bluuebunny/crossref_metadata_2025_split huggingface dataset:
Three phase slurry reactors
Authors: Chaudhari R. V. , Ramachandran P. A. 
Published: June 2004

AbstractThis article reviews the major developments in the engineering and design of three‐phase slurry catalytic reactors. A general theoretical analysis for predicting the overall rate of reaction in a slurry reactor for various kinetics is presented, incorporating all the transport effects. Modeling of semi‐batch reactors is discussed and design procedures are indicated. Some major correlations and methods for determining gas‐liquid and liquid‐solid mass transfer coefficients and effective diffusivity in liquid filled pores are reviewed. Slurry reactors are compared with other three‐phase reactors, such as trickle bed or packed bed reactors, and relative merits are pointed out.
Studies in the synthesis of control structures for chemical processes: Part II: Structural aspects and the synthesis of alternative feasible control schemes
Authors: Morari Manfred , Stephanopoulos George 
Published: June 2004

AbstractThe classification of control objectives and external disturbances in a chemical plant determines the extent of the optimizing and regulatory control structures (see Part I). In this article we discuss the structural design of alternative regulatory control schemes to satisfy the posed objective. Within the framework of hierarchical control, criteria are developed for the further decomposition of the process subsystems, reducing the combinatorial problem while not eliminating feasible control structures. We use structural models to describe the interactions among the units of a plant and the physicochemical phenomena occurring in the various units. The relevance of controllability and observability in the synthesis of control structures is discussed, and modified versions are used to develop all the alternative feasible regulatory structures in an algorithmic fashion. Various examples illustrate the developed concepts and strategies, including the application of the overall synthesis method to an integrated chemical plant.
Studies in the synthesis of control structures for chemical processes: Part III: Optimal selection of secondary measurements within the framework of state estimation in the presence of persistent unknown disturbances
Authors: Morari Manfred , Stephanopoulos George 
Published: June 2004

AbstractWhen primary control objectives cannot be measured directly, secondary measurements have to be selected and used in conjunction with estimators to infer the value of the unmeasurable variables. Unmeasured process disturbances (state excitation noise) are assumed to be of major importance, dominating the errors caused by measurement noise. Since the white noise assumption is generally insufficient for the persistent disturbances commonly occuring in the Chemical Engineering, environment, a nonstationary noise model has been employed, and is shown to yield superior estimations under these circumstances. New necessary and sufficient conditions have been developed for the observability of the dynamic system augmented to include the noise model.A variety of new measurement selection criteria is presented here, with the goal of minimizing estimation error. One class of criteria aims at minimizing the transient estimation error when a static estimator is used. The other class minimizes the measurement error caused by the unobservable subspace. The design of state reconstruction procedures (which are able to handle persistent unmeasured process disturbances) is explained in a stochastic and a deterministic framework. Finally, the synthesis of reduced order control schemes is discussed. The power of the selection criteria and the superiority of a Kalman filter design employing a nonstationary noise model is demonstrated in many examples.
Dynamics of bubbles and entrained particles in the rotating fluidized bed
Authors: Chevray Rene , Chan Yau Nam I. , Hill Frank B. 
Published: June 2004

AbstractTrajectories of bubbles and entrained particles in the rotating fluidized bed were obtained from equations expressing a balance among inertial, centrifugal, Coriolis, gravity and drag forces. The solutions led to information on the behavior of isolated bubbles, bubbles swarms and the elutriation characteristics of the rotating fluidized bed.
Electrically stimulated aerosol filtration in packed beds
Authors: Harriott G. M. , Saville D. A. 
Published: June 2004

AbstractSince charged particles are quite mobile in an electric field, charge is often added to aerosol particles to facilitate capture; indeed, provision for such charging is an indispensable part of electrostatic precipitators. Nevertheless, calculations disclose that a very slight amount of charge may suffice when the distance the aerosol particle must travel to the collector surface is small, contrary to the usual situation. In the experiments described, here, a model aerosol containing 0.5 μm polystyrene particles passed through a radioactive charge neutralizer to deliberately reduce the charge as much as practicable and then through a packed bed under the influence of a fairly large external electric field. Filtration efficiencies approaching 100% were obtained owing to the influence of the field on small amounts of residual charge.
Solvent losses in gas absorption. Solubility of methanol in compressed natural and synthetic gases
Authors: Lazalde‐Crabtree H. , Breedveld G. J. F. , Prausnitz J. M. 
Published: June 2004

