bluuebunny/crossref_metadata_2025 huggingface dataset:
Porosity distributions in a fluidized bed with an immersed obstacle
Authors: Bouillard J. X. , Lyczkowski R. W. , Gidaspow D.
Published: June 2004

Erosion in bubbling fluidized‐bed combustors is a serious issue that may affect their reliability and economics. Available evidence suggests that the key to understanding this erosion is detailed knowledge of the coupled and complex phenomena of solids circulation and bubble motion. A thin transparent “two‐dimensional” rectangular fluidized bed with an obstacle served as a rough model for a fluidized‐bed combustor. This model was studied experimentally and computationally using two hydrodynamic equation sets. The computed hydrodynamic results agree reasonably well with experimental data. Bubble frequencies and sizes compare well with those obtained from analyzing a high‐speed motion picture frame‐by‐frame. Time‐averaged porosities computed from both models agree with time‐averaged porosity distributions measured with a gamma‐ray densitometer. The principal diferences between the data and the computations in this paper are due to asymmetries present in the experiment and to the simplified solids rheology used in the hydrodynamic models.
Desorption processes: Supercritical fluid regeneration of activated carbon
Authors: Recasens F. , McCoy B. J. , Smith J. M.
Published: June 2004

Models are developed for isothermal desorption in a fixed bed of adsorbent particles. While more general models require numerical solution of the governing equations, two practically important cases have analytical solutions: (1) an equilibrium desorption model where the rate of desorption is controlled by external and intraparticle mass transfer; and (2) a kinetic model where external and intraparticle mass transfer and a first‐order irreversible desorption step control the overall process.

Recent experimental data (Tan and Liou, 1988) for the desorption of ethyl acetate from activated carbon with supercritical carbon dioxide are found to fit the local‐equilibrium model. Data for the effect of temperature on fractions desorbed indicate a reversal of the temperature dependence of the adsorption isotherm as the supercritical pressure is increased. This phenomenon is analogous to the observed cross‐over region for the effect of temperature on the solubility of a solid at supercritical conditions.
Plasma deposition of silicon nitride films in a radial‐flow reactor
Authors: Yoo Chue‐San , Dixon Anthony G.
Published: June 2004

Experimental data on silicon nitride film growth have been obtained from a radial‐flow, plasma‐enhanced chemical vapor deposition reactor. A nonisothermal mathematical model has been developed consisting of Navier‐Stokes, energy, and species balance equations taking into account the temperature dependence of physical properties. The model is predictive at various power input levels for film compositions and growth rates.
The continuous‐lumping method for vapor‐liquid equilibrium calculations
Authors: Moore Patrick K. , Anthony Rayford G.
Published: June 2004

The continuous‐lumping method is a refinement of continuous thermodynamics which does not depend upon the continuous‐mixture hypothesis. The method utilizes a generalized Fourier series expansion of a functional formulation of the equilibrium relations obtained by embedding the classical discrete equilibrium equations into generalized function space. The resulting method provides an effective means of reducing the number of parameters needed to describe a many‐component, complex mixture; furthermore, the method provides a straightforward means of converting the equilibrium equations to the new parameterized form. The error associated with the reduction in number of parameters can be easily estimated using the ratio convergence test for mathematical series. The theory of the method is first presented and the method is then used in an example calculation to illustrate the advantages of the method over pseudocomponent lumping and continuous thermodynamics. The method is useful particularly for mixtures described by chromatographic data.
Drop oscillations in liquid‐liquid systems
Authors: Basaran Osman A. , Scott Timothy C. , Byers Charles H.
Published: June 2004

When the ratio of the drop radius to the distance separating any two drops and the relative importance of gravitational to surface forces are both small, the small amplitude oscillations of a drop of one viscous fluid immersed in another fluid are governed by the nonlinear dispersion relation derived by Miller and Scriven (1968). The dispersion relation has been solved numerically to determine the character of oscillations for arbitrary values of drop size, physical properties of the two fluids, and interfacial tension. The new theoretical results determine the range of validity of the low‐viscosity approximation of Miller and Scriven, and are also shown to be essential for proper interpretation of many previously reported experimental results. New experimental measurements of natural frequencies of oscillation of water drops falling in 2‐ethyl‐1‐hexanol, a system having properties characteristic of many others in solvent extraction, agree well with the theoretical predictions when drop radius is smaller than a critical size. The frequencies of oscillations of larger drops are better described by the dispersion relation due to Subramanyam (1969), which accounts for the relative motion of the two phases.
Magnetic determination of axial catalyst temperature profiles
Authors: Cale T. S. , Merson J. A.
Published: June 2004

A magnetic thermometric method is used to determine cross‐sectional average axial catalyst temperature profiles for superparamagnetic neckel catalyst beds during ethane hydrogenolysis, an exothermic reaction. Each solid temperature profile is determined from an axial profile of cross‐sectional average magnetization and is represented by a polynomial. In turn, each magnetization profile is determined from voltage data obtained as the bed is moved through an AC permeameter. A Fredholm equation of the first kind, “regularized” using a minimum variance constraint, is inverted to determine the magnetization profile.

