Showing papers in "Canadian Journal of Chemical Engineering in 2011"

Chemistry and Applications of Nanocrystalline Cellulose and its Derivatives: a Nanotechnology Perspective

Abstract: Nanocrystalline cellulose (NCC) is an emerging renewable nanomaterial that holds promise in many different applications, such as in personal care, chemicals, foods, pharmaceuticals, etc. By appropriate modification of NCC, various functional nanomaterials with outstanding properties, or significantly improved physical, chemical, biological, as well as electronic properties can be developed. The nanoparticles are stabilised in aqueous suspension by negative charges on the surface, which are produced during the acid hydrolysis process. NCC suspensions can form a chiral nematic ordered phase beyond a critical concentration, i.e. NCC suspensions transform from an isotropic to an anisotropic chiral nematic liquid crystalline phase. Due to its nanoscale dimension and intrinsic physicochemical properties, NCC is a promising renewable biomaterial that can be used as a reinforcing component in high performance nanocomposites. Many new nanocomposite materials with attractive properties were obtained by the physical incorporation of NCC into a natural or synthetic polymeric matrix. Simple chemical modification on NCC surface can improve its dispersability in different solvents and expand its utilisation in nano-related applications, such as drug delivery, protein immobilisation, and inorganic reaction template. This review paper provides an overview on this emerging nanomaterial, focusing on the surface modification, properties and applications of NCC.

CFD simulation of stirred tanks: Comparison of turbulence models. Part I: Radial flow impellers

Abstract: A critical review of the published literature regarding the computational fluid dynamics (CFD) modelling of single-phase turbulent flow in stirred tank reactors is presented. In this part of review, CFD simulations of radial flow impellers (mainly disc turbine (DT)) in a fully baffled vessel operating in a turbulent regime have been presented. Simulated results obtained with different impeller modelling approaches (impeller boundary condition, multiple reference frame, computational snap shot and the sliding mesh approaches) and different turbulence models (standard k − e model, RNG k − e model, the Reynolds stress model (RSM) and large eddy simulation) have been compared with the in-house laser Doppler anemometry (LDA) experimental data. In addition, recently proposed modifications to the standard k − e models were also evaluated. The model predictions (of all the mean velocities, turbulent kinetic energy and its dissipation rate) have been compared with the experimental measurements at various locations in the tank. A discussion is presented to highlight strengths and weaknesses of currently used CFD models. A preliminary analysis of sensitivity of modelling assumptions in the k − e models and RSM has been carried out using LES database. The quantitative comparison of exact and modelled turbulence production, transport and dissipation terms has highlighted the reasons behind the partial success of various modifications of standard k − e model as well as RSM. The volume integral of predicted energy dissipation rate is compared with the energy input rate. Based on these results, suggestions have been made for the future work in this area.

Material advancements in supercapacitors: From activated carbon to carbon nanotube and graphene

Abstract: The electrochemical capacitor (EC), also known as supercapacitor, is an energy storage device possessing a near infinite life-cycle and high power density recognised to store energy in the double-layer or through pseudocapacitance as a result of an applied potential. Fundamental principles of charge storage in relation to the important physical and chemical characteristics of electrode materials are addressed in the following review, with carbon-made electrodes, specifically activated carbon, carbon fibres and aerogels, carbon nanotubes and graphene emphasised in regards to their enhancement of the characteristic energy and power densities of ECs. Pseudocapacitive materials, notably transition metal oxides and nitrides, and conducting polymers are remarked by the potential to further improve EC performance through synergistic effects and asymmetric design. Research towards gaining a better understanding of charge storage in sub-micropores, material design and improving the performance of alternative electrolytes are expected to greatly enhance the capabilities of these devices in the near future.

Modelling asphaltene deposition in turbulent pipeline flows

Abstract: Asphaltene deposition is one of the important problems of oil production that requires an accurate predictive modelling. We developed an asphaltene deposition model in a pipeline. The model is based on data, which are obtained by experiments performed in a Couette device, where the inner cylinder rotates, and deposition on the outer wall is studied. A detailed theoretical analysis of an applicability of a Couette device for imitation of the asphaltene deposition in a pipe flow is presented. The model developed is based on first principles and consists of the two major modules: (1) a sub-model describing the particle size distribution evolution in time in a Couette device, and along a pipe; (2) a sub-model for calculating the particle transport to the wall. A population balance model is employed for modelling the particle size evolution. A concept of the critical particle size is introduced; only particles that are smaller than the critical size can deposit. The model developed contains only three parameters that are determined experimentally using a Couette device. The model of asphaltene deposition in a Couette device allows accurate describing the deposit mass growth in time. Performance of the deposition model for a pipeline with the coefficients obtained by a laboratory Couette device is also illustrated. Le depot d'asphaltenes est un des problemes majeurs de l'industrie petroliere et necessite des modeles predictifs fiables. Nous avons developpe un modele de depot d'asphaltenes en conduite petroliere. Le modele est base sur des donnees obtenues experimentalement par un systeme Couette avec cylindre interieur tournant. Le depot sur les parois exterieures, fixes, est alors etudie. Une analyse theorique detaillee de l'applicabilite d'un systeme Couette a l'etude du depot d'asphaltenes en ecoulement dans une conduite petroliere est presentee. Le modele developpe est base sur des principes fondamentaux et consiste en deux principaux modules: (1) un premier module decrivant l'evolution de la distribution de taille des particules avec le temps dans un systeme Couette et le long d'une conduite, (2) un deuxieme module pour le calcul du transport des particules vers la paroi. Un modele d'equilibre de population (population balance model) est utilise pour modeliser l'evolution de la taille des particules. Un concept de « taille critique » est alors defini: seules les particules plus petites que cette taille peuvent se deposer. La modelisation contient seulement trois parametres qui sont determines experimentalement sur un appareil de type Couette. Le modele permet une description fiable de l'augmentation de la masse de depot avec le temps. Les resultats de ce modele appliques a une conduite petroliere avec les parametres obtenus en laboratoire sur un systeme Couette sont egalement demontres. © 2011 Canadian Society for Chemical Engineering

