bluuebunny/crossref_metadata_2025_split huggingface dataset:
Improving clay‐based tailings disposal: Case study on coal tailings
Authors: de Kretser Ross , Scales Peter J. , Boger David V. 
Published: June 2004

AbstractThe role of swelling clays in hindering the compressional dewatering characteristics of coal‐mine tailings is examined. The effects of electrolyte concentration and ion exchange in improving the shear and compressional rheology are compared. Suspensions studies include actual mine tailings (thickener feed and thickener underflow) as well as synthetic clay dispersions made from clay collected from the coal seam. It was shown that the most important parameter in controlling the properties of the tailings suspension is “controlled” dispersion in the presence of a Ca2+ electrolyte concentration in excess of that required to (1) prevent initial swelling and (2) provide full cation exchange of the clay. Under these electrolyte conditions, complete delamination of the clay did not occur, and both the dewatering and handling characteristics of the resultant suspensions improved dramatically.
Extracting effective diffusion parameters from drying experiments
Authors: Price Peter E. , Wang Sharon , Romdhane Ilyess Hadj 
Published: June 2004

AbstractThin polymer coatings produced from water‐ and organic‐solvent‐based precursor liquids are ubiquitous components of industrial and consumer products. Design and optimization of dryers for these coatings require accurate predictions of their drying rates. Accurate drying predictions for many polymer/solvent coatings require a satisfactory description of the polymer/solvent mutual diffusion coefficients. A method is proposed ot determine a satisfactory description of the diffusion coefficients by effective free‐volume theory parameters. The effective parameters are determined from gravimetric data measured in a bench‐scale drying apparatus. The application of the method to a poly(vinyl acetate)/toluene solution shows that the effective free‐volume parameters give diffusion coefficients that agree with published data. The method is also applied to a rubber‐based adhesive in industrial‐grade heptane by treating the complex adhesive as a pseudobinary solution. For both systems, the effective parameters lead to quantitatively accurate drying predictions in a pilot‐scale oven.
Control‐oriented modeling of sheet and film processes
Authors: Featherstone Andrew P. , Braatz Richard D. 
Published: June 2004

AbstractSheet and film processes pose a challenging identification and control problem due to high complexity, poor conditioning, and limited input–output data. The interaction between model accuracy and closed‐loop performance is explored for sheet and film processes using a model decomposition in terms of two static orthogonal matrices in series with a diagonal transfer‐function matrix. It is shown that the accuracy of the diagonal elements of the transfer‐function matrix directly specifies the closed‐loop performance achievable by a model‐based controller. This motivates the development of a combined identification and control procedure in which the controller is designed to be robust to model inaccuracies quantified during identification. The resulting controller is compared to an industrially accepted controller design method for two examples, including a simulated blown‐film process. Based on the theoretical results and simulations, it was concluded that the poor performance often reported for existing industrial sheet and film process‐control systems is likely due to signs of the model gains being incorrectly identified.
Design analysis for refolding monomeric protein
Authors: Kotlarski Nicholas , O'Neill Brian K. , Francis Geoffrey L. , Middelberg Anton P. J. 
Published: June 2004

AbstractRenaturation of protein expressed as inclusion bodies within Escherichia coli is a key step in many bioprocesses. Operating conditions for the refolding step dramatically affect the amount of protein product recoverd, and hence profoundly influence the process economics. The first systematic comparison of refolding conducted in batch, fed‐batch and continuous stirred‐tank reactors is provided. Refolding is modeled as kinetic competition between first‐order refolding (equilibrium reaction) and irreversible aggregation (second‐order). Simulations presented allow direct comparison between different flowsheets and refolding schemes using a dimensionless economic objective. As expected from examination of the reaction kinetics, batch operation is the most inefficient mode. For the base process considered, the overall cost of fed‐batch and continuous refolding is virtually identical (less than half than of the batch process). Reactor selection and optimization of refolding using overall economics are demonstrated to be vitally important.
Recovering deterministic behavior from experimental time series in mixing reactor
Authors: Letellier C. , Sceller L. Le , Gouesbet G. , Lusseyran F. , Kemoun A. , Izrar B. 
Published: June 2004

AbstractThe velocity field in a standard mixing reactor with a Rushton impeller is analyzed by using techniques from the theory of nonlinear dynamical systems. It is shown that the dynamical behavior contains a quasi‐periodic motion with three frequencies, fp, the frequency associated with the rotation of blades, fp/6, and a third frequency f'. Relying on an evaluation of the correlation dimension equal to 3.9, the phase space is likely to be at least four‐dimensional. Moreover, a set of four ordinary differential equations is indeed automatically obtained by using a global vector field reconstruction technique, confirming the existence of a 4–D‐deterministic behavior contributing to the dynamics of the system.
Temperature dependence of one‐component permeation through a silicalite‐1 membrane
Authors: Bakker Wridzer J. W. , Van Den Broeke Leo J. P. , Kapteijn Freek , Moulijn Jacob A. 
Published: June 2004

