bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical methods of solution for continuous countercurrent processes in the nonsteady state part II: Application of numerical methods
Authors: Tan K. S. , Spinner I. H. 
Published: June 2004

AbstractThe numerical methods developed in Part I are applied to a number of important countercurrent processes. Examples involving simultaneous input disturbances, distributed disturbances, Langmuir isotherms, and nonlinear coupled boundary conditions are tested. These examples, if solved by previous methods, would have required interpolation or iterative procedures, but are solved efficiently and accurately by the explicit algorithms and coding sequence developed in Part I.The solutions for a linear system are in excellent agreement with the analytic solution. Numerical solutions obtained from explicit algorithms based on a nonlinear rate expression also shows very good agreement with the analytic solutions of Thomas (1944) for a fixed bed process. In both cases good accuracy is obtained with as few as sixteen increments.
Collision rate of small particles in a homogeneous and isotropic turbulence
Authors: Yuu Shinichi 
Published: June 2004

AbstractA theoretical equation is derived for the collision rate of aerosol particles in a homogeneous and isotropic turbulent system. This equation takes into account the relative velocity between fluid and particles. The calculated results indicate that the relative velocity between fluid and particles is the main factor in the turbulent coagulation (agglomeration, coalescence) of unequally sized particles in an air flow. This hold true, even when the particle sizes are less than 1 micron. For particles of equal radii the coagulation coefficient reaches its minimum value, because the effect of motion relative to the fluid now becomes zero and only the spatial variation of turbulent motion remains to cause collisions between the particles. For particles following a fluid motion completely, as in a water stream, the equation for the collision rate reduces to the Saffman and Turner equation.
Olefins and BTX‐production by thermal cracking of hydrotreated vacuum gas oil and related fractions
Authors: Clymans P. J. , Froment G. F. , Berthelin M. , Trambouze P. 
Published: June 2004

AbstractAramco vacuum gas oil was catalytically hydrotreated to conversions of 20, 40 and 60%, and subsequently fractionated into naphtha, kerosene, gas oil, and hydrotreated vacuum gas oil. These fractions were thermally cracked to test their potential as feedstock for olefins and BTX production. The olefin yields from the hydrotreated vacuum gas oil obtained from hydrotreating with 40 and 60% conversion favorably compare with those of straight‐run naphthas. Cracking in conventional naphtha/atmospheric gas oil units becomes possible. The naphtha, kerosene and gas oil fractions are preferably added to standard refinery streams.
Initial value approach to a class of reaction‐diffusion systems
Authors: Namjoshi A. N. , Kulkarni B. D. , Doraiswamy L. K. 
Published: June 2004

AbstractNew sets of transformations that convert an original two‐point boundary value problem into an equivalent initial value problem have been proposed and illustrated in the solution of the diffusion‐reaction problem for a monodispersed catalyst pellet. The use of the transformations reduces the computational effort considerably. The method is especially useful in the analysis of more complex cases, such as bidispersed catalyst pellets, catalysts undergoing decay, and gas‐solid noncatalytic reactions where the use of the conventional numerical techniques is quite involved and cumbersome. The method is applied to some known and to some yet‐unresolved cases and the new results obtained are discussed.
Hindered diffusion of gases in “Leaky” membranes using the dusty gas model
Authors: Macelroy J. M. D. , Kelly J. J. 
Published: June 2004

AbstractThe modified Enskog theory of van Beijeren and Ernst for dense fluid mixtures of rigid spheres is applied to diffusion of inert, nonadsorbing gases in microporous “leaky” membranes. Utilizing the concept of a dense dusty gas, the resulting expressions for the permeability and flux ratio illustrate the influence of steric hindrance on the transport process. The results obtained serve as corrections to the original dusty gas model of Mason and others.
Development of improved bubble disruption and dispersion technique by an applied electric field method
Authors: Ogata Sumitoshi , Tan Kazushi , Nishijima Kiyoto , Chang Jen‐Shih 
Published: June 2004

AbstractWith the aid of nonuniform DC electric fields, an improved bubble disruption and dispersion technique has been developed for dielectric fluid bubble column reactors. The basic mechanisms which lead to bubble disruption and dispersion in the system have been studied both experimentally and theoretically. The influence of operating variables, liquid properties and electrode geometry on the present applied electric field method has been conducted. The efficiency of power consumption by using the present technique has also been revealed.
Calcination kinetics and surface area of dispersed limestone particles
Authors: Borgwardt R. H. 
Published: June 2004

AbstractThe 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.
Hydrodynamics of fluidization: Prediction of wall to bed heat transfer coefficients
Authors: Syamlal M. , Gidaspow Dimitri 
Published: June 2004

AbstractA 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.
Gas‐liquid mass transfer in fluidized particle beds
Authors: Nguyen‐Tien K. , Patwari A. N. , Schumpe A. , Deckwer W.‐D. 
Published: June 2004

