Showing papers in "Aiche Journal in 1978"

Synthesis of heat exchanger networks: I. Systematic generation of energy optimal networks

Abstract: A thermodynamically orientated method is presented for the synthesis of heat exchanger networks. With this method, the problem is solved in two stages. In the first stage, preliminary networks are generated which give maximum heat recovery. In the second stage, the most satisfactory final networks are evolved using the preliminary networks as starting points. In this paper, emphasis is given to the synthesis of the preliminary networks. Two four-stream examples are solved. In Part II, emphasis will be given to the synthesis of final networks.

Vapor‐liquid equilibria in multicomponent aqueous solutions of volatile weak electrolytes

Abstract: A molecular-thermodynamic correlation is established for calculating vapor-liquid equilibria in aqueous solutions containing one or more volatile electrolytes: ammonia, carbon dioxide, hydrogen sulfide, sulfur dioxide, and hydrogen cyanide. The correlation is similar to that presented in 1975, but the domain of application has been increased. The present correlation holds from about 0° to 170°C and for ionic strengths of about 6 molal; for the weak electrolytes considered here, this corresponds to total concentrations between 10 and 20 molal. To represent activities at these high concentrations, activity coefficients are expressed as a function of molality by Pitzer's equation. Required parameters are estimated from data reduction or from correlations. Special attention is given to the ternary systems ammonia-carbon dioxide-water and ammonia-hydrogen sulfide-water. Calculated equilibria are in satisfactory agreement with the severely limited experimental data now available.

Hydrodesulfurization of dibenzothiophene catalyzed by sulfided CoO-MoO3γ-Al2O3: The reaction network

Abstract: Kinetics experiments have determined the reaction network in the hydrodesulfurization of dibenzothiophene catalyzed by sulfided CoO-MoO3/γ-Al2O3 at 573°K and 102 atm The predominant reaction is a direct sulfur extrusion, giving biphenyl and hydrogen sulfide; the biphenyl is subsequently hydrogenated slowly to give cyclohexylbenzene and then bicyclohexyl Dibenzothiophene also undergoes a primary hydrogenation reaction preceding sulfur removal, but it is about one thousand times slower than the sulfur extrusion reaction

Evaluation of parameters for nonlinear thermodynamic models

Abstract: A method based on the maximum likelihood principle has been developed for the determination of model parameters from experimental data when all the measured variables are subject to error. In addition to the best estimates of the parameters, this method also yields information useful in selection of appropriate models and evaluation of the accuracy of the data. Application of the method is illustrated in the reduction of binary vapor-liquid equilibrium data.

Parametric studies in industrial distillation: Part I. Design comparisons

Abstract: Minimum cost surfaces compare eight distillation systems separating ternary feeds. The regions of optimality for various designs depend upon the species separated, but changes in feed composition have characteristic effects on the relative costs. These characteristic effects can be used to generate heuristics in the form of expected regions of optimality, based on composition and simple physical properties. The expected effects, however, are somewhat uncertain, because the costs of designs depend upon many variables in a complex way. Of all factors considered, the vapor requirements for a tower are perhaps the most important, but the tower operating pressure and the required tower should also be considered.

Perturbed hard chain theory for fluid mixtures: Thermodynamic properties for mixtures in natural gas and petroleum technology

Abstract: Perturbed-hard-chain theory for pure fluids, proposed previously by Beret, is modified slightly to yield better pure-component results. More important, it is extended to multicomponent mixtures. The perturbed-hard-chain theory is a synthesis of the polymer solution theories of Flory and Prigogine and the perturbed-hard-sphere theories of Alder and Barker and Henderson. The resulting equation of state is applicable to simple as well as complex molecules (for example, heptane, naphthalene, polystyrene). It can be used to calculate both gas and liquid phase properties. Extension of perturbed-hard-chain theory to mixtures is based on a one-fluid model without, however, making the usual assumption of random mixing. The perturbed-hard-chain theory has been applied to most fluids commonly encountered in natural-gas and petroleum refining operations. The theory gives good agreement with experiment for pure-component and fluid-mixture properties including vapor pressures, liquid densities, enthalpies, and K factors. Molecular parameters have been obtained for forty-five pure components and for more than sixty binary mixtures. Ternary and higher mixtures require no additional parameters.

