bluuebunny/crossref_metadata_2025_split huggingface dataset:
Adaptive generic model control: Dual composition control of distillation
Authors: Rani K. Yamuna , Gangiah K. 
Published: June 2004

AbstractGeneric model control (GMC) takes care of parametric mismatch for underdamped, closed‐loop specification, whereas robust generic model control (RGMC) can handle parametric mismatch for any closed‐loop specification. But, neither GMC nor RGMC is capable of compensating for structural mismatch. In this study, adaptive GMC(AGMC) and adaptive RGMC (ARGMC) structures are proposed, and their effectiveness over GMC and RGMC is demonstrated with several examples. AGMC exhibits better performance over ARGMC, GMC, and RGMC in all the cases of no process/model mismatch, parametric mismatch as well as structural mismatch.Distillation adaptive generic model control (DAGMC) structure is also proposed for dual composition control of distillation. Since embedding of distillation state‐space model in the basic GMC law is practically impossible, linear and nonlinear models are proposed with adaptation using distillation process data, and DAGMC is applied to two typical nontrivial distillation units. Nonlinear DAGMC exhibited better performance over linear DAGMC.
Explicit runaway criterion for catalytic reactors with transport limitations
Authors: Balakotaiah Vemuri , Luss Dan 
Published: June 2004

AbstractMost existing criteria for predicting parametric sensitivity or runaway in a catalytic reactor are based on a single‐phase model that does not account for interparticle heat and mass transfer resistances and intraparticle diffusion. Accounting for these effects, the simple criterion

defines the boundary of operating conditions, in which a catalytic reactor is insensitive to small perturbations. Here, r(Tf,Cf) is the intrinsic reaction rate at inlet conditions, dt(dp) and U(h) are the diameter of reactor tube (catalyst particle) and heat transfer coefficient between the fluid and tube wall (catalyst particle), respectively. The function f(ϕ0), where ϕ0 is the normalized Thiele modulus at inlet conditions, accounts for the effects of intraparticle diffusion. For the common case of equal coolant and feed temperatures, f(ϕ0) = 1 for ϕ0 < 0.5 and f(ϕ0) = 2 ϕ0 for ϕ0>0.5. The conservatism associated with the above criterion is comparable to the uncertainty involved in determining the parameters of the packed bed.
Effect of electrode surface area on chaotic attractor dimensions
Authors: Wang Ying , Hudson John L. 
Published: June 2004

AbstractAn experimental study of the dynamics of electrodissolution of iron in sulfuric acid is reported. The experiments were done under potentiostatic conditions with a rotating disk electrode as a function of two parameters, potential and electrode diameter. The dynamic behavior depends strongly on the latter parameter; with increasing electrode size we observe transitions from periodic oscillations to low‐order chaos to higher‐order chaos. The attractor dimension increases with increasing electrode size. In addition, for the large electrodes at more positive potentials, a secondary higher frequency oscillation also arises.
Comparing two neural networks for pattern based adaptive process control
Authors: Cooper Douglas J. , Megan Lawrence , Hinde Ralph F. 
Published: June 2004

AbstractAn adaptation strategy based on an analysis of patterns exhibited in the recent controller error history is presented. The strategy is a two parameter adaptation, where the gain and time constant of the controller's internal model are adjusted to make the closed loop error response match a target pattern. Both a back‐propagation network and a vector quantizer network (VQN) are compared as pattern analysis tools. This strategy is established for a number of model based controllers and is demonstrated here using the Generalized Predictive Control algorithm. Details of this set point tracking strategy are presented along with demonstrations on both simulated and real single loop processes that experience significant changes in process gain and time constant. Results show both networks to be equally capable at pattern recognition with the VQN's ease of training and implicit ability to assess the accuracy of the pattern match as deciding factors in network selection.
Automatic verification of sequential control systems using temporal logic
Authors: Moon Il , Powers Gary J. , Burch Jerry R. , Clarke Edmund M. 
Published: June 2004