CFD simulation of stirred tanks: Comparison of turbulence models (Part II: Axial flow impellers, multiple impellers and multiphase dispersions)

Abstract: In the first part of the review, published literature regarding the CFD modelling of single-phase turbulent flow in stirred tank reactors with radial flow impellers was critically analysed. A brief overview of different turbulence models (standard k − e model, RNG k − e model, the Reynolds stress model and large eddy simulation) as well as impeller baffle interaction models has been presented in the previous part. This part is concerned with the review of literature regarding CFD simulation of axial flow impellers. Comprehensive simulations have been carried out using various turbulence models and the model predictions (of all the mean velocities, turbulent kinetic energy and its dissipation rate) have been compared with the experimental measurements at various locations in the tank. The strengths and weaknesses of various turbulence models for axial flow impellers is presented. The quantitative comparison of exact and modelled turbulence production, transport and dissipation terms has highlighted the reasons behind the partial success of various modifications of standard k − e model as well as Reynolds stress model. Literature efforts on multiple impeller systems and multiphase systems have been discussed in a separate section. Based on these results, suggestions have been made for the future work in this area. Dans la premiere partie de l'etude, on a procede a une analyse critique de la litterature concernant la modelisation de la dynamique des fluides numerique de l'ecoulement turbulent a une phase dans les reacteurs a cuve agitee dotes de turbines a ecoulement radial. Une vue d'ensemble rapide des differents modeles de turbulence (modele standard k-e, modele RNG k-e, modele aux tensions de Reynolds et simulation des grandes echelles), ainsi que des modeles d'interaction des deflecteurs de turbine, a ete presentee dans la partie precedente. Cette partie se concentre sur l'analyse de la litterature concernant la simulation de DFN de turbines a ecoulement axial. Des simulations completes ont ete effectuees en utilisant plusieurs modeles de turbulence et les predictions des modeles (de toutes les vitesses moyennes, de l'energie cinetique turbulente et de son taux de dissipation) ont ete comparees aux donnees experimentales relevees a differents endroits de la cuve. On a presente les points forts et les points faibles de plusieurs modeles de turbulence concernant les turbines a ecoulement axial. La comparaison quantitative des donnees exactes et modelisees de la production, du transport et de la dissipation de la turbulence a mis en evidence les raisons qui expliquent la reussite partielle de plusieurs modifications apportees au modele standard k-e ainsi qu'au modele aux tensions de Reynolds. Une partie distincte est consacree a la discussion des resultats indiques dans la litterature concernant les systemes a roues multiples et les systemes multiphases. Sur la base de ces resultats, des etudes a venir dans ce domaine ont ete suggerees. © 2011 Canadian Society for Chemical Engineering

The CFD driven optimisation of a modified venturi for cavitational activity

Abstract: This work presents CFD-based optimisation of the important geometrical parameters of a cavitating venturi. The parameters for optimisation were selected based on the analysis of the steps involved in the cavitation process like cavity inception, cavity growth, and cavity collapse. It was seen that the ratio of the perimeter of the venturi to the cross-sectional area of its constriction quantifies the possible location of the inception of the cavity. The ratio of the throat length to its height (in the case of a slit venturi) controls the maximum size of the cavity and the angle of the divergence section controls the rate of collapse of a cavity. Based on the numerical study, it was concluded that a slit venturi (α = 2.7) with the slit length equal to its height (1:1) and a half angle of divergence section of 5.5° is an optimum geometry for best cavitational activity. Ce travail presente l'optimisation CFD-basee des parametres geometriques importants d'un venturi cavitation. Les parametres d'optimisation ont ete choisis bases sur l'analyse des etapes impliquees dans le processus de cavitation comme la creation de cavite, la croissance de cavite et l'ecroulement de cavite. On l'a vu que le rapport du perimetre du venturi a la section transversale de sa constriction (α) quantifie l'emplacement possible de la creation de la cavite. Le rapport de la longueur de gorge a sa hauteur (dans le cas d'une fente venturi) controle la taille maximale de la cavite et l'angle de la section de divergence controle la vitesse de l'ecroulement d'une cavite. Base sur l'etude numerique, on a conclu qu'une fente venturi (α = 2,7) avec la longueur de la fente egale a sa hauteur (1:1) et un demi-angle de la section de divergence de 5,5 est une geometrie optimum pour la meilleure activite de cavitation.

