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.

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.

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.

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.