The determination of the axial temperature profile for a reactor operating at 11.0% conversion is detailed. It provides a good test of the method used. Some limitations of the method are highlighted by attempts to analyze data from a reactor operating at complete conversion. The potential for model parameter estimation is discussed.
Bifurcation analysis in heterogeneous azeotropic distillation
Authors: Widagdo Soemantri , Seider Warren D. , Sebastian Donald H.
Published: June 2004

Parameterization with respect to the aqueous reflux ratio has been carried out for the steady‐state analysis of a tower to dehydrate secbutanol using disecondary butyl ether as the entrainer. With an equilibrium‐stage model, singularities are observed as the second liquid phase is introduced on the trays and regions of steady‐state multiplicity are demonstrated. Furthermore, a critical aqueous reflux ratio, in the vicinity of which two liquid phases are introduced on most of the trays, varies only slightly with the number of trays in the tower. The model predicts that the product purities and recoveries remain high using one‐third of the trays in the industrial SBA‐II tower. Bifurcation analysis for a single stage does not explain these observations, and the effect of recycle is suspected.
Dispersion and diffusion influences on yield in complex reaction networks
Authors: Liou Jiunn‐Shyan , Balakotaiah Vemuri , Luss Dan
Published: June 2004

Differences in the dispersion and/or catalytic pellet size between laboratory and commercial reactors, operating at the same average residence time, may lead to differences in the yield of a desired product. Bounds are developed for predicting the maximal design uncertainty introduced by these phenomena for a network consisting of an arbitrary number of irreversible first‐order reactions. A major advantage of these bounds is that they do not require any knowledge of the rate constants. It is shown that in a packed‐bed reactor, the fractional yield loss is smaller than:

where m − 1 is the number of reaction steps involved in converting a reactant to the desired product, σ is the dimensionless variance of the residence time density function, Bim is the Biot number, p2 = [(Vp/Sx)2(1/Deτ)], and τ is the average residence time.
Design and minimum reflux for heterogeneous azeotropic distillation columns
Authors: Pham Hoanh N. , Ryan Peter J. , Doherty Michael F.
Published: June 2004

A simple design technique for heterogeneous distillation columns has been developed. The underlying geometric conditions which govern minimum reflux are shown to share certain common features with homogeneous distillations, but differ in some important respects. It is shown that heterogeneous columns display some unusual sensitivities to the design parameters. The most notable being the drastic swings in the composition and temperature profiles with very small changes in the level of trace impurities in the product stream.
Axial distribution of solid holdup in bubble column for gas‐liquid‐solid systems
Authors: Matsumoto Toshitatsu , Hidaka Nobuyuki , Morooka Shigeharu
Published: June 2004

The axial distribution of solid holdup was investigated in a bubble column of 0.07 m in diameter and 4.25 m in height. The particle phase was glass beads of diameter 66, 118, 243, 465 or 1,300 μm. The effective slip velocity and the axial dispersion coefficient of the solid particles were evaluated in batch operation without solids feed and were correlated on the basis of mixing length theory. The equations obtained were applied to analyze axial profiles of particle concentration with a continuous feed of solids, and experimental data in the literature were simulated successfully over a wide range of solid concentration.
Mathematical analysis of two‐phase flow in low‐permeability porous media
Authors: Arastoopour Hamid , Semrau James
Published: June 2004

A one‐dimensional isothermal transient two‐phase flow model of gas and liquid in a low‐permeability medium has been developed from the general mass and momentum balances.

The characteristic roots of the governing differential equations are real and distinct. Therefore, solution of the flow equations may be attempted by a stable initial‐value finite‐difference scheme. A numerical solution was obtained using the method of lines.

Calculated two‐phase flow parameters are consistent with expected flow behavior and reflect the sensitivity of fluid flow to porosity, gas and liquid permeability, and capillary pressure in a tight sands porous medium. Calculated gas flow rates compared well with experimental data obtained at the Institute of Gas Technology (IGT) for low‐permeability sandstone.
Control mechanisms of fluidized solids circulation between adjacent vessels
Authors: Fox D. , Molodtsof Y. , Large J. F.
Published: June 2004

Many industrial proceses require the circulation of particles between reacting fluidized compartments at a stable, but flexible rate, so that the processes can be operated at different solids rates. In order to understand the phenomena involved in the circulation and its control, circulation of sand particles has been studied through a new experimental approach, using an open‐loop two compartment circulating system.

