A microfluidic route for synthesis of scandium oxide microspheres, their characterization and neutron activation.

Radioactive scandium-46 microspheres have applications in mapping flow in a chemical reactor through a technique known as radioactive particle tracking (RPT). In the present study a novel microfluidic method has been developed for synthesis of controlled size scandium oxide microspheres. An inline/in-situ mixing of the scandium precursor and gelling agents was implemented which makes the microfluidic platform amenable for truly continuous operation. Microspheres of size varying from 937 to 666 µm were produced by varying O/A ratio from 10 to 30. Perfectly spherical and monodispersed (PDI <10 %) microspheres were obtained at O/A 15 and beyond. The morphology, elemental composition, and structure of the microspheres were analysed by SEM, EDS and XRD, respectively. Subsequently the microspheres were irradiated with thermal neutrons in a nuclear reactor to obtain radioactive Sc-46 oxide microspheres. The activity produced on each Sc-46 microspheres with different sizes was in the range 19.5-34.0 MBq.

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.

Applications of the radiotracers in the industry: A review.

Radiotracer techniques are extensively used for troubleshooting, measuring hydrodynamic parameters and process visualization in industrial systems because of their many advantages over conventional tracer techniques. Most of these techniques are well established, and are routinely used in the industry around the world. This review discusses the general principles of the radiotracer methodology, commonly used applications of radiotracer in the industry, recent advances in the area, and the economic benefits accrued. Each application is illustrated with recently published case studies.

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.

Investigation of flow dynamics of wastewater in a pilot-scale constructed wetland using radiotracer technique.

Constructed wetlands (CWs) are used for the treatment of wastewater by natural processes. Knowledge of the flow dynamics of wastewater through the CWs is required to evaluate their performance, operation and design. The residence time distribution (RTD) approach was used to evaluate the above-mentioned parameters in a CW. The RTD of wastewater flowing through a pilot-scale CW was measured using Technetium-99 m (99mTc) as a radiotracer. The measured data were analyzed, and mean residence time and stagnant volumes were quantified under different operating conditions. A plug flow component in series along with a tank-in-series model with an exchange between the active and dead zones was used to simulate the measured RTD curves and investigate the flow dynamics of the flowing wastewater. The results of the study showed that the optimum flow rate and wastewater level in the CW was 2.3 m3/s and 0.6 m, respectively. Moreover, the results of the study will help in the operation and design of the existing wetland and design of new wetlands.

Investigation of flow dynamics of phosphate fertilizer production reactors using radiotracer technique.

Radiotracer investigations were carried out in two identical phosphoric acid production reactors and a triple super phosphate (TSP) production reactor in three different plants in Tunisia. The main objective of the study was to investigate and compare their flow behavior and identify flow abnormalities, if any. Residence time distribution (RTD) of the process material (ore pulp) was measured in the three reactors using Iodine-131. The measured RTDs were treated and analyzed to obtain flow parameters such as the mean residence time (MRT), dead volume, and extent of bypassing. The treated RTD curves were modeled using a suitable mathematical model, and the values of the parameters were obtained. The results of the investigations were used to evaluate and compare the flow performance of the reactors, quantify the degree of mixing, and visualize the prevailing flow patterns. The results of the investigations are expected to be used to make necessary modifications to enhance the efficiency and optimize the performance of the reactors or the production process.

Application of thin layer activation technique for monitoring corrosion of carbon steel in hydrocarbon processing environment.

Acidic crude oil transportation and processing in petroleum refining and petrochemical operations cause corrosion in the pipelines and associated components. Corrosion monitoring is invariably required to test and prove operational reliability. Thin Layer Activation (TLA) technique is a nuclear technique used for measurement of corrosion and erosion of materials. The technique involves irradiation of material with high energy ion beam from an accelerator and measurement of loss of radioactivity after the material is subjected to corrosive environment. In the present study, TLA technique has been used to monitor corrosion of carbon steel (CS) in crude oil environment at high temperature. Different CS coupons were irradiated with a 13 MeV proton beam to produce Cobalt-56 radioisotope on the surface of the coupons. The corrosion studies were carried out by subjecting the irradiated coupons to a corrosive environment, i.e, uninhibited straight run gas oil (SRGO) containing known amount of naphthenic acid (NA) at high temperature. The effects of different parameters, such as, concentration of NA, temperature and fluid velocity (rpm) on corrosion behaviour of CS were studied.

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.

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.

Investigation of flow dynamics of liquid phase in a pilot-scale trickle bed reactor using radiotracer technique.

A radiotracer investigation was carried out to measure residence time distribution (RTD) of liquid phase in a trickle bed reactor (TBR). The main objectives of the investigation were to investigate radial and axial mixing of the liquid phase, and evaluate performance of the liquid distributor/redistributor at different operating conditions. Mean residence times (MRTs), holdups (H) and fraction of flow flowing along different quadrants were estimated. The analysis of the measured RTD curves indicated radial non-uniform distribution of liquid phase across the beds. The overall RTD of the liquid phase, measured at the exit of the reactor was simulated using a multi-parameter axial dispersion with exchange model (ADEM), and model parameters were obtained. The results of model simulations indicated that the TBR behaved as a plug flow reactor at most of the operating conditions used in the investigation. The results of the investigation helped to improve the existing design as well as to design a full-scale industrial TBR for petroleum refining applications.

