bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nitrogen pollutant formation in a pulverized coal combustor: Effect of secondary stream swirl
Authors: Harding N. S. , Smoot L. D. , Hedman P. O. 
Published: June 2004

AbstractConcentrations of NO, NH3, and HCN, together with coal particle burnout and gas composition, were measured during combustion of a bituminous coal. Control of incoming secondary gas swirl level and overall stoichiometric ratio led to significant reductions in nitrogen oxide pollutant concentration. In‐situ measurements showed that coal particles were confined near the reactor center during rapid particle reaction. This took place in a locally fuel‐rich environment, producing near‐quantitative conversion of fuel‐nitrogen to NH3 and HCN, with some NO. Subsequent gas phase reactions of these nitrogen species were identified as important in establishing the ultimate NO concentration.
Optical fiber probe transit anemometer for particle velocity measurements in fluidized beds
Authors: Patrose B. , Caram H. S. 
Published: June 2004

AbstractA compact optical fiber probe to measure the velocity of solid particles in two‐phase flows was constructed. The probe has been used to measure particle velocities and obtain flow trajectories of solids in the distributor grid region of a two‐dimensional fluidized bed. Air was used as the fluidizing medium in a bed of glass beads of size ranging form 0.2 to 0.7 mm.Particle velocities were measured at corresponding points within a jet in the two‐dimensional bed, using the optical fiber probe and a Laser Doppler Velocimeter (LDV). The probe measurements compare well with the LDV results in the main jet region. Particle velocities were also measured with the probe in the dense phase region of the fluidized bed where measurements were not possible using LDV. The resulting flow maps clearly indicate solids circulation patterns around jets and identify dead zones formed on the distributor plate.
Approximate solutions to explosion kinetics
Authors: Aiken R. C. 
Published: June 2004

AbstractStiffness in combustion models is quite different from that in more conventional kinetic descriptions. The steady‐state approximation, so useful in other contexts, cannot be applied in the usual ad hoc manner but can be applied with attention to its origins in singular perturbation analysis. The magnitude and time scaling on the equations representing the isothermal kinetics of hydrogen combustion reveal distinct regions of the transient to which this approximation may naturally and successfully be made to reduce computation time. The steady‐state approximation is found to apply to some free radicals, but not all, and these can change between regions. An analytical solution to an important section of the transient is found and illustrates dramatically the power of the approach. The analysis may be applied a priori and leads to a stagewise efficient numerical solution.
Viscoelastic flow from a tube into a radial slit
Authors: Co Albert , Stewart W. E. 
Published: June 2004

AbstractThe viscoelastic flow from a tube into a radial slit between two parallel disks is investigated numerically by orthogonal collocation. A modified ZFD model and a generalized Newtonian fluid, with identical viscosity functions, are investigated. Results for these models indicate that fluid elasticity alters the velocity profiles significantly, but has little effect on the pressure profile in the radial flow region.
Analysis of evaporation of cadmium sulfide for manufacture of solar cells
Authors: Rocheleau R. E. , Baron B. N. , Russell T. W. F. 
Published: June 2004

AbstractVacuum sublimation of cadmium sulfide for manufacture of thin film solar cells was analyzed. The sublimation unit consisted of a two chamber cylindrical source bottle having a rate control orifice and exit nozzle. Coupled heat and mass balance equations were solved using appropriate rate equations for flow in the free molecular‐to‐viscous transition regime. The model equations predicted that heat transfer has a significant effect on sublimation rate. Experiments were carried out over a range of temperatures with several rate control orifices and exit nozzles. Quantitative agreement between measured rates and those calculated from the model equations was obtained.
An improved correlation for densities of compressed liquids and liquid mixtures
Authors: Thomson G. H. , Brobst K. R. , Hankinson R. W. 
Published: June 2004

