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Showing papers in "Aiche Journal in 1985"


Journal ArticleDOI
TL;DR: A general framework for analyzing flexibility in chemical process design is presented in this paper, which measures the size of the parameter space over which feasible steady-state operation of the plant can be attained by proper adjustment of the control variables.
Abstract: One of the key components of chemical plant operability is flexibility—the ability to operate over a range of conditions while satisfying performance specifications. A general framework for analyzing flexibility in chemical process design is presented in this paper. A quantitative index is proposed which measures the size of the parameter space over which feasible steady-state operation of the plant can be attained by proper adjustment of the control variables. The mathematical formulation of this index and a detailed study of its properties are presented. Application of the flexibility in design is illustrated with an example.

479 citations


Journal ArticleDOI
TL;DR: In this paper, a new procedure for synthesizing process flow sheets and base-case designs has been developed, which is evolutionary in nature and proceeds through a hierarchy of decision levels, where more fine structure is added to the flow sheet at each decision level.
Abstract: A new procedure for synthesizing process flow sheets and base-case designs has been developed. The procedure is evolutionary in nature and proceeds through a hierarchy of decision levels, where more fine structure is added to the flow sheet at each decision level. Heuristics are used to obtain some of the structural elements of the flow sheet, and other heuristics are used to make some of the decisions required at the various decision levels. In many cases, no heuristics are available, so that process alternatives are generated. The analysis protion of the procedure has strong focus on the economic tradeoffs that are associated with the significant design variables.

337 citations


Journal ArticleDOI
TL;DR: In this article, the hydrodynamics of cocurrent gas-liquid flow in packed beds is analyzed by extending the concept of relative permeability to the inertial regime, where the relative permeabilities of the gas and liquid phases are functions of the saturation of the liquid phase.
Abstract: The hydrodynamics of cocurrent gas-liquid flow in packed beds is analyzed by extending the concept of relative permeability to the inertial regime. The relative permeabilities of the gas and liquid phases are functions of the saturation of the liquid phase. These functions are found from an analysis of experimental data. The relations obtained are used to develop empirical correlations for predicting liquid holdup and pressure drop in gas-liquid cocurrent downflow in packed beds over a wide range of operating conditions. The correlations proposed give very good results when compared to experimental data yielding, in general, mean relative deviations lower than existing correlations. In addition, a new equation is proposed for predicting static holdup in packed beds which is based on a more physically realistic characteristic length than that used in previous studies.

276 citations


Journal ArticleDOI
TL;DR: In this paper, a method for predicting the film height and interfacial friction factor is presented for situations in which the liquid film flow rate is known, and a new measurement method for the height and pressure drop for vertical gas-liquid annular flows is presented.
Abstract: New measurements are presented for film height and pressure drop for vertical gas-liquid annular flows. Improved methods for predicting the film height and interfacial friction factor are developed for situations in which the liquid film flow rate is known.

270 citations


Journal ArticleDOI
TL;DR: In this article, two types of algorithms are proposed which rely on the assumption that critical points for feasible operation lie at vertices or extreme values of the uncertain parameters, and they are applied to several example problems to demonstrate both the use of the flexibility index in process design and the computational efficiency of the algorithms.
Abstract: Procedures for the numerical computation of an index for operational flexibility in chemical processes are considered. Two types of algorithms are proposed which rely on the assumption that critical points for feasible operation lie at vertices or extreme values of the uncertain parameters. The first algorithm is a direct search procedure that features a heuristic variant to avoid exhaustive enumeration of all vertices. The second algorithm employs an implicit enumeration scheme based on a lower bound for monotonic constraints. These algorithms are applied to several example problems to demonstrate both the use of the flexibility index in process design and the computational efficiency of the algorithms.