AbstractGas/liquid mass transfer has been studied in air/water fluidized beds of 0.05‐8 mm glass spheres in a 0.14 m diameter reactor. The volumetric mass transfer coefficients kL a were independent of bed height, and, for particle diameters up to 1 mm, decreased linearly with solids concentration. Low solids loadings as well as large diameter particles significantly increased kL and a, respectively, as compared to the two‐phase system.
Removal of colloidal particles in electroflotation
Authors: Fukui Yoshihiro , Yuu Shinichi 
Published: June 2004

AbstractThe collection mechanism of polystyrene latices of 0.6 μm in diameter in electroflotation has been examined both theoretically and experimentally as extension of our previous work (1980). To avoid the change of surface state of particle bubble, the experiment was conducted under the condition that the concentration of CTAB (cetyl trimethylammonium bromide), cationic surfactant in the solution, is within the 90% of its initial concentration. It is of interest that the theory predicts the collection efficiency to vary as d.
Vacancy solution theory of adsorption using Flory‐Huggins activity coefficient equations
Authors: Cochran T. W. , Kabel R. L. , Danner R. P. 
Published: June 2004

AbstractNew 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.
Longitudinal and lateral dispersion in packed beds: Effect of column length and particle size distribution
Authors: Han Neung‐Won , Bhakta Jayendra , Carbonell R. G. 
Published: June 2004

AbstractLongitudinal 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.
Chemical kinetics of carbon dioxide reactions with diethanolamine and diisopropanolamine in aqueous solutions
Authors: Savage D. W. , Kim C. J. 
Published: June 2004

AbstractDifferential rates of carbon dioxide absorption into aqueous monoethanolamine (MEA), diethanolamine (DEA), and diisopropanolamine (DIPA) were measured over a wide range of carbonation ratios. Analysis of the chemical‐reaction‐rate‐controlled data showed that the chemical reaction rates for all three aminoalcohols are first order with respect to the free‐amine concentration.
Carrier‐mediated transport across phospholipid‐composite membranes containing valinomycin
Authors: Sada Eizo , Katoh Shigeo , Terashima Masaaki , Takada Yoshihiro 
Published: June 2004

AbstractArtificial membranes containing a phospholipid and valinomycin were prepared. Valinomycin in these membranes acts as an ionophore (a mobile carrier for potassium ions) at a temperature above the phase transition point of the phospholipid. Experimental data were explained by the theory of carrier‐mediated transport accompanying formation of a carrier‐ion pair complex.
A hierarchical decision procedure for process synthesis
Authors: Douglas J. M. 
Published: June 2004

AbstractA 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.
A Simple Synthesis Method Based on Utility Bounding for Heat‐Integrated Distillation Sequences
Authors: Andrecovich M. J. , Westerberg A. W. 
Published: June 2004

AbstractIn this paper a new method is presented which will enable engineers to select better heat‐integrated distillation systems quickly and easily. The key to this method is making the assumption that QΔT, the product of the condenser or reboiler duty and the temperature difference between the reboiler and condenser, is constant for a single distillation task over a wide range of pressures. Using this assumption and the principles of multieffect distillation, a lower bound on the utility use for single distillation tasks and for distillation sequences is readily calculated for designs involving simple two‐product columns that may not be multieffected. This paper also describes methods which can be used to synthesize distillation systems which approach these bounds. Finally, an algorithm is presented which develops the least cost distillation system for separating a multicomponent feed. The methods in this paper are illustrated with a five‐component example problem.
High‐temperature mutual solubilities of hydrocarbons and water. Part II: Ethylbenzene, ethylcyclohexane, and n‐octane
Authors: Heidman J. L. , Tsonopoulos C. , Brady C. J. , Wilson G. M. 
Published: June 2004

AbstractIn 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.
Numerical simulation of a PSA system. Part I: Isothermal trace component system with linear equilibrium and finite mass transfer resistance
Authors: Raghavan N. S. , Hassan M. M. , Ruthven D. M. 
Published: June 2004

AbstractA numerical simulation of a pressure swing adsorption process is presented for a system in which a small concentration of an adsorbable component is separated from an inert carrier. Linear equilibrium and a linear rate expression are assumed. The model equations were solved by orthogonal collocation and by finite difference methods with consistent results. The theory is shown to provide a good representation of the experimental data of Mitchell and Shendalman (1973) for the system CO2‐He‐silica gel.
An NRTL model for representation and prediction of deviation from ideality in electrolyte solutions compared to the models of Chen (1982) and Pitzer (1973)
Authors: Ball F. X. , Fürst W. , Renon H. 
Published: June 2004