Internal boiling and superheating in vaporizing multicomponent droplets

Abstract: The vaporization and combustion of a miscible multicomponent droplet in a quiescent atmosphere is analyzed by assuming transient-diffusive transport within the droplet, quasi steady diffusive-convective transport in the gas phase, and ideal solution behavior for the mixture. Results on the vaporization of a binary droplet show that owing to the significant liquid phase diffusional resistance, the vaporization process approximately consists of an initial transient regime, an intermediate, diffusion limited, almost quasi steady regime, and a final volatility limited regime. It is further demonstrated that the entrapment of the volatile components within the rapidly heated droplet interior may lead to the initiation of either homogeneous or heterogeneous nucleation, which can result in the fragmentation of the parent droplet with the internal pressure buildup.

Synthesis of heat exchanger networks: II. Evolutionary generation of networks with various criteria of optimality

Abstract: An evolutionary method is presented for the synthesis of heat exchanger networks. Starting from feasible solutions which preferably exhibit maximum energy recovery,1 the method allows systematic promotion of desired design features such as low overall cost, suitability for starting-up procedures, observation of safety constraints, etc. Seven examples based on standard literature problems are used to illustrate the method.

Inferential control of processes: Part I. Steady state analysis and design

Abstract: Methods are presented for the design of a static estimator which infers unmeasurable product qualities from secondary measurements. The secondary measurements are selected so as to minimize the number of such measurements required to obtain an accurate estimate which is insensitive to modeling errors. Unlike previous work, the number of secondary measurements can be fewer than the number of unmeasured disturbances. If the statistics of the disturbances and/or measurement noise are available, this information can be incorporated into the design procedure to obtain an optimal static estimator. The design procedure is illustrated by application to a simulated industrial debutanizer. Data for the simulation were supplied by the Marathon Oil Company. Deviations in bottoms product quality are compared for the current control policy (maintenance of a stage temperature at its set point) and the inferential control system with the column subjected to representative feed composition disturbances. Results show that inferential control based on four, five, or six tray temperature measurements improves the steady state control performance by as much as 400%.

Optimum design of chemical plants with uncertain parameters

Abstract: A new strategy is proposed for the optimum design of chemical plants whose uncertain parameters are expressed as bounded variables. The design is such that the plant specifications will be met for any feasible values of the parameters while optimizing a weighted cost function which reflects the costs over the expected range of operation. The strategy is formulated as a nonlinear programme, and an efficient method of solution is derived for constraints which are monotonic with the parameters, a case which arises frequently in practice. The designs of a pipeline with a pump, of a reactor-separator system, and of a heat exchanger network, all with uncertain technical parameters, illustrate the effectiveness of the strategy for rational overdesign of a chemical plant.

A model for moving‐bed coal gasification reactors

Abstract: A steady state model of moving-bed coal gasification reactors has been developed. Model predictions are in agreement with published commercial plant data for Lurgi pressurized gasification reactors and a pilot plant slagging gasifier. The dependence of reactor performance on operating variables has been studied for Illinois and Wyoming coals. For a given coal, maximum efficiency is determined by the coal-to-oxygen feed ratio. The location of the maximum temperature, which defines the combustion zone, is an important operating variable. Efficient operation of the dry ash reactor cannot be carried out below a critical feed gas temperature because of insufficient gasification and excessive carbon loss in the ash.

The design of gas sparged devices for viscous liquid systems

Abstract: Design procedures for gas sparged contractors for both low and high viscosity liquids were developed to predict overall kLa. Bubble size close to the orifice, for moderately high gas rates, was found to increase at a rate proportional to one third power of gas rate and one tenth power of liquid viscosity. Bubble breakup phenomenon was shown to be related to liquid turbulence in the vessel rather than gas turbulence in the orifice. Procedures were developed through a simple liquid circulation model to obtain a criterion for the onset of bubble breakup. Results indicate that intense liquid mixing and high interfacial area can be achieved in low viscosity liquids by gas sparging alone. In high viscosity fluids, bubble breakup was not observed. The liquid circulation model predicts laminar flow at these experimental conditions over the complete range of gas rates observed.

Underground coal gasification

Abstract: Underground coal gasification (UCG) is a method whereby the mining and conversion of coal are accomplished in a single step. Many field tests of UCG have been operated worldwide since the 1930's with varying degrees of success; based on this experience (especially in the USSR and US), a field design which is applicable to a wide range of geological conditions and coal properties has evolved. This review discusses the rationale of this design and provides a physicochemical interpretation for the operation of a UCG system. Pertinent field and laboratory results as well as formal mathematical models of an in-situ gasifer are evaluated as part of the analysis. 158 references.