254 citations


Journal ArticleDOI
TL;DR: In this paper, the authors measured the rates of calcination of two types of limestones, ranging in particle size from 1 to 90 μm, over the temperature range 516 to 1,000°C.
Abstract: The rates of calcination of two types of limestones, ranging in particle size from 1 to 90 μm, were measured over the temperature range 516 to 1,000°C. A kinetic model based on the B.E.T. (Brunauer-Emmett-Teller method) surface area of the CaCO3 correlates the results over 5 orders of magnitude in reaction rate. The B.E.T. surface area of CaO formed by rapid calcination in dispersed-particle systems is 50 to 90 m2/g.

246 citations


Journal ArticleDOI
TL;DR: In this paper, longitudinal and lateral dispersion coefficients were measured at various axial positions in a packed bed in the Peclet number range from 102 to 104, and three different types of packings were used: uniform size particles, a narrow size distribution, and a wide size distribution.
Abstract: Longitudinal and lateral dispersion coefficients were measured at various axial positions in a packed bed in the Peclet number range from 102 to 104. Three different types of packings were used: uniform size particles, a narrow size distribution, and a wide size distribution. For the case of uniform particles the longitudinal dispersivities were found to be strong functions of position in the bed unless the dispersion length satisfies a constraint dependent on the value of the Peclet number. Generally, the larger the Peclet number, the larger the required length for constant axial dispersivities to be achieved. For the case of the wide size distribution, longitudinal dispersivities were larger than in the uniform particle case, and they required a longer dispersion length to achieve a constant value. This suggests a characteristic length for dispersion larger than the mean hydraulic radius. The lateral dispersivities were found to be insensitive to the distribution of particle sizes or location in the bed.

246 citations


Journal ArticleDOI
TL;DR: In this paper, the authors derived a nonlinear two-wave equation for long waves on the surface of vertical falling liquid films, valid within a range of moderate Reynolds numbers and reduced in some cases to other well-known equations.
Abstract: The method of integral relations is used to derive a nonlinear two-wave equation for long waves on the surface of vertical falling liquid films. This equation is valid within a range of moderate Reynolds numbers and and be reduced in some cases to other well-known equations. The theoretical results for the fastest growing waves are compared with the experimental results concerning velocities, wave numbers, and growth rates of the waves in the inception region. The validity of the theoretical assumptions is also confirmed by direct measurements of instantaneous velocity profiles in a wave liquid film. The results of the experimental investigation concerning nonlinear stationary waves and the evolution of initial solitary disturbances are presented.

245 citations


Journal ArticleDOI
TL;DR: A comprehensive review of fundamental gas-liquid-solid fluidization behavior can be found in this article, where the authors discuss the areas in which current knowledge is deficient and further research is needed.
Abstract: The successful design and operation of a gas-liquid-solid fluidized-bed system depend on the ability to accurately predict the fundamental properties of the system, specifically, the hydrodynamics, the mixing of individual phases, and the heat and mass transfer properties. Identification of the flow regimes under which the system operates is crucial to an understanding of both the variations of these properties and overall system performance. This timely, comprehensive review describes in a systematic manner the status of fundamental gas-liquid-solid fluidization behavior. This review also discusses the areas in which current knowledge is deficient and further research is needed.

239 citations


Journal ArticleDOI
TL;DR: In this article, a computer-aided particle tracking facility was used to measure solids motion in a fluidized bed, where a radioactive tracer particle was mixed with the solids in the bed and the gamma radiation from the tracer was continuously monitored by a large number of scintillation detectors located around the bed.
Abstract: Measurements of solids motion in a fluidized bed have been made in a computer-aided particle tracking facility. A radioactive tracer particle, dynamically identical to the solid particles to be studied, was mixed with the solids in thebed. The gamma radiation from the tracer was continuously monitored by a large number of scintillation detectors located around the bed, providing information on the tracer's instantaneous location. Prudent use was made of the purposely introduced redundant distance data to achieve improved accuracy. The recognition of the existence of secondary emission due to the interaction of the primary radiation and other system materials and the subsequent devising of a scheme to mitigate its effect contribute much to the success. Results for a bed with a uniform air distributor plate show the existence of two counter-rotating toroidal vortices whose relative sizes and strengths vary with the fluidizing velocity. Fluctuating motions at low frequencies ranging from 1.6 to 16 Hz have been observed at various locations in the bed.