AbstractClarke et al. (1986) have developed a model‐based verification method and have applied it to validation of VLSI circuits. We have used the method to test automatically the safety and operability of discrete chemical process control systems. The technique involves: (1) a “system model” describing the process and its software; (2) “assertions” in temporal logic expressing user‐supplied questions about the system behavior with respect to safety and operability; and (3) a “model checker” that determines if the system model satisfies each of the assertions and provides a counterexample to locate the error if one exists. Temporal logic is used for reasoning about occurrence of events over time. To reveal discrete event errors, we have applied the verification method to a simple combustion system and an alarm acknowledge system.
Adequacy of lumped parameter models for SCR reactors with monolith structure
Authors: Tronconi Enrico , Forzatti Pio 
Published: June 2004

AbstractTwo‐and one‐dimensional steady‐state isothermal mathematical models of monolith reactors for selective catalytic reduction (SCR) of NOx by NH3 are compared for circular, square and triangular geometry, as well as for linear and Rideal kinetics. Solutions for the two‐dimensional model demonstrate that, as the reaction rate decreases from infinity to zero, the Sherwood number varies from the values of the Nusselt number characteristic of the Graetz‐Nusselt problem with constant wall temperature to those with constant wall heat flux but with peripherally varying temperature. A lumped‐parameter treatment, based on similarity with the constant wall temperature heat transfer problem, agrees satisfactorily with the solutions for a far more expensive two‐dimensional model. The agreement is excellent for square channels, but the NH3 slip tends to be underestimated in the triangular geometry. The one‐dimensional model reproduces successfully experimental effects of the NH3/NO feed ratio, and of the area velocity and the size of monolith channels.
Parallel finite element computations on a network using NCS
Authors: Bertrand F. H. , Tanguy P. A. 
Published: June 2004

AbstractResearch has been carried out on the use of NCS (Network Computing System) to distribute the processing of a finite element application to multiple computers at once. Coarse‐grained parallelism of specific routines on loosely coupled CPUs has been implemented and tested. In a step‐by‐step fashion, the method of using NCS to convert finite element software POLY2D is explained for its application in parallel computing resources throughout a network. For the modeling of a simple conductive heat transfer problem, the distributed version of POLY2D on a homogeneous token ring network of nine Apollo workstations is used. Some timings given are compared to those obtained from a standard nondistributed simulation.
Semibatch reaction crystallization of benzoic acid
Authors: Slund Bengt L. Å , Rasmuson Å Ke C. 
Published: June 2004

AbstractAn experimental study of a semibatch reaction crystallization is presented. Dilute hydrochloric acid is fed to a stirred solution of sodium benzoate to crystallize benzoic acid. The weight mean size of the product crystals increases with increasing stirring rate, reaches a maximum, and then decreases again. Larger crystals may be produced if the reactant feed point is positioned close to the outlet stream of the impeller. At equal power input the influence of stirrer type is negligible. Decreasing reactant concentrations or feed rate increases the crystal size significantly. Experimental results are explained qualitatively focusing on nucleation and growth conditions and on feed point mixing. The feed point micromixing brings reactants together to generate supersaturation and allow for nucleation. Continued mixing, however, may partially dilute supersaturation before nucleation takes place or may restrict nuclei growth, thus promoting more efficient Ostwald ripening in the bulk. This may result in high bulk supersaturations which in turn hampers the dilution effects.
Agglomeration in a continuous MSMPR crystallizer
Authors: Tavare Narayan S. , Patwardhan V. 
Published: June 2004

AbstractExperimental responses from crystallization of copper sulfate pentahydrate, nickel ammonium sulfate, and soy protein in continuous MSMPR crystallizers were used to determine simultaneously crystal growth and nucleation rates and agglomeration kernels. Measured product crystal size distributions at steady state for all these systems were transformed into crystal volume coordinates to use two methods: moments analysis and optimization procedure for parameter characterization. An iterative nonlinear parameter estimation by optimization procedure was used to deduce the kinetic rate parameters in the solution of the agglomeration model in crystal volume coordinates, extended from the analysis by Liao and Hulburt (1976), from the translated data set for the product crystals. The kinetic results obtained for the copper sulfate pentahydrate system were correlated in terms of power law kinetic expressions depicting the effect of significant observable variables.
Alkaline hydrolysis of n‐butyl acetate with phase transfer catalyst aliquat 336
Authors: Asai Satoru , Nakamura Hidemi , Furuichi Yousuke 
Published: June 2004

