Determination Of Residence Time Distribution Research Articles

Determination of Residence Time Distribution in a Continuous Powder Mixing Process With Supervised and Unsupervised Modeling of In-line Near Infrared (NIR) Spectroscopic Data.

Successful implementation of continuous manufacturing processes requires robust methods to assess and control product quality in a real-time mode. In this study, the residence time distribution of a continuous powder mixing process was investigated via pulse tracer experiments using near infrared spectroscopy for tracer detection in an in-line mode. The residence time distribution was modeled by applying the continuous stirred tank reactor in series model for achieving the tracer (paracetamol) concentration profiles. Partial least squares discriminant analysis and principal component analysis of the near infrared spectroscopy data were applied to investigate both supervised and unsupervised chemometric modeling approaches. Additionally, the mean residence time for three powder systems was measured with different process settings. It was found that a significant change in the mean residence time occurred when comparing powder systems with different flowability and mixing process settings. This study also confirmed that the partial least squares discriminant analysis applied as a supervised chemometric model enabled an efficient and fast estimate of the mean residence time based on pulse tracer experiments.

Fluid dynamic analysis and residence time distribution determination for rectangular based spouted beds

Fluid dynamic characterization for a set of three serial rectangular based spouted beds (RBSB) using sawdust or turnip seeds, were made. In batch experiences, the minimum spouting velocity (Ums) and the maximum pressure drop (ΔPmax) were determined based on the bed height and moisture content. With respect to the continuous solid feed experiences, initially the conditions that allowed the stationary operation for 1, 2 and 3 beds connected in series, were determined. Following, injecting colored particles and with an image analysis it was possible to determine the residence time distribution (RTD). When compared with expressions from literature, good agreement was found for Ums, whereas for ΔPmax an expression is proposed that includes the sphericity of the particles. The RTDs were adjusted with the tank in series model, finding that the effects of solids feed rate, air flow and moisture content are significant for each solid RTD.

From powder to tablets: Investigation of residence time distributions in a continuous manufacturing process train as basis for continuous process verification

The essence of Continuous Manufacturing (CM) resides in the fact that continuous process units are directly connected to each other forming a continuous process train. The thorough understanding of material flow in this train based on suitable sensors, including on-line process analytical technologies and other sensors, is key in understanding the time-domain behavior of the system and the process. This real-time monitoring correlated with the time domain material flow behavior could be used to close control-loops. In practical terms, the implementation of such a control strategy is only feasible, if the overlying control system knows precisely what material is when and where at all times. Consequently, thorough knowledge of the residence time distribution (RTD) of the material throughout the whole manufacturing network needs to be established early on in development. Once RTD is well understood, its constant observation could also be used for continuous process verification purposes hinging on the argument that the flow pattern of the material is unchanged. As continuous processes that run over extended periods of time are susceptible to unforeseen incidents like equipment wear-out or clogging, drifts or shifts in RTD could indicate such issues early on.The presented work aims to demonstrate this proposed concept for an integrated wet-granulation CM process. To achieve this aim, three steps were completed: First, thorough RTD knowledge was generated, by inducing endogenous step-tests in active pharmaceutical ingredient (API) content in the range of ±30% at varying process conditions, and analyzing the material RTDs via NIRS analysis at four different locations in the line. Second, it was demonstrated that also low-level step tests of ±5% and even ±3% are sufficient for accurate RTD determination. This validated the possibility of continuous RTD assessment during (pre-)validation trials or even commercial manufacturing, as the drug product would comply with required quality characteristics (content uniformity, assay). In the third step, it was then demonstrated that recurring low-level step testing during routine manufacturing could be used as a way to determine the current system health, as observed changes in RTD indicated blockages and accidental material hold-up in the line. While deliberate changes in API content during commercial production might seem counter intuitive, they would actually aid in ensuring the production of quality product in a better way, than running at constant process settings over an extended period of time without the constant assessment of system health.

LIF or dye: Comparison of different tracing methods for granular solids

Determination of residence time distribution is considered essential for continuous pharmaceutical unit operations, in order to enable process understanding and control. A common way for determining residence times are tracer based methods, yet at the moment most realizations are found in liquid systems whereas use of those methods on granular samples is rarely encountered.Here, we compare two different methods for applying and detecting tracers in granular material processed in a pharmaceutical capsule-filling unit. As first method, a simple colorimetric procedure, i.e. using a dye and a camera as photometer is used. As second method, light induced fluorescence, i.e. using a fluorescent tracer material, a stimulating source and the camera as photometer again, is used.Both methods are tested and compared for their performance and appeared to be sufficient for the use in residence time distribution determination, yet none of the two proved to be superior. Consequently, side issues rather than analytic performance determined the final preference for the colorimetric method.