Experimental results show that the control of the circulation rate depends on three phenomena: the vertical resisting force in the fluidized compartments, the contraction of flow in the communication zone, and the bypass of gas between the compartments. For industrial purposes, the first appears to be predominant in the control of the solids rate. The second ensures neither the strict control of this rate nor the required flexibility. The link between the gas bypass and the circulation phenomena is explained and recommendations for the design and operation of circulating systems are given.
Sequential gas‐solid reactions
Authors: Fortini Arthur J. , Perlmutter Daniel D.
Published: June 2004

A model is developed describing consecutive gas‐solid reactions occurring in porous media. The model calls for independently measurable parameters and predicts two maxima in the reaction rate at intermediate conversions. The low temperature (350°C) reduction of hematite to iron in a hydrogen‐nitrogen atmosphere was used to test the model. The experimental data confirmed the expected rate maxima. The conversion predictions are very close to the data for conversions below 30%, but are systematically somewhat lower than the experimental values for higher levels of conversion. An explanation for the discrepancy is offered in terms of the description of the pore structure.
Melt blowing: General equation development and experimental verification
Authors: Uyttendaele Marc A. J. , Shambaugh Robert L.
Published: June 2004

A model has been developed for steady polymer melt blowing. This model includes the dominant effect that the forwarding air has upon the process. Inertial, gravitational and heat transfer effects are also included. The model equations are solved numerically with both Newtonian and viscoelastic (Phan‐Thien and Tanner) constitutive equations. The predicted results compare favorably with actual experimental data.
A study of multicomponent adsorption equilibria by liquid chromatography
Authors: Ching Chi Bun , Chu Khim Hoong , Ruthven Douglas M.
Published: June 2004

Equilibrium relations for the fructose‐dextran‐water system on silica gel have been determined by a liquid chromatographic method. The experimental procedure discussed provides a simple and straightforward means of determining adsorption equilibria. The ternary adsorption equilibria, derived from chromatographic retention time measurements of binary systems, are verified by the equilibrium theory developed by Gluekauf (1949).
Self‐consistent local composition model of electrolyte solutions
Authors: Ananth M. S. , Ramachandran Sunder
Published: June 2004

A self‐consistent local composition theory for the excess Gibbs free energy of a multicomponent electrolyte solution is developed. The theory incorporates correct pair counting, assumes that like‐charged ions cannot be nearest neighbors of each other, and accounts for the effect of second nearest neighbor interactions.

A perturbation analysis of the model, linear in the interaction parameters, is also carried out. For a given solvent and a given class of electrolyte the perturbed theory yields universal functions of molality, which can be weighted by suitable parameter values and added to give the desired property. The parameters can be expressed in a temperature‐independent form. This theory correlates very well the data on osmotic and activity coefficients in single‐solute aqueous solutions up to very high concentrations (up to 20 M) as well as over a range of temperatures.
Experiments on the conductivity of suspensions of ionically‐conductive spheres
Authors: Bashir Y. M. , Goddard J. D.
Published: June 2004

This is a report on the ionic conductivity of monodisperse, neutrally‐buoyant suspensions of ion‐exchange beads, both AC total‐ion conductivity and DC specific‐ion conductivity of an electrochemically‐active species. They represent the zero Péclet‐number and the large Péclet‐number limits of mass transfer, respectively.

A rotating disc electrode was employed for the DC studies and a well mixed conductivity cell for the AC—for particle volume fractions ϕ ranging from zero to about 45%. Novel techniques were developed for rapidly determining the particle AC conductivity and for modifying the relative conductivity α of ion‐exchange beads by poisoning with immobilely‐bound ions. For α values, 0.044⩽ α ⩽ 1.48, of this study Maxwell's classical relation is shown to be adequate for ϕ ⩽ 0.5, which is, in agreement with Turner (1973, 1976).

Our results for the DC conductivity differ somewhat from those of Andersen (1987) land show the weak dependence on particle Péclet number predicted by the dilute‐suspension theory of Nir and Acrivos (1976) for Pe ≫ 1.
Stress distribution in a packed bed above raceway cavities formed by an air jet
Authors: Apte Vivek B. , Wall Terry F. , Truelove John S.
Published: June 2004

The vertical stress profile in a packed bed above the cavities formed by an upward, high‐velocity air jet is estimated from a force balance analysis and static pressure measurements. The objective is to understand and determine the forces responsible for maintaining the cavity roof. Such cavities, formed in an iron blast furnace, adjacent to the hot air blast emanating from the tuyere pipes, are called raceways. A net upward force provided by the gas pressure drag and the support from the bed walls holds the raceway roof in its position. Abrupt changes in the stress and the gas velocity are observed near the roof. The zero vertical stress is also found close above the roof but fluctuates vertically with the raceway size, which varies irreversibly following a cyclic change in the blast rate.
Flue gas desulfurization by in‐duct dry scrubbing using calcium hydroxide
Authors: Rice Richard W. , Bond Gregory A.
Published: June 2004

No Absract.
Diagnostic model processor: Using deep knowledge for process fault diagnosis
Authors: Petti Thomas F. , Klein Jim , Dhurjati Prasad S.
Published: June 2004

Many recent attempts to use expert systems for process fault diagnosis have included information derived from deep knowledge. This information is generally implemented as a rule‐based expert system. Drawbacks of this architecture are a lack of generality, poor handling of novel situations, and a lack of transparency. An algorithm called the diagnostic model processor is introduced; it uses the satisfaction of model equations from process plants to arrive at the most likely fault condition. The method is generalized by the process model and diagnostic methodology being separated. The architecture addresses each of the shortcomings discussed. Experiments show that the methodology is capable of correctly identifying fault situations. Furthermore, information is derived from an a priori analysis technique, which is used to show the degree to which different faults can be discriminated based on the model equations available. The results of this analysis add further insight into the diagnoses provided by the diagnostic model processor.
Simple process equations, fixed‐point methods, and chaos
Authors: Lucia Angelo , Guo Xinzhou , Richey Paula J. , Derebail Ramnath
Published: June 2004

The chaotic behavior of fixed‐point methods for steady‐state process simulation is studied. It is shown that direct substitution and Newton's method exhibit all of the rich structure of chaos (period doubling, aperiodicity, fractal basin boundaries, and related properties) on simple process examples. These examples include finding roots to the Soave‐Redlich‐Kwong and Underwood equations, dew point and flash calculations for heterogeneous mixtures, and a simple process flowsheet.