AbstractA reasonable analytical procedure of the overall reaction rate for the phase transfer catalysis with mass transfer is discussed. Alkaline hydrolysis of n‐butyl acetate with a phase transfer catalyst Aliquat 336 (tricaprylmethylammonium chloride, Q+Cl−) was chosen as a model system and carried out in an agitated vessel with a flat interface. Overall reaction rates observed were proportional to the interfacial concentration of the actual reactant Q+OH− (the ion pair consisting of quaternary ammonium cation Q+ and OH−) for the hydrolysis in the organic phase. The interfacial concentration of Q+OH− was a unique function of bulk concentrations of the catalyst and NaOH, and the ionic strength of the aqueous solution. This behavior of the overall reaction rates was explained by the proposed model solution. The reaction rate constant, evaluated by fitting the rate data to the model prediction, was 47 m3/kmol·s at 298 K. It was 70 or more times greater than that of conventional alkaline hydrolysis in the aqueous phase.
Fraction of Pt surface covered with coke following hydrogenolysis of hexane
Authors: Rivera‐Latas F. J. , Betta R. A. Dalla , Boudart M. 
Published: June 2004

AbstractFollowing hydrogenolysis of n‐hexane on an alumina‐supported platinum catalyst, the surface of the metal is covered partially with carbonaceous residues or coke. The fraction of surface platinum not covered with coke has been found to be about one half by four independent techniques: titration of preadsorbed oxygen by dihydrogen, chemisorption of carbon monoxide, infrared spectroscopy of chemisorbed carbon monoxide, and hydrogenation rate of ethylene. The first of these techniques suggests itself as the simplest one for further studies of deactivation by coking of platinum catalysts.
Growth processes in bioreactors with external sources of biomass: Application of structured, continuum models
Authors: Fredrickson A. G. 
Published: June 2004

AbstractBatch, fed‐batch, and single‐stage CSTR bioreactors operate without external sources of biomass after they have been inoculated. However, other kinds of bioreactors, such as the second and subsequent reactors in a cascade of CSTRs, operate with continuous introduction of biomass from one or more external sources. The biomass in a bioreactor with an external source is not homogeneous with respect to past history of environmental conditions, and growth of this biomass is not balanced (steady‐state) growth even when the bioreactor operates in steady state. So‐called unstructured models of growth, which assume biomass to lack any internal structure or to have an invariant internal state, can give only a first approximation to the growth rate behavior of the biomass in a bioreactor with an external source of biomass. Structured models, which endow biomass with a changeable internal structure, are required to obtain more accurate predictions of growth rate behavior in such reactors. Introduction of structure is not sufficient for improved accuracy, however, and the fact that biomasses from different sources are remain segregated from one another must also be accounted for by any structured growth model used. This article presents, among others, the systems of different equations that result from application of the notions to the reactors of a cascade of CSTRs.
High‐temperature membrane reactor for catalytic gas‐solid reactions
Authors: Sloot H. J. , Smolders C. A. , Van Swaaij W. P. M. , Versteeg G. F. 
Published: June 2004

AbstractA mathematical model, based on the dusty‐gas model extended with surface diffusion, is presented that describes mass transport owing to molecular diffusion and viscous flow, as well as an instantaneous reversible reaction inside a membrane reactor. The reactants are fed to opposite sides of the membrane, considering masstransfer resistances in the gas phase outside the membrane. The Claus reaction is chosen as a model reaction to study this membrane reactor.The model is used to validate a previously presented simplified model. The simplified model predicts correct molar fluxes when it is very dilute and can therefore be considered a pseudo‐binary system. Occurrence of a maximum or a minimum in the pressure profile inside the membrane, in the absence of an overall pressure difference over the membrane, depends not only on the stoichiometry of the reaction but on mobilities of the different species.The Claus reaction is used to verify experimentally the transport model for a nonpermselective membrane reactor with a mean pore diameter of 350 nm. At 493 K and 542 K, molar fluxes experimentally determined are 10 to 20% lower than those predicted by the transport model. Conversions measured at pressures of 220 kPa and 500 kPa demonstrate that surface diffusion occurs as a transport mechanism despite the large pore diameter of the membrane. In the presence of a pressure difference over the membrane, there is a reasonable agreement between experimentally determined molar fluxes and those calculated by the transport model.
Analysis and design of melt and solution polycondensation processes
Authors: Jacobsen Lance L. , Ray W. Harmon 
Published: June 2004