Physical Modelling of Aluminum Refining Process Conducted in Batch Reactor with Rotary Impeller

The refining process is one of the essential stages of aluminum production. Its main aim is to remove hydrogen, that causes porosity and weakens the mechanical and physical properties of casting aluminum. The process is mainly conducted by purging inert gas through the liquid metal, using rotary impellers. The geometry of the impellers and the processing parameters, such as flow rate of gas and rotary impeller speed, influence the gas dispersion level, and therefore the efficiency of the process. Improving the process, and optimization of parameters, can be done by physical modelling. In this paper, the research was carried out with the use of a water model of batch reactor, testing three different rotary impellers. Varied methods were used: visualization, which can help to evaluate the level of dispersion of gas bubbles in liquid metal; determination of residence time distribution (RTD) curves, which was obtained by measuring the conductivity of NaCl tracer in the fluid; and indirect studies, completed by measuring the content of dissolved oxygen in water to simulate hydrogen desorption. The research was carried out for different processing parameters, such as flow rate of refining gas (5–25 L·min−1) and rotary impeller speed (3.33–8.33 s−1). The obtained results were presented graphically and discussed in detail.

Experimental Study on Pressure Drop and Flow Dispersion in Packed Bed of Natural Zeolite

The use of conventional correlation for pressure drop and dispersion coefficient calculation may result in inaccurate values for zeolite packed bed as the correlations are generally developed for regularly shaped and uniformly sized particles. To support the research on the application of modified natural zeolite as tar cracking catalyst, the research on the hydrodynamic behaviour of zeolite packed bed has been conducted. Experiments were carried out using a glass column with diameter of 37.8 mm. Natural zeolite with particle size of about 2.91 to 6.4 mm was applied as packing material in the column, and the bed height was varied at 9, 19 and 29 cm. Air was used as the fluid that flows through the bed and nitrogen was used as a tracer for residence time distribution determination. Air flow rates were in the range of 20 to 100 mL/s which correspond to the laminar-transitional flow regime. The pressure drops through the bed were in the range of 1.7 to 95.6 Pa, depending on the air flow rate and bed height. From these values, the parameters in the Ergun equation were estimated, taking into account the contribution by wall effect when the ratio of column to particle diameter is low. The viscous and inertial term constants in the Ergun equation calculated ranges from 179 to 199 and 1.41 to 1.47 respectively while the particle sphericity ranges from 0.56 to 0.59. The reactor Peclet number were determined to range from 5.2 to 5.5, which indicated significant deviation from a plug flow condition.

Experimental determination of residence time distribution in continuous dry granulation

With increasing importance of continuous manufacturing, the interest in integrating dry granulation into a continuous manufacturing line is growing. Residence time distribution measurements are of importance as they provide information about duration of materials within the process. These data enable traceability and are highly beneficial for developing control strategies. A digital image analysis system was used to determine the residence time distribution of two materials with different deformation behavior (brittle, plastic) in the milling unit of dry granulation systems. A colorant was added to the material (20%w/w iron oxide), which did not affect the material properties excessively, so the milling process could be mimicked well. Experimental designs were conducted to figure out which parameters effect the mean residence time strongly. Moreover, two types of dry granulation systems were contrasted. Longer mean residence times were obtained for the oscillating mill (OM) compared to the conical mill (CM). For co-processed microcrystalline cellulose residence times of 19.8–44.4s (OM) and 11.6–29.1s (CM) were measured, mainly influenced by the specific compaction force, the mill speed and roll speed. For dibasic calcium phosphate anhydrate residence times from 17.7–46.4 (OM) and 5.4–10.2s (CM) were measured, while here the specific compaction force, the mill speed and their interactions with the roll speed had an influence on the mean residence time.

Application of Raman Spectroscopy to Characterization of Residence Time Distribution and Online Monitoring of a Pilot‐Scale Tubular Reactor for Acrylic Acid Solution Polymerization

A pilot‐scale tubular reactor containing static mixers is equipped with several Raman probes in order to perform online monitoring of radical copolymerization of acrylic acid in aqueous solution. This setup allows determination of residence time distribution while polymerization reaction occurs, using sodium nitrate as a tracer. These results prove that the use of convenient static mixers allows obtaining a nearly perfect plug‐flow reactor in all explored conditions (reactive and nonreactive medium, between 0.001 and 1 Pa s viscosity). Furthermore, the dynamics of the pilot‐scale reactor is characterized. Experimental transient and steady‐state values are compared to predictions based both on residence time distribution and model of polymerization kinetics. The applicability of Raman spectroscopy to online monitoring of pilot‐scale reactors is demonstrated. image

Scandinavian baffle boiler design revisited

The aim of this paper is to examine whether the use of baffles in a combustion chamber, one of the well-known low-cost methods for the boiler performance improvement, can be enhanced. Modern day tools like computational fluid dynamics were not present at the time when these measures were invented, developed and successfully applied. The objective of this study is to determine the influence of location and length of a baffle in a furnace, for different mass flows, on gas residence time. The numerical simulations have been performed of a simple Scandinavian stove like furnace. The isothermal model is used, while air is used as a medium and turbulence is modeled by realizable k-epsilon model. The Lagrange particle tracking is used for the residence time distribution determination. The statistical analysis yielded the average residence time. The results of the computational fluid dynamics studies for different baffle positions, dimensions and flow rates show from up to 17% decrease to up to 13 % increase of residence time. The conclusion is that vertical position of the baffle is the most important factor, followed by the length of the baffle, while the least important showed to be the mass flow.