AbstractThe Tait equation has been extended and generalized to permit the calculation of densities of compressed liquids and their mixtures to a pressure of 68,950 kPa (10,000 psia) using only critical temperature, critical pressure, Soave‐Redlich‐Kwong acentric factor, saturation pressure, and saturated volume for a pure liquid or the corresponding mixture parameters for a liquid mixture. This correlation, together with the correlation developed by Hankinson and Thomson (1979) for saturated liquid densities, comprise COSTALD (COrresponding STAtes Liquid Density), an integrated method for estimating densities of nonpolar and slightly polar liquids and mixtures. The new correlation gave 0.446 average absolute percent error for 6,338 data points for nonpolar liquids, 2.57% error for 1352 data points for polar and quantum liquids, 0.369% error for 319 data points for LNG/LPG mixtures, and 1.61% error for all mixtures tested.
Decomposition strategy for designing flexible chemical plants
Authors: Grossmann I. E. , Halemane K. P. 
Published: June 2004

AbstractOne of the main computational problems faced in the optimal design of flexible chemical plants with multi‐period operation is the large number of decision variables that are involved in the corresponding nonlinear programming formulation. To overcome this difficulty, a decomposition technique based on a projection‐restriction strategy is suggested to exploit the block‐diagonal structure in the constraints. Successful application of this strategy requires an efficient method to find an initial feasible point, and the extension of current equation ordering algorithms for adding systematically inequality constraints that become active. General trends in the performance of the proposed decomposition technique are presented through an example.
Parametric sensitivity and runaway in tubular reactors
Authors: Morbidelli Massimo , Varma Arvind 
Published: June 2004

AbstractParametric sensitivity of tubular reactors is analyzed to provide critical values of the heat of reaction and heat transfer parameters defining runaway and stable operations for all positive‐order exothermic reactions with finite activation energies, and for all reactor inlet temperatures. Evaluation of the critical values does not involve any trial and error.
Distribution for maximum activity of a composite catalyst
Authors: Dadyburjor D. B. 
Published: June 2004

AbstractFor a catalyst composed of a more active component embedded in a less active (but not inert) and more diffuse matrix, an optimum distribution of the active component in the catalyst pellet may lead to significantly higher reaction rates per unit volume of pellet, compared with reaction rates using pellets with a uniformly distributed active component or with an active component concentrated on the outside or the inside of the pellet. The optimum distribution changes qualitatively with the physical parameters of the pellet and with changes in the rate constants and diffusion coefficients of the catalytic compoenents. This is relevant to the performance of coking zeolite/silica‐alumina catalysts in hydrocarbon cracking reactions.
Solution of recycle problems in a sequential modular approach
Authors: Pierucci S. J. , Ranzi E. M. , Biardi G. E. 
Published: June 2004

AbstractRecycle problems in a sequential modular approach are solved by adopting evolutionary models. When describing a process scheme by means of evolutionary models, a nonlinear algebraic system of equations is obtained. The resulting solution is utilized for updating the values of torn variables in the iterative solution of the scheme.
Experimental measurement of the thermal stability criteria for the low pressure methanol synthesis
Authors: Berty J. M. , Lenczyk J. P. , Shah S. M. 
Published: June 2004

AbstractThe mathematical basis was derived for the experimental measurement of the “Slope Condition” and of the “Dynamic Condition” of the thermal stability criteria in a laboratory‐scale internal recycle reactor. This work also resulted in clearer interpretations and simpler expressions for the two stability criteria. The method was experimentally demonstrated on the example of the low pressure methanol synthesis. Only seven experiments were needed to evaluate the stability criteria of this reaction for which the kinetics is unknown.
Time dependence of pressure in a bubbler tube
Authors: Gaigalas A. K. , Robertson Baldwin 
Published: June 2004

AbstractAn experimental and theoretical study is presented of the time dependence of air pressure in a bubbler tube used to measure the liquid level in a tank. The observed time dependence of the air pressure is a superposition of two components. The first component is a repeated slow rise and sudden fall in the air pressure that is associated with bubble growth and breakoff. It is the sudden breakoff that generates the second component consisting of damped oscillations associated with sound waves in the air interacting with an oscillating flow of the liquid. The air pressure during bubble growth is described theoretically. This result is combined with the gas law to predict the functional form of the slow pressure rise; this prediction agrees with experiment. An equation for the oscillation frequencies is derived, solved, and compared with experiment; agreement is within the measurement accuracy of 5%.
Photo‐assisted heterogeneous catalysis with optical fibers. Part III: Photoelectrodes
Authors: Marinangeli R. E. , Ollis D. F. 
Published: June 2004