For single variable problems, it is shown that direct substitution follows a classical period‐doubling route to chaos. On the other hand, the chaotic behavior of direct substitution and Newton's method on multivariable problems is considerably more complex, and can give the appearance that no organized route to chaos is followed. For example, for the dew point problems, truncated period doubling, odd periodic cycles, and chaotic behavior can be observed, within which are embedded narrow regions of global convergence. Many numerical results and geometric illustrations are presented.
Structure of plane underexpanded air jets into water
Authors: Loth Eric , Faeth Gerard M.
Published: June 2004

An experimental and numerical investigation of the structure of plane underexpanded turbulent air jets in water was conducted to characterize their structure and mixing properties. Measurements included void fraction profiles, static pressure distributions, entrainment rates, and high speed flow visualization. A locally homogeneous flow model was also developed with compressibility effects treated using an effective adapted jet condition. Static pressure measurements confirmed the presence of a shock‐wave‐containing external expansion region for underexpanded air jets in water, similar to results observed for underexpanded air jets in air. In addition, the plane jets exhibited half‐widths (based on void fractions) that were two to three times greater than half‐widths (based on scalar properties) observed for single‐phase jets. This behavior follows from the strong sensitivity of void fraction to mixing levels due to the large density ratio of the flow. Predictions of void fraction and mass entrainment were encouraging, but performance was found to be sensitive to initial conditions and effects of large‐scale unsteadiness near the jet exit.
Computation of flow patterns in circulating fluidized beds
Authors: Tsuo Yuan P. , Gidaspow D.
Published: June 2004

Flow regimes of dense‐phase vertical pneumatic transport of solids, referred to in the literature as circulating fluidized beds, have been computed using a generalization of the Navier‐Stokes equations for two fluids. In the less dense regime corresponding to volume fractions of solids of about 1%, the flow consists of centrally upward moving solids and downward moving clusters. The computations agree with observations made by high‐speed motion pictures and with measurements of radial solids concentrations and velocities. In the dense regime, corresponding to volume fractions of about 10%, a core‐annulus type of regime is obtained, with solids descending down at the wall. The computed voidage distributions and velocity profiles agree with measurement done at the Institute of Gas Technology.
Robust error‐in‐variables estimation using nonlinear programming techniques
Authors: Kim In‐Won , Liebman Michael J. , Edgar Thomas F.
Published: June 2004

For systems described by algebraic or differential equation models where all variables are subject to error, the error‐in‐variables method (EVM) for parameter estimation has been shown to be superior to standard least‐squares techniques. Previous EVM algorithms were developed assuming linear (or linearized) model equations. Unfortunately, many chemical engineering processes operate in strongly nonlinear regions where linear approximations may be inaccurate. In this paper, new algorithms using nonlinear programming techniques for the error‐in‐variables methods are proposed. In addition, a method for discerning when these methods are necessary is discussed. The proposed algorithms are compared to the least‐squares method and traditional error‐in‐variable approaches. Improved parameter estimates for several steady‐state nonlinear processes are demonstrated.
Platelet interaction with poly(ethylene oxide) networks
Authors: Chaikof Elliot L. , Merrill Edward W. , Coleman James E. , Ramberg Karen , Connolly Raymond J. , Callow Allan D.
Published: June 2004

Interpenetrating polymer networks (IPNs) of poly(ethylene oxide) (PEO) and a polyether substituted polysiloxane were synthesized containing variations of PEO content (35 and 65% dry network weight) and PEO systematically varied from low to high molecular weight (2,000, 8,000, and 20,000). Biocompatibility was assessed by measureing 111In platelet deposition in a baboon femoral ex vivo shunt. Mass transfer analysis revealed that platelet transport to PEO/polysiloxane surfaces was kinetically limited and correlated with both PEO content and molecular weight. Differences in material performance were noted particularly after the initial 30 min blood contact period. In mid and high PEO molecular weight networks (8,000 and 20,000), reduced platelet deposition was noted with increased PEO content. In materials of high PEO content (65%), mid and high PEO molecular weight samples had significantly lower levels of platelet adsorption than PDMS (60 min; p< 0.05) or networks of low PEO molecular weight, coded 2K‐65 (30 and 60 min; p < 0.05). The lowest level of platelet deposition was noted on 20K‐65 networks, less than one platelet per 1,000 μm2.
Protein partitioning in PEG/dextran aqueous two‐phase systems
Authors: Diamond Alan D. , Hsu James T.
Published: June 2004