AbstractPolycondensation processes include up to three distinct process stages: prepolymerization, polymerization, and finishing. One or more of these stages often have serious reaction rate limitations due to chemical equilibrium and the need to remove a condensate product. The problems arising in each process stage and the methods of designing each stage are unique. This article discusses many of the problems inherent to each process stage and basic design tools useful in designing each process stage. Two process design tools discussed are the mass‐transfer potential and pressure‐chain length plots. The application of these tools is illustrated through two design examples: nylon‐6,6 and poly (ethylene terephthalate) production.
Modeling of supercritical oxidation of aqueous wastes in a deep‐well reactor
Authors: Kodra Dusan , Balakotaiah Vemuri 
Published: June 2004

AbstractA mathematical model is developed for deep‐well oxidation of wastes in supercritical water. The model accounts for the variation of thermodynamic and transport properties with temperature and pressure. It is used to examine the steady‐state behavior of the supercritical‐water deep‐well oxidation reactors. The effects of inlet flow rate, heat losses from the reactor, inlet concentration of organics, oxygen injection depth, reactor length, inlet pressure, and inlet temperature on the exit conversion and the bottom temperature are examined. The simulations show that under practical conditions the capacity of the reactor is dictated by hydrodynamic considerations rather than the oxidation kinetics, and that obtaining temperatures of 10 to 50 K above critical temperature at the bottom of the reactor requires longer tubes and/or high inlet pressures. Heat losses to the earth can be modeled accurately by treating the earth as an infinite reservoir by properly choosing the effective heat‐transfer coefficient.
Two‐mode boiling on a horizontal heating wire
Authors: Lee D. J. , Lu S. M. 
Published: June 2004

AbstractTwo‐mode boiling on a horizontal heated wire immersed in a pool of liquid under atmospheric pressure has been investigated. Methanol, acetone, isopropanol, and isobutanol were boiled using wires made of tungsten (0.15, 0.50, 0.82, 1.01, and 1.55 mm dia.), tantalum (0.30 and 0.82 mm dia.), molybdenum (0.125 and 1.01 mm dia.) and titanium (1.01 and 1.55 mm dia.). Two‐mode boiling may be steady or unsteady. In steady two‐mode boiling, both modes of boiling are stationary on the wire. The applied current in this case is referred to as the equilibrium current. In this article a method devised to calculate this current is discussed. The calculated results agreed well with the experimental results. In unsteady two‐mode boiling, one of the two modes automatically takes over the other and boiling changes into a one‐mode boiling. A method to calculate this transition velocity is presented. The calculated results correlated well with the experimental work.
Modeling of the sulfidation of zinc‐titanium oxide sorbents with hydrogen sulfide
Authors: Lew Susan , Sarofim Adel F. , Flytzani‐Stephanopoulos Maria 
Published: June 2004

AbstractThe overlapping grain model was used to describe the sulfidation of zinc oxide and zinc‐titanium oxide powders at temperatures between 400–700°C in H2S‐H2‐N2 gas mixtures. Experimental data were collected under conditions free of mass‐transfer and pore diffusion limitations. Thus, the only resistances to reaction were due to intrinsic sulfidation kinetics (surface reaction) and diffusion through the product layer. The product layer diffusion coefficient was used as a fitting parameter in the model. As the relative amount of titanium in the sorbent was increased, the product layer diffusion coefficient decreased. Similar activation energies (26.6 kcal/mol) were obtained for the product layer diffusion coefficient of ZnO and Zn‐Ti‐O sulfidation. From the similarity in activation energies, it is proposed that for both types of sorbents diffusion occurs primarily through ZnS.
The modular multivariable controller: I: Steady‐state properties
Authors: Meadowcroft T. A. , Stephanopoulos G. , Brosilow C. 
Published: June 2004