AbstractThe concept of using optical fibers to distribute light within heterogeneous photo‐assisted catalysts is extended to photo‐electrochemical cells. The potential drop in a semiconductor photo‐electrode is predicted for various types of ohmic electrical contacts, and the optimum contact location is determined. The variation of electrical conductivity with temperature in non‐isothermal bundles of semiconductor‐coated optical fibers is considered.
Mass transfer between a turbulent fluid and a solid boundary: Linear theory
Authors: Campbell J. A. , Hanratt T. J. 
Published: June 2004

AbstractA linear form of the mass balance equation is used to determine how turbulent transport of mass to a solid wall is related to the fluctuating velocity field. It is found that at high Schmidt numbers the Reynolds transport is controlled by fluctuations of much lower frequency than the most energetic velocity fluctuations. The characteristic of the velocity field that emerges as being most important is the small frequency limiting value of the spectral function of the velocity fluctuations normal to the wall. However, the linear theory that is explored does not predict the correct dependency of the average and the mean‐squared deviation of the mass transfer coefficient on Schmidt number. A nonlinear analysis must be performed to examine fully the mechanism of turbulent mass transfer to a solid surface.
Kinetics of absorption of carbon dioxide into aqueous sodium sulfite solutions
Authors: Hikita Haruo , Asai Satoru , Yano Akinori , Nose Haruji 
Published: June 2004

AbstractThe rates of absorption of pure carbon dioxide into aqueous sodium sulfite solutions containing or not containing sodium sulfate were measured at 15, 25, 35 and 45°C and at atmospheric pressure using a liquid‐jet column, a wetted‐wall column, and a quiescent‐liquid absorber. The experimental results were analyzed by the chemical absorption theory based on the penetration model. The second‐order forward rate constants for the reaction between carbon dioxide and sulfite ion in aqueous solutions were calculated and correlated as a function of temperature and ionic strength of the solution. The chemical equilibrium constants for the reaction were also determined from the measurements of the total solubility of carbon dioxide in aqueous sodium sulfite solutions.
Carbon attrition during the fluidized combustion of a coal
Authors: Arena U. , D'Amore M. , Massimilla L. 
Published: June 2004

AbstractThe generation of carbon fines by attrition during the fluidized combustion of a bituminous coal has been studied by means of a 140mm ID fluidized‐bed combustor under variable excess air factor, bed temperature, fluidizing velocity and size of bed sand and coal. Results indicate that rates of attrited fines are roughly proportional to excess of gas velocity above the minimum for fluidization and bed carbon exposed surface. Attrition rate constant is affected by size of sand and, to a less extent, and particularly with finer coal, by bed temperature.
Absorption of sulfur dioxide into aqueous double slurries containing limestone and magnesium hydroxide
Authors: Sada E. , Kumazawa H. , Nishimura H. 
Published: June 2004

AbstractThe absorption of dilute SO2 into aqueous double slurries containing CaCO3 and Mg(OH)2 was carried out using a stirred tank with a plane gas‐liquid interface. The absorption rate increased and finally reached that under the completely gas‐film controlled conditions as the absorption process proceeded. The desulfurization process using the double slurry was formulated by a two‐reaction‐plane model in which there are no particles suspended in‐between the interface and the primary reaction plane. It was suggested from comparison of the experimental absorption rates with the theoretical predictions that 40 to 60% of the absorbed sulfur dioxide may be present as an effective magnesium sulfite ion pair.
Multivariable control of a wet‐grinding circuit
Authors: Hulbert D. G. , Woodburn E. T. 
Published: June 2004