Utilizing a modified form of the Flory‐Huggins theory of polymer solution thermodynamics, a generalized expression has been obtained for correlating protein partitioning in the polyethylene glycol (PEG)/dextran aqueous two‐phase systems. The expression relates the natural logarithm of the partition coefficient of the protein to the polymer concentration difference between the phases. The parameters of the relationship are a function of protein and phase forming polymer molecular weight, protein‐water, protein‐polymer and polymer‐water interaction parameters, and the electrostatic potential difference between the phases. The relationship was verified by partitioning 17 proteins covering a wide range of molecular weight in the tie lines of the above systems, along with data from the literature. This correlation will facilitate the selection and engineering scale‐up of aqueous two‐phase systems for biomolecule purification.
Development of a space‐charge transport model for ion‐exchange membranes
Authors: Guzmán‐Garcia Angel G. , Pintauro Peter N. , Verbrugge Mark W. , Hill Robert F.
Published: June 2004

A two‐dimensional, electrokinetic transport model that incorporates ionic hydration, orientation of solvent molecules by an applied electric field, and solvent dipole‐dipole interactions is developed. The model is used to simulate equilibrium and transport experiments for perfluorosulfonic acid membranes containing aqueous alkali metal sulfate solutions. The membrane is modeled as an array of cylindrical pores. Solution of the mathematical model requires that the membrane porosity, water partition coefficient, coion partition coefficient, water diffusion coefficients, and coion and counterion diffusion coefficients be known. Membrane coion and counterion diffusion coefficients were determined from free solution equivalent conductance data. All other parameters were determined experimentally for a Nafion (of E. I. du Pont de Nemours Inc.) cation‐exchange membrane and five 0.1 M alkali metal sulfate solutions. Experimental radiotracer data for coion absorption as well as for coion and water transport are compared with theoretical predictions to test the accuracy of the model.
Principles of dynamic balancing
Authors: Almasy Gedeon A.
Published: June 2004

The principles of static balancing, also called measurement error reconciliation (MER), have been generalized to transient conditions. An exactly linear dynamic balance model has been stated where flow variables are assumed to be stochastic processes with independent increments. With this model the residual error of static MER due to dynamic effects can be estimated. Dynamic balancing is proposed as the estimation of flow and inventory variables by Kalman filtering applied to the balance model. The error of estimates obtained in this way is significantly less than that for the static MER estimates, even if the process is nearly in steady state. The main problem of dynamic balancing is that it requires not only the redundant observation of flow variables but also the observation of inventory variables. Compatibility of MER and dynamic balancing has been shown.
Transport of aromatic molecules in NaY Zeolite powders
Authors: Chmelka B. F. , Gillis J. V. , Petersen E. E. , Radke C. J.
Published: June 2004

Xenon‐129 NMR is used to probe macroscopic distributions of aromatic molecules adsorbed in a packed bed of 1‐μm NaY zeolite particles. Relative rates of guest transport through the intracrystalline (micro) and intercrystalline (macro) pores play a unique role in the axial distribution of sorbate molecules, such as hexamethylbenzene, in a zeolite powder. Xenon‐129 NMR spectra show that a sharp HMB adsorption front advances through a bed of dehydrated NaY crystallites at 523 K. However, at 573 K or in the presence of coadsorbed water, HMB species disperse through the bed without forming a sharp boundary between adsorption zones.

When guest transport is controlled by pseudosteady‐state diffusion in the macropores, axial penetration of the bed by vapor‐phase guest species occurs in a sharp adsorption front. A shrinking‐core transport model then quantitatively estimates the intracrystalline diffusivities of HMB in dehydrated and partially hydrated NaY zeolite of 10−11 and 10−13 m2/s, respectively, at 523 K. Xenon‐129 NMR proves to be a powerful tool for probing adsorbed guest distribution in zeolites, allowing relative time scales to be established for transport of molecular guests in NaY powders.
New hypotheses for Mercury porosimetry with percolation approach
Authors: Park Churl‐Young , Ihm Son‐Ki
Published: June 2004

New hypotheses of no coalescence and no entrapment are proposed for mercury intrusion and extrusion. Pore structures are represented by a two‐dimensional lattice for bond percolation and the Rayleigh distribution function taken for the pore size distribution. Different modes of hysteresis are found with the new hypotheses and the effect of accessible probability on the hysteresis loop is analyzed. A bimodal size distribution with micropores and macropores is analyzed by considering the extent of overlapping and the sequence of connection between both distributions. Mercury entrapment is also predicted by considering the pressure difference between the applied and assigned pressures, as determined by the Washburn equation, as a parameter for mercury breakage. The applicability of the proposed hypotheses is demonstrated by showing that experimental data on an α‐alumina sample could be well correlated.
Optimizing the throughput of hazardous waste incinerators
Authors: Behmanesh Nasrin , Manousiouthakis Vasilios , Allen David T.
Published: June 2004