AbstractThe one‐component steady‐state permeation of gases through a silicalite‐1 zeolite composite membrane as a function of the temperature is studied from 190 to 680 K for light hydrocarbons, noble gases, and some inorganic gases. In general, with increasing temperature the permeance shows a maximum followed by a minimum. For gases weakly adsorbed the permeance has only a minimum and for gases strongly adsorbed only a maximum is observed in the permeance. The permeance for various gases, for a feed pressure of 101 kPa, span four orders of magnitude. The lowest permeation is for i‐butane at 300 K: a permeance of 0.07 × 10−8 mol. m−2.s−1.Pa−1. The highest value is observed for methane: a permeance of 70 × 10−8 mol. m−2.s−1.Pa−1 at about 240 K. A comparison between the isobars and the temperature dependence of the steady‐state permeance, both at 101 kPa, shows that at the temperature where the amount adsorbed vanishes the permeance starts to increase. The temperature dependence of the steady‐state fluxes through the silicalite‐1 membrane can be described only if two diffusion mechanisms are taken into account. For high occupancies the mass transport can be described by equilibrium adsorption followed by surface diffusion and for low occupancies the mass transport can be described by activated gaseous diffusion. With increasing temperature the mass‐transport mechanism shifts from the surface diffusion regime to the activated gaseous diffusion regime. With these two diffusivities modeling results agree well with experimental results for the one‐component flux through the silicalite‐1 zeolite membrane.
Constrained MPCI: A weak persistent excitation approach
Authors: Vuthandam Premkiran , Nikolaou Michael 
Published: June 2004

AbstractModel‐predictive control and identification (MPCI) introduced by Genceli and Nikolaou in 1996 is a novel approach to the identification of processes under constrained model‐predictive control. MPCI solves an on‐line optimization problem that involves (a) a standard MPC objective; (b) standard MPC constraints; and (c) persistent excitation (PE) constraints. The on‐line optimization problem is computationally demanding. To alleviate that problem, we take a frequency‐domain approach to formulating the PE constraints. This approach relies on the following fact: a signal is persistently exciting of order n, if its two‐sided power spectrum is nonzero at no fewer than n points. Therefore, persistently exciting input signals can be parametrized over a finite horizon as a sum of sinusoid terms with nonzero coefficients. Used in the MPCI framework, the last requirement generates a set of completely decoupled reverse‐convex constraints that are combinatorially tractable from a computational point of view. The effectiveness of the proposed MPCI method is demonstrated through simulations. For the SISO systems studied, computation of the global optimum could be handled combinatorially in real‐time using PC hardware.
Design and retrofit of sensor networks in process plants
Authors: Bagajewicz Miguel J. 
Published: June 2004

AbstractA novel procedure to find cost‐optimal sensor networks is proposed. Cost is minimized subject to qualifying constraints that are related to certain requirements of data reconciliation. One basic qualifying constraint is a desired level of precision of reconciled values for a selected set of variables. Since precision requirements lead to multiple solutions, other qualifying constraints are proposed. These constraints are availability, resilience, and error detectability. Definitions for these terms are given and their impact on the results is presented.
Pore‐structure optimization of calcium carbonate for enhanced sulfation
Authors: Mahuli Suhas K. , Agnihotri Rajeev , Chauk Shriniwas , Ghosh‐Dastidar Abhijit , Wei S.‐H. , Fan Liang‐Shih 
Published: June 2004

AbstractA modified CaCO3 sorbent with an open internal pore structure is prepared and its sulfation characteristics are investigated in an entrained flow reactor at high temperatures (900‐1,100°C) and short contact times (20–600 ms) using small particle sizes (< 5 μm). The most distinguishing feature of this modified carbonate (MC) is its 70–75% sulfation conversion within 0.5 s, which is substantially higher than any other sorbents published. The MC is prepared by carbonation‐precipitation from a calcium hydroxide suspension by optimizing the operating parameters to generate carbonate particles of the desired pore structural properties. The high initial surface area combined with its open pore structure and pore‐size distribution of its calcine contribute to its high reactivity. The calcined MC possesses a significant portion of its pore volume in the 50‐200 Å range. This size range represents an optimum pore size for sulfation since it provides a reasonably high surface area and is less susceptible than < 50 Å pore sizes, to pore filling, or pore‐mouth plugging due to the formation of higher molar volume CaSO4. Investigation with other carbonates reveals that a much higher portion of their calcines' porosity lies in the smaller pores, which leads to premature termination of sulfation. Results show the impact of internal pore structure on initial reactivity and ultimate sorbent conversion.
Collection efficiency model based on boundary‐layer characteristics for cyclones
Authors: Kim W. S. , Lee J. W. 
Published: June 2004