AbstractThe dynamic behavior of a pilot‐plant grinding circuit was modelled by relating three output variables that were representative of the conditions within the mill and the classifier to three input variables, namely feed rates of the solids, mill water, and sump water.A multivariable controller was designed, by the use of Inverse Nyquist Array techniques, for feedback control of the outputs by the inputs, and applied to the plant by a process‐control computer with the use of direct digital control.
Experimental measurements of the effect of viscosity on drag for liquid drops
Authors: Gillaspy P. H. , Hoffer T. E. 
Published: June 2004

AbstractThe drag coefficients of drops of various liquids falling in air were measured experimentally. The drag coefficient was linearly related to the viscosity in the Reynolds number and viscosity range measured. Measurements also suggested there is no difference between Newtonian and non‐Newtonian liquids.
Fault diagnosis in nonlinear chemical processes. Part II. Application to a chemical reactor
Authors: Watanabe K. , Himmelblau D. M. 
Published: June 2004

AbstractA two‐level strategy for fault detection and diagnosis developed in Part I is applied to a chemical reactor in which heptane is converted to toluene. Simulation of various faults demonstrates that the proposed strategy is valid, and that it also represents an improvement over fault diagnosis via an extended Kalman filter.
Reduced‐order steady‐state and dynamic models for separation processes. Part II. Application to nonlinear multicomponent systems
Authors: Cho Y. S. , Joseph B. 
Published: June 2004

AbstractIn Part I, a novel method for reducing the order of models for countercurrent staged separation systems was presented. In this paper, the method is applied to the modeling and simulation of nonlinear multicomponent distillation systems. Some additional properties of the model reduction procedure are derived. The accuracy of the approximation is established by comparison of the steady‐state profiles and transient responses to that of rigorous dynamic models. The results indicate that the proposed technique is an effective way of reducing the number of equations needed to model stagewise multicomponent separation systems.
Interfacial area, bubble coalescence and mass transfer in bubble column reactors
Authors: Miller D. N. 
Published: June 2004

AbstractRelationships are developed for determining interfacial areas as a function of bubble coalescence and for predicting liquid‐film‐controlled mass transfer in deep seal bubble column reactors. Interfacial area is inversely dependent on mean bubble size; the mass transfer constant is directly dependent on bubble size. A correction for enhancement due to liquid‐phase reaction must be applied, and enhancement is shown to decrease with increasing bubble size.Experimental measurements on the catalyzed rate of oxygen absorption from air in aqueous sodium sulfite solutions were made in a 0.299 m diameter × 9.14 m high glass column. Water and aqueous solutions of a surfactant and corn syrup were used to simulate ranges of surface tensions, densities, and viscosities. Perforated plates with 0.00635‐m holes and 2.85% open area were inserted at 1.524‐m spacing on half of the experimental runs to show the effects of gas redispersion. Two‐phase flow velocities were adjusted to cover ranges of interest in full‐scale, commercial bubble column reactor design.
Four environment model of mixing and chemical reaction. Part I. Model development
Authors: Mehta R. V. , Tarbell J. M. 
Published: June 2004

AbstractA new mathematical model (the four environment model) to describe turbulent flow chemical reactors with complex reactions and separate reactant feed streams is developed. The feed stream residence time distributions, the batch chemical kinetics, and a single turbulent micromixing parameter, which may be estimated from direct turbulence theory, are required as input information to the model. The model is computationally efficient as it involves only ordinary differential equations.
PVT analysis of a new cubic‐perturbed, hard‐sphere equation of state
Authors: Martin J. J. 
Published: June 2004

AbstractThe cubic‐perturbed, hard‐sphere equation of state proposed in 1980 by Ishikawa, Chung and Lu, has been analyzed by PVT criteria, as contrasted to the single component and multicomponent vapor‐liquid equilibria to which it was applied. The analysis compares its representation of the PVT behavior of substances with that of a simpler equation.
Modelling of rapidly‐mixed fast‐crosslinking exothermic polymerizations. Part I: Adiabatic temperature rise
Authors: Chella R. , Ottino J. M. 
Published: June 2004