AbstractExperimental results are reported for the solubility of methanol in compressed nitrogen, methane, ethane and carbon dioxide in the region −45° to +10°C and 17 to 62 bars.New and previously published experimental data are used to obtain (or estimate) second virial coefficients for all binary pairs in mixtures containing hydrogen, nitrogen, carbon monoxide, methane, ethane, propane, carbon dioxide, hydrogen sulfide and methanol. These coefficients, combined with experimental data for the vapor pressure of methanol and with Henry's constants, partial molar volumes and Margules coefficients for dissolved gases in methanol, yield a correlation for calculating solvent losses as a function of temperature, pressure and gas composition. For a large‐scale natural‐gas absorption process, these losses may represent a significant economic factor in plant design.
An introduction to the nonlinear theory of adsorptive reactors
Authors: Schweich Daniel , Villermaux Jacques , Sardin Michel 
Published: June 2004

AbstractCoupling between transient chemical reaction at equilibrium and a linear and isothermal chromatographic separation is studied when a nonlinear chemical mass action law is assumed to hold between the species. It is shown that the qualitative features of the chromatograms can be predicted by simple algebraic calculations. Two novel properties of the adsorptive (or chromatographic) reactor are demonstrated. The improvement of the theory, with regard to quantitative predictions, is discussed.
A single‐particle char gasification model
Authors: Srinivas B. , Amundson Neal R. 
Published: June 2004

AbstractA model is developed for the gasification of a single‐char particle in an environment of water, hydrogen, carbon dioxide, carbon monoxide and methane, existing in the gasification zone of a reactor. The model, consisting of the mass and energy conservation equations, together with the Stefan‐Maxwell relations includes the intraparticle effects and the change in internal surface area. It is found that the intraparticle effects and the surface area effects are significant and hence cannot be neglected, and the situation becomes more acute with increasing particle size and high temperatures. Comparisons with other models and existing empirical relations show that the model agrees well when diffusional effects are minimal, but at higher temperature and large pariticle size there is a significant difference. The model may be used to discriminate among various idealized models such as the homogeneous and the shrinking core model. The conyective terms in the Stefan‐Maxwell relations have negligible influence. The analysis can be directly used in the modeling studies of gasification reactors and will be so applied in a later paper.
An optimal arrangement of simultaneous linearized equations for general systems of interlinked, multistoged separators
Authors: Hidalgo S. R. , Correa V. A. , Gomez M. A. , Seader J. D. 
Published: June 2004

AbstractThe simultaneous solution of all the equations for a general system of interlinked, multistaged separators is considered. The interlinks may be simple streams or reciprocal streams, and a particular separator may have bypassing streams (for example, pumparounds). Algorithms are developed that automatically arrange the linearized equations so that for a Newton‐Raphson type of solution procedure using, for example, the Naphtali‐Sandholm technique, a minimum or nearly minimum number of nonzero blocks occur outside the tridiagonal band so that computational memory and time requirements are minimized. The nonzero and nonidentity blocks are stored in a single vector of variable dimension.
Sulfur dioxide transport through aqueous solutions: Part II. Experimental results and comparison with theory
Authors: Roberts Daryl L. , Friedlander Sheldon K. 
Published: June 2004

AbstractMeasurements were made of the steady state flux of sulfur dioxide through films of water and solutions of neutral and alkaline sodium salts (0.1 to 2.0 M sodium chloride, 10−3 to 3.0M sodium hydroxide, NaHSO3 or sodium sulfite) with sulfur dioxide partial pressures between 10 and 100Pa. In agreement with equilibrium theory (Part I), data from water and sodium chloride solutions show that HSO is responsible for 83 to 95% of the flux (facilitation factor F between 5 and 19). In alkaline solutions, HSO and other sulfur containing species cause F to be as large as 1 370. Equilibrium theory, however, overpredicts F by up to a factor of 7. The NEBLA (Part I) accounts for this deviation.
Throughflow drying and conditioning of beds of moist porous solids: A simple method for the quantitative prediction of moisture and temperature fronts
Authors: Basmadjian Diran 
Published: June 2004