AbstractIn cyclones, the boundary layer formed on the collecting‐wall surface acts as a barrier for particle migration toward the wall due to a decreased centrifugal force on particles inside the boundary layer. A new theory for high‐efficiency cyclones based on the boundary‐layer characteristics is presented. The cyclone was divided into two regions: the turbulent‐core region where the centrifugal force is large, and the near‐wall region where the centrifugal force is small. Particle trajectories in the turbulent‐core region are calculated from the mean fluid motion based on the quasi‐steady drag assumption, and the collection probability of particles in the near‐wall region is calculated by the deposition velocity that results from both turbulent diffusion and centrifugal force. The deposition velocity by centrifugal force was assumed equal to the equilibrium migration velocity at a certain point inside the boundary layer, and the distance to that point from the wall is assumed to be linearly proportional to the dimensionless‐particle relaxation time. When the proportional constant was determined by fitting the theoretical results to experimental data, the theory showed an excellent enhancement in predicting the variation of collection efficiency with the inlet flow velocity and particle size.
Isotope exchange technique for measurement of gas adsorption equilibria and kinetics
Authors: Rynders R. M. , Rao M. B. , Sircar S. 
Published: June 2004

AbstractThe isotope exchange technique (IET) can be used to simultaneously measure multicomponent gas adsorption equilibria and self‐diffusivities of the components in a single isothermal experiment without disturbing the overall adsorbed phase. An experimental protocol for the IET and corresponding data analysis procedures is described. Isotherms and self‐diffusivities for adsorption of N2 as a pure gas were measured on commercial samples of a carbon molecular sieve and a 4‐Å zeolite using IET, as well as those of O2 and N2 from their binary mixtures. The carbon molecular sieve did not exhibit thermo‐dynamic selectivity for air separation, but had a kinetic selectivity of O2 over N2 Mass‐transfer resistances for self‐diffusion of N2 and O2 on the carbon molecular sieve were controlled by pore mouth restrictions in the carbon, but those for adsorption of N2 into the 4‐Å zeolite by Fickian diffusion inside the adsorbent. A linear driving force model described the uptakes of N2 and O2 in the carbon molecular sieve. The Fickian diffusion model described the N2 uptake in the 4‐Å zeolite. Mass‐transfer coefficients for both O2 and N2 on the carbon molecular sieve increased linearly with increasing gas‐phase partial pressure of these gases, and the pressure of O2 did not affect mass‐transfer coefficients for N2. The self‐diffusivity of N2 in the 4‐Å zeolite decreased with increasing adsorbate loading.
Equilibrium and kinetics ofn– hexane sorption in pellets of 5A zeolite
Authors: Silva José A. C. , Rodrigues Alírio E. 
Published: June 2004

AbstractEquilibrium, diffusion, and fixed‐bed adsorption of n‐hexane in pellets of 5A zeolite (Rhone‐Poulenc) were studied between 373 and 573 K and at partial pressures up to 0.2 bar. Equilibrium data were obtained in a flow microbalance system. Diffusivity was studied simultaneously by gravimetric and ZLC techniques. Adsorption isotherms were satisfactorily described by a localized adsorption model developed by Nitta et al. (1984) with only one temperature‐dependent parameter (coefficient of Henry's law). The isosteric heat of adsorption is 14.2 kcal/mol.Kinetic data clearly show that macropore diffusion is the controlling mass‐transfer mechanism. Between 473 and 573 K, pore diffusivities range from 0.11 to 0.13 cm2/s in the system He‐nC6, and from 0.06 to 0.08 cm2/s in the system N2C6. The effect of partial pressure of sorbate, temperature, and total flow rate in the behavior of the fixed‐bed unit is shown. A simple mathematical model with equilibrium and diffusivity parameters obtained in this work predicts with good accuracy all fixed‐bed adsorption experiments.
Batch chemical process quality control applied to curing of composite materials
Authors: Thomas Matthew M. , Joseph Babu , Kardos John L. 
Published: June 2004

AbstractModel predictive control is used extensively to control continuous‐process systems. Application of a shrinking horizon model predictive control strategy is used to predict and control the end product quality of composite laminates produced by batch autoclave curing. The main contribution is the demonstration, using a laboratory‐scale autoclave, of the feasibility and advantages of a control strategy that adjusts the batch recipe on‐line to correct for unmeasured disturbance: entering the process. Readily available, on‐line secondary measurements are used in conjunction with the process model to predict (and hence control) quality‐related end product properties. On‐line monitoring is also used to monitor the process even after the possibility of on‐line correction has passed. The results show that this approach significantly reduces end product quality variance.
Novel swirl‐flow reactor for kinetic studies of semiconductor photocatalysis
Authors: Ray Ajay K. , Beenackers Antonie A. C. M. 
Published: June 2004