AbstractA lamellar mixing approach has been applied to the modelling of an imperfectly mixed, fast, crosslinking, exothermic polymerization. The model involves the solution of coupled nonlinear partial differential equations representing mass and energy transfer in locally structured lamellar domains with diffusion and reaction occurring between initially segregated lamellae.Several seemingly unusual features of experimental results can be explained qualitatively in terms of this simplified model. The phenomena investigated include: effect of variations in mixing, catalyst concentration (intrinsic reaction rate), and initial temperature for equal mixing conditions.
Distributed pore‐size model for sulfation of limestone
Authors: Christman P. G. , Edgar T. F. 
Published: June 2004

AbstractA model is proposed to study the reaction between a porous solid and a reactant gas resulting in solid and gaseous products. The model describes the reacting solid as a sphere made up of a distribution of randomly oriented open pores. The evolution of the pore‐size distribution is followed by use of a population balance, using a combination of the independent variables of time and location first presented by Dudukovic (1976). The macroscopic properties of the solid are obtained by integrating over the pore size distribution. The results of the population balance are used with a mass balance on the reacting gas to obtain rate and conversion data.The results of the model are compared to experimental data obtained for the sulfation of limestone (Ulerich et al., 1977). Both rate vs. conversion as well as conversion vs. time plots are presented, which serve as a more strenuous test of the model than either type of plot alone.
Effect of pressure fluctuation on coal combustion in large‐particle fluidized beds
Authors: Bywater R. J. , Chung P. M. 
Published: June 2004

AbstractAtmospheric fluidized‐bed combustors (AFBC) operate in the large‐particle (>1 mm) fluidization regime. Characteristics of this regime, combined with the fact that as much as 50% of the coal combustibles are volatiles, result in localization of the devolatilization and combustion of the volatilized gases to the neighborhood of the coal‐particle and volatile gas plumes arising from the injector region. The volatile gas plume resulting from the large‐particle fluidization dynamics wanders due to pressure fluctuations induced by bubble passage.The purpose of the present work is to determine the impact of these characteristics on the design of AFBC's. This has been accomplished by a linearized analysis of the governing equations to describe the periodic wandering of the volatiles plume diffusion flame and the corresponding fluctuation of the combustion rate. The flame oscillation increases the overall combustion rate above the steady‐state value. This increase diminishes with increasing fluctuation frequency until the flame becomes insensitive to the fluctuation in the high frequency limit.
Optimal control policy for substrate inhibited kinetics with enzyme deactivation in an isothermal CSTR
Authors: San Ka‐Yiu , Stephanopoulos Gregory 
Published: June 2004

AbstractA slow enzyme deactivation process taking place in parallel with the main enzymatic reaction in a continuous stirred‐tank reactor can cause a departure from the optimal operating conditions, or, even a reactor failure. One way of minimizing productivity losses and maintaining optimal reactor conditions is by properly manipulating the flow rate of the reactor. The optimal flow‐control policy for typical enzyme kinetics with parallel enzyme deactivation is derived. Both the complete and an approximate analytical solution are presented. The approximate solution, which is actually a quasisteady‐state solution, is a very good approximation when the deactivation process is slow compared to the main enzymatic reaction and can be easily implemented as a feedback control based on the current state of the reactor. If the deactivation kinetics is the same as that of the main reaction and the cost of the reactant is negligible compared to that of the product, the quasisteady‐state solution is indeed the exact solution.
Optimal process design under uncertainty
Authors: Halemane K. P. , Grossmann I. E. 
Published: June 2004

AbstractA rigorous mathematical formulation is presented for the problem of optimal design under uncertainty. This formulation involves a nonlinear infinite programming problem in which an optimization is performed on the set of design and control variables, such that the inequality constraints of the chemical plant are satisfied for every parameter value that belongs to a specified polyhedral region. To circumvent the problem of infinite dimensionality in the constraints, an equivalence for the feasibility condition is established which leads to a max‐min‐max constraint. It is shown that if the inequalities are convex, only the vertices in the polyhedron need to be considered to satisfy this constraint. Based on this feature, an algorithm is proposed which uses only a small subset of the vertices in an iterative multiperiod design formulation. Examples are presented to illustrate the application to flexible design problems.