AbstractA simple procedure previously developed for the prediction of fixed bed adiabatic sorption operations (Basmadjian, 1980b) has been extended to the throughflow drying and conditioning of beds of moist porous solids. The method eliminates time consuming numerical solutions of the model PDE's and yields satisfactory agreement with reported experimental data.
Transport accompanied by chemical reaction in stagnation flow
Authors: Balaraman K. S. , Mashelkar R. A. , Doraiswamy L. K. 
Published: June 2004

AbstractThere are many industrially important reactions in which the chemical kinetics and external diffusion govern the observed reaction rate, and the observed kinetics differ drastically from the true kinetics. This study shows that the forward stagnation flow region of a circular cylinder can be a convenient system for studying the true kinetics of a solid catalyzed reaction owing to its unique property of uniform accessibility.
A comprehensive model for fluidized bed coal combustors
Authors: Rajan Renga R. , Wen C. Y. 
Published: June 2004

AbstractA comprehensive model for the simulation of fluidized bed coal combustors (FBC) is developed, capable of predicting the combustion efficiency, char and limestone elutriation and the corresponding particle size distribution in the bed and in the entrained materials, solids withdrawal rate from the bed, bed temperature profile, sulfur dioxide retention, sulfur dioxide and NOx emissions, concentrations of oxygen, carbon monoxide, carbon dioxide, volatiles, sulfur dioxide and NOx along the combustor height. The model can also simulate combustors with varying cross section along the bed height. The performance of the model is compared with the data obtained from four different combustors. Agreement between the computed results and the data is good. The salient features in the model which need further investigation are pointed out.
Chlorination kinetics of zirconia in an RF chlorine plasma tail flame
Authors: Biceroglu O. , Gauvin W. H. 
Published: June 2004

AbstractThe chlorination kinetics of zirconia were studied in a single stationary particle reactor system. A plasma of pure chlorine generated by an induction torch provided both the high enthalpy field and the reacting gas. The influence on the rate of conversion of such parameters as temperature, chlorine concentration (in the presence of argon) and particle diameter and porosity were investigated. Based on experimental and theoretical studies, rate equations were developed under different rate controlling mechanisms.The chlorination of zirconia in the particle temperature range of 1 540° to 2 480°K obeyed a shrinking core reaction model. The reaction was chemically controlled below 1 950°K, and above this temperature both chemical and mass transfer resistances were important. The experimental results confirmed the theoretical analysis.
Application of a variable time‐step finite‐difference method for the one‐dimensional melting problem including the effect of subcooling
Authors: Yuen W. W. , Kleinman A. M. 
Published: June 2004

AbstractA new numerical method is proposed for the one‐dimensional melting problem. Unlike many of the existing numerical techniques which either immobilize the moving interface by a suitable coordinate transformation or search for the moving interface under a fixed grid, fixed‐time‐step finite‐difference formulation, the present method was a fixed grid, variable time‐step approach. Each time step in the computation is determined iteratively by requiring that the interface be located at a mesh point, one grid space from the previous interface location.Results of two sample calculations show that the present method is superior to the conventional finite‐difference method both in its accuracy and computational efficiency. The formulation is mathematically simple and can be applied with no difficulty to problems with nonplanar geometry and initial subcooling. The present method is applied to the analysis of the melting of a finite slab subjected to a constant heat flux boundary condition. Some interesting effects of initial subcooling on the physics of melting are illustrated and discussed.
Gas absorption with consecutive second‐order reactions
Authors: Huang D. T. ‐J. , Carberry J. J. , Varma A. 
Published: June 2004

