Residence time distribution studies using radiotracers in chemical industry—A review

A wireless-controlled lab-scale system for automated gamma column scanning and radiotracer applications

We present a novel wireless-controlled lab-scale system for gamma column scanning and radiotracer applications. The system utilizes a microcontroller for wireless movement of the source and detector along vertical and lateral axes. Acquired data is wirelessly transmitted to a handheld device, enabling real-time scan profiles. The system reduces scan duration, manpower involvement, and radiation exposure. Applicability to radiotracer applications, especially residence-time distribution measurements, is demonstrated. Finally, with its expanded scanning area and enhanced flexibility, the system holds potential for providing cost-effective solutions in both research and industrial settings.

Performance evaluation of a flighted rotary dryer for lateritic ore in concurrent configuration

The lateritic ore drying in the Cuban nickel producing industry is realized within flighted rotary dryers. In this investigation, performance indicators in regards to transfer of momentum, heat and mass were evaluated. The dryers operate in a concurrent configuration with combustion gas, at a productivity between 40 t h-1 and 50 t h-1. The distribution function of the residence time (RTD) was best fitted to a model of a multi-branch tanks-in-series system, theoretical residence time was 51 ± 2 min and experimental mean residence time 61 min, at a rate of 45 t h-1 and hydraulic efficiency 1.23, due to the presence of dead-zoon. Mass and energy balance was made following a "black box" model, as results, the specific fuel consumption was 27.25 ± 0.25 kg fuel t-1 of wet ore, specific energy consumption 79.66 ± 0.95 kg fuel t-1 of H2O evaporated, energy efficiency 97.28 ± 0.01 %, thermal efficiency 66.88 ± 0.71 % and drying efficiency 98.77 ± 0.12 %. Mathematical modelling was made using a system of differential equations, the rate of drying in falling rate period was estimated by Arrhenius equation, then, temperature profile and ore moisture content along the dryer was simulated. The model provided a successful predictive performance; for an inlet gas temperature between 850 °C and 900 °C, the ore moisture was reduced form 33.0 % (wet basis) to a range depending on the dryer productivity, from 3.0 % to 7.1 %. Designing a computerized system that implements these algorithms can benefit on efficiency and productivity of the production plant.

Investigation of Oxy-Fuel Combustion through Reactor Network and Residence Time Data

Oxy-fuel combustion is a promising strategy to minimize the environmental impact of combustion-based energy conversion. Simple and flexible tools are required to facilitate the successful integration of such strategies at the industrial level. This study couples measured residence time distribution with chemical reactor network analysis in a close-to-reality combustor. This provides detailed knowledge about the various mixing and reactive characteristics arising from the use of the two different oxidizing streams.

A hybrid model for multipoint real time potency observation in continuous direct compression manufacturing operations

The ongoing transition from batch to continuous manufacturing offers both challenges and opportunities in the field of oral solid dosage form production. In turn, Process Analytical Technology (PAT) offers a path towards the successful deployment of continuous tablet manufacturing in rotary tablet presses. One promising PAT tool for this endeavour is the NIR-derived potency measurement. However, the high degree of noise in the data may hamper the extraction of useful information. For this reason, this work focused on the implementation of an adaptive Kalman filter algorithm that incorporates and reconciles the potency prediction given by one or more NIR probes with those of a semi-mechanistic compartmental model developed for the application at hand. This approach allowed for more robust concentration estimations. Furthermore, it was observed that potency levels in multiple locations in the studied tablet press (including those in the finished tablets) could be appropriately inferred using a single in-line measurement data stream. This methodology thus opens the door to advanced process control applications.

Residence time distribution (RTD) revisited

Residence Time Distribution (RTD) theory is revisited and tracer technology discussed. The background of RTD following Danckwerts ideas is presented by introducing "distribution" functions for residence time, internal age and intensity function and how to experimentally obtain them with tracer techniques (curves C and F of Danckwerts). Compartment models to describe fluid flow in real reactors are reviewed and progressive modeling of chromatographic processes discussed in some detail. The shortcomings of Standard Dispersion Model (SDM) are addressed, the Taylor-Aris model discussed and the Wave Model of Westerterp's group introduced. The contribution of Computational Fluid Dynamics (CFD) is highlighted to calculate RTD from momentum and mass transport equations and to access spatial age distribution and degree of mixing. Finally smart RTD and future challenges are discussed.

Residence time distribution studies using radiotracers in a lab-scale distillation column: Experiments and modeling

The radiotracer's residence time distribution (RTD) is an important study of the performance of industrial process reactors.The application of radiotracers is the method used to diagnose the functioning of packed distillation columns. This paper presents the results of an experiment carried out using the Technitium-99 (Mo⁹⁹) radiotracer to determine the RTD in a laboratory-scale packed distillation column.The concentration of the radiotracer is monitored using eight scintillation detectors.The obtained data is treated for background correction, radioactive decay correction, starting point correction, filtering, and data extrapolation. After this preprocessing, two mathematical models are investigated on this data using International Atomic Energy Agency (IAEA) RTD software. The parameters of each model are optimized in oder to calculate the value of the RTD, and to determine the model which gives the best match with the experimental data. The appropriate model is than selected. Consequenly the one with the best match, is used to deduce the crucial parameter RTD in this experiment.

Explicit Residence Time Distribution of a Generalised Cascade of Continuous Stirred Tank Reactors for a Description of Short Recirculation Time (Bypassing)

The tanks-in-series model (TIS) is a popular model to describe the residence time distribution (RTD) of non-ideal continuously stirred tank reactors (CSTRs) with limited back-mixing. In this work, the TIS model was generalised to a cascade of n CSTRs with non-integer non-negative n. The resulting model describes non-ideal back-mixing with n > 1. However, the most interesting feature of the n-CSTR model is the ability to describe short recirculation times (bypassing) with n < 1 without the need of complex reactor networks. The n-CSTR model is the only model that connects the three fundamental RTDs occurring in reactor modelling by variation of a single shape parameter n: The unit impulse at n→0, the exponential RTD of an ideal CSTR at n = 1, and the delayed impulse of an ideal plug flow reactor at n→∞. The n-CSTR model can be used as a stand-alone model or as part of a reactor network. The bypassing material fraction for the regime n < 1 was analysed. Finally, a Fourier analysis of the n-CSTR was performed to predict the ability of a unit operation to filter out upstream fluctuations and to model the response to upstream set point changes.

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.