Performance of hydrocyclones with different geometries

Abstract: Hydrocyclones belong to an important group of equipments designed to solid–liquid or liquid–liquid separation in a centrifugal field. It is possible to adapt a hydrocyclone to the accomplishment of several industrial activities depending on the geometrical relations among its main dimensions. The operation and design of these devices are relatively simple; however, the flow inside them is very complex and its prediction is very difficult. For that reason, most models that are used to predict hydrocyclone performance are empirical ones. The objective of this work was to study the influence of geometric variables in the performance of hydrocyclones, using CFD and response surface techniques. The obtained results show that it was possible to find an optimum hydrocyclone design, that is, geometric relationships that lead to Euler number and cut size in minimum levels. Les hdrocyclones appartiennent a un groupe important d'equipements concus pour la separation solide-liquide ou liquide-liquide dans un champ centrifuge. Il est possible d'adapter un hydrocyclone a la realisation de plusieurs activites industrielles selon les relations geometriques dans ses dimensions principales. Le fonctionnement et la conception de ces dispositifs sont relativement simples; cependant, leur circulation interne est tres complexe et sa prediction est tres difficile. Pour cette raison, la plupart des modeles utilises pour predire le rendement des hydrocyclones sont des modeles empiriques. L'objectif de ce travail etait d'etudier l'influence des variables geometriques sur le rendement des hydrocyclones en utilisant une DFN et des techniques de surface de reponse. Les resultats obtenus indiquent qu'il etait possible de trouver une conception d'hydrocyclones optimale, c.-a-d. les relations geometriques qui menent au nombre d'Euler et a la mesure fixe a des niveaux minimaux. © 2011 Canadian Society for Chemical Engineering

An economically viable removal of methylene blue by adsorption on activated carbon prepared from rice husk

Abstract: Application of an agricultural waste material, rice husk, has been investigated for preparation of activated carbon. The rice husk-activated carbon (RHAC) was successfully utilised for the removal of a cationic dye, methylene blue (MB) from aqueous solutions. The activated carbon was prepared in presence of ZnCl2 as an activating agent under inert nitrogen atmosphere. RHAC was characterised for surface area, pore structural parameters, and point zero charge (pHZPC). The activated carbon was further characterised by Fourier transformation infrared (FT-IR) spectrometer, X-ray diffractometer (XRD), and scanning electron microscope (SEM). The effect of different parameters such as contact time and initial concentration, adsorbent dose, and temperature on removal of the dye from aqueous solutions was investigated. The experimental data fitted well in both the Freundlich and Langmuir isotherm models. The maximum adsorption capacity for MB was found to be 9.73 mg g−1 at 303 K. During the study of effect of adsorbent dose, almost a 100% removal was achieved at a higher dose of RHAC. Most of the experiments were carried out at an initial concentration of MB of 60 mg/L and at 303 K. Different thermodynamic parameters, viz., changes in free energy (G°), enthalpy (H°), and entropy (S°) have also been determined to explain feasibility of the process of removal. The sorption of MB on RHAC was found to be feasible, spontaneous, and endothermic in nature. On a analyse l'application d'un dechet agricole, l'ecorce de riz, pour la preparation de charbon actif. Le charbon actif d'ecorce de riz (CAER) a ete utilise avec succes pour le retrait d'un colorant cationique, le bleu de methylene (BM), de solutions aqueuses. Le charbon actif a ete prepare en presence de ZnCl2 comme activateur dans une atmosphere d'azote inerte. Le CAER etait caracterise pour la surface de contact, les parametres structurels des pores et le point de charge zero (pHZPC). Le charbon actif a ete davantage caracterise par un spectrometre infrarouge de transformee de Fourier (IR-TF), un diffractometre a rayons X (DRX) et un microscope electronique a balayage (MEB). On a analyse l'effet de differents parametres comme le temps de contact et la concentration initiale, la dose et la temperature de l'adsorbant lors du retrait du colorant des solutions aqueuses. Les donnees experimentales correspondaient bien a la fois avec les modeles isothermes de Freundlich et Langmuir. La capacite d'adsorption maximale du bleu de methylene etait de 9,73 mg g−1 a 303 K. Pendant l'etude de l'effet de la dose de l'adsorbant, on a atteint un retrait de presque 100% a une dose superieure de CAER. La plupart des experiences ont ete realisees a une concentration initiale de BM de 60 mg/L et a 303 K. Differents parametres thermodynamiques, viz., changements d'energie libre (G°), d'enthalpie (H°) et d'entropie (S°), ont egalement ete determines pour expliquer la faisabilite du processus de retrait. On a decouvert que la sorption du BM sur le CAER etait faisable, spontanee et de nature endothermique

Current challenges in the design and control of multiscale systems

Abstract: Multiscale modelling is a new emerging field in process systems engineering. Although the idea of linking events occurring across time and length scales is not new, the numerical solution of these models is challenging because of computational limitations and the difficulty in coupling modelling methods with different characteristics. Although an extensive set of tools are currently available to improve the performance of processes described using continuum models, most of these tools are not suitable to design and control a multiscale process. This work presents the approaches that are currently available to perform multiscale modelling and identifies the key challenges that need to be addressed to improve the performance of macroscopic processes by controlling events occurring at the atomistic, molecular and nanoscopic levels.

Numerical simulation of underground coal gasification using the CRIP method

Abstract: A three-dimensional simulation of the Underground coal gasification (UCG) process is studied in terms of the heat and mass transport phenomena and chemical kinetics in a coal seam during coal combustion by applying the controlled retracting injection point technique. The STARS module of the Computer Modelling Group software is used in this study. The gas species flow rate, cavity shapes, and temperature profile in the coal seam during gasification are investigated. The main motivation behind this study is to provide a simulation methodology by using a comprehensive porous media flow approach to understand the critical aspects of the UCG process. Une simulation tridimensionnelle du processus de gazeification in situ du charbon (UCG) est etudiee en fonction de la chaleur, des phenomenes de transport de la matiere ainsi que de la cinetique chimique dans une veine de charbon lors de sa combustion en appliquant la technique de retraction controlee du point d'injection. Le module STARS du logiciel informatique de modelisation du groupe est utilise dans cette etude. Le debit de l'espece de gaz, les formes de cavites, et profil de temperature dans la veine de charbon lors de la gazeification sont etudies. La principale motivation de cette etude est de fournir une methodologie de simulation en utilisant une approche globale de l'ecoulement en milieu poreux afin de comprendre les aspects critiques du processus de UCG.