A new thermodynamic representation of binary electrolyte solutions nonideality in the whole range of concentrations

Abstract: A system of equations based on the ionic atmosphere theory of Debye and Huckel, Born model contribution, and local compositions of the nonrandom two-liquid (NRTL) model is developed to represent isothermal activity coefficients, in the whole range of concentrations, for solutions in an undissociated solvent of a partially or completely dissociated electrolyte. The physical constants and the four adjustable parameters necessary to represent the osmotic coefficient, for fifteen strong aqueous electrolytic solutions, are given at 298.15°K and atmospheric pressure. Vapor-liquid equilibrium, for the hydrochloric acid-water system at 298.15°K, is represented for acid compositions ranging from infinite dilution to 18 M using a known dissociation constant and six parameters.

Particle turbulent diffusion in a dust laden round jet

Abstract: The turbulent diffusion mechanism of particles in a round air jet are studied both theoretically and experimentally, with particular attention to the relative velocity between particles and fluid, overshooting effect of particles, and the distributions of fluid properties in space. The results indicate that the particle diffusivity decreases with the increase of the particle inertia. In general, the turbulent diffusivity of particles in an air jet is smaller than that of fluid scalar quantities. The particle inertia and the fluid large eddies, which are expressed by the Stokes number and the integral scale, respectively, play an important role in the transport mechanism of particles.

Backmixing in gas‐liquid reactors

Abstract: This review evaluates the present state of the art on backmixing in gas-liquid and gas-liquid-solid reactors. A brief outline of numerous techniques for measuring residence time distribution (RTD) of various phases in a multiphase reactor is presented. This is followed by a brief description of differential and stagewise models for characterizing backmixing from RTD measurements. Both simple (that is, single-parameter axial dispersion model) and more complex (that is, two-, three-, or four-parameter models) models are evaluated. Backmixing characteristics of various gas-liquid columns such as trickle beds, spray columns, mechanically agitated columns, plate columns, fluidized bed columns, etc., are subsequently evaluated. The performance of a bubble column under various reaction conditions is analyzed. Criteria for the elimination of backmixing in packed-bed reactors are presented, and the effect of backmixing on the multiple steady states in a gas-liquid reactor is briefly reviewed. Finally, the scale-up problems associated with gas-liquid reactors with various degrees of backmixing and the recommendations for the future work in RTD and macromixing models are outlined.

Droplet size spectra generated in turbulent pipe flow of dilute liquid/liquid dispersions

Abstract: Experiments were carried out with water dispersed in hydrocarbons at various flow rates. The measured size spectra can be well represented by either an upper limit log-probability function or a Rosin-Rammler type of equation with constant parameters and only one variable, the maximum drop diameter dmax or d95. The latter can be predicted satisfactorily by a correlation based on the Hinze/Kolmogorov model of droplet breakup.

Selective copper recovery with two types of liquid membranes

Abstract: Copper can be selectively separated and concentrated by diffusion across liquid membranes. These membranes are effective either as thin films supported by porous polymer sheets or as liquid microcapsules or liquid surfactant membranes.

Semiempirical theory of surface tensions of pure normal alkanes and alcohols

Abstract: A comparison of experimental and theoretical surface tensions leads to a correlation between homogeneous fluid parameters and the inhomogeneous influence parameter c. From this correlation, it is possible to predict, to within excellent agreement with experiment, the surface tensions of normal alkanes and alcohols from bulk data only.

Adsorption rate on molecular sieving carbon by chromatography

Abstract: Diffusivities in the micropore and adsorption equilibrium constants were determined for neon, argon, krypton, xenon, nitrogen, methane, ethylene, ethane, propylene, propane, n-butane, and benzene on molecular sieving carbon by chromatographic measurement and moment analysis. Isosteric heat of adsorption was found to be 2.6 times heat of vaporization for the gases examined here. Two separate linear relations were obtained between activation energies of diffusion in micropore and isosteric heats of adsorption for rare gases, methane, and benzene, and for n-paraffin and n-olefin except methane.

A comprehensive experimental investigation of tubular entry flow of viscoelastic fluids: Part I. Vortex characteristics in stable flow

Abstract: The characteristics of a vortex found at the entry of a 2:1 and 4:1 contraction for viscoelastic fluids is investigated. Two distinct flow regimes are identified in the contraction flow field: a vortex growth regime and a divergent flow regime. In the vortex flow regime, rheological forces are found to dominate the flow, with the vortex detachment length being a linear function of the Weissenberg number. In the divergent flow regime, the flow is found to diverge at the center line upstream of the vortex detachment plane, and the vortex size decreases with increasing flow rates. Inertial forces are important in the divergent flow regime. The entry flow characteristics for the 2:1 and 4:1 contraction are quantified in terms of the vortex detachment length as a function of Reynolds and Weissenberg number over the range of 0:2 < N′Re < 200 and 0.10 < NWS < 0.7.

