing an aqueous phase in a continuous laboratory-scale bubble column at ambient conditions. The performance of the (198)Au-NPs as a radiotracer was compared with the results obtained with a conventional radiotracer i.e. bromine-82 ((82)Br) as ammonium bromide and found to be identical. A tank-in-series with backmixing model (TISBM) was used to simulate the RTDs of the aqueous phase and characterize flow in the bubble column.

Measurement of residence time distribution of liquid phase in an industrial-scale continuous pulp digester using radiotracer technique.

A series of radiotracer experiments was carried out to measure residence time distribution (RTD) of liquid phase (alkali) in an industrial-scale continuous pulp digester in a paper industry in India. Bromine-82 as ammonium bromide was used as a radiotracer. Experiments were carried out at different biomass and white liquor flow rates. The measured RTD data were treated and mean residence times in individual digester tubes as well in the whole digester were determined. The RTD was also analyzed to identify flow abnormalities and investigate flow dynamics of the liquid phase in the pulp digester. Flow channeling was observed in the first section (tube 1) of the digester. Both axial dispersion and tanks-in-series with backmixing models preceded with a plug flow component were used to simulate the measured RTD and quantify the degree of axial mixing. Based on the study, optimum conditions for operating the digester were proposed.

Residence time distribution measurements in a pilot-scale poison tank using radiotracer technique.

Various types of systems are used to control the reactivity and shutting down of a nuclear reactor during emergency and routine shutdown operations. Injection of boron solution (borated water) into the core of a reactor is one of the commonly used methods during emergency operation. A pilot-scale poison tank was designed and fabricated to simulate injection of boron poison into the core of a reactor along with coolant water. In order to design a full-scale poison tank, it was desired to characterize flow of liquid from the tank. Residence time distribution (RTD) measurement and analysis was adopted to characterize the flow dynamics. Radiotracer technique was applied to measure RTD of aqueous phase in the tank using Bromine-82 as a radiotracer. RTD measurements were carried out with two different modes of operation of the tank and at different flow rates. In Mode-1, the radiotracer was instantaneously injected at the inlet and monitored at the outlet, whereas in Mode-2, the tank was filled with radiotracer and its concentration was measured at the outlet. From the measured RTD curves, mean residence times (MRTs), dead volume and fraction of liquid pumped in with time were determined. The treated RTD curves were modeled using suitable mathematical models. An axial dispersion model with high degree of backmixing was found suitable to describe flow when operated in Mode-1, whereas a tanks-in-series model with backmixing was found suitable to describe flow of the poison in the tank when operated in Mode-2. The results were utilized to scale-up and design a full-scale poison tank for a nuclear reactor.