AbstractA new two‐phase swirl‐flow monolithic‐type reactor was designed to study the kinetics of heterogeneous photocatalytic processes on immobilized semiconductor catalysts. True kinetic rate constants for destruction of a textile dye were measured as a function of wavelength of light intensity and angle of incidence, catalyst layer thickness, and the effect of absorption of light by liquid film on the overall rate of photocatalytic degradation. Photocatalytic activities of two commercially available TiO2 catalysts (Degussa P25 and Hombikat UV 100) were also compared for different light intensities and catalyst layer thickness. Residence time distribution and mass‐transfer limitations were evaluated. This new reactor appears to be an attractive choice for kinetic studies of heterogeneous photocatalysis.
Microwave drying of softwood in an oversized waveguide: Theory and experiment
Authors: Perré Patrick , Turner Ian W. 
Published: June 2004

AbstractA comparison between experimental and theoretical results for the combined microwave and convective drying of softwood is presented. The microwave applicator used for the experiments was an oversized waveguide, and the results for both sapwood and heartwood were analyzed. To elucidate on the physics of the process at a fundamental level, a complete model is proposed, which considers the intricate link that transpires between the heat‐and mass‐transfer phenomena and the power distribution throughout the sample during drying. The resulting model, which uses a comprehensive 2‐D set of equations to describe the drying process, together with a complete 3‐D solution of the Maxwell equations within the waveguide in the time domain, can be used to investigate many aspects of dielectric drying. This research deals with the spatial variation of the power density within the material at various drying times and the effect of the anisotropy of the transfer properties on the shape and evolution of the power distribution. Most importantly, it focuses on the prediction of the location of hot spots and thermal runaway within the sample from the viewpoint of product quality. Strengths and weaknesses of the model are highlighted.
Transport analysis of diffusion‐induced bubble growth and collapse in viscous liquids
Authors: Venerus David C. , Yala Nadia 
Published: June 2004

AbstractTransport models of diffusion‐induced bubble growth and collapse in viscous liquids are developed and evaluated. A rigorous model for these important phenomena is formulated taking into account convective and diffusive mass transport, surface tension, and viscous and inertial effects. Predictions for bubble growth dynamics demonstrate the importance of viscous effects in the liquid surrounding the bubble for a wide range of conditions having relevance to polymer processing operations. It is also shown how previous models employing various approximations can be derived from the rigorous model by using different mathematical methods and dimensional analysis. Predicted bubble growth dynamics from the rigorous and approximate models are compared to establish the ranges of validity for two commonly used approximations. These comparisons indicate that models using a thin boundary‐layer approximation have a rather limited range of applicability. A new approximate model, based on a previously published result, gives reasonably accurate bubble growth rate predictions with a significant reduction in computational effort.
Synthesis of heat‐exchanger network by simulated annealing and NLP procedures
Authors: Athier G. , Floquet P. , Pibouleau L. , Domenech S. 
Published: June 2004

AbstractA two‐level procedure for heat‐exchanger network synthesis problems, which is related to structural optimization, is carried out by a simulated‐annealing procedure. The main control parameters, that is, the initial annealing temperature, the temperature length, and the temperature‐decreasing scheme, are extensively studied on the well‐known 10SP1 problem, and their values are used for solving a 5SP1 problem with forbidden matches and a larger scale problem, the 20SP1. In all cases, the structural search is initialized with the network involving only utilities. For each generated network, the operating conditions (temperatures and split rates) are optimized by an NLP procedure to minimize the sum of investment and operating costs. Particular attention is given to the size reduction of the NLP problem. The proposed procedure leads to a reduction by a factor of 3 of the problem size in terms of number of variables and constraints. This slave problem is solved by an SQP procedure from the IMSL Library.
Multiscale integration hybrid algorithms for homogeneous–heterogeneous reactors
Authors: Vlachos D. G. 
Published: June 2004

AbstractDespite many available models at different reactor length scales, no models exist for designing homogeneous–heterogeneous reactors from first principles by linking molecular with macroscopic scales. Hybrid algorithms, based on a domain decomposition method, are proposed to couple a continuum fluid‐phase transport/reaction model with a new efficient, real‐time surface Monte Carlo model suitable for stiff problems. These algorithms properly treat surface heterogeneities and morphology and provide the exact boundary condition to the continuum fluid‐phase model. In this way, molecular‐scale information is integrated into a macroscopic chemical system. The methods are applied at atmospheric pressure to a stagnant boundary layer near a catalytic surface where heterogeneities are caused by adsorbate–adsorbate interactions. Both steady‐state and transient simulations are performed. Such numerical methods have the potential for microscopic control of chemical processes through macroscopic control of experimental parameters. Applications to homogeneous–heterogeneous processes such as catalytic reactors, control of morphology of solid materials with atomic resolution, and corrosion processes are also discussed.