AbstractFor gas absorption accompanied by two consecutive second‐order reactions, the reaction factors of the film and penetration theories were solved by the orthogonal collocation method. For equivalent definition of the other physico‐chemical parameters, the reaction factors from the two theories differ only slightly. In film theory, it is shown that the film‐bulk boundary condition is of importance only for small values of M. It is also shown that the difference between the point yields of the film and penetration theories is generally small, although it is larger than the difference in reaction factors for the two theories.
Influence of condensable vapor on strength of powders
Authors: Elbirli B. , Vergara‐Edwards Luis , Coughlin Robert W. 
Published: June 2004

AbstractDiametrically different influences of small moisture contents upon strength are often measured in beds of different kinds of particles. Here we explain such opposing trends in terms of capillary forces exerted by condensed liquid rings at the points of particle contact. The effects of such rings are opposite for different particle shapes at the point of contact, namely, at spherical or at sharp angular contact points. In addition to the theoretical development, data are given for two different illustrative types of particles.
Heat and mass diffusion with chemical reaction: A moving boundary analysis in a particle
Authors: Essoh Djedjess C. , Klinzing George E. 
Published: June 2004

AbstractGoodman's integral heat and mass balance method is applied to the problem of a moving boundary in a spherical particle. The moving boundary was fixed by a suitable transformation for ease in solution. The mean value theorem was used to treat the nonlinearities when they occurred. Relations for the heat and mass boundary positions are obtained for the most general conditions. These expressions reduce in their limiting cases to known results.
The synthesis of distillation trains with heat integration
Authors: Morari Manfred , Faith Don C. 
Published: June 2004

AbstractDue to rising energy costs, there is an increasing need to include the goal of energy conservation as an integral part of process synthesis. This paper discusses the problem of finding the optimum sequence of distillation columns for separating a multicomponent mixture, when heat exchange is permitted between the columns. The major difficulties are associated with the nonserial nature of the problem, the large combinatorial variety and the size of the optimization task. The synthesis strategy presented here overcomes these problems by the use of a bounding technique together with the Lagrangian theory from nonlinear programming. Accurate lower bounds on the optimal costs permit the elimination of nonoptimal sequences with minimal computational effort.
The mixing of Granular solids in a rotary cylinder
Authors: Mu Jacob , Perlmutter D. D. 
Published: June 2004

AbstractA model is derived for solids mixing and material transport in a continucus flow rotary dryer or reactor. Detailed analysis of the particle motions in the turnover process provides an opportunity to apply well‐known reactor models to several subregions and to relate the overall results to different design geometries and operating conditions. The essential parameters of the model are the number of stages, the volume fractions of mixed flow and plug flow in each stage, the recycle ratio and the bypass ratio.
Studies in the synthesis of control structures for chemical processes: Part IV. Design of steady‐state optimizing control structures for chemical process units
Authors: Arkun Yaman , Stephanopoulos George 
Published: June 2004

AbstractThe design of the steady‐state optimizing control for a single unit is formulated within the framework of the nonlinear mathematical programming theory. Alternative implementational strategies are developed and a multilevel screening procedure is proposed to arrive at the best optimizing control configuration. Numerical examples on a fluid catalytic cracking unit and a distillation column demonstrate the systematic design and the synthesis of the most promising optimizing control structures for these systems.
Analysis of drop size distributions in lean liquid‐liquid dispersions
Authors: Narsimhan Ganesan , Ramkrishna Doraiswami , Gupta Jai P. 
Published: June 2004

AbstractExperimental measurements of transient drop size distributions in a stirred liquid‐liquid dispersion (with low dispersed phase fraction) have been used concomitantly with population balance theory to recover the transition probability of droplet breakage, based on a similarity concept. The data remarkably uphold the proposed similarity hypothesis, and the estimated probability function displays the same qualitative trend as the model due to Narsimhan et al. (1979).
A novel rotated disc electrode and time lag method for characterizing mass transport in liquid‐membrane systems
Authors: Gough David A. , Leypoldt John K. 
Published: June 2004