212 citations


Journal ArticleDOI
TL;DR: In this article, a nonequilibrium stage model is developed for the simulation of countercurrent multicomponent separation processes, where the component material and energy balance relations for each phase together with mass and energy transfer rate equations and equilibrium equations for the phase interface are solved to find the actual separation directly.
Abstract: A nonequilibrium stage model is developed for the simulation of countercurrent multicomponent separation processes. A feature of the model is that the component material and energy balance relations for each phase together with mass and energy transfer rate equations and equilibrium equations for the phase interface are solved to find the actual separation directly. Computations of stage efficiencies are entirely avoided. A procedure for solving the model equations simultaneously using Newton's method is outlined.

Journal ArticleDOI
TL;DR: A modification of van der Waals and Platteeuw's hydrate equilibrium model which incorporates the effect of spherical asymmetry is developed in this paper, where a corresponding states correlation is used to predict the deviation of Langmuir constants from ideal values.
Abstract: A modification of van der Waals and Platteeuw's hydrate equilibrium model which incorporates the effect of spherical asymmetry is developed. A corresponding states correlation is used to predict the deviation of Langmuir constants from ideal values. In this model the Kihara parameters obtained from hydrate equilibrium data agree well with those obtained from virial coefficient data.

Journal ArticleDOI
TL;DR: In this paper, Tsonopoulos and Wilson extended this analysis to the mutual solubilities of three C8 hydrocarbons (ethylbenzene, ethylcyclohexane, n-octane) and water, which have been measured at the three phase equilibrium pressure up to the critical temperatures (568, 561 and 539 K, respectively).
Abstract: In Part I (Tsonopoulos and Wilson, 1983), the mutual solubilities of three C6 hydrocarbons (benzene, cyclohexane, n-hexane) and water were experimentally investigated and, together with critically selected literature data, were correlated up to the three-phase critical end point. The present paper extends this analysis to the mutual solubilities of three C8 hydrocarbons (ethylbenzene, ethylcyclohexane, n-octane) and water, which have been measured at the three-phase equilibrium pressure up to the critical temperatures (568, 561 and 539 K, respectively). A thermodynamic analysis of these new measurements and of available literature data has been performed up to the three-phase critical end point. Information is also provided on vapor-phase equilibrium compositions. The solubility of hydrocarbons in water has been used to calculate Henry's constants, while the solubility and volatility of water in hydrocarbons has been successfully correlated with several modifications of the Redlich-Kwong equation of state.

Journal ArticleDOI
TL;DR: In this article, the problem of distillation sequence synthesis with heat integration is formulated and solved as a mixed integer linear superstructure optimization problem, and two alternatives for generating a superstructure are shown, then a formulation is presented which approximates the synthesis problem as a Mixed Integer Linear Programming (MILP) problem.
Abstract: In this paper the problem of distillation sequence synthesis with heat integration is formulated and solved as a mixed integer linear superstructure optimization problem. Allowing both conventional and multieffect distillation, two alternatives for generating a superstructure are shown, then a formulation is presented which approximates the synthesis problem as a mixed integer linear programming (MILP) problem. Examples illustrate the method. Reported computer times suggest that earlier algorithmic methods for discovering the better sequences among those allowed by the problem formulation, and without the option of multieffecting, are an order of magnitude slower than this approach.