Removal of strontium and barium from aqueous solutions by adsorption onto expanded perlite

Abstract: The adsorption of strontium and barium from aqueous solution onto expanded perlite (EP) has been investigated as a function of pH, contact time, adsorbent dosage, and temperature. Sorption experiments indicated that the sorption capacity was dependent on operating variables and the process was strongly pH-dependent. Equilibrium isotherm data were analysed using Langmuir, Freundlich, and Dubinin–Radushkevich isotherm models. The adsorption was well described by Langmuir isotherm model. The maximum adsorption capacity was found to be 1.14 and 2.486 mg/g for Sr (II) and Ba (II) from the Langmuir isotherm model at 20°C, respectively. Two simplified kinetic models viz. pseudo-first-order and pseudo-second-order models were tested to describe the adsorption process. The kinetic data indicated that adsorption fitted well with the pseudo-second-order kinetic model. Using the equilibrium constant value obtained at four (20, 30, 40, and 50°C) different temperatures, the thermodynamic parameters of the adsorption (ΔG°, ΔH°, and ΔS°) were also determined. The results showed that the adsorption of Sr (II) and Ba (II) ions on EP was exothermic and spontaneous.

Removal of solar red BA textile dye from aqueous solution by low cost barley husk: Equilibrium, kinetic and thermodynamic study

Abstract: The present study investigates the sorption potential of barley husk for the removal of solar red BA from aqueous solution. Sorption capacity, q (mg/g), of barley husk decreased with increasing initial dye concentration. The sorption equilibrium established within 90 min using 0.10 g biosorbent while it was prolonged to 135 min with increasing amount of biosorbent (0.25–0.50 g). The equilibrium data were fitted to Freundlich and Langmuir isotherms at different biosorbent doses. The results indicated the applicability of Freundlich isotherm at low-biosorbent dose. Pseudo-second-order kinetic model was found to be best fit to the biosorption data with three biosorbent doses. The equilibrium thermodynamic data for the adsorption of the dyes gave ΔG0 values −79.77 kJ/mol at 303 K indicated the process to be occurred spontaneously at low temperature. FTIR analysis and SEM imaging of biosorbent were also carried out. L'objectif de la presente etude est d'analyser le potentiel de sorption du son d'orge afin d'eliminer le BA rouge solaire contenu dans les solutions aqueuses. La capacite de sorption, q (mg/g), du son d'orge diminue lorsque les concentrations initiales de colorant augmentent. L'equilibre de sorption a ete etabli a 90 min en utilisant 0.10 g de biorsorbant, mais a ete prolonge a 135 min avec une plus grande quantite de biorsorbant (0.25 a 0.50 g). Les donnees relatives a l'equilibre ont ete harmonisees aux isothermes de Freundlich et Langmuir a differentes doses de biosorbant. Les resultats indiquent que l'isotherme de Freundlich est applicable avec de faibles doses de biosorbant. Selon les resultats, le modele cinetique de pseudo-second ordre correspond le mieux aux donnees de biosorption avec les trois doses de biosorbant. Les donnees de l'equilibre thermodynamique pour l'adsorption des colorants ont permis d'obtenir des valeurs de ΔG0 de −79.77 kJ/mol a 303 K, ce qui indique que le processus s'est deroule spontanement a faible temperature. Des analyses FTIR et une imagerie par MEB des biosorbants ont egalement ete realisees. © 2010 Canadian Society for Chemical Engineering

Effect of Tank Size on k L a and Mixing Time in Aerated Stirred Reactors With Non-Newtonian Fluids

Abstract: The most important scale-up parameters of aerated bioreactors are investigated in 42 and 340 L vessels, with water and various xanthan gum and carboxymethyl cellulose solutions. The study focuses mainly on mass transfer (kLa) measurements under various operating conditions. The relevance of existing correlations is discussed. The traditional viscosity-contribution approach appears unable to predict the changes in kLa during scale-up and an alternative formulation is proposed. The effect of rheology on power consumption and mixing time is in fair agreement with works published on this topic.

Density functional modelling in multiphase compositional hydrodynamics

Abstract: This work is essentially a review of a density functional approach in multiphase hydrodynamics developed by the authors during the last 15 years [Dinariev, J Appl Math Mech 1995;59(5):745-752; Dinariev, J Appl Math Mech 1998;62(3):397-405; Demyanov and Dinariev, Fluid Dynam 2004;39(6):933-944; Demianov et al., "Basics of the Density Functional Theory in Hydrodynamics," Fizmatlit, Moscow; 2009 (in Russian); Dinariev and Evseev, Fluid Dynam 2010;45(1 ):85-95]. The basic assumption is a representation of the entropy or the Helmholtz energy of the mixture as a functional that is dependent upon chemical component densities. The hydrodynamic system of equations (local conservation laws for chemical components, momentum, and energy) is used to describe multiphase processes, and the constitutive relations (expressions for stresses, diffusion, and heat fluxes) are derived from entropy growth requirement. The authors present the results of numerical simulations describing static and dynamic multiphase systems.