Determination of residence time distributions in different high pressure gasification processes by radioactive tracers

Abstract High-Pressure Partial Oxidation is a key technology for the usage of flare gases and heavy oil residues. At the test plant of TU Bergakademie Freiberg, it is possible to gasify different gaseous and liquid fuels at pressures up to 100 bar (g). Information on residence time distributions can be gained by using radioactive tracers. The results of measurements for different reactor geometries and feedstocks will be discussed in this paper. Results of radioactive residence time measurements depend strongly on reactor geometry and require different evaluation methods.

Residence time distribution of the electrodialyzer under electric field conditions

To avoid the membrane scaling during electrodialytic desalination of sparingly soluble salt solutions, the electrodialysis should be performed in a way that the vast majority of growing clusters is washed out from the module before the crystallization occurs (the residence time is lower than nucleation induction time). Such method requires the determination of residence time distribution (RTD) of the electrodialyzer. While available literature presents only RTD measured at no current conditions, with only water passing through the module, this study presents a method of measuring the RTD on the working electrodialyzer, when the applied current causes ion migration and electroosmotic water flux. The change in concentrate compartment RTD was confirmed for the linear flow velocity range of 0.38–0.84cm/s and current density range of 0–673A/m2. The hydrodynamic conditions inside the module were described using an open–open vessel dispersion model and it was shown that significant longitudinal dispersion is observed (on average D/uL=0.08). The current density distribution along the electrodialyzer was observed and quantified and the question of velocity distribution along the electrodialyzer was tackled.

Optimization of a continuous hybrid impeller mixer via computational fluid dynamics.

This paper presents the preliminary steps required for conducting experiments to obtain the optimal operating conditions of a hybrid impeller mixer and to determine the residence time distribution (RTD) using computational fluid dynamics (CFD). In this paper, impeller speed and clearance parameters are examined. The hybrid impeller mixer consists of a single Rushton turbine mounted above a single pitched blade turbine (PBT). Four impeller speeds, 50, 100, 150, and 200 rpm, and four impeller clearances, 25, 50, 75, and 100 mm, were the operation variables used in this study. CFD was utilized to initially screen the parameter ranges to reduce the number of actual experiments needed. Afterward, the residence time distribution (RTD) was determined using the respective parameters. Finally, the Fluent-predicted RTD and the experimentally measured RTD were compared. The CFD investigations revealed that an impeller speed of 50 rpm and an impeller clearance of 25 mm were not viable for experimental investigations and were thus eliminated from further analyses. The determination of RTD using a k-ε turbulence model was performed using CFD techniques. The multiple reference frame (MRF) was implemented and a steady state was initially achieved followed by a transient condition for RTD determination.

Residence time distribution determination in a submerged filter with and without aeration using a tracer

AbstractBACKGROUNDCommercial filter media are commonly regular in shape and the flow patterns can be predicted with simple tools. Using lava stones as filter media, this study analyzes the influence of particle size and aeration on the hydraulic behaviour of a submerged filter prior to biofilm colonization.RESULTSThe filter was packed, separately, with two different sizes of lava stones (4.7 and 9.5 mm) and operated under different hydraulic retention times to establish the causes of deviations from ideal models. Tracer curves were analyzed using two mathematical models (Axial Dispersion and Wolf and Resnick models). The curves show that the tracer appeared in the effluent in a shorter time than expected indicating an effective volume reduction. It was estimated that the dead volume of the filter with aeration was 83% and 22% for the filter without aeration.CONCLUSIONThe dead volume is caused, in the case of the filter with aeration, by the combination of two phenomena: the liquid volume displaced by the air bubbles and the turbulence caused by aeration generating preferential channelling along the filter media and creating large zones of stagnant liquid. In the case of the filter without aeration the volume reduction is caused by channels developed by the media irregular shape. © 2013 Society of Chemical Industry

Residence Time Distribution Determination of a Continuous Stirred Tank Reactor using Computational Fluid Dynamics and its Application on the Mathematical Modeling of Styrene Polymerization