Journal ArticleDOI
TL;DR: In this paper, a mathematical model is developed to describe the process of thermal regeneration in diesel-particulate monolithic filters, and the model shows that a typical regeneration cycle consists of four stages: preheating, ignition, transport-controlled combustion, and cooling.
Abstract: A mathematical model is developed to describe the process of thermal regeneration in diesel-particulate monolithic filters. The model shows that a typical regeneration cycle consists of four stages: preheating, ignition, transport-controlled combustion, and cooling. The total regeneration time and the peak temperature are the important regeneration characteristics and can be controlled by initial particulate loading, total filtration area, and channel wall thickness.

Journal ArticleDOI
TL;DR: In this paper, a computer model for a hot fluidized bed was developed and the large heat transfer coefficients characteristic of fluidized beds were computed without an enhancement of heat transfer by turbulence.
Abstract: A computer model for a hot fluidized bed was developed. The large heat transfer coefficients characteristic of fluidized beds were computed without an enhancement of heat transfer by turbulence. They agreed with measurements reported by Ozkaynak and Chen (1980) within the accuracy of estimated thermal conductivity of solids.

Journal ArticleDOI
TL;DR: In this article, the authors describe a procedure for the diffusion of charbon actifs in a mixture of 50/50 H 2 /CH 4 and CH 4 in deux produits de plus de 90% purete.
Abstract: Etude theorique et experimentale. En faisant varier de facon cyclique la pression d'un lit de charbon actif entre 3 et 500 psig (0,021 a 3,445 MPa), a la temperature ambiante, un melange 50/50 H 2 /CH 4 est separe en deux produits de plus de 90% de purete. Toutes les caracteristiques du procede peuvent etre predites par un modele de diffusion dans les pores

Journal ArticleDOI
TL;DR: In this paper, the vacancy solution model of adsorption in conjunction with the Flory-Huggins activity coefficient equations was used to predict gas-mixture equilibria better than any other model.
Abstract: New equations for the physical adsorption of gases on solids have been developed based on the vacancy solution model of adsorption in conjunction with the Flory-Huggins activity coefficient equations. The isotherm equation contains three regression parameters: a Henry's law constant, the limiting amount of adsorption, and a gas-solid interaction term. Pure-gas data over a range of temperature can be correlated using only five parameters. Gas-mixture equilibria can be predicted using only the parameters obtained from the pure-gas data. Pure-component, binary, and ternary adsorption equilibrium data on activated carbons, silica, and zeolites over a wide range of conditions have been used to evaluate the model. The results show that, except for a few systems, this model predicts gas-mixture equilibria better than any other model.

Journal ArticleDOI
TL;DR: In this article, the kinetics of carbon dioxide with mono-and diethanolamine in such nonaqueous solvents as methanol, ethanol, and 2-propanol and in water were studied using a stirred tank absorber with a plane gas-liquid interface at 303 K.
Abstract: The kinetics of the reaction of carbon dioxide with mono- and diethanolamine in such nonaqueous solvents as methanol, ethanol, and 2-propanol and in water were studied using a stirred tank absorber with a plane gas-liquid interface at 303 K. The reaction was found to be of first order with respect to carbon dioxide for every solvent. The order of reaction with respect to ethanolamine was found to be unity only for an aqueous solution of monoethanolamine and for the other solutions, ranged from 1.4 to 2, depending on the solvent species. The reaction order was increased in the order of water, methanol, ethanol, and 2-propanol. The variation of the reaction order with the solvent species could be explained in terms of a reaction scheme via a zwitterion. Almost linear dependence of the logarithm of the reaction rate constant on the solubility parameter of the solvent was derived.

Journal ArticleDOI
TL;DR: In this article, the authors studied the freeze-drying process under various operational policies through the use of a sorption-sublimation model and showed that the criterion used in terminating the freeze drying process is of extreme importance since it may lead to an undesirable water profile which may deteriorate the quality of the dried product.
Abstract: The freeze-drying process is studied under various operational policies through the use of a sorption-sublimation model. The operational policy that provides the shortest drying times keeps the pressure at its lowest value. The upper and lower heating plates are independently controlled so that the material constraints are encountered and held throughout the free water removal phase. Under certain conditions, and for the case of samples of small thickness, the sorbed water profiles may have segments whose bound water concentrations are higher than those at the start of the free water removal phase. It is shown that the criterion used in terminating the freeze-drying process is of extreme importance, since it may lead to an undesirable sorbed water profile which may deteriorate the quality of the dried product.