AbstractA time lag method is described for use with a membrane‐covered, rotated disc electrode that allows determination of the partitioning and diffusivity of small molecules in hydrophilic gel membranes and membrane permeability from a single measurement. This new technique takes into account the concentration boundary layer in the solution adjacent to the membrane and reaction at the electrode surface of solutes that are diffusion‐ or kinetic‐limited. Examples are given of the use of this method for characterizing mass transfer in a commercial cellulosic membrane with oxygen, hydroquinone, ferrocyanide, and glucose as solutes.
Kinetics of selective oxidation of toluene and methanol over supported V2O5‐alkalimetal sulfates
Authors: Sharma R. K. , Srivastava R. D. 
Published: June 2004

AbstractThe catalytic activity of supported V2O5‐alkalimetal sulfate catalysts was studied by oxidizing toluene and methanol to aldehydes and water. An isothermal, fixed‐bed reactor, operating at atmospheric pressure and temperatures of 320, 345, and 370°C, was used to obtain the reaction rate data for different partial pressure combinations of the reaction components of these two systems. Three different approaches, Langmuir‐Hinshelwood, Hinshelwood, and two‐step redox mechanisms, have been used to study the kinetics, with statistical data interpretation.
Oxygen mass transfer in bubble columns working at large gas and liquid flow rates
Authors: Alvarez‐Cuenca M. , Nerenberg M. A. 
Published: June 2004

AbstractOne of the most persistent obstacles in the study of oxygen mass transfer in bubble columns is the technical difficulty of using large liquid and gas flow rates economically. This experimental limitation is reflected in the present, very incomplete, understanding of the mass transfer characteristics of these two‐phase systems. In this work, a new experimental technique has been developed and used.The use of computer‐calculated concentration contour diagrams permitted a detailed study of the mass transfer characteristics of the zone near the distributor. No similar study has been reported in the literature until now. The ability of the axial dispersion and two‐zone models to describe the experimental data is analyzed.Finally, liquid side volumetric mass transfer coefficients have been calculated for both models. The results indicate that KLa increases, often linearly, with the superficial gas velocity. Furthermore, for the liquid‐phase range [0, 10] cm/s, KLa had a minimum at Vl ∼ 7.5 cm/s. For larger liquid superficial velocities, an increase in KLa was found. These observations were valid for the axial dispersion (ADM), plug flow (PFM) and two‐zone (T‐ZM) models.
Bacterial population dynamics in batch and continuous‐flow microbial reactors
Authors: Nishimura Y. , Bailey J. E. 
Published: June 2004

AbstractCalculations of the distribution of states in cell populations grown in well‐mixed, isothermal batch and continuous flow reactors are presented. By restricting the analysis to a class of bacteria for which cell division control may be modeled using overlapping timers, analytical results are obtained for many cell population characteristics in terms of the growth rate history. This required growth rate trajectory is evaluated using a separate overall reactor model. The simulation results conform qualitatively to available experimental data and suggest new experiments for further testing of the single‐cell model.
Effective diffusivity by the gas chromatography technique: Analysis and application to measurements of diffusion of various hydrocarbons in zeolite NaY
Authors: Hsu L.‐K. P. , Haynes H. W. 
Published: June 2004

AbstractThe gas chromatography technique was applied to measurements of diffusion of n‐butane in zeolite NaY. The linear chromatography theory failed to explain these results quantitatively, and a significant system nonlinearity was demonstrated. This nonlinearity is likely associated with non‐Fickian diffusion. Order of magnitude estimates of the diffusivity could still be obtained, however. Over the range of temperatures 105 to 240°C, the n‐butane diffusivities were in the range 10−8 to 10−6 cm2/s. Similar results were obtained with n‐hexane and calculated diffusivities were about an order of magnitude smaller than the corresponding n‐butane values. In contrast, limited experiments with cyclohexane, 2, 2‐dimethylbutane, and trans‐decalin were entirely consistent with the linear chromatography theory. At the measurement temperatures, the intracrystalline diffusion was too rapid to be detected in any of these systems. Attempts to operate at lower temperatures where diffusion might be significant were frustrated by extensive peak broadening and concomitant loss of detector response.