Scaling up of silverson rotor–stator mixers

Abstract: In-line rotor–stator mixers are widely applied in industry for the formulation of emulsion products; however, the current understanding of breakage/coalescence in such devices is limited. In this study the effect of rotor speed, flow rate and dispersed phase viscosity on drop size distributions in an industrial and in a lab scale in-line Silverson rotor–stator mixer were investigated. Silicone oils with viscosities of 9.4 and 339 mPa s at 1 wt.% were emulsified in surfactant solution. Sauter mean diameters were correlated with various parameters and it has been found that Weber number is the most appropriate scaling parameter. Energy dissipation rate is a marginally poorer scaling parameter and this term requires prior knowledge of the experimentally determined power constants. Based on these observations it seems sensible to use Weber number as the preferred scaling-up parameter.

Compatibilised ldpe/lldpe/nanoclay nanocomposites: i. structural, mechanical, and thermal properties

Abstract: Nanocomposites of LDPE/LLDPE/nanoclay have been prepared using a lab-scale co-rotating twin screw extruder. Using XRD, tensile testing, AFM, TGA, effects of some material properties and one processing parameter on mechanical and thermal properties of the prepared nanocomposites were evaluated. Tensile properties indicated that all the prepared nanocomposites exhibited a significant improvement in elastic modulus and toughness compared to pristine LDPE/LLDPE blends of the same composition. Thermal stability of nanocomposites in the air and nitrogen atmosphere was improved. XRD patterns and AFM micrographs showed semi-exfoliated and intercalated microstructures for the prepared nanocomposites with different orders of mixing. On a prepare des nanocomposites de polyethylene basse densite/polyethylene basse densite lineaire/nanoargile a l'aide d'une extrudeuse a deux vis a co-rotation a l'echelle laboratoire. A l'aide de la diffraction des rayons X, de l'essai de traction, de la microscopie a force atomique et de l'analyse gravimetrique par procede thermique, on a evalue les effets de certaines proprietes de materiaux et d'un parametre de traitement sur les proprietes mecaniques et thermiques des nanocomposites prepares. Les proprietes de traction ont indique que l'ensemble des nanocomposites prepares ont affiche une amelioration importante du module d'elasticite et de la tenacite comparativement au melange polyethylene basse densite/polyethylene basse densite lineaire original de meme composition. La stabilite thermique des nanocomposites dans l'air et de l'atmosphere d'azote a ete amelioree. Les modeles de diffraction des rayons X et les micrographies de microscopie a force atomique ont demontre des microstructures semi-exfoliees et intercalaires pour les nanocomposites prepares avec differents ordres de melange.

Power and flow characteristics of three rotor-stator heads

Abstract: In-line rotor-stators are used in a wide range of industrial applications—primarily for dispersion processes such as emulsification, deagglomeration. Three rotor-stator heads have been used to investigate their performance in breaking up of nanoparticle clusters within a large project. This article reports the findings of a part of this study aimed at investigating the flow and power characteristics in single phase to highlight the differences of three different mixer heads. Power characteristics are determined using the calorimetry allowing the characteristic power numbers for these devices to be obtained. These are also compared with CFD calculations. Flow characteristics are studied through numerical simulations.

Selection of simplified models: ii. development of a model selection criterion based on mean squared error

Abstract: Simplified models (SMs) with a reduced set of parameters are used in many practical situations, especially when the available data for parameter estimation are limited. A variety of candidate models are often considered during the model formulation, simplification, and parameter estimation processes. We propose a new criterion to help modellers select the best SM, so that predictions with lowest expected mean squared error can be obtained. The effectiveness of the proposed criterion for selecting simplified nonlinear univariate and multivariate models is demonstrated using Monte-Carlo simulations and is compared with the effectiveness of the Bayesian Information Criterion (BIC). Des modeles simplifies (MS) avec ensemble reduit de parametres sont utilises dans de nombreuses situations pratiques, particulierement lorsque les donnees disponibles pour l'estimation des parametres sont limitees. Divers modeles candidats sont souvent examines durant la formulation du modele, la simplification et l'estimation des parametres. Nous proposons un nouveau critere pour aider les modelisateurs a selectionner le meilleur MS et obtenir des predictions porteuses de l'erreur quadratique moyenne la plus faible. L'efficacite du critere propose pour la selection des modeles simplifies non lineaires a variable uniques et multiples est demontree en utilisant les simulations Monte-Carlo et comparee a l'efficacite du critere bayesian des informations (BIC).

A modified Peng–Robinson equation of state for phase equilibrium calculation of liquefied, synthetic natural gas, and gas condensate mixtures

Abstract: A modified Peng–Robinson equation of state, MPR2 EOS, is introduced by incorporating a new alpha function and a temperature dependent function for covolume, b. The modified cubic EOS has three input per each substance: critical temperature, critical pressure, and acentric factor. The coefficients of temperature dependence of the alpha and beta functions, relating to the parameters a and b of the new cubic EOS, are obtained by simultaneous fitting of saturated experimental vapour pressure and liquid density data for several pure components. The percent absolute average deviation (AAD%) of 1.38, 4.80 and 2.89 are obtained to correlation of the saturation vapour pressure, liquid density and vapour volume, respectively. Also the ADD% of 2.575 is computed for prediction of saturation enthalpy of vapourisation of the pure compounds. For calculation of phase equilibrium of mixture, the modified PR EOS is used for prediction of liquid density of the LNG mixtures. Also the new EOS is applied for construction of the phase envelop of synthetic natural gas, SNG, mixtures and calculation vapour–liquid equilibria of gas condensates. The results demonstrate that the new MPR2 EOS can be used for calculation of vapour–liquid equilibrium of pure components and mixtures with good accuracy.