AbstractThe modular multivariable controller (MMC) represents a multivariable controller design methodology which is based on the solution of multiobjective optimization problems using the strategy of lexicographic goal programming; priority‐driven, sequential satisfaction of objectives. This article formally introduces the concept of the MMC, analyzes its static characterstics, and proposes a specific methodology for the design of steady‐state MMCs. It is shown that the framework of MMC can explicitly handle all types of control objectives (for example, equality or inequality specifications on controlled outputs), and constraints on manipulations. Its priority‐driven, sequential satisfaction of control objectives leads to a modular, hierarchical structure of controllers with specific objectives. The modular character of MMC allows the explicit maintenance, tuning, and reconfiguration of multivariable control systems, while its hierarchical structure explicitly expresses engineering decisions and trade‐offs. Its static design incorporates uncertainty in process gains and automatic reconfiguration to account for failure in sensors and/or actuators. The design of an MMC for a heavy oil fractionator is presented to illustrate the controller's character and the proposed methodology for the design of static MMCs.
Nonlinear control of a batch polymerization reactor: An experimental study
Authors: Soroush Masoud , Kravaris Costas 
Published: June 2004

AbstractThis work studies the experimental application of the globally linearizing control (GLC) method to a batch polymerization reactor. The nonlinear controller is implemented on a microcomputer to start up the reactor and then track a precalculated optimal temperature profile. The reactor temperature is controlled by manipulating two coordinated inputs: power to an electrical heat and cooling water flow rate. A reduced‐order observer is used to estimate the concentration of initiator and monomer. Systematic tuning guidelines are proposed for the nonlinear control method. The experimental results show the excellent servo and regulatory performance of the nonlinear controller in the presence of modeling and observer initialization errors and active manipulated input constraints. Furthermore, in comparison to a conventional PID controller, the performance of the nonlinear controller is significantly superior, and its tuning is much easier.
Separation regions and processes of zeotropic and azeotropic ternary distillation
Authors: Stichlmair Johann G. , Herguijuela Juan‐Ramon 
Published: June 2004

AbstractThe rigorous calculation of top and bottom fractions of a multicomponent distillation is very time consuming and involved as it can only be done iteratively, and convergence problems are often encountered, especially in azeotropic systems. This article presents a method for the easy determination of possible top and bottom fractions of a ternary distillation. This method, which works for zeotropic as well as for azeotropic mixtures, is especially useful in the first steps of process synthesis and design since impossible separations can be determined and thus excluded from further analysis so that work can be concentrated on feasible processes. A very important application of the method developed in this article is to the design and analysis of processes for complete separation of binary azeotropic mixtures by use of an entrainer (for example, Azeotropic Distillation and Extractive Distillation). Knowledge of the separation regions in the distillation diagram allows for the development of a generalized process and the formulation of criteria for entrainer selection. The effectiveness of the method is demonstrated on a number of industrial important processes.
Real‐time qualitative analysis of the temporal shapes of (bio) process variables
Authors: Konstantinov Konstantin B. , Yoshida Toshiomi 
Published: June 2004

AbstractOne of the limitations of today's knowledge‐based (KB) systems for diagnostics and supervision is a lack of adequate temporal reasoning mechanisms. Most of these systems are designed primarily to operate with the current values of the process variables and, sometimes, with their derivatives. Such simple capabilities, however, are not always sufficient to identify some complex dynamic phenomena, which in many cases leave their own unique “stamp” on the process behavior, expressed in the form of characteristic temporal shapes of the related variables. To detect and diagnose adequately the events of interest, the KB system should be able to reason about the temporal shapes of the process variables. Although during manual supervision process operators rely heavily on such characteristic shapes as reliable symptoms of underlying phenomena, their exploitation has not been considered seriously by the designers of KB control systems. We propose a generic methodology for qualitative analysis of the temporal shapes of continuous process variables designed to be embedded into a real‐time KB environment. It is applicable to bioprocesses, as well as to other complex dynamic systems.