This work presents a linear, steady‐state model of a rotary kiln hazardous waste incinerator. Mass balance constraints, energy balance constraints, constraints typically imposed by incinerator permits, and constraints imposed by design limitations are all included in the model. The model is used to perform optimization studies, which maximize a measure of the incinerator's throughput. The sensitivity of the model to uncertainties in the chemical property values of the waste streams is also examined. For the spectrum of case studies examined, the optimal operating conditions are most sensitive to halogen content and water content of the wastes and are less sensitive to variations in heating value and nitrogen content.
Nonlinear analysis in process design
Authors: Seider Warren D. , Brengel David D. , Widagdo Soemantri
Published: June 2004

As steady‐state and dynamic simulators with optimal controllers have evolved, tools for nonlinear analysis have been developed by reactor and thermophysical property specialists. Designers lag behind in developing and utilizing these tools, as many design strategies assume idealized behavior even though processes contain an increasing number of nonlinear elements. This article examines the sources of the nonlinear elements, often associated with physical and chemical interactions, in designs and their control systems. Promising methods for nonlinear analysis are reviewed.

In each design activity, involving simulation, economic optimization, projections of controllability and operability, emphasis is on the sources of nonlinearities and solution methods. These are examined for the equality constraints and nonlinear programs in phase and chemical equilibria, in reactors and separators, and in the simulation and optimization of flowsheets. Also examined are the impact of non‐linear predictive control in screening designs and methods to insure operability, in the face of uncertainties.
Simulation of methane partial oxidation over silica‐supported MoO3 and V2O5
Authors: Amiridis Michael D. , Rekoske James E. , Dumesic James A. , Rudd Dale F. , Spencer Nicholas D. , Pereira Carmo J.
Published: June 2004

Microkinetic simulations have been carried out to describe the partial oxidation of methane over silica‐supported molybdena and vanadia. The objective of this study was to formulate a physically reasonable reaction network to capture the basic aspects of the surface catalytic chemistry and to use this network to link methane oxidation kinetics with the kinetics observed for the oxidation of subsequent gaseous products, i.e., methanol, formaldehyde, and carbon monoxide. The most abundant reactive intermediates on the catalyst surface are suggested to be oxygen and hydroxyl groups. This reaction network successfully predicts the catalytic activities, selectivities, activation energies, and reaction orders observed over silica‐supported molybdena and vanadia; and the microkinetic model also semiquantitatively explains the kinetic trends for related catalyst systems and is consistent with surface bonding energetics reported in the literature over various oxide catalysts. The microkinetic reaction network properly reduces to the more simple macrokinetic model reported previously for methane partial oxidation.
Bubble size prediction for rigid and flexible spargers
Authors: Geary Nicholas W. , Rice Richard G.
Published: June 2004

There exists a narrow operating window in bubble columns where the motion is so gentle that the normally dominating forces of coalescence and breakup no longer define the bubble size, hence formation dynamics must control. Elementary force balances are presented to predict bubble size, which compares favorably with experimental data and is shown to be applicable to both rigid and flexible spargers. The main focus is on the prediction and performance of a small‐holed flexisparger, for which it is proved that the gas momentum term is highly significant. Also, it is shown that the intermediate drag law is more appropriate than Stokes for forming bubbles.
Effect of scale of operation on CSD dynamics in evaporative crystallizers
Authors: Jager Johan , Kramer Herman J. M. , Scarlett Brian , De Jong Esso J. , De Wolf Sjoerd
Published: June 2004

Experimental measurements of the crystal‐size distribution (CSD) clearly indicate a pronounced difference in the dynamic behavior of a 20‐ and 970‐L continuous crystallizer that produces ammonium sulfate. The difference in their circulation time offers a probable explanation for this phenomenon. It causes different supersaturation profiles in the two crystallizers, which leads to internal fines dissolution in the large crystallizer. This contributes to the observed oscillations in the 970‐L crystallizer as opposed to the first‐order responses in the 20‐L crystallizer. To numerically study the effect of the supersaturation profile a dynamic model, from which the MSMPR (mixed suspension mixed product removal) assumption is omitted, is developed. Calculated supersaturation profiles differ considerably for the 20‐L, the 970‐L and an imaginary 50,000‐L continuous evaporative crystallizer. Coincident with changes in the supersaturation profiles, the numerical solution of the model indicates the tendency of large crystallizers to oscillate and supports this suggested explanation.
Data reconciliation in generalized linear dynamic systems
Authors: Darouach Mohamed , Zasadzinski Michel
Published: June 2004

A generalized linear dynamic model or singular model, for which the standard state space representation and the Kalman filtering cannot be applied, is used to develop a new algorithm to solve the linear dynamic material balance problem. This algorithm is based on the method developed in the steady‐state case and leads to a recursive scheme, which is very useful in real‐time processing. It reduces the computational problem such as singularities and round‐off errors that may occur in complex systems. Convergence conditions are given and verified for the dynamic material balance case.
Experimental study of reaction in a partially wetted catalytic pellet
Authors: Funk Gregory A. , Harold Michael P. , Ng Ka M.
Published: June 2004