Detailed investigation of non‐catalytic DPF regeneration

Abstract: The present investigation concerns the phenomena that occur during the non-catalytic regeneration of Diesel Particulate Filters (DPFs). The temperature evolution in the filter has been correlated to the emissions of CO, HC, NO, and NO2 during the loading and regeneration process. The emissions were assessed over both the diesel oxidation catalyst (DOC) and the DPF, in order to characterise the chemical species evolution inside the after-treatment line. Different regeneration temperatures, which have been found to have a strong impact on the evolution of the soot oxidation rate, have been assessed. Finally, the particulate emissions during regeneration have been measured on a number and size basis. La presente analyse concerne le phenomene qui se produit lors de la regeneration non catalytique des filtres a particules pour diesel (FPD). L'evolution de la temperature dans le filtre a ete en correlation avec les emissions de CO, HC, NO et NO2 lors du processus de chargement et de regeneration. Les emissions ont ete evaluees a la fois pour le catalyseur d'oxydation pour diesel (COD) et le FPD, dans le but de caracteriser l'evolution de l'espece chimique a l'interieur de la ligne post-traitement. On a evalue differentes temperatures de regeneration qui ont une forte incidence sur l'evolution du taux d'oxydation des suies. Enfin, les emissions de matieres particulaires lors de la regeneration ont ete mesurees sur une base de nombre et de taille.

Characteristics of batch rotor–stator mixer performance elucidated by shaft torque and angle resolved PIV measurements

Abstract: Characteristics of batch rotor–stator mixer performance are elucidated by shaft torque and angle resolved 2D PIV measurements obtained in a full-scale, custom build, bottom-mounted, rotor–stator mixer unit operating in the turbulent regime with water as working fluid. Measurements have been acquired at various rotor speeds corresponding to impeller based Reynolds numbers between 2.0 × 105 and 8.5 × 105. The use of a transparent Plexiglas stator facilitated PIV measurements inside and outside the stator as well as into the stator slots themselves. The governing mechanisms controlling the complex flow structures, flow rates, power dissipation, velocity fields, strain rate fields and turbulence intensity fields are explained, highlighting the influence on rotor–stator mixer performance. The results indicate that scale-up of mixing processes that depend on macro-scale phenomena should be based on constant rotor tip speed.

Optimising the lipid production of the green alga Neochloris oleoabundans using box–behnken experimental design

Abstract: A systematic approach involving factor grouping, factorial design and response surface analysis was demonstrated to be an effective method for studying the effects of a large number of nutrients on cell growth and lipid production of the green alga Neochloris oleoabundans for the purpose of medium optimisation. Box-Behnken experimental design (BBD) was used for factorial experimental design and response surface method (RSM) was used for data analysis. The optimised medium obtained was able to support a lipid yield of 641.4 mg lipid/L and a cell density of 2.54 g/L, which were 4.5- and 2.2-fold of that obtained with the basic medium, modified Bristol medium (MBM), respectively.

Equilibrium calculations for direct synthesis of dimethyl ether from syngas

Abstract: Thermodynamic analysis of single-step synthesis of dimethyl ether (DME) from syngas over a bi-functional catalyst (BFC) in a slurry bed reactor has been investigated as a function of temperature (200–240°C), pressure (20–50 bar), and composition feed ratio (H2/CO: 1–2). The BFC was prepared by physical mixing of CuO/ZnO/Al2O3 as a methanol synthesis catalyst and H-ZSM-5 as a methanol dehydration catalyst. The three reactions including methanol synthesis from CO and H2, methanol dehydration to DME and water–gas shift reaction were chosen as the independent reactions. The equilibrium thermodynamic analysis includes a theoretical model predicting the behaviour and a comparison to experimental results. Theoretical model calculations of thermodynamic equilibrium constants of the reactions and equilibrium composition of all components at different reaction temperature, pressure, and H2/CO ratio in feed are in good accordance with experimental values.

Rotary cement kiln coating estimator: Integrated modelling of kiln with shell temperature measurement