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.

Radiotracer investigations in pilot-scale soakers.

This paper describes a radiotracer investigation carried out to measure residence time distribution (RTD) of petroleum residues in pilot-scale soakers. The main objectives of the investigation were to evaluate the feasibility of using bromine-82 as dibromobiphenyl (DBBP) for tracing the petroleum residues (organic phase) as a radiotracer at elevated temperature and pressure, and to investigate the flow dynamics of the phase in the soaker at different operating and process conditions. The measured RTD was treated and mean residence times (MRTs) were determined. Tanks-in-series with backmixing model (TISBM) was used to simulate the measured RTD data. The results of model simulation indicated a high degree of backmixing in the soaker without baffles i.e. without sectionalizing the soaker. However, the introduction of perforated plates at various axial locations inside the soaker i.e. sectionalizing the soaker, reduces the extent of backmixing thus tending the flow towards plug flow.

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.

Radiotracer investigation in an industrial-scale oxidizer.

A radiotracer investigation was carried out in an industrial-scale oxidizer. The main objectives of the investigation were to measure residence time distribution (RTD) of organic process fluid, determine the mean residence time (MRT) and investigate the degree of axial mixing. Bromine-82 as p-dibromo biphenyl was used as a radiotracer for measuring RTD of the organic process fluid. The MRT of the fluid in the oxidizer was determined to be 390min. An ideal stirred tank model with a plug flow reactor in recirculation stream was used to simulate the measured RTD data and was found suitable for describing flow in the system. Based on the model simulation the mean residence times in oxidizer and recycle stream were estimated. The results of the investigation showed that the oxidizer behaved as a well-mixed reactor whereas the recycle stream behaved as a plug flow reactor.

Measurements of liquid phase residence time distributions in a pilot-scale continuous leaching reactor using radiotracer technique.

An alkaline based continuous leaching process is commonly used for extraction of uranium from uranium ore. The reactor in which the leaching process is carried out is called a continuous leaching reactor (CLR) and is expected to behave as a continuously stirred tank reactor (CSTR) for the liquid phase. A pilot-scale CLR used in a Technology Demonstration Pilot Plant (TDPP) was designed, installed and operated; and thus needed to be tested for its hydrodynamic behavior. A radiotracer investigation was carried out in the CLR for measurement of residence time distribution (RTD) of liquid phase with specific objectives to characterize the flow behavior of the reactor and validate its design. Bromine-82 as ammonium bromide was used as a radiotracer and about 40-60MBq activity was used in each run. The measured RTD curves were treated and mean residence times were determined and simulated using a tanks-in-series model. The result of simulation indicated no flow abnormality and the reactor behaved as an ideal CSTR for the range of the operating conditions used in the investigation.

Investigation of flow behaviour of coal particles in a pilot-scale fluidized bed gasifier (FBG) using radiotracer technique.

Knowledge of residence time distribution (RTD), mean residence time (MRT) and degree of axial mixing of solid phase is required for efficient operation of coal gasification process. Radiotracer technique was used to measure the RTD of coal particles in a pilot-scale fluidized bed gasifier (FBG). Two different radiotracers i.e. lanthanum-140 and gold-198 labeled coal particles (100 gm) were independently used as radiotracers. The radiotracer was instantaneously injected into the coal feed line and monitored at the ash extraction line at the bottom and gas outlet at the top of the gasifier using collimated scintillation detectors. The measured RTD data were treated and MRTs of coal/ash particles were determined. The treated data were simulated using tanks-in-series model. The simulation of RTD data indicated good degree of mixing with small fraction of the feed material bypassing/short-circuiting from the bottom of the gasifier. The results of the investigation were found useful for optimizing the design and operation of the FBG, and scale-up of the gasification process.

Application of 140La and 24Na as intrinsic radiotracers for investigating catalyst dynamics in FCCUs.

Instrumental neutron activation analysis (INAA) of fluid catalytic cracking (FCC) catalyst samples was carried out with an objective to identify activable elements and evaluate its suitability for use as an intrinsic radiotracer for tracing catalyst itself in Fluid Catalytic Cracking Units (FCCUs) used in petroleum refining. Two catalyst samples obtained from two different refineries were analyzed. Twelve different elements were identified in each catalyst sample and their respective concentrations were determined. From the recorded gamma-ray spectra, it was found that lanthanum-140 ((140)La) and sodium-24 ((24)Na) were the predominantly present and suitable radionuclides that could be used as radiotracers for tracing catalyst in FCCUs. Lanthanum being present in much higher concentration forms the major component of the radiotracer after irradiation. Based on the results of INAA, appropriate quantities of the catalyst samples were irradiated with neutrons to produce the desired amount of activity of lanthanum-140 and sodium-24 to be used as radiotracers for tracing the catalyst itself in a pilot as well as an industrial-scale FCCU. The residence time distribution (RTD) of catalyst was measured and analyzed to determine mean residence time (MRT). The axial dispersion model (ADM) was used to simulate the measured RTD data and investigate the degree of axial mixing. The results of the experiments were used to improve the design of pilot-scale FCCU and optimize the performance of the industrial-scale FCCU.