A single‐pellet reactor has been used to investigate the impact of partial external wetting on catalyst performance in a multiphase reaction system. The novel design simulates the local environment within a trickle‐bed reactor, and permits the direct measurement of the degree of wetting under reaction conditions. Experimental data of the hydrogenation of α‐methylstyrene (AMS) over a Pd/Al2O3 pellet provide unequivocal evidence of effectiveness enhancement by partial wetting, a predicted single‐pellet phenomenon (e.g., Harold and Ng, 1987; Funk et al., 1988, 1989). The overall reaction rate is an increasing (decreasing) function of the degree of wetting if the overall limiting reactant is more effectively supplied through the wetted (nonwetted) part of the surface. A maximum in the reaction rate can occur at an intermediate degree of wetting, signaling a transition from an overall AMS‐limited to hydrogen‐limited reaction. The dependence of the degree of wetting on the liquid flow rate for low reaction rates is consistent with a simple rivulet flow model. At higher reaction rates the degree of wetting decreases, with all other conditions fixed. Possible mechanisms for this interesting link between the degree of wetting and reaction are discussed.
Enhanced dispersion resulting from solute exchange between phases
Authors: Grosser Karen A. , Erickson Kenneth L. , Carbonell Ruben G.
Published: June 2004

The enhanced dispersion resulting from solute exchange between phases was investigated experimentally for the case of a long, cylindrical capillary tube, in which a stationary absorbing phase formed a thin annular film around a flowing fluid. Solute diffusion into the stationary phase was analyzed in detail to accurately determine the coupling of film diffusion and hydrodynamic effects. The experimental results and analyses showed an increase in dispersion relative to the usual Taylor effect. The increased dispersion was a function of the relative partitioning of solute between phases and was in quantitative agreement with predictions from previously published theoretical studies.
Eddy diffusivity for distillation sieve trays
Authors: Bennett Douglas L. , Grimm Henry J.
Published: June 2004

An understanding of the eddy diffusivity on a distillation tray is important to accurately predict the distillation tray efficiency from the point efficiency. This article presents a new correlation to predict liquid‐phase eddy diffusivity (De) on sieve trays. This correlation has been developed by modeling backmixing as the trajectory motion of liquid droplet elements through the two‐phase layer height on the tray. The trajectory model indicates that De is a strong function of the two‐phase layer height. An expression for froth height is derived.

The new De correlation offers two main improvements over existing literature correlations. First, this model is phenomenologically‐based and, therefore, not limited to air/water. Second, the new De correlation gives significantly lower average actual and relative errors and a lower standard deviation of the actual error than do other available correlations.
Molecular thermodynamics of solute‐polymer‐supercritical fluid systems
Authors: Shim Jae‐Jin , Johnston Keith P.
Published: June 2004

The distribution coefficients of the solutes (toluene, naphthalene, and phenanthrene) are reported at infinite dilution between silicone rubber and supercriticalfluid carbon dioxide. A new technique is described in which a thin film of polymer is coated and cross‐linked onto silica, and the distribution coefficient is measured rapidly by elution supercritical‐fluid chromatography. Because CO2 significantly enhances the solute's volatility and its diffusion coefficient in the polymer, it is possible to study solute‐polymer interactions at room temperature for nonvolatile compounds which would be difficult to study by conventional techniques such as gas chromatography. These infinite dilution data are used to determine solutepolymer interaction parameters to calculate phase diagrams over a wide concentration range. The residual, combinatorial, and cross‐link contributions to the solute activity coefficient in the polymer are discussed as a function of concentration. In addition, pronounced pressure and temperature effects are described in terms of experimentally measured solute partial molar volumes (to – 14 L/mol) and partial molar enthalpies (to – 850 kJ/mol) in the fluid phase.
Rotary kiln transport processes
Authors: Ferron John R. , Singh Dilip K.
Published: June 2004

Slow rotation of a cylindrical kiln, partially filled with powder or granular solid, produces a planar interface between the bulk of the solid and the gas phase, tilted at the angle of repose. Particles cascade downward on this plane, moving relatively freely and randomly, providing the principal mechanism for particulate diffusion and mixing in the kiln. The plane is also the most favorable location for chemical reactions that require efficient gas–solid heat and mass transfer. Conservation equations are constructed for planar and bulk regions, coupled by the particulate exchange produced by rotation. Sample problems of mixing and heat exchange illustrate problem formulation and useful simplifications. A penetration model predicts wall‐to‐bed heat transfer coefficients, leading to better agreement with experiment than is obtained when planar processes are omitted.
Rapid carbothermal reduction of boron oxide in a graphite transport reactor
Authors: Weimer Alan W. , Roach Raymond P. , Haney Christopher N. , Moore William G. , Rafaniello William
Published: June 2004

Uniform submicron crystals of B4C, boron‐enriched boron carbide, and B4C/TiB2 composite powders have been synthesized continuously by rapid carbothermal reduction at approximately 2,200 K in a 0.14 m ID × 1.68 m long pilot‐scale graphite transport reactor. A unique reactor design allowed for continuous feeding of a meltable boron oxide containing precursor, rapid heating rates that completed the carbothermal reduction reaction in seconds, and an expanded cooling that allowed for the precipitation in space of volatile excess boron oxides. Powder morphology resembled that of powder synthesized by laser pyrolysis of gaseous reactants. Rapid heating rates and minimized reaction times at high temperatures promoted nucleation with limited crystal growth. Dense parts fabricated from these powders had fine grains and extreme hardness.
Critical velocity correlations for slurry transport with non‐Newtonian fluids
Authors: Shah Subhash N. , Lord David L.
Published: June 2004