Journal ArticleDOI
TL;DR: In this article, a nonequilibrium stage model of countercurrent separation processes is used to predict composition and temperature profiles during binary and multicomponent distillation in wetted-wall and bubble-cap-tray columns.
Abstract: A nonequilibrium stage model of countercurrent separation processes is used to predict composition and temperature profiles during binary and multicomponent distillation in wetted-wall and bubble-cap-tray columns. The profiles predicted by the model are compared with experimental data for the binary systems benzene-toluene, ethanol-water, and acetone-chloroform and for the ternary systems benzene-toluene-ethylbenzene, acetone-methanol-water, methanol-isopropanol-water, acetone-methanol-ethanol, and benzene-toluene-m-xylene. The model does a very commendable job of predicting the composition profiles measured for these systems; average absolute differences between predicted and measured mole fractions are seldom greater than 4 mole percent and are often very much less.

Journal ArticleDOI
TL;DR: On etudie les ecoulements ascendants et descendants de bulles dans un tube de 100 mm de diametre, afin de voir si le meme modele mathematique s'applique dans les deux cas as discussed by the authors.
Abstract: On etudie les ecoulements ascendants et descendants de bulles dans un tube de 100 mm de diametre, afin de voir si le meme modele mathematique s'applique dans les deux cas

Journal ArticleDOI
TL;DR: In this paper, a lower bound on the utility use for single distillation tasks and for distillationsequences is derived for designs involving simple two product columns that may or may not be multieffected.
Abstract: In this paper a new method is presented which will enable engineers toselect better heat integrated distillation systems quickly and easily. The keyto this method is making the assumption that OAT, the product of thecondenser or reboiler duty and the temperature difference between the reboilerand condenser, is constant for a single distillation task over a wide range ofpressures. Using this assumption and the principles of multieffect distillation,a lower bound on the utility use for single distillation tasks and for distillationsequences is readily calculated for designs involving simple two productcolumns that may or may not be multieffected. This paper also describesmethods which can be used to synthesize distillation systems which approachthese bounds. Finally, an algorithm is presented which develops the least costdistillation system for separating a multicomponent feed. The methods in thispaper are illustrated with a five component example problem.UNIVERSITY LIBK/kRIESCARNEGIE-MELLON UNIVERSITYPITTSBURGH. PENNSYLVANIA 15?13

Journal ArticleDOI
TL;DR: In this paper, a robust version of the self-tuning regulator is developed, which requires relatively little knowledge of system characteristics (estimated order of transfer function polynomials and an upper bound for transportation delays).
Abstract: A robust version of the self-tuning regulator is developed. The regulator, which requires relatively little knowledge of system characteristics (estimated order of transfer function polynomials and an upper bound for transportation delays), has been shown to yield stable control and convergence for linear, time-invariant systems. Simulations and practical tests on a large pilot-scale process have shown that the inclusion of a variable forgetting factor and an “extended horizon” control criterion provides the regulator with a sufficient degree of robustness and flexibility to perform well in a nonlinear time-varying environment. The regulator makes use of intuitively easy-to-understand concepts and leaves few degrees of freedom for the potential user. Furthermore, extensive experiments and simulation studies have shown it to be insensitive to choice of initial conditions and dynamic characteristics set by the user.

Journal ArticleDOI
TL;DR: In this paper, the effect of liquid viscosity on the initiation of roll waves in a horizontal gas-liquid flow is analyzed by an analysis based on the calculation of the growth of long wavelength disturbances.
Abstract: Measurements of the effect of liquid viscosity on the initiation of roll waves in a horizontal gas-liquid flow are presented. These results are interpreted by an analysis based on the calculation of the growth of long wavelength disturbances.