Abstract The continuous operation of a stirred tank reactor for styrene polymerization was modeled. The proposed approach consists of an iterative procedure between two modules that considers the fluid-dynamics and kinetics respectively. The kinetic module considers a complex kinetic mechanism and is used to predict the time evolution of global variables, such as conversion and species concentrations, physicochemical properties and molecular structure characteristics of the final product. In order to obtain a 3D representation of the flow field, the simulation of the hydrodynamics of the reactor was carried out with the aid of a commercial computational fluid dynamics (CFD) software package. Because CFD is capable to predict the complete velocity distribution in a tank, it provided a good alternative to carry out residence time distribution (RTD) studies. It was found that the stimulus-response tracer method is reasonably accurate to obtain a complete RTD compared to the particle tracking method. The obtained RTD results showed a good agreement when validated with experimental data and literature information.From the estimates of the kinetic module and the RTD predictions, a statistical calculus allows the determination of the average properties at the reactor outlet. The convergence of the iterative procedure was tested and reasonable predictions were achieved for an industrial reactor.

Using tracer methods and experimental design approach for examination of hydrodynamic conditions in membrane separation modules

The possibility of application of fluorescein and radioactive 99mTc as tracers for determination of residence time distribution of liquid phase and for diagnosing hydrodynamic conditions in apparatuses for membrane separation was studied. Two different ultrafiltration systems with diverse arrangement of liquid flow: the apparatus with helical flow generated by the movable element (inner cylinder) and the tubular module with cross flow filtration, were tested by the RTD technique. The tracer studies were supplemented with modelling. The optimal conditions enabling to handle the plug flow-like structure in the helical apparatus were determined. The minimum of dimensionless variance (vard) was obtained at P=0.765bar, QR=121.88l/h and Ω=2887.5rpm. In spite of higher linear velocities attained in the tubular cross-flow module, the flow structure in the helical apparatus was more similar to the ideal plug flow pattern that was demonstrated by higher Peclet numbers and lower values of the dimensionless variance. Application of movable part and Couette–Taylor flow in the membrane apparatus may balance the advantages coming from high flow rates applied in cross-flow filtration systems minimising formation of the deposit on the membrane surface and reducing membrane fouling.

Hydrodynamics and batch biodegradation of phenol in an Internal Loop Airlift Reactor

Determination of Residence Time Distribution (RTD), oxygen volumetric mass transfer coefficient (kLa) and mixing pattern in an Internal Loop Airlift Reactor (ILALR) for both living and nonliving systems have been investigated in this paper. Optimal operating condition is found at a gas flow rate of 2 l min−1. The estimated kLa values for nonliving and living system at 27°C are 0.004 s−1 and 0.017 s−1 respectively. Batch biodegradation of phenol with an initial concentration of 300 mg l−1 by the mixed microbial culture occurs at a very high degradation rate (0.16 mg l−1 h−1).

Determination of Residence Time Distribution in Gas‐Phase Microreactors using Light Emitting (Quasi‐)Continuous Plasma Discharges

AbstractA novel technique for determining the residence time distribution in gas‐phase microreactors has been developed, which both minimizes flow distortions upon tracer injection and provides precise tracer detection with high temporal resolution. The methodology proposed has been demonstrated as a suitable means for characterizing gas‐phase microreactors by measurements on two idealized test reactors and two different ceramic plate microreactor modules.

Measurement of residence time distribution of a multicomponent system inside an ohmic heater using radio frequency identification

The residence time of the fastest particle through an ohmic heater should be known with a high degree of reliability to calculate the minimum lethality delivered to the product inside the heater. Many methods are available for the determination of residence time distribution (RTD) of particles inside heating systems, but the main limitation in all these methods is their inability to detect multiple particles. Radio frequency identification (RFID), which offers the possibility of tracking multiple particles inside the system, was used to measure the RTD of analog chicken particles in chicken chowmein inside an ohmic heating system. Results showed that the residence time of the fastest RFID tag embedded tracer inside the heater was as expected, higher than that associated with the laminar flow of a fluid in a tube, which is accepted by regulators in process filings. The experiment demonstrated that RFID could be successfully used to measure RTD under aseptic conditions and offers an innovative, time-saving technique for tracking multiple particles.

Numerical simulation of the residence time distribution in flotation cells

AbstractTwo methods for the numerical determination of residence time distributions (RTD) have been tested and proofed to be applicable. One has been used to obtain the RTD of solid particles in a laboratory size flotation machine. Emphasis has been laid on the influence of various parameters, e.g. numerical method, geometry or particle properties. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Residence Time Distribution in Granulation Drums on the Example of Industrial Carbon Black

AbstractThe present work describes systematic investigations into dry granulation of industrial carbon black with special regard to the residence time characteristics, using a continuously operated semitechnical bead‐forming drum. A novel experimental method and a model for the determination of residence time distribution of carbon black in the bead‐forming drum have been developed and very good agreement of model and experiment has been demonstrated.