Abstract: Coating thickness protection in the burning zone of a rotary cement kiln during operation is important from the viewpoint of the kiln productivity.In this paper, an integrated model is presented to estimate the coating thickness in the burning zone of a rotary cement kiln by using measuredprocess variables and scanned shell temperature. The model can simulate the variations of the system, thus the impact of different processvariables and environmental conditions on the coating thickness can be analysed. The presented steady­state model derived from heat and massbalance equations uses a plug flame model for simulation of gas and/or fuel oil burning. Moreover, the heat transfer value from shell to the outsideis improved by a quasi­dynamic method. Therefore, at first, the model predicts the inside temperature profile along the kiln, then by consideringtworesistantnodesbetweentemperaturesoftheinsideandoutside,thelattermeasuredbyshellscanner,itestimatestheformedcoatingthicknessin the burning zone. The estimation of the model was studied for three measured data sets taken from a modern commercial cement kiln. Theresultsconfirmthattheaverageabsoluteerrorforestimatingthecoatingthicknessforthecases1,2,and3are3.26,2.82,and2.21cm,respectively.La protection de l’ ´epaisseur du rev etement dans la zone de combustion d’un sˆ echoir rotatif pour cimenterie pendant le fonctionnement est´importantedupointdevuedelaproductivit ´edus echoir.Danscedocument,unmod´ eleint` egr´ ´eestpr esent´ ´epourestimerl’ ´epaisseurdurev ˆetementde la zone de combustion d’un s echoir rotatif pour cimenterie en utilisant des variables de fonctionnement et des mesures de la temp´ ´erature del’enveloppe. Le mod ele peut simuler les variations du syst` eme; par cons` equent, on peut analyser les cons´ ´equences des diff ´erentes variables defonctionnement et conditions environnementales sur l’ epaisseur du rev´ ˆetement. Le mod `ele en r ´egime permanent pr esent´ e, d´ eriv´ ´e des equations´de bilan de masse et d’ energie, fait usage d’un mod´ ele de flamme en` ecoulement piston pour la simulation de la combustion de gaz ou de mazout.´De plus, le transfert de chaleur de l’enveloppe a l’ext` ´erieur est am ´elior e par une m´ ethode quasi dynamique. Par cons´ ´equent, en premier lieu, lemod ele pr` ´edit le profil de la temp erature int´ ´erieure tout au long du s echoir, puis en consid´ erant la diff´ erence entre les temp´ eratures int´ erieures et´ext erieures, mesur´ ´ees par balayeur, l’ epaisseur du rev´ ˆetement form ´e est estim ee sur le plan local. La pr´ ediction du mod´ ele est examin` ee par trois´ensembles de donn ees qui proviennent d’un s´ echoir pour cimenterie commercial moderne. Les r´ esultats confirment que l’erreur absolue moyenne´pour estimer l’ ´epaisseur de rev ˆetement pour les cas 1, 2 et 3 sont 3,26, 2,82 et 2,21cm, respectivement.Keywords: rotary cement kiln, coating thickness, simulation, flame model

Flow regimes and vertical solids conveying in a spout-fluid bed with a draft tube

Abstract: Pressure fluctuation data were obtained in a semi-cylindrical spout-fluid bed with draft tube, and statistical analyses of them were employed to recognise flow regimes. Also, the effects of spouting-gas and auxiliary-gas velocities, and length of entrainment zone on solids loading ratio in a draft tube were examined. As a result, five flow regimes appeared by changing spouting-gas and auxiliary-gas velocities and it was found that the simplest method to determine flow regime is to measure pressure fluctuations in a draft tube. Moreover, solids loading ratio could be controlled flexibly by auxiliary-gas velocity and length of entrainment zone. Des donnees de variation de pression ont ete obtenues dans un lit fluidifie jaillissant semi-cylindrique avec tube de circulation et des analyses statistiques de ces donnees ont ete utilisees pour reconnaitre les regimes de debit. De plus, les effets des vitesses de gaz jaillissant et de gaz auxiliaire, ainsi que la longueur de la zone d'entrainement sur le rapport de charge des solides dans un tube de circulation ont ete analyses. Par consequent, cinq regimes de debit sont apparus en changeant les vitesses de gaz jaillissant et de gaz auxiliaire et on a decouvert que la plus simple methode pour determiner le regime de debit est de mesurer les fluctuations de la pression dans un tube de circulation. De plus, on pourrait controler le rapport de charge des solides avec souplesse par la vitesse de gaz auxiliaire et la longueur de la zone d'entrainement.

Prediction of enhancement factor for mass transfer coefficient in regular packed liquid–liquid extraction columns

Abstract: Mass transfer coefficients are one of the most important parameters for the design of liquid–liquid extraction columns. The mass transfer coefficients of single drops in a pilot structured packed column have been measured using toluene/acetic acid/water and n-butyl acetate/acetic acid/water systems. Current research shows that theoretical models have failed to predict mass transfer coefficient precisely and are not reliable for design. In this work an empirical correlation for prediction of enhancement factor is developed. Dispersed phase mass transfer coefficients predicted by the proposed correlation are in good compatibility with experimental results. Les cœfficients de transfert de masse figurent parmi les parametres les plus importants a prendre en compte lors de la conception de colonnes d'extraction liquide-liquide. Les cœfficients de transfert de masse de chaque goutte dans une colonne a garnissage structure pilote ont ete mesures grâce a des systemes a base de toluene/d'acide acetique/d'eau et d'acetate de n-butyle/d'acide acetique/et d'eau. La comparaison entre les modeles theoriques et les resultats experimentaux de cœfficients de transfert de masse a montre que ces modeles ne sont pas assez precis pour etre appliques a la conception. Dans cette recherche, les facteurs d'accentuation du cœfficient de diffusion ont ete determines experimentalement et une correlation empirique a ete atteinte pour le facteur d'accentuation. Les cœfficients de transfert de masse de la phase dispersee qui avait ete prevus grâce a la correlation proposee s'harmonisent bien aux resultats des experiences. © 2010 Canadian Society for Chemical Engineering

Removal of direct Red-31 and direct Orange-26 by low cost rice husk: Influence of immobilisation and pretreatments