Journal ArticleDOI
TL;DR: In this paper, experimentally determined char-air reaction rates and corresponding pore structures are compared to assess the applicability of a previously proposed random pore model and to extract pertinent chemical and physical parameters.
Abstract: Prior studies have demonstrated that char gasification rates vary with conversion, showing a maximum at an intermediate level. In this work experimentally determined char-air reaction rates and corresponding pore structures are compared to assess the applicability of a previously proposed random pore model and to extract pertinent chemical and physical parameters. Results on six different chars are presented and analyzed to obtain structure parameters, intrinsic kinetics, and activation energies. Agreement between two independent evaluations of the structure parameters demonstrates the degree of applicability of the random pore model and supports the view that rate variations with conversion are controlled by pore structural changes, even though overall rates also include contributions of intrinsic reactivity.

Journal ArticleDOI
TL;DR: In this paper, a water-filled sandstone was heated in microwaves and its drying rates and temperature profiles were measured, and a theoretical model was extended to predict the heat and mass transfer phenomena in microwave-heated porous materials.
Abstract: Our previous theoretical model was extended to predict the heat and mass transfer phenomena in microwave-heated porous materials. A water-filled sandstone was heated in microwaves and its drying rates and temperature profiles were measured. Predictions agree well with observations. Besides moisture loss rates and temperature profiles, the model also predicts local moisture content, gas densities, and pressure. These latter quantities were not measured in our work, but are of interest since they reveal the basic mechanisms of heat and mass transfer in internally heated porous media.

Journal ArticleDOI
TL;DR: A strategy for synthesizing regulatory control structures is developed within the framework provided by singular value decomposition (SVD).
Abstract: A strategy for synthesizing regulatory control structures is developed within the framework provided by singular value decomposition (SVD). Quantitative measures of interaction and sensitivity for the nodes, as well as for the entire system, are established with this method. The approach enables analysis of the control struture over a range of frequencies which are of practical importance for a particular processing unit, thus insuring that both static and dynamic effects are encompassed. In addition, this method allows the designer to identify the modeling aspects which are important in determining the performance of the synthesized control structures. A series of examples, presented in order of increasing complexity, demonstrate the usefulness and versatility of this procedure. The technique is implemented as an interactive computer package.

Journal ArticleDOI
TL;DR: In this article, a gas membrane is used to remove volatile solutes like hydrogen sulfide and sulfur dioxide from dilute aqueous solutions, supported by microporous hydrophobic hollow fibers.
Abstract: Gas membranes can be used to rapidly remove volatile solutes like hydrogen sulfide and sulfur dioxide from dilute aqueous solutions. The gas membranes are supported by microporous hydrophobic hollow fibers. The aqueous feed containing the volatile component flows down the fiber lumen, and an aqueous stripping solution bathes the outside fiber surface. Thus the membrane consists of gas trapped in the hydrophobic pores. The fluxes across these membranes, which can be much faster than those across polymer films, are consistent with a nonlinear mechanism which includes solute ionization.

Journal ArticleDOI
TL;DR: In this paper, a fine powder in a 0.15 m ID expanded top fluid bed with a ferromagnetic tracer was used to investigate solids mixing of a group.
Abstract: This study investigated solids mixing of a group A fine powder in a 0.15 m ID expanded top fluid bed with a ferromagnetic tracer. The superficial gas velocity was raised from 0.075 to 1.1 m/s, causing the bed to go through bubbling, slugging, and turbulent fluidization regimes. A countercurrent flow model described the data well at low gas velocities. The bed assumed a more homogeneous appearance at higher gas velocities; a one-dimensional axial dispersion model was used to correlate the data. Axial dispersion coefficients increased with gas velocity. The data agree well with literature data for low gas velocities.