AbstractA new method of representation of electrolyte solution nonideality is derived, on the basis of similar assumptions, from a model applied by Cruz and Renon (1978) to binary electrolyte solutions. In order to test the validity of the model for representation of strong electrolyte properties, parameters were fitted to osmotic coefficient data for single, completely dissociated salts in aqueous solutions and were used to calculate osmotic coefficients of mixed aqueous electrolytes. Results are compared with those given by Chen's local composition model (Chen et al., 1982; Aspen, 1983) and Pitzer's truncated model (Pitzer, 1973, 1979; Pitzer and Mayorga, 1973; Pitzer and Kim, 1974), the same number of adjustable parameters being used in each case.The average standard deviations for single electrolytes are within 1% in the case of 1–1 salts for the three models, and within 2% in the other cases, except for Chen's model (5%). As for predicted results, both local‐composition models yield standard deviations of less than 2%, while the accuracy given by the Pitzer model is better than 1.5%.
High performance displacement chromatography: Calculation and experimental verification of zone development
Authors: Frenz John , Horváth Csaba 
Published: June 2004

AbstractEffluent concentration profiles from high performance displacement chromatography were calculated by using the theory of equilibrium chromatography of Helfferich and Klein (1970). The close agreement between predictions of the theory neglecting mass transfer resistances and experimental results demonstrates that conditions close to ideal chromatography are attainable in HPLC. Individual adsorption isotherms, as measured by frontal development, closely followed Langmuirian behavior.
Synthesis of control structures by singular value analysis: Dynamic measures of sensitivity and interaction
Authors: Lau Henry , Alvarez Jesús , Jensen K. F. 
Published: June 2004

AbstractA 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.
A nonequilibrium stage model of multicomponent separation processes. Part I: Model description and method of solution
Authors: Krishnamurthy R. , Taylor R. 
Published: June 2004

AbstractA 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.
Partial molar excess properties, null spaces, and a new update for the hybrid method of chemical process design
Authors: Lucia Angelo 
Published: June 2004

AbstractA new thermodynamically consistent quasi‐Newton formula is proposed for building iterative representations of the approximated part of the Jacobian matrix in the hybrid method of chemical process design. This update exploits the fact that the excess enthalpy and activity coefficient functions are homogeneous functions of degree zero in mole numbers which, in turn, gives rise to a natural null space for the approximated part of the Jacobian matrix that is defined by the component molal flow rates. The new formula builds iterative approximated parts that satisfy this null space constraint in addition to the usual overall secant condition and the desired sparsity constraints.The new quasi‐Newton formula is derived using the variational calculus approach first for the nonsparse case. This solution is then extended to the sparse case.The new updating formula, which is applicable to any chemical process design problem that involves nonideal phase equilibria and/or enthalpy of mixing considerations, is compared to the modified Schubert update in the context of the hybrid method. It is also compared to an implementation of Newton's method in which the approximated part of the Jacobian matrix is calculated by finite differences. Using an adiabatic single stage flash problem for a binary mixture with strongly nonideal liquid phase behavior, it is shown that the new updating formula compares favorably with finite differencing and can result in solutions to problems for which the original hybrid method fails.
Longitudinal and lateral thermal dispersion in packed beds. Part II: Comparison between theory and experiment
Authors: Levec J. , Carbonell R. G. 
Published: June 2004

AbstractThe thermal response of a packed bed subject to step changes in fluid temperature was measured in the Peclet number range from 10 to 103. Fluid temperature and particle temperatures were measured independently at six different axial locations in the bed as a function of time. From the temperature breakthrough curves we were able to calculate the spatial separation between the fluid and solid temperature fronts. The measured values were higher by a factor of 2 to 3 than those predicted by traditional heat transfer models. Longitudinal effective thermal conductivities were also computed and compared to theoretical predictions. The new heat transfer model developed in a previous paper is able to account for these differences between experimental results and the predictions of the dispersionconcentric and continuous solid phase models used by previous investigators. Steady‐state experiments were used to measure lateral effective thermal conductivities. A temperature gradient was imposed at the top of the bed perpendicular to the flow direction and its spread was measured at different axial locations in the Peclet number range from 10 to 103. The predicted lateral effective thermal conductivities calculated using mass transfer data to estimate the hydrodynamic dispersion effect were significantly lower than the measured values. This is possibly due to the influence of viscosity and density gradients in the flow field in the packed bed.
An index for operational flexibility in chemical process design. Part I: Formulation and theory
Authors: Swaney R. E. , Grossmann I. E. 
Published: June 2004

AbstractOne 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.
An index for operational flexibility in chemical process design. Part II: Computational algorithms
Authors: Swaney R. E. , Grossmann I. E. 
Published: June 2004

AbstractProcedures 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.
A dynamic study of CO oxidation on supported platinum
Authors: Barshad Yoav , Gulari Erdogan 
Published: June 2004

AbstractCatalytic oxidation of CO on alumina‐supported platinum was studied in a tubular isothermal reactor with applied concentration transients. A completely automated reactor system capable of switching frequencies as high as 0.2 Hz was constructed.Concentration cycling resulted in reaction rates that were much higher than the maximum rate achievable at steady‐state operation. Mapping of the time‐averaged carbon dioxide production rate in the time‐period duty‐fraction plane, resulted in a unique global maximum. We find that the maximum in rate occurs when the switching times are comparable to the characteristic time of the surface reaction. Results of our experiments also rule out significant contribution from the Eley‐Rideal mechanism at the temperature range of this work (below 120°C).