Abstract: The aim of the present study is to investigate the influence of free, carboxymethyl cellulose (CMC) immobilised, PVA–alginate immobilised, and HCl treated rice husk on the removal of Direct Red-31 and Direct Orange-26 dyes. The biosorption capacity of the rice husk increased with HCl treatment (67.39 and 45.34 mg/g) and decreased with PVA–alginate immobilisation (9.73 and 10.03 mg/g) as compared to the free biomass (65.56 and 45.58 mg/g) at 200 mg/L dye concentration for Direct Red-31 and Direct Orange-26, respectively. Equilibrium data were best described by Langmuir Type 1 for Direct Red-31 and Direct Orange-26 (free, CMC immobilised, PVA–alginate immobilised, and HCl treated). Best correlation coefficients for Direct Red-31 and Direct Orange-26 using free, CMC immobilised, PVA–alginate immobilised, and HCl treated rice husk were obtained for pseudo-second order and Elovich kinetic models. Values of Gibbs free energy (ΔG°) and enthalpy change (ΔH°) indicated that reaction was spontaneous and endothermic in nature at the studied temperatures. FT-IR studies showed the involvement of carbonyl, carboxyl, and amide groups in the biosorption process. SEM exhibited the morphological changes on the biosorbent surface and BET analysis to determine the surface area is also carried out. Le but de la presente etude est d'etudier l'influence de la carboxymethylcellulose (CMC) immobilisee, du PVAL-alginate immobilise et de l'ecorce de riz traitee a l'acide chlorhydrique libres sur le retrait des colorants rouge direct-31 et orange direct-26. La capacite de biosorption de l'ecorce de riz a augmente avec le traitement a l'acide chlorhydrique (67.39 et 45.34 mg/g) et a diminue avec l'immobilisation du PVAL-alginate (9.73 et 10.03 mg/g) comparativement a la biomasse libre (65.56 et 45.58 mg/g, a une concentration de colorant de 200 mg/L) pour rouge direct-31 et orange direct-26 respectivement. Les donnees d'equilibre etaient mieux decrites par Langmuir de type 1 pour rouge direct-31 et orange direct-26 (CMC immobilisee, PVAL-alginate immobilise et traite a l'acide chlorhydrique libres). Les meilleurs cœfficients de correlation pour rouge direct-31 et orange direct-26 qui utilisent de la carboxymethylcellulose (CMC) immobilisee, du PVAL-alginate immobilise et de l'ecorce de riz traitee a l'acide chlorhydrique libres ont ete obtenus pour les modeles cinetiques d'Elovich et de pseudo second ordre. Les valeurs de changements d'energie libre de Gibbs (ΔGo) et d'enthalpie (ΔHo) ont indique que la reaction etait spontanee et de nature endothermique aux temperatures etudiees. Les etudes FTIR ont indique la participation des groupes carbonyle, carboxyle et amide dans le processus de biosorption. La MEB a expose les changements morphologiques sur la surface des biosorbants et l'analyse BET pour determiner la surface est egalement realisee.

Reduction of Cr(VI) to Cr(III) and removal of total chromium from wastewater using scrap iron in the form of zerovalent iron(ZVI): Batch and column studies

Abstract: This work experimentally investigates Cr(VI) reduction to Cr(III) using waste scrap iron in the form of zerovalent iron (ZVI) collected from the mechanical workshop of the Institute, both in batch and continuous operation. The reduction of Cr(VI) to Cr(III) was found to be complete (∼100%) depending on the experimental conditions. Lower pH values favour Cr(VI) reduction. Two concurrent reactions take place, that is reduction of Cr(VI) by Fe0 (ZVI) and by Fe2+ generated due to H+ corrosion of iron. Maximum around 22%, 11% and 2% Cr(III) remained dissolved in solution while the experiments were carried out at initial pH of 2, 4.67 and 7. Higher ZVI loading increases Cr(VI) reduction rate, however, consumption of iron is noted to be higher. The results indicate that the bed is exhausted rapidly at higher pH, initial Cr(VI) concentration and flow rate. This is attributable to predominance passivation of ZVI surface forming Cr(III)–Fe(III)-oxide layer. SEM analysis of ZVI before and after the experiments confirms formation of passive oxide on iron surface is responsible for deterioration of Cr(VI) reduction efficiency due to its blanketing effect.

Selection of simplified models: I. Analysis of model‐selection criteria using mean‐squared error

Abstract: Mean-squared error (MSE) is used to analyse nine commonly used model-selection criteria (MSC) for their performance when selecting simplified models (SMs). Expressions are derived to enable exact calculations of the probability that a particular MSC will select a SM. For several common MSC, the relative propensities to select SMs are independent of model structure and data. It is shown that MSC that are effective in preventing overfitting are prone to underfitting when information content of the data is low. In a subsequent article, results are extended to develop a new MSE-based MSC for selecting nonlinear multi-response SMs. L'erreur quadratique moyenne (EQM) est utilisee pour analyser neuf criteres de selection de modeles (CSM) couramment utilises pour leur rendement lors de la selection de modeles simplifies (MS). Des expressions sont trouvees pour permettre des calculs exacts de la probabilite qu'un CSM particulier choisisse un MS. Pour plusieurs CSM communs, les propensions relatives pour choisir des MS sont independantes de la structure et des donnees des modeles. On a demontre que les CSM qui sont efficaces pour empecher le surajustement sont enclins au sous-ajustement lorsque le contenu de l'information des donnees est faible. Dans un article ulterieur, les resultats sont etendus pour creer un nouveau CSM fonde sur l'EQM pour la selection de MS non lineaires a reponses multiples.

Solid suspension in stirred tanks: UVP measurements and CFD simulations

Abstract: Suspension of solids in stirred reactor is widely used for catalytic reactions, dissolution, etc. Quality of solid suspension is an important parameter required for the reliable design, optimum performance, and scale up of the system. Quality of suspension depends on local characteristics of solid velocity and hold up profiles. The present work was focused on investigating quality of solid suspension using ultrasound velocity profiler (UVP) measurements and CFD simulations. The slip velocity measurements carried out with UVP were used to evaluate different drag correlations used in CFD simulations. Results discussed in this work would be useful for extending the applications of CFD models for simulating large stirred slurry reactors.