Prediction of multicomponent ion exchange equilibria for the ternary system SO-NO-Cl from data of binary systems

Abstract: A framework is developed which provides predictions of multicomponent ion exchange equilibria from binary data. Experimental data are reported for the ion exchange equilibria of the binary systems SO42−-Cl−, SO42−-NO3−, and Cl−-NO3− on a strong base anion exchange resin. These systems exhibit nonideal characteristics in both phases, and the experimental characterization has been based on the reaction equilibrium constants and correlations for the activity coefficients in both phases. The exchanger phase activity coefficients are obtained from the well known Wilson (1964) model The predictions of the ternary system SO42−-NO3−-Cl− based solely on the binary data are consistent with the experimental data for this system.

Catalytic hydrogenation of cyclohexene: Part II. Liquid phase reaction on supported platinum in a gradientless slurry reactor

Abstract: The areal rate of liquid phase hydrogenation of cyclohexene on supported platinum catalysts does not depend on the nature of the support. Nor does it depend on particle size of the metal. The rate constant is independent of the nature of the solvent when the concentration of hydrogen in it is expressed as its measured or calculated solubility. All observations are compatible with the idea that the measured rate is that of chemisorption of dihydrogen on a metal surface covered with reactive hydrocarbon intermediates.

Liquid‐solid mass transfer in packed beds with downward concurrent gas‐liquid flow

Abstract: Mass transfer coefficients were determined by measuring the rate of solution of cylindrical 3 or 6 mm benzoic acid tablets into water in the presence of flowing nitrogen, helium, or argon. Gas flow rates varied from 0 to 1.6 kg/(m2·s) and liquid flow rates from 0.5 to 25 kg/(m2·s), resulting in hydrodynamic flow patterns varying from trickle to turbulent pulse types of flow. In the pulse regime, the mass transfer coefficient was markedly affected by gas flow rate but did not depend on gas density explicitly if correlated in terms of an energy dissipation function.

Transient gas-liquid flow in horizontal pipes: Modeling the flow pattern transitions

Abstract: The theory for predicting flow pattern transition under transient flow conditions is developed and compared with experiment. This work represents an extension of the methods presented by Taitel and Dukler (1976) for steady state flows. Under transient conditions, flow pattern transitions can take place at flow rates substantially different than would occur under steady flow conditions. In addition, flow patterns can appear which would not be expected for a slow change in flow rates along that same path. Methods are presented for predicting the flow rates at which flow pattern transitions will take place during flow transients. The method also reveals when spurious flow patterns will appear.

Bubble motion and mass transfer in non-Newtonian fluids: Part I. Single bubble in power law and Bingham fluids

Abstract: The Sherwood number and drag coefficient for a single gas bubble moving in a power law fluid and a Bingham plastic fluid are obtained using perturbation methods The perturbation parameters for power law and Bingham plastic fluids are m (= n – 1/2) and E (= R/U), respectively It is found that in the case of power law fluid, mass transfer and drag increase with increasing pseudoplasticity These theoretical results are found to be in good agreement with the available experimental data and the data obtained in the present study In the case of Bingham plastic fluid, mass transfer and drag are found to increase with increase in the Bingham number NB (= 2e) Contours of plug flow regions, where local stresses are less than the yield stress, are obtained as a function of the Bingham number NB These results qualitatively predict the zero terminal velocity observed for bubble motion in liquids with very high yield stress They are also in good agreement with the trends of the results obtained previously for solid sphere motion in Bingham plastic fluids

Real‐time estimation of aerobic batch fermentation biomass concentration by component balancing

Abstract: Real-time estimates of biomass concentration and growth rate in fermentation processes were obtained by performing a material balance on oxygen and employing a kinetic model for molecular oxygen utilization. A model containing yield and maintenance terms was satisfactory in fermentations where only the EMP and TCA pathways were utilized for glucose metabolism. However, model alterations based on metabolic energetics were required before accurate estimates were obtained for a metabolically complex fermentation producing bakers yeast.

Influence of polymer additives on the gas‐liquid mass transfer in stirred tanks

Abstract: The influence of polymer additives upon the gas-liquid mass transfer in stirred tanks is examined. While the addition of sodium carboxymethyl-cellulose brings about a reduction of the overall liquid side mass transport coefficient which is in line with the predictions by earlier works, the reduction of kLa in polyacrylamide solutions of equal viscosity is much stronger. This is explained by the viscoelasticity of the PAA solutions, and an empirical correlation is proposed.