Transport properties of various uncross‐linked and cross‐linked non‐Newtonian slurries in horizontal pipes are studied. Flow data are gathered in three long, different diameter, transparent horizontal pipes. Investigated are the effects of the pipe size, polymer concentration, fluid rheological properties, cross‐linking effects, particle size and density, solids concentration, fluid density, and slurry rate on the critical deposition velocities and particle resuspension velocities. It is found that critical deposition and resuspension velocities for the non‐Newtonian carrier fluids tested are significantly lower than those for water. Both velocities depend greatly on pipe size and particle density. Higher critical velocities are required to minimize settling (1) in larger pipe sizes and (2) for pumping solids denser than sand. For less viscous fluids, critical deposition and resuspension velocities increase slightly with increasing solids concentration. They are, however, independent of solids concentration for more viscous fluids.
Supercritical CO2 extraction of organic contaminants from aqueous streams
Authors: Ghonasgi D. , Gupta S. , Dooley K. M. , Knopf F. C.
Published: June 2004

Supercritical fluid extraction (SCFE) for the removal of organic toxins from water has been studied using a continuous‐flow view cell system. Distribution coefficients (ratio of mole fraction of contaminant in supercritical CO2 to mole fraction in the aqueous phase at equilibrium) have been determined for a homologous series of contaminants as individual components in pure water: benzene, phenol, p‐chlorophenol, and m‐cresol. Data were obtained at two temperatures (313 and 323 K) and over a pressure range of 9.65 to 17.23 MPa for each contaminant. The distribution coefficients of the contaminants follow a pattern that can be explained in terms of molecular interactions both with water in the aqueous phase (as quantified by the pure contaminant solubility in water) and with CO2 in the SCF phase (as quantified by the pure contaminant solubility in near‐critical CO2 and crossover phenomena in SCF CO2). These results have been accurately modeled using a hardsphere, perturbation‐theory‐based Carnahan‐Starling‐DeSantis‐Redlich‐Kwong equation of state and simple van der Waals mixing rules.
L‐serine obtained by methanol addition in batch crystallization
Authors: Charmolue Hervé , Rousseau Ronald W.
Published: June 2004

The solubility of L‐serine in water was measured as a function of temperature, and the solubility in methanol‐water solutions was determined as a function of temperature and methanol concentration. Solubility in aqueous solutions was found to be a linear function of temperature. Additionally, a statistical design of experiments was used to identify the kinetic variables that influence the purity of L‐serine crystals recovered by batch crystallization. Agitation and the rate at which super‐saturation was generated through cooling and methanol addition were found to influence the methanol content of the recovered crystals. The size of the recovered crystals also was found to depend on agitation and the rate at which methanol was added to the L‐serine mother liquor.
Water and ethanol sorption phenomena on starch
Authors: Lee Jay Y. , Westgate Paul J. , Ladisch Michael R.
Published: June 2004

The sorption behavior of water and ethanol on starch material has been investigated in relation to the adsorptive separation of water from ethanol. The adsorption isotherms of water‐starch, ethanol‐starch and water‐ethanol‐starch were measured using a Cahn electrobalance. Careful examination of the many sorption isotherm models resulted in selection of Sircar's model and the potential theory to best represent the isotherm data of water‐starch and ethanol‐starch adsorption. Experimental results showed that ethanol as well as water can adsorb on starch. The adsorption rate of ethanol, however, is much slower than that of water. This suggests that the selective removal of water from ethanol vapor in a packed‐bed adsorber is likely a rate‐dependent, not an equilibrium‐dependent, process.
Lattice relaxation in type I gas hydrates
Authors: Rodger P. M.
Published: June 2004

Computer simulations have been used to examine the approximations upon which the van der Waals‐Platteeuw theory of hydrate stability is based, and in particular, the extent to which the water lattice relaxes about the guest molecules. It is found that the behavior of the water lattice depends significantly on both the nature and number of guest molecules present—an effect that is neglected in the van der Waals‐Platteeuw theory. The simulations also indicate an important role for the repulsive guest‐host interactions in generating the mechanical stability of gas hydrates in the bulk. On the basis of these simulations, it is conjectured that surface interactions (particularly at a water/guest interface) are fundamental to the phase behavior of gas hydrates.
Trapping of solid particles at a wall in a turbulent flow
Authors: Young James B. , Hanratty Thomas J.
Published: June 2004

Studies of the motion of a dilute suspension of 100‐micron glass and stainless steel spheres in water flowing turbulently down a pipe revealed that they could be trapped in necklace formations that move slowly at a distance of less than one particle diameter from the wall. The tendency toward trapping increases with particle density and decreases with flow rate. The phenomenon is interpreted as occurring when the Saffman lift force toward the wall overcomes the ability of fluid turbulence to mix the particles. The location of the particles is dictated by a balance between the Saffman lift force and a wall‐induced force associated with the displacement of fluid as a particle moves parallel to the wall.